**表紙E_レイアウト 1 18/09/05 18:34 ページ 1

For New Technology NetworkR

TECHNICAL REVIEW No.85
Special Issue

corporation

Special issue on"Automotive Products and Electric Module Products"
October 2017

Automotive Products and Electric Module Products
corporation

This catalog is printed on recycled paper for environmental protection purposes.

ISSN 0915-0528 OSAKA, JAPAN

**表紙E_レイアウト 1 18/09/05 18:34 ページ 2

Osaka University forms"NTN Next Generation Research Alliance Laboratories."

NTN Corp (hereafter, NTN) formed the "NTN Next Generation Research Alliance Laboratory" within the Graduate Schoolof Engineering at the National University Corporation Osaka University (Headquartered in Suita-City, Osaka Prefecture,under the presidency of Dr. Shojiro Nishio; hereafter Osaka University) on September 1, for creating new business andaccelerating technical innovation.
NTN, which commemorates its 100th anniversary in March of 2018, is working on enhancing platform technologies toward
the next 100 years and creating new business by introducing new products into the new fields. NTN has formed the "NTN
Next Generation Research Alliance Laboratory" (hereafter, Laboratory) at the University by leveraging the Research Alliance
Laboratory system of Osaka University*. The specially-appointed professor, Yoshinobu Akamatsu, of the Graduate School ofEngineering at Osaka University (former NTN executive officer) will become the general manager and the Dean of the
Graduate School of Engineering at Osaka University, Prof. Toshihiro Tanaka, will become the deputy general manager of theLaboratory.
Together with Osaka University, NTN is conducting research and development of an innovative, artificial 3D cellulartissue. Using cell laminating technology with iPS-derived cells, in conjunction with NTN's own technology, a microscopic
coating applicator, the creation of new medicines and applications to regenerative medicine is possible. In addition, theLaboratory plans to initiate development of residual bearing life prediction by estimating damage to the bearings forautomobiles, rolling stock, machine tools, etc. Also the degradation of grease leveraging artificial intelligence (AI), as well as
achieving bearing operational trend management and failure prevention by applying multi-functional sensors is being studied.
NTN is also working on lightweight and compact product development by applying advanced simulation technology toward
energy saving and fuel efficiency for the automotive industry, as well as research for shorter development intervals.
Through activities in this Laboratory, NTN will enhance our partnership with Osaka University which possesses state-of-art
technology, work on research and development for strengthening platform technology, and create next-generation businesses
by incorporating the newest technology.
* A System aimed at the promotion of transfering research results into industries, advanced research activities and developmentof human resources for both industry and academia by mutual use of information, technology and facilities between businesses
and Osaka University in common fields.

NTN TECHNICAL REVIEW No.85
Printed and published in September 28, 2018

Yoshinori TERASAKA
Publisher Yoichiro MOCHIDA

EditorPublished by NTN Corporation
3-17, 1-chome, kyomachibori, Nishi-ku, Osaka,J apan

[Overview of NTN Next Generation Research Alliance Laboratory]
Name
Location
Open
General Manager

NTN Next Generation Research Alliance Laboratory
Graduate School of Engineering at Osaka University(2-1 Yamadaoka, Suita, Osaka 565-0871 Japan)
September 1, 2017
Yoshinobu Akamatsu

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R

TECHNICAL REVIEWSpecial Issue;
No.85 Automotive Products andElectric Module Products

corporation

NTN TECHNICAL REVIEW No.85
CONTENTS
Preface

For Automotive Products and Electric Module Products
1

Yoshinori TERASAKA

Issues on Electrification and Autonomous Driving for Automobiles
Contribution

Perspective

Tetsusei KURASHIKI

Dr. Eng. Associate Professor Management of Industry Technology,
Graduate School of Engineering, OSAKA UNIVERSITYNTN Approach toward the Electrification and Autonomous Driving
Koji KAMETAKA

2

14● Special Issue for Electric Module Products
Development of Electric Motor, Actuator Series

18

Kimihito USHIDA and Masashi NISHIMURA

Hub Module with Motor and Generator Function
Kentaro NISHIKAWA, Yuuji YADA, Yasuyuki FUJITA, Mitsuo KAWAMURA and Hiroki YABUTA

Influence of Vehicle Body Motion on the Effects of G-Vectoring Control
Yuta SUZUKI, Shuichi KOSAKA and Weipeng CHENG

26

33● Technical Articles and New Products
History of Constant Velocity Joints

40

Shinichi TAKABE

History of Axle Unit Bearings for Automobile

46

Daisuke NAKAULTAGE Tapered Roller Bearing for Automotive Application
Yasuhito FUJIKAKE, Takanori ISHIKAWA and Susumu MIYAIRIHigh Speed Rotation Ball Bearing for Pulley
Hayato KAWAGUCHI, Shouhei FUKAMA and Masaharu INOUE

Ultra Low Friction Sealed Ball Bearing for Transmission
Katsuaki SASAKI, Takahiro WAKUDA and Tomohiro SUGAI

Low Friction Hub Bearing

51

56

62

67

Makoto SEKI

Chain Tensioner for Motorcycle Engine

72

Kouichi ONIMARU

Light Weight Drive Shaft for FR vehicle “R series”
Tomoshige KOBAYASHI

Effects of Lubricant on Hydrogen-Related Rolling Contact Fatigue Life Improvement
Takayuki KAWAMURA

Relationship between Cage Stress and Degree of Freedom of Motion in Dynamic Analysis for Needle Roller Bearings

78

84

Naoto SHIBUTANI and Tomoya SAKAGUCHI90

Proposal of Low Fuel Consumption and High Functionality of Composite Material Products for Automobile

97

Kayo SAKAI, Tomonori YAMASHITA, Hajime ASADA and Takuya ISHII● Award Winning Products
Japan Powder Metallurgy Association Awards 2016 in the New Products Category (New Design)

Hybrid Magnetic Material Reactor Core for Booster

103

Hajime KATSUURA, Toshihiro TAKAKUSU, Shinya AMANO and Shouhei SUZUKI
Japan Powder Metallurgy Association Awards 2016 in the New Products Category (New Design)

Multi Layer BEARPHITE®

104
Takashi YAMAGUCHI, Toshihiko MOURI and Kazuki TAKAI

2016 “Cho” MONODZUKURI Innovative Parts and Components Award, Environmental Components Award

Low Torque Seal Ring

105

Kouzou KAKEHI, Takuya ISHII, Takumi KONDOU, Yuuki YAMAZOE and Souichirou YAMAMOTO

Our Line of New Technology
Our Line of New Product

106
107

*01-目次-巻頭言E_*01/目次/巻頭言 18/09/05 18:40 ページ 3

NTN TECHNICAL REVIEW No.85（2017）[ Preface ]A message for the special topic of"Automotive Products and Electric Module Products"

Yoshinori TERASAKAManaging Director

It has been a long time since the realization of a low-carbon society was called to address global warming,
environmental pollution, etc. and there is a strong demand for reduction of CO2 emissions. The governments ofFrance and UK both made an announcement "banning of fossil fuel automobiles after 2040 " indicating a clear
shift to EVs. The largest automotive market, China, has also shown similar moves, accelerating electrification ofvehicles and their various components, marking a major turning point in automotive components.
Furthermore, a separate, recent trend of the development of autonomous driving has made great strides
toward implementation by improving vehicle safety. With "level 2," partial implementation already introduced
into the market, it is assumed that "levels 3-5" will also be achieved very rapidly, requiring control units withhigher precision and faster responsiveness for various automotive components.
As the shift from engine vehicles to EVs accelerates, higher functionality will be required for NTN's coreproducts, such as bearings, hub bearings and constant velocity joints. Additionally, lower torque/higher
efficiency, as well as drastic weight reduction will be needed.

NTN has now developed "electric motors and actuators" with high precision and fast responsiveness, as analternative to conventional pneumatic and hydraulic products, taking advantage of NTN's core competence intribology, high-precision processing and analysis, and has launched them into the market as a standard catalog
products. These are modular products achieving unprecedented improvements in size and weight, which,coupled with supporting electric systems that integrate transmissions, in-vehicle pumps, various valves as wellas other components, contribute to the shift towards EVs and electrification.
As a new approach for accelerating the development of technology and creating new business, on
September 1st of this year, NTN established the "NTN Next Generation Research Alliance Laboratory" within
the Graduate School of Engineering at the National University Corporation Osaka University, making it aresearch and development center for next generation technology. This Laboratory will combine and integrate
NTN 's technology/engineering competency with the university's knowledge and intellectual base. Byleveraging artificial intelligence (AI), the Laboratory will work on the development of residual bearing life
prediction technology through the monitoring of the operational status of the rolling bearings applied toautomobiles, rolling stock, machine tools, etc. as well as establishing bearing operational trend management
and failure prevention technology by incorporating multi-functional sensors into bearings with the aim ofcreating new added value in bearings.

NTN will mark its 100th anniversary in March 2018. It is also the final year of the mid-term management planof "NTN 100" which NTN has been working on since 2015. While advancing the "Transformation and Building
Foundation for the Next 100 Years" that NTN is currently conducting alongside "NTN 100," NTN strives tocontribute to the sustainable development of society through new product development continuing "security andsafety" toward the next 100 years under NTN's philosophy that "We shall contribute to international society
through creating new technology and developing new products (For New Technology Network: Networking theWorld with New Technology)."-1-

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NTN TECHNICAL REVIEW No.85（2017）[ Contribution ]Issues on Electrification and Autonomous Driving
for Automobiles

Tetsusei KURASHIKI
Associate Professor, Business Engineering,
Graduate School of Engineering at Osaka University

An overview of large-scale R&D projects of our country in the manufacturing industry
field on automobiles was described. Technical issues and market forecast on next
generation-automobiles, special issues on electrification/autonomous driving, and theroadmap in the transportation field were also described with public information of eachministry in our country. It is important to develop additional value with cooperation ofindustry/academia/government aimed to solution-oriented “connected industries” basedon Japan’s high technologies and faculties in the manufacturing filed.

manufacturing industry in FY2017. It is organized insuch a way that manufacturing technology is
categorized into "resources," "material development,""component processing (manufacturing process)" and"finished product" The projects in those areas areplotted based on the development phases (basic
research, R&D, implementation/demonstration). The
size of the circles reflects the budget in FY2017 andcolor coded by sponsor ministry, such as Ministry of
Education, Culture, Sports, Science and Technology(MEXT), Cabinet Office and Ministry of Economy, andTrade and Industry (METI). The projects with abudget size of over 1 billion yen are depicted;
therefore, the chart can be considered as arepresentative summary of manufacturing industry
technology in Japan.
These projects span several years and include
elements of cooperation that are difficult to conduct bya single company. An example of large projects in theautomotive industry is "Innovative Structural Materials
Technology Development" promoted by the Cabinet
Office and METI. This is to support technology
development for drastic weight reduction oftransportation equipment (automobile, rolling stock,etc.) which has a significant impact on energy
consumption and CO2 emissions reduction,
specifically, development of light materials forachieving both high-functionality and costcompetitiveness such as innovative steel sheets/nonferrous metal/CFRP, development of high-function
magnets that allow higher efficiency motors, bonding
technology, and development of optimal methodology
for multi-material design, etc. The project spans 9years from FY2014 to FY2022 1), aiming for drastic

1. Introduction
As the mid-long term socio-economic challenges,
such as, declining population and global competition
that Japan faces toughen, creation of new added value
by innovation will become one of the driving forces toovercome these challenges.
The automotive industry, in particular, is one of theleading industries in Japan with strong international
competitiveness that earns foreign currencies, boasting
vast support industries and significant employment andis one of the principal pillars supporting regional
economies. It is also a national industry consistently
promoting an attitude of exploring quality, reliability andproductivity which has provided its workers with
opportunities to grow as human beings in its history forover 100 years.
In this paper, an overview of Japan's large projects
on technology development in manufacturing, center on
the automotive industry, and challenges in vehicle
electrification and autonomous driving is provided,
based upon public information from various
governmental organizations and NEDO. In addition,
policy concerns and the future direction of the mobility
area (autonomous driving, etc.) in "New Industrial
Structure Vision" published in May 2017 by the Ministryof Economy, Trade and Industry, is also presented.

2. Technology development projects in
manufacturing industry in JapanAs an example of the overall R&D projects, Fig. 1
shows an overview of the initiatives taken by theministries regarding technology development in the-2-

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Issues on Electrification and Autonomous Driving for Automobiles

METI Project

MEXT Project

CAO Strategic Innovation Promotion Program (SIP) (Based on the public information from the ministries)

Basic researchComponent
processing

・Joint technology
・3D printer・Print technology
・Laser processing, etc.
・Autonomous driving
technology
・Engine technology
・On-board battery
・Space/aircraft
・Robot・Housing
・Infrastructure
・Construction equipment
・Power generation area
・Electronics, etc.

Cross
sectoral

Implementation/demonstration[2013-2022]
SIP 3.49B yen[METI 2012-2021][2014-2018]
Advanced Low Carbon
Technology Research・Steelmaking, innovative and Development Program(ALCA)
steel sheet
MEXT 5.12B yen
・Non-ferrous metal material[2010-]
・Fine ceramics
Development of production
・Thermoelectric/insulator
technology for highmaterial
unctionality products
・Rare earth
using bio-material
Element
・Carbon fiber, CFRP
METI 2.1B yen
Technology development
Strategic・CNT, graphene[2016-2020]of innovative new
Project
・Cellulose nanofiber
structural material, etc.
MEXT 1.99B yen[2012-2021]
・Functional material, etc.
METI 3.6B yen

Finished productMaterialdevelopment

Resource
security

・Oil resource exploration
・Seabed mineral resource
・Artificial photosynthesis
・Hydrogen technology
・Resource recovery, etc.

R&D

Innovative energy saving Innovative hydrogen energy
storage/transportation, etc. Development of Technology
chemical process
technology development technology development for Environmentally Harmonized
METI 10B yen
Steelmaking Process
METI 2.19B yen

・Big data・AI・IoT
・Integrated system, etc.

[2013-2022]
SIP 4.0B yen[2014-2018]

Development o
next generation powerelectronics technology
METI 2.2B yen[2013-2019]
SIP 2.4B yen[2014-2018]

AIP: Advanced Integrated
Intelligence Platform Project
MEXT 7.11B yen[2016-]
SIP 2.62B yen[2015-2019]

METI 2.1B yen[2013-2017]

Development of
new technology to utilize
unused heat energy
METI 0.65B yen[2013-2022]

Development ofnext generation
structural material
system technology
METI 2.7B yen[2015-2019]

Monozukuri Revolution Programwith Three Dimensional
Molding Technology as Center Core

Development ofhigh-brilliance/high efficiency
next generation laser technology
METI 2.0B yen[2016-2020]※Amount is FY2017 budget

METI 0.35B yen
SIP 1.0B yen[2014-2018]

Development of ultra-low Development of R&D project on high performance
power consumption
high temperature monitoring system for maintenance,
management and renewal, etc.
optoelectronics
superconductiveof large-scale infrastructure Subsidized project for
implementation
implementation
METI 0.5B yen
system technology promotion technology
introduction of energy-saving[2017-2018]
METI 1.8B yen
METI 1.4B yen
construction machines[2012-2021][2016-2020]

Development of systems Development of Common
to address social issues Base Technology for
Practical Applicationsuch as infrastructure
maintenance, management, of Innovative Batteries Autonomous driving,
METI 2.9B yen
R&D/demonstration
renewal, etc.
[2016-2020]
project
METI 1B yen[2014-2018]
SIP 3.13B yen[2014-2018]

Development of cutting edg
functional materials bycomputer science technology
METI 2.4B yen[2016-2021]

METI 2.6B yen[2016-2018]
SIP 3.32B yen[2014-2018]

METI 1.41B yen[2014-2018]

Robotic Devices for Nursing Care
Development/Introduction/
Promotion Project
METI 1.64B yen [2013-2017]

Development of robotizedmarket application technology
METI 1.75B yen [2015-2019]

Development of crossDevelopment ofsectoral technology
next generation artificial
for promotion of IoT Social system promotion
intelligence/robot
METI 4.7B yen
core technology
project for promoting IoT[2016-2020]
METI 1.34B yen[2016-2018]

METI 4.5B yen [2015-2019]

Fig. 1 Overview of R&D projects of our country in manufacturing industry field based on public information of ministry

Leap from lithium-ion to innovative batteries

weight reduction (50% reduction in case of vehicle
bodies) and a reduction in CO2 emissions of
3.738million tons/year in FY2030.
For electrification, METI is promoting projects fordeveloping base technology for implementation of
innovative batteries1). This project accelerates R&D
for innovative batteries including advanced analyticaltechnology as international competition with Chineseand Korean manufacturers intensifies in the on-board
battery market (Fig. 2). The durability/safety and highenergy density, which are both required for on-board
batteries, are in a trade-off relationship. The plan
includes development of new materials that canachieve both requirements at a high level, as well asbatteries with energy density five times higher(500Wh/kg) than the current lithium-ion batteries,
including verification of no practical issues for onboard application in durability and safety by means oflarge trial cells of 5Ah with an overall aim to implement
the on-board innovative batteries by FY 2030. Details
will be described later in Chapter 4.
In the area of autonomous driving, an R&D/
demonstration project for the autonomous driving
system is underway. METI is conducting developmentof technologies and arrangement of business

By implementation of innovative batteries on board,
EV ranges will be equivalent to gasoline driven vehicles

2030
Innovative battery(zinc–air battery, etc.)

J-PARC

Range Approx. 500 km
Energy density: 500 Wh/kg

Around 2020
Advancedlithium ion Range: 250 - 300 km
battery
Energy density: 250 Wh/kg
Currentlithium ion
battery(Main analyticalresearch facilities)

SPring-8
Achieved by innovative
batteries with performance
significantly above limitationof lithium-ion batteries

Range: 120 - 200km
Energy density: 60-100 Wh/kg

Fig. 2 Research & development initiative for scientificinnovation of new generation batteries

environments required for social implementation ofadvanced autonomous driving systems shown in Fig. 3(controlled autonomous driving, truck platooning, etc.)
through demonstration projects including publicroads1). This project aims to establish truck platooning
technology and achieve over 10% of energy saving
per vehicle by FY2030. In addition, the Cabinet Office
is promoting projects focusing on four fields, namely,
R&D through large demonstration tests, businessdevelopment/business model build-up, regional
expansion/partnership among industry/ academia/-3-

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NTN TECHNICAL REVIEW No.85（2017）

government and international
partnership/standardization activities (Fig. 4) 2). R&D
is progressing so that the implementation of a system
to utilize traffic signal and traffic congestion
information (SAE Level 4) is achieved by 2025, using
look-ahead information from Intelligent Transportation
System (ITS). Details will be described later in
Chapter 5.

(1) User (elderly person,etc.) calls unmannedautonomous driving
vehicle and gets on board.

3. Challenges around next-generation
automobiles and market forecast
3.1 Challenges facing the automotive industry
The challenges surrounding the automotive
industry, such as restrictions due toenvironment/energy related issues and therequirement for addressing the aging society willcontinue to increase. According to "Automotive
Industry Strategy 2014," the challenges that the
automotive industry in Japan will face in the next 10 to
20 years are as follows 3) :Remote control/monitoring(2) Unmannedautonomous driving.

Control center(1) Environmental/energy restrictions(3) User gets off at the
final destination(home, etc.)(4) Unmanned autonomous
driving vehicle is automaticallysent backFrom the perspective of global environment
problems, the regulation on fuel efficiency andemission control will be stricter both from the program
and technology aspects.
From the energy security viewpoint, initiatives for
reduction of oil dependence including automobiles will
accelerate.

Finaldestination(home, etc.).

Controlled automatic driving
Expressway, etc.

(2) Increase in population/GDP per capita
The global population will increase to 8.1 billion by2025. Then the growth rate of global population will
reduce, except in Africa, and the population willremain at the same level or start decreasing by 2050.
The middle class in emerging countries will growdue to increases in population and economic growthwith GDP per capita approaching that of developed
countries after 2025.

MannedUnmanned
Unmanned

Truck platooning

Fig. 3 Image of verification for advanced autonomous
driving system
2015[I] Development ofautonomous driving system

・Research on dynamic map structure
・Method of transfer of authority
between driver and system
・Demonstration of communication
system between vehicle to vehicle,
road to vehicle, pedestrian to vehicle
・Information security enhancemen
technology, etc.

[II] Arrangement of basic
technology for reduction ofdeaths from traffic accidents/
traffic congestion

・Building simulation system forcalculating effect of accident reduction
・Verification of measurement methods
for effects of CO2 emission reduction[IV] Development of Advanced
Rapid Transit

・Development and verification of ART
vehicle control system
・Infrastructure information system(PICS, PTPS, etc.)

2016
Consolidation into 5 major challenges (consolidation/acceleration of R&D)

2014

[III] Building international alliance・Building framework for international
alliance/promotion of standardization
・Organizing globally open R&D
environment, etc.

2017(3) Aging society
Aging in developed countries and emerging
countries will advance by 2025 and 2035,
respectively. Global aging, except in Africa and India,
will advance by 2050 resulting in reduced numbers ofoperating vehicles and increased traffic accidents if noappropriate measures are taken.

2018(1) Dynamic map

・Global standards proposalof data format, etc. to ISO,etc.

(2) Information security

・Development of evaluation
method based on common
modeling, verification methodof simple signature, etc.

(3) HMI・Development of mutual
recognition andcommunication methods
among driver/vehicle/
pedestrians, etc.

(4) Urban overpopulation and regional depopulation
The total global urban population will increase to 4.5
billion in 2025, 5.3 billion in 2035 and 6.3 billion in
2050. With this urbanization, the social problems
caused by automobiles will become serious issues
and urban infrastructure/traffic systems will become an
important topic to be addressed.
After 2025, as depopulation takes place in regional
areas, the need for automobiles may increase.

Large-scaledemonstration
test forimplementation

Acceleration ofidentification ofissues and・Development of highly precise solutions forand low-cost infrastructure
implementing
radar for locating pedestrian
mainly 5 major
positions, etc.
challenges(4) Reduction of accidents
involving pedestrians(5) Emergence of new values(5) Advanced Rapid
Transit

Customers with diverse and new values (digital
native, borderless, ageless, etc.) will grow to become
the main automobile sales target.
The population born after the 1990s will exceed the
majority in 2035 (31% in 2025 and 70% in 2050).

・Incorporation of ART
development results for
implementation, etc.

・Enhancing relation with key
parties engaged in global
standards
・Implementation of measures for
improving International
understanding and social
receptivity

Fig. 4 Progress schedule of SIP-adus automated driving
for universal services-4-

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Issues on Electrification and Autonomous Driving for Automobiles

3.2 Prediction of adoption rate of the next
generation vehicles

adoption. Table 1 shows the adoption targets ofpassenger cars by vehicle type published by thegovernment 4). The target aimed for EVs and PHVs by2030 is up to 30%. This target is extremely aggressive
even when compared with the scenario laid out by theInternational Energy Agency (IEA), which is focusedon mitigation of global warming.
Fig. 6 shows the forecast of global vehicle sales by
IEA. IEA released their forecasts based on several
scenarios in Energy Technology Perspectives
announced in 2012. In the 2DS improved scenario(Fig. 6) where EVs and PHVs will be most adopted, it
is estimated that the market shares of HEVs/PHVs
and EVs will be approx. 28% and 4%, respectively in
2025, and approx. 52% and 11%, respectively in
2035. The governments in major countries have also
set adoption targets of EVs/PHVs in a magnitude ofmillions of vehicles and are actively promoting various
incentive programs such as support of charging
station infrastructure build-out (subsidies), support fordevelopment/facility investment for automotive/battery
industries, etc.
If Japan has to aim for early development ofadvanced market for EVs/PHVs while actively taking
measures to mitigate global warming, it is desirable toset the target level similar to the 2DS scenario basedon the targets shared in the Paris Agreement. Basedon the above, the EV/PHV Roadmap Study
Committee4) is studying the target setting andpotential programs for achieving 1 million (max.)
vehicles by 2020 on the premise of the efforts overand beyond those in the past by both public andprivate sectors and the maximum possible outcome.

Fig. 5 shows the vehicle sales forecast in majorcountries and regions 3). It is estimated that global
sales will exceed 100 million vehicles in 2025 alongwith the growth of population and economic
development in emerging countries and the market
size will reach approx. 250 trillion yen. As the overseas
automotive markets grow rapidly along with population
growth and income increase, the population in Japan
will decrease, which may lead to a significant impact
on the automotive industry in terms of the shrinkage ofthe domestic market and shortage of labor.
While adoption of electric vehicles is an importantsolution to the environment and energy restriction, theinternal combustion engine vehicles have strong costcompetitiveness and demand will grow, with their own
technology innovation, particularly in emerging
markets where motorization takes place. Therefore, astrategy with global market trends in mind is required.
In order for our automotive industry to be able toexpand its global market share and explore newmarkets, it is important to build the market
environment with no barriers so that optimal
investment and trade can be realized.
The increased adoption of next generation vehicles
is an important challenge for the automotive industrial
policy from the standpoint of increased energy
security, to better address the environmental demandand enhanced competitiveness of the automotive
industry. "Japan Revitalization Strategy Rev. 2015,"
aims to increase the ratio of next generation vehicles
in new car sales to 50-70% by 2030." Among next
generation vehicles, EVs, PHVs and FCVs have highimpact on CO2 emissions reduction, as well as
offering new added value such as using the
emergency power source in case of disasters;
therefore, the government is also supporting their(million vehicles) 120

300 (trillion yen)

250

100

200

80

150

60

Table 1 Government target of motorization
73.5%

30〜50%

Next Generation Vehicles

26.5%

50〜70%

Hybrid Vehicles (HVs)
Electric Vehicles (EVs)
Plug-in Hybrid Vehicles (PHVs)

22.2%

30〜40%

0.27％
0.34％

20〜30%

Fuel Cell Vehicles (FCVs)

0.01%

〜3%

Clean Diesel Vehicles (CDVs)

3.6%

5〜10%

ThailandIndonesia
MexicoSouth Africa
China
India

Passenger LDV sales (million)

RussiaBrazilAustralia

100

40

50

20

0

2035

2030

2025

2020

2015

2010

2005

2000

0

2015 (Actual) 2030 (Target)

Conventional Vehicles

South Korea
CanadaU.S.
EuropeJapan
Total number ofvehicles sold200

Electricity

150

Plug-in hybrid
dieselPlug-in hybrid
gasoline

100

Diesel hybrid

50

CNG/LPG

Fig. 5 Prospection of sales total for automobiles
by major countries and area

GasolinehybridDiesel

0
2000

Year

FCEV

2010

2020

2030

2040

2050

Gasoline

Source：IEA/ETP (Energy Technology Perspectives) 2012

Fig. 6 Prospection of number of vehicle purchases in the world-5-

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NTN TECHNICAL REVIEW No.85（2017）

manufacturers in pursuing extension of electric-only
driving range is the cost of batteries. It takes up the
major part of the cost difference with gasoline
powered vehicles, restricting driving range. Vigorous
R&D must be promoted for the ultimate solution ofrange extension. METI has been promoting"Advanced Technology Development of Lithium-Ion
Battery Application/Implementation Project" (FY20122016) aiming for advancing functionality of lithium-ion
batteries, which are the current mainstream batteries,
based on the roadmap in Fig. 7. It is said that theenergy density of lithium-ion batteries is approaching
the industry limit. Therefore, "Innovative Battery
Advanced Technology Basic Research Project"(FY2009-2015) was conducted to advance R&D ofinnovative batteries to significantly improve theperformance beyond the current lithium-ion battery
limit. This project is succeeded by a 5-year projectfrom FY2016 (Fig. 2) to establish advanced analysis
technology and basis technology for on-board
batteries. Fig. 8 shows the technology map ofinnovative batteries by NEDO 5). There is no clear
definition of innovative batteries; however, it shows
the relation between the capacity density and

4. Challenges of on-board batteries
4.1 Trends and challenges of R&D for batteries
EVs and PHVs, which run highly efficiently withelectric power and can be charged from external
power sources including renewable energy, are key
low-carbon technology and their growth rate isdetermined by the technology innovation of the onboard batteries.
Fig. 7 shows the secondary battery technology
roadmap developed by NEDO 5). It shows the directionof technology development with energy density andoutput density per unit weight, cost and life as
benchmarks. The batteries are classified by use, suchas "Output density focused secondary battery" for
HEVs and PHVs with LIB, and "Energy density
focused secondary battery" for EVs. The target values
for battery cost, energy density and output density
vary significantly depending on what to consider, suchas cells, modules or packs. From the standpoint ofcomparing materials/batteries, it is desirable toconsider cells; therefore, this published information isbased on the cells.
One of the major challenges for automotive

Applications ofsecondary batteries
Output density oriented
secondary battery
For HEVs with LIB
For PHEVs
Parameters of PHEVs(In case battery is used 60% of
the time in EV-mode driving)

Energy density oriented
secondary battery
For EV
Parameters offull-fledged EVs(In case battery is used
100% of the time)

Challenges inelement technology

Challenges ofsecondary batteries
Positive electrode
Electrolyte
Negative electrodeSeparator
Battery assembly technology

Enhancement of long-term basic/
fundamental technology

Other challenges(Numbers are for pack including BMU, etc.)

Present (as of end of 2012)

Around 2020

Energy density：30 〜 50Wh/kg，output density：1,400 〜 2,000W/kg
Cost：approx. 10 〜 15K yen/kＷｈ

200Wh/kg,2,500W/kg
approx. 20K yen/kWh

Calendar life：5 〜 10years，cycle life：2,000 〜 4,000

10 〜 15years，4,000 〜 6,000

Early adoption
Early adoption
60km
50kg
10kWh
200K yen

Energy density：60 〜 100Wh/kg，output density：330 〜 600W/kg
Cost：approx. 70 - 100K yen/kWh

250Wh/kg, 〜 1,500W/kg
Approx. 20K yen/kW or lessCalendar life：5 〜 10years，cycle life：500 〜 1,000

10 〜 15years，1,000 〜 1,500

Range
120 〜 200km：
On-board pack weight ：200 〜 300kg
On-board pack capacity ：16 〜 24kWh
Battery cost, vehicle cost：1.1 - 2.4M yen, 2.6 - 3.76M yen

Carbonic acid ester group solvent, etc.
Carbon group
Fine porous membrane

500Wh/kg, 〜 1,500W/kg
Approx. 10K yen/kWh

700Wh/kg, 〜 1,500W/kg
Approx. 5K yen/kWh

10 〜 15years，1,000 〜 1,500

10 〜 15years，1,000 〜 1,500

Full adoption

Early adoption

Current LIB

After 2030

Full adoption
Full adoption

Range： 25 〜 60km
On-board pack weight ： Approx. 100-180kg
On-board pack capacity ： 5 〜 12kWh
Battery cost
： 500K yen

Spinel Mn, group etc.

Around 2030

250 〜 350km
100 〜 140ｋg
25 〜 35kWh
500 - 800K yen, 2 - 2.3M yen

Advanced LIBLIB

Approx. 500km
80kg
40kWh
0.4, 1.9M yen

Approx. 700km
80kg
56kWh
0.28, 1.8M yen

Requires breakthroughHigher capacity/higher voltage, etc.
Fire retardant/high voltage resistance, etc.
Higher capacity, etc.
Composite material, higher-order structure/measures for higher output, etc.

Innovative battery

Metal air battery(Al, Li, Zn, etc.)
Metal negative electrode battery(Al, Ca, Mg, etc.)
Other

New battery material composite technology/electrode production technology/solid-liquid solid-solid interface formation technology, etc.
Clarification of interface response mechanism/mass transfer phenomenon, clarification of deterioration mechanism,
clarification of thermal stability, development of "in-situ observation" technology/electrode surface analysis technology, etc.
Improvement of safety as the system/resistance to environment, V2H/V2G, reuse/secondary use, recycle,
understanding of residual performance, charging technology, etc.

Fig. 7 NEDO Roadmap of secondary battery for automobiles-6-

*03-寄稿文E_*02/寄稿文 18/09/05 18:41 ページ 6

Issues on Electrification and Autonomous Driving for Automobiles

that it can be used for shifting power peak, backup
during blackout, utilizing night power, etc. byconnecting EVs to homes and office buildings. V2G(Vehicle to Grid) aims for reduction of tribo-electricfacilities of the entire smart grid, by using on-board
batteries of EVs parked during the night and holidays
by connecting them to the power grid of the concerned
region. In April 2014, "Charging-Discharging System
Guideline for Electric Vehicles" was developed toensure electric safety and compatibility between thevehicles and connecting devices for V2H which
supplies power to buildings and V2L (Vehicle to Load)which directly supplies power to electric devices. In
August 2015, Japan Electrical Safety & Environment
Technology Laboratory started "Certification of Power
Conditioner for V2H for Grid Interconnection(Certification of Protective Devices, etc. for GridInterface for Electric Vehicles, etc. On-board Batteries(for serial connection))" and adoption of V2X power
supply is being promoted by both the public andprivate sectors. Grid interconnection type that
optimally combines power from solar photovoltaic
electricity generation and power from batteries of EVs
and PHVs is also to be introduced to the market andits adoption is expected.
It is pointed out that the output fluctuation ofrenewable energy depending on the time of the day
and seasonal/weather conditions is one of the barriers
for adoption of renewable energy. If EVs do not holdenough power in their on-board batteries at the time
the users want to use them, the traveling range will beinsufficient and the convenience of using the vehicles
will be lost. Therefore, high energy density, low costand high storage capacity of on-board batteries areunavoidable challenges.
In the Great East Japan Earthquake, automobiles
were used as emergency power sources and forheating until energy infrastructure was recovered.
EVs/PHVs are able to supply power to the equivalentof a few days of consumption for average homes;
therefore, it is desirable to actively utilize this value,

5
Lithium ion battery

Operating voltage (V)4
Sodium ion
battery

3

Metal air battery

Lithium-sulfur battery

22,000Wh/kg

1
0

Metal negativeelectrode battery(Calcium, magnesium, aluminum, etc.)
0

200

400

600

800

1,000Wh/kg
500Wh/kg

1,000

1,200

Capacity density (Ah/kg)

Fig. 8 Technology map for new generation batteries(Relation between capacitance density and voltage)

operating voltage of the battery systems which havepotential to achieve the high performance required byaround 2030 that the current battery system cannot
achieve. Examples are metal-air batteries, lithium-sulfur
batteries and metal anode batteries. These innovative
battery systems are being considered to be adopted for
two usages (automotive and stationary) similar to thecurrent battery systems and gradually replace the latter.
However, each of these batteries has manytechnology challenges. According to NEDO TSC
Foresight 6), there is an issue of irreversibility ofdischarge products on the anode metal for metal-air
batteries which cause significant capacity degradation
when charge-discharge cycles are repeated. For
lithium-sulfur batteries, elution of polysulfide ion, which
is produced by charge-discharge cycles when organic
electrolytes are used, is known to cause reduction of
charge-discharge efficiency and shorter life. Metal
anode batteries also have issues of irreversibility ofelectrolyte elution at anode metal, similar to metal-air
batteries and lithium-sulfur batteries. As R&D forvarious innovative batteries is actively pursued globallyfor superior future battery candidates, it is necessary forJapan, to further accelerate R&D in government/
academia/industry for keeping and enhancing ourcompetitiveness in the automotive/battery industry.

4.2 Use of V2X functionality
One of the characteristics of EVs is the ability tostore power supplied from external sources to large
capacity batteries. Vehicles with the ability to supply
power externally can provide power to homes andfacilities via chargers with discharging capability.
Especially, the system which can provide power tohomes and buildings (V2X power supply) from EVs iscurrently gaining attention.
V2H (Vehicle to Home) shown in Fig. 9 indicatesPower grid
V2G
V2H
HEMS

Electric Vehicles

Electric Vehicles

Fig. 9 V2G, V2H (NEDO, 2015)-7-

*03-寄稿文E_*02/寄稿文 18/09/05 18:41 ページ 7

NTN TECHNICAL REVIEW No.85（2017）

Table 2 Definition of driving automation level

including as measures against disasters. However,just mentioning readiness for disasters alone does notconvey the message of specific advantages to theusers; therefore, it is necessary to clarify specificadvantages to the users and communities, andconvey the information in order to accelerate theiradoption.
In Japan, Agency for Natural Resources and Energy
has been leading the "Next Generation Energy/Social
System Demonstration Projects" for demonstration of
V2H and demand response technology. As we move
forward, initiatives for feeding back the results oftechnology demonstration through to implementation
into the real world are required based on the adoption
rate of EVs/PHVs and renewable energy, as well as
the restructuring trend of the power systems.

Level

Subject for monitoringandaddressing safe driving

Overview

Driver to perform all or partial driving tasks
SAE level 0
No automation¡Driver to perform all driving tasks

Driver¡System to perform driving subtasks related to vehicle
SAE level 1
Driver assistancecontrol of either front/back or left/right sides

Driver

SAE level 2¡System to perform driving subtasks related to vehicle
Partial automation control of both front/back and left/right sides

DriverAutonomous driving system to perform all driving tasks
SAE level 3
Conditional
automation

SAE level 4High automation

SAE level 5
Full automation

5. Current status and policy concerns
for autonomous driving¡System to perform all driving tasks(within limited area*)¡Drivers are expected to respond appropriately
to the system request to intervene in cases
where operation is difficult to proceed

System(Driver when
operation is difficult
to proceed)¡System to perform all driving tasks(within limited area※)

System¡Users are not expected to respond when
operation is difficult to proceed¡System to perform all driving tasks(not within limited areas※)

System¡User is not expected to respond when
operation is difficult to proceed※"Area" is not limited to the geographical area but includes environmental, traffic, speed
and time conditions, as well.

5.1 Trend of autonomous driving
Plan¡System to perform all driving tasks(not within limited areas※1)
Full
SAE
automation Level 5 ¡User is not expected to respond when operation isdifficult to proceed¡System to perform all driving tasks(within limited areas※1)
HighSAE
automation Level 4 ¡User is not expected to respond when
operation is difficult to proceed

By 2025 ※2¡System to perform all driving tasks
By 2020 ※2(within limited areas※1)
Conditional SAE
automation Level 3 ¡Drivers are expected to respond
appropriately to the system request tointervene in cases where operation is difficult to proceed
PartialSAE
automation Level 2¡System to perform driving subtasks
related to vehicle control of both front/back and left/right sides

2017¡System to perform driving subtasks
SAE
Driverrelated to vehicle control of either
assistance Level 1
front/back or left/right sides¡Driver to perform all driving
No
SAE
tasks
automation Level 0

Autonomous driving level changes depending on the road conditions

Implementation

In Japan, the 10th Traffic Safety Basic Plan (March,2016) stated "reducing deaths from traffic accidents to
2,500 or less and realizing the world’s safest roadtraffic" as the national objective. In 2016, deaths fromtraffic accidents decreased, the first time in two years,
to 3,904; however, significant efforts are required toachieve the national objective. Especially, traffic
accidents at intersections and those involving
pedestrians, bicycles and motor bikes are major
issues requiring a comprehensive approach including
improvement of traffic environment and awareness ofpedestrians, not only automobiles.
Autonomous driving levels and the definition ofautonomous running system/driving system to realize
autonomous driving can be found in SAE J 2016
determined by the U.S. SAE International in
September, 2016. The summary of definition is shownin Table 2 2). In any level, the driver can always
intervene in the system control.
Fig. 10 shows the expected timeframe for realizing
autonomous driving systems 2). It is expected that thesystem for SAE level 3 will be achieved by 2020 and
SAE level 4 by 2025, as the expected timeframe formarket introduction.
The new industries related to autonomous driving
are broad. Significant market expansion can be
expected around the digital infrastructure industry,
such as on-board sensors (cameras, radars, etc.), as
well as the information communication industry suchas on-board radio devices, street-side radio
communication equipment, mobile communication
devices, etc. In addition, the implementation andadoption of autonomous driving systems will drive the※1 "Area" is not limited to the geographical area, but includes environmental, traffic,
speed and time conditions, as well.
※2 Set as the timeframe for the government to aim so market introduction by theprivate companies can be achieved.

Fig. 10 Target of automated driving systememergence of new industries such as technology forthe generation of highly precise 3D maps, organizing
and operating information in diverse areas other thanautonomous driving systems, highly precise location
information services, etc.

5.2 Challenges and initiatives of autonomous driving
For achieving the national objective of reducing
deaths from traffic accidents, it is important to develop
and implement/promote driving assistance systems-8-

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Issues on Electrification and Autonomous Driving for Automobiles

SIP also promotes R&D around large-scaledemonstration tests. The plan includes a large-scaleand continuous demonstration test along expressways
spanning 300 km from Joban ExpresswayMetropolitan Expressway-Tomei Expressway to New
Tomei Expressway and surface roads around Odaiba
from FY2017 until the end of FY2018.
In addition, verification of the dynamic map,
mentioned in the above (1), will be conducted for its
implementation in the large-scale demonstration testfor verifying specification/accuracy of static highprecision map data and data
generation/update/distribution systems.
Regarding (2) HMI, evaluation method will beestablished for proposed standardization and data ofdriver conditions on test courses and public roads will
be collected and stored.
Regarding (3) Information Security, black box tests
are conducted to verify anti-hacking performanceusing vehicles from the participating manufacturers.
Regarding (4) Reduction of accidents involving
pedestrians, application with improvement of
positional accuracy and maps will be developed fromthe results obtained until FY2016 and the effect ofpedestrian-vehicle communication technology will bevalidated on public roads toward reduction of
accidents involving pedestrians.
Regarding (5) Advanced Rapid Transit, a specificproposal will be made including demonstration tests
on public roads for development of control technology
for ART (Advanced Rapid Transit system) vehicles
and realization of ART Information Center concept
which works together with the dynamic map.
In addition to the above promotion of R&D throughlarge-scale demonstration tests, businessand autonomous driving systems, deepen the data
analysis and simulation technology of deaths fromtraffic accidents and develop technology to predict andverify the effects of safety policy. It is also necessary
to promote technology development in the area of
coordination so that the SAE level 4 system can bemarketed by around 2025. Furthermore, challenges
include the implementation of next generationtransportation systems that contribute to our next
generation in view of the 2020 Tokyo
Olympic/Paralympic Games and having thedevelopment of Tokyo and aging society in mind, as
well as social acceptance and regulatory
consideration toward implementation.
In view of these points, "autonomous driving
system" in the Cabinet Office's SIP (Strategic
Innovation Promotion Program) sets the following 5
items of autonomous driving as the focused initiativefor FY2017 2).
(1) Dynamic map (map information integrating
information on the road structure and travelingcourse environment in addition to conventional
map information for generating the route in theautonomous driving system),(2) HMI (Human Machine Interface),(3) Information security, (move to next line)(4) Reduction of accidents involving pedestrians,(5) Advanced Rapid Transit
Fig. 11 shows the categories of R&D themes 2).
While the automotive industry conducts autonomous
system, etc. in competitive areas, SIP promotes
development and implementation of basic technology
and cooperative areas (related to cooperative
systems) which require initiatives based on
partnership between the public and private sectors.

[I] Development/verification of autonomous driving system

Transportation environment

Road traffic system
Recognition(5) System security enhancement
technology
Recognition

DriverDecision
Operation(4) HMI technology between driver andautonomous driving system
Decision
Operation(1) Advanced technology
for map information(dynamic map)

Competitionarea(2) Technology for
generating ITS
prediction information(3) Sensing capability
enhancement
technology

Vehicle(1) Method for estimating effect of reduction of deaths & national database sharing(2) Analysis of micro/macro data and simulation technology(3) Technology for visualizing CO2 emission from local traffic[II] Arrangement of basic technologies for reduction of deaths fromtraffic accidents/traffic congestion[III] Building international alliance(1) Organizing globally open
R&D environment andpromoting standardization(2) Promotion of social receptivityof autonomous driving system(3) Global package exporting
system(1) Enhanced local
management(2) Development of next
generation public road trafficsystem(3) Improvement andproliferation of accessibility[IV] Development of Advanced
Rapid Transit[V] Large-scale demonstration test
Cooperation area

(area of SIP initiatives)

Fig. 11 R&D theme of SIP-adus automated driving for universal services-9-

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NTN TECHNICAL REVIEW No.85（2017）

society where various people, organizations,
machines, technologies and states are connected toachieve Society 5.0, and create new added value andsolve social issues. The promotion of Connected
Industries is expected to encourage creation of value
and technology inheritance over the generations in theareas of "creating and maximizing added value",
which is Japan's manufacturing industry's challenge,and "maintaining and improving strong manufacturing
work sites" where shortage of labor is surfacing, byconnecting various industries, organizations, people,
things, technologies and data.
As an example, Fig. 13 shows common basic
technology such as AI and innovative
products/services by connected technologies andavailable data 7). By utilizing technology innovationsuch as AI and data, it will be possible to address"social/structural demands = customers' real needs." It
is desirable to realize rich society for each individualby taking advantage of new technology/data that leads
to solution of global challenges and Japan's economic
growth.
With the progress of the social implementation of
the fourth industry revolution technology, a new
industrial structure shift as depicted in Fig. 14 can beconsidered 7) by lowering the barriers among various
industries. With this, it is possible that a move tocreate a new service platform that swallows
completely different industries may expand.

development/business model build-up, regional
expansion/partnership amongindustry/academia/government and international
partnership/standardization activities are also
important. The value that Japan can obtain fromplaying the leading role is socially and industrially verylarge and should serve as a global contribution.

6. Strategy of mobility area in the New
Industrial Structure Vision
6.1 Society 5.0 and Connected Industries
As the fourth industrial revolution by disruptive
innovation such as IoT, big data and artificial
intelligence (AI) is underway, it is indispensable for the
public and private sectors to share the vision and work
strategically on what the economic and social impactof these developments are and what actions Japan
has to take. Under this recognition, METI formed "New
Industrial Structure Committee" (Chair: Motoshige Ito,
Professor at Tokyo University) under Industrial
Structure Council to develop vision that the public andprivate sectors can share and study the actions thatthe public and private sectors are required to take,and compiled and published the vision titled "New
Industrial Structure Vision: Japan as a future-oriented
country solving global challenges on an individual
basis" in May 2017 7). The following is an overview ofthis vision :In this Vision, it is expected to see new products/
services and a productivity revolution which will unfold
potential demand by social implementation of the
fourth industry revolution technology (IoT, big data, AI,
robots, etc.) which is considered to be the major key
for realizing Society 5.0 (ultra smart society) depicted
in Fig. 12 7). Among them, a new concept, "Connected
Industries" is proposed. It is a concept of industry

Technology

Agrariansociety

Informationsociety

Industrial society

Society 5.0
Super smart society

Each individuallydeveloped on its own< Change intechnology>First industrial
revolution
Acquired kinetic
energy(Steam engine)

Secondindustrial
revolution
Innovation of
kinetic energy(Electricity/motor)

・Creation of new added value by solution-oriented
various connections
・Changes induced by integration ofwhat were conventionally isolated
and conflicting
Emergence of new business models

Business
entityThing x Thing
Human x Machine x System
Enterprise x Enterprises
Human x Human(inheritance of knowledge and skillset)
Production x Consumption
On-site capability of Japan x digital
Diverse cooperation

Third industrial
revolution
Automation(Computer)

Mobility service by unmannedautonomous driving
Unmanned autonomous driving vehicles, etc.

Production
control
technology

Accident/
Near-miss incident
data

Safety/productivity improvement by early
detection of anomalies/symptoms,
Advanced insurance/ratings, etc.

Bio data

Drug discovery, Functional food,Advanced material manufacturing,
Bioenergy, etc.

Drugdevelopment
technology

Technology related
to nursing care
Health/medical data

Nursing care data
Individualized medication
Nursing care plan for self-dependent, etc.

Energy demand
Facility control
technology

Customer data

Energy demand response,
Watching service

FinTechProcurement/
logistic data,
financial market data

Credit based on transaction/payment data,
Asset management advice service
enhancement, etc.

Genome editing

Fig. 13 Common fundamental technology, Industrial coretechnology and data

Creation of

new society
Connected Industries Human-centric< Change inindustry >Related data Innovative products/services

Accident data,
Camera informationdata

Bio-informatics
Common basic
technology(AI, IoT, Robot)<Change of society>
Huntingsociety

Related data

Drive control
technology

Conventionaltransformational
centers(1) Automobile manufacturing

Fourth industrial revolution
Autonomous optimizationis achieved
AI autonomously makes
decision for optimal behavior
based on massive information

Social implementationof technology innovationby the fourth industrial
revolution

Transformational
centers in the fourthindustrial revolution

Supplier oftransportation
methods(2) Drone manufacturing

Transportationof humans(4) Traffic operation(bus/taxi, etc.)

Unmanned traffic service(5) Sharing businesses

Ride sharing service

Transportationof products(6) Logistical businesses(truck/train/drone, etc.)

Unmanned delivery service(3) Information services

Manufacturing of autonomous
driving vehicle/drone

Fig. 14 New transformation of industrial structure
in Industry 4.0

Fig. 12 Connected industries aimed for Society 5.0-10-*03-寄稿文E_*02/寄稿文 18/09/05 18:41 ページ 10

Issues on Electrification and Autonomous Driving for Automobiles

6.2 Strategy area "mobility"(4) Risk of social acceptanceIndustrial Structure Vision organizes strengths andopportunities that Japan should leverage in thefollowing three points:
・Accumulation of diverse and valuable "real data"(potential for creating new values from the real databy leveraging the ability to carefully learn from thefacts ongoing at user sites and market)
・Strength in "things" (ability to quickly adopt
advanced technology and renovate "things" andpotential to achieve new integration of hardware
and software)
・Early appearance and magnitude of new social
challenges (potential to discover solutions to makepeople happy and deploy them globally, earlier thananywhere else)
From the above points, it is determined that thefollowing four areas are strategic areas for Japan totake:(1) "Mobility", (2) Supply-chain, (3) Healthcare, (4)Living. Perspectives in the New Industrial Structure
Vision are described in the following:If significant accidents involving people occur
before autonomous vehicles and drones are
accepted into society, psychology of refusal andavoidance may become dominant. There is a riskof it not being implemented, even when technicallyfeasible, because of this social refusal.
As mentioned above, various risks can be anticipatedin each layer of mobility means, system network,
employment/labor and social acceptance as technology
advances. The New Industrial Structure Visionconsiders measures against them and incorporates
them into the roadmap.

6.4 Roadmap for "mobility of people"
Fig. 15 shows the direction of "mobility of people." 7)This is a conceptual diagram of providing safe anddiverse mobility services by autonomous mobility
means. In order to achieve autonomous driving, it isimportant to realize "recognition" and "decisions" forensuring safety, in particular, by combining software
such as algorithms and hardware such as sensor
devices. Fig. 16 shows the strengths and weaknessesof Japan in critical technology for "mobility of people." 7)
Since the importance of semiconductors will increase

6.3 Challenges of mobility of people and products
The goals for the 2030s include "safe mobility(reduction of traffic accidents)," "resolution for mobility
impaired individuals" and "effective use of commutingtime" for mobility of people, "resolution of imbalance oflabor supply/demand in industries such as logistics,""reduction of re-deliveries in the courier industry,""Expansion of coverage for emergency response during
disasters" and "Improvement of logistics for living
necessities on remote islands" for mobility of products,
and "mitigation of CO2 emissions in the transportation
sector" for both people and products. It is possible thatseveral social and structural challenges regarding"mobility" can be solved domestically and overseas byleveraging innovative technology and use of data.
On the other hand, the following potential risks may
surface:

Supply/demand matching system/operation management system

Indoor

IT/ICT infrastructure supporting
autonomous mobility means
Desire formobility

Desire formobility

Mobility robot
Indoor(+ a few kilometers in neighborhood)Autonomous driving vehicle (bus/taxi), train, etc.
Short distance - mid/long distanceFig. 15 Future trend of transportation of human

Element technology(1) Recognition(1) Security risk

Sensor devices
serving as "eyes"

Risk of accidents for passengers, surrounding
people and objects if autonomous vehicles anddrones are maliciously hacked and become
uncontrollable.

(2) Decision"Brain" todetermine
driving routes
and driving
operation(2) System risk (resonance of erroneous information)
Risk of paralyzed traffic systems and accidents
when autonomous vehicles share and amplify
erroneous information through the network.

(3) Operation
Mechanism
serving as"hands"(3) Risk of labor/employment/social security
Requirement for newly acquired skills and labor
conditions due to the changes in the industrial
structure. A risk that the labor/employment/social
security systems cannot adapt to these changes.

Strength/weakness

Competition status

Millimeter waves(detection of objects(barriers))△

Europe: 56%, U.S.: 34%, Japan: 10%

Camera(identification of objects(barriers))△

Israel's Mobileye exhibits overwhelming
presence and fierce competition, such as
acquisition announcement by U.S. Intel

Laser radar(detection of drivable terrain) △European suppliers account for the
majority of market share and presence ofJapanese suppliers is limited

Vehicles themselves(Source of drive data, whichis the key for algorithm
development)＊

Prominent companies are emerging inJapan, as well; however, the number islarger in Europe and U.S.

Electronically controlled
braking system(longitudinal control)×

Europe: 63%, U.S.: 22%, Japan: 9%

Electric power steering(lateral control)○

Japan: 55%, Europe: 41%, U.S.: 3%△

On-board microcomputers:
Europe: 35%, Japan: 33%, U.S.: 8%(4) Semiconductors
Platform supporting
On-board semiconductors
information processing* U.S. for the leader in semiconductors for AI

Fig. 16 Advantage and weakness of Japan in automateddriving technology-11-*03-寄稿文E_*02/寄稿文 18/09/05 18:41 ページ 11

NTN TECHNICAL REVIEW No.85（2017）

6.5 Roadmap of "mobility of products"

as the platform for supporting information processing,technology development for realizing ultra-high efficiency
AI processing, such as, on-board semiconductors as acommon platform for "recognition" will also be important.
Fig. 17 shows the roadmap calculated back fromthe target for "mobility of people" reviewed in the New
Industrial Structure Vision 7).
It is arranged by categorizing the programs into (i)Autonomous mobility means (edge), (ii) Platformsystem/infrastructure and (iii) Businessenvironment/rules in the short term (- 2018), mid-term(- 2020) and long term (2020 -). In addition totechnology development depicted in Fig. 17,
institutional reforms need to be accelerated in order tosolve the challenges in the mobility area.

Fig. 18 shows the direction of "mobility of products." 7)
It is a conceptual diagram of providing advanced
logistical services integrating diversified transportation
modes seamlessly from land to air. Fig. 19 shows theroadmap calculated back from the target for "mobilityof products." 7) In order to achieve truck platooning/
autonomous driving trucks, it is required to conduct
demonstration tests of truck platooning with succeeding
unmanned vehicles (on expressways, etc.), develop
technology for optimal configuration and managementof truck platooning, develop business environment for
operation rules and infrastructure, etc. Regarding
logistics by drones, it is required to develop technologythat allows drone operation out of sight, developmentof navigation and collision avoidance technologies,
certification of individual units and licensing of operators.

(i) Autonomous edge, (ii) System/infrastructure, (iii) Business/environment rules
Mid-term (- 2020)i○Demonstration test of
autonomous driving in
10 model areas

Achievement of mobility service
by unmanned autonomous
driving in specified regions

Expansion of service area/
marketing of unmannedautonomous driving○Realization of the Tokyo
Olympic/Paralympic project○Adoption of unmanned autonomous
driving (expansion of private
businesses), global standardizationof safety standards, etc.

○Support of technology development for AI semiconductors, etc. which will become the common
platform for "recognition" and "decisions" (realize with unmanned autonomous driving as the target)○Strategic utilization of driving video data, accident data, etcii○Selection of required
communication infrastructure○Deployment of required
communication infrastructure○Development of action planfor ensuring on-board security

iii

i
ii

○Study regulatory direction of ○Philosophy for the rules inoverall government policy
Road Traffic Law, etc./
Clarification of responsibilities
including insurance coverage○Development of guidelines forremote operation (1 to N)

Fig. 17 Roadmap of transportation of humanLong term (2020 -)Business development of truck
platooning with unmanned
succeeding trucks on expressways○Demonstration tests with
○Demonstration tests withsucceeding manned trucks toward
succeeding unmanned truck
unmanned truck platooning on
platooning on New Tomei
New Tomei Expressway
Expressway

technology used for truck platooning and results of the demonstration
tests and operating rules, etc.

i
ii

Deployment of merchandise delivery
by drones, out of sight in areas withpopulation including urban areas○Technology development andperformance evaluation criteria
development for navigation
management and collision
avoidance leveraging
Fukushima Robot Test Field○Establish navigation management ○Advanced and intelligent navigation
system and collision avoidance
management system and collision
technology to be used for drone
avoidance technology
logistics○Full-fledged social implementationof navigation management○Acquisition of global service market
with global standardization○Promotion of drone utilization by public and semi-public demands for inspection of critical/aged infrastructure○Requirements for flight above○Requirements for out-of-sight○Rules for navigation management
third party, etc. (standards for the ○Qualification system for operators
flight, etc.
units, operators and organizations)(standards for the units andand navigation managers
are reviewed and used for
operators) are reviewed and○System for certification, identification
establishing regulations
used for revision of Examination
and registration of units
procedures in accordance with
○Revision of Examination procedures
the Aviation Law in early FY2018
for flights above third parties inaccordance with the Aviation Law

Fig. 19 Roadmap of transportation of things

Initially: Delivery to remote islands
and mountainous areas

Drone

Office/residence

Warehouse/
store

Mainstream logistics
Anti-fall: Certification by performance
evaluation standards, etc.
Anti-collision: Improvement of anti-collision
technology, etc.

Hub
site

Autonomous driving truck

Automation of local logistics○Organize business environment for
infrastructure, etc. required for truck
platooning

Perform merchandise delivery bydrones, out of sight in areas
with no population

Operation/management system

Later: Delivery to broader areas
including urban area

○Expansion of distance and drivable
range of truck platooning on
expressways (between Tokyo andOsaka, etc.)○Organize requirements for, perform trial and review based on trial resultsof cargo transportation by passenger vehicles

iii○Study framework for international treaty

Mid-term (- 2020)
Realize truck platooning withunmanned succeeding trucks on
expresswaysiii ○Study business environment for infrastructure, etc. based on theTarget○Large-scale demonstrationof dynamic map○Global standardization of
expressway platform maps
and international deployment ○Deployment of platform maps
for prefectural roads and local○Deployment of platform maps
roads
for main national roads andregional roads

Initiatives (Drone)

Initiatives○Development of 3D precise
mapping of expressways

Short term (- 2018)

Timeframe

TargetTarget(i) Autonomous edge, (ii) System/infrastructure, (iii) Business/environment rules

Long term (2020 -)Initiatives (Truck platooning)

Short term (- 2018)

Hub
site
Truck platooning/autonomous driving truck＋ Automation of inter-region logistics

Fig. 18 Future trend of transportation of things-12-

Office/residence*03-寄稿文E_*02/寄稿文 18/09/05 18:41 ページ 12

Issues on Electrification and Autonomous Driving for Automobiles

References

7. Conclusion

1) Website of Ministry of Economy, Trade and Industry
2) Cabinet Office SIP Autonomous Driving System
R&D Plan (2017)3) Automotive Industry Strategy 2014, Automobile
Division, Manufacturing Industries Bureau, METI(2014)
4) EV/PHV Roadmap Investigative Committee Report(2016)
5) NEDO Secondary Battery Technology
Development Roadmap 2013 (2013)6）NEDO TSC Foresight, vol.5, (2015).
7) New Industrial Structure Vision, New Industrial
Structure Committee, METI (2017)

An overview of large-scale projects of technology
development in the manufacturing industry aroundautomation has been provided together withchallenges surrounding next generation vehicles andmarket forecasts, as well as trends and challenges of
on-board batteries/autonomous driving. In addition, abrief description of the study status and roadmap ofmobility area of New Industrial Vision was provided.
Although there are many challenges for vehicle
electrification and autonomous driving, I believe that it
is important for Japan to accelerate creation of new
added values by integrating wisdom and efforts ofindustry/academia/government, leveraging ourstrengths, namely, high "technology" and advanced"worksite capabilities" toward a new solution-oriented
industry society.
I would like to express gratitude to the members of
Ministry of Economy, Trade and Industry, Cabinet
Office and NEDO for their assistance in writing thisarticle.

<Author biography>

Tetsusei KURASHIKI
Associate Professor, Department of Management of Industry and Technology,
Graduate School of Engineering at Osaka University, Doctor (Engineering)
March, 1997
April, 1997 - March, 2004
April, 2004 - April, 2014
(May, 2011 - November, 2011
May, 2014 - September, 2016
October, 2016 - present

Doctor Course Completed, Manufacturing Processing Department, Division of Engineering,Osaka University Graduate School
Research Assistant, Graduate School of Engineering, Osaka University
Associate Professor, Department of Management of Industry and Technology,
Graduate School of Engineering at Osaka University
Visiting Professor, Catholic University of Leuven, Belgium)
Manufacturing Industries Technology Strategy Office, Manufacturing Industries Bureau, METI
Associate Professor, Department of Management of Industry and Technology,
Graduate School of Engineering at Osaka University[Major]Composite material engineering, reliability engineering, numerical simulation, functional creative design, risk management[Academic society and committee affiliations]Representative, The Society of Materials Science, Japan; Councilor, Advisory Committee Member,
The Textile Machinery Society of Japan; Representative, Japan Society for Composite Materials; Chief Manager,
Impact/damage assessment subcommittee, No. 180 Committee, Science Council of Japan, and others-13-*04_展望E_*03_展望new 18/09/05 18:43 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Perspective ]NTN Approach toward the Electrification
and Autonomous Driving

Koji KAMETAKA
130 years have passed since the automobile with the internal combustion engine
appeared on the market and it’s a convenient transportation, on the other hand, (1)the effect on carbon dioxide emission on global warming, and (2) economic loss
caused by heavy traffics and human damage caused by the accident. For the former,
strengthen the regulation of carbon dioxide emissions and automobile companies arelaunched the small engine with supercharger, diesel engine, hybrid vehicle (HEV /PHEV), electric vehicle (EV) etc. on the market. They are also promoting theelectrification and high efficiency of auxiliary machinery products for lower fuel consumption. For the latter, it isin the direction to obligate driving assistance such as automatic braking, and automobile companies are also
moving on to introducing autonomous driving technology on the market.
In order to contribute to these trends, NTN also developed a new electric motor / actuator. I introduce NTN's
efforts for electrification and autonomous driving including existing units and module products.

Automotive components are also becoming more
electrified, including the adoption of 48V for
improvement in fuel efficiency.
The critical challenges for the upcoming
improvement of fuel efficiency include electrificationand development of system/module products. In thisarticle, NTN's initiatives that contribute to theautomotive electrification and autonomous driving are
introduced.

1. Introduction
As mentioned in the abstract, automobiles are being
forced to change at an unprecedented pace.
Environmental requirements, in particular, are serious,
as various countries are planning to enforce very strict
CO2 emission regulations in 2020 or thereafter.
Automotive manufacturers which do not comply withthese regulations may face significant penalties. In
addition, since battery prices are still high, theadoption rate of electric vehicles is expected to be
slow and many research companies are predictingthat vehicles with internal combustion engines willremain at over 50%, even in 2050. Therefore,
automotive manufacturers are working on
improvement of thermal efficiency (currently at around
40% in the best-case scenario) together with
development of electric vehicles (EVs).
Regulation is particularly strict in Europe, enforcing
average CO2 emissions per company of 95 g/km in
2021. This means a fuel efficiency improvement of
38% compared to FY2008 levels is required;
therefore, automotive manufacturers are working hardfor development of next generation vehicles such as
hybrid vehicles (HEVs/PHEVs) with reduced CO2
emissions and better fuel efficiency, electric vehicles(EVs) and fuel cell vehicles (FCVs) which do not emit
CO2 at all, and their adoption over conventional fossil
fuel (gasoline/diesel) engine vehicles.

2. Development of electric motors andactuators, and examples of application
NTN has developed an "electric motor actuator"
series, with indispensable high versatility for by-wire
control which is expected to be widely used for driving
and control of vehicles.
Recently, autonomous driving and further
improvement of fuel efficiency are required in theautomotive industry, which is leading to vehicle
electrification including by-wire control for supporting
adoption and expansion of various systems for driving
and control.
In consideration of these market trends, NTN has
developed the "Electric motor and actuator" series bycombining its core technologies of bearings and ballscrews, design technology of motors and electronic
control technology for vehicle control. By achieving
standardization of components and specifications, and*Managing Executive Officer, Motorized Module Product Corporate General Manager-14-*04_展望E_*03_展望new 18/09/05 18:43 ページ 2

NTN Approach toward the Electrification and Autonomous Driving

2.1. Application example of electric motors andactuators
1) Electric variable valve timing unit

creating a line-up of different types and sizes,
individual design is no longer required anddevelopment turnaround time can be reduced.
The developed products can be adapted to various
on-board applications; however, they can also be
applied, not only to automotive, but also to muchbroader areas. NTN is aiming for early volume
production of these series, promoting global sales forvehicle on-board applications, then expand into otherdevices using actuators.
The line-up includes "parallel shaft type B II (Fig. 1),"
"coaxial hollow shaft type B III (Fig. 2) (Table 1) "andbrushless DC motor, SP Series, to meet therequirements of the applications.

An example of application for improved fuel efficiency
in internal combustion engines is the cam phaser,which realizes the Atkinson cycle by making the phasesof the crank shaft and cam shaft variable.
It was difficult to achieve precise control with theconventional hydraulic mechanism. Electrification canbe applied to the electric variable valve timing unit (Fig.
3) to realize this. The unit not only realizes precise
control but also contributes to light-weightedness due tothe electric motor and actuator.

2) Electric EGR valve unit
Another example of improved fuel efficiency in internal
combustion engines, which is similar to 1), is the electric
EGR valve unit (Fig. 4) which provides a mechanism for
improving fuel efficiency by cooling off and recirculating
exhaust gas. It can contribute to controllability, weight
reduction and reduction of valves size.

Motor

Linearmotionoutput shaft

Cam shaft

Ball screw

Fig. 1 Picture and structure of B@ series

Motor(+ reducer)

Table 1 Type of electric motor and actuator
Type

SprocketFeatures¡Lightweight by adopting resin housing
Parallel ¡Reverse input rotation prevention unit can beinstalled and be applied to parking brakes, etc.
1 shaft type
¡Add-on reducer unit which can be applied for(BⅡ)
large propulsion¡Embedded non-contact linear position sensor

2

Coaxialtype(BⅢ)

Fig. 3 Electric variable valve timing unit
Motor

¡Compact design by adoption of coaxial type¡Optimal size, torque and output by
polymerization composition of magnet and core
¡Standardization of magnet and coil which are
the main components of motors
Embedded non-contact linear position sensor

Valve
Reducermechanism

Fig. 4 Electric EGR valve unit
Motor
Hollow ball screwLinear motion
output shaft
Motor coilFig. 2 Picture and structure of B# series-15-

Planetary gear

*04_展望E_*03_展望new 18/09/05 18:43 ページ 3

NTN TECHNICAL REVIEW No.85（2017）from conventional engines and allows a fast and quiet
engine restart. Therefore, it is also adopted in Mild
Hybrid and its use is expected to be further expanded.

3. Other initiatives for autonomous
driving and electrification
1) Auto tensioner unit with variable damper mechanism
for ISG(Integrated Starter Generator)

2) Rear-wheel independent steering system
We have developed a "rear-wheel independent
steering system" which applies the steer-by-wire
steering system technology, allowing electronic controlof the steering system (Fig. 6).
The rear-wheel steering for vehicles is a mechanism
to stabilize vehicles in high-speed driving and improvecornering ability in mid-low speed driving, and theelectric actuator is used to drive rear-wheel steering.
The "left-right combined-type", which controls steeringwith one actuator lacks left-right toe angle control
function, and "left-right independent type" whichplaces actuators to the left and right to control steering
has a challenge of decreased driving performance due
to increase of unsprung weight.
NTN's "rear-wheel independent steering system"
allows left-right toe angle control although it is a leftright combined-type, and the actuator is mounted on
the vehicle body side. Furthermore, the maximum
steering rate of tires is improved to 10 degrees/second(conventionally 6 degrees/second) to improve theresponse of vehicle behavior in the case of high speed
driving and emergency avoidance. By achieving awider steering range of max. ±2.5 degrees for the tire
steering angle, the minimum radius of gyration has
become smaller, making it easier to park andcontributing to future autonomous driving.
By reducing the volume by approx. 60% comparedwith NTN's conventional product while maintaining thesame rigidity, the weight is reduced by approx. 30%,
improves ease of mounting on the vehicles. In
addition, since the developed product is left-right

We have developed an auto tensioner unit with avariable damper mechanism for ISG (Fig. 5) to be
used in engines with auto start/stop features.
Vehicles with auto start/stop mechanisms which
automatically stop the engine when the vehicles stopat traffic lights, etc., are increasing to improve fuelefficiency. The auto start/stop mechanism detects thedriver's starting operation to restart the engine, and"ISG method," in which the generator (power
generator) also works as the starter (ignition motor), is
the mainstream method for restarting. However, theconventional auto tensioner with ISG method which
adjusts the tension of accessory belt had to be set
either to ensure belt tension required for restarting
engine from auto-stop state, or to keep low belttension to improve fuel efficiency in normal driving.
The "auto tensioner unit with the variable damper
mechanism for ISG" allows optimal setting of thetensioner automatically depending on the engine
status, achieving both stability at restart of the engine
and fuel saving while driving.
It is a hydraulic auto tensioner with improved
internal design where the oil path is altered from theconventional oil path to one with less path resistance,
and the path is automatically switched depending on
the direction of force transmitted from the accessory
belt. With this mechanism, relatively low tension is
given while driving to improve fuel efficiency andinstantaneous high tension is achieved whenrestarting the engine.
In addition, this unit has common components with
NTN's conventional products without a switchingmechanism, ensuring compatibility when replacing theunits.
The belt drive ISG method does not requiresignificant design change for the accessory layout

Tensioner
Newly
developed
product(Oscillation pivot)
PulleyVolume: approx. 60% less
Weight: approx. 30% less

Conventional
product
Arm

Fig. 5 Auto tensioner unit with variable damper
mechanism for ISG

Fig. 6 Rear-wheel independent steering system-16-

*04_展望E_*03_展望new 18/09/05 18:43 ページ 4

NTN Approach toward the Electrification and Autonomous Driving"Mechanical clutch unit (MCU) for next-generation
steering" contributes to achievement of a backup
mechanism for direct adaptive steering. Its compact
configuration combining the electromagnetic clutch
and roller clutch releases the roller clutch when theelectromagnetic clutch is electrically driven while direct
adaptive steering is functioning, allowing transmissionof steering operation to the tires through electric
signals. On the other hand, when failure of direct
adaptive steering is detected, power to electromagnetic
clutch is shut off and the roller clutch is instantaneously
engaged so that the steering operation is mechanicallytransmitted to the tires. It has high reliability inmechanical engagement due to its high-load capacity
design.

combined-type and installed on the vehicle body side,
unsprung weight is not increased, resulting in no
impact on riding comfort.

3) Mechanical clutch unit (MCU) fornext-generation steering
NTN developed "mechanical clutch unit (MCU) fornext-generation steering (Fig. 7)" to be used in direct
adaptive steering developed by Nissan Motor
Company (hereafter, "Nissan") and started marketingin 2013.
The conventional steering system transmits thedriver's steering operation to the tires through theshaft. On the other hand, the direct adaptive steeringtransmits the driver's steering operation to the tires
through electric signals; therefore, there is no
mechanical link between steering and tires that may
be affected by road roughness, allowing agile andaccurate steering operation.
In addition, direct adaptive steering is equipped witha backup mechanism to mechanically connect thesteering wheel and tires in case of function failure
detection.

4. Conclusion
For electric vehicles and autonomous driving,motorized modules/system products are indispensablefor electrification of steering and control systems. It isan area where NTN's core competence, namely,
tribology technology, precise processing technology,
precision metering technology and analytics such as
simulation can be fully used.
While the automotive industry faces an unprecedented
time of changes in meeting challenges such as
maintaining/improving environment and improving
safety, we would be happy if NTN's technology andproducts can help meet[ing these challenges and becontribute to society.

Fig. 7 Mechanical clutch unit for next-generation steering

Photo of author

Koji KAMETAKAManaging Executive Officer
Corporate General Manager,
Motorized Module ProductHeadquarters-17-*05E_*15 18/09/05 18:44 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]Development of Electric Motor, Actuator Series

Kimihito USHIDA*
Masashi NISHIMURA*
Action to improve fuel economy by applying various electric devices is
accelerated while the fuel efficiency regulation of automobiles progress
globally. In addition, the practical use of autonomous driving technology will
advance, and it is predicted that by-wire system will be greatly advanced
mainly on the function of "running"," turning" and “stopping". Under such asituation, the application of electric actuators that operated for each function
with electrification and by-wire has been expanding. In this section, we
introduce the electric motor / actuator series developed by NTN.

1. Introduction(g/km) 6.9L/100km

160

CO2 emissions

Global warming has recently become a serious
problem. The impact of exhaust gas from automobiles
adding to global warming is increasing year by yearwith the increase of automobiles and vehicles fortransportation and distribution. For example,
emissions of CO2 from automobiles account for nearly
20% of total greenhouse gases. Reducing emission
gas is challenging. In November 2016 the Paris
Agreement, which is a new framework for preventing
global warming, took effect. Also initiatives for
reduction of greenhouse gases are accelerating inmany countries. For automobiles, Europe will adopt
the most stringent fuel efficiency regulation of 95g/km
of CO2 emissions by 2021 for passenger cars. The
U.S. is setting a goal of 100g/km of CO2 emissions
with 2025 being the last year for compliance for all
passenger cars and pickup trucks. Fig. 1 shows fuelefficiency regulations of various countries.
In order to meet these stringent regulations car
manufacturers are pursuing the electrification ofvehicles. This includes various aspects of fuelefficiency improvement for internal combustion engine
vehicles, such as motorizing on-board units whichhave historically been operated hydraulically for
reducing load to engines, in addition to developing
EVs and PHEVs.
On the other hand, reducing deaths from traffic
accidents is also a major social challenge. In Japan
SIP, (Strategic Innovation Promotion Program)headed by the Cabinet Office, is promoting initiatives

160g/km

China

140

U.S.

120

Japan
EU

100

130g/km
17.8km/L

80

17km/L
136g/km
41.4mpg
132g/km
5L/100km
116g/km
61.4mpg
89g/km20.3km/L
114g/km95g/km24.4km/L

4L/100km
93g/km3.2L/100km
74g/km

68 〜 78g/km (under study)
29.7 〜 34.km/L (under study)

60
2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030

(Year)

Fig. 1 Fuel consumption regulation 1)

for development of an autonomous driving system basedon the 10th Traffic Safety Basic Program. The goal of SIP
is to reduce deaths within 24 hours from traffic accidents
to 2,500 or less by 2020. It aims for the practical use of asemi-autonomous driving system (level 3) by 2020 when
the Tokyo Olympic/Paralympic games will be held, andcommercialization of full autonomous driving system after
the latter half of the 2020s.
Fig. 2 shows the definitions of automation levels
indicated in the SIP Autonomous Driving System R&D
Plan. Auto manufacturers are also working on thedevelopment of autonomous driving technology withimproved safety and the reduction of traffic accidents.
Autonomous technology is using motorized actuatorsfor by-wire control of fundamental functions ofautomobiles, including run, turn and stop. Motorized
actuator technology is becoming critically important.

*Business Promotion Dept., Motorized Module Product Headquarters-18-

*05E_*15 18/09/05 18:44 ページ 2

Development of Electric Motor, Actuator Series

Plan¡System performs all driving tasks(not within limited areas※1)
Full
SAE
automation Level 5 ¡User is not expected to respond when an operation isdifficult to maneuver¡System performs all driving tasks(within limited areas※1)
HighSAE
automation Level 4 ¡User is not expected to respond when
operation is difficult to maneuverBy 2025※2¡System performs all driving tasks
By 2020 ※2(within limited areas※1)
Conditional SAE
automation Level 3 ¡Drivers are expected to respond
appropriately to the system request tointervene in cases where operation is difficult to maneuverPartialSAE
automation Level 2¡System performs driving subtasks
related to vehicle control of both front/back and left/right sides

2017¡System performs driving subtasks
SAE
Driverrelated to vehicle control of either
assistance Level 1
front/back or left/right sides¡Driver performs all driving
No
SAE
tasks
automation Level 0

2. Introduction of the electric motor
and actuator series
Autonomous driving level changes depending on the road conditions

Implementation

NTN is developing an actuator series to meetrequirements of electrification of on-board units. The
product line-up includes the following series; parallel
shaft type B II Series, coaxial type B III Series and
BLDC motor (brushless DC motor) SP Series. The
series were designed to address various needs
without limiting applications in chassis, engines, andtransmission.
The following shows the configuration and featuresof each series:

2.1 B II Series
The B II Series is an electric actuator to reduce
motor rotation with respect to the gear pair in theparallel axes and convert rotation to linear motion witha ball screw. This Series is designed to allow optional
installation of a reverse input prevention unit. This isused for increasing driving force and keeping theposition by adding a planetary reducer unit between
the motor and gear pair in the parallel axes. It is also
lightweight due to manufacturing the case and gearwith resin.
Fig. 4 and 5 show the appearance and structure of
B II Series. Fig. 6 shows variations of B II Series andTable 1 shows the typical specifications of the B II
Series.

In all of the levels the driver should always be able to intervene in system control.
For the semi-autonomous driving system (level 3) and full automation system (level 4),
the timeframe has been set as the non-binding target for the government so that themarket introduction by private companies can be achieved.

Fig. 2 Automation level of autonomous driving 2)

As mentioned above, electrification of automotive
components is expanding while environmental
regulations are enhanced and autonomous driving
makes progress. In the past, electrification was
focused on comfort and convenience, such as power
windows, power door locks, power seats and power
mirrors. However, electrification is now underway invarious components of engine and transmission toachieve lower fuel consumption and increased safety.
Fig. 3 shows main electrification in vehicles.
In consideration of these changes surrounding
automobiles, NTN has developed the "Electric motor
and actuator" series. This was done by combining its
core technology of bearings and ball screws, design
technology of motors and electronic control technology
for vehicle control, in order to contribute to achieving asecure and safe society by improving fuel efficiency
and realizing autonomous driving. This article
describes the details of the series.

Fig. 4 Appearance of B@series
Table 1 Specification of B@series

Power seat

Wiper

Power steering
MirrorBrake booster

Power window
Seat belt pretensioner

Headlight beam adjustment

4WD coupling(Engine compartment)
Throttle valve, EGR valve, variable valve timing control,
A/C compressor, water pump, oil pump (for T/M),
supercharger

Motor

Stall current 46A

Rated output

Suspension
Parking brakeRear-wheel steering system (4WS)

Grill shutter

BII 00 (DC motor driven linear motion actuator)

Weight(For switching 2WD and 4WD)

ABS・ESC

Model number

EV, HEV system (Motor)

100W

Maximum thrust

1,400N-19-

400N

Response

0.2s／25mm

Control method(Stroke feedback PID position control)

Maximum speed

Fig. 3 Electrification of automotive

20W

Maximum output
Rated thrustPower door lock1.1 kg (not including harness/bracket)

192mm/s

*05E_*15 18/09/05 18:44 ページ 3

NTN TECHNICAL REVIEW No.85（2017）
Planetary reduction unit※
Motor
Storage part for sensor IC

Mounting boss

Reverse input prevention unit※

Out put shaft end
Boots

Rotation stopper end
Bearing unit for ball screw※Optional unit

Fig. 5 Structure of B@series

Model
Without
planetary
unit

With
planetaryunit

Without reverse
input prevention

BⅡ00

With reverse
input prevention

BⅡ01

Motor control ECU

Control current

Control current
Motor

Without reverse
input prevention

BⅡ10

With reverse
input prevention

BⅡ11

Lock motor

Planetary reducer
Stroke information

Drive gear

Lock plate

Sliding screw

Driven gear
Ball screw nut
Stroke sensor

Ball screw shaft

Rotationcontrol

Shaft coverFig. 6 Variation of B@series

Fig. 7 Block chart of B@series

Fig. 7 shows the operational block chart of B II
Series. The motor control ECU supplies control currents
to drive the motor, in which torque is amplified(reduced) by the planetary reducer and transmitted fromthe drive gear to the driven gear. The ball screw nut
fixed to the driven gear rotates which drives linear
motion of the ball screw shaft, which is restricted fromrotating. The travel amount is measured by the stroke
sensor and transmitted to ECU.
In the reverse input prevention unit, the rotation of
the locking motor is converted to linear motion with theslide screw and the rotation of the gear is regulated by
the lock plate installed on the slide screw that ispocket mounted on the drive gear.

it is directly installed in the components. Fig. 8 and 9
show the appearance and structure of B III Series.
Fig. 10 shows the operational block chart of B III
Series. The motor control ECU supplies and controls
the current that drives motor rotation. In cases wherea planetary reducer is attached, the torque will be
amplified. The rotational force is transmitted to the

2.2 B III Series
B III Series is a compact electric actuator combininga high output BLDC motor with the hollow structure,
which was developed by NTN, and a ball screw, byplacing a linear motion mechanism in the hollow areaof the motor. B III Series is best for applications where

Fig. 8 Appearance of B# series-20-*05E_*15 18/09/05 18:44 ページ 4

Development of Electric Motor, Actuator Series

various applications by changing thickness, expanding
diameters or increasing poles for faster rotation orlarger torque while maintaining standard components.
Table 2 shows the B III Series line-up and Fig. 12shows the performance curve of B III Series.

Hall sensor IC board

Higher rotation speed ⇒screw nut and the ball screw shaft which is restrictedfrom rotating and provides linear motion. The travel
amount is measured by the stroke sensor that is
integrated in the ball screw shaft and transmitted to
ECU.
B III Series is designed with standardized magnetic
circuit components such as magnet stator core coil(including bobbins) to create the Series line-up.
Specifically, as shown in Fig. 11, B III H, B III N and B
III W have the same core diameter with the only
difference being thickness. B III L is designed basedon B III N with only a change in the number of magnet
poles from 12 to 16. In this way, they can adapt to

Bus bar

BⅢH

ed
eas /
Incr metereddia reas
inc lespoThickn BⅢLof core:ess
doubleThof ickn
cor es
e: s
1/2

Tuned
windin by modifyingg specificatio
n

BⅢS

Tuned
windin by modifyingg specificationTralle / BⅢN w uned by modif
Sm meterindingda
specif ying
i
e
d duc
icationre lespo
BⅢW TunedTunewindin by modifyin
windind by modgg specg spe ifying
ificatiocificantion

Increased torque ⇒Fig. 11 Concept of B# series

Table 2 B# series line-up
Coupler for motor power
Stroke sensor IC board
Coupler for sensor signal

ModelnumberBⅢS

φ61ｘ45

140

107

1,300

15

BⅢR

φ70ｘ40

145

95

1,500

10

BⅢSP
Motor stator

Ball screw nut

BⅢRP
BⅢN

Hollow shaft ofball screw

BⅢNP
BⅢH

BⅢW
BⅢM

BⅢMP
BⅢL

Out put shaft

Linear motion performance

Outer
size
（mm）

BⅢLP

Speed at Thrust at
MaximumAllmaximum maximum
outputstroking
outputoutput（W）（mm）（mm/s） （N）

φ61ｘ53130

φ70ｘ4840

140

φ80ｘ4936155

φ80ｘ5748

135

φ80ｘ3518155

φ80ｘ689675

φ90ｘ50150□100ｘ83110

φ90ｘ5820
40

140

φ100ｘ91

15
31

110

12

3,300
3,800
3,200
7,400
1,600
3,700
3,800
9,300
3,600
9,000

15
10
10
10
10
30
10
10
40
40

※Planetary gear

Motor coil

※Optional unit
Fig. 9 Structure of B# series
Speed at maximum output mm/s

160

Motor control ECU
Control current
Motor
Stroke information

Planetary reducer

Ball screw nut
Stroke sensor

Ball screw shaft

Rotationcontrol

BⅡ(For reference only)

140

BⅢS

（φ61）

120

BⅢR

（φ70）

100

BⅢN

200W

80

（φ80）

BⅢM

100W

（φ90）

60
40
20

20W

0

BⅢL

（□100）

50W

0

2,000

4,000

6,000

8,000

Thrust at maximum output N

Motor coverFig. 10 Block chart of B# series

Fig. 12 Performance map of B# series-21-

10,000*05E_*15 18/09/05 18:44 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

2.3 SP Series
SP Series is a BLDC motor series developed by
NTN. It is designed based on the motor of the B III
Series, with a hollow motor structure which enables
incorporation of a reducer in the hollow space. As aresult, it can be applied as a thin and high-torquerotation actuator. Fig. 13 shows the appearance andFig. 14 shows the performance map of SP Series.

Rotation speed at maximum output min-1

Fig. 13 Appearance of SP motor series

4,000
3,500
3,000

Thin type
Standard typeLong type

200W

100W

2,500
2,000
1,500

50W

1,000
500
0
0.0

0.5

1.0

1.5

2.0

2.5
3.0
3.5
Torque at maximum output Nm

4.0

4.5

5.0

5.5

Fig. 14 Performance map of SP motor series

Table 3 Specification of motor

3. Performance cases of electric actuator

Model

Number of poles

The following is an evaluation of B III motor
performance as a representative case of electric
actuator performance.
The motor to be applied to B III actuator has
undergone magnetic circuit simulation using magnetic
analysis software during the design phase to obtain
the optimal shape. Table 3 shows the specifications of
the B III motor as a result of simulation.
Verification of motor performance to see if it is thesame as the analysis result through individual tests
using a prototype revealed that, the target
performance was achieved. The motor and theprototype performed at generally matching torques at
40Arms with slightly different rotation speed. Fig. 15
shows an example of simulation with magnetic field
analysis software (magnetic flux density vector map)
Fig. 16 shows the individual motor measurement
results.

Number of slots

1218Connection method

Star connection

Maximum output※

209 W

Phase current peak
Maximum torque※

Base rotation speed※

Maximum rotation speed※※Normal temperature performance (25˚C)

-22-

BⅢN

40Arms

2.41Nm

740min-12,170min-1

*05E_*15 18/09/05 18:45 ページ 6

Development of Electric Motor, Actuator Series

4. Possible applications of electric
actuators
The following describes possible applications for
NTN's electric actuator.

4.1 Transmission/electric shift selector
With AT and CVT, the shift lever is connected to thetransmission with linkage for shift selection. This shift
selection can be electrified by applying a B II actuatorto this part. When shift selection is electrified thedegree of freedom for placing the shift lever isincreased, enabling replacement of the shift lever withbuttons and dials. This also amplifies the degree of
freedom for design and layout around the driver’s
seat. It can also be used as an actuator for clutch
shifting for DCT (Dual Clutch Transmission), which isrecently expanding in Europe.
Fig. 17 shows an example of a B II actuator applied
to the transmission (CVT).

B II actuator

Fig. 15 Vector map of magnetic flux density

3

Shift position sensor

Actual measurement
Simulation result

2.5

Fig. 17 Shift actuator※The above picture is shown only as an example of application. It does
not indicate that it is provided to any specific auto manufacturer at thepresent time.

Torque Nm

21.5
1

4.2 Electric variable valve timing unit
With OHC engines intake/exhaust valves areoperated by a rotating cam shaft, which is driven by a
cam sprocket installed at the end of the cam shaft,which is driven by crank shaft rotation via a chain (Fig.
18). The variable valve timing control mechanism
controls the timing for operating intake/exhaust valves
by changing phases of these sprocket and cam shafts.
This improves fuel efficiency with high expansion ratio
cycle accomplished by improvement of intake
efficiency by optimizing the intake/exhaust valve
overlapping amount (Fig. 19) and late closure of theintake valve, etc.

0.5
0

0

500

1,000

1,500

Rotation speed min-1

2,000

2,500

Fig. 16 Torque characteristics of B#motor(sin-cos sensor control)-23-

*05E_*15 18/09/05 18:45 ページ 7

NTN TECHNICAL REVIEW No.85（2017）

By placing a reducer in the hollow space of thehollow motor of NTN's B III Series, the electric variable
valve timing mechanism can be made thinner,contributing to smaller engine sizes (Fig. 20).

Cam shaft

Cam sprocket
Crank shaft

Chain

Fig. 18 Camshaft driven structure of OHC engine
Sprocket

Valve lift

<Valve overlap is "0">Motor (+ reducer)

Fig. 20 Electric variable valve timing unit
ExhaustIntakeExhaust valve closed

4.3 Electric oil pump

Crank angle

Intake valve open

In general, AV and CVT use multiple wet disk
clutches which are hydraulically engaged/disengaged
to change gears. An oil pump is also used for
operating multiple disk clutches. Conventionally, oilpumps were mainly operated by engine rotation.
However, the use of electric oil pumps, which operate
without any impact from engine status, is increasing
due to introduction of auto start/stop mechanisms.
This is required because hydraulically operated oilpumps stop when engine stops. The use of electric oil
pumps increases fuel efficiency because they lower
load to the engine because engine does not have tooperate the oil pump.
When NTN's SP Series higher efficiency motor isapplied to this area electric oil pumps can be madesmaller (Fig. 21).

Valve lift

<Valve overlap is "positive">

IntakeExhaustIntake valve open
Valve overlap

Crank angle
Exhaust valve closed

Valve lift

<Valve overlap is "negative">

ExhaustIntakeCrank angle

Exhaust valve closed

Intake valve open

Fig. 19 Valve overlap 3)
Pump

Currently, this is done by installing a vane in the
sprocket and changing the angle of the vane
hydraulically to change the cam shaft phase attachedto the vane. However, the hydraulic system may notprovide sufficiently good operation when cold starting
due to high oil viscosity. Therefore, adoption of electricvariable valve timing mechanisms is expanding, which
control cam shaft phase by motor rotation The motor
and reducer are inserted between the sprocket andcam shaft to improve cold starting. Electrification withmotor driven mechanisms allows driving with efficientvalve timing that is not affected by the operating
temperature and allows the necessary operating angle
and operating speed can be obtained.

Motor

Fig. 21 Electric oil pump-24-

*05E_*15 18/09/05 18:45 ページ 8

Development of Electric Motor, Actuator Series

4.4 Electric hydraulic brake

5. Conclusion

Currently the brake pedal force of service brakeassist is supplied with a booster device that leverages
negative pressure produced with engine intake.
However, since EVs, where no engine exists, and
PHEVs and HVs, where engines do not run all thetime, cannot leverage engine negative pressure,electric motors and linear motion mechanisms areused to operate brake hydraulic cylinders for braking.
The use of a B III Series actuator, which
incorporates a ball screw into NTN's hollow motor,
contributes to the compact size of the electric
hydraulic brake system (Fig. 22).

NTN is engaged in the development of various
electric actuators and strives to contribute to thedevelopment of automobiles and a secure and safe
society by "smoothly" connecting and moving every
part in vehicles.

References
1) Nikkei Business Publications, Inc., "Environment and
Safety toward 2030", Nikkei Automotive, Issue No. 43,
March, 2016.
2) Cabinet Office SIP Autonomous Driving System R&D Plan
(2017)
3) Nikkei Business Publications, Inc., "Mechanism basics
briefing 1: Variable valve timing mechanism" Nikkei
Automotive Technology, Issue No. 105, July, 2014.

Master cylinder

Actuator

Fig. 22 Electric hydraulic brake unit

Photo of authors

Kimihito USHIDA

Masashi NISHIMURA

Business Promotion Dept.,
Motorized Module ProductHeadquarters

Business Promotion Dept.,
Motorized Module ProductHeadquarters-25-

*06E_*15 18/09/05 18:47 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Technical Article ]Hub Module with Motor and Generator Function

Kentaro NISHIKAWA*
Yasuyuki FUJITA*

Yuuji YADA*
Mitsuo KAWAMURA*
Hiroki YABUTA*As the regulation on fuel consumption and CO2 emissions being
strengthened, practical application of 48 V mild hybrid systems is expanding
mainly in Europe. The NTN is developing a HUB module that combines a Hubbearing and a Motor Generator in order to contribute to further fuel economy
improvement in combination with the existing 48 V system.

1. Introduction
Reduction of greenhouse gas emissions, mainly
CO2, as one of the causes of global warming, is a
global challenge. In the automotive industry, regulationof CO2 emissions from automobiles is becoming
tougher every year. Europe, in particular, is enhancing
regulations such that every auto manufacturer has tokeep average CO2 emissions to 95g/km or less in
2021 and 75 g/km or less in 2025. Fig. 1 shows thetrend of fuel efficiency regulations in various countries.
These regulations cannot be met with conventional
methods such as optimization of internal combustion
engines (ICE) and reduction of vehicle weight.
Therefore, auto manufacturers are working on
development and expansion of next generation
vehicles such as hybrid electric vehicles (HEVs),
battery-based electric vehicles (BEVs) and fuel cellvehicles (FCVs).
It is considered that the future vehicles will bemainly PHEVs, BEVs and FCVs; however, they havetheir own challenges such as cost, large battery
capacity, stability of power supply in some regions andbuilding infrastructure. Therefore, 48V Mild HEV (48V
MHEV) is gaining attention in Europe as a means tomeet rapidly approaching regulations. In Japan, strong
HEV is the mainstream technology, which is driven by
voltage higher than 48V, and there is little trend
toward the introduction of MHEV; however, Europe,
which has been working on improvement of fuelefficiency by increasing efficiency of ICE, is making
progress in development of MHEV as a HEV systemthat can be easily incorporated into existing vehicles.
There is a forecast that the market share of 48V
MHEV will reach 1.5 million or more, equivalent to
PHEV by 2025 3).
NTN is developing eHUB which is the HUB modulewith motor and generator for 48V MHEV, based on our
hub bearings (HUB), which has the leading global
share, applying our technology gained fromdevelopment of in-wheel motors (IWM) 4) and electricmodule products 5). In this paper, the product concept,
target specification and development status of eHUB
is introduced.

35

Fuel efficiency km/L

CO2 emission: 75 g/km or less

30

Japan

CO2 emission: 95g/km or less

U.S.

25

Europe
China

20
15
10
2014

2016

2018

2020

2022

2024

2026

Fig. 1 Fuel consumption targets of each country(Conversion from CO2 emission targets) 1), 2)*New Product Development R&D Center-26-

*06E_*15 18/09/05 18:47 ページ 2

Hub Module with Motor and Generator Function

addition to possibility of EV driving by installing higher
power output. Furthermore, P4 and P5 can realize allwheel driving and torque vectoring since they candrive the vehicle independent from ICE. P5 can further
drive left and right wheels independently, allowing
finer vehicle control. By combining these functions,even higher functionality can be accomplished. For
example, by combining P2 and P3 with P4 and P5, thedriving range of EV mode or all-wheel driving in EV
mode can be realized.
Different installation position significantly affects not
only the functions, but also installation cost and space.
P0, which can replace existing alternators, can beinstalled with little change in the surrounding structure,thus requires low implementation costs. P1, P2 andP3 require increased costs as surrounding
components of ICE and transmission (T/M) must be
significantly changed. P4 results in smaller cargospace. On the other hand, since P5 places M/G within
wheels, there is no space limitation.

2. 48V MHEV and vehicle function
2.1 48V MHEV
So far, various types of electric vehicles, from 12V
MHEVs to BEVs, have been introduced. Electricvehicles are adopting higher voltage, as higher motor
output and larger power capacity increases the CO2
emission reduction effect; however, it also brings
higher costs for safety measures and manufacturing
process, . The characteristics of 48V MHEVs lie
midway between strong HEVs and 12V MHEVs,
allowing simple measure of safety standards by using
a power supply of DC 60V or less.

2.2 Position of motor installation and vehicle
function
Position of motor/generator (M/G) installation in
HEVs can be categorized into P0, P1, P2, P3 and P4
as shown in Fig. 2. In addition, the so-called IWM
configuration, which places M/G around the wheels is
tentatively defined as P5 in this article.

3. Product concept
P3

P2

P1

P0

3.1. Structure
P5(eHUB)

P5
ICE

T/M
K1
Front

The developed product eHUB integrates stator of
M/G into HUB outer ring to rotate the hub ring and
M/G rotor as one unit with the rotation sensor inside
M/G. It is installed at the P5 position of B and C
segment vehicles providing driving assistance to ICE,
which is the main driving source, and regenerative
braking for deceleration. It has achieved small form
factor by limiting output power.
As shown in Fig. 3, it can be installed inside thebrake disk and between the brake disk and body. Thisarchitecture allows for installation similar toconventional HUB, without requiring major designchange.

P4

K0

ClutchRear

Fig. 2 Mounting position of hybrid system

Their characteristics are shown in Table 1. The
functions which can be achieved are different
depending on the installation positions. P0, P1 and P2
which can be directly connected to ICE do not requirea starter motor that allows auto start/stop functionality.
P2 and P3 which can be isolated from ICE by the
clutch K0 and P4 and P5 which operate drive shafts
can regenerate significant energy in deceleration, in

Outer diameter is equal or less thaninner diameter of brake disk
Location for
installation tovehicle bodySame installation
method as theconventional HUB

Table 1 Vehicle characteristics for each mounting positionof hybrid system
P0
Regenerative charging ○Auto start/stop○
Starting torque assistance○Accelerating torque assistance ○EV starting + creeping ×
EV coasting×
All wheel drive
×
Torque vectoring
×
Item

P1
○
○
○
○
×
×
×
×

P2
○
○
○
○
○
○
×
×

P3
○
×
○
○
○
○
×
×

P4
○
×
○
○
○
○
○
○

P5
○
×
○
○
○
○
○
○

Fig. 3 Mounting position of HUB module-27-

*06E_*15 18/09/05 18:47 ページ 3

NTN TECHNICAL REVIEW No.85（2017）

3.2 Function
P0

eHUB is installed on the driven wheels independent
from the main drive source which allows individual
driving/regenerating; therefore, drive assistance andregenerative braking can be controlled depending on
the driving conditions. While driving, the driven wheels
generate assisting driving force to reduce energy
consumption of the main drive source. While braking,the regenerative brake turns the braking energy that isreleased with conventional brakes as heat, into
reusable electric energy.
Fig. 4 shows the eHUB module configuration. eHUB
system consists of HUB module which integrates HUB
and M/G into a unit, on the left and right wheels, andmotor controller which operates M/G.

ICE

T/M

K0

Front

Rear

(a) P0+eHUB（P5）

HUB module (left wheel)

HUB

HUB module (right wheel)

M/G

Motor controller
OthersP0

P2

T/M
eHUB system

P5(eHUB)K0

P5(eHUB)

ICE

Front

Rear

(b) P0+P2+eHUB（P5）

Rotation
sensorFig. 5 Examples of eHUB system configuration

Seal
OthersTable 2 Target values of existing 48V MHEV systemwith eHUB

Fig. 4 eHUB system component

Vehicle system functions

Reduction ratio of CO2 emission

3.3 Target specification

System target values

25％
25％

Fuel efficiency improvement ratio

eHUB assumes installation on the rear wheels,
which are the driven wheels of 48V MHEV, based on
the front wheel drive vehicle. An example of a vehicle
system with eHUB installed is shown in Fig. 5.
M/G is integrated in the P0 position of Fig. 5 (a).
The excess energy from regenerative brake by M/Ginstalled on P0 is used by eHUB to contribute to thefuel efficiency.
In another example of P0 + P2 combination
depicted in Fig. 5 (b), further high functionality can beachieved such as improvement of vehicle
maneuverability in addition to fuel efficiency, such as
electric only all-wheel driving while isolating the engine
and deceleration with regenerative braking only.
Table 2 shows the target values of vehicle system
functions for the combination of the existing 48V
MHEV system vehicles and eHUB. The largest target
for development was set at reduction of CO2
emissions and improvement effects of fuel efficiency.
eHUB drives at maximum torque for acceleration
assistance and EV start + creep and at rated torquefor engine off-coasting. Table 3 shows eHUB target
specification to realize these functional improvements.
The effect of improvements in functionality by eHUBchanges depend on the vehicle style andperformance.

Braking method

4-wheel regenerative braking(non-hydraulic)

EV starting + creeping

Continuous for 10s or moreEngine off-coasting

Traction control (TCS)

Operated in 50 - 130km/h
Start assist

Acceleration assist
Attitude control

Table 3 Target specification of eHUB (per 1 wheel)
Item

Unit

ValuesMaximum operation frequency

min-1

2,600

Rated torqueNm

Maximum output

Maximum torqueOuter Diameter

-28-

kW

Nm

mm

10
60
20

φ160 or less

*06E_*15 18/09/05 18:47 ページ 4

Hub Module with Motor and Generator Function

4.2 Test vehicle

4. Development status

A test vehicle was created by installing eHUB on afront-wheel drive vehicle in segment B. Fig. 7 shows
the installation in the test vehicle. Fig. 7 (a) shows
installation of the HUB module on the vehicle. As
mentioned earlier, it offsets on the axial direction
compared to the existing HUB, and the installation partof the body and the brake disk are modified. Fig. 7 (b)shows the control system and battery installed in thevehicle compartment. The control system and battery
are installed in the rear seat and cargo space of thevehicle. The control unit, Micro Auto Box II (made by
dSPACE) was adopted for the motor controller, hybrid
controller and instrumentation system. For batteries
and inverters, commercially available units wereadopted. No dedicated electronic control unit (ECU)
was made, but rather a general-purpose unit was used
to create an environment of RCP (Rapid Prototype
Control) to prioritize the evaluation of HUB module.
In addition, in the test vehicle, no modifications weremade to ECU; therefore, ICE and eHUB are
independently controlled.

4.1 HUB module
Fig. 6 shows the structure of the prototype HUB
module and Table 4 shows the specifications. It was
designed with the maximum torque of 60Nm, rated
torque of 20Nm as a target and containing the outermost diameter of the HUB module to be within thebrake disk. Since it offsets approx. 50mm toward theaxial direction compared with the existing HUB, somemodifications to the body will be required. Upcoming
challenges include lightweight and compactness byhigher torque density and optimal design of HUB
module. The prototype aims for maximum output of
10kW. This was set to enable maximum rotational
speed required for achieving the maximum driving
speed of the existing vehicle. The current prototype
has a maximum output of 5kW; however, output of
10kW is achievable by changing internal specificationsof the motor.

Motor case

M/G rotor

Hub bolt

M/G stator
Seal
Surface mounted
on vehicle bodyConnector, case

HUB
Rotation sensor

Fig. 6 HUB module(a) Setting of HUB module
Table 4 Prototype specification
Item

Unit

Maximum operation frequency

min-1

Maximum output

Maximum torqueRated torque

kW

Nm
Nm

Outer Diametermm

Weight

kg

Width

mm

Values

10
2,600
60
20

φ159
115
13

5
1,200
60
25

Control device

Battery
BOX

Inverter(b) Control system and battery set in the test vehicle
Fig. 7 Setting eHUB in the test vehicle-29-

*06E_*15 18/09/05 18:47 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

4.3 Vehicle evaluation

Excluding vehicles with external charging capability
such as PHEVs and BEVs, the variation of battery
state of charge (SOC) before and after the fuelefficiency test must be as close as possible to zero. In
this test, we have explored conditions to make higher
improvements in fuel efficiency and low SOC variationby changing the control method for driving eHUB andregenerative timing.
The relation between fuel efficiency improvement
and SOC variation when the control conditions ofeHUB were changed is shown in Fig. 9. As SOC
variation becomes negative, fuel efficiency tends tofurther improve. Fig. 10 shows an enlarged viewof ±1% range in SOC variation. Fig. 11 showschanges in fuel consumption and SOC under thecondition that improvement on fuel efficiency is highand change of SOC is the lowest (condition A in Fig.
10) and Table 6 shows fuel efficiency of eachsegment and fuel efficiency with or without the ExHigh segment. Overall fuel efficiency was improved by
3% regardless of the Ex-High segment.
From the above, further improvement of fuelefficiency can be expected by optimizing energy
management, reducing weight and increasing
efficiency of eHUB.

Table 5 shows the vehicle evaluation items. The
impact on vehicle maneuverability is also evaluated, in
addition to the impact of fuel efficiency. The followingshows results of impact on fuel efficiency and traction
control among the evaluation items:

Table 5 Evaluation point of vehicle test
Test item

Alternative characteristics test

Fuel efficiency at constant speed driving

Fuel efficiency
improvement effectFuel economy mode driving
EV starting + creeping

Acceleration assist

Passing acceleration

Traction control[Start assist]Low friction road start

Stop→start

Low friction road straight running(corrective steering)Yaw traction control[Vehicle attitude stability] Steady state circular turning
Low friction road turning

SlalomDirect yaw control[Turning (steering ability)] Double lane change

4.3.1 Fuel efficiency improvement effect
For the mode running fuel consumption test, WLTC
(Worldwide harmonized Lightduty Test Cycle) mode
was adopted. In WLTC mode, as shown in Fig. 8, fuelefficiency is measured in 4 segments, namely, Low(urban area), Middle (suburban area), High(Expressway) and Ex-High (extra high speed). In
Japan, since extra high-speed driving is not frequent,
3 segments, namely, low, middle and high areevaluated and in Europe, all segments, including ExHigh, are evaluated for fuel efficiency. The standard
method for WLTC mode testing is "cold start" in whichtest starts with the vehicle engine in cold state;
however, in order to evaluate efficiency under many
conditions, we have used "hot start" with a warmed-up
engine.

Fuel efficiency
improvement ratio %With Ex-High

10
5
0
-5
-10

-5

0

5

Change of SOC %Fig. 9 Driving test result on WLTC mode

Fuel efficiency
improvement ratio %

Low

High

MiddleEx-High

100

50

0

Without Ex-High

15

8

150

Vehicle speed km/h

20Without Ex-High

6

With Ex-High

4

Condition A

2
0

-2

-1

-0.5

0

0.5

Change of SOC %
0

500

1,000

Time s

1,500

2,000

Fig. 10 Driving test result on WLTC mode
(Enlarged view)Fig. 8 Driving test result on WLTC mode

-30-

1

*06E_*15 18/09/05 18:47 ページ 6

Vehicle speed km/h

150

2Vehicle speed
Fuel consumption (without eHUB)
Fuel consumption (with eHUB)
Change of SOC

100

1

50

0

0

0

500

1,000

1,500

-1
2,000

Fuel consumption (L), change of SOC (%)

Hub Module with Motor and Generator Function

Test vehicle

Intended travelling line

Low friction roadFig. 12 Driving method of low friction road

Table 7 The condition of low friction road

Time sYaw angle control

Fig. 11 Driving test result on WLTC mode (condition A)

Stability control

Left wheel
Braking

No control

Unstability control

Right wheel
Driving̶̶Driving

Braking

Table 6 Section and fuel efficiency (condition A)
Change of SOC
(%)

3.40

0.05

Low
Each
segment

Middle

4.74

−0.27

Ex-Hi

2.30

0.22

High

3.40

Without Ex-High

3.81

With Ex-High

3.22

12

Stability control
No control
Unstability control

10

Yaw angle deg

Fuel efficiency
improvement ratio
(%)

−0.06
−0.28
−0.06

8
6
4
2
0

In order to reduce fuel consumption, EV mode
driving is effective under creep conditions such as
traffic jams and parking. Assuming a system of P0 +eHUB under Section 3.3, we verified possibility ofstarting and driving under 10 km/h with eHUB only.
We have confirmed that driving with eHUB only was
possible for approx. 180 seconds by starting in EV
mode on a flat ordinary road with asphalt, even if therequired driving torque changes depend on the vehicle
weight, road surface conditions, wind and slope.

05

Range m10

15

Fig. 13 Test result on low friction road

5. Conclusion
In this paper, development status of HUB modulewith motor/generator functions was introduced, which
can improve fuel efficiency and driving performance ofvehicles with 48V MHEV system, and with minorchanges to the vehicles. We tested the prototype
eHUB system on a test vehicle and obtained thefollowing results:

4.3.2 Traction control
In order to confirm its contribution to vehicle
stability, we verified straight-running ability on the roadwith different friction coefficients for left and right tires
at the road contact area. As shown in Fig. 12, thestraight-running test was conducted with a locked
steering angle on the road surface with a low friction
coefficient on the right side, measuring the deviationfrom the target running line as the yaw angle. The test
was conducted under three running conditions asshown in Table 7. Fig. 13 shows the test results. We
could confirm that, by driving eHUB with stability
control, vehicle deviation from the straight line was
reduced, improving straight line running.

● In WLTC mode, eHUB assistance is effective for
reducing fuel consumption● EV starting + creeping can be maintained for over
180 seconds● Straight line running ability is improved on low
friction roads
We will not only continue to improve eHUB, but also
study the effect of fuel efficiency improvement whencombined with the existing 48V MHEV and energy
management for commercialization.

-31-

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NTN TECHNICAL REVIEW No.85（2017）

References
1) Complete analysis of HEV and EV related markets, 2017,
Fuji Keizai, 30, 37.
2) Fourin Monthly Report on Global Automotive Technology
Research No. 34 (2), (2017), FOURIN, Inc.
3) Complete analysis of HEV and EV related markets, 2017,
Fuji Keizai, 5.
4) NTN TECHINICAL REVIEW No 79, (2011) 22-28.
5) NTN home page
http://www.ntn.co.jp/japan/news/new_products/
news201600042.html

Photo of authors

Kentaro NISHIKAWA

Yuuji YADA

Yasuyuki FUJITA

Mitsuo KAWAMURA

Hiroki YABUTA

New Product Development
R&D Center

New Product Development
R&D Center

New Product Development
R&D Center

New Product Development
R&D Center

New Product Development
R&D Center-32-

*07E_*15 18/09/05 18:49 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Technical Paper ]Influence of Vehicle Body Motion on the Effects of
G-Vectoring Control
Yuta SUZUKI**
Weipeng CHENG**
Shuichi KOSAKA**
G-Vectoring control (GVC) which controls longitudinal acceleration incoordination with lateral motion has been installed in an experimental
vehicle that can adjust the anti-dive mechanism. Only the pitch motion
characteristics of the vehicle body were changed during lane changes,
and the vehicle planar motion characteristics itself are kept
unchanged. Drivers’ steering model parameters during lane change forthe vehicle with/without GVC are identified. Then, the handling quality evaluations by the drivers are compared
and analyzed by using the driver parameters identified and the influence of the vehicle body motion on GVC
effect is investigated. It is found as a result of the study that the nose-dive pitch motion caused by the control isimportant for GVC to be effective in improving the vehicle handling quality.
Note) "G-Vectoring" is a registered mark of Hitachi Automotive Systems, Ltd.

objectively and quantitatively evaluated in cases when
dynamic coupling of roll motion and pitch motion may
have occurred or not 2), 3). This dynamic couplingwhen both a roll motion and pitch motion occur is adiagonal motion; hereafter known as diagonal roll
The above is the result of joint research with the
Kanagawa Institute of Technology.

1. Introduction
Recently electric vehicles have been gaining in
popularity. Due to this increase in popularity there is afocus on accurate and responsive motor-driven
controls, which can lead to higher energy efficiency
than gasoline engines, which can lead to anelimination of emission gases. Among other items, inwheel motors are able to further improve the accuracy
and responsiveness of independent driving andbraking control. This is due to the fact that the inwheel motor sends the driving and braking control
directly to the wheels.
In this paper, steering characteristics that a driver
feels are objectively and quantitatively evaluated bycomparing the cases when GVC is applied and not
applied. What GVC is, is when longitudinal
acceleration in connection with lateral motion of fulldrive-by-wire vehicles that have in-wheel motors
installed on all four wheels is applied 1). The test
vehicle can only change its pitch motion by changing
its suspension geometry and without changing its rollrigidity. That is, even when the vehicle motion on aplane surface is the same, the vehicle attitude in a 3Dview can be changed. Leveraging this characteristic,
the steering characteristics that a driver feels were

2. G-Vectoring Control
In this chapter, GVC is outlined. In the researchthus far, Emeritus Professor Abe, Professor
Yamakado etc. of Kanagawa Institute of Technology
have proposed the formula shown in (1) as the basic
control guideline for coupling longitudinal motion
depending on lateral motion. This is known as "GVectoring Control (GVC)", meaning integrated control
of longitudinal and lateral G vectors.

GXC = sgn Gy Gx(

Cxy) 1+ T G ………………（1）SyWhere, GXC is the acceleration command for
longitudinal acceleration of the vehicle, Cxy is thecontrol gain, Gy is lateral acceleration of the vehicle
・and G y is the lateral jerk information which is the firstorder derivative of vehicle lateral acceleration. This**Engineering Dept. Natural Energy Products Division**Advanced Technology R&D Center-33-

*07E_*15 18/09/05 18:49 ページ 2

NTN TECHNICAL REVIEW No.85（2017）control algorithm was derived from careful observationof driving maneuvers by expert drivers performing J
turns. As you can see from the formula, it is a very
simple algorithm, just multiplying the gain Cxy to theabsolute value of lateral jerk information y.
As shown in Fig.1, GVC accelerates/decelerates
according to vehicle lateral jerk information tosmoothly change the direction of combined
acceleration G. In this research, GVC of "onlydeceleration" at the bottom of Fig.1 was set as anevaluation object, while "no control (no GVC)" wasalso evaluated for comparison.

Fig. 2 Experimental vehicle

Table 1 Vehicle parameters
Steering

Turn-inSteady state

Name

Turn-out

SymbolWeightWheel baseDistance from the front wheel to center of gravity

Lateral jerk

Distance from the rear wheel to center of gravity
Front wheel tread
Rear wheel tread

Longitudinal
acceleration

Decelerate

Height of center of gravity

Accelerate

Valuesm

Yaw inertia moment709 [kg]l

2.05 [m]lf

1.012 [m]df1.415 [m]lr

1.038 [m]

dr

hs
hs

1.415 [m]0.417 [m]512 [kg・m2]

3.2 Change of suspension geometry adjustment
Decelerate

The test vehicle can change anti-dive/anti-squat
force by adjusting suspension geometry. When avehicle with double-wishbone suspension is viewed
from the side (Fig. 3), the intersection of the virtuallines coming from the upper and lower arms will be the"suspension rotation center." The angle between theline connecting this suspension rotation center and thecenter of the ground contact of the tire with the groundis called the "anti-dive angle (anti-squat angle)" in thisreport. When the same driving/braking force is given,
the larger this angle, the larger the "anti-lift force"
which presses the vehicle down or the "anti-squat
force" which lifts the vehicle up."Fig. 1 Schematic concept of GVC algorithm

3. Test vehicle
3.1 Vehicle parameters
The following is the description of the test vehicle.
The test vehicle shown in Fig. 2 has in-wheel motors
in all of its wheels and a steer-by-wire unit for the front
and rear; therefore, it provides 4-wheel independent
drive and 4-wheel independent steering.
This vehicle is equipped with 2 GNSS sensors on
the roof and a gyro sensor under the seat so that it
can sense highly accurate positional information andangular velocity to complement each other.
The steering angle is detected by a magnetic
encoder installed on the steering wheel. The inverter
installed at the front and rear of the vehicle provides
power to the motors in the wheels to generate torqueand detect rotational speed of the motors. Table 1
shows vehicle parameters.

Progressing
direction

Upper arm

Lower arm
Front

Xf・tanθf
Xf

θf

Rear

Suspension
rotation center

Xr・tanθr
θr
Xr

Fig. 3 Anti-dive/anti-squat geometry-34-

*07E_*15 18/09/05 18:49 ページ 3

Influence of Vehicle Body Motion on the Effects of G-Vectoring Control

The test vehicle shown in Fig. 2 can change theanti-dive angle from 0˚ to 30˚ in multiple stages. In thistest, braking force is applied to 4 wheels with GVC;
therefore, if the anti-dive angle is set larger than 0
degrees, "anti-squat force" is applied to the front
wheels and "anti-lift force" is applied to the rear
wheels which reduces the pitch motion.
In this paper, the steering characteristics that thedrivers feel and the impact of GVC on the vehicle
behavior were evaluated, by comparing the casewithout the reduction of pitch motion by setting theanti-dive angle to 0˚, and with the reduction of pitch
motion by setting the anti-dive angle to 30˚.

or without) GVC by identifying driver parameters fromdriver behavior (steering wheel maneuvering) andvehicle motion (lateral motion).
Expressing the relation between the steering angle
and lateral motion during a single lane change at aconstant speed as a transfer function, we obtainequation (2).

δy L 0 − (1 + τ h s )yh……………………（2）1+τ Ls

Where, δ is the steering angle, y is the lateralmotion and yL0 is the target lateral motion. In addition,
τL is an overall human delay (from the steeringcommand by LED to the time the driver actually starts
steering),τh is the time to focus on the forward view
(from the beginning to the end of lane change), h is
the steering gain (relative gain proportional to themagnitude of steering angle), and these three driverparameters were identified.
Describing the details of each parameter, h andτL
represent driver gain and responsiveness. For
example, when the steady gain of vehicle becomes
smaller, the driver increases gain h to create abalance. It can be considered that the driver iscontrolling the vehicle with confidence when the driverincreasesτL. The derivative control action timeτhindicates the drivers derivative control action andshould include driver control action predicted bylooking ahead.
From past research 4), it is known that τL is strongly
related to vehicle steering characteristics indicatingthat vehicles with largeτL can be driven with confidence,
which means the vehicle steering characteristics aregood.
The above flow can be expressed in the "humanvehicle system block diagram" shown in Fig 5.

4. Evaluation method of steeringcharacteristics
4.1. Test course
A single-lane change test was conducted toevaluate driver steering characteristics. The test was
conducted in a commonly used single lane change
course depicted in Fig. 4. The drivers enter the course
at 40 km/h and changed lanes while maintaining a
constant speed. The direction of lane change isdetermined at random immediately before the lanechange segment and indicated by turning on the LED
installed on the both sides of the windshield.

18[m]

=

2.5[m]

2.5[m]

Fig. 4 Single lane-change course
DriveryL0

4.2 Evaluation of steering characteristics usinga driver model

+
−

h
1+τLs

Steering angle δ hVehicleCourse error

Subjective evaluation by ordinary drivers tends tobe less reliable compared to expert drivers such as
test drivers. Therefore, objective and quantitativeevaluation of steering characteristics was conductedby using a simple driver model and identifying driverparameters.
The drivers adapt to the change of the vehicles
steering characteristics by maneuvering the steering
wheel to accomplish predetermined tasks. Therefore,
the driver parameters are considered to directly reflect
the change of steering characteristics. It should bepossible to conduct a quantitative evaluation of (with1+τ hsFig. 5 Simplified driver model

-35-

y

*07E_*15 18/09/05 18:49 ページ 4

NTN TECHNICAL REVIEW No.85（2017）

4.3 Identification of driver parameters

Table 2 Drivers for the forgoing test

In this chapter, a method for identifying driverparameters is described. Equation (2) can beconverted into equation (3).

Subjects

GenderAge

Drivingexperience

Driving
frequency

A

Male

22

4 years

Only weekends

C

Male

23

4 years(1 + τ L s)δ (s) = −h {(1+τ h s ) y (s) − y L0 (s )} ……（3）δ and y of equation (3) are replaced by δ* and y* ,where, δ* is the time history of human steering
maneuvers measured in the single lane change test(steering angle) and y* is the vehicle lateral motion
during that time. If the human steering model is close
to the actual human maneuvering, the left-hand sideand right-hand side of equation (3) should be close.
To obtain driver parametersτL ,τh , and h to makethem close, the performance function indicated inequation (4) is defined.

Steering angle ［deg］

2

dy*
dδ *
J = ∫ δ + τL+｛
h y*+ τ h
− yL 0 ｝ dt ……（4）
dt
dt
0
T

［

*

］

3 years

21

Male

E

4 years

23

Male

D

2 years

21

Male

B

EverydayEveryday

Only weekends
EverydayWithout GVC
With GVC

100
80
60
40
20
0
-20
-40
-60
-80
-100

0

0.5

1

1.5

2

2.5

3

3.5

4

2.5

3

3.5

4

2.5

3

3.5

4

2.5

3

3.5

4

Time ［s］

By solving equation (5) to minimize thisperformance function J , the parameters can be found.

Yaw rate ［deg/s］

40

∂J
∂J
∂J
= 0,
= 0,
= 0 …………………（5）∂ (hτ h )∂τ L
∂hIn this research,τL (overall human delay), from theabove parameters, is used as the evaluating
parameter.

30
20
10
0
-10
-20
-30
-40

0

0.5

1

1.5

2

Deceleration due to GVC ［N］

Time ［s］

5. Actual vehicle test
5.1 Preliminary test
Before evaluating the influence of GVC on thevehicle’s pitch motion, the effect of GVC itself wasverified in a single lane change test. The anti-diveangle was set to 0˚ for both the front and rear. The
following 5 subjects were chosen (Table 2). All ofthem were men in their 20s with different driving
experience and frequency. The test was conducted bycommunicating to them that the test can be
immediately terminated at their discretion, forexample, if they feel uncomfortable during the test.
Fig. 6 shows the comparison of the driver andvehicle motion with or without GVC in the time series
data. It can be seen that with GVC, the steering angle
is smaller and steering action is slower than without
GVC. The yaw rate is also smaller with GVC.
Then the driver parameterτL was identified. The
test results comparing the cases with and without
GVC for each subject are shown in Fig. 7.
For all subjects,τL with GVC is larger than without
GVC, which means that the drivers can drive more
confidently with GVC.

300
200
100
0
100
200
300

0

0.5

1

1.5

2

Time ［s］

Lateral motion ［m］

3
2.5
2
1.5
1
0.5
0
-0.5

0

0.5

1

1.5

2

Time ［s］

Fig. 6 Driver-vehicle behavior with/without GVC-36-

*07E_*15 18/09/05 18:49 ページ 5

Influence of Vehicle Body Motion on the Effects of G-Vectoring Control

pitch motion, namely, diagonal roll was observed.
Although longitudinal acceleration by GVC is verysmall (max. 0.06 m/s2), the waveform of the steering
angle is more stable with GVC. During this time,τL
was larger with GVC than without GVC for all subjects,
the same as during preliminary test (Fig. 8 (a)).
When the anti-dive angle was set to 30˚ (Fig. 9),anti-lift force and anti-squat force were produced by
GVC's braking force; therefore, pitch motion was
reduced and no diagonal roll was observed. The
waveforms of the steering angle and yaw rate weremore unstable than when the anti-dive angle was 0˚
and there were cases that τL was larger without GVC
than with GVC depending on the subject (Fig. 8 (b)).
From the above, we could confirm that even whenthe vehicle behavior is the same on a plane, GVC's
effect can differ depending on the pitch motion during
turns. It is conceivable that diagonal vehicle attitude isimportant, in addition to vehicle behavior as planar
motion, in order to achieve vehicle characteristics for
comfortable maneuvering for human drivers.

0.18
0.17
0.16

τL 0.15
[s]

0.14
0.13
0.12
0.11

Driver A

Driver B

Driver C

Without GVC

Driver D

Driver E

With GVC

Fig. 7 Effect of GVC on handling quality evaluatedby the driver parameter τL

5.2 Comparison of cases with and withoutanti-dive angle (anti-squad angle)
The influence on vehicle pitch motion relative to
GVC was evaluated by setting the anti-dive angle to 0˚
and 30˚ for both the front and rear. Four subjects
shown in Table 3 were chosen.
Fig. 9 and 10 shown on the next page are thegraphs that overlay the result data from one of the test
subjects.
When the anti-dive angle was set to 0˚ (Fig. 9), no
anti-lift force and anti-squat force was produced by
GVC's braking force; therefore, roll motion and diving

Table 3 Specifications of research participants
Subjects

GenderAge

Drivingexperience

A

Male

27

9 years

C

Male

22

4 years

B

D

0.28
0.27
0.26
0.25
0.24
0.23
L 0.22[s] 0.21
0.2
0.19
0.18
0.17
0.16

Male
Male

23
23

Driving
frequency
Everyday5 years

Only weekends

3 years

Only weekends

Everyday

0.28
0.27
0.26
0.25
0.24
0.23
L 0.22[s] 0.21
0.2
0.19
0.18
0.17
0.16

τ

τ

Driver A

Driver B

Without GVC

Driver C

Driver D

Driver A

With GVC

Driver B

Without GVC(a) Anti-dive angle : 0˚

Driver C

With GVC(b) Anti-dive angle : 30˚Fig. 8 Effect of anti-dive for driver parameterτL-37-

Driver D

*07E_*15 18/09/05 18:49 ページ 6

0

0.5

1

1.5

2

Time ［s］

2.5

3

3.5

4

2
1.5
1

0.5
0
0

0.5

1

1.5

2

Time ［s］

2.5

3

3.5

4

10
0
-10
-20
0

0.5

1

1.5

2

Time ［s］

2.5

3

3.5

0

0.3

0.5

1

1.5

2

Time ［s］

2.5

3

3.5

0
-0.1
-0.3

Lift
0

0.5

1

1.5

2

Time ［s］

2.5

3

3.5

Deceleration due to GVC［N］

Deceleration due to GVC
［N］

200
100
0

100
200
0.5

1

1.5

2

Time ［s］

2.5

3

3.5

4

0.8
0.6
0.4

Longitudinal acceleration［m/s2］

Longitudinal acceleration［m/s2］

0

0.2

0
-0.2
-0.4
-0.6
-0.8

0

0.5

1

1.5

2

Time ［s］

2.5

3

3.5

1.5

0

0.5

1

1.5

0

0.5

1

1.5

3.5

4

2

2.5

3

3.5

4

2

2.5

3

3.5

4

2

2.5

3

3.5

4

2

2.5

3

3.5

4

2

2.5

3

3.5

4

2

2.5

3

3.5

4

Time ［s］

30
20
10
0
-10
-20

Time ［s］

4
3
2
1
0

-1
-2
-3

0.3

4

Fig. 9 Driver-vehicle behavior with pitch motion freeTime ［s］

Dive

0.2
0.1
0
-0.1

Lift

-0.2
-0.3

4

300

300

1

3

-4

0.1

-0.2

0.5

2.5

0

4

Dive

0.2

0

2

Time ［s］

1

Pitch angle ［deg］

-4

1.5

0.5

Roll angle ［deg］

Roll angle ［deg］

1
0

1

2

-30

-1
-2
-3

0.5

1.5

4

4
3
2

0

3

Yaw rate ［deg/s］

Yaw rate ［deg/s］

20

Without GVC
With GVC

2.5

-0.5

30

-30

100
80
60
40
20
0
-20
-40
-60
-80
-100

Lateral motion ［m］

3
2.5

-0.5

Pitch angle ［deg］

Without GVC
With GVC

Steering angle ［deg］

100
80
60
40
20
0
-20
-40
-60
-80
-100

Lateral motion ［m］

Steering angle ［deg］

NTN TECHNICAL REVIEW No.85（2017）

0

0.5

1

1.5

0

0.5

1

1.5

0

0.5

1

1.5

Time ［s］

300
200
100
0
100
200
300

Time ［s］

0.8
0.6
0.4
0.2

0
-0.2
-0.4
-0.6
-0.8

Time ［s］

Fig. 10 Driver-vehicle behavior with pitch motion
restrained-38-

Influence of Vehicle Body Motion on the Effects of G-Vectoring Control

References

6. Conclusion

1) Rio Tanaka, Masato Abe et al. "Evaluation of steeringcharacteristics of G-Vectoring Control using in-wheel
motor electric vehicles," Proceedings for the Autumn
Meeting in 2016, No. 045
2) Rio Tanaka, Masato Abe et al. "Influence of vehicle
characteristics on G-Vectoring Control," Proceedings
for the Spring Meeting in 2017, No. 163
3) M.Yamakado, R. Tanaka etc "Influence of vehicle body
motion on the effects of G-Vectoring Control" IAVSD
2017 14-18 August4) Shota Abe, Masato Abe et al. "Influence of roll on
evaluation of driver steering characteristics,"
Proceedings for the Spring Meeting in 2015, No. 3115S

It was confirmed that the steering characteristics
that drivers feel can be improved by producing
longitudinal acceleration with GVC.
When pitch motion was not reduced withoutchanging roll rigidity, all drivers exhibited largerτLwith GVC; however, when pitch motion was reduced,
there were drivers with largerτL without GVC.
It was revealed that the diagonal roll produced bycoupling of roll and pitch motion during lane change isrequired to appropriately obtain the GVC effect.
It is necessary to consider 3D vehicle motion
including roll and pitch motion in addition to planar
motion, in order to achieve vehicle characteristics for
comfortable maneuvering by human drivers.

Photo of authors

Yuta SUZUKI

Weipeng CHENG

Shuichi KOSAKA

Chassis System
Engineering Department,
EV Module Headquarters

Chassis System
Engineering Department,
EV Module Headquarters

Driveline System
Engineering Department,
EV Module Headquarters-39-

*08E_03 18/09/05 18:50 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Technical Article ]History of Constant Velocity Joints

Shinichi TAKABE*

In 1963, Constant Velocity Joints (CVJ) have been started
production by NTN for the first time in Japan. NTN responded tochanges in the automobile industry and worked on the developmentof CVJ. And CVJ has grown to be the foundation product of NTN. In
this article, to celebrate the 100th Anniversary of NTN, I look back on
the history of CVJ.

The CVT originated when the Rzeppa joint wasdevised by Rzeppa (Hungary) in the 1930s, then in
1959, the Birfield joint was adopted in European
vehicles when front-wheel drive vehicles started
making major strides.
In 1963, NTN started manufacturing CVJs for the
first time in Japan. Currently, after over a half century,
CVJs are being manufactured globally in many sites,
totaling 720 million units (CVJs for automobiles as ofJune, 2017) (refer to Fig. 1).

1. Introduction
CVJ is a collective term for joints which smoothlytransmit power without rotational fluctuation when the
input shaft and output shaft rotate at any angle (workangle). Currently, it is commonly used as a driving
component for automobiles and industry machines;
however, it was originally initiated from therequirements of front wheel drive vehicles and evolved
together with the progress of vehicles and industry
machines.

Engineering
R&D
PlantsJ.V.

NTN-AT(Germany) 2006 Beijing
Seohan(China)Okayama Works 1982 -NTN-SNR Sibiu(Romania) 2009 -EuropeIwata Works 1973 Engineering
R&D

Fukuroi Works 2007 -Japan

NTE Crezancy(France) 2008 -TAIWAY(Taiwan)

North
America

NTK (North America)
2004 -

Asia

NNMI Chennai(India) 2011 NTE (France) 1998 Engineering (France)

Engineering(North America)

Kuwana Works 1963 -Shanghai NTN (China)
2003 Technical Center 2011 -NNMI Bawal(India) 2007 -NTN-BOWER(North America) 2016 -UNIDRIVE(Australia)

NMM (Mexico)
2016 SEOHAN-NTN(North America)

Guangzhou NTN(China) 2003 -NDI (North America) 1989 NDA (North America) 2017 -NMT (Thailand) 1998 Xiangyang NTN (China) 2015 -Fig. 1 Manufacturing & engineering location of CVJ*Drive Shaft Engineering Department, Automotive Business Headquarters

-40-

South
America

NDB (Brazil)
2011 -

*08E_03 18/09/05 18:50 ページ 2

History of Constant Velocity Joints

1959. This produced less vibration and noise anddrastically improved steering stability.
In Japan, front-wheel drive vehicles started gaining
attention and in 1963, Suzuki Suzulight adopted
NTN's ball-fixed joint (BJ) for the first time.
At that time, sliding CVJs, which slide in the axial
direction, did not exist. The overall mechanism wasrealized by BJ- was used on the wheel side, crossjoint, which was used on the differential gear side witha smaller work angle and slide spline installed on theshaft, which absorbed the sliding motion in the axial
direction.

2. Transition of vehicles and history of
CVJ
The drive system in automobiles has transitioned
with the time and NTN's CVJ has made significant
contributions in this transition. Table 1 reviews thehistory of CVJ with the transition of vehicles

2.1 Before the invention of CVJ (- 1960)
Currently, front-wheel drive vehicles account for the
majority in production; however, before 1960, most of
the vehicles were rear-wheel drive. With rear-wheel
drive vehicles, engine power is transmitted throughthe propeller shaft into the rear axle. Back then, bothrear wheels were directly connected to the shaft as
one unit and no independent vertical motion was
possible (rigid axle); therefore, the CVJ was not
required. The front wheels were used for steering
only, without transmitting engine power; therefore,
there was no need for CVJs here, either.

2.3 Market expansion of front-wheel vehicles(1965 -)
NTN developed a double offset joint (DOJ) with theability to slide on the axial direction to solve theproblem of vibration produced by the combination ofcross joint and slide spline. The drive shaft combining
BJ and DOJ was first adopted in Subaru 1000 by Fuji
Heavy Industries Ltd. (currently, Subaru Corporation)in 1965. This structure is the original form of the drive
shaft that is still used today (Fig. 2).

2.2 Appearance of CVJ (start of 1960s)
Before CVJs were developed, cross joints (Cardan
joint) were used for the drive shaft of front wheels offront-wheel drive vehicles and four-wheel drive
vehicles. However, it was not constant in velocity andproduced vibration and noise with a large work angle;
additionally steering stability during cornering wasbad. To solve these problems the Tracta joint, Weiss
joint, and Double Cardan joint, etc. were developed
however, their performance was not sufficient enoughfor the drive shaft of the front wheels.
Then in 1956, Hardy-Spicer in the UK developed
the Birfield joint, which was adopted by Austin Mini of
BMC and other front-wheel drive vehicles in Europe in

Differential
gear
Tire

Drive shaft (BJ+DOJ)

Fig. 2 Structure of driveshaft

Table 1 History of NTN CVJ
Decade 1960

1970

1980

1990

2000

Market/vehicle
trend●Second oil shock

Booming front-wheel● drive vehicles●●BJ (1963)●●Increase of AT vehicles●Introduction of HVs and EVs

Domestic front-wheel ●Increase of 4WD
drive vehicles●DOJ (1965)

Sliding●EBJ (1998)●UJ (1988)●EUJ (2002)●TJ (1983)●DOJ -RPC (1984)●DOJ- RPCF (1986)●AC-TJ (1987)●VU J (2012)

CFJ (2012)●REBJ (2015)●PTJ (2002)●REDJ (2015)●EDJ (2002)●ETJ (2002)●EPTJ (2005)

Fixed
Sliding●VBJ (2010)●SFJ (1997●FTJ (1989)

Propeller
shaft

Enhancement of fuel Efficiency
regulations●Increase of overseas production of Japanese auto manufacturers

Fixed
Drive
shaft

2010

●Expansion of emerging markets●First oil shock●HEBJ (2005)●LJ (1985)●HLJ (1997)●DOJ- RPCF (1987)●AC-TJ (1991)-41-●HEDJ (2005)●HETJ (2006)

*08E_03 18/09/05 18:50 ページ 3

NTN TECHNICAL REVIEW No.85（2017）

body, caused by the driver pressing the brake pedal
while transmission was set at D-range. NTN developed
DOJ-RPC and DOJ-RPCF which absorbed small
engine vibrations which solved this problem. In
addition, NTN started volume production of newly
structured sliding type CVJ with smaller sliding
resistance, and " (TJ)" in 1983, with wide adoption,
particularly with AT vehicles.
Today, TJ type CVJs are used on most AT vehicles.

In the 1970s, various auto manufacturers introduced
front-wheel drive vehicles into the market, which was
further accelerated by the second oil crisis in 1978. In
the 1980s, the need for quieter vehicles rose as the
production of front-wheel drive vehicles increased.
With improvements of CVJs, front-wheel drive vehicles
expanded into small car segments, Therefore, theneed for CVJs increased.

2.4 Emergence of IRS vehicles (1976 -)3.1 Low vibration sliding type CVJ (1983 -)Rear-drive vehicles transitioned from rigid axle toindependent rear suspension (IRS) to improve ride
comfort. Since IRS requires each rear wheel to moveindependently, CVJs were required on the drive shaft.
In 1976, Toyota Mark II adopted BJ and DOJ for the
first time as an IRS vehicle. Later, adoption of CVJ
increased in the propeller shaft of rear-wheel drive
vehicles with IRS for reducing vibration.

As the automobile evolved, requirements on comfort
and quietness also evolved. The following is thehistory of measures taken for reducing shudder of TJ
as an example of vehicle NVH (noise, vibration andharshness).

(1) TJ (1983 -)When TJ rotates with a wider angle, periodically,
fluctuating slide occurs between the roller and roller
groove on the outer ring, producing outer ring axial
force (induced thrust). This induced thrust may
produce shudder when resonated with the vibration ofengine mount during vehicle start and acceleration.

2.5 Expansion of 4-wheel drive vehicles (1980 -)Originally, 4-wheel drive was limited to off-roadvehicles; however, the introduction of Leone 4WD
from Fuji Heavy Industries Ltd. (currently, Subaru
Corporation) in 1972, and full-time 4WD vehicles from
European manufacturers in the 1980s, adoption of
4WD expanded to on-road vehicles. IRS was adopted
in the rear wheels of 4WD vehicles, and drive shafts
using CVJ on all wheels were required in the mid1980s.
As the adoption of 4WD expanded to on-roadvehicles, reduction of noise and vibration was
required, and adoption of sliding CVJs began
replacing the combination of cross joint and slide
spline on the propeller shaft.
Since the propeller shaft rotates at higher speeds
than the drive shaft, cross grooved joints (LJ) wereapplied because of little backlash and good rotationalbalance. Then, DOJ to absorb small vibrations, tripod
joints (TJ) with small sliding resistance and heatgeneration, and BJ for fixed CVJ usable at a wider
angle than cross joints were all adopted as they were
improved for use in the propeller shaft.
Increased usage of CVJs in on-road 4WD vehicles
proliferated to off-road 4WD vehicles, too.

(2) AC-TJ (1987 -)Gothic geometry was applied to the cross section of
the roller groove of the outer ring to make angularcontact with the roller, and induced thrust was induced
together with low-μ urea grease (refer to Fig. 3).

(3) FTJ (1989 -)Another roller (free ring) was installed outside theroller so that the free ring always maintains a certain
position against the roller groove, and induced thrust
was significantly reduced (refer to Fig. 4).

(4) SFJ (1997 -)Eliminated the flange on the roller groove of theouter ring prevents an increase of induced thrust
when the free ring end of FTJ strikes the flange on theroller groove of the outer ring (refer to Fig. 5).

(5) PTJ (2002 -)The journal cross section of the tripod was madeinto an irregular elliptical shape, and a freely swinging
roller cassette was incorporated to be contained within
the roller groove of the outer ring. Since the roller
cassette smoothly rolls maintaining a certain positionon the roller groove of the outer ring, even with awider angle, lower induced thrust can be always
maintained regardless of the work angle (refer toFig. 6).

3. Transition of CVJ technology
As CVJs significantly affect vehicle performance,
NTN has been contributing to improvement of vehicle
performance through improvement of CVJs.
Around 1980, automatic transmission (AT) started
outpacing manual transmission (MT) in Japan. AT
vehicles produced vibration while idling due to axial
vibration transmitted from the drive shaft to the vehicle-42-

*08E_03 18/09/05 18:50 ページ 4

History of Constant Velocity Joints

Table 2 Transition of max. angle of fixed CVJ
Max. work angle

Volume production start time

CVJ type

42.5˚

1963 -

BJ

46.5˚

1982 -

50˚1988 -

44.5˚
47˚

Fig. 3 Structure of AC-TJ

Fig. 4 Structure of FTJ

Fig. 5 Structure of SFJ

Fig. 6 Structure of PTJ

50˚

1980 1998 2012 -

BJ
BJ

EBJ
UJ

VUJ

Fig. 7 Structure of BJ

Fig. 8 Structure of EBJ

Fig. 9 Structure of UJ

Fig. 10 Structure of VUJ

3.2 Larger working angle(1) Fixed type CVJ (1980 -)The center of the differential gear and the center ofthe wheels are in different vertical and horizontal
positions; therefore, the CVJs on the wheel side anddifferential gear side would have a specific angle. The
CVJ on the wheel side would have a work angle,
which is a combination of this angle and the angle
created by steering. The turning radius of a vehicle isdetermined by the maximum work angle of the CVJs.
In order to reduce large turning radius due to a longer
wheel base and high common angle, CVJs are
required to provide a larger work angle.
The maximum work angle of BJ, originally 42.5˚,
was enlarged to 46.5˚, then an undercut free joint (UJ)
was developed to increase the angle further to 50˚,which was adopted in the Fuji Heavy Industries Ltd.
(currently, Subaru Corporation) Legacy. UJ has thesame component configuration as BJ, with a straightshape on the end of the ball groove of the outer wheel
and inner wheel to provide a larger angle.
In addition, the internal design has evolved with BJ
to EBJ (max. work angle: 47˚) and UJ to VUJ (max.
work angle: 50˚) refer to Table 2, Fig. 7 - Fig. 10.

3.3 Lightweight and compactness(1) First phase (1981 -)In order to adapt to vehicle specifications, CVJ
names and sizes were broken down into series insmaller increments.
The manufacturing process of the outer ring waschanged to induction hardening using medium carbon
steel rather than carburized steel to enhance thestrength allowing choice of smaller sizes.

(2) Second phase (1992 -)High strength shafts made of medium carbon boron
steel and long operating life urea grease weredeveloped to allow choice of CVJ with an even smaller
size than the first phase.

(2) Sliding type CVJ (1984 -)(3) Third phase (1998 -)CVJs on the differential gear side are also required
to provide a larger angle due to the increased
common angle and cope with work angle fluctuation
during bump and rebounding vehicle motion. The
original maximum work angle was increased from theoriginal 23˚ to 25˚ and a 30.5˚ design was also placed
into production.

In order to achieve lighter and smaller units
maintaining load carrying capacity equivalent to BJ,
EBJ was developed, increasing the number of balls
from 6 to 8 by reducing the ball size. This was
implemented in the Suzuki Cultus Crescent Wagon in
1998.
Also for sliding type CVJ, EDJ with 8 balls and ETJ
with renewed internal design were developed. EPTJ
-43-

*08E_03 18/09/05 18:50 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

was also placed into volume production, which is acompact version of PTJ.
On the other hand, on the propeller shaft side, HLJ
was developed by making LJ lighter and smaller, andincreasing sliding area. Also, HEBJ, HEDJ and HETJ
were developed by improving EBJ, EDJ and ETJ for
use on the propeller shaft.
Fig. 11 Structure of CFJ

3.4 Grease and CVJ boots
Originally, lithium soap grease with molybdenum
disulphide was used; however, improvement in
performance was made since the 1980s by focusing
on urea grease for "durability," "low vibration," "highefficiency" and "low heat generation." Highperformance urea grease with organic molybdenum,
etc. was developed and currently in use.
On the other hand, for CVJ boots, chloroprenerubber was used in the past; however, damage
occurred due to external wear and deterioration ofmaterial. Although some improvements in material anddesign were made, it was not sufficient for use on
fixed-type CVJ for front wheels.
Around 1985, boots made of thermal plasticizedpolyester elastomer (resin boots) were produced,
which drastically increased the life of boots. Today,
resin boots are used for almost all fixed-type CVJ, as
well as increased use for sliding type CVJ.

(3) Lightweight Rear Drive shaft "R-Series"
CVJ for front wheels is used as CVJ for rear drive
shafts. We have developed REBJ and REDJ
dedicated to rear wheels for rear-drive vehicles and
4WD pursing lightweight and compactness. We havesucceeded in reducing weight by 30% for the entire
drive shaft, including use of the hollow shaft as theintermediate shaft, compared to EBJ and EDJ, whichboast the world's highest level of lightweight andcompactness as CVJ for front wheels (refer to Fig. 12).

Fig. 12 Structure of light weight driveshaft for rear
(REBJ + hollow shaft + REDJ)

3.6 High functionality of drive shaft(1) Intermediate shafts with dynamic damper (DD)

3.5 High functionality of CVJ (2010 -)The following is a description of CVJs with higher
functionality.

Resonance may occur with natural bending
frequency of the intermediate shaft of the drive shaft
through engine vibration. DDs can be installed on theintermediate shaft as a means to shift the resonancefrequency.
Due to improved quietness of vehicles, demand for
reducing vibration of the drive shaft has been
diversified. Until the 1990s, DDs were used to absorb
one resonant frequency (1-mass spec); however,since the latter half of the 1990s, DDs to absorb 2
resonant frequencies (2 -mass spec) were applied.
Further, during the mid-2000s, dual mode DDs which
can solve 2 resonant frequencies with only one mass
were applied.

(1) Fixed-type CVJ, "VUJ"
The requirements for a larger maximum work angle
increased due to the increase of global demand for
SUVs. Therefore, VUJ was developed by making UJlighter and smaller with increased robustness, andplaced into volume production in 2012.

(2) Next generation high-efficiency fixed type
CVJ, "CFJ” 1)
As higher fuel efficiency is being explored forenvironmental measures and economy, we have been
pursuing improvement of transmission efficiency ofCVJs, in addition to reduction of weight for CVJ as
another contribution.
EBJ was developed, which reduced torque loss by
20% compared with BJ, and then OFJ was developed,
which reduced torque loss by 60% compared to that ofEBJ.
CFJ has a structure to alternate inclined ballgrooves from the outer ring and inner ring (crossgroove) to reduce internal friction for reducing torqueloss (refer to Fig. 11).

(2) Integrated hollow shaft
The drive shaft is required to have high rigidity;
however, thicker intermediate shafts for increasing
rigidity increase weight. Therefore, hollow intermediate
shafts were introduced to reduce weight.
Conventionally, intermediate shafts were made withshaft components for engaging CVJs welded on bothends of the pipe material. Currently, integrated hollow
shafts by swaging process have been used for volume
production since 2003.
-44-

*08E_03 18/09/05 18:50 ページ 6

History of Constant Velocity Joints(3) Isometric drive shaft

4. Future development

The drive shaft of front-wheel drive vehicles has
different lengths on the left and right sides because oftransmission placement. Taking rigidity balance of theleft and right may be limited, even when the thicknessof the intermediate shaft is changed. High output
vehicles may experience torque steer.
Therefore, outer wheel stem length of thedifferential side is made differently on the left
compared to the right (long shaft and short shaft), andthe intermediate shaft is made isometric to match thecommon angles of both sides. The long shaft outerring is connected to the differential gear throughbearings and brackets, etc.
The long shaft outer ring can be manufactured withintegrated cup and stem components, or cup andstem components may be manufactured separately
and welded together. The cup components arecommonly designed, and the stem components areindividually designed, based on the vehicle
specification. EBW outer rings with those components
welded by electron beam welding (EBW) have beenplaced in volume production since 2016 (refer to Fig.
13).

HEVs and EVs have emerged as the new drive
power; however, diesel engines and gasoline engines
are also changing every day. On the other hand,vehicle designs not only widely vary from light vehicles
to large passenger cars and SUVs, but also need tomeet the requirements of their individual dynamic
performance and ride comfort at a high level.
Although power types and vehicle designs vary,drive train structures evolve based on current
structures. The drive shaft is indispensable among
these, and has an increased role to play.
Performance required to the drive shaft may change
depending on the power type and vehicle design;
however, the basic elements are "lightweight," "highangle," "high rigidity," "quietness," "high efficiency"and "high speed." NTN strives to address theseelements by appropriately forecasting the needs, andpursuing development without delay for continuous
evolution.

5. Summary
Front-wheel drive vehicles, which were a revolutionary
drive system 50 years ago, are driven everywhere in theworld today. We are proud that NTN's CVJ has
contributed to the development of front-wheel drive
vehicles which were not imaginable 100 years ago.
I have reviewed the history of CVJ by taking theopportunity of NTN's 100th anniversary. Imagining theworld in 100 years from now, we would like to deliver
CVJs with evolution beyond imagination. NTN willcontinue growing with the history of CVJs in its
memory.

Inside section

Fig. 13 Combined by electron beam welding

References
Takeshi Ikeda: History of CVJ Design for Automobiles andRecent Technology NTN TECHNICAL REVIEW No. 70(2002) 8-17
1) Teruaki Fujio: Next generation high efficiency fixed-type
constant velocity joint "CFJ” NTN TECHNICAL REVIEW
No.81 (2013) 64-67

Photo of author

Shinichi TAKABE
Drive Shaft Engineering
Department, Automotive
Business Headquarters-45-

*09E_03 18/09/05 18:51 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Technical Article ]History of Axle Unit Bearings for Automobile

Daisuke NAKA*

Axle unit bearing has been innovated by integrating the surrounding components. This
article introduces the transition of bearing type and the latest NTN’s technology.

1. Introduction

2. Market needs

While rolling bearings for general use arestandardized by organizations such as ISO and JIS,rolling bearings for supporting vehicle wheels(hereinafter "axle unit bearings") have gone throughsignificant transitions over the years on theirtypes/materials and design specifications.
In addition, as environmental issues have become
the focus of the entire automotive industry, size,
weight and fuel efficiency of vehicle components arestrongly required to improve these environmental
concerns 1).
In parallel with the development of technologies toaddress these market requirements, theproduction/technology centers of NTN's axle unit
bearings have expanded globally (Fig. 1), which I
would like to review with its history and market needs.

The design specifications of axle unit bearings arediverse based on automotive manufacturer needs(mounting methods, allowable space and bearing
size, bearing load carrying capacity, friction, sealing
capability , rigidity and strength, etc.). Their historicaland current requirements can be categorized as follows:a) Ease of assemblyb) Simplification or elimination of bearing clearance
adjustmentc) Compactness and lightweight and large bearing
load carrying capacityd) Maintenance-free(Particularly, elimination of greasing operation andexternal seals for sealed bearings)e) Reduction of componentsf) Reduction of total cost including bearing units,
peripheral components and labor

Annecy/Ales/Seynod/Meythet Plants (France)
Mettmann Plant (Germany)

Canada Plant (Canada)
Nanjing Plant (China)

Sibiu Plant (Romania)

Elgin Plant (U.S.A.)
Iwata R&D Center (Japan)

Okayama Works (Japan)

NTN-SNR (France)

NCIC (China)

Chennai Plant (India)

NAC (U.S.A.)
Mexico Plant (Mexico)

Shanghai Plant (China)

Thailand Plant (Thailand)

Production (15 sites)

Curitiba Plant (Brazil)

Development/technology (4 sites)

Fig. 1 Axle unit bearing global production and R&D location*Automotive Unit Engineering Dept., Automotive Business Headquarters-46-

*09E_03 18/09/05 18:51 ページ 2

History of Axle Unit Bearings for Automobile

as hub and housing (knuckle) were integrated as aunit, evolving into GEN2 (GEN2 and later products asunits are called hub bearings at NTN, among the axle
unit bearings). NTN started development of GEN2 hubbearings in 1979 and volume production in 1983, thefirst being produced in Japan. GEN2 hub bearings
required integration of the hub flange and outer ring
raceway surface as a unit. This was achieved byapplying high frequency heat treatment to the
raceways, ensuring rolling fatigue life required forbearings, rotating bending fatigue strength required for
hub flanges, and fracture strength for expected large
load bearings from the road surface were met.
Adoption of GEN2 bearings by the automotive
manufacturers increased from the 1980s to 2000s as
its advantages are well recognized in the market.
Later, GEN2 evolved into GEN3 by integrating theinner ring, which improved ease of assembly of hub
bearings in the vehicle assembly line 1).
NTN started volume production of GEN3 in the mid1980s, the first being produced in Japan . Then, full
adoption of GEN3 started in the latter half of the
1990s and its wave rapidly propagated throughout theworld up until today.
In this case , GEN3 continued to evolve withsuperior specifications such as shaft-end tightening tofacilitate pre-load control and improving ease of
assembly in the vehicle assembly lines, as well as
improving reliability by integrating wheel velocity
sensors in the anti-lock brake system which prevents
damage from pebbles and corrosion from muddy/salty
water.

NTN has been developing and marketing volume
production of GEN1, GEN2 and GEN3 successfully
for approximately 40 years, responding to the above
requirements 2).

3. Transition of axle unit bearings
3.1 From standard bearings to GEN1
Until the 1970s, standard bearings conforming to
the ISO Standard were mainly used for axle unit
bearings, placing two deep groove ball bearings orconical rolling bearings on an axle and appropriately
selecting spacer rings and nut tightness to adjust theassembly clearance.
This method of using standard bearings had
limitations in weight and size; therefore, the market
needs for sealed/integrated bearings with potential for
a compact and light form factor increased, which
provided ease of assembly onto vehicles and did not
require clearance adjustment. In the late 1970s,
sealed double-row angular contact ball bearings(angular unit) and sealed double-row conical roller
bearings (taper unit), called GEN1, were introduced
into the market, and are still widely used as the axle
unit bearings for passenger cars even in the 21st
century. NTN produces GEN1 axle unit bearings indomestic plants, as well as overseas.

3.2 From GEN2 to GEN3
In the 1980s, the requirements for lightweight andcompact vehicle components increased. As a result,the peripheral components of axle unit bearings, such

Table 1 Characteristics of NTN axle unit bearings
Generation

Conventional

Volume production start time

GEN1

GEN2

GEN3

- 1970s

From latter half of 1970s

1983 -

From latter half of 1980s

Feature・Two single row
rolling bearings
are used・Two single row
rolling bearings
are integrated

・Mounting flange withmating component
and outer ring areintegrated

・Mounting flange with mating
component, outer ring andinner ring are integrated・Press fitting of bearings tomating component

Ease of assembly to vehicles

☆

☆☆

☆☆☆

☆☆☆☆

Compactness

☆

☆☆

☆☆☆

☆☆☆☆

☆
☆

☆☆
☆☆

☆☆☆
☆☆☆

☆☆☆☆
☆☆☆☆

☆

☆☆

☆☆☆

☆☆☆☆

Drive
wheel
Structure
Drivenwheel

RigidityPre-load control
Running torque

Superiority: ☆☆☆☆＞☆☆☆＞☆☆＞☆

-47-

*09E_03 18/09/05 18:51 ページ 3

NTN TECHNICAL REVIEW No.85（2017）(2) Grease

NTN has been responding to the demand of axle
unit bearings from the market based on specifictechnology accumulated over the years.
Table 1 on the previous page shows the transition
and features of NTN's axle unit bearings by
generation, including the period when two standard
bearings were used before integration.

Table 2 shows features of grease used in NTN's
axle unit bearings. NTN originally used highly refinedmineral oil as the base oil and urea-based organic
compound as thickener. Then, grease with improved
anti-corrosion properties was used as the standard
product. In addition, grease with improved lowtemperature tolerant properties was introduced forvolume production by blending additives to prevent
fretting wear when used for long-haul freight cartransportation in cold regions. Furthermore, withstricter fuel efficiency regulation planned to be
implemented by 2021 in Japan, U.S. and Europe, due
to the recent increase of fuel cost and environmental
issues such as global warming, low-torquespecification is required for axle unit bearings. To
meet the low torque requirements, NTN has
developed low-torque grease by modifying the baseoil/kinematic viscosity and consistency. This low
torque grease is currently in volume production.

3.3 Evolution of raceway material, grease and seals(1) Raceway material
NTN used high carbon chromium bearing steel for
inner/outer ring raceway materials for GEN1 axle unit
bearings. For outer rings and hub rings of GEN2 andGEN3, carbon steel with high frequency heat
treatment is used on the raceway, which contribute toincreased rolling operating life and forgeability. For
inner rings of GEN2 and GEN3, high carbon
chromium bearing steel is used, similar to GEN1.
Axle unit bearings use grease lubrication which iseasy to handle, contributes to simplified design ofsealing device and is most economical. Internal
grease for axle unit bearings is required to have thefollowing features:(1) Reduction of friction and wear(2) Extension of bearing life(3) Prevention of corrosion(3) Prevention of foreign materials from entering(5) Prevention of fretting wear

(3) Seals
Seals for axle unit bearings are required to have airtightness and low torque properties preventing muddy
water from penetrating from the operating
environment. Table 3 shows characteristics of seals
used in NTN's axle unit bearings. It shows theevolution from 2-lip seal that consist of only radial lips
to Hipack seals which improved sealing properties

Table 2 Characteristics of NTN axle unit greases

Performance

Conventional
greaseStandard grease

Grease with improved
fretting resistance

Low-torquegreaseAnti-corrosion property

☆

☆☆☆

☆☆☆

☆☆☆

Fretting resistance

☆☆

☆☆

☆☆☆

☆☆☆

☆☆

☆☆

☆☆

☆☆☆

TorqueSuperiority : ☆☆☆＞☆☆＞☆

Table 3 Characteristics of NTN axle unit seals
Hipack seal

2-lip seal

1-side lip seal

Anti- muddy water properties☆

☆☆

Grease leakage tolerance☆☆☆

Format2-side lip seal

2-side lip seal withmagnetic encoder

Performance

Cross-section

TorqueAnti-corrosion properties of seal land
Airtightness

☆☆☆
☆☆☆

☆☆☆

☆☆☆

☆☆

☆

☆☆☆

☆☆☆

☆☆☆

Superiority : ☆☆☆＞☆☆＞☆

-48-

*09E_03 18/09/05 18:51 ページ 4

History of Axle Unit Bearings for Automobile

against muddy water by adding side lips, as well as
significant anti-corrosion properties of the seal land byadding stainless steel slingers. Additionally, itachieved low-torque properties responding to theaforementioned low-torque requirement, by optimizing
seal lip sliding surfaces and developing grease
dedicated for seal lips. Furthermore, NTN has
extended volume production of value-added seals by
integrating magnetic encoders, vulcanizing magnetic
rubber on the side of the slinger.

Hub bearing (H/B)

Constant velocity joint (CVJ)

New joint method

Bolt for tightening

3.4 Next generation hub joint
Fig. 2 Structure of PCS-H/J

After the development of GEN3 for volume
production, NTN completed development of the next
generation hub bearings, GEN4, integrating constantvelocity joints (hereafter "CVJ"). This technology has
not been adopted since it requires significant
modification to the vehicle assembly lines at the
automanufacturers.
Therefore, NTN developed a new joint method for
CVJ and hub bearings which can be assembled
without changing the assembly lines at the automanufacturers and has achieved a significant
reduction in weight. The following is the introduction ofPress Connect Spline Hub Joint (PCS-H/J) (Fig. 2).
Conventionally, CVJ and hub bearings are engaged
with a spline and tightened with a nut. The spline teeth
are generally designed for interference fit with the

Hub ring
Hollow inside45

Nut : M22×1.25

L2

φ80

L1

100

45

Ｘ

Ｘ

Ｘ

Ｘ

Bolt: M12 x 1.25
100

35

Shortened CVJ stem length

Tooth contact condition(X - X cross section)

Tooth contact condition(X - X cross section)
H/B

Spline boundary

W1
W2

CVJ

Gap H/B

W2
W1

Gap

W1 ＜ W2

W1 ＞ W2
Tooth flank clearance

12% weight
reduction

φ80

100

helix angle to eliminate backlash, which requires long
spline fit length (L1 in Fig. 3 (a)). The new press
connect fit method finishes forming the spline bytightening a bolt, which results in a tighter interference
fit than the CVJ stem spline on the inner diameter ofthe hub bearings. This enables the torque to be
applied to the entire spline area, resulting in significant
reduction of spline fit length (L2 of Fig. 3 (b)).
Adopting the press connect method, PCS-H/J
achieves approx. 65% reduction in CVJ stem length,
12% reduction in weight (max) and no spline fit
backlash 3).

No tooth flank clearance

Tooth flank clearancea) Conventional structure

CVJb) PCS-H/J

Fig. 3 Example of The Application and Spline Cross Section of PCS-H/J-49-

Interference

*09E_03 18/09/05 18:51 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

4. Summary
NTN has been leading the evolution of axle unit
bearings for approximately 40 years, and throughexpansion of market share with the merger of NTNSNR in 2008, it has acquired the top share today.
This paper reviewed the history of axle unit bearingson the occasion of the 100th anniversary of NTN. Thisdevelopment is the result of efforts of the forerunners
which we are very proud of, and we strive to continue
this spirit of development while continuing to achieve
vehicles with higher functionality and better comfort,
setting our eyes on the next 100 years.

References
1) Eiji Funahashi, NTN Technical Review No. 70, 52-57,(2002).
2) Masao Kato, Hiroshi Morishita, Kenji Hibi, Kunishige
Ototake, NTN Bearing Engineer, NTN Technical
Review No. 52, 40-53, (1986).
3) Takayuki Norimatsu, Tsutomu Nagata, NTN Technical
Review No. 81, 58-63, (2013)

Photo of author

Daisuke NAKA
Automotive Unit Engineering Dept.,
Automotive Business
Headquarters-50-*10E_03 18/09/05 18:52 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]ULTAGE※1 Tapered Roller Bearing
for Automotive Application

Yasuhito FUJIKAKE*
Takanori ISHIKAWA*
Susumu MIYAIRI*NTN has developed the “ULTAGE Tapered Roller Bearing for Automotive
Application” that delivers the world's highest standard of high-load capacity andhigh-speed rotational performance with optimal internal design of bearing.
Tapered roller bearings for automobiles are used in transmission components such as transmissions anddifferentials, and need to have a high-load capacity to operate conditions that are becoming increasingly harsh inrecent years, including the greater loads due to higher power output of automobiles, as well as greater unbalanced
loads caused by the lower rigidity due to lightweight housings. The tapered roller bearings also need to provide low
torque required for lower fuel consumption and high-efficiency and high-speed rotational performance in low
temperature. The developed “ULTAGE Tapered Roller Bearing for Automotive Application” is a new, compact
series lineup that has been modified with optimal design technology for the shape of tapered rollers that maximize
the rolling operating life as used for the Large Size Tapered Roller Bearing. This design maximizes the potential
operating life with minimize of contact surface pressure between the rolling element (rollers) and raceway (innerand outer ring), even when there are high loads or unbalanced loads. It is introduced design and performance of“ULTAGE Tapered Roller Bearing for Automotive Application” contributing to fuel saving.

1. Introduction
As global warming and extreme weather associatedwith the increase of CO2 emissions are raised associal issues, initiatives for achieving a low carbon
society 1) has become an urgent issue. In line with thissocial environment, vehicle fuel efficiency standards
and regulations for CO2 emissions are becoming
stricter every year in many countries. 2), This forces
vehicle units such as transmissions and differential
gears to become smaller and lighter, which increases
the need for smaller bearings. As a result, long-life
bearings are required, even in more severe operating
conditions, such as increased loading on bearings andincreased unbalanced load due to the reduction of
rigidity in weight-reduced housings.
In response to these requirements, NTN developed
crowning optimization technology to maximize therolling fatigue life with high robustness, by minimizing
the rolling contact stress of roller bearings andapplying a special crowning shape (a shape where
the-diameter is gradually reduced by a few
micrometers toward the end) that suppresses
excessive pressure at the end of the contact area
(edge load) of the rolling elements 3).
NTN announced "Large ULTAGE Tapered Roller
Bearing for Industrial Machines" which applies thisdesign technology in 2014 4), and started volume
production of a series of standard products withbearing outer diameter of 280 mm or more.
NTN has now developed "ULTAGE Tapered Roller
Bearing for Automotive Applications" which applies the
improved optimization design technology thatmaximizes the rolling fatigue life to small tapered roller
bearings (with bearing outer diameters of 150 mm orless). In this paper, we will introduce the structure andcharacteristics of these bearings.

※1 ULTAGE® is the name created from the combination of "ultimate," signifying refinement, and "stage,” signifying
NTN’s intention that this series of products be employed in diverse applications, and is the general name for
NTN’s new generation of bearings that are noted for their industry-leading performance.

*Automotive Bearing Engineering Dept., Automotive Business Headquarters-51-

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NTN TECHNICAL REVIEW No.85（2017）

2. Structure

Large

Increase of temperature is
reduced by optimized shape

Contact stressFig. 1 shows the overall structure of the ULTAGE
Tapered Roller Bearing for Automotive Applications.
As shown in Fig. 1, contact stress is minimized byapplying a special crowning shape to the rollers. As aresult the temperature rise during bearing operationis reduced by optimizing the sliding contact of therollers with the inner ring and cage, in turn allowing
greater permitted rotational speed. Bearing steel forthese applications is adopted which is characterized
by improved cleanliness ,ease of thermal treatment
and global procurement. The specification where theaforementioned internal design optimization andstandard quenching are applied is called "standard
type." NTN also developed the "high functionality type"which combines NTN's proprietary FA thermal
treatment 5), as well, for use under severe lubrication
conditions such as ingress of hard foreign matter.

Small

Raceway axial direction widthFig. 2 Contact stress distribution on raceway

raceway. With ULTAGE Tapered Roller Bearings for
Automotive Applications, bearing operating life isimproved by suppressing excessive pressure at theedge of the contact area (edge load) and minimizing
the overall contact stress distribution by the adoptionof special crowning.

3.1 The mechanism of long operating life throughspecial crowning
Contact stress is
minimized by
optimized roller
shape

In the development of optimized crowning,
minimization of the internal maximum shear stress was
explored based on the basic concept of the rolling
fatigue life calculation that states "the probability ofinternal originated delamination increases when internal
shearing stress becomes large." Conventionally, thecrowning shape is distributed to the inner ring, outerring and rolling contact surface of the rolling elements
due to the restrictions of processing. In that case, roller
fatigue life is reduced when distribution of such shear
stress and contact stress is misaligned due to thedisplacement of crowning settings from the behavior of
the rollers during bearing operation. In contrast, if the
optimized special crowning shape is applied toonly therollers, such shear stress and contact stress areminimized regardless of the behavior of the rollers,
maximizing the potential roller fatigue life of theassociated bearings.

Outer
ring

Cage

Conventional tapered roller bearings 6)

ULTAGE Tapered Roller Bearings
for Automotive Application

Inner ring

RollerFig. 1 Structure of ULTAGE tapered roller bearing
for automotive application

3. Features
The following list shows the characteristics ofULTAGE Tapered Roller Bearings for Automotive
Applications in comparison with conventional tapered
roller bearings 6).
(1) High-load capacity at the world's highest level:
Basic dynamic load rating - 1.3 times(2) Long operating life (compared with the basic rating life):
Standard type - 2.5 times or more
High-functionality type - 3.8 times or more
(3) High speed rotational performance at the world's
highest level:
Permitted rotational speed - approx. 10%
improvement(4) Permitted inclination (magnitude of misalignment):
Permitted inclination - max. 4 times
Fig. 2 shows an example of the calculation of contact
stress distribution at the axial cross section of the

3.2 Special crowning analysis method
A new design method was introduced for the special
crowning shape to minimize contact stress. by an
optimization algorithm applied to a newly proposed
logarithmic function 3) with 3 newly introduced design
parameters, from "misalignment" and "applied load"
calculated from the actual operating conditions. With
this method, special crowning shapes can be quickly,
automatically and easily obtained, which was
traditionally complicated in the past. Fig. 3 shows acase study of running optimization of the special
crowing shape when minimization of the max. contact
stress is set as the objective function. The results from-52-

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ULTAGE Tapered Roller Bearing for Automotive Application

400

8
7

5

10

20

zm µm

30

40

50

5

200

0

4
3
0

300

100

Optimum
point

6

4

3

L10h=469h

500

10% life hMaximum contact stress GPa<Design parameter>
・K1: Curvature of crowning
・K2: Ratio of crowning width(Fixed in this optimization)
・zm: Amount of drop at the edge of crowning ※2(※2: Amount of reduction of radius when the
diameter of roller is reduced to the edge inmicrometers)

2

1

0

L10h=29.4h
Conventional
tapered roller bearing

ULTAGE
Tapered Roller Bearings
for Automotive Application[Standard type]Fig. 4 Clean oil life time test under high misalignment condition

K1

Type" has 469h of L10h, which is approx. 16 times theconventional tapered roller bearings and 6.5 times the
JIS calculated life. This is due to the optimization of
the contact stress distribution and adoption of special
crowning which eliminated edge loading.
When, for example, "Harris' Equation" 7) is applied
to these ULTAGE bearings with the long-life effectcharacteristics, even when misalignment increases,
the rolling fatigue life under high misalignment(0.002rad or more) does not exceed the permissible
contact stress rating and indicates 2.5 times life ormore compared to conventional tapered roller
bearings. ULTAGE Tapered Roller Bearings for
Automotive Applications adopts this theoretical life
comparison as the basic rated life comparison. When
this is converted to an increase of the basic dynamic
load capacity, it is equivalent to 1.3 times.

Fig. 3 Optimize by case-study of special crowning shapedifferent runs for exploring optimized solutions byseveral combinations of design parameters provide
the optimum point to minimize the max. contact stress,
as shown in Fig. 3, as well as the tolerance setting
considering the range for minimizing the impact of thecontact stress.

4. Bearing performance
4.1 Clean oil lubrication life test under highly
misaligned conditions
In order to determine the life level of ULTAGE
Tapered Roller Bearing for Automotive Applications, aclean oil life test was conducted under highly
misaligned conditions (0.002 rad), which is considered
to be the maximum level of misalignment under theoperating conditions of vehicles.

4.2 Life testing with contamination in the lubricant
Life tests under conditions of hard foreign objects inthe lubricant were conducted for NTN's conventional
long life ECO-top tapered roller bearings (long-life
type where carbonitriding treatment is applied to
carburized steel) and ULTAGE Tapered Roller
Bearings for Automotive Applications .
<Test conditions>●Bearing material heat treatment(1) ULTAGE: FA thermal treatment on bearing steel(2) ECO-Top: Carbonitriding treatment on
carburized steel●Load: 40% of basic dynamic load rating●Misalignment: None
●Rotational speed: 3,000min-1●Lubrication: ISO VG56 turbine oil●Foreign object condition: Hard gas-atomized powder
0.2g/L foreign object under NTN specification●Calculated operating life: 113.8h(a2 factor not considered)<Test conditions>●Bearing material heat treatment: SUJ2 standard
heat treatment●Load: 26% of basic dynamic load rating●Misalignment: 0.002rad●Rotational speed: 4,000min-1●Lubrication: Equivalent to ISO VG100 gear oil●JIS calculated operating life: 73h (a2 factor (lifeadjustment factor for special bearing properties)
not considered)Fig. 4 shows the test results. The result shows thatthe conventional tapered roller bearings do not satisfy
the JIS calculated operating life with 29.4h of 10% life
(L10h), as the edge originated surface damage
progresses under this test condition where edge load
is applied. On the other hand, ULTAGE Tapered
Roller Bearing for Automotive Application "Standard-53-

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NTN TECHNICAL REVIEW No.85（2017）

Outer ring temperature ˚C

120

25

Stable temperature range

20

80
60

10,100min -1

40

15

11,110min-1[Outer ring temperature]
ULTAGE Tapered Roller Bearings for Automotive Application 5[Outer ring temperature]
Conventional tapered roller bearings

20

Test rotational speed

0

2

4

Time h

6

8

10

0

Fig. 6 Temperature rise test
Table 1 Test results in stable region temperature summary
Rotational speed (min-1)

Using the calculated foreign object factor 0.0612, a2
factor of ULTAGE Tapered Roller Bearings for
Automotive Application [high functionality type] iscalculated.

ULTAGE Tapered Roller Bearings
for Automotive Applications
Conventional tapered
roller bearings➢32.8 (test result L10h / [113.8 (calculated
operating life) ×2.5 (ULTAGE life ratio) x 0.0612(foreign object factor)]≒1.9

10,10011,110

91℃

94.3℃

95.2℃

102℃

Bearings for Automotive Applications showed 94.3˚C
as the bearing average temperature in the stabletemperature range at 11,110min-1, which is 1.1 times
the permitted rotational speed, indicating a low rise intemperature compared with conventional tapered
roller bearings. Therefore, it is possible to improve thepermitted rotational speed of ULTAGE Tapered Roller
Bearings for Automotive Applications by 10%
compared to conventional products.

From the above result, a2=1.5 is adopted as aconservative value for the a2 factor of ULTAGE
Tapered Roller Bearings for Automotive Applications[high functionality type].

40

L10h=32.8h<Test conditions>●Load: 9% of basic dynamic load rating●Lubrication: ISO VG32 turbine oil

30

10% life h100

0➢19.5 (test result L10h) / [113.8 (calculated
operating life) ×2.8 (a2 factor)]=0.0612

20

Stable temperature range

Test rotational speed ×103 min-1

Fig. 5 shows the test results. Compared to theconventional long-life type ECO-Top tapered roller
bearings' 10% life (L10h) L10h=19.5h, ULTAGE Tapered
Roller Bearings for Automotive Application [highfunctionality type] exhibited L10h=32.8h, approx. 1.7
times longer life, due to nitration of FA heat treatment
and improvement of roller fatigue strength thoughgrain refinement.
Here, the a2 factor of ULTAGE Tapered Roller
Bearings for Automotive Applications [high functionality
type] is considered. With the life test result of ECO-Top
tapered roller bearings as the baseline, foreign object
factors of such a test is assumed.

L10h=19.5h

5. Compact/lightweight design
100

ECO-Toptapered roller bearings

Since ULTAGE Tapered Roller Bearings for
Automotive Applications can obtain long operating life
by minimizing contact stress, it is possible to achieve
a compact/lightweight design of bearings under thesame life conditions. In this section, an example of asmall/lightweight design study is shown.
The following is an example of a small/lightweight
design when ULTAGE specifications are applied tothe catalog standard type tapered roller bearings
32008X.
<Study conditions>●Load condition:
Maximum load during driving conditions(equivalent to 1st gear full torque)●Determination of life:
Calculated by JIS calculated operating life
using dynamic load ratings

ULTAGE
Tapered Roller Bearings
for Automotive Application[High-functionality type]Fig. 5 Life time test under contaminated lubrication condition

4.3 Rotational speed verification test.
A temperature rise test was conducted under thepermitted rotational speed.
Fig. 6 shows the result of the temperature rise test
and Table 1 shows the summary of the test results.
The conventional tapered roller bearings showed
95.2˚C as the bearing average temperature in thestable temperature range at 10,100min-1, which is thepermitted rotational speed. ULTAGE Tapered Roller-54-*10E_03 18/09/05 18:52 ページ 5

ULTAGE Tapered Roller Bearing for Automotive Application

Table 2 Study example of downsizing and lightweight of applying the ULTAGE tapered roller bearing for automotive application
Specification
Model number

Bearing size
Bearing weight (compared to conventional product)
Basic dynamic load rating Cr (N)Result of contact stress determination(equivalent to 1st full torque load)

Life ratio compared to conventional standard

Conventional
tapered roller bearings
32008XULTAGE Tapered Roller Bearings
for Automotive Application[High-functionality type]

φ30.162×φ62×16.002
0.226kg（17% reduction）

φ25×φ52×19.25
0.181kg（34% reduction）

Satisfied the standard[No edge load occurred]

Satisfied the standard[No edge load occurred]

17119/17244

φ40×φ68×19
0.273kg

Conventional:：50,000N

32205R

51,500N（Conventional:：39,000N） 50,000N（Conventional:：38,000N）

Satisfied the standard[However, edge load occurred]
19

ULTAGE Tapered Roller Bearings
for Automotive Application[Standard type]

1

1.10

16.002

1.90

19.25

●Determination of contact stress:
Satisfy the NTN standard●Selection of small/lightweight model number:
The most compact model number is selectedfrom the standard catalog series
Table 2 shows the study results. The ULTAGE
Tapered Roller Bearings for Automotive Applications[standard type] can achieve a 17% reduction in weight
while the ULTAGE Tapered Roller Bearings for
Automotive Application [high functionality type] canachieve a 34% reduction in weight.
In addition, reduced weight was also achieved inother model numbers with different sizes from theabove, as follows:●ULTAGE for Automotive Applications[standard type]: 15% - 30%●ULTAGE for Automotive Applications[high functionality type]: 30% - 45%

ø52

ø25

ø62

ø30.132

ø68

ø40

Cross section diagram

References
1) Ministry of Environment HP, A Proposal for Low
Carbon Energy for Achieving Low Carbon Society,http://www.env.go.jp/earth/ondanka/rmsuggestion.html
2) Ministry of Environment HP, Global Trend ofEnvironmental Tax on Vehicles,
http://www.env.go.jp/policy/tax/misc_jokyo.html
3) Hiroki Fujiwara, Tatsuo Kawase, Logarithmic Profile ofRollers in Roller Bearing and Optimization of theProfile, NTN TECHNICAL REVIEW, No.75 (2007),
140-148.
4) NTN Large Tapered Roller Bearings ULTAGE Metric
Series, Catalog, CAT. No.3035/J.
5) Chikara Ooki, Kikuo Maeda, Hirokazu Nakashima,
Improving Rolling Contact Fatigue Life of Bearing
SteelsThrough Grain Refinement, NTN TECHNICALREVIEW, No.71 (2003), 2-7.
6) NTN, Roller Bearings, Overview Catalog, CAT. No.
2202 - VII/J.
7) Harris, T. A., Rolling Bearing Analysis, Forth Edition,(2000), pp.728-729, John Wiley &Sons.

6. Conclusion
We believe that the "ULTAGE Tapered Roller
Bearing for Automotive Applications," which
contributes to a reduced burden on the environment
and fuel efficiency, is a new product that will be
installed on vehicles worldwide as the standard
product, and contribute to a low-carbon society.
Furthermore, NTN also developed new processing
technology in line with the new design technology,
establishing new technology for "Monozukuri."
NTN will continue to advance technologicalinnovation of tapered roller bearings for automotive
applications and contribute to the international
community through development of new products.

Photo of authors

Yasuhito FUJIKAKE

Takanori ISHIKAWA

Susumu MIYAIRI

Automotive Bearing
Engineering Dept.,
Automotive Business
Headquarters

Automotive Bearing
Engineering Dept.,
Automotive Business
Headquarters

Automotive Bearing
Engineering Dept.,
Automotive Business
Headquarters-55-

*11E_03 18/09/05 18:53 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]High Speed Rotation Ball Bearing for Pulley

Hayato KAWAGUCHI*
Shouhei FUKAMA*
Masaharu INOUE**
Layout of auxiliary belt becomes complicated by engine downsizing,and high speed rotation performance of pulley bearings accompanying
miniaturization of pulley diameter is required.
NTN has developed “High Speed Rotation Ball Bearing for Pulley”
capable of handling 20,000min-1 at outer ring rotation (by #6203).
This article introduces the feature and performance of the High Speed
Rotation Ball Bearing for Pulley.

1. Introduction

2. Characteristics

Due to a recent increase of small engines and ISGmounted vehicles focused on downsizing technology,
layout of engine auxiliary system has becomecomplex with greater restrictions on placement ofauxiliary belts and bearings for pulleys. Degree of
freedom for placement layout increases by reducing
pulley diameters; however, that forces the bearings forpulleys to rotate at higher speeds.
In addition, requirements for improving comfort andreliability of automobiles are demanding bearings forpulleys to acquire higher functionality such asmeasures against hooting noises when running cold
and protection against brittle flaking, as well as low
torque properties 1).
High Speed Rotation Ball Bearings for Pulleys arecapable of enduring up to 20,000 rotations (outerwheel rotation) per minute by suppressing a rise inheat by optimizing the cage, seal, inner/outer rings,
balls and grease.
At the same time, they achieved retaining andimproving measures against hooting noises whenrunning cold, protection against brittle flaking and low
torque properties.
This developed product is introduced in thefollowing:

The following are the characteristics of the High
Speed Rotation Ball Bearings for Pulleys:
High speed:
permitted rotational speed of 20,000min-1(in rotation with outer ring size of 6203)
Hooting noise when running cold:
no noise at -40˚C
Protection against brittle flaking:equivalent to the conventional product(under NTN test conditions)
Running torque:
10% reduction(compared to NTN conventional product)
Durability against high temperature:equivalent to the conventional product(under NTN test conditions)

3. Structure and performance
3.1 High speed
Fig. 1 shows issues associated with high speed
rotation of bearings for pulleys.
In high speed rotation, cages can deform due tocentrifugal force causing friction with steel balls andouter rings which produces heat. In addition, as thebearings for pulleys are used for outer ring rotation,**Automotive Bearing Engineering Dept., Automotive Business Headquarters**Application Engineering Dept., Automotive Business Headquarters-56-

*11E_03 18/09/05 18:53 ページ 2

High Speed Rotation Ball Bearing for Pulley

Deformationof cage

Cage deforms due to centrifugal force,
causing friction with steel balls and outer rings
which produces heat

Deformationof seal lip

Seal lips deform due to centrifugal force andseal reaction force changes⇒heat generationor sealing property loss

Shortage ofgrease supply

Shortage of grease supply due to centrifugal
force causes heat generation, seizure andreduction of bearing life

The rotation speed conditions for the conventional
resin cages were 15,000min-1, and were set to
20,000min-1 for the High Speed Rotation Ball
Bearings for Pulleys. We confirmed that the
deformation from the centrifugal force of the resin
cage for high-speed rotation, which underwent severer
rotational speed conditions, was reduced by approx.
30% compared to the conventional product at theedges A and B (Fig. 4) of the cage where the friction
with the outer ring and steel ball is suspected.

Rolling resistance increases due to highIncrease inrolling resistance speed rotation, causing heat generation,
seizure and reduction of bearing life

Outer ringThinning material
between pockets

Steel ball
Cage

Seal

Deformation
by centrifugal
force

Interference,heat generation

Inner ring

Fig. 1 Issues of bearing at high speed rotation

Thicker pocket
bottomPolyamid II(high rigidity resin material)

Polyamid I

centrifugal force is also applied to the seal lips,
causing heating or damage to seal properties due to achange of seal reaction force. Furthermore, seizure or
bearing life reduction may be caused by shortage ofgrease supply and increased rolling friction.
Due to these issues, the permitted rotational speedof bearings for pulley was conventionally around
15,000min-1.

(a) Conventional(b) High speed rotation
resin cageresin cage
Fig. 2 Cage shape (Comparison of current and developed)

Maximum
stressMaximum
stress

3.2. Design objectives of developed productThe cage, seal, inner/outer rings and steel balls of
the High Speed Rotation Ball Bearings for Pulleys(hereafter "developed product") are made to endure
high speed rotation.

15,000min-1

20,000min-1(a) Conventional(b) High speed rotation
resin cageresin cage
Fig. 3 Cage centrifugal analysis(Comparison of current and developed)

3.2.1 Cage
For the shape of cage of the developed product,resin cage developed for Grease Lubrication TypeHigh Speed Deep Groove Ball Bearings for EVs and
HEVs 2) was adopted.
Fig. 2 shows the comparison with the conventional
resin cages.
The following 3 points were improved to reduce
deformation during high-speed rotation.
(1) Thicker pocket bottom→ improvement of cage rigidity(2) Reduction of material between cage pockets→ reduction of centrifugal force(3) Adoption of high strength material→ improvement of cage rigidity
The results of centrifugal analysis of the cages areshown in Fig. 3 and 4.

Amount of deformation

30% reduction of deformation

B
A
Location of deformation

A

B

Conventional productDeveloped productFig. 4 Deformation amount of current and developed-57-

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NTN TECHNICAL REVIEW No.85（2017）

3.2.2 Seal

2.5
2

Seal reaction force N

Fig. 5 shows an overview of NTN's standard baring
seal for pulley.

Outer ring

1.5
1
0.5

Steel ball0

Lip behavior
due toLarge variation of centrifugal
reaction force in force
the high speed
rotation range

Interference max
Interference nom
Interference min
0

5,000

10,00020,00015,000

Rotational speed min-1(1) Grease lip

Fig. 6 Seal centrifugal force analysis (Current)
2.5(2) Main lip

Seal reaction force N(3) Dust lip
Inner ring

Fig. 5 NTN standard bearing seal for pulley

The standard bearing seal for pulley consists of 3 lips.

(1) Grease lip→ Penetration of grease to the area around themain lip is reduced by the labyrinth structurewith the inner seal groove to prevent greaseleakage

2

Interference max
Interference nom
Interference min
Small variation ofreaction force inthe high speed
rotation range

1
0.5
0

0

5,000

10,00015,000

Lip behavior
due tocentrifugal
force

20,000

Rotational speed min-1

Fig. 7 Seal centrifugal force analysis (Developed)(2) Main lip→ Prevention of grease leakage and penetration ofwater/dust, as well as low torque are ensured,maintaining interference even with centrifugal
force due to rotation of the outer ring

variance of seal reaction force is small, which reduces
heat generation at high rotational speed range evenwith different initial seal interference, as the center ofgravity of seal lips is optimized.
Seal interference and torque (calculated value) of
the conventional and developed products are shownin Fig. 8 and 9.
The seal interference of the developed product isincreased to improve the seal lip followability. On theother hand, lip rigidity is reduced, which achieved low
torque and low heat generation by optimizing the
thickness of the waist section of the seal lip.

(3) Dust lip→ Penetration of foreign objects from outside is
reduced by the labyrinth structure with the innerseal groove
Even when penetration occurs, they can beejected by the tapered shape of the dust lip
For the shape of the developed seal, the center ofgravity of the seal lip and thickness of the waist
section of the lip are optimized to minimize variation ofreaction force in the high-speed rotation range for
reducing heat and to keep low torque. The result ofanalysis of the seal reaction force is shown in Fig. 6
and 7.
With the conventional products, seal reaction force
tends to decrease when rotational speed increases
regardless of the initial seal interference, and heatgeneration due to seal interference becomes unstableeven at a high rotational speed range around
20,000min-1, because of large variance of seal
reaction force.
On the other hand, with the developed products,

Conventional productApprox. 40%
increase

Conventional
product

Developed
product

Developed productFig. 8 Seal calculation interference(Comparison of current and developed)-58-

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High Speed Rotation Ball Bearing for Pulley

Operating condition¡Low temperature¡Small radial load
¡Small belt winding angle

Conventional productDeveloped productSpecification of bearings¡Small gap¡Grease hardening

Axial vibration/self-excited
vibration of steel ballApprox. 60%
decrease

Axialvibration
vibration/self-excitedAxialof outer ring,vibrationof steelassemblybalresonanceof pulley
Conventional
product

Developed
product

Generation of air compressional wave

Fig. 9 Seal calculation torque(Comparison of current and developed)

Generation of abnormal noise(HOOT noise) in a cold condition

Fig. 10 Generation mechanism of hoot noise

3.2.3 Bearing internal specification
Bearing internal specification of the developed
product was set to maintain load carrying capacity
compared to the conventional product, and to
decrease PCD and reduce heat generation by revisingsteel ball size.
Table 1 shows the bearing internal specification.

Table 2 Grease characteristics comparison
Item
Base oilThickener

Base oil fluid point (˚C)
Worked penetration

Table 1 Internal specification comparison of current and developed
Specification

Conventional
bearings

Developed
bearings

Key dimensions (mm)* inner diameter x outer diameter x width

φ17×φ40×12←

Size and number of steel balls

9/32in × 7

17/64in × 8

Basic dynamic load rating (N)Basic static load rating (N)

9,600
4,600

Conventional Conventional Developed
grease (1)grease (2)grease
Ester

Ester + PAO
Urea

Ester + PAO

Urea

−42.5

−42.5

270

280

Urea

−50 or less286

3.3.2 Protection against brittle flaking
Brittle flaking is a singular flaking including
microstructural change which is observed in the
bearings used for accessories of automotive engines
and occasionally in the bearings for pulleys, as well.
Fig. 11 shows the presumed mechanism of thebrittle flaking 1) 3).
The developed product suppresses slipping of steel
balls and penetration of hydrogen by adjusting grease
additives and thermal treatment of inner/outer rings toensure protection against brittle flaking equivalent tothe conventional products.

9,500
4,700

3.3 Other requirements of bearings for pulleys
and their measures
3.3.1 Hooting noise when running cold
Hooting noise when running cold is a high pitch tone,
like a whistle generated when running in low
temperatures, known to be generated for a few seconds
from the bearings for pulleys when an engine starts.
Fig. 10 shows the presumed mechanism of thehooting noise. Since a decrease of grease
consistency in low temperatures is assumed to be thecause of the hooting noise, newly developed grease
with improved low temperature fluidity was adopted forthe developed product.
Table 2 shows a comparison of the greasecharacteristics for the conventional product anddeveloped product.
The developed grease lowered the fluid point in low
temperatures with softer consistency. This achieved
100% pass rate of hooting noise (no hooting noise)when running cold at -40˚C from 70% of theconventional products under the NTN measurement
conditions.

・Load, vibration
・Abrupt acceleration/deceleration
Causes・Temperature
・Grease・Gap

Sliding ofrolling
element

Breakage of oil film,
wear of raceway
Exposure of new surface
Generation of hydrogenfrom grease

LubricantRollingsurface

Exposure of new surface
Generation of hydrogen from grease
H

H

H

Tribochemical reaction

Penetration of hydrogen into steel

HH H

Crack propagation into raceway

Fig. 11 Generation mechanism of brittle flaking-59-

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NTN TECHNICAL REVIEW No.85（2017）

3.4. Evaluation results of developed product3.4.1 Test of elevation in temperature

3.4.2 High speed durability test
Durability at the rotational speed of 20,000min-1 was
confirmed. The test conditions are shown in Table 4
and the appearance of the test product after the test is
shown in Fig. 14,.
The durability equivalent to the conventional productwas confirmed after 400 hours of operating time
without flaking, seizure, damage or abnormal noise.

Elevation of temperature due to an increase inrotational speed was confirmed in the test. The test
conditions are shown in Table 3, appearance of testeris shown in Fig. 12 and the test results are shown in
Fig. 13, respectively.
Elevation of temperature of the developed productat 20,000min-1 was less than that of the conventional
product at 15,000min-1. The developed productachieved a permitted rotational speed of 20,000min-1.

Table 4 Test condition

Table 3 Test condition
Bearing size

6203

Radial load (N)Belt winding angle (˚)

960Atmosphere temperature (˚C)

Bearing size

6203

Radial load (N)Belt winding angle (˚)

960

180

Pulley rotational speed (min-1)

20,000Atmosphere temperature (˚C)

80

Operating time (h)

180

400

100
Inner ring

Outer ring

Idler pulley

Seal

Steel ballcage
Test sample

Driving pulleyFig. 14 Appearance of after test sample

Fig. 12 Temperature rising tester

Temperature of bearing inner ring ˚C

140

3.4.3 Running torque
Torque reduction effects were confirmed in the lowtemperature torque test. The test conditions areshown in Table 5 and the test results in Fig. 15.
The low temperature torque of the developed
product was confirmed to be approx. 15% lower thanthe conventional product.

Permissible rotational speed of conventional product: 15,000min-1

135
130
125

Table 5 Test condition

120
115
110

Conventional product

105
100

Developed product

0

5,000

10,00015,00020,00025,000

Pulley rotational speed (min-1)

Fig. 13 Temperature rising test result-60-

Bearing size

6203

Radial load (N)No-load(only the weight of test jig)

Inner ringrotational speed(min-1)

0→12,000(60s sweep)

Outer ring temperature
(˚C)

−40

*11E_03 18/09/05 18:53 ページ 6

High Speed Rotation Ball Bearing for Pulley

References

Approx. 15%
reduction

10.00

1) Takayuki Kawamura, Hidenobu Mikami, Developmentof Long Life Grease ‘NA103A’ for Automotive
Components, NTN TECHNICAL REVIEW, No. 75,(2007).
2) Masahiko Satoda, Goro Nakao, Grease LubricatedHigh-speed Deep Groove Ball Bearing for EV and HEV
Motor, NTEN TECHNICAL REVIEW No. 83 (2015).
3) Seiichi Nozaki, Koushirou Fujimoto, Kenji Tamada,
Brittle Flaking on Bearings for Electrical Instruments
and Auxiliary Devices and Life Extension of these
Bearings NTN TECHNICAL REVIEW No.61 (1992).

Conventional productDeveloped product

Torque N・cm

7.50

5.00

2.50

0.00

Conventional
product

Developed
product

Fig. 15 Torque measurement results at low temperature

4. Conclusion
In this paper, we have introduced the High Speed
Rotation Ball Bearings for Pulleys. This developed
product achieved outer ring rotational speed of
20,000min-1 with the size of 6203, and met therequirements of bearings for pulleys (measuresagainst hooting noises when running cold, protection
against brittle flaking and low torque properties),
simultaneously, by optimizing design of the cage, seal,
grease and bearing internal specifications.
The developed product is expected to contribute todownsizing and fuel efficiency of engines and will be
actively marketed. We are poised to promote
development of new products to meet therequirements of ongoing improvement of functionality.

Photo of authors

Hayato KAWAGUCHI

Shouhei FUKAMA

Masaharu INOUE

Automotive Bearing
Engineering Dept.,
Automotive Business
Headquarters

Automotive Bearing
Engineering Dept.,
Automotive Business
Headquarters

Application
Engineering Dept.,
Automotive Business
Headquarters-61-

*12E_03 18/09/05 18:54 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]Ultra Low Friction Sealed Ball Bearing
for Transmission

Katsuaki SASAKI*
Takahiro WAKUDA*
Tomohiro SUGAI**
Along with fuel-saving of automobiles, demands for lightweight, compact andlow torque are increasing. In this report, we will introduce characteristics andperformance of developed products with both low torque and long life of sealedball bearing for transmission to utilize tribology technology.

1. Introduction

3. Structure and performance

In order to mitigate life reduction under severe
bearing operating conditions, where hard foreign
objects such as gear wear particles are suspended intransmission lubricating oil, we have been improving
the tolerance of our bearings for foreign objects byadopting contact seals and applying special heat
treatment to special bearing material (open product) inorder to mitigate life reduction under severe bearing
operating conditions. However, bearings with contact
seals work against the trend of increasing fuel savings 1),
since they have increased bearing rotating torque dueto the seal sliding friction. In addition, special heat
treatment has a disadvantage of increased cost. NTN
has developed a new mechanism for ball bearings
with seals to achieve a significant reduction in runningtorque, while maintaining life equivalent to thebearings with special heat treatment, by leveraging
tribology technology. The following is a description ofsuch bearings.

3.1. Design methods of developed productOptimization of the following was the focus of
reducing friction of contact seals:
・Seal contact pressure
・Surface roughness
・Rubber hardness
In addition to the above, we have focused on a seal
shape with which the wedge film effect increases.
With this change, friction of the seal lip contact of thedeveloped product during t rotation was in thehydrodynamic lubrication range in the Stribeck curve(Fig. 1), as opposed to the case of the conventional
contact seal, where the friction of the seal lip contact
usually stays in the boundary/partial film lubrication.
This allows a drastic reduction of torque.

Mixedlubrication

Fluid
lubrication

Friction coefficient

Boundary
lubrication

2. Characteristics
The following are the characteristics of thedeveloped product:
・80% reduction of running torque (compared tobearings with contact seals)
・5 times or more of bearing life (compared to open
products)
・Support of high seal circumferential speed (50m/s
or more)・Prevention of harmful foreign objects from entering

Bearing characteristic number G

Fig. 1 Stribeck curve**Automotive Bearing Engineering Dept., Automotive Business Headquarters**Advanced Technical Research Center-62-

*12E_03 18/09/05 18:54 ページ 2

Ultra Low Friction Sealed Ball Bearing for Transmission

3.2 Objective of seal design

Table 1 Analysis condition

When multiple arc-shaped micro convexes areplaced evenly on the sliding surface of the seal lip(Fig. 2), a wedge film effect develops (Fig. 3) in an oil
lubricated environment, like that of transmissions,which leads to the friction coefficient being in thehydrodynamic lubrication range during rotation.
For the shape of the micro convexes, the optimized
shape drawn from our analysis "Fluid Lubrication
Analysis (Soft EHL Analysis) considering rubber-likeelasticity" (Fig. 4) was adopted. This achieved both
low torque and long operating life.
Fig. 5 shows an example of FEM analysis of thedeveloped product under the conditions in Table 1.
Fig. 6 shows the minimum film thickness obtained
from this analysis. It was verified that the minimum film
thickness in the temperature range of Fig. 6 is in thehydrodynamics lubrication range of the Stribeck curve(Fig. 1).

Rotational speed (min-1)

1,500

Lubricating oil

CVTF

Bearing temperature (˚C)

−40〜120

Fig. 5 Calculation result of oil film pressure distribution

Minimum oil film thickness μm

50
40
30
20
10
0
-40

Cross section ofdeveloped product

-20

0

20

40

60

80

100

120

140

Temperature ˚CFig. 6 Temperature and oil film thickness

Arc-shaped micro convexes(5 locations in the above figure)Fig. 2 Developed seal

3.3. Evaluation of developed productPressure distribution

An evaluation was conducted using test bearings
equivalent to the product with the representativemodel number 6010, which is the support bearing for
CVT vehicles with high market share.

Seal

Oil film

Direction of rotation

3.3.1 Running torque(1) Bearing temperature and running torque

Inner ring

Running torque was measured with varied bearing
temperatures. The test conditions are shown in Table
2 and measurement results in Fig. 7.
The developed product achieved 80% reduction of
torque (compared to the bearing with conventional

Fig. 3 Wedge film effect

Height of
micro convex

R ofmicro convex

Table 2 Test condition
Radial load
Rotational speed (min-1)

Interval between
micro convexes

Lubricating oil

Bearing temperature (˚C)

Fig. 4 Setting of micro convex

-63-

0.05C
1,500
CVTF
35〜120*12E_03 18/09/05 18:54 ページ 3

NTN TECHNICAL REVIEW No.85（2017）

Table 4 Test condition

contact seals) and low torque equivalent to bearings
with non-contact seals.

Radial load

0.05C

Rotational speed (min-1)

500−6,000

Lubricating oil

CVTF

Running torque N・mBearing temperature (˚C)

80

Developed
product

80%
reduction

Running torque N・mConventional
non-contact seal
Conventional
contact seal

0

20

40

60

80

100

120

140

Bearing temperature ˚C60-80%
reduction

Developed
product
Conventional
contact seal

Fig. 7 Bearing temperature and rotation torque
0

1,000

2,000

3,000

4,000

5,000

Rotation speed min(2) Interference and running torque(4) Running torque assuming oil splash by gears
Running torque was measured assuming oil splash
conditions. The test conditions are shown in Table 5
and measurement results in Fig. 10.
The developed product mitigated excessive oilpenetration due to the micro gap effect between the
micro convex shapes, resulting in stable torquetransition. On the other hand, the open productexhibited an increase of torque as oil stirring
resistance increased due to oil splash.

Table 3 Test condition
Radial load
Lubricating oil

Bearing temperature (˚C)

7,000

Fig. 9 Rotation speed and torque

Running torque was measured with variedinterferences. The test conditions are shown in Table
3 and measurement results in Fig. 8.
The developed product exhibited little change intorque, regardless of interference, due to wedge film
effects.

Rotational speed (min-1)

6,000

-1

0.04C
1,500
CVTF
40，80，120

Table 5 Test condition
Axial load
Running torque N・mLubricating oil

Bearing
temperature 40˚C

Bearing temperature (˚C)

Bearing
temperature 80˚C
Bearing
temperature 120˚C

Lower limit

Median

5,000
300ml of turbine oil VG32 was injected
Natural rise in temperature

Oil injection 300ml

Running torque N・m

Non-contact

0.09C

Rotational speed (min-1)

Upper limit

Seal interference mm

Fig. 8 Interference and rotation torque(3) Rotational speed and running torqueDeveloped
product
Open product0

Running torque was measured with varied rotational
speeds. The test conditions are shown in Table 4 andmeasurement results in Fig. 9.
The developed product achieved 60-80% reductionof torque (compared to the bearing with conventional
contact seals).

20

40

60

80 100 120 140 160 180 200 220

Time sFig. 10 Rotational torque under oil splash lubrication-64-

*12E_03 18/09/05 18:54 ページ 4

Ultra Low Friction Sealed Ball Bearing for Transmission

3.3.2 Life/durability test
(1) Life test under contaminated lubrication(2) Verification test under lubrication with alarge amount of different foreign objects

The effect on bearing life under contaminatedlubrication was verified for with the developed product.
The test conditions are shown in Table 6 andmeasurement results in Fig. 11 2) and 12.
The developed product suppressed penetration ofharmful foreign objects into the bearings through themicroconvex effect exhibited. No flaking in any
samples was found, even after suspending the test at
10 times the calculated operating life. Compared withthe open products in terms of L10 life, the developed
product achieved bearing life of 5 times or more. In
addition, no significant rubber wear of the micro convexes
was observed, maintaining low torque properties.

Tolerance against foreign objects was verified underlubrication with irregular foreign objects with different
particle diameters using a vertical type tester. The test
conditions are shown in Table 7 and measurement
results in Fig. 13.
It was verified that the developed product mitigatedpenetration of foreign objects into the bearings due tothe microconvex effect, even under lubrication withharder foreign objects than assumed. In addition, thepenetrated foreign objects were similar in particle
diameter and quantity to those in the bearings after
the life test under contaminated lubrication shown in(1).

Table 6 Test condition

Table 7 Test condition

0.33C

Radial load

Rotational speed (min-1)

2,000

Misalignment

2/1,000radLubricating oil

Bearing temperature (˚C)

CVTF immersion lubrication of shaft center
120

Condition offoreign objects
0.15 g/L

Axial load

0.05C

Lubricating oil
Bearing temperature (˚C)

Turbine oil VG10Natural rise in temperature

Condition offoreign objects
1.0g/L

Steel beads
up to 50μm 40wt%
50 to 100μm 30wt%
100 to 180μm 30wt%

Rotational speed (min-1)

Steel beads
up to 50μm 97wt%
50 to 100μm 3wt%

Cumulative damage probability %6

Operating time (h)
x 20

98

3,000

x 100

Open productDeveloped product

Life test under contaminated lubrication

Filled marks indicate suspended

90
80
70
60
50
40
30
20
10

2

L10
L50
e
1

Open product Developed product

102.0
182.6
3.23

Fig. 13 Appearance of inner ring surface after test

511.0
742.6
3.23

5

10

Life h

50

100

500

1,000

(3) Durability test under high seal circumferential speed
A durability test under high seal circumferential
speed was conducted. The test conditions are shownin Table 8 and measurement results in Fig. 14.
The developed product underwent the test until it
was suspended without any abnormal rise intemperature. In addition, no significant rubber wear of
the micro convexes was observed, maintaining low
torque properties.

Fig. 11 Bearing life under contaminated lubrication

x 20

x 100

Table 8 Test condition
Radial load

Fig. 12 Appearance of inner ring suface after test

Circumferential speed (m/s)
Lubricating oil
Bearing temperature (˚C)
Operating time (h)

-65-

0.05C
50
CVTF 7˚C × 100ml
Forced oil supply,
immersion lubrication of shaft center
Natural rise in temperature30

*12E_03 18/09/05 18:54 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

100
80

Bearing
temperature

60
40

Oil
temperature

20

Atmospheretemperature0

Axial load

0.05C

Lubricating oil

Turbine oil VG10

Operating time (s)Measured time until 100ml of oil flow went throughRotational speed (min-1)

0

5

10

15

20

Time h

25

30

35

40

Fig. 14 Seal high peripheral speed endurance(4) Durability test with sudden acceleration/
deceleration under lubrication
A durability test with sudden acceleration/deceleration
under lubrication was conducted. Table 9 shows thetest conditions.
The developed product underwent the test until it
was suspended without any abnormal rise intemperature or significant wear of micro convexes,
maintaining low torque properties. It was also verified
by soft EHL analysis that an oil film was formed
between the seal and inner ring at around 30-50rpm,
entering the hydrodynamic lubrication range.

Lubricating oil
Bearing temperature (˚C)
Operating time (h)8 times or moreof oil flow rate

Conventional
contact seal

Fig. 15 Oil through time

4. Conclusion
In this paper, we have introduced the technology of
Ultra-low Friction Sealed Ball Bearings fortransmissions. This developed product achieves highfunctionality and can be produced without newinvestment in machines or equipment. We plan toactively market this as the main product of NTN's ballbearings for transmissions.

0.05C
Alternately between 0 and 50
2s rising, 2s falling

CVTF 70˚C × 100ml
Forced oil supply,
immersion lubrication of shaft center
Natural rise in temperature

References

2.51) Ministry of Environment HP, Global Trend ofEnvironmental Tax on Vehicles,
http://www.env.go.jp/policy/tax/misc_jokyo.html
2) Takumi Fujita, Strategy of Rolling Contact Fatigue Life
Testing and Interpretation of Life Data, NTN
TECHNICAL REVIEW No. 84 (2016)

3.3.3 Oil flow rate
The oil flow rate of lubricating oil through thebearing was measured. The test conditions are shownin Table 10 and measurement results in Fig. 15.
It was verified that the developed product had
approx. 8 times more flow rate than the conventional
contact seal due to the micro gaps between micro
convexes of the seal lip.
With these properties, it can achieve an appropriate
supply of lubricating oil to the bearings, even with poor
lubrication.

Natural rise in temperature

Developed
product

Table 9 Test condition
Radial load
Circumferential speed
(m/s)

5,000

Bearing temperature (˚C)

Time 100 ml of oil goes through s

Temperature ˚C

Table 10 Test condition

Operationsuspended120

Photo of authors

Katsuaki SASAKI

Takahiro WAKUDA

Tomohiro SUGAI

Automotive Bearing
Engineering Dept.,
Automotive Business
Headquarters

Automotive Bearing
Engineering Dept.,
Automotive Business
Headquarters

Advanced TechnicalResearch Center-66-

*13E_03 18/09/05 18:55 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]Low Friction Hub Bearing

Makoto SEKI*

The fuel efficiency regulations has been strengthening, therefore thegood fuel efficiency is one of the important requirement from the field.
Based on this background, NTN has been developing the low friction hub
bearing continuously.
The hub bearing applicable to such around 50% low friction requirement
is introduced in this report.

1. Introduction

Outer seal
Hub bolt

Recentinitiatives to promote hybrid and electricvehicles over conventional vehicles, which use
engines as their source of power, are being actively
pursued. Hybrid vehicles combine engines andelectric motors to power the vehicle, while electricvehicles use electric motors. Global increase in fuelcosts and environmental issues, including global
warming, are some of the factors behind this initialive.
Reduction of energy required by vehicles is the focus
with plans for strict fuel efficiency regulations by 2021
in Japan, U.S., and Europe. Automotive companies
are competing every day to continually introducing
new technology into the global market.
NTN, which has a large market share in passenger
car hub bearings, is proposing various technology toachieve higher fuel efficiency 1), 2).
In this article NTN will introduce low friction hub
bearings which achieve a torque reduction of
approximately 50% by enhancing grease and seals.

Inner seal

Inner ring
Rolling element
Hub ring

Outer ring

Fig. 1 Structure example of generation 3 hub bearing

reduction of rolling resistance. For reduction of sliding
resistance, low friction seal rubber materialhas beendeveloped and seal structure and interference havebeen optimized.
This article focuses on new bearing internal grease
for further reduction of friction from rolling resistanceby reexamining base oil, kinematic viscosity, andconsistency, etc. Friction at the seals from sliding
resistance was also further reduced by developmentof new grease for application to the seal lips. By
reexamining seal structure, lip contact surface was
optimized and contact of the seal lips was reduced.

2. Initiative for low friction properties
Fig. 1 shows a structural example of a generation 3
hub bearings.
Friction of hub bearings can be divided into rolling
resistance of bearings and sliding resistance of seals,
approximately 50% each. As shown in Fig. 2, various
types of friction reduction technology have beendeveloped. These include optimization of bearing
specifications and use of resin as cage material for*Automotive Unit Engineering Dept., Automotive Business Headquarters-67-

*13E_03 18/09/05 18:55 ページ 2

NTN TECHNICAL REVIEW No.85（2017）

thickener was optimized to further reduce stirring
resistance as well.
Furthermore, in order to reduce fretting wear due tovibration during long-haul transportation, base oil witha low pour point and anti-wear agent were blended to
improve fretting properties in low temperatures.

Number of balls
Bearing
specification

Groove curvature

Bearing
Rolling
resistanceapprox. 50%

PreloadComposition of base oil
Bearing internal
greaseKinematic viscosityof base oil

Table 1 Concept of grease property

Consistency
Cage

Torque100％

Grease applied
to lipsGrease properties

Comparison with conventional productComposition of base oil

Base oil

Application of base oil with high viscosity index
Application of base oil with low pour point

Kinematic viscosity Low to room temperature: reducedHigh temperature: equivalent to conventional productof base oil

Kinematic viscosityof base oil
Consistency

Seal
Sliding
resistanceapprox. 50%

Material

Thickener

Interference
Seal lip

Covered in this article

Optimized

Additives

Contact condition

Application of anti-wear agent

2.1.2 Evaluation test

Number in contact

Running torque test of hub bearings with thedeveloped grease was conducted without seals.
The results are shown in Fig. 3. With a torquereduction rate of 24% compared to the conventional
product, the reduction of rolling viscosity resistancewith low viscosity properties of the bearing internal
grease was verified.
In addition, the reliability evaluation test shown in
Table 2 was conducted to verify the required
functions. The bearings with the developed grease
met the development objectives in all the test items,
satisfying the functional requirements for bearing
internal grease.

Fig. 2 Influence factor of bearing friction

2.1 Reduction of rolling resistance
2.1.1 Functional requirements and specificationsof developed grease
In addition to low friction properties, the following
functions are required for hub bearing internal grease.
(1) Long life without shortage of oil film and seizure
under the load, temperature and speed conditionsof hub bearings(2) Excellent fretting resistance in low temperatures(3) Sufficient anti-corrosion and leakage prevention
properties(4) Protection against penetration of foreign objects

Running torque ratio

1

Based on the above functional requirements, thespecifications of the newly developed grease were
determined as follows:
For reduction of torque, reducing kinematic viscosityof grease base oil and softening grease are general
methods to suppress stirring resistance; however, it
may cause bearing flaking and grease leakage by oil
film shortage. Especially, in high temperatures,
reduction of kinematic viscosity of base oil becomessignificant; therefore, the possibility of flaking may
increase.
Therefore, as shown in Table 1, in order to solve
poor lubrication conditions in high temperatures whilepursuing low friction, which is a contradictory
condition, at the same time base oil with high viscosity
index was applied. The kinematic viscosity of base oil
was designed to be reduced to room temperature or
lower, yet maintained at the level equivalent to theconventional product in high temperatures. In addition,

24% reduction

0.8
0.6
0.4
0.2
0

Conventional
product

Developed
product

Fig. 3 Rotation torque test (room temp.)

Table 2 Bearing grease reliability evaluation test
Test item

Result3 times or more than the rated life
Bearing life during vehicle turning*1
Seizure properties during
No seizure on bearing raceway surface
high-speed rotation*2
78% reduction of wear amountLow temperature fretting*3(compared to conventional product)*1 Turning load: 0.6G load condition*2 Rotational speed condition of vehicle velocity of 200km/h*3 Micro dynamic wear test under a -20˚C environment-68-

*13E_03 18/09/05 18:55 ページ 3

Low Friction Hub Bearing

2.2 Reduction of sliding resistance2.2.1 Functional requirements and specificationof developed seals

grease. The roughness of the seal surface wasdetermined in the range that produces friction
reduction effects and does not undermine tolerance
against muddy water and air-tightness.

Fig. 4 shows a structural example of the outer seal
and inner seal adopted in generation 3 hub bearings.
The outer seal shown in Fig. 4 (a) is a standard 3-lip
seal type. The inner seal shown in Fig. 4 (b) is a
Hypack type design of cassette type with the slinger
with stainless steel based sliding material integrated in
the unit. Since 50% of the friction of hub bearings
comes from the sliding resistance, improvement in this
aspect was pursued, while maintaining tolerance
against muddy water and air-tightness.
In this development, low friction was achieved by
optimization of seal lip contact (sliding) surface,development of grease dedicated for seal lip
application, and reduction of number of seal lip
contacts by optimizing the peripheral structure,compared to the conventional product.

2.2.3 Grease dedicated to seals
In general, grease applied to the tip of seal lips isthe same as the grease injected inside the bearings to
avoid adverse effects when mixed with each other.
However, we have developed grease dedicated toseals specially formulated for the requirements ofseals to reduce friction.
In the development of grease dedicated to seals,
the following two points were considered under theassumption of securing the basic seal performance.
Reduce sliding resistance by decreasing kinematic
viscosity of base oil.
Avoid any adverse effects to the function of the
bearings, even when mixed with internal grease.

2.2.4 Reduction of number of seal lip contacts
In general, a seal has a structure to possess 3 lips
in contact in order to secure required tolerance
against muddy water; however, we reduced thenumber of lips in contact to achieve lower friction.
Fig. 6 shows an example of seal structures of thedeveloped product. Deterioration of tolerance against
muddy water due to reduction of number of lip
contacts was avoided by placing a labyrinth structureon the outside and by arranging the seal shape.

Side lip A
Side lip B

Side lipSlinger

Radial lip

Middle lip(a) Outer seal(b) Inner seal

Fig. 4 Structure example of seal
Labyrinth
structure

2.2.2 Optimization of seal lip contact

Labyrinth lip

The conventional seal lip contact surface has evencontact to the circumference of the mating material,with no irregularities on the surface. On the other
hand, the developed product has micro irregularities
on the sliding surface or seal lip surface (Fig. 5).
These irregularities reduce the contact area with themating material and form sufficient oil film on thecontact surface since the recessed area can retain

Side lip
Radial lip(a) Outer seal(b) Inner seal

Fig. 6 Structure example of developed sealZ

Fig. 5 Seal lip surface (the enlargement from Z)-69-

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NTN TECHNICAL REVIEW No.85（2017）

2.2.5 Evaluation test

3. Performance of low friction hub bearings

Running torque test was conducted with theindividual seal. The results are shown in Fig. 7.
The developed product showed approximately 70%
torque reduction compared to the conventional
product by optimization of seal lip contact surface, andreduction of number of contacts and application ofgrease dedicated to seals. A significant reduction ofseal sliding resistance in rotation was achieved.
In addition, a reliability evaluation test against NTN
specifications shown in Table 3 was conducted toverify the required functions. Although the reduction of
number of lips may have caused deterioration oftolerance against muddy water, penetration of muddy
water into the contact lip area was reduced by setting
a labyrinth structure. The developed product achieved
equivalent tolerance against muddy water as theconventional product.

Fig. 8 shows the friction performance of hub
bearings combining the developed bearing internal
grease and low friction seal. Approximately 50%
reduction of friction was achieved with the entire hub
bearings by reducing rolling resistance and sliding
resistance of the outer/inner seals.
Fig. 9 shows the performance evaluation chart for
key functional requirement items of hub bearings.
The developed product achieved equal or better
performance compared to the conventional product inall required aspects. Particularly, as the fretting
resistance in low temperature has improved, thedeveloped bearings can be considered for use in more
severe environmental conditions.

1

Running torque ratio

Seal torque ratio

1
0.8
0.6

Approx. 70%
reduction

0.4

Sliding
resistance

0.5

Rolling
resistance0.2
0Conventional
product0Developed
product

Fig. 7 Rotation torque test (room temp.)

Approx. 50%
reduction

Conventional
product

Developed
product

Fig. 8 Friction performance of the hub bearing

Table 3 Low-friction seal reliability evaluation test

Low friction
property
5

Test item

ResultAirtightness*2

Equivalent to conventional product4

Heat resistance*3

Equivalent to conventional product3

Property against muddy water*1 Equivalent to conventional product*1 NTN test for tolerance against muddy water*2 NTN test for rotational airtightness*3 Use of dumbbell piece; 120˚C x 1,000 h grease immersion

Developed
product
Conventional
product

2
Bearinglife

10Fretting
resistance(low temperature

Properties against
muddy water

Fig. 9 Performance evaluation chart-70-

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Low Friction Hub Bearing

4. Summary
In order to meet the requirement of improved fuelefficiency, we have commercialized hub bearings withlower friction and reliability equivalent to conventional
products by developing bearing internal grease andlow friction seals for hub bearings. The bearing
internal grease has already been adopted by someauto-manufacturers.
We are poised to continue our efforts for lower
friction and higher reliability and contribute to society
by developing products that meet global needs.

References
1) Haruo Nagatani, Tsuyoshi Niwa, Application ofTopology Optimization and Shape Optimization for
Development of Hub-Bearing Lightening, NTN
TECHNICAL REVIEW No.73, (2005) 14-19.
2) Kiyotake Shibata, Takayuki Norimatsu, Technicaltrends and development products of axle bearings,
NTN TECHNICAL REVIEW No. 75 (2007) 29-35.

Photo of author

Makoto SEKI
Automotive Unit
Engineering Dept.,
Automotive Business
Headquarters-71-

*14E_03 18/09/05 18:56 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]Chain Tensioner for Motorcycle Engine

Kouichi ONIMARU*NTN has developed the hydraulic auto tensioner of timing belt drive andtiming chain drive unit for engine camshaft drive application.
Since 2004, NTN has started to supply timing chain tensioner for
motorcycle engine application.
Today I would like to introduce new technology of auto tensioner toreduce engine noise and increase durability performance.

1. Introduction
OHC engines use ribbed belts or chains to transmit
rotation of crank shafts to camshafts and synchronize
the timing of all these units. The auto tensioners areused to keep adequate tension of these ribbed belts
and chains which contribute to longer life and thequietness of engines.
For engines of motorcycles, chains are used more
often than ribbed belts for the above synchronization.
As such, auto tensioners for chains of motorcycles(hereafter, chain tensioners) are required to meetcertain functionality particular to motor cycle engines.
NTN has been developing and commercializing
chain tensioners that meet these requirements. This
article introduces the structure and characteristics ofchain tensioners for motorcycle engines.

Chain lever
Chain tensioner
Chain guideFig. 1 Layout example

On the contrary, if the chain tension is too low, chain
fluttering becomes larger, resulting in larger noise andvibration, as well as wear elongation. Therefore, theoptimized design of the chain tensioner, which adjusts
chain tension, is critical, requiring optimization of
damping force, etc. for each engine.
Usually, there is a time lag between the starting ofan engine and when lubricant oil reaches eachcomponent.
Chain tensioners with hydraulic damping
mechanisms may produce abnormal noise due tochain fluttering after starting the engine until oil is filled
into the high pressure chamber. Therefore, a no-backmechanism is required to prevent the chain from being
pushed in when the engine stops.

2. Current situation of chain tensioners
for motorcycle engines
2.1 System configuration and required functionality
When a chain is used for the above mentioned
synchronization of rotation, the chain is slide guided
by a chain lever and chain guide (Fig. 1). The sliding
resistance between those slide guides and the chain
creates friction loss; therefore, adequate chain tension
is critical. When the chain tension is too high, thefriction loss becomes larger, resulting in deteriorationof fuel efficiency, low output and, at worst, chain
rupture.

*Automotive Unit Engineering Dept., Automotive Business Headquarters-72-

*14E_03 18/09/05 18:56 ページ 2

Chain Tensioner for Motorcycle Engine

In addition, chain tensioners for motor cycles are
required to have the following functionality since they
are often installed by being inserted from outside ofthe engine.

3.1 Improvement of quietness and reliability1) Initial setting release mechanism fromoutside the engine

1) Buttress thread type chain tensioner

There are two types of structures to achieve a noback mechanism regarding quietness and reliability.
These structures are introduced in this paper.

The no-back mechanism (Fig. 3) utilizing a buttressthread with NTN proprietary technology makes it
possible to reduce chain fluttering. This is evenpossible with no oil supply to the chain tensioner
immediately after the engine starts and when no
damping force exists from oil hydraulics (Fig. 4 and 7).
The buttress threads enable the no-backmechanism, regardless of the position of the tensioner
tip when the engine stops; significantly contributing toquietness of the engine when it starts.
In addition, the frictional force of the buttressthreads also work as a part of the damping force
during normal operation, and not only when theengine starts (Table 1). In recent years, the load on

A chain tensioner is delivered with the initial setting
where the internal component is pushed into the cylinder.
The initial setting needs to be released, after thetensioner is installed to the engine, to allow the internal
component of the tensioner to be extended until it is incontact with the chain lever. Therefore, a mechanism torelease the initial setting (being pushed in) is required
either manually from outside or automatically (Fig. 2).

For motorcycles

For four-wheel vehicles

Buttress thread

Installed from outside of theengine, without requiring removalof the cover, allowing saving ofinternal space. No manual
operation from outside is possible
after installation, requiring an
automatic release mechanism of
the initial setting.

The entire mechanism is installedinside the engine.
Installation/removal requires
removal of the cover.
The initial setting is released byremoving the set pin of thetensioner before installing thecover.

Return spring

Fig. 2 Installation of chain tensioner

Fig. 3 Buttress thread type chain tensioner
Female thread: plunger

2) Prevention of fallout of internal components

Backlash: small
Male thread: screw rod

A mechanism to prevent fallout of internal
components into the engine is required in case chain
tensioners are removed for maintenance, etc.

2.2 Chain tensioners of other manufacturers
Mechanical chain tensioners have been used for
motor cycle engines with simple structures of springs
and ratchets or damping with friction force of screws.
<when pushed in><when extended>

Fig. 4 Operation of buttress thread

3. NTN chain tensioners
NTN has tackled the following challenges of thechain tensioners.
(1) Improvement of quietness and reliability(2) Compact/lightweight(3) Improvement of workability(4) Stability of hydraulic damping force

Table 1 Functions of each no-back mechanism
No-back mechanism-73-

Damping function No-back mechanism

Buttress threads

Hydraulic+(screw friction)

Stepless

Register ring

Hydraulic

Stepped*14E_03 18/09/05 18:56 ページ 3

NTN TECHNICAL REVIEW No.85（2017）

the chain tensioners immediately after starting theengine increases due to the increase in driving torqueof cam shafts, higher power output of engines, anddownsizing of oil pumps. In response to these trends,
NTN is marketing products with increased load
capability while maintaining the conventional
functionality of tensioners by reexamining the buttressthread specifications.

Extended direction
3rd thread
2nd thread
1st thread

Register ring

Fig. 6 Structure of ring type

Plunger
displacement

2) Register ring type chain tensioner

Small vibration fromearly stage of engine
start without hydraulics

Generation of hydraulicdamping force=>reduction of amplitude

Rotational
speed

NTN is also marketing chain tensioners withsimplified buttress thread functions with a structurethat allows a stepped no-back mechanism using thegrooves of the plunger outer perimeter and theregister ring (freed on the extended direction by thegrooves of the plunger outer perimeter and latched on
the return direction). As opposed to other productswith ratchet structure for the stepped no-backmechanism in the market, NTN products arecharacterized by the compact design by utilizing
elasticity of the ring placed concentrically with thechain tensioner plunger (Fig. 5).

Engine start

0

1

2

3

Time (s)4(a) Buttress thread

0

1

2

3

Time (s)4(b) Register ring

Fig. 7 Engine startup characteristic of each no-back mechanism

3.2 Compact/lightweightNTN has long been working on lightweight chain
tensioners by adopting cylinders made of aluminum;
however, we developed even lighter and morecompact chain tensioners which can be directly
installed on the engine with threads (self-mount type
chain tensioners,) and started marketing them in 2010
(Fig. 8). This product comes with male threads on thecylinder outer perimeter which can be screwed into thefemale threads on the engine for installation. Therefore,bolts and washers for installation of the conventional
products are no longer required, contributing to spacesaving, reduced weight and labor for installation on theengines. This product is particularly effective for motor
cycle engines because they have limited space in theengine, and chain tensioners are often installed fromoutside the engine. In addition, this product can be usedboth for the aforementioned buttress thread type andregister ring type.

Register ring
Plunger

Return spring

Fig. 5 Ring type chain tensioner

The traveling line of the chain (plunger position of
the tensioner) can vary depending on the temperatureand rotational speed. With the register ring type noback mechanism, the backlash amount until the noback mechanism starts functioning needs to be set sothat the axial movement of the plunger can follow thevariation of the traveling line of the chain. Caution tothis point is particularly needed for the motorcycle
engines which allow high-speed rotation range, andtherefore, produce significant variations of rotational
speed (Fig. 6).
The register ring also prevents the plunger to fall out
from the cylinder when it is completely extended, an
important role for motor cycle engines from a
maintenance standpoint, for which installation is often
accomplished from outside the engines.

Return spring(a) Buttress thread type(b) Register ring typeFig. 8 Self-mount type chain tensioner-74-

*14E_03 18/09/05 18:56 ページ 4

Chain Tensioner for Motorcycle Engine

3.3 Workability
1) Automatic release of initial setting(Initial setting status)
・The snap ring is shrunk and set into the grooves on
the plunger outer perimeter and cylinder innerperimeter.
・The plunger is pushed in the extended direction by
the internal return spring (Fig. 8) and kept in theinitial setting position.

For engines of four-wheel vehicles, the release of
the initial setting after installation of chain tensioners isaccomplished by removing the set pin of the chain
tensioner and then installing the front cover (Fig. 9).
However, motorcycle engines do not have working
space for removing the set pin after installation;
therefore, an easy and secure releasing mechanism isrequired. NTN addresses these challenges byadopting the mechanism shown in Fig. 10.

(Releasing initial setting)・With the load applied to the plunger, the snap ringmoves in the axial direction along with the groove of
the plunger as they move in the pushed-in direction.
・As the snap ring moves toward the cylinder grooveon the larger diameter side, the snap ring is
expanded.
・When the snap ring is expanded, it cannot preventthe plunger from being extended, releasing theinitial setting.

(Reapplying initial setting)・After the chain tensioner is removed from theengine for maintenance, etc., the initial setting canbe reset with the snap ring in place by pushing theplunger to the initial setting position.

Set pinFig. 9 Chain tensioner for automotive engines

This structure allows automatic release of the initial
setting by applying load with engine cranking, whichcauses displacement after the chain tensioner isinstalled onto the engine.

Engaged2) Prevention of fallout of internal components
With the register ring type chain tensioner, theregister ring works as a prevention mechanism
against fallout of the internal components. However,since the said component does not exist with thebuttress thread type, another snap ring shown in Fig.
11 is provided separately from the snap ring for initial
setting.

Plunger
CylinderSnap ring(Load on plunger)

Released

CylinderSnap ring(for preventing from fallout)
Snap ring(for initial setting)
PlungerFig. 10 Release mechanism of initial setting

Fig. 11 Prevention mechanism of parts falling off-75-

*14E_03 18/09/05 18:56 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

3.4 Stability of hydraulic damping force
1) Relief valve setting
Damping force N

1,400

For higher power output, motorcycle engines havehigher permitted rotational speed than four-wheel
vehicles. It is necessary for the hydraulic damping
mechanism to restrain the chain tension because of
the tendency of excessive damping force in the higher
rotational speed range. By controlling leak gaps withthe conventional simple hydraulic damping
mechanism, it is difficult to optimize the damping force
in the lower and higher rotational speed ranges. NTN
addressed these challenges by integrating a compact
relief valve in the chain tensioner (Fig. 12). The open
valve pressure of a relief valve can be changed with
the internal spring setting, allowing adjustments for
damping force appropriate to different engines. Thismechanism supports engines with higher permitted
rotational speed such as large and sports typemotorcycles; therefore, NTN chain tensioners areoften adopted.
Fig. 13 and 14 show the verification results of relief
valve effects. The tuning of damping force wasconducted under conditions of 100˚C/200 Hz.
Compared to the case when damping force isadjusted only by the leak gap (Fig. 13), adding a relief
valve produces stable damping force against variationof oil temperatures and frequency (=engine rotational
speed) (Fig. 14).
The comparison of the characteristics in the actual
test is shown in Fig. 15. Reduction of load in thehigher rotation range can be expected with the relief
valve setting.

50Hz
200Hz

1,200
1,000
800
600
400
200
0

40℃

Oil temperature

110℃

Fig. 13 Adjust with leak clearance (without relief valve)Damping force N

1,400

50Hz
200Hz

1,200
1,000
800
600
400
200
0

40℃

Oil temperature

110℃

Fig. 14 Adjust with relief valve

Input load on tensioner N

1,400
1,200
1,000

Without relief valve
With relief valve

800
600
400
200
0

Engine rotation speed

Fig. 15 Comparison of characteristics with or without
relief valve
Valve seat
Steel ball
Check valve(closed)SpringRelief valve(open)

2) Bleed mechanism setting
Hydraulic chain tensioners cannot satisfy thefunction if air is present in the oil pressure chamber.
Therefore, NTN has adopted various bleedingmechanisms so that they can be added to the best
location depending on usage (Fig. 16 and 17).

：Oil flow
CylinderPlungerHighpressurechamberFig. 12 Relief valve structure and oil flow-76-

*14E_03 18/09/05 18:56 ページ 6

Chain Tensioner for Motorcycle Engine

4. Conclusion

GrooveWe have been developing chain tensioners formotorcycle engines, particularly for higher power
output and sport vehicles, to satisfy requirements forfunctionality and reliability. Going forward, it isexpected that the requirements for chain tensioners
will be diversified, even for motorcycles possessing
environmental concerns.
NTN will continue to address these requirements
while developing chain tensioners for applications to
broader vehicle types.

Air

Fig. 16 Added bleed mechanism to relief valve

Air

References
Yoshiaki Ryouno, et al.: The Engine Part Technical
Trends and New Products for Engines, NTN
TECHNICAL REVIEW, 75 (2007) 62-71.
Seiji Sato: Technology Trends of Auto Tensioner, NTN
TECHNICAL REVIEW, 79 (2001) 83-89

Fig. 17 Added bleed mechanism to leak adjustment part

Photo of author

Kouichi ONIMARU
Automotive Unit
Engineering Dept.,
Automotive Business
Headquarters-77-

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]Light Weight Drive Shaft for FR vehicle“R series”

Tomoshige KOBAYASHI*

For the purpose of improving environmental performance, weight reduction is also required in the rear wheel
drive system which is often adopted for luxury cars.
In this paper, I introduce the features and performance of "Light weight drive shaft for FR vehicle" developed forrear wheel drive car.

1. Introduction

2. Structure and characteristics of thedeveloped productFor the driveshaft of front-wheel drive (FF) vehicles,
a fixed type constant velocity joint (CVJ), which cantake a wider work angle on the tire side and a sliding
type CVJ, which can slide in the axial direction on theengine side, are used.
On the other hand, rear-wheel drive (FR) vehicles
have a fixed axle (rigid axle that linearly connects bothwheels) suspension and an independent suspension
which allows each wheel on the same axle toindependently move vertically, depending on the roadconditions.
Independent suspension systems require a drive
shaft, since each axle is independent; however, it is
widely adopted by luxury cars as it offers superior
comfort and driving maneuverability.
Recently, luxury cars are also facing stricter
regulation of CO2 emissions, and therefore, reduced
weight and compactness are required for drive shaftsof rear-drive vehicles in order to improve fuelefficiency. NTN has developed "Lightweight Drive
Shaft for FR Vehicles" to meet these requirements.

In the past, NTN applied CVJ of the common designfor both FR vehicles and FF vehicles. However, thedrive shafts for rear-drive vehicles do not require thewide work angle for steering, and the CVJs for the tireside are only required to follow the vertical suspension
movement. By focusing on this fact, NTN has
developed a light and compact drive shaft for reardrive vehicles with a reduced maximum work angle,
dedicated to the rear-drive vehicles that can contributeto reduced weight and improved fuel efficiency.
The developed drive shaft consists of (1) newly
designed light/compact fixed CVJ, (2) sliding CVJ, (3)hollow shaft with reduced material that connects theformer two CVJs, and (4) compact boots with reduced
grease amount, achieving approximately 30%
reduction of weight compared to the conventional
product.
Configuration of the newly developed Lightweight
Rear Drive shaft "R-Series" is shown in Fig. 1.
The specification of the developed product and theweight reduction ratio compared with the conventional
product is shown in Table 1. Note that the weightcalculation excludes the stem section* from the(1) Lightweight fixed type CVJ
for rear-drive vehicles "REBJ"(3) Hollow shaft thinning type(thinning at the center)(2) Lightweight sliding type CVJ
for rear-drive vehicles "REDJ"

Stem section(4) Compact boots

Stem section

Fig. 1 Light weight drive shaft for FR vehicle “R series”*Drive Shaft Engineering Department, Automotive Business Headquarters-78-

Light Weight Drive Shaft for FR vehicle “R series”

Table 1 R series mass reduction rate
Developed product (R-Series)
Fixed type CVJ (REBJ)

Sliding type CVJ (REDJ)
Hollow shaft

Compact boots and injected grease
dedicated for rear-drive vehicles

Conventional product
EBJ

Weight reduction ratio
▲28％

EDJ
Solid shaft▲13％

Drive shaft
assembly
▲30％

▲53％

Boots and injected grease
for front CVJ

configuration shown in Fig. 1, since the installation
mechanism varies depending on user specifications.

▲36％

Table 2 Comparison of REBJ and EBJ*Stem section: shaft for engagement used for mounting the body

3. Lightweight fixed type CVJ for
rear-drive vehicles "REBJ"
The maximum work angle of the fixed type CVJ for
FF vehicles is set at 47 - 50 degrees to cope with thevertical movement of suspension and steering angle.
On the other hand, the fixed type CVJ for FR
vehicles can be set at 19 degrees or less working
angle, in most cases considering the practical use, as
it only needs to follow the vertical movement of thesuspension.
In the past, the fixed type CVJ for FR vehicles had
specifications common with the fixed type CVJ used
for FF vehicles. However, we have explored
light/compact design by optimizing the functions by 19
degrees or less.
The required functions are shown below:(1) Strength: equivalent to the conventional productwith a max work angle of 19 degrees or less
(2) Durability: equivalent to the conventional product(3) NVH performance: equivalent to the conventional
product

Item

Developed product
REBJ95

Conventional product
EBJ95

Max. work angle
(deg)

19

47

Outer diameter
(mm)

φ80.8

φ83.6

Ball diameter(mm)

φ15.081

φ15.081Weight(kg)

1.016
Ratio compared toconventional product: -28%

1.401

SUB-ASSY

Joint center

Developed
product(REBJ)
19deg

Joint center3.1 Characteristics
Table 2 shows the comparison of the developed
product "Lightweight fixed type CVJ for rear-drive
vehicles (REBJ)" and the conventional product "EBJ".
In this article, we focus on the newly designed fixed
type CVJ (REBJ) and the sliding type CVJ (REDJ), as
well as the compact boots that reduced the injectedgrease amount.
The following shows the focused design area
reexamined due to the change of the maximum work
angle from 47 degrees to 19 degrees or less.

Conventional
product
(EBJ)

47deg

Fig. 2 Comparison of Ball groove length (red line)

conventional product (Fig. 3).
In addition, the assembly method was improved
because of compact components.
The conventional product (EBJ) requires space forincorporating the cage at the bottom of the outer ringcup (L2) so that the cage can be installed at 90
degrees relative to the outer ring (Fig. 4).
On the other hand, the developed product (REBJ)
has a small undercut at the cup end of the outer ring;(1) Length in axial direction
The required ball groove length can be reduced as
the ball movement range becomes smaller due to the
reduced maximum work angle (Fig. 2).
Therefore, the length of various components in theaxial direction can be reduced compared to the-79-NTN TECHNICAL REVIEW No.85（2017）(2) Dimension of outer diameter

therefore, the cage can be incorporated horizontally,requiring less space at the bottom of the outer ringcup (L1).
The bottom of the outer ring cup only requires
minimum space to incline the cage to the angle
required for incorporating the ball (Fig. 5).
As described, the difference of the assembly method
also contributes to the reduction of weight and size.

As the max. work angle becomes smaller, input load
to various components are also reduced, allowing lessmaterial required for those components (Fig. 6).

Developed
product(REBJ)Developed
product(REBJ)
Conventional
product(EBJ)

Fig. 6 Comparison of Outer dia.
Conventional
product(EBJ)

3.2 Functional evaluation
Fig. 7 shows results from static torsional tests of thedeveloped product REBJ and the conventional
product EBJ (n=2 each). The light and compact REBJ
has the equivalent strength of EBJ.
Fig. 8 shows the results from the durability test.
Durability of the developed product REBJ sufficiently
achieved the development objectives, together withthe conventional product.

Fig. 3 Comparison of axial length
Developed product(REBJ)Breaking torque kN・mDevelopment objective
Conventional product(EBJ)

Fig. 4 Cage built-in method

Developed product(REBJ)

Conventional product(EBJ)

Fig. 7 Results of static torsional strength test
Interference between
cage and outer ring

CVJ
46deg

REBJ95

EBJ95

Built-in ball

No
1
2
3
4
1
2
3
4

Damage table/inspection time (h)
100
230
350

○：No error △：Slight error ×：Significant error：Development objective

Fig. 5 Built in ballFig. 8 Results of durability test-80-Light Weight Drive Shaft for FR vehicle “R series”

The following shows the focused design areas
which were reexamined due to the change in the
maximum work angle from 25 degrees to 19 degrees.

4. Lightweight sliding type CVJ for
rear-drive vehicles "REDJ"
There are various types of sliding type CVJs, which
are used paired with fixed CVJs. For luxury FR
vehicles, cross groove type and double offset type are
more preferred than triport type, as they require
minimum backlash in all drive systems.
EDJs used by NTN for FR vehicles are light andcompact; however, the maximum work angle is 25
degrees, and they were used for both FF and FR
vehicles, similar to the fixed type CVJ.
Therefore, we explored development of further
reduction in weight and size, also for the sliding type
CVJ, by optimizing the functions for a work angle of 19
degrees or less.
The required functions are described below, similar
to the fixed type CVJ.
(1) Strength: equivalent to the conventional productwith a max work angle of 19 degrees or less
(2) Durability: equivalent to the conventional product(3) NVH performance: equivalent to the conventional
product(1) Length in axial direction
The required ball groove length can be reduced as
the ball movement range decreases due to the
reduced maximum work angle (Fig. 9).
Developed product (REDJ)

19deg

Conventional product (EDJ)

25deg

4.1 Characteristics
Table 3 shows the comparison of the developed
product "Lightweight sliding type CVJ for rear-drive
vehicles (REDJ)" and the conventional product "EDJ".

Fig. 9 Comparison of Ball groove length (red line)

As the axial length (width) of the inner ring/cage isreduced, the outer ring cup length can also be
reduced (L1<L2), achieving compactness (Fig. 10).

Table 3 Comparison of REDJ and EDJ
ItemDeveloped product
REBJ95

Conventional product
EBJ95

Max. work angle
(deg)

19

25

Outer diameter
(mm)

φ79

φ82

Ball diameter(mm)

φ15.875

φ15.875

Weight(kg)

1.124
Ratio compared toconventional product: -13%

1.294

Developed
product(REDJ)SUB-ASSY

Conventional
product(EDJ)*Sliding length: 40 mm

L1

L2

Fig. 10 Comparison of Outer dia. and axial length-81-

NTN TECHNICAL REVIEW No.85（2017）(2) Dimensions of outer diameter

4.2 Functional evaluation

Similar to the fixed type CVJ (REBJ), as the max.
work angle is reduced, input load to various
components are also reduced, allowing less material
required for those components (Fig. 10).
Furthermore, as the max work angle is reduced, themoving range of the ball within the cage window is
reduced, which shortens the length of the cagewindow, as well as the angle of the cage outer
diameter tapered area.
Therefore, the cross-section of the cage pillar
increases, enhancing the cage strength, which makes
it possible to downsize the radial direction (Fig. 11).

Fig. 13 shows results from static torsional tests ofthe developed product REDJ and the conventional
product EDJ (n=2 each).
The light and compact REDJ has strength
equivalent to or better than the conventional product
EDJ.
Fig. 14 shows the results from the durability test.
The developed product REDJ has durability
equivalent to or better than the conventional product
EDJ.

12.5˚

Window length

Window length

9.5˚

Cage
enhancement

Breaking torque kN・mDevelopment objective

Developed product(REDJ)

Conventional product(EDJ)

Fig. 13 Results of static torsional strength test
Developed product(REDJ)

Conventional product(EDJ)

Fig. 11 Comparison of REDJ cage and EDJ cage

CVJ
REDJ95The detailed dimensions of each component are
determined by optimization through FEM stressanalysis and evaluation test for validating suitability.
Fig. 12 shows an example of FEM stress analysisof the cage. The developed product (REDJ) shows thesame level of stress balance as the conventional
product, while achieving compact size.

EDJ95

No
1
2
3
4
1
2
3
4

Damage table/inspection time (h)
100
230
350

○：Continued operation allowed
×：Continued operation not allowed：Development objective

Fig. 14 Results of durability test
High Stress

Developed product(REDJ)

Conventional product(EDJ)

Low StressFig. 12 FEM analysis of REDJ cage-82-

Light Weight Drive Shaft for FR vehicle “R series”

5. Boots

6. Conclusion

As the max work angle is reduced, the boots canalso be light and compact, which allow for a reduced
amount of injected grease, as the capacity is reduced(Fig. 15).
Table 4 shows the comparison of weight of theboots and the injected grease for the fixed type CVJ
and sliding type CVJ.

In this article, characteristics and performance of
the Lightweight Rear Drive shaft "R-Series"
development for rear-wheel drive vehicles arepresented.
Table 5 is a summary of the performance of thedeveloped products compared with general drive shafts
for rear-wheel drive vehicles. It shows that the developed
products, which achieved significant reduction of weight
while maintaining basic performance, are generally themost superior drive shafts.

Developed product

Table 5 Comparison of performance according to drive shaft
Fixed type+sliding type

Conventional productFig. 15 Miniaturization of boots

Item

Developed product Conventional product(REBJ＋REDJ)(EBJ＋EDJ)

Weight of boots (g)

62

120

Weight of grease (g)

151

215

Developed
product"R-Series"

BJ type+
TJ type

★★★

★★

★★

Durability life

★★★

★★

★★

Transmissibility

★★
★★★

★★
★★

★★
★★

WeightStrength

Table 4 Mass of boots and grease

Sliding type+sliding type

NVH

★★★

★★

LJ type+
LJ type★★

Superiority : ★★★＞★★

Recently, as requirements for improvement ofenvironmental performance also increases for luxury
cars, which often adopt rear-wheel drives, thisdeveloped product, which achieved significant weight
reduction is believed to meet the current needs.

References
Hiroshi Tone, Kenji Terada, Masamichi Nakamura
Summary of E Series, High Efficiency Constant
Velocity Joints,
NTN TECHNICAL REVIEW No.70 (2002) 18-23
Shin Tomogami
Technical Trend and Development Products ofConstant Velocity Universal JointNTN TECHNICAL REVIEW No.75 (2007) 10-15

Photo of author

Tomoshige KOBAYASHI
Automotive Business
Headquarters
Driveshaft Engineering
Department-83-

*16E_03 18/09/05 18:59 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Technical Article ]Effects of Lubricant on
Hydrogen-Related Rolling Contact Fatigue Life Improvement

Takayuki KAWAMURA*

Lubricant/water content
Sliding

H2

H

H

H

H

New steel surface

H2

In rolling bearings used under severe conditions such as automotive electricalinstruments and auxiliary device, an early bearing damage is occurred andaccompanied by unique white microstructures below the raceway subsurface. The
main cause is thought to be the result of hydrogen embrittlement. One of thepossible mechanisms of this flaking failure is due to metal contact between the steel
surfaces, i.e. exposing active fresh metal surfaces, by which the lubricants
decompose. Subsequently, hydrogen is generated and penetrates into steels. This
report introduces the outline of NTN’s hypothesis concerning about the hydrogenrelated failure mechanism and in addition, countermeasure by lubricant.

evidence with the most economically favorable
solution using lubricant technology among all
possibilities, from materials to lubrication.

1. Introduction
In the latter half of the 1980s and the beginning of
the 1990s, the drive belts for automotive engine
accessories and auxiliary devices were changed fromstandard V-belts to serpentine belts. During thetransformation to serpentine belts, early flaking wasobserved on the fixed bearing raceway of the engine
accessory bearings and caught the industry's attention 1).
Even if this flaking appears to be small, widespread
cracks with white microstructural change extend deep
through the circumferential cross section, which is apeculiar phenomenon that is not observed withconventional fatigue failures (Fig. 1).
Several hypotheses have been proposed based on
experimental verifications in order to pinpoint thecause of this peculiar flaking 2-5). The current leadingidea is hydrogen embrittlement, which is what NTN
also claims to be the cause of the flaking 6-8).
Today, failure due to flaking is decreasing in themarket mainly due to improvement of grease toprevent flaking 9). However, since this peculiar flaking
is still observed in applications such as bearings for
CVT and wind turbines bearings in addition to engine
accessories 6), 10), clarification of the detailed
mechanism of the flaking development and more
effective counter-measures are being investigated.
Presented in this article are hypotheses of themechanism of the peculiar flaking development andDirection of load

Appearance of flaking

Raceway

Peculiar microstructuralchangeCross section in thecircumferential direction

Fig. 1 Appearance of peculiar flaking failure
and its circumferential cross-section*Advanced Technical Research Center-84-

*16E_03 18/09/05 18:59 ページ 2

Effects of Lubricant on Hydrogen-Related Rolling Contact Fatigue Life Improvement

Also, as shown in Fig. 3, in the two-cylinder rolling
contact fatigue test after the hydrogen charge, early
cracking occurred under the influence of hydrogen.
When the injected hydrogen was significant, peculiar
white microstructural change similar to Fig. 1
appeared.
Based on these results, it is revealed that thefatigue strength is reduced, and peculiar widespreadflaking with white microstructural change occurs fromhydrogen embrittlement when the hydrogen
penetrates into the bearing steel. Therefore, we
consider this as hydrogen embrittlement flaking.
From the above, the mechanism of the hydrogen
embrittlement flaking that NTN considers is shown in
Fig. 4. To verify this hypothesis, it is necessary todemonstrate the possibility of hydrogen penetration
into the steel in an actual operating environment.

2. Characteristics of peculiar flaking and
its relation with hydrogen embrittlement
2.1 Characteristics of peculiar flaking
Table 1 shows a comparison of conditions leading
to the conventional fatigue microstructural change andpeculiar flaking with widespread white microstructuralchange under severe operating conditions. This table
implies that the peculiar flaking is significantly affectedby environmental factors such as hydrogen rather
than operating stress.

Table 1 Difference of occurrence condition
between peculiar and conventional flaking failure
Operating load/stress
Loading cycle

Peculiar flaking

Conventional flaking

Small

Less frequent
Large

Impact of lubricant

Large

More frequent
Small

Hydrogen charge

2.2 Reproduction of the deterioration of fatigue
strength and peculiar flaking with advanced
addition of hydrogen11)
Reproduction of reduced life and microstructuralchange with hydrogen was explored using test pieces
with hydrogen added in advance by the process ofcathodic charge. Fig. 2 shows the evaluation resultsof the ultrasonic wave fatigue test, which allows for ahigh-speed load for reducing dispersion of hydrogen
under testing. The test pieces charged with hydrogensignificantly reduced fatigue strength compared to thetest pieces without hydrogen. The larger the hydrogencontent, the larger the reduction of fatigue strength.

Pmax＝2.1GPa

Rotational speed：3,000min-1
Sliding ratio：2％
Raceway

Peculiar microstructuralchange occurredFig. 3 Photographs of surface cracks and theircircumferential cross sections after two cylinder rolling
contact fatigue test with hydrogen charge

1,400

No hydrogen charge

Stress amplitude MPa

1,200
Sliding due to driving with abrupt
Lubricant/water content acceleration/deceleration

1,000
0.1mA/cm2

Wear by metal contact(exposure of new steel surface)

Sliding

800

Tribochemical reaction

0.3mA/cm2

600

H2

H

H

H

H

H2

0.5mA/cm2400
1.E+04

1.E+05Generation of hydrogen by decompositionof lubricant/water
Penetration of hydrogen into steel

1.E+06

Loading cycle

1.E+07

New steel surface

1.E+08

Hydrogen embrittlement flaking

Fig. 4 Hydrogen embrittlement flaking failure mechanism

Fig. 2 Effects of hydrogen charge on stress amplitude
at ultrasonic fatigue testing-85-

*16E_03 18/09/05 18:59 ページ 3

NTN TECHNICAL REVIEW No.85（2017）
Detection ofhydrogenVacuum chamber

3. Verification of generation/ penetrationof hydrogen

Load

TMP

The source of hydrogen can be a lubricant that
contains hydrocarbon and water content in theatmosphere. Also, possible driving forces ofgeneration of hydrogen from lubricant and water
includes (1) sliding and vibration from abrupt
acceleration/deceleration while driving, (2) electricaleffects from electric currents and statics, and (3) fromsevere environments under which rolling bearings areused 12).
Presented below are the results from theinvestigation of effects of sliding on generation ofhydrogen and penetration into the steel.

Oil film
QMS

RP
ExhaustSteel ball

Motor

Test piece

Steel grade/flat plate

Material

SUS440C

Pmax

1.0GPa207mm/sSlide velocity

10-5PaIn order to verify generation of hydrogen throughsliding, a sliding test of ball-on-disk was conducted ina vacuum. Fig. 5 shows the results of hydrogendetection. It shows the change of generated hydrogen(red line) and the friction coefficient (blue line) whensliding-stopping is repeated three times. If we define
the amount of hydrogen generation as the increase inarea of hydrogen ion current during sliding, theamount of hydrogen generation is increasing as
sliding increases while the friction coefficient remains
almost constant. It is also revealed that hydrogen is
not generated immediately after the start of the first
test, but rather is generated immediately after the startof the second and third tests.
From these results, the following phenomenon is
deduced:(1) Usual bearing raceway surfaces are covered withan inactive oxide film 14). Friction from the initialsliding removes the oxide film, exposing an active
steel surface. Because of that, hydrogen is
generated in the mechanism shown in Fig. 4.
(2) Since the test is conducted in a vacuum, theamount of oxygen in the atmosphere is scarce.
The steel surface, once exposed, is only recovered
with a very thin oxide film that is easily removed in
the next sliding cycle.
(3) By repeating the sliding cycle, the friction surface
gradually becomes rougher making it easier toexpose a new steel surface This result of this is anincrease in the amount of generated hydrogen.
Therefore, if friction heat is considered to beequivalent to the friction coefficient because of theconstant load, generation of hydrogen is considered tobe affected by exposure of the new steel surface
rather than friction heat.

×10
6

Hydrogen ion current value A

-11

First

5

Sliding
Second

120%
UP

45%
UP

4

Third
0.6
0.5
0.4

3

0.3

2

0.2

1

0.1

0

0

300

600

900

Friction coefficient

Vacuum level

3.1 Verification of generation of hydrogenthrough sliding13)

Flat plate01,200 1,500 1,800

Time sFig. 5 Coefficient of friction vs. hydrogen generationfrom lubricant during sliding test in vacuum

3.2 Verification of penetration of hydrogenthrough sliding 13), 15)
In order to verify penetration of hydrogen into steel
through sliding, a sliding test of 3-balls-on-disk was
conducted in an oil bath similar to the actual
environment, using 5 different types of test oil. Fig. 6
shows the result of hydrogen detection. The tendency
that was observed was that the amount of hydrogen
penetrated into steel increased as friction increased.
In addition, in order to verify the impact of watercontent in the atmosphere, an abrasive wear test was
conducted under controlled humidity. This revealed
that the water content in the atmosphere works as the
supply source of hydrogen, increasing the amount ofhydrogen penetrated into steel as the volumetrichumidity (water content in the atmosphere) increases(Fig. 7).

-86-

*16E_03 18/09/05 18:59 ページ 4

Effects of Lubricant on Hydrogen-Related Rolling Contact Fatigue Life Improvement

These results imply that lubricant and water content
are decomposed by a tribochemical reaction 16) on thesteel surface that was newly exposed due to metal
contact, including sliding, generating hydrogen which
penetrated into the steel.

Load

Load

4. Preventative measures against
generation and penetration ofhydrogen from lubricants
The process of the effects of lubricant in the above
verification of the hydrogen embrittlement flaking
mechanism is "wear due to metal contact" and"tribochemical reaction". Therefore, with the additionof "anti-wear agent (action: reduction of wear underhigh-speed sliding)" and "corrosion inhibitor (action:formation of oxide film on the steel surface)" areconsidered to be effective as preventative measures.
The effect of addition of these agents was confirmedin the verification test of suppressing hydrogen
penetration from sliding and in the reproducibility test
using the actual bearings.

Oil bath

Load

Steel ballHydrogen analysis

Flat plate test piece
Test piece

Steel grade/flat plate

Material

SUJ2

4.1 Verification of suppressing penetration ofhydrogen from sliding 13)

Slide velocity

300mm/s

Oil temperature

100℃

Fig. 8 shows the result of hydrogen detection in thesliding test with anti-wear agent (organic zinc +organomolybdenum) or corrosion inhibitor(peroxomolybdate + tungstate) added to water-glycol
fluid for verifying the effect of the additives forsuppressing penetration of hydrogen due to sliding.
It was revealed that the amount of hydrogen in thesteel was low when any additive was used comparedto the fluid without additives and, in particular,
peroxomolybdate was effective for suppressinghydrogen penetration.

Pmax

3.0GPaTime

20h

Amount of hydrogenin the entire steel
wt-ppm1.2

0.8

No sliding
Water-glycol
Mineral oil

0.4

0

PAO
Ester
Ether

0

5

10

Depth of wear μm

15

20
1.2

Amount of hydrogenin the entire steel
wt-ppmFig. 6 Wear depth vs. amount of penetrated hydrogen
after sliding test in oil

0.8

Amount of diffusible hydrogenwt-ppm

0.20

0.15

0.10

Anti-wear agent

Peroxomolybdate0

Set to 20˚C

Tungstate

0

5

10

Depth of wear μm

1520Fig. 8 Effect of additive on prevention ofhydrogen penetration after sliding test in oil

0.05

0.00

No sliding
Oil with no additives

0.4

Set to 30˚C

0

5

10

15

20

25

4.2 Verification of reproducibility test using
actual bearings 17)

30

The effect of the prevention of hydrogen embrittlement
flaking with an anti-wear agent (organic zinc +organomolybdenum) and corrosion inhibitor(peroxomolybdate + tungstate), which had suppressed
the amount hydrogen penetration into the steel, wasVolumetric humidity g/m

3

Fig. 7 Absolute humidity vs. amount of penetratedhydrogen under an abrasive wear condition-87-*16E_03 18/09/05 18:59 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

evaluated under oil lubrication. Fig. 9 shows the
Weibull distribution of flaking life. It was verified that all
the failed bearings were caused by hydrogen
embrittlement flaking. The lubricant withperoxomolybdate and the anti-wear agent, , showed
longer life, especially with peroxomolybdate proving tobe especially effective.
In addition, Fig. 10 shows the analysis of oxygenon the inner ring surface in the depth direction after a
test using XPS (X-ray photoelectron spectroscopy). It

shows that peroxomolybdate, among corrosion
inhibitors, forms a thick oxide film.
From the above, we believe that peroxomolybdate
suppresses the exposure of the steel surface andgeneration/penetration of hydrogen as well as
achieving long life by reducing wear and forming athick oxide film, as shown in Fig. 11.
Oxide film

Load
Supporting bearings

Main shaft

Oil with no additives
Reaction film
Oil bath

Oil bath

Peroxomolybdate

New steelsurface

Oxide film

Rotation

Test bearing
Base oil

Water-glycol fluid（32mm2/s@40˚C）

Test bearing

Anti-wear agent

Needle roller bearing

Pmax

Fig. 11 Mechanism of tested additive action

2.61GPa

Oil temperature
Driving pattern

100˚C

Abrupt acceleration/deceleration＊（500⇔300min-1）

Cumulative damage probability %＊Repeating acceleration: 1s ⇒ constant speed: 1s ⇒ deceleration: 1s
99

5. Application of effective additives togrease 9)

L10=11.8h L10=27.1h

80

In order to verify the effects of peroxomolybdate in
the grease, an accelerated reproducibility test was
conducted using grease lubricated ball bearings with
anti-wear agent (organic zinc + organomolybdenum)
or corrosion inhibitor (peroxomolybdate) added to thebase grease. Fig. 12 shows the Weibull distribution offlaking life. It was verified that all the failed bearings
were caused by hydrogen embrittlement flaking. It was
revealed that the grease with peroxomolybdate
suppressed hydrogen embrittlement flaking similar tooil lubrication.

L10=44.7h

50
20
10
5

Tungstate

Oil with no additives

L10=11.2h

1101Anti-wear agent
Peroxomolybdate
Tungstate

102

103

Life hOxygen depth ratio %

60
50

XPS
(X-ray photoelectron spectroscopy)

40

Cumulative damage probability %Fig. 9 Weibull distributions of hydrogen-relatedrolling contact fatigue life

Oil with no additives
Peroxomolybdate
Tungstate

30
20
10
0

0

50

100

150

Sputtering depth nm

200

No additives

Anti-wear agent

Peroxomolybdate

99
80
50
20
10
5
1
101

Life h102

Fig. 12 Weibull distributions of hydrogen-related rolling
contact fatigue life under grease lubrication

Fig. 10 Oxygen depth profile on worn portion of inner ring raceway-88-*16E_03 18/09/05 18:59 ページ 6

Effects of Lubricant on Hydrogen-Related Rolling Contact Fatigue Life Improvement

5) Masamichi Shibata, Masao Goto, Noriyasu Oguma,
Tsuyoshi Mikami: A New Type of Microstructural
Change Due to Rolling Contact Fatigue on Bearings for
the Engine Auxiliary Devices, Koyo Engineering Journal,
150 (1996) 16.
6) Nobuo Kino, Takeshi Yamamoto, Keizo Otani, Noriko
Uchiyama: Analysis of Short Life Flaking due toHydrogen Embrittlement, Transactions of the Japan
Society of Mechanical Engineers (Series A) 70, 696(2004) 54.
7) H. Uyama, H. Yamada, H. Hidaka, N. Mitamura：The
Effects of Hydrogen on Microstructural Change andSurface Originated Flaking in Rolling Contact Fatigue,
Tribology Online, 6, 2 (2011) 123.
8) Toshiya Kinami: Effects of Hydrogen on Rolling Contact
Fatigue Phenomena due to Hydrogen Embrittlement,
Denkiseiko, 84, 1 (2013) 55.
9) Takayuki Kawamura, Hidenobu Mikami: Development ofLong Life Grease‘NA103A’ for Automotive Components, NTN
TECHNICAL REVIEW, No. 75 (2007) 116.
10）M. H. EVANS：White Structure Flaking (WSF) in Wind
Turbine Gearbox Bearings: Effects of Butterflies andWhite Etching Cracks (WECs), Material Science andTechnology, 28, 1 (2012) 3.
11) Hiroshi Hamada, Yukio Matsubara: The Influence ofHydrogen on Tension-Compression and Rolling Contact
Fatigue Properties of Bearing Steel, NTN Technical
Review, 74 (2006) 50.
12) Hideyuki Uyama: Effects of Hydrogen in Rolling
Bearings, Tribologist 60, 10 (2015) 658.
13) M. Kohara, T. Kawamura, M. Egami：Study on
Mechanism of Hydrogen Generation from Lubricants,
Tribology Transactions, 49 (2006) 53.
14) Yuji Yamamoto, Motohiro Kaneta: Tribology (2nd Ed.)
Ohmsha (2010) 11.
15) Motohiro Ito: The Influence of the Humidity and
Quantity of Hydrogen into Steel under the Abrasive
Wear, NTN Technical Review, 82 (2014) 88.
16) Shigeyuki Mori,, Hidetaka Nanao: Surface Chemistry inMicrotribology, Journal of the Surface Science Societyof Japan, 19, 6 (1998) 379.
17) M. Itoh, T. Kawamura, H. Mikami：Effects of Additives
on Hydrogen-Related Rolling Contact Fatigue Life
Improvement, International Tribology Conference,
Tokyo (2015) 748.

NTN developed its proprietary grease by leveraging
this technology and uses it widely for many
applications in preventing hydrogen embrittlement
flaking.

6. Conclusion
In this article, the mechanism of hydrogen
embrittlement flaking and the technology forpreventing it are discussed. Due to the increased
requirements on energy efficiency from the viewpointof environment protection, rolling bearings tend to be
lubricated under the conditions of a thin oil film, which
may induce metal contact (from use of base oil withlow viscosity). Therefore, the demand for a lubricant
with appropriate measures is increasing. Goingforward, it is expected that the requirement fordevelopment of a lubricant with refined design inchemical composition and characteristics for eachapplication will increase.
In addition, we consider that comprehensive
clarification of hydrogen embrittlement flaking will be
critical, not only from material or lubricant standpoints,
but also by quantitatively linking the operating
conditions of rolling bearings and event probability.

References
1) Seiichi Nozaki, Koushirou Fujimoto, Kenji Tamada:
Brittle Flaking on Bearings for Electrical Instruments and
Auxiliary Devices and Life Extension of these Bearings
NTN TECHNICAL REVIEW No.61 (1992) 36.
2) Kenji Tamada, Kikuo Maeda, Noriyuki Tsusima: A New
Type of Microstructural Change in Bearings for Electrical
Instruments and Auxiliary Devices of Automotive
Engines, NTN Technical Review, 61 (1992) 29.
3) K. Tamada, H. Tanaka：Occurrence of Brittle Flaking
on Bearings used for Automotive Electrical Instruments
and Auxiliary Devices, Wear, 199 (1996) 245.
4) Yasuo Murakami, Hiromichi Takemura, Michiharu Naka,
Takashi Ogawa, Tatsunobu Momono, Akira Iwamoto,
Shigeru Ishihara: Study on Fatigue Mechanism of
Bearings for Automotive Alternators, NSK Technical
Journal, 656 (1993) 1.

Photo of author

Takayuki KAWAMURA
Advanced TechnicalResearch Center-89-

*17E_03 18/09/05 19:00 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Technical Article ]Relationship between Cage Stress and Degree of Freedom of motion
in Dynamic Analysis for Needle Roller Bearings
Naoto SHIBUTANI*Tomoya SAKAGUCHI*
In dynamic analysis considering elastic deformation of cage, it requires
a long time to calculate cage stress. To shorten calculation time, a twodimensional analysis was conducted whose degrees of freedom of
motion were restricted to three. However, an influence of the restricted
degrees of freedom in this analysis was not clarified.
In this paper, the influence of the restricted degrees of freedom on
cage stress and its generating mechanism are discussed by calculating
both two-dimensional and three-dimensional analysis for needle roller
bearings in planetary gears.

planet gear in the planetary transmission, forcalculating the stress on the cage 3).
2-dimensional analysis of 3-degrees of freedom
provides a shorter calculation time compared with 3dimensional analysis of 6-degrees of freedom;
however, skew of raceway, rollers and cage cannot be
considered. In addition, the impact of the difference of
these degrees of freedom on the dynamic analysis of
the cage stress is not clear.
In this paper, we conduct 2-dimensional and 3dimensional dynamic analysis, considering the cage as
an elastic body against the bearings at the planet gear
support and clarify their differences. Together, we
examine the reason why the stress on the cage iscreated when autorotation speed, revolution speed andinput torque of the planet gear are changed.

1. Introduction
Generally, a rolling bearing consists of an inner ring,outer ring, multiple rolling elements and a cage. The
main role of the cage is to place the rolling elements anequal distance apart. If the number of rolling elements
is increased in order to increase the load carrying
capacity of the bearing, the bars of pockets in the cage
become too thin, increasing the risk of damage to thecage itself. Therefore, the bearing needs to be
designed to predict the stress applied on the cage.
Since measuring stress applied to the rotating cage is
not easy, prediction using dynamic analysis is aneffective method.
A bearing application where a large load is applied tothe cage is the support portion of the planet gear in theplanetary transmission. The reason why a large load isapplied is because the centrifugal acceleration from theplanetary motion is always applied to the bearings.
Suzuki et al. 1) reported factors that generate thrustforce and running torque due to roller skew by dynamic
analysis, including 3D behavior on needle roller
bearings under planetary motion. However, stress on
the cage is not considered as the cage is assumed to
be a rigid body.
Sakaguchi et al. 2) calculated stress on the cage bydynamic analysis of the bearings taking into
consideration elastic deformation of the cage. They
also explored 2-dimension dynamic analysis,
considering only 3-degrees of freedom on the radialplane wave for the bearings at the support area of the

2. Dynamic analysis model
As shown in Fig. 1 3), various loads act on the planet
gear, which is the subject of this analysis of theplanetary transmission. These loads determine the loadon the needle roller bearings which support the planetgear. In this paper, we study the impact of the degrees
of freedom of the motion when the stress on the cageof these bearings is obtained by dynamic analysis. The
dynamic analyses are conducted by 2-dimensional
analysis taking into consideration motion of only 3degrees of freedom on the radial plane, and 3dimensional analysis taking into consideration motionof 6-degrees of freedom.

*CAE Engineering Dept., Automotive Business Headquarters-90-*17E_03 18/09/05 19:00 ページ 2

Relationship between Cage Stress and Degree of Freedom of motion in Dynamic Analysis for Needle Roller Bearings

The calculation method of 2-dimensional analysis is
the same as the existing report 3)., introducing thefollowing 5 assumptions for simplification of theanalysis model. As a result, Fig. 1 can be simplified as
Fig. 2.
(1) The center of the inner ring raceway which is fixed
to the carrier moves on the circular orbit around thecarrier center at a constant speed. That is, thecarrier autorotates at a constant speed with its
center at a fixed position.
(2) The outer ring has degrees of freedom of 2 translation motion on the radial plane andautorotates at a constant speed.
(3) The roller and the cage have degrees of freedomof 2 -translation motion and 1-rotation motion on
the radial plane.
(4) The centrifugal force of the planet gear itself is only
supported by the bearings.
(5) The radial force components of the sun gear andring gear to the planet gear are assumed to bebalanced. Therefore, only the force generated by
the input torque of the transmission acts on the
direction of the planet gear revolution (Fig. 2).

On the other hand, key assumptions of 3dimensional dynamic analysis are as follows:(1) Motion of the inner ring and outer ring is the sameas the 2-dimensional analysis.
(2) The roller and cage have 6 degrees of freedom forthe motion.
(3) The outer ring has a flange face in contact with thecage.
(4) The cage can be in contact with the roller, outerring raceway and outer ring flange face.
(5) Assumptions (4) and (5) in the 2-dimensional
analysis also apply to the 3-dimensional analysis.
In the contact calculation of the roller and cage inthe 2-dimensional analysis, as shown in Fig. 3, theforce acting on the cage is applied to both ends of thelines set on the bar of the cage, and the lines set
according to the interference amount of the roller.

Force fromroller to cage

Bar

RollerContact line

FRingGear :Ring gear force

Ring gear

Fig. 3 Contact calculation method between roller andcage in two-dimensional analysis

Rotationplanetgear

yRotationx

Carrier force(input torque)On the other hand, in the contact calculation of theroller and cage in the 3-dimensional analysis, as
shown in Fig. 4, many nodes are placed on the cage
pocket surface which is in contact with the rollers, andthe forces that act on these nodes are calculated.
In addition to these assumptions, the calculation
methods for the contact area between the rollers andraceway, and between the cage and raceway are thesame as the existing reports 1), 3). These analyses
mentioned above consider all apparent forces(centrifugal force, inertia force, etc.).
Hereinafter, 2-dimensional analysis is referred toas "2D analysis", and 3-dimensional analysis as "3D
analysis."

Revolution

FPCent :Centrifugal force

FSunGear :Sun gear force
Sun gearFig. 1 Actual forces and motions on a planet gear 3)

Constant
speedplanet gear

Constant
revolution speed

FPCentComposite force
due to the gears(Reaction force
of input torque)

Contact plane

Centrifugal force

Marker for contact

Fig. 4 Contact calculation method between roller andcage in three-dimensional analysis

Fig. 2 Analyzed forces and motions on a planet gear 3)-91-

*17E_03 18/09/05 19:00 ページ 3

NTN TECHNICAL REVIEW No.85（2017）

2.0

3. Subject of analysis

three-dimensional analysis

Dimensionless stress

The specifications of the planetary transmission
mechanism and needle roller bearing, which are thesubject of analysis, are shown in Table 1. The cage isthe steel cage of the outer ring guided type (NTN's"KMJ-S" type). The operating conditions listed in thetable are the standard conditions of this analysis. In
addition, the input torque into the planetarytransmission mechanism assumes that it applies tothe carrier.

1.5

1.0

0.5

0.0

Operating conditions

Bearing
Planetary
specifications mechanism

Table 1 Specifications of needle roller bearing andplanetary gear system
Pitch circle diameter of sun gear (mm)Pitch circle diameter of planet gear (mm)Pitch circle diameter of ring gear (mm)Weight of planet gear (kg)Outer ring raceway diameter (mm)
Inner ring raceway diameter (mm)Roller diameter (mm)Roller effective length (mm)Number of rollers
Revolution speed of planet gear Nc, min-1
Autorotation speed of planet gear Np, min-1
Load acted on each bearing fromthe input torque (N)Lubricating oil
Typical temperature of lubricating oil (℃)

two-dimensional analysis

0

10,00020,00030,00040,00050,00060,000

Planet gear rotation speed Np, min-1

Fig. 5 Cage stress with various rotation speeds of planetgear (orbital rotation speeds of planet gear Nc=5,000 min-1)

95.3
28.7
152.7
0.05
19.85
13.85
2.997
13.8
11
5,000
17,000analysis. This is assumed to be the reason why thecage stress in 2D analysis is slightly higher than 3D
analysis.

4.2 Impact of revolution speed of planet gear
Fig. 6 shows the dimensionless maximum principal
stress of the cage when the autorotation speed of theplanet gear is fixed to 17,000min-1 and the revolution
speed of the planet gear is changed from 2,500min-1
to 20,000min-1. Even if the cage stress from the 2D
analysis is slightly higher than 3D analysis, thedifference between those analyses is small and thestress increases as the revolution speed increases.
This change of stress is nearly proportional to thesquares of revolution speed.
Comparing Fig. 5 and 6, the impact of revolution
speed of the planet gear on the cage stress is larger
than the autorotation speed of the planet gear.

300
Mineral oil
ISO VG100
100

4. Calculation results of cage stress
4.1 Impact of autorotation speed of planet gear
Fig. 5 shows the cage stress by 2D and 3D
analyses when the revolution speed of the planet gearis fixed to 5,000min-1 and the autorotation speed ofthe planet gear is changed from 11,000min-1 to53,000min-1. The vertical axis of the figure indicates adimensionless number with the maximum principal
stress divided by the fatigue strength of the material(dimensionless maximum principal stress). Even if thecage stress from the 2D analysis is slightly higher than
3D analysis, the difference between those analyses issmall and the stress increases as the autorotation
speed increases.
In the calculation of force acting on the bar of thecage in 2D analysis, as shown in Fig. 3, since the load
evaluation point is placed on the cross section of thebar center in the axial direction, the load evaluation
point is far from the base of the bar of the pocket
compared with the case of 3D analysis. As the cagestress increases at the base of the bar, the cagestress in 2D analysis is calculated higher than 3D

8

two-dimensional analysis
three-dimensional analysis

Dimensionless stress

7
6
5
4
3
2
1
0

0

5,000

10,00015,00020,00025,000

Planet gear rotation speed Np, min-1

Fig. 6 Cage stress with various orbital rotation speeds ofplanet gear (rotation speeds of planet gear Np=17,000 min-1)-92-

*17E_03 18/09/05 19:00 ページ 4

Relationship between Cage Stress and Degree of Freedom of motion in Dynamic Analysis for Needle Roller Bearings

4.3 Impact of input torqueFig. 7 shows the dimensionless maximum principal
stress of the cage when the revolution speed of theplanet gear is fixed to 5,000min-1, the autorotation
speed of the planet gear is fixed to 17,000min-1, andthe load that acts on each bearing by input torque ischanged from 0N to 1,200N. In 2D analysis, themaximum principal stress changed according to theload, but in 3D analysis the change is small. The
reason for this will be interpreted later.
In the above calculation, the calculation timerequired for 2D analysis was 1/10 - 1/30 of 3D
analysis, considerably shorter than 3D analysis.
Fig. 8 Result in two-dimensional analysis when the maximum
cage stress occurs at the planet gear orbital speed of 5,000 min-1

2.0

two-dimensional analysis

Dimensionless stressthree-dimensional analysis
1.5

1.0

0.5

0.0

0

500

1,000

1,500

Reaction force of input torque N

Fig. 7 Relationship between reaction force of input torqueand cage stress (rotation speeds of planet gear Np=17,000
min-1, orbital rotation speeds of planet gear Nc=5,000 min-1)

Fig. 9 Result in three-dimensional analysis when the maximum
cage stress occurs at the planet gear orbital speed of 5,000 min-1

The maximum principal stress occurred with thepocket at the exit of the load zone, different from 2D
analysis. Relatively high stress was also observed in
the load zone and with the pocket at 9 o'clock.
Compared to 2D analysis, even if the location of thepocket with the maximum principal stress wasdifferent, the location where relatively high cage stressoccurred, including the maximum principal stress,
were the same.
In these calculation results, the principal forces thatact on the cage are categorized into 5 items, as
shown in Fig. 10.
(1) FRfc: Force that acts on the front bar of the cage
pocket from the rollers, mainly by the centrifugal
force of the rollers(2) FRrc: Force that acts on the rear bar of the cage
pocket from the rollers, mainly by the centrifugal
force of the rollers(3) FRi: Force that acts on the cage from the rollers in
the load zone
(4) FFg: Friction force that acts on the cage from the

5. Cause of cage stressFig. 8 shows the calculation result at the instancewhen the principal stress of the cage became themaximum, when the revolution speed of the planetgear is at 5,000min-1 in 2D analysis. The bearings
revolve toward the right and the outer ring autorotatesclockwise. The center of rotation of the carrier is at thebottom of the figure and the centrifugal force acts
upward. Due to the centrifugal force of the planet gearand the input torque of right rotation, four rollers ataround the 5 o'clock position (indicates the position
within the bearing compared to a clock) support thebearing load. The maximum principal stress occurredat the second pocket from the exit of the load zone.
Other locations where relatively high stress occurred
were within the load zone and the pockets at 9 and 10
o'clock. On the other hand, Fig. 9 shows thecalculation result at the instance when the cage stressbecame the maximum, when the revolution speed was
at 5,000min-1 in 3D analysis.
-93-*17E_03 18/09/05 19:00 ページ 5

NTN TECHNICAL REVIEW No.85（2017）

Centrifugalforce② FRrc :Roller
forces acting on
the rear bar bycentrifugal force

Reaction force
of input torque① FRfc :Roller
forces acting on thefront bar bycentrifugal force

planet gear’s rotation● The maximum principal stress of the cage occurs
outside the load zone in both 2D and 3D analyses.
It can be explained that in 2D and 3D analyses ofrevolution speed of 5,000min-1, the collision of rollers
and the cage caused an increase of FRfc and FRi, togenerate high cage stress, and at 15,000min-1, thecentrifugal force due to high revolution speed
increased the impact of FRfc and FRrc, generating the
maximum principal stress in the non-load zones ofboth 2D and 3D analyses.

④ FFg :Friction force from gulding land
⑤ FNg :Normal force from guiding land

Load zone③ FRi :Roller forces in load zone

Fig. 10 Principal forces acting on cageouter ring guideway(5) FNg Normal force that acts on the cage from theouter ring guideway
In Fig. 8 and 9, either FRfc or FRrc occurred at almost
all of the pockets out of the load zone. Since thecenter position of the cage and the rotation speed canbe considered mostly constant, the forces andmoments that act on the cage can be considered asbalanced. Therefore, FRi should be balanced with themoments of FRfc, FRrc and FFg on the cage.
Based on this kind of dynamic characteristics, themechanism that the maximum principal stress occurs
can be explained as follows:● At the exit of the load zone, the roller is accelerated
by the centrifugal force colliding to the front (in the
direction of revolution) bar of the cage pocket. At
that time, FRfc surges.
● With the collision, autorotation of the cageincreases; however, since the rollers in the non-loadzone can move freely, change of FRrc is small.
● Since the rollers within the load zone cannot movefreely as they are caught in the raceways, theaccelerated cage and rollers collide, and the cage
decelerates. That is, FRi surges as it offsets themoment of FRfc
As a result, as the rollers out of the load zone
collide to the cage, FRfc and FRi surge and the stress ofthe pocket receiving these forces increases.
Next, Fig. 11 and 12 show the calculation results at
the instance when the cage stress became themaximum, when the revolution speed was at
15,000min-1 in 2D and 3D analyses. Compared withthe case of revolution speed of 5,000min-1, thefollowing is observed:● As the centrifugal force of the rollers is large, thecage stress is also high at 6 times.
● As the centrifugal force of the planet gear is also
large, the load zone is wider and the center of theload zone becomes closer to 6 o'clock.

Fig. 11 Result in two-dimensional analysis when the maximum
cage stress occurs at the planet gear orbital rotation speed of
15,000 min-1

Fig. 12 Result in three-dimensional analysis when the
maximum cage stress occurs at the planet gear orbital rotation
speed of 15,000 min-1-94-*17E_03 18/09/05 19:00 ページ 6

Relationship between Cage Stress and Degree of Freedom of motion in Dynamic Analysis for Needle Roller Bearings

respectively, under the conditions that revolution speedof the planet gear is 5,000min-1, autorotation speed is
17,000min-1, and the load applied to each bearing fromthe input torque is 300N. The characteristics of 3D
analysis when the force that acts on the cage iscalculated is that the distribution in the axial direction isconsidered, as shown in Fig. 16,. In this calculation offorces, skew of the rollers is considered as well.
The total forces that act on the cage from the rollers
in Fig. 15, and 16, are summarized as 61N in 2D
analysis and 31N in 3D analysis. It is considered thatthe difference comes from the skew of rollers as
described in the following.
Fig. 17, shows an image of the rollers colliding into
the cage in 2D and 3D analyses. In 2D analysis, theroller does not skew, even when the roller and the barof the cage collide. On the other hand, in 3D analysis
where skew of the rollers is considered, the rotation in
the direction of the skew also changes, not onlytranslational motion when the roller collides to the barof the cage pocket. Since it is rare that the peaks ofeach motion occur at the same time, the normal force
of collision is distributed on the time axis. That is, byconsidering the rotational motion the time that theroller and the bar of the cage are in contact is
extended. As a result, the maximum value observed
during collision in 3D analysis becomes smaller than
2D analysis.

6. Comparison of 2D and 3D analyses
In this chapter, we examine the difference intendency of stress change in 2D and 3D analyses
when the input torque described in 4.3 is changed.
First, we discuss the impact of change of the input
torque and the reason why this caused the cagestress change in 2D analysis.
Fig. 13 a) is the status of forces that act on the loadzone and cage, FRfc, FRrc and FRi , when the input
torque is small. When the input torque increases, as
shown in Fig. 13 b), the load zone moves to the rightside, which causes the non-load zone to move as well.
As a result, the difference between FRfc and FRrc
increases, which causes an increase of FRi forbalancing the moments of the cage. Since the collision
force of the roller exiting the load zone to the bar of
the cage pocket depends on acceleration of the roller
from the centrifugal force, as shown in Fig. 14, theangle at the exit of the load zone plays an importantrole, indicating that the collision force becomes larger
when the input torque is smaller.
As the force applied to the cage changes, the cagestress in 2D analysis changed as shown in Fig. 7 4).
Next, the reason why the cage stress did not change
in 3D analysis when the input torque changed is
discussed in detail.
The forces that act on the cage from the roller at the
instance when the maximum principal stress occurredin 2D and 3D analyses are shown in Fig. 15, and 16

Centrifugal
force

Reaction force
of input torque
FNfc
FNrc
FRl

Load zone

Rollera) Small input torqueLoad zoneb) Large input torqueFig. 15 Roller force on cage when the maximum cagestress occurs in two-dimensional analysis

Fig. 13 Load zone and principal forces acting on cageunder large and small reaction forces of input torques

Cage bar

Direction ofcollision

Centrifugal
force
RollerLoad zonea) Small input torqueLoad zoneb) Large input torqueFig. 14 Location of load zone and acceleration of roller
by centrifugal force under large and small reaction forcesof input torques

Fig. 16 Roller force on cage when the maximum cagestress occurs in three-dimensional analysis-95-

*17E_03 18/09/05 19:00 ページ 7

NTN TECHNICAL REVIEW No.85（2017）
Two-dimensional analysis

Three-dimensional analysis

stress was observed in 3D analysis. That is because
in 3D analysis, as skew of rollers is considered, theforce when the rollers collide into the cage isdistributed and the maximum value is reduced.
With the above study, it can be determined that in
2D analysis the impact force of collision tends to beoverestimated and the cage stress is calculated on thehigh side. If 2D analysis, which can be done in a
relatively short time, is conducted first to study cagestrength then the cage may be efficiently designed on
the safe side.
One point to note, in this analysis the damping
effect of lubricant which exists inside the bearings isignored. Therefore, the actual collision force should besmaller than the values obtained in this calculation;
however, their magnitude is unknown and remain atechnical challenge for the future.

cagerollerRoller collides with cage

Roller collides with cage
Normalforce

Cage bar deforms
by contact

Cage bar deforms
and roller skews

Roller leaves cage

Cage bar deforms
and roller skews

Roller leaves cage

8. Conclusion

Fig. 17 Difference in collision between roller and cage in
two-dimensional and three-dimensional analysis

Recently, a shorter time to market is required indesign and development of automotive components.
On the other hand, the importance of analyses isincreasing. Therefore, we would like to promote anefficient product development by fully grasping thecharacteristics of analysis assumptions in order toquickly deliver the analysis results.

This is the reason why the change of the cagestress was small when the input torque was changed
in 3D analysis.
In addition, although the roller which the centrifugal
force acts on remains in contact with the cage for a
relatively longer time, there does not appear to be acollision. Contact of the rollers in the non-load zone
and the cage are not collision-like either. Under thesesituations, even with or without the consideration ofrotational motion on the skew direction, the time ofcontact should remain almost the same. The reason
why the 3D analysis result was similar to 2D analysis
in Fig. 5 and 6 is because the cage stress was
dominated by the phenomenon of the relatively longcontact time, as mentioned above.

References
1) Atsushi Suzuki: Dynamic Analysis of Needle Roller
Bearings on Torque Loss, Transactions of the Japan
Society of Mechanical Engineers Series C, Vol. 79 No.
801, (2013) 1386-1395.
2) Sakaguchi, T., et al : Dynamic Analysis of Cage Stressin Tapered Roller Bearings, Proc. ASIATRIB 2006
Kanazawa, Japan，(2006) 649-650．
3) Tomoya Sakaguchi: Dynamic Analysis for Needle
Roller Bearings Under Planetary Motion, NTN
Technical Review No. 75, (2007) 94.
4) Naoto Shibutani: Dynamic Analysis for Needle Roller
Bearings Under Planetary Motion, Journal of Society ofAutomotive Engineers of Japan, Vol.71, No.9 (2017)97-101.

7. Summary
For the needle roller bearings under planetary
motion, 2D and 3D dynamic analyses wereconducted, taking into consideration elastic
deformation of the cage and the impact that degrees
of freedom of motion has on the cage stress was
examined.
As a result, when autorotation and revolution speedof the planet gear was changed, the trend that thestress increases as the rotational speed increases
was verified in both the 2D and 3D analyses. On theother hand, when the input torque was changed,
stress change due to the change in the load zone wasobserved in 2D analysis, but little change in cage

Photo of authors-96-

Naoto SHIBUTANITomoya SAKAGUCHICAE Engineering Dept.,
Automotive Business
Headquarters

CAE Engineering Dept.,
Automotive Business
Headquarters

*18E_03 18/09/05 19:01 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ New Product ]Proposal of Low Fuel Consumption andHigh Functionality of Composite Material Products for Automobile
Kayo SAKAI*
Hajime ASADA**

Tomonori YAMASHITA**
Takuya ISHII***We manufacture and sell composite material products molded fromresin and metal powder. These products are used in a wide variety offields because of their high degree of freedom in shape and their ability to
impart various functions. In this paper, we introduce composite material
products that contribute to low fuel consumption and high performance ofautomobiles.

1. Introduction

2. Seal rings for transmissions

NTN is manufacturing composite material products
using resin and metal powder as raw materials andcombining our own proprietary design at the affiliatedcompanies shown in Fig. 1. The composite material
products are used in broad fields as the compositionof resin, metal powder, and additives are changed
according to operating conditions. In addition, since
they are formed with molding, they have a high degreeof freedom for shaping, which provides good volume
production properties for products with complex
shapes. NTN is manufacturing and distributing oil
retaining bearings and plastic bearings containinghydrodynamic BEARPHITE, machine parts (such as
sliding parts), gears and cams, magnetic products(such as magnetic sensors), and reactors for broad
industries (such as automotive and industrial
machinery).
In this article we introduce composite material
products that contribute to fuel efficiency and highfunctionality for automotive applications.

Several resin based seal rings, with outer diametersfrom 15 to 60mm, are used in automobiletransmissions. Seal rings are required to have low
torque and low oil leak characteristics for fuelefficiency. NTN has developed a low torque seal ring 1)
made of PEEK (polyetheretherketone) with a 60%
reduction in torque by providing a V-shaped
lubrication groove on the side of the seal ring (Fig. 2),
low oil leakage equivalent to the conventionalgrooveless product, and started volume production.
However, as regulations on the fuel efficiency ofvehicles continues to become more strict, even lower
torque is required. With the developed productincorporating an optimized V-shape lubrication groovein low torque seal rings, we achieved an additional 10- 15% lower torque.
Seal rings are installed between the relative moving
shaft and housing in the hydraulic circuit of thetransmission. They seal oil and maintain pressure
within the hydraulic circuit, pressed against both the
housing inner diameter and the side wall of the shaft
groove with hydraulic pressure in a sliding motion(Fig. 3). The contact area between the seal ring andComposite Material Product Division

BEAREE®

NTN Engineering Plastics Corporation
Plastic bearings, inject molding products
Resin machining, coated parts

Abutment

Bearphite®, Nikamet®

NTN Advanced Materials Corporation
V-shape lubrication groove

Oil-impregnated sintered bearings, sintered machine parts
Magnetic Material Products, resin moldings

Hydrodynamic Bearphite®

NTN Manufacturing (Thailand) Co.,Ltd
Hydrodynamic bearing parts

Fig. 1 Composite material products of NTN group

Fig. 2 Low torque seal ring***New Material Development Dept. Composite Material Product Division***Composite Material Engineering Dept. Composite Material Product Division***Engineering Dept. NTN Engineering Plastics Corporation-97-

*18E_03 18/09/05 19:01 ページ 2

NTN TECHNICAL REVIEW No.85（2017）

Table 1 Test seal rings

Seal
rings

Hydraulic

Test seal rings
Shaft grooveside wall

Hydraulic

Lubricating oil

Housingシリ

Shape of side lubrication groove

Low torque seal ring V-shaped(conventional product)
12

Low torque seal ring
(developed product)

Shaft

V-shaped
24

Seal ring dimensions: outer diameter 45mm, thickness 2mm, width 2.4mm

Fig. 3 Operating state of seal ring

[Test conditions]

Seal ring tester: Hydraulic pressure: 0.4 - 1.2MPa, rotation speed: 2,000min-1
Iron-based housing/shaft: ATF (oil temperature 80˚C)side wall of the shaft groove is smaller than thecontact area between the seal ring and housing innersurface; therefore, when the housing or shaft rotates,
the seal ring side and side wall of the shaft groove
slide due to lower sliding resistance. Therefore,
providing lubrication grooves on the side of seal rings
is effective for torque reduction and manufacturers areworking on the design of their shapes.
NTN's low torque seal ring reduces torque as theedges of the V-shaped lubrication groove are underhigh pressure due to hydrodynamic effects. As thegroove is symmetric, the seal ring can be installed on
the shaft without concerns regarding direction.
Table 1 shows the conventional and developed low
torque seal rings and Fig. 4 shows the dependency of
torque on oil hydraulics.
The developed low torque seal ring showed a 10 15% torque reduction from the conventional product.
An increasing number of V-shaped lubrication
grooves is a factor in lower torque because ofelevated hydrodynamic effects; however, it can be afactor in increasing torque as the sliding area between
grooves increases as well. Therefore, optimization of
the number of lubrication grooves, as well as
optimization of width and length in the circumferential
direction were investigated for the developed product.

Low torque seal ring (conventional product)
Low torque seal ring (developed product)

0.14

Torque N・m

0.12
0.10
0.08
0.06
0.04
0.02

0

0.5

1

1.5

Hydraulic MPa

Fig. 4 Torque versus oil pressure

pumps was 20.8 million units and is expected to growto 34.75 million units in 2020 and 54.7 million units in
2025.
Fig. 5 shows the typical configuration of electricwater pumps. The rotor (which integrates the impeller,magnet and sliding bearing) is contained in the pumpchamber and the stator is placed facing the magnet.
The rotor is supported by the shaft via sliding
bearings. The magnetic field is generated byenergizing the stator which rotates the rotor, and theimpeller transports the coolant water out of the pumpchamber.

3. Plastic sliding bearings for electricwater pump

Coolant OUT

Electric water pumps are being installed on internal
combustion engine, hybrid, and electric vehicles, withthe trend of electrification and improved fuel efficiency
of vehicles. They have the advantage of arbitrarily
controlling flow as they are battery powered, and areused for cooling engines, inverters, and motors, aswell as for heating the cabins. BEAREE AS5704
sliding bearings 2), which use polyphenylenesulfide(PPS) blended with special filler, are adopted in theseelectric water pumps, contributing to energy saving.
The global market volume in 2015 of electric water

ImpellerThrust block

StatorMagnetThrust block

Coolant IN
Pump chamber
Shaft (fixed)

Sliding bearing

Fig. 5 Structure of electric water pump-98-

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Proposal of Low Fuel Consumption and High Functionality of Composite Material Products for Automobile

When the rotor operates, radial and axial loads are
generated in the inner diameter of the sliding bearing
and the shaft, as well as the ends of the sliding
bearings and thrust block slide.
For electric water pumps, carbon sliding bearings
have been traditionally used. The carbon sliding
bearings are tolerant to corrosion from the coolant andsingle-piece forming with the impeller is also possible;
however, the degree of freedom for shaping is low andcosts are high as they are made by machining from themolded material.
The plastic sliding bearings made of PPS are superior
in self-lubricity, chemical resistance, and are made by
injection molding, which brings a high degree of freedom
for design, including shaping and low cost. It is possible
to easily form lubrication grooves on the inner diameterand at the ends of the bearings, as well as the structure
for retaining the bearings with the impeller on the outer
diameter of the bearings (D-cut, protrusion, etc.) by
injection molding, making it possible to form a singlepiece with the impeller without machining.
The sliding bearings are required to have low-wear
properties, long operating life, and not damage/wear themating components in the coolant. Therefore, BEAREE
AS5704 sliding bearings shown in Fig. 6 were adopted.
The following is a list of features for these bearings.

[Test conditions]
700

0.6

600

0.4

500

0.2

400

0

300
200
100
0

BEAREE
AS5704PPS+
PPS+
Glass fiber Carbon fiber

PPS+
PTFE

Dynamic friction coefficient×10-8
mm3/(N・m)

Specific wear rate

Ring-on-disk type tester under water, room temperature
Contact stress: 0.4MPa Speed: 25m/min Mating material: SUS304 50h

Fig. 7 Relation between PPS bearing materials
and sliding property

4. Bearings for power windows and fan
motorsOil-impregnated sintered bearings are widely used in
automotive and industrial machinery applications, andthe materials are broadly categorized into bronze-based,iron-based, and bronze-iron-based. For applications
where high sliding properties are required for the
bearings, such as automotive electrical components for
power windows, fan motors, copiers, and laser printers,
bronze-based materials are the most appropriate.
However, due to the recent increase in copper prices,
NTN developed Bearphite CL 3) as a new material toreplace the bronze-based material by reducing the useof copper.
Bearphite CL is characterized by showing the same or
higher maximum permissible PV value when compared
to bronze-based material and the same or higher wear
resistance when compared to bronze-iron basedmaterial, all while reducing the use of copper by using
unique copper powder.
A thin copper film is formed on the surface by using aunique copper powder, which contributes to superior
sliding properties. Inexpensive iron powder is used
inside, which exhibits superior wear resistancecompared to a bronze-based material. The cross sectionof the bearings is shown in Fig. 8. The upper side of the
figure is the bearing bore diameter on which a thin layerof copper is formed, and iron powder is found inside.
Table 2 shows the chemical composition of
Bearphite CL. The copper content in the mixture isabout 20%; however, copper is exposed on the innerdiameter surface at about 60% or more.
Fig. 9. shows the results of measurement ofpermissible PV value for Bearphite CL.
From this result, it is revealed that Bearphite CLshows a friction coefficient equivalent to bronze-basedmaterial from the low PV value range, and maintains a
low friction coefficient up to the high PV value range.

[Features](1) Wear amount in the coolant water is 1/5 or lessthan the universal PPS sliding bearings.
(2) Low damage/wear properties for mating materials
such as stainless steel.
(3) High degree of freedom for design due to injection
molding.
(4) Usable in antifreeze, acidic, and alkaline fluid.
Fig. 7 shows the comparison of specific wear
amount and dynamic friction coefficient of BEAREE
AS5704 and the bearings of PPS blended with glass
fiber, carbon fiber and PTFE. The specific wear
amount of BEAREE AS5704 is small compared toother PPS bearings, at 1/5 or less of PPS+carbon
fiber bearings. In addition, the friction coefficient of
BEAREE AS5704 bearings is the lowest and stable.

Fig. 6 Plastic sliding bearings for electric water pump-99-

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NTN TECHNICAL REVIEW No.85（2017）

Therefore, it can be used in a broad PV value range.
The evaluation of wear resistance was conductedby measuring the dimensions of the bearing bore
diameter (wear amount) before and after the operation
test. The evaluation results are shown in Fig. 10.
The wear amount of the developed product is lessthan the bronze-based and bronze-iron based
products, which shows that the developed product has
excellent wear resistance.

5. Sliding bearings for AFS and EGR
Within a high temperature environment, lubricant canevaporate due to the heat which presents a risk ofcontamination; therefore, lubricants such as greasecannot be used in the sliding section. NTN is developing
self-lubricating sintering sliding material 4) by adding asignificant amount of graphite, which is a solid lubricant for
improving lubricity.
The self-lubricating sintered sliding material will be used
for AFS (Adaptive Front-Lighting System) (Fig. 11), whichbecomes very hot due to the heat of the head lamp, andbearings for valves of EGR (Exhaust Gas Recirculation)
units which are exposed to hot emission gases.

Copper thin layer

Iron powder

Fig. 8 Section of BEARPHITE CL
Table 2 Chemical components of BEARPHITE CL
Chemical composition wt%
Developed
product

Cu

Sn

C

Fe

15〜22

0.5〜2.5

0.5〜2.5

Remainder

Fig. 11 Self-lubricating sliding material (For AFS)

[Test conditions]

When a significant amount of graphite is added, thefluidity of the material powder is reduced due to the low
bulk density of graphite. This limits the shapes anddimensions that can be molded. In addition, even when
the shapes can be molded, the molding cycle may bedelayed, resulting in relatively high costs. The developed
self-lubricating sintering sliding material has a highdegree of freedom for shaping and productivity, evenwith the significant addition of graphite. This is done byincreasing the fluidity of specially treated graphite
powder. This developed product has superior low friction
properties and wear resistance, even in environments
where lubricants such as grease cannot be used.

・Shaft material: SUS420J2 ・Bearing size: ID 6 x OD 12 x Width 6mm
・Test temperature: room temperature
Bronze-iron based
Bronze-based
Bearphite CL
product (20%Cu)
product

Friction coefficient μ

0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00

0

50

100 150 200 250 300 350 400 450 500 550 600

PV value MPa・m/min

Fig. 9 Limit PV value of BEARPHITE CL[Features](1) Superior friction/wear properties in dry
environments(2) High degree of freedom for shaping is due tospecial graphite
Table 3 shows the chemical composition of thedeveloped product. More than double the amount ofgraphite is added when compared to the typicalbronze-based material.
The friction/wear test conditions of the selflubricating sintering sliding material are shown in
Table 4, and the test results are shown in Table 5.
The friction coefficient of the self-lubricating sintering
bearings was approx. half that of typical bronze-basedmaterials without oil impregnation. In addition, theBore surface wear amount μm[Test conditions]1098・Circumferential speed: 38m/min
・Contact pressure: 4.0MPa
・Bearing size: ID 6 x OD 12 x Width 6mm ・Shaft material: SUS420J2
・Test temperature: room temperature
・Test time: 8 hours

7
6
5
4
3
2
1
0

Bronze-based
product

Bronze-iron based
product (20%Cu)

Bearphite CL

Fig. 10 Abrasion resistance of BEARPHITE CL-100-

*18E_03 18/09/05 19:01 ページ 5

Proposal of Low Fuel Consumption and High Functionality of Composite Material Products for Automobile

wear resistance was improved by approx. 40 times
when compared to the typical bronze-based material.

current to which the performance can be maintained
are called superimposition characteristics. This isconsidered to be a particularly important index.
Generally in order to improve the superimposition
characteristics, a gap is created in the core; however,
the magnetic force leaked from the gap causes theincrease of performance loss and heat generation.
NTN's hybrid product improves superimposition
characteristics without creating a gap by combining
core components with different properties.
The widely used toroidal type is a reactor made of aring-shaped core with coils. To improve the DC
superimposition characteristics, a gap with an air layer
is required, which raises concerns of leakage flux. For
cooling, coils can be directly cooled, but the entire
reactor must be resin sealed for cooling the core.
Fig. 13 shows the newly developed EEP-type hybrid
reactor. The EEP-type reactor has a big opening fordrawing wires compared to the pot-shaped reactor.
In addition to the superior superimposition
characteristics of the gapless core of the pot-shaped
conventional product4), the developed productoptimized the shape of the core. This is done bychanging the cross-section shape closer to a square
which can utilize a larger area for reactor mounting forheat dissipation and to lower the profile for shortening
the heat dissipation path.

Table 3 Chemical components
Chemical composition %Material
Typical bronze-based material
Developed material

Cu

Sn

C

Remainder

7〜11

1〜2

Remainder

7〜11

4〜7

Table 4 Test conditions for friction and wear property(1) Friction test
Rotational speed (min-1)
Test sample dimensions (mm)(inner diameter ×outer
diameter × width)

1,000

450

φ6×φ12×6

φ6×φ12×6

SUJ2

SUS420J2

Mating material

Lubrication condition

15

98

Load (N)Test time (min)(2) Wear test

60
90
No oil impregnation No oil impregnation
(dry)
(dry)

Table 5 Specific wear rate and friction coefficient
Developed material Typical bronze-based material
Friction coefficientSpecific wear rate
m3 / (N・m)×10-12

0.2〜0.3

0.45

0.08

3.56

[Features]

6. Low-profile reactor(1) Excellent superimposition characteristics with
gapless core
(2) Low increase in temperature due to superior heatdissipation(3) Low profile

As part of the recent trend of electrification of
automotive components, many power supply devices
such as converters and inverters are now installed in
vehicles. Reactors are used to regulate voltage
among these power supply devices. In order to makethe power supply devices smaller, the use of highfrequency power is increasing. There are also
increased requirements for reactors to provide stable
and low-loss performance through the higher
frequency range.
A reactor consists of a core made of soft magnetic
material and wires wound around the core called acoil. When a current is supplied to the coil, a magnetic
force is generated in the core. Reactors are capable ofconverting the current in the coil into a magnetic force
and accumulating it in the core. They can thenreconvert the accumulated magnetic force to electric
current and release it from the coil. Reactors are used
to step the voltage up or down in the power supply
circuit by leveraging this conversion capability. As an
example of a reactor, NTN's pot-shaped hybrid reactor(hereafter, pot-shaped conventional product) is shownin Fig. 12.
Reactor performance degrades as the current
increases. The characteristics indicating the level of

Injection
molding core AS10
Compression
molding core AL60

Coil

Fig. 12 Pot type hybrid coreFig. 13 EEP type hybrid core-101-

*18E_03 18/09/05 19:01 ページ 6

NTN TECHNICAL REVIEW No.85（2017）
135 ℃

Table 6 shows a comparison of the developed
product, NTN's pot-shaped conventional product, andgeneral toroidal type product.
The analysis results of the developed product andthe pot-shaped conventional product are shown in
Table 7 and Fig. 14, and the analysis results of heatgeneration are shown in Fig. 15. The heat generation
analysis was conducted with an installation surface(bottom part) temperature of 60˚C assuming cold plate
mounting, and atmospheric temperature of 60˚C.
The developed product has similar superimposition
characteristics, loss and installation space (width anddepth) as the pot-shaped conventional product, with a
22% lower profile. In addition, the generated temperatureof the developed product was 117˚C (increase of 57°C)
compared with the conventional product of 134˚C(increase of 70˚C), improving heat dissipation
performance by approx. 19% by changing the shape ofthe mounting space and lowering the profile.

120
105
90
75

Developed product7. Conclusion
In this article, composite material products are
introduced which contribute to fuel efficiency throughsmaller and lighter form factors and high functionality,
such as improvements to sliding properties forautomotive applications.
Going forward, as electrification of vehicles andcomponent units advance, more rigorous requirementson these component units, as well as accelerated
transition from the conventional components tocomposite material products, are expected.
NTN strives to contribute to the development of theautomotive industry by providing products that match
market trends, not only by raising the added value of thecomponents, but also addressing modularizing andunitizing components, including the peripheral structure.

◎: Excellent

Developed
Pot-shaped
Toroidalproduct conventional product◎○◎○: Good

○
○
○

△
△
◎

△: Fair

Table 7 Iron loss and copper loss by magnetic field analysis
Dimensions (mm)Iron loss※
Copper loss※

Developed product Conventional product
W46×D44×H32
φ42×H41
3.1
3.4
13.1
13.3

References.
1) Kouzou Kakehi, Takumi Kondou, Takuya Ishii, Masato
Yoshino: Development of Low Torque Seal Ring for
Automotive Transmission, NTN TECHNICAL REVIEW,
No. 81 (2013) 68-73.
2) Norio Itoh, Takuya Ishii: Plastic Bearings for Electric
Pumps for Next Generation Battery Cells, NTN
TECHNICAL REVIEW, No. 77 (2009) 49-53.
3) Tomonori Yamashita: Copper-Iron-based Material
Equivalent to Bronze-based Material for Sintered, Oilimpregnated Bearings, NTN TECHNICAL REVIEW,
No. 82 (2014) 30-33.
4) Kayo Sakai, Eiichirou Shimazu, Takahiro Gotou,
Hajime Asada, Takuya Ishii: Product Introduction ofComposite Material for Automotive, NTN TECHNICALREVIEW, No.83 (2015) 54-59.

※With sinusoidal wave current of ripple rate 30% superimposed on DC 20A

Inductance μH

200
150
100

Developed product50

Conventional product

0 0

10

60

Fig. 15 Thermal analysis results

Table 6 Characteristics comparison
Heat dissipation performance
Leakage flux
Height of component

Conventional product

20

Superimposition current A

Fig. 14 DC bias characteristics

Photo of authors

Kayo SAKAI

Tomonori YAMASHITA

Hajime ASADA

Takuya ISHIINew Material Development
Dept. Composite Material
Product Division

Composite Material
Engineering Dept. Composite
Material Product Division

Composite Material
Engineering Dept. Composite
Material Product Division

Engineering Dept.
NTN Engineering Plastics
Corporation-102-

*19_21受賞案件E_*18,19_受賞案件 18/09/05 19:02 ページ 1

NTN TECHNICAL REVIEW No. 85（2017）

Award Winning Products
Japan Powder Metallurgy Association Awards 2016 in New Products Category (New Design)

Hybrid Magnetic Material Reactor Core for Booster
Hajime KATSUURA*

Shinya AMANO*

Shouhei SUZUKI*

Toshihiro TAKAKUSU**

1. Introduction

3. Features"Development of Hybrid magnetic material reactor core forbooster" received the 38th (2016) Industry Award from Japan
Powder Metallurgy Association.
Realization of optimized magnetic performance in the large
current/high frequency range, and miniaturization with a hybrid
structure of an amorphous powder compact and injected
amorphous powder was recognized.

The following shows the features of the hybrid magnet
material reactor coil core.
(1) No magnetic saturation compared to the conventional
ferrite material(2) Reduction of DC superimposition characteristic is less than
1/2, with a large current (300A) compared to theconventional ferrite material(3) Loss of high frequency (100kHz) is 1/10 of theconventional Fe-Si material

4. Effect
Compared to the conventional materials such as ferrite and
Fe-Si based material, the following effects can be obtained tocontribute to the miniaturization and performance
improvement of the devices:(1) 1/8 of volume(2) 2.6 times the maximum applied current (100A -> 260A)(3) 5 times the circuit operating frequency (10 kHz -> 50 kHz)

Fig. 1 Application example (MRI)

2. Structure
5. SummaryFig. 2 shows the structure of the hybrid magnet material
reactor coil core. Miniaturization and high magnetic
performance are optimized by a hybrid structure of anamorphous powder compact and injected amorphous powder,and optimized shaping from magnetic field analysis.
Injection moldingcore AS10

Since this product achieves properties not possible withsingle moldings by a hybrid structure of different moldings,
development for even broader applications is expected.

References

Compression moldingcore AL60

Yoshio Oki: Product Introduction and Complex Technology of Resin,
Sintered Metal and Magnet for Growth Markets, NTN TECHNICALREVIEW No. 82 (2014), 12-20

Fig. 2 Structure of Hybrid magnetic material reactor

Photo of authors**New Material Development Dept.
Composite Material Product Division**Mono-Zukuri Center,
NTN Advanced Materials Corporation

Hajime KATSUURA

Shinya AMANO

Shouhei SUZUKI

Toshihiro TAKAKUSUNew Material
Development Dept.
Composite Material
Product Division

New Material
Development Dept.
Composite Material
Product Division

New Material
Development Dept.
Composite Material
Product Division

Mono-Zukuri Center,
NTN Advanced Materials
Corporation-103-

*19_21受賞案件E_*18,19_受賞案件 18/09/05 19:02 ページ 2

NTN TECHNICAL REVIEW No. 85（2017）

Award Winning Products
Japan Powder Metallurgy Association Awards 2016 in New Products Category (New Design)

Multi Layer BEARPHITE®
Takashi YAMAGUCHI*

Toshihiko MOURI*

1. Introduction
NTN’s development of “Multilayer BEARPHITE®" received
the 38th (2016) Industry Award from Japan Powder
Metallurgy Association.
Our unique, dual layered, large bushing for construction
machinery was highly recognized because of its sliding
performance and wear resistance in the inner layer,
improved strength and ductility in the outer layer, eliminationof the need of CQT (Carburize, Quenching and Tempering)and finish machining.
"Multilayer BEARPHITE®" developed for joints ofhydraulic shovels (Fig. 1), etc. was recognized for achieving
low friction/wear resistance and high strength with low cost.

Kazuki TAKAI**

Outer
layer

Typical iron-based
structural material

Inner
layer

High-strength iron-based
structural material

Fig. 2 Structure of the Multi Layer BEARPHITE®

outer layer is made of strong and inexpensive iron-basedmaterial, blended with metal possessing a low melting point,
achieving the mechanical characteristics equivalent to theconventional products without carburizing and quenching.

Bearings for joints

3. Features
This product achieves a radial crushing strength of
500MPa or more without heat treatment such as quenching.
In addition, correction of dimensional distortion by a sizing
operation is enabled, eliminating the requirement ofmachining.

4. Summary
This product achieves both low friction/wear resistanceand strength by the integrated forming of different materials.
We strive to contribute to the market through thedevelopment of new products.

Fig. 1 Application example

2. Structure
The structure of multilayer BEARPHITE® is shown in Fig.

References

2.

Yosuke SUGAI, Toshihiko MOURI: Multilayer BEARPHITE, NTN
TECHNICAL REVIEW 80, (2012) 83-86.
Toshihiko MOURI, Yoshinori ITOU, Yosuke SUGAI, Eiji YUASA:Award Winning Products, NTN TECHNICAL REVIEW 84, (2016)
115.

This two-layer structure of different materials is made bypowder molding instead of press fitting or adhesion.
The inner layer is made of hard ferrous material, adding
copper to achieve both low friction and wear resistance. The

Photo of authors**New Material Development Dept.
Composite Material Product Division**Composite Material Engineering Dept.
Composite Material Product Division

Takashi YAMAGUCHI

Toshihiko MOURI

Kazuki TAKAI

New Material Development
Dept. Composite Material
Product Division

New Material Development
Dept. Composite Material
Product Division

Composite Material
Engineering Dept. Composite
Material Product Division-104-*19_21受賞案件E_*18,19_受賞案件 18/09/05 19:02 ページ 3

NTN TECHNICAL REVIEW No. 85（2017）

Award Winning Products
2016 “CHO” MONOZUKURI Innovative Parts and Components Awards,
Environmental Components Award

Low Torque Seal Ring
Kouzou KAKEHI*

Takuya ISHII*

Yuuki YAMAZOE*

Souichirou YAMAMOTO*

Takumi KONDOU**(1) 60% lower torque compared to our conventional seal ring(2) 1/10 of the wear(3) Equivalent low oil leakage properties

1. Introduction
NTN developed low torque seal rings 1) for automotivetransmissions (Fig. 1), achieving both low torque and low oilleakage, and started volume production. Recognized for its
contribution to high efficiency transmissions and vehicle fuelefficiency by lowering torque, it received the 2016 "CHO"MONOZUKURI Innovative Parts and Components Award,
Environmental Component Award sponsored by Nikkan
Kogyo Shimbun, Ltd.

Torque (for 2) N・m[Test conditions]Hydraulic pressure: 0.5-2MPa Rotation speed: 4,000min-1
ATF (oil temperature: 110˚C)
1.5
Conventional seal ring
Low torque seal ring
1.0

0.5

0.0
0.0

0.5

1.0

1.5

2.0

Hydraulic pressure MPa

2.5

Fig. 3 Torque versus oil pressure

Fig. 1 Automatic transmission

3. Summary
As the regulations on fuel efficiency will be further
enhanced, continued reduction of torque will be required. By
optimizing the V-shape lubrication groove even further, wehave achieved an additional 10 - 15% lower torque. We will
explore further reduction of torque to meet the market
demand.

2. Features
Fig. 2 shows the structure of the low torque seal ring. By
providing a V-shaped lubrication groove on the side of theconventional PEEK-based seal ring by injection molding,torque was reduced by 60% while maintaining the same low
oil leakage as the conventional product (Fig. 3). This is dueto the hydrodynamic effect that occurs at the edges of the Vshaped lubrication groove.
The low torque seal ring has the following featurescompared with the conventional seal ring:

References
Kouzou Kakehi, Takumi Kondou, Takuya Ishii, Masato Yoshino:
Development of Low Torque Seal Ring for Automotive
Transmission
NTN TECHNICAL REVIEW No. 81 (2013) 68-73

Abutment

Photo of author (representative)

V-shape lubrication groove**Engineering Dept.
NTN Engineering Plastics Corporation**Sales Engineering Dept.
Composite Material Product Division

Fig. 2 Shape of low torque seal ring
Kouzou KAKEHINTN Engineering Plastics
Corporation
Engineering Dept.

-105-*22_23製品紹介E_*20_26製品紹介 18/09/05 19:04 ページ 1

NTN TECHNICAL REVIEW No.85（2017）[ Our Line of New Products ]Thin Type High Precision Angle Sensor
Achieved high precision absolute angle sensing for rotational area ofindustrial machinery with thin and light components

Rubber magnet

Rubber magnet

8.2

Sub track

φ44

φ51.5

Main track

Core metal

Observe magnetization
pattern by pasting
magnet sheet
Core metal

Magnetic pattern

Sub track

Main track

Features(1) Easy miniaturization of rotational area and integration of wiring due to its thin and hollow structure(2) Low impact on response due to light and small inertia moment(3) High precision
Conventional product: angle precision ±0.2˚Developed product: angle precision ±0.1˚Structure

Applications

High precision magnetization of 2 magnetic tracks
with different number of polarized polar pairs(64/63 polar pairs)
Item
Magnet¡Encoder for detecting robot joint angle¡Encoder for detecting motor rotation angle
Magnetic
sensor

Double-track magnetic encoder
R64 (Radial type)
Rubber magnet

Number of polarized 64/63 polar pairs(128 poles/126 poles combining N and S poles)
polar bodies
Size

Outer diameter: φ51.5mm,
inner diameter: φ44mm, width: 8.2mm

Weight10.7g

Inertia moment
Operatingtemperature

Bearing

6.3×10-6 kg m2

Double-track magnetic encoder−40 〜 +120℃

Application of bearings-106-

*22_23製品紹介E_*20_26製品紹介 18/09/05 19:04 ページ 2

NTN TECHNICAL REVIEW No.85（2017）[ Our Line of New Products ]Double row asymmetric self-aligning roller bearings
for main shaft of wind turbines
Long life and improved wear-resistance characteristics
by double row asymmetrical design of rollers
Outer ring

Rear row roller

Front row roller

Inner ring

Cage

Features

Structure(1) Long life:

Achieved long life and improved wear resistanceproperties by efficiently sharing load by front and rearrows in double-row asymmetrical design of rollers

improvement of approx. 2.5 times of calculated life(2) Wear resistance:
improved wear resistance by approx. 30% reduction of
PV value

Front row roller(rotor head side)(3) Compactness and lightweight:
design capability for bearings with life equivalent tothat of conventional products, with approx. 10% lessbore diameter and approx. 30% less weight

Rear row roller(generator side)

L1

L2

Applications¡Main bearings for wind turbines(Bearing application)
Main bearings

Generatorα1α2Wind load(axial load)▷ Contact angle ：α2 ＞α1

α1：Contact angle of front row
α2：Contact angle of rear row▷ Roller length： L2 ＞ L1

L1：Roller length of front row
L2：Roller length of rear row
Rotor head

Cross section

Internal structure of wind power generator-107-