NO.

89
NTN
TECHNICALREVIEW
2022 - 2023
Special Issue
Strengthening the Services andSolutions Business andResponding to the Shift to EVs andAutomotive Electriﬁcation

NTN TECHNICAL REVIEWSpecial Issue
No.89

Strengthening the Services andSolutions Business andResponding to the Shift to EVs andAutomotive Electrification

NTN TECHNICAL REVIEW No.89
CONTENTS

Preface

Contribution

Special Issue“Strengthening the Services and Solutions Business and Responding to the Shift to EVs and Automotive Electrification.”

1

The Current Situation of Condition Monitoring and Diagnosis of Machine Systems

2

Masaki EGAMI

Tsuyoshi INOUE, Ph.D. Professor, Department of Mechanical Systems Engineering, Graduate School of Engineering, Nagoya University

Service and Solution Related Technologies
Efforts for Service & Solution Business in NTN

23

Hiroyuki KUREBAYASHI

Development of Remaining Useful Life Prediction Technology for Rolling Bearings Under Flaking Progression

29

Development of Sensor Integrated Bearing“Talking Bearings ”

35

Development of Multi Track Magnetic Encoder Integrated Rolling Bearing

41

Development of Sensor Integrated Bearing Unit for Machine Tool Spindles

47

Bearing Diagnostic Edge Application for Industrial IoT Platforms

53

Masashi KITAITM

Yasuyuki FUKUSHIMA, Tomomi GOTO, Yosuke TOYOGUCHI, Daigo IKKE, Kohei MATSUBAYASHI
Hiroshi OKUMURA, Hiroyoshi ITO, Yasuyuki HAMAKITA

Shohei HASHIZUME, Yudai NAKANO, Daichi KONDO, Yoji OHGUCHI, Yohei YAMAMOTO
Yudai NAKANO, Takashi HASEBA

EV and Electrification-Ready Technologies
ｓ Activities for Electric Vehicle and Electrification of Automobile
NTN’

58

Introduction of Rolling Bearings for Electric Drives Corresponding of Automobiles

65

Evolution of Fixed Constant Velocity Joint that Contributes to Environmental Protection

73

Introduction of Composite Material Products Used in Electrical Auxiliaries for Automobile

79

Ikuya TATEOKA

Takashi KAWAI, Tomohisa UOZUMIMasashi FUNAHASHI, Teruaki FUJIO, Ritsuki SAKIHARAKen YASUDA, Shinji KOMATSUBARA

Evaluation and Analysis Techniques
A Life Estimation Method of Peeling in Rolling Bearings Under Mixed Lubrication Conditions

85

Development of Technical Calculation Systems for Rolling Bearings

91

Naoya HASEGAWA, Takumi FUJITA, Michimasa UCHIDATE, Masayoshi ABO
Tomomi ISHIKAWA, Hiroyasu HIRUKAWA, Mariko IZUMI, Cedric BURNET

New Product Introduction
Development of Feeder“TRINITTE”for Picking Robots

96

Shuhei MATSUI

Product Introduction of Compact Torque Diode (TDL8)

99

Masayuki OHARA

Application Examples of the Wrist Joint Module“i-WRIST ”
TM

Yuzuru TANAKA

102

Award Winning Products
Low Friction HUB Bearing Ⅲ

106

High Speed Deep Groove Ball Bearing for EV/HEV107

Development of Super Long-Life Tapered Roller Bearings for Automobile108

Low Friction Technology of Sealed Ball Bearings for Transmission

109

Estimation Method of Micropitting Life from S-N Curve Established by Residual Stress Measurements andNumerical Contact Analysis

110

DLC Coating Spherical Roller Bearing for Wind Turbine Main Shaft

111

Makoto SEKI

Goro NAKAO, Katsuaki SASAKI, Yukihiro ISHIDA, Kazunori MURANUSHI
Hiroki FUJIWARA, Takashi KAWAI, Chikara OHKI

Tomohiro SUGAI, Katsuaki SASAKI, Takahiro WAKUDA

Naoya HASEGAWA, Takumi FUJITA, Michimasa UCHIDATE, Masayoshi ABO, Hiroshi KINOSHITA
Kazumasa SEKO, Takashi YAMAMOTO, Masaki NAKANISHIPreface
Special Issue“Strengthening the Services and Solutions Business andResponding to the Shift to EVs and Automotive Electrification.”

Executive Officer, CTO (Chief Technical Officer)

Masaki EGAMI

Against the backdrop of global warming and climate change issues, global efforts to achieve net-zerogreenhouse gas emissions, or carbon neutrality, are gaining pace. NTN is committed to contributing to
the realization of a carbon-neutral society. We are promoting research and development with a focus
on our material issues of realizing a sustainable society powered by natural energy and of reducing
energy loss. We also have advanced CAE technology, which aids us as we design our products andstudy technologies. CAE enhances the reliability of our products and our ability to make proposals
to our customers. In this issue, we feature our efforts in the areas of (1) Service and Solution Related
Technologies, (2) EV and Electrification-Ready Technologies, and (3) Evaluation and Analysis Techniques.
We also introduce three of our new products and six products and technologies that have received
external awards.
In Special Feature 1, we introduce technologies and products that contribute to the spread of wind
power generation and help improve the productivity of operating equipment. The use of wind power
generation systems is expanding globally. Key tasks are to ensure their stable operation and to curb
power generation costs. NTN has contributed to the stable operation of wind power generationequipment and reduction of operating costs by providing Wind DoctorTM. This monitoring service
remotely collects and monitors vibration and other data from wind power generation equipment andnotifies customers of anomalies and changes, thereby reducing the need for operation management andmaintenance. We have also developed technologies and products that contribute to the stable operationof equipment and improved productivity, such as rolling bearings with built-in sensors, including Talking
BearingsTM, portable vibroscopes, and bearing diagnostics applications compatible with the EdgecrossTM
IoT platform. We will introduce these technologies and products here.
In Special Feature 2, we introduce our technologies and products for bearings, hub bearings, andconstant velocity joints for automotive electrification. The pursuit of carbon neutrality is driving a rapid
shift toward automotive electrification. A key task in this is to stretch the cruising range of EVs. This inturn calls for smaller and more efficient onboard components, including key components such as thoseused in e-Axles. NTN has been contributing to the reduction of energy loss in vehicles by bringing new
products to the market that deliver smaller sizes and greater efficiency in bearings, hub bearings, andconstant velocity joints. We have also been developing highly functional and efficient modular productsthat take advantage of our core technologies in tribology, mechanical design, and mechatronics,
such as electric ball screw units, electric oil pumps, and the Ra-sHUBTM, a hub bearing with a steering
mechanism. We will introduce these technologies and products here.
Special Feature 3 introduces Evaluation and Analysis Techniques that use CAE for rolling bearing
design and bearing operating life estimation. Proposing, in a timely manner, competitive products aligned
to market trends and customer needs calls for greater sophistication and higher efficiency in productdesign work and product performance evaluation. This paper introduces a newly developed integrated
technical calculation system for rolling bearings and a CAE calculation system that semi-automates
the design process of hub bearings. In addition, we introduce analysis technology that enables reliablebearing design under conditions where oil film formation is insufficient. This technology addresses theshift toward lower viscosity lubricants which stems from the demand for more efficient machines.
We hope that our technologies and products introduced in this issue will help bring about a carbonneutral society. Guided by our corporate philosophy “For New Technology Network: Connecting theworld through new technologies”, we shall contribute to international society through creating newtechnologies and developing new products. We will work toward the further development of industry,
while coexisting with nature, through research and development activities centered on carbon neutrality.

NTN TECHNICAL REVIEW No.89

1

Contribution

The Current Situation of Condition Monitoring and
Diagnosis of Machine Systems

Tsuyoshi INOUE
Ph.D. Professor, Department of Mechanical Systems Engineering, Graduate School of Engineering, Nagoya University

Recently, condition monitoring and diagnosis technologies for machine systems havebeen rapidly developing and attracting attention. This paper first reviews the recent
trends in condition monitoring and diagnosis of mechanical systems, referring to thestandardization activities of ISO/TC 108/SC 5, in which the author has been involved formany years. Subsequently, this paper introduces the recent trends in asset management andcondition monitoring, condition monitoring and diagnosis of wind power generation, IoT for predictive maintenance,and condition monitoring and diagnosis using 1DCAE as the latest topics. Finally, some topics regarding condition
monitoring and diagnosis of machine systems and bearings at domestic conferences in the past few years have been
introduced.

1. Introduction
I have been involved in ISO standardization
activities for ISO/TC 108/SC 5 Condition Monitoringand Diagnostics of Mechanical Systems since 2004.
I will first briefly review the standardization activities
of ISO/TC 108/SC 5 and then give an overview ofrecent developments in condition monitoring anddiagnostics of mechanical systems. The first half ofthe paper (Chapters 2 and 3) is mainly based on acommentary article1) written and published in thejournal “Nondestructive Inspection” in 2020, with an
update based on information from the last two years.
The latter half of the paper (Chapters 4 to 7)
will cover recent trends in asset management andcondition monitoring, condition monitoring anddiagnostics for wind power generation, IoT for
predictive maintenance, and condition monitoring anddiagnostics using 1DCAE. Finally, we will introduce
some content from presentations at domestic
academic conferences in the past few years that relate
to condition monitoring and diagnostics of bearings.

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NTN TECHNICAL REVIEW No.89

2. International Trends in Condition Monitoringand Diagnostics of Machine Systems1)
2.1 Scope of ISO TC 108/SC 5
ISO/TC 108/SC 5 is officially called “Condition
monitoring and diagnostics of machine systems”. The
purpose and scope of SC 5 provided on the website2)
are as shown below.
Standardization of the procedures, processes andequipment requirements uniquely related to theactivity of condition monitoring and diagnostics ofmachine systems is an important part of all programswith selected physical parameters associated with
an operating machine system are periodically or
continuously monitored, measured and recorded forthe interim purpose of reducing, analyzing, comparing
and displaying the data and information obtained
to support decisions related to the operation andmaintenance of the machine system．
2.2 Working Group for ISO TC 108/SC 5
The working groups (WGs) established in ISO/TC
108/SC 5 as of September 2022 are listed in Table 1
and introduced individually below.
AG E: This is a working group for discussing theoverall strategic plan for SC 5. Here, the overall
direction of international standardization of SC 5, how
to proceed with the work of each working group, andthe establishment and dissolution of working groups
are examined and discussed. The initial draft of thepreliminary work item (PWI), which assumes that a
new working group will be established in the future, isalso considered here.

Table 1 Working Group2) of ISO/TC 108/SC 5(as of September 2022)
WG

Technical field

AG E

Strategic planning

WG 7

Training and accreditation in the field ofcondition monitoring and diagnostics

WG 11

Thermal imaging

WG 16

Condition monitoring anddiagnostics of wind turbines

WG 17

Condition monitoring anddiagnostics applications

WG 18

Condition monitoring management

WG 7: This working group focuses on the training
and certification of condition monitoring technicians.
It has developed a series of standards for training andcertification. In addition to ISO 18436-1:2021, which
covers the entire range, it has published standards
for condition monitoring technicians for individual
technologies which include ISO 18436-2:2014
Vibration condition monitoring and diagnostics, ISO
18436-4:2014 Field lubricant analysis, ISO 184365:2012 Lubricant laboratory technician/analyst, ISO
18436-6:2021 Acoustic emission, ISO 18436-7:2014
Thermography, and ISO 18436-8:2013 Ultrasound. In
Japan, certification of machinery condition monitoring
technicians based on these 18436 series, has been inpreviously in place, details of which are described in
Chapter 3.
WG 11 Thermal Imaging: This working groupfocuses on condition monitoring and diagnostic
techniques using thermal imaging. It has published
ISO standards for general procedures in ISO 184341:2008 and for interpretation of images in ISO 184342:2019, where images of bearing anomaly detection
are also presented. It is currently considering thestandardization of optical gas imaging. In addition
to WG11, which focuses on thermal imaging, whichwere previously in many other working groups on
condition monitoring and diagnostic techniques(WG3 Performance monitoring and diagnostics,
WG4 Tribology, WG10 Condition monitoring anddiagnostics of electrical equipment, WG14 Acoustic
techniques, WG15 Ultrasound diagnostics, etc.).
However, each of these has finished publishing the
ISO standards that are currently required and has
therefore been disbanded. Information on these
disbanded working groups is shown in Table 2. If
the need arises for a new ISO standard in the same
field, or if a major revision of the current ISO standard
becomes necessary, we plan to reopen the Working
Groups.

WG 16 Wind turbines, WG 17 Applications: These
working groups focus on condition monitoring anddiagnostics for individual machines. WG16 hascompleted the standardization of ISO 16079-1:
2017 General Guidelines and ISO 16079-2: 2020
Monitoring the drivetrain. The latter describes themonitoring and diagnosis of bearings and gears forwind turbines. As its name suggests, WG17 covers
a wide range of applications. It has published thestandard ISO 19283:2020 Hydroelectric generating
units and has started the standardization ofreciprocating compressors.
WG 18 Asset Management: This is a new working
group launched in 2019 that, as of September
2022, is the most active. The condition monitoringand diagnostics of mechanical systems havetraditionally been done mainly by the engineers who
directly handle machines. However, the need forstandardization that also incorporates the perspectiveof asset management systems, has been raised at
SC 5 international meetings (see Section 2.3) for the
past 10 years. Now, under the strong leadership of thecurrent SC5 chairman, the working group has begun
studying and vigorously promoting the standardizationof asset management systems with a specific focus onmechanical systems. The standards being examinedare (1) accreditation of condition monitoring
managers, (2) accreditation of condition monitoring
auditors, and (3) physical asset management.
2.3 International meetings for ISO TC 108/SC 5
In ISO standardization, international meetings
play an important role as forums for reviewing andreflecting ballot comments on draft standardization
texts and for considering the next standards. The firstinternational meeting of SC 5 was held in 1994, and23 meetings were held up to 2019. Table 3 shows
the years and venues of the conference. The 24th
meeting was originally scheduled to be held in
New York in September 2020 but was postponed(and subsequently canceled) for the first time due toglobal restrictions on international travel arising fromthe COVID-19 pandemic that began in March 2020. It
was held later in May 2022 as the first online meeting.
In 2023, with the pandemic now largely under control,
Japan will host the meeting in Kyoto, which will be thefirst in-person meeting in four years.

NTN TECHNICAL REVIEW No.89

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The Current Situation of Condition Monitoring and Diagnosis of Machine Systems
Table 2 Working groups established in SC 51) 2)

Table 3 List of SC 5 International Conferences1)

WG

Technical field

1st

1994

Swansea

UK

2nd

1995

LondonUK

AG A

Vibration condition monitoring procedures andinstrumentation used for diagnostics

3rd

1996

SydneyAU

WG 1

Terminology

4th

1997

Berlin

DE

5th

1998

TasmaniaAU

WG 2

Data interpretation and diagnostics techniques

6th

1999

Copenhagen

DK

WG 3

Performance monitoring and diagnostics

7th

2000

Nanjing

CN

WG 4

Tribology-based monitoring and diagnostics

8th

2001

ViennaAS

WG 5

Prognostics

9th

2002

Minden, NV

USA

10th

2003

Paris

FR

JWG 6

Formats and methods for communicating,presenting and displaying relevant informationand data

11th

2004

London

UK

12th

2005

Dania Beach, FL

USA

WG 8

Condition monitoring and diagnostics ofmachines

13th

2007

Prague

CZ

14th

2008

Kyoto

JP

WG 10

Condition monitoring and diagnostics ofelectrical equipment

15th

2009

Copenhagen

DK

16th

2010

LondonUK

WG 14

Acoustic techniques (Acoustic emissions)

17th

2011

SydneyAU

WG 15

Ultrasound

18th

2013

Berlin

DE

19th

2014

Paris

FR

20th

2016

Sydney

AU

21st

2017

London

UK

22nd

2018

Helsinki

FI

23rd

2019

Copenhagen

DK

24th

2022

Online25th

2023

Kyoto (scheduled)

For these working groups, items to be discussed toconsider future projects or new areas of work are includedin each yearʼs meeting. These are examined, along withconsidering the resumption of activities.

JP

2.4 ISO TC 108/SC 5: Status of activities andoutlook
The latest SC 5 activities can be found on the ISO
Website. The current chairman is Mr. L. Hitchcock(SA), the fourth chairman. The secretary is Mr. A.
Rashid (SA). As of September 2022, the P-members(Participation members) consisted of 23 countries
and regions, while O-members (Observer members)consisted of 12 countries and regions.
Fig. 1 shows the status of SC 5 standards as of
September 2022. SC 5 has published 28 international
standards. Five standards are in the process of being
established or revised.

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NTN TECHNICAL REVIEW No.89

Fig. 1 Standardization Activities as of September 2022
SC 5 began with the concept of “Condition
Monitoring and Diagnostics.” As the work ofstandardization progressed from 1994 to around2011, there was an overall shared recognition among
Japan, the United States, Europe, and other countries
in terms of the background, needs, and objectives ofthis concept. However, around 2012, while the original
concept was retained, (the background, needs, andobjectives of condition monitoring and diagnostics
as recognized and advocated by the SC5 members in
Europe and the United States) gradually expanded.
They have long recognized the need for and value ofcondition monitoring and diagnostics standards thatshould be used by engineers and management froman asset management standpoint. Now that the firstround of standardization of the basic technologies
of SC 5 has been finished, the activities of SC 5
show signs of a shift toward such new standards forcondition monitoring and diagnostics.
As of September 2022, as shown in Table 1, SC
5 has the following active working groups: Training
and Accreditation WG 7, Thermal Imaging WG 11,Wind Turbines WG 16, Applied Technology WG 17,
and Asset Management WG 18. As mentioned in theprevious section, the WG on foundational technologies(currently WG 11) is to be disbanded after completing
standardization. The future activities of SC 5 will
mainly take two directions: applied technology (WG16
and 17) and asset management (WG18). In particular,
the current chairman of SC 5 has strongly indicatedthe latter direction based on the aforementioned
background. This shift has been clear in the past
three international meetings, as SC 5 currently has
liaisons with IEC TC 56 Dependability and ISO/TC 251
Asset management in the opposite direction. WG18
is expected to be the center of SC 5 activities shortly.
However, TC 108/SC 5 has not yet reached a mutual
understanding or recognition concerning the asset
management of mechanical systems proposed by TC
108/SC 5 concerning the 55000 series, which is the
major ISO standard for asset management. It is also
clear that TC 108/SC 5 itself has yet to define theideal state of condition monitoring management formechanical systems.
In Japan, the needs and expectations for asset
management of mechanical systems are alreadyincreasing, and one can sense that interest in theactivities of SC 5/WG18 is growing rapidly. On theother hand, the ISO/TC 108/SC 5 National Committee
does not yet have a fully shared understanding of
the background, needs, and expanding objectives ofcondition monitoring and diagnostics from an asset
management perspective. The start of considerationof several ISO standards in asset management(WG 18) was approved at the 23rd International
Conference (Copenhagen) and will be considered atthe 25th Kyoto Conference. For the above reasons,the current ISO/TC 108/SC 5 National Committee
may not be able to adequately respond to thesestandardizations. To address this, the ISO/TC 108/SC
5 National Committee has recently started to engage
with the Japan Association of Asset Management(JAAM) and is preparing to start mutual participationin committee activities. The committee is also
considering adding asset management experts asmembers if necessary or restructuring the structure of
the ISO/TC 108/SC 5 National Committee. We hopethat experts from related companies in Japan who
are interested in asset management for condition
monitoring of mechanical systems will participate
in the ISO/TC 108/SC 5 National Committee orinternational meetings and share their views.

3. Engineer Accreditation Programs andCourses1)
3.1 Machine Condition Monitoring Qualification
Accreditation Project
To evaluate the technical competence of individuals
in a globally consistent and objective manner,
accreditation of machinery condition monitoring anddiagnostics technicians is conducted based on the ISO
18436 series (qualification of machinery condition
monitoring and diagnostics technicians) developedby ISO/TC 108/SC 5/WG 7.1) In Japan, accreditation
has been implemented for vibration, tribology, andthermography.
ISO 18436-2 (vibration) was published first in
2003. The ISO 18436 standard series continued insteady succession with ISO 18436-4 (field lubricant
analysis), ISO 18436-6 (acoustic emissions) and ISO
18436-7 (thermography). ISO 18436-5 (laboratory
lubricant analysis) followed in 2012 and ISO 184368 (ultrasound) was published in 2013. It should be
noted that in ISO 18436-2 (vibration) the overall field
is divided into categories Ⅰ through Ⅳ (category Ⅳ
is recognized as equivalent to a professional engineer
or doctor of Engineering), whereas all other fields
are divided into categories Ⅰ through Ⅲ. In addition,although the redefinition of vibration as Category Ⅰ
to Ⅲ has been proposed and periodically consideredat SC 5 international meetings, for the sake of clarityand ease of understanding of the overall categories,
the original category system has been maintained due
to opposition from countries that have already been
implementing the system for nearly 20 years.
The accreditation system for the qualificationof technicians who perform condition monitoring

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The Current Situation of Condition Monitoring and Diagnosis of Machine Systems
and diagnostics of machines (vibration) has been
implemented by the Japan Society of MechanicalEngineers (JSME3)) since June 2004. A total of 5 472
persons have been certified by the 37th examination
to be held in August 2022. In Category Ⅰ, the numberof qualified personnel is 819. In Category Ⅱ, it is 4 557.
In Category Ⅲ it is 434. On average, around 10 people
receive accreditation in Category Ⅰ, 100 in Category
Ⅱ, and 20 to 30 in Category Ⅲ. In addition, 41 people
have received accreditation in Category Ⅳ, which is
positioned as equivalent to a Doctor of Engineering or
a professional engineer. This shows the high level ofengineers involved in vibration technology in Japan. It
is hoped that those who aspire to work internationallyas engineers, will take up the challenge of Category Ⅲ
and Ⅳ.
The accreditation system for the qualificationof technicians who perform condition monitoringand diagnostics of machines (tribology) has been
implemented for Categories Ⅰ-Ⅲ since FY2009
through joint certification by JSME3) and the JapaneseSociety of Tribologists (JAST). As of September 2022, a
total of 1 421 persons have been certified. (In Category
Ⅰ, the number of qualified personnel is 1 176. In
Category Ⅱ, it is 234, and in Category Ⅲ it is 11.)
The qualification examinations for technicians who
perform condition monitoring and diagnostics ofmachines (thermography) have been conducted by
the Japanese Society for Non-Destructive Inspection(JSNDI) for Category Ⅰ since FY2016 and forCategory Ⅱ since FY2018. A total of 206 people (173
and 33 for Categories Ⅰ and Ⅱ, respectively) havepassed the examination as of September 2022.
JSNDI (Certification Division for CM Engineers)and JSME (Japan Society for Machine Monitoring
Engineers) have formed a partnership for
administering the accreditation of condition
monitoring4). For example, JSME sponsors meetingsof the Condition Monitoring and Vibration Diagnostics
Engineer Community. It provides a forum fordisseminating information on condition monitoring
and for exchange among qualified engineers, including
JSNDIʼs qualified CM engineers and other relatedparties4).
3.2 Workshop on condition monitoring anddiagnostics techniques
The ISO/TC 108/SC 5 National Committeeorganizes and holds a seminar entitled “A Must for
Global Engineers! Monitoring and Diagnostics of
Mechanical Systems, Fundamentals, Practical KnowHow, Application Examples and Standards” (hosted
by JSME). The content includes an introduction of
the SC5 standards and engineer accreditation for
condition monitoring, diagnostics using vibration,
lubricant analysis, thermal image analysis, introductionof basic technologies for acoustic emissions (AE),diagnosis of large rotating machinery, diagnosis ofwind turbines (mainly bearings), current indication
diagnosis (added from 2019), and comprehensive
diagnosis (added from 2021). The first seminar washeld in Tokyo in October 2007 (30 participants). The

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NTN TECHNICAL REVIEW No.89

second seminar was held in Osaka in October 2007
(15 participants). After a hiatus following the above
two seminars, the third seminar was held in Tokyo in
September 2016 (29 participants). The fourth seminar
was held in September 2018 (44 participants), andthe fifth in September 2019 (53 participants).
A book was written based on the contents of the
5th seminar. Entitled “Condition Monitoring and
Diagnostic Techniques for Mechanical Systems”, it
was published in June 2021 (edited by Inoue andHyodo, Japan Society of Mechanical Engineers,
Corona Publishing).5) The 6th seminar was held online
in November 2021 (150 participants) using this bookas the textbook. In fiscal 2022, this workshop was
expanded and held in two rounds in November, one
for beginners and the other for intermediate-level
students. The last three seminars have been fully
booked, highlighting the growing need for and interestin this technology with the arrival of the IoT (Internetof Things) era. We will continue to educate people
about this field and introduce the activities of the ISO/TC 108/SC 5 National Committee. I hope that throughthese seminars and publications, people will learn thefundamentals of technology in this field.

4. Condition Monitoring and AssetManagement6)-14)
4.1 Europe: Trends in IoT and Asset Management
Ten years have passed since IoT and Industry
4.0 were proposed in the 2010s, and these terms
and concepts have spread widely. In Europe
and the United States, these technologies have
evolved through deep integration with equipment
diagnostics and asset management. This year, Kawaisummarized equipment diagnostics and IoT in Europe
in comparison with Japan as follows.6) In Japan,
discussions tend to focus on the use of data obtained
from equipment in a single factory or company. In
contrast, in Europe, the European Integrated Data
Infrastructure Project GAIA-X represents the European
Data Economy Area. In recognition of the strategic
utility of data, GAIA-X integrates various cloudservices of companies on a single system, enabling
interoperability through a standardized authentication
mechanism that facilitates data exchange acrossindustries (Data Economy Area).
It is expected that manufacturers will evolve to amodel of providing services to customers. Globally,
the customerʼs usage environment will become
a complex system environment that includes not
only their own products but also those of othercompanies.8) Japan will be no exception to this trend.
As a result, manufacturers will be required to manage
the entire life cycle of the userʼs usage environment
as they provide services. It is thus expected that
manufacturers will need to collect data generated
from the entire userʼs usage environment, including
competitorsʼ products. In particular, sharing andutilizing data from the operation and maintenancephases, which have not been visualized until now,
will become a new and important area of researchand development. It is clear that data collaboration
involving users will be key.8)
Let us briefly touch on the report “Applying theInternet of Things (IoT) to Manufacturing” 6) 9) which
Siemens has compiled on Industrial IoT (IIoT), thecollection and centralization of large amounts ofmachine data from industrial sites. Fig. 2 shows the
major use cases that manufacturers can implement
to maximize the added value and ROI (return on
investment) to their businesses, modeled in six levels
of IIoT maturity. It is recommended that the IIoT
be introduced at the basic level, which is relatively
easy to handle, and then gradually expanded toachieve greater value. It is interesting to note thatthe first asset management and asset maintenanceare specifically listed as condition monitoring,asset performance management, and predictive
maintenance. We will give an overview of these here.
Asset management condition monitoring uses
a centralized IoT system to monitor specificparameters (temperature, vibration, pressure, etc.)
and key performance indicators (KPIs). It tracks theoperational status of all connected assets and, shoulda problem occur, takes corrective action before that
asset fails, thereby maximizing uptime of criticalassets. In this way, condition monitoring ensurestransparency into the health and performance ofassets at locations around the world.
In asset performance management, KPIs areused to monitor and track the condition andstatus of machines and identify machines that are
not performing adequately in terms of efficiency
and productivity. In addition, asset performance
management applications using IoT can improve
performance by making changes to production linesthat deviate from optimal operating conditions. In thisway, production is accelerated, and positive effects
spill over to resource allocation, time-to-market, andcustomer satisfaction. In addition, KPIs are fine-tuned
each time to identify machine performance moreaccurately, and machines are continuously adjusted
based on real-time data to improve performance. In
this way, asset performance management improves
overall equipment and corporate profits.
Predictive maintenance in asset maintenancedynamically collects and analyzes machine healthand performance data. It then identifies parts thathave reached key thresholds, determines when
maintenance or replacement is required, and performs
maintenance only when necessary. This eliminates
the need for scheduled maintenance and significantly
reduces unscheduled maintenance. As a result,predictive maintenance can reduce unscheduled
downtime, lower maintenance costs, improve quality,
productivity, asset uptime, availability, and production,and extend the service life of machines. For more
information, including other topics of interest, pleaserefer to the report.

Fig. 2 Siemens Digital Maturity Model6) 9)
Kawai stated that when he attended COMADEM(Condition Monitoring and Diagnostic Engineering
Management),10) a traditional international conferencein the field of condition monitoring and diagnosis,
he noticed that many of the presentations by Asian
researchers were on individual diagnostic techniques,
while those by Western researchers were mostly
about asset management.6) This shows how in Europe
and the U.S., research has already expanded in scope
to include not only equipment management using
diagnostics of anomalies, but also how to realize
managerial cost reductions based on such data, taking
into consideration the costs of installing diagnostics
equipment and conducting diagnostics necessary
for that purpose. This point is consistent with thetrend of thinking among Western experts, which
the author himself has experienced and felt throughthe standardization activities of ISO/TC 108/SC 5.
Japanese engineers and researchers must quickly
recognize this global trend so that they can respond
appropriately.
4.2 Trends in Japan: Maintenance Optimum
Strategic Management System (MOSMS)11)-14)
In Japan, the Japan Institute of Plant Maintenance(JIPM) has been continuously and actively involvedin equipment management. Fig. 3 shows the historyof facilities management in Japan, based on the
introduction material of the association11). Facilities
management technology continues to expand, as canbe seen in the background and history of MOSMS,
which integrates these technologies and incorporates
asset management.

Fig. 3 History of facility maintenance in Japan11)

NTN TECHNICAL REVIEW No.89

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The Current Situation of Condition Monitoring and Diagnosis of Machine Systems■ Estimated number of employees(manufacturing and maintenance, thousands)
Manufacturing
5 000

4 887 4 792

Maintenance
4 577

808
4 235 4 386

610

4 000

4 365
629
3 739

3 000
2 000

474

527
388

796

900
700

4 067

514

(From maintenance performance survey)

2010 2011 2012 2013 2014 2015 2016 2017
Manufacturing
departments

this way, the system aims for to align maintenancemanagement, which aims to balance risk and cost,with planned maintenance using technology forcontinuous improvement.

500
300

Maintenancedepartments

Fig. 4 Number of employees in manufacturingand maintenance departments11)
Fig. 4 shows the number of employees in the
manufacturing and maintenance departments.11) The
results show that the introduction of new equipment
has recently decreased. As this has happened, there
has been a growing shift toward maintaining andoperating existing equipment as well as possible.
Therefore, it can be said we are in the age of
maintenance.
Given this trend, in 2006, JIPM proposed and started
the Maintenance Optimum Strategic Management
System (MOSMS).12) 13) Its aim was to build amaintenance system that matched management
theory and technology theory through a consistentconcept for dealing both with loss (issues that havealready occurred) and risk (possibility that such issues
may occur in the future). This system clarifies therelationship between the PDCA cycle of management
and the PDCA cycle of maintenance (Fig. 5). In
particular, it emphasizes that in order for maintenanceto be integrated with management, a plan must be
created that is logical from a management perspective
and it must be ensured that maintenance follows theplan (maintenance management).13) It is necessary to
fully align management and maintenance to create a
grand design for maintenance (a maintenance planoffering maximum advantage from a management
perspective). MOSMS is a “made in Japan” systemthat has been developed for this very purpose.
MOSMS lists P (productivity), Q (quality), C (cost),
D (delivery time), S (safety), M (motivation), andE (environment) as loss/risk categories, aiming
to minimize these loss/risk categories as a resultof facility management. The target group is the
middle rank (managerial level), which is the sameas the target group for asset management in ISO/TC 108/SC 5/WG 18 described in the previous
section. To link management and maintenance, as
shown in Fig. 5, loss/risk management and facility
maintenance strategies are incorporated into the P(plan) of the management PDCA cycle. The D (do)of the management PDCA cycle and the P (plan) of
the MOSMS PDCA cycle are linked with each other,
the C (check) and A (act) of both PDCA cycles arealso linked through evaluation of each other.14) In

8

NTN TECHNICAL REVIEW No.89

Fig. 5 Linking management and conservation
through MOSMS14)

5. Current status of wind power
generation and trends in condition
monitoring and diagnostics15)-21)
Let us look at wind power generation systems, oneof the main systems subject to condition monitoringand diagnostics, and trends in this area.
5.1 Wind power producer trends15) 16)
The following is a summary of a report issued by
Accenture15) 16) this fiscal year. Over the past decade,efforts to reduce the Levelized Cost of Electricity(LCOE) of onshore and offshore wind power have
expanded and intensified. This has ushered in a digital
revolution in the wind power industry. Global onshore
wind power generation capacity has risen sharply
over the past decade, from 178 GW in 2010 to 594
GW in 2019. Offshore wind power is also growing
rapidly, reaching 29 GW of global capacity in 2019.
Fig. 6 shows global offshore wind power capacity andprojected short-term growth rates. The power market
is investing heavily in offshore wind power, whichcurrently accounts for only about 5 % of global wind
power capacity, but with the scale and growth rate of
the project, some predict that offshore wind power
capacity will nearly triple over the next five years.

Fig. 6 Global Offshore Wind Power Capacity andProjected Short-Term Growth15)

5.2 Condition monitoring and diagnostics of windturbines15) 16)
In the wind power business, LCOE has been
improved by increasing turbine size (from 2 MW
to 12 MW in 10 years in the UK16)), reducing
capital investment per MW, and increasing facility
utilization (from 30 % to over 40 % in the UK16)).
Accordingly, operation and maintenance (Operation& Maintenance, O&M) costs in the LCOE of wind
power plants have gradually increased in relative
terms and now exceed one-third of the life cycle
costs. As a result, there has recently been a growinginterest in achieving productivity gains and cost
reductions for O&M processes, and digital technology
has been identified as one of the key determinants of
its success. Accenture has conducted a survey of 11
leading onshore and offshore wind energy companies
and identified six key O&M use cases. The results ofthe study on the impact of advanced digital tools on
process improvement for these six key O&M use cases
are shown in Fig. 7.

Fig. 7 Degree of impact of advanced digitaltechnologies on key O&M use cases andbreakdown of surveyed companiesʼ ratings15)
Three of the six major O&M use cases are related
to condition monitoring. Applying advanced digital
tools to these three cases offers very high potential
for improvement. The following sections provide an
overview of three of these use cases individually.
• Alerts, Alarms, Warnings, and Faults: Types ofalerts and faults are analyzed to identify trends
and patterns for equipment condition analysis,
work prioritization, etc. These are incorporated
into response time guidelines to minimize loss ofgeneration and cost. The control room monitors
alarms and warnings and determines the response.
The performance engineering team takes chargeof the cause and relevance of alarms and faults,
while the asset management team and O&M team
identify follow-up actions and prioritize responses.
• Troubleshooting and minor corrective maintenance(CM): The process of investigating and repairing
incidents remotely or in the field to reduce

downtime and increase power generation. An
operations team monitors plant performanceand remotely investigates reported incidents,
coordinates field inspections, and handles
subsequent activities based on work instructions.
• Failure prediction and major component
replacement: Condition monitoring tools andalgorithms are used to understand the risk ofmajor component failure within a pre-specified
time frame. Setting up an optimally timed
major component replacement process reduces
downtime and maintenance activities, resulting incost savings and increased power generation.
In addition, this study comprehensively analyzes thecases above and clarifies the following key findings
related to the current role, potential and challenges ofdigital technology in O&M.15) 16)
Most of the companies surveyed see digitaltechnology as having an important role in fault
prediction, alerts and warnings, and trouble shooting.
All companies have implemented appropriate custombuilt solutions, and many of them would like todevelop further functionality. In this regard, a business
opportunity has arisen for third-party companies toprovide O&M insight services that power producers
can implement in their current environments.
• Integrating data of all types throughout the O&M
process enables the addition of rich contexts toanalytics to create added value. However, becauseof the low quality of data and the lack of dataengineering skills, few companies have achieved
this.
• Many companies are willing to improve their O&M
processes by learning from past activities andinformation, such as alert responses and service
records. In reality, however, the lack of time and ofeasy-to-use digital tools makes this difficult to do.
• As for data, data owners, such as owners, power
generators, and OEMs (or O&M service providers),
are reluctant to share the data and the insights
derived from it. Therefore, third-party companies
need to clearly define the ownership of the dataand consider and provide a partnership model forjointly developing software and tools.
Going forward, based on the abovementioned
recognition, advanced digital technologies will be
used to devise and build mechanisms for successful
data sharing. There will be a rapid global shift toachieve increased productivity and cost reduction for
the O&M process of wind power generation. In thisregard, condition monitoring and diagnostics will play
an important role.

NTN TECHNICAL REVIEW No.89

9

BladeControl andpower electronics
Main shaft / bearings systems
Main
shaft
Hub

Nacelle

0.60
0.50
0.40
0.30
0.20
0.10
0.00

Fig. 9 Trends in wind turbine failure andaccident rates17)
Table 4 Breakdown of Failure and Accident Factors(FY 2016)17)
Failure andaccident
factors

Breakdown offactors

Number ofoccurrences

Percentage
of total

Strong winds

0

0.0 %

Lightning

34

9.1 %

Air turbulence

19

5.1 %

Low
temperatures/
freezing

0

0.0 %Flooding

7

1.9 %

Other

12

3.2 %

Design flaw

3

0.8 %

Manufacturing
flaw

17

4.5 %

Construction
flaw

13

3.5 %

Human factor

Inadequate
maintenance

23

6.1 %

SystemfailureSystem failure

17

4.5 %

Under
investigation

6

1.6 %

Unable toidentify

108

28.9 %

Other*

115

30.7 %

374

100 %Naturalphenomenon

PitchsystemTower

YawsystemGear box

Mechanicalbrake

Oil hydraulics/
Powergenerator cooling system

Fig. 8 Example of windmill equipment configuration

17)

Fig. 9 shows the trends in the failure and accident
rates for the wind turbines cooperating with thesurvey (the same survey method has been in placesince around 2012, and the rates have remained
almost constant.)17) Table 4 shows a breakdown of
the causes of failures and accidents in fiscal 2016.
Among the factors related to condition monitoringand diagnosis, “inadequate maintenance” (6.1 %), a“human factor”, was relatively common. Comparedto past surveys, the “Other” category in the “Cause
unknown/other” category, which is related to condition
monitoring and diagnosis, has increased significantly.
This “Other” category was mainly reported as longterm deterioration. The same trend has continued inrecent years, indicating an increase in the number of
failures and accidents due to the deterioration of windturbines after a certain number of years.

10

0.70

20
04
20
05
20
06
20
07
20
08
20
09
20
10
20
11
20
12
20
13
20
14
20
15
20
16

5.3 Wind Power Condition Monitoring and
Diagnostics Trends in Japan(from the NEDO Report)17)
In Japan, a few years ago, NEDO summarized its
research results in “R&D of Technologies for Wind
Power and Other Natural Energies, R&D for Advanced
Practical Use of Wind Turbine, smart maintenancetechnology R&D (analysis) (fatigue prediction, etc.).”17)
The following is a brief overview of the research
results.
Fig. 8 shows an example of a basic wind turbine
component configuration. In this report, to contributeto the development of maintenance methods
for highly efficient rotating (drive train, control
equipment) and non-rotating (tower, etc.) systems,
data was collected on wind turbine failures andaccidents, the circumstances and causes of theiroccurrence was analyzed, along with analyzing
maintenance methods. The report also summarizes
the maintenance methods of existing wind turbines inJapan and overseas, as well as the measures taken in
response to failure accidents.

Failure/accident rate (times/year/unit)

The Current Situation of Condition Monitoring and Diagnosis of Machine Systems

NTN TECHNICAL REVIEW No.89

Failure inwind turbine

Unknowncause/Other

Total* “Other” of “Cause unknown/other” is mainly reported as“long-term deterioration”

Other Over all Blade Hub 0.5 %System 16.5 % 2.6 % 7.1 %Aerodynamic brakelinkage device
0.7 %
2.8 %
Mechanical brake
Joint
1.6 %
1.9 %
Pitch control unit
11.5 %
Foundation
Main shaft /0.5%
bearings
Sensors
1.2 %4.2 %Gear box
7.8 %Oil hydraulics
Power
4.0 %
generator
Electrical
Control
Yaw 2.8 %Windequipment
unit
anemometer device
17.9 %
12.2 %
0.2 %4.0 %5.4 Condition monitoring technology for windturbines17)
5.4.1 SCADA and wind turbine CMS

Fig. 10 Summary of wind turbine failures andaccidents by site of occurrence (FY2016)17)
Fig. 10 shows a summary of wind turbine failures
and accidents by site (FY2016). The most common
failure/accident categories were “electrical unit” (17.9%), “other” (16.5 %), “control unit” (12.2 %), and “pitch
control unit” (11.5 %). In the evaluation by operation
period, “blades”, “pitch control unit”, “gearbox”,“control unit”, and “electrical unit” accounted for a
relatively high number of failures of wind turbines that
had been in operation for “10 years or longer”. In mostcases, the longer the operation period, the greater
the number of failures. In the past survey results, thenumber of failures and accidents tended to increase
with the length of operation period for parts withmechanical drive mechanisms such as the pitch
control device, gearbox, and yaw device. In contrast,
the number of failures and accidents tended to behigher for blades, generators, electrical devices, andcontrol devices regardless of the length of operation
period. This is because the former are mechanicaldevices, while the latter are electrical devices.
Mechanical fatigue (including the effect of turbulence)is thought to be the main cause of the former failures,
while lightning strikes are often the cause of the latter.
The NEDO report also mentions that the data owners
are not willing to share their data. The same trend canbe seen in the situation in Europe described in theprevious section. In addition, a serious shortage ofengineers who can work on O&M of wind turbines has
been reported worldwide.

Fig. 11 SCADA and condition monitoring (CMS)
system for wind turbines17)
Fig. 11 shows the supervisory control and dataacquisition (SCADA) system and condition monitoring
system (CMS), which are the core systems forwind turbine operation and control. The actual
relationship between CMS and SCADA is organized
as an integrated image. Together with the operational
status data of each device collected by the CMS,
Operational data obtained by the SCADA system is
indispensable for evaluating the condition of windturbine components and equipment. As for thenecessity of CMS for wind turbines, the failure rateof gearboxes, generators, and converters, which aremajor components of wind turbines, is reported to behigher than those of the same type and capacity usedin other industries. As the output of a wind turbine
fluctuates with wind conditions, the load constantly
changes due to turbulence and blade position anddeformation. In addition to these load fluctuations,wind turbines with higher output and larger sizes
tend to have lighter equipment components, which
can increase the probability of failure and accelerate
fatigue. It is therefore important to constantly monitor
the equipment condition (load and response values)
to detect and address anomalies as early as possible(application of condition-based maintenance). It isalso important to use digital technology to evaluate
and predict the impact of load fluctuations on theequipment and to take measures for operation andmaintenance in advance (remaining service life
evaluation).

NTN TECHNICAL REVIEW No.89

11

The Current Situation of Condition Monitoring and Diagnosis of Machine Systems
5.4.2 CMS technology for wind turbines
The failure modes of wind turbines and diagnostic
techniques are shown in Fig. 12. Most of themonitoring technologies applied to wind turbine
CMS are based on existing condition monitoring
technologies. The CMS of wind turbines ischaracterized by the high need for online monitoring
because the operation and maintenance of many
wind turbines must be performed at a distance fromthe site. Table 5 shows the results of a survey ofdetection technologies in the current wind turbine
CMS in terms of online monitoring and diagnostic
effectiveness. While the development and applicationof new CMS technology specifically for wind turbines
is not necessary, given the shortage of real-world
examples there are major obstacles to wind turbine
CMS in terms of providing qualified failure diagnosis
through online monitoring.

12

Table 5 Anomaly detection technologies, target sites,
and characteristics of wind turbines17)
No

CM technology

cost

onlinecommercial

failurediagnosis

track
recordwind turbine
components

1

thermocouple

low

○

×

in usebearing
generatorsconverter
nacelletransformer

2

particlecounter
methodlow○×in usegearboxbearing3

vibration
analysis

low

○

○

in usemain shaft
main shaft
bearings
gearboxgenerator
nacelletower
foundation

4

ultrasonic
exploration

low tomedium○×

undertesting

tower
blade

5

electricalsignal(e.g., discharge
measurement)

low

○

×

in usepower
generator

6

vibroacoustic
analysismedium○××

blade shaft
bearing
gearboxgenerator

7

lubricating oil
component
analysis
methodmediumto high×○×

gearboxbearing8

acoustic
emission

high

○

×

×

blade shaft
bearing
gearboxgenerator
tower

9

twisting
vibration(encoderbased)

low

○

×

under
testing

shaft
gearboxFig. 12 Failure modes at general plants and applied
condition monitoring techniques used forwind turbine CMS17)

10

optical fiber
strain gages

extremely
high

○

×

in useblade

5.4.3 Condition monitoring and prediction of main
bearings for wind turbines
As the main bearings of wind turbines are used
under low-speed conditions, vibration caused bydamage is itself small. In laboratory tests, it is possible
to detect changes in vibration levels even in the very
early stages of damage. In actual wind turbines,
however, peripheral equipment generates vibration
at a level that can bring severe damage to the main
bearings. Transmission of this vibration from theperiphery hinders the detection of damage to themain bearings. A key task in detecting damage tothe main bearing is to improve the signal-to-noise
ratio by suppressing this vibrational disturbance. To
address this issue, this report17) develops a detection
method that highly integrates frequency band
splitting, a physical method, and machine learningalgorithms, a statistical method. As shown in Fig. 13,
we have demonstrated that the method can be used
to properly detect and diagnose initial damage to themain bearing.

11

thermography

extremely
high

○

×

×

blade shaft
main shaft
bearings
gearboxgenerator
converter
nacelletransformer

12

shaft torquemeasurement

extremely
high

○

×

under
testing

blade shaft
main shaft
bearings

13

shock pulse
method

low

○

×

×

bearing
gearboxNTN TECHNICAL REVIEW No.89

The same report17) also attempted to construct amethod for predicting the residual life of wind turbine
main bearings. By proposing an equation relating
the equivalent distance between wind turbines andthe load coefficient that reflects the effect of wakes(areas of lower velocity than the main flow that
occur downstream of objects placed in the flow), it ispossible to evaluate the bearing-rated life as shown in
Table 6.

Fig. 13 Damage detection of the main bearing of awind turbine17)
Table 6 Predicted and actual comparison of rated life17)WindturbineDistance
between
Actualequivalent
rated life
wind
(years)turbines(km)

Load
coefficient

Predicted
rated life
(years)Unit 4

16

0.3

1.55

14

Unit 5

17

0.3

1.51

16

Unit 19

10

0.2

1.72

9

Unit 20

8

0.2

1.75

8

5.4.4 Wind Turbine Tower Anomaly Detection
On March 12, 2013, a wind turbine nacelle fell fromthe top of the wind turbine support tower at windturbine No. 3 on the Taikoyama wind farm in Japan.
This was due to a fatigue fracture of the tower casing
just below the flange. Investigation of the accident
revealed that the cause of the fatigue fracture wasa stress concentration in the tower casing due todamage to the tower top bolt installed in the flange at
the top of the tower. Similar past accidents occurring
as anomalies characteristic of wind turbines include:a blade fallout in Falkenberg, Sweden, in 2009; an
accident at the Lemnhult wind farm south of Vetlanda,
Sweden, in December 2015; and an accident at the
Auwahi wind farm on Ulupalakua Ranch on the south
coast of Maui, Hawaii, USA in October 2016. In thecase of the collapse accident at the Taikoyama wind
farm, no anomalies were detected during routine
inspections before the accident, and fatigue fracture
occurred in a short period. In response to this accident,
a method was developed for detecting anomalies in

0.010
0.00800.00600.00400.00200.0

080 120 170 420 680
Axial force (Nm)(a) Torque change

Mahalanobis Distance(b) Diagnostic results for Unit 4 on the Unit 5 model.

Mahalanobis Distance(a) Diagnostic results for Unit 5 on the Unit 20 model.

tower top bolts at an early stage and evaluating axial
force.17) The MT system (Maharonobis-Taguchi) T
method (3), a type of multivariate analysis method,
was used to detect abnormal bolts. The results of
the analysis using the second-order derivative of thestrain variation are shown in Fig. 14. When the torquewas 680 N-m, the value exceeded the threshold value,indicating that it was possible to determine whether
the bolt was abnormal or normal, and the accuracyof the determination could be maintained even when
the rotor orientation changed (from -45°to 45°).

0.010
0.00800.00600.00400.00200.0-45 -22.5 0 22.5 45
Rotor load position( °)(b) Rotor orientation

Fig. 14 Early anomaly detection method for windturbine tower top bolts by Mahalanobis
distance17)
5.4.5 Example of standard for wind turbine CMS17) 18)
Here we will introduce the standard for windturbine CMS using the Guideline for the Certificationof Condition Monitoring Systems for Wind Turbines
Edition 201318) published by GL (Germanischer Lloyd)
as an example. The scope and objects of application of
the CMS for wind turbines are mainly the drive train,main bearings, gearboxes, and generators. In addition
to these, the CMS also covers the tower, blades,
main bearings, gearbox lubrication oil, foundations,and other parts of the wind turbine. Monitoringdata for wind power generation equipment include
load (power generation or torque), shaft speed,
temperature in the nacelle, bearing temperature,generator winding temperature, oil temperature, andoil pressure. Other environmental data, such as windspeed, wind direction, and outside temperature, arealso required to be measured when available.
Table 4.1 Ref.18) shows the number of sensors
required for a wind turbine CMS. It states that at leastsix sensors are required to monitor the vibration stateof the drive train of a wind turbine equipped with agearbox. The required frequency bandwidth starts
from fairly low speeds and has a wide range. Table 4.2
in Ref.18) shows a list of methods for using the signals
acquired from each sensor in a wind turbine CMS. It
requires the application of various analysis methods
for each site in order to deal with frequencies,
vibration modes, and corresponding anomaly modes.

NTN TECHNICAL REVIEW No.89

13

The Current Situation of Condition Monitoring and Diagnosis of Machine Systems
6. Predictive Maintenance and IoT19)
This is a citation from the article “IoT for Predictive
Maintenance” compiled by Mr. Sako, a long-timemember of the ISO/TC 108/SC 5 National Committee,
in 202019).
6.1 Key Points for Building a Predictive Maintenance
IoT System
Predictive maintenance is also called conditionbased maintenance or condition monitoring
maintenance. It is a maintenance method that uses
diagnostics techniques to measure and monitor thecondition of facilities and equipment to understandor predict the degree of deterioration and takeappropriate maintenance measures. The key points of
IoT include:• selection of sensors for detecting anomalies,• selection of optimal signal processing methods andanalysis methods,• determination of information collection methods,• determination of monitoring methods,• and automation of analysis and diagnosis.
Several development items are needed to promote
IoT for predictive maintenance. Here, we take“visualization of equipment conditions (as quantitativevalues)” as an example. Technological development
for visualization of facility conditions (as quantitativevalues) includes expansion of target facilities foranomaly detection, improvement of detection
accuracy, and more efficient and easier detection. To
this end, it is important to first clarify the equipment
to be monitored, the failure mode, the requiredprediction level (lead time), the difficulty of stopping
the equipment, and the time when the equipment canbe stopped. At the same time, it is necessary to clarify
the measurement location and available sensor types.
The procedure includes identifying a sensing
method capable of detecting anomalies throughlaboratory testing and determining evaluation indicesand threshold values for good or bad judgment
through field testing using the same method. Table 7
shows the application status of the diagnostic
techniques developed by Sako et al. for rotating
equipment19). The diagnostic techniques have been
comprehensively applied to a wide range of objects.
In his contribution19), Sako further describes indetail the diagnostic technologies for rolling bearings,
plain bearings, and motor current symptom analysis(MCSA) for the IoT of predictive maintenance. Here,we will focus on “diagnostic technology for rolling
bearings”.
6.2 Diagnostics techniques for rolling bearings forpredictive maintenanceAs shown in Fig. 15, rolling bearing anomalies
generate vibration and sound in various frequency
ranges19). These can be roughly classified into two
categories: structure-borne, such as vibration and AE(acoustic emission), and airborne, such as acoustic.
Sound is further divided into audible sounds andinaudible sounds above 20 kHz.

14

NTN TECHNICAL REVIEW No.89

6.2.1 Diagnostics using the vibration method19)
One of the signals used to diagnose anomalies
in rolling bearings is vibration acceleration. This
acceleration is further divided into two maincategories: acceleration in the high-frequency
range of 10 k to 30 kHz and acceleration in the lowfrequency range of 1 k to 10 kHz.
Fig. 16 shows an example of bearing diagnostic
results from the field. This is the acceleration
spectrum of a 6310 deep groove ball bearing whenfalse brinelling occurred in the inner ring due topropagating vibration from adjacent equipment.
As shown in Fig. 15, a frequency of 14 KHz was
generated in the zone indicated as high-frequency
acceleration. This is an example of how even a small
flaw could be detected by acceleration in the highfrequency range.
Fig. 17 compares the trends of acceleration values
in the high-frequency range for the six cases that
resulted in bearing failure. The average value in thenormal state is set to 1.0. The vertical axis shows theratio of the acceleration to the normal value, and thehorizontal axis shows the time elapsed from the time
when the condition began to change. Each bearingshows an exponential upward curve. It took three to
six months to reach the relative standard of caution(4.0 times), and about six months for the anomaly toarise (8.0 times). When the bearings were replaced
after about six months, small defects were observed.
It is explained that the variations in the degradation
speed of each bearing relates to differences inlubrication conditions and bearing load.
As deterioration progresses from this state, a lowfrequency acceleration spectrum in the 2 k to 3 kHz
range is generated in addition to the high-frequency
acceleration. This is the natural frequency of the
bearing outer ring. The explanation for this is thatthe progressive deterioration of the bearing results
in a higher excitation force, which vibrates the entire
bearing and generates natural frequencies. The trendof acceleration values in the low-frequency range wasalso investigated in four cases.19) As with the highfrequency range shown in Fig. 17, an exponential
upward curve was drawn, leading to bearing
replacement within approximately one to threemonths after the change was observed.
Furthermore, as bearing deterioration progresses,changes in vibration velocity also occur. A comparisonof velocity trends in seven cases of bearing failure due
to increased velocity shows an exponential increase
curve similar to that in the high-frequency range. Thechange in velocity value is so rapid, however, about
one or two weeks after the vibration velocity begins
to increase, the bearing can be said to have reacheda terminally degraded state that requires it to be
replaced.19)
The conclusion is that although the residual life ofbearings can be predicted in several frequency ranges,
monitoring using acceleration in the high-frequency
range may be essential for critical facilities wherecontinuous operation must not be interrupted.

Table 7 Application of Diagnostic Techniques toRotating Equipment19)

mediumand highspeed
rotationslidingbearing

gear

coupling
belt

acoustics
AE

audiblerange

ultrasoundelectric
current(MCSA)

×

○

○

△

○

○

○

○

poor
lubrication

×

○

○

○

○

○

○

○

wear

×

○

○

○

○

○

○

○

looseness/rattle

×

○

○

×

○

○

○

○
○

seizing

×

○

○

○

○

○

○

fatiguespalling

×

×

○

×

○

×

○

poor
lubrication

×

×

○

△

○

×

○

wear

×

×

○

×

○

×

○

looseness/rattle

×

×

×

×

○

×

○

seizing

×

×

○

△

○

×

blowers,
pumps,
compressors,
motors, etc.

○

seizing×○ :Kepstrum

○

○

△

×

○ :Kepstrum

○

○

△

fatigue×○ :Kepstrum

○

×

△

contamination
by foreign
matter×○ :Kepstrum

○

×

△

oil whirl

○

×

×

×

×

×

×

oil whip

○

×

×

×

×

×

×

pitching

△

○

○

○

○

○

○

○

spalling

△

○

○

○

○

○

○

○

scratching

△

○

○

○

○

○

○

○

meshinganomaly

△

○

×

×

○

○

○

○

misalignment

○

×

×

×

×

×

×

○

slack

○

×

×

×

×

×

×

○

overstretching

×

×

×

△

×

×

×

○

imbalance

○

×

×

×

×

×

×

○

rotating stall

○

×

×

×

×

×

×
×

turbines,
compressors,dieselengines, etc.

surging

○

×

×

×

×

×

cavitation

×

○

×

×

○

○

contact

×○ :Kepstrum

×

×

○

○

○

bend

○

×

×

×

×

×

×

eccentricity

○

×

×

×

×

×

×

• AMD
speed
criteria• AMD
rollingbearing
criteria• Noisereduction
methodfor inverter
motors• SOAP
method,ferrographymethod• Lighttransmission
method(MD-410L:
currently
discontinued)

Remarks

applicableequipment

agitators,
extruders,rolls, paper
machines, etc.

rubbing

blade

axis

lubricanttemperature
analysisfatiguespalling

rollingbearing
low
speed
rotation(severalhundredrpm orless)vibration
vibration vibration
velocity acceleration

Sensoryobservation
Structuralpropagation

20

30

50

70

100 200 300 500 700 1k

reduction
gears, speed
increasers,
etc.

3k

5k

7k

blowers,
pumps, etc.
ventilator
ventilator

○

pump

×

screw
compressor

10k 20k 30k 50k 70k 100k 200k 300k 500k 700k 1M

Audible range (hearing with auscultation rod)
Vibration velocity

Low range
acceleration

Inaudible range
High frequency
acceleration(Brg acceleration)

Audible acoustics
Rattling vibration due to bearing flaws (4)y=e0.0006x

8.00

⑥

y=e0.0003xy=e0.0004x

7.00
6.00

⑤

5.00

③

① ②

④

4.00
3.00
2.00

0

1 000 2 000 3 000 4 000 5 000 6 000 7 000 8 000

Elapsed time from change point Hr

Fig. 17 Bearing degradation curve at high frequency
range acceleration19)

Shaking detection by palpation

Airborne
propagation
Rollingbearing
acoustics

2k

9.00

6 months

1.00

Frequency Hz
10

3 months

10.00

0.00

• Application
to equipment
for whichvibration isdifficult tomeasure(cannedpumps,
axial flow
fans, etc.)•
Measurement
at power
supply panels• Non-contact
measurement• Operation
for moving
equipment(LM Guide,etc.)• Thermal
imaging
cameraFig. 16 Acceleration spectrum during false brinelling19)

Multiplier to normal

type ofanomaly(example.)machineelement

Acoustic emission(AE)

Ultrasonicacoustics
Ultra soundNatural frequency of bearing outer ring (3) Contact noise between bearing steel (2) Crack propagation sound of bearing steel (1)Fig. 15 Vibration and acoustics generated by rolling
bearings19)

6.2.2 Diagnosis by AE method19)
The AE method is the method that enables theearliest detection of anomalies in rolling bearings.
Fig. 18 shows the results of an accelerated life test at
750 rpm. The horizontal axis shows the test time, andthe vertical axis shows the event rate for both AE andacceleration of vibration (ACC). AE captures rolling
bearing anomalies earlier than the high-frequency
accelerations shown in Fig. 17. The explanation
given19) for this is that fatigue causes spalling on the
bearing steel from its internal starting point, andas it progresses to the surface of the raceway, AE
occurs at the time of the spalling occurring whereas
acceleration occurs after the rolling elements havebegun to collide with the spalling on the orbital planesurface. In the case of spalling with a surface causesuch as that due to oil film rupture or indentation, thetwo occur almost simultaneously.
Fig. 19 compares the AE spectra of the exfoliation
propagation and slit cracks. The AE spectrum of the
exfoliation propagation has a prominent frequency
component between 100 k and 500 kHz, whereas the
AE spectrum of the slit flaw has almost no component
above 100 kHz. Thus, AE can also capture thedifference in anomaly modes of rolling bearings in theearly stage.
The AE method is also superior in the low-speed
speed range. In the low-speed range, where theproduct of bearing bore diameter d (mm) androtational speed N (rpm) (dN value) is less than 2.0
× 104, the shock signal level of vibration acceleration
decreases and is buried in the noise level, making
it generally difficult to distinguish between normal
and abnormal conditions. In contrast, the AE method

NTN TECHNICAL REVIEW No.89

15

The Current Situation of Condition Monitoring and Diagnosis of Machine Systems
is an effective measurement method because it isindependent of rotation speed.

event rate Pieces/10 min

10 000

ACC
AE

1 000
100
10
1
0

0

100

710

810

910

Time min

1 010 1 100

θ dB

At the time ofdelamination
progress-36 dB-72 dB

0500 KHz

Frequency

Amplitude

Amplitude

Fig. 18 Accelerated life test results and diagnosis by AE19)

1 MHz

θ dB

time ofslit flaw-36 dB-72 dB

0500 KHz

Frequency

1 MHz

Fig. 19 AE spectra during exfoliation propagationand slit flaw19)
6.2.3 Other19)
The AE method requires a couplant to be applied
between the equipment surface and the sensor
surface. It is difficult to obtain a stable signal in cases
where this is strongly affected by unevenness orcurvature of the installation surface. For equipmentthat has conventionally been difficult to diagnose
due to such drawbacks, the authors have developed
a non-contact detection method using ultrasonicmicrophones. Using 20 k to 100 kHz ultrasonicacoustics, it has been shown that bearing separation
anomalies can be detected in the same way as with
the AE method, even at low rotational speeds of65 rpm. The ultrasonic acoustic method was applied
to detect rolling contact fatigue exfoliation of roll
support bearings in a solvent gas environment where
AE could not be used due to couplant leakage. In
addition, AE is also used to diagnose abnormalities in
low-speed rotating equipment, such as contact withthe extruder body, pitching of reduction gear gears,
and bearing rattling in agitators19).

7. Trends in Condition Monitoring and
Diagnostics Using 1DCAE
Kawai, a leading domestic expert who has been
engaged in condition monitoring and diagnosis ofmachinery for many years in Japan, provides anintroduction “On Diagnostic Methods for Equipment
Using Physical Models – Application to Digital Twins”21)
in the opening article of the 2022 JSME Dynamics,

16

NTN TECHNICAL REVIEW No.89

Measurement and Control Division Newsletter. In
this article, Mr. Kawai summarizes the process ofincorporating 1DCAE software into the equipment
diagnosis that he has been working on for many years.
1DCAE is a generic term for CAE methods and toolsthat have been rapidly spreading and developing inrecent years and their design support concepts.22) It
can be applied from the upstream stage of productdevelopment because it accurately captures thefundamental nature of the target. It can be expressedin a simple and clear format and can be used forevaluation and analysis. The article explains how
modeling the target system with 1DCAE software (inthe case of this data, Modelica is used) is useful forequipment diagnosis, and shows examples of system
and anomaly modeling (Table 8) that Mr. Kawai has
been working on.
As a concrete example, the model of anelectromagnetic brake is shown. It is explained thata system such as an electromagnetic brake, which
combines complex physical phenomena consisting ofdynamics, magnetic circuits, and electric circuits, canbe easily modeled by the 1DCAE software (Fig. 20).
Here, it is explained that the wear of the armature
increases the clearance between it and the plate, andthat the resulting effects on other physical quantities
can be simulated in a variety of simple ways. Fig. 21
shows the effect of the clearance on the time variationof the current at the start of energization. In thesame example, he states that the simulation andexperimental results align very well. Thus, he argues,
modeling the system and anomalies with 1DCAE
software makes it easy to analyze the system behavior
when anomalies occur in the system. The interested
reader is advised to view the material, which isavailable free of charge from the departmentʼs
website.
Some examples of modeling of mechanical systems
using 1DCAE software are shown below. Kashiwase etal.23) modeled a capacitor motor using the magnetic
circuit method and conducted an analysis using 1DCAE
software (Modelica). A coupled system (Fig. 22)
connecting an electric motor model and a rotating
shaft model was used to perform a coupled simulation(Fig. 23) relating the vibration of the rotating shaft
and the current of the power supply. This is expected
to enable more detailed diagnosis of the electricmotor.
Furthermore, Kashiwase et al. constructed a basicmodel for three-phase induction motors, which arewidely used in plants, based on the magnetic circuit
method, which consists of a stator, rotor, air gap, andother components, and a model that can be coupledwith a rotating shaft24). The validity of the modelusing 1DCAE software was verified by comparing its
electromagnetic behavior with FEM analysis, and theresults showed promise for simulation application toelectric motor diagnosis. Fig. 24 shows the winding
currents in each phase. Although the pulsation of the
1DCAE model (Modelica) is larger, it was confirmedthat the overall behavior can be reproduced,
according to the report.

Table 8 System and Anomaly Modeling Examples21)

control valve

biting, sensor offset

compressor

leakagecogeneration systemdecrease in efficiency, clogging,and heat transfer coefficient due
to debris

crankshaft

bearing rattling

rotational axis
systemrotor disproportion, bearing flaw,
bearing rattlingcoupling

misalignment, miscoupling

journal bearings

wear and its evolution(residual life estimation)screw compressor

bearing rattling, leakage

electromagnetic
brake

wear

gear mechanism

gear wear

3D printerfailure of fan for cooling(control in case of anomaly)

1.2
1.0

Electric current [A]anomaly

0.8

0.2 mm
0.3 mm
0.5 mm0.75 mm

0.6
0.4
0.2
0.0
0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

Time [s]experiment
1.2
1.0

Electric current [A]target system

0.8

0.2 mm
0.3 mm
0.5 mm0.75 mm

0.6
0.4
0.2
0.0
0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

Time [s]simulation

Fig. 21 Current change at the start of energization(effect of clearance)21)

energized state
dynamics model

magnetic circuit model

electric circuit modelFig. 20 Electromagnetic brake model21)
Fig. 22 Modelica model of motor and shaft system23)

NTN TECHNICAL REVIEW No.89

17

The Current Situation of Condition Monitoring and Diagnosis of Machine Systems

8. Research Trends in Condition Monitoringand Diagnosis of Bearings in Japan

Displacement of Motor Shaft
Displacement [m]5.0E-13
2.5E-13-0.0E+00-2.5E-13-5.0E-13

Time [s]Spectrum

Amplitude

1.2E-13
1.0E-138.0E-14
6.0E-14
4.0E-142.0E-140.0E+00
050

100 150 200 250 300 350 400

Frequency [Hz]

8
6
4
2
0
-2
-4
-6
-8

lu

lv

lw

Current [A]Current [A]Fig. 23 Vibration analysis results of motor and shaft
system23)

00.005 0.01 0.015 0.02

Time [s]

8
6
4
2
0
-2
-4
-6
-8

lu

0

lv

lw

0.005 0.01 0.015 0.02

Time [s]Fig. 24 Stator current (unsteady) (1DCAE and FEM)24)
Another study25) modeled gear pairs and gear
tooth wear, which are typical power transmission
mechanisms, using 1DCAE software (Modelica).
The model was used to estimate how the vibration
characteristics of the gear pair changed due to wearon the tooth flanks, and also to verify the results using
actual equipment.
In this regard, modeling of mechanical systems
using 1DCAE software has been used extensively
in recent years. The results of 1DCAE modeling ofvarious mechanical systems were presented in across-divisional OS organized at the 2022 annual
conference of the Japan Society of MechanicalEngineers (JSME). As mentioned above, the use of
1DCAE software as a modeling method for condition
monitoring and diagnosis of mechanical systems is
expected to advance further.

18

NTN TECHNICAL REVIEW No.89

8.1 National Scientific Conference on Condition
Monitoring and Diagnosis
Finally, I would like to review research trends in thisfield in Japan. In Japan, the representative academic
societies for this field are the Japan Society of
Mechanical Engineers, the Japanese Society for NonDestructive Inspection, the Society of Plant Engineers
Japan, and the Japanese Society of Tribologists.
Among the conferences held by these academic
societies are the Dynamics and Design Conferenceof the Dynamics, Measurement and Control Divisionof the Japan Society of Mechanical Engineers20) andthe Symposium on Evaluation and Diagnosis, which
is held jointly by the Dynamics, Measurement andControl Division of the Japan Society of MechanicalEngineers, the Society of Plant Engineers Japan,
and the Japanese Society of Tribologists. Numerous
condition monitoring and diagnostics research results
are published every year.
The following is a list of articles and papers
presented at these conferences over the past year or
two, focusing on bearing-related topics.
8.2 Examples of AI-based diagnostic techniques
In the field of bearing anomaly diagnosis, there havebeen recent studies on the use of AI technology for
intelligent and automated diagnostics techniques.
Deep learning, with its high feature extraction
capability has been garnering attention in theequipment diagnosis field in particular. In Japan,
Maeda et al. have been working on AI-based bearing
diagnosis. In one recent example, after removing
noise from vibration signals measured for bearing
diagnostics using a statistical information filter, thespectrum of the vibration signal was converted into aquadratic array (equivalent to image information). The
method automatically performed feature extraction
and state classification using a convolutional neuralnetwork (CNN), which is a type of deep learning26).
The results of various validation tests showed thatthe proposed method can achieve highly accurate
automatic diagnostics of bearings even in noisy
environments.
8.3 Examples of lubricant film evaluation techniques
Takeda et al. have verified the effect of differencesin lubricant composition on bearing life by using athrust ball bearing operating life test machine. The
test observed the lifetime until the thrust ball bearing
actually failed as a test piece. In addition, the effectof lubricant degradation on bearing life has also beenverified by observing the thickness of the lubricant
film after bearing failure in new oil and life tests using
a lubricant film visualization system. Recently, as a
new oil film evaluation method, an ECR (ElectricalContact Resistance) observation circuit was attachedThrice ACC (convenient method)
1

Rep. ACC

to the lubricant film visualization system (Fig. 25) toelectrically evaluate and observe the oil film condition,and the observation principle and results werereported27).

0.8

Twice ACC
(usual method)

0.6
0.2
0

Thrice ACC(usual method)

Once ACC(usual method)

0.4

0

1

2

3

4

5

6

7

8

9 10 11 12 13 14 15Time [hr]Fig. 26 Analysis of URIs with low signal-to-noise
ratios using a simplified method to improve
periodicity extraction of rolling behavior28)

8.4 Examples of diagnostic techniques using
ultrasound and acoustics
Wakabayashi et al. reported the efficacy of theultrasonic echo method for condition monitoringof bearings. They studied the early detection of
anomalies in oil-lubricated bearings by applying
autocorrelation analysis to the time variation ofultrasonic reflection intensity (URI). The higher theperiodicity of the URI waveform, the better the
rolling behavior of the bearing. Research has also
been conducted recently into the applicability of
the ultrasonic echo method to a grease-lubricatedbearing (6210 deep groove ball bearing). It was
shown that the method can detect rolling behavior
inside the bearing during operation and grease
removal and replenishment on the orbital plane in theactual working condition by performing two analyses
based on autocorrelation for the time variation of
the URI. In addition, methods were investigated forextracting periodicity of rolling behavior in URIs withlow signal-to-noise ratio (S/N ratio), which is often
obtained when diagnosing abnormalities in greaselubricated bearings by ultrasonic echo method. A
comprehensive method and a simplified method weredeveloped as methods to improve multiple analyses
by autocorrelation, and it was clarified that they wereeffective (Fig. 26)28).

1

Amplitude [V]Fig. 25 Equipment for electrical evaluation andobservation of bearing oil film condition27)

For highly accurate acoustic diagnosis of bearings,
Takada has proposed a new method for improving thesignal-to-noise ratio. Recently, he applied this method
to failure detection of rolling bearings and confirmed
its effectiveness.29) In particular, the effectivenessof this method was demonstrated by applying it tooperating conditions with low dN values, which are
generally considered difficult to diagnose (Fig. 27).
Furthermore, the S/N ratio improvement method using
an adaptive line enhancer, which is one of the adaptive
signal processing methods, was used as a subject forcomparison, which shows that the proposed method
was effective.

: Applied Data
: Not Applied Data

0.5
0
-0.5
-1

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5Time [s]Fig. 27 Time series data obtained by applying the
proposed method and an anti-aliasing filter(low-pass filter with a cutoff frequency of
40 [kHz]) to the measured rotating noise of abearing with outer ring failure29)
8.5 Examples of data collection techniques for
initial failure processes
Conventional research into the diagnostics ofbearings often involves scratching the inner orouter rings beforehand. In actual bearing condition
diagnostics, however, it is necessary to detect theearliest signs of any anomalies that could eventuallylead to failure. Inoue et al. focused on this point.
With the aim of collecting bearing data from thenormal state to the occurrence of failure in a timeefficient manner, they created a rotating device with avibratory mechanism that can apply displacement of
any frequency to the rotating shaft. They conductedvibration experiments on deep groove ball bearings as
the targets for inducing failure30). Failure progression

NTN TECHNICAL REVIEW No.89

19

The Current Situation of Condition Monitoring and Diagnosis of Machine Systems
was evaluated using acceleration data from the normal
state to the occurrence of initial defects (Fig. 28).
The degree of failure to the actual bearing was thenconfirmed by cut-off disassembly inspection.

Acceleration [m/s2]

0.20
0.15
0.10
0.05
0.00

0

10

20

0

10

20

30

40

50

60

70

30

40

50

60

70

Frequency [Hz]Acceleration [m/s2]

0.20
0.15
0.10
0.05
0.00

Frequency [Hz]Fig. 28 Envelope spectrum of acceleration signal(upper) before vibration, (lower) after
vibration30)

9. Conclusion
In this article, entitled “Trends in Condition
Monitoring and Diagnosis of Mechanical Systems”,
the author first describes the recent activities andtrends in ISO/TC 108/SC 5 condition monitoring anddiagnosis of mechanical systems with which he isinvolved1). Those interested to know more about thehistorical background to this subject may refer to theseries of documents 31)-34) compiled by the TC 108/SC 5 National Committee Chairman at that time.
Going forward, the international standardizationof condition monitoring and diagnosis of bearings
is expected to continue. It will develop along withthe standardization of condition monitoring asset
management in connection with the standardizationof individual machines. We look forward to continued
cooperation from all parties concerned.
Next, the status of condition monitoring and asset
management in Japan and overseas is described,
with a focus on the IoT. This field is expected to be
one of the biggest areas of development globally inthe field of condition monitoring and diagnosis. The
paper describes IoT-based condition monitoring anddiagnostics and predictive maintenance in wind power
generation projects. With the wind power generation
business undergoing full-fledged development inJapan with the installation of large floating offshore
wind turbines, condition monitoring techniques thatinvolve linkage to a digital twin are being developed.

20

NTN TECHNICAL REVIEW No.89

We look forward to seeing the development of thesefields in Japan.
In addition, the author also focuses on the trendof condition monitoring and diagnosis using 1DCAE
modeling of target machines in relation to thecondition monitoring technology using the digitaltwin described above. This field is also being actively
researched in Japan, and its future trends will beworth watching.
Finally, the research and publication trends
in the field of bearing condition monitoring anddiagnostics in Japan are described. Recently, thepublished proceedings of academic conferences
have tended to be extremely short. This makes it
necessary to actually visit the conference and listen
to live presentations. In the wake of social distancing
measures adopted during the COVID-19 pandemic,
academic conferences are adopting hybrid formats of
online and face-to-face meetings. I hope that there
will be a resumption in people visiting academic
conferences, exploring the latest trends, and engaging
in lively exchanges with researchers and technicians invarious fields.
The above is an introduction to the trends incondition monitoring and diagnostics of mechanicalsystems in the direction of this authorʼs interest andconcern, which it is hoped may be of some reference.
The author wishes to thank the Japanese Society for
Non-Destructive Inspection for granting permission to
include the citation in the first half of this paper1). For
providing information in the latter part of this paper,
I would like to express my gratitude to Mr. Hitoshi
Sakakida, ISO/TC 108/SC 5 committee member andformerly of Toshiba Corporation, Mr. Keita Ishimitsu
of JERA Co., Inc, Mr. Takashi Sako, formerly of Asahi
Kasei Corporation, to the Japan Institute of Plant
Maintenance, and to Professor Tadao Kawai of Osaka
Metropolitan University.
References
1) Tsuyoshi Inoue and Koji Hyodo, History and Current
Situation of ISO Standards on Condition Monitoringand Diagnostics of Machines and Activity of ISO/TC 108/SC 5 (Special issue on trends in condition
monitoring and diagnosis technology), Journal of theJapanese Society for Non-destructive Inspection, Vol.
69, No. 9 Sep, (2020) 442-448.
2) ISO/TC 108/SC 5 Condition monitoring anddiagnostics of machine systems website, https://www.iso.org/committee/51538.html
3) The Japan Society of Mechanical Engineers (JSME)
Certification Program for Machine Condition
Monitoring (Vibration, Tribology)
https://www.jsme.or.jp/jotaiweb/
4) Japanese Society for Non-Destructive Inspection
Certification System for Machine Condition
Monitoring and Diagnosis Engineers (Thermography)
http://www.jsndi.jp/quali_cation/index12n.html
5) Tsuyoshi Inoue and Koji Hyodo, editors, The
Japan Society of Mechanical Engineers, Condition
Monitoring and Diagnostic Techniques for Mechanical
Systems, Corona, 2021.

6)

T. Kawai, Equipment Diagnosis in the Continuing IoTEra, Journal of Economic Maintenance Tribology, No.
685, (2022) 26-29.
7) What is GAIA-X, a European cloud data infrastructure
initiative involving GAFAM, Fintech Journal, SB
Creative, 2021/04
https://www.sbbit.jp/article/cont1/56622
8) GAIA-X and Catena-X: The Rise of a Huge Ecosystemthrough Impact Data Linkage̶DX in Manufacturing:
For Promoting Servitization, Nomura ResearchInstitute, Column, 2022/07.
https://www.nri.com/jp/knowledge/blog/lst/2022/iis/
fujino/0727_1
9) Applying the Internet of Things to manufacturing 8
IoT use cases to boost ROI (IoT (Internet of Things)
adoption in the manufacturing industry, 8 IoT use
cases to improve ROI), Siemens website
https://resources.sw.siemens.com/ja-JP/e-book-8industrial-iot-use-cases-for-manufacturing-2
10) COMADEM (Condition Monitoring and Diagnostic
Engineering Management)
http://www.comadem.com/
11) Japan Institute of Plant Maintenance12) Strategic Maintenance Management System(MOSMS), Japan Institute of Plant Maintenancehttps://www.jipm.or.jp/report/?ca=113) Maintenance Science for Management, Japan
Institute of Plant Maintenance14) Hybrid of “Field Capability” and “MaintenanceManagement Capability”, Utilization of MOSMS“MOSMS”, Japan Institute of Plant Maintenance, 200815) Survey on the use of digital technology in wind power
generation, jointly conducted with The Offshore
Renewable Energy (ORE), Accenture and ORE
Catapult, UK
https://www.accenture.com/_acnmedia/PDF-151/
Accenture-210164-ORE-WindCatapult-POV-LCS-JP.
pdf16) Using Digital Technology in Wind Power Generation
Learning from Overseas Case Studies, Wind Power
Generation / Regional Industry Development andthe Use of Digital Technology (Online Seminar),
Accenture, May 13, 2022.
17) New Energy and Industrial Technology Development
Organization (NEDO), FY2013-FY2017 Result Report,
Research and Development of Wind Power andOther Renewable Energy Technologies, Research andDevelopment of Advanced Practical Application ofWind Power Generation, Research and Developmentof Smart Maintenance Technology (Analysis) (Fatigue
Prediction, etc.), February 2018.
18) Service Specification DNVGL-SE-0439, Certificationof Condition Monitoring, DNV• GL 2016, GL(Germanischer Lloyd)19) Takashi Sako, On IoT for predictive maintenance,
Plant engineer: Technology for new generationengineers & Information Magazine, Japan Institute of
Plant Maintenance, 52-4, (2020) 32-45
20) The Japan Society of Mechanical Engineers (JSME)
Dynamics, Measurement and Control Division web
page
https://www.jsme.or.jp/dmc/

21) Tadao Kawai, on a diagnostic method of equipmentusing physical models - Development to digitaltwin, Newsletter of the Japan Society of MechanicalEngineers, Dynamics, Measurement and Control
Division, No. 70 (July 2022) (available from thedivision website).
22) Koichi Ohtomi, and Takehiro Hato, Design Innovation
Applying 1DCAE, Toshiba Review Vol. 67. No. 7,(2012)
23) Shoichi Kashiwase and Kenji Ozaki, “Development of a
Model-Based Diagnostic Method for Electric Motors”,
Dynamics and Design Conference 2021, September
2021, 442.
24) Shoichi Kashiwase, Kenji Ozaki, Hiroaki Makino,
Development of a Model-Based Diagnostic Method
for Electric Motors, 19th Symposium on Evaluation
and Diagnosis, 208, 2021
25) Tadao Kawai, Yoshihiro Yamamoto, Tatsuro Ishibashi,
Estimation of Gear Wear Using a Physical Model,
Dynamics and Design Conference 2022, September
2022, 239
26) Linghe Maeda, Haihong Tang, Shanpeng Chen, Keishi
Mori, Yuji Yonekura, Intelligent State Diagnosis of
Bearings Using Statistical Information Filter andDeep Learning, 19th Symposium on Evaluation andDiagnosis, 106, 2021
27) Yusuke Takeda, Noriaki Satonaga, Masaya Kano,
Takashi Watanabe, Tomoyuki Sonoda, An Evaluation
and Observation Method of Oil Film Condition
by Electrical Contact Resistance Method, 19th
Symposium on Evaluation and Diagnosis, 210, 2021
28) Toshiaki Wakabayashi, Takahiro Nakatsu, Hideki
Yamasaki, Application of Ultrasonic Echo Techniqueto Diagnostic Evaluation of Grease Lubricated Bearing- Method of Detecting Periodicity in Rolling Behavior-,
19th Symposium on Evaluation and Diagnosis, 211,
2021
29) Hirotomo Takada, Hiromitsu Ohta, Shuji Miyazaki,
Daisuke Matsuo, Mirai Ohmori, Satoshi Shimizu,
High Precision Acoustic Diagnosis Method for LowSpeed Rolling Element Bearing, 19th Symposium on
Evaluation and Diagnosis, 202, 2021
30) Yuto Inoue, Tsuyoshi Inoue, Promotion Controlof Rolling Bearing Failure, 19th Symposium on
Evaluation and Diagnosis, 203, 2021
31) Hitoshi Sakakida, Takuzo Iwatsubo, The trend of
ISO/TC108/SC5 Mechanical Vibration and ShockCondition Monitoring and Diagnostics of Machines,
Proceedings of the 1st Symposium on Evaluation andDiagnosis, (2002) 32-36.
32) Hitoshi Sakakida, The trend of ISO/TC108/SC5
Condition Monitoring and Diagnostics of Machines,
Proceedings of the 5th Symposium on Evaluation andDiagnosis, (2006) 7-11.
33) Hitoshi Sakakida, The trend of ISO/TC108/SC5
Condition Monitoring and Diagnostics of Machines,
Newsletter of the Japan Society of MechanicalEngineers, (2007) 1.
34) Tsuyoshi Inoue, Present situation and trend of the ISO
standards for condition monitoring and diagnostics
of machines (TC108/SC5), Turbomachinery 39(5),(2011) 304-312.

NTN TECHNICAL REVIEW No.89

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The Current Situation of Condition Monitoring and Diagnosis of Machine Systems

Author Profile

Tsuyoshi Inoue
Ph.D. Professor, Department of Mechanical Systems Engineering, Graduate School of Engineering, Nagoya University

Academic and professional background
1993
Completed masterʼs program in Electronic and Mechanical Engineering, Graduate
School of Engineering, Nagoya University
1993-1995
Okuma Corporation
1995-2001
Assistant Professor, Faculty of Engineering, Nagoya University
2000
Doctor of Engineering (Nagoya University)
2001-2005
Lecturer, Graduate School of Engineering, Nagoya University
2004-2012
ISO / TC108 / SC5 National Committee Secretary
2005-2012
Assistant Professor, Graduate School of Engineering, Nagoya University(renamed Associate Professor in 2007)2012 - Present Professor, Graduate School of Engineering, Nagoya University
2012 - Present Chair, ISO / TC108 / SC5 National Committee
2013 - Present Chairman, Multibody Dynamics Council
2017 - Present ASME Journal of Computational and Nonlinear Dynamics Associate Editor
2018 - Present Director, Creation Plaza, School of Engineering, Nagoya University
2018 - Present Delegate, Turbomachinery Society of Japan
2021 - Present Vice-Chairman, Standard Project Committee, Japan Society of Mechanical Engineers
2022
Head of the Dynamics, Measurement and Control Division, Japan Society of MechanicalEngineers
Specialties• Mechanical mechanics, vibration engineering, nonlinear dynamics, vibration control• Explanation and use of vibration phenomena, in particular those caused by nonlinearity
Academic societies
Japan Society of Mechanical Engineers, Turbomachinery Society of Japan, Japan Society for Design
Engineering
The Japanese Society of Tribologists, ASME
Major awards and commendations
Fiscal 2000
Japan Society of Mechanical Engineers Japan Society of Mechanical Engineers Award
for Encouragement of ResearchFiscal 2006
The Japan Society of Mechanical Engineers, Dynamics, Measurement and Control
Division, Division Contribution Award
Fiscal 2013
Turbomachinery Society of Japan Award (Technology Award)
Fiscal 2016
Turbomachinery Society of Japan Award (Best Paper Award)
Fiscal 2018
Project Award, Tokai Branch, Japan Society of Mechanical Engineers
Fiscal 2019
Turbomachinery Society of Japan Award (Best Paper Award)
Fiscal 2020
Tokai Branch Distinguished Service Award, Japan Society of Mechanical Engineers
Fiscal 2020
25th Engineering Education Award, Japan Society for Engineering Education
Fiscal 2021
Turbomachinery Society of Japan Award (Best Paper Award)
Fiscal 2022
Japan Society of Mechanical Engineers (JSME) Medal for Outstanding Paper（2 papers）
Fiscal 2022
The Japan Society of Mechanical Engineers (JSME) Standard Project Award
Contribution Award

22

NTN TECHNICAL REVIEW No.89

Prospects

Efforts for Service & Solution Business in NTN

Hiroyuki KUREBAYASHI*
Rolling bearings are fundamental mechanical parts working in various
equipment that support our life activities. The failures on mechanical
Bearing
parts in the industrial equipment cause a stop of the equipment and
life
cycle
Bearing
supply management
induce a considerable amount of profit loss. It is important to monitor
service
Condition
the condition of temperature or vibration around the bearings, inmonitoring
order to prevent the unexpected stop of the equipment. NTN develops
bearings with sensing functions and provides condition monitoring service of the bearings. We are willing toprovide the service & solution, which is valuable to solve the customerʼs problems by using the sensing data.
Maintenance

1. Introduction
Machinery and equipment that have rotating
mechanisms support the abundant lives of people
today. Many of the machines and equipment used to
manufacture transport machinery such as automobiles
and railroads, as well as air-conditioning equipment
and household electrical appliances are equippedwith rotating mechanisms. Rolling bearings (hereafter,
bearings) are one of the major components used inthese rotating mechanisms. Bearings must rotatesmoothly while supporting the rotating shaft and beable to operate in a stable manner for long periods oftime. Although improvements in bearing performancecontinue, it is said that bearings are the cause of 30 %of all machinery and equipment failures1).
Since profit is lost when equipment stops due todefects in machine parts at the production site, it isimportant to monitor the temperature and vibration
around the bearing to prevent defects from occurring.
Furthermore, in the automotive sector, bearing
condition monitoring will become essential as growth
in autonomous driving results in people moving fromownership of automobiles to sharing them, in addition
to the development of infrastructure to support
autonomous vehicles.
As mentioned above, it is necessary to develop
a method (providing services) to use bearings ina stable manner for extended periods of time, notjust develop technology (providing products) forthe bearings themselves. In response to this, NTN
provides solutions that combine both products andservices that focus on bearing technology:• High-performance products that integrate sensing
functions with bearings (products)• Services that provide users with informationsuch as bearing condition diagnosis, appropriate
methods of use, and replacement periods (services)
Here, I will introduce an overview of the service andsolution business that NTN is working on and discuss
the future prospects. More detailed information
about the technology and applicable products will be

introduced separately in other articles in this technicalreview.

2. Sensing around the bearing
NTN has developed a bearing with a sensor thatcombines bearing and sensing functions with the aimof responding to the following customer needs:(1) Integrated multi-functions for bearings(2) Improved reliability for machinery, equipment,
and parts as well as support for maintenance(1) Implementation within compact machines
such as motors and pumps. Incorporating a sensing
function in the bearing provides an effective methodof saving space and reducing the person-hours for
assembly, etc. Sensing functions are used to measuresuch things as the rotational speed, rotational angle,
and load around the bearing, and are used to control
the operation of machinery.
(2) Implementation within large equipment thatmust operate in a stable manner and run for longconsecutive periods of time. Sensors embedded
into the bearing are used to monitor the bearingʼsoperating conditions, and to provide information
about bearing condition diagnosis such as whether
it is damaged. This aims to prevent unforeseen
problems and minimize stoppage time due to failure.
To diagnose the condition of a bearing, it is necessary
to sense such factors as its temperature, vibration(noise) and lubrication conditions (oil film thickness,grease degradation, foreign object contamination).
If production equipment or infrastructure-related
equipment suddenly stops operating, this will have asignificant impact on business operators and society.
Therefore, there is a strong demand in these sectors
for a bearing that will not fail, or at the very least anunderstanding of a suitable replacement period. NTN
provides technical services that achieve a high levelof accuracy in predicting and detecting when a failure
will occur. These services prove useful to customers inpreventing equipment-related problems and production
downtime.

* Deputy Corporate General Manager, Industrial Business Headquarters

NTN TECHNICAL REVIEW No.89

23

Efforts for Service & Solution Business in NTN

3.1 Rotation sensor bearing
The rotation sensor bearing is constructed byincorporating a magnetic sensor and magnetic
encoder in the bearing as shown in Fig. 1, and NTN
has created a lineup of several standard deep grooveball bearing numbers. Since a magnetic sensor isused, it is resistant to contamination compared withgeneral optical sensors and can also be used in hightemperature environments. This type of bearing isused to control the drive motor on forklifts and forwheel slip prevention control.

of accuracy. For example, when passing over a sectionof asphalt road covered in gravel, the rotational speed
changes spectrum varies2) as shown in Fig. 3. Using
this type of high-resolution signal can further enhance
the functionality of automotive control.
400
350

Frequency Hz

3. Implementation example of a bearing
with a sensor

300

Road covered in fine gravel

250
200
150
100
50
0
0

Magnetic sensor(Hall IC)

50

100

150

200

Run m

250

300

Fig. 3 Variance in speed change spectrum while driving2)
Sensor basic configuration
Magnetic
field
Bz

Hall IC
Magnetic encoder(NS-pole alternating
magnetization)

Fig. 1 Rotation sensor bearing2)
3.2 Automobile wheel speed sensor
A magnetic sensor to detect the wheel speed isfitted onto the bearings of automobile wheels (hubbearings) and used for controlling ABS (anti-lockbraking system). The seal on the hub bearing has abuilt-in rubber magnetization ring, which provides
high durability and prevents deterioration aroundthe wheel over an extended period even in harshenvironments. NTN has also developed the Hub
Bearing with an Integrated High-Resolution Rotation
Sensor2) that uses a magnetic sensor provided with aninterpolation function (Fig. 2).
For drive wheel

3.3 Multi Track Magnetic Ring for absolute angle
sensing
NTN has developed the Multi Track Magnetic
Ring3) as shown in Fig. 4. This magnetic ring is soldas a detection target for use in combination with amagnetic sensor for absolute angle detection. The
magnetic sensorʼs advanced interpolation function
and Multi Track Magnetic Ringʼs highly accurate
magnetic pattern make it possible to detect a single
revolution (360 degrees) with an angle resolutionof over 100 thousand divisions. Since it is magnetic,
it has superior environmental resistance whencompared to optical sensors, and its compact
configuration is suitable for saving space. It is used asa control sensor on robot joints and various types ofmotors.
Sub track (63 polar pairs)
Main track (64 polar pairs)
Rubber magnetic
material

Magnetic sheet is affixed toshow magnetization pattern

For driven wheel(b) Magnetization pattern

Core(a) External appearance

Fig. 2 Hub Bearing with an Integrated High-Resolution
Rotation Sensor2)
Wheel rotation signals include the impact oftire conditions (such as the air pressure) and roadconditions. Analyzing high resolution rotation signals
makes it possible for us to detect the differences intire conditions and road conditions with a greater level

24

NTN TECHNICAL REVIEW No.89(c) Illustrated
magnetization patternFig. 4 Multi Track Magnetic Ring: Radial
magnetization type3)

3.4 Sensor Integrated Bearing Unit for Machine Tool
SpindlesThe main shaft unit on a machine tool must supportcondition monitoring and IoT in addition to having
the fundamental ability of high speed, high rigidity,
and high accuracy, etc. NTN has developed the “Sensor
Integrated Bearing Unit” for Machine Tool Spindles,
which has various sensors integrated into the outerring spacer adjacent to the bearing to monitor theconditions inside the bearing and has a load detection
function and wireless communication function (Fig. 5)4).
These sensors detect deteriorating lubrication
conditions and signs of damage from vibration andtemperature sensing information to prevent defects.
Alternatively, they have been proposed for use inadjusting machining conditions by monitoring suchfactors as forming load and bearing pre-load amount.
Outer ring spacer(Various sensors are integrated)

Spindlebearing

4. Efforts for condition monitoring services
4.1 Trends in condition monitoring
In recent years, the concept of assessment
management, which targets the maintenancemanagement and operation of infrastructure suchas roads and buildings, is also being expanded to themachinery and equipment sector, and extensively
applied to areas from machine condition monitoring topart procurement control. In terms of the equipment
maintenance method, there has been a shift towards
CBM (condition-based maintenance, predictive
maintenance) from the conventional TBM (time-based
maintenance, preventive maintenance) method (Fig. 7).
Under such circumstances, efforts to monitor
bearing conditions during operation, detect signs ofdefects and then provide measures before problems
arise have attracted a great deal of interest.

Spindlebearing

Inner ring
spacerFig. 5 “Sensor Integrated Bearing Unit” for Machine
Tool Spindles4)
3.5 Talking BearingTM
NTN has developed a “Talking BearingTM” as theultimate form of a bearing integrated with sensing
functions (Fig. 6)5). This bearing has the same external
dimensions as a standard number bearing but also
has vibration, temperature, and rotation sensors aswell as a power generator, signal processing circuit
and wireless communication unit incorporated into
the bearing. The bearing generates power as it rotates
and results from sensors are sent wirelessly, allowing
the bearing to “talk” and convey information.
Currently, space is required to incorporate theelectronic circuit and power generator so there is alimit to the viable bearing size. However, the progress
being made in miniaturizing sensor devices andthe improvements in power saving will lead to theimplementation of much smaller diameter bearings
that use this concept in the future.
Electronic circuit board(Includes sensors and wireless device)
Material
to protect
circuitFig. 6 Talking BearingTM

Fig. 7 From time-based maintenance tocondition-based maintenance.
4.2 Introducing a condition monitoring system forfactory equipment
To operate large machinery and equipment,
continuous operation pumps and generators, etc.,
in a stable manner for extended periods of time it isvital to conduct suitable maintenance work based on
bearing condition monitoring, diagnosis technology
and the conditions. At large-scale equipment andimportant production lines, comprehensive condition
monitoring systems are introduced while regularinspection and daily maintenance work is conducted
constantly together with records for operation andmaintenance. In this manner, all companies haveestablished a condition monitoring and operation
management system for their entire factory to prevent
problems with large equipment.
In contrast, operation management is often
conducted individually for each machine when looking
at small-scale equipment. This creates the problem ofmaking it difficult to introduce condition monitoringmachinery and connect it to a unified systemfor operation because factories with small-scaleequipment use a mix of partially optimized systems
throughout the factory.
An IoT platform has been proposed to solve thistype of problem. The IoT platform is introduced toeach piece of equipment and then applications suchas measurement software are run on the equipment

NTN TECHNICAL REVIEW No.89

25

Efforts for Service & Solution Business in NTN
to make it easier for data and communication to besent between equipment as well as stored data to be
managed at a central location and facilitate mutual
use of such stored data.
NTN has developed a bearing diagnostic application(Fig. 8) that runs on Edgecross6), which is an IoT
platform. This application is provided as a condition
monitoring tool that requires no internet connection
or detailed settings7). See the commentary section for
more information about this application.

conditions and maintenance work cannot be
conducted easily. For this reason, remote monitoring
using a condition monitoring system (CMS) is
necessary, and the use of this type of system has
spread throughout Japan.
Mainbearing

Rotor

GearboxGenerator

Nacelle

Blade

Tower

Fig. 10 Large wind turbine structure

Fig. 8 Bearing diagnostic application
4.3 Portable Vibroscope
When personnel regularly take measurements atfixed points on equipment as they patrol and monitor
their worksite where TBM (time-based maintenance)is performed, there is a demand for a measuring
instrument that is easy to carry around and that caneasily record data. The NTN Portable Vibroscope8),
as shown in Fig. 9, is a useful tool for this type of
application.
Personnel can connect the device to a tablet PC ora smartphone, then measure and record vibrations at
the equipment to determine the conditions based on
predefined criteria or analyze condition trends. If theobserved data needs to be analyzed in more detail,a frequency analysis function is used to enable suchthings as coupling damage and bearing damage to bediagnosed.

Plans are underway in Japan to introduce large
wind turbines with the aim of creating offshore windturbine projects in the region of 10 GW by 2030 and
30 to 45 GW by 2040. One of the technical challenges
in this area is reducing the cost of power generation,and targets were indicated to achieve 8 to 9 yen per
kWh using seabed-mounted offshore wind turbines. To
achieve this, significant importance has been placedon reducing the cost of operation and maintenance(O&M), which accounts for 36 % of the lifetime cost ofwind turbines (Fig. 11).

Fig. 11 Lowering the cost of offshore wind turbines(Source: Found in documentation from the
Ministry of Economy, Trade and Industry9))

Fig. 9 NTN Portable Vibroscope
4.4 Trends in condition monitoring with large windturbines
Large wind turbines, as shown in Fig. 10, areinstalled at a height of over 60 meters above groundlevel and are often operated in difficult to accesslocations such as along the coast and in mountainous
areas. Weather conditions can also restrict work on
wind turbines so it is not easy to know the equipment

26

NTN TECHNICAL REVIEW No.89

4.5 Wind DoctorTM, a condition monitoring system
for wind turbines
NTN released Condition Monitoring System (CMS)for Wind Turbines “Wind DoctorTM” for sale in 2012.
Currently, this system is in operation at around 300
wind turbines throughout Japan10) 11). Wind DoctorTM
provides a monitoring service as shown in Fig. 12.
Sensors installed on the wind turbine are used toremotely collect and store data such as vibrations
on a regular basis for monitoring purposes. If an
abnormality or change is detected, the system
will promptly send information to the customer.

Customers using this monitoring service can use
this information for operation management andmaintenance work on their wind turbines.
As discussed above, offshore wind turbines are
more difficult to access than those built on land, andremote condition monitoring of key components suchas bearings is particularly important for offshore windturbines. Furthermore, it is believed necessary to
evolve and support condition monitoring systems sothat they can adapt to the weather conditions uniqueto Japan, such as typhoons and winter storms over
the Sea of Japan, which are said to be the strongest in
the world.
NTN has selected the two projects of “nextgeneration wind turbine technology development”
and “offshore wind turbine operation maintenanceenhanced functionality” for NEDO Green Innovation
Fund Projects12) and started activities on theseprojects from FY202213). These projects promotetechnological research and development fromboth sides of “products” and “services” in terms ofdeveloping improvements for bearings and enhancing
the functionality of CMS.
Data is automaticallycollected

Data is stored,
automatic diagnosis

Monitoring
analysisDatacollection
systemInformation
and results arereported
Assists O&M for wind turbines

Fig. 12 Wind DoctorTM monitoring service

uses observed data from the actual machine and is
working on the continuous operation of this system. At
the same time, we are focusing on developing sensor
devices for collecting sensing information centeredon bearings, as well as providing measurement tools,
which we consider to be especially important.
5.2 Solutions provided by NTN
The following types of information are required byequipment operation sites to monitor the conditions
and sense around the bearing.
(1) The decision about whether operating conditions
are suitable or not(2) The estimated progress of damage if it has
occurredTechnology shown below is required to provide
this information and requires a great deal of timeand effort such as expert level training and much
experience.
• Fundamental knowledge of bearings and condition
diagnosis technology• Sensing technology and signal processing
technology• Technology to automate condition assessment,such as AI diagnosis• Expertise in issues unique to bearings
Business operators who run equipment needcondition diagnosis information for the entire
machine, not just for the bearing condition. Therefore,
comprehensive assessment technology thatincorporates information from around the machineis required. Furthermore, depending on the uniquecharacteristics of the operated equipment, we may
also be able to consider operations that combine
information from a wide range of fields. For example,
we may be able to use various data such as weather
data, financial data, social events, or currency
exchange information and apply it to data analysis
for equipment operation management through tasks
such as considering procurement costs and the timingof repairs.

5. Efforts for the solution business
5.1 Using sensing data
Generally, condition monitoring systems diagnose
equipment conditions using diagnosis parameters
derived from such things as vibration data measured
around bearings. It is possible to calculate many
diagnosis parameters, but it is difficult to selectparameters that are viable for diagnosis because they
are different for each piece of equipment.
If diagnosis parameters have previously been
selected through observation and experience, anda large volume of data has been stored that shows
the relationship between the measured data anddamage, then it is possible to teach an AI system toautomatically select viable diagnosis parameters. Also,
analyzing cases of observed damage and defects canalso improve the design of machinery and equipment
and their operation method. The more we can store
actual data from the machine, the greater we can
improve accuracy in assessing the conditions relating
to the equipment.
NTN continues to build a system that stores andFig. 13 Service & Solution Business in NTN
Many business operators feel it is important tofocus on operation and management that uses
collected data rather than spending the effort tobuild and maintain a monitoring system. As shownin Fig. 13, NTN will continue to develop services
that provide solutions that can be used in business

NTN TECHNICAL REVIEW No.89

27

Efforts for Service & Solution Business in NTN
operations, such as equipment maintenance planning,by extracting information beneficial to the customer
and information required to resolve problems throughactivities such as monitoring the condition of bearings
incorporated in equipment.
5.3 Development of wind turbine maintenance businessIn addition to condition diagnosis based on CMS forwind turbines, NTN is working to optimize operationand maintenance and its use in operation control.
In the long term, we will develop long operating
life bearings by analyzing CMS data and cases ofbearing damage, while promoting the provision of a
total service for aftermarket bearings and inspection
maintenance to reduce O&M costs for offshore windturbines.
In the wind turbine sector, NTN has started
an initiative14) in the maintenance business incollaboration with Hokutaku Co., Ltd. By optimizing
the operation and maintenance of wind turbines
based on CMS information (smart maintenance) andcollaborating on the development and procurement ofbearings, and operation and maintenance services, as
shown in Fig. 14, NTN will achieve bearing life cycle
management and continue to contribute to society.

Data Acquisition System

Wind power Companies

Fig. 14 Bearing life cycle management

6. Summary
NTN not only sells products but also provides
services to resolve customer problems. Efforts inthis area will be focused on developing softwarethat analyzes sensor signals and software that
controls machinery to create new value. Additionally,
we will provide aftermarket bearings and develop
improvements in new bearings based on collected
information and build life cycle management forbearings centered on bearings and their monitoring
information.
In the future, we will build a business model thatuses this big data and promote service and solution
business that will lead to improved NTN brand value.
References
1) Japan Lubricating Oil Society, Lubrication
Management Optimization Promotion
Investigation Report, 1995.
2) Kentaro Nishikawa, Toru Takahashi, C. Duret,
Hub Bearing with an Integrated High-Resolution
Rotation Sensor, NTN TECHNICAL REVIEW,
No.81, (2013)52.

28

NTN TECHNICAL REVIEW No.89

3)

Takashi Koike, Yasuyuki Fukushima, Yusuke
Shibuya, Hiroyoshi Itou, Development of Multi
Track Magnetic Ring for High Accuracy Absolute
Angle Detection, NTN TECHNICAL REVIEW,
No.86, (2018) 45.
4) Shohei Hashizume, Yusuke Shibuya, Daichi
Kondo, Yohei Yamamoto, Hiroyuki Iwanaga,
Development of Sensor Integrated Bearing Unit
for Machine Tool Spindles, NTN TECHNICALREVIEW, No.88, (2020) 33.
5) NTN, Press Release, NTN Develops Sensor
Integrated Bearing “Talking BearingTM”.
https://www.ntn.co.jp/japan/news/new_
products/news202200041.html
6) Edgecross Consortium,
https://www.edgecross.org/
7) NTN, Press Release, Extension on Period toProvide Free Trial Version of Bearing Diagnostic
Application.
https://www.ntn.co.jp/japan/news/new_
products/news202200022.html
8) NTN, Portable Vibroscope, NTN TECHNICALREVIEW, No. 87, (2019) 106.
9) METI, R&D and Public Implementation Plan
Formulated for “Cost Reductions for Offshore
Wind Power Generation” Projects
https://www.meti.go.jp/shingikai/sankoshin/green_
innovation/green_power/pdf/001_04_00.pdf10) Makoto Miyazaki, Wataru Hatakeyama,
Application of Condition Monitoring System(CMS) for Wind Turbines, NTN TECHNICALREVIEW, No.86, (2018) 40.
11) Katsuyoshi Suzuki, Deployment and Improved
Reliability of the Condition Monitoring System forWind Turbines, NTN TECHNICAL REVIEW, No.88,(2020)111.
12) NEDO, Started Green Innovation Fund Project“Offshore Wind Turbine Cost Reduction”.
https://www.nedo.go.jp/news/press/
AA5_101505.html
13) NEDO, Business Overview Documentation of“Green Innovation Fund/Offshore Wind Turbine
Cost Reduction” Project.
https://www.nedo.go.jp/content/100941539.pdf
14) NTN, Press Release, NTN Starts Maintenance
Service for Wind Turbines.
https://www.ntn.co.jp/japan/news/press/
news202200031.html

Photo of author

Hiroyuki KUREBAYASHI
Deputy Corporate
General Manager,
Industrial Business
Headquarters

Commentary

Development of Remaining Useful Life Prediction
Technology for Rolling Bearings Under Flaking Progression

Masashi KITAI*In recent years, due to aging equipment and the lack of maintenance personnel, there is increasing
interest in advanced predictive maintenance, and rolling bearings are attracting attention as a target. In
general, rolling bearings are replaced when some kind of damage occurs. However, in some cases where
maintenance is not easy, they may continue to be used even after the damage has occurred as long as it
does not affect peripheral equipment. This paper introduces a developing AI method for predicting theremaining useful life of rolling bearings under flaking progression.

1. Introduction
Interest is growing for enhanced functionality andautomation of maintenance technologies amid the
backdrop of increased maintenance costs due tolong-term deterioration and the increasing burden
on workers due to the lack of maintenance personnel
in manufacturing, infrastructure and similar related
equipment. In recent years much attention has
been given to technology relating to “predictive
maintenance”, a method which involves detecting
abnormal signs of operation so that maintenance canthen be performed. This method is more efficient than
“preventive maintenance”, which involves regularly
maintaining equipment regardless of its condition or“corrective maintenance”, which involves maintaining
equipment after a failure has occurred. NTN has
increased activity in this area by introducing thesetechnologies in maintenance using IoT and AI1).
Rolling bearings are machine elements that is vitalto equipment and are a key element in supporting
machine rotation. In cases of equipment failure, it
is said that roughly 30 % of failures are caused byrolling bearings2). Based on this fact, it is desirable
to estimate the condition of rolling bearings andrepair or replace them at the proper time to reduce
maintenance costs for the entire machine.
Vibration acceleration is often used to diagnoserolling bearings because it can be measured without
interrupting the machine and is highly sensitive todamage3). Diagnostic methods that use vibration
acceleration predict damage conditions using statistics
such as the root mean square value and kurtosis, aswell as specifying areas of damage using frequency
analysis. There has been much recent activity in R&D
development to predict the damage conditions andremaining useful life of rolling bearings in line with thedevelopment of AI technology such as deeplearning4), 5), 6).

This paper introduces AI technology7) developed to
predict remaining useful life up to when it is necessary
to replace the bearings and is applicable to rolling
bearings after damage has occurred.

2. Development background
Generally, the life of a rolling bearing is often
considered to be when some type of damage occurs
on the bearing raceway surface, such as flaking or
indentation. However, depending on the environmentand conditions in which the bearing is used, it is noteasy to replace rolling bearings and these bearings
may continue to be used even after minor damage
has occurred because of the significant maintenancecosts involved.
If rolling bearing damage progresses, there will
be a sudden increase in vibration, which will cause
damage to the machine as well as other elements andwill likely lead to increased downtime. Therefore, it isdesirable to be able to predict the remaining usefullife up to when the bearing needs to be replacedby estimating the extent of damage on the rolling
bearing (hereafter, damage condition). However, mostresearch into remaining useful life prediction of rolling
bearings mentioned above does not describe thedamage condition of rolling bearings.
Therefore, this paper will introduce the technologythat was developed with the aim of predicting theremaining useful life with high accuracy, by expressinga regression model of the relationship between thedamage condition and remaining useful life for rolling
bearings where damage is in progress.

* Advanced Technology R&D Center

NTN TECHNICAL REVIEW No.89

29

Development of Remaining Useful Life Prediction Technology for Rolling Bearings Under Flaking Progression

4. Characteristics of development
technology

Fig. 1 shows the relationship between the operatingtime and vibration when using a cylindrical roller
bearing. Operation continued until the circumferential
length of flaking that occurred on the inner ring
raceway surface exceeded the rolling element pitch
length8). The horizontal axis shows the load count
while the vertical axis shows the change relative to theroot mean square (RMS) initial value of the vibration
acceleration (RMS relative value). The figure also
shows an external view of the flaking on the inner ring
raceway surface for a specific time. Flaking occurred
at a load count of approximately 900 thousand times.
Flaking on the raceway surface first develops mostly
in the axial direction (range A in Fig. 1), and when thelength of flaking in the axial direction reaches the rolling
element contact length, flaking mostly progresses
along the circumference after this (the direction inwhich the rolling element moves) (range B in Fig. 1).
RMS increases quickly while flaking progresses in theaxial direction, and while flaking mostly progresses
along the circumference, RMS increases slower
and fluctuations follow the same trend. As flaking
progresses further, if the length of flaking along thecircumference reaches the rolling element pitch length(range C in Fig. 1), RMS increases rapidly once again
and the fluctuation range also increases.
When this type of vibration increases, displacement
between the inner and outer rings of the rolling
bearing increases the risk of exceeding the range ofacceptable clearance for peripheral components,
which will result in damage to the peripheral
components. Consequently, it is best to stop
operation before the flaking circumferential length
reaches the rolling element pitch length. This study
regarded the bearing replacement time to be when
the circumferential flaking length reaches half of therolling element pitch length.

This chapter describes the overview for development
technology.
4.1 Development technology
Fig. 2 shows an overview of development technology.
Development technology consists of a combination of
Feature Fusion Network (FFN)7) as indicated in section
4.2 and Hierarchical Bayesian Regression, HBR9) as
indicated in section 4.3. Using a short time Fouriertransform (STFT) (see Fig. 3)10) spectrogram to input
vibration acceleration time series data, FFN can predict
maximum circumferential flaking length (hereafter,
flaking size) and remaining useful life (hereafter, SS
remaining life) as a snapshot (a single output for asingle input data set). Next, from the flaking size andSS remaining life predicted by FFN, HBR can be used
to output the remaining useful life regression equation,
remaining useful life and its distribution.
Measurement
data
Pre-processing
Spectrogram

Flaking size

Remaining useful life curve

Fig. 2 Development model overview

Traveling direction of rolling element

Fourier transform

A

30

B

C

20

0

50

100

150

200

Load count x 106 times

250

Fig. 1 Relationship between flaking progress andvibration acceleration8)

30

Time
Time series waveform

High

Low
Time
Spectrogram

Fig. 3 Illustration of short time Fourier transform

10
0

…

Frequency

Amplitude
RMS relative value

40

SS remaining useful life

Amplitude

3. Flaking progress and vibration
acceleration on rolling bearings

NTN TECHNICAL REVIEW No.89

4.2 Feature Fusion Network
FFN is a regression method based on a convolutional
neural network (CNN)11) in deep learning and is often
used for image recognition. Fig. 4 shows an illustrationof FFN. Normal CNN directly predicts corresponding
objective variables just from data input at the time of
the measurement. FFN calculates a deterioration index(a normalized index in a range of 0 to 1 for the state ofdeterioration) at each point in time from data input frommultiple times in the past. The deterioration index isthen vectorized with a measured permutation to createa deterioration index vector, which is then used as anintermediate variable with the aim of improving theprediction accuracy of the objective variables (flaking
size and SS remaining useful life).
Objective variables

Feature vector

Feature vector

Deterioration index vector

Deterioration index

Input data
(Measurement point)

5. Evaluation test
5.1 Test equipment and measurement data
A schematic drawing for test equipment used toevaluate development technology is shown in Fig. 5,
while test conditions are shown in Table. 17). A cylindricalroller bearing (number NU224, bore diameter 120 mm,
outer diameter 215 mm) was used as the test bearing.
Operation continued until the bearing reached its limit
of use after the initial flaking that occurred on the
bearing raceway surface, and both vibration accelerationand flaking size were measured at regular intervals.
Measurements were taken for a sample of 33 bearings.
Fig. 6 shows the relationship between the operatingtime and RMS from when the initial flaking occurred oneach bearing sample until the bearing reached its limit ofuse. Fig. 7 shows the relationship between the operatingtime and flaking size. At the end of flaking progress,
RMS fluctuated significantly, and this made it difficult
to accurately know the flaking conditions. Despite thefact that all 33 bearing samples were tested under thesame operating conditions, the remaining useful life, up
to when the bearing limit of use was reached, differedsignificantly among the bearing samples. Therefore, inorder to improve the accuracy of predicting remaining
useful life, it is necessary to consider fluctuations infeature quantities of vibration acceleration as well as
individual differences in remaining useful life.

Input data
(Measurement point + past)

Vibrational acceleration
sensorRolling bearing

Fig. 4 Feature fusion network overview
4.3 Hierarchical Bayesian regression
Since the previously mentioned SS remaining usefullife is predicted with a snapshot, the predicted valuechanges for each measurement time. In practical use,
the regression curve for remaining useful life is definedby a monotonically decreasing function because itis preferable for the remaining useful life predictedvalue to monotonically decrease as operating time
elapses. In addition to the above, HBR was used7) asa method to consider variations between individual
bearings during this development. HBR uses all pastdata before the measurement point to obtain theremaining useful life and regression curve. Morespecifically, differences in individual bearings are
assumed to vary based on a probability distribution
so that individual remaining useful life regression
curves can be handled for each bearing. This enables
relatively accurate predictions for remaining useful life
output at the end, even for individual bearings whose
SS remaining useful life greatly deviates from theaverage obtained from all learned data.

SpindleHousing

Load

Fig. 5 Test equipment7)
Table 1 Test conditions7)
Rolling bearing

Cylindrical roller bearing (number: NU224)

Main shaft
500 min-1
rotational speed
Radial load

90 kN

Measurement
data

Vibration acceleration (vertical direction)

Bearing sample
quantity

33 pieces

NTN TECHNICAL REVIEW No.89

31

Flaking size mm

Fig. 6 Relationship between operating time and RMS

Operating time hFig. 7 Relationship between operating time andflaking size
5.2 Evaluation metrics
2
The coefficient of determination R was used in the2evaluation metrics of the development method. R is
an indicator of the degree to which a predicted valueof the objective variables (flaking size or remaining
useful life in this case) matches the actual value(hereafter, true value), and is shown in equation (1)below.
R =1−
2

Σ nk −1(yk−ŷk)2Σ nk =1(yk−y)2(1)

Here, yk and ŷk denote the true value and predictedvalue of the objective variables at measurement time k,
respectively. Furthermore, y denotes the true value
average of the objective variables while n denotes the2number of data. R can be a value of 1 or less, and thelarger the value (closer to 1), the higher the prediction
2
accuracy. R was calculated for each bearing sample,
and both the average and variation of predicted values
calculated using leave-one-out cross-validation12)
were evaluated. Furthermore, the whole range,from when flaking occurred until it was necessary
to replace the bearing, was divided into two ranges
which were the early stage and late stage. Both ofthese stages were evaluated. Here, the range in which
flaking mostly progressed in the axial direction was
taken to be the early stage, while the range in which
flaking progressed along the circumference was taken
to be the late stage.

32

NTN TECHNICAL REVIEW No.89

R2 Score (Coefficient ofdetermination)

Operating time h

5.3 Flaking size and SS remaining useful life
prediction results using FFN
This section provides a comparison of FFN with thevarious regression methods and evaluates the accuracyof predicting flaking size and SS remaining useful life.
Kernel Ridge (KR)13), Random Forest (RF)14), Support
Vector Regression (SVR)15), Neural Network (DNN)16)
with 4 hidden layers, and CNN were used as comparison
methods. Similar to the development method, CNN
inputs the vibration acceleration spectrogram and does
not consider past data. Moreover, for KR, RF, SVR and
DNN, statistics in the time domain, frequency domain
and cepstral domain (RMS, maximum value, peak factor,
kurtosis, skewness, RMS after envelope processing17))
were used as inputs after various band pass filtering wereapplied to vibration acceleration. Hyper-parameters ofthe development method and comparison methods
were then selected as optimal values using 5-fold crossvalidation12).
Fig. 8 shows a box plot of comparison results for theaccuracy of predicting flaking size, while Fig. 9 showsa box plot of comparison results for the accuracy of
predicting SS remaining useful life.

1.0：Early stage：Late stage：Average

0.5
0.0

-0.5
-1.0

KR

RF

SVR

DNN

CNN

FFN

Fig. 8 Flaking size prediction accuracy (w/o HBR)7), 17)

R2 Score (Coefficient ofdetermination)

RMS m/s2

Development of Remaining Useful Life Prediction Technology for Rolling Bearings Under Flaking Progression

1.0：Early stage：Late stage：Average

0.5
0.0

-0.5
-1.0

KR

RF

SVR

DNN

CNN

FFN

Fig. 9 SS remaining useful life prediction accuracy(w/o HBR)7), 17)
All four methods, excluding KR and DNN, had
2
an average R of 0.7 or higher for the flaking
size prediction during the early stage of flaking
progression. In particular, FFN prediction accuracy2
had the highest value. Additionally, the average R
for CNN and FFN was high during the late stage offlaking progression. However, because CNN prediction
accuracy worsened for specific samples, on average
CNN was significantly lower than FFN. Therefore, FFN
has the highest prediction accuracy for predicting theflaking size.

5.4 Remaining useful life curve using thedevelopment method
Fig. 10 shows the relationship for the median andprediction distribution of the remaining useful life
curve and damage progression using HBR. In thisfigure, measured data in the range used for HBR
learning is shown to the left of the red dotted line.
Measured data in the prediction range is shown to
the right of the red dotted line. The black line shows
the prediction curve using HBR. Furthermore, thedark grey area shows a 50 % level of confidence
range while the light grey area shows a 95 % level ofconfidence range. The three graphs in the figure show
prediction results for remaining useful life at points
where 10 %, 20 % and 50 % data was measured outof all measurement data for the bearing from the left,
respectively. A dashed line is also shown in the figure
to represent the limit of use (life criteria) as definedin chapter 3. The prediction curve approaches thetrue value and the range for the level of confidence
became narrower as measurement data increased
with the progression of damage. Therefore, therelationship between remaining useful life and damage
progression using HBR can be expressed as a curvewith a prediction distribution (reliability of predictedvalues). Furthermore, increasing measurement data
improved the remaining useful life prediction accuracy
and increased the reliability of the predicted value.
Fig. 11 shows a box plot of remaining useful life
prediction accuracy due to the development method(the combination of FFN and HBR). For comparison,
the figure shows the prediction results for RF and HBR
combined, CNN and HBR combined, and FFN by itself.
During the damage early stage, the development
method has improved accuracy in comparison withthe other methods. In particular, the interquartile
range becomes smaller, confirming that variation in
the bearing sample is smaller. This method also hasa high prediction accuracy compared with the othermethods during the damage late stage, with the2
only average R exceeding 0.5. Therefore, using thedevelopment method can predict remaining useful life
with high accuracy more than conventional methods.

Measurement Prediction

Remaining useful life

the early stage of flaking progression compared with
KR, RF and SVR. Among these three methods, FFN
had the highest prediction accuracy. All methods had
a lower prediction accuracy during the late stage offlaking progression compared with the early stage offlaking progression. However, RF and the development
method maintained a comparatively high accuracy
out of all the methods.
Based on these results, we can see that FFN
maintains a high prediction accuracy for both flaking
size and SS remaining useful life in comparison withthe other general regression methods.

Measurement Prediction Measurement Prediction

60

60

60

40

Limit of use 40
20

Limit of use 40
20

20
0

0
10 20
Number of measurement
data: 10 %

0

0
10 20
Number of measurement
data: 20 %0

Limit of use

0
10 20
Number of measurement
data: 50 %Flaking size

Fig. 10 Relationship between flaking progression
and remaining useful life prediction distribution7)

R2 Score (Coefficient ofdetermination)

The three methods DNN, CNN and FFN have a highR2 for the SS remaining useful life prediction during

1.0：Early stage：Late stage：Average

0.5
0.0

-0.5
-1.0

RF＋HBR

CNN＋HBRFFN
Development(w/o HBR)
methodFig. 11 Remaining useful life prediction accuracy7)

6. Summary
This paper compared and verified general machinelearning methods and their performance for aremaining useful life prediction method developed totarget rolling bearings after damage has occurred. It
confirmed that using the development method canpredict the remaining useful life with high accuracy
until the time the rolling bearing needs to be replaced
after damage has occurred. Therefore, use of thisdevelopment method enables us to obtain a guideline
for using rolling bearings in the range where thedisplacement between the inner and outer rings does
not exceed the acceptable clearance for peripheral
components even when operation is continued after
flaking has occurred on a rolling bearing. Equipment
such as pumps and fans used in special environments
are an example of equipment that continue to be
used even after the rolling bearings are damaged. In
the future, NTN will continue working on increasing
the versatility of this development technology while
contributing to the reduction of maintenance costs on
various equipment.

NTN TECHNICAL REVIEW No.89

33

Development of Remaining Useful Life Prediction Technology for Rolling Bearings Under Flaking Progression
References
1) METI, “Collection of Advanced Studies in Smart
Security”, April 2022.
https://www.meti.go.jp/policy/safety_security/
industrial_safety/smart_industrial_safety/
jireisyu_r3.pdf, (See 2022-8-10).
2) Japan Lubricating Oil Society, “Lubrication
Management Optimization Promotion
Investigation Report”, 1995.
3) ISO10816-3:2009/Amd1:2017, “Mechanicalvibration -Evaluation of machine vibration bymeasurements on no-rotating parts -Part3:
Industrial machines with nominal power above 15
kW and nominal speeds between 120 r/min and15000 r/min when measured in situ -Amendment
1”，(2017).
4) Y. Lei, N. Li, L. Guo, N. Li, T. Yan and J. Lin,
“Machinery health prognostics: A systematic
review from data acquisition to RUL prediction”,
Mechanical Systems and Signal Processing,vol.104, (2018) 799-834.
5) S. Ramezani, A. Moini and M. Riahi, “Prognostics
and health management in machinery: A review ofmethodologies for RUL prediction and roadmap”,
International journal of industrial engineering &management science, vol.6, issue 1, (2019) 38-61.
6) Z. Xia, Q. Guan, Y. Gao, X. Chen and X. Zhai,“Review on remaining useful life prediction
methods of bearing”, 2020 11th international
conference on prognostics and system healthmanagement (PHM-2020 Jinan), (2020) 429433.
7) M. Kitai, T. Kobayashi, H. Fujiwara, R. Tani,
M. Numao and K. Fukui, “A framework forpredicting remaining useful life curve of rolling
bearings under defect progression based onneural network and Bayesian method”, IEEE
Access, vol.9, (2021) 62642-62652.
8) M. Kitai, H. Tsutsui, R. Tani and T. Sakaguchi“Investigation into the Relationship between
Bearing Damage Progression and Vibration
Feature Quantities”, Tribology Congress, Spring
2019, Tokyo, (2019) 1-2.

Photo of author

Masashi KITAIAdvanced
Technology
R&D Center

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9)

M. S. Hamada, A. G. Wilson and C. S. Reese,“Bayesian Reliability”, Springer (2018).
10) J. Allen, “Short term spectral analysis, synthesis,
and modification by discrete Fourier transform”,

IEEE transactions on acoustics, speech, andsignal processing, vol.25, no.3, (1977) 235-238.
11) Y. LeCun, L. Bottou, Y. Bengio and P. Haffner,“Gradient-based learning applied to document
recognition”, Proc. of the IEEE, (1998) 1-46.
12) C. M. Bishop, “Pattern recognition and machinelearning”, Springer, (2006) 32-33.
13) C. Saunders, A. Gammerman and V. Vovk, “Ridge
regression learning algorithm in dual variables”,
Proceedings of the 15th international conferenceon machine learning, (1998) 515-521.
14) L. Breiman “Random forests”, Machine learning,vol.45, (2001), 5-32.
15) V. N. Vapnik, “Statistical learning theory”, Wiley,(1998).
16) D. E. Rumelhart, G. E. Hinton and R. J. Williams,“Learning representations by back-propagating
errors”, Nature, vol.323, (1986) 533-536.
17) M. Kitai, Y. Akamatsu, R. Tani, H. Fujiwara,
M. Numao and K. Fukui, “Remaining useful life
curve prediction of rolling bearings under defectprogression based on hierarchical Bayesian
regression”, Proc. European conference on
artificial intelligence 2020, (2020) 2986-2992.

Commentary

Development of Sensor Integrated Bearing“ Talking BearingsTM ”

Yasuyuki FUKUSHIMA*
Yosuke TOYOGUCHI*
Kohei MATSUBAYASHI*

Tomomi GOTO*
Daigo IKKE*

There has been a growing demand for equipment condition monitoring using
IoT technology to reduce equipment downtime and improve production
efficiency. NTN has developed Talking BearingsTM that integrate sensors,a power generation unit, and a wireless device to standard bearings, inorder to meet this demand. This paper introduces the features, structure, and performance test results of thedeveloped bearing.

1. Introduction
There has been an increased demand to reduce
equipment downtime as much as possible to increase
production efficiency1). Similar strong demands havebeen made to increase utilization even in power
generation facilities and infrastructure. To respond tothese demands, it is effective to monitor equipment
conditions to prevent sudden equipment stoppages
and plan for maintenance and part replacement
periods2) 3).
NTN has developed the “Condition Monitoring
System for Wind Turbines (Wind DoctorTM)”4), the“Sensor Integrated Bearing Unit” for Machine Tool
Spindles5), the “Bearing Diagnostic Application
for Industrial IoT Platforms”6), and the “Portable
Vibroscope”7) as shown in Fig. 1 to meet the needsof condition monitoring at this type of equipment.
We have also been releasing devices and analysis
software to the market for the purpose of bearing
condition monitoring.
It is important to provide devices that are extremely
useful and can detect bearing conditions with highsensitivity to achieve a condition monitoring service
that will bring a high level of satisfaction to users.
Rolling bearings are incorporated into all kinds ofmachines such as transport machinery, household
appliances and industrial machinery to support
rotation. Including sensors in rolling bearings is
considered to be an ideal data collection element formonitoring the condition of machines.
With this in mind, NTN has developed the sensor
integrated bearing “Talking BearingTM” with built-in
sensors, a power generation unit and wireless device
in a standard bearing**, without changing the bearing
size and load carrying capacity. This paper introduces
the structure of this developed product, its features,and results from performance tests.

The “Talking BearingTM” detects the bearing
condition using sensors and sends the sensor
information wirelessly so its name is derived fromthe fact that we can understand the condition of the
bearing as though it is talking to us.
**Rolling bearings that comply with international standards interms of their boundary dimensions and type(a) Condition Monitoring System forWind Turbines「Wind DoctorTM」(b) For Machine Tool Spindles“Sensor Integrated Bearing Unit”(c) Portable
Vibroscope

Fig. 1 Products used for condition monitoring* New Product Development R&D Center

NTN TECHNICAL REVIEW No.89

35

Development of Sensor Integrated Bearing “Talking BearingsTM”
2. Features and structure
2.1 Features
This section provides the main features of thedeveloped product.
(1) Advanced condition monitoring and abnormality
diagnosis
The sensors are built into the bearing so they can
detect bearing conditions with greater sensitivity thanif the sensors had been installed on equipment. Thiscan diagnose abnormalities early.
(2) Compatibility
Sensors, a power generation unit and wireless device
have been built into a standard bearing withoutchanging the bearing dimensions or load carrying
capacity. This makes it easy to replace bearings used
on existing equipment.
(3) Very convenient
The sensors and wireless devices operate using thepower generated by bearing rotation to automaticallysend sensor information wirelessly. This requires nocables to supply power or transmit data.
2.2 Structure
2.2.1 Overall structure
The structure of the developed product is shownin Fig. 2. A power generator and electronic circuit
substrate are arranged at one end of the bearing
used at the inner ring rotation. A stator is fixed tothe bearing outer ring and coils are held in place by
the stator. A rotor (a magnetic ring that is alternately
magnetized by the N and S-poles) is also fixed tothe bearing inner ring. AC voltage is generated in thecoils by the action of electromagnetic induction as
the inner and outer bearing rings rotate relative toeach other. The electronic circuit substrate, which ismounted with circuits, sensors and wireless devices,
is fixed to the bearing outer ring via the stator andalso sealed with material that protects the electronic
circuit.
Electronic circuit
substrate

StatorRotor(Magnetic ring)

Material to protect
electronic circuit

Fig. 2 Structure of Sensor Integrated Bearing“Talking BearingsTM”

36

NTN TECHNICAL REVIEW No.89

2.2.2 Electronic circuit
A functional block diagram and power supply circuit
block diagram for the developed product are shown in
Fig. 3 and Fig. 4, respectively. AC voltage generated
by the power generator is input to the power supply
circuit. The power supply circuit rectifies AC voltage
into DC current, and also steps down any voltage
obtained beyond what is required to the designatedvoltage. Following this, a fixed voltage required forsensor and wireless module operation is obtainedusing a step-up/step-down DC-DC converter. The
fixed voltage activates the sensors, and the obtained
sensor signals are sent by radio waves through thewireless device.
Electronic circuit
Power generator

Power supply circuit

Sensors

Wireless device

Fig. 3 Functional block diagram for developed
product

Power supply circuit
Rectifier circuit

Voltage limiting circuit

Step-up/step-down
DC-DC converter

Fig. 4 Power supply circuit block diagram

3. Specifications
Table 1 shows the specifications for the developed
product. Such things as acceleration, temperatureand rotational speed are provided in the tablefor items to detect the condition of the bearing.
Among these items, rotational speed is obtained byprocessing the AC current waveform generated by thepower generator without using a dedicated sensor.
Furthermore, the operating temperature range is
set to -40 to 85 ℃ with consideration for the heat
resistant temperature of the electronic components
mounted in the circuit.
The wireless device uses Bluetooth Low Energy(2.4 GHz) telecommunication standard. Modes(monitoring mode and analysis mode) are selectedbased on the application to enable sensing.
Monitoring mode assumes that monitoring is
performed continuously and over an extended
period, and sends data obtained for temperature,acceleration and rotational speed at intervals of 0.1
seconds. During this time, acceleration sent in thismode is the RMS value. Analysis mode acquires andsends acceleration data for a given sample number toenable the frequency to be analyzed by the receiver.
In addition, switching between monitoring mode andanalysis mode can be done using dedicated software
installed on a computer.

Usage conditions

Communication

Sensing

Bearing

Table 1 Specifications for Sensor Integrated Bearing“Talking BearingsTM”
Type

Deep Groove Ball Bearing

Number63-series, bore diameter code 14 or
higher

Acceleration

Radial detection direction
Detection range of ±50 G
Frequency band from 11 kHz (3 dB)
Sensitivity 40 mV/G

TemperatureC
Detection range of -50 to 150 °Rotational
speed

Resolution of 16.7 min-1

Standard

Bluetooth Low Energy(2.4 GHz)

Transmitted
data[Monitoring mode]
Temperature, acceleration(RMS value), rotational speed(communication interval: 0.1 second)[Analysis mode]
Acceleration

Allowable
rotational
speed

Conforms to bearing number

Rated load

Conforms to bearing number

Rotational
speed thatcan betransmitted

500 min-1 or more

Operatingtemperature
range

C-40 to 85 °and Fig. 7 show examples of displaying data formonitoring mode and analysis mode, respectively.
Monitoring mode displays the change over time foracceleration, temperature and rotational speed. Also,
when acquired data exceeds a pre-defined threshold,a warning will display. Analysis mode displays theacceleration time waveform and frequency analysis
results.
(1) Data is saved to a data logger then imported

Data loggerPC(2) Data is imported directly to a tablet or PC
Developed
product
Tablet or PC

Fig. 5 Communication configuration examples

Fig. 6 Example of data displayed in monitoring mode

4. Examples of use
Fig. 5 shows communication configuration
examples for the developed product. When constantly
monitoring the equipment conditions for a long
period of time, the amount of received data will be
extremely large so it is best to send the data to a
device such as a data logger that can store a large
volume of data, and configure the device to ensure it
can import the data to a computer or similar terminal.
Moreover, when wanting to carry a computer or tablet
into the workplace each time to check the conditionof the equipment, a configuration that allows directcommunication with the computer or tablet iseffective. The developed product can communicate
with devices that comply with telecommunication
standards without needing to change the installed
communication program, enabling the appropriate
usage method to be selected as required.
The use of dedicated software enables thedeveloped product to communicate with a computeror similar device to display sensor data. Fig. 6

Fig. 7 Example of data displayed in analysis mode

5. Performance test
5.1 Vibration detection performance
To check the vibration detection performance ofthe developed product, an abnormal bearing with adefect resembling spalling (simulated spalling) on the
raceway surface was used. This abnormal bearing wascompared with a normal bearing without any defects
to observe the vibration detected by the built-in
sensor. The vibration detection performance was also
compared using the acceleration sensor provided on
the outside of the bearing (hereafter, external sensor)
and the built-in sensor.

NTN TECHNICAL REVIEW No.89

37

Development of Sensor Integrated Bearing “Talking BearingsTM”
5.1.1 Test machine and test conditions
Fig. 8 shows a schematic drawing of the testing
equipment. The bearing being tested is rotated by ashaft fitted to the inner ring of the bearing. A radialload also acts on the bearing being tested througha stand that sways on a pivot point. The externalsensor is installed on the stand, and its specifications
are provided in Table 2. The external sensor iscompared with the built-in sensor (see Table 1), andtheir detection range is about the same. However,
the external sensor has a wider frequency band. The
acting radial load was set to 784 N. This load is quite
small when compared to the basic dynamic load
rating of 115 kN for deep groove ball bearing 6314.
Bearing being tested

Table 3 Specifications for the bearing being tested
Normal bearing

Abnormal bearing

Bearing

Deep groove ball bearing 6314

Seal

Non-contact type (one side)

GreaseThickening agent: Urea-based
Base oil: Poly-alpha olefin

Simulatedspalling

No

1 location at the bottomof the groove on the outerring raceway surface
φ0.87 × depth of 0.1 mm

φ 0.87
Rotating shaft

0.1 mmRaceway
surface

Position of built-in
acceleration sensor
External sensor

Stand

Load

Position ofsimulated spalling

Simulatedspalling
Outer ring

Fig. 9 Schematic drawing of simulated spalling

Pivot

Fig. 8 Schematic drawing of testing equipment
5.1.2 Bearing being tested
Table 3 provides the specifications for the bearing
being tested and Fig. 9 shows a schematic drawingof the simulated spalling formed on the bearing
outer ring. Cylindrical-shaped simulated spalling wasformed at 1 location at the bottom of the groove on
the outer ring raceway surface, and its size was set
based on the size of the contact ellipse due to elastic
deformation of the bearing parts. More specifically,
the diameter of the simulated spalling was set to 0.87
mm, which is twice the diameter of the contact ellipse
minor axis when the test radial load of 784 N was
applied. Fig. 10 shows an external photo of actual
spalling that occurred during the damage end stage,as an example of spalling that occurs on a bearing. The
size of the simulated spalling was made sufficiently
small in comparison to end stage spalling with the aimof evaluating vibration detection performance during
the initial stages of damage.
Table 2 Specifications for the external sensor
External
sensor38

Detection range±60 G

Frequency band

3 Hz to 25 kHz（3 dB）

Sensitivity

100 mV/GNTN TECHNICAL REVIEW No.89

5 mm

Fig. 10 Example of spalling damage
5.1.3 Test results
Fig. 11 shows the built-in sensor output whenrotating the normal sensor and abnormal sensor at
2 000 min-1. Each time the rolling element passes
the simulated spalling on the abnormal bearing, anobvious spike in acceleration was detected. If a defectof about the same size as the simulated spalling
created this time occurs on the raceway, it would bepossible to detect an obvious abnormality with thedeveloped product.
Next, Fig. 12 shows a comparison between thebuilt-in sensor and external sensor for the acceleration
measured at the abnormal bearing. Fig. 12 shows
the results of conducting envelope processing andfrequency analysis (fast Fourier analysis) on the data
output in Fig. 13. Finally, Fig. 13 lists the rotational
speed (103 Hz) of the rolling element relative to theouter ring and the higher-order rotational speeds. The

sensor output when the rolling element passes thesimulated spalling is greater for the built-in sensor
in comparison with the external sensor. Frequency
analysis also shows that the built-in sensor is moresensitive and can better detect vibration at highfrequency.

12

4
0
-4
-8
-12

0

20

40

60

80

100

Fig. 11 Comparison of normal bearing and abnormal
bearing built-in sensor output

12
8

Acceleration G

Built-in sensor
External sensor

Bearing Rotational
speed 2 000 min-1

4 000

30

3 000

20

2 000
Built-in (temperature sensor)
External (thermocouple)
Rotational speed

10

0

2

4

6

1 000

8

0

Fig. 14 Comparison of temperature taken with thebuilt-in sensor and external thermocouple

-4
-8
0

20

40

60

80

100

Time ms

Fig. 12 Comparison of acceleration for built-in sensor
and external sensor with abnormal bearing

1

Acceleration G

40

Time h00.8

Built-in sensor
External sensor

103 Hz206 Hz0.6

309 Hz0.4

412 Hz

0.2
0

5 000

0

4

-12

Temperature ℃

Time ms

50

Rotational speed min-1

Acceleration G

Abnormal bearing
Normal bearing

Bearing Rotational
speed 2 000 min-1

8

and it was measured using the testing equipment
shown in Fig. 8. The rotational speed was taken as being
up to the allowable rotational speed of 4 600 min-1(value listed in the NTN catalog) for deep groove ballbearing 6314 (grease lubrication, non-contact seal).
Measurements were taken by repeatedly increasing
rotation and holding for two hours at increments ofaround 1 000 min-1. Measurement results are shownin Fig. 14. The results show that there is no significant
difference in the values measured with both sensors
in either the transient region after rotation wasincreased or the steady-state region when rotation
was held. Thus, the developed product has the same
temperature detection performance as when affixinga thermocouple to the bearing outer ring.

0

200

400

600

800

1 000

Frequency Hz

Fig. 13 Comparison of frequency analysis for built-in
sensor and external sensor
5.2 Temperature detection performance
Measured values taken from a thermocouple affixed
to the outer circumferential surface of the bearing
outer ring were compared with measured values takenfrom the built-in temperature sensor. The bearing
being tested was the normal bearing shown in Table 3,

5.3 Temperature increase characteristics
Fig. 15 shows the generated power and runningtorque of the developed product in relation torotational speed. Here, the generated power is thesum of the power consumed by the circuit and thepower loss from the power generator. Also, therunning torque is equivalent to the running torqueof the entire bearing with built-in sensor, including
the friction loss during bearing rotation and thegenerated power mentioned above. Fig. 15 shows
the values measured after holding for two hours at
each rotational speed. The generated power is small
at 1 to 2 % in contrast with the power loss of theentire bearing calculated from the running torqueand rotational speed, and incorporating the power
generator and circuit into the bearing is also estimatedto have a minor effect on the bearing temperature.
Fig. 16 shows the results measured for thetemperature on the actual bearing. The bearing
temperature was measured with a thermocouple
affixed to the outer ring outer circumferential surface
and the built-in sensor. Fig. 16 shows the value
increase from ambient temperature after holding fortwo hours at each rotational speed. There was no
significant difference between the standard bearing
and developed product, showing that the developed
product has the same temperature increasecharacteristics as the standard bearing.

NTN TECHNICAL REVIEW No.89

39

Development of Sensor Integrated Bearing “Talking BearingsTM”

Running torque
Generated power

100

400

50

200

0

0

1 000

2 000

6. Summary

600

3 000

4 000

0
5 000

Generated power mW

Running torque mN･m

150

Rotational speed min-1

Rise in outer ring temperature ℃

Fig. 15 Generated power and running torque for thedeveloped product

20
Standard bearing
Developed product

15
10
5
0

0

1 000

2 000

3 000

4 000

5 000

Rotational speed min-1

Fig. 16 Temperature increase characteristics for thedeveloped product and standard bearing

To respond to efforts towards reducing downtime atmanufacturing sites, NTN has developed the Sensor
Integrated Bearing “Talking BearingTM” which has
sensors, a power generation unit and wireless device
built into a standard bearing. The performance of
this product was verified in this paper. We predictthat demand for equipment condition monitoring will
increase in the near future, and further improvements
in functionality will be required. NTN will continue
to develop equipment condition monitoring andcontribute towards improving production efficiency
through its improvements in the function of “Talking
BearingTM” and releasing products in the market.
References
1) Japan Institute of Plant Maintenance, 2021
Maintenance Investigation Report Summary(June 2022)
2) Sohei Yamada, Shigetoshi Noritake, Investigation
to Optimize Manufacturing and Logistics Sites
Using Sensing Technology, Journal of The Japan
Society of Mechanical Engineers, Vol.123,
No.1223(2020)19-21.
3) Hou Jinyama, Smart Equipment Condition
Monitoring & Diagnosis Technology in the IoT/AI
Age, System/Control/Information, Vol.65, No.4
（2021）113-118.
4) Makoto Miyazaki, Wataru Hatakeyama,
Application of Condition Monitoring System forWind Turbines, NTN TECHNICAL REVIEW, No.86,(2018) 40-44.
5) Shohei Hashizume, Yusuke Shibuya, Daichi
Kondo, Yohei Yamamoto, Hiroyuki Iwanaga,
Development of Sensor Integrated Bearing Unit
for Machine Tool Spindles, NTN TECHNICALREVIEW, No.88 (2020) 33-37.
6) Hiroyuki Iwanaga, Development of Edge
Application for Bearing Diagnosis, Inspection
Technology, March 2022 Edition, 32-34.
7) Our Line of New Product, Portable Vibroscope,
NTN TECHNICAL REVIEW, No. 87 (2019) 106.

Photo of authors

40

Yasuyuki FUKUSHIMA

Tomomi GOTO

Yosuke TOYOGUCHI

Daigo IKKE

Kohei MATSUBAYASHINew ProductDevelopment R&D
Center

New ProductDevelopment R&D
Center

New ProductDevelopment R&D
Center

New ProductDevelopment R&D
Center

New ProductDevelopment R&D
CenterNTN TECHNICAL REVIEW No.89

Commentary

Development of Multi Track Magnetic Encoder Integrated
Rolling Bearing

Hiroshi OKUMURA*
Hiroyoshi ITO*
Yasuyuki HAMAKITA*
The robot industry has been expanding on the back of market demand for
improved productivity and labor saving as the countermeasures of diminishingworking population. Especially, the demand of small robots such as collaborative
robots that work with human labors and service robots has been increasing.
Through the recent trend, market requirements for the robots have been getting
higher and more diversified.
NTN has developed the “Multi Track Magnetic Encoder Integrated Rolling Bearing” based on the technologyof the “Multi Track Magnetic Ring” for rotary encoders. The bearing is suitable for robot joints and performs
high-precision angle detection as well as the shaft support. This report introduces the features, structure,and performance of the bearing.

1. Introduction
The use of robots to perform work instead ofhumans is on the increase throughout the world in
all industrial manufacturing sectors, including forautomobile manufacture1) 2). In recent years we haveexperienced significant social problems such as thedecline in the working-age population ratio due tothe decreasing birthrate and aging population as
well as slow production activity due to the increase
in COVID-19 infections, prompting the increased
introduction of robots. Industrial robots installed in
production lines, robots that work in locations awayfrom humans, and small robots such as collaborative
robots and service robots are on the increase, while
the structure of robots and the work they do has
become increasingly diverse.
Vertical articulated robots (Fig. 1) that move similar
to the arms of a human are typical, and such robots
must transport a workpiece with high accuracy andspeed to a determined position. To achieve this, thejoint mechanism must be able to support the motorʼsrotating shaft while detecting its rotational speed,
rotational direction, and absolute angle with a highlevel of accuracy to achieve the correct position. In
addition to servo motors and reducers, robots use
bearings to support rotation and rotary encoders todetect rotational conditions3).
Furthermore, recent joint mechanisms must support
the diverse trends as mentioned above, and to becompact, lightweight, be assembled from as fewer
parts as possible to reduce man-hours to build themand have a high environmental resistance so they canbe used in various operating conditions.
So far NTN has commercialized the highly accurate
and compact Multi Track Magnetic Ring for use indetecting the absolute angle and rotational speed
for the robot joint mechanisms4). The Multi Track
Magnetic Ring, in combination with the magnetic
sensor IC, forms a magnetic rotary encoder thatprovides high environmental resistance.
The application of this technology contributes
to greater improved performance for robot joint
mechanisms, so NTN has developed a new “Multi
Track Magnetic Encoder Integrated Rolling Bearing”(hereafter, developed product) that brings together
the bearing, the Multi Track Magnetic Ring, andmagnetic sensor IC in a single unit. The developed
product supports the rotation of the shaft while
detecting the rotational speed, rotational direction
and absolute angle as a rotary encoder. Bringing
together the bearing and magnetic rotary encoder
in a single unit can make the robot joint mechanism
more compact and reduce the man-hours required
for assembly and setup in the robot manufacturing
process. The developed productʼs features, structure
and test results are introduced below.
Axis 5: Wrist bend

Axis 6: Wrist rotation

Axis 2: Lower arm

Axis 4: Wrist turn

Axis 3: Upper arm

Axis 1: Turn

Fig. 1 6 axes vertical articulated robot* Robotics & Sensing Engineering Dept., Industrial Business Headquarters

NTN TECHNICAL REVIEW No.89

41

Development of Multi Track Magnetic Encoder Integrated Rolling Bearing
2. Developed product structure and features
The developed product is a unit composed of adeep groove ball bearing, Multi Track Magnetic Ring,and magnetic sensor IC (Fig. 2).
The Multi Track Magnetic Ring is attached tothe inner ring of the deep groove ball bearing. The
magnetic sensor IC is attached to the outer ring of
the deep groove ball bearing through the sensor
housing. The developed product can be used for joint
mechanisms on the robot as shown in Fig. 3. The
Multi Track Magnetic Ring rotates as the axis rotates,
and to correspond to the rotation the magnetic sensor
IC reads the change in magnetic poles. This enables
the developed product to detect the rotational
speed, rotational direction, and absolute angle. Data
detected by the magnetic sensor IC is transmitted
to a motor driver prepared by the user, then used for
positioning the robot joint mechanisms (Fig. 4).

Deep Groove Ball
Bearing

Multi Track
Magnetic Ring

Magnetic
sensor IC

Rotary encoder unit

Deep Groove Ball
Bearing

Rotary encoder unit

Multi Track Magnetic Encoder
Integrated Rolling Bearing

Fig. 2 Configuration of major components for the Multi Track
Magnetic Encoder Integrated Rolling Bearing

The developed product is a compact unit that uses
technology to integrate the rotation detection unit
and bearing that NTN has developed for conventionalrotation sensor bearings (Fig. 5), which are wellestablished for use in transportation machinery5). It
has the same bearing bore diameter, outer diameter,
width, and load rating as a standard bearing without
the rotation detection unit, making it compatible withstandard bearings. This unitʼs features are shown in (1)to (4) below. Table 1 also shows the specifications forthe developed product using deep groove ball bearing
6907.
(1) Can support shaft rotation and provide highaccuracy angle detection.
The developed product detects rotational speed,
rotational direction, and absolute angle while supporting
shaft rotation. Configuring parameters in the magnetic
sensor IC enables a maximum high accuracy output of
20 bits (resolution of approximately 0.00034°).
(2) Contributes towards making the robot joint
mechanism compact and lightweight.
Integrating the deep groove ball bearing, Multi Track
Magnetic Ring and magnetic sensor IC means that acoupling to connect the joint mechanism and rotary
encoder is not needed. This enables a reduction in
the joint mechanism shaft length, the use of fewer
components, and results in producing a more compact
and lighter joint mechanism (Fig. 6).
(3) Can reduce man-hours for robot assembly and setup.
As mentioned above in (2), integrating components
can reduce the number of robot components, which
reduces man-hours required for assembly. It alsomeans that the user does not have to perform setup
such as adjusting output signals required for whenassembling the magnetic ring and magnetic sensor, so
man-hours can be reduced.
(4) Affected less by the surrounding environment andhigh environmental resistance.
The developed product is a magnetic rotary
encoder that detects the rotational speed, rotational
direction and absolute angle using magnetism. In
comparison with optical rotary encoders that use lightfor detection, it is affected less by the surrounding
environment such as temperature changes, dust, andoil, and has a high environmental resistance6).
Host controller
Motor driver
Robot joint mechanisms
Servo motor
ReducerAngle information

Rotaryencoder unit

Operation instructions

Rotational shaft
Robot arm

Fig. 3 Positions where the Multi Track Magnetic Encoder
Integrated Rolling Bearing can be used42

NTN TECHNICAL REVIEW No.89

Fig. 4 Schematic drawing of positioning for robot
joint mechanisms using the Multi Track
Magnetic Encoder Integrated Rolling Bearing3. Absolute angle detection principles
and resolution

Fig. 5 Rotation sensor bearing(NTN conventional product)
Bearing

Joint
Couplingmechanism

Bearing

Rotary encoder(a) Conventional

Multi Track
Magnetic Encoder
Integrated Rolling
Bearing(b)Developed
product

3.1 Multi Track Magnetic Ring and magnetic sensor IC
The Multi Track Magnetic Ring (Fig. 7, Fig. 8) is composedof a core press-formed from thin steel plates and rubbermaterial that contains a magnetic material (hereafter, rubber
magnetic material). The rubber magnetic material is adhered
to the core by vulcanization. Two magnetic tracks withdifferent number of polar pairs for the N-pole and S-pole
are formed on the outer diameter circumferential surface ofthe rubber magnetic material for the radial magnetization
type, and the width surface for the axial magnetization type.
For a 64/63 polar pair Multi Track Magnetic Ring, the main
track is magnetized with N-pole S-pole 64 polar pairs andthe sub track is magnetized with 63 polar pairs.
The magnetic sensor IC arranged opposite the Multi
Track Magnetic Ring is equipped with two detection
units that face the main track and sub track, and an
absolute angle calculation unit. For example, IC (iC-MU)
manufactured by iC-Haus can be used (Fig. 9).
Sub track (63 polar pairs)
Main track (64 polar pairs)
Rubber magnetic
material

Using the developed product enables the rotary encoder to be
integrated into the joint mechanism

Fig. 6 Adopting the Multi Track Magnetic Encoder
Integrated Rolling Bearing reduces
the number of components required
for the robot joint mechanism,and makes it more compact
Table 1 Specifications for the Multi Track
Magnetic Encoder Integrated Rolling Bearing(deep groove ball bearing 6907)
Item

Specifications

Deep Groove Ball Bearing

6907（ID35×OD55×10）

Wiring connector
height

6 mm (protrusion amount frombearing outside diameter surface)

Encoder unit width

10.5 mm

Multi Track Magnetic Ring 64/63 polar pairs, 1.28 mm pitch
Magnetic sensor IC

iC-MU

Allowable rotational speed

6 000 min-1

Angle resolution

Max. 20 bits

Detection information

Rotational speed, rotational
direction, absolute angle

Angle detection error± 0.1゜

Power supply voltage

DC 5 V

Current consumption

60 mA

Signal format

ABZ，SPI，BiSS，SSI

Operating temperaturerange

ー25 to ＋110 ℃

Magnetization pattern view
through magnetic sheet(b)Magnetization patternCore(a)External
appearance(c)Illustrated magnetization patternFig. 7 Multi Track Magnetic Ring:
Radial magnetization typeCore

Rubber magnetic(a)Externalmaterial
appearance(c)Illustrated magnetization
patternFig. 8 Multi Track Magnetic Ring: Axial magnetization typeFig. 9 Illustration of combining the Multi Track
Magnetic Ring with iC-MU series(images provided by iC-Haus GmbH)NTN TECHNICAL REVIEW No.89

43

Development of Multi Track Magnetic Encoder Integrated Rolling Bearing
3.2 Absolute angle detection principles and resolution
This section explains the absolute angle detection
principles (Fig. 10) and resolution with the 64/63
polar pair Multi Track Magnetic Ring as an example.
For the 64/63 polar pair Multi Track Magnetic
Ring, at each rotation the output signal of the period
corresponding to magnetization polar pairs 64 fromdetection unit 1 of the magnetic sensor IC, andmagnetization polar pairs 63 from detection unit
2 are obtained. These output signals have a phasedifference of one polar pair for each rotation so
calculating this phase difference enables the absolute
angle to be detected. Thus, on a magnetic pair with64 polar pairs, it is possible to detect at what polar
pair the position lies.
By accurately reading the magnetic strength
between polar pairs with the magnetic sensor IC,
12 bit multiplication is possible. Therefore, angle
information for one polar pair can be divided into
212 sections, and together with 64 polar pairs (26),
18 bit (resolution of approximately 0.0014°) angle
information can be output8). Magnetic sensor IC
parameters can be configured to also enable up to 20
bit (resolution of approximately 0.00034°) output.
Angle information output from the sensor isdependent upon the magnetic pitch accuracy. To beable to detect the absolute angle and achieve this kindof high angle accuracy, it is necessary to sufficiently
magnetize two magnetic tracks with a different
number of magnetized polar pairs. NTN has developed
original magnetization technology to provide highly
precise control of the magnetic pitch for eachmagnetic pole on the Multi Track Magnetic Ring9).
Magnetic sensor
Detection Unit 1
Detection Unit 2

4. Evaluation test
4.1 Absolute angle detection error
The absolute angle detection error was measured forthe developed product using deep groove ball bearing
6907. Table 2 shows the measurement conditions
and Fig. 11 shows the measurement results. The
developed product uses both a Multi Track Magnetic
Ring and magnetic sensor IC, and these items areattached to a deep groove ball bearing with good
accuracy to achieve high accuracy detection of theabsolute angle. Under the measurement conditions
shown in Table 2, an absolute angle detection error of± 0.1°or less was obtained.
4.2 Resistance to electromagnetic noise
The developed product achieves a compact unit
composed of few elements as possible, including
a deep groove ball bearing, Multi Track Magnetic
Ring, magnetic sensor IC and circuit substrate, andcontributes towards a more compact and lightweightrobot joint mechanism. To investigate its resistance tovarious noise assumed at the robot joint mechanism,
an electromagnetic noise test was conducted. This
test results show that the developed product has
resistance to EMC Standards (IEC 61000-6-2) for
industrial environments10) (Table 3, Fig. 12).
Table 2 Absolute angle detection error measurement
conditions for Multi Track Magnetic Encoder
Integrated Rolling Bearing(deep groove ball bearing 6907)
Item

Conditions

Power supply voltage

DC 5 V

Rotational speed

5 min-1

Measurement angle

360°

Measurement temperature

Room temperature

Number of polar pairs

64/63 polar pairs

Multi Track Magnetic Ring

S

N

S

N

S

N

S

N

S

N

S

N

S

N
S

S
N

N
S

S
N

N
S

64 polar pairs
63 polar pairs

S N
Output Voltage of
detection unit 1
Output Voltage of
detection unit 2
Linear Conversion of output
Voltage of detection unit 1
Linear Conversion of output
Voltage of detection unit 2
Phase difference between
detection unit 1 and 2

Rotation angle

0°

360°

Angle detection error deg.

Fig. 10 Absolute angle detection principles

0.3
0.2
0.1
0
-0.1
-0.2
-0.3

0

30

60

90

120

150

180

210

240

270

300

330

360

Rotation angle (position) deg.

Fig. 11 Absolute angle detection error measurement results of Multi Track Magnetic Encoder Integrated Rolling Bearing

44

NTN TECHNICAL REVIEW No.89

A. Static electricity discharge caused
by electrification frompeople and materials, etc.

5. Developed product examples of application
The developed product can be used for compact
robot joint mechanisms, such as collaborative robots
and service robots using the features introduced in thispaper. Additionally, it can also be used in general servo
motors by replacing the analog rotary encoders, suchas optical rotary encoders and resolvers (Fig. 13).
For example, optical rotary encoders requirebarriers to prevent the intrusion of dust and oil to thelight emitter and light receiver, as well as the internalareas of the encoder so it is difficult to make themcompact. Furthermore, resolvers require high accuracy
arrangement of many coils in the coil unit which is a
key component to achieving high resolution, so they
have a complex shape, and it is difficult to make themcompact. Additionally, resolvers must have an R/Dconverter to convert the output signal to digital.
In contrast, the developed product only requires a
Multi Track Magnetic Ring and magnetic sensor IC tocreate the magnetic rotary encoder. This produces a
simple structure in comparison with an optical rotary
encoder or resolver, which can contribute towards
making robot joint mechanisms and servo motors
more compact and lighter in weight. The developed
product also outputs digital signals, so an R/Dconverter or similar device is not necessary, so it iseasy to make the system compact and lightweight.

Circuitsubstrate

B. Magnetic field
caused by power
supply line,transformer,etc.

Deep Groove Ball Rotary encoder unit
Bearing
Electromagnetic noise charged directly to circuit substrate
C. Electromagnetic waves
caused by wireless device
antenna, household appliances,
etc.
Electromagnetic noise

D. Electromagnetic waves
caused by wireless device
antenna, household
appliances, etc.

Electromagnetic noise
charged directly tocircuit substrate &Electromagnetic noise
charged to circuit
substrate via signal line
and power supply line

Deep Groove Rotary
Ball Bearing encoder
unit

Electromagnetic noisecaused by electricmotor turning on/off
and lightning strike,etc.

Deep Groove
Ball Bearing

Rotaryencoderunit

Signal processing
equipment such as
decoder

E. Electromagnetic field fluctuation
due to lightning surge
Signal processing
equipment such as
decoder

Electromagnetic noise
charged to circuit substrate
via signal line and power
F. Reverse electromotive
supply line from otherforce generated bymachinery or outdoor
switching of machinery
power line

Fig. 13 Servo motorthat uses coils, etc.

Fig. 12 Types of electromagnetic noise
Table 3 Resistance evaluation test to electromagnetic noise
Test
No.
1
2
3
4
5
6

Test standards and name
IEC 61000-4-2 : 2008
Electrostatic discharge immunity test
IEC 61000-4-4 : 2012
Burst immunity test
IEC 61000-4-5 : 2014
Surge immunity test
IEC 61000-4-8 : 2009
Power frequency magnetic field immunity test
IEC 61000-4-6 : 2013
Radio frequency conducted disturbances immunity test
IEC 61000-4-3 : 2006
Radiated, radio-frequency electromagnetic field immunity test

Assumedelectromagnetic
noise

Test conditions

A in Fig. 12

4 kV

F in Fig. 12

1 kV

E in Fig. 12

1 kV

B in Fig. 12
D in Fig. 12
C and Din Fig.12

Results

No damage possible
to conform with
EMC standards(IEC 61000-6-2)

30 A/m(50 Hz/60 Hz)
10 V
0.15 to 80 MHz
10 V/m（80 to 1 000 MHz）
3 V/m (1.4 to 6.0 GHz)NTN TECHNICAL REVIEW No.89

45

Development of Multi Track Magnetic Encoder Integrated Rolling Bearing
6. Expanding the developed product series
The developed product can be applied to compact
robot joint mechanisms such as collaborative robots
and service robots. In addition to using the deep
groove ball bearing 6907 introduced in this paper,
NTN plans to expand the series from bearing bore
diameter 15 mm to 45 mm.

7. Summary
The demand for robots, including collaborative
robots and service robots, is on the increase, andmarket demands are becoming more sophisticatedand diverse.
To respond to the above needs, NTN has developed
a Multi Track Magnetic Encoder Integrated Rolling
Bearing that integrates a deep groove ball bearing andmagnetic rotary encoder using Multi Track Magnetic
Ring technology. This enables robots that are morecompact and lightweight while also reducing manhours to assemble and setup the robots.
NTN will continue to work on developing
products that contribute to further improvementsin performance of industrial machinery, including
robots, and support the advancement of technology
for further enriching peopleʼs lives and technology forprotecting the global environment.

Photo of authors

46

Hiroshi OKUMURA

Hiroyoshi ITO

Yasuyuki HAMAKITA

Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters

Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters

Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters

NTN TECHNICAL REVIEW No.89

References
１） Keiichi Ueda, Technical Trend of the Precision
Bearings for Machine Tools, Tool Engineer, Vol. 60
No. 16, (2019) 41-43.
２） Makoto Oebisu, Hiromichi Kokumai, Yasuyoshi
Hayashi, Masato Tsujihashi, Technical Trend
and Features of the Bearing for Robot, NTN
TECHNICAL REVIEW, No.86, (2018) 34-39.
３） Hiromichi Kokumai, Hideaki Tanaka, Kosuke
Suzuki, Yuichiro Kawakami, Approach to
Development of Robot Joint-related Products,
NTN TECHNICAL REVIEW, No.88, (2020) 27-32.
４） Takashi Koike, Yasuyuki Fukushima, Yusuke
Shibuya, Hiroyoshi Itou, Development of Multi
Track Magnetic Ring for High Accuracy Absolute
Angle Detection, NTN TECHNICAL REVIEW,
No.86, (2018) 45-49.
５） Hiroyoshi Itou, Takashi Koike, Bearings with
Rotational Sensors, NTN TECHNICAL REVIEW,
No. 69, (2001) 108-116.
６） Yasuyoshi Hayashi, Development of Robotic
Joint-Related Products, Bearing & Motion-TechMagazine, No.035, (2022) 25-27.
７） iC-Haus GmbH，iC-MU off-axis nonius encoderwith integrated hall sensors８） Shoji Itomi, Hiroyoshi Itou, NTN Sensor Units forConstruction Machine, NTN TECHNICAL REVIEW,
No. 76, (2008) 118-125.
９） Takashi Koike, Yasuyuki Fukushima, Yusuke
Shibuya, High Accuracy Absolute Angle Sensor
for Use in Absolute Angle Detection on Robot
Joints, Vol. 62 No. 3, (2018) 55.
10）Electromagnetic compatibility (EMC) - Part
6-2，Generic standards – Immunity standard for（2016）．
industrial environments IEC 61000-6-2，

Prospects

Development of Sensor Integrated Bearing Unit for
Machine Tool Spindles

Shohei HASHIZUME*
Daichi KONDO**
Yohei YAMAMOTO***

Yudai NAKANO*
Yoji OHGUCHI**

Machine tools are sometimes called the “Mother Machine” or “Motherof Industry” and have been supporting manufacturing all over the world.
They are required for not only fundamental features like high speed, highrigidity, and super precision, but also condition monitoring and “Connected
Industries” related technology. In 2018, NTN developed the “Sensor
Integrated Bearing Unit for Machine Tool Spindles”, and additionally,
applied the load detection function and wireless system to the unit in 2020.
NTN has recently added the data receiver unit which collects the data from the “Sensor Integrated Bearing
Unit” in machine tool spindles and the software for data communication. This report introduces thefeatures, structure, and performance of the unit, and offers communication examples between the unit andmachine tools.

1. Introduction
Amid significant changes in the global environmentand social structure, the industrial world has beentackling various social challenges, such as achievingcarbon neutrality to slow down global warming,achieving sustainable development goals (SDGs),
and improving production to further enrich peopleʼs
lives, by integrating new technology created in the
4th industrial revolution (Industry 4.0) into coretechnologies developed over many years.
Among these technologies, machine tools1) 2) that
support manufacturing in various industries, including
the automotive, aircraft, medical and IT sectors, arebeing promoted to further improve basic performance interms of “high speed, high durability and high accuracy”
as a response to energy loss reduction and work force
reduction. Productivity improvements and manpower
reductions using IoT technology are underway.
NTN has developed the “Sensor Integrated Bearing
Unit” for Machine Tool Spindles (hereafter, this bearingunit)3), which has sensors built into the spacer, acomponent of a bearing unit. This enables sensing of thetemperature and vibration around the bearing raceway
surface, making it possible for advanced condition
monitoring of machine tools. NTN showcased areference exhibit of this at the 29th Japan International
Machine Tool Fair (JIMTOF 2018) held in 2018. A loaddetection function was also added to this bearing unit
together with wireless operation4) in 2020.
We have also added a data receiving unit that
acquires data detected by the sensors on thisbearing unit at the exterior of the spindle as well as

communication software to send and receive the datawith the aim of further improving the usefulness of
this bearing unit. This bearing unitʼs characteristics,
structure, performance test results for load and othersensors, and how to connect it to machine tools aredescribed below.

2. Functions and purpose of the sensor
integrated bearing unit
Table 1 shows the functions and purpose of thisbearing unit. When a bearing that supports therotation of the spindle (hereafter, spindle bearing),
a key component on machine tools, is damaged,
operation at the machine tool stops and the spindle
must be replaced; this significantly lowers productivity.
Due to this fact, there is a growing need to detect thisdamage early on. Furthermore, it will be even morenecessary in the future to increase the productivityof machine tools and to minimize the dependence
on individual expertise in machining monitoring in
response to the aging of skilled personnel and thedecline in the working-age population ratio. This
bearing unit is expected to contribute towards theseneeds while also contributing towards achieving
sustainable development goals (SDGs).
For example, if we detect the machine load appliedon the spindle, and use this information for machining
monitoring, we can optimize the machine conditions
such as cutting depth, feed, and rotational speed.
This is expected to provide increased machining
quality and productivity. Furthermore, this bearing
unit detects tool and workpiece collision to reduce* Robotics & Sensing Engineering Dept., Industrial Business Headquarters ** New Product Development R&D Center*** Product Design Dept., Industrial Business Headquarters

NTN TECHNICAL REVIEW No.89

47

Development of Sensor Integrated Bearing Unit for Machine Tool Spindles
Table 1 Functions & purpose of the sensor integrated bearing unit

Function(1)

Detects external loads
applied to the spindle(3)

Monitors temperature changes
in the spindle bearing

Connection to SDGs

• To see sudden rises in preload that
occurs before bearing seizure, and to
detect signs of bearing seizure early on• To make it easier to manage preload
on bearings after the spindle has been
installed, and to reduce assembly
manhours for the spindle

Detects preload for spindle
bearing(While spindle is rotating
and after spindle has been
installed)(2)

Purpose

Implementation
methodLoad
Sensor• To detect machining load applied
to the spindle, and contributetowards improved machining quality
and productivity using machining
monitoring• To detect collisions between the tool
and workpiece, reduce damage tothe spindle bearing, and use it toinvestigate the cause of the damage

Temperature
Sensor• To monitor the bearing raceway
surface and lubrication conditions(4)

Monitors vibration changes inthe spindle bearing

Vibration
Sensor(5)

No need for an externallyconnected cable or wiring
space for power supply

Independent
Power supply(6)

External connection for datatransmission
No need for cable or wiring
space

Wireless
Module• Improve productivity,
and reduce energy
loss throughoptimized production• Reduce defective
workpieces (waste)• Contribute towards
automation andmanpower reduction• To monitor the bearing raceway surface• To detect collisions between the tool
and workpiece, reduce damage tothe spindle bearing, and use it toinvestigate the cause of the damage• To reduce man-hours to assemble
the spindle• To eliminate the need to change thestructure of the spindle• Reduce energy loss
with independent
power supply andimproved productivity

Workpiece

Workpiece

Workpiece

Workpiece

Fig. 1 Illustration of sensor integrated bearing unit application
Example of improving machining quality by linking machining data to each product of a machine tool48

NTN TECHNICAL REVIEW No.89

damage to the spindle bearing, uses real-time
information to determine the cause of the damage,and as shown in Fig. 1, links machining data for eachmanufactured product to both improve machining
quality and promptly investigate the reason why adefect occurred.

Sensor Integrated Bearing Unit

Load applied to tool
when machining

Housing
SpindleTool

3. Structure and specificationsof the sensor integrated bearing unit

BearingOuter ring spacer

Load sensor, vibration sensor,
temperature sensor

Wireless module Inner ring Processing
spacercircuitRotor and stator
Independent power
supplyFig. 3 Example of application for the sensor integrated
bearing unit on a machine tool spindle
3.2 Specifications
Table 2 shows the specifications for this bearing
unit. It lists load, temperature, and vibration
acceleration for sensing items. Bluetooth Low
Energy (2.4 GHz) is used for the telecommunication
standards to allow for a lower power consumption at
the wireless module and to make it more compact.
The operating temperature range is set to -20 to 70 ℃
with consideration for the allowable temperature ofelectronic components mounted on the module.

SpacerBearing

Table 2 Specifications for the sensor integrated
bearing unit

Sensing

3.1 Structure
Fig. 2 shows a structural illustration of this bearing
unit. This bearing unit comprises a set of angularcontact ball bearings arranged back-to-back withan outer ring spacer and inner ring spacer provided
between the angular contact ball bearings. The outerring spacer and inner ring spacer are equipped withsensors, circuits to process data detected by thesensors, a wireless module, and an independent
power supply.
The independent power supply uses anelectromagnetic induction generator. A stator
consisting of a coil and yoke is built into the outerring spacer, and a rotor with alternately magnetized
N and S-poles is attached to the inner ring spacer.
Electromagnetic induction is generated by the relativerotation of the outer ring spacer and inner ring spacer
which generates the power required to run thesensors and circuits.
Fig. 3 shows an example of application for thisbearing unit on a machine tool spindle. Factors suchas the internal clearance and the difference between
the width of the inner ring spacer and outer ring
spacer are adjusted to apply preload on the bearing.
This maintains high rigidity at the bearing which
ultimately improves machining quality. With thisstructure, bearing preload and the load applied to thetool during machining act on the outer ring spacer so
a load sensor is provided on the outer ring spacer ofthis bearing unit.
The sensors, circuits, and an independent power
supply are built into this bearing unit in a compact
way;this enables it to achieve the same dimensions as
a conventional outer ring spacer without sensors.

Type

Ultra-high speed angular contact
ball bearings with ceramic balls(Equivalent to 5S-2LA-HSE014)
Double row back-to-backarrangement

Bore diameter ×
outer diameter ×
width

φ70 ×φ110 × 20 (per row) mm

Inner ring spacerbore diameter ×
outer ring spacer
outer diameter ×
width

φ70 ×φ110 × 40 mm

Load

Maximum detection load: 45 kN

Temperature

Detection range: - 40 to 125 ℃

Vibrational
acceleration

Detection range: ± 50 G
Response frequency band:
up to 11 kHz

Independent power
supplyElectromagnetic induction
generator

Communication
standard

Bluetooth Low Energy（2.4 GHz）

Operating temperature
range- 20 to 70 ℃

Fig. 2 Structural illustration of sensor
integrated bearing unit

NTN TECHNICAL REVIEW No.89

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Development of Sensor Integrated Bearing Unit for Machine Tool Spindles
4. Connecting to equipment

5. Evaluation test

Fig. 4 shows an schematic example of using thedata communication capabilities of this bearing unit.
Data detected by the sensors is transmitted wirelessly
from the wireless module built into the outer ring
spacer to the data receiving unit provided with a USB
antenna for data reception. The data receiving unit,
the customerʼs machine tool and server are connectedby a LAN cable so that data can be verified.
Data transmitted from the wireless module consistsof 3 types of data; these are load, temperature, andvibration detected by each sensor. Since each data
type is constantly transmitted to the connected
equipment, it is expected that it will be used tocontrol, monitor conditions as the spindle bearing, andprovide predictive maintenance to machine tools that
require a high level of response.
A separate connection program is required
to connect the data receiving unit to dedicatedequipment. However, if the system uses an IoT
platform, it has the advantage of making the system
more versatile and easier to connect. NTN provides“Bearing Diagnostic Edge Application” for Industrial
IoT Platforms5) to support efforts in this area.
This bearing unit has an independent power
supply to feed power to the unit and can transmit
data wirelessly, which makes it easy to use in an IoTenvironment.

This section introduces the test results for the load,
temperature, and vibration sensor built into thisbearing unit.
Fig. 5 shows the evaluated spindle that simulated
the machine tool spindle. This bearing unit wasassembled onto this evaluated spindle and then theevaluation test was carried out. This bearing unit
wirelessly transmitted data detected by the sensors toa receiver installed externally on the spindle using thewireless module.

Data receiving
USB antenna

Data receiving unit
(Single-board computer)

Machining center spindle
lessly)ion (wire

nsmissData traWireless
ModuleSensorPower supply

Independent
power supply

Data transmission(Wired, LAN cable, etc.)

Load
Vibration
Temperature

Sensor Integrated Bearing Unit
ServerMachine tool (machining center)Fig. 4 Example of using the sensor integrated bearing unit

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NTN TECHNICAL REVIEW No.89

Load parameters

600

Drive
motor

18 000

Unit incorporated sensor (load)
Rotational speed

16 000400

14 000200

12 0000

10 000

-200

8 000

-400
0:00

0:05

0:10

0:15

0:20

0:25

0:30

Rotational speed min-1

800

6 000

Operating time min

Area where bearing unit ismountedFig. 5 Structure of evaluated spindle
5.1 Verifying load and temperature responsivenessduring an acceleration/deceleration test
An acceleration/deceleration test was carried out
in which the rotational speed was changed, assuming
the actual operation conditions of a machine tool.
Table 3 shows the test conditions and Fig 6 shows
the test results for load and temperature. It was
confirmed that this bearing unit can detect changes
in bearing preload and temperature for fluctuationsin the rotational speed. It was also confirmed that it
has a higher temperature sensitivity than an externalsensor.
Table 3 Acceleration/deceleration test conditions

Test bearing

φ70 ×φ110 × 20
Equivalent to 5S-2LA-HSE014(Ultra-high speed angular contact ballbearing with ceramic balls)

PreloadmethodFixed position preload (preload of 750 N
after spindle installation)

Rotational
speed

6 000 → 10 000 → 6 000 → 8 000 min-1

Lubrication
methodAir-oil lubrication

Lubricating
amount0.03 mL/10 min

Lubricating oil

ISO VG32

Lubricating
airflow rate

30 NL/min

Fluid coolingchannelYes, room temperature tuning

Axis position

Horizontal axis

Temperature °C

25

Housing outer circumferential surface(thermocouple)
Unit incorporated sensor (temperature)
Rotational speed

18 000
16 00024

14 00023

12 00022

10 000

21

8 000

20
0:00

0:05

0:10

0:15

0:20

0:25

0:30

Rotational speed min-1

26

6 000

Operating time min

Fig. 6 Acceleration/deceleration test results
5.2 Indentation bearing vibration verification test
To tackle the detection of an abnormality on abearing that uses a vibration sensor, damage (anindentation) was simulated on the bearing raceway
surface. Then a vibration verification test was carriedout on the evaluated spindle in Fig. 5 with the same
condition as for the acceleration/deceleration test.
Table 4 shows the test conditions and Fig. 7 shows a
3D illustration of the simulated damage (indentation)
created on the bearing raceway surface. During thetest, the vibration on the outer circumferential surfaceof the evaluated spindle housing was measured at thesame time together with the vibration detected by thevibration sensor built into the outer ring spacer, andboth measurements were compared. For a vibrationof 5 000 min-1 at the test bearing, while checking
components with frequency that matches the innerring damage, feature quantities of the sensor built into
the outer ring spacer were greater than at the housing
outer circumferential surface, showing that the signal
to noise ratio improved (Fig. 8). The vibration sensor
built into the outer ring spacer is considered to beable to detect damage on the bearing with better
accuracy.

NTN TECHNICAL REVIEW No.89

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Development of Sensor Integrated Bearing Unit for Machine Tool Spindles
Table 4 Vibration verification test conditions
Test bearing

Equivalent to φ70 ×φ110 × 20 5S-2LA-HSE014(Ultra-high speed angular contact ballbearing with ceramic balls)

PreloadmethodFixed position preload (preload of 750 N
after spindle installation)

Rotational
speed

5 000 min-1

Lubrication
methodAir-oil lubrication

Simulateddamage(Indentation)

1 location on inner ring raceway surface
Depth of 6 µm

Simulated damage(indentation)

Comparison of feature quantities
for inner ring damage frequency

Fig. 7 3D illustration of the simulated damage (indentation)
created on the bearing raceway surface

3

2

1

0

External vibration
sensor

Built-in vibration
sensor

6. Summary
Trials are underway to use and introduce sensing
technology on machine tools, against the backdropof the rising demand for condition monitoring andmachining monitoring.
To meet this demand, NTN is making progress with
developing the “Sensor Integrated Bearing Unit for
Machine Tool Spindles”, which has a built-in wirelessfunction and can detect load, temperature, and vibration.
NTN has also made proposals for new methods toconnect developed products and machine tools.
We will continue to repeatedly evaluate this bearing
unit through operation tests for its practical use andpromote further improvements and refinements to its
function. Furthermore, we will also work on establishing
more advanced condition monitoring and predictive
maintenance technology by combining this bearing unit
with AI technology. These efforts will support the efficient
operation of machine tools.
We intend to work on developing technology thatwill enrich the lives of people and be ecologicallyfriendly in support of sustainable development goals(SDGs) for the future.
References

１） Naoki Matsumori, Keiichi Ueda, Technical Trendof the Precision Bearings for Machine Tools, NTN
TECHNICAL REVIEW, No.84, (2016) 40.
２） Keiichi Ueda, Technical Trend of the Precision
Bearings for Machine Tools, Bearing & Motion
Tech, September 2016 Edition, No.002, 33.
３） Shohei Hashizume, Yasuyuki Fukushima, Yusuke
Shibuya, Yohei Yamamoto, Development of Sensor
Integrated Bearing Unit for Machine Tool Spindles,
NTN TECHNICAL REVIEW, No.86, (2018) 50.
４） Shohei Hashizume, Yusuke Shibuya, Daichi Kondo,
Yohei Yamamoto, Hiroyuki Iwanaga, Developmentof Sensor Integrated Bearing Unit for Machine
Tool Spindles, NTN TECHNICAL REVIEW, No.88(2020) 33.
５） Hiroyuki Iwanaga, Development of Edge
Application for Bearing Diagnosis, Inspection
Technology, March 2022 Edition, Vol.27 No.3, 32.

Fig. 8 Indentation bearing vibration verification test results
Photo of authors

52

Shohei HASHIZUMEYudai NAKANO

Daichi KONDO

Yoji OHGUCHI

Yohei YAMAMOTO

Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters

Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters

New ProductDevelopment R&D
Center

New ProductDevelopment R&D
CenterProduct Design Dept.,
Industrial Business
Headquarters

NTN TECHNICAL REVIEW No.89

New
Products

Bearing Diagnostic Edge Application for Industrial IoT
Platforms

Yudai NAKANO*
Takashi HASEBA*
In an effort to realize a smart and efficient factory, IoT-based
condition monitoring systems are attracting attention in recent
years. Rolling bearings are used to support the rotation ofNormal Attention Caution Warning
production equipment. We need to monitor bearing conditions toprevent unplanned downtime due to bearing damage.
NTN bearing diagnostic edge application
NTN has developed a bearing diagnostic edge application forindustrial IoT platforms to monitor bearing conditions using vibration data. In this article, we introduce thefeatures and application examples of the bearing diagnostic edge application.

1. Introduction
There is a rising demand for predictive maintenancefor production equipment, against the backdrop of
manpower reduction and improved productivity at
production equipment. Manufacturers are preferringto transition to condition-based maintenance from theconventional time-based maintenance implemented
at production sites1).
At the production site, it is necessary to minimize
downtime that occurs due to equipment stoppages
so that productivity can be improved. Therefore, wemust apply monitoring technology that will allow
us to quantitatively understand conditions such as
equipment deterioration and failure, and quickly
detect abnormalities that have occurred so thatmaintenance can be performed.
A method to achieve this is monitoring the conditionof production equipment through the use of anindustrial IoT (Internet of Things) platform.
NTN has developed an edge application forindustrial IoT platforms that can diagnose production
equipment bearings through the use of vibration
data. This paper introduces the features of thisedge application and examples of its application at
production sites.

2. Condition monitoring at the production site
2.1 Industrial IoT platforms
Industrial IoT platforms refer to IoT systeminfrastructure in the industrial sector. In the
manufacturing industry, various equipment at the
production site is connected via a network, and the
production process is monitored and controlled. This
allows improvements to be made to productivity ateach step of production.

Fig. 1 shows a schematic drawing of an industrial
IoT platform. This schematic drawing shows how theindustrial IoT platform, edge application and IT system
are linked at the production site.
IT system

Edge Application
Data analysis/AI
Industrial IoT Platforms
Data collection, data management and external system linkup

Production site
Machine tool, PLC, sensors, etc.

Fig. 1 Schematic drawing of industrial IoT platform
An industrial IoT platform connects to equipment
at the production site and collects data relating toequipment operation. An edge application receives
the data collected from the industrial IoT platform
and analyzes it. The analysis results processed here
are then sent to the production site equipment andhost IT system. The IT system takes on the role ofcomprehensively managing the various information
for the production site, and systems such as theEnterprise Resource Planning (ERP) system or
Manufacturing Execution System (MES) can be used
for this task.
Using this industrial IoT platform optimizes
management tasks and provides visualization of the
production site in terms of monitoring the operation* Robotics & Sensing Engineering Dept., Industrial Business Headquarters

NTN TECHNICAL REVIEW No.89

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Bearing Diagnostic Edge Application for Industrial IoT Platforms
and conditions of production equipment.
2.2 Monitoring the condition of bearings
Bearings are precision machine parts where highaccuracy and quality are critical for proper function
and long life. They are installed for use on several
types of equipment to support the rotation ofmachinery.
If a bearing is damaged, the equipment must be
stopped to perform inspection and repairs, which
lowers productivity. Therefore, it is important tomonitor bearing conditions to perform maintenancework at an appropriate time.
A method of diagnosing the bearing using vibration
data is often used to monitor bearing conditions2).
Table 1 shows the types of bearing diagnosis using
this vibration method. Two types are available todiagnose bearings: simple diagnosis and precision
diagnosis.
Table 1 Types of bearing diagnosis
Type

Diagnosis method

Simplediagnosis• Absolute value determination(Evaluated in line with standards/
standard values)• Same type comparison(Evaluated by comparing with the same
type of equipment/machines under thesame conditions)• Trend management(Determine abnormalities by constantly
observing trends)

Precision
diagnosis• Estimates damage positions on bearing
and extent of damage with frequency
analysis (FFT, etc.)*Requires various bearing information

Simple diagnosis monitors changes in thecondition over time and the degree of deviation fromhealthy conditions. Methods include absolute value
determination in line with predetermined criteria
and standards, compariative analysis that involves
comparing the same type of equipment and machines,
and trend management in which constant observation
is implemented. Simple diagnosis is used to properly
understand the bearing condition and create
maintenance plans for equipment based on diagnosis
results, which can prevent such things as unscheduled
equipment stoppages due to bearing damage.
Meanwhile, precision diagnosis is performed whenfurther analysis is required based on the results ofsimple diagnosis. Fast Fourier transform (FFT) andsimilar can be used to analyze the vibration spectrum
to estimate where the bearing is damaged andthe extent of the damage. However, to analyze therelationship between the spectrum and the positionof damage, various bearing factors such as the rolling
element raceway diameter, rolling element diameter,
number of rolling elements, and the contact angle, as

54

NTN TECHNICAL REVIEW No.89

well as information about the shaft rotational speed
are required.

3. Bearing diagnostic edge application
As a bearing manufacturer, NTN has developed a
condition monitoring system (CMS) for wind turbines
using our knowledge about bearing damage alongwith sensing technology and diagnosis technology
developed over many years and released this forsale as “WindDoctorTM”3). Currently, we are providing
a condition monitoring service using this systemon over 250 wind turbines throughout Japan. This
technology was used to develop a bearing diagnostic
edge application using real-time processing functions
from Edgecross4), which is an industrial IoT platform(hereafter, bearing diagnostic application).
3.1 Features
The main features of the bearing diagnostic
application are shown below.
(1) Realtime diagnosis
The application includes NTN proprietary diagnosis
algorithms to automatically collect vibration data for
analysis and diagnosis purposes. Up to 16 locations
are diagnosed within at least 3 seconds using a single
bearing diagnostic application license. This enables
users to know any changes in the bearing condition
that may appear in a short amount of time and can
detect abnormalities early on.
(2) Automatic threshold generation
Thresholds are automatically generated to identify
the bearing conditions based on learned data. Thiseliminates work to configure thresholds that require
an experienced operator.
(3) Provides diagnosis not limited to certain bearing
numbers
It is not necessary to configure such things as
bearing factors and rotational speed. Therefore, theapplication can be used even if you do not know thenumber of the bearing installed on the equipment or
the rotational speed.
(4) Rating scale for bearing health condition
Diagnosis results display 4 ratings (Normal,
Attention, Caution, and Warning) in text and color
on the display screen of the bearing diagnostic
application. Therefore, it is possible to easily know the
bearing condition without the operator performing
detailed analysis.

Attention

Fig. 2 Device configuration for bearing diagnostic applicationPC

Edgecross

PLC

Attention

Fig. 3 Coolant pump diagnosis process

NTN TECHNICAL REVIEW No.89

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Bearing Diagnostic Edge Application for Industrial IoT Platforms
3.2 Usage configuration
The devices required to use the bearing diagnostic
application are a PC installed with Windows operating
system, a vibration sensor, and a data logger.
Edgecross basic software and the bearing diagnostic
application can be used after installing them onto the
PC (Fig. 2).
The bearing diagnostic application can also run
in standalone mode for convenience of use at the
production site.

4. Example of application on coolant
pumpsThis section introduces an example of using
the bearing diagnostic application to monitor theconditions of a coolant pump at the production site.
4.1 Challenges of inspection work
If a coolant pump that supplies coolant toequipment fails, it will lead to production line
stoppages. To mitigate this type of situation, operators
either regularly perform inspection work on theequipment or perform such work depending on thesituation. However, this inspection work relies on theexperience of the operator so there are times when an
operator may fail to notice a problem with the coolant
pump. To prevent this type of situation, it is necessary
to evaluate the bearing conditions automatically andquantitatively (whether damage has occurred and its
extent, etc.) based on the operational status of thecoolant pump expressed in a numerical format.
4.2 Introducing the bearing diagnostic application
Fig. 3 shows the device configuration andmeasurement/diagnosis procedure for this example.
The bearing diagnostic application is organized suchthat it links to the coolant pump control PLC and thedisplay via Edgecross. Operation information such as
the rotational speed, pressure and temperature aredisplayed on the coolant pump control panel display
in addition to diagnosis results from the bearing
diagnostic application.
In this example, operators receive information about
the coolant pump operational status at the same time
the bearing conditions are checked, which reduces
the amount of inspection work the operator must
do. Furthermore, the bearing diagnostic application
constantly monitors the bearing conditions, enabling
any bearing abnormalities or development of damage
to be quantitatively evaluated. If any signs of damage
are discovered on the bearing, control is switched
to lower the load on the coolant pump based on
the diagnosis results, which is expected to delay the
progress of damage on the bearing.

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NTN TECHNICAL REVIEW No.89

5. Proof of concept build support service
When introducing the system to the production site,
proof of concept (PoC) is performed to validate theeffectiveness of introducing the system in advance.
Sensors and equipment used for the PoC step are
prepared by the user. However, when introducing thebearing diagnostic application, users were unable toprepare equipment such as vibration sensors and dataloggers, and it was sometimes difficult to implement
PoC. Due to this fact, NTN provides a “PoC build
support service”5) in collaboration with EdgecrossConsortium4), in which the user can borrow a setof the devices that need to be prepared. They areborrowed for a fixed period at no cost to the user.
Fig. 4 shows a flowchart up to the point of starting
PoC operation for the PoC build support service.
This service includes an interview concerning what
equipment needs to be diagnosed and any issues
to address, followed by a decision on the PoC
implementation details and NTN work support details.
For users who are concerned about how to set up thedevices, NTN also helps set up peripheral devices andconfigure the bearing diagnostic application.
This service has been favorably received by users
who have used it, describing how they were able toquickly start PoC and were able to understand how
it operates. Even after the PoC build support service
ended, many users continued to use the bearing
diagnostic application.

Apply for the proof of concept build
support service

Interview held about requirements
and issues (Web)Loan of PoC Kit, assistance to set
up at production site

Start PoC operation
Fig. 4 PoC build support service flowchart

6. Summary
This paper introduced the bearing diagnostic edge
application used for industrial IoT platforms. It also
showed the introduction of the bearing diagnostic
edge application at a production site using an
example of application on cooling pumps. The bearing
diagnostic edge application is not limited to theexample shown in this paper and is used by a variety
of users. We will continue to develop products withenhanced functionality in the future, provide service
solutions that meet the needs of our users, andcontribute towards improving productivity in eachindustry.
References
1) METI, The State of Government Initiatives for
Promoting Smart Security, (December 2020)
https://www.meti.go.jp/policy/safety_security/
industrial_safety/smart_industrial_safety_
symposium/images/meti_goto.pdf
2) ISO 20816-1:2016, Mechanical vibration- Measurement and evaluation of machine
vibration - Part 1.
3) Makoto Miyazaki, Wataru Hatakeyama,
Application of Condition Monitoring System forWind Turbines, NTN TECHNICAL REVIEW, No.86,(2018) 40-44.
4) Edgecross Consortium, Edgecross Consortium
Official Homepage.
https://www.edgecross.org/ja/
5) Edgecross Consortium, PoC Build Support
Service, Edgecross Consortium Official
Homepage.
https://www.edgecross.org/ja/dounyu_kentou/
poc.html

Photo of authors

Yudai NAKANOTakashi HASEBA

Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters

Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters

NTN TECHNICAL REVIEW No.89

57

Prospects

NTNʼs Activities for the Electric Vehicle andElectrification of Automobiles

Ikuya TATEOKA *With the Paris Agreement of 2015, countries around the world are stepping up efforts to become carbon
neutral. Major countries such as Japan, the U.S., and the EU are aiming to achieve carbon neutrality
before 2050 by expanding the introduction of clean energy and reforming their industrial structures. The
automotive industries are accelerating the development and expansion of sales of electric vehicles thatcan reduce the generation of exhaust gas. This paper introduces NTNʼs products for energy-saving andelectrification of automobile. The products contribute to carbon neutrality.

Against the background of global warming,
international efforts are accelerating toward achieving
a decarbonized society, or, as it also known, carbon
neutrality. The Paris Agreement adopted at the 21stConference of the Parties to the United Nations
Framework Convention on Climate Change (COP21)
in December 2015 set a long-term goal of limitingC
global average temperature increase to less than 2 °above pre-industrial levels, with a further commitment
C below pre-industrial levels.
toward a target of 1.5 °To achieve this goal, the Paris Agreement targets
early limits of greenhouse gas emissions and theachievement of carbon neutrality in the second half ofC
the century. Furthermore, at COP26 in 2021, the 1.5 °target was stated not as an aspirational target but as ashared global goal.
Based on the Paris Agreement, Japanʼs Ministryof Economy, Trade and Industry (METI) has led theformulation of a “Green Growth Strategy for Carbon
Neutrality by 2050”. The strategy calls for 100 %electric vehicles in new car sales by 2035 as one of thegreen growth strategies in the automotive industry,
one of 14 sectors expected to grow in the future. The
development and sales of electric vehicles, includingEVs, are expected to accelerate in the future as part ofefforts toward carbon neutrality. Fig. 1 shows trendsin automobile production and production forecasts forelectric vehicles.
The trend of CASE (Fig. 2), which collectively refers
to Connected, Autonomous, Shared, and Electric(electrification), has come to the forefront as theprominent development trend in the automotive
industry. For example, in the field of automateddriving, the spread of various systems that support
driving and drive control , turning, and stopping,which are the basic functions of automobiles, hasbeen accompanied by a shift toward electrification,
mainly through the use of by-wire systems. Against
the backdrop of these trends, NTN is focusing oncontributing to carbon neutrality and CASE bydeveloping energy-saving and electrificationcompatible products.
120

Automobile production(Millions of units)

1. Introduction

100

ICE

80

FCV

60

HEV
BEV

40
20
0

2017 2019 2021 2023 2025 2027 2029 2031 2033

Fig. 1 Automobile production volume forecast1)■ Linking with IoT-enabled society,smartphones, etc.

■ Providing various services such as

in-car entertainment

Autonomous driving ■ Realizing a society with zero traffic accidents■ Use of IoT/AI technologies■ Evolution of sensing technology

Sharing■ From Ownership to Sharing■ Change in business model to a shared services businessElectrification■ Policy demands for improved environmental

Fig. 2 Overview of CASE automotive trends* Deputy Corporate General Manager, Automotive Business Headquarters

58

NTN TECHNICAL REVIEW No.89

performance■ Spread of EVs/HEVs/PHEVs

2. Market Trends and Responding to These Needs
with NTNʼs Research and Development
Table 1 shows market trends in the automotive
industry, technological trends, and the products that
NTN is developing to respond to market needs. A
key challenge in electrification is to extend range
while reducing power consumption. This is driving
an increase in demand for compact, lightweight,
low torque, and high efficiency components. Thereis also a growing demand for high-speed rotation
drive motors to obtain higher motor output withthe same size. Furthermore, as the overall weight ofthe drive unit is reduced and the housing becomesthinner, the rolling bearings are required to suppress
creep phenomenon (whereby the mating surfacesof the housing and bearing gradually shift due todeformation of the outer ring caused by the load).
In addition, to increase the efficiency of electric
auxiliary equipment, there is a trend toward using
lower viscosity lubricant and reducing the amountof lubricant supplied. The increasing use of rolling
bearings under dilute lubrication conditions canincrease the risk of premature bearing failure due tohydrogen embrittlement. NTN has developed longlife technology to prevent early bearing failure due
to hydrogen embrittlement by applying new steel
materials and special heat treatment technology.2)
On the other hand, many automakers expect that as
the transition to higher levels of autonomous driving
frees people from driving, it will increase demand
for roomy, quiet vehicle interior space. This creates aneed to improve flexibility in the layout of batteries
and electric drive units, and to design componentsthat contribute to the effective use of space. The
increasing demand for SUVs in the global market

and the trend toward longer wheelbases to increase
battery capacity are increasing the minimum turning
radius of vehicles. NTN is developing CVJs withhigher angles and rear-wheel steering mechanisms
to address this trend. In addition, to pursue safety
and comfort, it is necessary to work on drive motors,
brakes, suspension, steering, and system control thatcombines these components. NTN is also working
to develop module type products for electrification
by utilizing its core technologies in tribology, bearing
design technology, mechatronics, and other areas. The
following is a list of representative products developed
by NTN.

3. Automotive products developed for
EV and electrification
3.1 Deep groove ball bearing for high-speed
rotation

The market for e-Axles is expanding due to theelectrification of automobiles. Deep groove ballbearings, which support the motor shaft of e-Axles
and the directly connected motor of reduction gears,
are required to support high-speed rotation. As
the rotational speed of deep groove ball bearings
increases, centrifugal force causes contact between
the cage pockets of the resin cage and the rolling
elements (balls), which may result in seizure.
In response to this, we developed a high-speed
deep groove ball bearing for EV/HEV with a newshaped resin cage that takes into account the
deformation of the cage during high-speed rotation.
We found conditions where d mn = 180 × 104
operation is possible with oil lubrication3). Here, d mn isthe product of the rolling bearing pitch diameter androtational speed, and the unit is mm/min-1.

Table 1 NTN-developed products that respond to market trends/technological trends/market needs
for automotive electrification
Market trend

Technology trends
Downsizing andlightweighting

Acceleration ofelectrification
andenergy saving

Low torqueDeveloped products that meet market needs
・Needle bearing unit for planetary gear reducers
・Creepless bearings
・Deep groove ball bearings with ultra-low friction seals
・Low Friction HUB Bearing Ⅳ

Higher efficiency

・Higher efficiency fixed constant velocity joint CFJ

Higher speeds

・High Speed Deep Groove Ball Bearing for EV/HEV

Lower viscosity
lubricating oil

・Hydrogen Embrittlement Resistant Bearings

Pursuing comfort

Drive stability

・Hub Bearing Modules with Rear Steering Function Ra-sHUBTM

Pursuing safety

Improving electronic
control technology

・Ball screw drive modules for electronic hydraulic brakes
・Electric oil pumps

NTN TECHNICAL REVIEW No.89

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NTNʼs Activities for Electric Vehicle and Electrification of Automobile
The new shape resin cage has the following features.
Fig. 3 shows the appearance of the new shape resin
cage.
(1) Adoption of high-strength materials⇒ Improved rigidity and hot strength of cage(2) Thickening of the pocket bottom to suppress
deformation⇒ Improved rigidity of the cage ring(3) Thinned wall between cage pockets(weight reduction)⇒ Reduction of centrifugal force deformation(4) Installation of oil grooves on the inner surface ofthe cage pockets⇒ Improved lubricity of cage and rolling elements

3.3 Needle bearing unit for planetary gear reducers
The needle bearing unit for coaxial e-Axle planetary
gear reducers (Fig. 4) are compact in the axial
direction. Planetary gear reducers with sun and ringgears in parallel on the same axis tend to use smalldiameter, long-shaft planetary shafts. The bearings
must be durable under high-speed rotation, dilutelubrication, and moment load conditions. Here we
introduce needle bearings for planetary gear reducers
that meet these needs.

Bearing

Sun gear

Pinion wheel(a) Conventional product(b) New model productFig. 3 Exterior photo of resin cage
3.2 Deep groove ball bearing with ultra-low friction seal
We developed a deep groove ball bearing with ultralow friction seal that reduces running torque by 80 %compared to the conventional contact sealed types byadopting a unique shaped low friction seal.
Rolling bearings used in electric drives such as
e-Axles require not only long operating life but
also lower torque. The conventional approach topreventing bearing operating life reduction caused
by intrusion of hard foreign matter, such as gear wear
particles generated in the reduction gears, has been
to use contact sealed type bearings. But the problem
with this was that the seal comes into contact withthe bearing inner ring, which generates drag torqueduring rotation. In addition, the contact sealed type
bearing is difficult to use in recent EV and HEV
applications, which require high-speed rotation, due
to the limitation of the circumferential speed limit of
the seal.
Deep groove ball bearings with ultra-low friction
seals employ a newly developed contact seal witharc-shaped (half-cylindrical shaped) micro convexes
at equal intervals on the sliding contact zone of theseal lip to reduce running torque by 80 % compared
to conventional products. This achieves a low-torqueeffect comparable to that of ball bearings with noncontact seals. During rotation, the wedge film effectof the micro convexes forms an oil film between thesliding surfaces of the seal and inner ring, significantly
reducing seal drag torque despite the fact that it isa contact type seal. Furthermore, since the micro
convexes on the seal lip are extremely small, they can
prevent the intrusion of hard foreign matter harmful tothe bearing, even through the lubricating oil, without
the reduction of bearing operating life.

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NTN TECHNICAL REVIEW No.89

Ring gear

Fig. 4 Structure of co-axial type e-Axle planetary gear reducer
Needle bearing units for planetary gear reducers(bearing unit in Fig. 4) consist of rollers, cage, andshaft. The features of each component are as follows.
(1) Rollers (high carbon chromium steel, special
heat treatment)
The crowning shape required for the function
was optimized, reducing the maximum contact
stress in a moment load environment.
(2) Cage (low carbon steel, carburized)
Improved cage fatigue strength by changing
materials, optimizing weld geometry, andselecting the appropriateheat treatment(an improvement of 1.2 times compared toconventional products)(3) Shaft (low carbon steel, special heat treatment)
Plastic deformation is reduced by selecting amaterial containing a lower amount of alloy
components related to hardenability and by
optimizing heat treatment (an improvementof 70 % compared to conventional products).
The amount of retained austenite in the surface
layer and surface hardness were optimized to
improve durability.

3.4 Low Friction HUB Bearings
Over the years, NTN has conducted research anddevelopment in pursuit of lighter weight, longer
operating life, and higher efficiency for hub bearings
that support tire rotation. We have promoted theunitization of bearings and peripheral components,
contributing to lower fuel consumption andimproved ease of assembly through downsizing
and lightweighting. We have developed productswith longer operating life and lower torque throughimprovements in areas such as materials, heat
treatment, grease, and seal structure. Table 2 shows
the Transition of improvements in low friction HUB
bearings.4)
Recently, to respond to the global demand for
improved fuel efficiency of automobiles and stricter
CO2 emission regulations, we have worked to further
reduce torque by developing the Low Friction HUB
Bearing Ⅳ” (Fig. 5). The Low Friction HUB Bearing
Ⅳ features a seal coating grease with a special
thickening agent that reduces the running torque ofthe seal by 38 % compared to conventional grease
while maintaining functions such as resistance against
environmental contamination and low temperatures.
Currently, the sealʼs performance is being evaluated,
and the product will be introduced to the market
as soon as possible. Furthermore, by optimizing
the internal preload of the bearing and combining
elemental technologies up to the Low Friction HUB
Bearing Ⅲ5) (Table 2) developed in 2019, the bearing
running torque was reduced by 67 % compared to
Low Friction HUB Bearing Ⅰ.
Table 2 Transition of Improvements to Low Friction
HUB Bearings

Bearing

Low-torque technology
application factor

Ⅰ

Ⅱ

Bearing
specifications,preload

Ⅲ

Ⅳ

〇

◎

Bearing interior
grease○◎←Seal coating grease

○

←

◎

←

←

←

Lip contact status

○

←

←

Number of lip
contacts○←←

Lip design
Seal

Low Friction HUB Bearings○

Optimization of
bearing pre-load[Outer seal][Inner seal]

New seal coating grease- Special thickening agent- Base oil, additive improvement

Fig. 5 Low Friction HUB Bearing Ⅳ
3.5 Higher efficiency fixed constant velocity joint CFJ6)
Power from engines and motors is transmitted tothe tires via variable speed reducers and differentials
through drive shafts. A key challenge for improving
fuel efficiency and electricity costs in automobiles
will be to reduce the torque loss of these powertransmission paths.
The drive shaft consists of two constant velocity
joints (CVJ), a fixed type and a sliding type, connectedby a shaft, with a typical torque loss ratio of
approximately 1 %. Here, we introduce the CFJ, whichuses a proprietary spherical cross groove structure
to reduce the torque loss ratio by more than 50 %compared to conventional products.
Fig. 6 shows the structure of the CFJ, which consistsof an inner and outer ring with raceway grooves(tracks), eight balls that transmit rotational torque,and a cage that holds the balls. The torque loss of the
CVJ is caused by energy loss due to friction between
the parts. To reduce this internal friction, the CFJ has
arc-shaped tracks on the inner and outer rings inclinedin the axial direction and adjacent tracks arranged in
mirror-image symmetry. In the conventional product,
the load (F1 and F2 in the figure) of the ball pushing
the cage is directed in one direction on all tracks.
However, in the CFJ, the above-mentioned structure
pushes the cage in different directions, so the internal
forces cancel each other out on adjacent tracks,
significantly reducing friction between internal parts
compared to conventional products.
Outer ring（

：direction of the force of the ball pushing the cage）

Balls (8)Cage
Inner ring〇：First return improvement, ◎：Additional improvement

Raceway groove (track)[Spherical cross-groove structure]

Fig. 6 CFJ structure and internal forces

NTN TECHNICAL REVIEW No.89

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NTNʼs Activities for Electric Vehicle and Electrification of Automobile
CFJ achieved a torque loss ratio of less than 0.4 % (areduction of 50 % or more compared to conventional
products) at an operating angle of 9 degrees,
enabling world-class transmission efficiency. The
difference in efficiency from conventional products is
known to yield corresponding improvements in fuelconsumption and electricity costs. CFJ, which enteredmass production in 2022, is expected to be a new
product that can greatly contribute to decarbonizationin the future.
3.6 Ball screw and ball screw drive module forelectronic hydraulic brake
NTN has a strong track record in ball screws, oneof our core technologies, for automotive applications
starting in 2004, when mass production began. The
features of NTN ball screws include (1) linear motion
conversion efficiency of 90 % or higher, (2) highload capacity (Fig. 7), and (3) improved positioning
and position retention due to the high reliabilityof circulating parts. Table 3 shows examples ofapplications of NTN ball screws.

As a modular product using ball screws, we
introduce the ball screw drive module for electronic
hydraulic brakes shown in Fig. 8. It is used in thebrakes of vehicles such as EVs and HEVs as aregenerative mechanism that recovers kinetic energy
during vehicle braking as electrical energy. To enableefficient recovery of kinetic energy as electricity, it isimportant to optimize the distribution of regenerativeand hydraulic brakes so that they can instantly
respond to changing braking effort. To address
this issue, NTN has utilized its ball screw producttechnology to develop a ball screw drive module forelectric hydraulic brakes that uses a motor drive toenable precise control of hydraulic brakes. We beganmass production in 2012.
Input gear

Aluminum case

Output gear

Motor

Ball screw nut
High-load
capacity design

Conventional
designBearings

Ball size

Lead
Ball screw shaft
Shaft anti rotation sleeve

Compared to the lead, ball size is maximized, enabling higher load
carrying capacity (about twice that of NTN conventional products)

Fig. 7 Features of NTN ball screws
Table 3 Examples of applications of NTN ball screws
Location of
application

Ball screw

AMT shift unit

Variable valve
lift mechanism

Electronic
hydraulic brake
AMT：Automated Manual Transmission

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NTN TECHNICAL REVIEW No.89

Fig. 8Fig. 8 Structure of the ball screw drive module forelectronic hydraulic brake
As automatic braking becomes mandatory andmore sophisticated, more responsive brakes will be
required. Electric hydraulic brake systems are also
being increasingly used to improve fuel efficiency
and electricity costs. We believe that there will be a
growing need for our ball screws and ball screw drive
modules for electronic hydraulic brakes, which cancontribute to a higher response of automatic brakes.
3.7 Electric oil pump
In ATs and CVTs, the clutch is operated hydraulicallywhen starting and shifting gears. This hydraulicpressure is normally supplied by a mechanical oilpump driven by the engine. Electric oil pumps are
increasingly being used to improve fuel efficiency by
reducing oil pump drive loss and to secure hydraulicpressure and lubrication when the engine is stopped in
vehicles equipped with a start-stop function. In recent
years, the e-Axle, which integrates a motor, inverter,and reduction gearbox, has been used increasingly asa drive motor for EVs. The use of oil-cooled systems
for cooling motors is expanding, as they offer a
superior cooling effect to water-cooled systems
and contribute to higher efficiency and smaller
motors. It is expected that electric oil pumps will be
increasingly used in electric vehicles. In response tothis technological trend, NTN is developing an electricoil pump that can help enhance vehicle environmental
performance (Fig. 9, Table 4).
Controller case(+direct coupler)

Bus bar

PCB(printed circuit board)

Pump cover

Pump rotor

Motor rotor

Motor stator

Fig. 9 Electric oil pump structure
Table 4 Electric oil pump specifications
Item

Details

Pump(1) 30 W or less (when used for idle stop)

output(2) 30-300 W (when used for e-Axle, etc.)

Voltage

12 V (to 48 V)

HydraulicpumpTrochoid pumps (vane pumps)

Control

PWM (CAN compatible)

Features- Lightweight and compact design
achieved by the use of BLDC motors- Aluminum body for improved heatdissipation- Equipped with a rotation sensor tohandle various operating conditions (lowtemperature, low RPM, etc.)

3.8 Hub Bearing Module with Rear Steering Adjust
Function “Ra-sHUBTM”
The hub bearing “Ra-sHUBTM” with rear steering
adjust function (Fig. 10) utilizes the strengths of our
hub bearing base technology. We developed this as asteering system that adjusts to the driving conditionof the vehicle, controlling the wheel steering angle
and improving turning performance at low speeds
and increasing vehicle stability at medium and highspeeds.
Although first applied to mass-produced vehicles
in the 1980s, rear-wheel steering systems were notwidely used at that time because it was widely feltthat the vehicle responded unnaturally to the driverʼsoperation of the steering wheel. In recent years,
however, advanced control technology has madeit possible to suppress the sense of an unnatural

response. Adoption is increasing, particularly in luxury
and sports cars. In addition, EVs tend to have a longer
wheelbase and larger turning radius in order to securebattery installation space. There is a limit to reducing
the vehicle radius of gyration by increasing thesteering angle of the front wheels, and a rear-wheel
steering system can assist in this reduction.
Conventional rear-wheel steering systems arelimited to undercarriage structures such as multi-link
systems. Structurally this made it difficult to achievea large operating angle. The “Ra-sHUBTM” integrates
the steering shaft in the hub bearing with the steering
mechanism, enabling installation in the same manneras conventional hub bearings, while maintaining acompact design. Regardless of the undercarriage
structure that is chosen, it can be mounted on rigid
axle structures such as torsion beams, and canbe applied to rear-wheel steering systems withindependent left and right wheels and large operating
angles. Furthermore, the steering function can behoused in the wheelhouse, enabling effective use of
space inside the vehicle.
Advantages of the rear-wheel steering system using“Ra-sHUBTM” include the following.
(1) Reduction of vehicle turning radius(2) Mounted on the left and right wheels,
independent control of the steering angle(3) Improved driving safety (vehicle attitude control)(4) Improved fuel economy (reduced driving
resistance)

Base

Actuator

Steering axis

Hub bearing

Fig. 10 Ra-sHUBTM (prototype)

NTN TECHNICAL REVIEW No.89

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NTNʼs Activities for Electric Vehicle and Electrification of Automobile
4. Conclusion
In the automotive industry, technologies are being
developed for carbon neutrality and CASE. This has
driven changes in demand for the bearings, hub
bearings, CVJs, and electric module products that weoffer. NTN has been quick to identify these market
trends, developing high value-added productswith original technologies that lead to customer
satisfaction. In this paper, we have introduced some ofour recently developed products and technologies to
respond to EVs and electrification in the automotive
industry. In the future, we will continue to contributeto the promotion of carbon neutrality and the further
development of the automotive industry through thedevelopment of new technologies and new products.
References

１） S&P Global Mobility Data (January 2023) + NTNForecast

２） NTN website, “Hydrogen Embrittlement ResistantBearings” developed

https://www.ntn.co.jp/japan/news/new_products/
news202100038.html
３） NTN website, Nippon Brand Award of 2021
“CHO” MONODZUKURI Innovative Parts andComponents Award
https://www.ntn.co.jp/japan/news/press/
news202100067.html
４） Makoto Seki, Low Friction HUB Bearing, NTN
TECHNICAL REVIEW, No. 85, (2017) 67-71.
５） Makoto Seki, Low Friction HUB Bearing Ⅲ, NTN
TECHNICAL REVIEW, No. 87, (2019) 63-67.
６） Teruaki Fujio, Next Generation High Efficiency
Fixed Constant Velocity Joint “CFJ”, NTN
TECHNICAL REVIEW No. 81, (2013) 64-67.

Photo of author

Ikuya TATEOKA
Deputy Corporate
General Manager,
Automotive Business
Headquarters

64

NTN TECHNICAL REVIEW No.89

Commentary

Introduction of Rolling Bearings for Electric Drives
Corresponding of Automobiles

Takashi KAWAI *Tomohisa UOZUMI **Continued electrification of automobiles has introduced the need for electric drive bearings with new anddiverse performance capabilities. This article introduces the efforts made at NTN to design rolling bearings
specifically to meet these requirements.

1. Introduction
The automotive industry is undergoing an
unprecedented transition from gas powered to fully
electric vehicles. The shift to electric vehicles (EVs) isaccelerating worldwide as one solution on the path toachieving carbon neutrality1). Rolling bearings, which
support power transmission in electric drives, are a
key component. They must respond to the demandfor higher speeds in addition to smaller size, lighter
weight, and lower torque. Here NTN introduces rolling
bearings for electric drives that have been designed
specifically to meet these requirements.

Fig. 2 shows an example of an “e-Axle”. An e-Axle
is a drive unit which integrates a motor, inverter, andreduction gear for electric vehicles (EVs). An e-Axle witha parallel three-axis structure uses two bearings forthe motor and six bearings for the gear reducer. Fig. 3
shows a typical example of a parallel triaxial e-Axle witha rolling bearing arrangement supporting the motor andreduction gearbox. Since the combination of the motor
torque and reduction ratio affects the bearing load oneach axis of the reducer, deep groove ball bearings andtapered roller bearings are used on the second andthird axes, depending on the load.

2. Performance Requirements of
Rolling Bearings for Electric Drives

Motor

There are two main types of rolling bearings forautomobiles: deep groove ball bearings and tapered
roller bearings. These rolling bearings consist of thefour parts shown in Fig. 1 (inner ring, outer ring,rolling elements [balls and tapered rollers], andcage) and sometimes seals. With the recent shift toelectric vehicles, bearings are required to have new
performance characteristics to meet the operating
conditions.
Seal

ReducerFig. 2 Example of e-Axle structure and arrangementof rolling bearings3)

Outer ring

Cage
Deep
groove ballbearings
appliedRolling
element(a) Deep groove ballbearings

Inner ring(b) Tapered roller
bearings

Fig. 1 Rolling bearing cross-section and part names

2)(a) Using deep groove ballbearing for all

Taperedrollerbearings
applied(b) Using tapered roller bearingsin shaft 2 and shaft 3

Fig. 3 Example of rolling bearing arrangement
in a simplified cross-sectional view of an e-Axle(motor and reduction gear)4)* Automotive Bearing Engineering Dept., Automotive Bearing Products Unit, Automotive Business Headquarters** NTN BEARINGS (UK) LTD.

NTN TECHNICAL REVIEW No.89

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Introduction of Rolling Bearings for Electric Drives Corresponding of Automobiles
The rolling bearings used in each of the e-Axleʼsaxes are required to have the following performance
characteristics.
(1) To meet the demands for higher power output
and downsizing of the e-Axle, driving motors areoperating at higher speeds. The deep groove ballbearings that support the motor shaft and the
directly connected motor shaft of the first reducer
shaft are required to offer high-speed performance.
(2) As bearing raceways become thinner due tothe e-Axle becoming smaller, creep (a sliding
phenomenon in which the outer ring rotates relative
to the housing) is more likely to occur on the outer
diameter of the outer ring. Each reduction gear
shaft must therefore have anti-creep measures.
(3) The high voltage of the batteries used in e-Axle
motors requires countermeasures against electricalpitting of the bearings (a phenomenon in whichelectrical discharge occurs in the bearing, causing
microscopic melting of the raceway surface) in the
motor shaft and the first shaft of the reduction gear.
(4) To improve the efficiency of the e-Axle under low
viscosity lubricating oil, the tapered roller bearing
supporting the second shaft of the reducer requires
heat generation countermeasures at the area of
sliding contact on the large end rib.
(5) The increased bearing load associated with thehigher output of the e-Axle requires the tapered
roller bearings supporting the second and third
shafts of the reducer to have a higher load carrying
capacity than conventional bearings.
Table 1 summarizes the performance requirements for
e-Axle rolling bearings.
Table 1 Performance Requirements for e-Axle rolling
bearings
Markettrend

Technology
trendsPerformance requirements forrolling bearings

Low torque3.1 Deep groove ball bearing
with ultra-low friction seal
Higher efficiency 4.1 Low temperature rise andlow torque tapered roller
bearing
Support for high-speed

Higher speed

3.2 Deep groove ball bearing

Environment
for high-speed rotation
ally friendly
technology Downsizing and Improved creep resistancelightweighting 3.3 Creepless bearings
Motor-driven
electrification Higher voltage Preventing electrical pitting
3.4 Ceramic rolling element
HigherShareddeep groove ball bearings
frequency

3. Introduction of high-performance
deep groove ball bearings
This section introduces the technology NTN has
developed for deep groove ball bearings to meet theperformance requirements for e-Axles as shown in
Table 1.
3.1 Deep groove ball bearing with ultra-low friction seal
Due to increased demand for higher efficiency
and more compact e-Axles, the deep groove ballbearings used in these applications are required tohave both high operating life and low operating torque.
Optimizing e-Axle bearing operating life requires
preventing hard particulate material present in the
lubricating oil of the application from contaminating
the bearing rolling surfaces. Although contact seals canprevent the intrusion of particulate contamination, it
is difficult to optimize both bearing life and operating
torque with this seal type because sliding torque (which
accounts for most of the running torque for deep
groove ball bearings with contact seals) is generated
at the contact area between the seal lip and the innerring.
NTNʼs newly developed ultra-low friction seal5)
employs a contact-type seal with arc-shaped(half-cylindrical shaped) microscopic convexes at equalintervals on the sliding contact area of the seal lip, asshown in Fig. 4. During rotation, the wedge film effectof the microscopic convexes forms an oil film (Fig. 5)
between the sliding surfaces of the seal and inner ring,
significantly reducing seal drag torque compared toa more conventional contact-type seal. Furthermore,because the clearance between the seal and the innerring sliding surface is extremely small, the intrusion ofparticulate contamination of a size that would affectbearing operating life can be prevented.
Under the conditions shown in Table 2, NTN
compared running torque between the ultra-low
friction seal and conventional contact/non-contact
seals. As shown in Fig. 6, The running torque of the ballbearing with ultra-low friction seals was 80 % lower
than that of the ball bearing with contact seals dueto the wedge film effect of the micro convexes on theseal lip. Running torque of the ball bearing with ultralow friction seal was also equivalent to that of the ballbearing with non-contact seals.

Lower viscosity and Lower temperature risesmaller volume of 4.1 Low temperature rise and low
torque tapered roller bearings
lubricating oil
Long operating life

High reliability 4.2 Tapered roller bearings withlong operating life

66

NTN TECHNICAL REVIEW No.89

Arc-shaped micro convexes (5 points in the upper cutout)

Fig. 4 Cross section of deep groove ball bearing withultra-low friction seal5)

Arc-shaped micro
convexes
Pressure distribution

Seal
Oil film

3.2 Deep groove ball bearing for high speeds
By adopting a new shape of resin cage that takes
into account the deformation of the cage duringhigh-speed rotation, NTN found operation was
possible under oil lubrication at d mn*1 = 180 × 104.
Here NTN introduces a high-speed deep groove ballbearing for EV/HEV that uses high-speed rotation
technology.6) 7)*1 Bearing rolling elements pitch diameter and rotational speed
mm min-1

Inner ring
Direction of rotation

Fig. 5 Diagram of wedge film effect5)
Table 2 Test condition5)
Test bearing

6010 equivalent

Radial load

Basic dynamic load rating of 5 %(JIS B 1518:2013)

Rotational speed

1 500 min-1

Bearing temperature

35 to 120 C

Lubricating oil

CVTF(1) Adoption of high-strength materials⇒ Improved rigidity and strength of cage(2) Thickening of the pocket bottom to suppress
deformation⇒ Improved rigidity of cage ring(3) Thinned wall between cage pockets (weight reduction)⇒ Reduction of centrifugal force deformation(4) Installation of oil grooves on the inner surface ofthe cage pockets⇒ Improved lubricity of cage and rolling elements

Deep groove ball bearing with ultra-low friction seal
Ball bearing with non-contact seal
Ball bearing with contact seal
0.40

Running torque N･m

0.35

A temperature rise qualification test (oil lubrication)
was conducted on high-speed deep groove ballbearings for EVs and HEVs under the conditions shownin Table 3. Fig. 8 shows the test results. The outerring temperature of the high-speed deep groove ballbearings could be operated stably below the upper
temperature limit for d mn values up to 180 × 104.

0.30
0.25

80 %
reduction

0.20
0.15
0.10
0.05
0.00

Deep groove ball bearings, which support the motor
shaft of e-Axles and the directly connected motorof first axis reduction gears, are required to support
high rotational speeds. As the rotational speed ofdeep groove ball bearings increases, centrifugal force
causes contact between the cage pockets of the resin
cage and the rolling elements (balls), which may result
in seizure.
In response to this, NTN developed high-speed
deep groove ball bearings for EVs and HEVs by adding
improvements (1-4) to the resin cage.
Fig. 7 shows a comparison between theconventional and improved resin cage.

Table 3 Test condition2)
0

20

40

60

80

100

Bearing temperature °
C

120

140

Fig. 6 Relationship between running torque andbearing temperature5)(a) Conventional resin cage

Tested bearing
characteristics

Basic dynamic load rating= 16 800 N(JIS B 1518:2013)

Radial load

264.5 N

Axial load

147 N

Rotational speed

d mn 160 to 180×104(b) Modified resin cage

Fig. 7 Exterior of resin cage for high-speed deep groove ball bearings for EV/HEV 4)

NTN TECHNICAL REVIEW No.89

67

Relative percentage of outerring temperature

Introduction of Rolling Bearings for Electric Drives Corresponding of Automobiles

Undercut

Judgment
upper limit
temperature

100
95
90
85
80

0

160

170

180

dmn ×104

Fig. 8 Relationship between d mn and outer ringtemperature2)
Recently, by optimizing the lubrication conditions
and the internal elements of the bearing, NTN has
confirmed that the deep groove ball bearing can
support high-speed rotation with a d mn value of 220
× 10 4 8).
3.3 Creepless bearing
As bearing raceways become thinner due to thedemand for smaller and lighter e-Axles, the rigidity ofthe outer ring decreases, increasing the likelihood ofrippling deformation on the outer ring outer diametersurface as the rolling element passes through. This
repetition results in a progressive wave that causes
the outer ring to rotate relative to the housing(progressive wave type creep).10)
The structure of the creepless bearing that NTN
has developed is shown in Fig. 9. As shown in Fig. 10,
by providing a full-width arc-shaped relief area on a
portion of the outer ring outer diameter surface, thehousing inner diameter surface and outer ring outer
diameter surface lose contact when the undercut of
the outer ring is positioned in the load-bearing zone,
thereby blocking the transmission of traveling waves.
This suppresses creep. Although creep occurs when
the undercut of the outer ring is positioned in the
non-load-bearing zone, creep stops at that position
when the undercut of the outer ring moves to theload-bearing zone. Therefore, when the bearing isassembled into the housing, there is no need to alignthe undercut with the load-bearing zone. The only
design change is in the undercut of the outer ringouter diameter, making it easy to replace an existing
bearing.
Creep rate evaluation tests were conducted on
creepless bearings and standard deep groove ballbearings11) under the conditions shown in Table 4 ina testing machine for inducing creep. The test results
are shown in Fig. 11. The creep rate of the standard
deep groove ball bearing tended to increase withincreasing load. By contrast, it was confirmed thatcreep did not occur in the creepless bearing under anyof the loading conditions due to the effect of the outerring undercut.

Fig. 9 Cross section of creepless bearings9)

Red line part:
Outer
diametershape of outerring underload

Housing

9)68

NTN TECHNICAL REVIEW No.89

Undercut

No contact with
deformation of outer
diameter surface

Fig. 10 Relationship between creepless bearing
outer ring shape and housing9)
Table 4 Test condition9)6208

Radial load

Basic dynamic load rating(JIS B 1518:2013)
10 % - 40 %Inner ring rotational speed

6 000 min-1

Lubricating oil

CVTF

Bearing outer ringtemperature

50 ℃

Creep speed Degree/min

Bearing number

100Standard type deep
groove ball bearing
Creepless bearing

80
60
40

Creep speed zero

20
0

0

10

20

30

40

50

Radial load (ratio to basic dynamic load rating) %Fig. 11 Creep speed evaluation test results9)

Table 5 Test condition14)

3.4 Ceramic rolling element deep groove ball bearings

Bearing being tested
Rolling element

Fig. 12 Ceramic rolling element deep groove ball bearings
Inverter-driven motors are shifting toward higher
power output and smaller size, and the drive power
supplies are becoming higher voltage. In the case of
inverter drives, a potential difference is generated
between the shaft and housing. The oil film that forms
between the bearing raceways and rolling elements is
known to break down, causing damage due to electricaldischarge. 12) 13) The higher the voltage, the greater the
potential difference generated, which increases the riskof bearing damage due to dielectric breakdown. This
leads to acoustic deterioration and a shorter operating
life. As a countermeasure, a ceramic rolling element
deep groove ball bearing (Fig. 12) using silicon nitride
ceramic balls as rolling elements can be applied toinsulate the inner and outer ring raceways and preventthe occurrence of electrical pitting.
Rolling tests were conducted under the conditions
shown in Table 5 on the test machine shown in Fig. 13
to investigate bearing spalling life in an energizedenvironment. The results are shown in Table 6.
Compared to standard ball bearings using steel balls,
the ceramic rolling element deep groove ball bearing
can suppress the occurrence of spalling on the rolling
element surface due to electrical pitting.
Testbearing

Pulley

Pin A

Pin B
Supportbearing

Insulating
material

Fig. 13 Rolling life test machine

Deep Groove Ball Bearing(6203)
Steel ball

Ceramic ballGreaseNon-conductive grease

Amount of grease injected (g)0.86

Rotational speed (min-1)

0-20 000(rapid acceleration/
deceleration)

Atmosphere

Room temperature

Pulley load (N)1 617

Bearing load (N)Current (A)

2 332
0.5

Stopping conditions−

Vibration 10 times initial level

Table 6 Rolling life test results for energized state14)
Life (h)Spalling area

Deep groove ball bearings(steel balls)

19.6

ball

Deep groove ball bearings(ceramic balls)

>200

None

4. Introduction of high-performance
tapered roller bearings
Fig. 14 shows the structure of a tapered roller
bearing. Compared to ball bearings, tapered roller
bearings can support higher radial and axial loads,
but also generate more torque. NTN has developed atapered roller bearing that achieves both low torque(low temperature rise) and long operating life by
optimizing the geometry of the rolling surfaces andthe inner ring large end rib face. 16)
Inner ring large
end rib
Outer
ring

Cage

Inner
ring
Rolling element (tapered
roller bearing)

Fig. 14 Structure of tapered roller bearing15)
4.1 Low Temperature Rise and Low Torque
Tapered Roller Bearing
The lubricating oil used in e-Axles is becoming lower
in viscosity and volume in order to achieve higher
efficiency in automobiles. When standard tapered
roller bearings are used under these conditions, it
becomes difficult for an oil film to form in the sliding
contact area of the bearing rib, increasing the risk of
rapid temperature rise. Our newly developed Low

NTN TECHNICAL REVIEW No.89

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Introduction of Rolling Bearings for Electric Drives Corresponding of Automobiles
Temperature Rise and Low Torque Tapered Roller
Bearing improves anti-galling and reduces torque bymaking the design changes described in (1) to (4)below (Figs. 15 and 16).

Tapered roller pitch
circle diameter(1) Compact design oftapered roller pitch
circle diameter

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NTN TECHNICAL REVIEW No.89

Table 7 Test bearing16)
Standard tapered roller
bearing 32007X
18

13.5

φ58.5

Scale
drawing of
bearing
crosssection

Low Temperature
Rise and Low Torque
Tapered Roller Bearing

φ34

A rotary torque test was carried out under theconditions shown in Table 8 to compare performance
between a conventional tapered roller bearing11) andthe Low Temperature Rise and Low Torque Tapered
Roller Bearing shown in Table 7. The test results
are shown in Fig. 17. The Low Temperature Rise
and Low Torque Tapered Roller Bearing achieved asignificant torque reduction of 66 % compared to theconventional design.
Temperature rise characteristics were evaluatedfor the two types of bearings shown in Table 7 under
the conditions shown in Table 9. In this test, tosimulate an oil starved environment in the e-Axle, thebearings were operated after only an extremely small
amount of lubricating oil was applied to the bearing
surface. The bearings were tested until the outer ring
C. The test results aretemperature reached 100 °C for theshown in Fig. 18. The time to reach 100 °Low Temperature Rise and Low Torque Tapered Roller
Bearing was approximately 10 times longer whencompared to the standard tapered roller bearing.

Fig. 16 Structure of “Low Temperature Rise and Low
Torque Tapered Roller Bearing”16)

φ62(1) Compact size and low torque enabled bytapered roller and reduced pitch diameter(2) Reduced clearance between cage inner ring andinner ring cone front face rib outer diameter
reduces torque caused by agitation of lubricatingoil(3) Recessed shape added to large diameter end ofcage pocket improves lubricity(4) Optimal shape of tapered roller end face andinner ring large end rib face improves lubricity(4) Optimal shape between
the tapered roller end
face and inner ring large
end rib(2) Smaller clearance
between cage innerdiameter and innerring small side rib
outer diameter

φ35

Fig. 15 Exterior of Low Temperature Rise and Low
Torque Tapered Roller Bearing16)(3) Concave shape
applied to pocket
large side edgeSize

φ35 φ62 18

φ34 φ58.5 13.5

Dynamic
load rating

46 000 N

28 500 N

Cage

Standard steel plate cage

New shape resin cage

Table 8 Test condition16)
Axial load

3 000 N

Rotational speed

5 000 min-1

Lubrication conditions

Oil bath
ATF (50 °C)

Table 9 Test condition16)
Lubricating oil conditions

ATF (25 °C)

Inner ring large end rib plane
contact stress

Approx. 200 MPa

Inner ring large end rib planesliding velocity

Approx. 2.5 m/s

Roller Bearings to achieve a dynamic load rating whichis 1.3x higher than conventional product and a rated
life which is 2.5x higher.*2 The geometry of the contact
area on the inner ring large end rib surface was also
optimized to improve the allowable rotational speed
by approximately 10 %*3.

50
40

66 %
reduction30*2: Comparison with tapered roller bearings to which thebasic dynamic load rating is applied according to JapaneseIndustrial Standards B 1518:2013.

20
10
0

Standard
tapered roller
bearing*3: Comparison with tapered roller bearings in NTN Corporation
Ball and Roller Bearings Catalog (CAT.No.2203/J 20.08.199
NI/NI)

Low Temperature Rise
and Low Torque Tapered
Roller Bearing

Fig. 17 Tapered roller bearing running torque test results
Time for outer ring temperature toreach 100 °
Cs

16)

800
700

Fig. 20 compares the contact stress distribution of
ULTAGE Tapered Roller Bearings and a conventional
tapered roller bearing design.11) The ULTAGE Tapered
Roller Bearings do not have excessive stress (edgestress) at the edge of the contact area due to the
optimized crowning geometry.

600
500
400

Large

Approx. 10
times

Standard tapered roller bearings
ULTAGE Tapered Roller Bearing

300
200
100
0

Standard
tapered roller
bearing

Low Temperature Rise
and Low Torque Tapered
Roller Bearing

Fig. 18 Tapered roller bearing temperature rise
evaluation test results16)
4.2 Long operating life tapered roller bearings
Here we introduce ULTAGE Tapered Roller
Bearings,15) which feature an optimized internalbearing design to achieve high load capacity andhigh-speed rotational performance (Fig. 19).

Contact stress

Running torque N･cm

60

Small

Rolling contact surface of tapered
roller Shaft direction widthFig. 20 Contact stress distribution on the raceway
surface of a tapered roller bearing15)
Service life tests were conducted under the highmisalignment (0.002 rad) conditions (Table 10)
assumed for e-Axle. Fig. 21 shows the test results.
The ULTAGE Tapered Roller Bearings achieves a long
operating life approximately 16 times longer thanthat of standard tapered roller bearings due to theuniformity of the contact stress distribution.
Table 10 Test condition15)

Fig. 19 ULTAGE Tapered Roller Bearing

15)

ULTAGE Tapered Roller Bearings use optimized
tapered roller surface geometry to maximize bearing
operating life. (This technique, which involves
reducing the diameter of tapered rollers toward
the end in micrometer increments, is known as“crowning.”) Roller crowning allows for uniform
contact stress between the rolling elements and the
raceways when an unbalanced load is applied. This
design technology has enabled ULTAGE Tapered

Test bearing size

φ23×φ55×20

Bearing material heat
treatment

Standard bearing steel heat
treatment

Test load

Basic dynamic load rating of 26 %(JIS B 1518:2013)

Misalignment

0.002 radRotational speed

4 000 min-1

Lubricating oil

ISO VG100 gear oil
equivalent

JIS basic rating life

73 hours

NTN TECHNICAL REVIEW No.89

71

Introduction of Rolling Bearings for Electric Drives Corresponding of Automobiles
8)

500

400

300

L10h
h

Approx. 16
times

200

100

0

Standard
tapered roller
bearing

ULTAGE Tapered Roller
Bearing for Automotive
Application

Fig. 21 Clean oil life test results for tapered roller bearings
under high misalignment conditions15)

5. Conclusion
As the shift to electric vehicles (EVs) continues aspart of the pursuit of carbon neutrality, the functions
required of bearings are becoming more diverse. In
this article, NTN introduced rolling bearings for electric
drives that can meet the technical requirementsof e-Axles. Looking towards the future, NTN willcontinue to develop technologies that anticipate theevolving needs of the automotive market.
References
1) Ministry of the Environment website,
Decarbonization Portal,
https://ondankataisaku.env.go.jp/carbon_
neutral/2) Takashi Kawai, Introduction of Recent Rolling
Bearings for Automotive Applications,
Automotive Technology, Vol. 9, No. 10, (2022)
43-50.
3) NTN Corporation to expand mass production anddelivery of high-speed deep groove ball bearings
for EVs and HEVs, 2020
https://www.ntn.co.jp/japan/news/new_
products/news202000044.html
4) Takashi Kawai, Introduction of Rolling Bearings
for EVs (Electric Vehicles), Journal of Economic
Maintenance Tribology, No. 692, (2022) 37-44.
5) Katsuaki Sasaki, Takahiro Wakuda, Tomohiro
Sugai, Ultra-low Friction Sealed Ball Bearing forTransmission, NTN TECHNICAL REVIEW, No. 85,(2017) 62-66.
6) Katsuaki Sasaki, Technical Trend of High-Speed
Deep Groove Ball Bearings for Motors, Monthly
Tribology, No.404, (2021) 12-15.
7) NTN Corporation wins Nippon Brand Award of2021 “CHO” MONODZUKURI Innovative Parts
and Components Award, 2021
https://www.ntn.co.jp/japan/news/press/
news202100067.html

72

NTN TECHNICAL REVIEW No.89

NTN Corporation achieves high-speed rotation of
2.2M with deep groove ball bearings for EVs andHEVs, 2022
https://www.ntn.co.jp/japan/news/new_
products/news202200027.html
9) Hayato Kawaguchi, Toshiki Masuda, Marina
Nagata, Toshitaka Kawai, Creepless Bearings,
NTN TECHNICAL REVIEW, No. 88, (2021) 66-70.
10) Tsuyoshi Niwa, A Creep Mechanism of Rolling
Bearings, NTN TECHNICAL REVIEW, No. 81,(2013) 100-103.
11) NTN Corporation Ball and Roller Bearings Catalog(CAT.No.2203/J 20.08.199 NI/NI), 2020
12) Shoji Noguchi, Electric Pitting Prevention
Technology for Rolling Bearings, Monthly
Tribology, No.320, (2012) 18-20.
13) Yoshinori Isomura, Tatsuo Maetani, Akihiko
Watanabe, Keisaku Nakano, et al., A Study ofElectrical Pitting for Small Ball Bearing of PWM
Inverter Drive (Part 2), The Tribologist, Vol. 58,
No. 1, (2013) 46-51.
14) Takayuki Kawamura, Hiroki Fujiwara, and Koya
Ohira, New Technology of Rolling Bearings
contributing to Low Fuel Consumption ofAutomobiles, NTN TECHNICAL REVIEW, No. 87,(2019) 85-91.
15) Yasuhito Fujikake, Takanori Ishikawa, Susumu
Miyairi, ULTAGE Tapered Roller Bearing for
Automotive Application, NTN TECHNICALREVIEW, No. 85, (2017) 51-55.
16) Yasuhito Fujikake, Takanori Ishikawa, Low
Temperature Rise and Low Torque Tapered Roller
Bearings, NTN TECHNICAL REVIEW, No. 88, (2021)
71-76.

Photo of authors

Takashi KAWAI

Tomohisa UOZUMIAutomotive Bearing NTN BEARINGS (UK)LTD.
Engineering Dept.,
Automotive Bearing
Products Unit,
Automotive Business
Headquarters

Commentary

Evolution of Fixed Constant Velocity Joint thatContributes to Environmental Protection

Masashi FUNAHASHI *Teruaki FUJIO *Ritsuki SAKIHARA *In 1963 NTN commercialized the constant velocity joint for the firsttime in Japan. Since then, NTN has continued to develop new products
in order to adapt to the environmental policy which changes with thetimes. This article looks back on the evolution of NTNʼs fixed constantvelocity joints and explains about two types of high efficiency fixed constant velocity joints applied for the
evolving EV market of the future.

1. Introduction
Drive shafts used for power transmission in
automobiles can be divided into two types. Fixed
constant velocity joints (“fixed CVJs”) are attachedto the tire side and can take a large angle as the tirerolls. Sliding constant velocity joints (“sliding CVJs”)
are attached to the powertrain unit side and can takean angle and slide with vertical movement of thevehicle body (Fig. 1). NTN has been developing drive
shafts that are compact, lightweight, high-angle, lowvibration, and has made continuous improvements
using tribology, materials, mechanical design andother technologies. On the other hand, as abnormal
weather conditions have occurred due to global
warming caused by increased CO2 emissions, theimpact of human activity on the environment is being
taken up as a social problem making it increasingly
important to find a new approach to environmental
conservation. Since the Kyoto Protocol wasestablished in 1997, the international community has
worked to advance global warming countermeasures.
To achieve the global average temperature
increase target set in the Paris Agreement of 2015,
efforts to realize a decarbonized society by 2050
are accelerating around the world. Against thatbackground, in recent years the use of high-efficiency(low heat generation) drive shafts has been attracting
attention.
This paper focuses on fixed CVJs, for which there
is a greater need for improvement from the market.
We introduce the evolution of CVJs that NTN iscontinuously developing in response to the changes
in automobiles associated with environmental
protection.

2. Market trends/needs
As the drive toward decarbonization continues,
each year countries around the world are tightening
their standards for CO2 emissions and fuel efficiency
of automobiles. There is a continuing need forlightweighting and higher efficiency of all components
used in automobiles. In addition, the automotive
industry is rapidly shifting from conventional internal
combustion engine vehicles to electric vehicles (EVs)which are expected to have a longer cruising range. In
addition, changes in vehicle layout such as changes in
the position of the powertrain unit and extension of
the wheelbase are expected in order to provide spacefor large capacity batteries. (Fig. 2)
Slidi

ng ty

pe C

VJ
Fixe

d ty

Dri

ve

pe C

VJ

sha

ft

Fig. 1 Arrangement of fixed CVJs at the drive shaft* CVJ Development Dept., CVJ Products Unit, Automotive Business Headquarters

NTN TECHNICAL REVIEW No.89

73

Evolution of Fixed Constant Velocity Joint that Contributes to Environmental Protection

Powertrain
unit

Extended wheelbase

Powertrain
unit

Side of vehicle
Drive shaft

Drive shaft

Powertrain
unit

Powertrain
unit

Top of vehicle

Fig. 2 Image of EV drive shaft arrangement
In this context, the functions required of drive
shafts are (1) higher efficiency, smaller size, andlighter weight to help reduce fuel consumption andelectricity costs, and (2) a higher operating angle(higher steering angle) to control the increase inturning radius due to an extended wheelbase anda higher working angle due to the need to securebattery space. One particular issue has been that fixed
CVJs are less efficient than sliding CVJs in terms of therequired functions and structure. NTN is continuously
developing fixed CVJs to meet these market trends
and needs.

In 1956, Hardy Spicer (U.K.) developed a fixed CVJ
that could transmit power at constant velocity evenwhen the operating angle was increased. This enabled
the front wheels of a car to have both steeringand driving functions. NTN formed a technology
alliance with Hardy Spicer in 1962, through which
we developed the BJ (maximum operating angle
42.5 degrees) for the Suzulight Van FE (Suzuki Motor
Corp., Fig. 4). In 1964, the first vehicle equipped witha fixed CVJ that was successfully mass-produced inJapan was introduced to the market (Fig. 5). This
greatly improved handling stability, which had beena problem for FF and 4WD vehicles, and contributed
greatly to the popularization of automobiles in Japan.
Later, to meet the rapidly expanding demand for
fixed CVJs and the increasing need for higher steering
angles in vehicles, NTN developed BJ-L (Fig. 6), which
expanded the maximum operating angle from 42.5
degrees to 46.5 degrees while maintaining the outer
diameter. NTN achieved this by changing the fixed CVJouter ring material from carburized steel to induction
hardened midcarbon steel, and by making an optimalhigh angle design. Mass production of the BJ-L fixed
CVJ began in 1982, is still used as the basic design
today, and continues to evolve to capture the market
needs of small size, lightweight, high efficiency, andhigh angle.

3. Evolution of NTN fixed CVJs1)2)4)5)
3.1 Development of CVJs in Japan
Before the 1960s, automobiles developed mainly
as rear-wheel drive (FR) vehicles, while front-wheel
drive (FF) and four-wheel drive (4WD) vehicles
were also developed to improve comfort and driving
performance, etc. In FF and 4WD vehicles, powerfrom the engine is transmitted to the front wheels.
Drive components are therefore required to be abletransmit power at constant speed even if the tires aresteered. The cardan joint (cross shaft coupling, Fig. 3)
used at that time was an unequal-velocity joint thatcaused large rotational fluctuations between the input
and output shafts when the operating angle increased,
resulting in unstable steering operation during driving.

Fig. 4 Suzulight Van FE (Suzuki Motor Corp.)

Fig. 5 Exterior of CVJ mounted on Suzulight Van FE

Fig. 3 Cardan Joint (cross shaft coupling)
Fig. 6 BJ-L exterior74

NTN TECHNICAL REVIEW No.89

3.2 The shift towards more compact, lightweight,
high-efficiency CVJs
The evolution of fixed type CVJs is shown in Fig. 7.
The first evolution was to change the lubricant
sealed inside the CVJ from lithium-based grease
to urea-based grease, thereby achieving a longer
operating life. The fixed CVJ (BJ-L compact) is
4 % smaller and 8 % lighter than the BJ-L while
maintaining the maximum operating angle of 46.5
degrees. Mass production began in 1992.
The next evolution was the E-series fixed CVJ(“EBJ”; Fig. 8), which achieved further downsizing
and weight reduction. To reduce the size while
maintaining the same load carrying capacity as the
BJ-L, the outer diameter size was reduced and thenumber of balls was increased from six to eight. The
EBJ is 13 % smaller and 20 % lighter than the BJ-L,
and it improved the torque loss ratio by 30 % (higher
efficiency). Mass production of the EBJ began in 1998.
The torque loss ratio was further improved by 20 %with the EBJ-S, by optimizing the internal clearance
and applying low-friction grease to the EBJ. Mass
production of the EBJ-S began in 2020.

Fig. 8 Exterior of EBJ, EBJ-S
In 2022, NTN began mass production of the highefficiency fixed CVJ “CFJ”.3) This was the first CVJ
to adopt NTNʼs proprietary spherical cross groove
structure (the “proprietary structure”) as a further
evolution of the EBJ. The same outer diameter andmass as the EBJ were maintained while the torqueloss ratio was improved by more than 50 %. CFJs will
be introduced in detail in Chapter 4.

Standard typeHigh-angle type

BJ-L

BJ-L
compact

EBJ

EBJ-S

CFJ

UJ

UJ compact

VUJ

Developed
product

No. of balls

6

6

8

8

8

6

6

6

8

Maximum
operating
angle

46.5
degrees46.5
degrees47
degrees47
degrees47
degrees50
degrees50
degrees50
degrees52
degreesStart ofmass
production

1982

1992

1998

2020

2022

1988

1992

2007

ー

Lightweight,
higherefficiency

100 %Efficiency

Function

Developed
product
52 degrees

99 %Compact

Standard
type
Compact

High-angle
type

-10 %

0%

10 %

20 %

30 %

Mass Reduction Rate

Fig. 7 Evolution of fixed type CVJs

NTN TECHNICAL REVIEW No.89

75

Evolution of Fixed Constant Velocity Joint that Contributes to Environmental Protection
3.3 Increasing the operating angle of CVJs
As FF vehicles became larger in the 1980s and 4WD
vehicles increased in number, the need to reducethe minimum turning radius drove demand for fixed
CVJs with a high operating angle. In 1988, NTN
began mass production of UJ, which has a maximum
operating angle of 50 degrees. To ensure high angle
functionality, mass production of UJ began with a
4 % increase in diameter and an 8 % increase inmass compared to BJ-L. In 1992, UJ (small size) was
developed that achieved an outer diameter and massequivalent to BJ-L by applying urea-based long-lifegrease (Fig. 7).
In 2007, NTN began mass production of VUJ,
which has the same six balls as UJ, but is smaller andlighter due to the optimized strength of each partand the application of long-life grease. In 2022, NTN
completed basic development of a 52-degreehigh-angle fixed CVJ [developed product] based on
CFJ technology. Compared to the UJs (compact type)developed since the 1990s, the VUJ is 4 % smallerand 8 % lighter, while the 52-degree high-angle fixed
CVJ [developed product] is 10 % smaller and 16 %lighter, with a torque loss ratio improvement of over
50 % (Fig. 7).

4.1.1 Features(1) Arc-shaped tracks on the inner and outer rings are
inclined in the axial direction, with adjacent tracks
arranged in mirror-image symmetry (Fig. 10).
(2) The slopes of the inner and outer ring tracks
cross each other and the ball is placed at theintersection (Fig. 11).
The torque loss of a CVJ is equivalent to the energy
lost due to the frictional forces that occur between
the parts during torque transmission. In the case of
EBJ, among the internal forces of the CVJ that occur
during torque transmission, the direction of the forceof the ball pushing the cage is the same for all balls.
The cage is pushed in one direction and contacts
the outer and inner rings. On the other hand, theunique structure of the CFJ causes the force of theball pushing the cage to be in the opposite direction
for adjacent balls, which cancels out the force on thecage and significantly reduces the contact force withthe outer ring and inner ring (Fig. 12). This reduces
the frictional force between the cage and the outerand inner rings, resulting in the worldʼs highest level of
efficiency.

Track

4. Helping to reduce environmental impact
with higher efficiency fixed type CVJs
To meet vehicle requirements, NTN offers two typesof fixed CVJs: a standard type and a high-angle typewith different maximum operating angles, as shown in
Fig. 7.
This chapter introduces the standard high-efficiency
fixed CVJ “CFJ” and the high-angle type 52-degree
fixed CVJ [developed product] to show how
improvements in the efficiency of fixed CVJs can help
to reduce environmental impact.
4.1 High-efficiency fixed CVJ “CFJ”3) (standard type)
The CFJ is a fixed CVJ with a maximum operating
angle of 47 degrees that achieves the worldʼs highest
level of efficiency through the adoption of a uniquestructure (Fig. 9) with the aim of reducing automobile
CO2 emissions and improving fuel efficiency. The
torque loss ratio is reduced by 50 % or more while
maintaining the same outer diameter and mass as the
EBJ (conventional product), which has achieved theworldʼs highest levels of compactness and lightweight.

Fig. 10 Image of track shape

Fig. 11 Arrangement of track and ball

Outer
ring
Ball

Cage
Inner
ring

Fig. 9 Configuration of CFJ

76

NTN TECHNICAL REVIEW No.89

EBJ

CFJ

Direction of the force of the ball pushing the cage

Fig. 12 Comparison of internal force

Torque loss ratio %Blue line: conventional product (EBJ)Red line: CFJ
Continuous line: During normal driving
Dotted line: During regenerative driving

0

3

6

9

Operating angle deg

1215Fig. 13 Comparison of torque loss ratios
4.1.3 Efficiency of Fixed CVJs and Estimated Effects
on Vehicles
The efficiency of the drive shaft, the component thattransfers power from the engine to the tires, directly
affects the fuel efficiency and electricity consumptionof a vehicle. In addition, it has an even greater impact
on hybrid vehicles and EVs that have regenerative
braking for recovering energy during deceleration.
Performing a detailed calculation for CFJ, we findthat in the case of a gasoline vehicle, fuel efficiency
improves by 0.62 % and CO2 emissions decrease by
0.96 g/km compared with EBJ (fuel efficiency: 17.6km/L) when the vehicle weighs approximately 1.5
tons and the drive shaft is installed at a 9-degree
angle under the WLTP（Worldwide Harmonized Light
Vehicle Test Procedure）conditions. BEV (electric
power consumption: 155 Wh/km) improves electric
power consumption by 0.90 % (Table 1).
Table 1 Effects on automobiles (EBJ ratios)
Fuel and electricity
cost Improvement rate

CO2 Emission
Reduction

Gasoline
vehicle0.62 % UP-0.96 g/km

HEV

0.76 % UP-1.12 g/km

BEV

0.90 % UP―<Test conditions>
Setting angle: 9 degrees
Vehicle: fuel efficiency 17.6 km/L; power consumption 155 Wh/km
Vehicle weight: approx. 1.5 tons; driving conditions: WLTP

4.2 52 degrees fixed type CVJ (high-angle type)[developed product]
This product is a high-angle, high-efficiency fixed
CVJ. As well as offering a high operating angle that islarger than the maximum operating angle of the VUJ(maximum operating angle: 50 degrees), it offers highefficiency and is compact and lightweight.
4.2.1 Features
By adopting a unique structure similar to that of the
CFJ, it is possible to reduce the force generated inside
the CVJ during torque loading (internal force) and to
improve the load carrying capacity at high operating
angles. In addition, NTN changed the track shape in
the area where the ball moves toward the outer ring
aperture at high operating angles. This secured therolling path length of the ball to align with the contact
point between the ball and the track at operating
angles exceeding 50 degrees. The cage, which is theweakest part of the fixed CVJ at high operating angles,
was made smaller yet higher angle was achievedby optimizing the shape and changing the material.
As a result, a 6 % reduction in size and an 8 %weight reduction were achieved while increasing the
maximum operating angle by 2 degrees compared to
the VUJ (Fig. 14).
VUJ

Developed productFig. 14 Design comparison
4.2.2 Function- Efficiency (torque loss ratio)
By adopting a unique structure, the torqueloss ratio was improved by more than 50 % in all
angular regions compared to the VUJ (Fig. 15).

Conventional product (VUJ)

Torque loss ratio %4.1.2 Function
Fig. 13 shows the measurement results of torqueloss ratio. The torque loss ratio was reduced by morethan 50 % compared to the conventional productnot only during normal driving, but also during theregenerative driving that occurs in vehicles such as
EVs.

Developed product

0

3

6

9

Operating angle deg

1215Fig. 15 Comparison of torque loss ratios

NTN TECHNICAL REVIEW No.89

77

Evolution of Fixed Constant Velocity Joint that Contributes to Environmental Protection

Breakage torque Nm- Strength at high operating angles
By using a unique structure, modifying the track
shape, optimizing the cage shape, and changing
the materials, we achieved a 6 % reduction insize and 9 % reduction in weight compared to the
VUJ, while achieving the same strength at highoperating angles (Fig. 16).

Conventional product(VUJ)

Developed
product

Fig. 16 High angle static torsional strength comparison

5. Summary
This paper touched on the evolution of fixed CVJs
that contribute to reducing environmental impact, andintroduced products NTN has developed in responseto the changing times and their effectiveness. To
realize a global decarbonized society, automobiles areundergoing a once-in-a-century transformation. CVJs
are required to provide enhanced functions to respondflexibly to this transformation. As a constant velocity
joint manufacturer, NTN will target demand for EVs,
which will continue to expand going forward so that
we can contribute to the realization of a decarbonizedsociety and reduce environmental impact. We willcontinue to develop CVJs that are small, lightweight,
high-performance, and have excellent quietness
with optimal strength and durability tailored to
the locations of their application and to vehicle
characteristics.

Photo of authors

Masashi FUNAHASHI

Teruaki FUJIO

Ritsuki SAKIHARA

CVJ Development
CVJ Development
CVJ Development
Dept.,
Dept.,
Dept.,CVJ Products Unit,
CVJ Products Unit,
CVJ Products Unit,
Automotive Business Automotive Business Automotive Business
Headquarters
Headquarters
Headquarters

78

NTN TECHNICAL REVIEW No.89

References

１） Takeshi Ikeda, History of CVJ Design for

Automobiles and Recent Technology, NTN
TECHNICAL REVIEW, No. 70, (2002) 8-17.
２） Shin Tomogami, Technical Trends in Constant
Velocity Universal Joints and the Development ofRelated Products, NTN TECHNICAL REVIEW, No.
75, (2007) 10-15.
３） Teruaki Fujio, Next Generation High Efficiency
Fixed Constant Velocity Joint “CFJ”, NTN
TECHNICAL REVIEW, No. 81, (2013) 64-67.
４） Shinichi Takabe, History of Constant Velocity
Joints, NTN TECHNICAL REVIEW, No. 85, (2017)40-45.
５） Tatsuro Sugiyama, History of Developmentof Constant Velocity Joint Aiming at Low Fuel
Consumption, NTN TECHNICAL REVIEW, No. 87,(2019) 59-62.

New
Products

Introduction of Composite Material Products Used inElectrical Auxiliaries for Automobile

Ken YASUDA *Shinji KOMATSUBARA **The Composite Material Product Division at NTN has developed bearings, mechanical parts, and module
products. These products make full use of tribology and are made of multi materials such as: resins,
sintered metals, magnetic materials. In this article, we mainly introduce products for thermal managementin automobiles.

1. Introduction
In recent years, the automotive industry has been
in development of various technologies focused on
the keyword of CASE. For example, motors and otherpower sources, inverters, and DC-DC converters
are being developed for electrification. Meanwhile,cameras, sensors, and ECUs that integrate and control
these accessories and their parts, are being developed
for autonomous driving. As these accessories become
smaller and lighter to improve the fuel efficiency andpower consumption of automobiles, heat dissipation
has become more difficult to manage due to the risein heat generation of new automobile components.
The addition of electrical and electronic devices thatgenerate large amounts of heat due to high-speed,large-capacity communications (such as 5G) havemade thermal management of the entire automobile
an important theme for ensuring reliability. The shift toelectric vehicles has also created new market demand
for a quiet vehicle interior that offers a recreational
environment free from the noise of a conventional
engine.
This paper introduces examples of applications forcomposite material products and how they contributeto higher efficiency of accessories as they relate
to thermal management of automobiles, and to
improved cabin comfort.

2. Elastomer main shaft seal for electriccompressors
The accessories related to thermal management
are critical to the range and battery life of electricvehicles. This has led to the increased market demandfor energy-saving and high-efficiency performance.

These accessories contain various sliding parts madeof high polymer materials (elastomers and resins) andtheir tribological properties are important.
While conventional internal combustion engine
vehicles use belt-driven compressors powered by theengine, electric vehicles such as HEVs, PHEVs, andEVs use electric compressors. Electric compressors
are used for cooling the cabin in HEVs and PHEVs,
and for temperature control for batteries and othercomponents – in addition to air conditioning in EVs.
There are two types of compressors: scroll type andswash plate type.
Scroll type compressors are used because of theirsuperior quietness. Scroll compressors use a main
shaft seal that seals the refrigerant and refrigeratingmachine oil. NTN has developed a low-torque,
low-leakage, BEAREE TP5300 main shaft seal that
contributes to power savings and higher efficiency.
2.1 Structure of electric scroll compressors
A cross section of an electric scroll compressor isshown in Fig. 1. The refrigerant is compressed by the
gyrating motion of the movable scroll, which is opposedto the fixed scroll. The movable scroll is driven by therotation of the main shaft, and is supported by ballbearings. The main shaft seal has an inner diameterof about 20 mm with lips on both the inner and outercircumference to reduce leakage of refrigerant andrefrigerating machine oil to the rotor side.
In EVs, electric compressors are used not only forheating and cooling, but also for the temperature
management of batteries and other components.
As a result, they operate for longer durations thanin internal combustion engine vehicles. This has
led to the need to improve the durability of electriccompressors.

* Plastics Engineering Dept., Composite Material Product Division** Hydrodynamic Bearing Engineering Dept., Composite Material Product Division

NTN TECHNICAL REVIEW No.89

79

Introduction of Composite Material Products Used in Electrical Auxiliaries for Automobile

Stator

Rotor

Fixed scroll

Compression
chamber

Ball bearing

Main shaft

TP5300 and PTFE with filler, on a disc type testingmachine. The BEAREE TP5300 has specific wear ratethat is approximately one-fourth that of PTFE with filler.
0.15

PTFE main shaft seal
(conventional product)
BEAREE TP5300 main
shaft seal

Torque N･m

0.12

Main shaft seal

Cross
sectionLip

Movable scroll

0.09
0.06
0.03

Discharge valve

Fig. 1 Cross section of electric scroll compressors

Table 1 BEAREE TP5300 and PTFE main shaft seal
performance comparison
Item

BEAREE TP5300
main shaft seal

PTFE main shaft seal
(Conventional
product)

Base resin

Thermoplastic
elastomer

PTFE

Processing
methodInjection molding

Compression molding+ machining

Flexibility ofshapedesign◎△Torque

◎

〇

Leak

〇

〇

Durability

◎

△

Cost

◎

△

◎ : Excellent 〇 : Good △ : Acceptable

2.3 Friction and wear characteristics
Fig. 2 shows the torque measurement results of the
shaft seal in refrigerating machine oil. The torque of the
BEAREE TP5300 shaft seal is 15 % to 25 % lower thanthat of the PTFE shaft seal, and the TP5300 seal has
lower oil leakage. The oil leakage of the TP5300 seal isequivalent to the PTFE seal (less than 1 mL/min).
Fig. 3 shows the results of a wear test for BEAREE

80

NTN TECHNICAL REVIEW No.89

0

0.2

0.4

0.6

0.8

1

Oil hydraulics MPa<Test conditions>
PAG oil, Oil temperature 100 °C
Oil hydraulics 0.3 to 0.8 MPa
Rotation speed 7 500 min-1, Steel main shaft

Fig. 2 Torque measurement results
15

Specific wear rate

×10-8 mm3/(N･m)

2.2 Features of the BEAREE TP5300 main shaft seal
NTNʼs BEAREE TP5300 main shaft seal is madeof a composite material that is formulated with afilling material in a thermoplastic elastomer – offering
excellent friction and wear characteristics. Its flexibility(low elasticity) offers advantages such as low torqueand low leakage. The lip reaction force caused by theinterference with the shaft is small, and the lip tip (innerand outer sides) easily follow the shaft and housing.
Further torque reduction is achieved by optimizing thelip design (thickness, angle, length, etc.).
Table 1 shows a performance comparison with aconventional polytetrafluoroethylene resin (PTFE) shaft
seal. While conventional PTFE shaft seals are machined,
the BEAREE TP5300 shaft seals can be injection
molded, offering better design flexibility and reduction
in manufacturing costs.

0.00

10

5

-75 ％
0

BEAREE TP5300

PTFE with filler<Test conditions>
Ring on disc type testing machine, PAG oil, Room temperature
Surface pressure 0.3 MPa, Speed 1 m/s
Opposing material SUJ2, 50 hFig. 3 Wear test results

3. Low torque plastic sliding bearings forelectric water pump
Electric vehicles are equipped with an electric water
pump that circulates cooling water, and an electriccompressor for thermal management. Sliding bearings
used in these pumps require even lower friction
coefficients for lower fuel and power consumption.
NTN has developed a low torque plastic bearing
with a significantly reduced friction coefficient incooling water. This bearing features special lubrication
grooves on the thrust surface of a PPS sliding bearing.
This bearing is made of a proprietary composite
material1)2) that combines materials such as
polyphenylenesulfide (PPS), polytetrafluoroethylene
resin (PTFE), and carbon fiber (CF).

3.1 Role and structure of electric water pump
Electric water pumps are classified by high-flow,
medium-flow, and low-flow types, with each type
having a different purpose in a vehicle. The highflow type electric water pump is used for engine
cooling, the medium-flow type is used for cooling thebatteries, motors, and inverters, while the low-flow
type is used for cooling and heating intercoolers andexhaust gas recirculation equipment.
Fig. 4 shows a cross section of a typical electricwater pump. The rotor includes: the impeller, magnet,
and sliding bearing, and is found in the pump housing.
Meanwhile, the stator is arranged opposite themagnet and is freely supported by the shaft throughthe sliding bearing. The magnetic field generated
by the energization of the stator causes the rotor torotate about the shaft. Since the impeller is integrated
with the rotor, the impeller rotates as the rotor
rotates, and the cooling water is sucked into the pumphousing.
The inner diameter of the sliding bearing is about 4
to 10 mm. During rotor rotation, radial and axial loads
are generated. This causes the inner diameter surface
and shaft of the sliding bearing, and the thrust surface
and the thrust pad, to slide in the cooling water. The
sliding bearing is pressed against the thrust pad on
the impeller side, and the axial load is larger than
the radial load. The frictional resistance of the thrustsurface is thus greater than that of the inner diametersurface. To reduce the frictional resistance of thesliding bearing, it is therefore necessary to reduce thefrictional resistance of the thrust surface.
Cooling water OUT
StatorThrust pad
Thrust pad
Pump chamber
Shaft (fixed)
Cooling water
IN

Rotor
(rotation)

Impeller

MagnetSliding bearing

Slidingbearing

In general, a rectangular lubrication groove shownin Table 2(b) is used as a lubrication groove on thethrust surface in sliding bearings for electric water
pumps. This rectangular lubrication groove penetrates
radially from the bearing bore to the outer diameter.
The cross section has a simple rectangular shape, so it
is conventionally applied to machined products suchas the carbon sliding bearings used in water pumps.
NTNʼs low torque plastic bearings instead havespecial lubrication grooves on the thrust surface of
the PPS sliding bearing, as shown in Table 2(a). These
special lubrication grooves have a shape that enables
material transfer during injection molding. As shownin Fig. 5, the special lubrication grooves are designed
so that the grooves gradually become shallower inthe counter-rotational direction of the bearing. This
causes cooling water to be forced into the shallower
grooves during bearing rotation, and generatepressure by the hydrodynamic effect. As a result, thecooling water can easily penetrate the thrust sliding
surfaces of the bearing.
Fig. 6 shows the dynamic friction coefficient incooling water for three types of PPS sliding bearings
with three shapes of thrust surface: one with special
lubrication grooves, one without lubrication grooves,and one with rectangular lubrication grooves on thethrust surface. The dynamic friction coefficient of the
PPS sliding bearing with special lubrication grooves
is 65 % lower than that without lubrication grooves,and 30 % lower than that with rectangular lubrication
grooves.
Table 2 Shape of lubrication grooves on thrustsurface of each thrust bearing
Item

Thrustsurfacelubrication
grooveshape(a) Special(b) Rectangular (c) No
lubrication
lubrication
lubrication
groovegroovesgrooves
Rotational
directionof bearing

Slidingarea ratio

0.88

0.95

1 (reference)

Pressure,
MPa

1.06

1.00

0.93

Note: Surface pressure is the value in the test (load 128 N)
described below.

Fig. 4 Structure of electric water pump
3.2 Bearing thrust surface lubrication groove shapeSliding bearings in electric water pumps maintainlow friction and low wear under good lubrication
conditions (high speed and low load). However, during
startup, shutdown, and when there is localized water
film loss during operation, the friction coefficientincreases due to contact between the sliding bearing
and the thrust pad – increasing the likelihood of wear.
As a countermeasure, lubrication grooves are included
on the thrust surface of the sliding bearing.

Pressure
高圧
Thrust pad
スラスト受

摺動面
Sliding surface

Bearing

軸受（スラスト面）(thrust surface)
軸受回転方向Rotational directionof bearing

冷却水がDirection of coolingwater being pushed
押し込まれる方向

Special lubrication groove
特殊潤滑溝

Fig. 5 Hydrodynamic effect from special
lubrication grooves
NTN TECHNICAL REVIEW No.89

81

0.03

-30 ％

0.02
0.01
0

0.03

10

0.02

-34 ％
5

0

(a) Special(b) Rectangular (c) No lubrication
lubrication groove lubrication grooves
grooves<Test conditions>
Ring on disc type testing machine cooling water (ethylene
glycol 50 % concentration), Room temperature, 128 N load
(surface pressure approx. 1 MPa), Speed 125 m/min, Opposing
material SUS304

Fig. 6 Relationship between shape of lubrication
grooves on thrust surface and dynamic friction
coefficient
3.3 Friction and wear characteristics
Fig. 7 shows the results of friction and wear tests
in cooling water for a low torque PPS sliding bearing,
and a conventional carbon sliding bearing with threerectangular lubrication grooves as shown in Table 2 (b).
The low-torque plastic bearing (with special lubrication
grooves) had a 34 % lower coefficient of dynamic
friction and 1/10 th the specific wear rate as comparedto the carbon sliding bearing (rectangular lubrication
grooves). This difference in the dynamic friction
coefficient is similar to the results for the rectangularlubrication groove and the special lubrication groove
shown in Fig. 6.
Low torque plastic bearings are made of PPS
composite material with fillers suitable for sliding incooling water. These bearings have special lubrication
grooves on the thrust surface, which provide lower
friction and wear characteristics compared to carbon
sliding bearings (rectangular lubrication grooves).
Low-torque plastic bearings have various otherexcellent properties, as shown in Table 3.

0.01

-90 ％

Low torqueplastic bearing(special
lubrication
groove)Carbon sliding
bearings(rectangularlubrication
groove)0.00

Dynamic friction coefficient

-65 ％

0.04

15

○

0.05

■ Specific wear rate
×10-8 mm3/(N･m)

Dynamic friction coefficientIntroduction of Composite Material Products Used in Electrical Auxiliaries for Automobile<Test conditions>
Ring on disc type testing machine, Cooling water (ethylene
glycol 50 % concentration), Room temperature, 128 N load
(surface pressure approx. 1 MPa), Speed 125 m/min, Opposing
material SUS304, 50 hFig. 7 Friction and wear characteristics of each typeof sliding bearing
Table 3 Comparison of properties of each type of
sliding bearing
Item

Low torque plastic
bearing(special lubrication
groove)Carbon sliding
bearings(rectangularlubrication groove)

Processing
methodInjection molding

Machining

Chemicalresistance◎◎

Impactresistance〇△Flexibility ofshapedesign◎△Friction
properties(in coolingwater)◎〇

Wear
resistance(in coolingwater)

◎

〇

Cost

◎

△

◎ : Excellent 〇 : Good △ : Acceptable

4. Sintered hydrodynamic BEARPHITE
headlight cooling fan
In conventional internal combustion engine vehicles,
the sound from interior accessories is typically lessnoticeable due to the noise of an internal combustion
engine. With no more engine noise, the electrificationof automobiles has led to a growing demand for
quieter interior accessories reliable over a wide rangeof temperatures.
In recent years, energy-saving and long-life LED
lights have entered the mainstream for headlights.

82

NTN TECHNICAL REVIEW No.89

These require higher current to provide a visible lightintensity, but subsequently result in a large amountof heat generated in the LED circuit board. The needfor thermal management is therefore increasing,and the cooling fan motor used for heat dissipation(Fig. 8) must have stable performance over a wideC)
temperature range, from low temperatures (- 40 °C).
to high temperatures (100 °NTN has developed a hydrodynamic bearing,
Hydrodynamic BEARPHITE (Fig. 9), that meets theserequirements and is quiet over a wide temperature
range.

Fig. 9 Hydrodynamic BEARPHITE
4.1 Excellent quietness
Hydrodynamic BEARPHITE is a type of oilimpregnated sintered bearing manufactured bypowder metallurgy and has herringbone-shapedhydrodynamic grooves on the bearing inner diameter(Fig. 10). The hydrodynamic effect generated by shaft
rotation forms an oil film in the bearing clearance andsupports the shaft and bearing without contact.
Fig. 11 shows the results of determining thepresence or absence of contact between the shaft andHydrodynamic BEARPHITE by the electrical resistancemethod. This is done to confirm the difference in oilfilm formation depending on the presence or absenceof hydrodynamic grooves. Based on the detectedvoltage, the oil film formation rate was set to 0 % for
the contact state and to 100 % for the non-contact
state. These results indicate that hydrodynamic
grooves can support the shaft without contact.

10 000
8 000
6 000
4 000
2 000
0
10 000
8 000
6 000
4 000
2 000
0

100

Oil film formation rate % Oil film formation rate %Rotational speed r/min

Fig. 8 Cooling fan motor

Fig. 10 Hydrodynamic BEARPHITE inner surface(red outlined areas: hydrodynamic grooves)

Rotational speed r/min

Hydrodynamic BEARPHITE

Oil ﬁlm formation rate

80
60
40
20

Rotational speed

0

100
80

Oil ﬁlm formation rate

60
40
20

Rotational speed

30 s

0

Fig. 11 Difference in oil film formation depending on
presence or absence of hydrodynamic grooves(upper: no hydrodynamic grooves;lower: with hydrodynamic grooves)
Where a drop in oil film pressure is a concern3),
Hydrodynamic BEARPHITE generally remains quiet at
low rotational speeds. This is why it is popularly usedin cooling fan motors for information equipment, suchas thin-type notebook PCs and mobile terminals. It isalso being used in cooling fan motors for headlights
because of its excellent quietness over a wide rangeof rotational speeds, from low to high speeds.
4.2 High reliability over a wide temperature range
In headlights, the bearing performance remains
stable because of the minimum change in lubricant
viscosity expected, over the wide temperature
range required for headlights. A significant drop in
lubricant viscosity at high temperatures reduces thehydrodynamic pressure effect generated by shaft
rotation. However, the Hydrodynamic BEARPHITE,
which applies a less viscous lubricating oil that
decreases at high temperatures, offers excellent
temperature characteristics when compared toconventional products. (Fig. 12)

NTN TECHNICAL REVIEW No.89

83

Introduction of Composite Material Products Used in Electrical Auxiliaries for Automobile
5. Conclusion

Viscosity

Developed
product
Conventional
product

35 ％ increase

40 ℃
100 ℃
Temperature

Fig. 12 Relationship between lubricating
oil temperature and viscosity

Eccentricity ratio

Fig. 13 shows the eccentricity ratio calculation
C).
results of the shaft at high temperatures (100 °The eccentricity ratio is the ratio of shaft center
displacement to radial clearance, and a lower
eccentricity ratio means a larger minimum film
thickness. The Hydrodynamic BEARPHITE cansignificantly reduce the eccentricity ratio as compared
to conventional products, ensuring better bearing
reliability over a wide range of temperatures.

References

１） Takuya Ishii, Ken Yasuda, The Latest Technology

of Resin for Automobiles and Aircraft, Technical
Information Institute (2016) 167.
２） Ken Yasuda, Technology of Plastic Sliding
Bearings for Electric Water Pumps, Monthly
Tribology, May 2021, No. 405 (2021) 32.
３） Shinji Komatsubara, Hydrodynamic BEARPHITE
Bearings for Thin Cooling Fan Motors, NTN
TECHNICAL REVIEW, No.88 (2021) 44-45.

-37 ％Developed
product

This paper introduces a case in which NTNʼsbearings and elemental parts made of resin, sinteredmetal, and other materials were adopted to saveenergy in automobiles and provide a comfortablecabin interior.
Thermal management has become vital to thedevelopment of vehicle electrification, autonomous
driving, and connected automobiles. The UN-R51
international standard for four-wheeled vehicle noise
has entered Phase 3 and is becoming stricter. In Phase3, tire noise is taken into account, and the noise level
during driving is required to be reduced from the levelof a vacuum cleaner in Phase 2 to that of a washingmachine. In addition, in a future where autonomous
driving frees drivers from driving operations, it isexpected that the demand for a quieter interior space
will rise.
We will continue developing products andtechnologies that are key to improving thermal
management and vehicle interior habitability, thereby
contributing to the development of a mobile society
with vehicles at its core.

Conventional
product

Fig. 13 Eccentricity ratio calculation results
Furthermore, as a feature of the powder metallurgy
process, Hydrodynamic BEARPHITE can retain ample
lubricant in the pores on the bearing surface layer
and inside the pores (Fig. 14). Therefore, even if theassumed operating temperature range is exceeded,
there is an effect of suppressing seizure due to thecontact between the shaft and the Hydrodynamic
BEARPHITE.

Photo of authors

Pore (black area)

0.1 mmFig. 14 Surface condition of Hydrodynamic BEARPHITE84

NTN TECHNICAL REVIEW No.89

Ken YASUDA

Shinji KOMATSUBARA

Plastics Engineering
Dept.,
Composite Material
Product Division

Hydrodynamic
Bearing Engineering
Dept.,
Composite Material
Product DivisionPaperA Life Estimation Method of Peeling in Rolling
Bearings Under Mixed Lubrication Conditions

Naoya HASEGAWA *Takumi FUJITA **Michimasa UCHIDATE ***Masayoshi ABO ****

Peeling, which consists of spalls and cracks with the size of about 10 µm, is one of the failures of rolling
bearings under boundary and mixed lubrication conditions. In the past, we introduced a life estimation methodof peeling which is applicable to boundary lubrication and rolling conditions without slip. In this report, we
introduce an updated life estimation method which is applicable to mixed lubrication conditions. The updated
method applies a contact analysis based on the load-sharing theory of Johnson et al. This enables us toestimate peeling lives with consideration of the effect of oil film on supporting the load under mixed lubrication
conditions. We evaluated the accuracy of the updated method by rolling contact testing. The accuracy of life
estimation by the updated method was improved as compared with that of the previous method.

1. Introduction
International efforts toward carbon neutrality are
expected to further accelerate the use of low viscosity
lubricating oil for reducing friction in machineryand automobiles. Low viscosity lubricating oils will
increase opportunities for use in boundary lubricationof rolling bearings (hereafter “bearings”) and mixed
lubrication conditions (hereafter “severe lubrication
conditions”). Improving the reliability of bearings
under these conditions is thus expected to be an
important technical issue in the future.
Peeling is a typical example of bearing failure that
occurs under dilute lubrication conditions. It refers toa dense area of spalling and cracks of about 10 µm in
size.1) Peeling tends to occur under certain conditions,such as severe lubrication conditions, where the rollingsurface oil film parameter Λ (the ratio of the minimum
film thickness of the rolling area determined by EHL
theory to the square root of the root-mean-squareroughness of the two surfaces) is low. The cause isthought to be cyclic stress acting on the direct contact
area of the surface roughness (hereafter “the realcontact area”). In addition, the authorsʼ research2, 3)
shows that the initial notches of peeling occur
because of notch formed by plastic deformation due
to the action of the cyclic stress mentioned above.
To examine the reliability of bearings under dilutelubrication conditions, it is necessary to estimate
the life as affected by peeling (hereafter the “peelinglife”). If the peeling life can be estimated, the surface
roughness and lubricant of the bearing can be selected
appropriately. In addition, it can also be applied to thedesign of the surface roughness and lubricating oil
viscosity of the bearing necessary to balance reliability

and low torque, which can also help reduce friction
for bearing users. In the previous report, the authors
introduced a peeling life estimation method5) thatthey independently developed,4) but its application
was limited to boundary lubrication conditions. In thispaper, we present a peeling life estimation method
applicable to mixed lubrication conditions, along withthe results of validating its estimation accuracy.6)
The term “peeling” is customarily used by Japanese
domestic bearing manufacturers, while the term
“micropitting” is commonly used outside Japan.

2. Conventional peeling life estimation
method5)
2.1 Procedure for life estimation

Fig. 1 shows the procedure for estimating peelinglife. In Step 1, rolling fatigue tests are carried out
under various operating conditions to obtain a historyof peeling life (hereafter “stress history”) and thestress acting on the rolling surface (von Mises stressacting on the depth of 0.5 µm directly below thetrue contact area, hereafter “surface stress”). Surface
stress is reduced during operation by decreasing thesurface roughness of the rolling surface and generating
compression residual stress (hereafter “running-in”).
The surface stress is thus estimated using the results ofcontact stress analysis and residual stress measurement
using the surface roughness measured for eachconstant load.
The von Mises stress at a depth of 0.5 µm was used
for life estimation as the von Mises stress tended tobe highest at a depth of 0.5 µm regardless of the test
conditions.5) In Step 2, the peeling S-N curve (StressNumber of cycles to failure) was obtained from the* Advanced Technology R&D Center ** Product and Business Strategic Planning Dept.
*** Faculty of Science and Engineering, Iwate University **** School of Engineering, University of Hyogo

NTN TECHNICAL REVIEW No.89

85

A Life Estimation Method of Peeling in Rolling Bearings Under Mixed Lubrication Conditions[Step 2 Create S-N curve][Step 1 Collect data for peeling life and stress history]
Stress-life data of experiment 1

Stress-life data of experiment 2
Stress-life data of experiment 3

StressPeeling

Regression
analysis

StressStress-life data of experiment 4…

Number of cycles[Step 3 Preliminary test under the conditionsof the subject for life estimation]
Obtain stress history data up to
the limited loading cycles Nex
StressAssume constant stress after Nex

Peeling life

[Step 4 Life calculation]

Map with S-N curve(Apply Minerʼs rule)

Nex

Estimated peeling life

Number of cycles

Fig. 1 Flow of the estimation method of peeling life4)
peeling life and stress history data obtained in Step 1
by regression analysis. In Step 3, a rolling fatigue test
simulating the operating conditions to be estimated(hereafter the “preliminary test”) is conducted toestimate the peeling life under arbitrary conditions, andthe stress history under those conditions is obtained.
The preliminary test is conducted up to the number ofloading cycles when the flexibility stops, Nex (about 104
cycles). It is assumed that the surface stress does notchange after that time. Finally, in Step 4, the peelinglife is estimated using the stress history and S-N curve
obtained in Step 3.
In Steps 2 and 4 of this procedure, the degree of
fatigue (the ratio of the total number of loads to thelifetime) is calculated using Minerʼs law from the stresshistory. The concept adopted is that peeling occurs
when the degree of fatigue reaches 100 %.
For surface stress, the average value of von Mises
stress acting at a depth of 0.5 µm below the individual
real contact area is used. To obtain this, the normal
stress component σ̂j and the shear stress component τ̂jkof the triaxial stress acting substantially at a depth of 0.5µm below the true contact area are first determined by
the following equations (1) and (2).

σ̂j = σj, con + σj, res(1)τ̂ jk = τjk, con + τjk, res(2)( j = x, y, z, k = x, y, z, j ≠ k, τjk = τkj )Here, the subscript “con” indicates the contact
stress obtained by contact stress analysis, and “res”
indicates the residual stress obtained by residual
stress measurement. In addition, x represents thecircumferential direction, y the axial direction, and z
the depth direction in the rolling surface. The triaxial
stress components obtained in equations (1) and (2)86

NTN TECHNICAL REVIEW No.89

are then substituted into equation (3) below to obtainthe von Mises stress at a depth of 0.5 µm at the realcontact area, and the surface stress is obtained as theaverage of these values.

σvm=√ {(σ − σ ) + (σ − σ ) + (σ − σ ) + 6 (τ + τ + τ )}
1
2

x

y

2

y

z

2

z

x

2

2
xy

2
yz

2
zx

(3)

Although this estimation method requires preliminary
testing, the life can be estimated in a few hours,
including preliminary testing. By using the data fromthe preliminary tests, it is possible to perform a life
estimation that accurately reflects running-in behavior
under a wide variety of conditions that are difficult tosimulate. Another feature of this method is that it takes
into account the effect of residual stress on the life. The
S-N curves should be prepared for each steel grade andheat treatment of rolling parts.

3. Improved method of contact stress analysis
for application to mixed lubrication conditions
3.1 Overview of contact stress analysis

Under mixed lubrication conditions, the effect ofload support by the oil film cannot be ignored. In thispaper, to apply the peeling life estimation method
described above to mixed lubrication conditions, thecontact stress analysis for estimating surface stress
was enhanced to a method7) that can consider theeffect of load support by the oil film. In this analysis,
the load sharing theory8) of Johnson et al. is applied.
The load on the rolling parts is considered to be sharedby the oil film and the true contact area at a certain
ratio, as shown in Fig. 2. The pressure distribution on
the rolling surface is therefore obtained as the sum of

the pressure distributions of the oil film and the truecontact area. The pressure distributions of the oil film
and the true contact area are determined separately
by convergence calculations with the load sharing
ratio of the oil film as an unknown quantity. The
convergence condition here is that the mass of theoil film in the clearance between two rough surfaces
is equal to the mass of oil film formed between
two smooth surfaces when the sharing load of oil isapplied.
Hereafter, the procedure of this analysis is describedwith reference to Fig. 3. In Step 1, the load sharing
ratio of the oil film to the load W on the rolling area
is set as α. Then, the central oil film thickness hc,
the distribution of oil film pressure Pf (x, y), and theelastic deformation of the two surfaces are calculated
under the condition in which the sharing load of oil
αW is applied to smooth surfaces. An arbitrary initialvalue is set for α in this calculation. The central oil
film thickness hc is calculated with the formula9) ofcentral oil film thickness of Chittenden et al, and thecorrection coefficient 10) due to shear heating. The oilfilm pressure Pf (x, y) and the elastic deformation are
assumed to be equal to them when the two surfaces
contact with the load αW, and are obtained by thecontact calculation program11) using the boundary
element method. This is based on the fact thatthe spike of oil film pressure under high pressure
conditions (several GPa) is small and negligible.12)
Besides, the lubrication regime of rolling bearings is
generally the E-V (Elastic-Variable viscosity) regime
in which the viscosity of the oil increases with the risein pressure and the deformation of the rolling surface
due to hydraulic pressure cannot be ignored. However,under conditions where α is close to 0, the lubrication
regime is not E-V regime. In that case, the Chittenden
et al. formula cannot be applied. Nevertheless, theerror of analysis due to applying the formula ofChittenden et al. may be small as the influence of theoil film on the load support is small when α is close to
0. In Step 2, the three-dimensional roughness dataof the rolling surface actually measured in advanceis added to the shape of the two surfaces after theelastic deformation obtained in Step 1, and the roughsurface shape of the deformed state due to the actionof hydraulic pressure (hereafter, the rough surface

Oil film pressure Pf (x, y) Lubricating oil

shape oftwo surfaces
after elastic
deformation(Step 1 results)

Pre-measured
threedimensionalroughnessα

Load

Oil Truefilm contact
area

Axis

Surfaceroughness

Oil
film
True contact area

Fig. 2 Concept of load sharing theory
shape after hydraulic action) is created.
In Step 3, the remaining load (1 − α)W is applied
to the rough surface shape after the hydraulic action,and the distribution of pressure Pa (x, y) at the truecontact area and the average clearance hm, rough of thetwo surfaces are calculated using the same contact
calculation program as in Step 1. The average clearance
hm, rough is calculated by the following equations.
(4)hm, rough = ∫A hrough (x, y) dxdy / A

In the formula (4), A is the area of the region where
the oil film pressure Pf (x, y) is greater than 0 in Step
1. In addition, the clearance at the true contact
area is set to 0. In Step 4, we examine whether thecentral oil film thickness hc found in Step 1 is equal
to the average clearance hm, rough found in Step 3. If it
is not equal, we return to Step 1 and correct α. Thisis the convergence condition of the contact stressanalysis, and is based on the idea that the mass of
the lubricating oil drawn in between the two surfaces
does not change regardless of the surface roughnessof the two surfaces (law of conservation of mass). In
Step 5, the pressure distribution P (x, y) on the rollingsurface when the total load W is applied is determinedas the sum of Pf (x, y) and Pa (x, y), then the elasticity
solution of Boussinesq13) is applied to the obtainedpressure distribution. In this way, the distribution ofinternal stresses (triaxial stress components) below
the rolling surface is calculated.

3.2 Validity of contact stress analysis

The value of the load sharing ratio α and surface
stress of the oil film obtained by this analysis method
was verified to match the index of oil film formability
obtained in the rolling fatigue test and the residual stress

True contact area pressure
Pa (x, y)

Clearance: hrough (x, y)

hc = hm, rough ?

No

Yes
α

W : Load on rolling parts
α : Oil film load sharing ratio(0 < α < 1)

when rolling under αW・elastic deformation
・oil film pressure Pf (x, y)・center oil film thickness hc

Enlargementof rolling area

arecalculated

Rough surface shapeafter oil hydraulics action

After the oil hydraulics action, the remaining load isapplied to the rough surface shape andare・True contact area pressurePa (x, y)・Average clearance of the two surfaces hm, rough calculatedhm, rough =∫A hrough (x, y) dxdy / A
A: Area of oil film pressure Pf (x, y) > 0

・Calculate the pressure P (x, y) on the rollingsurface when the total load W is applied
P (x, y) = Pf (x, y) + Pa (x, y)・Apply elasticity solution to P (x, y) andcalculate internal stress distribution

correction of αFig. 3 Contact Stress Analysis Procedure7)

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A Life Estimation Method of Peeling in Rolling Bearings Under Mixed Lubrication Conditions
change of the test piece.7) Although details are omitted
in this paper, it has been confirmed that the analyticalvalues of α and surface stress are generally consistent
with the test data. Fig. 4 shows, as an example of
the results of the study, the relationship between theestimated value of the surface stress of the rollingsurface and the measured value of the residual stress in
the rolling fatigue test.
The rolling fatigue tests were conducted in a tworoller testing machine, as described below, with a
gradually decreasing rotational speed starting at
900 min-1. The test was interrupted each time when
the rotational speed was changed, and the threedimensional roughness and residual stress of the rollingsurface were measured at each interruption. From thesemeasurements, the surface stress during the test at
each rotational speed was estimated. Fig. 4 shows thatthe surface stress (estimated value) during operation
exceeded the yield stress of the test piece at a rotational
speed of 125 min-1. The residual stress (measured value)
increased during operation at a rotational speed of 125
min-1. These results are consistent with the predictionof the contact analysis that the rolling surface shows
plastic deformation at 125 min-1 and the validation of theresidual stress measurements.
Rotational speed min-1

Residual stress(measurement value) GPa

0.65

250

125

0.625

3

Surface stress(right shaft)

Residual
0.6
stress(left shaft)

2.5

2

0.575

Yield stress
1.5

0.55
?:4.5〜3.2
0.525

0

200

?:2.1
400

?:1.4
600

800

1 000

Surface stress(estimation value) GPa

900〜
500

1

Overall test time s

Fig. 4 Relationship between surface stress estimatedby contact stress analysis and measured
residual stress7)

4. Life estimation overall accuracy verification
4.1 Rolling fatigue test

To verify the accuracy of the new life estimation
method, rolling fatigue tests were carried out with thetwo-roller testing machine shown in Fig. 5. The drive
roller and the driven roller were cylindrical with anouter diameter of φ 40 mm and a thickness of 12 mm.
A radius of 60 mm was applied to the drive roller onlyin the axial direction. A felt pad impregnated withlubricating oil was used to lubricate the roller test pieceby contacting it from below. The material of the roller
test piece was SUJ2, which was subjected to standard
quench-hardening and tempering so that the surface
hardness was about 63 HRC. Table 1 shows the test
conditions. Testing was carried out under varying
conditions in terms of the surface roughness of therolling surface, the rotation speed, the maximum
hertzian contact surface pressure, and the lubricating
oil type. The Λ of Nos. 6 and 7 tests is more than 0.5,
which corresponds to the mixed lubrication condition.
Since it is easy for peeling to occur in the driven
roller, which has low surface roughness, the life wasdetermined from the occurrence of the peeling on thedriven roller. In principle, each test was interrupted
at 102 cycles, 103 cycles, 5 × 103 cycles, 104 cycles,
and 105 cycles at load. At these interruptions andbefore the test, the three-dimensional roughness
measurement of the drive roller and the driven roller
and the residual stress measurement of the driven
roller were performed. The stress history of thedriven roller was obtained from the collected data. In
addition, the occurrence status of the peeling of thedriven roller was observed with an optical microscopeat the time of interruption. The total number of loads
when the ratio of the area of the occurrence of micro
spalling and cracks to the area of the observation fieldof view (hereinafter referred to as the peeling area
ratio) reached 0.5 % or more at six different places in
the rolling surface was taken as the actual life Lact ofthe peeling. If the peeling area ratio was less than
0.5 % at 105 cycles, the test was continued until 0.5 %was reached.

Table 1 Test conditions of the two-roller test6)
Test
No.
1
2
3
4
5
6
7
8
9
10
11

88

Surface roughness (Ra) µm
Drive roller

Driven roller

2 000

0.75
0.50
0.75
0.40
0.35

NTN TECHNICAL REVIEW No.89

Rotational
speed
min-1

0.02

500
2 000
2 000
500
1 000
2 000

Maximum
Hertzian contactpressure GPa
2.3
1.6

LubricantSynthetic oil
(PAO)

2.3
Mineral oil
2.3

Synthetic oil(PAO)

Dynamic
viscosity(40 ℃ ) mm2/s

Oil film
parameter
Λ

0.11

32.6
47.7

0.12
0.06
0.17
0.52
0.87

6.8

0.15

6.2

0.17
0.24

6.2

Drive roller

Load

Felt pad for
lubrication
Driven roller

MotorFig. 5 Two-roller testing machine2)
4.2 Method for verification of overall estimation accuracy
Peeling life was estimated for the two-roller testingmachines Nos. 1 to 11 shown in Table 1 by theprocedure shown in Fig. 1. The life was estimated withand without considering the load sharing theory in thecontact stress analysis, and the accuracy of the life
estimation was compared between the two cases. The
estimated peeling life Lest for each test was calculated
from the stress history up to 104 cycles. For the life
estimation with load sharing theory, S-N curves weregenerated using the test data except for Nos. 7 and
8, which were used for the calculation of Lest. In thecase of life estimations where the load sharing theory
was not considered, Lest was calculated using the S-N
curve that had already been created in a previous
report.5) The overall accuracy of the life estimation
was examined using the life ratio (Lact / Lest) between Lestand the actual life of the peeling, Lact , which was finallyobtained in the test.

also shown in the figure. In the case of Fig. 6 (a)without consideration of load sharing theory, theoverall accuracy of life estimation for tests Nos. 6 and7, which were conducted under mixed lubrication
conditions, was lower than that of the other tests,
and the error in estimated life relative to actual life(the error is calculated as the largest value or thereciprocal of the minimum value of Lact / Lest Lact /Lest) was 20 times. On the other hand, when the loadsharing theory is taken into account in Fig. 6 (b), theerror in the estimated overall accuracy for tests Nos. 6
and 7 is less than five times, indicating that the overall
accuracy of life estimation under mixed lubrication
conditions is improved. Considering that the life ofbearings generally varies by a factor of 10 or more
under the same conditions14) , the overall accuracyof the life estimation in the case of the load sharing
theory is considered to be at a sufficiently high levelfor practical use.

6. Summary
This article has presented an improved peeling life
estimation method applicable to mixed lubrication
conditions and the results of validation of the overall
accuracy of the life estimation.
1) In this estimation method, a method of contact
stress analysis that applies load sharing theory is
employed, and the effect of lubrication conditions
on peeling life is considered.
2) The maximum error of the peeling life obtainedby this estimation method is less than 5 times of
the actual life, and the accuracy of the peeling life
estimation under mixed lubrication conditions is
improved compared to the conventional method.
The overall accuracy of the above is sufficiently
high for practical use as a peeling life estimation
method for bearings.

5. Results
Fig. 6 shows the relationship between the estimatedlife Lest and the actual life Lact. The median, minimum,and maximum values of the life ratio (Lact / Lest) are

10

10

Test No. 1

1

11

5
9

2

3

Lact / Lest

0.1
8

0.01
0.01

4

0.1

7

6

Median value: 1.07
Minimum value: 0.39
Maximum value: 20.00

1

10Life estimation Lest’×106 times

Life estimation Lest’×106 times

10

11

1

5
8

0.01
0.01

9

6
10

7

4
0.1

2

3

0.1

Test No. 1

Lact / LestMedian value: 1.07
Minimum value: 0.20
Maximum value: 2.22

110Actual life Lact’×10 times

Actual life Lact’×10 times(a) Load sharing theory not considered(b) Load sharing theory considered66

Fig. 6 Relationship between estimated peeling lives and actual peeling lives6)
NTN TECHNICAL REVIEW No.89

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A Life Estimation Method of Peeling in Rolling Bearings Under Mixed Lubrication Conditions
It should be noted that the scope of application ofthis estimation method is currently limited to purerolling conditions. Going forward, we will work tofurther improve the accuracy of the estimation andextend it to conditions where there is slip on therolling surface. This estimation technique will be used
to provide customer value in the form of improved
bearing reliability and higher machine efficiency.
This paper summarizes the content of thepresentation “Estimation Method of Micropitting
Life from S-N Curve Established by Residual StressMeasurements and Numerical Contact Analysis, 2ndReport” in the Proceedings of Tribology Congress2021 Spring Tokyo, which was organized by theJapanese Society of Tribologists and the presentation“Validation of Contact Stress Analysis of Rolling
Surface under Mixed Lubrication” in the Proceedingsof Tribology Congress 2022 Spring Tokyo. (Somefigures and tables have been translated into Japaneseand rearranged.) We thank the Japanese Society of
Tribologists for their kind permission to publish thispaper.
References
1) Noriyuki Tsushima, Hirokazu Nakashima, Hiroshi
Kashimura: Typical Failures of Bearings, NTN
TECHNICAL REVIEW, No. 57 (1990) 59.
2) Naoya Hasegawa, Takumi Fujita, Michimasa
Uchidate, Masayoshi Abo: Mechanism for
Initiation of Peeling in Rolling Contact andthe Effect of Black Oxide Treatment on the
Suppression of Peeling (Part 1), The Tribologist,
63, 8, (2018) 551.
3) Naoya Hasegawa, Takumi Fujita, Michimasa
Uchidate, Masayoshi Abo, Mechanism for
Initiation of Peeling in Rolling Contact andthe Effect of Black Oxide Treatment on the
Suppression of Peeling (Part 2), The Tribologist,
63, 9, (2018) 618.
4) N. Hasegawa, T. Fujita, M. Uchidate, M. Abo, andH. Kinoshita: Initiation Mechanism of Peeling in
Rolling Bearings, and Its Life Estimation Method,NTN TECHNICAL REVIEW, No. 88, (2021) 77.
5) N. Hasegawa. T. Fujita, M. Uchidate, M. Abo & H.
Kinoshita, Estimation Method of Micropitting Life

from S-N Curve Established by Residual StressMeasurements and Numerical Contact Analysis,
Tribology Online, 14, 3, (2019) 131.
6) N. Hasegawa, T. Fujita, M. Uchidate, and M.
Abo: Estimation Method of Micropitting Life
from S-N Curve Established by Residual StressMeasurements and Numerical Contact Analysis,
2nd Report, Proceedings of Tribology Congress2021 Spring Tokyo, (2021) B22.
7) N. Hasegawa, T. Fujita, and M. Uchidate:
Validation of Contact Stress Analysis of Rolling
Surface under Mixed Lubrication, Proceedings ofTribology Congress 2022 Spring Tokyo, (2022)
F118) K. L. Johnson, J. A. Greenwood & S. Y. Poon,
A Simple Theory of Asperity Contact inElasstohydrodynamic Lubrication, Wear, 19,(1972) 91-108.
9) R. J. Chittenden, D. Dowson, J. F. Dunn & C. M.
Taylor, A Theoretical Analysis of the Isothermal
Elstohydrodynamic Lubrication of Concentrated
Contacts, II. General Case, With Lubricant
Entrainment Along Either Principal Axis of the
Hertzian Contact Ellipse or at some Intermediate
Angle, Proc. Roy. Soc. Lond., A, 397, (1985) 271294.
10) M. K. Ghosh and R. K. Pandey, Thermal
Elastohydrodynamic Lubrication of Heavily
Loaded Line Contacts-An Efficient Inlet Zone
Analysis, Trans. ASME, J. Tribol., 120-1, (1998)
119-125.
11) M. Uchidate, Comparison of Contact Conditions
Obtained by Direct Simulation with Statistical
Analysis for Normally Distributed Isotropic
Surfaces, Surface Topography: Metrology andProperties, 6, 3, (2018) 034003.
12) H. Takada and R. Aihara, Life and Reliability of
Rolling Bearings, Nikkan Kogyo Shimbun, (2005)
161.
13) K. L. Johnson, Contact Mechanics, Cambridge
University Press, Cambridge, (1985) 51.
14) Rolling Bearing Operating Life Study Group,
Influence of Load and Lubricant on the Life of
Rolling Bearing, The Tribologist, 61, 9, (2016)607

Photo of authors

90

Naoya HASEGAWA

Takumi FUJITA

Michimasa UCHIDATE

Masayoshi ABO

Advanced
Technology R&D
CenterProduct andBusiness Strategic
Planning Dept.

Faculty of Scienceand Engineering,
Iwate University

School ofEngineering,
University of Hyogo

NTN TECHNICAL REVIEW No.89

Commentary

Development of Technical Calculation Systems for
Rolling Bearings

Tomomi ISHIKAWA *Mariko IZUMI *Hiroyasu HIRUKAWA *Cedric BURNET **The performance requirements for rolling bearings are diverse, and the pace of this diversification has
accelerated in recent years due to environmental concerns and other factors. The use of Computer-Aided
Engineering (CAE) technology is indispensable for NTN to respond quickly to these requirements. Twotechnical calculation systems developed by NTN to improve the efficiency and sophistication of rolling
bearing design will be introduced in this technical review.

1. Introduction
Introduce a wide variety of competitive bearing
products to the market that consider market trends
and customer needs in a timely manner, it is necessary
to improve the sophistication and efficiency of productdevelopment work. To this end, NTN is promoting theuse of Computer-Aided Engineering (CAE) technology.
In October 2018, NTN established the CAE Researchand Development Center1) to accelerate our researchand development of CAE technology.
In the past, NTN used both commercial softwareand the NTN-proprietary CAE system for bearing
product development work. There were several
challenges for efficient design, such that engineers
were required to select and use multiple, unlinked
subsystems repeatedly based on their specificapplications to derive design values that met thedesign requirements. Furthermore, even routine Finite
Element Method (FEM) analysis had to be carried out
by a Computer-Aided Engineering (CAE) specialists.
To improve the efficiency of the entire development
process, NTN developed two systems: SharcNT, an
integrated technical calculation system for rolling
bearings that consolidates existing calculation systems
with additional features, and ABICS, an integrated
calculation automation system that automates thedesign work of third-generation (GEN3) hub bearings.
This paper describes an overview of these systems.

2. Integrated technical calculation system
for rolling bearings
2.1 Background
Rolling bearings are an essential machine element
used in mechanical systems. They require a long
operating life, low torque, high stiffness, highprecision, and other performance capabilities. In
recent years, energy saving and decarbonization havebeen advanced to achieve carbon neutrality. This
has led to greater diversity in rolling bearing design
to meet required specifications and performanceneeds. For example, electrified automobiles andvarious industrial machines require smaller, lighter
bearings with ultra-high speed specifications, whilewind power generation requires larger bearings withlong operating lives as wind turbines become larger
and are used offshore. NTN must adapt to thesemarket trends and customer needs; there are strong
demands for highly reliable, high-performance bearing
designs and shorter design lead times. The use of CAE
technology is essential to meet these demands.
In the initial stage of designing rolling bearings,
life and internal bearing load calculations basedon theoretical calculations are used as the primaryperformance evaluation. In recent years, calculation
models have become larger, more complex, and moresophisticated. Calculations of entire applications,
including power transmission mechanisms, andcalculations considering elastic deformation aroundthe bearing are essential.
NTN developed SharcNT (Shaft, Housing and Roller
Coupling with NTN Technology), NTNʼs proprietary
integrated technical calculation system for rolling
bearings, to enable designers to design reliable,
high-performance bearings quickly using CAE
technology.
2.2 Global integration of calculation systems
In the past, NTN conducted design studies byutilizing multiple calculation systems according to
the design requirements of rolling bearings. However,making full use of multiple systems required a certain
level of experience. Therefore, SharcNT was developedby combining the main calculation functions of NTNʼsconventional calculation systems (Fig. 1) based ona system developed and used by NTN subsidiarycompany NTN-SNR.

* CAE R&D Center** NTN-SNR ROULEMENTS Research, Innovation & Development

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Development of Technical Calculation Systems for Rolling Bearings
In addition to the calculation functions required for
performance evaluation such as bearing operating life,
bearing load, load distribution, contact stress, bearing
stiffness, and bearing torque, SharcNT can constructa multi-axis calculation model in which bearings arearranged using an intuitive graphical user interface(GUI) (Fig. 2).
Integration of multiple systems made it possible fordesigners to perform a wide variety of calculations
within a single system and acquire skills andexperience more easily.

Base system

To understand the internal load of the bearing
obtained by calculation, it is necessary to confirm
how the shaft displaces with deformation due toconditions such as gear load and bearing position.
Depending on the structure, it may be extremely
difficult to verify the calculation results using only thenumerical information shown for each power flow.
Fig. 3 shows an example of a calculation for the
gearbox. The calculation model is displayed in a
3D model, and the vector of the internal load andthe displacement of the axis on the model can be
confirmed visually. In addition, detailed resultsfor each bearing are output as various graphs andnumerical data. These improvements make it easierfor the user to grasp the characteristics of thecalculation conditions.

All calculation functions

Fig. 1 Integration of calculation systems

Fig. 3 Calculation for entire applications
Fig. 2 Integrated technical calculation system SharcNT
2.3 Calculation for entire applications
In recent years, gearbox manufacturers havediversified their products to cater the wider needsof the markets, for example to meet the varying
requirements of the automobile market which
provides gasoline vehicles, hybrid vehicles, andelectric vehicles, ranging from simple structures tomulti-stage and complex structures. When bearings
used in more complex structures are examinedthroughout their application, the calculation model
becomes complex. It is not only difficult to understandand verify the calculation results, but it is also difficult
to do so in a short period of time. Even in the case ofcomplex structures, one must accurately and quickly
grasp the bearing characteristics.
To enable complex gearbox construction, SharcNT
makes it possible to create a calculation modelwith many parallel and orthogonal axes to analyze
the bearing in detail while taking into account thepower flow (power transmission path). In addition,
the overall life of the bearing can be determined by
setting the duration of time that the bearing spends
at each operating condition. In addition, advanced
calculations that consider elastic deformation aroundthe bearing, which will be discussed in the next
section, can be completed in a short time.

92

NTN TECHNICAL REVIEW No.89

2.4 Calculation that considers bearing elastic
deformation
Normally, the internal bearing loads are calculatedon the assumption that the contact between
the rolling element and the raceway surface willcause infinitesimal deformation. However, in some
applications, the stiffness of the housing is low (due tothin thickness, aluminum alloy, etc.), and the internalload of the bearing cannot be accurately determined
unless the elastic deformation of the outer ring andthe housing is considered. In this case, although it
is possible to use FEM to perform calculations thatconsider the elastic deformation of the outer ring andhousing, high-precision calculations demand expertiseand involve a series of calculations, which takes time.
SharcNT has a function2) that can consider elastic
deformation of the outer ring and the entire housing
as a contracted stiffness matrix (“virtual spring”),
which can be combined with the contact calculation
between each rolling element and a raceway with
relevant degrees of freedom. This function allows
calculation that takes elastic deformation of the outerring and housing into account at higher calculation
speeds when compared to FEM.
Calculations can also be performed that consider
elastic deformation of the inner ring and shaft using
the “virtual spring”. However, the fit between the
inner ring and the shaft is usually highly rigid whencompared to the fit between the outer ring and the
housing, and it is often sufficient to consider only thedeflection of the shaft. In such cases, the calculation
time can be shortened by modeling the shaft with thebeam element3).

3. Integrated calculation automation
system for hub bearings
3.1 Background to development
Hub bearings are used in automobile undercarriages
to support the rotation of the vehicleʼs wheels. Since
the late 1970s, hub bearings have evolved into unit
products incorporating peripheral components.4)
This was done in response to market demands
for easier bearing assembly into vehicles, bearing
downsizing, reducing bearing weight, and higher
bearing performance (load-carrying capacity,
low-torque performance, resistance against muddy
water, stiffness, strength, etc.). Currently, thepredominant hub bearing is the 3-generation hub
bearing called GEN3 shown in Fig. 4.
Hub bolt

Outer seal
Inner seal
Rolling
element

Innerring
Hub ring

Outer
ring

Fig. 4 GEN3 hub bearing
In the design of unitized GEN3 hub bearings,
automobile manufacturers require a balance between
long bearing operating life and high stiffness on the
one hand and compactness and light weight on theother. While a larger bearing size is required to reduce
contact stress and increase stiffness to improve
bearing life and steering stability, smaller bearing sizeand lighter weight is optimal for vehicle fuel efficiency.
In addition to these bearing design optimization tasks,
CAD and FEM analyses are also required in the design
process. All of these tasks are performed by human
workers and required a long time to complete.
To solve these problems, NTN developed an
integrated calculation automation system Axle
Bearing Integrated Calculation System (ABICS) for hub
bearings that automates each area of design work andshortens the design and lead time.
3.2 System overview
To automate the various tasks required for thedesign study of hub bearings, NTN developed the
ABICS (Fig. 5), which has the following four primaryfunctions.
• Search function for optimal bearing specifications• Automatic creation of 3D shape models• Automatic execution of FEM analysis• Data management

The use of this system enables designers to performtasks that were previously performed by separate
people in charge of each task. This further reduces
design and lead time through automation. Details ofeach function are described in the following sections.

Obtaincustomerrequirement

Bearing
specification
design3D modelcreationStress andstiffness FEM
analysis

Search function for
optimal bearing
specifications

Automatic creation of
3D shape models

Optimal value search
programBearingcharacteristic
calculation program

Bearingcharacteristic
calculation program

Automated creationof 3D shape models
programDesignreview
completion

Reportcreation

Automatic execution of FEM analysis
Automated pre-processing
program

Automated post-processing
program

FEM analysis job management
Program system

User interface & data management“ABICS”: Integrated calculation automation system for axle bearings

Fig. 5 ABICS system overview
3.3 Search function for optimal bearing
specifications
In the past, when determining the bearing
characteristics of a hub bearing, the NTN designer
would repeatedly change each parameter andcalculate the characteristics until the required
characteristics (life, internal mass (mass within acertain area around the rolling element), internal
stiffness, torque, etc.) had been met (Fig. 6 left).
Multiple calculation tools for each characteristic wereused for the characteristic calculation. The human
work therefore required time for both the search for
optimal results and the calculations.
In ABICS, NTN has created a bearing characteristic
calculation program that combines these calculation
tools. An optimal value search function (Fig. 6, right)
has been developed to automatically select desired
values for specifications.
Conventional

This system

Bearing specification
assumptions

Optimal value search program

Various bearing characteristic
calculations

Bearing characteristic
calculation program

Fig. 6 Optimization of bearing specifications
The optimal value search program employs agenetic algorithm (GA), which is classified as AI. For
the search, the desired bearing characteristics to be
optimized are set as the objective function and thedesign parameters that affect the characteristicsof the objective function are set as explanatory
variables. Under these conditions, the explanatory
variables selected by the GA are sent from the optimal

NTN TECHNICAL REVIEW No.89

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Development of Technical Calculation Systems for Rolling Bearings

Operating life

value search program to the bearing characteristic
calculation program, where bearing characteristics arecalculated. The characteristic values are returned tothe optimal value search program, and the GA selects
new explanatory variables. This iterative process
results in optimal values.
An example of an optimal value search is shown in
Fig. 7. The objective function is set to the conflicting
properties of life and internal mass, and the
explanatory variables are the three design parameters
related to these two properties. Fig. 7 shows theresults of the search. The Pareto solution for the
bearing life relative to the mass (marked in red)determines the candidates of optimal values. Basedon the results, the designer selects the value thatmeets the customerʼs required characteristics. In thisexample, about 34 000 calculations are required tofind the optimal value by exhaustive search, where thesearch for the optimal value is completed in about 300
calculations (marked in blue) with GA. In addition to
the computational cost, automation of the search also
reduced the work time required of personnel.

Internal mass

Fig. 7 Example of optimal value search
3.4 Automatic creation of 3D shape models
In the past, a CAD specialist created the 3D shapemodel required for FEM analysis and drawing(Fig. 8, top) based on previously-determined bearing
specifications. Since CAD work was done manually
by dedicated personnel, model creation was time
consuming. In addition, there was time spent waitingfor preliminary meetings with designers and for thecompletion of work in progress.
In the ABICS, an automatic 3D shape model creation
program has been developed to automate this model
creation process (Fig. 8, bottom). The program
has a variety of shape templates and automaticallycreates a 3D shape model by automatically inputting
dimensions derived from bearing characteristics
obtained from the optimal value search function
and the bearing characteristic calculation program
described in the previous section. In the case of
shapes for which it is difficult to create templates, theprogram automatically creates a similar shape andthen allows manual modification.

94

NTN TECHNICAL REVIEW No.89<Conventional>

Bearing
specification

CAD
specialist

3D shape
model<This system>

Bearing specification

Shape templates

3D shape
model

Fig. 8 Creation of 3D shape model
3.5 Automatic execution of FEM analysis
In the past, based on a previously-created 3D
shape model, a CAE specialist would perform thepre-processing, calculation execution, and postprocessing required for FEM analysis stress andstiffness characterization5) (Fig. 9, top). As withthe other tasks described above, time was required
to complete these tasks due to the skill level ofthe specialist, prior discussions with the design
engineer, and waiting time before starting the work.
A program and system were created to automate
these tasks, and an automatic FEM analysis
execution function (Fig. 9, bottom) was developed.
Details of each program are shown below.
• Automated pre-processing program
Automatically create a mesh for each part of the
3D shape model to be analyzed, combine theperipheral components necessary for analysis, andset the boundary conditions.
• Automated post-processing program
The system automatically obtains characteristic
values of stress and stiffness from calculation results,
obtains contour plots, checks calculation logs, etc.
• FEM analysis job management program / system
Computers to execute each of the above programs
and FEM calculation jobs are automaticallyassigned according to the computer utilization
status. Fig. 10 shows this job management
system. Jobs are distributed from the ABICS
server to the job management computer (thecomputer executing this program) based on
the input information of the user computer.
From the job management computer, jobs
are allocated according to the usage status ofmultiple computers prepared for pre-processing,calculation execution, and post-processing.
This system reduces the waiting time for jobs
and improves the availability of computers andsoftware licenses used for FEM analysis.

<Conventional>

3D shape model

Pre-processing

Execution of
calculation

Postprocessing

In addition, design reports can be automaticallygenerated based on the stored input/output results,
reducing the time spent by designers and shortening
lead times.

4. Conclusion
CAD specialist

CAE expert<This system>

3D shape model

Pre-processing Execution of
calculation

Postprocessing

Fig. 9 FEM analysis workJobtransmission

User PC

ABICS
SystemserverReturnresults

Job transmission

Pre-processing
Return results

Jobmanagement
PC

Execution of
calculation

Post-processing

Fig. 10 FEM analysis job management system

This paper introduces the integrated technicalcalculation system SharcNT, which is used toevaluate the performance of rolling bearings, andthe integrated calculation automation system ABICS,
which automates the design work of GEN3 hubbearings.
Going forward, NTN will continue to research,develop, and utilize CAE technology to further
enhance the sophistication and efficiency of productdevelopment operations. As we do so, we will build astructure that will enable us to quickly bring to market
the bearings that the market demands.
References
1) An Introduction to the CAE R&D Center, NTN
TECHNICAL REVIEW, No. 87, (2019) Back cover.
2) Rolling Bearing Theory and Practice Guidebook(Cat. No. 9600/J), NTN, (2022) 254-255.
3) Rolling Bearing Theory and Practice Guidebook(Cat. No. 9600/J), NTN, (2022) 253.
4) Makoto Seki, History of Development of Axle
Bearing Aiming at Low Fuel Consumption, NTN
TECHNICAL REVIEW, No. 87, (2019) 55-58.
5) A. Imoo, FEM Analysis of Hub Bearing, NTN
TECHNICAL REVIEW, No.70, (2002) 70-73.

3.6 Data management function
All ABICS usage information (input/output results,etc.) is stored and managed in a database. Information
designed with ABICS can thus be capitalized on andused effectively. The search function makes it easy toview past design results, while the input data used in
calculations can be reused, enabling efficient redesign
when improving products.

Photo of authors

Tomomi ISHIKAWA Hiroyasu HIRUKAWACAE R&D Center

CAE R&D Center

Mariko IZUMICedric BURNET

CAE R&D Center

NTN-SNRROULEMENTS
Research, Innovation& Development

NTN TECHNICAL REVIEW No.89

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New
Technology

Development of Feeder “ TRINITTE ” forPicking Robots

Shuhei MATSUI*NTN has developed a new parts feeder (TRINITTE) that combines aconventional parts feeder and a rotating disk and is developing it into afield that transcends the field of the conventional parts feeder.
In this article, I will explain the outline, features and specifications of
TRINITTE.

1. Introduction
There has been a rapid expansion in automationand manpower reduction globally using industrial
robots with the aim of increasing productivity at
the manufacturing site. This situation has occurredbecause of the diversification of consumer needs,
and the shift from mass production to “high-mix
low-volume production”. For parts feeders, there is aneed to reduce production changeover time due tothe support for a wide variety of workpieces, and aneed to decrease brief stoppages in production due toworkpiece jamming (improve availability factor).
For the conventional parts feeder and picking robot
combination, the workpieces are selected and sorted
in a bowl feeder were stored in straight feeders, adelivery mechanism used to deliver each workpiece,
and then the workpieces were picked up by a picking
robot. This setup had issues, which were that only
certain workpieces could be handled, many working
components were required, and workpieces became
jammed when sorting or storing them inside feeders.
However, parts supply devices are now being soldfor robots on the premise that sensing technology isused in combination with picking robots. Parts supply
devices for robots use 3-axis vibration technology
to change the posture of workpieces in the picking
area and to separate workpieces if they are too close
to each other, and a camera is used to detect theworkpiece position so that the picking robot can pickup the workpiece. The issue with this setup is that if
a workpiece with a pickable posture is not present in
the picking area, the machine operates to change theposture, so the robot stops during this time.
NTN has developed TRINITTE to solve these issues.

* NTN Technical Service Corp., Precision Equipment Division96

NTN TECHNICAL REVIEW No.89

2. Overview
Fig. 1 shows the system configuration. TRINITTE
comprises a motor-driven rotating disk arrangedon the outer circumference of a conventional bowl
feeder, and an encoder attached to the rotating disk.
A camera and picking robot are connected to thesystem so that the picking robot can import pulse
signals output from TRINITTE and image processing
signals obtained from the camera.
The following explains the full sequence of thepicking system that combines TRINITTE with a robot.
Workpieces deposited in the bowl are sorted ina single-row single-layer arrangement by the bowl
feeder, then supplied onto the rotating disk. The
workpieces supplied onto the rotating disk are picked
up without stopping the rotating disk using a robot
arc conveyor tracking function*1, then supplied to
the next process. Any workpieces that could not bepicked up are also collected inside the bowl feeder via
a workpiece collection opening located on the rotating
disk. These recovered workpieces are once again
supplied via the bowl feeder onto the rotating disk.
*1 Vision sensors are used to detect the position of a workpieceat any position on the rotating disk. This information andinformation from the encoder is used by the robot so that it
can follow the rotating disk and pick up the workpiece fromthe disk.

Camera

Scalar robot

Workpiece sortand supply
Picking

Bowl

Rotating disk
TRINITTE main body

Workpiece collection opening

Fig. 1 System configuration

In addition to supplying workpieces to the robot
using the rotating disk, this product has a simple andcompact structure that can also separate workpieces
and recover unpicked workpieces, enabling it toperform three tasks in a single unit.
Increasing the rotational speed of the rotating
disk more than the supply speed of the bowl feeder
enables workpieces that are ejected in a joinedmanner to be separated, making it easier for the robot
to pick up. Workpieces that could not be picked upby the robot are also collected inside the bowl so thatthey can be supplied once again onto the rotating disk
(Fig. 3).

3. Features
TRINITTE has the following features.
(1) Saves space
TRINITTE is different to conventional parts feeders
and uses a rotating disk to supply workpieces, so
it does not require a straight feeder, a chute or aworkpiece separating mechanism. Therefore, as
shown in Fig. 2, the number of working components
can be reduced to cut the footprint by approximately
30 %.

Attachment
Rotating disk

Workpiece

Bowl
Conventional parts feeder(a) Workpiece separation
Workpiece
collection opening

Separating mechanism
Chute

Workpiece

Rotating disk
Bowl

Straight feeder

30 %reduction

TRINITTE

Fig.2 Comparison of size between conventional parts
feeder and TRINITTE(b) Workpiece recovery
Fig. 3 Workpiece separation and recovery(2) Reduces brief stoppages
Conventional parts feeders use an attachment witha complex structure installed on the bowl feeder toarrange the posture of workpieces in the bowl feeder.
This complex structure makes it easy for workpieces
to become jammed when they are caught on theattachment, etc.
TRINITTE links the vision system and picking robot
together so that the attachment installed on the bowl
feeder has only a simple structure to perform tasks
such as aligning the orientation of workpieces. Since
the attachment can be simplified, continuous supplyof stable parts is achieved.
(3) Reduces robot wait time
TRINITTE ensures that workpieces are aligned sothat their orientation matches in a single-row

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Development of Feeder “TRINITTE” for Picking Robots
single-layer arrangement and enables a continuous
supply of workpieces at the picking area of the picking
robot. Therefore, workpieces on the rotating disk
can always be picked up and the robot can continue
picking up workpieces. Furthermore, as mentioned
previously, the use of an arc conveyor tracking
function on the picking robot enables constantoperation without stopping the rotating disk, so thisincreases the equipment availability factor.
(4) Improves versatility
TRINITTE can simplify the attachment installed on
the bowl feeder, which makes it possible to support awide variety of workpieces (Fig. 4) by making simple
adjustments only, without changing the bowl feeder.
This can reduce the time required for productionchangeover.
Additionally, workpieces that could not be stored
and could not be supported with conventional parts
feeders, or irregular-shaped workpieces can now be
supported, demonstrating that this is a device withhigh versatility.

(a) Fuses(b) Resin bushing

4. Specifications
TRINITTE has a lineup of 3 distinct types of bowl
sizes according to the size of the workpiece. Table 1
shows the main specifications.
Table 1 Specifications
Part number
Dimensions

K-UP301
K-UP302
K-UP303
Length 350 mm Length 500 mm Length 700 mm
Width 350 mm Width 500 mm Width 700 mm
Height 320 mm Height 370 mm Height 510 mm
φ190 mm φ320 mm φ420 mm

Bowl diameter
Power supply
AC200 V 50/60 Hz
voltage
Mass
38 kg
85 kg
200 kgOuter
φ344 mm φ494 mm φ694 mm
diameterRotating Rotational
1.3 to 6.5 min-1
count
disk
Rotational
0.05 to 0.20 m/s
0.05 to 0.30 m/s
speed
Part number ofcontroller for bowl
K-ECL25
K-ECH45
feeder (manufactured
by NTN)
Part number ofcontroller for motor
DSCD15JC(Manufactured by
Oriental Motor)
Encoder part number
E6B2-CWZ1X 1000P/RO.5M(Manufactured by
Omron)

5. Summary(c) Connectors(d) Resin blocks

Fig. 4 A wide variety of workpieces are supported
using the same bowl

Photo of author

Shuhei MATSUINTN Technical
Service Corp.,
Precision Equipment
Division98

NTN TECHNICAL REVIEW No.89

This paper explained the outline, features, andspecifications of TRINITTE.
In the future, we will investigate new applications ofuse, such as special uses that matchuser requirements
and the development of new sizes.
The Precision Equipment Division will work on
supporting the changing situation in which workpieces
are becoming more diverse, such as their increasing
miniaturization and complexity, and achieve stable
and continuous operation for the supply of parts
so that we can continue to contribute towards theautomation of production equipment using robots.

New
Technology

Product Introduction of Compact Torque Diode(TDL8)

Masayuki OHARA *NTN manufactures a “torque diode” that transmits rotation torque fromthe input shaft to the output shaft. But does not transmit the torquefrom the output shaft, which is the reverse input, to the input shaft.This
article introduces the technology of the compact and lightweight torquediode “TDL8” which has an outer ring diameter of 1/3 (10 mm) and aweight of 1/14 (5 g) as compared with conventional product “TDL28”.

1. Introduction

2. Torque diode structure and features

NTN produces a torque diode used in reverse
input prevention mechanisms and drop prevention
mechanisms. This product is used between two powertransmission shafts such as a motor and transmission.
This is a reverse input blocking clutch that transmits
the running torque from the input shaft to the output
shaft and locks the running torque from the output
shaft, preventing it from being transmitted to the
input shaft. Due to this ability, it has been given thename “torque + diode” from the rectifying action of
the torque. Since it does not require electric power
when compared with an electromagnetic brake, thisenables energy to be saved at mounted machinery.
It is also unaffected by power outages which is an
excellent safety feature. The torque diode (hereafter,
TDL) is introduced below (Fig. 1).
Running torquetransmission
direction

Input shaft

Running torquetransmission
direction

TDL comprises an outer ring, inner ring, cage, rollers,
spring and side plate, and is used with an input shaft
prepared by the user (Fig. 2). The running torque of the
input shaft is transmitted to the output shaft integrated
with the inner ring (hereafter, output shaft). The rollers
and spring lock the output shaft when the input shaft is
not rotating to block reverse input.
Side plate
Rollers
SpringOuter ring

Output shaft(Integrated with
inner ring)

Cage

Input shaft(Produced by user)

Input shaft

Output shaft

Output shaft

Running torque from the
input shaft is transmitted
to the output shaft for
both forward and reverse
rotational directions.

When attempting to rotate
the output shaft, theoutput shaft will not rotate
and running torque is nottransmitted to the input shaft.

B-O-B cross-sectional drawing

A-A cross-sectional drawing

Fig. 2 TDL structure

Fig. 1 TDL function* Product Design Dept., Industrial Business Headquarters

NTN TECHNICAL REVIEW No.89

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Product Introduction of Compact Torque Diode (TDL8)
3. Operating principle

4. TDL8 structure and features

This section explains the operating principle of how
TDL transmits running torque from the input shaft tothe output shaft. It also uses a structural drawing of aconventional product “TDL28” to show how the rollers
lock the output shaft (Fig. 3).
When the input shaft is motionless and not rotating,there is clearance between the input shaft and output
shaft. The rollers are making contact with the outerring bore diameter and the output shaft so there is norotation (Fig. 3 (a)).
When the input shaft rotates from a motionlessstate, 1) the cage connected to the input shaft pushes
the rollers to release the lock. Then 2) the input shaft
and output shaft make contact, and 3) the output
shaft rotates (Fig. 3 (b)).
When attempting to rotate from the output shaft,the spring pushes two rollers against a wedge formedby the outer ring bore diameter and output shaft
cam surface. This locks rotation in both the forward
and reverse directions and prevents the shaft fromrotating (Fig. 3 (c)).
Contact (lock)
Outer ring

Rollers Clearance

Fig. 4 shows the structure of the compact andlightweight torque diode “TDL8”. “TDL8” uses a
proprietary shaped C-type spring that enables it
to save more space than “TDL28”, a conventional
product that uses a coiled spring. This enables
smaller rollers to be used because many rollers canbe inserted. This achieves a 10 mm outer ring outer
diameter that is 1/3 the size and a 5 g weight that is
1/14 that of the conventional product “TDL28”, whilestill maintaining the allowable load torque.
The structure and features of the compact andlightweight torque diode “TDL8” are listed below
against the conventional product “TDL28”.
1. Changed from a coiled spring to a proprietary
shaped C-type spring.
2. Many rollers are inserted, enabling smaller roller
sizes, which reduces the overall size and weightof TDL.
RollersC-typespringCage
Outputshaft

Coiled spring

Clearance
Input shaft
2-sidedwidth
sectionInput shaft(a) When motionless
1) Lock released

2) Contact

3) Rotation(b) When transmitting runningtorque from the input shaft
Contact (lock)
Wedge formedby outer ring bore
diameter andoutput shaft

Clearance

Rotation notpossibleFig. 3 TDL operating principle

NTN TECHNICAL REVIEW No.89

5. Example of application
TDL is used in as applications like reverse input
prevention mechanisms. This will prevent unintended
rotation from the output shaft and drop prevention
mechanisms (Fig. 5) for the purpose of maintaining
safety when stopping rotation from the input shaft at
the time of a power outage, etc.
It is also installed in automobile seat lifter
mechanisms (Fig. 6). These systems are used to lift orlower an automobile seat surface by operating a leverwhen adjusting the height of the seat. It will also allow
a user to maintain the height of the seat when notoperating the lever.
Point of application

HandleClearance(c) When running torque from the output shaft is blocked

100

Fig. 4 TDL8 structure

WeightWeight Weight
When the handle (input shaft) is
rotated, the output shaft rotates
and the weight rises.

If the handle is not
rotated, the output shaft
locks so the weight does
not fall.

Fig. 5 Example of application in drop prevention mechanism

Point ofapplication
Load due toweight ofpassenger
Seat surface

Link gear section

Seat movement

Link

The torque diode prevents the link from fallingover to maintain the seat position.

Fig. 6 Example of application on automobile seat

6. Summary
The compact and lightweight torque diode “TDL8”
achieves a significantly smaller and lighter product incomparison with the conventional product “TDL28”,
and is a product that contributes towards making
mounted machinery smaller, lighter and require lessenergy.
In the future, NTN will continue to aim to make thisproduct more compact, lightweight and provide higher
efficiency, and also achieve a sustainable “NAMERAKA
Society” by saving energy.
References

１） NTN Catalog Clutch Related Products CAT.
No.6405/J．

Photo of author

Masayuki OHARA
Product Design
Dept.,
Industrial Business
Headquarters

NTN TECHNICAL REVIEW No.89

101

New
Technology

Application Examples of the Wrist Joint Module“i-WRISTTM”

Yuzuru TANAKA*
NTN developed an angle control equipment system applying a parallel
link mechanism, a constant velocity joint1)-7). We started mass production
under the product name of the “i-WRISTTM” in August 20188).
We have improved its functions to meet the needs of customers and havelaunched it on the market with the target of automating and reducing
manual work9). The features of the i-WRISTTM like “high-speed angle
control” are useful in the appearance inspection process of complexshaped parts. We would like to introduce application examples that showsuch advantageous features of the i-WRISTTM.

1. Introduction
Due to the reduction in the working population,
aging of skilled workers, and rise in personnel
expenses, the range of application for robots has
spread from work mostly involving tasks that placeda heavy load on operators and extremely dangerous
work, such as transporting heavy objects and welding,to more detailed manual labor work. Among thesemore detailed jobs, appearance inspection still relies
heavily on manual labor, and there is an increased
demand to automate this type of work. However,conventional robots cannot achieve the speedof visual checks performed by humans, and theautomation of appearance inspection for complex
shaped parts is particularly lagging.
NTN has proposed the application of Wrist Joint
Module “i-WRISTTM” to automate tasks handled byhumans. i-WRISTTM has received high praise for its
strength in “high-speed angle control”, and examples
of its use in projects to automate visual inspection
have increased.

2. i-WRISTTM overview
i-WRISTTM is a robotic module product that achieves
smooth movement like a human wrist. Fig. 1 showsa schematic drawing of the i-WRISTTM unit. The
i-WRISTTM unit comprises a parallel link mechanismand drive mechanism. The drive mechanism
determines angle orientation in 2degrees of freedom(bending angle and swing angle) at the parallel
link mechanism for high-speed and high precision
positioning within hemispherical areas. Furthermore,
cables can be passed through the internal space of theparallel link mechanism, so the cables do not become
twisted even when swing operation is repeated in thesame direction.

Fig. 1 Schematic drawing of i-WRISTTM unit

3. Features of i-WRISTTM in use at the
production site
The use of robots at the production site poses
problems for some managers who give comments
such as “we installed robots but are not satisfied
with the cycle time”, “robots are difficult to operate
and hard to master” and “we have no space to installrobots.” To solve these problems, NTN proposes a
configuration9) that combines i-WRISTTM with a linear
actuator or rotation actuator. The features of this areshown below.
(1) Fast motion
The moment of inertia at the entire movablesection is small, and the robot can move to the target
orientation along the shortest route. Therefore, thissetup can be particularly effective for work that
requires fine movement, something that conventional
robots do not do well.
(2) Easy of use
Even operators who do not have expert knowledgeof robot language can easily operate this setup using
a dedicated console.

* Robotics & Sensing Engineering Dept., Industrial Business Headquarters

102

NTN TECHNICAL REVIEW No.89

(3) No singularity point
There is no need to create an operation program
to avoid the singularity point, as is the case witharticulated robots.
(4) Offline teaching
NTN provides a PC-based teaching tool to specify
points on a 3D model and configure operating
patterns9).

resolved using the features of i-WRISTTM. For example,
as shown in Fig. 3, inspection processes that haveso far required the use of two robots can now be
configured using a single i-WRISTTM unit, and this has
been evaluated as achieving the required cycle timeand has been adopted for use. Below introduces more
specific examples of the application in appearance
inspection.

(5) Space-saving
In combination with a linear actuator or rotation
actuator, the machine can be compactly configured,
which allows this setup to be installed in a space
where a operator worked9).
Fig. 2 shows examples of application for i-WRISTTM.
Among such applications, i-WRISTTM is often used
in appearance inspection machines equipped withcameras and lighting. An example of this is shown
below.

Appearance inspection

Grease dispensing

Fig. 2 Example of applications for i-WRISTTM

4. Example of applications for i-WRISTTM
in appearance inspection
During appearance inspection of workpieces thathave a 3D shape or complex shape, such as castingparts and resin molded parts, humans can quickly andskillfully visual inspection multiple locations of theworkpiece from various angles while changing how
lighting is shone onto the workpiece and the angleof the workpiece. This type of high-speed inspection
is exceedingly difficult to automate. However, many
examples exist in which this difficulty has been(a) With conventional robots(b) With i-WRISTTM

Fig. 3 Example of application at the production site
4.1 Example of application for casting parts
During appearance inspection of small castingparts, such as for an automotive compressor as
shown in Fig. 4 (a), appearance inspection of 0.2
seconds per single point -- about 2.5 times the speedof conventional robots -- was achieved. Fig. 5 shows
an example of the configuration for this system.
This configuration involves mounting a camera onto
i-WRISTTM and controlling the angle, while a rotation
actuator and linear actuators are used to position
the workpiece. The rotation actuator rotates theworkpiece while images are captured from multiple
directions. This enables high-speed inspection for
defects such as surface scratches, dents, and residualdebris inside bore holes. This configuration can also
make the machine more compact.
During appearance inspection of large casting parts
such as for an engine block or transmission case as
shown in Fig. 4 (b), appearance inspection of 0.3
seconds per single point was achieved. Fig. 6 shows
an example of the configuration for this system.
This configuration involves mounting a camera
onto i-WRISTTM installed at an incline and using arotation actuator and linear actuators to position theworkpiece. Installing i-WRISTTM at an incline enables
images to be taken of the workpiece while looking up
at the workpiece from below. This enables high-speed
inspection for defects such as scratches on unevensurfaces at the side of the workpiece, dents, andresidual debris inside bore holes.

(a) Small casting part(b) Large casting partFig. 4 Casting parts

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Application Examples of the Wrist Joint Module “i-WRISTTM”

Fig. 5 System configuration example (1)Fig. 6 System configuration example (2)4.2 Example of application for automotive resin
molded parts
During appearance inspection of automotive resin
molded parts integrated with various sensors asshown in Fig. 7, visual inspection of 0.3 seconds per
single point was achieved. Fig. 8 shows an example ofthe configuration for this system. This configuration
involves fixing the camera and lighting while a chuck
mounted onto i-WRISTTM holds the workpiece. The
workpiece is positioned using i-WRISTTM, a linear
actuator and a rotation actuator. The use of a rotation
actuator achieves a compact system configurationthat can minutely change the positioning of theworkpiece while rotating it for a single revolution at
the same position. This configuration enables thesystem to inspect the appearance of surface (forscratches, bubbles and burrs) and check whether any
connector pins and sensor parts are missing.

Fig. 7 Resin molded part104

NTN TECHNICAL REVIEW No.89

Fig. 8 System configuration example (3)4.3 Example of application for automotive electronic
control unit
With the electronification of automobiles,
examples of appearance inspection have increased
for automotive electronic control units, such as gearboxes integrated with electronic circuit boards asshown in Fig. 9. This type of unit has sections whereimages are difficult to capture, such as the back of
circuit boards, so a person visually inspects blind spotsthat are difficult to see while changing the angle. The
system configuration shown in Fig. 6 enables images
to be captured of electronic control units, including
the back of circuit boards from multiple directions.
The illumination angle can be finely adjusted onto thecircuit board using i-WRISTTM so that light shines onto
blind spots. This enables inspection of blind spots atthe back of the circuit board (the soldered surface) as
shown in Fig. 10. In this example an inspection speedof 0.3 seconds per single point was achieved to checkfor missing parts on electronic circuit boards, andfor appearance defects on the resin surface such as
scratches, dents, and burrs.

Blind spot
(Back of circuitboard)

Fig. 9 Electronic control unit Fig. 10 Example of captured image(back of circuit board)
4.4 Through-hole and screw-hole internal inspection
There is also a high demand for automating
inspection of burrs and residual debris inside throughholes and screw-holes. Using the pivot movement of
the i-WRISTTM enables the angle to be changed while
maintaining working distance from the camera to
the reference point by linked i-WRISTTM and linear
actuators. Using this action enables images to be
captured as shown in Fig. 11. This can make it easy toinspect the entire inside diameter surface of a hole.

and create examples of applications to contribute toautomating and optimizing the production site andstabilize quality.

Reference point

Fig. 11 Pivot movement

5. Efforts to increase the range ofapplication for i-WRISTTM
Amid the launch of i-WRISTTM to the market, we
received praise for i-WRISTTM high speed operation, andits excellent ability to work without singularity points,
which is a challenge for conventional robots. At thesame time, we received many requests for i-WRISTTM tohandle similar payloads as conventional robots and haveinvestigated methods to achieve this.
Until now, maximum load capacity was restricted to
1 kg so that i-WRISTTM could be used at high speed.
However, we developed a new grade that increases
the maximum payload to 3 kg by establishing a modethat optimizes the control method to match the load
capacity. As a result, it is now possible to mount largescale lighting and multiple lighting onto i-WRISTTM forappearance inspection. Using large-scale lighting enables
images to be captured over a large area in a single shot,
and this reduces the number of inspection points, whichleads to a shorter cycle time. Furthermore, using multiple
lighting increases the variation of how lighting can beshone onto a work piece being inspected. This provides
support for work pieces that are difficult to inspect.
In addition to appearance inspection applications,
i-WRISTTM can be applied to such as the deburring
process in which the machining load acts on the end
effector, and the welding process in which the end
effector weight is large.

6. Summary
This paper introduced examples of appearance
inspection using high-speed angle control, which is astrength of i-WRISTTM. Using i-WRISTTM can replacesight checks that are difficult to automate and achievea cycle time that cannot otherwise be achieved withconventional robots.
In the future, there will be greater demand forautomating complex work performed by humans, suchas deburring and assembly to accompany the decreasein the working population. i-WRISTTM introduced here is arobotic module product that can achieve automation ofmanual work at a work speed and smooth movement likehuman hands. NTN will continue to improve performance

References
1) Keisuke Sone, Hiroshi Isobe, Koji Yamada, WideAngle Active Link Equipment, NTN TECHNICALREVIEW, No. 71, (2003) 70-73.
2) Hiroshi Isobe, Yukihiro Nishio, Parallel Link High
Speed Angle Control Equipment (PHACE), NTN
TECHNICAL REVIEW, No. 80, (2012) 42-47.
3) Hiroshi Isobe, Yukihiro Nishio, Keisuke Sone, Hiroyuki
Yamada, Yoshio Fujikawa, Parallel Link High Speed
Angle Control Equipment, Proceedings of the Japan
Society for Precision Engineering Spring Meeting in
2013, (2013) 809- 810.
4) Hiroshi Isobe, Yukihiro Nishio, Seigo Sakata, Naoya
Konagai, Hiroyuki Yamada, Yoshio Fujikawa, Parallel
Link High Speed Angle Control Equipment Implementation on Grease Application Equipment -,Proceedings of the Japan Society for Precision
Engineering Spring Meeting in 2014, (2014) 10871088.
5) Naoya Konagai, Hiroshi Isobe, Seigo Sakata, Kenzou
Nose, Hiroyuki Yamada, Yoshio Fujikawa, Parallel Link
High Speed Angle Control Equipment, Proceedingsof the Japan Society for Precision Engineering Spring
Meeting in 2015, (2015) 605-606.
6) Kenzou Nose, Hiroshi Isobe, Seigo Sakata, Naoki
Marui, Naoya Konagai, Parallel Link High Speed
Angle Control Equipment - Enhancement of
Performance by Improvement, Proceedings of
the Japan Society for Precision Engineering Spring
Meeting in 2016, (2016) 483-484.
7) Kenzou Nose, Hiroshi Isobe, Seigo Sakata, Speeding
Up of Parallel Link Angle Control Equipment, NTN
TECHNICAL REVIEW, No. 84, (2016) 96-101.
8) Keisuke Kazuno, Hiroshi Isobe, Jun Midoumae,
Yuki Shimura, Masayuki Ohara, Development of“i-WRISTTM” Wrist Joint Module, NTN TECHNICALREVIEW, No. 86, (2018) 22-27.
9) Keisuke Kazuno, Hiroshi Isobe, Masaki Kagami, Jun
Midomae, Yuki Shimura, Seigo Sakata, Yukihiro
Nishio, Naoki Marui, Application Examples andFunction Improvements of the Wrist Joint Module“i-WRISTTM”, NTN TECHNICAL REVIEW, No.88,(2020) 105-110.
Photo of author

Yuzuru TANAKA
Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters
NTN TECHNICAL REVIEW No.89

105

AwardWinning
Products

2020“CHO” MONODZUKURI Innovative Parts and Components Award,
Mobility Components Award

Low Friction HUB Bearing Ⅲ
Makoto SEKI

The “Low Friction HUB Bearing Ⅲ”1), which reduces
rotational friction while driving by 62 % comparedwith conventional products, received the 2020 “CHO”
MONODZUKURI Innovative Parts and Components
Award, Mobility Components Award sponsored by
MONODZUKURI. Nippon. Conference and Nikkan
Kogyo Shimbun, Ltd.
NTN developed bearing internal grease in pursuit of
low friction, and combined with the latest low friction
seals, was able to reduce rotational friction by 62 %when compared with conventional products2). Using
this product on the wheels at both sides of a vehicle
is expected to improve vehicle fuel efficiency byapproximately 0.53 %.

２. Structure
Fig. 1 shows a schematic drawing of Low Friction
HUB Bearing Ⅲ.

《New development》● Low friction grease・Low viscosity base oil
・Revised additive● Low friction seal
・Labyrinth structure
・Seal dedicated grease is applied
・Optimized lip contact[Outer seal][Inner seal]
Assist lip

Labyrinth
Assist lip

Slinger

Running torque comparison

1. Introduction

Hub bearing (overall)
Running torque is reduced by 62 %1

Sealfriction
0.50Bearingfriction

-70 %

NTN
conventional
product

Low Friction HUB
Bearing Ⅲ(Developed product)

Fig. 2 Hub bearing running torque comparison(an example)

4. Summary
To support stricter emission regulations on CO2
and improve vehicle fuel efficiency throughout
the world, NTN has developed a hub bearing withsignificantly lower friction over conventional products
while meeting the requirements for service life andstrength. NTN will continue to develop the market
for this product, which is expected to improve vehicle
fuel and power consumption efficiency, and also
contribute towards reducing the impact on the global
environment.
References
1) Makoto Seki, Low Friction HUB Bearing Ⅲ,
NTN TECHNICAL REVIEW, No.87, (2019) 63-67.
2) Makoto Seki, Low Friction HUB Bearing,NTN TECHNICAL REVIEW, No.85, (2017) 67-71.

Fig. 1 Structure of Low Friction HUB Bearing Ⅲ

3. Features

Photo of author

The following are the features of Low Friction HUB
Bearing Ⅲ.
(1) Application of newly developed low friction
grease(2) Application of new seal structure with labyrinth(3) Application of seal dedicated grease(4) Optimization of seal lip contact surface
As shown in Fig. 2, these features reduce bearing
friction and outer/inner seal friction to achieve a runningtorque reduction of 62 % for the entire hub bearing.

106

NTN TECHNICAL REVIEW No.89-56 %Makoto SEKI
Axle Unit Products
Development Dept.,
Axle Products Unit,
Automotive Business
Headquarters

AwardWinning
Products

Nippon Brand Award of 2021 “CHO” MONODZUKURI Innovative Parts
and Components Award

High Speed Deep Groove Ball Bearing for EV/HEV
Katsuaki SASAKI

1. Introduction
NTNʼs “High Speed Deep Groove Ball Bearing for EV/HEV”1),
has achieved the worldʼs highest level of allowable speed by
the Nippon Brand Award of 2021 “CHO” MONODZUKURI
Innovative Parts and Components Award sponsored by
MONODZUKURI. Nippon. Conference and Nikkan Kogyo
Shimbun, Ltd.
This product was developed using technology that optimizes
the shape and material of the bearing cage to minimize theenergy lost due to friction. As motors become smaller andfaster to accommodate the continued electrification of theindustry, there is a growing need for bearings that can support
high-speed rotation of 1.8 million d mn*1.
Furthermore, with the aim of improving performance ofdeep groove ball bearings, high regard is placed on such things
as the creativity of designers and development concepts
that provide verification of results after planning detailed
improvements.

2. Structure
Fig. 1 shows a schematic drawing of a cage for the High
Speed Deep Groove Ball Bearing for EV/HEV.

Yukihiro ISHIDA

Large

Standard
cage

Developed
cage
Optimized material
removalFig. 1 Structure of developed cage

3. Features
NTNʼs “High Speed Deep Groove Ball Bearing for EV/HEV”
contains the following features:(1) The worldʼs highest allowable speed of 1.8 million d mn
: Over 3 times that of a standard deep groove ballbearingStandard cage
Developed cage

Ball interference

Small

Cage pocket clearance0

Increased thickness(strength)
Optimized lubrication
grooveKazunori MURANUSHI(2) Superior cage strength (compared to standard cage)
1.6 times: Tensile strength: Centrifugal force deformation
1/8: Heat resistance temperature improved by 30 °C
Fig. 2 shows the results of analyzing the amount of cage
deformation (outer radial displacement) due to centrifugal
force under bearing inner ring rotating conditions. NTNʼs“High Speed Deep Groove Ball Bearing for EV/HEV” has an
optimized resin material and resin cage design that preventsball interference at high speeds. Note that the developed
product can operate at speeds up to 3 times higher than aconventional bearing and still maintain sufficient clearancewith the cage pocket. This also prevents increased bearing
torque and temperature rise during operation.

Outer radialdisplacement

Goro NAKAO

10 000

20 00030 000Inner ring rotational speed [min-1]

Fig.2 Difference in deformation due to centrifugal force(standard cage vs. developed “high speed” cage)

4. Summary
Increasing the speed of the motor is the most effective wayof improving EV motor efficiency. This product responds todemands from customers to increase the speed of bearings,
and also contributes towards achieving a decarbonizedsociety. Furthermore, NTN has recently achieved a d mn valueof 2.2 million due to the optimization of heat balance.2) In the
future, NTN will continue to support the need for increased
allowable speeds using our expert knowledge in high speed
operating technology.
References
1） Masahiko Satoda, Goro Nakao, Grease Lubricated Highspeed Deep Groove Ball Bearing for EV and HEV Motor,
NTN TECHNICAL REVIEW, No.83, (2015) 81-85.
2） Single page in Nikkan Kogyo Shimbun dated April 28, 2022.

Photo of authors*1

Goro NAKAO

Katsuaki SASAKI

Yukihiro ISHIDA

d mn value refers to an index that represents
bearing rotational performance, and is thebearing pitch diameter (mm) × rotational
speed (min-1).

Kazunori MURANUSHI

Automotive Bearing
Automotive Bearing
Automotive Bearing
Automotive Bearing
Engineering Dept.,
Engineering Dept.,
Engineering Dept.,
Engineering Dept.,
Automotive Bearing Products Unit, Automotive Bearing Products Unit, Automotive Bearing Products Unit, Automotive Bearing Products Unit,
Automotive Business Headquarters Automotive Business Headquarters Automotive Business Headquarters Automotive Business Headquarters

NTN TECHNICAL REVIEW No.89

107

AwardWinning
Products

2020 Japanese Society of Tribologists (JAST) Technology Award

Development of Super Long-Life Tapered Roller
Bearings for Automobile
Hiroki FUJIWARA

Takashi KAWAI

1. Introduction

Chikara OHKI

3. Features

NTN has developed “Super Long-Life” Tapered Roller
Bearings that can be used on automobile transmissions anddifferentials as well as in electric drive devices (reducers for
e-Axle). This product received the 2020 Technology Award
from the Japanese Society of Tribologists.
This bearing has an increased resistance to misalignmentand contamination and a higher allowable speed. Theseadvancements are possible due to improvements madeto the shape of sliding contact areas, the heat treatment
method for grain refinement of crystal grain in bearing steel,and the technology used to design the shape of rollers thatminimizes the contact stress at the rolling contact surfaceof roller elements and the raceway surface. These factors
enable the automobile drive device to be more compact
and lighter in weight, which has been praised for its ability
to improve both fuel and power consumption efficiency.
The product that received the award was commercialized
as “ULTAGE Tapered Roller Bearing for Automotive
Application” (Fig. 1).

Fig. 1 ULTAGE Tapered Roller Bearing for Automotive Application

2. Structure
Fig. 2 shows a schematic drawing of ULTAGE
Tapered Roller Bearing for Automotive Application.
Optimized shape of the sliding contact area
provides control for temperature increases1)

Optimized roller
shape minimizes
the contact
surface pressure2)

Outer
ring

(1) The worldʼs highest level in high-load capacity: Basic dynamic load rating4) 1.3 times(2) Long operating life (comparing basic rating life4)): Standard heat treated type 2.5 times or more
: Grain refinement heat treated type 3.8 times or more
(3) The worldʼs highest level in high rotational speed
performance: Allowable speed5) Improvement of approx. 10 %(4) Allowable misalignment5) (misalignment amount): Allowable misalignment Up to 4 times

4. Summary
This product was developed to allow for longer
operating life for tapered roller bearings. The bearing
can also be made smaller dimensionally and achieve
the same previous service life. This contributes tomaking automobile drive devices smaller and lighter,and can also make automobiles more efficient interms of fuel and power consumption. Furthermore,
the longer operating life technology we havedeveloped for this product can also be applied toother areas, which we hope will greatly contributetowards higher optimization of various machines andachieve carbon neutrality.
References
1) Yasuhito Fujikake, Takanori Ishikawa, Susumu
Miyairi, ULTAGE Tapered Roller Bearing for
Automotive Application, NTN TECHNICALREVIEW, No. 85, (2017) 51-55.
２) H. Fujiwara et al., Optimized Logarithmic Roller
Crowning Design of Cylindrical Roller Bearings
and Its Experimental Demonstration, Tribol.
Trans., 53 (2010) 909-916.
３) C. Ooki, Improving Rolling Contact Fatigue Life of
Bearing Steels Through Grain Refinement, SAE
Technical Paper Series, 2004-01-0634.
４) JIS B 1518 (2013)５) NTN “Ball and Roller Bearings Catalog” (CAT. No. 2203/J)
Photo of authors

Cage

Application of grain refinement
heat treatment improves surface
initiated damage life3)

Inner
ring

RollerFig. 2 Structure of ULTAGE Tapered Roller Bearing for
Automotive Application

108

NTN TECHNICAL REVIEW No.89

Hiroki FUJIWARA

Takashi KAWAI

Chikara OHKI

CAE R&D Center

Automotive Bearing
Engineering Dept.,
Automotive Bearing Products Unit,
Automotive Business Headquarters

Advanced
Technology R&D
CenterAwardWinning
Products

2021 Japanese Society of Tribologists (JAST) Technology Award

Low Friction Technology of Sealed Ball Bearings forTransmission
Katsuaki SASAKI Takahiro WAKUDA

1. Introduction
Lower torque and long operating life are needed forautomotive transmission bearings to achieve carbon
neutrality. The lubricating oil inside a transmission
has contaminants such as gear wear debris which
can cause the service life of a rolling bearing to
decline. Therefore, countermeasures are provided
using methods such as ① preventing contaminantsfrom entering the bearing using a contact seal and ②
applying special heat treatment to the rolling bearing
ring to improve the service life against contaminants.
However, ① places restrictions on the allowable speed
due to increased running torque due to the seal andheat generated at the seal. Furthermore, ② is not
sufficiently effective at suppressing the decline inservice life in comparison with the bearing service life
in an environment with no contaminants.
To respond to these issues, NTN has developed
technology to reduce running torque while
maintaining sufficient service life even whencontaminants are present in the lubricating oil1,2). This
technology received the “2021 Japanese Society of
Tribologists Technology Award”, which is given for
excellent new technology in the field of tribology. This
paper introduces this technology.

2. Overview of award-winning technology
With conventional contact seals, the seal sliding
surface contacts the inner ring and because a sufficientoil film does not form at the operational speed range,
there is a comparatively high drag resistance torqueat the seal. In contrast, this technology provides arcshaped micro convexities on the contact seal sliding
surface as shown in Fig. 1. These micro convexities
generate a fluid film due to the “wedge film effect”
between the seal sliding surface and inner ring under
oil lubrication. This results in a fluid lubrication state at
the operational speed range which reduces the runningtorque by 80 % when compared to conventional
contact seals, as shown in Fig. 2. This can achieve
the same low torque performance as a non-contact
seal despite it being a contact seal. Furthermore, theconvexities are of a micro height so they can prevent
contaminants of sizes that would cause the service life
to decline from entering the bearing. This enables thebearing to maintain a service life equal to a bearing
used in an environment with no contaminants.

Bearing running torque N . m

Tomohiro SUGAI

0.4

Developed seal
Conventional non-contact seal

0.3

Conventional contact seal

0.2
0.1
0.0
20

40

60

80

100

120

140

Bearing temperature °C

Fig. 2 Bearing running torque experimental results
Additionally, this seal reduces sliding heat generated
at the seal contact area so it can also be used underperipheral speed conditions that are two or moretimes greater than that of a conventional contact seal.

3. Summary
This technology can reduce the running torque oftransmission bearings while maintaining sufficient
service life even with contaminants in the lubricatingoil. This can contribute towards better fuel economy
in automobiles. Furthermore, the bearing size can besmaller due to improved reliability which can makeautomobiles lighter in weight. It can also respond to
the demand for speed increases that accompany theelectrification of vehicles.
References
1） Katsuaki Sasaki, Takahiro Wakuda, Tomohiro
Sugai, Ultra-Low Friction Sealed Ball Bearing forTransmission, NTN TECHNICAL REVIEW, No.85,(2017) 62-66.
2） Tomohiro Sugai, Katsuaki Sasaki, Takahiro Wakuda,
Low Friction Technology of Sealed Ball Bearings
for Transmission, Tribology Congress, 2022 Spring
Tokyo Proceedings, (2022) B6 85-86.
Photo of authors

Tomohiro SUGAI Katsuaki SASAKI Takahiro WAKUDA
Arc-shaped
micro convexity

Fig. 1 Schematic drawing of developed seal

Advanced
Technology R&D
CenterAutomotive Bearing Automotive Bearing
Engineering Dept.,
Engineering Dept.,
Automotive Bearing Automotive Bearing
Products Unit,
Products Unit,
Automotive Business Automotive Business
Headquarters
Headquarters
NTN TECHNICAL REVIEW No.89

109

AwardWinning
Products

2021 Japanese Society of Tribologists (JAST) Best Paper Award

Estimation Method of Micropitting Life from S-NCurve Established by Residual Stress Measurements
and Numerical Contact Analysis
Takumi FUJITA

Michimasa UCHIDATE

1. Introduction
The above-mentioned paper1) submitted to
the Japanese Society of Tribologists (non-profit
organization) academic journal “Tribology Online”
received the 2021 Best Paper Award. The content of
this paper is introduced below.

2. Overview
Peeling (referred to as micropitting in the paper)is the typical damage seen on bearings under severe
lubrication conditions. It refers to a concentration of
micro spalling caused by cyclic contact of projections
on rough surface. This paper proposed a new peelinglife estimation method utilizing experimental results.
This method estimates the peeling life using thefollowing procedure.
1) A rolling fatigue test is conducted under various
operating conditions. Time series data (hereafter,
stress history) for cyclic stress at areas ofprojection contact and peeling life during each testis acquired. The stress history is estimated using
the measurement results of surface roughness
and residual stress during the operation.
2) Regression analysis is performed on the obtained
data, and a S-N curve that shows the relationshipbetween cyclic stress and peeling life is created.
3) A preliminary test simulating the subject
operating conditions is conducted. Stress history
under those conditions is obtained. The peelinglife is then estimated using the S-N curve createdin 2) above and Minerʼs rule.
To estimate peeling life under various conditions,actual measured data was utilized to increase theprecision of life estimation. Furthermore, anotherfeature of this method is that it considers the effectof residual stress on life, something that was difficult
to do in the past. However, it must be noted that theapplication range of this estimation method is limited
to pure rolling and boundary lubrication conditions.
Fig. 11) shows the relationship between the actual
life Lact and the peeling life Lest estimated using thismethod. The median, minimum value and maximum

Masayoshi ABO

Hiroshi KINOSHITA

value of the life ratio (Lact / Lest) is 0.89, 0.49 and 1.82
respectively. This precision is comparable to or better
than the generally used spalling life estimation of therolling bearing. This method is considered sufficiently
applicable as an estimation method for peeling life.

Estimated life (Lest)×106 cycles

Naoya HASEGAWA

10

4
1

1

8

3

9

2

Lact / Lest (All test)

6

0.1

0.01
0.01

7

Median: 0.89
Min.: 0.49
Max.: 1.82

5

0.1

1

Fig. 1 Relationship between estimated life and actual life1)

3. Summary
Even greater progress is expected in the future toachieve higher efficiency of machines for achievingcarbon neutrality by lowering the viscosity of
lubricating oils. This increases the likelihood ofbearings being used under thin lubrication conditions.
Life estimation under conditions similar to those usedin this study will become an important technology for
maintaining the reliability of bearing life prediction. In
the future, NTN will strive to increase the application
range of this estimation method and further improve
its accuracy.
References
1） N. Hasegawa, T. Fujita, M. Uchidate, M. Abo & H.
Kinoshita: Estimation Method of Micropitting Life
from S-N Curve Established by Residual StressMeasurements and Numerical Contact Analysis,
Tribology Online, 14, 3 (2019) 131.

Photo of authors

Naoya HASEGAWA
Advanced
Technology R&D
Center110

Takumi FUJITA

Michimasa UCHIDATE

Masayoshi ABO

Hiroshi KINOSHITA

Product and Business Faculty of Science andEngineering,
Strategic Planning
Iwate University
Dept.

School ofEngineering,
University of Hyogo

School ofEngineering,
University of Hyogo

NTN TECHNICAL REVIEW No.89

10

Actual life (Lact)×106 cycles

AwardWinning
Products

2021 New Energy Awards, New Energy Foundation Chairman Award(products and services category)

DLC Coating Spherical Roller Bearing for Wind Turbine
Main Shaft

Kazumasa SEKO

Takashi YAMAMOTO

1. Introduction“DLC Coating Spherical Roller Bearing for Wind
Turbine Main Shaft” received the “New Energy
Foundation Chairman Award (products and services
category)” of the 2021 New Energy Awards sponsoredby the New Energy Foundation.
The award-winning product substantially improves
the wear resistance of the raceway surface and rolling
contact surface of rolling elements by applying a
DLC (diamond-like carbon) coating* to the rolling
contact surface of rolling elements. This has beenhighly regarded for its significant contribution towards
improving the reliability of wind turbines.

Masaki NAKANISHI

confirmed that wear depth on the outer ring raceway
surface was suppressed by 1/9 or less in comparison witha conventional product (Fig. 2).
Test bearing

Wear depth progress
50 h
50 h
100 h
100 h

Conventional product

20
20

30
30

40
40

50
50

10
10

20
20

30
30

40
40

50
50

50 h
50 h

DLC coating product2. Structure

10
10Wear depth µm
Wear depth µm

100 h
100 h

* A hard film consisting of a mixture of a diamond structure andgraphite structure

150 h
150 h
0
0

150 h
150 h
0
0

Wear depth µm
Wear depth µm

Fig. 2 Wear test results

Fig. 1 shows the structure of the DLC Coating
Spherical Roller Bearing for Wind Turbine Main Shaft.
RollerCage

DLC coating

Outer
ring

Inner
ring

Suppresses wear due to the DLC coating on therolling contact surface of rolling elements

Fig. 1 DLC Coating Spherical Roller Bearing for Wind
Turbine Main Shaft

3. Features
When there is insufficient lubrication during operation
with conventional spherical roller bearings, metal on theroller raceway surface and rolling contact surface of rolling
elements makes contact, resulting in wear on the raceway
surface. This contact and resultant wear causes spallingand cracks to occur.
The DLC Coating Spherical Roller Bearing for Wind
Turbine Main Shaft can suppress wear on the raceway
surface even under harsh lubrication conditions byapplying a DLC coating. The DLC coating has a 3-layer
structure that provides excellent adhesion to the basematerial on the rolling contact surface of rolling elements.
During a wear test on smaller sized bearings, NTN

4. Summary
The main bearings on a wind turbine repeatedly rotateand stop based on wind conditions, and are used underharsh lubrication conditions. Moreover, replacing the main
bearings is not an easy task. Therefore, it is necessary to
avoid spalling and cracks due to wear on the main bearings
because such factors are directly linked to a drop in thereliability of wind turbines.
DLC Coating Spherical Roller Bearing for Wind Turbine
Main Shaft is a product that responds to these issues, andcan contribute towards improving the reliability of windturbines by developing the market for this type of product.
References
1） Michio Hori, Yusuke Yamada, New Products andImproved Reliability of Main Bearings for Wind
Turbine Generators, NTN TECHNICAL REVIEW,
No.88, (2021) 15-20.
Photo of authors

Kazumasa SEKO Takashi YAMAMOTO Masaki NAKANISHI
Application
Engineering Dept.,
Industrial Business
Headquarters

Product Design
Dept.,
Industrial Business
Headquarters

Advanced
Technology R&D
CenterNTN TECHNICAL REVIEW No.89

111

NTN TECHNICAL REVIEW No.89
Printed and published in December 25, 2023

Editor Masaki EGAMI

Publisher Tatsuo NAGAO

Published by NTN Corporation
Daibiru-Honkan Bldg., 3-6-32, Nakanoshima,
Kita-Ku, Osaka 530-0005, Japan

Printed by Daishinsha Delight Inc.

No part of this publication may be reprinted
or reproduced without the prior permissionof the copyright owner.

112

NTN TECHNICAL REVIEW No.89

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ISSN 0915-0528ⓒ NTN Corporation 2023
CAT.No.ZE089 23.12.005 DS/DS