Special Issue;
Efforts for the Environment
December 2009ISSN 0915-0528 OSAKA, JAPANR

TECHNICAL REVIEW
No.77

corporation

Special Issue:
Efforts for the Environment

NTN TECHNICAL REVIEW No.77
CONTENTS

Yoshikazu FUKUMURA

Preface1● Activity for Reducing Environmental Impact
Initiatives for Environmental Conservation
Masakazu HIRATA and Noboru UMEMOTO

Approach on Environment by SNR
Didier SEPULCHRE DE CONDE and Jean-Hervé BULIT

2
10● Environment-responsive Production Engineering
An Approach the Reduction of Environmental Loads in the Material Processing
Akira SERA, Hisatsune SAITO, Kenichi NAKANO and Syunsuke MAKINO

Improvement the Work Environment with Factory Robot
Shigeki MATSUSHITA and Genji NAGURA● Environmentally-friendly Products and Technology
Market Trend of Wind Turbine and Bearing Technologies
Nobuyuki NINOYU, Souichi YAGI and Tsuyoshi NIWA

Eco-friendly Products Development SNR Roulements
Siegfried RUHLAND, Ludovic SAUNIER, Cynthia TSEN, Bernard LIATARD and Gérald MIRABEL

Actuator for Electromechanical Brake
Tatsuya YAMASAKI, Masaaki EGUCHI and Yusuke MAKINOElectric Ball Screw Actuator for Automotive
Yoshinori IKEDA and Hirakazu YOSHIDA

Plastic Bearings of Electric Pump for the Next Generation Cell
Norio ITOH and Takuya ISHII

Low-torque Roller Lifter Unit
Masashi NISHIMURA

Hub Bearing for Automobiles for Saving Resources
Isao HIRAI

V-series Hub Joint
Mitsuru UMEKIDA and Yuuichi ASANO

Extreme High Load Capacity Tapered Roller Bearings
Takashi UENO and Tomoki MATSUSHITANew Spherical Roller Bearings “ULTAGE” Series Type EA and EMYukihisa TSUMORI

Compact Free type Torque Diode
Shoji ITOMICharacteristics and Applications of DLC films
Kouya OOHIRA

Optimized Radius of Roller Large End Face in Tapered Roller Bearings
Hiroki FUJIWARA, Takashi TSUJIMOTO and Kazuto YAMAUCHI

Round-table talk

Advance and Future of Analysis Technology for Constant Velocity Joints

18
22

28
34
42
47
51
56
62
67
73
81
86
90
96

106

● Our Line of Award Winning Products"2009 'CHO' MONOZUKURI Innovative Components Awards" Encouragement Award

High Capacity Tapered Roller Bearing

110

Takashi UENO
"2008 'CHO' MONOZUKURI Innovative Components Awards" Automotive Component Award

Constant Velocity Steering Joint (CSJ)

111

Kenta YAMAZAKI"2008 Resource Recycling Technology and Systems" Encouragement Award

Development of Briquetting Machine and Accomplishment Recycling System for Steelmaking Dust

112

Shozo GOTO, Ikuo YAMADA and Katsutoshi MURAMATSU

Our Line of New Products

114

NTN TECHNICAL REVIEW No.77（2009）[ Preface ]To the New Issue Featuring Efforts
for the Environment

Yoshikazu FUKUMURAManaging Director

The concentration of greenhouse gases in the atmosphere has increased by about 30% since theonset of the Industrial Revolution. If the emission of greenhouse gases continues at this rate, the rise intemperature is expected to reach almost twice what it was before the Industrial Revolution by the end of
the 21st century.
At the end of 2009, the 15th United Nations Climate Change Conference (COP15) was held in
Copenhagen where medium and long-term reduction goals were discussed. In every country, efforts arebeing made to reduce greenhouse gases. Developments in electric cars and other next-generation
automobiles, solar and wind power generation, and other new energy fields must also be actively
advanced.
Given these circumstances, on July 1, 2009 we established a New Products and Intellectual Property
Strategy Department at NTN as a division that keeps future growth in mind. It is responsible for longterm business strategies that emphasize the global environment, energy conservation and resource
conservation in the fields of natural energy and electric cars, for example. In addition to utilizing ourcompany’s fundamental technologies, this department will promote collaboration between industry,
academia and government, as well as with different business fields. The department will also seek toaccelerate the development of new products for automobile parts and industrial machinery that meet therequirements of new energy fields, for example.
In our efforts at NTN, we are prioritizing the development of fundamental technologies with the goal of
reducing environmental burdens and the development of products that are considerate of theenvironment in our efforts at NTN.
With the protection of the global environment, the creation of a recycling-based society and theenhancement of environmental management systems as key issues, we are working to raise the levelsof our environmental management activities at our production facilities. In particular, we are making
great efforts to reduce CO2 emissions in our industrial activities.
In this publication, we introduce “Activities for reducing Environmental Impacts,” “Engineering that is
Responsive to the Environment” and “Environmentally-Friendly Products and Technologies” of NTN and
SNR, a company that has joined the NTN Group and is headquartered in France. After a roundtablediscussion with Dr. Kimata, a former NTN director, ” we also introduced three developed products thathave received prizes in the current and previous fiscal year (two ‘CHO’ MONODZUKURI Innovative
Components Awards and one Resource Recycling Technology and Systems Encouragement Award).
The NTN corporate philosophy is “For New Technology Network: Our contribution to the global
community lies in our creation of new technologies and development of new products.” In our new “NTN2010 for The Next Step” medium-term management plan for the next two years from April 2010, we willseek to realize a management core that is not dependent on scale. In order to achieve “harmony withthe global environment,” we will promote the development of products that are better for theenvironment and contribute to the sustainable development of society.

-1-

NTN TECHNICAL REVIEW No.77（2009）[ Technical Article ]Initiatives for Environmental Conservation

Masakazu HIRATA*
Noboru UMEMOTO*At NTN, we have been conducting our corporate activities basedon the NTN Environmental Policy and seeking harmony with theglobal environment through systematic and continuous initiatives
to reduce impacts on the environment. In this article, we introduce
our efforts to reduce CO2 in manufacturing and other efforts for theenvironment in research and development, as well as in ourcontributions to society.

At NTN, our entire group is working together toreduce the emissions of CO2 in order to prevent global
warming and decrease the production of waste.
Bearings and constant velocity joints, which reduce theamount of energy loss caused by friction, arefundamentally green products, These products are also
contributing to the preservation of the environment
through their application in fields such as wind power
generation, which uses natural energy, and rollingstock, which is a green means of transportation. When
we build new factories, we are effectively using naturalenergy through the incorporation of solar power
generation and wind power generation, and adopting
manufacturing processes that include environmentallyfriendly manufacturing methods that eliminate the useof oil. We are also building more compact productionlines and reducing waste through the installation ofgrinding sludge briquetters. As a result of these efforts,
we are establishing factories that are considerate ofand good for the global environment.
In ;past publications, we have primarily introduced
our new products and technologies. Recently,
however, preservation of the global environment andthe depletion of petroleum energy resources havebecome major concerns. For these reasons,businesses are also expected to reduce theiremissions of greenhouse gases and adopt activities
that are good for the global environment. In thisarticle, we explain NTN’s efforts for the environment,
focusing on our efforts to reduce CO2 emissions inparticular.

1. Fundamental environmental
policies and goals
We have established the NTN Environmental Policy(Table 1), making “harmony with the global
environment” the top priority of our company, and weare advancing efforts to preserve the environment withthe following four policies as guides for our activities.
i) Develop and sell products that are good for theenvironmentii) Reduce impacts on the environment: work to
improve energy efficiency and carefully manage
substances that have environmental impacts inevery aspect of our business, from manufacturing to
distribution and sales, in order to reduce impacts on
the environmentiii) Build comprehensive systems for legal complianceand environmental managementiv) Contribute to society and protect the naturalenvironment
In order to advance and realize this environmental
policy, we have built an environmental management
structure for our entire group that is centered on our
Companywide Environmental Management
Committee. We are setting environmental targets
every year for three areas—preserving the global
environment, creating a recycling society, andmaintaining and improving environmental
management systems (Table 2), and we areadvancing our efforts for the environment as planned.

*Innovation and Intellectual Property Strategy Headquarters Environment Strategy Dept.

-2-

Initiatives for Environmental Conservation

Table 1 NTN Environmental Policy
At the NTN group, we make harmony with the global environment our top priority, and we are continuously reducing
the impacts on the environment caused by our business activities. We are also striving to constantly contribute to thesustainable development of society.
1. Develop and sell products that are good for the environment¡We will utilize high-precision manufacturing and tribological technologies and develop environmentally-friendly products.
By providing these products to society, we will also contribute to promoting energy conservation around the world.
2. Reduce impacts on the environment¡As we strive to help prevent global warming, we will seek to improve energy efficiency in every aspect of our businessactivities, from the procurement of raw materials, parts and other goods to manufacturing, distribution and sales.
¡We will focus on the effective use of resources and strive to reduce waste by thoroughly implementing the 3Rs (reduce,reuse, recycle).
¡In addition to comprehensively managing substances with environmental impacts that are used in products andmanufacturing processes, we will actively seek to replace chemical substances that are suspected of being harmful withalternative substances, and we will strive to prevent pollution of the environment.
3. Build comprehensive systems for legal compliance and environmental management¡Starting with a foundation of strict compliance with laws and regulations, we will also establish and abide by voluntarystandards and in-house regulations that are more stringent in order to respond proactively to the needs of communities
and our customers.
¡In addition to preparing systems and operation methods for environmental management, by conducting environmental
audits we will seek to maintain and improve our environmental management systems. In addition, we will publicize
information about the status of our efforts toward the environment and promote communication with the public.
¡Through environmental education, internal bulletins and other efforts, we will seek to make every person working at an
NTN location aware of our Environmental Policy, and we will seek to increase their awareness of environmental
protection.
4. Contribute to society and protect the natural environment¡By actively participating in programs that contribute to local communities and support efforts to protect the naturalenvironment, we will promote interaction with neighboring communities and reduce our environmental impact.

Table 2 Environmental targets in fiscal 2009 and fiscal 2010

Maintaining and improving
Creating a recycling
environmental management systems
organization

Preserving
the global environment

Goal
Reduction of
CO2 emissions

2009 fiscal year targets¡Total CO2 emissions: 250,000 tons/year¡Total CO2 emissions: 317,000 tons/year¡CO2 emissions per basic unit: –8% compared to FY1997¡CO2 emissions per basic unit: –25% compared to FY1997

Overseas ¡CO2 emissions per basic unit: +3% compared to FY2006¡CO2 emissions per basic unit: –15% compared to FY2006

Japan¡Conversion from halon to CO2 fire extinguishers: 70 units(54 unchanged units at the end of FY2009)

Prevention of air,water and soil
pollution2010 fiscal year targets

Japan ¡Reduction in the handling of substances subject to the
PRTR Law: –38% compared to FY2006¡Soil testing and purification after the closing of our
Takarazuka facility¡Elimination of all halon fire extinguishers¡Reduction in the handling of substances subject to the
PRTR Law: –40% compared to FY2006¡Compliance with the revised Soil Pollution Countermeasures Law

Participation in efforts¡Promotion of local revegetation efforts
to protect the naturalJapan(corporate forest stewardship, etc.)
environment
Reduction ofwaste production

Japan¡Advance zero emissions: seek a recycling rate of 99.5%¡Advance zero emissions: seek a recycling rate of 99.5%¡Reduce landfill waste to 25 tons/month or less

¡Reduce landfill waste to 25 tons/month or lessOver- ¡Advance zero emissions: seek a recycling rate of 96.3%
seas¡Weight of purchased paper: –50% compared to FY1998¡Reduce styrene foam: –92.4% compared to FY1999¡Reduce styrene foam: –96.1% compared to FY1999

Japan

Internal systems

Japan¡Prepare system for the acquisition of certification atOvernew locations
seas

Promote green
procurement¡Enforce thorough compliance with our green procurement
standards in our supply chain¡Handle investigations of substances with environmental
impacts reliably (begin the application of a REACHJapan
compliant system)¡Advance auditing of substances with environmental impacts(internal auditing, auditing of suppliers)¡Continue inspection of incoming materials

Promote environmental¡Support supplier efforts to obtain ISO14001 and similar
management in ourJapancertifications: 90% certification rate
supply chain
Japan¡Achieve zero emissions: seek a recycling rate of 98.3%¡Weight of purchased paper: –46.2% compared to FY1998

Preservation of
resources

Comply with new laws
and regulations−¡Revised Law Concerning the Rational Use of Energy,
revised PRTR Law-3-¡Acquire ISO14001 certification at all locations worldwide−¡Certification of all suppliers−

NTN TECHNICAL REVIEW No.77（2009）

established a plan to reduce the CO2 emissions of all
our locations by about 20,000 tons, which isequivalent to about 6% of our total emissions in the2007 fiscal year.

2. Efforts for the environment in our
production activities
The majority of our efforts toward our environmental
targets, including preservation of the global
environment and creation of a recycling society, occur
at our production sites. In this article, we introduce ourefforts for the environment in our production activities,
focusing on efforts to reduce CO2 emissions inparticular.

[Changes in the amount of CO2 emissions andthe basic unit]
We can say that the basic unit of CO2 emissions for
our Japanese locations by fiscal year tended todecrease, and our energy efficiency, which affects
CO2 emissions, had been improving annually through2007. The basic unit for the 2007 fiscal year was 1.46,
which was an 18% improvement compared to the1997 fiscal year, so we achieved our target.
Between the 2003 and 2007 fiscal years, our CO2
emissions continuously increased each year as we
also increased our production volume. However, in the2008 fiscal year, as a result of the rapid decrease inproduction from the second half of the fiscal year, thebasic unit increased because our energy use did not
decline correspondingly with production volume.
Our CO2 emissions and energy consumption by
power source for the 2004 and 2008 fiscal years areshown in Figs. 2 and 3, as well as Table 3. These
illustrations make clear that the majority of our CO2
emissions are the result of the use of electric power,
and that the amount resulting from oil use decreased
from the 2004 fiscal year to the 2008 fiscal year.
Compared to the 2004 fiscal year, kerosene use
decreased, while natural gas use doubled in the 2008
fiscal year (Table 3). The use of thermal processing
furnaces and other fuel conversion, as well as thereplacement of air conditioning equipment, were thecauses of this switch from kerosene to natural gas andelectricity.

2.1 Efforts to reduce CO2 emissions
At the Third Conference of the Parties (COP3) of
the Framework Convention on Climate Change held in
1997, when consensus was reached on numerical
CO2 reduction values for each country, considerationin Japan about efforts for countermeasures against
global warming began immediately. The JapaneseFederation of Economic Organizations established avoluntary environmental action plan for industry in
1997.
At NTN, we have participated in this voluntary
environmental action plan and the CO2 emissions
targets set by the Japan Bearing Industrial
Association, which set the target basic unit* foremissions for the 2010 fiscal as 13% less than that of
the 1997 fiscal year. We voluntarily set an even higher
reduction target of 25 in an effort to further reduce
CO2 emissions.
* The basic unit is the total amount of CO2 emissions (in tons)
per million yen of added value of production.

The first commitment period of the Kyoto Protocol
began in 2008, and the importance of setting targets
for total CO2 emissions has increased. The CO2
emissions for our corporate group have increased
yearly, but in March 2008 we added a target for the
total emission of CO2 from our locations in Japan.
The CO2 generated by our group is the result of our
production activities. In order to achieve our target for
total emissions, in April 2008 we initiated a CO2
Reduction Project to investigate the potential to further
reduce CO2 emissions from our factories and initiate
efforts to do so. The activities of this project wereconducted for one year, and included the acquisitionof information about the latest energy conserving
technologies and their incorporation, the exchange of
information about examples of improved energy
conservation and the incorporation of conservationequipment being undertaken at each manufacturinglocation, as well as the discussion of such
implementation plans at other locations. Additionally,
we examined the thermal processing furnaces of othercompanies and invited outside experts to introduce
technologies to us. Based on these efforts, we

Emission amounts(in units of 10,000 tons)

Basic unit
(tons of CO2 per million yen)
2.0

60.0
45.0

1.5
Emission amounts
Basic unit

2008

2007

2006

2005

2004

2003

2002

0.0

2001

0.0

2000

0.5

1999

15.0

1998

1.0

1997

30.0

Year

Fig. 1 Change in total CO2 emissions and CO2
emissions rate (At operating sites in Japan)-4-Initiatives for Environmental Conservation

We will describe examples of energy conservation
improvements that we have implemented as a resultof these efforts, as well as examples of our own
independent efforts.
At our Iwata Works in 2006, in addition to installingin-house power generation equipment, we are alsousing a pipeline (Fig. 4) to carry the hot water emitted
by this equipment to our constant velocity joint factory.
Through heat exchange, we are able to heat thefacility in the winter, for example, reducing CO2
emissions by about 1,500 tons in a single winterseason. We have also been able to reduce the fuelcosts from using kerosene boilers.
In 2008, through an energy service company(ESCO), we undertook the replacement of an air
compressor with the latest model of turbo compressor(Fig. 5), as well as adopted a system to control thenumber of units and an intake cooler. We also
implemented countermeasures for air pipe leaks andimproved air flow. As a result of these efforts, wepredict CO2 reductions of 4,000 tons per year startingin the 2009 fiscal year.

Oil, 8%Gas, 12%

Total CO2
emissions:
310,000
tons/year

Electricity, 80%

Fig. 2 CO2 emissions by power source (2004)
Oil, 6%
Gas, 13%

Total CO2
emissions:
310,000
tons/year

Electricity, 81%

Fig. 3 CO2 emissions by power source (2008)
Table 3 Energy consumption by power source
Type of energy

2004 fiscal year

2008 fiscal year

Electricity (GWh)

510

520

LPG
Butane (tons)
Gas
Propane

7,310

6,810

Natural gas (km3)

3,220

6,330

Heavy oil (kL)

3,520

2,620

Kerosene (kL)

4,250

2,590

Gasoline (kL)

160

160

Light oil (kL)

130

130

Oil

Fig. 4 Wastewater pipeline and heat exchanger
at Iwata Works[Efforts to reduce CO2 emissions at production
plants]With the goal of reducing CO2 emissions caused byour production activities, since 2005 we havecontinuously received energy conservation
diagnostics assisted by the New Energy and Industrial
Technology Development Organization (NEDO) toreceive advice about problem points and proposals for
significant reform measures from the perspectives ofexperts. With this guidance, we have been draftingenergy conservation improvement plans.

Fig. 5 High-efficiency screw compressor at Iwata Works-5-

NTN TECHNICAL REVIEW No.77（2009）

At our Kuwana Works, we are advancing theconversion to natural gas as the fuel used for heat
treatment facilities. We made the conversion of 22
facilities in 2005, reducing the amount of CO2
generated due to heat treatment by about 10%. We
are continuing this fuel conversion at present.
At our Okayama Works, in 2008, we received a
grant from the Ministry of Economy, Trade andIndustry (2008 Leading Model Business for the
Adoption and Popularization of Load Leveling
Equipment). We used this to install a new thermal airconditioning system (Fig. 6). We also replaced aconventional absorption water cooler and heater thatwas powered by kerosene with a high-efficiency
electric turbo refrigerator. By using these with athermal storage system that uses electricity late atnight, which makes for operation that is even more
efficient and as inexpensive as possible, we are able
to achieve both CO2 and cost reductions. By using
clathrate hydrate slurry, which is a thermal storage
medium that has twice the thermal storage capacity ofwater, we have increased thermal storage efficiency
and reduced energy use in the transportation of themedium. By incorporating this system, we expect toreduce CO2 emissions by 1,000 tons per year.
In 2008, NTN Kongo Corporation received a grantfrom the Ministry of the Environment, and installed
high-efficiency equipment, including air-conditioning(Fig. 7), lighting, compressors and air blowers at its
four factories through an ESCO business. As a part ofreceiving subsidies for these projects, we joined theMinistry of the Environment’s voluntary Domestic
Emissions Trading System in the 2009 fiscal year, andwe have agreed to a CO2 reduction target of 3,000
tons per year.
To increase energy conservation in lighting, in 2007
we replaced 185 mercury lamps with high-efficiency
metal hydride lamps in the heat treatment plant of our
Kuwana Works (Fig. 8), resulting in a reduction of 185
tons of CO2 per year. At NTN Casting Corp., we
installed inverter fluorescent lamps and made otherefforts to increase the efficiency of the lighting there.
By doing this, we have reduced CO2 emissions by 690
tons per year. At Hikari Seiki Industry Co., Ltd., in2007 we replaced all the existing lighting within thefactory with inverter fluorescent lamps, which arebrighter and better for the environment, resulting in a
reduction of the total number of lamps from 520 to 392
and increased efficiency.
At every NTN location, we are also implementing air
leak countermeasures (Fig. 9). Through the utilizationof leak detectors, we are conducting regularinspections of air pipes for leaks and making
improvements as necessary.

Fig. 6 A thermal storage tower for the new air
conditioning system installed at Okayama Works

Fig. 7 Turbo refrigerator and cooling tower for the airconditioning system at NTN Kongo Corporation

Fig. 8 Metal hydride lamps at a heat treatment plantof Kuwana Works

Fig. 9 Check by air leak detector-6-Initiatives for Environmental Conservation

Through the combination of large-scale energy
conservation improvements and small-scale energy
conservation activities, we are striving to reduce CO2
emissions at NTN.

development divisions, in cooperation with ourbusiness partners, are now advancing thedevelopment of materials that do not contain thissubstance.

2.2 Waste reduction and resource preservation

2.4 Environmental Guidelines for theconstruction of new factories and structures

In order to reduce waste products, we are seeking
to achieve a final target rate of 100% recycling, andwe are promoting the recycling of resources. In the2008 fiscal year, our results were mixed as we
achieved a recycling rate in Japan of 99.6%, which ishigher than our target of 99%, but we failed to achieve
our reduction target overseas. At the same time that
we are reducing the production of waste, we are also
advancing the development of recycling equipment. In
the 2008 fiscal year, the technology for “thedevelopment of a briquetting device for dust from ironand steel and the creation of a recycling system” that
we developed jointly with Daiwa Steel Corporation, an
electric arc furnace manufacturer, received an
encouragement award for Resource Recycling
Technologies and Systems from the Clean Japan
Center, which is a foundation that is affiliated with the
Ministry of Economy, Trade and Industry.

We have established guidelines for the constructionof new factories and structures in order to contributeto the prevention of global warming by reducing CO2
emissions and with the goal of reducing energy costs.

[Environmental Guidelines](1) Use solar and wind power generation to provide
electricity for offices and kitchens (Fig. 10)(2) Adopt all-electrical kitchens and EcoCute energyconserving hot water supply equipment(3) For office buildings, plant vegetation on roofs andinstall film that reflects light and heat on windows(4) Ensure that building roofs have heat reflecting
paint or two layers(5) Use lighting with motion sensors in places where
people pass infrequently and there are no safetyconcerns(6) Utilize natural light(7) Ensure the use of use stratified (displacement) airconditioning systems(8) Use air-conditioning systems with thermal storage
that take advantage of low outdoor temperaturesand low electricity costs at night(9) Investigate the incorporation of in-house power
generation systems that use natural gas and theuse of the excess heat generated by such
equipment (in cases where heat-use needs arehigh and natural gas infrastructure is available)(10) Prohibit the use of incandescent light bulbs (useinverter florescent lamps and compact fluorescentbulbs)

2.3 Promotion of green procurement
We have established Green Procurement
Standards, and we are striving to protect theenvironment and improve the environmental
performance of our products in cooperation with ourbusiness partners. In order to comply fully withregulations and laws related to substances withenvironmental impacts, including the RoHS and ELV
directives and the REACH regulations of theEuropean Union (EU), we have created systems forthe analysis of incoming parts and materials, andspecialized internal auditing systems for substanceswith environmental burdens.
The EU’s REACH regulations, which came into
effect in June 2007, require manufacturers andimporters to register and evaluate the safety of all
substances, compounds and chemicals that are
known to be emitted from products that are to be usedin the EU. At our group, we have prepared a list of 19
chemicals that are included in grease and otherproducts that we export to the EU in amounts of one
ton or more annually, and we confirmed that the
manufacturers of all the raw materials conductedpreliminary registration. 15 substances of very highconcern (SVHC), which are substances that are
carcinogenic or bioaccumulative, were listed by theEuropean Chemicals Agency in October 2008. Since
one of these substances, phthalate ester, has been
contained in rubber tools and CVJ boots, ourFig. 10 Wind power generator at the first factoryof NTN Mie Corporation-7-

NTN TECHNICAL REVIEW No.77（2009）(11) Prohibit the use of mercury lamps (adopt the useof high-efficiency metal halide lamps)(12) Prohibit the running of vending machines at night(install timers)(corporate forest) where people can interact withnature. At our Okayama Works as well, we signed a
Kigyo to kyodo no mori zukuri (public-corporate forestplanting) agreement with Mimasaka City, Okayama
Prefecture in August 2008. For five years until March
2013, we are being allowed to borrow about 3.5
hectares of forests owned by the city, and we areadvancing efforts to improve the forest there as an
NTN Kigyo No Mori. At both of these Works, we havebeen undertaking efforts to preserve forests incooperation with local governments until now, but withthese agreements, we are further expanding the scaleof our activities. These restored forests will provide
places of comfort not only for local residents, but theyshould also allow our employees and their families
good opportunities to interact with nature.

3. Efforts for the environment in thedevelopment of products
Bearings, constant velocity joints and our othermain products make great use of tribological
technologies. They serve to reduce friction and wear
in rotating parts and the parts that transmit force fromrotation. As such, these can be said to beenvironmentally-friendly products or “green” goods.
In other articles in this journal, we introduce highefficiency CVJs and DLCs that are the fruits of ourfriction reduction technologies, resource-conserving
hub bearings that utilize our technologies fordesigning to conserve resources and otherenvironmental products and technologies.
As indicated in the previous section, the eliminationof substances with environmental impacts from our
products is an important issue. We have alreadyachieved compliance with the RoHS and ELV
directives, so now we will rapidly advancecountermeasures for the substances of very highconcern (SVHC) defined in the REACH regulations.
In the future, it can be said that the most important
issue from the perspective of product development isthe extent that we can reduce environmental impact
caused by products in their manufacture, use anddisposal. From the development stage we will strive to(1) design to suppress the generation of CO2 in the
manufacturing process, (2) design to reduce material
loss, (3) reduce the quantity of rare metals used, and(4) decrease energy loss during use (conserve
energy). As a part of these efforts, we have begun topromote life cycle assessment (LCA), which is amethod of quantitative evaluation. We are currently
investigating manufacturing processes, but the next
step can be thought to be LCA evaluation of products
when they are in use.

5. Conclusion
At NTN we are focusing our abilities onenvironmental preservation in everything frommanufacturing processes to products themselves,
including their distribution, use and disposal. When weare building new factories and facilities, we make theincorporation of natural energy, including solar andwind power, a fundamental policy. We are actively
incorporating natural energy as one means of
reducing CO2 emissions. In the 2008 fiscal year, weinstalled 94-kW of solar power generation equipmentat our Kuwana Works (Fig. 11) and 62-kW at our Mie
Works. So far, we have installed 10 solar power
generators, 14 wind power generators and 13 hybrid
generators that combine wind and solar power.
Together, these generators save the equivalent of 290
tons of CO2 emissions per year (Fig. 12).
At NTN, our dream is to use the power of the wind
and the sun to manufacture bearings, and provide
bearings that conserve resources and energy to thegreatest extent possible. We will continue our daily
efforts to reduce environmental burdens in everythingfrom manufacturing processes to the products
themselves, including their distribution, use anddisposal.

4. Efforts to contribute to society
At every NTN location we are promoting efforts tocontribute to society in cooperation with local
communities.
One such effort is tree-planting. For example, at our
Iwata Works, we agreed in July 2008 to join the
Shizuoka Mirai No Mori Supporter (supporters of
Shizuoka’s future forests) system with the Iwata Cityand Shizuoka Prefecture. In this system, we areundertaking activities at an NTN Kigyo no mori-8-Initiatives for Environmental Conservation

Fig. 11 Solar power generation system at Kuwana Works

700

Cumulative output kW

600

Cumulative natural energy

500
400

Solar

300
200

Wind power

100
0
2003

2004

2005

2006

2007

2008

Fiscal year

Fig. 12. Natural energy output

Photo of authors

Masakazu HIRATA

Noboru UMEMOTO

Innovation and Intellectual
Property Strategy Headquarters
Environment Strategy Dept.

Innovation and Intellectual
Property Strategy Headquarters
Environment Strategy Dept.

-9-

NTN TECHNICAL REVIEW No.77（2009）[ Technical Article ]Efforts for the Environment by SNR

Didier SEPULCHRE DE CONDE**
Jean-Hervé BULIT**

When we think about it bearings are present everywhere in our daily
lives, from household appliances to aerospace applications not tomention in the automotive market. By reducing the energy needs ofmany things around us, bearings play a major role in supporting
sustainable development. Since 1994, at SNR Roulements, we haveintegrated environmental concerns into our development.
Environmental policy is a major focus for SNR Roulements for not only
ecological reasons, but also for economic and image reasons. That is
why our environmental policy is being implemented from our head office
down to all our workshops and suppliers.

1. EMS of SNR

2. Corporate organization

Since its foundation, SNR has kept an establishedISO 14001-complying environmental management
system (EMS) for its all operation sites. This EMS isbased on a particular portion of the quality
management system of SNR commonly applicable tofunctions and business operations (documentation,
education, audit management, etc.).
This EMS is the very basis of the environmental
policy of SNR, and SNR wishes to fulfill its
environmental objective through continued
improvement activities according to the basic principleof PDCA (Plan, Do, Check, Action). The corporate
annual guideline of SNR is established according to its
environmental policy, guidance for its shareholders,possible environmental impacts resulting from its
business activities, new ecology-related legal
regulations, and results of internal and external audits.
This annual guideline constitutes the basis forplanning with all the SNR operation sites, thereby
SNR is maintaining follow-up activities for progress
and performance of projects by referring to various
indices.
Since 1999, all the SNR operation sites have beenregistered as “multi-sites” defined in ISO 14001,
where the latest update took place in 2008.

In SNR, the Environmental Management Division
belongs to the Quality Management Department, andis under the directly supervision of the President. Fig.
1 schematically illustrates the organizational chart of
the Environment Management Division of SNR.
In each SNR base within France, a responsible
engineer functioning as an environment manager is
responsible for smooth operation of EMS in his/her
site, by enhancing knowledge about his/her specialty
and expanding the scope of his/her role andresponsibility.
SNR Annecy Head Office & Plant includes a
production plant and research division for bearing
products, product and machine test center, including a
production engineering division and an engineering
service division (including laboratory and precision
measurement center). In each division, the “ecology
promoter” as a coordinator plays the role of “operationsite environment manager”.
In SNR overseas operation sites, the responsibility
about environmental issues is assigned to quality
managers.
The “Environment Manager in the Head Office”
chairs the regular meetings in which environment
managers from all the SNR operation sites participate.
He/she always checks that the operation and activities
about SNR EMS are executed as planned.

**NTN-SNR ROULEMENTS President**NTN-SNR ROULEMENTS Environment Div. Manager-10-Efforts for the Environment by SNR

SNR has developed excellent environmental system
tools (environmental database, dedicatedenvironmental analysis software, and ecology-related
legal regulations monitoring software), and has beenutilizing these tools to support its routine
environmental analysis activities and help implement
common use of its environmental data by all theoperation sites.

3. Production of bearings and resultant
environmental impacts
Fig. 2 schematically illustrates factors in bearing
production activities that can lead to environmental
impacts.
As a result of investigation at each SNR operation
site, the following aspects of the bearing production
process that may lead to environmental impacts havebeen identified:qEnergy consumption resulting from production
activities and building heating
qConsumption of water and chemical substancesused for production process and coolant supply or
chilling equipment
qRelease of evaporated water and volatile chemical
substances into atmosphere
qSolid waste typically occurring from turning andgrinding processes
qWastewater from rinsing machine; waste liquid
associated with the production process or process
liquidQuality Management Dept.
Assistant
Quality
Management
System Div.

Customer
Quality Div.

EnvironmentDiv.

Division Chief Meeting

Production
plant

Quality &Environment Div.

Environmental
Technologies

Ecology
Promoter

Ecology
Promoter

Ecology
Promoter[Steps in Bearing Production Process](1) Production of bearing rings through forming ofblanks (tubes or bars of particular lengths) bymachining or press process(2) Heat treatment(3) Grinding, and super-finishing(4) Assembly (bearing ring, rolling elements, andcage)(5) Prefilling with grease or fitting of seal, depending
on bearing type.

Person Responsible in Each Base

Ecology Promoter(doubles as Quality Manger)

Fig. 1 Organization of SNR Environmental Management
Department

Impacting Factors

Resources

Atmosphere

Steel material: 1.27 kg
Energy: 3.65 kWh
Electricity: 3.03 kWhNatural gas: 0.62 kWh
Water consumption: 3.38 L* Others: 0.12 g

Evaporation

1 kg of bearing product

Waste
Water
Industrial waste (hazardous): 0.18 kg
Grinding sludge: 0.07 kg
Industrial waste (non-hazardous): 0.07 kg
Metal waste: 0.32 kg

Industrial wastewater: 0.21 L
Sanitary sewage: 0.9 L* Others: Examples include grease, seal, resin, coolant, and rinse liquid.

Fig. 2 Environmental impacts-11-

NTN TECHNICAL REVIEW No.77（2009）

past several years. Fig. 4 provides the type of basic
unit for energy consumed for building heating at SNR
as well as the trend in energy consumption for building
heating at SNR over past several years.

4. Reduction in energy consumption
Typical examples of energy consumption reduction
efforts of SNR are as follows:(1) An existing conventional air-compressor has been
replaced with a high-efficiency screw-type aircompressor; the compressed air line is inspected
for air leakage at regular intervals (Meythet Plant).
(2) An exhaust system has been installed in a facility
where oil mist of higher concentration was present.
During winter in particular, fresh air is supplied to
the workplace, thereby significantly improving theenvironment of the work station. As a result, theoverall electricity consumption previously needed
for the exhaust system in the entire works as well
as boiler gas consumption have been reduced
considerably (Meythet Plant).
(3) Improved employee awareness for reduction inenergy on idle or inactive equipment (all SNR
plants and offices).
(4) Two aged fuel-firing boilers have been replacedwith one novel gas-firing boiler, thereby improving
the environment in the workplace and reducing theenergy consumption (Annecy Head Office-Plant).
Fig. 3 shows the type of basic unit for energy
consumed for processing in SNR as well as the trend
in energy consumption for processing in SNR over

5. Reduction in CO2 emissions
To be able to assess the contribution of SNR’s CO2
emissions reduction efforts to mitigation ofgreenhouse effect, we have translated the amounts ofour energy consumptions in electricity, oil and gas into
corresponding “CO2 emissions”.
In terms of CO2 emissions, the reduction in energies
consumed by SNR is equivalent, if its production
output remains unchanged, to approximately 3,400
tons reduction in CO2 emissions. Please note that thisreduction is limited only to the SNR operation sites inFrance. Fig. 5 graphically plots the trend in CO2emissions at SNR over past several years.

CO2 emissions Tons

17000
16000
15000
14000
13000
2005

2006

Basic unit MWh/kO

0.76

2007

2008

Year

Fig. 5 Discharge of CO2

0.74

0.72

6. Reduction in water consumption

0.7
2005

2006

2007

Year

Typical efforts so far made by SNR in reducing
water consumption are presented below:(1) A certain portion of the aged water-cooled salt bathheat-treatment plant has been replaced with a newhardening plant, and for the remaining portion of
the existing heat-treatment plant, the rinsing
system situated downstream the heat-treatment
process has been modified into an overflow
design, thereby reducing water consumption(Annecy Plant).
(2) A new cooling tower has been introduced into thecoolant water system for metal working process tohelp reduce the risk of bleeding bacteria anddecreasing water consumption (Meythet Plant).
Fig. 6 illustrates the type of basic unit for water
consumption at SNR as well as the trend in water
consumption at SNR over past several years.

2008

Basic unit
MHz/average temperature

Fig. 3 Energy of processing

2.6
2.4
2.2
2
1.8
1.6
1.4
2005

2006

2007

Year

2008

Fig. 4 Energy of heating-12-

Efforts for the Environment by SNR

compounds used at SNR as well as the trend inorganic compound emissions into atmosphere at SNRover past several years.

Basic unit m3/kO

1
0.96
0.92

8. Reduction in amount of industrial
wastewater

0.88
0.84

Ordinary municipal wastewater treatment facilities
are intended to treat household wastewater, and will
not able to treat all pollutants occurring from industrial
wastewater (a pollutant may pass the soil in a
wastewater treatment facility and can be released into
the environment). To address this problem, it isnecessary that wastewater from the production
processes at SNR (in particular, the barrel polishingprocess) is preprocessed within the plant before being
released to the nearby municipal wastewater
treatment facility). Typical examples of our efforts for
reducing emissions of our industrial wastewater tooutside facilities are as follows:(1) Heavily contaminated rinse water from heattreatment process is treated in special wastewater
treatment equipment rather than being directly
released into the municipal wastewater treatment
facility (Annecy Plant).
(2) Previously, wastewater was directly released into a
wastewater treatment plant. Now, wastewater
having undergone treatment with a highperformance filter is returned to a reservoir andreused. This arrangement positively contributes toreduction in wastewater emission and freshwater
consumption (Meythet Plant).

0.8
2005

2006

2007

2008

Year

Fig. 6 Consumption of water

7. Reduction in organic compounds
emissions into atmosphere
When exposed to sunlight, pollutants such asvolatile organic compounds (VOCs) in atmospherenear ground will generate photochemical substancesthat can adversely affect human health andvegetation. In bearing production processes at SNR,
VOCs can typically occur from use of volatile oil, CFC
or alcohol employed for rinsing and degreasing of
bearing parts.
Some of our efforts for reducing emissions oforganic compounds are described below:(1) Oil solvent used in final rinsing step within bearing
production has been superseded with a lessvolatile type (at all operation sites of SNR).
(2) Previously, CFC was used for rinsing bearings
before non-destructive inspection. This substancehas been superseded with a detergent (Argonay
Plant).
Through these efforts, all SNR operation sites within
France alone achieved reduction of about 152 tons interms of VOCs emitted into atmosphere.
Figs. 7 and 8 show the type of basic unit for organic

250

Emissions Tons

Basic unit kg/kO

1.50

1.00

0.50

0.00

200

150

100

50
2006
2007

Year

2006
2007

2008

Year

Fig. 7 Organic compound2008

Fig. 8 Emission of organic compound to atmosphere-13-

NTN TECHNICAL REVIEW No.77（2009）

Fig. 9 illustrates the type of basic unit for reuse ofindustrial wastewater at SNR as well as the trend inreuse of industrial wastewater at SNR over past
several years.
Amount of industrial wastewater can be converted
into amount of household wastewater in terms of
population (number of residents). Thus, theachievement by efforts of SNR in mitigating
environmental impacts in this period through reductionin emissions of wastewater including industrial
wastewater is equivalent to reduction of household
wastewater consumed by 590 residents.
Currently, the amount of wastewater released from
SNR is as small as the amount of household
wastewater from only 160 residents. Fig. 10 illustrates
the trend of amount of industrial wastewater from SNRover several years, wherein the amounts of industrial
wastewater are shown as converted into the amounts
released by residents of ordinary households.

9. Management of wastes
Industrial wastes occurring from worksites of
production plants can be classified into “nonhazardous wastes” that can be treated together withhousehold wastes; and “hazardous wastes” that mustbe treated in a special plant. Non-hazardous wastes
from industrial processes are more frequently recycledcompared to ordinary household wastes. Because thistype of wastes typically consists of paper, carton,
plastic and glass materials, 90% of them can berecycled. At the same time, SNR has been proceedingwith research that will help convert certain hazardous
industrial wastes into recyclable-materials. Figs. 11
and 12 show the amounts of non-hazardous andhazardous industrial wastes occurring from SNR over
several years.

38

Basic unit kg/kO

Basic unit m3/kO

0.15

0.1

0.05

0
2005

36

34

32
2006

2007

Year

2005

2007

Year

Fig. 9 Reuse of industrial wastewater

2008

Fig. 11 Innocuous waste

55

800
700

Basic unit kg/kO

Equivalent usage
Population

2006

2008

600
500
400
300
200
100
0
2005

50

45

40
2005

2006

2007

Year

2006

2007

2008

Year

Fig. 10 Conversion to household use (number of people)
from industrial use (wastewater)

Fig. 12 Harmful waste

-14-

2008

Efforts for the Environment by SNR

been conducting various surveys about industrial
waste.

10. Ecology-improving technologies
of SNR

10.1 Test for steam condenser

SNR has long been committed to development andimprovement in bearing designs, as well as
improvement in bearing product manufacturing
processes: each commitment positively contributing tobetter ecology. Some ecology-improving techniques
unique to SNR are summarized below:

Waste liquid essentially comprises water. For thisreason, a steam condenser separates water fromcontaminated liquid through evaporation.
SNR Alès plant has tested an advanced steam
condenser. Thanks to the resultant findings, SNR can
now calculate data about performance andenvironmental impacts of a given steam condenser,
and has begun assessment of positive effects
obtained from a particular steam condenser. Fig. 13
schematically illustrates the operating principle of thesteam condenser tested.

[Examples of development and improvement]• Improvement in performance of steel material
Reduction in bearing size helps reduce amount of
raw material consumed.
• Optimization of internal structure
Reduced friction in bearing helps reduce the energy
needed to drive the associated machinery.
• Improved grease quality
Reduction in amount of prefilled grease helps
reduce amount of chemical substanceconsumption.
• Optimized seal performanceLonger bearing life and reduced grease loss.
• Compliance with REACH
SNR assures that it uses the registered chemical
substances only.

10.2 Test for biological purification unit
Waste liquid from a rinsing reservoir contains a verylarge portion of waste oil. On our biological purification
unit, the oil-containing waste liquid is transferred to abiological reactor where the oil content in the liquid iseliminated by bacteria, and then the purified liquid isreturned to the rinsing machine. The effectiveness of
this demonstration plant has been verified in the SNR
Annecy Plant. Fig. 14 shows a schematic illustrationof this biological purification unit.

[Examples of improved production processes]• Turning process was replaced with forging process:consequently, the amount of metal mass removed
from blank has been much reduced.
• Improvement in heat-treatment process has led tomitigated deformation of bearing rings.
Consequently, grinding allowance and energy
consumption in grinding process have been much
reduced.
• Having been supported by CETIM (Centre
Technique des industries Mécaniques), SNR has

10.3 Grinding sludge briquetting
Sludge occurring from the grinding process contains
not only steel powder but also coolant. Thus, this typeof sludge is categorized into hazardous wastes. In the
SNR Seynod Plant, grinding sludge is divided into
coolant and grinding powder, and then the grinding
powder portion is compressed into solid briquettes.
Being recyclable, these briquettes are reused in asteel manufacturer.

Bio-activating
agent tank

(3)
(4)

Compressed air

M(5)Detergenttank

pH-adjusting
liquid tank

Bio-reactor

Waste liquid
inlet
Deposition
liquid outlet(6)

Condensate
outlet(1)(2)(1) Recuperator(4) Compressor ROOTS(6) Deposition storage

Rinsing reservoir

Fig. 14 Biological purification unit

(2) Evaporator(3) Water separator(5) Immersion type exchanger

Fig. 13 Principle of VACUDEST-15-

NTN TECHNICAL REVIEW No.77（2009）

Incorporating an NTN proprietary technology forsludge briquetting (Fig. 15), the process has alreadybeen implemented in the SNR’s mass-production line.
In addition, SNR has been testing techniques forbriquetting other sludge types.

12. Promotion for Eco-consciousness
To help the SNR employees become more
conscious about their ecology-associated activities,
SNR has been keeping a basic eco-education
program for its newly hired employees. In particular,
SNR provides special eco-education curriculum for its
employees working in sites of higher environmental
risk within SNR.
SNR is also committed to support of ecoconsciousness promoting activities outside SNR. For
example, SNR engineers and technicians have been
actively presenting ecology-related lectures atuniversities (Ecole Centrale de Lyon, Polytech
Savoie), local science festivals, and ecology-centeredspecial seminars (World Bearing Association (BWA),
and ADEME). Fig. 17 shows a picture of an SNR
booth at a local exhibition. Also, SNR has been
supporting the development of a specialized vehicle
for an inter-college eco-run race (vehicles compete fora maximum range run with 1 liter of fuel). Fig. 18
shows a vehicle competing in the eco-run race. This
vehicle utilizes SNR-made wheel bearings.

Fig. 15 Grinding sludge briquetter

11. Investments into ecology-improving
activities
In order to continue its ecology-improving activities,
SNR has invested approximately 5 million euro in the
2005-2008 period. Fig. 16 shows a breakdown of theinvestments by objective for ecological improvement:

Considerations about
treatment and storageof waste
4.4%

Considerations about
discharge of rainwater
1.3%
Noise control
1.7%
Risk avoidance:
total ban on use of
PCB-containing
transformers
39%

Considerations about
release into atmosphere
7.4%

Fig. 17 SNR booth at local exhibition

Risk avoidance:
Safe storage oforganic
substances
1.2%
Decontamination of soil
15.4%
Risk avoidance:
prevention of
Legionnaires’ disease
5.6%
Energy-saving
measures
6.5%

Control over releaseof industrial
wastewater
8.1%
Survey about applicablelaws and regulations,and necessary actions
9.3%

Fig. 16 Investments

Fig. 18 Fuel-efficient vehicle with SNR-made wheel
bearings at the Shell Eco-Marathon®

-16-

Efforts for the Environment by SNR

13. Conclusion
The achievements in ecology-improving activities
described above have resulted from the long years of
eco-conscious commitments of SNR employees, anddemonstrate that the EMS system of SNR has been
beneficial.
Beginning in 1999, all the operation sites of SNR in
France, as well as those in Brazil and Romania, haveacquired ISO 14001 certification. By closely
monitoring its carbon footprint, SNR is making strides
to improve its effects on the global environment.

Photo of authors

Didier SEPULCHRE DE CONDENTN-SNR ROULEMENTS President

Jean-Hervé BULIT
NTN-SNR ROULEMENTS Environment Div. Manager-17-

NTN TECHNICAL REVIEW No.77（2009）[ Technical Article ]Efforts for the Reduction of Environmental Impacts
in Material Processing

Akira SERA*
Kenichi NAKANO*

Hisatsune SAITO*
Syunsuke MAKINO*

We developed a forging processing technique that uses a whitelubricant to achieve both the reduction of environmental loads andthe improvement of the operating environment in the forging
process.
We introduce a technology to reduce forging billet weightvariation and thea technology that improves yield rate by changing
the product shape and the forging process.

Wishing to help conserve the global environment,
NTN has been increasing the use of white lubricants.
This paper describes its efforts to mitigate
environmental impacts through use of white lubricants.

1. Use of white lubricant in forging process
for constant velocity joint parts
Recently, every manufacturer has been increasingly
required to combat the challenge of environmental
issues. For example, in the forging process forconstant velocity joint parts within Japan’s bearing
manufacturers, graphite lubricants (lubricants
prepared by dispersing graphite powder into water ormineral oil) have been superseded with whitelubricants (water solution primarily comprising organicacid salt and polymer) in an attempt to mitigate
environmental impacts and improve working
environments in production plants.
Generally, graphite lubricants have been used in the
hot forging process because of their better
performance in terms of lubricity, die-releasing
capability, and die life. However, these lubricants havedrawbacks: a work site involving a graphite lubricant
can readily get dirty; contaminating oil deriving from apress slide gib may not be readily separated: graphite
lubricant mixed with an excessive amount of oil can
exhibit deteriorated lubricating performance andneeds to be replaced, and the contaminated lubricant
will make an industrial waste. To sum up, use of thislubricant type can lead to a heavy environmental
impact.
In contrast, white lubricants can help improve work
environments in forging process, be readily separated
from oil, and readily recovered. Thus, use of thislubricant type can help greatly reduce occurrence ofindustrial wastes.

1.1 Features of white lubricantsWhite lubricants are water-soluble lubricants eachessentially comprising of organic acid salt and apolymer. Their features are summarized in Table 1
below.

Table 1 The characteristic of white lubricantsWhite lubricant
LubricantPolymerbased

Carbonic
acid-based

Water
glass-based

Characteristics

Phthalate
Major components Alkyl maleate Phosphate Silicate glass
Colloidal silica
Sulfonate
Cooling
performance

△

×

△

Drying readiness

△

△

△

Oil recovering
quality◎△△◎：Excellent○：Good△：Acceptable

×：PoorNOTE 1) Various white lubricant types are available, including
polymer-based, carbonic acid-based, and water glass-based
types. Manufacturers of these lubricants have beencommitted to development, aiming at the optimization ofadvantages of each lubricant type.
NOTE 2) Aqueous solution of organic acid salt is transparent. Afterapplied to a set of dies and heated to an appropriate
temperature, an aqueous solution containing such anorganic acid salt will form a whitish lubricant film after its
water content has evaporated.

*Production Engineering R&D Center-18-

Efforts for the Reduction of Environmental Impacts in Material Processing

air blowing time to determine a temperature range
where a dry lubricant film readily occurs (Table 3). An
attempt was then made to quantify necessary
lubricating conditions.
Fig. 2 shows a view of lubricant film formed on apunch used to forge an outer race of fixed constantvelocity joint.
To be able to determine an optimal set of lubricant
film forming conditions, we have first definedconditions about duration and timing for applying
lubricant as well as conditions of blowing air. The
relevance of these conditions was verified by
performing a series of tests on work-pieces being
forged. Consequently, we have achieved good results
about quality of forging-formed products and extended
die life.
As described above, we have adopted a whitelubricant in our forging process for NTN constant joint
outer race primarily to improve work environments
through the selection of an appropriate forging
lubricant, control for die temperature, and lubrication
conditions. Consequently, we have achieved
improvement in work environments. We wish to further
extend forging die life and expand a line of applicablebearing numbers and sizes.

1.2 Performance of graphite lubricants ascompared with that of white lubricants
NTN has compared performance of graphite
lubricants with that of white lubricants, in terms offorging-lubrication performance, workability-improving
capability, and safety. These results are summarizedin Table 2. Graphite lubricants excel in forginglubrication performance. In contrast, white lubricants
boast better workability-improving capability andsafety. Therefore, so that white lubricants are morecommonly used in forging process, their forginglubrication performance needs to be improved to alevel equivalent to that of graphite lubricants.

Table 2 Comparison of capability Graphitewith white lubricant
GraphiteWhite
lubricant lubricant

Function
ForgingLubricity, die release property
lubrication
performance Die life

Workabilityimproving
capability

Safety◎：Excellent

◎

△

◎

△

Working conditions

×◎

Die setup, die change○○

Putrefaction resistance
Maintainability against
seizure on sliding surfaces
and lubricant path
Immunity against fire

△

◎

○

△

○：Good×△：Acceptable◎
×：PoorTable 3 The film situation by die temperature during the test
State of lubricant film formed on die

1.3 Lubrication conditions setup and test result

Die temperature

Any white lubricant exhibits a satisfactory lubricating
effect only when it has formed a dry lubricant film. To
be able to form an appropriate dry lubricant film,
relevant control of die temperature is critical.
Therefore, we have studied various working conditions
that can help achieve formation of optimal lubricant
film and evaluated these conditions.
Fig. 1 shows an example plot of die temperature
measurements taken during hot forging processes.
First, we have adjusted lubricant application time andRoom temperature Water content in lubricant does not evaporate,
to low temperature and the lubricant remains in liquid state.
Water content in lubricant evaporates and alubricant film is eventually formed: however,this process takes an extended time.

Appropriate
temperature

Water content in lubricant evaporates quickly
and a lubricant film occurs promptly.

High
temperature

Droplets of lubricant rolling on the die surface are
repelled from the surface, not being deposited on
the die surface to form a lubricant film.

Measurements of die surface temperature

Temperature ˚C

High

Low
temperature

Punch
Dies

Low
0

60

120

180

240

300

360

Fig. 2 The film situation of the Punch for the Outer Race Joint

420

Time sec.

Fig. 1 Example of the result for die temperature check-19-

NTN TECHNICAL REVIEW No.77（2009）

2. Minimization of variation in weightof forging blanks

Shear press
properIn order to cope with an increasing rise in raw
material prices and help conserve the global
environment, demands have been rising for lighter
product designs, improved yields with parts that
constitute final products, and introduction of near-netshape forging techniques.
The forging process for constant velocity joint parts
begins with a shearing step as illustrated in Fig. 3.
Since the shearing is the first step in the entire mass
reduction process, it is critical that the blanks being
processed have a much more precise weight. Our
efforts exercised for this objective are hereunder
described.
Incidentally, to be able to minimize variation in theweight of forging blanks, it is necessary to minimize
variation in feed length and outside diameter of thesteel bar work piece being sheared.

Steel barwork piece
Pinch rollers

Fig. 4 The outside drawing of a shear press with Feed
Forward System of Bar O/D

Shearing blade
Fixed tool
Movable tool
Steel barwork piece

Sizing stopper

Fig. 5 The image drawing of Shear Tooling

Turning

Cold forging

Bonderite
treatment

Preforging

Precoating

Forging process
Shearing

Bar diametermeasuring rig

2.2 Countermeasure against variation in billet
weight(1) Countermeasure against variation in entire
billet length

Fig. 3 The Forging process

2.1 Overview of shear press (bar diametermeasuring rig) and shear tooling(Possible cause) At the beginning of shearing
operation, the steel bar was bent by the downward
motion of the movable tool. The bar was sheared
even though its positioning was, at the time,
unstable.
(Remedy) We have modified the form of sizing
stopper and shear tooling so that any steel bar isreliably sheared in a stable horizontal position.

Fig. 4 schematically illustrates the appearance of
our shear press equipped with a bar diametermeasuring rig. This machine comprises of the shear
press proper, a steel bar feeder, and a bar diametermeasuring rig. Before shearing, the bar diametermeasuring rig scans the entire area of the steel bar tomeasure the outside diameter and supplies thesemeasurements to the controller. When a change in theoutside diameter is detected, the sizing stopper isshifted accordingly to trigger a weight compensation
operation.
Fig. 5 shows the constitution of the shear tooling.
The steel bar shearing procedure consists of insertionof the steel bar from the fixed side of the tooling to thesizing stopper, lowering the movable side of thetooling to shear the steel bar, and removing theseparate work pieces from the tooling. The separate
blanks obtained from shearing are hereunder called“billets”.

(2) Method for correcting variation in steel bar
outside diameter(Cause) The outside diameter can vary even steel
bars belong to a same lot (Ex.: if the true diameterof dia. 70 x 100 (nominal) steel bar work piece is70.1 mm, then the true weight of this work piece
will be 11 g greater).
(Remedy) Using the bar diameter measuring rig in
Fig. 4, we scanned the entire area of the steel bar
work piece to determine the variation in the outside
diameter of the steel bar. Then, we determined thedeviation in bar diameter relative to the targeted
outside diameter and attempted to make weightcompensation for the billets by adjusting the lengthof billets so that the as-obtained billets weigh thesame as specimens of targeted outside diameter.
-20-

Efforts for the Reduction of Environmental Impacts in Material Processing

Taking a dia. 69.5 mm steel bar material type as amodel, we have investigated currently achievabledimensions and attempted to minimize variation in theentire length and outside diameter with the billets
obtained from the steel bar material. Consequently,
we have succeeded in limiting the variation in weightof the billets by approximately 60% as shown in Fig. 6.
We, NTN, have been not only attempting to realize
lighter bearing designs but also committed to various
development works that help mitigate environmental
impacts through reduction in the amount of materials
used through improvement in machining techniques
for our bearing products. One representative example
of our commitment is the above-mentioned near-netshape technique adopted in our forging line, wherein
the feed stroke for the steel bar work piece isregulated based on the trend in the measurements
obtained from the outside diameter measuring
equipment in order to minimize variation in the weightof resultant billets. NTN people in charge of forging
technology have been making efforts to develop novel
technologies to help realize better ecoconscious
manufacturing practices.
Comparison in terms of variation in weightwith and without compensation

GreaterweightBillet weightacceptable quality, Typical examples of these efforts
include:(1) Improved product design that can help delete amachining step for the forged surface while the forgedwork piece positively satisfies needed functions(2) Realization of not only extended die life but also
the introduction of near-net-shape techniques bysuperseding the conventional forging process witha novel forging process (this new forging process
technique is realized through introduction of newtechniques including a novel analysis technique.)(3) Realization of more compact and lighter productdesigns whose performance is equivalent to that itsof conventional design, beginning with the review
of designs of conventional constant velocity
bearing products
Fig. 7 shows some examples of new NTN constantvelocity joint products that reflect our efforts in (1)through (3) above. NTN has positively achieved
mitigation in its environmental impacts throughreduction in material used and alleviation inmachining-derived environmental impacts. These
contributing techniques include more common use offorging technique to delete certain machining steps
including turning, reduction in mass possibly removed
by turning, and introduction of more compact andlighter product designs.
We will further remain committed to develop andmanufacture ecofriendly bearing products through thedevelopment of new techniques aimed at reducing theamount of materials used, mitigating environmental
impacts from postforging process, reducing or deletingmachining steps, and creating lighter weight productdesigns by introducing multi-material designs.

0

Lower
weightW/o compensation

0

100

200

W/ compensation

300

400

Permissible range

500

600

700

Number of data sets

Fig. 6 Weight variation before and after used by Feed
Forward System of Bar O/D.

Fig. 7 Variation of Constant Velocity Joint parts

3. Efforts of NTN for improved yield withgood constant velocity joint products
and reduction in materials used
As a part of our commitment to reduction inenvironmental impacts, NTN has been challenged witha variety of objectives that include reduction in theamount of materials used in components of NTN
products, reduction in the energy consumed during
manufacture of these components, and waste
reduction. This challenge also applies to the
manufacturing of inner races and outer races for NTN
constant velocity joint products. To fulfill theserequirements, NTN has been involved with efforts for
improved yield for constant velocity joint products of

Photo of authors

Akira SERA
Production Engineering
R&D Center-21-

Hisatsune SAITO Kenichi NAKAJIMA Syunsuke MAKINO
Production Engineering
R&D Center

Production Engineering
R&D Center

Production Engineering
R&D Center

NTN TECHNICAL REVIEW No.77（2009）[ Technical Article ]Improvement of Work Environmentswith the Use of Factory Robots

Shigeki MATSUSHITA*Genji NAGURA*

Human sense and experience are necessary for assembling processes.
Therefore, automation (mechanization) has been difficult. We used sensor,
robot, and simulation technologies, which have made remarkable advancesin recent years, and succeeded in improving working environments in theassembly process for constant velocity joints (CVJ).
We introduce this case in this article.

(2) Unique shapes of finished CVJ products

1. Introduction

Because each CVJ is designed for a particularfunction, the individual components of CVJ’s and thefinal products are diverse in shape. Thus, ordinarytransfer systems are not readily capable of handlingfinished CVJ products creating a necessity for humanoperators to transport these products.
With a larger finished CVJ product weighing
approximately 10 kg, and the operators involved will
experience heavy physical burden while transferring awork piece from a particular process to a downstream
process or while changing the orientation of a workpiece.

Constant velocity joints (hereinafter called CVJs)
are a major product of NTN and are used in many
automobiles as a means of power transmission.
In a typical CVJ assembly process in NTN, 12 to 16
parts are assembled in sequence to form the final
product. Fig. 1 schematically illustrates a typical CVJ
assembly process.
NTN regards steps 1 through 3, which arecommon to various CVJ types, as the start-up
assembly process and steps 4 through 6, which canvary depending on the CVJ type processed, as thecompletion assembly process.
NTN mass-produces a variety of its CVJ products.
However, a larger portion of its CVJ assembly isachieved through manual operation because ofreasons described below. Thus, these jobs are difficult
to execute and pose a heavy burden on the operators.

(3) Precision phase-matching procedure
Many CVJ components (rubber boot, shaft, innerring, outer ring, etc.) have to be assembled into final
products, being fully phase-matched between
components.
These components each have unique geometricalfeatures including cut-outs and projections in snap-fit
joints and boot receiving joints and these features areused for convenience to achieve an optimal phasematch between components during assembly of CVJ
product. The allowance for snap-fit is very small
and/or snap-fit joints consist of soft and a hardmaterial components forcing NTN to rely on
experienced operators to manually assemble thecomponents and remain conscious of phase matching
between components involved.
During manual assembly work of a CVJ product, an
operator assembles components into a final product(1) Unique shapes of CVJ components
Many CVJ components are prone to deformation
because of their material and/or shapes, including therubber boot, resin boot, and ring-shaped boot band
made of a thin metal strip.
To be able to automatically install these difficult
components, there will be orientation and alignment
challenges during component feeding and handlingthroughout assembly. In conventional practice,
position (orientation) of components is visuallychecked, and components are manually transferred
and assembled.

*Production Engineering R&D Center-22-

Improvement of Work Environments with the Use of Factory Robots

while matching phases of the components involved
based on visual detection and handling touch. In
contrast, to be able to utilize an automatic assembly
system for a CVJ product, it is necessary to first detect
the phases of all the components involved and relay
the data to downstream processes so that thecomponents can be assembled in correct phases.

I/B boot+ small band

Creating such a system that produces reliable results
poses a great challenge for producing reliable results.
To address the above mentioned challenges, NTN
has committed to improving work environments in CVJ
assembly facilities by deleting high difficulty and highburden steps. For this purpose, NTN has developed
an automated CVJ assembly process incorporating a
6-axis vertical multi-joint robot that is virtually capableof human motions (hereinafter simply called the“robot”).

O/B boot+ small band

2. Approaches to automation throughuse of robot

1

I/B inner ring

The objective of the robot-assisted CVJ assemblyline recently developed is “the elimination of humanactivities by automation with robot.” It is intended tomitigate the work load on human operators, and to doso, NTN has executed the following four approaches:

Clip

2

Snap ring(1) Analysis of work flow

O/B sub-assy

In considering the assembly process involving
robots, each manual process step within the wholeprocess has been analyzed and numericallyassessed. Based on this obtained knowledge,
challenging jobs done by experienced operators havebeen replaced with automated industrial robots.

3

O/Blarge band

4(2) Greater scope of applicability
A coordinated operation is performed using of arobot featuring greater degree of freedom of motion
while maintaining a simple station for the operator toassist the robot. Consequently, delicate work, whichcannot be achieved with a robot alone, is possible,
leading to a greater productivity through cooperation.

I/B outer ring5

I/B large band(3) More reliable work piece transfer operation
Through the introduction of a more compact, lighter
robot hand as well as optimization for speed andrange of robot hand motion, the reliability of robot
assisted word has been improved. Consequently,
product transfer operation, which was once a largely
physical burdening manual process, has now been
reduced with robot use.

(4) Numerical control of force-sensitive operation
Start-up
assembly
process

1 Boot and small band are inserted over the shaft.
2 I/B inner ring and O/B clip are fitted.
3 I/B snap ring and O/B sub-assy are installed.

Completionassembly
process

4 OB large band is inserted over the sub-assy.
5 I/B outer ring is inserted, and the boot is fitted.
6 I/B large band is inserted, and both bands areform-fitted.

Inspection
process

Where the worker used to do operations by feel orexperience, the robots allow for much more controlled
operation and gather data during the process as
feedback for further engineering.
To help proceed with these approaches, NTN has
executed robot motion simulation by gathering loading
analysis data from manual operation and using a 3Dmodel. As a result, NTN is now capable of checking
equipment layout and potential interference onequipment and running cycle times before equipment
installation. Thus, NTN has achieved not only optimal

7 Functions and appearance of product are inspected.

NOTE) "Inboard (I/B)" means the engine-side of CVJ having been
installed onto a car body and "outboard (O/B)" means thewheel-side of installed CVJ.

Fig. 1 Standard CVJ assembly processss-23-

NTN TECHNICAL REVIEW No.77（2009）assembly procedure and equipment layout but also a
reduction in the development period for thisequipment.
Fig. 2 shows a view of the 3D robot motion
simulation system.

Fig. 3 Intelligent parts supply device

Fig. 2 Robot simulation

3. Challenges and solutions about
automated CVJ assembly process
NTN has identified the following four major
challenges with the robot-assisted CVJ assembly
process. This section describes these challenges andtheir corresponding solutions.
(1) Detection of component orientation(2) Automated snap-fitting work for serrated
components(3) Automated assembly work for difficult-to-handleshaped components(4) Improved efficiency in robot-assisted operation

Phase information

Fig. 4 Tripod and phase information

3.2 Automated snap-fitting work for serrated
components

3.1 Detection of component orientation

The majority of CVJ components must be
assembled with their phases matching. Like many
steps in CVJ production, the snap-fitting step forjoining serrated components poses a challenge tomake automated assembly work for CVJ production
possible.
As shown in Fig. 5, the outer circumference of bothends of the shaft as well as the inner bore of the innerring, which receives one end of the shaft, are serrated.
Manual phase-matching with the two serrated
components is a delicate procedure where mismatchof phases is prone to occur.
To address this issue, NTN has developed two
techniques for snap-fitting with these two serrated
components, and is applying one technique according
to the shape of the components.

To run a problem-free automated assembly,
orientation-related data of each component, including
position (location), phase, and orientation (front orback), must be correctly sensed.
To address this challenge, NTN has developed aunique intelligent parts feeder capable of correctly
orienting/aligning parts. This parts feeder system
captures images of CVJ components, makes
judgment about position (location), phase, andorientation (front or back) of individual CVJ
components based on the captured images andtransmits the resultant judgment information to therobot. The system always places individualcomponents arranged in a same orientation into asame location. By this development, reliability in partstransfer with a robot has been much improved, and, atthe same time, has eliminated work issues for theoperator with respect to aligning parts. Fig. 3 shows aview of the intelligent parts feeder. Fig. 4 illustrates acaptured image of parts.
-24-

Improvement of Work Environments with the Use of Factory Robots

Serrated outer circumference of shaft

possible only when the phases of both components
are correctly matched. In other words, the rubber bootcannot be fitted over the outer ring simply with pressfitting force. Fig. 6 shows the profiles of TJ boot andouter ring—two members that will constitute a joint.
Previously, an experienced NTN operator has beencommitted to this work, making fine-adjustment efforts
based on his/her experience and including information
on angle of force and location of pivot point.
Therefore, NTN has analyzed boot fitting motions of
its experienced operators to develop numerical data,and has a robot to trace the trajectories of motions ofthese operators. Consequently, NTN has realized areliable robot-assisted rubber boot fitting work for its
CVJ assembly process.

Shaft

Inner
ring

Serrated bore of inner ring

Fig. 5 Serration fitting portion(1) Exploration-based method
Two serrated components are brought into contact,
then, while the state of phase-matching is being
explored, they are snap-fitted with each other. A
delicate sensor reacting to correct phase-matching
between both components sends an electrical signal
by another sensor which outputs the signal as an
insertion trigger signal.

Boot bore

Outer ring outer circumference(2) Measurement-based method
First, the profile of serration on each of bothcomponents is measured with a sensor. By referringto the resultant phase information, the serrated shaft
end is fitt into the correspondingly serrated bore of
inner ring.

Fig. 6 Shape of TJ boot bore and outer ring O.D.

(3) Boot band form-fitting work
Through form-fitting, the quick-locking boot band
used in NTN's CVJ secures the rubber boot when its
retainer is appropriately set. Previously, a delicate
form-fitting process was necessary for the boot band
made of thin metal strip (this component can readily
get deformed); therefore, manual operation was
mandatory in order to reliably ensure better quality
and productivity.
Fig. 7 shows shapes of the small and large bootbands.

3.3 Automated assembly work for difficult-tohandle-shaped components(1) Boot band insertion work
In this work, the boot band is fit over the outercircumference of a particular small diameter section ofrubber boot. Reliability of this operation poses achallenge as two components of very different
shape—rubber boot and sheet metal boot band—are
joined together.
To address this issue, NTN has invented a uniqueassembly system in which a guide jig dedicated toband insertion is installed onto an auxiliary station sothat the band and rubber boot after undergoing shapecorrection are joined together.
Because both components are joined together only
after correction for shape, this system positively
improves reliability and repeatability of the boot band
insertion work.

Small dia. quick-locking
boot band
Large dia. quick-locking
boot band

Fig. 7 Shape of one-touch boot band(2) Rubber boot fitting work
In this work, the outer ring is fit into a particularlarge diameter section of rubber boot. Note that theboot bore and outer ring outer circumference are eachuniquely shaped: therefore, successful insertion is-25-

NTN TECHNICAL REVIEW No.77（2009）

To sum up, one robot unit can be applied to aplurality of processes, and previously unavoidable
time loss for hand change has been eliminated.

NTN has attempted to supersede this complicatedmanual operation with a robot-assisted automatedarrangement, and has learned that a special robot
hand is necessary and exact tracing of necessary
human operators’ motions is impossible. Though
beginning with the original motions of humanoperators, NTN has revised/reorganized thenecessary motions to develop motions suitable forrobot-assisted automation. Consequently, a robotassisted rubber band fitting operation has beenrealized which boasts more efficient and reliable
operation compared with procedure that could havebeen achieved by simply tracing human operators’
motions.

4. Positive effects of development ofrobot-assisted CVJ assembly line
NTN has adopted its newly developed robotassisted CVJ assembly technology to all the CVJ
assembly lines within its factory; consequently, fullautomation of CVJ assembly has been realized. Fig. 9shows a view of the robot-assisted CVJ assembly line
installed in NTN factory.
The effects of this development are elimination or
mitigation of the burden of highly difficult operations
and high-load operations associated with the transferof heavy work pieces, each being the challenge withconventional assembly practice. They also provided
improved work environments, as well as 60% laborsaving compared with conventional assembly
practices.
In addition, the intelligent part feeder checks theparts while they are loaded into the assembly robot,
thereby misassembling the CVJ is prevented,
positively helping improve the quality of NTN CVJ
products.

3.4 Improved efficiency in robot-assisted
operation
To be able to fully utilize robot technology in its CVJ
assembly process, NTN has developed a unique
combined robot hand system.
When an industrial robot system is used forautomated production, the robot itself uses a pluralityof robot hands that can be changed between.
However, this practice of changing hands leads tounavoidable time loss.
To address this problem, NTN has developed aunique combined multi-functional robot hand system.
This robot hand system not only combines a pluralityof robot hands but also is designed such that eachindividual hand when active does not interfere with a
CVJ component or peripheral equipment.
Furthermore, the individual hands are driven by acommon single drive, allowing the entire system to becompact and light-weight.
Fig. 8 shows the combined robot hand system thatis capable of chucking a boot and a small band at one
time.

Fig. 9 CVJ robot assembly line

Fig. 8 Operation of combined robot hand
(Upper: boot chuck, Lower: small band chuck)-26-

Improvement of Work Environments with the Use of Factory Robots

5. Conclusion
NTN believes that robot-assisted assembly lines willcontinue to be further sophisticated, diversifying into
various configurations to meet contemporary needs.
While performance of industrial robots has been
increasingly enhanced, NTN thinks that robot users
need to deepen their knowledge about robot
technology and improve their skills in utilizing robots.
Thus, NTN will remain committed to thedevelopment of robot technology that can be applied
to not only CVJ assembly processes but also all the
production processes for NTN products, and wishes toestablish a production system that is safe and poses
the least burden to human workers and helps improve
work environments.

Photo of authors

Shigeki MATSUSHITAGenji NAGURA

Production Engineering
R&D Center

Production Engineering
R&D Center-27-

NTN TECHNICAL REVIEW No.77（2009）[ Technical Article ]Market Trends
for Wind Turbine and Bearing Technologies

Nobuyuki NINOYU*
Souichi YAGI**
Tsuyoshi NIWA***
Wind power generation, which contributes to the preventionof global warming, is being actively introduced to theworldwide market as a clean energy source. Bearings are
increasing in size accordingly with the growth in the size ofwind power generation equipment. Evaluation tests of bearings that simulate actual performance areimportant for selecting suitable bearings, but they are becoming difficult with equipment that is verylarge, so conducting structural analysis, including for shafts and bearing housings, for example, isnecessary. This article introduces some of these analysis techniques.

Being a clean energy source that does not emit CO2,
wind power generation plants are widely appreciatedaround the world, and their installed capacity has been
increasing by more than 20% every year 1).
As the market for wind power generation plants has
been steadily expanding, more advanced wind turbine
technologies have been increasingly developed. The
current development efforts are focused on scale-up
and offshore production of wind turbines. This report
describes the current market trend for wind turbines
and typical examples of the newest bearing
technologies for wind turbines.

1. Introduction

Total electricity generation capacity

The total electricity generation capacity of wind
power generation plants worldwide reached 122 GW
as of the end of 2008 business year, and according toa report, this value means a 30% increase over the
BY2007 level.
Fig. 1 graphically plots the trends in the total wind
power electricity generation capacities of the world andmajor participating nations in the BY2004–2008 period.
During this period, three major nations—USA,
Germany and China—accounted for approximately
50% of the total installed capacity. In particular, thetotal installed capacity significantly increased in USA
and China in the same period. 50% of the increase in
newly installed capacity in the world in BY2008 is
accounted for by USA and China.

2. Market trend
2.1 Scale-up
In 1985, the rated output of a typical wind turbinewith rotor diameter 15 m stood at 50 kW. About twenty
years later, mass-production began with a larger windturbine that boasts a rotor diameter of 126 m and is
rated at 5,000 kW (5 MW).
In the engineering aspect, the contributing factorsthat have helped realize scale-up of wind turbines are
improved mechanical strength for rotor blades byintroduction of carbon fiber monolithic impregnatedstructure, advancement in mechanical strength design
and analysis technique for the structures of tower andnacelle, and progress in design and production
techniques for producing larger wind turbine bearings.

(MW)
Others

140000China
Germany
The United States

120000100000
80000
60000
40000
20000
0

2004

2005

2006

2007

2008

Year

Fig. 1 Cumulative global wind power development***Application Engineering Dept. Industrial Sales headquarters***Industrial Sales headquarters***Product Design Dept. Industrial Sales headquarters-28-

Market Trends for Wind Turbine and Bearing Technologies

at seabed) and a sailing type (floating platform structure
can freely move on the ocean surface). Research into asailing type platform is attracting attentions as thisplatform type appears to be promising because offshore
areas in Japan are often much deeper and Japan’slong-established shipbuilding technologies can beapplied to these sailing type structures.

Research works for super-large wind turbine designs
are in progress in particular for offshore wind turbine
power generators that are rated at 10 MW to 20 MW.

2.2 Offshore site production
Few sites are available on land where the windprofile is appropriate for wind power generation. For
this reason, offshore wind farms site production has
been increasing, especially in Europe. Fig. 2 shows anexample of typical offshore wind farm in Europe.

3. Applicable bearing technologies
3.1 Efforts for analysis techniques for large bearings
3.1.1 Main-shaft bearing
To cope with the scale-up of wind turbines, the sizes
must be larger for the bearings that support the main
shaft, speed-up gearing and generator. In particular,
the larger main-shaft bearings that support the larger
rotors often measure 2,000 mm OD or greater, andtheir types include self-aligning roller bearing, double
row tapered roller bearing, and cylindrical roller bearing.
To be able to determine the final specifications for amain-shaft bearing, an intended bearing needs to betested by running on a test rig that can simulate theintended wind turbine so that the bearing in question
can stably perform for an extended period. However, asimulation test of the bearing in question on an actual
wind turbine requires a large test facility, higher costand longer preparation period before actual test, and,
therefore, cannot be readily executed. To address thisissue, NTN has been performing not only simulation
tests on an actual wind turbine but also finite element
method-based structural analysis for the bearings andauxiliaries including the bearing housing and bearing
bed so that a more reliable bearing design is achieved.
Figs. 4 and 5 show a result of the analysis with amain-shaft model. By an external force, the bearing aswell as the bearing housing and shaft get deformed.
A larger wind turbine develops greater deformation
owing to the greater external load it receives, andgreater this deformation on the wind turbine more
adversely affects the bearing clearance. Therefore, it isnecessary to take into account this deformation for

Fig. 2 Under construction of offshore wind turbine

2.2.1 Offshore wind power generation programsin Europe
In Europe, there is a vast spread of continental
shelves down to a depth of 40 m, and wind farms areoften constructed on seabed foundation. In particular in
the north Europe, there are large scale offshore windfarm projects 2). Fig. 3 maps the currently present
offshore wind farm projects in the north Europe
scheduled in the timeframe up to the year 2020.
Offshore wind farmprojects in Europe(up to 2020)
The United Kingdom: 40 GW
Germany : 15 GW
Netherlands : 6 GW
Denmark : 4 GW
Belgium: 2.5 GW
Sweden: 1.5 GW

Fig. 3 Plan of offshore wind farms in north Europe

2.2.2 Offshore wind power generation programsin Japan
In Japan, application of seabed foundation for windfarms is difficult owing to topographical limitations.
Therefore, joint industry-university teams have beendeveloping floating platform wind power generation
plants. Note that floating platform plants can be
categorized into an anchor-secured type (floating
platform structure is secured with the anchoring point

Fig. 4 Main shaft model-29-

NTN TECHNICAL REVIEW No.77（2009）

correct analysis of the main-shaft system. NTN
performs design reviews after taking into account theeffect of deformation on the entire wind turbine
structure, and then finalizes the bearing specification
optimized for the wind turbine in question. Fig. 5 shows
an example of the structure for a bearing that supports
the main shaft in nacelle, wherein the bearing structure
comprises a double row tapered roller bearing in theblade side and a cylindrical roller bearing in the speedup gearing side. Fig. 6 provides structural diagrams of
the bearings used in this analysis model.
The diagrams in Fig. 7 show the results of theanalysis of the effect of deformation on the bearing
housing and other structural members. In Fig. 7, theload distribution pattern over the rolling elements isshown for each of two assumptions—where
deformation is taken into account and where it is nottaken into account.
In FEM analysis procedures, an “elastic body”
element is used for the deformation analysis. If theelement is assumed to be a “rigid body”, thencalculations are possible without taking into accountdeformation.
The diagrams in Fig. 7 show that when deformation
on a bearing housing and bearing are taken into
account, the load zone expands and, consequently,
load peak is mitigated, meaning the overall load
imposed over the rolling elements is reduced.
Compared with the “solid body” scenario, the bearing

life resulting from the “elastic body” scenario isapparently longer—the life of tapered roller bearing isapproximately 20% longer and that of cylindrical roller
bearing is 10% longer.
It is true that deformation helped increase bearing
life in the example above. However, deformation in
Tapered roller bearing row 1 in Fig. 5: 34 rollers
3

4

5

400

6

30

31

Load [kN]

1 2
500

34

33

32

7

27 28
25 26
29

300
200

8
9

100

24

10 11
12

0

23

13
15

16

17 18 19 20Life ratio =

14

21

22

Elastic body
Rigid bodyelastic body
= 1.2
rigid body

Tapered roller bearing row 2 in Fig. 5: 34 rollers

32

4

5

400

27 28
25 26
29

300

7

200
8
9

100
0

24

10 11
12

Speed-upgearing side

3

6

Blade side

Load [kN]

1 2
500

34

30

31

33

23

13

16

17 18 19 20

21

22

3

15

Rolling element
Nos. (1–34)

14

12

Cylindrical roller bearings row 3 in Fig. 5: 27 rollers
Double row
tapered roller bearings(ID 750, OD1,100)

Cylindricalroller bearings(ID 710, OD1,050)

Load [kN]

1
27
1200

26

2

3

4

25

24

Fig. 5 Analysis example of main shaft model

6

23

5

800

7

22

400

21

9

20

8

0

19

10

18

12

15

16

17

Fig. 6 Bearing structures for analysis

14

Elastic body
Rigid body

Cylindricalroller bearings

13

Double row tapered
roller bearings

11

Rolling element
Nos. (1–27)

Life ratio =elastic body
= 1.1
rigid bodyFig. 7 Load distribution of each rolling elements-30-

Market Trends for Wind Turbine and Bearing Technologies

other scenarios can lead to reduced bearing life.
Therefore, NTN is executing deformation analysis forthe entire wind turbine system in order to design an
optimal bearing for the main shaft on wind turbine.

Fig. 10 schematically illustrates the calculation
result. If the deformation on the carrier and planetary
gear resulting from the input torque is taken into
account, the load acting on the rolling elements in rows
1 through 4 on the two double row cylindrical roller
bearings is mitigated, compared with a case where
deformation is not taken into account. Compared with acase where deformation is not taken into account, thecalculated bearing life with deformation being taken
into account more closely matches the actual life
obtained from the bearings installed to an actual windturbine. In our test, the life of the two double row
cylindrical roller bearings with deformation taken into
account was approximately 50% longer compared witha case where deformation was not taken into account.

3.1.2 Planet bearing for speed-up gearing
Figs. 8, 9 and 10 provide information obtained fromstructural analysis with bearings incorporated into
speed-up gearings in larger 2-2.5 MW class windturbines. Note that through this analysis, thespecification for relevant planet bearing has beendeveloped while taking into account the magnitude ofpossible deformation on the carrier, pinion shaft andplanetary gearing.
Fig. 9 shows an analysis example of the deformation
mode with planetary gearing wherein gear load andcentrifugal force are imposed onto the planetary
gearing.
In the main mode, the force resulting from twotangential loads Ft shown in Fig. 7 acts on the bearing
as a radial load. Consequently, the outer ring isdeformed by two radial loads Fr, thereby the load zone
expands.

0.6
0.5

Fr
Ft
Double row cylindrical roller bearings
Rows 12 34

Pinion shaft

0.4
0.3
0.2

Input torque

0.1
Centrifugal
force

0.0

CarrierPlanet gear

Fig. 8 Planet gear

2

19 80

3

Second row
17

40

11

12

16

8

13

15

7

8

13

6

7

14

16

40
20
0

6

14

3

5

5

0

2

60

Fourth row

20

1

17

40

15

19 80
18

4

4

17

elastic body
= 1.5
rigid body

9

12

10

Fig. 10 Load distribution of each low

-31-

11

16

16
15

14

13

10

Total life ratio =

10

13

9
3

12

2

60

Third row

88

Elastic body
Rigid body

11

15

0

7

7

14

20

6

6

1

3

5

5

19 80
18

2

60

40
20

1

4

4

17

60

0

Rolling element
Nos. (1–19)

18

9First row

1

9

19 80

Fig. 9 Analysis example of planet gear

10

Load [kN]
18

Ft

Fr

11

12

NTN TECHNICAL REVIEW No.77（2009）

measured value on a particular point (point A in Fig.
12) where the inclination of the inner ring is greatest.
In the test result data in Table 1, the difference
between the pre-run analytical value and measured
value is 5%, which qualifies as a fairly good match. In
contrast, the difference between a post-run analyticalvalue and a measured value is as great as 25%. A
result of a post-run analysis is provided below. For thisanalysis, the heat transfer coefficient was determinedbased on the temperature rise on the inner and outerrings, and the coefficient was applied to the thermal
analysis about the increase in bearing preload andchange in bearing rigidity resulting from operation of
the bearing.
The bearing housing in Fig. 13 houses a double row
tapered roller bearing. This analysis model was
continuously run thereby resulting in a temperature

3.1.3 Thermal analysis
When assessing the performance of bearings
incorporated into larger wind turbines, thermal
deformation needs to be taken into account. Fig. 11
shows an example of a bearing model that was
subjected to our thermal analysis. In the analysis work,
the temperature distribution over the entire model was
determined based on the heat release performance ofthe bearing as a heat source. Through analysis for a
combination of heat and structure, it will be possible todevelop bearing specifications that better reflect
operating conditions of bearings installed on actual
wind turbines. Note that in the thermal analysis work,
the thermal characteristics including the heat transfer
coefficient and heat release coefficient are affected byvarious factors including surface properties of the
bearings, the weather, the ambient temperature, thehumidity and the wind velocity. Therefore, we haveattempted to improve precision of thermal analysis byfeeding back data obtained from field tests. This effort
is later described.

0.50mm
0.40
0.30
0.20
0.10

Blade side

0.0

50

-0.10

45

Reducer side

-0.20
40
-0.30

Point A

35

-0.40

30

-0.50

Fig. 12 Example of FEM analysis

25
20

Table 1 Test result

15

Displacement on point A (mm)Fig. 11 Example of heat transfer analysis

Pre-runPost-runAnalytical value

0.403

0.326

3.2 Simulation on actual wind turbines

Measured value

0.424

0.259

NTN owns and operates a unique test facility that is
capable of simulating performance of super large
bearings for the main shaft of a 2–2.5 MW class windturbine while subjecting the bearing to a load that will
occur on an actual wind turbine. Utilizing this facility,
NTN has been performing tests on the bearings
simultaneously with FEM analysis to improve precisionof FEM analysis, so that the bearing development
period is shortened.
Fig. 12 shows an example of results of the FEM
analysis with a bearing model (double row tapered
roller bearing: 2,000 mm pitch diameter with roller set)for 2–2.5 MW class wind turbine, wherein a momentload of 1700 kN-m was applied to the inner ring.
Table 1 summarizes the information about acomparison between analytical results of FEM and

Difference

5%

25%

Temperature distribution on
surface of bearing housing

Directly above double row
tapered roller bearing

50
45
40
35
30
25
20
15

Fig. 13 Analysis model-32-

Market Trends for Wind Turbine and Bearing Technologies

Based on the estimated analytical value oftemperature difference across the inner ring and outer
ring, as given in Table 2, the decrease in bearing
clearance on the running bearing was estimated, andthen, adequate initial bearing clearance has been
accordingly determined. As a result, the difference
between analytical value and measured value has
decreased to 1%.
Considering the findings obtained from theseanalytical results, NTN has developed an optimalbearing design that has been installed in an actual
wind turbine and is reliably running.

distribution on the bearing and bearing box to beanalyzed.
Incidentally, for an estimation of temperature
distribution on the bearing through thermal analysis,tuning (a technique that approximates analytical results
to measured values obtained by experiment) was
employed. More specifically, with this technique,temperatures measured on various test points on the
bearing of an actual wind turbine are incorporated into
analytical results to adjust the heat transfer coefficient
thereby increasing the reliability of the temperature
distribution analysis.
The example of bearing temperature distribution
inside a bearing housing in Fig. 14 reflects measured
values for ambient temperature, nacelle insidetemperature, and temperature on the outercircumference surface of the outer ring. Table 2
summarizes information about the comparison
between analytical result of thermal analysis andmeasured values.
Double row tapered roller bearing

4. Conclusion
Wind power generation as a clean energy source
has been increasing its output. The quantity of installed
offshore wind turbine plants will further increase. At thesame time, wind turbines will increasingly feature
greater output and larger size, while they are required
to withstand severer natural elements more reliably.
In this context, the bearing designs adopted for windturbines need not only to satisfy conventional
standards but also to be optimized for intended windturbines through wind turbine-specific detailed analysis
technique and review of analysis result.
Wishing to contribute to development of wind power
generation which is a new energy source possibly
helping prevent global warming, NTN will further
develop and stably supply highly reliable and durable
bearing products.

Housing

Shaft

Fig. 14 Example of thermal analysis
Table 2 Bearing temperature distribution
Temperature difference
across inner ringand outer ring (˚C)

Temperature on outercircumference surfaceof outer ring (˚C)

Analytical value

2.2

50.5

Measured value

Not measured

50.0
1%(Post-tuning difference)

Difference−

References
1) BTM Consult ApS International Wind Energy
Development World Market Update 2008
2) SCOTTISH Development International: Offshore Wind
Power Generation in Scotland and the UK

Photo of authors

Nobuyuki NINOYU

Souichi YAGI

Tsuyoshi NIWA

Application Engineering Dept.
Industrial Sales headquarters

Industrial Sales
headquarters

Product Design Dept.
Industrial Sales headquarters-33-

NTN TECHNICAL REVIEW No.77（2009）[ Technical Article ]Eco-friendly Product Development
at SNR Roulements

Siegfried RUHLAND***
Ludovic SAUNIER***
Cynthia TSEN***
Bernard LIATARD***
Gérald MIRABEL***The reduction of CO2 emissions is being promoted in Europe, and every automobile company isconsidering various measures to achieve this goal. "Mass reduction" and "torque reduction" areeffective ways to decrease CO2 emissions, and automobile and parts makers are challenging thelimits every day, including awith existing products. SNR products that contribute to "mass reduction"and "torque reduction" are introduced in this article.

2.1.1 Design activities for automotive hub bearings

1. Preface

Under the loading conditions (rotational bending
force, hub bolt tightening torque, etc.) possibly acting
on bearings installed in actual cars, we have analyzed
the stresses occurring on H/B. Fig. 1 shows ananalysis model used. As can be understood from thisdiagram, we have learned that the maximum stressoccurs on both the flange tightening area and thechamfer area at the base of flange. Therefore, whendeveloping the new bearing design, we have shifted a
portion of the mass of the hub from a low stress region
to a high stress region to mitigate stress concentrationon the hub while not altering the design of critical areas
including the raceway surface, disk and wheel
receiving area.

CO2 emissions control has been posing a challenge
to any manufacturer in attempting to addressenvironmental issues including global warming. To beable to contribute to CO2 emissions reduction, theautomotive industry has been committed to design andproduce lighter, lower-torque automotive parts to help
improve the fuel efficiency of cars they manufacture. In
this article, SNR will present its technologies for lighter
weight and lower torque in their automotive hub
bearings transmission bearings and suspension
bearings.

2. Efforts for lighter bearing designs
This section describes the efforts of SNR for its
automotive hub bearing (hereinafter H/B) products andwater pump bearing products.

Low stress region

High stress region

2.1 Automotive hub bearings
Based on a novel concept, SNR has developed
unique H/B designs that can be applied to flanged 2nd
generation and 3rd generation hub bearings forsupporting brake disks and wheel rims. Throughoptimized shape design for H/B, the newly developed
H/B products boast 15% weight reduction while
keeping excellent strength and durability.

Fig. 1 Stress analysis on the hub bearing*SNR Product Innovation & Mechatronic**SNR Automotive Transmission Engineering-34-***SNR Automotive Equipment EngineeringEco-friendly Product Development at SNR Roulements

Fig. 2 shows shapes of a conventional design andthe new optimized design. The new hub design
features a unique flange shape, each of its bolt-down
segments being reinforced with two ribs. With thisdesign, the mass of outer ring has been reduced by
20% and that of entire H/B by 15%. This weight
reduction will mean a maximum weight reduction of
1,300 g per automobile axle.

2.2 Water pump bearing for automobile
Fig. 4 shows an appearance of a conventional water
pump for cooling an automotive engine, and Fig. 5schematically illustrates the structure of the water
pump. Many present-day water pumps used for coolingmodern automotive engines incorporate integral shaft
bearings that have a raceway surface on their shaftswith their inner ring deleted.
With a conventional structure in Fig. 5, the belttension poses an offset load onto the bearing andcauses the contact pressure to be greater. This
problem in turn poses a challenge in providing longer
life for the bearing. At the same time, resultant
misalignment of the bearing relative to the shaft cancause water to pass the seal and enter the bearing.
Consequently, the grease can leak out of the bearing,leading to poor lubrication of the bearing. The bearing
can then develop abnormal noise and/or exhibit
excessively short life.

20% weight
reduction

Fig. 2 Conventional design (left) and new optimized
design (right)

2.1.2 Performance of new optimized design
As described above, the new optimized design
boasts a much reduced weight, while its rigidity isequivalent to that of conventional designs.
Furthermore, because the bolt-down segments are
reinforced with ribs, the stress occurring at the flangebase of the new design is 35% smaller as shown in
Fig. 3.

Drain hole
Seal

Pulley35% reduction
in stress

Pump rotor

StressDrive shaft

Hub (pulley sheet)
Pump bodyFig. 4 View of Water pump

Conventional design

Load from belt

New optimized design

Fig. 3 Stress analysis results

Integral shaft bearing

Fig. 5 Water pump structure-35-

NTN TECHNICAL REVIEW No.77（2009）

Through improvement in our production technology,
we have integrated the bearing and flange with theshaft, thereby we have successfully achieved anincrease in load carrying capacity of bearing, increasein pump capacity, longer bearing life, lower noise
emission and lighter weight. Fig. 8 summarizes
changes in appearance and weight of water pumpbearing over several years.

2.2.1 Structure of new bearing
In order to achieve lower running noise, lighter
weight and longer bearing life, we have developed anovel external bearing that has a shaft integrated witha flange. Fig. 6 shows a view of this novel externalbearing, and Fig. 7 schematically illustrates the
structure of this bearing. This structure ensures thatthe tension from the drive belt acts on the center ofbearing, helping prevent misalignment of the bearing
relative to the shaft. Compared with conventional
designs, the contact pressure between the balls andraceway surface on this bearing is lower, leading to
improved bearing durability. In addition, because our
new bearing is free from bearing-shaft misalignment
which will develop moment load, the balls will roll at thebottom of groove, resulting in lower running noiseoccurrence.

2.2.2 Determination of contact pressure occurring
between balls and raceway surface
So that a water pump on an automobile remains
operative without any need for repair until theautomobile reaches the end of its useful service life,
the life of water pump bearing needs to satisfy 3×105

Load from belt
Flange

Shaft

External bearing

Fig. 6 View of external bearing

Fig. 7 Structure of external bearing

Drive belt for auxiliaries is directly engaged with the outer ring; this arrangement
helps realize a space-saving pump design.
Use of larger balls helps reduce contact pressure, mitigating adverse effect ofpress-fitting operation.
21%

Greater pump capacity
Longer life
Weight reduction

Optimization of water pump

Improvements• Greater load carrying
capacity with bearing• Pump capacity• Bearing life
• Noise level• Weight

571g
2004

Years

2008

Fig. 8 Process of water pump bearing

-36-

451g

Eco-friendly Product Development at SNR Roulements

km of automobile’s total travel distance. In order for agiven water pump bearing design to satisfy this life
requirement, its internal design needs to be finalized sothat the contact pressure at any portion in it does notexceed fatigue limit of that portion. To this end, it isalso important to optimize tightening allowance of theseal, amount of prefilled grease, and location ofprefilled grease.
We have studied various parameters including
bearing life, temperature, parts tolerances, minimum
and maximum clearances, and tightening allowance,
executed functional test, and various tests with thepump lifetime tester shown in Fig. 9, thereby we haveestablished the design standard that satisfies thebearing life requirement.

automotive transmission is greatly affected by torqueloss occurring from an inactive idler gear: therefore,
bearing torque poses a critical factor in the torque loss
on the transmission.
The efforts SNR has so far made with its
transmission bearings in order to reduce CO2
emissions are as follows:(1) The inner and outer rings and rolling elements ofour bearings made of the standard steel material
100Cr6 are now subjected to a special heat
treatment process. Consequently, thesecomponents boast longer life even under severe
lubricating conditions.
(2) Development of unique self-lubricating bearings forautomotive gearboxes (Fig. 10 shows examples ofself-lubricating bearing lubricated with solid
lubricant).
(3) Decreased torque by superseding sliding bearings
for idler gear with rolling bearings such as caged
needle roller bearing.
(4) Optimized bearing design through analysis for load
and torque on transmission bearing by using newly
developed engineering computation software (asimulation model is shown in Fig. 11).
(5) Reduced frictional torque through improved internal
design for bearings.

Fig. 9 View of pump lifetime test

3. Efforts for bearing products of lower
torqueThis section describes our efforts for low torquedesigns with automotive transmission bearings, hub
bearings and suspension bearings.

3.1 Automotive transmission bearings

Fig. 10 Autonomous bearings using solid lubricant

Various improvement activities have been performedby people involved in automotive technologies to help
improve operability of automotive transmissions andreduce CO2 emissions from automobiles. To promotevarious automotive transmission systems, SNR has
been committed to lighter weight, higher efficiency(lower torque) transmission bearing designs.
Approx. 50% of torque loss occurring on a given
automotive transmission results from stirring-induced
resistance with lubricating oil. Therefore, anappropriate choice of lubricating oil is one of importantconsiderations in achieving lower torque on an
automotive transmission, and a currently more favored
combination is a use of minimum amount of low
viscosity lubricating oil. Incidentally, efficiency of anFig. 11 Transmission simulation-37-

NTN TECHNICAL REVIEW No.77（2009）

our bearing boasts improved seizure resistance.
Furthermore, filtering function of our bearing is virtuallyequivalent to that of conventional bearing design, andthe width of our bearing can be smaller. Our bearing
design can be applied to produce compact, light-weighttransmission bearing products.

3.2 Low torque ball bearings
To reduce friction-induced torque loss on an
automotive transmission, use of a ball bearing rather
than a tapered roller bearing is advantageous.
However, since load carrying capacity of a ball bearing
is smaller compared with a tapered roller bearing, thesize of ball bearing tends to be larger so that thebearing can satisfy targeted life. Incidentally, theordinary fracture mode of transmission bearing issurface damage starting from a dent mark on the
raceway owing to lubricant contaminated with foreign
matter, rather than fatigue failure of bearing material.
Therefore, to prevent ingress of foreign matter into abearing to ensure longer bearing life, a bearing having
filter seals shown in Fig. 12 is used. Filter seals need
to be optimally designed so that they not only provide
good filtering performance but also allow lubricating oil
to be introduced into the bearing to lubricate and cool
down the bearing.
Many bearings with filter seals feature an increased
bearing width dimension to accommodate an additionalelastomer filter seal; however, this configuration leads
to increased frictional torque on bearing. A novel
design developed by SNR, as shown in Fig. 13 has aclipped double polyamide cage that has filteringfunction. The advantages of this design are as follows:

Fig. 12 Bearing with filter seals
Oil flow

15.5

Clipped double
polyamide cage

Fig. 13 Bearing with double filter seals into a clippeddouble polyamid cage

Filtering effect and oil flow

(1) Compact and light-weight design is possible.
(2) Labyrinth clearance between the cage andraceway can be controlled at higher precision.
(3) Provision of two oil inlets helps increaselubricating oil flow into the bearing.
(4) Reduced cost
The result of comparison between our newly
developed double seal design and a conventional seal
design is described below.
Fig. 14 illustrates results of measurement of oil flow
through a bearing under oil bath lubrication
environment. The data mapped along the vertical axis
represent filtering effect and oil flow that passes a filterand contribute to lubrication. Compared with aconventional filter seal, our newly developed double
filter seals boast better lubrication efficiency as more
oil flows through the bearing though the filtering effectis roughly same.
Fig. 15 illustrates a result of comparing runningtorque of our newly developed bearing with double
filter seals to that of conventional bearing. Torqueoccurring inside the bearing including rolling resistanceis virtually the same with both bearing types;
notwithstanding, the total torque on our new bearing
design has been reduced by 65% because the torques
occurring on the seals has been greatly reduced. Also,
heat buildup in our bearing is mitigated; consequently,

Filtering effect
Oil flow

Filter seal
(conventional
design)Doublefilter seals(new design)

Fig. 14 Efficiency against pollution

Running torque N・m

0.350
Bearing interior
Seal

0.300
0.250

65%
reduction

0.200
0.150
0.100
0.050
0.000

Conventional
designNew design

Fig. 15 Torque test results-38-

Eco-friendly Product Development at SNR Roulementsfrom this diagram, the bearing products of SNR boast
25 to 50% reduction in torque loss, compared withcompetitor’s products.
25% reduction in torque loss with transmission
bearings means 2 g/km reduction in CO2 emissions per
vehicle. In addition, use of low torque tapered roller
bearings helps improve seizure resistance as well as
quality of shift-change operation.

3.3 Low torque tapered roller bearings
Tapered roller bearings are often used astransmission bearings because they can carry agreater combined axial and radial load compared withother bearing types of similar size. However, reduction
in frictional torque occurring on this bearing type posesa challenge.
The SNR tapered roller bearings for automotivetransmissions boasts decreased frictional torquethrough adoption of NTN’s design and production
technologies for low torque tapered roller bearings.
The advantages of these SNR products can be defined
as follows:(1) Special heat treatment process helps improve
fatigue strength and resistance against dent markthat can result from foreign matter in lubricant.
(2) Adoption of polyamide cage in which shear friction
with oil is lower, compared with that in standard
steel sheet cages(3) Improved design for bearing interior in order toimprove load carrying capacity and rigidity andmitigate misalignment and frictional torque(optimized number and size of rollers, and special
crowning on raceway surface and rolling surface)(4) Optimization of contact locations between inner ringflange surface, rollers, and raceway surface(5) Reduction in surface roughness of inner ring flange
surface and roller end faces to reduce frictional
torque on roller end faces

3.4 Automotive hub bearings
About 50% of frictional torque occurring on a wheel
bearing results from sliding friction on contact surfaceof seal(s). Therefore, the use of hub bearings featuring
reduced sliding resistance is effective in reducing theCO2 emissions from the vehicle that incorporates low
friction wheel bearings. However, reduced frictional
resistance on a given seal often means jeopardized
sealing performance of that seal. Therefore, there has
been a challenge of meeting conflicting needs for
reduced frictional resistance and improved sealing
performance.
SNR has developed a unique tribological effectcapable seal that boasts approx. 11% reduction insliding resistance and 22% improvement in sealing
performance, by improving lubrication quality on thesliding surface of seal lip. As SNR has applied theabove-mentioned development concept to its currently
present seal products, cost reduction and reduced
development lead time have been achieved.

3.4.1 Advantages of tribological effect-capable
seal products

Fig. 16 graphically plots information aboutcomparisons of SNR's tapered roller bearing fortransmission and a competitor’s tapered roller bearing,wherein the running speeds data of these bearings areplotted along the horizontal axis. As can be understoodOn our newly developed tribological effect-capable
seals, the lip sliding surface of the slinger is uniquely
shaped so that oil film is readily formed on it.

1.0

Running torque N・mCompetitor’s tapered roller bearing
0.8

0.6

0.4

SNR low torque tapered roller bearing
0.2

0
0

200

400

600

800

1000

1200

Running speed

1400

min-1

Fig. 16 Torque measurements with rotations

-39-

1600

1800

2000

NTN TECHNICAL REVIEW No.77（2009）

Consequently, lower torque and mitigation of heatbuildup have been achieved. Fig. 17 illustrates across-sectional plan of our seal, and a view of thecontact area of the slinger. Micro-pores present in thiscontact area help form an oil film between the seal lip
and slinger, and the oil film reduces friction on the seal
lip. Furthermore, these micro-pores prevent wear
caused by ingress and trapping of foreign matters.

3.5 Automotive suspension bearings
To be able to operate without problems under
severe operating conditions (environments such as
muddy water), a sealed strut bearing needs to feature
improved reliability and sealing performance. In
challenging this issue, SNR has developed a unique
low torque sealed strut bearing complete with a floating
seal in order to satisfy requirements for both an
improvement in running torque and sealing
performance (Fig. 21).

3.4.2 Performance of tribological effect-capable seal
Figs. 18 and 19 show running torque and test
results of a muddy water bearing life test withconventional seal and our newly developed tribologicaleffect-capable seal. Owing to reduced resistance on
seal, the running torque has decreased by 11%, andthe muddy water bearing life has increased by 22%.

3.5.1 Features of sealed strut bearings
Muddy water resistance of a bearing is governed bylip performance of its seal. Therefore, it is important todevelop a seal that is capable of satisfying both better
sealing performance and stabler running torqueperformance. To address this challenge, we haverecently developed a novel low torque sealed strut
bearing complete with a floating seal. Fig. 20 shows aconventional design, and Fig. 21 illustrates our new
design. For comparison purpose, Fig. 22 shows astructure of a different design, that is, an overmolded
lip seal.

Micro-pores

Enlarged view ofcontact area
on slinger

Fig. 17 Seal shape on the slinger

Torque N・m

0.7

11% reduction
in runningtorque

0.6
0.5
0.4

Seal area
Bearing area

0.3

Fig. 20 Usual design

0.2
0.1
0

Conventional
designTribologicaleffect-capable seal

Muddy water bearing life hFig. 18 Comparison of rotational friction between
development seal and current one

700
600

22%

500

Fig. 21 SNR design: floating seal

400
300
200
100
0

Conventional design

Tribologicaleffect-capable seal

Fig. 19 Comparison of muddy water resistance between
development seal and current one
Fig. 22 Competitor design: overmolded lip seal-40-

Eco-friendly Product Development at SNR Roulements

3.5.2 Test results

4. Afterword

Fig. 23 illustrates the contribution of a seal onto therunning torque of a strut bearing. Compared with aconventional design, the running torque on our newly
developed floating seal (SNR design in Fig. 21) is 18%
greater; compared with an overmolded lip seal, therunning torque on our new seal design is 50% smaller.
Fig. 24 provides results of muddy water test.
Compared with the conventional design, our newly
developed floating seal (SNR design in Fig. 21) boasts
greatly improved sealing performance that helps
positively reduce water ingress into the bearing.
Though excellent in initial sealing performance, theovermolded lip seal experiences wear of theovermolded lip: the SNR’s newly developed design
boasts 38% smaller water ingress.

This article has provided an overview about lighterweight, lower-torque, and eco-friendly automotive
bearing technologies of SNR. We have beencommitted to development of new technologies andproducts, aiming at further progress in light-weight andlow-torque bearing designs, and, at the same time,remains involved in long-term projects for hybrid
electric vehicles and pure electric vehicles.

Reduction in water ingress %Running torqueSeal area
Bearing area

50% reduction
in running torqueUsualdesignSNRdesign38% reduction
in water ingress

Overmolded
designUsual
designFig. 23 Torque test results

SNR
designOvermolded
designFig. 24 Muddy water test results

Photo of authors

Siegfried RUHLAND

Ludovic SAUNIER

Cynthia TSEN

Bernard LIATARD

Gérald MIRABELSNR Product Innovation& Mechatronic

SNR Product Innovation& Mechatronic

SNR Product Innovation& Mechatronic

SNR Automotive
Transmission Engineering

SNR Automotive
Equipment Engineering-41-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Actuator for Electromechanical Brakes

Tatsuya YAMASAKI**
Masaaki EGUCHI**
Yusuke MAKINO**Electromechanical brakes (EMB) have some advantages, such as
vehicle safety improvement and simple system. In electric vehicles andhybrid electric vehicles, which have received much attention in recent
years, applying EMB and controlling them in coordination withregenerative braking is expected to improve fuel economy. On the other
hand, it is desirable that the brakes be compact and lightweight, because
they are installed under the springs of the vehicles. NTN has developeda small actuator for EMBs with our original linear motion device.

friendliness. There has been a mounting need in themarket for an electrically actuated electromechanicalbraking system, as a means for solving these issues.
However, conventional electromechanical braking
systems, which use a ballscrew or ball-ramp for a linear
motion device, require a reducer mechanism to obtaina greater reduction ratio; thus, a compact actuator
design for this purpose has been difficult to realize.
By using its propriety linear motion mechanism, NTN
has developed a compact actuator forelectromechanical brakes 3). In this paper, we provide
information about our actuator for an electromagnetic
brake, whose performance has been improved by
optimization of its internal design.

1. Introduction
The brake system plays a critical role in the safe
operation of any automobile. Recently, carmanufacturers have been improving the safety of theircars through improvements in ABS, ESC and brakeassist systems that have resulted from improvements
in hydraulic control technologies1), 2).
Incidentally, while concerns about the global
environment have been mounting an increasing
number of electric motor-driven cars such as HybridElectric Vehicles (HEV), which boast better fueleconomy, and Electric Vehicles (EV), which do not use
any fossil fuels, have been marketed and will see everincreasing demand.
On HEV’s and EV’s a regenerative braking system
recovers energy during the deceleration process by
allowing an electric motor to function as a generator.
To be able to recover energy more efficiently, it isnecessary to further improve control over mechanicaland regenerative braking systems. In addition, on an
HEV or EV, the negative pressure occurring on theengine is insufficient or cannot be used; therefore, if aconventional braking system is used a separate
negative pressure generating system will be needed.
To sum up, it is difficult with conventional braking
systems to readily solve difficult issues, such as brakes
with more sophisticated functions and improved eco-

2. Structure of actuator for electromagnetic brake
2.1 Linear motion device(planet roller screw mechanism)
The constitution and operating principle of our linear
motion device are hereunder described. As shown in
Fig. 1, our linear motion device comprises of a sunroller, planet rollers, outer ring, carrier, support pins,
springs, and bearings. The planet rollers are
circumferentially arranged at equal intervals between
the sun roller that functions as an input means and theaxially sliding outer ring that functions as an output**Automotive Module Product Development Dept. New Product Development R&D Center**Mechatronics Research Dept. New Product Development R&D Center-42-

Actuator for Electromechanical Brakes

Support pin

support bearing

Caliper (housing)

Projection

Revolution of planet roller
Rotation of planet roller

Planet roller
Revolution
support bearing
Rotation

Friction-typetransmission
Sun roller (input)
Outer ring (output)
Springs

Rotation of sun roller

CarrierFig. 1 Schematic of linear motion device

Load exerted by the outer ringmeans. Torque on the sun roller is transmitted to theplanet rollers through friction. The outer circumferenceof each planet roller has an external thread or
circumferential groove that engages with an internal
thread on the bore surface of the outer ring; wherein
the pitch of the internal thread on the bore surface ofthe outer ring is the same as that of the external threador circumferential groove on each planet roller but thelead of internal thread on the outer ring is reversed tothat of the external thread or circumferential groove oneach planet roller. The carrier that supports the planet
rollers is supported by the caliper (housing) such that it
can rotate, but does not slide in the axial direction.
With this construction, when the sun roller rotates theplanet rollers revolve while rotating, thereby the rotary
motion of the sun roller is finally translated into theaxial slide motion of the outer ring.
Next, let us describe a means for providing a normalload that is necessary to permit a friction-typetransmission of torque from the sun roller to the planet
rollers. In a report from a previous issue of the NTN
Technical Review, the necessary normal load wasprovided by positioning the planetary rollers between
the sun roller and outer ring by a shrink-fitting
technique 3). With our new development, the planetaryrollers are forced into contact with the sun roller bymeans of a spring force being applied by the springs
connected to both ends of the support pin. At the sametime, the contact areas between the planetary rollers
and the outer ring are each designed to form a ramp
having a particular flank angle; consequently, when an
axial load acts on the outer ring as shown in Fig. 2, theramp-type contact surface exerts a load that forces thecorresponding planet roller toward the sun roller.
This structure helps mitigate the effect of adimensional change owing to a worn torquetransmission surface to the normal load; thereby, aThrustLoad exerted by the sun roller

Fig. 2 Load acting on planet roller

stable load acts along a normal line. In addition,
through optimization of the flank angle between theplanet roller and the outer ring, reliable torquetransmission is achieved without causing excessive
slippage between the sun roller and the planet rollers
even when a very high load is acting on the sun roller
and the planet rollers.

2.2 Electromagnetic brake unit
Fig. 3 schematically illustrates our electromagnetic
brake unit designed for the front wheels of a 1500 ccclass vehicle. To configure this brake unit, we haveincorporated our linear motion device, described inSec. 2.1, into the caliper together with an electric motor
such that the entire axial length of the brake unit isshorter. The linear motion device and the driving motor
are arranged in parallel, where the motor transmits
driving power to the linear motion device through agear train. Main specifications of this new EMB unit aresummarized in Table 1. Note that the driving motor forthis actuator has been designed by NTN Fig. 4
illustrates the structure of this motor, and Table 2
summarizes major specifications of this motor.
-43-

NTN TECHNICAL REVIEW No.77（2009）

Linear motion Caliper (housing)device

Gears

70m
m

Brake pad

Wheel
137

84.5mmMotor

mm

Brake disk

Fig. 3 Schematic of EMB unit

Table 1 Specifications of EMB unit
Specification

Max. thrust force

30kN

Load retaining
function.

None

Size
(excluding pad clamp)

−

5.6kg

−

Mass

3.1 Efficiency

Equivalent to that of front wheelsfor 1,500 cc-class vehicle
This setting may be changed to“Yes” by appropriately altering
the specifications for threadingfor planet rollers and outer ring.

137mm×70mm×84.5mm(excluding pads)

3. Performance

Remarks

Lubrication system Grease lubrication

Fig. 5 illustrates the interrelation between motor
torque, thrust force and efficiency. Note that thecalculated values in Fig. 5 have been determined byapplying the efficiency calculation method presented ina previous issue of NTN Technical Review 3). The
experimental values fairly match the calculated values.
Thus, our EMB unit performs as designed.

−

φ70

Thrust kN

Stator

40

80

30

60

20

40

10
ThrustEfficiency

Output shaft
Rotor

0
0

Efficiency %Characteristic20

Calculated Experimental

0
0.2

0.4

0.6

0.8

1

Torque Nm

54.5

Fig. 5 Efficiency of EMB unit (developed)

Fig. 4 Structure of motor

3.2 Thrust variation rate

Table 2 Specifications of motor
Characteristic

Specification

Type

DC brushlessSize

φ70×54.5

Voltage applied

12V

Max. running speed

5000min-1 (w/load)

Max. torque0.8Nm

By adopting the caliper shape shown in Fig. 3 andby using a pad and disk used on an actual brakesystem, the variation rate of thrust was assessed. Fig.
6 shows the results of the assessment obtained byapplying a constant voltage (12 V) to the EMB unit
placed in an ambient temperature of 20˚C. Table 3
summarizes the response times and thrust variation
rates defined by expressions (1) through (4).
-44-Actuator for Electromechanical Brakes

ThrustThrustVoltage applied

Voltage applied

40

Thrust kN, Voltage applied v

Thrust kN, Voltage applied v

40

Fa
30

0.75Fa
20

10

0
-0.1

t0

t1

t1'

0

0.1

Fa
30

20

10

t2
0.2

t3
0

0.3

t4
0

t5
0.1

0.2

Time sec

Time sec(a) During thrust increase (initial clearance: 0.0 mm)(b) During thrust decrease

0.3

Fig. 6 Thrust variation rate of EMB unit (developed)

Table 3 Response time and thrust variation rate
CharacteristicTime

Thrust variation rate

During thrustincrease

0.172 s(=ΔtINC)

170 kN/s(=VINC)

During thrust
decrease

0.146 s(=ΔtDEC)

221 kN/s(=VDEC)

3.3 Durability
Table 4 summarizes the characteristics tested in the
durability test that has been performed in accordancewith JASO C 448-89 that specifies the bench test
method for the disk brake caliper assembly of apassenger car. Our new design has satisfied the
durability requirements for all the characteristics
summarized in Table 4.

ΔtINC＝t1−t0 ……………………………………… (1)ΔtDEC＝t5−t3 ……………………………………… (2)Table 4 Durability test

0.75・Fa
VINC＝―――― ……… … … … …………………… (3)t1'−t1

Characteristics tested
Torque durability

Braking torque Equivalent to 0.6G
Number of braking cycles 20×104

Fa
VDEC＝―――― ………………………………………(4)t5−t4High thrust durability

Magnitude of thrust 30 kN
Number of thrust applications 1×104

Normal temperature
actuation durability

Temperature 4〜35˚C
Magnitude of thrust 15 kN
Number of thrust applications 50×104

High temperature
actuation durability

Temperature 120˚C
Magnitude of thrust 15 kN
Number of thrust applications 7×104

Vibration durability

Vibration acceleration ±20G (vertical direction)
Vibration frequency 60 Hz
Number of vibration applications 500×104：Max. thrust force = 30 kN：Actuation start point (during thrust increase)：Thrust increase start point：75% maximum thrust reached point(during thrust increase)t2：Maximum thrust reached point
t3：Actuation start point (during thrust decrease)t4：Thrust decrease start pointt5：Brake release end point
VDEC ：Thrust variation rate (thrust decrease rate)
VINC ：Thrust variation rate (thrust increase rate)
ΔtDEC ：Time (during thrust decrease)
ΔtINC ：Time (during thrust increase)
Fa
t0
t1'
t1

-45-

Test parameters

NTN TECHNICAL REVIEW No.77（2009）

4. Conclusion
This paper has presented our unique actuator, which
incorporates NTN’s propriety linear motion device for acompact electromagnetic brake.
As electric motor-driven cars such as HEV and EV
become more commonly used, there will be anincreasing need for electromechanical brake systems.
NTN will further improve durability and response speedof the actuator so that it can be reliably used onelectromagnetic brakes.

References
1) Tomohiko Adachi: Trends in Electronic Stability
Control (ESC) Systems, Journal of the Society ofAutomotive Engineers of Japan, Vol. 60, No.12 (2006)
28-33 (Japanese)
2) Bo Cheng, Tetsuo Taniguchi, Tadashi Hatano, Toshiya
Hirose: Effects of Brake Assistance Systems in
Emergency Situations, Proceedings of the Society ofAutomotive Engineers of Japan Annual Congress No.
20065894 (2006) (Japanese)
3) T. Yamasaki, M. Eguchi and M. Makino: Developmentof an Electromechanical Brake, NTN Technical
Review No. 75 (2007) 53-61

Photo of authors

Tatsuya YAMASAKI

Masaaki EGUCHI

Yusuke MAKINO

Automotive Module ProductDevelopment Dept.
New Product Development
R&D Center

Automotive Module ProductDevelopment Dept.
New Product Development
R&D Center

Mechatronics Research Dept.
New Product Development
R&D Center-46-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Electric Ball Screw Actuators for Automobiles

Yoshinori IKEDA*
Hirakazu YOSHIDA*
In the automotive market, many new hybrid cars and low -fuel consumption and low -emission engines have been developed toreduce CO2 and to produce cleaner exhaust. At the same time,
many projects are advancing to achieve more car amenities andsafer driving using quicker and more reliable electric motor drives. NTN had already developed a
new electric ball screw for use in automatic manual transmission and engine control. Building on
this, we have developed an electric ball screw actuator with modularized peripheral parts. This
article introduces the structure and the features of this ball screw actuator unit.

1. Introduction

2. Structure of the actuator

Control-by-wire technologies for automobiles are
becoming more commonly adopted with one typicalexample being the by-wire throttle control system.
Recently though, certain cars have adopted brake-bywire technology. Control-by-wire technologies havebeen ever evolving in an effort to achieve better
comfort and safety in operating vehicles.
Recently, NTN has developed a high-response,
high-thrust, electrically driven ballscrew actuator for
automobiles (hereinafter referred to as “actuator”) thatcan be adopted for control-by-wire systems.
This paper hereunder describes the structure andfeatures of this actuator.

Fig. 1 shows the structure of our actuator.
The ballscrew is coupled with an electric motor via
an involute spline formed at one end of the ballscrew
shaft to transmit torque from the motor.
At the other end of the ballscrew shaft, a double row
angular ball bearing is situated securely in analuminum case. The ballscrew and actuator aresynchronized by means of an interlocking arm. Acrossboth ends of the actuating shaft, linear ball bearingsand oil seals are arranged symmetrically.
The linear ball bearings support the actuating shaft
while developing only minimum friction so that theactuating shaft can slide in the axial direction. The oil
seals situated around the linear ball bearings prevent
ingress of foreign material into the aluminum case. An
actuating wire is connected to the coupling member atthe end of the actuating shaft.

Actuating shaft
Coupling member

Oil seal
Boot

Linear ball bearing

Oil seal
Shaft cap

Interlocking arm
Double row angular contact ball bearings
Lock nut

DC motor

Aluminum case
Ballscrew nut

Ballscrew shaft

Fig. 1 Structure of actuator*Automotive Sales Headquarters Automotive Engineering Dept.

-47-

Involute spline

NTN TECHNICAL REVIEW No.77（2009）as 32%; in contrast, the efficiency of the ballscrew
adopted in our actuator is very high, standing at 92%.
Fig. 5 shows the linear ball bearings that support
both ends of the actuating shaft. The actuating shaft is
supported by the linear ball bearings in rolling contact,
thereby the resultant lower friction helps the actuating
shaft to move smoothly.

3. Advantages of our actuator
Fig. 2 shows our actuator, and Fig. 3 shows theballscrew for our actuator.
The actuator has undergone various tests
simulating various environmental conditions including
water, snow, mud, gravel, and dust along withvibration and impact testing. Through these tests, theactuator has been progressively improved and now
boasts a higher degree of reliability. The actuator
boasts the following advantages:

Table 1 Spec. of ballscrew(1) Highly efficient ballscrew and lower friction
moving parts help achieve a higher degree of
response and greater thrust force.
(2) Sufficient corrosion resistance, and dust-proof& water-proof performance

Shaft diameter

Lead

Lead angle

14.5mm4mm

4˚47'

Efficiency in forward rotation

100
92% 90
80
70
60
50
40
30
20
10
0

Ball screw

Efficiency %(Friction coefficient: 0.005)

These advantages are described below:

Efficiency in reverse rotation(Benchmark)Sliding screw(Friction coefficient: 0.1)

Efficiency in forward rotation
0

1

2

3

4

5

6

Lead angle deg

Fig. 4 Efficiency of ballscrew

Fig. 2 Ballscrew actuator

Fig. 5 Liner ball bearing

3.2 Corrosion resistance, dust-proof &water-proof performance
Any automotive actuator needs to perform as
designed for a prolonged period under various
environmental conditions. Our actuator, in particular,
has an actuating shaft that is exposed outside thecase; therefore, both ends of the shaft are provided
with reciprocating motion-capable oil seals to prevent
ingress of foreign material.
For enhanced corrosion resistance, the actuating
shaft is provided with special plating. Furthermore, theactuating shaft is equipped with a boot and shaft cap
so that the shaft is not directly exposed to the ambientair (Fig. 6).

Fig. 3 Ballscrew for actuator

3.1 Higher efficiency and lower friction
We have set up the specifications for our actuatorso that the conversion efficiency of motion of theballscrew adopted, from both forward and reverse
rotation directions, is 90% or greater. The actuating
shaft can be readily moved by hand thanks to its lowfriction design.
Table 1 provides the specifications for theballscrew. Fig. 4 graphically plots the theoretical
efficiency of the ballscrew. At a lead angle of 4°47’,
the efficiency with a benchmark sliding screw is as low-48-

Electric Ball Screw Actuators for Automobiles

Oil seal
Actuating shaft

Actuator

Shaft cap

Moving part

Load cell
Fixed part

Direction ofload application

Boot

Linear ball bearing (2 pos.)Fig. 6 Structure of sealing of shaft

Fig. 7 Appearance of thrust force test

4. Evaluation test
Generated axial thrust force N

3000

In an effort to develop a highly reliable
electromechanical actuator, we have performed
various tests to verify that our actuator has sufficientperformance and reliability. The major characteristics
tested are described below:

4.1 Thrust force test
The load torque on a ballscrew can be determinedwith the following expression:

2500
2000
1500
1200N
1000
500
0
3.5

P・L
T＝―――― ………………………………………(1)
2π・η

4.5

Sliding screw
Time

sec.

Fig. 8 Thrust force measurement

where,
T ： Load torque (N-m)
P ： Axial load (N)L ： Lead of ballscrew (m)η ： Efficiency 0.92
Using the result from expression (1), the thrust force
can be determined with expression (2) below:

have fabricated a special durability tester that uses anadditional ballscrew responsible for applying a
constant load to an actuator sample. Fig. 9 shows aview of this tester. We performed a durability test for anumber of loading cycles that is equivalent to the lifeof a car while applying the maximum expectedworking load to each actuator sample and, after
completion of the durability test, we performed an
actuator response test.

T・2π・η
P＝――――― ……………………………………(2)L
For the thrust force test, a load cell was inserted
between the coupling member and a fixed part asshown in Fig. 7 to measure the load.
The result of the thrust force measurement isplotted in Fig. 8. We have verified that the theoretical
calculated value of 1,200 N is achieved with ourballscrew. The thrust force available from a sliding
screw whose size is similar to that of our ballscrew isapproximately 1/3 that of our ballscrew.

Load applying device
MotionActuator

Backward end sensor

4.2 Durability test in severe environment
We have subjected the actuator samples to a
durability test under severe environmental conditions
with a high-temperature ambience while applying apredetermined load to each actuator sample. So that a
constant load is applied to an operating actuator, we

Load cell

Backward end sensor

Fig. 9 Appearance of durability test

-49-

NTN TECHNICAL REVIEW No.77（2009）

Fig. 10shows results of the response test obtained
from actuator samples before and after the durability
test. Our actuator having undergone a severe
durability test still boasts a higher level of responsecompared with the pre-test level and its post-test
response shows no deterioration.
From these findings we have determined that evenafter having undergone a durability test under severe
environmental conditions the performance of ouractuator is as good as the pre-tested level.

5. Conclusion
We have presented information about our unique,automotive electromechanical ballscrew-driven
actuator that adopts various mechanical elementrelated technologies for realizing higher response andgreater thrust force.
With electromechanical moving parts increasingly
being used in recent automobile designs, more
automobile designers have been considering use ofballscrew-driven mechanisms that can be actuatedwith smaller electric motors. Thus, our ballscrew
actuator products will find a greater market share.
To be able to further improve the lighter-weight andenhanced functionality designs for its automotive
electromechanical ballscrew actuator products, NTN iscommitted to improvements in not only elementaryparts such as the ballscrew but also auxiliarycomponents such as sensors and electric motors.
Through these efforts, NTN will help expand the scopeof applications of its ballscrew actuator products.

20
15

Location mm

10

After
durability test

5

0.16 sec

0-5

Before-10 durability test
-15
-20
0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time sec.

Fig. 10 Example of operating time measurement

References
1) K. Tateishi and K. Kazuno: Ball-screw for AutomatedManual Transmissions, NTN Technical Review No. 73(2005) 72-75
2) K. Kazuno: Ball-screw Unit for Variable Valve Eventand Lift Systems, NTN Technical Review No. 75(2007) 72-77

4.3 Combined cyclic corrosion test
Our actuator was placed in the combined cyclic
corrosion tester and each sample was subjected torepeated environmental cycles. Each cycle consistedof a salt water spray, high-temperature drying, and ahigh-temperature high-humidity condition to verify
corrosion resistance of our actuator under severe
environmental conditions.
Fig. 11 shows the appearance of our actuator
having undergone the combined cyclic corrosion test.
The interior of our actuator having undergone thesevere test does not show any problems such as rustor water ingress; the characteristics of the post-test
actuator do not show any signs of problem.

Photos of authors

Fig. 11 Internal condition after cyclic corrosion test

-50-

Yoshinori IKEDA

Hirakazu YOSHIDA

Automotive Sales Headquarters
Automotive Engineering Dept.

Automotive Sales Headquarters
Automotive Engineering Dept.

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Plastic Bearings for Electric Pumps
for Next Generation Battery Cells

Norio ITOH*
Takuya ISHII*

In order to reduce CO2 emissions, devices with next generation
battery cells are being introduced or are already on the market.
Fuel cell co-generation systems, electric evehicles and hybrid
vehicles have electric pumps to circulate cooling water in thecooling systems for the cells and motors. BEAREE AS5704
bearings, which have excellent self-lubricity, chemical resistance and high flexibility in design, areused in these electric pumps. This article introduces the characteristics and applications of BEAREE
AS5704 bearings.

into a fuel-cell stack that generates electricity byelectrochemical reaction. Electrochemical reaction
taking place in a fuel-cell stack is an exothermic
reaction; therefore, the cooling system (which
circulates cooling water) that regulates the temperatureinside the cell stack to a constant level is driven by anelectromechanical pump. The typical requirements forthis electromechanical pump are high efficiency andcompact size. In order to satisfy these requirements,
the electromechanical pump adopted is often a magnet
drive-type centrifugal pump.

1. Preface
To help reduce CO2 emissions, unconventional
apparatuses that do not burn fossil fuels have been
increasingly marketed recently, and the need forapparatuses incorporating next generation battery cells
has been mounting. The most common applications
introducing these novel apparatuses include fuel-cellcogeneration systems in the industrial and homeelectric appliances fields and electric vehicles andhybrid electric vehicles in the automotive engineering
field. Each of the cooling systems that mitigate heatbuildup in these apparatuses has a built-in
electromechanical pump that circulates cooling water.
This article provides information about resin sliding
bearings suitable for electromechanical pumps and thetypical applications of such bearings are included.

2.2 Cooling systems on electric vehicles (EV)and hybrid electric vehicles (HEV)
On conventional automobiles driven by internal
combustion engines (ICE), a centrifugal pump is used
to circulate radiator coolant to cool down the ICE,
wherein rotary motion on the engine is input to thepump shaft via a drive belt.
Incidentally, any EV does not have an ICE, and an
ICE on HEV is shut down in idling stop mode:
therefore, an electromechanical pump is needed toactuate a cooling system for battery cells and/or
electric motor. The electromechanical pump used forthis purpose is often a magnet drive-type centrifugalpump.

2. Electromechanical pumps forvarious systems
2.1 Fuel-cell cogeneration system1)
By the electrochemical reaction between hydrogenand oxygen, a fuel-cell generates electricity. The
oxygen it uses is derived from air, while the hydrogen it
uses is obtained by reforming the air with a reformer:
the so-obtained oxygen and hydrogen are introduced*Engineering Dept. NTN Engineering Plastics Corporation-51-

NTN TECHNICAL REVIEW No.77（2009）

lubricating slots on the bore surface and end face ofthe bearing and a retaining feature (D-shaped cutout,
projection, etc.) on the outer circumference of the
bearing to help securely engage the bearing with the
impeller (see Fig. 2).
Without undergoing any machining process, a resinmade sliding bearing can be formed together with an
integrated impeller.
When a resin sliding bearing runs, a radial load andan axial load act on it, thereby causing sliding contact
between the bearing bore and stationary shaft andbetween the bearing end face and thrust force carrying
face . The material used for this resin sliding bearing is
NTN BEAREE AS5704.

3. Construction of electromechanical pump
Generally, pumps transport fluids such as water,
liquid fuels, lubricating oils, organic solvents, and acidic
and alkali liquids. Three major pump operation types
are available: centrifugal, volumetric rotary andvolumetric reciprocating types, wherein their rotary
shafts are supported by bearings. When the fluid
transported by a pump is water, or acidic or alkali
liquid, an ordinary metal bearing can develop a
corrosion problem: to address this issue, carbon sliding
bearings and resin sliding bearings may be used 2).
Resin sliding bearings boast better self-lubricating
performance and chemical resistance. In particular,
injection-molded components of sliding bearing boast
greater freedom of design for factors including shape.

Retaining feature(D-shaped cutout)

3.1 Magnet drive-type centrifugal pump
Fig. 1 shows a structure of a typical magnet drivetype centrifugal pump. With this structure, the magnets
installed onto the motor shaft rotate to cause theirmagnetic force to rotate the impeller integrated with themagnets in the casing, thereby causing the pump totransport the fluid.

Lubricating slot
(4 pos.)Fig. 2 Bearing

Fluid OUT
Casing4. BEAREE AS5704 resin bearing
MagnetCasingBearing

Thrust bearing

4.1 Features

Motor shaft

The BEAREE AS5704 resin sliding bearing consistsof PPS (polyphenylene sulfide) blended with a special
filler.

Electric
motor

Fluid
IN

<Advantages>(1) Compared with a general-purpose PPS resin
sliding bearing, wear of our bearing in water is
20% or lower.
(2) Low wear or abrasion on a mating material suchas stainless steel(3) BEAREE AS5704 bearing boasts greater
freedom of design in shape due to injection
molding.
(4) Can be used even in anti-freeze liquid, or acidic
or alkaline liquid

Stationary shaft
Impeller

MagnetFig. 1 Structure of magnet drive centrifugal pump

3.2 Resin sliding bearing
Conventional magnet drive type centrifugal pumps
often use carbon sliding bearings. A carbon sliding
bearing can be molded together with an impeller;
however, because this bearing component is obtained
only by machining a molded blank, the form factor
flexibility of this work piece is limited. Therefore, thisbearing type requires improvement in its resistance toimpact-induced cracking and reduction of costs.
Through an injection molding process, geometricalfeatures can be readily formed on a resin-made sliding
bearing, and the examples of such features include

4.2 Basic physical characteristics
Table 1 summarizes the basic physical characteristics
of BEAREE AS5704 material.

-52-

Plastic Bearings for Electric Pumps for Next Generation Battery Cells

Table 1 Basic characteristics of BEAREE AS5704
Test method

Characteristics

Specific gravity
ASTM D792
Tensile strength
ASTM D638
Elongation
Bending strength
ASTM D790
Bending elastic modulus
Linear expansion
TMA method
coefficient
Rockwell hardness

ASTM D785

Table 3 provides a comparison of performance ofsliding bearings made of these materials. Using PPS
resin as a base material, the BEAREE AS5704 bearing
excels in chemical resistance and dimensional stability
after having absorbed water.

Unit of
Characteristic
measurement
value
―
MPa
%
MPa
GPa
1/˚C

1.64
54
0.7
103
10
MD : 2.0×10-5
CD : 4.5×10-5

R scaleTable 3 Comparison of features various bearings
Bearing type

112
Process used

ASTM D256
J/m(Notch type)※The values given above are representative values.
Izod impact strength27

4.3 Comparison of various bearings(resin materials)
Examples of materials of typical resin sliding
bearings used in liquid include phenol resins and PTFE
(polytetrafluoroethylene) resins. To compare wear
resistance characteristics of these materials with thoseof BEAREE AS5704 and carbon material, we have
performed an underwater wear test. Table 2
summarizes the test conditions applied, and Fig. 3
shows specific wear NOTE) of various bearing materials.
BEAREE AS5704 boasts superior wear resistanceand has lower friction compared with the carbon
material.

Test equipment

Underwater ring on disk type

Bearing pressure

0.4 MPa
25 m/min（Hv200，0.4μmRa）
SUS304

Environment

Water(normal temperature, no temperature control)

Test time

50h

Specific wear ×10-8mm3/（N・m）

Sliding velocity
Mating material

400
300
200
100
0

CarbonPhenol
resin

PTFE
resin

(including graphite)(including graphite)

○

△

×

◎

◎

△

◎

○

×

△

○

○

×

×

○

○

○

○

×

◎

×

○

×

Price

◎

×

○

×

Under the test conditions summarized in Table 2,comparison test for friction wear characteristics has
been performed for BEAREE AS5704 and three PPSresin based bearing materials (PPS + fiber glass, PPS+ carbon fiber, and PPS + PTFE). Fig. 4 shows thetime-dependent variation in dynamic friction
coefficients of these materials, and Fig. 5 provides the
specific wear of these materials.
BEAREE AS5704 boasts the lowest dynamic friction
coefficient, and the value of this coefficient remains
stable. Furthermore, the specific wear of BEAREE
AS5704 is less than 20% of the PPS resin blended
with carbon fiber coefficient. The wear depth on themating material (SUS 304) that underwent the test has
been measured. As a result, the wear depth on themating material tested with the PPS resin blended withcarbon fiber was approximately 5 µm. In contrast, themating material tested with BEAREE AS5704 did not
develop any wear (Figs. 6 and 7).

500

BEAREE
AS5704◎4.4 Comparison to PPS resin bearing

Table 2 Wear test condition
Content

Wear resistance(underwater)
ChemicalresistanceDimensional stabilityof material having
absorbed water
Resistance to cracking
due to impact
Resistance to deformation due to impact
Degree ofFreedom of design◎：Excellent ○：Good △：Acceptable ×：Not acceptable

NOTE) “Specific wear” means a wear volume per unit sliding
distance or per unit load calculated from wear before andafter the test. Smaller specific wear means smaller wear.

Characteristics

BEAREE Carbon Phenol resin PTFE resin(including graphite) (including graphite)
AS5704
Injection
Injection compremolding Machining ssion molding Machining

Fig. 3 Specific wear of various bearings-53-

NTN TECHNICAL REVIEW No.77（2009）

4.5 Limiting PV value of BEAREE AS5704
BEAREE AS5704

Two sets of velocity conditions summarized in Table
4 were tested. Under each set of conditions, thebearing pressure was increased by 1 MPa per hour.
The limiting bearing pressure was recorded as thepressure at which the wear exceeded 20 µm or thesliding surface melted. Table 5 summarizes limiting PV
values calculated from the test velocity and limiting
bearing pressure.

PPS resin + fiber glass

Dynamic friction coefficient

PPS resin + carbon fiber
PPS resin + PTFE resin
0.8

0.6

0.4

Table 4 Limit PV test condition

0.2

Characteristics
0.0

0

10

20

30

40

50

Time hSliding velocity 100，300 m/min

Fig. 4 Coefficient of dynamic friction of PPS bearings

Mating material SUS304（Hv200，0.4μmRa）
Environment

Specific wear ×10-8mm3/（N・m）

Content

Test equipment Underwater high-speed ring on disk type

Antifreeze (normal temperature, no temperature control)

500

Table 5 Limiting PV value
400

300

Sliding velocity (V)Limiting bearing
pressure (P)Limiting PV value

100m/min

7 MPa

700 MPa・m/min

300m/min

3 MPa

900 MPa・m/min

200
100

4.6 Wear curve of BEAREE AS5704
0

BEAREE
AS5704

PPS resin +fiber glass

PPS resin +carbon fiber

Under the test conditions summarized in Table 6,
the time-dependent wear on BEAREE AS 5704
specimen were measured; then the wear curve in Fig.
8 was plotted. This plot shows an initial wear phasebeginning at the start of test and ending at 50
operating hours. After that point, the wear curve
exhibits steady wear state and shows virtually no
increase in the wear.

PPS resin +PTFE resin

Fig. 5 Specific wear of PPS bearings

Sliding area

Table 6 Wear test condition
Characteristics

Content

Test equipment Underwater high-speed ring on disk type

1mm

Bearing pressure 1.15 MPa
Sliding velocity

Fig. 6 Surface roughness of mating material after test

170 m/min

Mating material SUS304（Hv200，0.4μmRa）
Environment
Test time

Sliding area

1mm

Fig. 7 Surface roughness of mating material after test

-54-

Antifreeze (normal temperature, no temperature control)
500hPlastic Bearings for Electric Pumps for Next Generation Battery Cells

Because its base material and filler are highly
resistant to chemicals, FL3700 remains impervious tovirtually all chemicals, and therefore is used inchemical pumps.
For food machinery applications, the bearing resinmaterial must not be black in color. Therefore, FL3642,
which is pale yellow, is adopted 4).

Wear μm

30

20

10

7. Afterword
0
0

100

200

300

400

EVs and EHVs will be more commonly used in the
future. Consequently, demand for electromechanicalpumps used on these vehicles will further expand.
These electromechanical pumps need to be more
efficient, have longer service life and feature much
more compact size. Therefore, performance of resin
sliding bearings for these pumps need to be further
improved. To address these challenges, we are going
to continue our research and development efforts forour resin sliding bearings so that we can further
improve the sliding mechanism with our bearing
products to improve their functionality. We believe thatdemands for resin sliding bearings will further increase
in applications that require low friction and low wear
characteristics. We hope this report may help deliveruseful information to people involved in thisengineering field.

500

Time hFig. 8 Wear curve

5. Considerations about use of resin
sliding bearings
When setting up the clearance between a resin
sliding bearing and a mating shaft, it is necessary toconsider the linear expansion coefficient of the resinmaterial. Generally, linear expansion coefficients ofresin materials are greater than those of metalmaterials. For example, in a case where the material of
an impeller integrated with a bearing is a metal, or
there is a temperature gradient across the bearing andthe impeller, resulting in heat generation at the sliding
area, the bearing expands toward its bore side. In thiscase, incorrect bearing clearance design can lead toelimination of bearing clearance to the mating shaft,and this in turn can lead to abnormally severe wear on
the bearing and mating shaft 3).

References
1) O. Tajima: Development Status of Proton Exchange
Membrane Fuel Cells (PEFC) 2, Denki (2004) 35(Japanese)
2) T. Hayashi: Machine Parts and Elements, Japan
Plastics Vol. 57, No. 4 (2006) 50 (Japanese)3) NTN Corporation Editing Team: Understanding
Bearings (2007) 154
4) Oki and T. Ishii: Tribological Properties of PTFE
Composite Materials in Water, Monthly Tribology Vol.
13, No. 12 (1999) 48 (Japanese)

6. Special materials for difficult applications
Electromechanical pumps have been used invarious industrial fields and environments. In addition
to BEAREE AS5704, NTN offers the BEAREE FL3700
and FL3642 lines of products made from PTFE resin
as base material for difficult applications (Table 7).
Table 7 Bearings under special condition
Bearing

Base material

Advantages

BEARI FL3700

PTFE resin

Chemical resistance

BEARI FL3642

PTFE resin

Non-black color: may be used incontact with food or drinking water.

Photos of authors-55-

Norio ITOH

Takuya ISHII

Engneering dept.
NTN Engneering Plastics Co.,ltd

Engneering dept.
NTN Engneering Plastics Co.,ltd

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Low-torque Roller Lifter Unit

Masashi NISHIMURA*

The demand for improved fuel consumption and exhaust emissions
control in cars has increased on a global basis in recent years. Automobile
companies are working to develop gasoline direct-injection engines as one
means to achieve new fuel efficiency targets. Other demands include
increasing the fuel pressure and reducing the friction in the fuelcompression process in the high-pressure fuel pumps used for directinjection engines. NTN has developed a low-torque roller lifter unit that responds to these demands.
This report introduces the features of this NTN low-torque roller lifter unit.

better compared with the FY2004 level 2).
To address this situation, automakers have beencommitted to development of hybrid electric vehicles
and electric vehicles; as well as fuel economy
improvement through techniques including variable
valve system and idling stop. Direct-injection gasoline
engine also appears to be a particularly promisingmeans.
Direct-injection engines are characterized by thefact that air alone is drawn into cylinders andcompressed. Fuel is compressed by a fuel pump is
directly injected into the cylinders where the fuel isfired. In contrast with conventional engines that draw
air-fuel mixture generated in an intake pipe into thecylinders (port injection), direct-injection engines are
said to develop better fuel economy owing tooperation of the following reasons 3), 4).

1. Introduction
EU has decided to enact in 2012 its CO2 emissions
regulation according to average CO2 emission perpassenger car of 130 g/km or lower, which means
20% reduction relative to the present emissions level.
Also, USA has established targets for improved fueleconomy which include average 40% improvement infuel economy by fiscal year 2020 in terms of theamount of gasoline consumed by passenger cars orcompact trucks 1). Thus, NTN believes that the needfor more fuel-efficient cars will increase and more
stringent emissions standards will be introduced.
In Japan, a new fuel economy standard (see Table
1) has been legislated whose deadline is set at fiscal
year 2015: accordingly, the fuel economy ofpassenger cars in Japan in FY2015 will be 23.5%(1) Improved anti-knock properties to allow for ahigher compression ratio (greater engine power).
(2) Accurate control of the air/fuel ratio(3) Reduced pumping loss at a lower load range

Table 1 2015 year fuel-efficient target(Improvement rate compare with 2004) 2)
Car type

Actual value Estimated value
for FY2004
for FY2015

Improvement in fueleconomy over
FY2004 level

Passenger car 13.6
（km/R） 16.8
（km/R）

23.5%

8.3（km/R） 8.9（km/R）

7.2%（km/R） 15.2
（km/R）
Compact truck 13.5

12.6%

Compact bus*Needle Roller Bearing Engineering Dept. Automotive Sales Headquarters-56-

Low-torque Roller Lifter Unithigh as 20 MPa 5) in order to improve combustion
efficiency. It appears that much higher injection
pressure will be increasingly adopted.
A higher fuel injection pressure means a greaterload exerted onto the lifter. A conventional lifter, inparticular, whose contact surface to the cam is asliding surface can experience deterioration in fueleconomy owing to greater friction with the cam.
At the same time, to be able to adopt higher fuelpressure, it will be necessary to increase a number of
cam-operated compression cycles (increased cam
cyclic rate and increased number of high points oncam) as well as a cam lift. To cope with thesechanges, the outer circumference length of cam needs
to be longer if the base circle dimension of cam
remains unchanged. Consequently, the bearing usedin this type of application needs to be capable ofhigher running speeds.

2. Peripheral structure around directinjection engine and typicalapplications of roller lifter unit
Fig. 1 shows an appearance of a roller lifter unit
while Fig. 2 illustrates a structure around a fuel pumpon a direct injection engine. Fig. 3 provides a view oftypical application of a roller lifter unit.
In combination with a cam, a roller lifter unit situatedin a fuel pump drive on a direct injection engine
transmits rotary motion of the engine shaft to areciprocating plunger.
Previously, most commonly used roller lifter units
had a sliding surface in contact with a cam. Now,certain automakers are adopting rolling type roller lifter
units in order to reduce friction loss from contact witha cam and to allow a cam to be able to run at a higher
speed.
Usually, on a direct injection engine, the fuel isinjected with a pressure of 4 to 13 MPa. On certain
direct injection engines, the injection pressure is as

Fuel pump

Fig. 1 Appearance of roller lifter unit

Fig. 2 Direct injection engine, fuel pump

Roller lift unit
Fuel pump

Mating guide hole
Intake camshaft

Fuel pump driving cam

Fig. 3 Application of roller lifter unit

-57-

NTN TECHNICAL REVIEW No.77（2009）

complement roller type bearing.
Furthermore, NTN has optimized wall thicknessesof various areas of the casing of its roller lifter unit sothat the casing features lighter weight while
maintaining necessary mechanical strength. Thus,
NTN has reduced the inertial force occurring on its
roller lifter unit in reciprocating motion so that its roller
lifter unit can more accurately follow the motion of cam
running at higher speed.
Fig. 4 shows the specification for NTN low-torqueroller lifter unit.

3. Structure and advantages of NTN
Low Torque Roller Lift Unit
As mentioned above, more common roller lifter units
previously used have sliding contact surface that is incontact with a cam: certain automakers are usingroller lifter units incorporating rolling bearings in orderto mitigate friction loss. The rolling bearings used forthis purpose are full complement roller bearings
because of their excellent load bearing performanceand longer life*1. However, full complement roller
bearings can pose problems such as heat buildup andincreased running torque. Intermittent loading by the
cam as well as inclination occurring from the gap
between the roller lifter unit and mating guide hole willlead to skew on the rollers. This skew will cause thebearing to develop lateral runout , which triggers theabove-mentioned problems.
In order to mitigate lateral runout on the bearing forroller lifter unit, NTN has adopted a caged roller
bearing to inhibit skew occurrence on the rollers,
reduce running torque on the bearing, and improvehigh-speed durability of the roller lifter unit. Also, NTN
has adopted FA treatment which is NTN’s propriety
heat treatment technique to improve bearing life,
thereby NTN has achieved a calculated bearing lifethat is equivalent to or better than that of full

4. Evaluation by performance
Higher fuel temperature means a greater load
applied to the lifter. In particular, on conventional
lifters whose contact surface to the cam is a sliding
surface. The friction on the contact surface will begreater and can cause deterioration in fuel economy.
Furthermore, to help achieve higher fuel pressure, thelifter needs to be more durable at higher speed.
In order to evaluate the performance of our roller
lifter unit, NTN measured torques and temperature
increases on the bearing. The section below presents
some portion of information about our tests forevaluating our roller lifter unit.

[Outer ring][Rollers]
FA treatment

30[Cage][Detent pin]*2[Shaft]Special induction
heat-treated
Hollow shaft[light-weight design]

φ26[Casing]

Bearing size: ID 8 ×OD 16×W18 (in mm)

Fig. 4 Specification of NTN low-torque roller lifter unit
*1: “Full complement roller bearing” means a roller bearing type not having a cage. Though this bearing type boasts greater load rating
because of a greater number of rollers for a given bearing size, but can develop problems such as skew proneness of rollers because
the rollers are not guided by a cage.
*2: The detent pin slides in the groove formed in the mating guide hole to prevent the roller lifter from rotating in the circumferential
direction on the casing.

-58-

Low-torque Roller Lifter Unit

4.1 Torque measuring operation

4.1.2 Result of torque measurement

NTN measured torques on bearings in lifter units todetermine the reduction of friction loss using NTN low
torque caged roller lifter compared to conventionalsliding type lifters and full complement roller type lifter
units.

Fig. 6 Graphically plots the resultant torquemeasurements.
From Fig. 6, our findings are apparent; incomparison with a sliding type lifter, NTN’s standard
torque roller lifter unit (caged type) boasts an 85%
reduction in starting torque and 73 to 86% reduction inrunning torque. Also, in comparison with a fullcomplement roller type, NTN’s standard torque roller
lifter unit exhibits 8 to 29% torque reductions invarious measuring conditions.

4.1.1 Torque measuring conditions
Table 2 summarizes the conditions for our torquemeasuring test and Fig. 5 schematically illustrates thetest rig used.

Table 2 Rotational torque measurement conditions

Loading
conditions

500 N, 1,000 N (Measurement was performed
with starting torque set at 500 N.)

Bearing
speed*4

1000min-1，3000min-1，6000min-1，9000min-1
The starting toque at start-up phase, where
acceleration from 0 to 3,000 min-1 takes place,
was measured (with outer ring rotated*5).

Lubrication

Lubricating oil: engine oil with dynamic viscosityof 0W-20
Lubricating temperature: ordinary temperature
Lubricating system: splash lubrication (oil level:
centerline of drive roll)

Running torque(full complement roller type)
Torque ratio(relative to full complement roller type)Running torque (caged type)Running torque(relative to sliding type lifter)
Torque ratio (relative to sliding type lifter)

1.4

1

1.2

0.8

1
0.8

0.6

0.6

0.4

0.4
0.2

0.2
0

1000

3000

6000

Bearing speed

Running torque(full complement roller type)
Torque ratio(relative to full complement roller type)Running torque (caged type)Running torque(relative to sliding type lifter)
Torque ratio (relative to sliding type lifter)

1

Running torque N・m

1.4
1.2

0.8

1
0.8

0.6

0.6

0.4

0.4

0.2

0.2
0

1000

3000

6000

Bearing speed

Load

Running torque

Torque meter

Temperature measuring point(end face of shaft)

9000

0

min-1

Caged type
Full complement roller type
Relative to sliding type lifterStarting torque N・mElectric motor

0

min-1

Running torque (at load 1000 N)*3 Because the contact surface of sliding type lifter in contact with thecam is a flat face of cylindrical tappet, the diameter and height of
the tappet are given here.
*4 Means running speed of outer ring of rolling bearings (caged type,full complement roller type). Measurement on sliding type lifter was
taken while allowing the drive roll to run at a running speed
equivalent to that for measuring bearing speed of rolling bearing.
*5 A test method where the drive roll is brought into contact with theouter circumference of outer ring to allow the outer ring to turn in
response to the rotary motion of the drive roll. (The outer ring isallowed to rotate on the roller lifter unit installed on an actual
automotive fuel pump.)

Samples being tested

9000

Relative torque ratiosof caged type

Samplesbeing tested• Rolling bearing (caged type)
Size: ID 8×OD 16×W18 (in mm)• Rolling bearing (full complement roller type)
Size: ID 7.67×OD 16×W16 (in mm)• Sliding type lifterSize: D 30×H 25 (in mm)*3

Running torque (at load 500 N)

Drive roll

1.4
1.2
1
0.8
0.6
0.4
0.2
0

Fig. 5 Diagrammatic illustration of test machine

Fig. 6 Result of rotational torque measurement-59-

Relative torque ratiosof caged type

Torque tester (outer ring rotation tester completewith a torque meter)

Running torque N・m

Test
equipment

NTN TECHNICAL REVIEW No.77（2009）

4.2 Temperature-rise test
Temperature rise tests for bearings on roller lifter
units have been performed to verify the excellent highspeed durability of NTN’s caged low torque unit
compared to complement roller type lifter units.

4.2.1 Temperature-rise test conditions
Table 3 summarizes the test conditions adopted.

Table 3 Temperature-rise test condition
TesterOuter ring rotation tester (See Fig. 5.)

Samplesbeing tested• Rolling bearing (caged type)
Size: ID 8×OD 16×W18 (in mm)• Rolling bearing (full complement roller type)
Size: ID 7.67×OD 16×W16 (in mm)

Loading
conditions

P/C=0.22*Relative to rolling bearing (caged type)

Bearing
speed

Eight incremental steps: 4,500, 9,000, 13,500,
18,000, 22,500, 27,000, 31,500 and 36,000 min-1(with outer ring rotated)

Lubrication

Lubricating oil: engine oil with dynamic viscosityof 0W-20
Lubricating temperature: ordinary temperature,lubricating oil flow rate: 150 ml/min
Lubricating system: circulating lubrication

Fig. 8 Appearance of test sample(Full complement roller type)

4.3 Bearing life test
The bearing of the NTN’s low torque roller lifter unit
is a caged type. Accordingly, the number of rollers inthis type is unavoidably smaller compared with the fullcomplement roller type causing its load bearing
capacity to be lower and expected service life is to be
shorter. In order to address a problem of shorter
bearing life on the NTN’s low torque roller lifter unit,
NTN is subjecting the rollers to our unique FA
treatment and the shaft to special induction heating
treatment as previously described in Sec. 3. NTN has
performed a life test on the bearing section in questionin order to verify the effectiveness of these life
extending measures.

4.2.2 Results of temperature-rise test
Fig. 7 graphically plots comparison of temperaturerise on the samples tested and Fig. 8 shows a view of
seizure on a rolling bearing (full complement rollertype) having undergone the test.
The full complement roller type has developed
seizure as a result of lateral runout of its bearing at
18,000min-1. In contrast, the NTN’s standard low
torque roller lifter unit (caged type) has not developed
seizure up to 36,000 min-1. Thus, we have verified thatthe high speed durability, in terms of maximum
allowable running speed, of the caged type is morethan twice as much as that of the full complement
roller type.

4.3.1 Test conditions for bearing life test
Table 4 summarizes the test conditions applied forthe life test.
Table 4 Life test conditions
Test
equipment

Outer ring rotation tester (See Fig. 5.)

Samplesbeing tested• Rolling bearing (caged type)
Size: ID 8×OD 16×W18 (in mm)

Loading
conditions
Bearing
speed

Full complement roller type hasdeveloped seizure at 18,000 min-1.
Temperature rise ˚C

60
50

Lubrication

Calculated
life per JIS

97h(Information) Calculated life for full complement
roller type is 203 hours.

40
30
20
10
0

4,500

9,000

13,50018,000 22,500 27,000

31,500 36,000

Bearing speed min-1

Fig. 7 Comparison of temperature-rise(Full complement roller type)-60-

28000min-1 (with outer ring rotated)
Lubricating oil: engine oil with dynamic viscosityof 0W-20
Lubricating temperature: ordinary temperature,lubricating oil flow rate: 150 ml/min
Lubricating system: circulating lubrication

Caged type
Full complement roller type

P/C=0.22

Low-torque Roller Lifter Unit

4.3.2 Result of bearing life test

5. Conclusion

Fig. 9 shows graphical plotting of the result of ourbearing life test.
NTN has have subjected the rollers to FA treatment
and the shaft to a unique induction heat treatment
process. The results have verified that the standard
rating life of our bearing stands at 1,370 hours, whichis 14 times as long of a life value calculated according
to a JIS method (97 hours).
When assuming that the average engine speed is
3,000 min-1 (equivalent to average running speed of
7,500 min-1 at the bearing of roller lifter unit*6), theaverage load acting on the bearing is 1,000 N*7, andthe above-mentioned life value calculated per a JIS
standard is multiplied by 14, then the resultant bearing
life for our roller lifter unit stands at 5×104 hours andthis life coincides with a life of 27 years*8. Assumingthat the useful life of an average passenger car is 15
years, the NTN’s bearing well satisfies this useful life
requirement.

This paper has presented information about NTN’s
low torque roller lifter unit and associated technology.
The size of market will further expand for direct
injection engines as one of potential measures for
improving fuel economy for automobiles. To address
this trend, NTN will further market its low torque roller
lifter products as well as enhance their functionality.

References
1) Website of Japan Automobile Manufacturers
Association, Inc. (JAMA)
2) Website of Ministry of Land, Infrastructure, Transport
and Tourism
3) H. Ando: Technical Prospects of Gasoline Direct
Injection Engines, Engine Technology Review Vol. 1,
No. 1 April 2009, 18-23
4) T. Sena and Y. Katsuragi, Introduction to Engine
Science, first edition, Grand Prix Publishing, (1997)
173–183 (Japanese)5) Direct Injection, Car Mechanism Encyclopedia Engine
Volume, August 2009 special issue 111–115(Japanese)

Cumulative failure probability %*6 Assumptions: This speed is equivalent to cam running speedof 1,500 min-1, and the cam outside circumference length isfive times as long as the bearing outside circumference
length.
*7 Assumptions: The fuel pressure is set at 13 MPa, and thepump plunger diameter measures 10 mm.
*8 Assumption: The average daily use time for an average
passenger car is 5 hours.

95
90
80
70
60
50
40
30
20
10
5

8

9

1
103

1.5

Life

2
103

2.5

3

h

Fig. 9 Life test result

Photo of author

Masashi NISHIMURA
Needle Roller Bearing
Engineering Dept.
Automotive Sales Headquarters-61-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Hub Bearings for Automobiles that Conserve Resources

Isao HIRAI*

Automotive parts are being expected to respond to environmental
issues such as global warming and to effectively use natural
resources. This article introduces our hub bearings for automobiles
that conserve resources in order to meet these demands. They aredesigned to be lighter than conventional products and to reduce theamounts of materials used in order to improve the yield from thematerials during processing.

1. Preface

2. Structure and features

One of the leading environmental issues today is
global warming. To help in the prevention of global
warming it is necessary to reduce the emissions ofgreen house gases - in particular, CO2. Therefore, in
the auto industry around the world there is an everincreasing need for light-weight, low friction designs
that will lead to lower energy consumption on cars
during travel as well as a reduction in the amount ofmaterials consumed during car manufacturing.
Believing that coexistence with the global
environment is its most urgent challenge, NTN has
long been committed to efforts for designing lighter,lower-friction car components. We have developed aunique hub bearing, which is one of the underbody carcomponents. In this paper we are going to present
information about this novel “resource-saving
automotive hub bearing design” that features a
reduction in the amount of materials consumed in
production while boasting functions and characteristics
equivalent to or better than those of conventional hub
bearing products.

In developing our “resource-saving automotive hub
bearing design”, we have adopted the Gen3 hubbearing for non-driven wheels (rear wheels on front
drive vehicles) as a model case. In this development
work we have attempted to meet the following targets:• Compatibility with conventional designs in termsof mounting dimensions• 10% or more weight reduction compared withconventional designs• At least 20% reduction in the materials used forthe hub and outer rings whose masses accountfor a large portion of the bearing product• Functions including rolling fatigue life, mechanicalstrength and rigidity of our novel hub bearing
design are equivalent to or better than those of
conventional designs, even though our hub
bearing design does not adopt special materials
and/or heat treatment technique.
• Production cost equivalent to that of conventional
designs
To fulfill these targets, we have improved forging
techniques in the manufacturing aspect, and fully
utilized structural analysis techniques including FEM in
the design aspect. We have optimized the bearing
shape so that the amount of material scrapped in theforging process and the amount of material removed in
the machining process are minimized, while still*Axle Unit Engineering Dept. Automotive Sales Headquarters-62-

Hub Bearings for Automobiles that Conserve Resources

somewhat larger than the flange design, and then thework piece is punched to the final flange shape, andthis technique also leads to deteriorated material yield.
In order to achieve not only improved material yield
but also a lighter hub ring, we have developed a hub
bearing shape shown in Fig. 5. In finalizing this shape,
we have adopted an FEM analysis technique to
optimize the mechanical strength and forgeability of the
hub flange. More specifically, concaves of a larger
radius are included in the outer circumference of the
hub flange so that the convexes on the outercircumference are readily formed during the forging
process and the number of portions which can later
develop intermittent cutting during the turning process(which means deteriorated workability).

maintaining functionality of the hub bearing. Thus, wehave achieved a light weight hub bearing product aswell as a reduction in the amount of materials
consumed in production.

2.1 Hub flange
Fig. 1 shows a typical example of the structure of a
Gen3 hub bearing for a non-driven wheel. The hub ringas a rotary body has a hub flange that functions as amount for installing the wheel and brake disk. The mostcommonly used hub flanges are disk type hub flanges
such as a one shown in Fig. 2. Light-weight hub flange
products are available; examples of which include a
hub flange having lightening holes as shown in Fig. 3
and a cross shaped hub flange (non-common shape)
shown in Fig. 4.
A hub ring is prepared by obtaining a work blankfrom a round steel bar and then subjecting the blank toforging, turning, heat treatment and grinding
processes. The ratio of the mass of the steel blankwork loaded into the forging process to the mass of thefinished hub ring is known as “material yield”.
The lightening holes shown in Fig. 3 are formed bypunching during the forging process. Despite its
lightening effect, this technique leads to deteriorated
material yield. When a cross shaped hub flange ismanufactured, a work blank is first forged into a shape

Lightening hole

Hub bolt holeFig. 3 Lighter holes in hub flange

Hub bolt

Hub flange

Outer
ring

Non-common
flange shape
Rolling
elements

Hub ring
Inner ring

Hub pilot

Outer ring pilot

Fig. 1 Structure of Gen3 hub bearing for non-driven wheel

Fig. 4 Cross shaped hub flange

Outer ring flange

Concave on outercircumference
Convex on outercircumference

Hub flange

Fig. 2 Round shaped hub flange

Hub flange

Fig. 5 Shape of developed hub bearing-63-

NTN TECHNICAL REVIEW No.77（2009）

To address this problem, ramps are formed during theforging process at both ends on each pilot tooth along
the circumferential direction as shown in Fig. 8. This
arrangement helps not only mitigate the impact that
occurs when the cutting tool comes into contact withthe pilot teeth but also inhibits the occurrence of burrs,
thereby extending the life of the cutting tool anddecreasing the number of machining steps.
Furthermore, as can be understood from Fig. 7, thepilot is situated in a location whose phase is the sameas that of a concave on the outer circumference of our
hub flange; consequently, the difference in crosssectional area between a convex and a concave on theouter circumference of our hub flange is minimized andforgeability of the hub flange is improved.

2.2 Hub pilot
The hub ring is provided with a hub pilot that serves
as a guide for the wheel and brake disk installation on
the hub. Previously, the outer circumference of the hub
was machined to generate a hub pilot in the form of acylindrical-sectioned belt as shown in Fig. 6, and themass removed by the machining process was
scrapped as chips.
In the case of our newly developed hub bearing, toachieve lightening as well as reduce the portion
removed by machining, the previous pilot (cylindricalsectioned belt) has been superseded with anintermittent hub pilot shown in Fig. 7 that consists of aplurality of teeth formed by forging.
An intermittent pilot shape can contribute tolightening as well as improved material yield owing to a
reduction in surface being machined. However, thisfeature necessitates intermittent cutting, which leads toshorter tool life. At the same time, because this pilot
shape involves an increased number of edges on thework piece, a chamfering process is needed to remove
burrs.

Intermittent hub pilot

Ramps are formed at both ends on eachpilot tooth along the circumferential direction.

Fig. 8 Measure for intermittent cutting of hub pilot

2.3 Outer ring pilot
When a hub bearing is installed to the car body(suspension), the outer ring of the hub bearing offers amounting point to the car body. The outer ring has aring pilot that serves as a guide.
We have again chosen an intermittent configuration
for the outer ring pilot on our hub bearing in order toreduce the area being machined and realize a lighter
outer ring design. However, unlike the hub pilot, theinner bore of the outer ring pilot is fitted with a seal thatprevents ingress of water and dust into the hub
bearing. Therefore, as can be understood from theviews given in Fig. 9, the inner edge of the outer ringpilot is continuous while the outer edge features adiscontinuous form.
Incidentally, we have adopted a continuousmachined surface around the flange of outer ring pilot
in order to improve accuracy for installing the hub
bearing and prevent corrosion of the flange surface
due to the ingress of muddy water. Like in the case of
the hub pilot, areas subject to intermittent cutting on

Hub pilot

Fig. 6 Example of conventional shaped hub pilot

Intermittent hub pilot

Convex on outercircumference

Concave on outercircumference

Fig. 7 Discontinuous shaped hub pilot-64-Hub Bearings for Automobiles that Conserve Resources

Convex on outercircumference

Discontinuous outerring pilot
Seal

Machined surface onouter circumference

3. Evaluation test
We first performed the theoretical review by FEM
analysis technique of our novel “resource-saving
automotive hub bearing design” that reflects thepreviously mentioned lightening technique and material
consumption reduction technique. Then, we havesubjected the prototype to a bench test looking at fivecharacteristics, whereby we can verify that our new
design is equivalent to the conventional design interms of functionality:(1) Bearing rolling fatigue life: life (durability) test forbearing subjected to turning load on the car(2) Fatigue strength of hub flange: fatigue strength test(3) Rigidity of hub bearing: rigidity measurement(4) Mechanical strength of hub bearing: static strength
test(5) Rotational balance of non-common shape flange:
unbalance measurement

Enlarged view

Outer circumference surface

Inside bore surface

3.1 Bearing life (durability) test for bearing
subjected to turning load on the car

Continuous machined surface
adjacent to the flange, aroundentire circumference

The findings from the bearing life test are given in
Table 1. The measured rolling fatigue life of our new
design is more than six time as long as the targeted
rating life. Thus, it has been proven that our new
bearing design has sufficient durability.

Fig. 9 Shape of outer ring pilot

the outer ring pilot have outward inclined ramps formedby forging in order to help extend the useful life of the
cutting tool used.
As can be understood from Fig. 9, the portions beingmachined on the outer circumference of the outer ringpilot are situated in the same phases as those of theconvexes on the outer circumference on the hubflange. This arrangement is intended to promote easeof installation of the hub bearing to the car body andimprove mechanical strength and rigidity of theinstallation. Because projection of the outer ring flange
is small, we can give priority to this objective rather
than improvement in its forgeability as described inSec. 2.2.

Table 1 Results of durability test with curving moment
Subject of evaluation

ResultConventional design

At least six times as long as rating life

3.2 Fatigue strength test
As summarized in Table 2, the samples have been
run for a number of revolutions in excess of a target
number. Though having undergone a test whose runtime was longer than that of a conventional hub flange
design, our newly developed hub flange has notdeveloped any fractures, thereby we have determinedthat our new design has sufficiently high fatigue
strength.

2.4 Lightening and reduced material consumption
As a result of the reduction in material consumption
and improved material yield, our new design has
achieved the following improvements overconventional designs: approximately 10% weight
reduction of the hub bearing, approximately 20%
reduction in material consumption with the hub ringand outer ring, and approximately 30% reduction in the
total amount of material scrapped as a result ofmachining for the hub ring and outer ring.

Table 2 Results of fatigue strength test
Subject of evaluation
New design
Conventional
design-65-

ResultNumber of revolutions at least 1.9 times
as many as the targeted value
No fracture on flange
Number of revolutions at least 1.7 times
as many as the targeted value
No fracture on flange

NTN TECHNICAL REVIEW No.77（2009）

From these findings, we are sure that our novel“resource-saving automotive hub bearing design” hasfunctions equivalent to those of conventional hub
bearing designs. The chart in Fig. 10 provides acomparison between our new hub bearing design andconventional design in terms of functionality andadvantages in manufacture.

3.3 Rigidity measurement
Table 3 summarizes the results of the rigidity
measurement. The rigidity of our newly developed hubflange is virtually equivalent to that of a conventional
design.
Table 3 Measurement of stiffness with curving moment
Subject of evaluation

Rigidity of tilted hub flange kN/˚

New design

21

Conventional design22

4. Afterword
To be able to contribute to the reduction of CO2
emissions, NTN has designed a unique hub bearing
product that boasts lighter weight through improved
design as well as a reduction in materials consumed
through an improved forging technique.
The applicable specification for individual NTN hub
bearings can vary depending on the vehicle type
and/or location of use. It is possible that all theconsiderations described in this document may not beapplicable for the intended usage; notwithstanding,
NTN will as necessary expand the scope of
applicability of this product line. NTN is going tointegrate its already proven “hub bearing with built-in
high-sealing low-torque seal” technology with its novel“resource-saving automotive hub bearing” technology
described above. Through these efforts, NTN will
promote the reduction in weight and friction for hub
bearings and thereby will further contribute to
reductions in energy consumption by cars in travel aswell as proceeding with development of novel ecoconscious technologies.

3.4 Static strength test
The mechanical strength required for our bearing inthe static strength test is that the bearing does notdevelop a fracture when subjected to a lateral G loadof 2.0 in the vehicle turning mode (side collisionsituation where the wheel has hit a curb). As can beunderstood from the information given in Table 4, ournew bearing design satisfies the load requirement andhas mechanical strength equivalent to that ofconventional bearing designs.
Table 4 Result of static strength test
Subject of evaluation Lateral G in turning mode equivalent to fracture load
New design

2.4

Conventional design

2.4

3.5 Unbalance measurement
To be able to determine the magnitude of effects ofa non-common hub flange shape on the rotationalbalance of the hub ring, the unbalance of the hub ringneeds to be measured. The resultant unbalance is of
this design is better than G16 per JIS B 0905 and thislevel well satisfies G40, which is the levelrecommended by the same JIS (Japanese Industrial
Standard) for quality of balance with automotive
wheels.
LighterweightRotationalbalance

References
1) K. Shibata and T. Norimatsu: Technical Trends in Axle
Bearings and the Development of Related Products,
NTN Technical Review No. 75 (2007) 29-35

New design
Conventional design
Reducedmaterial input

Photo of author
Mechanicalstrength

Waste
reduction

Cost

Rigidity

Isao HIRAI

Bearing life

BetterFig. 10 Image for comparison

Axle Unit Engineering Dept.
Automotive Sales Headquarters-66-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]V-series Hub Joint

Mitsuru UMEKIDA**
Yuuichi ASANO**

To improve fuel efficiency, reducing the weight of axle units isdesirable. NTN has developed various hub- bearing and CV joint
products to meet this requirement. This report introduces the Vseries hub joint, which is an integrated hub-bearing and CV joint
crafted using NTN’s original press-cut fitting. This productachieves a lighter weight through integration of a hub- bearing
and a CV joint

in particular, H/J products adopting press cut fitting
technique are referred to as V series H/J products.
NTN has developed two types of V series H/Jproducts: “non-separable type” that boasts the lightest
weight, and a “separable type” that features separable
construction that allows a bearing user to be able torepair the purchased bearing product easily.
This report hereunder describes the information
about the press cut fitting technique as well as the
structural features of “non-separable type” and“separable type” of V series H/J products.

1. Preface
A typical environmental issue to be addressed today
is global warming. Recently, emissions reduction ofCO2, the most abundant greenhouse gas, has beenposing a challenge that needs to be addressed
urgently. The car-manufacturing industry around theworld has been committed to develop cars with better
fuel efficiency in order to help reduce CO2 emissions
from their products. As a result of this, the global
market for hybrid electric vehicles has been
dramatically expanding.
In this paper, we will provide information about our V
series hub joint products (hereinafter, may be simply
referred to as V series H/J) that are modularized
products each obtained by joining a hub bearing(hereinafter, may be referred to as H/B) with a constantvelocity joint (hereinafter, may be referred to as CVJ)
by a “press-cut fitting” technique that is NTN’s propriety
joining technique; consequently, the V series hub joints
boast improved ease of assembly and productivity forour clients as well as a 12% weight reduction
compared with conventional products.

2.1 Previous fitting technique
A previous NTN fitting technique for H/B’s with CVJ’s
is hereunder described. Fig. 1 illustrates the structureof NTN’s previous serration fitting joint. Both the outercircumference of the outer ring stem of the CVJ and
the inside bore surface of the H/B are serrated. Torqueis transmitted via the serrated joint between bothserrated members. Also, the CVJ is secured to the H/Bwith a hub nut tightened onto the threaded end of CVJ
outer ring stem.
Torque transmission from CVJ to H/B takes place at
the contact surfaces between tooth flanks of bothserrated portions. However, because of the limitation ofmachining accuracy with both members (difference intooth pitch between both serrated parts), it is difficult torealize a tight fit between both members.

2. Structure and advantages
Hub joints (hereinafter, may be referred to as H/J)
are products each integrally comprising H/B and CVJ;**C.V.Joint Engineering Dept. Automotive Sales Headquarters**Axle Unit Engineering Dept. Automotive Sales Headquarters-67-

NTN TECHNICAL REVIEW No.77（2009）

As explained above, the serrated joint of theprevious method fails to evenly bear the torque andtherefore, the design length of the mesh between bothserrations has to be longer.

Consequently, variation in the gap between toothflanks can occur as shown in Fig. 2, and excessive
play can occur on the joint in the circumferential
direction with the previous fitting technique.
There has been a method available for eliminating
circumferential play between CVJ and H/B, that is, theprovision of a helix angle on the serration of the CVJ.
However, this method has its drawbacks. As nonuniformity in contact pressure occurs across the tip
side and the root side of the serrated shafts, the entire
tooth surface on the serrated shaft may fail to uniformly
bear the load owing to the difference between the tooth
pitch of the CVJ side serration and that of the H/B.

2.2 Joint formed by press cut fitting techniqueWith the previous fitting method, both the CVJ andH/B are serrated. In contrast, with our press cut fitting
method the CVJ outer ring alone is provided with a
special serration as shown in Fig. 3, while the inside
bore of H/B remains cylindrical.
With our press cut fitting system, the CVJ outer ringstem is hardened through heat-treatment, while theinside bore surface of the H/B is not hardened so that
there remains a difference in hardness between the
CVJ outer ring stem and inside bore surface of the
H/B. Consequently, when the CVJ outer ring stem isfitted into the H/B inside bore, the serration on the CVJ
outer ring stem generates serrations on the inside bore
surface of the H/B. NTN calls this unique fitting method“press cut fitting”.
During the press cut fitting process, the inside bore
surface of the H/B is serrated as this surface is underelastic deformation. As a result, the ridges found on the
CVJ outer ring stem fit into the grooves formed on theinside bore surface of the H/B while a tightening
allowance is present between the ridges and grooves.
Thus, a preload is exerted onto the resultant joint, andthe CVJ outer ring stem is tightly fitted within the inside
bore of the H/B as illustrated in Fig. 4.

Serration on outer circumference of outer ring stem of
CVJ is engaged with serration on inside bore of H/B.

H/B

CVJ outer ring stem
CVJ is secured with hub nut.

Fig. 1 Fitting by serration (previous method)[CVJ outer ring stem]• Special serration (grooves and ridges)• Hardened through heat-treatment[Inside bore surface of H/B]
• Cylindrical form (before fitting)• Non-hardened (not heat-treated)

Fig. 3 Press cut fitting (before fitting)Gap between
tooth flanks

Boundary of serration

No gap between tooth flanks

Variation in gap between tooth flanks

Fig. 2 Contact condition of teeth (previous method)

Fig. 4 Contact condition of teeth (Press cut fitting)-68-V-series Hub Joint

As a result of this unique fitting method, the torqueinput is uniformly borne by all the teeth and toothflanks, and the allowable torque capacity of this joint isgreater, thereby the necessary length of mesh between
serrations can be much shorter compared with theprevious fitting method.

Caulked area on stem end
Rear face of outer ring

2.3 Structure of V-series hub joint
As previously mentioned, the V-series H/J products
subjected to press cut fitting method can be
categorized into “non-separable type” and “separable
type”. The structures of these product types are
hereunder described.

Oscillation-capablecaulked area

Fig. 5 V-series H/J (Non-separable type)2.3.1 Non-separable H/Jon the contact surfaces is effective in preventing
occurrence of the stick-slip sound.
Unlike the previous structure, the joint formed by ourpress cutting fitting method is resistant against
accidental disengagement, and is capable ofcontrolling the axial pressing force during the press
cutting fitting process; thereby, the bearing pressure on
the contact surfaces between the CVJ and the H/B canbe reduced. Thus, our press cut fitting method is usefulin preventing the stick-slip sound.

The “non-separable type” products boast lighter
weight through integration of the H/B with the CVJ. Fig.
5 shows a cross-sectional view of a V-series nonseparable H/J product.
As previously mentioned, both members in a joint
remain in full a contact state, and do not come apartwhile the hub joint is running because a preload
remains applied to the joint. Nevertheless, to prevent
accidental disengagement of the CVJ outer ring stemin a non-separable type from the H/B, the outer end of
the CVJ outer ring stem is coined to secure the CVJ to
the H/B.
The V-series H/J products boast lighter weightbecause the length of meshed serration is shortercompared with previous products and they do not havea hub nut.
With the previous fitting method (Fig. 1), whentorque from the CVJ is input to the H/B and sudden slip
develops on the contact surfaces between theoscillation-capable coined area of the H/B and the rearface of CVJ outer ring, a unique noise known as “stickslip sound” can occur. Reduction in bearing pressure[Structure and features of non-separable H/B]
Fig. 6 shows the structure and features of NTN nonseparable H/B.
1 Press cut fitting: No gap between contact surfacesof serration on H/B and that on CVJ
2 Deletion of flange on H/B outer ring, that is, a flange
for installing a knuckle: Adoption of a press-fitting
technique for weight reduction
3 Deletion of hub pilot: Lighter weight (Area A on
flange outer circumference shown in Fig. 6 serves
as a pilot)

6 Coining at stem end.
1 Press cut fitting
4 Reduced bearing pressure on contact surfaces between H/B and CVJ

5 V series CVJ
A

2 Deletion of H/B outer ring flange

3 Deletion of hub pilot

Fig. 6 Structure and characteristics of V-series H/J Non-separable type-69-

NTN TECHNICAL REVIEW No.77（2009）

4 Reduced bearing pressure on contact surfaces
between H/B and CVJ: Structure to prevent stickslip sound5 V series CVJ
6 Coining at stem end

allow the CVJ outer ring stem to be pulled in, the H/B
has an inside wall and the CVJ outer ring stem has athreaded hole along its centerline to accept this bolt.
This unique structure allows the H/B to be separated
from and reinstalled to the CVJ as necessary.
As mentioned previously, a joint formed by our press
cut fitting technique is preloaded and as a result theH/B cannot be readily separated from the CVJ, unlike
the joint obtained from the previous method describedin Sec. 2.1; this drawback remains true when the H/B
is reinstalled to the CVJ. The unique advantage of our
newly developed “separable” hub joint is being able todisassemble and reassemble the joint, which theprocedures for our “separable” design are briefly
described below.

2.3.2 Separable H/J
A hub joint consists of a constant velocity joint
integrated with a hub bearing. To help realize easy
repair work for a marketed hub bearing, NTN has
developed a “separable” hub joint design that is
capable of disassembly and reassembly. Figs. 7 and 8
show the structure of our separable hub joint.
To allow the H/B to be separated from the CVJ, theCVJ outer ring stem is secured by fastening a bolt,
instead of coining at the stem end on the nonseparable H/J. This bolt is also used to retract the CVJ
outer ring stem into the inside bore of the H/B during
the reassembly procedure for the separable H/J. To<Disassembly procedure>
Referring to Fig. 9, fit the stem push-out bolt into thethreaded hole on the CVJ outer ring, and then mountthe pulley extractor onto the H/B. Turn the stem pushout bolt to push out the CVJ outer ring stem. Then, theH/B can be separated from the CVJ.

Stem push-out bolt

Bolt
HB inside wall

Threaded hole

Pulley extractor

Fig. 7 V-series H/J (Separable type)Fig. 9 Separate method of separable type

Stem pull-in bolt
Press cut fitting

Phase-matching guide slot for reassembly

Fig. 8 Structure and characteristics of V-series H/J (Separable type)-70-

V-series Hub Joint

specimens.
The non-separable product has sufficiently hightorsional strength as the specimens of non-separable
design satisfy the strength target while the press-fit
allowance (difference between the outside diameter ofserration on CVJ outer ring stem and the inside
diameter of H/B) remains in the standard range.

<Reassembly procedure>
The joint formed by our press cut fitting technique isa tight-fitting joint that’s being preloaded. If a H/B isseparated from a CVJ, it will be impossible to readily
reestablish circumferential phase-matching between
the ridges on CVJ outer ring stem and the grooves on
the H/B. To address this drawback, the entrance toinside bore of the H/B in our “separable” design has aphase-matching guide slot that is geometricallysituated in a circle greater than the one defined by theridges of the serration on the CVJ outer ring stem.
For reassembly, the CVJ outer ring stem is guided
along the guide slot on the H/B, and the stem pull-in
bolt is tightened to a recommended tightening torque.

Fracture torqueStatic torsional strength

Guide slot on H/B

TargetStandard pressfitting allowance

Press-fitting allowance for press cut fitting techniqueFig. 11 Static torsional strength test

Serration on CVJ
Phase-matching guide slot for reassembly(2) Bi-directional torsional fatigue strength test(with non-separable type)Fig. 12 graphically plots the test result from the bidirectional torsional strength test with non-separable
specimens.
Assessment has been performed with two types of
CVJ samples whose operating angles are 0 degreeand 43 degrees respectively. Both sample types havewithstood a targeted number of load applications andhave exhibited sufficient durability.

Stem pull-in bolt

Fig. 10 Re-assemble method of separable type
Bi-directional torsional fatigue strength

Torque loading

3. Function assessment test
The functions required of a joint formed by press cut
fitting technique are sufficient static torsional strength,
torsional fatigue strength against torque transmitted
from the CVJ to the H/B, and durability of the joint
against a bending moment that occurs when the CVJ is
operating at a greater angle.
In the assessment test, we used a CVJ whose press
cut fitting joint that has sufficiently great static torsional
strength and tested the CVJ samples under the test
conditions that led to a fracture of the press cut fitting
joint.

θ＝0˚

Targetθ＝43˚

Number of repeated cycles

Fig. 12 Bi-directional torsional fatigue strength test

(1) Static torsional strength test(with non-separable type)Fig. 11 graphically plots the test result from thestatic torsional strength test with non-separable-71-

NTN TECHNICAL REVIEW No.77（2009）(3) Static torsional strength test (separable type)

4. Afterword

Fig. 13 shows the test result from the static torsional
test with separable specimens.
Static torsional strength has been assessed withsamples having undergone disassembly/reassembly
cycles. The samples having undergone
disassembly/assembly cycles do not show any
evidence of deterioration in mechanical strength, andboast sufficient mechanical strength.

NTN has successfully developed the V series hub
joint products that feature lighter weights by integratinga hub bearing with a constant velocity joint through
NTN’s propriety press cut fitting technique. The V
series hub joints are categorized into two types: “nonseparable” type boasting a light-weight design and a“separable” type featuring easy repair work. This paper
has presented information about the structures andadvantages of both types. By fully utilizing thetechnology described above, we will continue to remaincommitted to the development of novel corner module
products for hybrid electric vehicles and electricvehicles.

Torque loading

Static torsional strength: Separable

TargetNo separation/
reassembly cycle

One separation/
reassembly cycle

Five separation/
reassembly cycle

Fig. 13 Static torsional strength test (Separable type)

Photo of authors

Mitsuru UMEKIDA

Yuuichi ASANO

Axle Unit Engineering Dept.
Automotive Sales Headquarters

C.V. Joint Engineering Dept.
Automotive Sales Headquarters-72-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Extremely High Load Capacity Tapered Roller Bearings

Takashi UENO*
Tomoki MATSUSHITA*
Standard tapered
roller bearing

Extreme high load
capacity bearing

NTN developed a tapered roller bearing with extremely high load
capacity to improve the fuel efficiency of cars. This new bearing
has improved capacity from increasing the number and length of
the rollers. This bearing is used for transmissions and differential
gears. This article introduces the design and performance of thisproduct that we have developed.

development, the NTN extreme high load capacity
tapered roller bearing products boast much decreased
bearing pressure with a bearing under load; longer
bearing life under severe lubricating conditions orcontaminated lubricating conditions; and higher rigidity.
This paper describes the structure and advantages ofthis newly developed bearing product.

1. Foreword
People around the world have been increasingly
concerned with prevention of global warming andimprovement in air quality. In this context, the level ofallowable vehicle emissions has been increasingly
more stringent, and a Japanese target value for
improvement in fuel economy for cars has been
established—average 23.5% improvement in fueleconomy by the end of fiscal year 2015 relative to thefiscal year 2004 level 1). While automakers have been
more deeply committed to efforts for improved fueleconomy, engineering people specializing in
automotive transmission and differential gearing havebeen attempting to use less viscous oil and morecompact, lighter weight designs aimed at reduced
friction of automotive transmissions and differentials.
To help contribute to this trend, the bearing industry
has been challenged with a life and rigidity requirement
for compact, light-weight bearings. To address thesechallenges, NTN has developed and marketed a line ofextreme high load capacity tapered roller bearing
products 2), which result in lighter, more compact
bearings at the same bearing life or a longer bearing
life bearing size.
These new products feature longer rollers: the lengthof rollers has been maximized by further incorporating
new engineering improvements into the cage and innerring of the NTN’s already developed high load capacity
tapered roller bearings. As a result of this new

2. Structure of NTN extreme high load
capacity tapered roller bearing
Previous NTN high load capacity tapered roller
bearings are characterized by a smaller clearance
between the cage and outer ring as well as a greater
cage pitch circle diameter—these features areintended to ensure presence of spaces sufficient for
the width of cage bars and reduced distances between
rollers. Consequently, the number of rollers in any NTN
high load capacity tapered roller bearing is virtuallyequivalent to that of a similarly sized full complement
roller bearing.
In addition to these structural features of theprevious high load capacity bearing products, ournewly developed extreme high load capacity tapered
roller bearings (the example in the right in Fig. 1) havea resin cage and maximized-length rollers, and areavailable in two structural types: (1) bearing without
inner ring small side rib, and (2) bearing with inner ringsmall side rib.

*Automotive Engineering Dept. Automotive Sales Headquarters-73-

NTN TECHNICAL REVIEW No.77（2009）

Standard tapered roller bearing

High load capacity bearing

Extreme high load capacity bearing

Clearance between
outer ring and cage

Smaller clearance
between outer ring and cage

Smaller clearance between outer ring and cage

Resin

Steel plate

Lock
structure
Roller length extended bylength of small side rib

Without inner ringsmall side rib
1 Structure without inner ring small side rib
Cage bar widthCage bar width
Resin

Clearance
between rollers

Clearance
between rollers(Smaller)

With inner ringsmall side rib

2 Structure with inner ring small side rib

Fig. 1 Structure of extreme high capacity tapered roller bearing

allowable cage protrusion is not exceeded.
(3) Lock structure using teeth on cage: So that an innerring/rollers/cage ASSY can remain non-separable,
a lock structure is provided which consists of teethon the large diameter side on cage, wherein theseteeth are engaged with the grooves formed on theouter circumference of inner ring large side rib.

2.1 Bearings without inner ring small side rib
Fig. 2 schematically shows the structure of a bearing
without an inner ring small side rib, and Fig. 3
illustrates a 3D model of this bearing.
A bearing design without an inner ring small side rib
is intended to be used in space constrained
applications where the additional geometry required forthe rib would make the overall bearing too large. The
features of this bearing structure are as summarized
below:(1) Cage: The small side rib has a minimum width justsufficient for satisfying the mechanical strength
required of it.
(2) Roller length: The length of rollers may be
increased to the maximum width of inner and outerring raceways provided that the maximum

Dimension ofcage protrusion

2.2 Bearings with inner ring small side rib
Fig. 4 shows one example of a bearing structurewith an inner ring small side rib.
There may be cases where the dimension of innerring width can be increased even though the allowabledimension of protrusion of cage is limited. Then, thebearing with inner ring small side rib may be adopted,
and its features are described below.

(3) Lock structure withteeth on cage(1) Smaller dimension(thinner) of cage
small diameterside rib(2) Roller length is maximized to maximum allowableinner ring raceway width.

Fig. 2 Structure of extreme high capacity tapered roller
bearing without inner ring small side rib

Fig. 3 3D model of Extreme High Capacity tapered roller
bearing-74-

Extremely High Load Capacity Tapered Roller Bearings

Dimension ofcage protrusion

which can occur from metal-to-metal contact under acondition where formation of oil film is difficult, hasbeen prevented and bearing life has been extended.
¡Useful life under contaminated lubrication conditionis extended.
The use of an increased number of longer rollers
helps reduce the maximum bearing stress, limiting thesize of dent mark caused by trapped foreign matter.
The stress occurring on the raised material around adent mark is also reduced thereby resulting in longer
life under contaminated lubrication conditions.

(1) Roller length is maximized to maximum
allowable outer ring raceway width.

(2) Smaller dimension(thinner) of cage
small diameterside rib(3) Inner ring small rib is added.

Fig. 4 Structure of extreme high capacity tapered roller
bearing with inner ring small side rib

4. Performance of NTN extreme highload capacity tapered roller bearings
The NTN extreme high load capacity tapered roller
bearing differs from other NTN tapered roller bearingsin having an increased number of longer rollers and alock structure on the large side diameter of the cage.
To study the effects of these special features on the
bearing, we have performed a function assessment
test comparing the standard tapered roller bearing andextreme high load capacity tapered roller bearing(without inner ring small side rib) shown in Table 1.

(1) Cage: The cage is designed with the minimum rib
width necessary to satisfy the mechanical strength
required of the cage small diameter rib under theintended bearing operation conditions.
(2) Roller length: The length of rollers are maximized
while leaving sufficient room for the small rib andhaving a cage small end protrusion which isacceptable.

(1) Result of pumping performance test

3. Features of NTN extreme high load
capacity tapered roller bearings

The NTN extreme high load capacity tapered roller
bearing features a unique lock structure on the larger
diameter side of cage as well as increased number ofrollers and roller length. Fig. 5 provides visualcomparison between both bearing types in terms of thespace volume. It is apparent that the clearance
between rollers is smaller on the NTN extreme highload capacity tapered roller bearing owing to increasein the number of rollers and as a result, the spacevolume in the bearing is smaller.
We have compared the flow rates of lubricating oil
flowing through both bearing types in running mode.
Fig. 6 schematically illustrates concept of the pumping
performance test. When a bearing is run with theinterior of bearing and housing filled with lubricating oil,a pumping function takes place on the bearing, thereby
the lubricating oil flows from the large diameter side of
the bearing. Fig. 7 graphically plots the measured
amounts of lubricating oil pumped through the bearings
after operating for a fixed duration. Though having asmaller space volume within its interior, the NTN
extreme high load capacity tapered roller bearing offers
a flow rate comparable to that of the standard roller
bearing sample.

Thanks to increase in quantity and length of rollers,
the NTN extreme high load capacity tapered roller
bearings boast functions improved over the NTN
standard tapered roller bearing products, and theexamples of improvement in functions are as described
below:(1) Greater load rating¡Basic dynamic load rating: 16% increase at
maximum (64% increase at maximum in calculated
life)¡Basic static load rating: 21% increase at maximum(21% increase at maximum in safety factor)(2) Greater rigidity¡Bearing rigidity: 14% improvement at maximum(14% reduction at maximum in elastic displacement)(3) Longer bearing life
¡Useful life under clean oil lubrication condition isextended.
The use of an increased number of longer rollers
helps reduce the maximum bearing stress, leading toan increased oil film thickness and alleviation of stressthat occurs in a metal-to-metal contact mode.
Consequently, occurrence of surface initiated flaking,(2) Roller settling performance comparison test
When an NTN extreme high load capacity tapered
roller bearing without inner ring small rib is used, the-75-

NTN TECHNICAL REVIEW No.77（2009）

Table 1 Comparison of bearing internal designStandard tapered roller bearing

High load capacity bearing

Dimension of cage protrusion
1.5max.

Extreme high load capacity bearing

Dimension of cage protrusion
1.5max.

16.25

Dimension of cage protrusion
1.5max.

16.25

16.25

φ25

φ52

φ25

φ52

φ25

φ52

Schematicview

φ25×φ52×16.25

Bearing size
Load rating

Basic dynamic load rating Cr =31.5kN(comparison withstandard tapered
roller bearing)

Basic dynamic load rating Cr =34.0kN(8% increase)

Basic dynamic load rating Cr =36.5kN(16% increase)

Basic static load rating C0r =34.0kN

Basic static load rating C0r =37.0kN(9% increase)

Basic static load rating C0r =41.0kN(21% increase)

Number of rollers

16 rollers

17 rollers

17 rollers

Length of rollers

10.5mm

10.5mm

11.8mmCage material

Steel plate

Steel plate

Resin

0.6m

1.1m

Space

Amount delivered ml

20

m

m

(a) Standard tapered
roller bearing(b) Extreme high load
capacity bearing

15

Loading conditions: Axial load Fa=500N
Bearing speed: 1500 min-1
Lubrication: ATF

10

5

Fig. 5 Space volume of bearing inside0Standard tapered
roller bearing

Extreme high load
capacity bearing

Fig. 7 Test result of oil flow
Initial level oflubricating oil

Nroller settling performance in the bearing may differ
from that of other tapered roller bearings because of
absence of inner ring small side rib that otherwise
limits the location of rollers.
Let us describe roller settling performance. When an
inner ring assembly is fitted into an outer ring fromabove, a clearance will occur on the inner ring largeside rib since the length of rollers is usually smaller
than the inner ring raceway width (see Fig. 8).
Because the rollers in a running bearing rotate while
being guided by the inner ring large side rib surface,
the bearing needs to be subjected to a seating
operation in order to allow the rollers to shift to normal

Fa

Fig. 6 Evaluation of oil flow through bearing inside-76-Extremely High Load Capacity Tapered Roller Bearings

revolutions. The reason the NTN extreme high load
capacity tapered roller bearing achieves good roller
settlement performance can be explained as follows:
Fig. 11 provides schematic diagrams for situations
where the rollers in both NTN extreme high load
capacity tapered roller bearing and standard tapered
roller bearing are in settled state.
On the NTN standard tapered roller bearing, thedimension of roller displacement is limited by the end
face of inner ring small side rib. In this state, the cageremains in contact with the roller large diameter side
end faces of rollers: consequently, as soon as break-in
operation begins, working forces occur between
associated components and generate a thrust thatforces each roller toward the inner ring large side rib;
thereby while this thrust continues to lift up the cage,
the rollers shift toward the inner ring large side rib.
In contrast, on the NTN extreme capacity tapered
roller bearing, the dimension of roller displacement islimited by the end face of cage pocket small diameterside. As soon as break-in operation begins, the rollers
shift toward the inner ring large side rib by a distanceequivalent to the distance between the rollers and cage
pockets, causing them to come into contact with thecage pocket large side end faces; then like in a
movement on the standard tapered roller bearing, thelocations where they remain in contact with the innerring large side rib surface (considered fully seated).
The lower the number of bearing revolutions needed
for the bearing to be fully seated means easier preload
setting for the bearing.
Fig. 9 schematically illustrates the test method used
for investigating roller seating performance on the NTN
extreme high load capacity tapered roller bearing, andFig. 10 graphically plots the test results for roller
seating performance. The test result in Fig. 10 showsthat the rollers in the NTN extreme high load capacity
tapered roller bearing fulfill settlement in about five
revolutions while the rollers in the standard tapered
roller bearing reaches settlement in about 13

Some clearance

No clearance(a) Before seating
operation(b) After seating
operation

Fig. 8 TClearance change between inner
raceway width and roller

Dial gage
Dimension of sinking of inner ring μm

WeightBearing
being tested

Outer ring
housing

Loading conditions: Axial load Fa=302 N
Measuring method: Dimension of inner ring displacement resulting from revolutions of bearing is measured.

20

15

10
Extreme high load capacity bearing
Standard tapered roller bearing
50Completion ofroller settlement

05Completion ofroller settlement

10

15

20

Revolution

Fig. 9 Testing method of roller settlingFig. 10 Test results of roller settling

Clearance between roller and cage pocket

Clearance between roller and cage pocket

Clearance between roller
and inner ring large side rib

Clearance between roller
and inner ring large side rib

Position of settled roller(a) Standard tapered roller bearing(b) Extreme high load capacity bearing

Fig. 11 Clearance to determine roller seating characteristics-77-

NTN TECHNICAL REVIEW No.77（2009）

rollers shift to the inner ring large side rib end face
while lifting up the cage.
As described above, the dimension of roller
displacement in the extreme high load capacity tapered
roller bearing is greater owing to the structure of thisbearing: at the earlier stage of break-in operation, therollers alone, independent of the cage, shift toward
inner ring large side rib; thereby the shift per revolutionof the bearing is greater and the rollers will settle in ashorter time.

load capacity tapered roller bearing: Table 3
summarizes the parameters adopted for calculating therunning torque of bearing samples.
The high load capacity tapered roller bearing boasts
16.2% reduction in bearing weight and 2% reduction inrunning torque.
Adoption of the NTN extreme high load capacity
design helps achieve 25.3% reduction in bearing
weight and 7.5% reduction in running torque. Thus thistapered roller bearing technology contributes to thegoal of reduced size (more compact), lighter weight,
and reduced torque.

5. Compact, light-weight design
technique for NTN extreme high load
capacity tapered roller Bearing

Table 3 Calculation condition of rotating torque

Demands will continue to grow for improved fueleconomy and riding comfort with automobiles, as wellas higher engine power and greater number oftransmission speeds. To help satisfy these demands,
automotive bearings have to be capable ofwithstanding greater loads with no changes to theenvelope dimensions, or feature compact size andlighter weight with a given load bearing capacity. In thispaper, Table 2 below summarizes technical data forstudies into compact size, lighter weight design for asame set of a given load bearing capacity and a given
shaft diameter. Because a compact size, lighter weight
design helps a tapered roller bearing to achieve lower
running torque, this paper includes the facts about thebearing torque reduction with the NTN extreme highRadial load Fr

5000N

Axial load Fa

5000N

Bearing speed

5000min-1

Lubrication

ATF

Lubricating oil temperature

90˚C

Table 2 Study of down sizing under same load capacity
Standard tapered roller bearing

High load capacity bearing

Basic dynamic load rating Cr=31.5kN

Load rating
Bearing size
Bearing mass
(reduction in comparison withstandard tapered roller bearing)Calculation result
for running torque※(reduction in comparison withstandard tapered roller bearing)

Extreme high load capacity bearing

Basic static load rating C0r=34.0kN

φ25×φ52×16.25

φ25×φ49.3×15.4

φ25×φ49×15

0.154kg

0.129kg(16.2% reduction)

0.115kg(25.3% reduction)

0.293Nm

0.287Nm(2.0% reduction)

0.271Nm(7.5% reduction)

Dimension of cage protrusion 1.5 max

Dimension of cage protrusion 1.5 max

Dimension of cage protrusion 1.5 max
16.25

15.4

15

φ25

φ49

φ25

φ49.3

φ25

φ52

Schematic view

※Does not include stirring resistance on lubricating oil.

-78-

Extremely High Load Capacity Tapered Roller Bearings

sufficiently high oil resistance performance.
If our extreme high load capacity tapered roller
bearing is used in a lubricating oil that does not containa lot of phosphorus or sulfur content, it is possible toadopt PA46 (polyamide 46) or PA66 (polyamide 66)
each often used as a resin material for a bearing cage.

6. About special cage structure
By adoption of toothed lock structure on the large
diameter side and narrower rib on the small diameterside on the cage of the NTN extreme high load
capacity tapered roller bearing, the length of rollers canbe maximized. The shape of this cage is very unique,and the cage cannot be shaped with steel plate:therefore, it is made of a resin. Information about theresin used for this purpose and mechanical study
about the special cage structure are hereunderdiscussed.

(2) Dynamic analysis of extreme high load
capacity cage
We have attempted to determine the mechanicalstrength needed for the cage small diameter side ribthat is a unique feature of the cage for the NTN
extreme high load capacity tapered roller bearing, andhave found a minimum necessary rib width. To be able
to determine the stress occurring on the cage in therunning bearing, we have used an NTN-developed 3D
dynamic analysis tool for tapered roller bearings 3).
Fig. 13 shows one typical example of model for
dynamic analysis of tapered roller bearing. This
diagram shows that the largest stress occurs at thesmall diameter side rib among various areas on the
cage. In designing the small diameter side rib on thecage, we have determined the size of rib that has
necessary mechanical strength by reflecting thefindings obtained from the dynamic analysis.

(1) Resin material
Lubricating oil in a transmission and/or differential
sometimes contains phosphorus or sulfur content as
extreme pressure additive which are known to be
detrimental to some resin materials. Therefore, theresin material for the cage needs to be resistantagainst oils containing these additives.
When considering ease of assembly into bearing
and durability in bearing, each needed for a material oftapered roller bearing cage, the resin material of thecage also needs to have excellent physical properties
including mechanical strength, toughness and heat
resistance. Beginning with these considerations, NTN
has performed a necessary research and has
successfully developed a PPS (polyphenylene sulfide)resin cage that features physical properties needed forthe cage on the NTN extreme high load capacity
tapered roller bearing.
Fig. 12 graphically plots the results of oil resistancetest with various resin cage materials. The PPS resin
does not exhibit deterioration in tensile breaking
strength even after undergoing immersion for 2,000
hours: it is apparent that this resin material has

Inlet to load zone
(small diameter side rib)Area subject tomaximum stressTensile breaking strength %Fig. 13 Model of dynamic analyzed bearing

4.0

PA66

PA46

PPS

3.5
3.0
2.5
2.0
1.5
1.0
0

500

1000

1500

2000

Immersion time h
Oil bath: differential oil GL-5, oil temperature 150˚C

Fig. 12 Test result of oil resistance-79-

NTN TECHNICAL REVIEW No.77（2009）

7. Conclusion
As the challenge to prevent global warming andimprove air quality continues, people committed toautomotive technologies have been more strenuously
involved in improving fuel economy. Thus, demand forsmaller, lower torque, longer-life automotive bearings
will continue to increase.
This paper has presented information about the“NTN extreme high load capacity tapered roller
bearing” that boasts compact size, lighter weight andhigher rigidity by reflecting novel bearing design
techniques—“maximized roller length” and “adoptionof newly developed resin cage”—in the NTN high load
capacity tapered roller bearing that has been alreadyrunning on actual automobiles.
By remaining committed to development of bearing
technologies and products, NTN will further cope withincreasingly demanding operating conditions anddiversifying structures where NTN bearing products will
be used.

References
1) Website of Ministry of Land, Infrastructure, Transport
and Tourism
http://www.mlit.go.jp/kisha/kisha07/09/090702_.htm
2) T. Tsujimoto and J. Mochizuki: High Capacity Tapered
Roller Bearings, NTN Technical Review No. 73 (2005)
30-39
3) K. Harada and T. Sakaguchi: Dynamic Analysis of aHigh-Load Capacity Tapered Roller Bearing, NTN
Technical Review No. 73 (2005) 20-29

Photo of authors

Takashi UENO

Tomoki MATSUSHITA

Automotive Engineering Dept.
Automotive Sales Headquarters

Automotive Engineering Dept.
Automotive Sales Headquarters-80-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]New ULTAGE Series
EA and EM Types of Spherical Roller Bearings

Yukihisa TSUMORI*
For spherical roller bearings that are used in industrial machinery,
including construction equipment and iron and steel facilities, we haveachieved the world’s best load capacity and possible rotation speed
through major revisions to the internal design. We began sales of thesebearings as the new ULTAGE series of models in March 2009, allowing
us to contribute further to creating a society that is more harmonious
with the environment.

1. Introduction

2. Structure of new self-aligning roller
bearings in ULTAGE Series

In contribution to realization of the ecology-oriented
society, novel technologies have been developed inevery technical field for industrial machinery.
The bearings used on rotary mechanisms inindustrial machines need to satisfy requirements for
improvements in “bearing life”, “load capacity”, “highspeed performance”, and “handling quality”. NTN has
been marketing the “ULTAGE*” Series bearing
products that boast the world’s best performance tomeet these requirements. The “ULTAGE” Series line ofbearing products already includes product series for
precision angular ball bearings and cylindrical roller
bearings intended for use on machine tool main
spindles.
Recently, NTN has added new standard productseries to the ULTAGE Series: they are new selfaligning roller bearings, EA Type (pressed steel cage)and EM Type (machined copper alloy cage) eachboasting higher load capacity and longer life.

Fig. 1 shows the structure of the NTN conventional
Type B self-aligning roller bearing. The structure of thisroller bearing is unique in that the bearing has
asymmetric rollers, and its inner ring center rib bears
the thrust induced by the running bearing. Due to being
guided by the inner ring center rib, the running rollers
are maintained in stable attitude. This structure isappropriate for larger bearings and high-speed
bearings.
At the same time, recent needs for self-aligning roller
bearings, other than high-speed capability, are longer
life and greater rigidity. To cope with these needs,
bearing manufacturers have been developing bearing
products with improved cage shape and more amply
sized rollers.

*“ULTAGE” (a name created from the combination of“ultimate,” signifying refinement, and “stage,” signifying
NTN’s intention that this series of products beemployed in diverse applications) is the general namefor NTN’s new generation of bearings that are noted fortheir industry-leading performance.

Pressedsteel cage

AsymmetricrollerInner ring
center rib
Induced thrustFig. 1 Spherical roller bearings (type B)*Product Design Dept. Industrial Sales headquarters-81-

NTN TECHNICAL REVIEW No.77（2009）

Tble 1 Comparison of spherical roller bearing type
Type

Type B

Type CType E

Rollers

Asymmetric roller

Symmetrical rollers

Symmetrical rollers

Cage

Pressed steel

Pressed steel

Resin molding

Center rib

Yes

None (w/guide ring)

None

Crosssectional
plan

greater load.
In addition, by adoption of novel cage featuring
higher rigidity and simplified form, it has become
possible to delete the inner ring center rib andincorporate a maximum number of rollers of maximized
length.
As shown in Fig. 3, the pressed steel cage in theType EA bearing guides the rollers with its both end
faces. In addition, four tabs (protrusions) situated in thecage pocket shown in Fig. 4 help stabilize the attitudeof rollers while the bearing is running and generatesmooth lubricating oil flow in the bearing (Fig. 5).
Furthermore, the entire surface of pressed steel cageis subjected to a special surface treatment to improvewear resistance of the cage.
Fig. 6 shows the structure and features of the Type

Table 1 provides information about comparison ofseveral self-aligning roller bearing types. In order tocope with the above-mentioned needs for higher load
capacity bearing products, NTN has been seriesproducing unique self-aligning roller bearings with theinner ring center rib deleted. They are the Type C selfaligning roller bearings having a guide ring and theType E self-aligning roller bearings whose rollers arestabilized in terms of attitude with the resin cage. NTN
will include these types in the ULTAGE Series bearing
products.
Fig. 2 shows the structure and features of the newly
developed ULTAGE Series Type EA bearing. Both
Types EA and EM employ symmetric rollers, wherein
the diameter and length of the rollers have beenmaximized so that the bearings can withstand a much

Rollers･ Larger rollers･ Maximized roller length･ Maximum number of rollers

Outer rings･ With oil inlets and oil groove･ Optional curvature

Cage･ Window-type pressed steel cage･ Cage end faces function as guides･ Special surface treatment

Inner ring･ No rib required･ Optional curvature

Fig. 2 Ultage series type EA spherical roller bearings

Four cage pockettabs stabilize theroller position.

Oil pathCage end faces function as guides

Fig. 3 Cage guide type of
EA spherical roller bearings

Fig. 4 Design of cage pocket tabs

-82-

Fig. 5 View of oil path

New ULTAGE Series EA and EM Types of Spherical Roller Bearings

Outer rings• With oil inlets and oil groove• Optional curvature

Rollers• Larger rollers• Maximized roller length• Maximum number of rollers

Inner ring
• W/outer rib• Optional curvature

Cage• One-piece machined cage
• Roller guide typeFig. 6 Ultage series type EM spherical roller bearings

Basic dynamic load rating kN

300
250
200
150
100
50
0

One-piece machined cage

Fig. 7 Cage type of EM spherical roller bearings

EA(New design)CompanyA

Company
B

CompanyC

Fig. 8 Catalogue comparison of basic dynamic load
rating (Cr)22216(φ80×φ140×33)

EM bearing and Fig. 7 illustrates the machined hightensile brass cage. This cage adopts roller guide typein order to stabilize the attitude of rollers while thebearing is running. The right half and left half of thecage constitute a non-separable body and the innerring has the outer rib in order to prevent loss of rollers.
The Type EM bearing is particularly advantageous inapplications subject to severe vibrations and impacts.
The dimensions in a Type EM bearing are same as
those of an equivalently sized Type EA bearing.

Basic static load rating kN

300
250
200
150
100
50
0

3. Advantages of ULTAGE Series selfaligning roller bearings

EA(New design)CompanyA

Company
B

CompanyC

Fig. 9 Catalogue comparison of basic static load rating(Cor)
22216(φ80×φ140×33)

3.1 Load capacity
Maximized roller diameter and maximized number ofrollers help the Types EA and EM bearings achieve theworld’s highest load capacity.
(1) Basic dynamic load rating: Comparison withcompetitors’ products is summarized in Fig. 8.
(2) Basic static load rating: Comparison withcompetitors’ products is summarized in Fig. 9.

Allowable speed min-1

5,000

3.2 Allowable speed
Employing a high-rigidity, pressed steel cage type,the Types EA and EM bearings boast the world’s
highest allowable speed as compared with thecompetitors’ catalogue values given in Fig. 10.

Oil
4,000

Grease
3,000
2,000

1,000
0

EA
(New design)CompanyA

Company
B

CompanyC

Fig. 10 Catalogue comparison of allowable speed
22216(φ80×φ140×33)-83-

NTN TECHNICAL REVIEW No.77（2009）

reduction means an approximately 30% reduction inboth bearing volume and mass. NTN believes that thisachievement will positively help machine designers
design lighter, much compact industrial machines.

Fig. 11 graphically plots test results for bearing
temperature rise under circulation lubrication condition.
It is apparent that the temperature rise on the Types
EA and EM bearings is limited compared with thecompetitors’ bearings, while the running torque is low.

Outer ring temperature ˚C

3.5 Improved handling quality
Introduction of a simple-shaped window typepressed steel cage helps simplify assembly,
disassembly, and greasing works.
(1) Easy grease application to roller surfaces (Fig. 12)

90
EA (New design)Company A
Company B

80
70
60
50
40

0

2000

4000

Bearing speed

6000

8000

min-1

Fig. 11 Test results of temperature rise22216(φ80×φ140×33)

3.3 Operating temperature range

Fig. 12 Grease application

Thanks to adoption of a special heat-treatment
technique, the maximum allowable operating
temperature is set as high as 200°C.

(2) Projection of rollers from the cage is small, androllers smoothly return to their normal state. Thus,
the disassembly/reassembly procedure for the
bearing is simple (Fig. 13).

3.4 Compact and lightweight design
By developing the Types EA and EM bearings, NTN
has achieved the following improvements over theprevious designs: 65% increase at maximum in basic
dynamic load rating, 35% increase at maximum instatic load rating, and 20% increase at maximum inallowable bearing speed.
A higher load capacity design technique helps
achieve a line of compact and lightweight bearing
products. Table 2 summarizes an NTN’s attempt torealize such an improved bearing product. By applying
this design technique, the size of conventional bearing
No. 22220B (dia. 100×dia. 180×46 in mm) can be
reduced to that of a product of the new series—
22218EA (dia. 90×dia. 160×40 in mm): this size

Fig. 3 Assembly / disassembly
Tble 2 Example, compact and lightweight
Model No.
22220B(Conventional design)

22218EA(New design)

Load rating(kN)

Boundary
dimensions(mm)

Bearing
volume
(cm3)

Mass
(kg)

Cr

Cor

315

415 φ100×φ180×46

810

4.95

385

398

φ90×φ160×40

600

3.28

△25%

△34%

-84-

New ULTAGE Series EA and EM Types of Spherical Roller Bearings

4. Inclusion into standard ULTAGE
Series products

5. Conclusion

NTN has developed an improved functionality
version of its standard self-aligning roller bearing
The ULTAGE Series Types EA and EM self-aligning
products, and added these improved products to its
roller bearing products are now available in all the
ULTAGE Series—that is NTN’s next generation
series range with outside diameter 420 mm or smaller.
bearing product series.
NTN is going to modify the conventional types (B, C,
Industrial machinery technologies have been
and E) to the new ULTAGE standards. For details, theincreasingly innovated to help realize the ecologyreaders are encouraged to contact the NTN.
oriented society. NTN believes that the new bearing
For the bearing number system for the new
products in the ULTAGE Series that boast greater load
ULTAGE Series products, see an example of bearing
capacity and higher speed positively satisfy demanding
number shown below:
market needs for lighter weight, smaller size andlonger life.
●Bearing Number
NTN will remain committed todevelopment of bearing products of anext generation, through further
improvement, realization of advanced
Internal clearance code
C3: C3 clearancefunctionality and lower cost in order to
No code: Normal clearance
cope with diversifying market needs.

222 20 EA K D1 C3

Oil inlet/oil groove code
D1: With oil inlet/oil groove(D1 specification only)
W33: With oil inlet/oil groove(European market specification)

Raceway configuration code
No code: Cylindrical bore
K: Tapered bore

Type code
EA: Window-type pressed steel cage
(EM: One-piece machined high-tension brass cage)

Bore diameter code
Dimension series code

Photo of author

Yukihisa TSUMORI
Product Design Dept.
Industrial Sales
headquarters-85-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Compact Free-type Torque Diode

Shoji ITOMI*NTN developed a free-type torque diode that rotates the output shaft
by turning the input shaft , but does not rotate the input shaft by turning
the output shaft. Recently, NTN has developed a small and light freetype torque diode that we call a “compact free-type torque diode.” This
report introduces the structure and function of this product.

The features of the newly developed compact free
type torque diode product can be summarized asfollows:

1. Preface
Free type torque diodes (TDF) are often used as an
automatic switching mechanism to switch overbetween electromechanical mode and manual modeon rotary equipment and as a safety-protection
mechanism for electric motors. To be able to expand
the scope of applications of this product line, NTN has
developed the “Compact Free Type Torque Diode” thatcan be used on compact precision equipment.

2. Dimensions and features
Figs. 1 and 2 provide information for comparison insize between the NTN newly developed product andconventional product.
The size of the newly developed product is 1/3 assmall as that of the conventional product.

10Outer ring

New design

Fig. 1 Comparison of size of developed productand current productCam face

New design

φ30.5

Output shaft

φ10

φ10

φ4

φ4

Input shaft

16.7

Conventional
designConventional design

Fig. 2 Comparison of size of developed product and current product*Application Engineering Dept. Industrial Sales headquarters-86-Compact Free-type Torque Diodeclutch can be categorized into two clear-cut types
according to the behavior of the clutch in response toreverse input situation: “locked rotation type” thatprevents torque transmission to the input shaft, and“free-rotation” type whose output shaft turns freely anddoes not transmits torque to the input shaft.
Now, Table 1 summarizes the relation oftransmission of rotational torque from the input shaft tothe output shaft on a free type torque diode.
Figs. 3 and 4 illustrate the structure and operating
principle of the newly developed compact free type
torque diode.
The outer ring is coupled to the input ring, remaining
capable of transmitting the rotational torque from the
input shaft; and the inner bore surface of outer ring has
a cam face. The cage retains the rollers and balls,
wherein the balls are forced to the outer ring end faceand bearing cover side face by spring force.

[Features](1) A portion of the output shaft also serves as a
cam face: consequently, the size of output shaft
×10 mmhas been greatly reduced to OD 10 mm×(1/3 reduction, compared to the conventional
product).
(2) Now, the housing and input shaft are made ofresin: consequently, the newly developed
product weighs mere 28 g (2/5 reduction
compared to the conventional product).
(3) The area of sliding surfaces has been reduced
to decrease the running torque* (resultant
torque is 5 mN-m or smaller; 1/25 reduction
compared to the conventional product).
(*The running torque mentioned here is a torque on the
product in unloaded state.)(4) Now, the housing is made of a resin; thereby
the shape of mount area of the housing can be
designed with greater freedom.

Table 1 Relation of input and output shaft rotationof Free type Torque Diode

3. Operating principle of free type
torque diodeInput shaft“Torque diode” can be defined as a reverse input
blocking mechanical clutch that transmits rotational
torque from the input shaft to the output shaft but does
not transmit rotational torque from the output shaft tothe input shaft. The reverse input blocking mechanicalSprings

Rollers

Output shaft

Rotation

Rotation(When the input shaft is turned, the output shaft rotates too.)
Does not rotate.

Rotation(When the output shaft is turned, the output shaft alone rotates.)

Outer ring end face Bearing cover side face
Outer ring

Rotational input from the input shaft causes theouter ring to rotate, thereby the output shaft rotates.

Ball

Capable ofbidirectional rotation

Capable ofbidirectional rotation

Contact

Output shaft

Input shaft

Cage

Fig. 3 Case of input shaft rotating
RollerRotational input from theoutput shaft

The output shaft remains at a standstill:
the input shaft does not rotate.
No contact

Fig. 4 Case of output shaft rotating (Input shaft not rotating)-87-

NTN TECHNICAL REVIEW No.77（2009）

Variation in the torque transmission path isdescribed below between a case where the torque isinput from the input shaft and another case where thetorque is input from the output shaft.

4. Endurance test
By using the forward-reverse rotation test machine
illustrated in Fig. 5 and applying the endurance test
conditions summarized in Table 2, durability of the
newly developed Compact Free Type Torque Diodehas been investigated by turning the input shaft in
forward and reverse directions to turn the output shaft.
Table 3 summarizes the tests result obtained. Thereis not much difference found in the running torque,state of internal structure. And backlash between,
before, and after operation for 11×104 cycles with the
newly developed Compact Free Type Torque Diode;this new product has proved its good durability.

3.1 Case where rotational torque is input fromthe input shaft
When the input shaft turns, the outer ring coupledwith the input shaft rotates; and the cage rotates in a
direction same as that of the outer ring at a speed
about 1/2 as fast as that of the outer ring. The balls
retained by the cage roll on the outer ring end face andbearing cover side face; the rollers shift to the outerring end face owing to difference in rotational speed
between the outer ring and cage, and then locked
between the outer ring cam face and output shaft; andthe output shaft rotates together with the outer ring
(Fig. 3).

Table 2 Test condition of endurance test
Running speed 100min-1
Forward and reverse rotation test machine(see Fig. 5)
One operating cycle consists of one forward rotation
Operating pattern (1 sec.), one standstill (0.5 sec.), one reverse rotation(1 sec.) and one standstill (0.5 sec.).
Test equipment

3.2 Case where rotational torque is input fromthe output shaft
When rotational torque is input from the output shaft,the rollers are held in location where they do not comeinto contact with the outer ring cam face; thereby, therollers are not engaged with the outer ring cam face;consequently, even when the output shaft rotates, theinput shaft does not rotate (Fig. 4).

Torque loading 50mN･cm (Loading is governed with a bidirectional
torque limiter.)Temperature

Room temperature
φ4 mm needle pin is used
Output shaft Dia. (hardness number: HRC60 or greater).

NOTE) After having stopped rotation, the input shaft isturned slightly in the reverse direction: consequently,
the rollers come off the cam face and take a relation
shown in Fig. 4; and then rotation of the output shaft is
not transmitted to the input shaft any more.

Table 3 Test results
Running time

110,000 cycles (61 hours)

Rotational torque Remains at 3 mN･cm, no change between before
with no load applied and after test operation.
State inside
the productVery minor wear on contact surfaces
No apparent variation in the amount of residual grease

Backlash

No variation between before and after test operation

Compact Free Type Torque Diode
Output shaft

Input shaft

Bidirectional torque limiter (load)

Fig. 5 Forward and reverse rotation test machine-88-

Electric motor (input)

Compact Free-type Torque Diode

5. Intended application
The product will be conveniently used for switchingover between motor-driven mode and manual mode forlens zooming functions on still cameras and video
cameras.

6. Conclusion
Previously, switch-over between electromechanicalmode and manual mode for rotary mechanism has
been achieved by switching over between paths fortransmitting rotational motion by actuating an electromechanical component such as an electromagnetic
clutch or a manually operated component such as ahand lever. Use of a free type torque diode helps
realize automatic switch-over between these modes
without using an electrical switch.
The newly developed NTN Compact Free TypeTorque Diode helps realize automatic switch-overbetween electromechanical mode and manual modefor small-sized mechanisms. NTN will not only remaincommitted to efforts for cost reduction and function
improvement, but also propose other applications to beable to support activities to develop low energyconsumption equipment.

Photo of author

Shoji ITOMI
Application Engineering Dept.
Industrial Sales
headquarters-89-

NTN TECHNICAL REVIEW No.77（2009）[ New Product ]Characteristics and Applications of DLC films

Kouya OOHIRA*
From the view point of environmental and energy issues,
vigorous efforts have been put into research and development
activities for tribological coating films in order to reduce friction andwear of sliding surfaces. In particular, diamond-like carbon (DLC)
coatings have superior low-friction and anti-wear properties
compared to other coating films, and they are attracting a greatamount of attention from tribology researchers and engineers. he friction and wear properties of DLC
films, however, depend on their use conditions as well as their production processes, and therefore itis necessary to choose appropriate DLC films according to their use conditions and engineering
purposes. This article introduces various properties of DLC films.

sliding in nitrogen gas or a vacuum, a-C:H(hydrogenated amorphous carbon), which is ahydrogen-rich DLC, exhibits an extremely low friction
coefficient of 0.001 1), 2); another report says that ta-C
(tetrahedral amorphous carbon), which is a hydrogenfree DLC, exhibits low friction when lubricated with oilin an automotive gasoline engine 3). A variety of DLC
films are available, and their sliding properties can varysignificantly depending on coating method and/or
conditions and the operating environment. Therefore,
the optimal DLC film design must be selected based on
the expected operating conditions. The following article
describes various properties of DLC films andexamples of their application to molding dies.

1. Introduction
NTN Group strives to reduce its environmental
footprint and thus remains committed to continued
mitigation of environmental impacts caused by its
corporate activities through improving energy efficiency
and utilization of resources in its production activities.
As an example, bearing engineers have been
proposing reduced use of rare materials, such as Mo,
included in bearing lubricant, as well as reduction in
the amount and viscosity of the lubricating oil usedwhich, result in lower bearing torque. However, theseattempts can result in deteriorated lubrication of the
bearing components, and conventional techniques
may fail to sufficiently lubricate the bearing
components involved.
Surface modification appears to be a promisingtechnique that can dramatically improve the tribologicalcharacteristics of bearing components. Bearing
engineers have been considering the adoption ofvarious hard films in order to alleviate friction and wear
on sliding surfaces within bearings. In particular,
Diamond-Like Carbon (DLC) film boasts higher
hardness, excellent wear resistance, and lower friction
coefficient and has been applied to automotive parts,
dies, and tools.
There are various reports available about
applications of DLC films: examples state that when

2. Features of DLC films
2.1 What is DLC film?
A DLC film can be defined as an amorphous film
(Fig. 3) consisting of an irregular mixture of diamondatoms that form sp3 bonds (diamond structure shownin Fig. 1) and diamond atoms that form sp2 bonds(graphite structure shown in Fig. 2). To provide aconcept diagram that helps to better explain DLC films,
Frrai and Robertson 4) have proposed a ternary phase
diagram such as given in Fig. 4. In this diagram, thecorner at the top represents diamond, the lower left
corner graphite, and the lower right corner hydrogen.

*Elemental Technological R&D Center-90-

Characteristics and Applications of DLC films

Table 1 summarizes the general physical propertiesof carbon materials including graphite, diamond, and
DLC films. Data for Young’s modulus, hardness
number, and the electrical characteristics of DLC film
are similar to those of diamond, and the thermal
conductivity of DLC film is similar to that of graphite.
The variation in physical property values of DLC films
exist due to variation in proportion of sp3 bonds to sp2bonds and hydrogen content 5, 6, 7).
Table 1 Comparison of characteristics of carbon material

Fig. 1 Structure of diamondFig. 2 Structure of graphite

Graphite

Diamond

DLC

Specific gravity

2.25

3.52

1.0〜3.0

Specific electric
resistance (Ω・cm)

10-3

1012〜1016

109〜14

Thermal conductivity(W/cm/K)

0.4〜2.1

1000〜2000

0.2〜30Lattice constant(nm)a=0.2456c=0.6708(interlayer)

a=0.3567…

…

…

Young’s modulus
(GPa)

…

1000〜2000

100〜800

Hardness number(Hv)…

10000〜12000 1000〜8000

Oxidation starttemperature

400〜450600

300〜500

2.2 Coating methods for forming DLC films
DLC films can be created from solid carbon orhydrocarbon gases such as methane, acetylene andbenzene and are usually formed in a vacuum chamber.
Depending on the carbon source used, the DLC film
falls within one of the following two categories:

sp2

sp3

(1) PVD: Physical Vapor Deposition
Fig. 3 Structure of DLC films

A process that uses solid carbon as a starting
material, wherein solid carbon is evaporated and thenthe resultant carbon vapor is allowed to deposit on asubstrate to form the DLC film.

ta-C ：Tetrahedral amorphous carbon
a-C：Amorphous carbon
a-C:H ：Hydrogenated amorphous carbon
ta-C:H ：Hydrogenated ta-C
sp3(2) CVD: Chemical Vapor Deposition
A process that uses hydrocarbon gas as a starting
material, wherein the gas is decomposed in a vacuum
chamber and then the resultant carbon vapor isallowed to deposit on a substrate to form the DLC film.

Diamondta-C
ta-C:H
a-C:H
a-C
Graphite
Glassy carbon
Pyrocarbon

sp2

By using solid carbon as an evaporation source, thePVD process can produce a DLC film solely composedof carbon. In contrast, since the CVD process useshydrocarbon gas as a starting material, the resultant
DLC film unavoidably contains hydrogen atoms ofapproximately 15 to 50 atm%. Either the PVD or CVD
processes can be applied in various methods. Fig. 5
summarizes typical coating processes applied to form
DLC films.

Organic polymer
Organic gas

H

Fig. 4 Classification of amorphous carbon-91-

NTN TECHNICAL REVIEW No.77（2009）

Table 2 lists several general physical characteristics
of DLC films formed by various coating processes. It
has been known that characteristics of synthesized
DLC films can vary greatly depending on starting
materials, atomic elements added, and coating
conditions 5, 6, 7).
The UBMS (Unbalanced Magnetron Sputtering)process listed in Table 2 is one type of sputtering
process, and is characterized by an unbalanced
magnetic field that is employed to expand a plasma
layer in the vicinity of the substrate. Because theplasma density near the substrate is increased, the ion
assist effect (ions are allowed to collide the substrate)is enhanced; consequently, the film characteristics
including density and adhesion are improved 8).

resultant carbon vapor is ionized and is allowed todeposit on the sample surface to which a negative bias
voltage is applied. As a result, a DLC film with a higher
degree of adhesion is formed 5).
In a plasma CVD process, hydrocarbon gas (suchas methane, acetylene, benzene, etc.) is decomposedin a vacuum chamber to generate hydrocarbon ionsthat are accelerated and allowed to collide into asubstrate to which negative voltage is applied resulting
in the DLC film. Because of using gas as a starting
material, the CVD process features better “coverage”
and is suitable for forming a DLC film on samples withcomplex geometry. Also, with this process, a DLC filmof uniform thickness can be formed without the need toreorient the sample.

The AIP (Arc Ion Plating) process uses a solidcarbon cathode and the chamber inner wall as an
anode in order to trigger an arc discharge and allow
carbon on the target surface to evaporate. The

2.3 Comparison of DLC films with various otherhard coatings
2.3.1 Characteristics in general
Table 3 summarizes the characteristics of DLC films
and other hard coatings. DLC films boast particularlyhigh hardness and excel in anti-seizure quality.
However, DLC films have an unavoidable drawbackthat is, poor adhesion to a substrate. Poor adhesion
occurs because stresses within a DLC film are high,and carbon atoms, which are chemically stable, do notreadily coagulate with a dissimilar material. Therefore,
improved DLC film adhesion poses an engineering
challenge.

Sputtering process
Arc ion plating process
PVD
process

Ion vapor deposition process

2.3.2 Friction wear resistanceIon beam process

Using the NTN Savin type wear test rig, NTN has
evaluated the sliding characteristics of DLC films(formed with UBMS process) and of various other
nitride coatings.
This test rig is designed to maintain sliding contact
between the flat test piece and a driven rotating
cylinder which is crowned. Fig. 6 illustrates theconfiguration of the NTN Savin test rig, and Table 4summarizes the test conditions applied. The test rig
uses a crowned cylinder so that uneven contact does
not occur between the test piece and cylinder, thusachieving a much more accurate assessment of thefilm’s wear resistance. Fig. 7 summarizes the test
results, where the specific wear has been calculated
based on the width of wear marks found on the test
piece and the friction coefficients that have been
determined based on friction values measured with theload cell.
The specific wear of DLC film is 1/6 or lesscompared with that of TiN, which was the best of thenitride films tested. In addition, the friction coefficient of
DLC film is about 0.2 while the friction coefficients ofother hard films fall in a range of 0.4 to 0.8, indicating
the DLC film features excellent friction characteristics.

Laser abrasion process
Plasma CVD process
CVD
process

Thermal CVD process
Photo CVD process

Fig. 5 Classification of coating methods

Table 2 Characteristics of various DLC films
PVD process

CVD process

UBMS process

AIP process

Plasma CVD process

Coating material

Solid carbon

Solid carbon

Hydrocarbon gas

Coating
temperature (˚C)

＜250

＜300

＜200

Hardness
number (Hv）

2000〜5000

5000〜8000

1000〜2000

Surface roughness

○

△

◎

Coverage△△◎

Adhesion◎○○

Wear resistance

◎

○

△

Cost

△

△

○

-92-

Characteristics and Applications of DLC films

Table 3 Characteristics of DLC films and other hard coatings
Hardness
Corrosion Oxidation
Seizurenumber (Hv) resistance resistance resistanceFilm type

Color

DLC

Gray to black

1000〜8000○○

Adhesion

Applications◎△

Cutting tools, dies, functional films

TiN

Gold

2000〜2400

○

○

○

◎

Cutting tools, dies, jewelry

ZrN

White gold

2000〜2200

○

△

△

○

Jewelry

CrN

Silver white

2000〜2200

◎

○

◎

◎

Machine parts/components, dies

TiC

Silver white

3200〜3800

△

△

○

○

Cutting tools, dies

TiCN

Purple to gray3000〜3500

△

△

○

○

Cutting tools, dies

TialN

Purple to black

2300〜2500

○

◎

○

○

Cutting tools, dies, jewelry

Thus, the DLC film appears to be a promising meansfor creating a highly wear-resistant surface treatment
used on machine parts/components, dies, and tools.

3. Coating method-dependent variationin characteristics of DLC films
3.1 Sliding wear characteristics

WeightLoad cell

Test piece
Matingmaterial

Fig. 6 Wear test rig

Test
piece

Hardened SUS440C stainless steel, OD 48 mm,
thickness 7mm, surface roughness 0.005 mmRa

Matingmaterial

Quenched and tempered SUJ2 steel, curvature R60 mm,
hardness Hv784, surface roughness 0.01 mmRa

Load

50 N (max. contact pressure 0.5 GPa)）

Speed

0.05 m/s

Time

3 min (sliding distance 9 m)

Specific wear ×10-10mm3/(N・m)

Table 4 Test conditions

40000

1

32000

0.8

24000

0.6

16000

0.4

8000

0.2

0

0
DLC

TiN

TiSiAlN TiCN

TiAlN

CrN

0.5

400

0.4

300

0.3

200

0.2

100

0.1
0

0

A（UBMS）

Friction coefficient at the end of test

Specific wear ×10-10mm3/(N・m)Environment Under blowing of dry air, temperature 0–20%RH

500

Friction coefficient at the end of test

Fig. 8 plots the NTN Savin type wear test results ofthree DLC film samples, wherein the DLC films ofthese samples were prepared by UBMS process, AIP
process, and plasma CVD process previously
described in Sec. 2.2. Table 5 summarizes the coating
methods, hardness numbers and thicknesses of thesesamples. The test conditions are the same as thosespecified in Sec. 2.3.2 except in that the test duration
was changed to 30 minutes.
It is apparent that among three DLC film types, the
UBMS process boasts best wear resistance and the
AIP process features the lowest friction coefficient.

B（AIP）C（CVD)

Fig. 8 Wear property and coefficient of frictionof each specimen
Table 5 Coating method, hardness, thickness of DLC films
Test piece

CrAlN CrSiN

Fig. 7 Wear property and coefficient of friction of eachspecimen specimens-93-

Coating method Hardness, Gpa

Thickness, μm

A

UBMS

26

1.2

B

AIP

53

1.0

C

CVD

15

2.0

NTN TECHNICAL REVIEW No.77（2009）(1) Higher substrate hardness (created by nitriding,shot peening, etc.)(2) Surface pre-treatment (by chemical etching,abrasive blasting, etc.)(3) Adoption of an intermediate layer that is highly
affinitive to both the substrate and DLC film
Through adoption of techniques best suited for theintended operating conditions, a DLC film will positively
adhere to a substrate.
As described above, DLC films can have diverse
characteristics depending on coating method andconditions adopted. The optimal coating method andconditions for forming a DLC film need to be selectedaccording to the intended application and performancerequirements.

3.2 Power of adhesion to substrate
NTN performed an adhesion evaluation test per the
Rockwell indentation test method to determine
adhesion of the DLC films which were tested in Sec.
3.1 to substrates. The Rockwell indentation test forcesa cylindrical diamond indenter into each DLC film
sample under a particular load (1,470 N) to form an
indentation mark on the film. The quality of adhesion of
the DLC film to a substrate has been evaluated basedon the evidence of cracking or flaking of the filmaround the indentation mark. Figs. 9 through 11 show
the resulting test samples.
In this evaluation, DLC film (A) has not developed
cracking or flaking: DLC film (B) has developed radialcracks, though not flaking: DLC film (C) has exhibitedsevere flaking around the indentation.
Generally, DLC films are prone to peeling because
their hardness is very high and internal stress exists:
therefore realization of reliable adhesion to a substrateposes an engineering challenge. Techniques for
improving film-to-substrate adhesion include:

4. Applications to dies-DLC film application
to dies for sintered metal moldings
In molding/forming work for sintered copper alloyparts, tungsten carbide dies are usually used becauseof their excellent wear resistance. However, in this typeof work, excessive wear is occasionally observed on
the dies even though the tungsten carbine material
boasts significantly higher hardness compared with thecopper alloy material. As a result, dies of much longer
life have been increasingly needed. To address thischallenge, NTN has attempted to adopt DLC films thatprovide much greater wear resistance.
Using the NTN Savin type wear test rig, NTN has
evaluated wear resistance of non-coated tungsten
carbide test pieces and tungsten carbide test pieces
coated with a DLC film. The DLC film used was formed
using the UBMS method. Table 6 summarizes the test
conditions applied; Figs. 12 and 13 show wear marks
found on the sliding surfaces; and Figs. 14 and 15 plot
the resultant profile measurements on the worn
surfaces of the test pieces.
The tungsten carbide-only test piece has exhibited a
noticeable wear mark on its sliding surface eventhough it has undergone sliding contact with a sinteredcopper alloy member (a relatively soft material). The
maximum depth of wear has reached 0.8 mm. In
contrast, the test piece consisting of tungsten carbide

0.1mm

Fig. 9 Indentation of DLC film(A)0.1mm

Fig. 10 Indentation of DLC film(B)Table 6 Test conditions
Test
piece

Tungsten carbide (WC-Co), OD 48 mm, thickness 7 mm,
surface roughness 0.005 mmRa

Matingmaterial

Sintered copper alloy (Cu58%, Fe40%),
surface roughness 0.3 mmRa

Load

50 N

Speed

0.1 m/sTime

30 min (sliding distance 180 m)

Environment Under blowing of dry air, temperature 0–20%RH

Fig. 11 Indentation of DLC film(C)-94-Characteristics and Applications of DLC films

Test point for shape measurement

Test point for shape measurement

0.3mm

0.3mm

Fig. 12 Wear of sliding part (WC)

Fig. 13 Wear of sliding part (WC + DLC film)

Fig. 14 Surface profile of wear (WC)

Fig. 15 Surface profile of wear (WC + DLC films)

coated with DLC film exhibited a wear depth of 0.04
µm which is 1/20 that of the uncoated test piece. The
DLC film has helped dramatically reduce wear on thetungsten carbide test piece.
The reason tungsten carbide (WC-Co) wears as aresult of sliding against the softer sintered copper alloy
may be because the copper atoms diffuse into thecobalt particles at the contact interface. The cobalt
particles act as a binder in the tungsten carbide
structure. As a result of this diffusion, the Cu
concentration between the WC and Co particles
increases, thereby deterioration the mechanicalstrength of the tungsten carbide structure. By coating
the surface of a tungsten carbide die with a DLC film,
which does not readily react with copper atoms while
maintaining wear resistance, wear on the die is much
reduced. In addition, based on endurance test resultswith a die used commercially for sintered copper alloy,
it has been verified that the life of the die coated with
the DLC film is much longer compared with a noncoated die of a same geometry.

References
1) A. Erdemir et al., SAE Paper, 2000-01-0518
2) J. Andersson et al., Wear, 254 (2003), 1070-1075
3) M. Kano et al.: Proceedings of The Third Asia
International Conference on Tribology, October 2006,
Kanazawa, 399
4) A.C. Ferrari, J. Robertson, Phys. Rev., B61, 14095(2000)
5) M. Ikenaga (ed.), Film Technologies for Advanced
Functionality, Nikkan Kogyo Shimbun (2007)(Japanese)
6) N. Otake, Surfaces, Vol. 45, No. 9, 22-35 (2007)(Japanese)
7) M. Ikenaga and H. Suzuki, Principles of Super Hard
Films Made through Dry Processing and their
Industrial Applications, Nikkan Kogyo Shimbun (2000)(Japanese)
8) N. Otake: Application and Technology of DLC Films“Evolving Industrial Applications and Future
Technologies of Diamond-Like Carbon,” CMC
Publishing Co., Ltd. (2007) (Japanese)

Photo of author

5. Conclusion
As described above, the DLC film treatment is atechnique that is effective in extending life of dies andtools. Boasting a higher degree of wear resistance andlower friction, the DLC coating provides a promisingtechnology that helps address environmental andenergy issues. NTN will attempt to further develop thistechnology and expand the scope of its applications.

Kouya OOHIRA
Elemental Technological
R&D Center-95-

NTN TECHNICAL REVIEW No.77（2009）[ Technical Paper ]Optimized Radius of Roller Large End Facein Tapered Roller Bearings

Hiroki FUJIWARA***Takashi TSUJIMOTO***
Kazuto YAMAUCHI***Tapered roller bearings can support heavy combined radial and thrustloads, and are widely used for automobiles, railcars and industrial
machines. The bearings have an inner ring rib into which the large endsof rollers are thrust, and the contacts are accompanied with rolling-sliding
motions. The arge ends of rollers and the rib surfaces are spherical andconical in shape, respectively. The typical lubrication regime of thecontact is elastohydrodynamic lubrication (EHL). However, some surface damage may occur if the oil film formation
is insufficient due to low-rotational and/or heavy-load operations. The film thickness should be thick enough toprevent damage in a given operating condition. In this paper, an EHL numerical model is developed inconsideration of both asperity contact and roller skewing. A parameter study shows that to form thicker oil films the
optimum radius of the large end face of a roller is about 85% that of the rib face conical surface.

large end face and the cone flange.
Fig. 1 (a) shows a cross-sectional view of a tapered
roller bearing. The cone flange face usually consists ofa part of a conical surface perpendicular to the bearing
axis, while the roller large end face comprises a part ofspherical surface. This condition results in roller endflange face point contact resulting in the highest
pressures. The cone flange face may possess aconcave surface matches the contour of the roller
large end face. In this situation, the pressure between
these two faces will be smallest. However, even small
rotations of the roller on the y-axis (see Fig. 1 (a)) inthis condition can cause the edge of the roller large
end face to come into contact with the cone flange
face, possibly damaging the roller or the cone flange
face. To avoid this problem, the radius of curvature on
the roller large end face is designed to be somewhat
smaller than that of cone flange face. Note thatrotational motion on the y-axis is referred to as“skewing” while rotational motion on the x-axis is called“tilting”.
At the roller end-flange contact a sufficiently thick oilfilm may not be readily formed when the bearing runs
at lower speeds or is insufficiently lubricated.
Consequently, frictional torque on the bearing will

1. Preface
A basic tapered roller bearing consists of acompliment of tapered rollers that are arranged
between inner and outer rings having conicalraceways. The inner and outer ring of a tapered roller
bearing is commonly referred to as a cone and a cup
respectively. Because tapered roller bearings can
support both a relatively high radial load and a singledirectional axial load, they are widely used in drive
systems in automobiles and railway cars, steel millmachines, and other industrial applications. The apexof the inner and outer ring raceways and the roller
contact surfaces of a tapered roller bearing converge
on the bearing centerline. The rollers develop purerolling motion without sliding on the conical raceway
surfaces. However, when a radial load acts on the
bearing, an axial component force occurs on the rollers
due to a disparity in angles between the inner andouter ring raceways. As a typical means for bearing
this force, a cone flange is provided. As a result, thelarge end face of each roller is guided while being
forced to the cone flange. Though each roller
undergoes pure rolling motion on the raceway surface,
there remains rolling-sliding contact between the roller*Elemental Technological R&D Center **Automotive Sales Headquarters Automotive Engineering Dept. ***Graduate School of Engineering Osaka Univercity

Modify the Japan Society of Mechanical Engineers. C. Journal (Vol. 75, 2009), pp-2319-2326.

-96-

rm

rB

mean flow model 4).
Incidentally, a tapered roller has a tendency to skew
even if factors such as misalignment are not present,
as pointed out by Harada et al. 6). However, so far,there have been few examples of EHL analysis thatconsider roller skewing. Furthermore, there have beenno examples of experiments to optimize the radius of
the roller large end face. We recently performed EHL
analysis considering roller skewing. Based on the
results obtained from this work, we now propose an
optimal radius for the roller large end face in order toform a reliable lubricating oil film. This optimal radius
will be verified through a series of experiments.

lglr(a) Radial cross-section and legend

2. Analysis of elastohydrodynamic
lubrication (EHL) between roller end
and flange faces
2.1 Isothermal EHL analysis
EHL analysis was conducted for the contact area
between the roller large end and cone flange face oftapered roller bearings. The velocity, bearing load, andlubricating oil viscosity used for this analysis wereselected in order to minimize heat generation at thecontact area. Therefore, the temperature condition forthis analysis was assumed to be isothermal.
Specifically, the following assumptions were made:• Adequate lubrication exists.
• Heat generation in the lubricating oil due toshearing is ignored.
Equations involving the following variables are
solved simultaneously:• Reynolds’ equation• Elastic deformation derived from semi-infinite elastic
contact theory• High-pressure viscosity properties of the lubricatingoil• Balance between force and moment
As shown in Fig. 1 (b), in the entire region ofcontact, both roller end face and flange face have avelocity distribution in the x and y directions.
Therefore, the Reynolds’ equation needs to incorporate
considerations about stretch terms ( 3rd and 4th terms
in the right-hand side in expression (1)). Consequently,
the Reynolds’ equation will be expressed as:(b) Mode of contact between roller large end face andcone guide flange, and associated coordinates system

Fig. 1 Tapered roller bearing

increase and under higher loads sliding will occur atthe contact surfaces. This will increase the possibilityof surface damage or seizure at these areas. Note thatthe situation where mating components haveinsufficient lubrication is known as “starvation”.
So far, the mode of contact between the roller large
end face and the cone flange face has been reviewed
through experimental methods and theoreticalanalysis. The experimental methods include thefollowing examples. Yamada performed a series ofexperiments to study the effects of surface roughness
on oil film formation at lower speeds. This resulted inachieving lower torque at these contact surfaces
through reduction in surface roughness of the roller
end face and flange face 1). Okamoto, et al. attempted
to reduce the distance from the roller large end-flange
face contact point to the cone raceway. The intent was
to reduce the slip ratio of these components in order toimprove their anti-seizure properties 2).
There are many examples of applying EHL(Elastohydrodynamic Lubrication) analysis. Jiang, et al.
performed thermal EHL analysis with non-Newtonian
fluids and discussed the relationship between the
shape of the contact area and the oil film thickness 3).
Nishida, et al. performed EHL analysis under a mixed
lubrication condition 5) by introducing the Patir-Cheng（∂ρh3 ∂p∂x

12η ∂x） （＋∂ρh3 ∂p∂y12η ∂y

）

∂(ρh)
∂(ρh)
∂vm
∂um
= um
＋ρh
＋ρh
＋ vm
…（1）
∂x
∂y
∂y
∂x
where, h stands for clearance, ηviscosity of
lubricating oil, p pressure, ρdensity of lubricating oil,um and vm x-direction component and y-direction-97-

NTN TECHNICAL REVIEW No.77（2009）

component of the mean velocity at the contact area
between roller large end face and flange face,respectively.
To investigate the high-pressure viscosity property of
the lubricating oil, Houpert converted the formula given
by Rolelands into the SI system 7). This formula
incorporates considerations for temperature change.
However, because our study was intended to determine
the isothermal viscosity of the lubricating oil, we haveignored the terms associated with temperature andhave adopted the following expression:

｛

［

z

h
provided that, whenA1=1.899
α1=0.98
α2=0.92
α3=0.05
A2=1.126
then, the Reynolds formula (1) will be modified asfollows:

（

∂

］｝

＋vm

＋ρh

……………（4）

F2.5
kc =

α1

σ

exp −α2

φs= A2 exp −0.25

h

σ

σ

＋α3

h

σ

∂um
∂x
∂vm

2

when

F2.5

when

ρh3 ∂p12η ∂y）∂（ρφsy）∂y＋ρσφsy…………（7）（ ）（ ）∂ ur−ui∂x2∂ ur−ui

hc

σ

5

hc

∞

= hc t−

σ

σ

8√
2

σ

hc 2

σ
2

π
（Nβσ)

15

hc

……………………………（8）

｛

hc

σ

f *（t）dt……………（9）σ…………………（10）β, Patir-Cheng offers the following
hc 6.804hwhen c ＜4σσhwhen c ＞4σ…………………（11）4.4086×10-5 4−=

0where, hc stands for the oil film thickness at the
midpoint. For values of N, β and σ, available
research so far has attempted to define them in theform of Nβσand σ/β. Greenwood-Tripp haveassumed that Nβσ= 0.03 to 0.05 10). We also assumeNβσ= 0.05. Incidentally, Patir-Cheng assumes that σ/β= 100 12): however, through our experience, we
believe thatσ/β= 20 is a reasonable assumption.
Bearing engineers believe through experience thatthe boundary friction coefficient μa related with contact
surface between roller large end face and flange face
falls in a range of 0.12 to 0.15. For this study, we haveassumed μa = 0.12.

hσσ＋ρσφsxapproximation 12):………………（5）（ ） ｛ （ ）（ ）｝（ ）φs= A1

h

φy

∂y

2

For function F2.5

and that the roller large end face is a smooth surface;
and when adopting the shear flow factor 11) that resultsfrom these assumptions and is defined as:
h

∂

（ ）
（ ）∫（ ）
（ ）
（）
（ ）
（）

We adopted the mean flow model of Patir-Cheng 4)
to be able to determine the effects of surface
roughness, and introduced the mixed fluid lubrication
theory 10) of Greenwood-Tripp. Incidentally, with these
two models, surface roughness is handled in aprobabilistic manner. In other words, the abovementioned methods have a low probability ofcalculating results for pressure and film thickness
distribution that agree with results obtained from thoseof a fixed contact area.
In our study, we only considered isotropic roughness
in the Patir-Cheng’s mean flow model 4). Whenassuming that the pressure flow factor is defined as:

）

∂y

vr−vi

＋

pa= kc E'F2.5

2.2 Effects of surface roughness

σ

） （
＋

∂y
2
∂y
If surface asperities of mating components come into
contact then the resultant contact pressure can be,
based on Greenwood-Tripp theory 10), expressed as:

where, v means the kinematic viscosity (mm2/s), and mviscosity slope constant appearing in Walther-ASTM
formula 9).

（12η ∂x∂(ρh)＋ρhwhere, α0represents the viscosity-pressure coefficient,and is given by the following Wu-Klaus-Duda formula 8):

φx=φy =1−0.90exp −0.56

ρh3 ∂p∂(ρh) ur−ui ∂（ρφsx）
σ
= um
＋
∂x
2
∂x

where, η0 stands for atmospheric viscosity andis expressed as:α0z=………………………（3）5.1×10-9（lnη0＋9.67）

h

φx

∂x

η=η0 exp［lnη0＋9.67］−1＋（l＋5.1×10-9p） …（2）α0=（0.1657＋0.2332log10v）m×10-8

＞5

σ

≤5

h

＞5
σ
………………（6）-98-

Optimized Radius of Roller Large End Face in Tapered Roller Bearings

2.3 Boundary conditions

φ

rB

rm

In ordinary EHL analysis works, researchers choose
an evaluation region whose size is several times larger
than the area of projected Hertzian contact surfaces sothat the projected pressure at the outer fringes in thisregion is zero. By contrast, when studying roller large
end-flange contact, the region of generated oil film
(hatched area in Fig. 1(b)) is not sufficiently large
relative to the size of Hertzian contact surfaces.
Therefore, we have introduced the boundary conditions
defined below.
The contact pressure occurs only in the region
where the roller large end face contacts the flat surfaceof the cone flange face. The contact pressure in otherregions is assumed to be zero.

2.4 Assumptions about motions
We developed the following assumptions about the
motions of the rollers, inner and outer rings:• Angular velocities of the rollers and inner and outerrings occur due to the mechanical relationshipbetween them.
• Centrifugal force and gravitational force can beignored.
• Interface between the rolling surfaces of the roller andraceways and between the rollers and the cage do
not affect roller skewing.
• The rollers do not tilt.
• Skewing occurs due to the oil film pressure
distribution between the roller large end face andcone flange face, traction, and metal-to-metal friction
between surface roughness asperities.

Fig. 2 Skewing of roller

this rotational motion of rollers are described below,
wherein the center of rotation is assumed to be at thecenter of gravity of the roller.
When referring to the coordinates system given in
Fig. 1, the moment of force Mh deriving from pressure
on the oil film p can be calculated by the expression
below:

3. Skewing on rollers in EHL mode∫
∫xpdxdy ………………………………（12）Mh=Generally, under an EHL (Elastohydrodynamic
Lubrication) condition, the pressure on the oil film
gradually increases at the fluid inlet side, and suddenly
drops at the outlet of the Hertzian contact area.
Consequently, the pressure gradient along the oil film
is asymmetric relative to the center of contact.
Because of this, a moment is created between thecontacting objects. This moment will cause the rollers
to skew as shown in illustrated in Fig. 2. While slip ofapproximately 20% is occurring between the roller
large end face and cone flange, a moment of force
deriving from traction is also occurring. Furthermore, if
metal-to-metal contact is present, the resultant
frictional force also contributes to the occurrence of amoment. Each roller turns such that balance isachieved among the pressure on the oil film, thetractional force from the oil film, the frictional force frommetal-to-metal contact, and the outer force (force
acting on the cone flange). The moments taking part inwherein, the origin is defined as the intersection
point of the x-axis and y-axis in Fig. 1 (b).
The magnitude of the moment caused by thetractional force can be determined in the following
manner: from the experiment by Ono et al. 13), themaximum tractional coefficient μt, max is determined asfollows:
0.09
×α0 p whenα0 p≤ 25
25……（13）
0.09
μt, max=
whenα0 p＞25
25
where, α0 stands for the viscosity-pressure coefficient.
Since the maximum projected skewing angle is as
small as approximately 0.05 degrees, the slip ratio s
can be calculated with the following expression,
ignoring minor variation by skewing:
μt, max=-99-

NTN TECHNICAL REVIEW No.77（2009）ur−uis（x, y）=

4. Calculation results………………………（14）（ur＋ui）/2

4.1 One detailed example of calculations

where, ur and ui represent the velocity at the roller
large end face and the velocity at the cone flange facerespectively. If the slip ratio leading to the maximum
tractional coefficient is taken as smax, then the tractionalcoefficient μt can be determined, by adopting thecircular-model of Lee-Hamrock 14), with the following
expression:μt =s / smax
2
1＋（s / smax）

Calculations were performed under the analysis
conditions summarized in Table 1, and the results areshown in Fig. 3. The R ratio of roller large end facegiven in Table 1 can be defined as rm/rB, using theassociated codes in Fig. 1. The analysis conditions inTable 1 correspond to a situation where lubricating oil

μt, max ………………（15）Table 1 Analysis condition
Cup tapered angle
Roller tapered angle
R ratio of roller large end face
Roller length
Young's modulus
Poisson ratio
Oil kinematic viscosity at 40˚C
Oil kinematic viscosity at 100˚C
Oil density…
Viscosity - pressure coefficient

Therefore, the tractional force Ft is defined as:
Ft =μt ∬pdxdy……………………………（16）Then, when assuming that the distance between the
ontact point to the center of gravity of the roller is lg,
the tractional moment Mt can be expressed as:
Mt = lg Ft……………………………………（17）The frictional force resulting from metal-to-metal
contact can be investigated using the Greenwood-Tripptheory 10). When assuming the boundary frictionalcoefficient as μa and the apparent contact area as A0,
then the frictional force Fa on the asperity contact
surface can be expressed as:
Fa=μa A0 pa………………………………（18）

Rotating speed
Rib load
Oil temperature
Root mean square roughnessof roller large end face
Root mean square roughnessof cone back face rib

deg.
deg.
mm
GPa
mm2/s
mm2/s
kg/m3
Pa-1
min-1
N
˚C

57.62
8.5
0.8
13.52
208
0.3
32.2
5.45
850
1.93〜10-8
2000
200
40

µm

0.025

µm

0.1

The moment Ma deriving from Fa is:
Ma= lg Fa…………………………………（19）When a roller begins skewing, the contact point
between the roller large end face and cone flange
shifts, and the vector of the contact force no longer
intersects the center of the roller. As a result, theflange generates moment Mr that helps reduceskewing. When the distance in the x-direction between
the roller flange contact point and center of the roller(i.e. the distance the contact point shifts), is taken aslshift, Mr can be defined as follows:(a) Oil film pressure distribution

Mr= lshift P…………………………………（20）where, P is load on rib. Then, the geometrical
relationship between lshift and the skewing angleφcanbe expressed as:lshift =rB（rm−lg）
sinφ
rB−rm

…………………（21）where, rm, rB and lg are lengths shown in Figs. 1 and 2.
Finally, skewing angleφcan be determined by solving
the expression below:
Mh ＋ Mt ＋ Ma ＋ Mr = 0…………………（22）μm(b) Oil film thickness distribution

Fig. 3 Result of EHL analysis between roller large end
face and cone flange face-100-

Optimized Radius of Roller Large End Face in Tapered Roller Bearingsof viscosity grade ISO VG32 is kept at 40˚C, pure axial
load of 9.8 kN is applied to the tapered roller bearing
30306D, and the inner ring is allowed to run at 2,000
min-1.
Fig. 3 (a) provides an oil film pressure distribution
diagram. Fig. 3 (b) shows an oil film thickness
distribution diagram. The x and y -axis in these
diagrams are the same as those in Fig. 1 (b), and theregion enclosed with solid lines is the zone where
lubricating oil film formation can occur. The two faces
generally shift in the positive direction along the x-axis.
As shown in Fig. 3 (a), a pressure spike indicative of
EHL occurs at the location near the exit of the fluid
flow. A skewing angle of -0.019˚ of the roller is present,
an angle at which oil film tends to occur due to a wedge
film effect. The point of maximum oil film pressure has
shifted by 0.2 mm in the positive direction along the xaxis due to skewing. As a result, the inlet oil flow area
is greater than if the roller was not skewed. As shownin Fig. 3 (b), the deformed region constitutes an oval
having its long axis in the x-direction, which is the major
flow direction of the lubricating oil. There is ahorseshoe-shaped neck at the oil flow outlet. Unlike a
one-way oil flow situation, the oil film profile is not
symmetric along the x-axis at y = 0.

experimental results of Harada et al., “EHL” stands forcalculation results obtained from our EHL analysis
technique previously described in this paper, and “HL”
indicates a results of fluid lubrication analysis on roller
large end flange performed by Harada et al. assuming
an isoviscosity-rigid body region. Compared withvalues associated with “HL”, the values obtained from
“EHL” are more similar to the experimental results.
This is because with “HL” results, the force as anintegral of pressure is significantly shifted toward thefluid inlet path since elastic deformation is notconsidered. In contrast, with “EHL” results, the oil film
pressure is approximately the same as the Hertz
pressure; thereby, the force (i.e. integral of pressure)acts on a point situated near the contact center.
The calculated effects of the rotational speed
qualitatively differ from the experimental results. In thecalculated results, a greater rotating speed leads to agreater magnitude of the skewing angle for both “EHL”
and “HL”. However, at lower rotational speeds (e.g.
1,000 min-1), the experimental skewing angle closely
matches that obtained from EHL analysis. From thesefindings, we believe that at low rotational speeds,
where starvation seems not to be present, the resultsof our EHL analysis technique well represents theexperimentally determined lubrication state.
Furthermore, we reason that the experimentallyobtained skewing angle is smaller than that obtained
from the EHL technique because experimentally athigh pressure, the pressure at the inlet oil flow pathdrops due to starvation causing the moment derived
from the oil film pressure to drops.

4.2 Experimental verification of skewing angle
Harada et al. measured the skewing angle on arunning 32310 tapered roller bearing 6). The resultant
report states that a skewing angle was calculated using
the roller large end face/cone flange face contact
program. This program simulates an isoviscosity-rigid
body region but there was a discrepancy in magnitude.
Harada et al. think this is because in the experimental
study, a high viscosity-elastic body region was used incontrast to the calculation-based study, whichassumed an isoviscosity-rigid body region.
We compared the experimental result of Harada etal. with the calculation results obtained from our
method described in this paper. The results aregraphically plotted in Fig. 4. In this chart, “Exp.” areSkewing angle deg

0.07

Behavior of fluid flow is primarily governed by thepressure gradient across and velocity between two
faces. Roughness asperities within the pressure
gradient will result in localized pressure variation. In
addition, fluid in the troughs of a rough surface will
move along with the surface: affecting the oil flow ratecaused by relative motion between the faces, resulting
in a substantial decrease of the oil film thickness.
Consequently, the expected flow will vary. By adopting
a pressure flow rate coefficient and a shear flow rate
coefficient in the Patir-Cheng mean flow model 4), we
can quantitatively determine the effects of 2D (twodimensional) surface roughness.
The “pressure flow rate coefficient” can be definedas the ratio of the mean pressure flow on a roughsurface to that on smooth surface. The “shear flow rate
coefficient” is similar but with additional flow caused bya shift of the rough surface. Both the pressure flow rate
coefficient and the flow rate are affected by directionalparameters associated with roughness. For

Exp.1000 min-1

0.06
0.05

Exp.2000 min-1
Exp.3000 min-1

0.04
0.03
0.02

EHL1000 min-1
EHL2000 min-1
EHL3000 min-1

0.01

HL1000 min-1

0

-0.01

4.3 Effects of surface roughness

HL2000 min-1

0

50

100

150

200

HL3000 min-1

Rib load

Fig. 4 Comparison between experimental and calculatedof skewing angle-101-

NTN TECHNICAL REVIEW No.77（2009）

convenience of discussion, we will deal with isotropic
surface roughness.
Taking the values in Table 1 to define surface
roughness, we have determined changes in the oil film
thickness caused by the presence/absence ofroughness. Fig. 5 plots the resultant change of the oilfilm thickness.
Using the same conditions, the samples including
factors for surface roughness have exhibited
somewhat larger minimum oil film thickness.
In the roller large end-flange contact mode, the cone
flange has higher surface roughness and surface
velocity. As a result, it seems that the additional oil flowcaused by the shifting of the surface roughness of therib is greater than the inward oil flow restricted by thesurface roughness of the roller large end face. Also,
the amount of oil flowing into the contact area is higher,
leading to a thicker oil film.

5. Optimal end face R ratio resulting
from oil film forming capability
So far, proposed factors triggering seizure ofcontacting objects include critical oil film thickness,
temperature and frictional loss. Note that regardless of
the underlying cause, metal-to-metal contact must be
avoided to prevent seizure. Therefore, a maximum
possible oil film is preferred. In order to maximize theoil film thickness in a bearing, we have attempted to
optimize the roller end face R ratio. Because theoptimal roller end face R ratio appears to be governedby bearing operating conditions, we have calculated
the oil film thickness using velocity, viscosity and load
as parameters.
Fig. 6 includes examples of plotting the relationshipbetween roller large end face R ratio and oil film
thickness, with several sets of operating parameters.
These charts show the following trends:(1) Regardless of the combination of operating
parameters, there is a particular R ratio that leads
to a maximum oil film thickness. However, the oilfilm thickness can suddenly decrease when the R
ratio is increased above the optimum value (though
R ratios smaller than the optimum value do not leadto as drastic a decrease).
(2) The R ratio that leads to a minimal oil film thickness
appears to be least affected by rotating speed andviscosity (except for cases with a high viscosity
lubricating oil).
Now, let us discuss the relationships we havelearned so far concerning velocity, viscosity andoptimal R ratio with our tapered roller bearings.

Center oil film thickness
µm

1
0.8
0.6
0.4

Smooth
0.2

Rough
0
0

500

1000

1500

2000

Rotating speed min-1(a) Central oil film thickness
Minimum oil film thickness
µm

0.5
0.4
0.3

5.1 Effects of velocity
As shown in Fig. 6 (a), at a rotational speed of 500
min-1, the minimum oil film thickness is largest when the
R ratio is 93%; with a higher rotating speed, the optimal
R ratio is somewhat smaller, standing at 88% at 4,000
min-1. However, at the lower rotational speed range
where the oil film thickness is smaller, the variation inminimum oil film thickness near the optimal R ratio issmaller. Therefore, we think it is not necessary toseriously consider the effects of rotating speed for
optimal R ratio at low rotational speeds.

0.2

Smooth
0.1

Rough
0
0

500

1000

1500

2000

Rotating speed min-1(b) Minimum oil film thickness
Bearing: 30306D
Rib load: 200 N
Kinematic viscosity of lubricating oil: 32.2 mm2/s

Fig. 5 Effect of surface roughness on oil film thickness

5.2 Effects of viscosity
In Fig. 6 (b), the minimum oil film thickness is largest
when the R ratio is 78% and the kinematic viscosity is
335 mm2/s. Because the magnitude of the oil film
thickness is large in this case, the viscosity of the
lubricating oil is not an important factor when pertaining
to oil film formation and R ratio. On the other hand, atlower viscosities where the oil film thickness is small, the-102-

Minimum oil film thicknessµm

Optimized Radius of Roller Large End Face in Tapered Roller Bearings

to design the R ratio smaller than the optimal value since
the oil film thickness decreases dramatically when the R
ratio exceeds the optimal value, but much less so when
the R ratio is less than the optimum value.

0.64000 min-1

0.53000 min-1

0.4

2000 min-1

0.3

1500 min-1

0.2

5.4 Experimental verification

1000 min-1
500 min-1

0.1
0
70

80

90

We produced tapered roller bearing samples withvarying roller end face R ratios—97%, 91.7% and 80%.
We analyzed the temperature rise of the outer ring withincreasing outer ring rotational speeds. Fig. 7 shows aplot of the measured bearing temperatures. Typically,flange faces are super-finished. However, the flange
faces in these samples were ground so that the effects
of lubrication would be more apparent. Excessive heatbuildup occurred in the samples with 97% R ratios
running at 2,000 min-1 and 91.7% R ratios running at
3,000 min-1. It was determined that these samples weregenerating an excessive amount of heat, too high forrecommended operation. In contrast, samples with 80%
R ratios proved to be able to run at 5,000 min-1 without
excessive heat generation. In the previous sections, wedemonstrated through analysis that oil film thickness is
optimized by selecting an R ratio of 85% or smaller.
Through experimental verification, we proved theappropriateness of our analytical results.

100

R ratio of roller large end face %2

335 mm2/s
117 mm2/s

1.5

32 mm2/s

1

11 mm2/s
0.5
05.5 mm2/s
70

80

90

100

R ratio of roller large end face %(b) Effect of oil kinematic viscosity
Bearing speed: 2,000 min-1
Rib load: 200 N
0.5
20N

0.4

100N
0.3

200N

0.2

350N

0.1

500N
160

0

70

80

90

Bearing temperature ˚C

Minimum oil film thicknessµm

Minimum oil film thicknessµm(a) Effect of rotating speed
Rib load: 200 N
Kinematic viscosity: 32 mm2/s

100

R ratio of roller large end face %(c) Effect of rib load
Bearing speed: 2,000 min-1
Kinematic viscosity: 32 mm2/s

Fig. 6 Relationship between R ratio of roller large
end face and minimum oil film thickness

140
120
100
80
60

R ratio 97%

40

R ratio 91.7%

20

R ratio 80%

0effect of the viscosity of the lubricating oil on the optimal
R ratio is small.

0

2000

4000

6000

Rotating speed min-1
Bearing: 30306D
Radial load: 19.6 kN
Axial load: 6.9 kN
Lubricating oil viscosity grade: ISO VG 56

5.3 Effects of load
From Fig. 6 (c), it is apparent that increasing the loadcauses the optimal R ratio to be smaller. Furthermore,
under higher loads, the minimum oil film thickness
resulting from an R ratio greater than optimal will besmaller. Therefore, when the oil film thickness is smaller
and the rib load is higher, the R ratio needs to besmaller.
In summary, based on our results of the optimal R
ratio and oil film formation, it is not necessary to give
particular considerations to the effects of velocity and/or
viscosity, assuming the operating conditions in ourstudy. It is reasonable to set the R ratio to approximately
85% for a high load situation and to approximately 95%
for a low load situation. At the same time, it is desirably

Fig. 7 Results of measured bearing temperature: Effects
of R ratio of the roller large end face-103-

NTN TECHNICAL REVIEW No.77（2009）

References

6. Conclusion

1) T. Yamada, Torque Control and Operational Improvement ofTapered Roller Bearings, SAE Technical Paper Series,(1986), 860726.
2) Y. Okamoto and T. Tsujimoto: ECO-Top Tapered Roller
Bearings, NTN Technical Review No. 68 (2000) 34-38.
3) X. Jiang et al., Thermal Non-Newtonian EHL Analysis of RibRoller End Contact in Tapered Roller Bearings, Transactionsof the ASME, Journal of Tribology, 117 (1995), 646-654.
4) N. Patir and H.S. Cheng, An Average Flow Model for
Determining Effects of Three-Dimensional Roughness on
Partial Hydrodynamic Lubrication, Transactions of the ASME,
Journal of Lubrication Technology, 100 (1978), 12-17.
5) H. Nishida et. al., Analysis of mixed lubrications between the
Large End Faces of Tapered Roller Bearings and Ribs,
Proceedings of the Fall 2001 Tribology Conference in
Utsunomiya, (2001), 277-278. (Japanese)
6) K. Harada and T. Sakaguchi, Rolling Element Skew inDynamic Analysis for Tapered roller Bearings, Proceedings of
The Third Asia International Conference on Tribology, (2006),
647-548.
7) L. Houpert, New Results of Traction Force Calculations in
Elastohydrodynamic Contacts, Trans. ASME, J. Tribol., 107-2(1985), 241-248.
8) C.S. Wu, E.E. Klaus and J.L. Duda, Development of a Method
for the Prediction of Pressure-Viscosity Coefficients ofLubricating Oils Based on Free-Volume Theory, Trans. ASME,
J. Tribol., 111-1 (1989), 121-128.
9) ASTM, Annual Book of ASTM Standards, Section 5, Vol.05.01
Petroleum Products, Lubricants, and Fossil Fuels, (1987),
197.
10) J.A. Greenwood and J.H. Tripp, The Contact of Two
Nominally Flat Rough Surfaces, Proceedings of IMechE, 185(1970-71), 625-633.
11) N. Patir and H.S. Cheng, Application of Average Flow Modelto Lubrication Between Rough Sliding Surfaces, Trans.
ASME, J. Lub. Tech., 101 (1979), 220-230.
12) N. Patir and H.S. Cheng, Effect of Surface Roughness
Orientation on the Central Film Thickness in E.H.D. Contacts,
Proc. of 5TH Leeds-Lyon Symp. on Tribol., (1978), 15-21.
13) N. Ohno et al.: Effect of Bulk Modulus of Solidified Oils underHigh Pressure on Tractional Behavior, Journal of JapaneseSociety of Tribologists, Vol. 38 (1993), 927-934 (Japanese)
14) R.T. Lee and B.J. Hamrock, A Circular Non-Newtonian Fluid
Model: Part I - Used in Elasto-hydrodynamic Lubrication,
Transactions of the ASME, Journal of Tribology, 112 (1990),
486-496.

Studying roller large end-flange face contact on
tapered roller bearings, we performed isothermal EHL
analysis while considering roller skewing. We
discovered the following characteristics about
lubrication at the roller large end-flange face:• Assuming isotropic surface roughness, the magnitudeof oil film thickness will be greater when surface
roughness is taken into account.
• If an EHL condition is assumed, the calculated valueof the roller skewing angle is smaller than thatobtained without considering deformation of thecontacting elements; it more closely matches theactual measured value.
In addition, we discovered the following design
guidelines for end face R ratios to maximize thelubricant oil film thickness:• The optimal end face R ratio that helps maximize thelubricating oil film thickness can vary depending on
the rotational speed, lubricating oil viscosity and loadconditions. Basically, it should be approximately 85%
for high load situation. However, once the end face R
ratio exceeds the optimal value, the oil film thickness
suddenly decreases. Therefore, the design end face
R ratio should be smaller than the optimal value.
• Tapered roller bearings can experience operational
problems when the oil film thickness is very low. If the
low oil film thickness is due to low speed or low oil
viscosity, then the optimal end face R ratio has little
affect.
From these studies it is desirable to design the roller
with an end face R ratio of approximately 85% at most.
This will allow the tapered roller bearing to operateproperly under heavy loads.
In preparing this technical paper, the authors have revised
Transactions of the Japan Society of Mechanical Engineers(Trans. Jpn. Soc. Mech. Eng.), Book C, Vol. 75 (2009), pp. 23192326.

Photo of authors

Hiroki FUJIWARA

Takashi TSUJIMOTO

Kazut0 YAMAUCHI

Elemental Technological
R&D Center

Automotive Sales Headquarters
Automotive Engineering Dept.

Graduate School of Engineering
Osaka Univercity-104-

-105-

NTN TECHNICAL REVIEW No.77（2009）[ Discussion ]Advances in and the Future of Analysis Techniques
for Constant Velocity Joints

Participants
Kei Kimata

Former Director

Masakazu Hirata
Yoshinori Terasaka
Hisaaki Kura
Shin Tomogami
Kisao Yamazaki
Teruaki Fujio
Masashi Funahashi
Kazuhiko Yoshida(Intellectual Property Strategy Department)(C.V.Joint Engineering Dept.)(C.V.Joint Engineering Dept.)(C.V.Joint Engineering Dept.)(C.V.Joint Engineering Dept.)(C.V.Joint Engineering Dept.)(C.V.Joint Engineering Dept.)(New Product Development R&D Center)

Kei Kimata Former Director

Hirata: Former Director Kimata received a doctoral degree in engineering from
Nagoya University in December 2008 with a thesis entitled “Research related toanalysis methods for ball-type constant-velocity joints.” Before Dr. Kimata retired
from our company in 1998, he had, for example, been the chief of our bearing
technology research laboratory and the president of NTN Engineering Plastics
Corporation. He also served as a corporate director. Since retiring, he hascontinued his research, which culminated with his dissertation at the age of 72.
Today, Dr. Kimata, who is one of our great predecessors, joins us in a discussion
about the “Advances in and the future of analysis techniques for constant velocity
joints” with some of our young engineers.

Tomogami: The three young engineers here today
helped Dr. Kimata with the numerical analysis usedin the completion of his thesis. As they advanced thisnumerical analysis, they were able to study his
theories, so this was a valuable experience for them.
We are very grateful for this.
Currently, we are also working on applying thisanalysis to the development of constant-velocity
joints (hereafter, “CVJ”) in order to accelerate
development. MSC. Adams* (hereafter, “Adams”),
which is a commercially-available general-purpose
software application for dynamic mechanism
analysis, is being used as one means for analysis. I
would like to ask Dr. Kimata for his opinions
regarding the differences between his own “ball-type
constant-velocity joint analysis method” and Adams.

Masakazu Hirata

Differences between the “ball-type constantvelocity joints analysis method” and Adams
Kimata: The main contents of my thesis are related tothe static analysis and dynamic analysis of ball-type
CVJs. As equations of motion for dynamic analysis, I
used Euler’s equations of motion. Adams is generalpurpose software for the dynamic analysis ofmechanisms, and it is supposed to use Lagrange’s
equations of motion, so I think that theirfundamentals for dynamic analysis are the same.
I believe that in order to correctly interpret datafrom numerical analysis, it is necessary to haveknowledge about analytical theory. Even when using
Adams, I think that analytical theory related to CVJs
is useful when interpreting the results.
Static analysis is very useful in understanding thefundamental characteristics of CVJ. I think that it isalso useful in understanding the results of dynamic
analysis.

(*Registered trademark of MSC. Software)-106-

Advances in and the Future of Analysis Techniques for Constant Velocity Joints

From the left, Yoshida, Tomogami, Terasaka, Fujio, Funahashi, Yamazaki and Kura

Funahashi: I think that analysis using Adams is valuable
during the initial investigation of new structures.
However, the fact is that there are many cases where
numerical analysis is difficult when plastic
deformation and destruction occur. The pursuit ofboth mechanism analysis and finite element analysis
is necessary. Particularly in miniaturization, the ratioof plastic deformation volume increases making
analysis complex. I want to apply the power of youth
to resolving this.

About the application of analysis technology
Tomogami: In other words, regarding the results thatcome from analysis using Adams, it is important tohave the sense to always verify whether or not they
are valid in consideration of analytical theory. In ourdevelopment—particularly in the development ofparts for automobiles—I believe the main approachhas been a method that involves the creation of
prototypes, their evaluation and the consideration of
the results, or, in other words, trial and error. I
wonder, however, how our young colleagues feel
about this way of proceeding.

Terasaka: That is a reassuring statement (laughs).

Improving analysis technologies for the future
Yamazaki: Through analysis it is possible to evaluate theperformance of a product without creating a
prototype, so I think this has the effect of reducing
development time and cutting costs. On the other
hand, since there is uncertainty as to whether the
results are accurate and whether phenomena havebeen suitably simulated, I think it is necessary toproceed by using both analysis and experimentation
skillfully.

Kimata: For the improvement of analysis technologies,
efforts in elastic-plastic analysis are necessary. Are
efforts in the engineering division advancing?
Fujio: I think that, for CVJ development in particular,
analysis must be undertaken related to the failure of
CVJs caused by plastic deformation where inner andouter rims contact balls. I want to accelerate
development by applying dynamic finite element
analysis in the analysis of these parts.

Fujio: In the process of development, we conduct
analysis, of course. In particular, when we aredesigning a new CVJ, for example, to investigate
how the internal contact load differs in comparison
with an existing product, we analyze using Adams.
Analysis is convenient because it allows conditions to
be changed easily. Adams is also useful because it
allows the visualization of the internal force vectors
from calculation results.
I believe that even though development should be
advanced with analysis in the lead, at present we stillcannot say that we are able to accurately simulate
every phenomenon, so in the future I want toinvestigate new methods.

Hirata: At the Elemental Technology Research &Development Center, as one fundamental
technology, we are also striving to develop coupledanalysis that combines the dynamic analysis ofmechanisms comprised of multiple parts anddeformation analysis of those comprising parts.
Kimata: Being able to process mechanism analysis
based on dynamics and elastic-plastic finite element
analysis in one program would be good. However, at
this point realizing this is going to be very difficult.
High-speed computers with great processing
capacity are necessary for dynamic analysis.

-107-

NTN TECHNICAL REVIEW No.77（2009）

Seeking the strength conditions with dynamic
analysis and using these as input conditions to
conduct elastic-plastic analyses with a finite elements
approach and then applying this procedure
repeatedly might be the only way.

The future of constant-velocity joints
Tomogami: Now I would like to change the topic anddiscuss future technologies for constant-velocity
joints. As you all know, environmental considerations
have become an extremely important theme even forautomobiles. As parts for the driving force ofautomobiles, CVJs are said to be mature products. In
order to meet the needs of customers, however, weare still working on issues that include making themlighter and more compact and further increasing theirtorque transfer performance.

Funahashi: I also feel this way. I think that at present
conducting analyses at each small step is probably
the most suitable.
Yoshida: In CVJ testing, there is a semi-torsional test inwhich it is twisted and fractured in low-speed fixedrevolution conditions. In order to clarify thisdestruction mechanism, we are working on dynamic
elastic-plastic finite element analysis. This model is
at a level that allows the semi-torsional fracture
mechanism to be simulated qualitatively. Currently
we are striving to improve this model to allow
quantitative simulation.

Terasaka: Make them lighter, make them smaller, andmake them thinner. In every case, we must consider
rigidity and deformation, but I think that it is difficult toinvestigate thoroughly enough to be able to identify
the limits. Do you have any suggestions for how toapproach this?

Kimata: I hope that you will continue your efforts for CVJ
elastic-plastic analysis as a manufacturer thatspecializes in CVJs.

Kimata: I think that in design it is important that you focus
on reducing the concentration of stress. I think theapproach of increasing the number of balls, which
NTN is advancing, is also one solution (E Series
CVJs).
By making the balls smaller in size and bearing theforce with numerous balls, the stress at the point ofload can be decreased. By reducing theconcentration of stress, the possibility of usingmaterials other than steel also arises. Incidentally,
have you been able to utilize resin materials inconstant-velocity joints yet?

How to advance efficient development
Tomogami: If we want to further increase the speed ofdevelopment, I believe that we must apply the latest
technologies for analysis. Could our young engineers
who are advancing our development work receive
some advice from you, Dr. Kimata?
Kura: We also discussed this earlier, but wheninterpreting data, I wonder if the way to advance tothe next step will differ depending on the approach tothe interpretation of data from dynamic analysis andexperimentation.

Yoshida: In propeller shaft assemblies, by using CFRP
shafts, weight has been reduced and the use of two
joints has been made possible where three joints had
been used before.

Kimata: Well, accurately evaluating the data isnecessary. In addition, I think that grasping themechanisms that produce that data is important. A
graph of the results of dynamic analysis iscomplicated, but the results of static analysis aretransformed by the impact of the friction generated
by rotational movement. Looking at the data fromthat analysis and the dynamic analysis together cansometimes make it easier to understand. By
considering and investigating how the friction
worked, I have had the experience of being able toeasily interpret a dynamic analysis graph that had
appeared complicated at first glance.
In analysis, it is easier to understand if we start by
thinking about a model that has been simplified asmuch as possible. In some senses, I think that inanalysis, while considering the necessary conditions,the crucial point is how much it can be simplified.

Yamazaki: In the case of drive shafts, since the axial
diameter is fine and the input torque is greatcompared to propeller shafts, contact surfacepressure and shear stress are higher. At present, wehave not yet utilized resin materials in high-strengthparts such as drive shafts, but we are investigating
the possibility of application.
Hirata: Among non-ferrous materials, ceramic also has ahigh modulus of elasticity and high strength, so weare considering its application in strong parts.
Tomogami: It is a light and appealing material, but
pliability, processing characteristics and cost areissues at this time.
Kimata: For these reasons, I think that the age of steel
continues…

-108-

Advances in and the Future of Analysis Techniques for Constant Velocity Joints

Hirata: Considering the long-term, I believe that there
probably is a need to work with new materials
besides steel, and the current state is that we areadvancing efforts from the standpoint of elemental
technologies. Looking to the future, I am convincedthat we must work with these new materials.

Yamazaki: Recently, HL treatment of balls for CVJs that
we have developed is an example of this. By
combining HL treatment of balls for CVJs with greasethat has been matched to this, we are able toachieve a great reduction in torque loss.

Encouragement for young engineers
Kura: Have you ever investigated sliding type constantvelocity joints, for example, which are completely
different from ball-type CVJs?

Terasaka: We have enjoyed discussing a variety of
topics, but we have come to the end of our time.
During your many years of research anddevelopment work, including analysis related toconstant-velocity joints, I expect that you have also
run into a few walls. One of the things you said wasto start by simplifying things to think about them. At
times when you have a problem and think that things
are difficult, are there any other kinds of things thatform the basis for your thinking?

Kimata: I have investigated TJ-type CVJs, but it did not
go well in the end. With two-way sliding, I think that itis probably difficult to achieve an oil film. Friction
increases obviously. For bearing large loads, with the
exception of parts like cages that must be madesliding, rolling or rolling-sliding is probably better. The
reason for this is that the lubrication characteristics
are better.

Kimata: I believe that it is returning to the fundamentals
to think about the problem. By practicing returning to
the fundamentals, I believe that you will gain avariety of cognitive abilities.

Hirata: In the application of sliding for CVJs, I haveinvestigated surface modifications and greases, but,
as you say, with rolling-sliding, the grease isreplenished well, while with sliding only, the grease isexpelled, reducing performance in my experience.

Terasaka: For example, when test results disagree with atheory that you have devised, what is a good way toproceed?

Kura: So we should think about new joints as we use
rolling-sliding skillfully.

Kimata: You should probably check and confirm
everything thoroughly. Was there a mistake in thetest procedures? You have to return to thefundamentals and reconsider even when conducting
analysis. The greatest danger is becoming
overconfident and believing that there are no
mistakes in what you have done. I have also had
many failures, but the important thing has always
been returning to the basics to think and reviewing toconfirm that there are no contradictions in the theory.

Kimata: It would be good if there was a sliding material
with low friction and high load capacity, but…

To further increase performance
Tomogami: Please give us some advice about how tofurther improve the performance of CVJs.
Kimata: It might be obvious, but I think it is minimizing
the coefficient of friction of the contact surface asmuch as possible. I think that inside CVJs, thecoefficient of friction is not fixed, but rather depends
on the relative movement (sliding or rolling-sliding)conditions of the contact parts. They change
depending on the conditions of the contact surfaces
and the grease.
For this reason, I think that surface modification isa good method.

Hirata: Today you have given us the opportunity toparticipate in this valuable and lengthy discussion.
Thank you very much.
Everyone: Thank you very much.

-109-

NTN TECHNICAL REVIEW No. 77（2009）

Presentation of award-winning articles“2009 ‘CHO’ MONOZUKURI Innovative Components Awards”
Encouragement Award

High Capacity Tapered Roller Bearing

Takashi UENO

Clearance between outer ring and cage

1. Introduction
NTN “High Capacity Tapered Roller Bearing” won an
Encouragement Award in “CHO MONOZUKURI Innovative
Parts and Components Award 2009” sponsored by The
Conference for the Promotion of MONOZUKURI and
Nikkan Kogyo Shimbun Ltd., Japan’s leading business andindustry newspaper publisher (and backed up by Ministryof Economy, Trade and Industry in Japan, and The Japan
Chamber of Commerce and Industry).
With bearing size unchanged, this novel high capacity
tapered roller bearing design boasts a 10% increase at
maximum basic dynamic load rating (37% increase at
maximum calculated bearing life), 15% increase at
maximum basic static load rating (15% increase in safety
factor) and 10% increase at maximum bearing rigidity(10% reduction at maximum elastic displacement). This
novel tapered roller bearing also features lower contactpressure and has exhibited longer life even in a difficult
lubricating environment where the bearing is lubricatedwith a low viscosity lubricating oil 1).

Cage bar widthStandard tapered
roller bearing
Clearance
between rollers
Smaller clearance between
outer ring and cage

Cage bar width(Same dimension)

Extreme high load
capacity bearing
Smaller clearance
between rollers

Fig. 1 Structure of high capacity tapered roller bearing[Left: Standard tapered roller bearing Right: High capacity tapered roller bearing]

2. Structure of NTN high capacity
tapered roller bearing

Fig. 2 Figure of high capacity tapered roller bearing

The NTN high capacity tapered roller bearing featuresa unique structure which include: a smaller clearance
between the cage and outer ring combined with a larger
pitch circle diameter with the cage, helps the cage to besituated nearer to the outer ring. Therefore, the roller-toroller clearance has been reduced to maximize thenumber of rollers (a number same as that on a fullcomplement roller bearing of a same size) while the cagebar width dimension remains same as that on the NTN
standard tapered roller bearing (see Figs. 1 and 2).

bearings will feature much reduced size, weight, andrunning torque. Thus, NTN is going to more positively
market this line of bearings as products that willcontribute to better fuel economy on automobiles.

References
1) T. Tsujimoto and J. Mochizuki: High Capacity Tapered
Roller Bearings, NTN Technical Review No. 73 (2005)
20-29

3. Conclusion
Photo of author

Boasting longer life and higher rigidity, the NTN highcapacity tapered roller bearings will help solve challenges
occurring from needs for much improved fuel economy
with automobiles. By additionally adopting NTN’s
propriety FA heat treatment technique to help designunique tapered roller bearings of longer life and lower
torque, the new NTN high capacity tapered roller

Takashi UENO
Automotive Engineering Dept.
Automotive Sales Headquarters-110-

NTN TECHNICAL REVIEW No. 77（2009）

Presentation of award-winning articles“2008 ‘CHO’ MONOZUKURI Innovative Components Awards”
Automotive Component Award

Constant Velocity Steering Joint (CSJ)
Development
Kenta YAMAZAKI

1. Introduction

3. Features of constant velocity
steering joint CSJ

NTN “Constant Velocity Steering Joint (CSJ)” won an
Automotive Component Award in “CHO MONOZUKURI
Innovative Parts and Components Award 2008” sponsoredby The Conference for the Promotion of MONOZUKURI
and Nikkan Kogyo Shimbun Ltd., Japan’s leading businessand industry newspaper publisher (and backed up by
Ministry of Economy, Trade and Industry in Japan, and
The Japan Chamber of Commerce and Industry).
The CSJ satisfies otherwise conflicting requirements
for “smooth rotation” and “reduced play on steering
wheel” through provision of a special preloadingmechanism within the joint to eliminate backlash on the
joint and optimization of internal design.
Compared with the double Cardan joint, which is aconventional constant velocity steering joint (hereinafterreferred to as “D-CJ”), NTN CSJ are about half the weightand volume which can run at a constant speed in theoperating range (0-48 C˚) without developing backlash.
Thus, the NTN CJS helps car steering system designers
flexibly design the steering system layout.

Results of comparison of performance of the NTN CSJ
with conventional constant velocity steering joint (D-CJ)
are summarized below 2):
1) Result of comparison in terms of rotational backlash
As shown in Fig. 2, compared with the D-CJ, the CSJ
boast smaller hysteresis and higher rigidity.
2) Result of comparison in terms of rotational torqueFig. 3 graphically plots the relation between rotational
angle and rotational torque. There is no significant
variation in the rotational torque of CSJ. In other words,
the NTN CSJ has characteristics needed for an
automotive steering joint.
++

Rotational torque

Torque loading

CSJ
D-CJ

Low torsional rigidity,
and high hysteresis

0
Higher torsional
rigidity0-

2. Structure of constant velocity
steering joint CSJ

CSJ
D-CJ

0

60

120

180

240

300

360

Rotational angle-

0+

Torsional angle

Fig. 2 Rotational bach lash

The basic structure of CSJ 1) comprises as a basis, theBJ, (ball type constant velocity joint) that is frequently
used for driveshaft a plunger, and a spherical plate
incorporated into the BJ (see Fig. 1). The spring force ofthe plunger causes the inner ring to shift rightward in thisdiagram; thereby the balls always remain in contact withthe surfaces of ball grooves on the inner and outer rings;
as a result, clearances between related parts are
eliminated in order to inhibit rotational backlash.

Fig. 3 Rotational torque4. Conclusion
Being the world’s first ball type constant velocity steering
joint product, the NTN CSJ boasts not only great
functionality but also significant reduction in both weightand size—approximately 50% reduction compared with the
NTN’s conventional D-CJ. This novel constant velocity
steering joint will positively contribute to mitigation ofenvironmental impacts possibly caused by automobiles.

References

Outer ring

1) K. Yamazaki: Constant Velocity Steering Joint (CSJ),NTN Technical Review No. 73 (2005) 84-87

Spherical plate
Cage

Ball

Photo of author
Inner ring
Axial displacement
Plunger

Kenta YAMAZAKI
C.V. Joint Engineering Dept.
Automotive Sales Headquarters

Fig. 1 Structure to reduce rotational play-111-

NTN TECHNICAL REVIEW No. 77（2009）

Presentation of award-winning articles“2008 Resource Recycling Technology and Systems”
Encouragement Award

Development of a Briquetting Machine and theConstruction of a Recycling System
for Steelmaking Dust
Shouzo GOTO*

Ikuo YAMADA**

Katsutoshi MURAMATSU***

mixture is pelletized. The resultant pellets are formed intocylindrical briquettes by pressure, without using glue, andthen the resultant briquettes are loaded into an electric
In Japan, approximately 500,000 tons of steelmaking
furnace together with steel scraps.
dust annually occurs in steelmaking electric furnace
Because the carbon content included in the briquettes
plants. This type of “waste” has been traditionallyservesas a fuel/reducing agent, NTN’s new recycling
disposed of by landfill, dezincification or reuse.
systemboasts higher degree of melting efficiency. In
Now, disposal by landfill poses problems—increasingly
addition,
the density of steel content in the briquettes
limited availability of landfill sites and mounting costs.
obtainedfrom the NTN’s novel steelmaking dust recycling
Incidentally, costs for dezincification are high, including
system is high compared with the previous methods.
expenses needed for transportation. Therefore, it isthus, more iron content will be melted in the molten bathnecessary to reduce the amounts of steelmaking dust to
and recovered as an iron. Note that with previous
be disposed of.
steelmaking dust disposal methods, steelmaking dust
Various recycling techniques for steelmaking dust have
either unmodified or pelletized was fed into an electricbeen proposed. However, to be able to improve melting
steelmaking furnace.
efficiency and cost-effectiveness, NTN has chosen
This new development has already resulted in
DAIWA STEEL CORPORATION as a partner.
improved
economy, total elimination in amount ofConsequently, the team has successfully developed adisposal by landfill and improved electricity use in theunique steelmaking dust recycling method that realizes
NTN Group. The resultant recycling ratio of steelmaking
both mitigation in environmental impacts and reduction indust (increase in recovered iron material) has helped
costs.
decrease the amount of steelmaking dust being
In the newly developed recycling system, which is
subjected to dezincification. Thereby, NTN has been
schematically illustrated in Fig. 1 below, carbon andcontributing
to mitigation in environmental impacts
water are added to steelmaking dust, and then the
resulting from its manufacturing
activities.
Recycling of steel products
While environmental conservation
Scrap
poses challenges to manufacturers,
Recycling of steelmaking dust
this novel steelmaking dust
occurring from electric furnace
Dust Exhaust gas
briquetting system has been
Briquette
positively contributing to realization(1) Electric(φ150×120H)(2) Filter
furnaceof the recycling-oriented society.
Steel products

Overview

Steelmaking dust

Photo of author (Representative)
Carbon(3) Pelletizer
Water

Iron component

Pellets(5) Dezincification plant
Metal zinc

Shouzo GOTOH(4) NTN steelmaking dust briquetting machine

Fig. 1 Briquetting Machine and Recycling System for Steelmaking Dust
*Fomer Production Engineering R&D Center**Production Engineering R&D Center-112-

Fomer Production Engineering.
R&D Center***Elemental Technological R&D Center

-113-

NTN TECHNICAL REVIEW No.77（2009）[ New Products Information ]Intelligent In-wheel Unit
Integration of electric motor, brake and sensor as well as size reduction
in in-wheel unit contribute to optimal energy regeneration and vehicle
stability control, and improved driving performance.

Features

Applications(1) Improvement in both fuel economy anddriving safety(2) Much improved freedom in designing vehicle
itself and automotive components(3) Car maneuverability can be tailored according
to users’ needs.

¡Electric vehicles, fuel cell vehicles

Construction
Electromechanical brake

In-wheel motor

Hub bearing
Load sensor
Sensor information
Steering angle
Accelerator opening

In-wheel motor
Electromechanicalbrake
Load sensor

Wheel speed (motor speed)
Driving power (motor current)
Braking power
Ground load

Motor control
Brake control

Vehiclecontroller

Steering angle control
Suspension control

Cornering force-114-New Products Information

Wide-Range High-Resolution Small Sensor
Integrated Hub Bearing
Two sets of control signals are available to contribute to improvementin precision and reliability in vehicle safety control.

Features

Construction(1) The built-in sensor covers the entire
speed range from extremely low to highspeed regions: will contribute to
mitigation of load in signal processing.
(2) Running speed detection at higher
resolution (40 times as accuratecompared with a previous detection
system): now, the motion of wheel isdetected to accuracy in steps of mm.
(3) Now, judgment on whether the wheel isrunning forward or reverse is possible:
also, fall motion in hill launch mode ispossible.
(4) Use of a compact sensor contributes tosize reduction of hub bearing product.

Magnetic encoder

High-resolution sensor

High-resolution signal (40 times as high comparedwith conventional signal) and ABS signal
Magnetic poles onmagnetic encoder
ABS signal for highspeed travel

Applications

High-resolution signal
for low-speed travel

Wheel hub bearings for passenger cars
¡Car attitude control¡Hill hold control-115-

NTN TECHNICAL REVIEW No.77（2009）

High Efficiency Fixed TypeConstant Velocity Joint (EUJ-S)
Positively assists in fuel efficiency of cars thanks to 30% reduction in torque transmission loss!
Compact, light-weight constant velocity joint products capableof higher operating angle (50 degrees).

Features (comparison with conventional products)

Construction- Advantages over conventional
products (EUJ) -(1) Torque transmission loss: Reduced byapprox. 30%(2) Strength/Durability: Same level(3) Max. working angle: Same level (50˚)¡Design of internal structure has been
optimized to reduce friction loss that
results from contact between internal
components in joint.
¡Use of newly developed low-µ grease andadoption of surface modification
technique for metal components help
decrease friction loss.

Applications¡Automotive drive shaft

Sliding type constant velocity joint

Fixed Type Constant Velocity Joint(EUJ-S)

Outer ring

Tire

-116-

Cage

Ball

Inner ringNew Products Information

High Efficiency and Low Heat Generation Ten Ball
Constant Velocity Joint (HELJ) for Propeller Shafts
Realization of reduced torque loss, limited heat generation and light weight!
Contributes to higher functionality and improved fuel economy!

Features (comparison with conventional products)

Construction(1) High efficiency: Torque loss reduced by
50%(2) Low heat generation: Temperature rise
reduced by 50%(3) Light weight: Mass reduced by 5%- Advantages over conventional products (HLJ) ¡Optimally angled ball slots helps reduce frictional
resistance occurring on balls in axially shifting motion;consequently, heat generation on balls is mitigated.
¡ Smaller diameter balls are adopted: number of balls has
been increased from six to ten: the size and weight of
inner ring, outer ring and cage have been much
reduced.

Applications

Ball slots inclined in
opposite directions¡ Automotive drive shaft(Propeller shafts on FR and 4WD vehicles)

Inner
ring

Ball

Cage Outerring

New product (HELJ)
Number of balls: 10

Conventional
product (HLJ)
Number of balls: 6

Propeller shafts

Comparison using
cross-sectional view

-117-

NTN TECHNICAL REVIEW No.77（2009）

Long Life Ball Screw for Actuators
Longer life in spite of compact, light-weight design. Contributes to realization ofelectromechanical design that contributes to better fuel efficiency.

New product

Conventional productFeatures (comparison with conventional products)

Construction(1) Life: Improved by 6 times(compared to the same size product)(2) Size: Down sized axially by 7%(compared to products with similar life)(3) Mass: Reduced by 30%(compared to products with similar life)¡Balls whose size is greater than that of lead
Maximized ball size helps increase load
capacity of ball-screw.

Applications¡Automotive continuous variable valve
mechanism and electromechanical actuatornr sectio

ActuatoBall screw[New product][Conventional product]

Lead
Lead < ball size

Lead
Lead > ball size

Locker arm
Control shaft
Output cam
Link
Valve lifter

Link

Driveshaft
Valve

-118-

New Products Information

Ultra Low Torque Back-up Roll Unit
for Tension Levelers
Much reduced torque contributes to improvement in productivity
and alleviation in environmental impact!

Features (comparison with conventional products)

Construction(1) Rotational torque: Reduced by 40%(2) Temperature rise: Reduced by 20%

Low torque needle roller bearing

Applications¡Steel sheet production equipment, Tension
levelers

Novel seal structure (spacer and O-ring)

Back-up roll unit

Steel sheet

Intermediate roll unit
Work roll unit
Wind up-119-

NTN TECHNICAL REVIEW No.77（2009）

Two Way Sorting Feeder
Parts feeding mechanism derived from new concept contributes
to improvement in productivity!

Features

Construction(1) Feeding in two opposing directions
A well conceived mounting system for apair of leaf springs can realize parts
feeding in two opposing directions.
(2) Increasing speed/Decreasing speed
Speed can be varied for the attachment
section that aligns and feeds parts.
(3) Transfer of vibration to the sloped chute
Congestion of parts within the chute isprevented.

Parts feedingmechanism

Forward direction: Feed direction with bawl feeder
Reverse direction: Feed direction with parts feeding mechanism

Applications¡Aligning and feeding of automotive parts,
parts for electric equipment, and parts for
medical equipment, etc.
Increasing speed/
Decreasing speed-120-

Sloped chuteNew Products Information

New-Type One-Way Clutch for Office Equipment(NCT)
This one-way clutch can be readily built into a resin-built component, while
maintaining highly reliable clutching function!

Features

Construction(1) Can be integrated with a resin-built
component.
(Detents are situated on the outercircumference of outer ring.)(2) Improved handling ease
• Cage cover is thermally caulked to theouter ring to form a single component(non-separable type).
• Orientation for assembly can be
identified by color-coding (lockdirection is clearly indicated on the
product).
• Lock direction can be altered by simply
reversing the orientation for installingthe clutch.
(3) Higher reliability and durability• Equivalent with the unit type (NCZ)
one-way clutch(4) Capability for bearing radial load
• The cage bore surface on the clutch
bears radial load.

φ12Thermal caulking(5 pos.)

Detent6φ

7Outer ring flange

Outer ring

Cage with built-in cover

Applications¡Paper feeding section in printers andphotocopiers
Paper output tray

Applicable areas

Paper feeding tray

-121-