For New Technology Network

R

Special Issue
Automotive Products
for Electric, Autonomous and Low Fuel Consumption
November 2019ISSN 0915-0528 OSAKA, JAPANIntroduction to CAE R&D Center
In October, 2018, CAE R&D Center was established to enhance the R&D and
Manufacturing operations and increase the efficiency of various departments (Design,
Development, Prototyping, Testing, Manufacturing, etc.), reorganizing the existing CAE
Department.
CAE (Computer Aided Engineering) is a technology to validate if the planned product/peripheral structure
satisfies the required performance by computer simulation. This helps us to improve design accuracy where
design validation was conventionally difficult. This even allows us to study the design safety factors of products
including the peripheral components. By simulating fabrication of prototypes and experiment/evaluation of the
prototypes in advance, we can reduce the number of prototype builds and testing to improve the efficiency ofdesign/experiment and provide costreductions.
The recent improvements of CAE have been remarkable and CAE technology has been introduced andenhanced in all the industrial fields. NTN Next Generation Research Alliance Laboratory at Osaka University
also adopts CAE in its research projects for establishing next generation technologies and quickly applying
them to products.
By reducing the R&D man-hours with CAE technology, researchers and engineers are allowed to dedicate
themselves to higher-value activities. The development period can be reduced and competitive products canbe introduced to the market faster. As NTN transforms its operations from the development of single products
to modules and system products, we are appling technology to more complex mechanisms and simulations ofcomposite and different materials.
As an example of CAE simulation technology, the following are some of the calculations of the force applied
from rolling elements to the cage in bearings used to support transmissions which are the power transmitting
devices in automobiles. CAE simulation technology enables the following:· Calculation of the load acting on each rolling element in the bearings of a moving automobile.
· Calculation of the force from the above rolling elements to the cage and the generated stress.
⇒ These calculations help optimize the number and diameters of the rolling elements and improve the bearing
load capacity by precisely determining the required strength of the cage.

Simulation of force applied to cage of transmission bearings and initiation ofstress

TECHNICAL REVIEW
No.87

Special Issue
Automotive Products for Electric,
Autonomous and Low Fuel Consumption

corporation

NTN TECHNICAL REVIEW No.87
CONTENTS

Preface
Contribution
Perspective

Automotive Products for Electric, Autonomous and Low Fuel Consumption
Yoshinori TERASAKA

Perspective for Advanced Vehicle Technology into CASE Era
Hideo INOUE

Professor, Faculty of Creative Engineering, Chair of Department of Vehicle System Engineering,
Kanagawa Institute of Technology

NTN's Approach and Effort for CASE

1
2
13

Koji KAMETAKA

Special Issue for Modular Products for Electric and Autonomous for Automobiles
Hub Bearing Module with Steering Adjust Function

18

Satoshi UTSUNOMIYA, Norio ISHIHARA, Yuusuke OOHATA, Atsushi ITO

Hub Bearing Module with Motor and Generator Function
Kentaro NISHIKAWA, Mitsuo KAWAMURA, Hiroki YABUTA, Atsushi ITO

Development of Control Platform for Electric Module24
30

Tatsuji INOUE, Kazuhiro AOSHIMA, Yuichi SUGIMOTO, Keigo MOTOKUBO

Introduction of Sensor Modular Products and Technologies for Autonomous Driving and Electrification of Automobiles
Yasuyuki FUKUSHIMA, Hiroyuki HAKAMATA, Christophe DURET

Vehicle Motion Control with In-Wheel-Motors

37
44

Junichi HIRATA, Yuta SUZUKI

Automotive Products for Low Fuel Consumption

History of Development of Bearings for Automobiles Aiming at Low Fuel Consumption
Takashi YASUNISHI

History of Development of Axle Bearings Aiming at Low Fuel Consumption
Makoto SEKI

History of Development of Constant Velocity Joints Aiming at Low Fuel Consumption
Tatsuro SUGIYAMALow Friction Hub Bearing Ⅲ

50
55
59
63

Makoto SEKI

Fuel-efficient Compact Chain Tensioner

68

Kouichi ONIMARU, Ikumi AGATA

Fixed Constant Velocity Joint with Ultra High Angle and High Efficiency“CFJ-W”
Masashi FUNAHASHI, Mika KOHARA

Compact Plunging CVJ for Propeller Shaft“HEDJ-P”

74
80

Masazumi KOBAYASHINew Technology of Rolling Bearings contributing to Low Fuel Consumption of Automobiles
Takayuki KAWAMURA, Hiroki FUJIWARA, Kouya OOHIRA

Verification of Torque Reduction for Low Torque Seal Ring by Fluid Analysis
Takuya ISHII, Tomohiko OBATA

Analysis of Dynamics of Hub Bearings under Moment Loads
Tomoya SAKAGUCHI, Naoto SHIBUTANI

85
92
97

Award Winning Products

2018“CHO”MONODZUKURI Component Award, Mobility Components Award,
Ultra-low Friction Sealed Ball Bearing for Transmission

104

The 28th Nikkei Global Environmental Technology Awards, Award for Excellence,
Micro Hydro Turbine

105

Katsuaki SASAKI, Takahiro WAKUDA, Tomohiro SUGAI

Masatoshi MIZUTANI, Fumihiko MATSUURA, Tomoya KAWAI, Hiroki MUKAI, Takashi ITO,
Tomomi GOTO, Yasunari KANAMURA, Kanta KIMURA, Kouji TATEISHI

Our Line of New ProductHandy Type Failure Detection Device
N3 N-CUBE, Container Type Transportable Independent Power Supply

106
107

Preface

A message for the special issue on “Automotive Products
for Electric, Autonomous and Low Fuel Consumption”

Representative Executive Officer,
Senior Managing Executive Officer and CTO (Chief Technology Officer)

Yoshinori TERASAKA
The automotive industry is facing a huge transformation period. All the companies in the world associatedwith automobiles are in the midst of fierce competition in technology, performance and cost, in an industry
which is swept away by the market trend characterized by “CASE,” such as the agreement of controlling
global average temperature at the COP 21 Paris Agreement, electrification to improved fuel economy asa response to global warming, autonomous driving providing improved safety and the idea of a sharedeconomy.
We are a bearing manufacturer with 100 years of history since its foundation; however, we have beenproactive in advanced development ahead of the market trend so that we can achieve “sustainable growth”
and be a “surviving company” into the next generation. The origin of NTN’s development is our corecompetence including tribology technology but we have also expanded our development philosophy fromoriginal development to partnership with third parties.
Our foundation is our core competence in tribology. We think that this core competence continuously
enhances the companys value when it is applied to new products. In our company, the Advanced Technology
R&D Center is in charge of core technology, New Product Development R&D Center is in charge of new
product development and the Process Engineering R&D Center is in charge of manufacturing technology.
The NTN Next Generation Research Alliance Laboratory at Osaka University was founded in 2017 forresearch of next generation technologies which are expected to grow in the future such as AI and IoT. The
NTN Next Generation Research Alliance Laboratory is responsible for incorporating those technologies as
our new core competence, and for the training of our researchers. In addition, the CAE R&D Center was
newly founded in October, 2018. Its purpose is to advance simulation technologies we have been developing
to work on tasks such as engineering challenges of all NTN groups, faster development/refinement andaccuracy improvement. Since simulation technologies are a research area to be further actively pursued, weare continuing our research at the NTN Next Generation Research Alliance Laboratory, as well as elevating
the applicability of these technologies to our development and using them in our products.
We have also realized vehicle autonomous driving and electrification, with advanced development ofmodule and system products, which increased our value in the industry. Those products include IWM (Inwheel motor systems), among others, such as electrical module products that can be used for electricalaccessory devices such as oil pumps, water pumps and vacuum pumps. There are also multifunctional
products such as eHUB and sHUB, which consist of axle bearings (our main product), motor and controller.
We are also contemplating development of “sensorized bearings” . With the integration of special sensors,
we can transform wheel bearing operations offering service solutions such as status monitoring and fault
prevention using the output of those sensors and analyzing them with advanced programs equipped with an
AI algorithm.
We have been preparing for the drastic transformation of the automotive industry by reorganizing our R&D
and production systems. We believe that the success of our challenge of “sustainable growth” and being a“surviving company” depends on how we can achieve competitive products fast, taking advantage of thetechnologies and know-how accumulated so far. The foundation for this challenge is our mid-term businessplan “NTN100” of 2015. In “DRIVE NTN100” of 2018, we set a plan to promote new products.
We would be grateful if these plans can contribute to further development of the entire industry.

NTN TECHNICAL REVIEW No.87

1

Contribution

Perspective for Advanced Vehicle Technology into CASE Era

Hideo INOUE
Professor, Faculty of Creative Engineering, Chair of Department of Vehicle System Engineering,
Kanagawa Institute of Technology

What is the CASE (Connected, Autonomous, Shared & Services, Electric)1)era?
The integration of information and mobility has begun a paradigm change that will
drastically change the ecosystem of people, cars, and transportation society, and it
can be said that it is a borderless competition and collaborative era of Silicon Valley
players, European car manufactures, new comers, and developing countries. Looking
back on the history of automotive technology, I would like to discuss this perspectivewith you based on the examples of the evolution of safety, deepening driving, andmobility city systems that are the foundation of the eco-system.

1. Introduction
Automobiles have contributed to the developmentof industry and culture by expanding free and safe
transportation of people and goods since the endof the 19th century. In 1885, Karl Benz of Germany
succeeded in running a 3-wheel vehicle with a newly
invented gasoline engine on a public road. The
glorious first-ever automobile’s name was Benz Patent
Motorwagen. It created the basic form of the current
automobile. In 1908, the king of automobiles, Henry
Ford, introduced the mass-production “Model T,” ashe “wanted a vehicle as fast as a train that can run
anywhere like a horse,” which created an “automotive
revolution.”
And today, the environment surrounding theautomotive industry is in a foregoing period of a large
paradigm shift, such as diversification of power train
led by electrification, global competition of autonomous
driving, acceleration of “intelligent vehicles with IoT”
and transformation of “ownership and use of vehicles”
as can be seen in “emergence of sharing services.”
From the perspective of the global industry
competition, energy, IT and automotive industries
are actively partnering with each other across theborders for innovation and acquisition of new businesssegments while competing with each other. Even inthis environment, however, we cannot overlook thefact that Tesla’s fast growth quickly achieved entry
to the automotive industry from Silicon Valley, by notjust building an EV but by building a vehicle platform
through electrification that cannot be achieved by theconventional internal combustion engine power train.
Tesla created a vehicle with very high fundamental
performance that is fun, comfortable and attractive toconsumers.
2

NTN TECHNICAL REVIEW No.87

Also, the European automotive industry, led byGermany, is diligently working on the evolution ofenvironment-friendly, comfortable, easy-to-drive
and intelligent vehicles incorporating advanced
technologies such as drive assistance and connectivity
backed up by the respective state through thecollaboration among the industry, academia andgovernment. In addition, these new trends havepotential to quickly expand to the automotive markets
of emerging countries such as China, India and SouthEast Asian countries. The Japanese automotive
industry also needs to be competitive to win inthis paradigm shift both in global competition andcompetition with other industries such as IT.
These global trends can be interpreted as asolution to the compelling social problems such as
global warming, traffic jams/accidents, declining
birthrate and an aging population while achieving arich and comfortable mobility society. In other words,
the automotive innovations with better and smartervehicles are the “primary units” and “driving force” forenriching the communities and the citizens (Fig. 1).

Electrification

Intelligence

Driving&
Mobility

Traffic
Accidents

Innovation
Aging
Society

Lightweight/rational
vehicle package

Traffic
Jam

Information

Fig.1 Direction of vehicle innovation

leadership, its own core technology is needed.
Thus, the ecosystem raised by CASE can also be
expressed as the cyber physical system (Fig. 2)5).

Near-miss incident data and accident
prediction analysis
Evolution of the map for dynamic application
Predition simulations of traffic congestion
etc.

Runningenvironment database

Human factor database

Fig. 2 Example of cyber physical system

The cyber physical system is a system of cyber
space (virtual space) and physical space (real space)highly integrated by ICT.
I highly expect the automotive industry to achieveself-transformation and take the leadership of otherindustries by putting the people (citizens) in the centerof mobility (Fig. 3).
・Vehicle innovation drives social system reform

Toward new
ecosystem

Renewable energy
Electricity/
infrastructure industry

Distributed power

Grid power

Evolution of social infrastructure

(3)

BEMS
HEMS

?

Environment/energymsCollaboration with other industries(1)

Horizontal specialization

lo
b

(2)

al

st
an

da

rd
s

/n

or

Battery

Automobile
industry

G“The real automobile innovation is starting now!”“Vehicle development” and “human development” with“integration of advancement and foundation” will makeor break is not an overstatement.
Now, let me discuss the perspective raised in thetitle of this paper by looking back at the ITS (Intelligent
Transport System) activities so far. Although CASE
(Connected, Autonomous, Shared & Services, Electric)
is a term that expresses the current paradigm shiftof the automotive and IT industries well, it is not so
different from the change nurtured by the long ITS
activities aiming for the “sustainable mobility society.”
The biggest difference is the automotive industry isforced to make a big transformation in the era of new
entrants from the IT industry of Silicon Valley such as
GAFA2), energy industry and new industries throughelectrification and autonomous driving. However, thiswas also included in the discussion of ITS activities, as
it expressed the importance for the automotive industry
to have a perspective of an ecosystem consisting ofpeople, transportation community and the use ICT(Information and Communication Technology) for
building a rich and comfortable mobility community(maximizing) by solving social problems (minimizing)such as traffic accidents/jams, energy/environment andaging society3), 4). Then, what are the real differences?
· The evolution of electrification, autonomous driving
and ICT raised the expectation that the dream of amobility community may come true
· It revealed the change cannot be coped with using
the conventional framework of the automotive
industry alone and a new ecosystem from both theindustrial and social system perspectives needs to bebuilt· A ubiquitous and global borderless era facilitated by
the Internet made it easier for the new entrants toplay with new ideas· Due to all of the above, the design structure of theautomobile itself, needs to be innovated
Are the above not the real differences from theperspective of the history of the automotive industry?
This also shows the conventional structure andmechanism of production is close to the limit and a
new S curve needs to be built for breaking the limit
representing the needs of the times. Although thethreat from IT, energy and new industries exist, theautomotive industry should not take them as the entire
picture. The real challenge is:· if the automotive industry can transform itself, and· if the automotive industry can take the leadershipwhile repeating collaboration and competition withother industries,
aiming for a comfortable and rich mobility community.
In order for the automotive industry to take the

Vehicleinnovation

Information?

IT industry

Fig. 3 Relationship among industries

In this paper, I would like to think about the mobility
community of the 21st century together with thereaders, introducing cases from the viewpoints of“driving” and “mobility” on how the ecosystem andcyber physical system in this mobility change in the eraof CASE.

NTN TECHNICAL REVIEW No.87

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Perspective for Advanced Vehicle Technology into CASE Era

2. Autonomous Driving; “Unity of Rider
and Horse” and “Driving Intelligence
Aiming for Further Safety”
2.1 W hat Are “Autonomous Driving” and “Driving
Intelligence”?
Information on autonomous driving technology isconstantly publicized at the media, industry and state levelin the world. Although with rather excessive expectation,
the autonomous driving technology is promoting a big
dream in the mobility community where the people haveforesight of innovation in vehicles, transportation systemand even information services.
Let us track down the history of autonomous driving.
Leonardo da Vinci dreamed of an autonomous driving
vehicle when he thought of a mechanical vehicle. In
the 1960s to 1970s, the first smart car “Stanford Craft”
was conceived for investigation of the lunar surface.
Long cables were equipped for a video camera andremote control which contributed to obstacle avoidancetechnology and higher image processing performancelater in the development. However, the biggest impact on
the automotive industry and society came as autonomous
driving vehicles from colleges and companies participating
at two DARPA (Defense Advanced Research Projects
Agency) Challenges subsequent autonomous driving
vehicle from Google. Google has continued the driving
experiment on public roads since 2010, totaling 700
thousand miles (approx. 1,130 thousand km) by April,2014. In Europe, state level projects such as HAVEit
are making progress through a collaborative framework
among industry, academia and government6). In 2013,
Daimler announced that it would introduce autonomous
driving vehicles into the market by 2020, disclosing thatits vehicle traveled autonomously on a German publicroad for over 100 km. Furthermore, European project
PEGASUS recently created and proposed a framework
for the development and evaluation process based on
systematic driving scenarios. Also recently reported isthe announcement of establishing a research center forautonomous driving taxis by the U.S. car sharing company
Uber, and a plan of an on-demand autonomous car
service from Google. As such, the competition of researchand development has heated up with participants
worldwide from the automotive, IT, car sharing service
and logistics industry which combine engineering andbusiness operations with the actual introduction reportedlyaround 2020. When we consider the advantage/valueof autonomous driving from the viewpoint of the social
challenges,(1) Improvement of traffic flow (reduction of congestion/
CO2)(2) Reduction of accidents due to human errors(carelessness/distraction/fatigue)
4

NTN TECHNICAL REVIEW No.87(3) R eduction of accidents due to health problems/
unconsciousness(4) S afe driving under low visibility (nighttime/rain/snow)(5) R eduction of accidents by aged drivers/securingmeans of transportation (decline of driving ability due
to physical impairment)(6) Improvement of comfort by reduction of driving load
can be expected. However, “autonomous driving” is notnecessarily “safe” all of sudden. I think there is “gooddriving” and “bad driving” for “autonomous driving,”
as well. With the technology today, it should not bedifficult to run the vehicles automatically, however,“good driving” is a different matter. Driving by anexpert driver requires observation of the surrounding
environment predicting possible changes based on
the knowledge, experience, and understanding of his/her own vehicle’s behavior and motion characteristics
with prediction of possible outcomes. The driver
enjoys the value of transportation, freely, safely andcomfortably by doing all of the above but it is not aseasy for a machine to do that on behalf of humanbeings. Recognition of the surroundings is not
sufficient. It requires “driving intelligence.” Also, neither
people nor machines are 100% safe or trustworthy.
They grew (learn from each other) by enhancing theiradvantages and complementing disadvantages toimprove the driving quality by continuously creating“better” and “safer” driving operation under various
driving conditions. Regardless of who drives thevehicle, people or machines, safe driving technique
is common. Therefore, I think incorporating more
“driving intelligence” into the vehicles and driving its
evolution specifically is the most important challenge.
In the history of mankind, the relationship between
machines and people is commonplace. There has
been a lot of evolution when transportation changed
from the horse to vehicle; however, there are things
horses can do but vehicles cannot. I do not think thevehicles have achieved the value of so-called “unityof rider and horse” such as the “safety instinct where
the horse would not jump off from the cliff even if therider instructs so and running with comfort together,”“ability of the rider, who may or may not want to drive,
to communicate and act on the context of the willsof each other between the rider and the horse,” and“not to be isolated in the communication between theriders.”In the context of CASE, this aspect of “driving” isnot largely raised. In addition, we cannot ignore
the development of the people (drivers) and traffic
environment (infrastructure) along with the developmentof vehicles in the context of the relationship among thepeople, vehicles and traffic environment. As mentioned
before, the driving technique of an expert driver

The safe driving technology has evolved fromcollision safety to preventative safety. The recent ideaof “integrated safety,”8) which covers the entire safetyphases from the normal driving phase to collision andrescue/emergency response phase for reviewing andresponding is an important philosophy showing “there isno compromise for safety.” With this philosophy, adoptionof a driving support system that recognizes the driving
surrounding environment and obstacles using sensors
such as cameras and radar expanded very quickly.
Devices such as collision damage reduction/preventative
automated brake systems are deployed in many products
as their benefit is easily recognized and its adoption isrecently expanded even in light vehicles under the nameof AEB (Automated Emergency Brake). This way, thecapability of accident avoidance is a little over a second
before collision, such as rear-end collision, has greatly
improved. On the other hand, systems for reducing
the driving load during normal operation have been
deployed, such as the ACC (Adaptive Cruise Control),
LKA (Lane Keeping Assist) and LDW (Lane Departure
Warning (& Prevention)). From the safety standpoint,
driving phases consist of the “normal driving” phasefor smooth driving without any risk and the “emergency

・Learn from knowledge and experience of mature drivers
10sec

5sec

（1）
Decide how to drive

1sec

100msec

Accident occurs
10msec（2）
Read hidden risk potential（3）Emergency avoidance

Information knowledge/experience (machine learning)/
external information (map.V2X)

Collision avoidance PCS Damage reduction PCS
Onboard sensor recognition

High performance sensor
Innovation of sensing/recognition/decision algorithm
Vehicle speed
Look ahead km/h
20Acquire information of/getting closer to knowledge/
experience of a good driver2.
5
hit sece l onine ds/v ahe
eh ad
icl
1s
es
eco
/p
n
Imm d ahe ede
a
edia
str
te o d
ian
bsta
cle s

2.2 Driving Intelligence Aiming for Further Safety
2.2.1 Driving Support System and Autonomous
Driving Technology

avoidance” phase, which is a few seconds before
potential collision and with increased potential/apparent
risk. In the former phase, it is necessary to drive withcaution while predicting potential risks as the driving
schools often teach with “risk predictive driving” (Fig. 4).
So far, the driving support system has been effective in“normal driving” and “emergency avoidance” phases. As
the autonomous driving technology evolves, we must
not overlook the technology of “look-ahead driving”
that corresponds to the risk increasing phase. Also, as
mentioned earlier, since 90% of the traffic accidents arecaused by human errors, the evolution of driving support
systems to deal with the various causes, such as
elderly drivers, distraction, health problems, distracted,
congestion, etc. is expected. However, adding individual
systems will not be effective. It should be necessary tocomplement driver errors by the autonomous /intelligent
driving systematically.

Intersection/
ad
ead
d ah
he
crossingda
Vehicle trajectoryonec
Stopped vehicle
5s
Tail end of traffic jam
Roadgradient
Road surface μRoad condition Traffic
Merge
control information
10 s

Room ahead
m

econ

W

comes from the information learned under various
driving conditions and knowledge accumulated over along driving experience. An expert driver internalizes
the dynamic vehicle motion reaction against the driving
maneuver and holds it as “driving intelligence” in thephysical model. Therefore, the driving technique of anexpert driver can be understood as a cyber physicalsystem integrating the “experience/knowledge information
model” and “physical model of vehicle motion.” Is this“driving intelligence” not the important aspect where
the autonomous driving technology makes the realdifference?
Recognizing these challenges, I would like to step into
the discussion of the evolution of “safe driving technique”
and “autonomous driving with unity of rider and horse(shared control)” based on “driving intelligence,” which
can be interpreted as the instinct of a vehicle, not only
remaining in the generalized concept of “autonomous
driving.”
The following is based on the research anddevelopment conducted since 2011 on a collaborative
framework between universities and industry “Driving
Intelligence System to Enhance Safe and Secured Traffic
Society for Elderly Drivers”7) which is the theme adopted
by the “Japan Science and Technology Agency (JST)Strategic Innovation Promotion Program (SIP)” and myown view.

300

200

60

100

100

Fig. 4 Concept of risk phases for preventative safety (SIP)9)2.2.2 Driving Intelligence with Risk Prediction
Capability
Now, how can we specifically capture the driving
intelligence? First, it is essential to “observe well” thesurrounding environment, namely, improve the abilityof “recognition” with sensing technologies. In addition,
it is necessary to create the basic drive planning ability
such as generating the path to the destination from therecognized information10) and pass around the stopped
vehicles. In addition essential drive planning and risk
prediction intelligence will be required by looking ahead
and anticipating risks (Fig. 5).
Map
information

Recognized
information

Potential objects
Hidden risk potential (pedestrians running out)

Near-miss incident
weighting factor(Risk predictive driving)
Visible risk potential (following vehicles ahead/avoiding parked cars/passing pedestrians)(Normal driving)
Basic running potential (course trace/entry into intersection)

To motion optimization
calculation section

Fig. 5 Layered structure of risk predictive control (SIP)11)
NTN TECHNICAL REVIEW No.87

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Perspective for Advanced Vehicle Technology into CASE Era

Risks include apparent risk such as a bicycle
or pedestrian who is visible but “may” change thebehavior in the next instance, and potential risk suchas a pedestrian who is hidden and may jump out frombehind a stopped vehicle. There are two important
points for making the risk prediction technology. The
first is the model to define the possibility of collisiona few seconds away while running and to physically
express the present margin toward the risk. There aresome methods such as the potential field, but this is an
important model expression for generating the optimum
driving path with smaller risk and control of the vehicle
speed. The second is the learning process based on
the experienced running information. The ontologicalapproach based on rich information is also necessary inorder to determine the risk from the apparent conditions.
Building prediction model’s integrating the physicalmodel and information model is a new challenge
for the automotive industry. The “near-miss incident
data”12), 13) currently accumulated at Tokyo University ofAgriculture and Technology is very useful as a sourceof information. Since this is the information source
determining risk events such as “emergency brake wasapplied even if it did not lead to accidents,” learning thedata may lead to risk prediction. As described above, it
is indispensable to implement the intelligent behavior of
people, such as feeling “somewhat risky” from generalobservation and slowing down, to the machine (vehicle)
for evolution of safety and technical challenge calledautonomous driving.
Fig. 6 shows the physical model expressing therisk as the potential field (hereafter, “risk potential”)
in the SIP project. By making the space information
recognized by various peripheral monitoring sensors
risk potential, the risk image of driving environment
such as the parked vehicles can be continuously
presented as the physical expression. Furthermore,this potential field facilitates driving control since it can
optimize the target course and speed (I am omitting thedetailed explanation. Refer to the reference for more
information)14).

2.3 Near-Miss Incident Database andInformation Risk Model
We learned a lot from the near-miss incident datain the SIP project15). We made progress in building the“Data Driven Risk Prediction Model” which predicts therisk potential in the future from the near-miss incident
empirical data, not only from the risk potential of thephysical model. Fig. 7 shows the framework leading to
the risk prediction control built in this project16).
Determination of risk values
Scenario category· Structured data
· Annotation, etc.
· Ordinary road...
· Rear end (vehicle to vehicle)· Pedestrian· Bicycle

Road traffic
context
and driving
behavior

Determining weighting
factors of risk values fromvarious environmental
factors and LHP fromdriving behavior risk
factors by multiple
regression equation

Risk prediction
values from driving
environmental factors
Determination of LHP
Future risk factor
values from individual
driving behavior

Traffic context
risk andevaluationof driving
behavior

Calculation of total-SCT

Cruising
speed
Determination ofweighting factor ofrisk potentials

Fig. 7 Framework of data-driven risk predictive control

The causes and effects of “driving behavior factors” and“driving environmental factors” to the near-miss incident
events are expressed by the quantitative indices, LHP(Long-term Hazard Potential) and Rv (Risk value). These
2 risk quantitative values are determined by the data
between approx. 10 seconds and 3 seconds before therisk events. The value of these not-so-complex quantitative
indices, LHP and Rv, which show 2 key non-stationary
factors of the “human drivers” and “driving environment” invehicle driving is significant. Furthermore, by incorporatingthem in the virtual driving/traffic simulation to make ita framework of prediction from near-miss incidents toaccidents, we could make probabilistic predictions from the“risk prediction control,” such as “risk predictive driving.”
Fig. 8 shows an example of its results16).
Pedestrians and bicycles accidents → near-miss incidents werereduced to 1/4 through risk predictive control and accidents were reduced to 1/50
Without risk

Approx. 10 km of public predictive control(AEB/autonomous
roads around Kanagawa driving)
Institute of Technology
were modeledWith risk predictive
control (SIP)

20%

Total
7,486
incidents
80%

Near-miss incidents rate
→reduced to 1/4

Without risk
predictive control(AEB/autonomous
driving)With risk predictive
control (SIP)

2%(Only vehicles)

Total
211
accidents
98%

Accident rate

→reduced to 1/50

Fig. 6 Optimization of target trajectory by risk potential

6

NTN TECHNICAL REVIEW No.87

Fig. 8 Prediction of risk predictive control throughdriving/traffic simulation

The machines are only used by the people whentrusted. As mentioned earlier, the people may wantto drive or may not when tired or under monotonous
situation. Elderly people feel uncomfortable driving,
recognizing poor physical conditions. Enabling them todrive worry-free to the destination should be the role of theintelligent machine, not taking away the driving privilege
from the elderly people. The benefit of cars is not only
providing means of flexible transportation but also driving
pleasure. Use of machines by people has an aspectof stimulus to the instinct where the people become
active and motivated. Recently, “use of information”
significantly expanded through the use of smartphones.
If the information provides value for “knowing,” “things”
have value “to be seen, touched and felt.” The question is
not to determine which is better, but the important point
they both offer in common is if the context the machinesprovide can be understood by the people who use them(or easily understood). This does not immediately jump
into the discussion of HMI (Human/Machine Interface)or driver monitor, but rather, we have to check if themachines provide the outcomes (performance) that meetor exceed expectation of the people who use them (thisis the baseline for the trust). The machines should predictthe result (performance), provide the context of their action
to the people and be understood. In this context, theDriving
intelligence

Model steering angle

Machine driving(an expert driver)

Assistance adjustment
mechanism
Steering reaction
force(Look-ahead driving, risk prediction)

Actualsteering angle

Traffic
environment

Elderly driver(Reflect driver’s conditions)

Driving characteristics(response time, etc.)

Physical condition(fatigue, sleep, etc.)

Fig. 9 Haptic Steering Shared Control
Number of drivers［-］

2.4 A
 utonomous Driving with Unity of Rider andHorse (Shared Control)17)-19)

smartphones are ahead. The vehicles are still behind thecurve. By providing the road conditions and recognition
that the machines determine optimal as rational as possible
to the people and expressing them through the steering
wheel, acceleration and braking which the people cantouch and feel while the frontal view that the people cansee and understand, the machines can become closer tothe horses. It is imperative not to add new interfaces andincrease the load of driving. Can the context of driving befirmly grasped and communicated to the people? This isalso what is expected from the intelligence of autonomous
driving (i.e. driving intelligence).
An example of the research achievements of SIP projectis shown in the following. Fig. 9 shows a conceptual
diagram of Haptic Steering Shared Control11). It aims for
guiding the vehicle to a better course trace by applying thedifference between the steering operation modeled afteran expert driver and steering operation of a real person
to the steering torque reaction force. It revealed that thiscontrol improves both traceability of the model course andsmooth operation (Fig. 10)14), 20), 21).

8
7

N=13

W/O control

6With control

5
4
3

Good

2
1
0

0.60

0.50

0.40

0.30

0.20

0.10

0.00

Tracing performance of model path=RMS of tracing error [m]Number of drivers［-］

We have simulated intersections and jumping-out ofpedestrians and bicycles on public roads of approx. 10
km around the Kanagawa Institute of Technology andbuilt a virtual model considering the LHP and Rv indices.
This dynamic simulation result shows a reduction ofnear-miss incidents to approx 1/4 (total of 7,486 nearmiss incidents) and a reduction of accidents to approx
1/50 by the introduction of risk prediction control (slowing
down by risk predictive driving). This result indicates thedifference between “autonomous driving to apply brakeafter observation (recognition)” and “driving intelligenceof slowing down by looking ahead for something jumpingout from the visible environment.” This kind of simulated
effect prediction does not have enough credibility, yet, as
the history of weather forecast shows. However, it showsa direction of risk prediction technology both as thesystem control technology and as the digital twin virtual
validation technology integrating the “information model”
and the “physical model.” This framework that we could
build this time is important but we have to note that thisdatabase might not be effective in the area/country where
the traffic environment is different, similar to the fact thatthe people familiar with the area can drive effectively. Our
challenge is how to build near-miss incident database foreach community and how to structure them.

6
5

N=13

W/O control
With control

4
3

Good

2
1
0

0.3

0.25

0.2

0.15

0.1

0.05

0

Smoothness of driving = RMS of steering angle velocity [rad/s]

Fig. 10 Effectiveness of Haptic Steering Shared Control

NTN TECHNICAL REVIEW No.87

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Perspective for Advanced Vehicle Technology into CASE Era

I have discussed “driving intelligence aiming for
further safety” and “autonomous driving with unity ofrider and horse” in the evolution of autonomous driving
technology as my expectation. I welcome participationof those who share my view in this discussion.

3. Connected; Mobility Ecosystem
Connected by Information
3.1 Overview
Now, let us think about the transformation oftransportation system as the ecosystem of people,
vehicle and traffic environment. That is, MaaS (Mobility
as a Service). The possibility of service businesses
is unlimited in the cyber physical network where
information and mobility are integrated. Services touse multiple means of transportation in an integrated
fashion are beginning and expected to grow worldwide.
In Finland and Singapore, collection of traffic
information and creation of database for dynamic
communication are led at the government level. The
initiatives at ITS include solution of mobility divide, thatis, safe mobility and active life support of elderly anddisabled people who are vulnerable road users, andrevitalization of local communities and improvementof QOL (Quality of Life) of citizens. Therefore, theconcept of “provision of equal mobility to everybody” isalso important.
The above is an example focused on theinformation/software aspects but formation of
ecosystem as an infrastructure that includes IoT andphysical space is also important as the information andmobility are integrated. Let me introduce a researchand development project in Singapore, “TUMCREATE,”
as an evolution of mobility from transformation oftransportation system.

3.2 TUMCREATE
A project of Technical University of Munich,
TUMCREATE (TUM: Technical University of Munich),
adopted by the CREATE (Campus for Research
Excellence and Technological Enterprise) programof Singapore’s National Research Foundation is agood research example that shows a new mobility
community.
This project is joined by Singapore’s NTU (Nanyang
Technological University) and thus contributing to
the development of young Asian engineers. The firstphase was conducted from 2010 to 2016 with thetheme of “The Center for Electromobility in Megacity”
and the second phase is being conducted from 2016
to 2021 under the theme of “Towards the Ultimate
Public Transport System.” Over 100 engineers andresearchers will participate in this project from both
universities and the professors from the Technical8

NTN TECHNICAL REVIEW No.87

University of Munich are also stationed in Singapore
dedicated to 5 years of research.
In the first phase, NTU’s engineers learned thearchitecture of vehicles including package design as
the foundation of automotive engineering, in addition
to building an EV. They also digested the foundation of
the electric motor system such as the design of battery
pack and test bed and fabricated a research vehicle
taxi EV suitable for megacities in South East Asia,
called EVA (Fig. 11).

(Source: TUMCREATE website)

Fig. 11 TUMCREATE EVA – Tropical taxi EV 22）

In addition, they conducted simulation of the traffic
conditions in Singapore, as well as to the simulation of
the battery management in the vehicle. They even built
a data management system for optimization of driving
and battery charging.
The research theme of the second phase is traffic
congestion, energy and security in Singapore, which isprecisely the solution aimed at problems of megacities
in the new ecosystem proposed by the ITS activities.
First, the mobility called SRT (Semi Rapid Transit)
System is planned, which uses units of 30 person
capacity to form a flexible caravan of autonomous
driving. This is a mobility capability aimed for increased
efficiency in urban transportation, between MRT(Mass Rapid Transit) System which is high speed/highcapacity with sparse passengers and a bus service
which is slow and low capacity (Fig. 12).

(Source: TUMCREATE website)

Fig. 12 Semi Rapid Transit System 22）

Naturally, the electric vehicle with the technology
developed in phase 1 is used. The SRT System ischaracterized by the following, in addition to theservice offering of seamless use of multiple means oftransportation (mobility X).
 ultifunctional capability by autonomous driving as·Mthe module lean urban environment by electric vehicles·C ynamic and flexible passenger transporting·D
capability up to 10 units (300 passengers) in a
caravan during peak hours
 uick response to demand reducing wasted time·Q uick loading/unloading at the SRT stops·Q
Next, the SRT-MODULE is not a stand-alone project
but a component of an integrated ecosystem with SRTCENTRAL, SRT-INFRASTRUCTURE, SRT-CONNECT
and SRT-POWER (Fig. 13, 14).
The SRT vehicle unit is designed with userfriendly features, such as an air curtain to contain theconditioned air in the vehicle while loading/unloading,
all wheel independent steering mechanism for a small
turning radius and easy parallel parking (Fig. 15), lowfloor and guidance technology with road projection foreasy access, adopting many novel ideas.

(Source: TUMCREATE website)

Fig. 15 All wheel steering system 22）

They can be evaluated/designed on the virtual space
using VR (Virtual Reality). The most spectacular point isthat they have built a dynamic simulation of the entire cityof Singapore, called CityMoS (Fig. 16).
This is the system with layers of power system, sensor
network and a traffic system for the entire city not only
providing simulation (virtual world) but also actual data
sensing (real world), so it is built as a cyber physicalsystem. In other words, the city-state of Singapore itself,
as the “Cyber City,” has become an intelligent system.

(Source: TUMCREATE website)

Fig. 16 SRT – CENTRAL (CityMoS) 22）(Source: TUMCREATE website)

Fig. 13 Semi-Rapid Transit(SRT) System 22）

As an advisor of this project, I am impressed withthe young engineers of TUM and NTU who are excitedand confidently working on their respective R&D
subjects. Post doctoral researchers, doctors, professors
and engineers of NTU from the international allianceare increasing their capabilities through automotive
design and manufacturing while acquiring a high skill
set of the cyber physical system. The level of these
R&D activities is equivalent to forefront R&D activities
at large corporations. Some companies seem toparticipate in the actual manufacturing process but
most of the basic design is decided by this project.
Also, the project offers a powerful human development
opportunity for young engineers.

3.3 Disaster-Resilient Ecosystem for Japan(Source: TUMCREATE website)

Fig. 14 SRT-MODULE 22）

In this Chapter, I have only mentioned good projects
from the overseas but now I would like to mention
universal concepts originated from Japan which (in myopinion) should also work worldwide.
In the era of Heisei, Japan was struck by many
disasters and many people had a bad experience.
NTN TECHNICAL REVIEW No.87

9

Perspective for Advanced Vehicle Technology into CASE Era

However, the Japanese culture had strength toovercome these disasters. Based on these lessons, wehave to build an ecosystem suitable for Japan in theera of Reiwa, which is highly active in normal period
and resilient to disasters.
In the Great East Japan Earthquake of March 11,
2011, the entire nation of Japan grieved over the deathof many people. I would like to express my deepest
sympathy to the deceased and encourage the people
who are working hard in the aftermath.
Personally, I also experienced the earthquake
on March 11, when I was holding a conference in
Sendai. I experienced the infrastructure risk firsthand.
An experience of loss of social infrastructure withinformation completely blocked, energy risk ofelectric power and gasoline, disruption of meansof transportation, lack of food and water, etc. The
following is an unofficial proposal we made to thegovernment and business community, which isbased on my own note of lessons I learned as oneof the citizens working on the mobility industry andcontribution from colleagues.

· Building autonomous and distributed mobile wirelesscommunication network→ Use vehicles as the temporary wireless tandem
stations for ad-hoc communication network using
WiFi functionality during disasters or in remoteareas, as a limited emergency communication
system.
M
ulti-fuelrange extender·→Effective during normal and disaster periods.
· Automatic driving system for remote control andautonomous driving→The questions of security need to be addressed,
but remote control driving is effective during
disasters. Vehicles with ability to run on bad terrainsuch as SUVs are also effective.

3.3.1 Lessons from the Experience ofInfrastructure Risk

4. Summary· Mobile phones did not work as the base stations
were dysfunctional.
→ Internet and WiFi spots are effective. Distributionoptimized ad-hoc base stations are needed.
· It was unfortunate that a Prius generator could not
be used for 12V output. (Toyota provided this featuresoon after the disaster.)→ Electrification means having optimum battery
capacity; yet, having generators is also important.
Especially a multi-fuel generator.
R
eal-time
mobility connection information is·required on how to coordinate public transportation,
automobiles and other mobility modal.
· Autonomous distributed power management system
is also required, not only overall optimization such as
the power grid.
· It is important to “have the ability to communicate withstrangers,” “take action when scared” and “believe in
one’s own sense of risk.”

3.3.2 Proposal for Disaster-Resilient System· Locally generated/locally consumed distributed
energy community→ Autonomous management of local power systemfor energy saving and efficient use based on
management of local energy information such asa stationary battery. Control of demand and supply
balance with the power grid by dynamic pricing
during normal operation.
10

NTN TECHNICAL REVIEW No.87

Some of the above have made good progress
but having built the cyber physical ecosystem withautonomous and distributed system in addition to
overall optimization system must be particularly
important for the ecosystem of Japan where many
disasters strike.

In this paper, we have discussed the evolutionof advanced automobile technologies toward theera of CASE and evolution of ecosystem of people,
automobile and traffic environment, although thediscussion may have been generalized towards theend. For example, the discussion included much of
my personal views, which may not reflect the trends ofthe time objectively. We are certainly in the midst of aonce in a century paradigm shift and we should havea sense of urgency as global competition intensifies;
however, this change is an inevitable result of evolution
and is also important to have originality in our visionand ideas based on the Japanese culture and history,
for the requirements of the mobility society andautomotive technologies. I believe that these views andideas will have a positive global impact.

References

13) Pongsathorn Raksincharoensak, Drive Recorder1) https://mb-live.jp/mercedes-benz/case/

Database for Accident/Incident Study and Its Potential for2) https://ja.wikipedia.org/wiki/GAFA

Active Safety Development, FOT-NET Workshop Tokyo

3) Okazaki Teruo, Watanabe Hiroyuki, Oohata Akira, Inoue

Japan, (October 13 2013).

Hideo, Amano Kaoru, Chapter 9. Technology Diffusion
and Development, Climate Change Mitigation - A
Balanced Approach to Climate Change - , Yamaguchi
Mitsutsune(Ed.), Springer,(2012), 179-221.
4) Teruo Okazaki, Hiroyuki Watanabe, Akira Oohata,Hideo

14) Hideo Inoue, et al, “Intelligent Driving System for Safer
Automobiles”, Journal of Information Processing, Vol.25,(November 2016).
15) Wongwaiwit, P., Raksincharoensak, P., Michitsuji,Y., “Analysis on Pedestrian and Bicycle Behavior in

Inoue, Kaoru Amano, Climate Change Mitigation

Unsignalized Intersection Based on Near-Miss Incident- a Balanced Approach to Climate Change - Edited

Database”, Proceedings of 20th JSME Transportation andby Mitsutsune Yamaguchi, Chapter 9 Technology

Logistics Conference, (2011), 19-22.

Dissemination/Development, Maruzen Publishing, (2013),
213-238.
5) Hideo Inoue, et al. Intelligent Vehicles for Super Mature
Society, Symposium of the Society of Automotive
Engineers of Japan (No. 06-14) Presentation on “Latest16) Hideo Inoue, Mohanad El-Haji, Thomas Freudenmann,
Haipeng Zhang, Pongsathorn Raksincharoensak,
Yuichi Saito, “Validation Methodology to Establish Safe
Autonomous Driving Algorithms with a High DriverTechnology Innovation of Autonomous Driving” (May,

Acceptance Using a Virtual Environment”, FAST-zero,2014).

(September 2019).

6) Bauer, E. et al., “PRORETA3 : An Integrated Approachto Collision Avoidance and Vehicle Automation”,
Automatisierungstechnik, Vol. 60, No.12, (2012), 755-765.
7) Hideo Inoue, Masao Nagai, et.al, Driving Intelligence
System to Enhance Safe and Secured Traffic Society for17) Abbink, D. A., Mulder, M. and Boer, E. “Haptic Shared
Control: smoothly shifting control authority”, Cognitive
Technology Work, Vol.14, (2012), 19/28.
18) Diomidis Katzourakis, Claes Olsson, Nenad Lazic andElderly Drivers, 2014 JSAE Annual Congress(Spring),

Mathias Lidberg, “Driver Steering Override Strategies

Yokohama Japan, (May 22 2014).

for Steering Based Active Safety Systems”, Proceedings

8) Toyota Motor Corp. News Release, “Toyota Strengthens
Efforts to Develop Safe Vehicles - Integrated Safety
Management Concept Forms Base of New Safety
Technologies -” (August, 2006).
https://global.toyota/jp/detail/1532213
9) Hideo Inoue, et al. Vehicle Intelligence toward Agingof 2nd International Symposium on Future Active Safety
Technology Towards Zero-Traffic Accidents (FAST-zero'13) , Paper no. 20134591, (2013), 1-7.
19) Ryota Nishimura, Takahiro Wada, and Seiji Sugiyama,“Haptic Shared Control in Steering Operation BasedSociety, Japan Science and Technology Agency (JST)on Cooperative Status Between a Driver and a Driver

Strategic Innovation Promotion Program (SIP), Interim

Assistance System”, Journal of Human-Robot Interaction,

Report Symposium, presentation material, (January,2015).
10) Kim, W., Kim, D., Yi, K and Kim, H. J., “Development of aVol.4, No.3, (2015), 19-37.
20) Shintaro Inoue, Hideo Inoue, Hiroyuki Aikawa,
Raksincharoensak Pongsathorn, Study on Human-

Path-Tracking Control System Based on Model Predictive

Machine Shared Driving System Using DYC and Steering

Control Using Infrastructure Sensors”, Vehicle System

Assistance (Second Report), Transactions of Society of

Dynamics, Vol.50, No.6, (2012), 100-1023.

Automotive Engineers of Japan, Vol. 48, No. 1, 20174062,

11) Hideo Inoue, et al. Autonomous Driving Intelligence(January, 2017), 111-118.

System to Enhance Safe and Secured Traffic Society for21) Shintaro Inoue, Yutaka Hirano, Hideo Inoue, Takumi

Elderly Drivers, Japan Science and Technology Agency

Ozawa, Raksincharoensak Pongsathorn, Study on(JST) Strategic Innovation Promotion Program (SIP)

Human-Machine Shared Driving System Using DYC

Symposium, presentation material, (September, 2016).

and Steering Assistance - Effectiveness of Assistance12) Hideo Inoue, Research into ADAS with Driving Intelligence

on Elderly Drivers in Course Tracking Maneuver -,for Future Innovation, 26th IEEE International ElectronTransactions of Society of Automotive Engineers ofDevice Meeting 2014, Keynote Speech, (15 December2014), 1.3.1-1.3.7.

Japan, Vol. 47, No. 3, 20164339, (May, 2016), 734-737.
22) https://www.tum-create.edu.sg/

NTN TECHNICAL REVIEW No.87

11

Perspective for Advanced Vehicle Technology into CASE Era〈 Author Biography 〉

Hideo Inoue
Professor, Faculty of Creative Engineering, Chair of Department of Vehicle System Engineering,
Kanagawa Institute of Technology
1978

Graduated from Mechanical Engineering, Faculty of Science and Engineering, Waseda
University

1978

Joined Toyota Motor Corporation

1997

Head of BR-Vehicle Control Room1998

Head of No. 2 Vehicle Engineering Dept. Vehicle Control Development Room

2004

Manager, Integrated System Development Dept.

2008

Head of Advanced Technology Strategy Room (Equivalent to Dept. Head)2013

Manager, FP Advanced Vehicle Research (Equivalent to Dept. Head)2016

Professor, Faculty of Creative Engineering, Chair of Department of Vehicle System
Engineering, Kanagawa Institute of Technology

2017

Director, Advanced Vehicle Research Institute, Head of Automotive Technology Center,
Kanagawa Institute of Technology

2018

Dean of Faculty of Creative Engineering

2011-present

Project Manager, “Autonomous Driving Intelligence System to Enhance Safe and Secured
Traffic Society for Elderly Drivers” which is the theme adopted by the “Japan Science andTechnology Agency (JST) Strategic Innovation Promotion Program (SIP)”

2013-present

Visiting Professor, Division of Advanced Mechanical Systems Engineering, Institute ofEngineering (Graduate School), Tokyo University of Agriculture and Technology

2013-present

Advisory Committee Member, TUMCREATE, a Germany-Singapore International
Partnership Project

2018-present

Project Leader, “Development of Autonomous Driving Evaluation Environment
Maintenance Method in Virtual Space” which is adopted in the“Strategic Innovation Promotion Program (SIP), Phase 2 Autonomous Driving (System andService Enhancement)”[Specialty]
Vehicle motion control, driving assistance/autonomous driving, advanced safety/preventative safety,
vehicle integrated control, etc.

[Society Activity]
2017-present

Reviewer of technical papers, Member of Activity Safety Committee, Society of Automotive
Engineers of Japan, Inc.

2018-present

Delegate, Society of Automotive Engineers of Japan, Inc.
Member, Technical Paper Editorial Committee[Awards]

12

1992

FISITA Paper Award, Development of Vehicle Integrated Control System

1998

Japan Society for the Promotion of Machine Industry, 31st Minister of International Tradeand Industry Award “Development of a sideslip prevention rolling stock stability control
system”

2009

The US Government Award from NHTSA for Special Appreciation for contributions to thedevelopment and popularization of safety technology

2016

The Japan Society of Mechanical Engineers, Transportation and Logistics Award forAchievement

NTN TECHNICAL REVIEW No.87

Perspective

NTN's Approach and Effort for CASE

Koji KAMETAKA*

Currently, it is said that automotive industry enters a phase of major change which comes “once in a century”.
One of the representative development trends is CASE.
"CASE" consists from initials of Connected (External connection), Autonomous (Autonomous driving), Shared& Services (Car sharing and service or Car sharing only) and Electric (Electrical vehicles).
CASE is advocated by Dr. Dieter Zetsche (ex-CEO of Daimler AG) at Paris Motor Show 2016.
This paper introduces our developing activities with this major trend which we are greatly concerned with.

1. Introduction
Automobiles are a useful means of transportation,
but a significant change to electrification is now
underway due to recent environmental issues.
Autonomous driving is another area of research fora safer and more efficient transportation system.
Research of autonomous driving involves both control
of a single vehicle and a safe and highly efficientautonomous driving system that incorporates various
types of information. Particularly in Japan, with a large
aging society, autonomous driving should be effectivemeans in avoiding accidents.
In addition, the car sharing system is also
expanding, particularly in urban environments where
automobiles are being shared instead of owned.
As such, the automobile industry is in an era oftransformation so-called “once in a century”, which is
driving an alliance among automobile manufacturers inorder to reduce the burden of development expenses.
As new entrants are making strides into autonomous
driving from outside the automobile industry, suchas communication companies, it is not clear from theconsumers who the decision makers of the automotive
industry will be in the future.
The impact of these large trends on productdevelopment is significant for NTN, and as a result wehave been developing electric module products. We
have also conducted development of energy savingfeatures on the existing products.
This paper describes our approach for developmentof new electric module products to support CASE,
which is depicted in Fig. 1, as well as an overview of
new development to our existing products for faster,

more reliable, quieter and more durable operation in
addition to our continuous efforts to reduce size/weight
and lower friction.
■ Connection with IoT communities,
smartphones, etc.
■ Offering of various services such asentertainment in the vehicle■ Achieving zero traffic accidents■ Use of IoT/AI technologies■ Evolution of sensing technology■ From ownership to sharing■ Transformation of business model
toward sharing service business■ Requirement for policy of improved
environment■ Adoption of EV/HEV/PHEV

Fig. 1 Overview of CASE for automobile

2. Approach to Support CASE
2.1 D
 evelopment of the Electric Actuator and Its
Applications
NTN has developed the “Electric Motor andActuator” series, which is essential for by-wire control
that is expected to be widely used for vehicle drive andcontrol.
Significant electrification is now underway in the* Executive Officer, Deputy Corporate General Manager, Automotive Business Headquarters, General Manager, Electric Module Products Division

NTN TECHNICAL REVIEW No.87

13

NTN's Approach and Effort for CASE

automotive industry, particularly with by-wire control
as the core technology along with the various systems
that support drive and control, in response to therequirements needed for autonomous driving andimproved fuel efficiency.
To address such market trends, NTN developed
the “Electric Motor and Actuator” series shown in
Table 1 and Fig. 2, combining its core technology
of bearings and ball screws with motor design andelectronic control technology for controlling vehicles.
The product line-up features common components
and specifications with a variety of shapes and sizes,
which eliminates the need for individual designs andreduces development time.
The developed products can be applied to various
on-board applications, but should be applicable fora wider range of fields in the future that is beyond
automotive. NTN is aiming to establish early volume
production and promote global distribution for on-board
applications first, and then expand applications toother devices that use actuators.
Table 1 Types of electric actuators
Type

Feature1

Parallel shaft
Type B II• Lightweight with resin housing• Can be equipped with a reverse input
rotation prevention unit that can beused for parking brakes, etc.
• Add-on reducer unit that can be used
for high-thrust applications• Integrated non-contact linear position
sensor2• Compact design with coaxial
configuration• Optimum size, torque and output by
Coaxial Hollow
layering the magnet and core
Shaft Type B III• Common magnets and coils that are(Fig. 2)the core components of motors• Integrated non-contact linear position
sensor

Hollow ball screw

and higher energy savings electric oil pump, which
requirement is met by the pump that uses NTN’s“Electric Motor and Actuator.”
In addition, the ZEV (Zero Emission Vehicle)
regulations in the U.S. and China, for example, require
EV mode driving of approx. 50 km or more for HEVs
and PHEVs, which is only met by electric oil pumps
with higher output than those for idling stop.

2.2 Module Product with Added Functionality
for Axle Bearings
2.2.1 Hub Bearing with Motor Generator
Function “eHUB”“eHUB (Fig. 3)” is a product already developed
which combines a motor generator with a hub bearing
to support wheel rotation. As improvement of fuelefficiency of vehicles progresses and regulation of CO2
emission is strengthened, the adoption of the “48V
Mild Hybrid System” (hereafter, 48V MHEV), which
improves fuel efficiency by adding power at start or
acceleration of vehicles, has increased.
The “48V MHEV” is a system that uses the engine
as the main power source and provides additional
power using a small motor while driving the engine
when starting and accelerating. Also, the energy
can be recovered as electric power in deceleration(regeneration) resulting in even better fuel efficiency.
When “eHUB”s are used for front-wheel drive
vehicles they are also mounted on the rear wheels(non-driven wheels) to provide driving assist powerwith the motor in order to reduce engine load and also
act as power generators to regenerate energy into
electric power when decelerating. When “eHUB” iscombined with the “48V MHEV” already in use (suchas starter generators), an improvement of up to 25%
in fuel efficiency is expected compared to conventional
vehicles with only engines. It can also be used for EV
creep and vehicle stability control on slippery roads (lowfriction roads).

Motor
Brake disc

Direct output
shaft
Motor coil

Outer diameter less than the innerdiameter of brake disk

Motor generator

Planetary gear

Fig. 2 External view and configuration of Coaxial
Hollow Shaft Type B III

2.1.1 Electric Oil Pump for Transmission
An example of this development is the electric oilpump for idling stop function. Idling stop is provided
as one of the methods to reduce fuel consumption
and requires a lightweight/compact, more efficient14

NTN TECHNICAL REVIEW No.87

Hub bearing

Fig. 3 Cross-section of Hub Bearing with
Motor Generator Function

2.2.2 Hub Bearing with Steering Assist Function“sHUB”
NTN has developed a hub bearing with a steering
assist function, “sHUB”, which integrates the hub
bearing and steering angle adjustment mechanism.
“sHUB” combines motor and motion control
technology with the design and manufacturing
technology that has been acquired over many years
with the development of the hub bearing, which NTN
has the No. 1 global share.
With conventional vehicles, the tires and the steering
device placed on the front wheels are mechanicallyconnected and therefore the turning angles of both
front tires are fixed to the angle of the steering wheel
being operated. While driving it was not possible tochange to an optimal setting for each driving condition,such as driving straight or cornering.
“sHUB” (shown in Fig. 4) is a module productthat can correct the steering angle at the left andright wheels separately and be installed onto avehicle’s front wheel steering and the suspension
system without replacing the existing steering device.
Optimum correction of the turning angles of each tirebased on the data on the speed and steering wheel
operating angle while driving improves the cornering
performance and high-speed stability, as well as
vehicle stability in emergency against skidding, forexample, and fuel efficiency.
It is expected that “sHUB” will be used as part of asystem to provide a safer risk avoidance performancein full-autonomous driving vehicles and it is anticipatedthat this product will expand in the market in the future.

KnuckleController

Actuator

Steering axis

3. Improvement of the Existing
Products for Reduced Size/Weightand Lower Friction
3.1 “Ultra-low Friction Sealed Ball Bearing” forTransmission
NTN developed the “Ultra-low Friction Sealed Ball
Bearing” for automotive transmissions that reduces
rotating torque by 80% compared to the conventional
contact sealed type bearing by adopting a proprietary
shape of the ultra-low friction seal.
Lower torque is required for better fuel efficiency
in addition to a longer life for transmission bearings
used for automobiles. Use of the contact sealed typewas standard for longer operating life by preventing
hard foreign objects, such as wear debris from thegears in the transmission, to penetrate the bearings.
However, this resulted in drag torque due to the seal
contacting the inner ring when rotating. Furthermore, inapplications where high-speed rotation is required, suchas recent EVs and HEVs, use of the contact sealed
type was difficult due to the restriction of the peripheral
speed limit of the seal.
“Ultra-low Friction Sealed Ball Bearing” has achieved
an 80% rotating torque reduction compared toconventional products and provides a low torque effectequivalent to that of the non-contact sealed type. Thisis achieved by adopting a newly developed contact
type seal which arranges arc-shaped (half-cylindrical)
micro convexes at evenly spaced intervals on the sliding
contact section of the seal lip, as shown in Fig. 5.
During rotation an oil film is formed between the sliding
surfaces of the seal and inner ring due to the wedge film
effect of the micro convexes. This significantly reduces
the drag torque of the seal, even if it is a contact
sealed type. Also, because the seal lip convexes aremicroscopic, they allow lubricant to pass through but
prevent harmful hard foreign matter from entering thebearing, which contributes to longer bearing life.

Hub bearing

Fig. 4 General structure of Hub Bearing with
Steering Assist Function
Cross-section view of thedeveloped productArc-shaped micro convexes(5 convexes are shown in the above cut view)Fig. 5 General structure of “Ultra-low Friction Sealed
Ball Bearing” for Transmission

NTN TECHNICAL REVIEW No.87

15

NTN's Approach and Effort for CASE

3.2 ULTAGE Tapered Roller Bearings for
Automotive Application“ULTAGE Tapered Roller Bearing for Automotive
Application (Fig. 6)” is introduced in the following
paragraphs, which delivers the world’s highest standard
load capacity and rotational speed performance by
optimizing the internal design of the bearing.
Tapered roller bearings for automobiles are used incomponents such as transmissions and differentials, andneed to have a high-load capacity in order to operate inconditions that are becoming increasingly more harsh,
including greater loads due to a higher power output, as
well as greater unbalanced loads caused by the lower
rigidity due to lightweight housings. The bearings alsoneed to provide the low torque required for lower fuelconsumption and high-efficiency and high-speed rotational
performance with a low temperature rise.
“ULTAGE Tapered Roller Bearing for Automotive
Application” improved on the optimal design technologythat maximizes the rolling operating life developed for
the Large Size Tapered Roller Bearing and applied it to
the compact series lineup. This was done to realize themaximum potential of the bearing operating life evenunder increased and high unbalanced loads by making thecontact stress even between the rolling elements (rollers)
and the raceways (inner/outer rings).
This developed product has realized a load capacity
1.3 times higher and a rated life over 2.5 times longer
than the conventional product. In addition, the permitted
rotational speed increased by approximately 10% to offer
the world’s highest level in load capacity and rotational
speed performance by optimizing the sliding contact zone
between the rollers, inner ring and cage.

satisfying the basic performance, such as operating lifeand strength.
NTN has been researching and developing hub bearings
for many years in pursuit of lighter weight, longer operating
life, and higher efficiency. We have also promoted to unitize
bearings and components (GEN1 to GEN3) to improve fuelefficiency and ease of assembling by making them smaller
and lighter. We also developed hub bearings with longer
operating life and lower friction by improving materials,
greases, seals, and other items, for use in the global
market. Today, NTN has the world’s largest market share in
hub bearings.
“Low Friction Hub Bearing III” reduces rotational
friction by 62% compared to the conventional productand improves the fuel efficiency by approximately 0.53%,
by developing a low friction grease as shown in Fig. 7.
The newly developed product has improved operating
life and resistance to fretting wear in low temperature. In
addition, by optimizing the preload inside the hub bearing,the developed product reduces the rotational frictionof the bearing itself while still maintaining the required
performance.

<New development>● Low friction grease•Lower viscosity of base oil•Thickener improvement•Revised additive contents
Reduce bearing
rotational friction

Labyrinth lip● Low friction seal
•Labyrinth structure•Lip contact optimization•Application of seal grease

Slinger

Reduce sealrotational friction［Outer seal］ ［Inner seal］

LabyrinthLabyrinth lip

Fig. 7 Low Friction Hub Bearing III

3.4 C
 ompact Plunging Type Constant Velocity
Joint for Propeller Shafts “HEDJ-P”

Fig. 6 ULTAGE Tapered Roller Bearing for Automotive
Application

3.3 “Low Friction Hub Bearing III” Reducing
Rotational Friction by 62%“Low Friction Hub Bearing III” reduces rotational friction
by 62% compared to the conventional product and isintroduced in the following paragraphs.
Hub bearings that support wheel rotation are now being
required to further reduce rotational friction in addition to16

NTN TECHNICAL REVIEW No.87“HEDJ-P” (Fig. 8) is a plunging type constant velocity
joint for propeller shafts that achieves the world’s highest
level of compactness and lightweight with 17% weight
reduction and 6% decrease in outer ring outer diameter
when compared to conventional products.
Propeller shafts are used on vehicles, such as ones
with 4WD, and take the role of transferring transmission
rotation to the front and rear of the vehicle, as shown in
Fig. 9. Also, constant velocity joints for propeller shafts
have increased in application as there is now an increaseemphasis on NVH (Noise, Vibration and Harshness) for
luxury passenger vehicles as well as SUVs (Sports
Utility Vehicle).
The conventional HEDJ, which this development
was based on, provides excellent balanced NVH

characteristics, as well as easy mounting ability on avehicle since a greater slide amount and operating angle
can be used, which improves the flexibility of vehicle
layout and is suitable for use on SUVs which use large
angles.
NTN has been widely distributing HEDJ’s, which havebeen adopted by a great number of users around theworld since the first product roll out. The newly developed“HEDJ-P” is redesigned based on the conventional HEDJin order to make the outer ring even more compact andthe inner ring thinner for dedicated use with propeller
shafts. As a result, it achieved 17% weight reduction
and 6% reduction in the size of the outer diameter while
maintaining the same performance as the HEDJ.

4. Conclusion
This paper introduced NTN’s current development
and products regarding one of the main development
trends, CASE (Connected, Autonomous, Shared &Services, Electric), which represents a “once in a
century” transformation of the automotive industry.
We described our approach for development of
new electric module products, as well as an overview
of new development items to our existing products
for faster, more reliable, quieter and more longer
life operation in addition to our continuous efforts to
reduce size/weight and lower friction.
Numerous items in development are based on
NTN’s core competency of tribology technology,
high-precision processing technology, high-precision
measurement technology and analytical technology
such as simulation, as well as our alliance withexternal agencies in view of increased speed andexpansion of fields of application.
We hope to provide a major contribution to thedevelopment of the automotive industry and to thecommunity at large through our technologies andproducts.

Fig. 8 Compact Plunging Type Constant Velocity Joint for
Propeller Shafts HEDJ-P

Fig. 9 Application of Compact Plunging Type Constant
Velocity Joint for Propeller Shafts HEDJ-P

Photo of author

Koji KAMETAKA
Executive Officer
Deputy Corporate General
Manager, Automotive Business
Headquarters,
General Manager, Electric
Module Products Division

NTN TECHNICAL REVIEW No.87

17

New Products

Hub Bearing Module with Steering Adjust Function

Satoshi UTSUNOMIYA*
Yuusuke OOHATA*

Norio ISHIHARA*
Atsushi ITO*

We have developed a hub bearing module, ‘sHUB’ with steering adjust
function incorporating the steering angle adjustment mechanism in the
hub bearing. We demonstrated that the prototype successfully modified thesteering angles of the left and right wheel independently according to thedriving situation of the vehicle and the operation of the driver. The developed
hub bearing module will hence make a significant contribution to the dynamic
performance improvement of the vehicle.

1. Introduction
In conventional vehicles the tires and the steering
device placed on the front wheels are mechanicallyconnected and therefore the turning angles of both front
tires are fixed to the angle of the steering wheel being
operated. When making a big turn at slow speed, theturning radii of the right and left wheels are significantly
different. Therefore, in order for a smooth turn theyshould follow the Ackermann geometry (larger angle forthe inner wheel with smaller angle for the outer wheel).
On the other hand, parallel or reverse Ackermann
geometry is suggested to improve the turning
performance in mid to high-speed maneuvers.
The Ackermann characteristics are determined by thegeometric configuration of the steering device; therefore,
volume production vehicles choose to emphasize either
maneuverability at low speed or turning ability at highspeed depending on the vehicle concept.
Also, the toe angle of the outer wheel, which
supports a heavy load while turning at mid to highspeed, is passively controlled by the damping
characteristics of the suspension bushings; however,
it is more desirable to actively control the optimum
steering geometry based on the turning radius andturning acceleration.
As the top manufacturer of hub bearings, NTN has
developed a brand new “Hub Bearing with Steering
Assist Function” (hereafter, sHUB®)1) which combines amechanism that adjusts the steering angle of the tireson the hub bearing, for actively controlling the steeringgeometry depending on the driving conditions whilesolving the above mentioned trade-off.
sHUB provides safe and comfortable driving by*New Product Development R&D Center

18

NTN TECHNICAL REVIEW No.87

controlling the left and right wheels independently
to the optimum angles depending on the running
conditions of the vehicle. This module system improves
straight-running and cornering stability and contributes
to risk avoidance in emergencies, for example whena wheel skids on a low-μ road surface. In normal
driving conditions it contributes to energy saving byminimizing the cornering drag while turning in a curve.
It could also be applied to avoidance maneuvering inupcoming autonomous driving vehicles.
Fig. 1 shows an overview of how sHUBs are
installed on a vehicle. They can be installed on vehicles
together with the existing steering devices without
making large modifications to the suspension system.
The controller of sHUBs independently calculates andcontrols the target angles of the sHUBs on the left andright wheels based on the vehicle information, such as
the vehicle speed and steering angle.
Range of angle foradjustments±3.5°

VehicleActuator
Existing
steering
systemSteering
operation
Vehiclespeed

KnuckleSteering
axis

Controller

Fig. 1 Vehicle with sHUB installed (on front wheels)

2. Concept
The following parameters were set as the designconcept for achieving improved vehicle dynamic
performance, as well as safe and comfortable driving.

(1) Installed on the left and right wheels in order toindependently control steering angles of bothwheels(2) Optimum control to the best angles depending on
the driving conditions
・Energy saving driving minimizing cornering drag・Maintain vehicle stability even in an emergency
situation, such as risk avoidance(3) Able to be installed on the driven wheels (frontor rear wheels) of existing vehicles regardless ofthe type of steering/suspension systems without
requiring a large modification(4) Compact and lightweight based on the optimum
internal design
Fig. 2 shows the appearance of the prototype (forright wheel) to be used with the strut type suspension
for front wheels. As shown in Fig. 3, the small size
allows installation on both front wheels of a vehicle
without modifying the surrounding structure, such as
the suspension.

Steering axis of sHUB
Kingpin axis

Lower arm
Contact pointwith groundFig. 4 Basic design of sHUB installed on front wheel

Fig. 5 shows an example of sHUB installed on therear wheel. Similar to the case of the front wheels, it
can be installed with modification only to the knuckle.
In this case, the suspension system is a regular rigid
axle (torsion beam). The rear wheel steering was easily
achieved by merely installing sHUB on the torsion
beam where the hub bearing is normally installed.

Actuator

KnuckleSteering axis

Steering axis of sHUB
Actuator
Hub bearing

Fig. 2 Prototype of sHUB

Hub bearing

Fig. 5 sHUB installed on rear wheel

3. Configuration and Specification
3.1 Components
Fig. 6 shows the components of sHUB. sHUB iscomprised of an actuator, hub bearing and knuckle.
The function of the respective components is
described as follows:

sHUB

sHUB

Fig. 3 sHUBs installed on front wheels

Fig. 4 shows the basic design of sHUB when it isinstalled on the front wheel. The kingpin axis which isthe central axis of the tire during normal steering andthe steering axis of sHUB are two different axes. It was
designed so that those two axes cross at the groundsurface. With this structure the amount of sliding
is reduced by the steering-assist of sHUB, which
improves safety.

・Actuator
Fixed to knuckle and steers hub bearing
・Hub bearing
Rotary support of tire; rotary support of the steering
axis of sHUB against the knuckle
・Knuckle
Connection with vehicle suspension

NTN TECHNICAL REVIEW No.87

19

Hub Bearing Module with Steering Adjust Function

4. Basic Performance Test

KnuckleSteering axis

A C-segment rear-wheel drive vehicle was chosen
as the test vehicle with the sHUBs described in
Section 3.2 being installed on the front wheels.

4.1 Frequency Response Characteristics Test

KnuckleHub bearing

Fig. 6 Components of sHUB

The motor of the actuator is controlled by thecontroller based on an input, such as the vehicle
speed and steering wheel angle in order to achieve
the best tire angle. The rotation from the motor,
through the reducer, is converted to linear motion by
the trapezoidal screw, which drives the end of the arm
installed on the hub bearing and steers the tire aroundthe steering axis.
The reverse input from the tire due to the reaction
force from the ground is blocked by the self-lockmechanism of the trapezoidal screw. Therefore, power
consumption of the motor can be saved.

3.2 Specification
Table 1 shows the specification of the prototype,which was designed for front wheels of a C-segment
vehicles with rear wheel drive. The weight of the
prototype was 13.8 kg, which only adds 5 kg or less tothe standard components (knuckle and hub bearing) of
the original vehicle.
Table 1

Specification of prototype

Item
Maximum steering torqueSupply voltage

Values350 Nm
24 V

Maximum steering angle±3.5 deg

Maximum steering angular speed

16 deg/s

Weight13.8 kg20

NTN TECHNICAL REVIEW No.87

Steering angle deg

ArmActuator

Steering angle deg

Trapezoidal screw

Steering angle deg

Motor

Hub bearing

Speed
reducer

Steering angle deg

Hub bearing

A frequency response characteristics test was
conducted in a stationary state by mounting the front
wheels of the sHUB installed on the vehicle to a turntable.
The actual angles were verified by giving an angle
command in the form of a sinusoidal wave (0.5 deg. of
amplitude and 1, 2, 4, 6 and 8 Hz of frequencies).
Fig. 7 shows the test results. The dashed curve
indicates the command angle and the solid curve
indicates the actual angle of sHUB. As the frequency
increased, the delay of the actual angle against thecommand angle increased; however, the maximum
frequency in practical use is 5 Hz or less and in thisrange the delay of the actual angle from the commandangle was 0.025 sec or less, which is sufficiently small.

Steering angle deg

Actuator

1

1 Hz

0.5
0
Command angle-0.5

Actual angle

-1
1

2 Hz

0.5
0
-0.5
-1
1

4 Hz

0.5
0
-0.5
-1
1

6 Hz

0.5
0
-0.5
-1
1

8 Hz

0.5
0
-0.5
-1

0

250

500

750

Time ms

Fig. 7 Frequency response characteristics

1,000

4.2 Steering Response Speed Test

Steering angle deg

Standard hub bearing

0.4

sHUB

0.3
0.2
0.1
0

0

500

1,000

1,500

2,000

Moment load Nm

4
3

Fig. 10 Flange angle

2

Command1value

5. Vehicle Motion Control by the Front
Wheel Steering

0
-1
-2

Actual measurement-3-4Time sFig. 8 Command value and measured value ofsteering angle

Fig. 9 shows the steering response speed of sHUB
against the steering torque. As the steering torqueincreased, the steering response speed decreased.
However, it satisfied the target response time of 10 deg/sor more in the entire range of the steering torque.
Steering response speed deg/s

Hub flange angle deg

0.5

The steering response speed was obtained bysteering the sHUB while a steering torque is applied tothe hub bearing. The command value shown in Fig. 8(dashed line) was given to the controller to determine
the steering response speed of sHUB. The steering
response speed was determined from the slope of theactual measurement (solid line).

25
20
15
10
5
0

0

100

200

300

400

500

Steering torque Nm

Fig. 9 Relationship between steering torque andsteering response speed

4.3 Rigidity Test
The rigidity of the axle of a turning vehicle wasverified against a moment load being applied to thetires. Fig. 10 shows the flange angles of a standard
hub bearing and sHUB for the same type of vehicle forcomparison of moment rigidity.
As a result of the optimization of internal
specification of the hub bearing, which is a componentof sHUB, steering axis support bearing and bearing
preload, the flange angle of sHUB increased 5%compared with standard hub bearings in the high-load
range.

A joint development with Yamakado/Kano Laboratoryof Kanagawa Institute of Technology was conducted
for verification of effective control method of sHUB.
“Control to Improve Transient Response” which
improves the vehicle response in transient mode and“Control to Improve Turning Characteristics” which
optimizes the lateral skidding angle of the tires in a
steady turn of a vehicle were developed.

5.1 Control to Improve Transient Response2), 3)
This control adjusts time constants of 3 responses,
namely, lateral skidding angle, yaw rate and lateral
acceleration against the vehicle speed and steeringby the correction of steering operation of sHUB for
improvement of vehicle dynamic performance.
In order to verify the improvement of the vehicle
responsiveness by this control law, a “pulse steering
input” test was conducted using a test vehicle withsHUB according to the “Transient Response Test
Procedures for Passenger Cars (JASO Z110:2003).”4)
A test condition of 80 km/h vehicle speed and atriangular wave with pulse width of 0.5 s for drivers
steering operation was used.
The results of frequency response of yaw rate andlateral acceleration against the steering wheel angle
are shown in Fig. 11.
By using this control, it revealed that the vehicle
responsiveness against steering operation improved,
as the peak value increased and the phase lag
improved, both for yaw rate and lateral accelerationin the frequency range (0.5 to 2.0 Hz) of the steering
wheel angle, which is equivalent to normal driving.

NTN TECHNICAL REVIEW No.87

21

Hub Bearing Module with Steering Adjust Function

5.2 Control to Improve Turning Characteristics (SAHS)5)
Gain 1/s
Gain 1/s

0.70.70.60.6

0.20.2Control
ControltotoImprove
Improve
TransientTransientResponse
Response

Gain m/s 2 /deg
Gain m/s 2 /deg

0.80.80.50.50.40.40.30.30.20.20.00.00.10.1

1 1

0.10.10.05
0.05

Without
controlWithout
control

0.10.1

Without
controlWithout
control

0 00.10.1

1010

1 1

1010

9090

Control
ControltotoImprove
Improve
TransientTransientResponse
Response

6060
3030
0 0

-30-30Without-60-60 Without

Phase deg
Phase deg

9090

Phase deg
Phase deg

Control
ControltotoImprove
Improve
TransientTransientResponse
Response

0.15
0.15

control
control-90-900.10.1

Control
ControltotoImprove
Improve
TransientTransientResponse
Response

6060
3030
0 0
-30-30Without-60-60 Without
control
control

1 1-90-900.10.11010

1 1Frequency
FrequencyHzHz

1010

Frequency
FrequencyHzHz(a)Yaw rate(b)Lateral acceleration

The following shows the control law to efficiently utilize
the maximum tire performance in response to the load
shift during turns, in the entire speed range from ultralow speed to mid/high speed when the load shift on theleft and right wheels increases. This control law is called
SAHS (Super Ackermann Hub Steer).
When a running vehicle makes a turn, load shift
between the left and right wheels and lateral skidding
occur. When the load on the inner wheel and outer wheel
during a turn are represented by and respectively,
and the lateral skid angle by , (inner wheel: , outerwheel: ), then the relationship between the cornering
force and lateral skid angle is similar against the changeof the load, which can be depicted as Fig. 14.

Fig. 11 Test result of frequency response characteristics

80km/hInner wheel

μWi

K

0
2.5m

Outer wheel

μWo

Cornering force

Next, the change of vehicle behavior was evaluatedwith the actual vehicle, with and without this control,by conducting a single lane change at the speed of 80
km/h on an asphalt course shown in Fig. 12. Fig. 13
shows the change of yaw rate and lateral accelerationin the test. It revealed that this control decreases therequired steering wheel operation and improves the
response of yaw rate and lateral acceleration.

βi

βn

βo

2μWi / K

2μWo / K

Lateral skidding angle
2.5m

15m

15m

Fig. 14 Relationship between lateral skidding angle
and cornering force

15m

Fig. 12 Actual driving test course (single lane change)

Yaw rate deg/s

40

Without control
Control to Improve
Transient Response

30
20
10
0
-10
-20
-30

2

Lateral acceleration G

50

1.5
1
0.5
0
-0.5
-1

-40
-50
-120 -90 -60 -30 0

30 60 90 120-1.5-120 -90 -60 -30 0

30 60 90 120

Steering angle deg

Steering angle deg(a)Yaw rate

Without control
Control to Improve
Transient Response(b)Lateral acceleration

Fig. 13 Test result (yaw rate and lateral acceleration)

22

NTN TECHNICAL REVIEW No.87

In SAHS control, the lateral skidding angle of theinner wheel is decreased and that of the outer wheel
is increased by sHUB so that the loads on the rightwheel and left wheel become equal(to thedirection of the arrows in Fig. 14). With this control, thesum of the cornering forces can be increased withoutchanging the average steering angles of the left andright wheels, utilizing both tires effectively during turns. In
other words, at ultra-low speed where lateral acceleration(load shift) can be ignored, the control realizes an ideal
Ackermann geometry and at mid/high-speed where lateral
acceleration increases, reverse Ackermann geometry isfollowed.
An evaluation test was conducted for verifying theeffect of SAHS using a test vehicle with sHUB. Fig. 15
shows the layout of the test course. The change of vehicle
behavior was evaluated with and without this control byinputting a steering maneuver ramping up to 130 degrees
at 0.5 sec intervals starting from point A after straightrunning at a speed of 50 km/h. The control parameters
were determined based on the sensitivity evaluation
during driving.

Moving forward, we will study control methods to takeadvantage of sHUB more effectively for its application
on many vehicles including being applied for the driving
wheels. We believe in the high potential of sHUB for
increasing the driving degrees of freedom in the “steering
by wire” system which is expected to be a technology ofthe future in order to increase responsiveness even more,
as it can apply corrective control at the closest position
from the contact point between the tire and the ground.

2.5m
Point A

Fig. 15 J-turn test course layout

Fig. 16 shows the result of test. Without the control,
the ratio of skidding angle against tire load (burden
on the tire) is significantly different between the innerand outer wheels. On the other hand, with the control
the load is equivalent between the inner and outerwheels. Therefore, the force from both tires is efficiently
transmitted on the road surface. As a result, the turning
radius decreased as shown in Fig. 17.

References
1) NTN’s home pagehttps://www.ntn.co.jp/japan/news/new_products/
news201800050.html.
2) Norio Ishihara, Mitsunori Ishibashi, Hirokazu Ooba,
Atsushi Ito, Makoto Yamakado, Yoshio Kano, Masato
Abe, Hub Bearing with Integrated Active Front Steering

n=4 for each

4

Inner wheel32Outer wheel

1
0

0

1

2

3

4

Time s5Lateral skidding
angle/tire load deg/kN

Lateral skidding
angle/tire load deg/kN

Function that Improves Vehicle Dynamic Performance,
n=4 for each43Ishibashi, Makoto Yamakado, Yoshio Kano, Masato Abe,
Hub Bearing with Steering Function that Improves Vehicle

10(2018) 20185263.
3) Norio Ishihara, Hirokazu Ooba, Atsushi Ito, Mitsunori

Inner wheel Outer wheel

2

Proceedings of Society of Automotive Engineers of Japan,

0

1

2

3

4

5

Time s(a)Without control(b)SAHS

Fig. 16 Test result (load on tires)

Dynamic Performance, NTN TECHNICAL REVIEW, No.
86, (2018) 84-90.
4) JASO Z110:2003 “Automotive Standard: Transient
Response Test Procedures for Passenger Cars”.
5) Norio Ishihara, Mitsunori Ishibashi, Hirokazu Ooba,

Y mAtsushi Ito, Makoto Yamakado, Yoshio Kano, Masato
45
40
35
30
25
20
15
10
5
0
-5

n=3 for each

Abe, Hub Bearing with Integrated Active Front Steering
Function that Improves Vehicle Dynamic Performance [2ndReport], Proceedings of Society of Automotive Engineersof Japan, (2019) 20191269.

Without control
SAHS
0Photo of authors

5 10 15 20 25 30 35 40 45 50

X m

Fig. 17 Test result (driving trajectory)

6. Conclusion
Structure, specification and basic performance of the“Hub Bearing with Steering Assist Function (sHUB®)” wereintroduced.
Also, it was confirmed that two control methods (Control
to Improve Transient Response and Control to Improve
Turning Characteristics (SAHS)) can significantly improvethe vehicle characteristics by applying correction to thesteering angles of the left and right wheels against thedriver’s steering operation for improved vehicle dynamic
performance, as shown in the driving test with sHUB
installed on an actual C-segment vehicle. In addition, weare currently working on building an integrated control
combining these two control methods.

Satoshi UTSUNOMIYANorio ISHIHARANew Product Development
R&D Center

New Product Development
R&D Center

Yuusuke OOHATA

Atsushi ITO

New Product Development
R&D Center

New Product Development
R&D Center

NTN TECHNICAL REVIEW No.87

23

Technical Article

Hub Bearing Module with Motor and Generator Function

Kentaro NISHIKAWA*
Hiroki YABUTA*

Mitsuo KAWAMURA*
Atsushi ITO*NTN has developed the hub bearing module combined with a motor generator,‘eHUB’. This module is mounted on an existing vehicle with less modification of
the chassis. It will make a contribution to the improvement of the fuel efficiency
and vehicle dynamics practically when it is applied to a 48V mild hybrid vehicle.
This article focuses on the improvement of the vehicle dynamics.

1. Introduction

Number of
production vehicles Millions

As environmental regulations are strengthened globally,each country has established stringent regulations
for automobiles toward reduction of CO2 emissions.
Along with this trend, the electrification of automobiles
has been accelerating with the active developmentof hybrid vehicles including plug-in, battery powered
electric vehicles and fuel cell vehicles. Fig. 1 shows
the production forecast of passenger vehicles globally.
48V mild hybrid vehicles (hereafter, 48V MHEV) are
expected to grow to 25% of all the production vehicles
by 2025 since electrical handling is easy and theimplementation costs are low. It is known however,that the rate of improvement of fuel efficiency is about
15% maximum even if the effect to fuel cost against
implementation costs are large. The implementation
rate of these vehicles in terms of low fuel consumption
such as electric vehicles and plug-in hybrid vehicles
is expected to be slow due to the promulgationof infrastructure, battery supply and cost issues. ;Improvement of fuel efficiency of 48V MHEVs, which
are expected to grow faster, is required to address thestrengthening regulatory requirements on fuel efficiency
in the near term.
120
100

BEV
HEV
MHEV
ICE

80
60
40
20
0
2015

2020

2025

Fig. 1 Production forecast of global passenger vehicles(Our own analysis and forecast based on IHS Markit)*New Product Development R&D Center

24

NTN TECHNICAL REVIEW No.87

Therefore, NTN has developed a Hub Bearing with
Motor Generator Function (hereafter, eHUB), to beinstalled on the rear wheels (driven wheels) of front
wheel-driven 48V MHEVs1). The following shows thedevelopment concept of eHUB.
(1) Improved fuel efficiency of 48V MHEV vehicles(2) Improved vehicle dynamic performance(3) Installable on existing suspension systems
In the previous article, we reported that the eHUB
improved fuel efficiency by 3.2% in WLTC mode when
installed on the rear wheels of a front wheel-driven
internal combustion engine vehicle (ICE vehicle)1).
Additionally, eHUB can drive the left and right wheels
independently with good responsiveness as it transmits
torque directly to the wheel, and controls regenerative
torque. These characteristics contribute to driving stability
and ride comfort. In this article, improvement of vehicle
dynamic performance based on the independent controlof eHUBs on the left and right wheels is discussed,
focusing on concept (2) above.

2. Basic Configuration
2.1 Structure and Specification
We set the following goal for the size of the outer
diameter so that it can be installed on an existing
suspension system.
・Outer diameter less than the inner diameter of brake
disk・Same axial length as a conventional hub bearing
A three-phase brushless DC motor was adopted toobtain as much output as possible in a limited amountof space. Table 1 shows the specification of the eHUB
used for evaluations. The prototype eHUB was larger than
the target size (width) requiring modification to the test
vehicle. NTN is currently working on size modifications to
the design achieving the same output and results.

Table 1 Specification of eHUB
Item

Target value

Existing
vehiclesystemPrototype

Controller unit

Appearance

eHUB

Transmission ICE
48Vbattery
Front

Outer diameter mm

φ 160

φ 159

Width mm(Hub bolts not included)

80

126

Weight kg

10

Rear

Fig. 2 Power train configuration of the test vehicle
Table 2 Test vehicle specification
14

Driving voltage V

48

48

Maximum output kW

5.0

4.5

Maximum torque Nm

60.0

59.2

Maximum rotational speed min-1(Equivalent vehicle speed km/h)

1,700
(200)

1,200
(130)

2.2 Test Vehicle
Improvement of vehicle dynamic performance
was reviewed by installing the eHUB on the front
wheel-driven application of a B segment vehicle.
The vehicle used for measuring fuel efficiency in theprevious report was used for this test. The power
train configuration is shown in Fig. 2 and the vehicle
specification is shown in Table 2. A commerciallyavailable internal combustion engine vehicle (ICEvehicle) was modified to install the eHUB on the rear
wheels. As shown in Fig. 3, the torsion beam was
modified to install the eHUB and existing hydraulicbrakes. The controller unit and battery were installedin the rear seating area and cargo space (Fig. 4). The
eHUB was built as a control system independent fromthe existing vehicle system, that obtains informationsuch as steering angle, acceleration and speed fromthe vehicle. Commercially available products wereused for the 48V battery and controller unit, building
an environment where the control model created for
simulation can be directly evaluated with the actual
vehicle.

Item

Specification

RemarkDriving method

Front
wheel-driven

Main drive power

ICE

Transmission type

MT

Number of passengers

2

Tire size

195/45/R17

Vehicle weight kg

1,207

ABS system

OFF

Electronic stability control
systemOFF

eHUB

Prototype

Refer to Table 1

eHUB installation

Rear wheels(left and right)

Torsion beam ismodified

Rear seats were
removed

No loadTorsion beam (modified)Hydraulic brakeeHUB

Fig. 3 eHUB installed

NTN TECHNICAL REVIEW No.87

25

Hub Bearing Module with Motor and Generator Function

48V battery

Controller

Inverter(2 units)

Where,: time constant of yaw moment response [s]: steady gain of yaw moment response: required yaw moment [Nm]Fig. 4 Controller unit and battery

3. Direct Yaw Moment Control (DYC)
We worked on vehicle dynamic control taking
advantage of the benefits of eHUB, which can drive
the left and right wheels independently and regenerateenergy. Vehicle dynamic performance can be improved
by appropriately operating eHUB depending on thevehicle information such as the speed, steering angles
and changing the vehicle behavior.
The approach to actively producing different
driving inputs to the left and right wheels to directly
control the vehicle yaw moment is called Direct Yaw
Moment Control (hereafter, DYC)2), 3). DYC is expected
to improve the responsiveness of yaw rate against
steering and vehicle maneuverability on slippery roadsurfaces such as roads with compacted snow or ice.
An approach to produce yaw moment from thedifference of driving inputs to the left and right wheels
to compensate for the difference between the target
yaw rate and vehicle yaw rate is known as the DYC
yaw rate response. The target yaw rateis expressedby Equation (1) in conventional DYC.

Equation (2) shows that the yaw moment isdetermined depending on the steering angular velocity
and angular acceleration in the conventional DYC.
By adjusting α and β to maximize the effect of DYC,
the yaw moment becomes large due to the term that
depends on the steering angular velocity, resulting
in the required maximum torque of several hundredsof Nm per wheel, on both wheels. Therefore, theconventional DYC cannot be applied to eHUB, which
has the maximum torque of a magnitude of tens Nm.
Therefore, we focused on the stability ofmaneuverability on slippery roads and adjusted thecontrol parameters for improving the yaw rate responseat the beginning of steering operation. If we set β = αin Equation (1), the target yaw rate can be expressedby Equation (3) and the required yaw moment by
Equation (4), respectively, improving the torqueresponse against the steering angular acceleration.
This enables improved response to the initial steering
operation even with relatively low torque.

Where,: target yaw rate [rad/s]: steering angle [rad]: natural frequency of yaw rate response: damping ratio of yaw rate response: time constant of yaw rate response [s]: steady gain of yaw rate response: control parameter of natural frequency: control parameter of damping ratio
Equation (1) shows that the natural frequency anddamping ratio of the yaw rate response to steering can
be changed by arbitrarily setting the control parameters
necessary to achieve
α and β. The yaw moment
this yaw rate is expressed by Equation (2).

26

NTN TECHNICAL REVIEW No.87

The yaw motion of the initial steering operation isenhanced when α > 1, and suppressed when α < 1.
Torque of the eHUB to achieve the yaw moment ofEquation (4) is Equation (5).

Where,: rear wheel tread [m]: dynamic effective radius of tire [m]: torque of eHUB (left and right) [Nm]Fig. 5 shows the result of the simulation for therequired torque against the steering angles. In theordinary DYC, the torque is determined according to
the change of steering angular velocity and steering

360

100

270

75

180

50

90

25

0

0

Steering angle
Torque Nm

Steering angle/
angular acceleration deg deg/s/s

-25

-90
0.8

1

1.2

1.4

1.6

1.8

2

2.2

Steering angularacceleration
Required torque(ordinary DYC)
Required torque(DYC for eHUB)

Time sFig. 5 Torque of eHUB against steering
Speedadjustment zone

Release of acceleration pedal

μ=0.20

4m
4m
5m

10m

Fig. 6 Driving condition

Lateral distance m

0

Without control
DYC (α=1.2)
DYC (α =0.8)

1
2
3
4
5
6
0

10

30

20

40

50

Longitudinal distance m

Fig. 7 Vehicle driving trajectory30
20

Yaw rate deg/s

angular acceleration. In contrast, in the DYC for theeHUB, since the torque responds to the change ofsteering angular acceleration, the increase in torqueis faster compared with ordinary DYC. A driving test ofa single lane change on a low μ road was conductedusing this method for setting parameters. As shownin Fig. 6, the vehicle’s speed is adjusted to 30 km/h
in the speed adjustment zone and the acceleration
pedal is released at a predetermined point to coast
for a lane change. Fig. 7 shows the driving trajectoryof the vehicle. The figure shows an average of 3 runs
under the same conditions. Without control and with
DYC (α = 0.8), the vehicle turned wide when steering
back (at around 20 - 30 m in the figure), but the vehicle
with DYC (α = 1.2) turned smoothly and remained
stable. Fig. 8 shows the change of yaw rate against
the steering angle. Applying DYC (α = 1.2) improved
traceability of yaw rate to steering angle and theamount of steering significantly reduced compared to
the vehicle without control. That means that the vehicle
behavior responds well to the steering operation andthe vehicle turns more easily. On the other hand, in thecase of DYC (α =0.8), the amount of steering is almost
the same as the case without control but the area
inside the curve is larger. That means that the yaw rate
response is delayed against the steering operation,
the vehicle behavior does not respond well and thevehicle turns less easily. As such, we could verify thateven a small amount of torque, such as the eHUB, canchange the vehicle behavior by driving/regenerating
the left and right wheels separately.

10
0
-10

Without control
DYC(α=1.2)-20

DYC(α=0.8)

-30
180

90

0

-90

-180

Steering angle deg

Fig. 8 Change of yaw rate against steering angle

4. Longitudinal Acceleration Control
According To Lateral Acceleration
DYC in the previous Chapter is effective when
the friction coefficient between the tire and the roadsurface is low. However, these driving conditions arelimited so another method for controlling vehicles morecohesively with longitudinal and lateral acceleration
is being proposed by adding longitudinal accelerationaccording to lateral acceleration4).
Fig. 9 shows a graphical representation of
longitudinal and lateral acceleration during turns ofeveryday drivers and expert drivers in regular driving
conditions. Ordinary drivers tend to decelerate before
a turn and only maneuver the steering wheel whileturning. Therefore, the lateral acceleration abruptly
changes after deceleration as shown in (a) in the
figure. The passengers feel significant change ofinertial force that may cause carsickness or discomfort.
On the other hand, expert drivers adjust acceleration/
deceleration along with steering operation, whichmakes the combined acceleration of longitudinal andlateral acceleration transition along with a smooth
curve. Therefore, the passengers feel a smootherchange of inertial force and a improved comfort level5).
The driving technique of expert drivers can beachieved by adding longitudinal acceleration to lateral
acceleration, which can be expressed in Equation (6).
The left and right torque from the eHUBs are the same
to realize this and can be expressed in Equation (7).

NTN TECHNICAL REVIEW No.87

27

Deceleration

Lateral acceleration

Acceleration

Deceleration(a) Ordinary driver

Lateral acceleration(b) Expert driverFig. 9 Lateral/longitudinal acceleration during a turn(graphical representation)

Where,: vehicle lateral acceleration [m/s2]: vehicle lateral jerk (time derivative of) [m/s3]: vehicle target longitudinal acceleration [m/s2]: first-order lag time constant [s]: vehicle weight [kg]: control parameter of longitudinal acceleration
Fig. 10 shows the graphic representing longitudinal
acceleration control. The longitudinal accelerationis controlled with the torque produced by eHUB
according to lateral acceleration. Deceleration is added
when the vehicle enters into a curve so that the load
moves from the rear wheels to the front wheels andthe yaw moment to assist turning is created. On theother hand, acceleration is added when the vehicle
exits from the curve so that the load moves from thefront wheels to the rear wheels and the yaw moment torestore the vehicle stability is created.

Fig. 11 shows the result of the driving test with anactual vehicle similar to that in Chapter 3 to verify theeffect of the longitudinal acceleration control throughdrive/regenerating brake control of the eHUB. Twocontrol conditions were used: without control andlongitudinal acceleration control. The results show
an average of 3 runs, similar to the test with DYC.
The longitudinal/lateral acceleration transitioned in asmooth curve when longitudinal acceleration control
was applied.
These results suggest high potential for improvementof vehicle dynamic performance if appropriate vehicle
operation is implemented, even with a motor/generatorof small output such as eHUB. In the next stage,
we will build an integrated control combining DYC,
longitudinal acceleration control and optimum logic forfuel efficiency, etc.

0Longitudinal acceleration G

Acceleration

Longitudinal acceleration

Longitudinal acceleration

Hub Bearing Module with Motor and Generator Function

Without control
Longitudinal
acceleration control

-0.02
-0.04
-0.06
-0.08
-0.1
-0.12
-0.3

-0.2

-0.1

0

0.1

0.2

Fig. 11 Result of longitudinal acceleration control driving

Concept of control
Lateralacceleration

Exit(acceleration)

Lateral jerk
Steadyturn

Vehicle acceleration
by eHUB

Entry(deceleration)

Torque of eHUB
(left)Torque of eHUB
(right)Longitudinal acceleration
control

Fig. 10 Concept of longitudinal acceleration control

28

NTN TECHNICAL REVIEW No.87

0.3

Lateral acceleration G

Entry Steady Exitturn

References

5. Conclusion
In this paper, the effect of vehicle dynamic control
was verified with the eHUB, which improves fuelefficiency and driving performance of 48V MHEVs
without significant modification to the vehicles, and thefollowing result was obtained.
(1) Direct Yaw Moment Control
It was verified that DYC with higher sensitivity to thesteering angular acceleration was effective for thestability of driving trajectory and the reduction of theamount of steering in a single lane change on a low
μ road.
(2) Longitudinal Acceleration Control Coupled with
Lateral Acceleration
It was verified that application of longitudinal
acceleration, which is said to contribute to theimprovement of ride comfort, was effective for thesmoother change of lateral/longitudinal combined
acceleration and the improvement of ride comfort insteering.

1) Kentaro Nishikawa, Yuuji Yada, Yasuyuki Fujita, Mitsuo
Kawamura, Hiroki Yabuta, Hub Module with Motor andGenerator Function, NTN TECHNICAL REVIEW, No. 85,(2017) 26-32.
2) Masato Abe, Automotive Vehicle Dynamics (2nd Edition),
Tokyo Denki University Press (2012) 236-247.
3) Ryou Yukishima, Yusuke Makino, Hidenori Karasawa,Takeshi Kanda, Aiko Myouki, Tomohiro Sugai, Katsunori
Satou, Two Motor On-board Drive System,NTN TECHNICAL REVIEW, No. 83, (2015) 20-25.
4) Yuta Suzuki, Weipeng Cheng, Shuichi Kosaka, Influence of
Vehicle Body Motion on the Effects of G-Vectoring Control,
NTN TECHNICAL REVIEW, No. 85, (2017) 33-39.
5) Makoto Yamakado, Junya Takahashi, Shinjiro Saito, Masato
Abe, New Vehicle Dynamics Control Concept “G-Vectoring”
for Enhancement of Safe Driving, Hitachi Review, (2009)46-49.

In the next phase, we will work on improvementof the eHUB for higher output and higher efficiency
to enhance the effect of reduced fuel consumption,
as well as the improvement of vehicle dynamic
performance for practical applications.

Photo of authors

Kentaro NISHIKAWA

Mitsuo KAWAMURA

Hiroki YABUTA

Atsushi ITO

New Product Development
R&D Center

New Product Development
R&D Center

New Product Development
R&D Center

New Product Development
R&D Center

NTN TECHNICAL REVIEW No.87

29

Technical Article

Development of Control Platform for Electric Module

Tatsuji INOUE*
Kazuhiro AOSHIMA*
Yuichi SUGIMOTO* Keigo MOTOKUBO*
In the automotive industry, the development of CASE (Connected, Autonomous,
Shared & services, Electric) has proceeded. Many devices (such as cameras,
sensors, actuators, motors, etc.) are used for autonomous driving and electrification.
And the software for controlling those devices increase year by year. The functionalsafety standard ISO 26262 has been established and development to ensure safety
is proceeding. However the development which is based on ISO 26262 requires
larger number of people, costs, and much more skills than conventional development which is based on IATF
16949. NTN is developing electric motors, actuators, and controllers that contribute to electrification and By-wiresystem. In this article, we introduce the development of control platform for NTN electric motors and actuators.

1. Introduction
Various companies are developing initiatives forConnected, Autonomous, Shared & Services, andElectric (CASE) with the aim of reducing traffic accidents,
providing safe and secure freedom of transportation,
usefulness to users and environmental measures.
NTN, in view of these trends, has developed auniversal series of electric modules containing various
motors and actuators so that we can contribute to the“Autonomous” and “Electric” aspect of CASE. NTN
achieves this through the use of our core expertise andtechnologies which includes bearings and ball screws,
as well as our research into the design technology of
motors and control technology of vehicles. The following
are descriptions related to some of the electric modules
we have developed as well as their proposed uses.

・For use in applications where it will be directly
installed on components

Fig. 1 Outlook of B II Series (B II 00)

1) Overview of Electric Module Series(1) B II Series (Fig. 1)・Electric actuator using paired gears to reduce thespeed and convert rotation motion to linear motion
through the use of a ball screw・Through the use of optional components such as aplanetary reducer or a reverse lock out, the driving
power can be increased as well as the ability tomaintain actuator position(2) B III Series (Fig. 2)
・A compact electric actuator that combines a highoutput brushless DC motor, a ball screw and alinear motion mechanism within a hollow structure.

* Business Promotion Department, Electric Module Products Division, Automotive Business Headquarters

30

NTN TECHNICAL REVIEW No.87

Fig. 2 Outlook of B III Series (B III N)

(3) SP Series (Fig. 3)・ Brushless DC motor series・ For use in applications that require a thin and high torquerotational actuator. This is based on the hollow motor
structure of the BIII series but with a reducer in the hollow
part.

2. Background of Control Platform
Development
The electric module series was developed as a
product line-up for applications such as chassis,
engine and transmission, and are selected to meet
the application specification. Various software versions
have been developed for different applications by using
the existing asset, which created the following issues:
・Complexity due to many changes, enhancements,
and reproduction of code
・Side effect of software changes causing degradationand failure of existing functions

Fig. 3 Outlook of SP Series2) E xamples of proposed uses of Electric Module
Series(1) Transmissions as an electronic shift selector (B II Series)
The shift lever of both AT and CVT are usuallyconnected to the transmission with a mechanical wire,
etc. for selecting the shift position. Using the B II Series
module it would be possible to electrify the shifting of thetransmission.
(2) Electric hydraulic brake (B III Series)
Applying the coaxial type B III Series with built-inball screw to the master cylinder shaft contributes toreducing the overall size of an electric hydraulic brakesystem(3) Electric variable valve timing control (SP Series)
Space efficient electric variable valve timing mechanism
can be created by incorporating the SP Series into cam
shafts(4) Electric oil pump (SP Series)
Integrating a thin and highly efficient SP motor andcontroller contributes to reducing the size of an electric
oil pump
With the development of the different Electric Module
Series, the software needed to support each Electric
Module and application also needed to be developed, which
increased man-hours for development and maintenance.
Failure rate was also increased due to the complexity ofthe electronic system, in addition to increased risk of new
failure modes due to the application of new technologies.
Out of these backgrounds, the Automotive Standard for
Functional Safety, ISO 26262 was issued. It became
imperative to build a new process for efficient softwaredevelopment not only to cope with the requirements of
ISO 26262 but also to address the need of software
support for each application of electric module series.

To address the issues of the conventional
development approach of using the existing asset
and to cope with ISO 26262, we decided to analyze
the current situation and introduce two development
methods.

1) Development of software product line
The characteristics of the Electric Module seriesof products were defined by the external variability(characteristics/values of the system viewed fromoutside) and the internal variability (elements tocompose a system). Using a variety of systems andsoftware it was possible analyze the dependencies
and differences between the Electric Module productseries. As a result, the software product line wasintroduced, which is effective at reducing the numberof man-hours by creating a core asset of software, andfor improving quality by repetitive use of the core asset.
This is further described in Section 3.2 in details.

2) Model Based Development
In general, it is said that validation by simulation
during the requirement definition and basic designphases reduces the man-hours of test phase and rework(Fig. 4).

MBD by simulation
Requirement
definition
Architecture
designDetailed
designTest by people
with actual
Efficient design
machine through verification

Implementation

Efficient test
processof simulation

Fig. 4 Shift of development to design process

NTN TECHNICAL REVIEW No.87

31

Development of Control Platform for Electric Module

is subject to quality management, and is based on
the internal process that conforms with IATF 16949,
adding Automotive SPICE (system development
process model for on-board systems) which is highly
compatible with ISO 26262 (Fig. 5). The followingshows the features.

Conventionally, simulation of responsiveness, etc.
was conducted by spreadsheet software, which had
its own limitations. In order to increase the simulation
accuracy and to understand the basic characteristics
of a motor at the design phase, JMAG*1 is used for
motor design.
It is also required to conduct simulation of thesystem including controller (motor control part) andplant (JMAG-RT*2 model created from JMAG).
As ISO 26262 also suggests validation using
simulation, fault injection test*3, which intentionallycreates faults in the model, can be easily conductedin shorter time and at less cost than using actualmachines. Validation by simulation can also be
conducted at the requirement definition phase. We
decided to use the Model Based Development toaddress the above.
We are currently conducting the development of
the Control Platform using these two development
methods, which is described in the following Chapter.

・Since Automotive SPICE only defines the framework,requirements on methods and safety specified by
ISO 26262 are incorporated into the process tomake it compliant to the standard.
Process
definition (where work ﬂow is specified)・is made available to software developers at any
time, using EPF Composer (a tool that defines thedevelopment process and converts it to HTML) via
the Intranet (Fig. 6).
・The software process is separately defined for coreasset development and new product developmentaligned with the Product Line newly introduced for
efficient development of software (Section 3.2).
・The following was introduced mainly for validationof motor control in the Model Based Development(Section 3.3):
In the system requirement phase: MILS*4
In the software design phase: MILS, RCP*5*1: JMAG: Simulation software made by JSOL for development of electric
equipment design*2: JMAG-RT: A high-speed and high-accuracy plant model for systemlevel simulation derived from the FEA model*3: Fault injection test: Validation to review if the system turns into a safe
condition as designed, by intentionally injecting
faults*4: MILS: Model In the Loop Simulation; Simulation that operates thecontrol specification written in the model, combining with theplant model*5: RCP: Raid Control Prototype; Validation of the actual machine subject
to control, which incorporates the control specification written in
the model into the general purpose controller

3. Control Platform Development
3.1 Overview of Process
The entire process was built with compliance tothe functional safety standard ISO 26262, which

Electric Module Series
Simulation

By wire*b

SafetyMechanicalclutch unit
Ball screw drive
module for electric
hydraulic brake

Software Product Line

Development
process foron-board system

Electric hydraulic brake
Electric shift selector

MBD (Model Based Development)*c

Proposed
applications

Electric parking brake
Electric variable valve
timing unit*aElectric EGR valve
SP motor
Electric oil pump*a Automotive SPICE: process improvement model for on-board system development*b SURIAWASE: Strategy that Ministry of Economy, Trade and Industry (METI) compiled to enhance harmonization by taking advantage of a model-based
development (MBD) process that uses virtual simulations instead of physical machines.
*c SOTIF: safety of the intended functionality

Fig. 5 Foundation of the development process

32

NTN TECHNICAL REVIEW No.87

1) Development of core asset

Development process
Development
Core asset

Product planning/requirement
extraction process
Merging of individual product asset is required
DE_domain̲engineering_process_group
Merging not required
Requirement
management DB

Individual
product asset

AE_application_engineering_process_group(1) The common part and variable part of the productgroup (Fig. 8) are created by the feature model thatdefines the variability of functions and features which
are used to generate the base of the configuration
model (model to select the product properties)(2) Reusable assets are incorporating into the deliverables(requirement specification, architecture, Simulink®
model, codes) which helps develop the feature modelof the common and variable parts of the product group2) New product development
Domain engineering process(Core asset development process)DE.SWE.06̲software test (D)CMP.16_software test

SUP.02_verification

・Product group software requirement specification
・Product group software safety requirement

Subject to merge

Individual product asset (release branch)

Software test speciﬁcation

Core asset (development branch)

Progress information(plan/implementation)

Example of process description

Fig. 6 Process definition created by EPF

3.2 Software Product LineThe Software Product Line is a method to analyze
the products to be developed and to categorize certain
portions into the common part and product specificpart. Using this method, the common part is definedas assets to be reused and the product specific partis developed efficiently. It is effective in reducing thedevelopment period and man-hours while improving
quality. In applying the Software Product Line, thescope (range of specifications that covers a productgroup) was defined as the existing motor series. The
deliverables were defined as the software requirements,
architecture, detailed design specification, Simulink®*6(3) The requirement specifications of the new product areclassified into “common part/variable part” and “productspecific part”(4) The common/variable parts of the requirement
specification of new products are selected from theconfiguration model(5) The configuration model created in (4) and based on thereusable assets created in the core asset development(2) is loaded into the Binding Tool. This is then used
for binding and deliverables based on the required
specification of the new product(6) The deliverables for the product specific part are newly
created(7) The deliverables to conform to the new productrequirements are created by combining the deliverables
extracted from the core asset (5) and the deliverables
newly created for the product specific parts (6)Product specific part
Product A

Common part

Variable part

Product D
Product B
Product Cmodel, hand implementation code and test specification.
The ﬂow of the Software Product Line is explained in thefollowing, along with Fig. 7.

Fig. 8 Common part and variable part

*6: Simulink®: Block diagram environment for Model-Based Design
developed by MathWorks
Quality review
Definition of variability(3)Management

Feature model
Configuration(4)

Configuration
model

Requirement specificationof the product group
Core asset

Requirement specification

Core asset (reusable asset)

Hand implementation code

Architecture

Detailed design document

Test specification

Architecture of the
product group(5)(6) (7)

Introduction

Simulink model
Feature enhancement/
modification(1) (2)

Support offunctional safety

Variability analysis
Reusable asset

Define characteristicsof the product group
Select characteristics
of a productAdd individual
specification
Extract only the requirement
specifications that correspondto the selected characteristics

Work
requestExtract only the elements that
correspond to the selectedcharacteristics

Buildout
Subcontractors

UpdateSubmitUpdate

Review of changes

Binding[Support tool]feature IDE

Process
definition

New productProduct A

Product B

Requirement specification

Requirement specification

Requirement specification

Architecture

Architecture

Architecture

Detailed design document

Detailed design document

Detailed design document

Simulink model

Simulink model

Simulink model

Hand implementation code

Hand implementation code

Hand implementation code

Test specification

Test specification

Test specification

Development
environment(Redmine,SVN,···)
SubmitUpdateDevelopment
support toolFig. 7 Total view of Software Product LineNTN TECHNICAL REVIEW No.87

33

Development of Control Platform for Electric Module

3.3.1 Result of Simulation and Future Plan

Tools could be created in-house in a short time, byusing FeatureIDE an open source product for creating
the feature model and configuration model anddeveloping the Binding Tool.
We used a sample core asset for binding (5) andverified that the required deliverables were extracted.
With this, we completed creating the mechanism of theprocess.
Currently, we are converting the requirement
specifications and architectures of the existingproducts into parts to be reused. In this process, since
the difference (variability) needs to be considered fordesign and implementation, some of them need to bemodified before turning them into parts.
In the Product Line, since specifying and managing
the variability that exist in the product group areimportant, we plan to thoroughly analyze thedifferences (variability) of the software platform forfunctional safety under development to make thedesign easily reusable.

As the target of simulation, in MILS, JMAG and RCP,
the relative error of N-T and I-T characteristics, which
are regarded as the basic characteristics of the motor,
were set to ±10%.
Firstly, the motor control (vector control) algorithm
was modeled reverse engineered from the existing
C source code, to create the controller model by
Simulink®. The vector control algorithm that wasmodeled was bound to the motor model (JMAG-RT)in order to conduct MILS with the general purpose
controller. This control was connected to the inverter
and motor to be evaluated and RCP was conducted.
The comparison of N-T and I-T characteristics
from MILS and RCP (Fig. 10) revealed that theI-T characteristics almost matched and the N-T
characteristics were within ±10% when no load
was applied but as the current increased, the N-T
characteristics exceeded ±10%. Since the motor phasevoltage dropped by 1.73V against the power source
voltage of 12V, the voltage drop may have occurred
due to the internal resistance or wiring resistancein the inverter used in RCP (Fig. 11). We plan toinvestigate the cause of this error by comparing thetheoretical calculation and the actual measurement of
the voltage drop due to internal resistance, etc. andimprove the model.

3.3 Model Based Development
In order to verify the system to conduct simulation of
the controller model, where the motor control algorithm
and the controlled objects are incorporated into theplant model, the Model Based Development wasapplied.
In the process definition, the process was identified
with system requirement review phase, softwarearchitecture design phase and simulation (MILS, RCP)in the detailed design phase (Fig. 9).

Functional safety concept
Control model

Controlled
object model

Extraction/analysis of requirements
Specification for technology
safety requirements

System validation test
Safety validation
System integration test
Integration of items and test

System design

Control model

Software test
Verification of safety
requirements

Requirement definition
Controlled Specification for safety
requirements
object model
Software architecture
designControl model

Integration evaluation

Detailed design

CodingPlanned to be introduced
ACG

Control model

Actual controlled
objectFig. 9 V-shape development model

34

NTN TECHNICAL REVIEW No.87

Actual controller
Virtual controlled object
Made by dSPACE

Unit test

In case of a single motor

General purpose controller
Made by dSPACE

Controlled
object model

C code3.3.2 Result of Controller Model and Future Plan
MILS

JMAG

2.0

RCP

Torque Nm

1.5

1.0

0.5

0.0

0

500

1,000

1,500

2,000

2,500

3,000

Rotational speed min-1

N-T characteristics
JMAG

2.0

MILS

RCP

1) Required model elements are edited (added/
deleted) by the Matlab script2) Required model is selected by the Variant
SubSystem and Configurable SubSystem3) Processing is dynamically selected by If/Switch
Case SubSystem and Switch block

Torque Nm

1.5

1.0

0.5

0.0

0

5

10

15

20

25

Phase current Arms

I-T characteristics

Fig. 10 Simulation result (N-T, I-T characteristics)

13

Supply voltage12［V］

12

1.73
［V］

11
10

U phasevoltage

Voltage V

9
8
7
6
5
4
3
2
1
0

0

0.002

0.004

0.006

0.008

In the controller model, we are promoting the useof the core asset (reusable asset) anticipating theforthcoming auto code generation. As one subsystemmeets multiple requirements, the subsystems wererecreated to correspond to each requirement in therequirement specification.
Then, the switch of subsystems where made in threepatterns based on “with/without” requirement. The
three patterns determine the binding time dependingon “when” the variability is realized for each subsystem(Fig. 12).

0.01

Switch is applied at the design phase for 1), code
generation or compiling phase for 2) and software
execution phase for 3). The model unit test was
defined in the process to verify the output result per
SubSystem.
By conducting the simulation test per subsystem,
faults can be removed before implementation with
auto code generation. The model based development
comes with a rich set of test tools; however, in order
to eliminate variance of quality of manual tests and for
efficiency purposes, a tool for automatic testing thatworks with different tools was developed. This enabled
automatic generation of test specifications, simulation
models and test results, easy retesting and recordingof evidence (Fig. 13).
For applying auto code generation to the productsin the coming years, we will prepare the environment
and process for conducting verification of consistency
between the model and codes (Back to Back testing)required by ISO 26262 (SILS, PILS).

0.012

Time sFig. 11 U phase voltage when phase current effective
value is 25Arms

NTN TECHNICAL REVIEW No.87

35

Development of Control Platform for Electric Module(Example) Unnecessary subsystems andsignals are deleted in the implementation
stage

1. Required model
elements are edited by
the Matlab script(Example) Necessary subsystems
are “selected” in the implementation
stage(Example) Processing of a subsystem can beisolated by a compilation switch even after the codes
are output

2. Required model is selected by the Variant SubSystem andConfigurable SubSystem

3. Processing is dynamically selected by If/Switch Case SubSystem and Switch block(Example) The constant value toswitch processing is “selected” in theimplementation stage(Example) Processing of a subsystem can beisolated by switching the constant value even after
the codes are output(Example) Processing of a subsystem canbe isolated by switching the command
value even at the execution phase
Binding time

When subsystems
are implemented

When compiled

When linked

When installed

When activatedWhen executed

Fig. 12 Relationship of replacement measures between the binding time and Simulink® subsystem

Model is automaticallygenerated from the test
specification
Test specification

Automatic execution of the simulation

4. Conclusion
NTN will continue developing electric module
products, which can be applied to various applications
efficiently, taking advantage of our base technologies,
and contribute to the promotion of autonomous driving
and electrification, which is evolving in the automotive
industry.
Photo of authors

Waveforms of input values
and expected values
Tatsuji INOUE

Kazuhiro AOSHIMABusiness Promotion
Department
Electric Module Products
Division
Automotive Business
Headquarters

Business Promotion
Department
Electric Module Products
Division
Automotive Business
Headquarters

Yuichi SUGIMOTO

Keigo MOTOKUBO

Business Promotion
Department
Electric Module Products
Division
Automotive Business
Headquarters

Business Promotion
Department
Electric Module Products
Division
Automotive Business
Headquarters

Waveforms of
expected values
and results
The red circles
indicate deviationfrom the expectedvaluesFig. 13 Flow of unit test tool of automatic model

36

NTN TECHNICAL REVIEW No.87

New Products

Introduction of Sensor Modular Products and Technologies forAutonomous Driving and Electrification of Automobiles
Yasuyuki FUKUSHIMA* Hiroyuki HAKAMATA*
Christophe DURET**
This article describes what NTN is challenging to meet the emerging
requirements on automobiles, ‘CASE’ , focusing on newly developed sensor
modular products and technologies applied to the existing automotive bearings.

1. Automotive Market Trend and NTN’s
Approach
The automotive industry is facing a significant
transformation period that only happens once ina century. Responses to the new requirements of“CASE” are needed, in addition to the improvementof conventional vehicle performance: “driving”,“turning” and “braking”. CASE stands for “Connected”,“Autonomous”, “Shared & Services” and “Electric”1)-3).
・Connected
Exchange of information between an automobileand everything else connected to the network, suchas roads, homes, dealers and other automobiles via
wireless transmission pathways such as 5G networks.
・Autonomous
Autonomous vehicle driving represented by vehicle
driving assistance and driverless taxis.
・Shared & Services
Sharing and service offerings including MaaS
(Mobility as a Service).
・Electric
Not only the electric power train of electric vehicles(EVs), but also electrification of every moving
element of vehicles.
NTN provides the automotive sector with hubbearings and CVJs (driveshaft), and module productsthat incorporate them. Hub bearings are importantcomponents in many vehicles that support rotation of
the wheels and are equipped with ABS sensors (wheel
rotational speed sensors) to detect the rotational
speed of each wheel. NTN-SNR has been leading thefield of wheel speed active sensing technology sincethe 1990s, by developing a technology to integrate therubber magnet with the seal of hub bearings (ASB®:
Active Sensor Bearing; shown in Fig. 1) as the global
standard4). In this article, NTN’s sensor products/
technologies that can satisfy the new requirementsof CASE are introduced, which have been developed
after the above mentioned technology.

Rubber magnet
integrated seal

Fig. 1 ASB® (Active Sensor Bearing) hub bearing

2. Hub Bearing with Integrated High
Resolution Rotation Sensor
NTN developed the “Hub Bearing with Integrated
High Resolution Rotation Sensor” 6) which is equippedwith wheel speed sensor technology that achievesa max. 40 times higher resolution by using a highresolution rotation sensor (MPS40S)5), withoutchanging the specification of the conventional hub
bearing. The improved resolution promotes accurate
estimation of the tire and road conditions. The Hub
Bearing with Integrated High Resolution Rotation
Sensor is shown in Fig. 2. In this section, an overview
and the evolution of the Hub Bearing with Integrated
High Resolution Rotation Sensor are discussed, withfocus on its application to autonomous driving.

*New Product Development R&D Center** NTN-SNR ROULEMENTS Research & Innovation Mechatronics

NTN TECHNICAL REVIEW No.87

37

Introduction of Sensor Modular Products and Technologies for Autonomous Driving and Electrification of Automobiles

Fig. 2 Hub Bearing with Integrated High Resolution
Rotation Sensor

2.1 O verview of Hub Bearing with Integrated High
Resolution Rotation Sensor
An overview of the Hub Bearing with Integrated High
Resolution Rotation Sensor equipped with the high-resolution
rotation sensor (MPS40S) is shown in Fig. 3. The highresolution rotation sensor, which is the detection component,
is molded together with the fixing core grid with resin, andpress fit onto the stationary ring (outer ring). The component
to be detected is a magnetic ring with alternating Northand South-poles (48 poles total), which is press fit onto therotating ring (inner ring). The high-resolution rotation sensor(MPS40S) creates high resolution output signals by electricallyinterpolating (multiplying) the length of the pole-pair of themagnetic ring. The multiplier can be set up to 40 times, with
output of 1,920 pulses/rotation.

extracting the rotational speed variation of one tire rotation. The
data is extracted under the condition that the driving speed
is constant in order to obtain highly accurate information. The
rotational speed variation patterns are generated from thesignals of multiple rotations to reduce the random noise thatcomes from the road surface while the vehicle is running. The
rotational speed variation patterns obtained this way provide
characteristic waveforms dependent on the tread patterns. It isestimated that they show the rotational speed variation causedby the deformation of the tread when the tread comes in contact
with or separates from the road surface. In high speed driving,
the deformation of the tread cannot be captured easily because
the tire-specific vibration mode becomes dominant. Therefore,
the detection accuracy can be increased by obtaining data inlow speed driving. The conventional ABS sensor cannot extract
the rotational speed variation with sufficient resolution since it
provides much fewer pulses per rotation. Therefore, the signals
from the high-resolution rotational sensor can be used toincrease accuracy of the estimation of the tire and road surface
conditions. Sections 2.2.1 to 2.2.5 discuss the result of test
verification with different conditions of the tire, such as a foreign
object inserted in the tread, tire type, wear, air pressure, as well
as different conditions of the road surface. The multiplier of thehigh-resolution rotational sensor was set to 10 (output of 480
pulses from AB phase per rotation).
Detected rotational speed variation

Asynchronouschange (drift-like)

Rotation synchronization
component

Change of rigidity due to temperature

Road surface/tire variation
Tread pattern

Deformation/expansion due to rotation

Roundness of tire

Tire

High resolution sensor(IC, processing circuit)

RandomWear

Inserted foreign object

Internal pressure (temperature)
Wheel load

Resin moldCondition (dry/wet)Road surface

Roughness, friction coefficient
Vehicle driving condition

Magnetic ring

Power train friction resistance/change of input torqueFig. 4 Information contained in the rotational speed
variation components
Seal

Magnetic encoder

Seal with magnetic encoder

T(1)Rotation output
signalFig. 3 Overview of Hub Bearing with Integrated High
Resolution Rotation Sensor

Measurementof rotational
pulsesT (n)NTN has been working on the approach to estimate the tireand road conditions by extracting and analyzing the informationof the changes of the rotational speed from the wheel rotation
signals of a running vehicle using the Hub Bearing with an
Integrated High Resolution Rotation Sensor. The rotational
speed variation includes information about the variation of theroad surface/tire and vehicle propulsion condition, as shownin Fig. 4. Fig. 5 shows an example of signal processing for
obtaining the rotational speed variation. The tire and roadconditions are estimated by analyzing patterns obtained by38

NTN TECHNICAL REVIEW No.87

Rotational speed variation

2.2 A
 pplication to Estimation of Tire/Road Conditions

T(2)

T(3)

T(959) T(960)

One rotation of tire (480 pulses)
Calculationof wheel
speed
v (n)

Analysisof speedvariation

Informationof roadsurface/tire

5

0

-5

96

192

288

394

480

576

672

768

864

Number of pulses

Fig. 5 Example of rotation pulse signal processing

960

Autocorrelation value

To simulate the condition of foreign objects inthe tire, a screw was set between the treads of thetire without puncturing it (Fig. 6). Fig. 7 shows therotational speed variation patterns with and without ascrew. A part of the rotational speed variation patternsignificantly changed due to the presence of theforeign object in the tread, verifying the difference ofrotational speed variation patterns with/without theforeign object.

Autocorrelation value

2.2.1 Detection of Foreign Objects in the
Tire Tread

0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8

Tire A

96

192

288

394

480

576

672

768

864

960

864

960

Number of pulses
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8

Tire B

96

192

288

394

480

576

672

768

Number of pulses

Fig. 8 Comparison of autocorrelation patterns of 2 typesof tread patterns

2.2.3 Detection of Tire Wear

Fig. 6 A screw is inserted in the tread

With screw

Rotational speed variation

Without screw

0

-5

0

96

192

5

Number of pulses

Fig. 7 Comparison of rotational speed variation patterns
with and without the screw

2.2.2 Detection of Tire Types
Improvement in vehicle safety and fuel consumption
can be expected by optimally controlling propulsion/
braking based on the characteristics of the detected
tire type. Two types of tires, A and B, which havedifferent tread patterns, were prepared. The
rotational speed variation patterns of tires A and B
were obtained, and in order to clearly observe thecharacteristics of the tread patterns, an autocorrelation
value (cyclic nature of signals) was calculated byshifting the phase of each rotational speed variation
pattern, and the resulting patterns were compared (Fig.
8). The autocorrelation pattern of each tire is clearly
different, which verified that the tire types could be
differentiated.

Tread depth of 8mm

0

-5

288

Rotational speed variation

Rotational speed variation

5

Fig. 9 shows the results of the rotational speed
variation patterns of two sets of tires with the sametread pattern and different tread depths of 8 mm
and 2 mm. It was verified that the amplitude level ofthe rotational speed variation patterns are different
depending on the tread depth.

100

200

300

400

500

600

700

800

900

Number of pulses
5

Tread depth of 2mm

0

-5

100

200

300

400

500

600

700

800

900

Number of pulses

Fig. 9 Comparison of rotational speed variation patterns
with different tread depths

2.2.4 Detection of Air Pressure
Tires with eight levels of air pressure (0.14, 0.15,
0.16, 0.17, 0.18, 0.2, 0.23, 0.26 MPa; the standard levelis 0.23 MPa) were prepared to obtain rotational speed
variation patterns of four wheels (FL: front left, FR:
front right, RL: rear left and RR: rear right). To verify
the difference due to the air pressure levels, the crosscorrelation values (similarity of signals) of the rotational
speed variation patterns of different air pressures
versus the variation patterns at the air pressure of 0.23
MPa were calculated and plotted in Fig. 10. As the
air pressure changes, the contact position between
the tread and the road changes and the rotational
NTN TECHNICAL REVIEW No.87

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Introduction of Sensor Modular Products and Technologies for Autonomous Driving and Electrification of Automobiles

speed variation pattern changes; therefore, the crosscorrelation values decrease. From this test result, it
was verified that the change of air pressure could be
detected from the relative change of rotational speed
variation patterns.

Cross-correlation value

1.2
1
0.8
0.6
0.4

FL

0.2

FR

0

RL

-0.2

RR

-0.4
-0.6
0.1

0.15

0.2

0.25

0.3

Air pressure ［Mpa］

Fig. 10 Comparison of cross-correlation values withdifferent air pressures

2.2.5 Estimation of Road Conditions
Fig. 11 shows the cross-correlation values of therotational speed variation patterns of an asphalt paved
road and a road with compacted snow; the baseline
rotational speed variation pattern was obtained from adifferent asphalt paved road. When the friction coefficientof the tire and road surface decreases, the crosscorrelation value also decreases, which verifies thepossibility of detecting the change of road conditions.
1

FL
RL

Cross-correlation value

0.9
0.8

FR
RR

0.7
0.6
0.5

3. Application of high-resolution
rotation sensor technology
NTN has bearings with rotation sensors7) in its
product line. Therefore, NTN developed bearings
with high-resolution rotation sensors by combining
the high-resolution rotation sensor technology withbearings similar to the case of hub bearings. In
addition, NTN promotes CASE by proposing use of themagnetized ring, which is the key component of thehigh-resolution rotation sensors.

0.4
0.3

3.1 Bearing with High-Resolution Rotation Sensor

0.2
0.1
0

Asphalt paved road

Road with compacted snow

Fig. 11 Comparison of cross-correlation values withdifferent road conditions

2.3 A
 pplication to Autonomous and Shared &Services
For autonomous driving, especially automated vehicle
parking, accurate information is needed about thetraveling distance of a vehicle so that the vehicle canmove exactly to the desired position. This information canbe gathered by detecting the rotation of the wheels. The
wheel speed sensors widely used today do not output arotation pulse until the wheel rotates approximately four
centimeters or more. That means that vehicle movementof a few centimeters cannot be detected; the vehicle
may contact an obstacle due to detection error of thevehicle position based on the wheel rotation. When40

high-resolution rotation sensor technology is applied,
the rotation signal frequency increases by a factor of
forty (maximum of approx. 1.4 kHz) compared with theconventional wheel rotation speed sensor, with the output
of a rotation pulse when the wheel travels approximately
1mm. This has the potential to contribute to riding
comfort and improve operating stability. This technology
is expected to address the requirements of autonomous
driving.
Autonomous driving vehicles where users do not drive,and shared vehicles which a large unspecified number ofdrivers drive only for a short time present problems thatthe users may not become aware of, namely risky vehicle
conditions such as tire wear and low tire pressure. As
mentioned above, this technology can detect the variationin the contact condition between the tires and the roadsurface based on the resulting rotational speed variationand provide the information of the conditions to the users
and administrators. This helps prevent accidents andenables scheduled maintenance, as well as secures thesafety of autonomous driving and shared vehicles andimproves their availability.

NTN TECHNICAL REVIEW No.87

In autonomous driving, it is necessary to recognize theenvironment surrounding the vehicle as accurately as
possible. The components currently used to accomplish
this, such as cameras, LiDAR and millimeter-wave radars,
are listed in Table 1 with their respective characteristics7).
Table 1 Sensors for recognizing the surrounding environment
Sensor type

Range

Advantage

Disadvantage

Camera300m

Resolution
Color
identification

Poor
Environmental
resistance

LiDAR

200-300m

Distancefinding
performance

Poor
Environmental
resistanceMillimeterwave radar

200-300m

Speed
measurement
Environmental
resistance

Resolution

Created based on Reference 7)

LiDAR acquires distance data by measuring the timeof the reﬂected light from two-dimensional scanningof a near-infrared laser beam. Currently, rotating
mirrors are used to scan the laser light. Although
the development of non-mechanical light scanningtechnology is expected that uses no mechanicalmovement or rotating components for achieving lightand compact LiDAR with high reliability, challenges
remain for both wide scanning angles and stability.
The rotating mirror scanning method requires
accurate detection of the rotational angle of the rotating
mirror in high resolution for further segmentation of
the distance data for the scanned surface. Currently,
application of magnetic rotational angle sensors has
begun for mass production automobiles consideringboth the environment and cost.
NTN is proposing the “Bearing with High-Resolution
Rotation Sensor” using the MPS40S sensor for thisapplication8). Fig. 12 shows the appearance of the
Bearing with High-Resolution Rotation Sensor. The
MPS40S sensor is certified by the reliability test for
automotive electronic components, AECQ100, which
proves its high environmental performance. It also has
a compact structure that allows installation in the same
way as conventional bearings. Therefore, information
on rotation and angle can be acquired with highaccuracy by simply replacing the existing bearings.
For example, it can be used in the application where
highly accurate angle detection is required with small
and light form factor such as LiDAR of the rotational
mirror scanning type. NTN is prepared to apply thistechnology in a broad range of applications in vehicle
electrification.

Fig. 12 Bearing with High-Resolution Rotation Sensor

3.2 Tube Type High Resolution Rotation Sensor
When the Bearing with High-Resolution Rotation
Sensor discussed in Section 3.1 is used in a muddy
water or oily environment, the magnetic detection
elements need to be protected by a waterproof/oil
proof structure, because the sensor detects magnetic
fields by Hall elements. NTN started proposing the useof the Tube Type High Resolution Rotation Sensor (Fig.
13) where the elements and peripheral circuits aresealed by a tube-shaped thin laminate structure. NTN’s
proposal began in Europe, where it is beginning to be
used on agricultural tractors and small autonomous
buses. With this sensor, high-resolution pulse signals
can be acquired by a factor of 4 to 200 more times
over the N-S magnetic pole pair width (standard widthis 5 mm). Table 2 shows the key specifications. The
multiplication factor, magnetic pole width, sensor
size and mounting method can be customized, whichallows its use in broad applications.
.

Fig. 13 Tube Type High Resolution Rotation Sensor
Table 2 Key specifications of Tube Type High Resolution
Rotation Sensor
Size (excluding wiring)Φ 15.2 × L73mm

OutputTwo-phase square wave
(phase A, phase B)

Input voltage range

8-32V

Magnetic pole width

5mm(1, 2.5 mm selectable)

Air gap

3 mm or less

Waterproof structure

IP67

3.3 Multi-track Magnetic Ring9)
The next topic to be discussed is the application of
the multi-track magnetic ring (Fig. 14) in car sharing.
The driver of a shared vehicle needs to adjust the seatposition and the mirror angle every time he/she drives
depending on his/her physical size or preference. If
electric adjustment mechanisms such as power seatand the position data are available, the vehicle can
automatically adjust to the driver-specific seat position.
A driver who uses a vehicle sharing service can register
NTN TECHNICAL REVIEW No.87

41

Introduction of Sensor Modular Products and Technologies for Autonomous Driving and Electrification of Automobiles

his/her seat position setting data into the cloud and thevehicle can set the adjustment position the next timehe/she drives the car using that data and the electricadjustment mechanism. An angle sensor is required toreproduce the rotational angle of the electric actuator
for adjustment. Drivers often feel discomfort when theseat position is off even a little bit. The Bearing with
High-Resolution Rotation Sensor, which provides highresolution and accuracy, along with an angle detection
system equipped with a multi-track magnetic ring for
acquiring absolute angle without initialization, can beused in these situations.
The multi-track magnetic ring has two magnetic tracks
with a different number of pole pairs and can detectabsolute angle with high accuracy (±0.1°) and resolution
without the need of initialization, by the dedicatedmagnetic sensor using the difference of the number ofpole pairs. A series of radial type (magnetized on thecircumferential direction) and axial type rings (magnetizedin the axial direction) as well as different numbers ofpole pairs are available to be used depending on theapplication and layout.

a) Radial typeb) Axial typeFig. 14 Multi-track magnetic ring

3.4 R otation angle sensor as an alternative toresolvers
Electrification of vehicle power trains, such as in hybrid
electric vehicles (HEVs) and electric vehicles (EVs), is
expected to grow due to the trends of global environment
protection (including legal regulations), and innovative
battery technology reducing cost and improving
performance. Along with the drivetrain, accessories arebeing electrified like those that use the power generated
by the internal combustion engine, such as the air
conditioner, and devices that use negative enginepressure and hydraulic pressure, such as the brake.
Together with the trends of electrification, complianceto international standard ISO 26262 is required regarding
vehicle functional safety. This standard requires
measures on the vehicle system, hardware, and software
depending on the ASIL (Automotive Safety Integrity
Level) considering the severity of any risk factors. They
are ranked from A to D depending on the probability of42

NTN TECHNICAL REVIEW No.87

exposure, controllability and severity. For items that directly
involve lives, such as the EPS (Electric Power Steering),
where the highest safety is required, measures of ASIL-D
are mandatory. For example, misdetection of angles ofa motor, which is controlled by detecting the rotation
angle, may result in a major functional loss. In this case,the functional loss is prevented by redundancy, placing
multiple detectors. For redundancy, if multiple detectors of
the same type are implemented, they may fail altogether
with the same cause; therefore, implementing detectors
with different detection methods will be a safer choice.
Redundancy of rotation angle detection is expected tobe achieved by inexpensive and highly accurate rotation
angle sensor technology, to respond to the demand offunctional safety. Currently, resolvers are widely used as
the rotation angle detection sensors for motors; however,magnetic type rotation angle sensors are attracting
attention as a redundancy sensor due to their cost anddetection method.
Resolvers are widely adopted for controlling motors
for propulsion, and have become an inexpensive andsecure detection means due to the volume production
effect and broad adoption of processing circuits withsignal processing hardware. Magnetic-type rotation
angle sensors for automotive applications have also
been widely adopted as wheel speed sensors and crankangle sensors, but they are not cost competitive against
resolvers for achieving highly accurate absolute angle
detection functionality.
NTN developed a new rotation angle sensor combining
a magnetic ring that uses special magnetization
technology and an inexpensive magnetic sensor.
Absolute angles can be calculated from the output
signals of sine/cosine waves according to the rotation
angles, and highly accurate angle information can beacquired by the proprietary magnetization technology
and signal processing. Fig. 15 shows the external viewof the developed Bearing with High-Resolution Rotation
Sensor.

Fig. 15 Bearing with rotational angle sensor

4. Summary
In this article, NTN’s activities around bearings,
and bearing module products/technologies to respondto the new demands of CASE are discussed. Thesedemands can significantly change the businessstructure of the automotive industry, as part of atransformation that happens once in a century. Table 3
shows the summary of the discussion. These products/
technologies are required in global markets including
Japan. NTN, as a group, will continue to devote
ourselves to this development.
Table 3 Summary of NTN sensor related products for CASE
Hub Bearing withan Integrated
High Resolution
Rotation Sensor

Hub Bearing withan Integrated
Rotation Sensor

Tube Type High
Resolution Rotation
SensorMulti-Track
Magnetic Ring

Connected

○

○

○

○

Autonomous

○

○

○

○

Shared &Services

○

○

○
○

Electric

Rotation Angle Sensor
as an alternative to
Resolvers○○

References1) 	Journal of Society of Automotive Engineers of Japan, Vol.
73, No. 7 (2019).
2) 	CASE Revolution; Automotive Industry of 2030, Nikkei
Publishing Inc., (2018).
3) 	Age of CASE; Exploring New Mobility, Jihyo Co., Ltd.
(2018).
4) 	ASB Technology
https://www.ntn-snr.com/sites/default/files/2017-03/
technologie_asb_en.pdf.
5) NTN TECHNICAL REVIEW No.75（2007）36-41.
6) NTN TECHNICAL REVIEW No.81（2013）52-57.
7) 	Three Kingdom Saga of Onboard Sensors, Nikkei
Electronics, March Issue, 2018 (2018).
8) NTN TECHNICAL REVIEW No.78（2010）70-76.
9) NTN TECHNICAL REVIEW No.86（2018）45-49.

Photo of authors

Yasuyuki
FUKUSHIMA

Hiroyuki
HAKAMATA

Christophe
DURET

New Product Development
R&D Center

New Product Development
R&D Center

NTN-SNR ROULEMENTS
Research & Innovation
Mechatronics

NTN TECHNICAL REVIEW No.87

43

Technical Article

Vehicle Motion Control with In-Wheel-Motors

Junichi HIRATA*
Yuta SUZUKI*
A vehicle equipped with In-Wheel-Motors can control the braking / driving
force independently in the left and right wheels. NTN has developed a vehicle
motion control that balances turning performance and attitude stability byadjusting the braking / driving force of the In-Wheel-Motors according to thedriving attitude of the vehicle. This paper mainly introduces, among the developed vehicle motion control, theeffect of yaw moment control that we verified by the actual vehicle test.

1. Introduction
Recently, various policies for promoting electricvehicles (EVs) as a measure to solve environmental
issues such as global warming and air pollution havebeen put in place globally1). With EVs, the driving
power source changes from the conventional internal
combustion engine to electric motors, which alsoenables active use of regenerative braking2),3).
The methods for using the motor for driving vehicles
include on-board method4) which places the motor
on the body and transmits the power to the tires via
driveshafts and in-wheel motor method5) which places
the motor inside the wheels and transmits the power
to the tires directly without the use of driveshafts.
Adopting the in-wheel motor method means that thebraking/driving power to the left and right wheels canbe independent, responsive and precisely controlled
because the driveshaft is not used.
NTN developed vehicle motion control technology
to improve both the turning performance and attitude
stability by controlling the braking/driving power of inwheel motor (hereafter IWM) according to the vehicle
driving conditions. In this article, the effect of the yaw
moment control is introduced from the developed
vehicle motion control technology, among others.

the torque commanded to IWM when skidding begins.
The turning performance improvement control andattitude stability control are the blocks to control thevehicle yaw moment.
The concept of the yaw moment control operationis shown in Fig. 2. The vehicle in Fig. 2 is equippedwith IWM on the front wheels, similar to the test
vehicle introduced in Chapter 3. The yaw moment isgenerated to the vehicle by creating different braking/driving powers to the left and right front wheels (orange
arrows in Fig. 2). When the yaw moment is createdto the same direction as the turning direction of thevehicle, turns can be assisted (Fig. 2 (a)). When theyaw moment is created to the opposite direction of theturning direction of the vehicle, excessive turns suchas the spinning can be reduced (Fig. 2 (b)).
The control shown in Fig. 1 is integrated so thatthese 4 blocks can seamlessly work together.
Integrated control

Input
Steering angle
Vehicle speed
Yaw rate
Vehicle rotation speedetc.

Turning
performance
improvement
control
Torque command,
etc.
Attitude stability
control
Torque command,etc.

μμ estimation

Gy, etc.

OutputTorque command

Skidding condition

Anti-skid control

2. Vehicle Motion Control
Fig. 1 shows the block diagram of integrated control,
which is the developed vehicle motion control. The
integrated control consists of 4 functional blocks.
The μ estimation is the block to estimate the friction
coefficient of the road surface and the anti-skid control
is the block to control the skidding of tires by reducing* Engineering Dept., EV Module Division

44

NTN TECHNICAL REVIEW No.87

Fig. 1 Block diagram of integrated control

IWM

IWM
Weight 30kg
With control

Without control(a) Turning assist
Fig. 4 In-wheel motor (IWM)
Table 1 Vehicle specification
Overall length
Without control

With control(b) Control of Spin

Overall width

1.69m

Wheel base

2.36m

Tread front/rear

1.46m/1.47m

Vehicle weight

Approx. 1,200 kg

Driving method

Front wheel IWM

Maximum output

60 kW(30 kW × 2 wheels)

Battery type

Lithium ion battery

Fig. 2 Concept of yaw moment control

3. Actual Vehicle Test
In this Chapter, the verification result of the effectof the developed control is introduced from an actual
vehicle test.

3.1 Test Vehicle
Fig. 3 shows the vehicle used in the test. IWMs
(Fig. 4) were installed on the front wheels of a Suzuki
Splash (front wheel driven) to convert it into an EV.
Table 1 shows the vehicle specification.

3.775m

3.2 Verification of Turning Performance
Improvement Effect
The effect of turning assist by turning performance
improvement control was verified by driving the slalom
course shown in Fig. 5 at a speed of 50 km/h. As
shown in Fig. 6, the delay from the steering operation
to the generation of vehicle yaw rate was reduced
from 75 ms to 60 ms and the amplitude of the steering
angle was also reduced from 300 deg. to 270 deg.
by applying the control. This result revealed that theturning performance improved from the control.

Pylon

50km/hμ=1.015m

Fig. 5 Slalom course

Fig. 3 Test vehicle

NTN TECHNICAL REVIEW No.87

45

200

40

100

20

75ms

0

0

300deg
-100

-20

-200

-40
0

μ

1

Time s2

Steering angle

Pylon

Yaw rate deg/s

Steering angle deg

Vehicle Motion Control with In-Wheel-Motors

m

20
μ=1.0

(18

m)

60km/h3

Yaw rate

200

40

100

20

60ms

0

0

270deg
-100

-20

-200

-40
0

μ

Fig. 7 J-turn course
Yaw rate deg/s

Steering angle deg(a) Without control

1Time s2

Steering angle

3

Yaw rate

Fig. 8 J-turn(b) With control
50

Fig. 6 Slalom test result40

3.3 Verification of Attitude Stability
Improvement Effect

30

Y m

The vehicle condition representing turning instability
can be categorized into plow (drift out) where thevehicle is pushed outside of the course as it turns
around the curve and spin where the vehicle is pulledinside the curve. The attitude stability control to control
these conditions is developed and its effect wasverified using a test vehicle.

20

10

Traveling direction

0-20

3.3.1 Control of Plow
The effect of the plow control by the attitude stability
control was verified by driving the J-turn course in Fig.
7. The pylons were placed in the position with a 20 m
radius, to make the J-turn target radius of 18 m. The
vehicle speed entering the course is approx. 60 km/h.
Fig. 8 shows the vehicle in the driving test and Fig.
9 shows the driving trajectory. Fig. 9 shows that thevehicle without control significantly deviated from thecourse whereas the vehicle with control was on the
track proving that the plow was reduced by the control.

46

NTN TECHNICAL REVIEW No.87

-10

0

10

20

30

X m

μ

Without control

With control

Fig. 9 J-turn test result

3.3.2 Control of Spin
The vehicle test with a steering maneuver to induce
spinning was conducted at a vehicle speed of 60 km/h
to verify the effect of attitude stability control against
spinning and the yaw rates and driving trajectories withand without control were compared. Fig. 10 shows thetest result. In the case where no control was applied,the yaw rate continued to increase inducing a spinning
condition even if the steering angle was reduced at
2 1/2 seconds. The trajectory also indicates spinning

300

120

Yaw rate increases

200

80

100

40

0

0

-100

-40

-200

-80

-300

Yaw rate deg/s

Steering angle deg

condition as the turning radius suddenly became small.
On the other hand, when control was applied, the yaw
rate turned to zero as the steering angle returned tozero after 3 seconds without causing spinning andthe vehicle was under control as the driver intended
to steer it. The trajectory also shows stable driving
without unsteady behavior.

-120
0

1

2

3

4

5

Time sμ

Steering angle

Yaw rate

spin while driving and tire lock while braking (Fig. 1).
A start/acceleration test was conducted on a roadsurface equivalent to frozen roads (friction coefficient
μ = 0.2: course design value) to verify the anti-skid
control effect. When anti-skid control is not applied,giving a large driving torque command to IWM creates
spinning of the driving wheels preventing good
acceleration.
Fig. 11 shows the wheel speed of both front
wheels, vehicle speed is measured by GNSS
(Global Navigation Satellite System) and the vehicle
longitudinal acceleration as the vehicle starts moving.
The driving wheels steadily rotate at a rate slightly
faster than the GNSS vehicle speed (maintains theconstant skid rate) without remarkable skidding,
producing acceleration equivalent to the course design
value of 0.2 (≈ 2m/s2) to the vehicle. This confirmedthat the driving power was securely transmitted to theroad surface with the anti-skid control.

80

100

40

0

0

-100

-40

-200

-80

-300

-120
0

1

2

3

4

μ

Yaw rate

15

6

10

4

5

2
0
0

0.5

1

1.5

2

2.5

3

Time sμ

Steering angle

8

0

5

Time s20

Wheel speed(right front wheel)
Vehicle speed(GNSS)

Longitudinal acceleration m/s2

120

Yaw ratedecreases

200

Speed km/h

300

Yaw rate deg/s

Steering angle deg(a) Without control

Wheel speed(left front wheel)
Longitudinal
acceleration

Fig. 11 Low μ road starting test result(b) With control

3.5 Integrated Control
20

The integrated control integrates all of the controls
introduced in the previous Sections so that they work
seamlessly together. The following are the effect of theintegrated control on a high μ road and low μ road.

Spinning occurred
without control

10

Y m

Traveling direction

0

3.5.1 High μ Road (dry asphalt surface)
-10
-10

0

10

20

30

40

50

X m

μ

Without control

With control(c) Vehicle driving trajectory
Fig. 10 Stability evaluation test result

3.4 Anti-Skid Control
In order to make the yaw moment control effective,
it is important to ensure the braking/driving powerof the front wheels (braking/driving torque of IWM)
is securely transmitted to the road surface. For thatreason, anti-skid control is applied to prevent tire

The effect of the integrated control was verified on
the high μ road in the double lane change course
shown in Fig. 12. The vehicle speed entering thecourse was 60 km/h. Fig. 13 shows the test results.
Fig. 13 reveals that the steering angle and thedelay of the yaw rate are both reduced by the effectof the turning performance improvement control at
the first steering maneuver immediately after entering
the course (at around 1 second). In the latter half ofthe course (after 2 seconds), the yaw rate follows thesteering operation preventing spinning from occurring
due to the effect of the attitude stability control. The
driving trajectories also show that the vehicle without
control significantly deviated from the course whereas
NTN TECHNICAL REVIEW No.87

47

Vehicle Motion Control with In-Wheel-Motors

the vehicle with control could follow the targeted
course. Fig. 14 shows the vehicle attitude when it
exited the course. The vehicle without control shows
the spinning behavior heading in the lateral direction
from the course but the vehicle with control maintained
a stable vehicle attitude, proving the effect of thecontrol.

3m

Pylon at exit

60km/h
Pylon

μ=1.0

13.5m

(a) Without control

13.5m

Fig. 12 Double lane change course120

Yaw rate remains large

200

80

100

40

0

0

-100

-40

-200

-80

Steering angle Large

-300
0

1

Yaw rate deg/s

Steering angle deg

300

-120

2

3

4

Time sSteering angleμPylon at exit

Yaw rate(a) Without control(b) With control
Fig. 14 Vehicle attitude during double lane change test120

Yaw rate follows
the steering
operation

200
100

80
40

0

0
-100

-40

Steering angle
Small

-200
-300
0

1

2

-80

Yaw rate deg/s

Steering angle deg

300

-120

3

4

Time sμ

Steering angle

Yaw rate(b) With control

Y m

20
10

Pylon at exit
Traveling
direction

0
-10
-20

-10

0

10

20

30

40

X m

μ

Without control

With control(c) Vehicle driving trajectory
Fig. 13 Double lane change test result

48

NTN TECHNICAL REVIEW No.87

50

3.5.2 Low μ Road (equivalent to frozen road μ = 0.2)
The integrated control has a function to estimate theroad surface μ (Fig. 1) to detect the change of the roadsurface μ from different kinds of information, such as
the vehicle behavior, and automatically adjust various
parameters to control the vehicle not only for high μ
roads but also low μ roads. The effect of the low μ roadwas verified on the road surface equivalent to a frozen
road (μ = 0.2) by setting a single lane change course
as shown in Fig. 15. The vehicle speed entering thecourse was 40 km/h.
Fig. 16 shows the driving trajectories. No differenceswere noted in the vehicle trajectory by steering
operation immediately after entering the course
between the vehicles with and without control;
however, in the latter half of the course, the vehicle
without control showed a spinning behavior, similar tothe high μ road, significantly deviating from the course.
On the other hand, the vehicle with control could drive
the course without spinning behavior. This result showsthat the developed integrated control is effective with achange to the road surface friction coefficient and canhandle the low μ road instantaneously, as well as thehigh μ road.

4. Conclusion
In this article, the effect of the yaw moment control isintroduced from the vehicle motion control technologies
developed by NTN. We will further explore thepossibilities of control with IWM through developmentof vehicle motion control using IWM.

2.5m

40km/h

10m

μ=0.2

Pylon

Fig. 15 Single lane change course

References
1) Ministry of the Environment, Ministry of Economy, Tradeand Industry, Ministry of Land, Infrastructure, Transport
and Tourism, Next-Generation Automobile Guidebook

10

Y m

2017-2018 (2018).
5

Traveling direction2) Kimura et al., Development of New-generation e-POWER
Hybrid Powertrain, Nissan Technical Review, No 80, (2017)
6-14.

0

3) Tomokazu Honda, Development of Handling Performance
-5
-20

-10

0

10

20

30

X m

μ

Without control

40

Control for SPORT HYBRID SH-AWD, Proceedings of
the Society of Automotive Engineers of Japan Annual
Congress. No. 102-14, (2014) 25-28.

With control

4) Yukishima et al., Two Motor On-board Drive System, NTN
TECHNICAL REVIEW, No. 83, (2015) 20-25.

Fig. 16 Single lane change test result5) Itoh et al., In-Wheel Motor System, NTN TECHNICALREVIEW, No. 79, (2011) 9-16.

Photo of authors

Junichi HIRATA

Yuta SUZUKI

Engineering Dept.
EV Module Division

Engineering Dept.
EV Module Division

NTN TECHNICAL REVIEW No.87

49

Technical Article (1)History of Development of Bearings for Automobiles Aiming at
Low Fuel Consumption
Takashi YASUNISHI*

Hybrid vehicle/Electric vehicles (HEV/EV) that represent the next-generation
vehicles, future expansion are expected.
On the other hand, in emerging countries such as Asia and Africa, there is
still high demand for conventional vehicles (engine type) on a global basis due
to population growth. In addition, from the point of environmental regulation, each automotive manufacturer
is focusing on the development of vehicles with low environmental impact. We will introduce the history of thedevelopment as a bearing for automobiles, about “Low Fuel Consumption” required for automobiles.

1. Introduction
Since the structure of bearings for automotive use
are simple, specification differences are not often
noticeable by appearance. However, a look at thehistory of bearing specifications from the 1980’s tillpresent reveal that basic performance continued
to evolve ahead of market needs. In this article thetransition of automotive bearing technology (deepgroove ball bearing and tapered roller bearing) is
introduced up to the latest specification in regards to
low fuel consumption (low torque).

2. History of Development of Bearings
for Automotive Use
2.1 Deep Groove Ball Bearing
In response to the market demands of high efficiency
multi-stage AT and CVT, the functionality of the deep
groove ball bearing, mainly used for transmission, hasbeen improved. This includes high-speed use and lower
torque. In addition to requirements of being compact,
lightweight and a long operating life, bearings for driving
motors of electric vehicles also face similar specification
demands.
The demand for lower torque is met with a compact
and lightweight design. This is achieved with thematerial and thermal treatment, change of internal
design specification and improvement of components
such as the seal, cage and grease (Fig. 1).
Table 1 shows the characteristics of the structure andperformance of each specification of deep groove ballbearings. Fig. 2 shows the history of technology sincethe 1980s comparing the running torque.
The deep groove ball bearings used for transmission* Automotive Bearing Engineering Dept., Automotive Business Headquarters

50

NTN TECHNICAL REVIEW No.87

were generally the open type without a shield or seal.
However, contact seals (LU seal/LH seal) are now
adopted to prevent reduction of operating life due topenetrating hard foreign objects contained in the oil.
Bearings with contact seals have higher torque thanthe open type due to the sliding nature of the seal so
the open type is used when the requirement for lower
torque is critical. Improvements of material and thermal
treatment have been made to achieve longer operating
life even in an environment where foreign objects may
penetrate.
The latest specification (LE Seal) developed has
improved seal material and seal lip geometry achieving
low torque while maintaining the seal performance.
These improvements result in lower torque equivalent
to non-contact type seal under oil lubrication.

Low torque

Seal

Cage

Material/thermal
treatment

GreaseInternal design

Long operating life
Compactness/lightweight
Low torqueFig. 1 Deep groove ball bearing and characteristics

Table 1 Characteristics of deep groove ball bearing1)
Specification ofdeveloped productSpecification of standard typeType and code

Shield typeOpen type

Seal typeNon-contact type ZZ

Contact type LU

Low torque type LH

Low torque type LE

No shield or seal toseal the bearing.

Metallic shield isfixed on the outerring to form labyrinth
seal with the seal
groove of the inner
ring.

Seal of steel platewith synthetic
rubber adhered byvulcanization is fixed
to the outer ring andthe tip of the seal isin contact with theseal groove of theinner ring for sealing
the bearing.

The same basic
structure as LU
with improved seal
tip to reduce thecontact force andachieve low torqueby providing slits foravoiding absorption.

Low torque is achieved
with non-contact sealby creating a wedge
film effect of fluid under
the oil lubrication
environment by
providing multiple
arc-shaped micro
convexes on thesliding surface of theseal tip.

Low torque

☆☆☆

☆☆☆

☆

☆☆

☆☆☆

Dust proof

ー

☆

☆☆☆

☆☆☆

☆☆☆

High speed

☆☆☆

☆☆☆

☆

☆☆

☆☆☆

Structure

Comparisonofperformance

Seal type

Order of superiority: excellent ☆☆☆＞☆☆＞☆ poor

Deep Groove Ball Bearing*The effect of compactness from the technology for long operating life is converted into torque

Running torque ratio

100Standard type(Contact type LU)
100

Ultra low friction seal
LE sealResin cage for highspeed operation
Low torque cage50
LH sealStandard type(Open type) 18

Impro

veme

Improvem

nt of sent of ope

n typeTM*

Material/thermal
treatment
0

1980

1990

ealed

type

Specification of
bearings with ultra
low friction seals 12 *TA*
Material/thermal
treatment
2000

2020
Year

2010

Fig. 2 Transition of development of deep groove ball bearings2)

NTN TECHNICAL REVIEW No.87

51

History of Development of Bearings for Automobiles Aiming at Low Fuel Consumption

2.2 Tapered Roller Bearing
Tapered roller bearings used for transmission anddifferential gears have more design elements than deep
groove ball bearings. As a result, various characteristics
brought by the design parameters have been explored. In
addition to lower torque, improvements on materials andthermal treatment as well as long operating life has beenachieved (Fig. 3).
In this Section, improvements on the internal design
and material/thermal treatment are discussed in
the transition to lower torque. The ST specification,
which reduced the torque by improving the sliding
characteristics of the rollers, was established forthe improvement of internal design. This is primarily
accomplished with special shape and processing of theinner ring collar. As for the improvement of the material/
thermal treatment, special thermal treatment was applied
to the carburized steel as the base. This contributes tolong operating life due to an increase in retained austenite
on the surface of the raceway. (The torque calculation
result due to compactness is shown in Fig. 4.)
The ECO-Top specification was later establishedwith improvements to micro curvature (crowning) of
inner/outer ring raceway and development of products
which integrated this technology and other material/
thermal treatment technology. Furthermore, the stirring
resistance of oil was significantly reduced by changing
the design of steel plate cage. In the latest specification,
ULTAGE*1 Tapered Roller Bearing for Automotive
Application was developed with improved designof crowning and establishing of volume production

processing technology. This also addresses the needs
for being lightweight and compact for the recent
application of HEVs/EVs.
In addition, the long-life thermal treatment “FAprocess” was developed based on the bearing steel
globally available for procurement. The ULTAGE Tapered
Roller Bearing has achieved an increased operating
life and a significant torque reduction compared to thestandard specification (Fig. 4). Improvements suchas optimization of contact stress distribution, which is
mentioned later, contribute to the longer life.
Low torque

Cage

Material/thermal
treatment

RollerLubricating oil
Internal design

Long operating life
Compactness/lightweight
Low torqueFig. 3 Tapered roller bearing and characteristics*1 ULTAGE® is a 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.
Additionally, ULTAGE® is also the general name for NTN’s new
generation of bearings that are noted for their industry-leading
performance.

Tapered roller bearings*The effect of compactness from the technology for long operating life is converted into torque

100

Imp

Standard type
100

rov

ent

ST

4T *

Running torque ratioemSpecial process forinner ring collar part
of i

nte

rna

l de

sig

n

ET *

Imp

rove

men

t of

mat

eria

l/the

ETA *

rma

l tre

atm

Low torque cage

50

ent

Inte
imp grationrov
em of iment
pof m rovem
ECO-Top *eaterial nt of i/thenrma ternalFA *l tre desatm ign
andent
FA+STX *Low torque cage

Internal design

Special crowning
0

1980

1990

2000

2010
2),3)

Fig. 4 Transition of development of tapered roller bearing

52

NTN TECHNICAL REVIEW No.87

ULTAGE
40 *

2020
Year

3. Introduction of Next-Generation
Bearings for Automotive Use

3.1 Ultra Low Friction Sealed Ball Bearing4)
In order to prevent reduction of operating life due tosevere environments where hard foreign objects arepresent in the transmission lubrication oil, contact typeseals are generally used. Contact type seals increase
resistance to foreign objects such as the wear particles
from gears. However, bearings with contact seals havelarger torque due to the sliding resistance of the seal.
The LE Seal optimizes the shape and material of theseal to achieve low torque while maintaining the sealing
effect of the contact seal. This seal successfully reduces
running torque and raises the circumferential speed
limit. It accomplishes this by promoting formation of oil
film between the seal lip and the sliding surface of the
bearing inner ring for fluid lubrication condition, from thepressure wedge effect of the arc-shaped (half-cylindricalshaped) micro convexes (Fig. 5) placed on the sliding
contact section of the seal lip (Table 2, Fig. 6).

Running torque

The following is the introduction of the next-generation
deep groove ball bearings for automotive use for “lowfuel consumption” and the latest development of tapered
roller bearings.

Developed product
Conventional non-contact type seal
Conventional contact type seal

Reduction of
80%

0

20

40

60

80

100

120

140

Bearing temperature °C

Fig. 6 Relation between bearing temperature andrunning torque3.2 ULTAGE Tapered Roller Bearing for
Automotive Application5)
Tapered roller bearings used in the power train suchas the transmission and differential gears are required
to be small and light, in addition to having long
operating life and low torque.
ULTAGE Tapered Roller Bearing for Automotive
Application is introduced in the following, which
delivers the world’s highest standard of high-load
capacity and high-speed rotational performance withrobust crowning optimization technology to maximize
the rolling fatigue life of bearing (Fig. 7).

Reduce temperature riseby optimized shape

Outer
ring

Minimize contact
stress by
optimized roller
shape

Seal
Inner
ring
Outer ring

Cross-section view of thedeveloped productArc-shaped micro convexes

Fig. 5 Characteristics of ultra low friction sealed ballbearing(1) Reduction of 80% or more of running torque (compared tocontact type seal)(2) Support of high circumferential speed of 50 m/s or more
(3) Prevention of harmful foreign objects from penetrating

Table 2 Test condition
Condition

Radial load

0.05 C (C: dynamic load rating)-1

Inner ring

RollerFig. 7 Structure of ULTAGE tapered roller bearing forautomotive application

Features of developed product

Item

Cage

Rotational speed (min )1,500

Lubricating oil

CVT fluid

Bearing temperature (°C)

35-120Features of developed product(1) World’s highest standard of high-load capacity
・Basic dynamic load rating - 1.3 times*(2) Long operating life (compared with the basic rating life)
・Standard type (bearing steel; standard quenching)
2.5 times or more*・High-functionality type (FA process)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** Comparison of standard catalog values

NTN TECHNICAL REVIEW No.87

53

History of Development of Bearings for Automobiles Aiming at Low Fuel Consumption

LargeContact stressStandard tapered roller bearing
ULTAGE tapered roller bearing forautomotive application

Standard tapered
roller bearing

Rolling raceway axial direction widthFig. 8 Contact stress distribution on the raceway

1

100

ULTAGE tapered
roller bearing forautomotive application
50［Test condition］

Test model No.: 30306D(Φ30×Φ72×20.75)
Load: Fr=19.1kN, Fa=6.4kN
Lubricating oil: VG56 (detergent oil)0

Rotational speed min-1

Fig. 10 Seizure resistance test (temperature rising test)

4. Conclusion
The development history of bearings for automotive
application was reviewed from the viewpoint of
reducing torque. As we have been proposing productsahead of market needs through the developmentof various technologies, we intend to support the
coming stricter and rapidly changing demands. We
hope we can continue to contribute to society, so that
we will continue to be indispensable in the quest fordevelopment of more environmentally friendly, more
comfortable and more useful next-generation vehicles.

References

Ratio: 1.0 ［Test condition］(Standard) Test bearing size(with specification of equivalent operation life)
Standard: Φ28.6×Φ57.2×17.5
ULTAGE: Φ22×Φ47.7×14.6
Load: Fa=4.0kN
Temperature: 80°C (oil)Lubricating oil: GL-5 (75W-80)

2) Hirokazu Nakashima, Trends in Materials and Heat
Treatments for Rolling Bearings, NTN TECHNICALREVIEW, No. 76 (2008), 10-16.
3) Chikara Ohki, Development of High Performance Bearing
with Strengthened Grain Refinement, NTN TECHNICALREVIEW, No. 78 (2010), 128.
4) Katsuaki Sasaki, Takahiro Wakuda, Tomohiro Sugai, Ultralow Friction Sealed Ball Bearing for Transmission, NTN
TECHNICAL REVIEW, No. 85 (2017), 62-66.
5) Yasuhito Fujikake, Takanori Ishikawa, Susumu Miyairi:
ULTAGE Tapered Roller Bearing for Automotive Application,
NTN TECHNICAL REVIEW, No. 85 (2017) 51-55.

Photo of author

0.5

Reductionof 60%
0Standard tapered
roller bearing

ULTAGE tapered roller bearing
for automotive application

Fig. 9 Running torque ratio of bearings

54

Temperature risingcharacteristics 1/3

1) NTN Catalog CAT. No. 3015- Ⅳ , P2

Small

Running torque ratio

150

Outer ring temperature °C

The contact stress at the rolling contact area of thetapered roller bearing was minimized and a special crowning
shape to reduce the excessive pressure on the edge ofthe contact area (edge load) was applied to the rollers.
Fig. 8 shows an example of calculation of contact stress
distribution at the axial cross section of raceway. WithULTAGE Tapered Roller Bearing for Automotive Application,
the bearing operating life is improved by suppressing theedge load at the edge of the contact area and equalizing theoverall contact stress distribution by the adoption of special
crowning.
In addition, because of the long operating life effect due
to equalized contact stress distribution, the bearing canbe designed for smaller and lighter form factor under thesame operating life. Using a compact and lightweight design
while maintaining operating life and the restriction of contactpressure, the bearing running torque was reduced by 60%
compared to the standard bearing (Fig. 9).
Furthermore, superior seizure resistance property wasconfirmed with the temperature rise of 1/3 of the standard
bearing in the temperature rising test, as shown in Fig. 10.
Optimization of the shape of the collar and the roller end
surface shown in Fig. 7 resulted in the superior seizure
resistance property.

NTN TECHNICAL REVIEW No.87

Takashi YASUNISHI
Automotive Bearing
Engineering Dept.
Automotive Business
Headquarters

Technical Article (2)History of Development of Axle Bearings Aiming at
Low Fuel Consumption
Makoto SEKI*

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

1. Introduction
While roller bearings for general use are regulated
by standards such as ISO and JIS, roller bearings forsupporting vehicle wheels (axle unit bearings) havegone through significant transitions over the years.
Also, in recent years restrictions on size, weight,
fuel consumption, and environmental consciousnessof automotive components have been imposed1).
The axle unit bearings have evolved to meet thoserequirements. In this article, the history of thesedevelopments is discussed, focusing on reduction ofweight and fuel consumption (low torque) of axle unit
bearings.

2. Overview of Market Demand for Axle
Unit Bearings
The design specifications of axle unit bearings arediversely based on automotive manufacturer needs(mounting methods, allowable space and bearing
size, bearing load carrying capacity, low torqueperformance, muddy water resistance, rigidity andstrength, etc.). Their past and current requirements
can be categorized as follows:a) Ease of assemblyb) Simplification or elimination of bearing clearance
adjustmentc) Compact, lightweight and large load carrying
capacityd) Maintenance-freeParticularly, elimination of greasing operation andexternal seal for sealed bearingse) Reduction of quantity of componentsf ) Overall cost reduction including bearing units,
secondary components and labor cost

* Automotive Unit Engineering Dept., Automotive Business Headquarters

Responding to the above requirements, NTN has
been developing and marketing the production of the
1st generation, 2nd generation and 3rd generation
products (GEN1, GEN2 and GEN3) for approximately
40 years2).
In addition, environmental regulations havebeen introduced in many countries with continuous
enhancements. This demands the improvement offuel efficiency to reduce CO2 emissions. Therefore,
lightweight and low torque products are required foraxle unit bearings, in addition to the above mentioned
requirements.

3. History of Axle Unit Bearings
3.1 History of Bearing Type
Until the 1970s, placing two single row roller
bearings was the norm. However, the single row roller
bearing had limitations for reducing the weight andsize. Therefore, the evolution of unitized products wasdone to ease assembly, which had the potential toaccommodate the weight and packaging requirements.
The first of such products were the Sealed Double
Row Angular Contact Ball Bearing (Angular Unit) andSealed Double Row Taper Roller Bearing (Tapered Unit),
then named GEN1 bearings. These were widely usedin the themed to late 1970s. In the 1980s, the bearings
were unitized with their secondary components, suchas hubs and housings (knuckles) to reduce the numberof components. This also aided in the efforts to reduceweight, which eventually resulted in the GEN2 bearing.
The aim to further reduce the amount of individualcomponents led to the creation of the GEN3 bearing.
Because the GEN3 bearing encompassed morecomponents than the previous GEN2, the installation of
the axle unit bearing on the vehicle assembly line wassimplified.
Table 1 shows the transition and characteristics of
NTN’s axle unit bearings by generation, including thetime when two single row bearings were used (before
unitization efforts began).
NTN TECHNICAL REVIEW No.87

55

History of Development of Axle Bearings Aiming at Low Fuel Consumption

Through the multiple generations of bearings, moresecondary components have been incorporated into thesingle product. This helped reduce the total number ofindividual components contributing to a more compact
design and overall lighter axle weight. Similarly, as the axle
unit bearings evolved with further unitization, press fitting
the inner/outer rings onto the secondary components is nolonger necessary. On driven bearings, fixing the inner ringby swaging it makes preload management easier resulting
in significant reduction of variability. This improved preload
optimization to achieve reduction of running torque.

hub bearing bore diameter. This enables the torque to be
applied to the entire spline area, resulting in significant
reduction of spline fit length.
The adoption of the PCS H/J method achieves about a
65% reduction in CVJ stem length and a 12% reduction inweight (max.). This is due to the hollow structure of the hub
ring inner diameter, conversion of nut to bolt, etc., and no
spline fit backlash3).
Hub bearing (H/B)

Constant velocity joint (CVJ)

3.2 Development of Next Generation Hub Joint
After the creation of the GEN3 for production, NTN
completed the development of the next generation axle
unit bearing: the GEN4. This bearing combines the axle
unit bearing with the constant velocity joint (CVJ). This
technology has not been adopted because it requires
significant modification to the vehicle assembly lines at the
auto manufacturers.
Therefore, NTN developed a new assembly method for
CVJ and axle unit bearings, which can be done withoutchanging the assembly lines at the auto manufacturers.
The Press Connect Hub Joint (PCS H/J) method achieves
a significant reduction in weight (Fig. 1).
Conventionally, the CVJ and axle unit bearing areconnected with a spline and tightened with a nut. The
spline teeth are generally designed for interference fit withthe helix angle to eliminate backlash, which requires a long
spline fit length. The new press connect fit method finishes
securing the spline by tightening a bolt, which results ina tighter interference fit than the CVJ stem spline on the

New joint method

Bolts for tightening

Fig. 1 Structure of PCS H/J

3.3 Development of Lightweight Bearings
As mentioned above, NTN has been reducing thesize and weight of the entire axle structure throughmultiple generations of increasingly unitized axle unit
bearings. However, after the adoption of the GEN3 as
the mainstream product, further weight reduction of the
bearing was required, but unitization has become moredifficult.

Table 1 Transition and Characteristics of NTN’s Axle Unit Bearings by Generation
Generation

Conventional

GEN1

GEN2

GEN3

Start of production- 1970s

Mid - 1970s

1983 -

Mid - 1980s -DrivenWheel

Structure
NonDriven
Wheel

Feature・Two single row roller
bearings.

・Combined two single row
roller bearings.

・Integrated mounting
flange and outer ring.

・Integrated mounting flange
and outer ring, inner ring.
・No need to press bearing tomating component.

Ease of Assembly to Vehicles

☆

☆☆

☆☆☆

☆☆☆☆

Compactness

☆

☆☆

☆☆☆

☆☆☆☆

Rigidity
Preload Control

☆
☆

☆☆
☆☆

☆☆☆
☆☆☆

☆☆☆☆
☆☆☆☆

Running Torque

☆

☆☆

☆☆☆

☆☆☆☆

Order of Superiority: Excellent ☆☆☆☆＞☆☆☆＞☆☆＞☆ Poor56

NTN TECHNICAL REVIEW No.87

3.4 Development of Torque Reduction

Requirements for the GEN3 axle unit bearing, as thestrength member, are different from those for the individual
bearing, in terms of strength of hub ring, strength of outer
ring, overall bearing rigidity, etc. Weight reduction was
required while maintaining these strengths, particularly
with GEN3. The weight of the hub ring and outer ringaccount for more than a half of the entire unit, so optimizal
design of these components is very important for reducing
weight.
NTN uses FEM analysis to determine weight abatement
while maintaining the strength and rigidity to satisfy therequired functionality. In the past, the optimal shape wasdeveloped using topology optimization4). An ultra-light
hub bearing shape shown in Fig. 2 was also developed.
Therefore, NTN employs the accumulated technologies toprovide the optimal shape for the minimum weight, while
meeting the required specifications.

Reduction of torque has always been required foraxle unit bearings to improve the vehicle fuel efficiency.
However, the requirements are becoming stricter since
many countries introduced environmental regulations.
NTN has developed various low torque products
to respond to market demands for hub bearing
applications. Fig. 3 shows the progression of hub
bearings reducing torque.
The torque of axle unit bearings consists of rolling
resistance from the rolling balls that follows the rotationof the bearing and the sliding resistance of the seal,
which is equipped to seal the bearing. Each represents
approximately 50% of the entire torque. Therefore,
reducing them is the general approach to reducing theoverall torque.

3.4.1 History of Grease Development
The rolling resistance of the bearing is determinedby the bearing design and the grease contained in
the bearing. The bearing design is optimized to satisfy
the customer’s demands. The grease contained in the
bearing has been developed over many years basedon the needs of the customers and the market.
Fig. 2 Shape of developed product by topology
optimization

GEN2
GEN2

Torque/weightGEN3
Low Friction Hub
Bearing I

GEN3
Low Friction Hub
Bearing II

GEN3
Low Friction Hub
Bearing III

Standard grease
Base oil: mineral oil

Improved grease forlow temperature fretting
resistanceLow friction grease
Base oil: mineral oil +synthetic oil
Ultra low friction grease
Base oil: synthetic oil

Hypack seal

3-lip seal

Torque(Seal)GEN3
GEN3

PCS H/J

Torque(Grease)Hub bearing

GEN1
GEN1

1980

1990

Low friction
rubbermaterial
2-side lip
seal

2000

Seal withridgedstructure
Lip contact
surface
optimization
Greasededicated forLabyrinth
seal
seal

2010

Decade2020* Lower position in the graph shows lower fuel consumption(evolution of lower torque/lighter weight)

Fig. 3 History of development of hub bearings
NTN TECHNICAL REVIEW No.87

57

History of Development of Axle Bearings Aiming at Low Fuel Consumption

The standard grease used in production currently
is based on that used for GEN1 production, withimprovements made to better its rust resistanceproperties. In the mid-2010s low friction grease wasdeveloped5) and used on vehicles requiring lower
torque. In 2019 the ultra-low friction grease was createdfurther reducing torque. The difference between thethree greases are the base oils. The standard grease
uses mineral oil, the low friction grease uses a mixtureof mineral oil and synthetic oil and the ultra-low friction
grease uses synthetic oil. Adopting superior base oil
can reduce the viscosity resistance in the low to mid
temperature range and, in turn, reduce torque. NTN
has been optimizing, not only the base oil, but also thethickener and additives which compose the grease,improving the torque property and other grease
properties.

3.4.2 History of Seal Development
Various elements of seal sliding resistance havebeen developed and introduced to the market, such as
the optimization of the seal design structure, rubbermaterial, lip contact surface, lip rigidity, etc. without
degrading the seal property. By incorporating theseelements, the seal torque has been significantly
reduced compared to previous seals.
Further torque reduction can be achieved by
reducing the number of lips in contact with the rotating
components. However, this would degrade the seal
function. A new seal was developed adopting alabyrinth structure to combat these issues5).
For the driven wheels, CVJ does not have to beinserted in the inner diameter. Therefore, a designthat seals the inboard side (vehicle side) with a cap is
implemented, as shown in Fig. 4, which significantly
reduces torque by eliminating one of the two seals of
the conventional unit.

4. Summary
NTN has been working to develop axle unit bearingsfor over 40 years and has expanded its market withthe merger of NTN-SNR in 2008, which has enabled
its market share has grown to the top. By continuously
working to meet the market’s needs, we are able tooffer products with lower weights and torque than in
the past while maintaining reliability. We are excited
to continue our development of the next generation of
products with new ideas for further reduction of weight
and torque.
In this article, we have reviewed the history of axle
unit bearings development focusing on reduction ofweight and torque. We owe this to the efforts of ourpioneers, which we are very proud of, and hope tocontinue these efforts to construct vehicles with greater
functionality and comfort.

References
1) Eiji Funahashi, NTN TECHNICAL REVIEW, No. 70, (2002)
52-57.
2) Masao Kato, Hiroshi Morishita, Kenji Hibi, Kunishige
Ototake, NTN TECHNICAL REVIEW, No. 52, (1986) 40-53.
3) Takayuki Norimatsu, Tsutomu Nagata, NTN TECHNICALREVIEW, No. 81, (2013) 58-63.
4) Haruo Nagatani, Tsuyoshi Niwa, NTN TECHNICALREVIEW, No.73, (2005) 14-19.
5) Makoto Seki, NTN TECHNICAL REVIEW, No. 85, (2017)67-71.

Eliminates the inner seal bysealing cap

Photo of author

Magnetic encoder

Fig. 4 Example of sealing cap structure
Makoto SEKI
Automotive Unit Engineering
Dept.
Automotive Business
Headquarters

58

NTN TECHNICAL REVIEW No.87

Technical Article (3)History of Development of Constant Velocity Joints
Aiming at Low Fuel Consumption
Tatsuro SUGIYAMA*NTN commercialized the constant velocity joint for the first time inJapan in 1963, and after that, worked on lightweight, compact and highefficiency to meet the evolving needs of automobiles. This article looks
back on the history of NTN's constant velocity joints contributing to lower fuel consumption in automobiles.

1. Introduction

2. Market Trend/Need

Recently, environmental concerns such as global
warming have been highlighted globally. For reducing
CO2 emissions, which is the main factor of global
warming, auto manufacturers are working on various
aspects to reduce fuel consumption.
Under these circumstances, reducing weight andimproving torque transmission efficiency are required,for lower fuel consumption, to the Constant Velocity
Joint (hereafter, CVJ), which is a component totransmit the vehicle power.
The power from the vehicle engine is transmitted
to the tires through the transmission, differential anddriveshaft. The CVJ is used to smoothly transmit torqueat the same rotational speed when the input and outputof the driveshaft rotate at an arbitrary work angle. As
shown in Fig. 1, “the sliding type CVJ” which can slidein the axial direction is used on the differential side ofthe driveshaft and “the fixed type CVJ” which has alarger work angle is used on the tire side.

The CVJ has contributed to solving challenges
that automobiles face such as safety, environmental
protection, low fuel consumption, and ride comfort.
Historically, the fixed CVJ was required for its
reduced weight and compactness and then later
addressed the increased efficiency requirement.
The sliding CVJ was required for its low vibration
characteristics and then later addressed therequirement of lightweight and compactness.
Improvements to the grease for CVJ lubrication,higher shaft strength and development of thelightweight E-series have greatly contributed to theabove development requirements of CVJs and highefficiency, contributing to lower fuel consumption ofvehicles.

Sliding type CVJ
Shaft

Input axis

Fixed type CVJ

Output axis

3. History of Development of CVJ1)-3)
3.1 Before Development of CVJ
Vehicles before the 1960s were mostly front engine/
rear drive type where power was transmitted to therear wheels through a rigid axle and a CVJ was notnecessary. A CVJ was not necessary for the front
wheels either, as they were used only for steering, notfor driving.

3.2 Adoption of CVJ to Automobiles(in the 1960s)

Driveshaft

Fig. 1 Placement of driveshaft

In front wheel drive (FF) vehicles and 4-wheel drive(4WD) vehicles, the power is transmitted to the front
wheels; therefore, a driveshaft to steer and transmit
driving power became necessary. Initially, a cross joint(Cardan joint) was used for the driveshaft. However,since it was not a constant velocity joint, the cross joint
produced vibration and noise while driving with a large
work angle and steering stability during cornering waspoor.

* CVJ Development Dept., Automotive Business Headquarters

NTN TECHNICAL REVIEW No.87

59

History of Development of Constant Velocity Joints Aiming at Low Fuel Consumption

Date

CVJ
Production
Quantity

1960s(3.2-3)*

Production
began
1963

1980s
(3.3)*

100 millionth
produced in
1986

2000s
(3.4-6)*

Sliding type CVJ

Shaft
GreaseBJ

DOJ

Shaft w/standard material
Lithium based grease

TJ
DOJ-RPCF

Early 1990s(3.4)*

Late 1990s(3.4)*

Fixed type CVJ

Boron steel shaft

BJ

DOJ,TJ

Downsizing

Downsizing

200 millionth
produced in
1997

Urea based grease

EBJ
E-Series
EDJ,ETJ

400 millionth
produced in
2007

Hollow shaft

E-Series

PTJ

Low friction (μ) grease

Low vibration

2010s(3.7)*

2020s(3.8)*

800 millionth
produced in2018
1 billionth
predicted in
2022

Designed for rear

Designed for rear

REBJ

REDJ

R-Series

R-Series

CFJ
High efficiency

New CVJ

Lightweight

CompactHighefficiency
Low vibration* ( ) following the date indicates the corresponding paragraph in the document text
Fig. 2 History of development of NTN’s light weight, compact and high efficiency CVJ

To solve these problems, the Weiss joint, and Double
Cardan joint, etc. were developed as the pseudo constantvelocity joint; however, their performance was not
sufficient enough for the driveshaft of automobiles.
Then, Hardy-Spicer in the UK developed the Birfield
joint (BJ) which is a predecessor of the current CVJ for
automobiles and NTN introduced that technology intheir products. At that time, the sliding motion in the axial
direction was absorbed by the slide spline installed on theshaft, but the sliding double offset joint (DOJ) developed
by NTN provided smooth sliding. These CVJs weresuperior in performance and reliability, improving driving
stability significantly, and contributed to the developmentof FF vehicles.
Fig. 2 shows the history of development of NTN’slightweight, compact and highly efficient CVJ.

3.3 Application to FF vehicles (1963 -)When automobile manufacturers started developing FF
vehicles at full scale, NTN worked with Suzulight (Suzuki)
to develop the BJ in 1963 and succeeded with volume
production of CVJs for the first time in Japan. Then in
1965, the BJ+DOJ, which is the current driveshaft style,
was first adopted by the Subaru 1000 model vehicle.
In the 1970s, various auto manufacturers introduced FF
vehicles into the market. The second oil crisis of 197860

NTN TECHNICAL REVIEW No.87

accelerated the adoption of FF vehicles and the demandfor NTN’s CVJs expanded. In addition, NTN’s CVJs greatly
contributed to the expansion of the front engine/rear drive(FR) vehicles, which introduced independent suspension,from the rigid axle style, for improved ride comfort and thedevelopment and expansion of 4WD vehicles.

3.4 Lightweight and Compactness (1990 -), E-Series
The manufacturing process of the outer ring of CVJs
was changed to induction hardening using medium carbon
steel rather than carburized steel to increase strength andreduce weight. Also, urea-based grease was developed tofacilitate a long operating life. With these developments, inaround 1992, NTN started providing driveshafts of one size
smaller and lighter than the conventional products.
Furthermore, from around 1995, NTN started thenext phase of development of fixed/sliding type CVJ for
lightweight/compactness and from 1998, started market
introduction of the E-Series CVJ. The E-Series CVJ (EBJ)
which is the fixed type CVJ, was developed by reducing theball size and increasing the number of balls from 6 to 8 inorder to achieve lighter and smaller units, while maintaining
the load carrying capacity equivalent to BJ. Along with
this, the sliding type CVJ, “EDJ” was also developed byincreasing the number of balls from 6 to 8.
The internal design of the roller type sliding TJ wasFixed type CVJ

Sliding type CVJ

Outer diameter

WeightWeight1963 -

Weight kg

Outer diameter mm

Outer diameter

1992 -

1998 -

1983 -

1992 -

2002 -

Fig. 3 Transition of outer diameter and weight of CVJ (example of the initial #87 size)

also improved at the same time to achieve a smaller
unit without degrading strength from the inherent longer
operating life than ball type, resulting in the developmentof “ETJ.”
The transition of reduction of weight and size mentioned
above is shown as a comparison with the size #87 fixed
type BJ and sliding type TJ as the baseline (Fig. 3). The
size #87 was downsized to size #82 by application of
long-life grease and high-strength shaft and then further
reduction equivalent to 2 sizes by introduction of E-Series.
Compared to the initial volume production, the current
product achieved 13% reduction in size and 23% reduction
in weight for fixed type BJ and 12% reduction in size and
17% reduction in weight for sliding type TJ.

3.5 Low Vibration Driveshaft
Along with the development of automobiles, the need for
comfort and quietness increased for improved ride comfort,
which increased the demand for low vibration sliding type
CVJ.
The first developed sliding type CVJ was the ball type
DOJ which had large sliding resistance. In 1984, the sliding
resistance was successfully reduced by the adoptionof *RPCF cage which has a structure to allow a small
amount of ball rolling in the axial direction to absorb small
amplitude vibrations.
In 1983 the roller type tripod joint (TJ), which was a
newly structured sliding CVJ, was developed. Becauseof its structure of rolling rollers, sliding resistance wassignificantly reduced compared to DOJ and its adoption
by FF AT vehicles expanded due to issues with idlingvibration.
Later, TJ was also improved and in 2002, low vibration
sliding type CVJ “PTJ” was developed, which allowed
rollers to roll smoothly, even in the high work angle range,
by combining elliptical trunnion journal shape and roller
cassette, for addressing further low vibration and low

sliding resistance (Fig. 4). The history of the developmentof the sliding type CVJ reduced sliding resistance,
which contributed to the reduction of vibration and fuelconsumption of vehicles over time.
*RPCF cage: Cage with a structure to allow movement
between the cage and inner ring by opening a gap in the axial
direction between them, which allows a ball to roll by opening
gap between the cage window and the ball.

Trunnion journal

Fig. 4 Structure of PTJ

3.6 Lightweight Shaft (Hollow Shaft)
The shaft is a component to transmit power, connecting
the fixed type CVJ and the sliding type CVJ. After
achieving reduction of weight by enhancing the strengthof the material of the solid shaft, a hollow shaft wasdeveloped, which increased rigidity and reduced weight.
Volume production of hollow shaft started from the 2000s.
The hollow pipe raw material shown in Fig. 5 wasprocessed to have the both ends squeezed so they can beinserted to the inner rings of a CVJ. Applying a hollow shaft
achieved 20-30% reduction of weight compared with theconventional solid shaft with the same torsional stiffness.
Raw material (steel pipe)

Shape after processing

Fig. 5 Structure of hollow shaft
NTN TECHNICAL REVIEW No.87

61

History of Development of Constant Velocity Joints Aiming at Low Fuel Consumption

3.7 Light and Compact Rear CVJ (R-Series)4)
Conventionally, commonly designed CVJs wereused for the rear driveshaft of FR vehicles and front
driveshaft of FF vehicles. However, since the reardriveshaft of FR vehicles does not require a highwork angle, a light and compact R-Series CVJ wasdeveloped specifically for rear driveshafts, as shownin Fig. 6. Together with the adoption of the hollow
shaft and compact boot with less grease, the R-Series
accomplished approx. 30% weight reduction comparedwith the conventional product.
REBJ

Hollow shaft

REDJ

Fig. 6 Structure of R-Series

3.8 D evelopment of High Efficiency Fixed
Type CVJ (CFJ)5)
In 2013, a structure to reduce sliding resistanceamong the internal components of the fixed type CVJ
was developed, as the current structure was causing
increased friction loss and thus reduced transmission
efficiency as the angle increased. “CFJ” shown in
Fig. 7 places the adjacent arc-shaped tracks mirrorsymmetrically, so that the forces that the balls pushon the cage with are alternately directed to the openside of the outer ring and the opposite side. These
forces have the same magnitude and opposite
directions; therefore, they are canceled out resulting in
reduced axial displacement of the cage. This design
significantly reduces the contact force of the sphericalparts between the cage and the outer ring, as well as
between the cage and the inner ring. As a result, thetorque loss rate against the EBJ improved by approx.
50% (work angle of 9 deg) achieving the world's
highest level of efficiency, contributing to low fuelconsumption.

Outer ring

4. Future Development
Although electric vehicles (EVs) are gaining traction,
which changes the driving method, the requirement
for the driveshaft will stay the same. Therefore,
we will continue developing light, compact, highly
efficient and quiet CVJs while optimizing strength anddurability suitable for the application, use and vehicle
characteristics by anticipating the future trends andneeds of vehicles.

5. Summary
In this article, the history of the development of
the constant velocity joint (CVJ) for driveshaft, which
was aimed for low fuel consumption, was reviewed.
The performance of vehicles is constantly improving.
The functional improvement of constant velocity
joints directly and indirectly contribute to this vehicle
performance, and therefore, NTN will continue
developing and supplying CVJs that contribute tovehicle development and are friendly to the global
environment.

References
1) Takeshi Ikeda, History of CVJ Design for Automobiles andRecent Technology, NTN TECHNICAL REVIEW, No. 70,(2002) 8-17.
2) Shin Tomogami, Technical Trends in Constant Velocity
Universal Joints and the Development of Related Products,
NTN TECHNICAL REVIEW, No. 75, (2007) 10-15.
3) Shinichi Takabe, History of Constant Velocity Joints, NTN
TECHNICAL REVIEW, No. 85, (2017) 40-45.
4) Tomoshige Kobayashi, Light Weight Drive Shaft for FR
vehicle “R series,” NTN TECHNICAL REVIEW, No. 85,(2017) 78-83.
5) Teruaki Fujio, Next-generation High Efficiency Fixed TypeConstant Velocity Joint “CFJ,” NTN TECHNICAL REVIEW,
No. 81, (2013) 64-67.

Photo of author

Ball
Cage

Inner ring

Fig. 7 Structure of CFJ
Tatsuro SUGIYAMACVJ Development Dept.
Automotive Business
Headquarters

62

NTN TECHNICAL REVIEW No.87

New Products

Low Friction Hub Bearing III

Makoto SEKI*

The Fuel efficiency regulations have been strengthening, therefore the goodfuel efficiency is one of the important requirements from the field. Based on thisbackground, NTN has been developing the low friction Hub Bearing continuously.
The Low Friction Hub bearing III applicable to such around 60% low torquerequirement is introduced in this report.

1. Introduction
Recently, regulations on fuel efficiency and CO2
emissions have been enhanced globally which has
increased the importance of vehicle energy consumption
reduction. As a result hub bearings that support wheel
rotation are required to further reduce running torque in
addition to satisfying basic performance such as operating
life and strength.
NTN, which has a high share of hub bearings forvehicles, has long been dedicated to R&D of low
consumption technologies for hub bearings. NTN has
proposed various technologies to achieve the objective1)-3).
In this article Low Friction Hub Bearing III is discussed
which reduced running torque by 62% when compared toconventional products. It accomplishes this by combining
existing items with newly developed grease for reducing
torque.

Outer seal
Hub bolt

Inner seal
Rolling element

Inner ring

Hub ring

Outer ring

Fig. 1 Example of the 3rd generation hub bearing
structure
Number of balls/diameter/
pitch circle diameter
Bearing
specification

PreloadGroove radiusBase oil composition (traction)

2. Development of Low Torque Hub
Bearings

Bearing

2.1 S
 tructure of Hub Bearings and Contributing
Factors for Increasing Torque

Rolling
resistanceApprox.
50%

An example of the 3rd generation hub bearings isshown in Fig. 1.
The torque of hub bearings consists of rolling resistanceof the bearing and the sliding resistance of the seals (outerseal and inner seal). Each of them represents approx.
50% of the entire torque. Various reduction technologies
have been developed for each of the contributing factors
shown in Fig. 2. For rolling resistance, optimization of
bearing specifications and improvement of bearing
internal grease are included. For sliding resistance,
improvement of seal rubber material and improvement ofseal structure and seal interference are included.

Base oil kinematic viscosity

Torque100%

Bearing internal
greaseConsistency
Thickener composition
Additive

Cage

Material
DesignBase oil composition (traction)
Base oil kinematic viscosity

Grease applied
to lips

Consistency
Thickener composition
Additive

Seal
Sliding
resistanceApprox.
50%

Material
Interference
Seal lip

Lip design
Contact condition
Number of lips in contact

Fig. 2 Contributing factors of bearing torque* Automotive Unit Engineering Dept., Automotive Business Headquarters

NTN TECHNICAL REVIEW No.87

63

Low Friction Hub Bearing III

2.2 Transition of Low Friction Hub Bearings

adoption of low friction seals were applied to achieve asignificant reduction.
The newly developed Low Friction Hub Bearing III
further reduced the torque to achieve a 62% reduction
compared to conventional products. This reduction was
accomplished by applying the specifications developedin the past and newly developed grease which
improved the bearing internal grease used in the Low
Friction Hub Bearing II.

NTN has been developing and proposing design
specifications for reducing torque. The hub bearings
have evolved into Low Friction Hub Bearing I, II and III
by applying these design specifications.
An overview of the evolution is shown in Table 1 andtorque reduction ratios to the conventional products areshown in Fig. 3. For Low Friction Hub Bearing I, design
optimization was mainly applied and for Low Friction
Hub Bearing II, improvement of injected grease andTable 1 Transition of Low Friction Hub Bearings
Low Friction Hub Bearing

Applied low torque technologies

I

II

III

○

←

◎ * Further improvement

Bearing internal grease○◎ * Further improvement

Grease applied to lips

○

←

←

←

Lip contact condition○←

Number of lips in contact○←

Bearing specification

Bearing○

Lip design

Seal

Friction ratio

1

-62%

0.8
0.6
0.4
0.2
0

Conventional product(1st half of the 2000s)

Low Friction
Hub Bearing I(2009)

Low Friction
Hub Bearing II(2017)

Fig. 3 Transition of development for torque reduction

64

NTN TECHNICAL REVIEW No.87

Low Friction
Hub Bearing III(Developed product)3. Newly Developed Grease(Reduction of Rolling Resistance)
3.1 F unctional Requirements and Specificationsof the Developed Grease
The internal grease of hub bearings is required tohave the following functions in addition to low friction.
(1) Maintain long operating life by providing sufficientoil film and preventing seizure under the load,
temperature and speed conditions of hub
bearings(2) Provide superior fretting resistance under low
temperature(3) Sufficient rust resistance and leakage resistanceBased on the above requirements, the specificationof the developed grease was determined as follows:
The final concept of the developed grease is shown in
Table 2.

to secure long-term lubricity in the high load region,
resulting in an operating life equivalent to or better thanconventional products.

3.1.2 Fretting Resistance under Low
Temperature
In the long-haul transportation of newly
manufactured vehicles on railroad freight cars, small
vibrations are generated between the raceway and therolling elements of a hub bearing. As shown by the redarrows in Fig. 4, these vibrations squeeze out grease
between the raceway and rolling elements creating
metal-to-metal contact causing fretting wear. Fretting
wear becomes more significant in low temperature
conditions where grease tends to be harder and fluidity
decreases. If a vehicle in this condition is driven,
abnormal noise may be generated.
In order to ensure grease fluidity in low temperature,base oil of low pour point is applied and thickener
and additive were optimized resulting in improved low
temperature fretting performance.

3.1.1 Reduction of Friction While Maintaining
Bearing Operating Life
A microscopic view of the rolling contact point
between the ball and groove includes the element ofsliding as well. As a result, grease with base oil for
reduced kinematic viscosity and low traction coefficient
was applied to reduce friction caused by sliding.
When kinematic viscosity of the base oil of thegrease is reduced, the risk of insufficient oil film
increases. This results in damage to the raceway, asa trade-off condition. Attention is especially required inhigh load condition as the bearing temperature rises
and the grease base oil viscosity further decreases.
Low traction base oil was used to control the locallyrising temperature for maintaining sufficient oil film
thickness and high viscosity index. Vaporization
resistance and oxidation resistance were improved

Table 2 Concept of developed grease
Grease property

Comparison with the conventional
product

Base oil・High viscosity index
・Superior vaporization resistance andoxidation resistance・Low pour point
・Low traction

Base oil kinematic
viscosity

・Low to room temperature: reduce・High temperature: aim for equivalent
to conventional product

Thickener

・Improved composition for low friction

Additive・Selection of additives to compensate
the disadvantages brought in bychange of base oil

The condition caused by shaking of the vehicle on the railroad freight car
during the long-haul transportation. The resultant motion while the freight car
passes over the rail joints. (Vehicle is fixed on the bed of the freight car)
Vehicles intransportation

Tire

Top part of the groove

Small vibrations between the raceway
and the rolling elements

Bottom part of the groove
Example of fretting wear on the
bearing raceway surface

Fig. 4 Mechanism to produce fretting wear
NTN TECHNICAL REVIEW No.87

65

Low Friction Hub Bearing III

3.2 Evaluation Test
A running torque test was conducted with a hub
bearing filled with the developed grease and seals withthe rubber lip removed.
The result is shown in Fig. 5. The ratio of
torque reduction reached to 56% compared to theconventional product (initial 3rd generation hub
bearing), validating the reduction effect of rolling
resistance of the improved bearing internal grease.
A reliability evaluation test was also conducted toverify the required functionality, as shown in Table 3.
The bearing with the developed grease satisfied all thedevelopment objectives in the test items, fulfilling all
the functions required of the bearing internal grease.

Running torque ratio

1
0.8

Bearing running torquereduction by 56%

0.6

4. Ultra Low Friction Seal
(Reduction of Sliding Resistance)
The structures of the outer seal and the inner seal
adopted by the initial 3rd generation hub bearings(conventional seal) and low friction seals are comparedin Fig. 6.
Generally, three contacting lips are used to ensure
necessary protection against muddy water. However,
low friction seals use less contacting lips to further
reduce friction. Protection against muddy water,which is degraded by reduction of contacting lips, ispreserved by introducing a labyrinth structure andelaborating the lip shape.
Reduction of friction is not only due to the structure
but also the rubber material with low friction coefficient,
optimized design of the lip contact surface andapplication of grease dedicated to the lips. Altogether,
these items contributed to a reduction of 70% of seal
torque compared to conventional products as shown in
Fig. 7.

0.4

Conventional seal

Low friction seal

0.2
0Conventional productDeveloped product

Outer
seal

Fig. 5 Running torque test (room temperature)
Table 3 Bearing internal grease reliability evaluation test
ResultBearing life fromvehicle turns*1

More than 3 times over the
rated operating life

Seizure duringhigh-speed rotation*2

No trace of seizure on the
bearing raceway surface

Low temperature fretting*3

Wear rate
Reduction of 80% compared tothe conventional grease*1 Turning load: 0.6 G load condition*2 Rotating speed condition when the vehicle speed is
200 km/h*3 Wear test with small vibrations under the environmentof -20°C

Inner
seal

Fig. 6 Structure of conventional seal and low friction seal

1

Seal torquereduction by 70%

0.8

Seal torque ratio

Test item

0.6
0.4
0.2
0

Conventional seal

Low friction seal

Fig. 7 Seal torque test (room temperature)66

NTN TECHNICAL REVIEW No.87

5. Low Friction Hub Bearing III¥6. Conclusion

The newly developed bearing internal grease wascombined with the existing low friction seal. Fig. 8
shows the running torque ratio of this bearing. By
reducing rolling resistance and sliding resistance ofboth inner seal and outer seal, 62% of torque reduction
effect was obtained for the entire hub bearing.
Fig. 9 shows the performance evaluation chart ofthe main functional requirements of hub bearings.
It shows that the developed product performed
equivalent to or superior to the conventional product inall the functional requirements. The developed productshould also be adequate in applications with more
severe environments as the fretting resistance in low
temperature has significantly improved. In addition, theLow Friction Hub Bearing III decreases the preload
upper limit by narrowing the preload range to reduceand stabilize the running torque.

In response to the demand for low fuel consumption,
new bearing internal grease was developed andcombined with the existing technology to introduce
Low Friction Hub Bearing III to the market. It has
reliability equivalent or greater than the existingproducts while reducing torque. Some of thetechnology used in the developed product is alreadyadopted by auto manufacturers.
We will continue to strive to contribute to society
and develop products to address the global need forfurther torque reduction and improved reliability.

References
1) Haruo Nagatani, Tsuyoshi Niwa, Application of Topology
Optimization and Shape Optimization for Development of
Hub-Bearing Lightening, NTN TECHNICAL REVIEW, No.
73, (2005) 14-19.

Hub bearing (total)
Reduction of approx. 60%of running torque

Axle Bearings and the Development of Related Products,
NTN TECHNICAL REVIEW, No. 75, (2007) 29-35.
3) Makoto Seki, Low Friction Hub Bearing, NTN TECHNICALREVIEW, No. 85, (2017) 67-71.

1

Running torque ratio2) Kiyotake Shibata, Takayuki Norimatsu, Technical Trends inSeal
sliding
resistance

-62%

0.5

-70%

Bearingrolling
resistance-56%
0Conventional product

Low Friction
Hub Bearing III(Developed product)

Fig. 8 Example of running torque ratio of hub bearings
Low torque

Low Friction
Hub Bearing III(Developed product)

Photo of author

Conventional productFretting resistance(low temperature)

Bearing life

Poor 1 ←← 3 →→ 5 Excellent

Makoto SEKI
Protection against muddy water

Fig. 9 Performance evaluation chart

Automotive Unit
Engineering Dept.
Automotive Business
Headquarters

NTN TECHNICAL REVIEW No.87

67

New Products

Fuel-efficient Compact Chain Tensioner

Kouichi ONIMARU*
Ikumi AGATA**The fuel efficiency regulations have been forwarded, therefore the automotive
industry is developing electrical technology. On the other hand, efforts are being
made to reduce engine fuel consumption.
Based on this background, The "Fuel-efficient compact chain tensioner" that
achieves downsizing and a significant reduction of oil supply for a hydraulic chain
tensioner that adjusts the tension of the timing chain is introduced in this report.

1. Introduction
Recently, regulations on vehicle fuel efficiency andgas emissions have been intensified considering
the impact on the global environment, with further
regulatory developments planned globally in the
coming years.
Therefore, development of electrified technologies,
including hybrid technology, is actively pursued in theautomotive industry. More efficient internal combustion
engines are also being pursued.
NTN develops and manufactures auto tensioners
used for timing belt systems and timing chain systems,
which transmit the rotation of the crankshaft ofinternal combustion engines (hereafter, “engines”)
synchronously to the cam shafts and accessory belt
systems for driving accessory devices1).
The role of an auto tensioner is to appropriately
maintain the tension of the belts and chains to reduce
the system noise and extend operating life. It also
contributes to low fuel consumption by reducing system
friction through selecting the optimum specifications to
fit particular engines.
NTN has developed a “Fuel-efficient Compact Chain
Tensioner” (hereafter, “Chain Tensioner”) (Fig. 1) as a
product to contribute to lower fuel consumption fromtiming chain systems.
In general, the chain tensioner used in vehicle
engines employs a damping mechanism using
engine oil supplied from the engine. The aim of NTN’s
development was to reduce the energy loss and fuelconsumption by significantly reducing the amount of* Automotive Unit Engineering Dept., Automotive Business Headquarters** Automotive Testing Dept., Automotive Business Headquarters

68

NTN TECHNICAL REVIEW No.87

engine oil used by the chain tensioner so that the loadof the oil pump, which supplies engine oil to the entire
engine, is reduced.
In addition, this development included simplificationof the internal structure of the tensioner itself for
reducing its size and weight to address the market
demand for cost reduction. In this article, the structureand features of NTN’s developed chain tensioner are
introduced.

Cam sprocket

Chain tensioner

Timing chain
Chain lever
Chain guide

Crank sprocket

Fig. 1 Example of chain system layout

2. Structure

3. Features

Simplified diagrams of the structure of the developed
product and the conventional product are shown in
Fig. 2 and 3. The developed product uses a newly
adopted oil circulating structure and oil storage
structure, described later in section three. Adoptionof an oil storage structure helped eliminate the antibacklash mechanism shown in Fig. 3 to simplify the
structure. Also, modification of the return spring toa conical spring helped reduce the total length andachieve a more compact size. In case the plunger
thrust power is insufficient in certain applications, anassist spring, also shown in Fig. 3, can be added for
additional power.

The features of NTN’s chain tensioner are listed
below, compared to our conventional chain tensioner:(1) Reduction of the oil amount used by adoption ofoil circulating structure: 1/10 or less
(2) Activation of damping force from the initial stage
by adoption of oil storage structure: elimination ofanti-backlash mechanism(3) Compactness by modification of internal
structure (Fig. 4): reduction of total length by
18%, reduction of weight by 10% or more

CylinderPlunger(Mounting side)

Reduction by 18%
Weight reduction of 10% or more by the internal parts

Oil supply port
(Cylinder and plunger)

3.1 Contribution to Low Fuel Consumption by
Adoption of Oil Circulating Structure

Check valve(Pressure chamber)

Fig. 4 Compact and light structure

Assist spring (purple)
Return spring (green)

Valve seat
Steel ball
Valve spring
Valve retainer

Check valve

Fig. 2 Structure of Fuel-efficient Compact Chain Tensioner
Groove on cylinder bore

Groove on plunger outer
diameter
Register ring

Conventionally, the oil supplied to the chain
tensioner is released from the tensioner through thegap between the outer diameter of the plunger andthe cylinder bore (leak gap) when damping force isgenerated. The released oil is stored in the oil pan
below the engine to be re-supplied to various parts ofthe engine by the oil pump. The oil pump is required tohave the supply capacity to also return the oil released
from the tensioner.
In contrast, the developed product can significantly
reduce the amount of oil released out of the tensioner
by returning the oil that leaks out through the leak gap(when damping force is generated) back inside theplunger through a side hole on the outer circumferenceof the plunger (Fig. 5). This enables a significant
reduction of the necessary amount of supplied oil
while maintaining high reliability and durability as theconventional product. The reduction of the amount of
oil used reduces the load the pump is required to drive,
which can reduce the size of the oil pump, leading tolower fuel consumption from the engine.

Anti-backlash mechanism
Check valve
Oil supply port

Fig. 3 Structure of conventional chain tensioner
NTN TECHNICAL REVIEW No.87

69

Fuel-efficient Compact Chain Tensioner

Oil flow in the conventional product

Noise suppression on the conventional product after the engine starts

Check valve

Plunger
All of oil amount isreleased outside
the tensioner

Anti-backlashmechanism isrequired due toshortage of oil in thepressure chamberas the plunger isextendedAnti-backlash mechanism(register ring type)
Supply side

Pressure chamber→ : Oil flow

Oil flow in the developed product<When chain tension is high>When plunger is returned

Pressure chamber: no oil supply

Noise suppression on the developed product after the engine starts<When chain tension is low>
When plunger is extended

Oil storage
d
nde

e
Ext
ed

d

end
Ext

rne

u
Ret

Leak gap

Oil that leaked out of thepressure chamber returns
inside the plunger

Oil supply side (oil storage)

Oil is supplied from inside
the plunger to the pressurechamberFig. 5 Oil circulation structure

3.2 Structure benefit from oil storage
A hydraulic chain tensioner generates the required
damping force for adjusting the chain tension using oil
supplied from the oil pump. However, as mentioned
later, when the engine stops, the oil pump also stops
supplying oil, which causes a delay of oil supply
to the chain tensioner when the engine restarts.
Conventionally, a mechanical anti-backlash mechanism
was required to suppress abnormal noise generated
due to insufficient tension from the above-mentioned
delay for a few seconds after the engine starts.
The developed product adopts a structure to store
oil inside the plunger to eliminate the anti-backlashmechanism. By adopting this structure, this stored oil
is used until oil is supplied from the oil pump to thechain tensioner after the engine starts to compensate
the delay of oil supply, producing appropriate damping
force immediately after the engine starts (Fig. 6).
Therefore, undesirable noise can be mitigated evenwhen the anti-backlash mechanism is eliminated.

3.3 Compactness/lightweight Design
The developed product achieved reduction of axial
length by 18% and reduction of weight by over 10%
compared to the conventional product by modifying the70

NTN TECHNICAL REVIEW No.87

The oil storage supplies oil to the pressure chamber
until supply oil comes from the engine to suppress theabnormal noise when the engine starts

Fig. 6 Oil storage structureinternal specifications and simplifying the structure/
The following are some examples of adopted designs.
1) Size reduction of internal spring (Fig. 7)
The total length of the internal spring was reduced
by adopting a conical return spring as the main spring.
In addition, providing an assist spring on the outer
perimeter made it possible to cope with a wide rangeof thrust requirements.

Reduction

Adoption of conical spring

Fig. 7 Spring shape

Assist spring2) Streamlined cylinder
Eliminating the anti-backlash mechanism also
eliminated the need for the register ring and multiple
grooves on the outer diameter of the plunger. The
groove to accommodate the register ring on thecylinder bore is not required any more, making it
possible to streamline the cylinder outer diameter.
(Additional notes)(1) Anti-backlash mechanism (conventional product)
A mechanism to suppress vibration of the timing
chain due to no oil supply immediately after the engine
starts even when no damping force is produced on the
chain tensioner. NTN has two mechanisms: a buttressthread type, which uses the frictional force of the screw
and has small backlash and quiet operation, and aregister ring type, which has a simplified structure witha ring and stepped grooves1), 2).
(2) Role of the check valve (Fig. 8)・When the chain has tension, the plunger is pushed
back and the pressure of the pressure chamber(a) becomes higher than the oil supply pressure(b), the check valve is closed and damping force isproduced.
・When the chain loses tension, the plunger isextended and the pressure of the pressurechamber (a) becomes lower than the oil supply
pressure (b), and the steel ball moves and oil flows
into the pressure chamber.
<When chain tension is high><When chain tension is low>

b

b

a

a
Check valve closed

Oil inflow

Pressure a>b

Pressure a<b

When the engine starts, oil is re-supplied to the chain
tensioner through the piping, which causes a delay
before the chain tensioner is supplied with oil again.

Chain tensioner
Cam sprocket
Timing chain
Engine is running

Crank sprocket
Oil pump

Engine stops
Oil pan and oil

Fig. 9 Concept of oil supply

4. Functional Evaluation
4.1 Comparison of oil consumption
To evaluate the oil circulating structure, which is afeature of the developed product, operation with theactual product was simulated to measure the amountof oil released from the chain tensioner (oil consumed)
under vibration and the result was compared with theconventional product. During the test, oil was supplied
to the chain tensioner and the orientation of thesample was horizontal (Fig. 10). Below is an exampleof the evaluation conditions and the evaluation result.
The comparison was made with the samples having
an equivalent damping capacity (load generated when
vibration was applied).
<Example of the evaluation conditions>: ± 0.2mm
・Amplitude of applied vibration
Frequencyofappliedvibration:
100Hz・: 0.2MPa
・Supply oil pressure: SAE 10W-30
・Oil type: 35°C, 100°C
・Oil temperature
Measurementofoilamount:30s
・Fig. 8 Role of check valve(3) Delay of oil supply when the engine starts (Fig. 9)
In general, oil is supplied to the chain tensioner
by the oil pump, which pumps out oil in the oil pan
located at the bottom of the engine. Since rotationof the oil pump usually works together with rotationof the engine, oil is not supplied while the engine
stops. Therefore, oil in the piping of the engine drops
back into the oil pan a while after the engine stops.
NTN TECHNICAL REVIEW No.87

71

Fuel-efficient Compact Chain Tensioner

Plunger displacement

Applied vibration

Released oil
Hydraulic
Input load pressure

Engine rotational speed

Measurement of released oil(= used) amountFig. 10 Measurement of used oil amountThe developed product could reduce oil consumption
to 1/10 or less compared with a conventional productwith the equivalent damping capacity (Fig. 11).

0s

5s

10s

15s

20s

25s

30s

(2) Plunger is extended

Amplitude: small(1)

Amplitude: large
Used oil amount under vibration cc/30s

180
160
140

Conventional product

Reduction by 97%

Developed product
1.5s

120
100
80
60

2.5s

3s

1s

2s

3s

Too large vibration
immediately after start-up(unacceptable case)

Reduction by 95%
(1)

40

(2)

20
0

Oil temperature : 35°C

Oil temperature : 100°C

Fig. 11 Measurement result of used oil amount

4.2 Evaluation at Start-up of the Engine
In order to verify the impact of eliminating the antibacklash mechanism and verify the function of the oil
storage structure, a test was conducted simulating theengine start-up using the actual engine. By verifying
the displacement of the plunger and the input load,
the effect of the aforementioned delay of oil supply atthe engine start-up was determined. The following aresome examples of the evaluation results.
When the plunger is quickly extended due to thestart-up of the engine (the condition from (1) to (2)in Fig. 12) and no oil is supplied from the engine,
damping force is produced by internal oil stored in theoil storage giving an appropriate tension to the chain,in an early stage, which suppressed the vibration of
the chain (amplitude of the plunger displacement). The
result verified that the anti-backlash mechanism canbe eliminated.

72

2sTime from start-up of theengine until oil hydraulics
produce pressure on the oil path

NTN TECHNICAL REVIEW No.87

Plunger is extended at start-up
Oil storage

Fig. 12 Result of evaluation of behavior at start-up of
the engine

4.3 Oil Hydraulics Damping Property
A dynamic characteristics evaluation test was
conducted to evaluate the dynamic reaction forceof the chain tensioner when vibration is applied toindex the basic damping force of the hydraulic chain
tensioner. In the dynamic characteristics evaluation,
the load generated by the applied vibration is verified
while supplying oil to the chain tensioner; therefore,
the impact of various parameters such as the leakgap, check valve load and spring load can be verified.
The evaluation can be conducted on the platform
simulating the operation with the engine. The following
is an example of the evaluation conditions:<Evaluation conditions>・Amplitude of applied vibration
・Frequency of applied vibration
・Supply oil pressure
・Oil type・Oil temperature: ± 0.2mm: -200Hz: 0.3MPa: SAE 10W-30: 35°C

Fig. 13 shows the comparison of the evaluation
results of the developed and conventional product.
The developed product shows load generation up tohigher frequencies, similar to the conventional product,
which verifies good followability? and basic damping
capacity. The maximum and minimum values in Fig. 13
are the results obtained from the Lissajous figure (Fig.
14 Amplitude-Generated Load) at various frequencies.
Developed product5. Conclusion
In this article, the Fuel-efficient Compact Chain
Tensioner was introduced. The developed productachieved reduced oil consumption in the tensioner to
1/10 or less, compared to the conventional product.
The functionality of the conventional product wasmaintained by adopting the structure to circulate
oil in the tensioner, which contributes to lower fuelconsumption of the engine by reducing the load to theoil pump. In addition, the developed product achieved
a reduction in length by 18% and a reduction of weightby 10% by simplifying the structure and reducing thesize of the tensioner.
We will devote ourselves to further development andpromote product development for higher functionality.

Conventional productLoad NMax. value

References
1) Seiji Sato, Technology Trends in Auto Tensioners, NTN
TECHNICAL REVIEW, No. 79, (2011) 83-89.
2) Kouichi Onimaru, Chain Tensioner for Motorcycle Engine,

Min. value

0

50

100

150

NTN TECHNICAL REVIEW, No. 85, (2017) 72-77.

200

Frequency of applied vibration Hz

Fig. 13 Dynamic characteristics evaluation test result

Load NMax. value
Min. value

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

Amplitude of applied vibration mm

Fig. 14 Lissajous figure (developed product)

Photo of authors

Kouichi ONIMARU

Ikumi AGATA

Automotive Unit
Engineering Dept.
Automotive Business
Headquarters

Automotive Testing Dept.
Automotive Business
Headquarters

NTN TECHNICAL REVIEW No.87

73

New Products

Fixed Constant Velocity Joint with Ultra High Angle andHigh Efficiency “CFJ-W”
Masashi FUNAHASHI*
Mika KOHARA*

Maximumworking angle
55°

In the future, it is increasingly required to improve the energy efficiency of
automotive parts and the added value of automobiles. So, by applying NTN's
proprietary technology, we have developed the fixed constant velocity joint "CFJ-W"
with the highest maximum working angle and high efficiency in the world.

1. Introduction
In 2015, parties agreed via the Paris Agreement, tomaintain the average global temperature rise attributed
to greenhouse gas emissions from human activities,
to below 2 degrees Celsius. Automobiles account for
approx. 18% of the CO2 emissions of energy origin,and therefore, energy efficiency improvement of
automotive components is an urgent issue1).
At the same time, longer wheelbases for larger
passenger compartments, and larger size tires fordriving stability, have become the vehicle trend. These
trends affect the vehicle’s minimum turning radius andrequire a larger wheel angle in order to maintain thesame turning radius of conventional vehicles.
The wheel angle is determined by vehicle design
restrictions and the maximum bending angle (hereafter,“maximum working angle”) of the fixed type constantvelocity joint (hereafter, “fixed type CVJ”) installed on
the tire side.
So in this article, the fixed type CVJ, “CFJ-W”, isintroduced. The CFJ-W has the world’s highest level ofboth efficiency and working angle and can contribute to
the reduction of CO2 emissions, deliver larger passenger
compartments and increase vehicle driving stability.

2. About the Driveshaft
The driveshaft is a component that smoothly transmits
engine power (both rotation and torque), to the tires atconstant speed, even when the input shaft (differential
gear shaft) and the output shaft (wheel shaft) are rotatedat an angle. In general, the driveshaft consists of a fixed
type CVJ, a sliding type CVJ, and a shaft to connect them
together (Fig. 1). The fixed type CVJ can have a large
working angle, but cannot slide in the axial direction; thesliding type CVJ has a small working angle, but allows for* CVJ Development Dept., Automotive Business Headquarters

74

NTN TECHNICAL REVIEW No.87

movement in the axial direction.
In 1997, ahead of the competition, NTN developed
the “EBJ (with a maximum working angle of 47°)2)”,
a light, compact and highly efficient joint. Then in2012, for a light, compact, wide-angle, fixed type CVJ,NTN started production of the “VUJ (with a maximum
working angle of 50°)”. Also in 2012, NTN introduced
the “CFJ (with a maximum working angle of 47°)3)”,
which through NTN proprietary design, reduced torqueloss by half in comparison to NTN’s EBJ. As such,
NTN has shown a track record of improving on joint
efficiencies and widening angles.

Tire

Driveshaft

Differential gear

Output axis

Input axis

Sliding type CVJ
Shaft
Fixed type CVJ

Fig. 1 Placement of driveshaft

3. CFJ-W Structure and Features
3.1 Structure
The CFJ-W basically follows the structure of theexisting already developed CFJ; it consists of an innerrace and an outer race, both of which have raceway
grooves (hereafter, “tracks”) for the 8 balls thattransmit running torque, a cage that holds the balls
and a boot that can operate to the maximum working
angle of 55° (Fig. 2).

Outer ring

Track

Cage
Boot

Ball

Inner ring
Outer ring

Fig. 2 Structure of CFJ-W

3.2 Features
Adopting NTN’s proprietary spherical cross groove
structure technology (Fig. 3) made it possible toreduce the force generated within CVJ (internal force)
upon torque load, as well as to increase the load
carrying capacity. This enabled smooth operationof the CVJ internal components, even under toughoperating conditions. Additionally, applying NTN’s
technology helped the CFJ-W achieve the world’s
largest maximum working angle and transmission
efficiency, while maintaining an outer race diameter
and weight similar to a conventional high-angle fixed
type CVJ (i.e. VUJ). (Table 1 and Fig. 4)
To ensure quality, the associated boot shape wasredesigned to withstand the wider CFJ-W angle, while
maintaining outer race diameter dimensions that areequivalent to those of conventional boots.

Inner ring

Feature 1: The arc-shaped tracks of the inner and outer rings are tilted in
the axial direction, and adjacent tracks are mirrored.
Feature 2: The inner track and the outer track cross the slope of eachother, and the ball is placed at the intersection.

Fig. 3 Spherical cross groove structure
Table 1 Comparison of VUJ and CFJ-W
Item

Conventional Product
VUJ92

Developed Product
CFJ92W

Max. Working
Angle (°)

50

55

Outer Race
Outer Diameter
mm

Φ87.8

Φ88

Number of
Balls

6

8

Ball Diametermm

Φ17.462Φ15.081Weight kg

1.64

1.60

Torque Loss-

Over 50% reduction
compared to theconventional productOuter ring
Boot outer diameter
outer diameter

VUJ92 (Maximum working angle 50 degrees)

CFJ92W (Maximum working angle 55 degrees)Fig. 4 Appearance of VUJ and CFJ-W

NTN TECHNICAL REVIEW No.87

75

Fixed Constant Velocity Joint with Ultra High Angle and High Efficiency “CFJ-W”

Within conventional joint (i.e. EBJs, VUJs) structures,
the ball tracks on the inner and outer race are formed
in an arc shape (shown in Fig. 5), with the arc centers
offset in opposite directions from each other from thecenter of the joint. On the other hand, the CFJ-W innerand outer races’ arc-shaped track centers are notoffset, but slanted in the axial direction, with adjacent
tracks symmetrically placed with the angles of theinner and outer race tracks crossing each other (shownin Fig. 6). This ensures the functionality of the CVJ andgreatly contributes to the achievement of both a large
maximum working angle (working angle of over 50
degrees) and high efficiency.

Load produced by
the balls pushing
the cage

F
F

Fig. 5 Structure of EBJ (conventional product),internal force

Load produced by
the balls pushing
the cage

F2

VUJ (Conventional product)
CFJ-W (Developed product)“Reduced” contact force
Reductionby 24%“No” contact force

Normal operating range

F1High angle range

Fig. 7 Analysis result of spherical contact force

F1
F2
Outer ring
Track on theload side

Outer ring
Track on theload side

Fig. 6 Structure of CFJ and CFJ-W, internal force

761) CVJ Internal ForceAs mentioned above, the CFJ-W has adjacent arcshaped tracks axially inclined and placed symmetricallyrelative to each other. The intended affect for this design
is to have the adjacent balls push the cage in opposite
directions, canceling out the resultant forces that suppress
the axial displacement of the cage (shown in Fig. 6). Thissignificantly reduces the spherical contact force between
the cage and outer race, and between the cage and inner
race, which greatly improves torque loss ratio.
Also, it is known that as the CVJ working angle
increases, the load produced inside the CVJ increases
independent of torque input4). Along with this increasedload, the load on the CVJ internal components also
increases resulting in increased heat and degraded
strength. At the high working angle range, the CFJ-W’s
spherical cross groove structure reduces the contact force
produced inside the CVJ. As evidenced by the sphericalcontact force analysis in Fig. 7, the aforementioned
structure nearly eliminates the contact force in the normal
operating range. Even at the high working angle range,close to the maximum working angle, the contact force isreduced in comparison to that of the conventional product,
contributing to the achievement of functionality in therange beyond 50 degrees.

Spherical contact force

3.3 Achieving High Efficiency & a Large Maximum
Working Angle (50 Degrees-Plus)NTN TECHNICAL REVIEW No.87

2) Load Carrying Capacity
For achieving a maximum working angle beyond 50
degrees, it is important to control deformation of theinternal components. Internal component deformation
is mainly a product of ball and track contact at highworking angles and high torque inputs. Therefore, itis necessary to keep sufficient track depth at the highworking angle range. The CFJ-W’s spherical crossgroove structure positions the CFJ-W inner and outer
races’ arc-shaped track center in the same plane as
the center of the joint which ensures the same track
depth at any range (Fig. 8 hatched area), improving
the load carrying capacity of the CFJ-W at the highworking angle range. This differs from that of theconventional joint which has the inherent problem of
reduced track depth at the high working angle range.

Enlarged3) Grease
NTN has developed various high-functional greases
内輪トラック深さ in various CVJ types and applications. In
used selectively
order to achieve a 50-plus degree maximum working angle
and high efficiency, internal force reduction as well as
lubrication improvement is required.
By optimizing the thickener and additive, which resulted
inoutstanding
grease fluidity and lower friction respectively,
外輪トラック深さ
the CFJ-W grease reduced the friction coefficient in the
SRV (vibration/friction/wear) test, as shown in Fig. 9. In the
Torque Loss Test (Fig. 9) for an EBJ (conventional joint),
this grease showed a 22% improvement in performance in
内輪トラック深さ
comparison
to the general-purpose grease’s performancein the same test. This supports that this grease’s use in a
CFJ-W, can further reduce torque loss and heat generation.

外輪トラック深さ

Joint under evaluation: EBJ (conventional product)

Inner ring track depth

Torque loss rate

Inner ring track depth

Friction coefficient
Improvedby 22%

General purpose grease

Applied grease

Fig. 9 Comparison of torque loss rate by grease

Outer ring track depth
Outer ring track depth

Enlarged view of EBJ (conventional product)
Inner ring track depth
Inner ring track depth

Outer ring track depth
Outer ring track depth

Enlarged view of developed productFig. 8 Comparison of track depths

4) Functional Evaluation
The results of the CFJ-W (developed joint) and VUJ(conventional joint) dynamic high-angle torsional strength
evaluation, transmission efficiency (torque loss rate)evaluation and temperature rise characteristics (joint
surface temperature) are shown in Fig. 10, Fig. 11 and Fig.
12, respectively of the developed product, CFJ-W, and theconventional product, VUJ, are shown in Fig. 10, Fig. 11
and Fig. 12, respectively.
At high angles, close to the maximum working angle, the
CFJ-W and VUJ show equivalent strength. Transmission
efficiency evaluation confirmed similar performances
between the CFJ-W and the current high-efficiency fixed
type CVJ, the CFJ; the torque loss was reduced by over
50% at any angle range in comparison to the VUJ (thecurrent high-angle fixed type CVJ). Additionally, thetemperature rise characteristics comparison show a 55%
joint surface temperature reduction between the CFJ-W
and CFJ.
These results show that the CFJ-W has the world’s
highest level of efficiency in its normal operating range,
as well as low temperature rise and sufficient strength at
the severe operating conditions of working angles over 50
degrees.
NTN TECHNICAL REVIEW No.87

77

Fixed Constant Velocity Joint with Ultra High Angle and High Efficiency “CFJ-W”

performance requirements of other fixed type CVJs,
specifically the following items:(1) D urability and Sealability:
equivalent to the conventional joint(2) Compactness:
equivalent to the conventional joint
 o clamp interference:(3) N
no clamp interference at the maximum angle

Breakage torqueEquivalent

4.1 Durability
VUJ (Conventional product)

CFJ-W (Developed product)

Fig. 10 Comparison of high-angle torsional strengths

CFJ-W (Developed product)
CFJ
Torque loss rate

VUJ (Conventional product)
EBJ (Conventional product)
Reduction by
over 50%

0

2

4

6

8

10

12

14

Joint angle (degree)

Joint surface temperature

Fig. 11 Comparison of torque loss rates

Reduction by 55%

VUJ (Conventional product)

An appropriate boot bellow length is required toensure boot durability. There are different approaches
to accomplish this, such as increasing the number ofconvolutes, increasing the boot large diameter anddecreasing the boot small diameter. However, each ofthese techniques brings unfavorable consequencessuch as:(1) increasing vehicle space needed for bootpackaging and installation(2) decreasing boot flexibility(3) increasing the friction between adjacent bootconvolutes(4) increasing the chance of interference of the small
diameter inner convolute with the IC shaft(5) increasing the axial load on the clamp when theboot bellows are retracted
The boot developed for the CFJ-W addressed all
the aforementioned issues through the addition ofmultiple, smaller multiple convolutes on both ends ofthe boot with these convolutes the same size as thoseused by conventional boots (as indicated by the circles
in Fig. 13). In addition, to protect against friction atlarger working angles, when considering the increased
contact surface pressure between convolutes, a suitablematerial was selected. As a result, this boot achieved
comparable durability to conventional boots.

!"

CFJ-W (Developed product)

Fig. 12 Comparison of joint surface temperatures

4. Development of CFJ-W DedicatedResin Boot
Since this joint achieved the maximum working
angle of 55 degrees, which is the world’s greatest forvehicles’ front driveshafts, the boot applied also had
to match this capability. This boot would be required
to withstand angles higher than that of a conventional
high-angle boot (for 50 degrees) and demanded bootshape improvements.
The CFJ-W boot needed to achieve the ultra-highworking angle, while meeting the same functional and78

NTN TECHNICAL REVIEW No.87

Fig. 13 Sectional view of the boot(working angle: 0 degrees)4.2 C lamp Compactness and Interference
Control
CVJ boots are designed considering interferencewith the joint and peripheral components, in addition
to needing to be flexible at higher working angles.
The bellow of the CFJ-W boot was designed with the
optimum ratio of large and small diameter convolutes
to achieve a small packaging requirement, even at highangle operations. Also, this design, while allowing the
bellow to be convoluted on the outer diameter of theouter race, including the addition of the small convolutes
with no clamp interference, protects the boot from being
damaged by the clamp (as shown in Fig. 14).
Clamp

5. Conclusion
In this article, the features and performance of“CFJ-W” were introduced; the CFJ-W achieves boththe “world’s highest maximum working angle of 55
degrees” and “reduction of approx. 50% of torqueloss rate in comparison to the conventional CVJ(VUJ)” by improving the load carrying capacity ofeach component and enhancing lubrication of NTN’s
proprietary “CFJ” product, which was announced in
2012.
This developed product can be applied to the front
wheels of 4-wheel drive vehicles, while achieving thesame minimum turning radius as the rear wheel drive
vehicles, as well as to reduce the adverse impact onfuel consumption due to increase of vehicle weight.
NTN hopes to introduce this product globally as theworld’s benchmark for fixed type CVJs, achieving both
high functionality and low CO2 emission which arebecoming increasingly required for vehicles globally.

References
1) IEA, CO2 emissions from fuel combustion,(2018).
2) Keisuke Sone, Kazuhiko Hozumi, High Efficiency
Compact Fixed Constant Velocity Universal Joints (EBJ),NTN TECHNICAL REVIEW, No. 66, (1997) 28-31.
3) Teruaki Fujio, Next-generation High Efficiency Fixed TypeConstant Velocity Joint “CFJ,” NTN TECHNICAL REVIEW,
No. 81, (2013) 64-67.
4) Yoshihiko Hayama, Dynamic Analysis of Forces Generated
on Internal Parts for Ball Type Constant Velocity Joint,
NTN TECHNICAL REVIEW, No. 70, (2002) 36-43.

Fig. 14 Sectional view of the boot(working angle: 55 degrees)

Photo of authors

Masashi FUNAHASHI

Mika KOHARACVJ Development Dept.
Automotive Business
Headquarters

CVJ Development Dept.
Automotive Business
Headquarters

NTN TECHNICAL REVIEW No.87

79

New ProductsCompact Plunging CVJ for Propeller Shaft “HEDJ-P”

Masazumi KOBAYASHI*

Constant velocity joints for propeller shaft have been applied to 4WD
and FR vehicles since the 1970s. And further small size and lightweight are desired to CVJ for propeller shaft.
This article introduces the new product “HEDJ-P” for propeller shaft.

1. Introduction
Propeller shafts are used on a variety of vehicles
and take the role of transferring transmission rotation
to the front and rear driving shafts, as shown in Fig.
1. Application of the constant velocity joint (CVJ) for
propeller shafts has recently increased in Luxury Car
and SUV’s applications due to emphasis on reducing
NVH (Noise, Vibration and Harshness) and ongoing
demands to further reduce size and weight for lower
fuel consumption.
Although NTN has existing production of compact
and lightweight sliding type propeller shaft CVJ
joints, known as “HEDJ” here we introduce the new“HEDJ-P”. This new joint is dedicated for propeller
shafts to address the need for further size and weight
reductions and has achieved the world’s highest levelin these categories.

Fig. 1 Application of CVJ for propeller shaft

2. Features of CVJ for Propeller Shafts1)-3)
NTN’s CVJ was first adopted for propeller shafts ofautomotive vehicles in the first half of the 1970s. The
demand significantly increased from the latter half ofthe 1980s with a increased need of high functionalityand diversification of vehicles. Due to noise and ride
* CVJ Development Dept., Automotive Business Headquarters

80

NTN TECHNICAL REVIEW No.87

comfort requirements of 4WD vehicles and complex
powertrain configurations CVJs have been adopted
replacing the conventional Cardan joint (not constantvelocity joint, using cross shaft). Fig. 2 shows the
manufacturing timeline of NTN’s CVJs for propeller
shafts.
The main operating conditions of CVJ are rotation,load torque and work angle. The propeller shaft
transmits power between the transmission anddifferential and the driveshaft transmits power between
the differential and the wheels. With the position of thepropeller shaft the rotational speed is higher and theload torque is smaller than the driveshaft. In general,the propeller shaft does not require a large work
angle as the driveshaft due to its layout and functional
requirements.
NTN has a lineup of various types and sizes of
the CVJs for propeller shafts to meet the increase inpropeller shaft structures and functional requirements
in vehicles. Initially the design was common with CVJ’s
for driveshafts (BJ/DOJ/TJ/LJ); however, addressing
the market demand for high speed rotation, CVJs
modifications of internal clearance and surface
treatment were offered as the CVJs for propeller
shafts (conventional series). CVJs for driveshafts weremodified to be more compact/light type, E-Series(EBJ/EDJ/ETJ), to address the demand for smaller
and lighter components. In addition, H-Series forsupporting high speed operation are enhanced toaddress the needs of every type of vehicles (Fig. 3).
An appropriate sliding type CVJ must be selectedbased on the required sliding amount, outer diameter
size, characteristics and operating condition. Table 1
shows the main basic performance of H-Series sliding
type CVJs and a comparison of their characteristics.

1970s

1990s

1980s

2000s

2010s

2020s

Adoption of FF vehicles
Adoption of 4WD vehicles
Improvement ofvibration characteristics
by application of CVJ

Increased variation of
CVJ for propeller shafts

Further reduction of size and weightfor propeller shafts by designing CVJ’s
dedicated for propeller shafts

Reduction of size and weight of
CVJ for propeller shafts

DOJ

HEDJ
LJ

HLJ

Non-constantvelocity joint such as
Cardan joint

H-Series

This developed product

HETJ

TJ
Conventional series

HEDJ-P

BJ

HEBJ

Fig. 2 Manufacturing timeline of CVJ for propeller shafts

CVJ for propeller shafts

Fixed type

BJ

Sliding type

HEBJ

DOJ

H ED J

H ETJ

TJ

LJ

H LJ

H-Series: support of high-speed operation

Conventional series

BJ7 5

BJ87

DO J7 5

H-Series

B J 1 00

H E B J87

H E B J100

D OJ 8 7

H E D J71

H E D J82

H E D J95

T J7 5TJ79

H E TJ71

H E TJ75

H E TJ79

L J7 5

LJ87

H LJ75H LJ95

H LJ1 09

L J 95

L J10 9Fig. 3 Type and size of CVJ for propeller shafts

NTN TECHNICAL REVIEW No.87

81

Compact Plunging CVJ for Propeller Shaft “HEDJ-P”

Table 1 Comparison of characteristics of various sliding type CVJs
Sliding type
HEDJ

HETJ

Sliding amount

+++

+++

++

Allowed angle

+++

+

++

High speed operation

++

+

+++

Heat generation

++

+++

+

Sliding resistance
NVH
characteristics Induced force

++

+++

+

8th order

3rd order

6th/3rd order

Backlash

HLJ

Axial

++

+

+++

Radial+++++++++: Excellent ++: Good +: Fair

3. Structure and Features of Developed
Product
The newly developed HEDJ-P is redesign of theconventional HEDJ to make the outer ring even morecompact and the inner ring thinner for dedicated use
with propeller shafts.
As shown in Table 1, HEDJ has relatively superiorbalance of NVH characteristics and large sliding
amount/angle. These attributes contribute to theincreased degree of freedom for vehicle design andease of mounting on vehicles. It is suitable especiallyfor SUVs which have larger operating angles,
and adopted by many vehicle models. That is thereason why it was selected as the base of the newdevelopment.

Cage
Steel ballOuter ring

Inner ring

Fig. 4 Structure of the developed product3.1 Structure
The joint itself consists of an inner ring, outer ring,
cage and 8 steel balls, as shown in Fig. 4, similar tothe conventional HEDJ.
For the cage, the RPCF cage was adopted so that it
can absorb small vibrations of vehicles, similar to theconventional product. Fig. 5 shows the structure of the
RPCF cage. The RPCF cage has a clearance between
the steel ball and the cage pocket and a cylindricalpart on the inner diameter of the cage so that the
inner ring and the cage can mutually move in the axial
direction.
This allows the small vehicle vibrations to beabsorbed in the joint, blocking the vibrations.

LC

Cage inner diameter cylinder part

RC: radius of cage inner sphere
Ri: radius of inner ring outer spheredw: diameter of steel ball
LC: cage pocket width
RC ≒ Ri
LC ＞ dw

Fig. 5 Structure of RPCF cage82

NTN TECHNICAL REVIEW No.87

3.2 Compactness/lightweight

Conventional
product
HEDJ

Fig. 6 Comparison of developed product andconventional product

80
70

6%
60

Outer diameter mm

300

200

100

0

Conventional product Developed product
HEDJ71HEDJ71P

Fig. 8 Comparison of weights

3.3 Functional Evaluation
Fig. 9 shows the result of the static torsional strength
test of the developed product HEDJ71P.
HEDJ71P has sufficient static torsional strengthcompared to the conventional product.

Reduction of inner ring/
cage widths

Developed
product
HEDJ-P

50
40

17%

400

Breakage torqueThinner
inner ring500

Development target

Reduction of outer
diameter/PCD

600

Weight g

Since the inner ring and cage of the conventional
HEDJ are common with EDJ for driveshafts, themaximum work angle of the joint alone (without theboot installed) is 25 degrees.
On the other hand, CVJs for propeller shafts only
require the maximum work angle of around 10 degrees
for vehicle assembly (with the boot installed) andaround 15 degrees for the joint alone.
HEDJ-P focused on the functions required by thepropeller shafts limiting the maximum work angle to 15
degrees and to achieve reduction of outer diameter by
6%, weight by 17% while maintaining the equivalent
performance as HEDJ in the same operating range.
This was achieved by reducing the outer diameter ofthe outer ring and PCD (ball pitch circle
diameter),
プロペラシャフト用小型しゅう動式ＣＶＪ「ＨＥＤＪ-Ｐ」
thinning the inner ring and reducing the widths of inner
Compact plunging CVJ for propeller shaft 「HEDJ-P」
ring and the cage.
Fig. 6 shows a comparison of the developed
product with the conventional HEDJ, Fig. 7 shows acomparison of the outer diameters, and Fig. 8 shows acomparison of weights.

N=1

30 DRIVESHAFT ENGINEERING DEPT.
20
100Conventional product Developed product
HEDJ71HEDJ71P

Fig. 7 Comparison of outer diameters

N=3

Fig. 9 Static torsional strength test result(mounting angle: 15°)

Fig. 10 shows an example of the results from thedurability test.
HEDJ71P has sufficient durability compared to theconventional product.
CVJ type

ドライブシャフト技術部

N=2

Operating time

Developed
product
HEDJ71P
Conventional
product
HEDJ71○：No problem△：Minor problem

Fig. 10 High-speed rotation durability test result

The temperature rise characteristics which are used as
an index of high-speed performance is shown in Fig. 11.
HEDJ71P shows about 30% lower temperature riseNTN TECHNICAL REVIEW No.87

83

Compact Plunging CVJ for Propeller Shaft “HEDJ-P”

than the conventional product, revealing superior highspeed performance.
30

Conventional product HEDJ71
20

10

0
4,000

5,000

6,000

45%

Torque loss rate

Temperature rise °C

Developed product HEDJ71P

7,000

8,000

Conventional product Developed product
HEDJ71HEDJ71P

Rotational speed rpm

Fig. 11 Temperature rise characteristics (inner ring driven)

Table 2 shows other performance evaluation
results. It shows that the developed product performed
equivalent to the conventional product in all items.
Table 2 Other performance
Evaluation item

Developed productSliding resistance

Equivalent to HEDJ

Induced force

Equivalent to HEDJ

Radial backlash

Equivalent to HEDJ

Axial backlash

Equivalent to HEDJ

Bending torqueEquivalent to HEDJ

Fig. 12 Calculation result of torque loss rate
(inner ring driven)

4. Conclusion
The structure, features and performance of thecompact sliding type CVJ for propeller shafts “HEDJ-P”
were introduced in this article.
The demand for CVJs for propeller shafts continues
to grow along with the recent popularity of SUVs and
4WD vehicles. The developed product has achieved
the world’s highest level of size and weight reduction
and is expected to be globally adopted as it contributes
to increased degree of freedom for vehicle design andlow fuel consumption at high-speed operation.

3.4 Transmission Efficiency Analysis Result
The following is an introduction of the optimization of
the internal design to achieve the highest level of size
and weight while keeping performance.
Since CVJ for propeller shafts is used in highspeed rotation, the most critical issue is how to containheat generation of the joint. Some of the methods forcontaining heat generation of the joint include surface
treatment of the internal components and applicationof temperature controlling grease. However, it would
achieve higher propeller shaft performance if heat canbe contained by the optimum design of the joint.
Since the temperature rise inside the joint is causedby friction among internal components, an analysis of
the torque loss within the joint was conducted using themechanism analysis. The results are shown in Fig. 12.
It revealed that the developed product reduced torqueloss rate by approx. 45% compared to the conventional
product. It also matches with the result of the actual
temperature rise test shown in Fig. 11, in that thetemperature rise of the developed product is small.

References
1) Akio Sakaguchi, Yoshimasa Ushioda, Masahide Miyata etal., Constant Velocity Universal Joints for Propeller Shafts,
NTN TECHNICAL REVIEW No. 66, (1997) 37-44.
2) Tomoshige Kobayashi, Teruaki Fujio, Summary of E
Series, Constant Velocity Joint for Propeller Shaft, NTN
TECHNICAL REVIEW No. 73, (2005) 88-91.
3) Shinichi Takabe, History of Constant Velocity Joints, NTN
TECHNICAL REVIEW, No. 85 (2017) 40-45.

Photo of author

Masazumi KOBAYASHICVJ Development Dept.
Automotive Business
Headquarters

84

NTN TECHNICAL REVIEW No.87

Technical Article

New Technology of Rolling Bearings Contributing to
Low Fuel Consumption of Automobiles
Takayuki KAWAMURA*
Kouya OOHIRA*

Hiroki FUJIWARA*

To reduce the fuel consumption of automobiles, rolling bearings are required to be lighter,smaller and have lower torque. Additionally, for electric automobiles, the rolling bearings thatare used at high speed rotation and prevent electrolytic corrosion are also required.
In this paper, the technologies for these requirements are explained from the viewpoints of lubrication, numericalanalysis, and materials.

1. Introduction
Recently, development of automobiles is drasticallyshifting from the conventional vehicles with an engine
as the power source to hybrid vehicles (HEV and
PHEV), which combine the engine and motor, fuel cellvehicles (FCV) and electric vehicles (BEV) which are
driven only by motor. One of the reasons for this trend
is the stricter global regulations on fuel consumption
originated from environmental issues such as air
pollution and global warming. Emphasis on reductionof CO2 emissions while driving vehicles continues
and enhanced regulations on fuel consumption takeeffect in Japan, the U.S., Europe and China toward2021. Therefore, auto manufacturers and automotive
component manufacturers are racing to introduce
new technologies successively into the global market.
On the other hand, engines are also used in HEVs
and PHEVs; therefore, improvement of fuel/electricity
efficiency is a critical challenge, too.
Based on the above situation, this article introduces“new technologies contributing to low fuel consumptionof vehicles” with rolling bearings.

2. Challenges of Rolling Bearings
Regarding Low Fuel Consumption
Approximately 100 to 150 bearings are used
in a vehicle and rolling bearings are some of thecomponents required for safe and comfortable
driving. Rolling bearings are used in many parts ofa vehicle, such as engine peripheral, transmission,various motors as accessories and driving axle units.
There are broadly two characteristics for reducing
fuel consumption of conventional vehicles poweredby engines. One is lower torque and the other iscompactness and lightweight for reducing the vehicle

weight.
The requirements for rolling bearings toward
electrification of vehicles include high-speed
technology to support high-speed rotation of motors
and avoidance of electrical corrosion in the vehicles
with complex electrical current paths.
There may be other technological challenges
specific to HEVs and PHEVs, as well as to FCVs
and BEVs, but the main challenges overall are (1)lower torque, (2) compactness and lightweight, (3)high-speed rotation and (4) avoidance of electricalcorrosion, which are inherent from electrification.
The following are the topics of the discussion in thisarticle on those challenges:(1) Lower torque: While grease lubricated rolling bearings
are frequently used in vehicles, improvement ofgrease technology made a significant contribution
to reducing torque. This article will discuss thosecases.
(2) Compactness/lightweight: Technologies discussed
in the past article1) for improvement of materials/
thermal treatments are making a good track recordof results for contributing to compactness/lightweight.
This article discusses improvement of bearing load
carrying capacity by numerical analysis.
(3) High-speed rotation: High-speed rotation is usually
supported by ball bearings and an accurate
understanding of cage transformation in high-speed
rotation is required. In this article, some cases ofnumerical analysis are discussed.
(4) Avoidance of electrical corrosion: While insulating
film may be applied on the outer diameter of the
raceway, this article discusses about ceramic ballbearings which are expected to provide highly reliable
insulation capability and significant weight reduction.

* Advanced Technology R&D Center

NTN TECHNICAL REVIEW No.87

85

New Technology of Rolling Bearings Contributing to Low Fuel Consumption of Automobiles

3. Lower Torque

Cage

Reduction of torque is required to grease lubricatedrolling bearings from the viewpoint of energy efficiency
and resource conservation. Reducing viscosity of grease
base oil can reduce torque. However, a simple reductionof viscosity is not effective as it degrades the oil film
formation and increases the risk of reduced bearing life.
The following is an introduction of bearing torque reduction
technology based on rheology characteristics of grease2).

3.1 Relation of State of Existence of Grease Within
Ball Bearings and Bearing TorqueThe state of existence of grease within ball bearings
can be broadly divided into a churning state where grease
churning continues and torque is high and a channelingstate where most grease is squeezed out from the rolling
elements and torque is low. To observe the difference
between those states, the condition of grease adhesion
inside the bearing was investigated using X-ray CT, which
is becoming a standard method for observing grease
behavior.
Inner/outer rings, balls, cage and seals made of resin
were used for the bearing to be observed, so that X-ray
can be transmitted. For a better contrast between thegrease and the other materials, 5% tungsten (by weight)
was added in the grease as a tracer. As shown in Fig. 1,
state of existence of grease between the balls and cage
pocket was observed running the grease lubricatedbearing while torque is measured. In the initial stage (after
5 hours of operation) where the bearing was stopped
in the churning state (torque: 13 Nmm) and when the
bearing was assumed to reach the channeling state after
a long hours (23 hours) of operation (torque: 5 Nmm). It
revealed that there was a large difference in the amountof grease between the balls and the cage pockets
between the two states, as shown in Fig. 2.
<Resin-made bearing torque measurement condition>
6204, 25 °C, Fa=19.6 N, 3,600 min-1
20

Bearing torque Nmm

Churning state
15

10

5

Channeling state
0

0

5

10

15

20

25

Operating time hFig. 1 Chronological change of bearing torque of resin
made bearing86

NTN TECHNICAL REVIEW No.87

Ball
GreaseChurning state(Torque: 13 Nmm)

Channeling state(Torque: 5 Nmm)

Fig. 2 State of grease adhesion in resin made bearing(between ball and cage pocket surface)

3.2 Basic Concept of Lowering Torque by
GreaseThe observation of X-ray CT revealed that shear
stress of grease between the balls and the cage
pocket surface needs to be reduced in order to reduce
torque in grease lubrication. That is, two points,
namely, 1) reduction of grease viscosity and 2) fastertransition to channeling state, are effective. The
following is an example of verification of these effects
by using 4 types (grease A to D) of grease for rolling
bearings (Table 1).
Table 1 Sample grease
Grease A Grease B Grease C Grease D
Thickener

Base
oil

Type
Kinematic
viscosity
mm2/s (40°C)

Consistency

Lithium
soap

Urea

Urea

Synthetic Synthetic Synthetic
oil
oil
oil

Urea
Mineral
oil

25

40

23

95

250

250

280

290

1) Reduction of Grease Viscosity
Grease viscosity is a function of grease shear
velocity, therefore viscosity needs to be reduced in theshear velocity zone between the balls and the cage
pocket surface under the operating condition of rolling
bearings. If the balls are assumed to be at the centerof the cage pockets and the inner ring of a ball bearing(6204) rotates at 1,800-10,000 min-1, then the grease
shear velocity of the cage pocket is 24,000-130,000 s-1.
Fig. 3 shows the relation between the shear stressat the cage pocket obtained by calculating the actual
grease viscosity measured with a rheometer multipliedby the shear velocity, and the bearing torque actually
measured at the initial stage of operation. Except for
grease D at 1,800 min-1, the more the shear stress, thegreater the bearing torque in all the conditions (anygrease types and rotational speeds). Reduction ofgrease viscosity at the shear velocity equivalent to thecage pockets and reduction of shear stress between
the balls and the cage pocket surface are effective for
reducing torque.

<Bearing torque measurement condition>
6204, 25 °C, Fa=19.6 N, 1,800-10,000 min-1

Loss modulus （G’’）

Storage modulus （G’）

Thickener
G’
G”

tanδ = G ” / G ’Stress（τ）

Yield stress( tanδ =1 )Fig. 4 Example of measurement of yield stress byrheometer<Bearing torque measurement condition>
6204, 25 °C, Fa=19.6 N, 1,800 min-1
Grease A（Yield stress：1,425 Pa）
Grease B（Yield stress：898 Pa）
Grease C（Yield stress：1,757 Pa）
Grease D（Yield stress：1,756 Pa）
60
50
40
30
20
10

0

40

80

120

Time minFig. 5 Relationship between grease yield stress andbearing torque-1

Bearing torque Nmm

Base oil

06050Change of network structure of thickener

Bearing torque Nmm2) Faster Transition to Channeling StateIn grease lubrication, the difference between
the churning state and channeling state has amajor impact on bearing torque. For low torque, thechanneling state, where the grease between the balls
and the cage pocket surface is quickly squeezed out,
is more desirable. Grease D at 1,800 min-1 in Fig. 3 isconsidered to be in the channeling state and the otherconditions are considered to be in the churning state.
By changing angle of oscillation with the rheometer,
the storage modulus G’, which indicates grease
property as solid, and the loss modulus G’, whichindicates the grease property as liquid, are measured
and the shear stress, where the ratio of those two(tan δ = G” /G’) is 1, is obtained as the yield stress(Fig. 4). As shown in Fig. 5, it was verified that thegrease with high yield stress (grease C and D) can
transition from the churning state (high torque) to thechanneling state (low torque) within the operating timeof 120 min., the grease with low yield stress (grease A
and B) cannot transition to the channeling state (lowtorque).
The grease in the bearing with a rotating innerring moves from the raceway surface to the innerdiameter of the outer ring by the centrifugal force andstays there as agglomeration. It is assumed that theagglomerated grease or oil separated from it flows
back to the raceway lubricating the bearing3). As shownin Fig. 6, it is considered that the grease agglomerated
on the inner diameter of the outer ring with higher yieldstress is harder to move to the raceway surface byvibration and temperature rise, allowing more stablechanneling state.

*1,800 min data

40

Cross section of outer ring
Grease A

30

Grease B

20

Grease C

10

Grease D0
1,000

10,000

Rolling
element

100,000

Shear stress Pa

Fig. 3 Relationship between bearing torque and cage
pocket shear stress

Grease with high yield stress(harder to move to raceway surface)

Grease with low yield stress(easier to move to raceway surface)Fig. 6 Schematic diagram of grease flow agglomerated
on the inner diameter of outer ringNTN TECHNICAL REVIEW No.87

87

New Technology of Rolling Bearings Contributing to Low Fuel Consumption of Automobiles

3.3 Application to Grease for Hub Bearings
NTN is developing different types of greasefor various applications based on the low torquetechnologies by grease described in 3.2. As an example,
the case of application of the grease for hub bearings,
which has particularly strong demand for low torqueamong automotive components4) is introduced.
In this development, reduction of grease shear stressbetween the raceway and rolling elements is alsoelaborated in addition to the reduction of the grease
shear stress between the balls and cage pocket surface.
(1) Reduction of Grease Shear Stress Between the Balls
and Cage Pocket Surface
Fig. 7 and 8 show the comparison of the grease
viscosity and yield stress between the conventional
product and the developed product. The developed
product provides lower viscosity and higher yield stressin the shear velocity zone above 2,000 s-1, which
is important in hub bearings, than the conventional
product, as a result of elaboration on grease
composition. Control of these physical properties madeit possible to reduce grease shear stress between theballs and cage pocket surface and achieve low torque.

(2) Reduction of Grease Shear Stress Between
Raceway and Rolling Elements
With ball bearings, it is known that the small sliding
between the raceway and the rolling elements, whichis called differential slips and spins, cause friction(traction)5). Fig. 9 shows the investigation resultof the impact of the molecular structure of grease
composition on the traction. It was revealed that thetraction can be reduced by reducing circular/branching
structure in the molecular structure of the base oil andmaking the straight-chain structure as the dominant
structure. The developed product improved themolecular structure in addition to the rheology propertyof the grease for achieving torque reduction.
<Traction measurement condition>
25°C, 0.65 GPa, 0.2 ⇒ 1.0 m/s (3% slip)

Steel ballGreaseSteel disc<Grease viscosity measurement condition>
Cone-plate rheometer, 25°C, 1 ⇒ 8,000 s-1, steady flow
Conventional
product

Grease viscosity Pa • s

10,000Conventional product
1,000

More circular/branch structure withlarge friction

Developed product100
10Developed
product

1
0.1

1

10

100

1,000

Less circular/branch structure withsmall friction

10,000

Shear velocity s - 1

Fig. 7 Relationship between shear velocity and grease
viscosity

100

Conventional product10t an δ

Developed product

1

0.06
0.04
0.02

1

10

Rolling speed m/s

100

1,000

10,000

Shear stress Pa

Fig. 8 Measurement result of yield stress

88

Developed product
0.08

0.00
0.1

0.1

0.01
10

Conventional product0.10

Traction coefficient<Yield stress measurement condition>
Parallel plate rheometer, 25°C, 1 Hz, 10 ⇒ 3,000 Pa

0.12

NTN TECHNICAL REVIEW No.87

Fig. 9 Relationship between molecular structure ofgrease component and traction

4. Compactness/lightweight

5. High-speed Rotation

For low fuel consumption, it is necessary to reduce
the size and weight of each individual component of avehicle. In case of rolling bearings, a simple downsizing
causes reduction of system life. Therefore, past efforts
were focused on the improvement of material to reduce
the size while maintaining the required system life1). In
this article, a technology for long system life is introduced,
with a new viewpoint of changing the design of the
bearing internal shape, which contributes to downsizing.
The rolling element and raceway are in line contact asthey are basically cylinders; however, if they are madeof simple cylinders, excessive stress is concentrated on
both ends of the contact called “edge load.” Therefore,
the radii of both ends of the rolling elements and raceway
are reduced by a few μ m, called “crowning.” Edgeloading can be prevented by applying large crowning
even in the misaligned condition; however, that causes
large maximum stress at the center of the roller, causing
reduction of operating life. Although the theoretical shape
to minimize the maximum stress while preventing theedge load was known to be a logarithmic curve, the ideal
curve could not be actually processed and the impact of
misalignment, which is realistically unavoidable could not
be eliminated. NTN developed a proprietary logarithmic
function formula for crowning with improved degree ofdesign freedom, as well as an automated design method
using mathematical optimization method6).
Fig. 10 shows a diagram of the distribution of stress.
The logarithmic crowning reduces the edge stress even
if the amount of processing at the edges is almost thesame as the conventional crowning, resulting in longer
operating life. By using this technology, compact and lightbearings can be developed maintaining equivalent life
as the conventional products, which contribute to lower
torque and lower fuel consumption.

The motor, as the power source of an EV, becomeslarger if designed with the low speed/high torquespecification; therefore, it is designed with the high speed/
low torque specification for compactness and the required
torque is created by reducing the speed. This requires
the rolling bearings for EV motors to support high-speed
rotation.
The type of bearings suitable for high-speed operation
is ball bearings. Resin made cages, which exhibit superior
self-lubricating property, are frequently used to reduce
friction loss. An ordinary resin-made cage has a shapeasymmetric with respect to the axial direction called a “snapcage,” as shown in Fig. 11. The pocket has an open end in
the axial direction where a ball is snapped in. The claws on
the open end of the pocket can open to the outer diameterside when operated in high speed, by the centrifugal force,as shown in Fig. 12, with deformation like flower petals. This
type of deformation of claws can interfere with the balls andouter ring, causing an increased friction loss and wear.

R
30

Drop quantity μm

Drop quantity μm

30
25
20
15
10

-6.0 -4.0 -2.0

0.0

2.0

4.0

4.09 GPa
2.0 6 G Pa
-6.0 -4.0 -2.0

0

2.0

4.0

6.0

Coordination in the bus line direction mm

Depth mmDepth mm

15
10

0

6.0

Coordination in the bus line direction mm
0
0.1
0.2
0.3

20

5

5
0

25

-6.0 -4.0 -2.0

0.0

2.0

4.0

6.0

Coordination in the bus line direction mm
0
0.1
0.2
0.3

2.08 GPa

1.6
1.2

2.05 G Pa-6.0 -4.0 -2.0

GPa
2.0

0

0.8
2.0

4.0

6.0

Coordination in the bus line direction mm

0.4
0.0

(a) Conventional crowning (b) Logarithmic crowning
Fig. 10 Crowning geometry and distribution of Mises
equivalent stresses7)

Open end side

Opposite to open end side

Fig. 11 Resin made snap cage

Fig. 12 Example of deformation analysis of resin madesnap cage

Therefore, the thickness of the claw portion was
reduced for lightweight and the rigidity of the ring
portion on the opposite side of the open end was
reduced to allow deformation of the ring to the outer
diameter direction, to decrease the impact of thedeformation of the claws. Fig. 13 shows the deformationof the cages of the conventional structure and thedeveloped product in high-speed rotation. In the case of
the snap cage, the limitation of the high-speed rotation
is not in the cage strength but in the local deformationof the claws. Noticing this fact, the challenge was solved
not by providing high rigidity to prevent deformation
but conversely, by making the entire piece a flexible
structure. For example, the permitted rotational speed ofoil lubricated 6206 is 13,000 min-1; however, adoption of thistechnology achieved a normal operation of 17,000 min-1.
NTN TECHNICAL REVIEW No.87

89

New Technology of Rolling Bearings Contributing to Low Fuel Consumption of Automobiles(a) Conventional cage(b) Developed cage

Fig. 13 Example of deformation analysis due tocentrifugal force and cage shape

Even higher speed can be achieved by adopting a
cage that prevents deformation of the pocket and its
surrounding by integrating axially divided components
snapped into one8).

terminal A and B are activated. Table 2 shows the test
condition. The test was conducted by applying a constantcurrent (0.5 A) under quick acceleration condition guided
by the inner ring (in case of the bearing with ceramic balls
made of silicon nitride, the applied voltage was set to 30 V).
Table 3 shows the test results.
As shown in Table 3, the ceramic balls made of silicon
nitride can contain peeling of rolling element surface due
to electrical corrosion, since they are insulating body,compared to the steel balls. Therefore, the ceramicballs made of silicon nitride with insulation capability are
expected to be used in the bearings of various types ofmotors used in the next generation vehicles, which will be
widely adopted such as HEVs, PHEVs and EVs.
Terminal A

Terminal B

Bearing under test

Support bearing

6. Avoidance of Electrical Corrosion
While insulating film made by resin or ceramics may
be applied on the outer diameter of the raceway forpreventing electrical corrosion of rolling bearings, thisarticle discusses about ceramic balls which are expected
to provide highly reliable insulation capability andsignificant weight reduction.
A type of damages incurred to the bearings used in
motors and generators is called electrical corrosion. The
electrical corrosion is a phenomenon of damage on therolling surface by sparks generated at the rolling contact
by the electrical current that flows into the bearing. The
metallographic structure is deteriorated by the spark
generated at the rolling contacts, resulting in vibration,
noise and flaking.
Devices equipped with motors, for instance, use carbon
brushes for grounding the shaft or shut down the electricalcurrent from the bearings by shaft insulator, etc. However,each of them has issues in durability, such as wear ofcarbon brushes during operation and thermal degradationof resin, if resin insulator is used for shutting down theelectrical current. As a method to solve these issues, ahybrid bearing, where ceramic balls made of silicon nitride
are incorporated in the raceway made of steel, is effective.
To verify the insulation capability of the hybrid bearing
with the ceramic balls made of silicon nitride, a bearing
peel life test was conducted under current carrying
condition using direct current, as an example. Fig.
14 shows an outline of the test equipment. This test
equipment supports the rotational shaft by the bearing
under the test and a support bearing. The housing is
divided into 2 parts by the insulation. The electricalcurrent flows from the terminal A → bearing under test →rotational shaft → support bearing → terminal B when the90

NTN TECHNICAL REVIEW No.87

Insulation

Pulley(driven by belt)

Fig. 14 Peeling life tester under current carrying condition
Table 2 Test condition
Bearing under test

Deep groove ball bearing (6203)

Rolling element

Steel ballGreaseCeramic ball

Nonconductive grease

Amount of injectedgrease (g)Rotational speed(min-1)

Quick acceleration/
deceleration from 0 to 20,000

Atmosphere

Room temperature

0.86

Pulley load (N)1,617

Bearing load (N)2,332Current (A)Stopping condition

0.5-

When the vibration is 10 times than initial condition

Table 3 Peeling life test results
Life (h)Peeling region

Steel ball

19.6

Ball

Ceramic ball

> 200

None

In addition to the solution for avoidance of electricalcorrosion, ceramic balls are also effective for reducing
weight. The specific gravity of the ceramic made of silicon
nitride is around 40% of the bearing steel; therefore,
applying ceramic balls made of silicon nitride for rolling
elements makes the bearing lighter than an ordinary
bearing with the raceway and rolling elements made ofbearing steel (SUJ2). In addition, lighter rolling elements
contribute to reduction of centrifugal force applied to therolling elements during rotation of the bearing, which

0.5

SUJ2 (Fixed) -SUJ２ (Rotation)

Si3N4 (Fixed) -Si3N4 (Rotation)

0.4

Friction coefficienthelps support the increasing demand of higher speed
motors for HEVs, PHEVs and EVs.
In case of deep groove ball bearing 6206, applying ceramicballs made of silicon nitride for rolling elements makes the
hybrid bearing lighter than the ordinary bearing with the
raceway and rolling elements made of bearing steel (SUJ2)
by approx. 10%. As shown in Fig. 15, applying ceramic balls
made of silicon nitride for hub bearings reduced the weight byapprox. 13%, contributing to low fuel consumption of vehicles.

SUJ2 (Fixed) -Si3N4 (Rotation)

0.3
0.2
0.1
0
0

200

400

600

800

1,000

1,200

1,400

1,600

Load (N)Fig. 16 Seizure resistance test result

7. Conclusion

Fig. 15 1st generation hub bearing (using ceramic balls)

In addition, ceramic made of silicon nitride is chemicallystable which is expected to help reduce oxidative
deterioration of lubricant between the raceway made ofbearing steel and the rolling elements and improve antigalling property by avoiding adhesion if the rolling elements
made of bearing steel are replaced with the ceramic madeof silicon nitride.
The seizure resistance property was evaluated in the
combination of steel ball (SUJ2) and ceramic ball made ofsilicon nitride (Si3N4) using a four-ball friction tester. The test
condition is shown in Table 4 and the test result is shownin Fig. 16. Four-ball friction testing uses three fixed balls on
which a rolling ball rotates. Seizure resistance property wasevaluated by running the tester for a minute at a constantload and when the friction coefficient did not increase, theload was increased. The test was stopped when the friction
coefficient rose more than 5 times the initial condition when
the seizure occurred. As shown in Fig. 16, a combinationof steel balls and a ceramic ball made of silicon nitride
indicated the best seizure resistance property.
Since seizure resistance property improves when steel isused for inner/outer rings and ceramic made of silicon nitride
is used for rolling elements, low fuel consumption of vehicles
can be expected by reduced use of lubricant and therefore,
low torque effect.

New technologies contributing to low fuel consumptionof vehicles, such as design technology by numericalanalysis for rolling bearings, weight reduction technologies
and low torque technologies were discussed. The hope isthese new technologies help support measures against
the environmental issues such as global warming andglobal tendency of fuel cost increase.

References
1) Nakashima: Trends in Materials and Heat Treatments for Rolling
Bearings, NTN TECHNICAL REVIEW, No. 76 (2008) 10.
2) Kondo, Kawamura: Impact of grease rheology property on
bearing torque, Japanese Society of Tribologists, Proceedings
for Tribology Conference 2017 Spring Tokyo, F17.
3) Kawamura: Research on the Lubrication Mechanism of Greasefor High Speed Bearings, NTN TECHNICAL REVIEW, No. 76(2008) 39.
4) Seki: Low Friction Hub Bearing III, NTN TECHNICAL REVIEW,
No. 87 (2019) 63-67.
5) Muraki: Illustrated Tribology Science of Friction and Lubrication
Technology, Nikkan Kogyo Shimbun, Ltd., 221.
6) Fujiwara, Kawase: Logarithmic Profile of Rollers in Roller
Bearing and Optimization of the Profile, Transactions of the
JSME C, 72 (2006), 3022.
7) Fujiwara, Yamauchi: Experimental Comparison Between
Partially Crowned and Logarithmic Roller Profiles in Cylindrical
Roller Bearings, Transactions of the JSME C, 74 (2008), 2308.
8) Katagiri, Naito: Next Generation Deep Groove Ball Bearing forHigh-Speed Servomotor, NTN TECHNICAL REVIEW, No. 72(2004) 45.

Photo of authors

Table 4 Test condition
Test equipment

Four-ball friction tester

Material of balls
under test

Steel ball (SUJ2), ceramic ball (Si3N4)

Ball size (inch)

3/4

Lubricating oil

Turbine oil grade 68

Lubricating condition

Dipping

Atmosphere

Room temperature

Slide velocity (m/s)

0.86

Stopping condition

When the friction coefficient rose morethan 5 times from the initial condition

Takayuki KAWAMURA

Hiroki FUJIWARA

Kouya OOHIRA

Advanced Technology
R&D Center

Advanced Technology
R&D Center

Advanced Technology
R&D Center

NTN TECHNICAL REVIEW No.87

91

Technical Article

Verification of Torque Reduction for Low Torque Seal Ringby Fluid Analysis
Takuya ISHII*
Tomohiko OBATA**
Seal rings

In order to achieve demands of fuel consumption standard, seal rings forautomotive transmission are required to further reduce torque and oil leak. NTN
developed “Low Torque Seal Ring” and started mass production. It has V-shaped
lubrication grooves, which reduces torque by 60% in comparison with conventional
products. This article introduces fluid analysis results of torque reduction by V-shaped lubrication grooves in “Low
Torque Seal Ring”.

1. Introduction
Multiple seal rings made of resin with outer
diameters ranging from 15-60 mm are used in vehicletransmissions (AT, CVT, etc.). These seal rings are
required to have low torque and low oil leakage
properties to achieve low fuel consumption of vehicles.
In order to respond to this requirement, NTN developed“Low Torque Seal Ring”1), 2) made of polyether ether
ketone (PEEK) resin with a V-shaped lubrication
groove and started volume production (Fig. 1).
The number and shape of the V-shaped lubrication
grooves was optimized by fluid analysis andexperiments to further reduce torque of the low torqueseal ring. This article introduces the verification resultof the fluid analysis regarding the reduction of torquefor the low torque seal ring.
Abutment
V-shaped lubrication groove

are pushed to both the inner surface of the housing
and the side wall of the shaft groove by oil hydraulics
sealing oil and maintaining the pressure inside the oil
hydraulic circuit, as they slide.
The required performance of the seal rings is low
torque, low oil leakage and high wear resistance. Whentorque is reduced, transmission efficiency increases
achieving higher energy efficiency. Reduced oil leakage
leads to a more efficient and smaller oil-hydraulicpump which results in higher energy efficiency. To
maintain low torque and low oil leakage operation andrealize long operating life, seal rings are required to bewear resistant and at the same time prevent wear of
the mating component which the seal rings slide on.
Fig. 2 shows the operation of NTN’s conventional
product which has a rectangular cross section. Since
the contact area of the seal ring and the side wall of
the shaft groove is smaller than the contact area of theseal ring and the inner surface of the housing, the seal
ring slides on the side wall of the shaft groove. It is
this side wall of the shaft groove that has lower sliding
resistance when the shaft or the housing rotates. Oilleakage is small as the seal ring has area contact withthe side wall of the shaft groove.

2. Role and Operation of the Seal Ring
Oil is sealed by the seal ring that slides on themoving components. Seal rings are installed between
the shaft and housing that moves in relative motion
within the oil hydraulic circuits of transmissions. They
* Precision Plastics Engineering Dept., Composite Material Product Division** Advanced Technology R&D Center

92

NTN TECHNICAL REVIEW No.87

Seal ringSide wall of
shaft groove

Fig. 1 Low torque seal ring

Lubricating oil

Housing：Hydraulicpressure

Shaft

Fig. 2 Operation of seal ring

3.1 Features
The Low Torque Seal Ring realized low torque andlow oil leakage by installing a V-shaped lubrication
groove on the surface of the seal ring which slides
on the side wall of the shaft groove. It uses BEAREE
PK5301, which is a material made of PEEK resin withspecial additives. It has V-shaped lubrication grooves on
the side formed by injection molding and the abutment
is made of complex shape. Oil leakage from theabutment is reduced, by making it a complex shape.
The Low Torque Seal Ring has the following featurescompared with NTN’s conventional product.
(Features)(1) Reduction of torque by up to 60%(2) 1/10 the wear rate(3) Equivalent low oil leakage property

3.2 Comparison of the Lubrication Groove
Shapes
3.2.1 Torque Measurement Results
Table 1 shows a comparison of torque using 3
types of seal rings with different shapes of lubrication
grooves and without grooves. Fig. 3 shows an outlineof the test equipment. Torque was measured bycirculating oil between two seal rings installed on theshaft grooves, applying oil pressure and rotating the
housing.
Table 1 Seal rings under test
Seal rings under test

Shape of the lubrication grooves on the side

V-shaped lubrication
grooves(12 on one side)
Square-shaped
lubrication grooves(12 on one side)
No lubrication
grooves
Seal ring size: OD: 50 mm, thickness: 1.6 mm, width: 1.5 mm

Seal rings

Housing (rotating)

Motor

Torquemeter

Axis

Hydraulicpower unit
(oil circulation)

Fig. 4 shows the relation between the oil hydraulics
and torque. The measured torque for two seal rings
was divided by 2 to obtain torque for one seal ring. The
seal ring with the V-shaped lubrication grooves showed
lower torque than the seal ring without grooves (NTN’sconventional product) by 60-70% and the seal ringwith square-shaped lubrication grooves by 20%.
[Test condition]
Oil hydraulics: 0.5-2 MPa,
rotation speed: 4,000 min-1, ATF: 110°C
S45C Housing/shaft
0.9

Torque (for one seal ring) Nm

3. Low Torque Seal Ring

No grooves (conventional product)
Square-shaped lubrication grooves
V-shaped lubrication grooves

0.6

0.3

0.0
0.0

0.5

1.0

1.5

2.0

2.5

Oil hydraulics MPa

Fig. 4 Relationship between oil hydraulics and torque3.2.2 Fluid Analysis Results
As the reason for lower torque, it is assumed thatapplication of the V-shaped lubrication grooves which
reduced the contact area between the seal ring andside wall of the shaft groove promoted lubrication of
the sliding surface. The difference of torque between
two different shapes of the grooves is attributed to thedifference of lubricating conditions. This was verified by
fluid analysis.
Fig. 5 shows the analysis result of the model
extracting fluid region of one lubrication groove. With
the V-shaped lubrication groove, oil film pressure at
one end of the groove is high due to a hydrodynamic
effect. This axial force due to oil film pressure is in
the opposite direction from the force that the seal
ring is pressed on the side wall of the shaft grooveby oil hydraulics; therefore, it reduced the latter force.
It is also assumed that oil flowed from the end of the
lubrication groove onto the sliding surface between
the lubrication grooves due to difference of pressure
helped reduce torque. On the other hand, the highpressure observed in the V-shaped lubrication groove
is not observed in the square-shaped lubrication
groove.

Fig. 3 Outline of test equipment

NTN TECHNICAL REVIEW No.87

93

Verification of Torque Reduction for Low Torque Seal Ring by Fluid Analysis[Analysis condition]
Oil film thickness: 5 μm, oil hydraulics: 2 MPa,
rotation speed: 4,000 min-1, ATF(20°C)

Groove angle

Groove depth[View from the arrow A]

V-shaped lubrication groove

Groove length

Distance
betweengrooves

Direction of axial rotation
Groove width

Square-shaped lubrication groove[Enlarged view of B]

Fig. 6 Analysis of seal ring (24 grooves)
Direction of axial rotation

High

PressurePa

Fig. 5 Oil film pressure distribution on sliding surface

4. Verification of Torque Reduction by
Optimization of V-Shaped Lubrication
Grooves
4.1 Fluid Analysis Condition
The torque measurement result and oil film pressure
distribution on the sliding surface revealed that theforce appearing at the end of the V-shaped lubrication
grooves is in the opposite direction from the force
due to oil film pressure (oil film reaction force) which
contributed to a reduction of torque. When the oil film
reaction force is greater, the torque is lower. So, it isassumed that the greater the number of the V-shaped
lubrication grooves and the wider the groove widths, thegreater the oil film reaction force. Therefore, this wasverified by the fluid analysis.
Fig. 6 shows the definition of the length, width,
depth, angle of, and the distance between V-shaped
lubrication grooves of the seal ring in the analysis.
The size was set as: OD: 44 mm, thickness: 2 mm
and width: 2.3 mm. The fluid region of one V-shaped
lubrication groove of the seal ring was modeledwith fluid analysis and the oil film pressure due tohydrodynamic effect was integrated to obtain the oilfilm reaction force of one groove. The product of thisforce and the number of grooves was defined as the oilfilm reaction force for one seal ring and a comparisonof different conditions was made. Note that the oil film
pressure at the contact area of the side of the seal ringand the side wall of the shaft groove was ignored, as
this is very small compared to the V-shaped lubrication
groove. In this analysis, the oil film thickness on thesliding surface was assumed to be constant at 5 μm,
for ease of calculation, and the operating condition
was defined as ATF pressure: 0.6 MPa, temperature:
20°C and rotation speed: 10,000 min-1.
94

NTN TECHNICAL REVIEW No.87

4.2 Fluid Analysis Results
4.2.1 Number of V-Shaped Lubrication Grooves
Oil film reaction force of one seal ring was obtainedby fluid analysis for seal rings with 12 and 24 V-shaped
lubrication grooves on one side. The distance between
V-shaped lubrication grooves was the same and thelength was changed between 12 and 24 grooves. The
groove angle was also the same but the groove depths
are different to allow for 12 or 24 grooves.
Fig. 7 shows the oil film reaction force of seal rings with
12 and 24 V-shaped lubrication grooves. As estimated, it
was verified that the oil film reaction force is larger as thenumber of grooves is greater. Therefore, the greater thenumber of grooves, the better for reducing torque.
3

Oil film reaction force N

Low

2

1

0

12 grooves

24 grooves

Fig. 7 Number of grooves and oil film reaction force

However, when the number of grooves increases, thenumber of the spaces between the grooves increases,
too, which increases the contact area between the sideof the seal ring and the side wall of the shaft groove,
which result in higher torque. Therefore, there should
be an optimum number of grooves for the minimum
torque. To verify this, seal rings with a varying number ofgrooves were made and the torque measured. The seal
ring size was: OD: 51 mm, thickness: 2.4 mm, width: 2.3mm and the number of grooves: 12-30 on one side. The
distance between grooves, groove width and groove
angle were the same so the groove lengths and depths
were different depending on the number of grooves.
The measurement condition was: ATF pressure: 1 MPa,
temperature: 80°C, rotation speed: 2,000 min-1.

Fig. 8 shows the relation between the number of grooves
and torque. Torque was reduced toward 24 grooves but
increased at 30. The measurement results matched with theaforementioned concept, verifying that there is an optimum
value for the number of grooves. Since the number ofgrooves is restricted by design and manufacturing reasons
depending on the outer diameter, NTN’s Low Torque Seal
Rings are lined up with the optimum number of V-shaped
lubrication grooves by outer diameter.

Torque (for one seal ring) Nm

0.3

0.2

0.1

4.2.3 Angle of V-Shaped Lubrication Grooves
The oil film reaction force was obtained using fluid
analysis, by increasing or decreasing the angle of the
V-shaped lubrication grooves based on the seal ringwith 24 grooves on one side described in 4.2.1. Since
the distance between the grooves and the groove
length and width were the same, only the groove depth
is different based on the change of angles.
Fig. 10 shows the relation between the groove angle
and oil film reaction force. The horizontal axis is a ratioof angle against the base angle. Within the range ofthis test, the oil film reaction force is almost the same
regardless of the groove angles. Similarly, there is no
impact to the groove depth. These results revealed
that the number of grooves must be emphasized in thedesign of the V-shaped lubrication grooves, and thegroove angle and depth do not need to be considered,if they are in the appropriate range.
3

0.0
15

25

35

Number of grooves

Fig. 8 Relationship between number of grooves and torque4.2.2 Width of V-Shaped Lubrication Grooves
The oil film reaction force was obtained by fluid analysis
for seal rings with V-shaped lubrication grooves withwidths ranging from 0.2 to 0.7 mm. The number of grooves
was 24 on one side and all the sizes are the same except
for the groove width.
Fig. 9 shows the relation between the groove widthand oil film reaction force. The verification result obtained
matched with the estimate, as the groove width increased,
the oil film reaction force increased. However, excessive
groove width was found to cause increased oil leakage.
Therefore, the groove width must be determined for eachcase, considering the size of housing and the shaft,eccentricity, wear amount of seal ring and housing, etc.

Oil film reaction force N

3

2

1

Oil film reaction force N

5

2

1

0
0

1

2

(Base)
Ratio of angle against the base angle

Fig. 10 Relationship between groove angle and oil film
reaction force

4.3 R esult of Torque Measurement with the
Optimum V-Shaped Lubrication Grooves
The number and the shape of the V-shaped
lubrication grooves are optimized based on the above
fluid analysis. Fig. 11 shows a comparison of torquefrom the seal ring with 12 V-shaped lubrication grooves
discussed in Section 3.2 and the seal ring with the 24
optimized V-shaped lubrication grooves. The seal ringwith 24 optimized grooves showed torque reduction of
10-15% compared to the seal ring with 12 grooves3), 4).
A seal ring that was of the following size was used forcomparison: OD: 45 mm, thickness: 2 mm, width: 2.4
mm.

0
0.0

0.3

0.6

0.9

Groove width mm

Fig. 9 Relationship between groove width and oil film
reaction force
NTN TECHNICAL REVIEW No.87

95

Verification of Torque Reduction for Low Torque Seal Ring by Fluid Analysis

References[Test condition]
Oil hydraulics: 0.4-1.2 MPa,
rotation speed: 2,000 min-1, ATF: 80°C
Steel base housing/shaft

Torque (for one seal ring) Nm

0.15

Seal ring with 12 grooves
Seal ring with 24 grooves
0.10

0.05

0.00
0.0

0.5

1.0

1.5

Oil hydraulics MPa

Fig. 11 Relationship between oil hydraulics and torque5. Summary
This article introduced the verification result of thefluid analysis regarding reduction of torque of the
Low Torque Seal Ring. The number and the shapeof V-shaped lubrication grooves are optimized basedon the fluid analysis and experiments to successfully
reduce torque even further. Adoption of the Low TorqueSeal Rings is well in progress as they could respondto the requirement of low fuel consumption of vehicles.
We strive for further reduction of torque as we move
forward.
Requirements for energy efficiency are increasing inmany areas. We are poised to increase the speed ofdevelopment for enhancing the performance of resin
sliding components by adopting analytical approaches
such as fluid analysis.

Photo of authors

Takuya ISHII

Tomohiko OBATA

Precision Plastics
Engineering Dept.
Composite Material Product
Division

Advanced Technology
R&D Center

96

NTN TECHNICAL REVIEW No.87

1) Kouzou Kakehi, Takumi Kondou, Takuya Ishii,
Masato Yoshino: Development of Low TorqueSeal Ring for Automotive Transmission, NTN
TECHNICAL REVIEW No. 81 (2013) 68.
2) Takuya Ishii: Lower Torque of Seal Ring for
Automotive Transmission, Journal of Society ofAutomotive Engineers of Japan Vol 71, No. 9 (2017)81.
3) Takuya Ishii: Lower Torque of Seal Ring forTransmission, Automotive Technology Vol. 6, No. 1(2018) 69.
4) K ayo Sakai, Tomonori Yamashita, Hajime Asada,
Takuya Ishii: Proposal of Low Fuel Consumptionand High Functionality of Composite Material
Products for Automobile, NTN TECHNICALREVIEW No. 85 (2017) 97.

Technical Article

Analysis of Dynamics of Hub Bearings under Moment Loads

Tomoya SAKAGUCHI*
Naoto SHIBUTANI*
Stiffness of hub bearings is an important factor for vehicle handlingstability. Analysis and measurements for the hub bearing stiffness havebeen done only under non-rotating inner ring conditions but not done
under rotating inner ring conditions. Hence, the authors have examined
the rotating hub bearing stiffness by using a bearing dynamic analysis
system “IBDAS”. This examination shows that rotating hub bearing
stiffness coincides with the nonrotating one and hysteresis, that is response delay, exists in displacement curves of
inner ring alignment angle against varying moment.

1. Introduction
Even as automated driving technology develops andcomputers control steering, vehicle handling stability
continues to be an important aspect. That is becauseeven with the most advanced computer system if thevehicle response to the steering signal is too slow, thenthe vehicle will have difficulty driving along the desired
path. On the other hand, the stiffness of hub bearings
that support the tires of the vehicle is one of the factorsthat affects vehicle handling stability1), 2). Therefore,
designing the stiffness of hub bearings appropriately is
an important subject.
In general, measuring stiffness of hub bearings
is done without rotating the shaft2). Although, it isexpected that stiffness with a rotating shaft does notdiffer from the static rigidity, it is not confirmed, yet.
To determine if this is valid, dynamic analysis of therelationship between the shaft rotation speed andstiffness of hub bearings was established using an
integrated dynamic analysis system “IBDAS”3), which
NTN has been developing for the analysis of roller
bearings4). In this article, the results obtained fromthese dynamic analyses are reported.

2. Product to Be Analyzed
A hub bearing consists of two rows of balls and acage, as shown in Fig. 1. The inner ring on the inboard
side is fixed to the hub ring and a certain axial preload
is applied to the balls. Therefore, in this report, therotation system configured with the double row angularcontact ball bearing specified in Table 1 is calculated.

The operating condition of the bearing is shown in
Table 2 and the load acting point and coordinate
system of analysis are shown in Fig. 2. This condition
assumes a hub bearing of a vehicle, which runs at aconstant speed where moment, axial load and radialload periodically change.
Hub bolt

Flanged outer ring

Hub ring

Inner ringCage/ball

Seal
Seal

Outboard side

Inboard side

Fig. 1 Example of hub bearings5)
Table 1: Bearing specification
Ball diameter (mm)11.1

Number of balls

16

Pitch diameter of ball set (mm)61

Contact angle (deg)35

Distance between rows of balls (mm)18.2

Preload (N)5,400* CAE R&D Center

NTN TECHNICAL REVIEW No.87

97

Analysis of Dynamics of Hub Bearings under Moment Loads

Table 2: Operation condition
Vehicle speed (km/h)

10, 50, 100

Moment (N mm)−600×103 - 600×103

Axial load Fa (N)−1,890 - 1,890

Radial load Fr (N)1,820 - 3,750

Load acting point (mm)10.4Load variation frequency (Hz)1, 10, 50

In order to dynamically analyze the motion of the ballbearing system with the above degrees of freedom,
normal force and tangential force at the contact between
the ball/raceway and the ball/cage must be appropriately
calculated. The following are the respective methods ofcalculation. In addition, moments of the balls generated byvarious forces are also calculated, as required.

3.1 Contact Point Between Balls/Raceway
Normal force is obtained assuming that the contactpressure follows Hertz Theory. In calculating tangential
force, the distribution of contact pressure on the major axisof the contact ellipse and sliding velocity are consideredas shown in Fig. 3 for an appropriate expression of
3-dimensional ball motion6). The specific calculating
method is as follows:
The normal load on one of the nth pieces sliced along
the major axis of the contact ellipse under hertzianpressure can be obtained by integrating the contactpressure along the direction of the minor axis, thenintegrating it along the major axis within the range ofthe particular sliced piece and can be expressed in thefollowing equation:

MomentOutboard side

Inboard side

Fig. 2 Load acting position and coordinate system ofanalysis

3. Method of Analysis
Temporal waveform of the inclining angle of theoperating hub bearing under moment load was
calculated using an integrated dynamic analysis
system “IBDAS”3), which is NTN’s proprietary
development for analysis of roller bearings.
The degrees of freedom of motion set for the
analytical model and the constraint conditions are
as shown in Table 3. The outer ring of the bearing isfixed in the space and the inner ring has degrees of
freedom of motion excluding rotation. The inner ring
was given the weight and the inertial moment of hub
ring. The balls and the cage have 3 translational and3 rotating degrees of freedom. IBDAS can take into
account the elastic deformation of the cage using themode synthesis method. This analysis gives a total of
56 deformation modes to each cage.
Table 3: Degrees of freedom of motion and constraint
conditions within the analytical model

98

Outer ring

Degrees of freedom: None (fixed)

Inner ring

Degrees of freedom: 3 translational, 2 rotating
Constraint: rotation at a constant speed

Ball

Degrees of freedom: 3 translational, 3 rotating

Cage

Degrees of freedom: 3 translational, 3 rotating
Elastic deformation: 56 modes

NTN TECHNICAL REVIEW No.87(1)

Where,
is the normal force acted on the th
is the normal force of the entire contact
section,area and is the section number (0 to n-1).

Slice

Outer ringContact ellipse

Ball

Contact surface
Direction of ball revolution
Center line of outer ring

Fig. 3 Calculation model of the contact area between ais the normal force actingball and outer ring (is theon the th section from the outer ring,sliding velocity of the th section of the ball against
outer ring)6)

For the tangential force, the following 3 types of force
elements, which can be assumed in the contact area
under oil lubrication, were considered.
1. Traction*1
2. Rolling viscosity resistance*2
3. Oil film force on the rolling direction*3

Where,
is the translational velocity vector of thecenter of the ball,is the angular velocity vectorof the ball,is the position vector from the centerof the ball to the th section surface, race is thetranslational velocity vector of the center of raceway,

Since hub bearings are lubricated by grease, thisreport assumed that the above 3 types of force elements
are determined only by the base oil of the grease. The
following is an outline of calculation of each force element:
Force acting on each section was calculated using
the following equation, assuming that it would act in the
opposite direction of the sliding velocity vector of the ballsurface against the raceway.

race is the angular velocity vector of the raceway,
and racecj is the position vector from the center ofthe raceway to the th section surface. The method for
obtaining the position of the section surface within thecontact ellipse is based on the Jones method9).
The sliding velocity vector of the section on the ball, has a component of the axial direction
surface,in addition to the rolling direction, as shown in Fig. 5.
Therefore, there is a force acting in the direction ofmajor axis of the contact ellipse.

(2)
Where
is the force acting on the ball,is thefriction coefficient and the subscript represents the thsection. The arrow on top means that it is a vector.
under
ﬂuid lubrication was obtained using the calculation
method that considers the property of lubricating oil7),
under boundary lubrication was obtained by afunction with only slide-roll ratio*4 andunder mixed
lubrication was obtained by interpolating between thosefriction coefficients proportionally to the film parameter8).
The friction coefficient greatly depends on the slideroll ratio even under ﬂuid lubrication, as shown in thecalculation example in Fig. 4.
0.1

Traction coefficient

0.08
0.06
0.04
0.02
0

0

0.005

0.01

Black: Sliding velocity component in the rolling direction
Blue: Sliding velocity component in the axial direction
Red: Sliding velocity vector

Fig. 5 Example of sliding velocity vector on the ball surface

The rolling viscosity resistance acts in the opposite
direction of rolling direction against the ball and the
raceway. Since it is the force from the lubricating
film, it was assumed that this only occurs under ﬂuid
lubrication where lubricating film is formed. And themagnitude of the rolling viscosity resistance FR was
obtained, using the equations for10), 11) the case ofhigh pressure viscosity elastic body range (PE) andhigh pressure viscosity rigid body range (PR). The
case of isobaric viscosity rigid body range (IR) is also
used selectively, depending on the result of the range
determination12).

0.015

Slide-roll ratio(4)

Fig. 4 Example of traction coefficient

The sliding velocity vector of the ball surface against the
raceway

was obtained using the following equation:
race

race

racecj(3)*1 On two objects in rolling/sliding contact, this is the tangential force which actson the opposite direction from the rolling direction at the higher speed side
and on the same direction as the rolling direction at the lower speed side.
*2 This is the force caused by shear force of oil film which acts in the direction
to prevent rolling of two objects in rolling contact, under oil lubrication.
*3 This is the force that acts on the rolling direction due to the oil film pressurethat acts on two objects in rolling contact under oil lubrication. This is
generated as the center of oil film pressure shifts to the upstream side.
*4 Sliding velocity of the contact surface divided by the average velocity of thecontact surface.

Where,
is the coefficient of thermal correction,is the effective radius,
is the material parameter,is the velocity parameter,is the load parameter,is the section width,
is the equivalent elastic
modulus and the subscript
refers to the section
where the contact pressure is the greatest.
The oil film force on the rolling directionwas
obtained using the following equation10) from the rollingviscosity resistance12).

NTN TECHNICAL REVIEW No.87

99

Analysis of Dynamics of Hub Bearings under Moment Loads

0.10

(5)
0.05

Inclining angle deg

Where,
is the radius from the rotational axis of
the ball to the th section of the contact area.
As the distribution of forces in the contact ellipse
and their 3D effect are put into consideration, thecalculation result of rotation and revolution velocity ofthe balls from IBDAS closely matches6) the calculation
result from Jones Theory9).

0.00

100 km/h-0.05

50 km/h
10 km/h

-0.10
-0.8

-0.4

3.2 Contact Point Between Balls/Cage

0.0

0.4

It was assumed that the normal force,, thatcorresponds to the interference amount, , isgenerated following the Hertz Theory meaning thesurface of the cage is divided into finite elements andthose nodes geometrically interfere with the balls.
(6)
Where,
is the non-linear spring constant in
the Hertz Theory.
In calculating tangential force, only force from sliding
friction was considered, as sliding is the only force
between the balls and the cage. Sliding friction force
was obtained by the following equation.

Fig. 6 Calculation result of the inclining angle of the innerring to the applied moment in each vehicle speed(load variation frequency: 50 Hz)

Fig. 7 shows the calculation result of the inclining angleof the inner ring on the applied moment, when the load
variation frequency is changed to 3 different levels withvehicle speed of 10 km/h. The slopes of the lines of theinclining angles of the inner ring on the applied moment
remain the same, revealing that the rigidity of hub
bearings does not depend on the load variation frequency.
0.10

(7)

0.05

Inclining angle deg

Where,
is the friction coefficient andis thesliding velocity vector of the ball surface against thecage pocket. For, 0.06 was used in this calculation.

0.00

1 Hz
-0.05

10 Hz

4. Calculation Result
Fig. 6 shows the calculation result of the inclining
angle of the inner ring on the applied moment in eachvehicle speed. The load variation frequency is 50 Hz.
It revealed that the waveform of the inclining angle ofthe inner ring on the applied moment has hysteresis.
It also revealed that the slopes of the lines for eachvehicle speed (compliance) are, although withhysteresis, the same. From these results, it was
revealed that the rigidity of hub bearings, which is
the inverse number of compliance, is also mutually
the same regardless of vehicle speed.

100

NTN TECHNICAL REVIEW No.87

0.8

Moment kNm

50 Hz
-0.10
-0.8

-0.4

0.0

0.4

0.8

Moment kNm

Fig. 7 Calculation result of the inclining angle of the innerring to each load variation frequency(vehicle speed: 10 km/h)

On the other hand, hysteresis is also observed in thelines of Fig. 7. The hysteresis of the inclining angle ofthe inner ring on the applied moment means that theincrease of lateral displacement of the body lags a little
behind the tire lateral force input from the ground. If lateraldisplacement of body against steering is considered, itmeans the peak of the lateral displacement appears alittle late. This reduces vehicle handling stability.
Therefore, the effect of driving conditions on themagnitude of hysteresis is determined by examining
the difference of the inclining angle at the moment
0.3 kNm. It is defined as the ﬂuctuation range, asshown in Fig. 8.

0.06

Inclining angle deg

Fluctuation range WH
0.04

PR
PF

e

0.02

ti

on

c
ire

of

ch

ge

an

D

Di

on

i

ct

re

0.00
0.0

Direction of change ofinclination of inner ring

g
an

h
fc

1 Hz
10 Hz
50 Hz

o

0.2

0.4

0.6

Moment kNm

Fig. 8 Definition of fluctuation range, which indicatesthe magnitude of hysteresis of inclining angle ofthe inner ring against the moment(Points PF and PR are used in Chapter 5)

Load variation frequency Hz

Fig. 9 shows the ﬂuctuation range of the inclining
angle of the inner ring when vehicle speed and load
variation frequency are both changed. As shown in Fig.
9, the ﬂuctuation range increased as the vehicle speed
reduced and the load variation frequency increased.

50

6.7

4.1

3.0

10

4.2

1.3

0.7

1

0.9

1.3

0.3

10

50

100

Vehicle speed km/h

Fig. 9 Calculation result of fluctuation range of inclining
angle of the inner ring against the moment
when vehicle speed and load variation frequency
are changed (bubble diameter is proportional tofluctuation range, numbers next to bubbles are
fluctuation range(deg/103))

5. Examination
The following discusses the mechanism of how
ﬂuctuation range,, affects the waveform of theinclining angle of the inner ring on the applied moment.
The reason for the ﬂuctuation range is shown in
Fig. 10. The force in the direction of the major axis of
the contact ellipse created between the ball and the
raceway hinders the movement of the ball in the radialplane. This mechanism is described below, focusing
on the forces that act on the upper right ball of Fig. 10.

Fig. 10 Overall concept of the normal force and tractionthat act on the balls from the raceway when the
inner ring inclines counterclockwise

The typical state of forces that act on the upper rightball of Fig. 10 is shown in Fig. 11. First, Fig. 11 a) shows
the state where the inner ring continues to rotate while theinclining angle of the inner ring remains constant. In thiscase, since the inner ring is rotating with the same inclining
angle of the inner ring, the center of the ball is positionedon the line that connects the centers of the grooves of theinner and outer rings. The normal forces,and,which act on the ball from the inner/outer rings are alignedon the same axis and remain balanced (here, the centrifugal
force is ignored for ease of explanation). The forces thatact on the ball from the inner/outer raceways act only in the
direction of the roller, not having the surface component in
the figure.
Fig. 11 b) shows the state immediately after the inclining
angle of the inner ring increases its magnitude in the
counter clockwise direction, where the ball transition is not
sufficient. In this case, the normal force,, from the innerring changes its direction as shown in the figure (here,, that acts on the ball from the inner ring is ignored
force,
for ease of explanation). The resulting force that acts on theball from the raceway will be toward upper left as shown in
the figure.
Immediately after this, the ball moves in the radialplane and the force that acts on the ball and the momentbalance out, as shown in Fig. 11 c). As the ball moves, themagnitude and direction ofandchange and theforces that act on the ball from the inner/outer rings,
and, start moving in the upper right direction. Due to theseforces, the center of the ball cannot move to the line thatconnects the centers of the inner/outer raceway grooves,
not as Fig. 11 a).
Next, a case where the inclining angle of the inner ring is
the same as Fig. 11 c), but the moment is decreasing and
NTN TECHNICAL REVIEW No.87

101

Analysis of Dynamics of Hub Bearings under Moment Loads

the inclining angle of the inner ring changes in the clockwise
direction is considered. Let us consider the case of PR as
the PF point in Fig. 8. The force that acts on the point PR canbe described in Fig. 12. Since the forces that act on the ballfrom the inner/outer rings act in the lower left direction, theball remains toward to lower left from the line that connects
the centers of the inner/outer raceway grooves. The angle ofalso becomes smaller. As a result, the magnitude of the
moment the ball induces on the inner ring is smaller thanFig. 11 c) meaning the moment at the point PR in Fig. 8 issmaller than the point PF.
As seen above, due to the forces acting in the major axis
direction of the contact ellipse, the center position of theball where the inclining angle of the inner ring cannot reachthe ball position where the inclining angle of the inner ringis constant. And this force produces the ﬂuctuation range ofthe inclining angle of the inner ring.
Center of outer ring groove

Center of ball

Change of inclining angle ofinner ring

Fig. 12 Normal force and traction that act on the balls
from the raceway when the inner ring inclines
clockwise

The ﬂuctuation range,, correlates with the magnitudeof the force in the major axis direction of the contact ellipsethat acts on the ball, as mentioned above. This magnitude
of force greatly depends on the slide-roll ratio as shown in
Fig. 4. The slide-roll ratio on the ball surface, , is a ratioof the sliding velocity on the ball surface,, over the
rolling velocity of the contact area,, and is given in thefollowing equation:

Center of inner ring groovea) Inner ring is rotating when inclining angle is constant(8)
For simplification, slide-roll ratio at the pure rolling
position (no sliding in the rolling direction) in the contact
area between the ball and raceway is considered. In
this case, the sliding velocity and the rolling velocity areproportional to the load variation frequency, load , andthe vehicle speed, , respectively. The slide-roll ratio, ,can be expressed as follows:
load

Resultant force

Change of inclining angle ofinner ring

Change of inclining angle ofinner ringb) Immediately after increaseof inclining anglec) A little after increase of
inclining angle

Fig. 11 Normal force and traction that act on the balls
from the raceway when the inner ring inclines
counterclockwise102

NTN TECHNICAL REVIEW No.87(9)

Therefore, it can be concluded that the increaseof load and decrease of
result in the increase of
the slide-roll ratio , friction coefficient , force and, which corresponds with theﬂuctuation range
trend in Fig. 9.
The above is a discussion of pure rolling position
within the rolling contact area. At the position where
sliding velocity exists in the rolling direction, thenumerator of Equation (8) includes the sliding velocity
component in the rolling direction which slightly
reduces the impact of load on . However, since thesliding velocity component in the major axis direction
increases, the forces in the major axis still increases.

References

6. Conclusion
The rigidity of hub bearings with inner ring rotation
was analyzed using the dynamic analysis system,
IBDAS. As a result, it was verified that the rigidityof hub bearings does not depend on the rotational
speed of the inner ring and variation frequency ofthe moment. It was also verified that the waveform of
the inclining angle of the inner ring over the varying
moment has hysteresis. The reason for this hysteresis
is because of the traction in the direction of major axisof the contact ellipse created between the ball andthe raceway. Increasing the load variation frequency
and decreasing the vehicle velocity (decreasing therotational speed of the shaft) increases traction in the
major axis direction of the contact ellipse, ultimately
increasing the hysteresis range.
The above hysteresis can be interpreted as thedelay of response of hub bearing angle to the changeof moment. In order to increase vehicle handlingstability, it is desirable to reduce this delay. We willcontinue further analysis using CAE technology todeveloping hub bearings with reduced hysteresis.

1) Eiji Funahashi, History of Hub Bearings and Recent
Technology, NTN TECHNICAL REVIEW, No. 70, (2002)
52.
2) Takayasu Takubo, Evaluation Bench Tests for Hub
Bearings, NTN TECHNICAL REVIEW, No. 70, (2002) 74.
3) Mariko Sekiya, Integrated Bearing Dynamic Analysis
System (IBDAS), NTN TECHNICAL REVIEW, No. 79,(2011) 119.
4) N. Shibutani, D. Imada, T. Sakaguchi, Dynamic
Characteristic of Moment Stiffness of Hub Bearing,
Proceedings of the 8th Asian Conference on Multibody
Dynamics, (2016).
5) NTN Corp. Hub Bearings Catalog, CAT. No. 4601/J.
6) Tomoya Sakaguchi, Mariko Izumi, Tomoya Nakamura,Toshiya Kimura, Masaharu Uchiumi, Dynamic Analysis
of Ball Bearings for Turbopumps Considering Forceand Moment due to Liquid Hydrogen, The 68th
Turbomachinery Society of Japan Conference in Okinawa(2012) 203.
7) Masayoshi Muraki, Yoshitsugu Kimura, Study on Traction
Property of Lubricating Oil (2nd Report), Journal of Japan
Society of Lubrication Engineers, 28, (1983) 753.
8) T. Sakaguchi, K. Harada, Dynamic Analysis of Cage
Behavior in a Tapered Roller Bearing, J. Tribol, 128, (2006)
604.
9) A. B. Jones, A General Theory for Elastically Constrained
Ball and Radial Roller Bearings Under Arbitrary Load andSpeed Conditions, Trans. ASME, J. Basic Engineering, 82,(1960) 309.
10) R. S. Zhou, M. R. Hoeprich, Torque of Tapered Roller
Bearings, J. Tribol., 113, (1991) 590.
11) L. Houpert, Piezoviscous-Rigid Rolling and Sliding
Traction Forces, Application: The Rolling Element-Cage
Pocket Contact, J. Tribol., 109, (1987) 363.
12) Tomoya Sakaguchi, Calculation Methods of Forces andCage Stresses in Roller Bearings, Doctoral Dissertation,
Nagaoka University of Technology Institutional
Repository (2018).

Photo of authors

Tomoya SAKAGUCHI

Naoto SHIBUTANICAE R&D Center

CAE R&D Center

NTN TECHNICAL REVIEW No.87

103

Award Winning Products
NTN received the 2018 “CHO” MONODZUKURI Innovative Parts and Components Award, and Mobility Components Award

Ultra Low Friction Sealed Ball Bearing for Transmission
Takahiro WAKUDA

1. Introduction“Ultra low Friction Sealed Ball Bearing forTransmission” was developed. This reduces friction ofan application by controlling the fluid lubrication with a
new design of a proprietary shaped seal lip.
This product received the Mobility Components Awardof the 2018 “CHO” MONODZUKURI Innovative Parts
and Components Award sponsored by MONODZUKURI
Nippon Conference and Nikkan Kogyo Shimbun, Ltd.
This breakthrough idea achieves both low torqueand long operating life simultaneously. The results ofthis study are based on an unprecedented unique seal
philosophy and verified through theory and experiments.

Tomohiro SUGAIThis long-life bearing has 5 times or more operating
life than a product with special heat treatment.
Developed product
Conventional non-contact type seal
Conventional contact type seal

Running torqueKatsuaki SASAKI

Reduction by

Measurement ofrunning torque

80%

0

20

40

60

80

100

120

Bearing temperature °C

Life under lubrication withforeign objects

95
90
80
70
60
50
40
30
20

140

Special heat
treatment(No seal)

Developed product(Standard heat treatment+ developed seal)

Standard heat
treatment(No seal)

105No peeling observed inany unit, suspended

LIFE(h)2. Structure
A general structure of the “Ultra Low Friction Sealed
Ball Bearing” is shown below:

Cross-section view ofthe developed productArc-shaped micro convexes(5 convexes are shown in the above cut view)

3. Features
The developed product has the following features:(1) Fluid lubrication seal (equivalent to open product)
Reduction of running torque by 80%(compared to contact type seal)(2) Longer operational life in comparison to productwith special heat treatment 5
times or longer bearing life
(compared to open product)(3) World’s highest seal circumferential speed
performance
Seal circumferential speed of 50 m/s or more(4) Sealing properties are equivalent to or better
than the conventional contact type seal
Prevention of penetration from harmful foreign
objects

4. Summary
The low torque seal has adoptied a new mechanism
design to produce a wedge film effect for the seal lip. This
creates a low torque equivalent to non-contact type sealed
bearings and long operational life that is better than the
products with special heat treatment. It exhibits excellent
seal durability, even under high rotational speed conditions.
This makes this contact type seal suitable for high-speed
rotation required by EV/HEV. It is less costly than the
bearing with special heat treatment. An active market
deployment is planned.

References
1) Tomohiro Sugai, Lubrication Mechanism of Low Friction
Seal of Ball Bearing for Transmission, NTN TECHNICALREVIEW 86, (2018) 78-83.
2) Takumi Fujita, Strategy of Rolling Contact Fatigue Life
Testing and Interpretation of Life Data, NTN TECHNICALREVIEW 84, (2016) 74-79.

Photo of authors

Note: “Open product” is a designation of open type bearing with no seal

The low torque equivalent to non-contact sealed
bearings was verified through analysis and experiment.
The optimum seal shape was developed to prevent
harmful foreign objects from penetrating into bearing.
104

NTN TECHNICAL REVIEW No.87

Katsuaki SASAKI

Takahiro WAKUDA

Tomohiro SUGAI

Automotive Bearing
Engineering Dept.
Automotive Business
Headquarters

Automotive Bearing
Engineering Dept.
Automotive Business
Headquarters

Advanced Technology
R&D CenterAward Winning Products
NTN received the Award for Excellence of the 28th Nikkei Global Environmental Technology Awards

Micro Hydro Turbine
Masatoshi MIZUTANI*

Fumihiko MATSUURA*

Tomomi GOTO*

Tomoya KAWAI**

Yasunari KANAMURA*

Hiroki MUKAI*

Kanta KIMURA*

Takashi ITO*
Kouji TATEISHI*

1. Introduction

3. Product Specifications of Typical Models

The Micro Hydro Turbine (Fig. 1) received theAward for Excellence of 2018 (28th) Nikkei Global
Environmental Technology Awards hosted by Nikkei
Inc. The Turbine starts generating power by simply
placing it in an existing water channel. It is very friendly
to the global environment and is contributing to SDGs
on a global scale. Features include a highly efficient
blade shape that captures water energy and ability
to increase generating power. This was evaluated byplacing multiple units in series or parallel in the samewater channel.

The model with the blade diameter of 90 cm
achieves a rated output of 1 kW when the flow rate is 2
m/sec (Table 1).
Table 1 Product specifications of typical models
Turbine type

Propeller hydro turbine for small water
flow

Generator type

Permanent magnet synchronous
generator

Blade diameter

60 cm, 90 cm, 130 cm

Rated power output
Recommended
water channel
Size/weight

1 kW (90 cm model at flow rate of 2 m/s)
Width 100 cm or more,
depth 100 cm or more
H 190 cm × W 230 cm* × D 170 cm, 170 kg* Varied depending on the width of water channel

4. SummaryFig. 1 Micro Hydro Turbine

2. Configuration
Fig. 2 shows the product configuration. It consists ofhigh efficiency blades which connects to a generator
and beams for installation on water channels. There
are two types of controllers for power generation,
one for charging batteries as an independent powersource and the other for connecting to the grid so thatgenerated power can be sold. This makes the productversatile to respond to broad market requirements for
power generation.

Existing hydro turbines in the market by othermanufactures require major construction work to create
different water levels. The issue with major construction
is its cost and damage to the environment. The NTN
Micro Hydro Turbine can be installed by simply placing
the unit on a water channel with the beams to fit thewidth of the water channel, which can solve the issue
construction causes to the environment. This unit canbe expected to be used in many fields by utilizing
agricultural and industrial water promoting local
generation and consumption of renewable energy.

References
1) Tomoya Kawai et al.: Micro Hydro Turbine, NTN
TECHNICAL REVIEW No. 84, (2016) 28-33.

Generator

Battery or
grid connection

2) Takashi Itou et al.: Grid Connectable NTN Micro Hydro
Turbine, NTN TECHNICAL REVIEW No. 86, (2018) 102107.

Photo of author (representative)
Strut
Support beamController
BladeFig. 2 Configuration of Micro Hydro Turbine* Engineering Dept., Green Energy Products Division** Business Promotion Dept., Green Energy Products Division

Kouji TATEISHI*NTN TECHNICAL REVIEW No.87

105

Our Line of New Products

NTN Portable VibroscopeThis Compact and light sensor unit enables measurement of vibration in various places*Magnet (accessory)
Power button

Vibration sensor

Thread size M6 (P = 1), depth 4 mm
Can be attached with glue or magnet (accessory)*

Features(1) Light and compact
The Sensor, power and WiFi wireless units are integrated into a single package(overall dimensions/weight: W 41 mm × D 36 mm × H 87 mm, 145 g).

(2) Easy measurement
This unit allows for smart devices that support iOS to measure vibration data.

(3) Determines abnormalities
Using OA and FFT methods the user is able to determine abnormalities of bearings via dedicated applications,
identifying damaged parts when abnormalities are detected.
Ease of use by graphic display of the measurement history and storage in the smart device allowing forcontinuous access to the condition of the equipment.

(4) Dust and water resistant
IP65 enclosure to assist with portable usage.

Application· Failure detection, vibration measurement, analysis and trend management of bearings

Support bearing forconveyor

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NTN TECHNICAL REVIEW No.87

Motor

Main spindle ofmachining centerOur Line of New Products“N3 N-CUBE,” Container Type Transportable Independent Power Supply
Power generation and storage devices by natural energy (wind, water and solar light)
for quick installation

Solar panel
Hydro turbine(1)Transportation/
installation

Battery Wind
turbineWind turbine setup(2)Open(3)Start power
generation

Concept model

Workflow from installation to start of power generation

Features(1) During an emergency response such as natural disasters, the provided space can be used as storage forsupplies or as a living space.
(2) Transportable independent power supply and storage unit with power generation by natural energy (wind, water,and solar light).
(3) Compact package of devices for easy storage(4) Quick installation and prompt start of power generation/supply

Standard specification
Product type

Application
・Power supply to
medical devices

12-feet container(L 3.7 m × W 2.4 m × H 2.5 m)

Means of
Truck, freight vessel and helicoptertransportation

MedicineWind turbine: 0.5 kW, hydro turbine: 1.0 kW,
Power devices solar power generator: 0.9 kW,
battery: 8.6 kWh
Installationtime

1 hour by 2 persons

Survival wind Wind turbine and solar power generator: 30 m/s*1,
speed/flowhydro turbine: 2 m/s*2
rate*1 Extreme wind speed *2 Maximum water flow

Food

Living・Power supply for cooking/storage equipment
・Supply of emergency
stock・Supply of drinking water

・Provide space・Power supply for
information devices
・Charging forsmartphones
・Power supply to toilets
and air conditioners

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