Prospects

NTNʼs Activities for the Electric Vehicle andElectrification of Automobiles

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

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

Automobile production(Millions of units)

1. Introduction

100

ICE

80

FCV

60

HEV
BEV

40
20
0

2017 2019 2021 2023 2025 2027 2029 2031 2033

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

■ Providing various services such as

in-car entertainment

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

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

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

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NTN TECHNICAL REVIEW No.89

performance■ Spread of EVs/HEVs/PHEVs

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

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

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

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

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

Technology trends
Downsizing andlightweighting

Acceleration ofelectrification
andenergy saving

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

Higher efficiency

・Higher efficiency fixed constant velocity joint CFJ

Higher speeds

・High Speed Deep Groove Ball Bearing for EV/HEV

Lower viscosity
lubricating oil

・Hydrogen Embrittlement Resistant Bearings

Pursuing comfort

Drive stability

・Hub Bearing Modules with Rear Steering Function Ra-sHUBTM

Pursuing safety

Improving electronic
control technology

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

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

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

Bearing

Sun gear

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

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Ring gear

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

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

Bearing

Low-torque technology
application factor

Ⅰ

Ⅱ

Bearing
specifications,preload

Ⅲ

Ⅳ

〇

◎

Bearing interior
grease○◎←Seal coating grease

○

←

◎

←

←

←

Lip contact status

○

←

←

Number of lip
contacts○←←

Lip design
Seal

Low Friction HUB Bearings○

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

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

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

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

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

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

Fig. 6 CFJ structure and internal forces

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

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

Aluminum case

Output gear

Motor

Ball screw nut
High-load
capacity design

Conventional
designBearings

Ball size

Lead
Ball screw shaft
Shaft anti rotation sleeve

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

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

Ball screw

AMT shift unit

Variable valve
lift mechanism

Electronic
hydraulic brake
AMT：Automated Manual Transmission

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

Bus bar

PCB(printed circuit board)

Pump cover

Pump rotor

Motor rotor

Motor stator

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

Details

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

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

Voltage

12 V (to 48 V)

HydraulicpumpTrochoid pumps (vane pumps)

Control

PWM (CAN compatible)

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

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

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

Base

Actuator

Steering axis

Hub bearing

Fig. 10 Ra-sHUBTM (prototype)

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

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

２） NTN website, “Hydrogen Embrittlement ResistantBearings” developed

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

Photo of author

Ikuya TATEOKA
Deputy Corporate
General Manager,
Automotive Business
Headquarters

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NTN TECHNICAL REVIEW No.89