OUTLOOKTechnological Trends and Outlook of Automotive Bearing
K. YOKOTA

The automotive industry is said to be facing a once-in-a-century time of major change, as represented by the
key words of CASE (Connected, Autonomous, Shared, Electric). Among these, further enhancement of bearing
performances in response to expanding electric motorization and also new mechanisms and sensing technologies
for advancing autonomous driving technologies are required.
This paper introduces JTEKT’ s automotive bearing technologies responding to these needs.
Key Words: automotive bearing, trends, bearing technology, tribology

1. Introduction

Passenger car sales, mill cars

The auto industry is said to be facing a once-in-acentury time of great change represented by the keywords“Connected, Autonomous, Shared, Electric.” Automakers
and auto parts makers face the major issues of responding
to such change.
Of these keywords, “Electric” in particular is
triggering structural change, and has the biggest impact
on our bearing products. It goes without saying thatworldwide environmental regulations are pushing electricmotorization. In Europe, for example, the CO2 emission
regulation of 130 g/km will become 95 g/km in 2021.
Moreover, due to regulations regarding zero-emission cars
and new energy cars as well as sales promotion measures,
it is predicted that electric vehicles such as EV/PHV/HV
will increase to 35% of the global number of passenger
vehicle sales in 2030 (Fig. 1).

175
FCV

150
EV
100

PHV

In line with this electric motorization, the performances
required of bearings are changing. For example, compared
to conventional engine-powered vehicles, the electric
powertrains of EV/PHV/HVs must endure dramaticallyhigher rotational speed and solve the new issue of electric
pitting. Moreover, in addition to changes in required
bearing types and proportions, there is a need to further
reduce torque, as well as reduce size and weight.
Meanwhile, vehicles equipped with engines willcontinue to account for a major percentage of sales due
to factors such as the predicted rise in engine-powered
vehicles in newly-emerging countries and global
expansion of PHV/HVs. We cannot overlook initiatives
to increase reliability and reduce torque for bearings usedin these engine-powered vehicles. Moreover, we are also
engaging in product development completely different
from before in response to electric motorization in the
broad sense; i.e. sophistication of motor-based control.
This report will introduce development trends ofautomotive bearings responding to the abovementioned
electric motorization trend, and JTEKT’s bearing products
which satisfy functions and performance requirements
as well as the evaluation technologies by individual
application (Fig. 2).

HV

50
ICE
0
2015 2020

2030

2040

2050

2060

Source: IEA “EPT (Energy Technical Perspectives) 2017”

Fig. 1 Global car sales forecasts by car type

JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)25

Technological Trends and Outlook of Automotive Bearing

Improved reliability
2025
Response to electric motorization• Sensing HUB• Ball screw for electric brakes
2020• Electric pitting preventive bearing• Ball bearing with suppressed creep wear
• HUB with low• High rotational speed SBB
friction torque seal (grease lubrication）• HUB for IWM
Low friction torque• BB with ultra-low friction torque seal
• TRB with outer ring oil sump
• BB for wave reduction gear
• Outer ring anti-creep BB• Low friction torque resin cage thrust NRB• High rotational speed BB• Long-life NRB for planetary gears(oil lubrication)• Improved HUB seal reliability• Next-generation ultra-low friction torque TRB• BB for electric supercharger• TRB with a resin cage
preventing seizure

2015• BB for ISG

2010• Low friction torque grease for HUBs

Size/weight
reduction• High axial load-compatible low friction torque ball bearing• High-speed BB for HV• Low friction torque BB• Thrust NRB for thin lubrication• Lightweight low friction for differentials• Ultra-low friction torque TRB
torque HUB• Super-lightweight HUB• Low friction torque(LFT-IV)TRB (LFT-III) • Low friction torque thrust NRB
2010

2015

2020

2025

Fig. 2 Development trends of automotive bearings

2. Bearings for Powertrains
2. 1 Response to Electrification of Powertrains
The powertrain could be considered to have changed
the most due to the impact of electric motorization. There
are powertrains such as those of PHVs and HVs whereby
the engine and motor are used in combination, as wellas powertrains such as those of EVs, which only convey
the motor output as driving force. Both are electric
powertrains using the motor as a power source, which
had never been used as a power source before, and are
predicted to increase significantly moving forward.
In the case of such electric powertrains, as the levelof output’s dependence on the motor increases, needfor high-speed motor rotation grows to achieve higher
output as well as reduce size and weight. To meet suchneeds, JTEKT developed a high rotational speed ballbearing (Fig. 3). When conventional ball bearings were
subjected to high rotational speed, centrifugal force would
cause cage deformation, and heat generation caused byinterference between the cage and balls would result inbearing seizure. In contrast, the high rotational speed ballbearing features a cage consisting of two identical resin
parts which hold the balls from both sides, minimizing
cage deformation upon high-speed rotation, as well as
reducing heat generation by eliminating interference withballs. This design enables the bearing to accommodate ahigh rotational speed of 2 million d mn ＊1 or more under oil
lubrication conditions (Figs. 4 & 5).
＊1 d mn value: Bearing P.C.D. (mm)× rotational speed (min-1)

26

Fig. 3 High rotational speed ball bearing

Moreover, the operating environment of motor bearings
differs from that of conventional gear support bearings,
and sometimes an electric current flows between the innerand outer rings due to a potential difference created by
the motor. Damage referred to as “electric pitting” occurs
on the contact surfaces between the inner ring and therolling element as well as between the rolling element
and the outer ring when electric currents flow between
them (Fig. 6), and there is a possibility of this leading
to abnormal noise or premature failure if the damage
progresses.
For industrial applications, as a means of preventing
the passage of electricity through insulation, we
commercialized bearings coated with resin molding or
ceramic, ceramic ball bearings, etc. (Fig. 7). However, forautomotive applications, these bearings have problems in
cost, durability, and mass productivity. As such, JTEKT
is engaging in the development of a ball bearing using a
special coating for preventing electric pitting for electric
powertrains. The special coating is applied to this ball

JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)

Cage deformation amount, mm

Technological Trends and Outlook of Automotive Bearing

0.5Standard cage

Rotational speed: MAX. 50 000 min1
Temperature: 120 C

0.4
0.3

Deformation limit for interference
between pocket and ball

0.2

Two-piece cage

0.1
0

0

10 000

20 00030 00040 000

0

50

100

150

200

Rotational speed,
50 000 min1
250

d mn，
×104

Standard cageTwo-piece cage

Fig. 4 Results of high-speed performance (cage deformation) evaluation
Radial load: 1 600 N

Resin
mold

Ceramic
coating

Ceramic
balls

Cost

△

×

×

Durability

△

◎

◎

Mass productivity

△

×

◎

Type

Oil temperature: Room temperatureStandard cage

120

Shape

Developed cage

100
80

Features

Outer ring temperature, °C

140

60
40

Judgment ◎: Extremely good, 〇: Good, △: Normal, ×:Bad

20
0Fig. 7 Existing electric pitting preventive bearing0

10 000

20 00030 00040 000

Rotational speed, min1

Fig. 5 Results of high-speed performance (outer ringtemperature) evaluation

Special coating

Fig. 8 Ball bearing coated with special coating for preventing
electric pitting
Fig. 6 Electric pitting on raceway

bearing’s O.D. surface and is unlike any used previously(Fig. 8).

2. 2 Response to Gear Trains
Many bearings are used not only in the speed reduction
mechanisms of electric powertrains, but also to support
gears in gear trains of current AT/MT/CVT, etc. To
achieve high efficiency of the unit, low friction torque,
as well as size/weight reduction are required of suchbearings. Particularly in the case of electric powertrains,there is a strong demand for thin section ball bearings at
the same time as a response to high-speed motor rotation.
However, durability issues, such as life and creep wear,
JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)

existed.
Bearings used in gear trains are normally lubricatedwith oil sealed into the unit. As such, when used foran extended period of time, abrasion powder from thegear, etc. may infiltrate into the bearing, and shorten
bearing life. Potential countermeasures for this issue
are increasing bearing size, and adding a seal to prevent
infiltration of abrasion powder, etc. into the bearing.
However, increasing size conflicts with the need to reduce
size and weight, while adding a seal conflicts with theneed to reduce torque.
In response to these issues, JTEKT developed aball bearing with a low friction torque seal capable ofaccommodating high-speed rotation. By optimizing seal
lip shape, we succeeded in reducing the force that the27Technological Trends and Outlook of Automotive Bearing

seal tightens the shaft with, and practically halved seal
torque (Figs. 9, 10 & 11). Moreover, by bearing size
reduction enabled by the effect of improved bearing life
against contaminants, the weight was reduced by around
50% compared to conventional open-type bearings(Figs. 12 & 13).

50% Weight reduction

19
u72

16
（3）
u30

Conventional
product(open type)

u62
（10）
Developed
product

Fig. 13 Example of weight reduction

Fig. 9 Ball bearing with ultra-low friction torque seal
<FEM study result>
Minimize permanent set in
fatigue by distributing stress＊Stress caused
by interference

Conventional seal (RKB seal)

Developed seal

Another issue associated with thin section ball bearings
is that they are susceptible to creep caused by strain
under large radial loads. Creep caused by strain is aphenomenon whereby, in the case of general inner ringrotation, outer ring strain and its adhesion to the housing
occur continuously whenever the rolling element passeson the outer ring raceway, causing the outer ring to rotate
in the bearing rotational direction relative to the housing(Fig. 14). When creep occurs, wear progresses between
the bearing and the housing. Therefore, abnormal noiseand premature failure may occur due to displacement of
the bearing axis or large inclination.

Fig. 10 Results of CAE analysis

Direction of
Direction of rolling
progress ofelement movement
outer ring creep
caused by strain
Rolling element load

Radial load: 0.1C
Rotational speed: 1 000 - 10 000 min1
Temperature: 20℃

Unidirectional load
Rolling
element
Inner ringrotational direction
Outer
ring

Conventional product
Seal torque, N•m

Developed product

40%

50%

Direction of outerring creep
0

2 000

4 000

6 000

8 000

10 000

Rotational speed, min1

Housing

BondedportionStrain occurs in the circumferential direction

Fig. 14 Mechanism of creep occurrence

Fig. 11 Results of seal torque evaluation
Radial load: 0.5C
Rotational speed: 3 000 min1
Temperature: 80℃
B10 life/calculated life

4.0 times or larger

Standard Conventional
product
product(open type) (sealed type)

Developed
product

Fig. 12 Life test results in contaminated oil

28

The conventional countermeasure was to thicken theouter ring to suppress outer ring strain. However, thisconflicted with size/weight reduction needs, and led tolarger, heavier units. As a solution, JTEKT quantitatively
analyzed the creep occurrence mechanism using CAE andby experimental verifications, and then, became the firstin the world to adopt a structure with an ultra-shallow
groove in the center of the outer ring O.D. (Fig. 15). This
groove makes the distances from the contact points of theballs and the outer ring raceway to the contact point of
the outer ring O.D. and the housing equivalent to thoseof a bearing with a thicker outer raceway (which was theconventional solution), and minimizes the effect of outerring strain on the housing (Figs. 16 & 17).
JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)Technological Trends and Outlook of Automotive BearingFig. 15 Anti-creep bearing
Reduced outerring thickness
Housing

GrooveaConventional
product

Conventional
product(w/thicker outer ring)b

Developed
product

Fig. 16 Characteristics of developed bearing

continued technical development to overcome theseissues. Particularly in the case of the electric powertrain,
low-viscosity lubricating oil is used in small quantity inorder to improve unit efficiency, and bearing performancewith such lubricating oil could be a potential issue. In
response to this, JTEKT developed an ultra-low friction
torque tapered roller bearing, LFT-IV, which also offers
improved anti-seizure performance (Fig. 18).
Focusing our efforts on reducing tapered roller bearing
torque, we applied the technology we developed to thecreation of the LFT (Low Friction Torque) series. The
LFT-IV bearing adopts a resin cage with a high degreeof design freedom, and has achieved 65% less rotating
torque than standard models by strengthening the function
to control oil inflow into the bearing. Additionally, in theoil groove in the cage, oil accumulates when the bearing
rotation is stopped, and is released from the groove whenbearing rotation starts. Thus, three times longer oil-freeseizure time was achieved compared to the conventional
TRB (Fig. 19).
Specially shaped bearing face
⇒Reduce oil inflow through controlling oil flow along the face
Flow separation from the cage
generates a low pressure zone

Oil groove⇒Minimize oil
shortage

Radial load: 4 kN

1.2

Outer ring

Creep amount, ratio

1
Cage

0.8
0.6

Oil flow analysis result

0.4

Fig. 18 Ultra-low friction torque tapered roller bearing(LFT-IV)

0.2
0Conventional
product

Conventional
product(w/thicker outer ring)

Developed
product

Rotational speed: 8 000 min1
Axial load: 3 kN

This new model eliminated the conventional need forincreasing outer ring thickness used as a countermeasure
for creep and made the size and weight reduction of the
reduction gear possible.
As mentioned above, many ball bearings are usedin electric powertrains. However, in final gear support
parts, etc. which support high power output, sometimes
large size ball bearings are required. On the other hand,tapered roller bearings have higher load capacity than ballbearings. Therefore, if a tapered roller bearing is usedinstead of a ball bearing, it is possible to reduce bearing
size and weight in the high load portions. However, since
tapered roller bearings have larger rotating torque andlower anti-seizure performance than ball bearings, JTEKTJTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)

Seizure time ratio

4

Fig. 17 Comparison of creep amount3 times longer
3
2
1
0

Conventional
product

Developed
product

Fig. 19 Seizure test result

Furthermore, as a technology to support rotation of ballbearings under large gear load, JTEKT developed a highaxial load compatible bearing with asymmetrical inner/outer rings (Fig. 20). Specifically speaking, by expanding
raceway depth on the axial load side, we have improved
axial load capacity by 80% compared to the conventional29

Technological Trends and Outlook of Automotive Bearing

Expansion of raceway
depth on axial load side
(improvement of shoulder overriding resistance)

Countermeasure ①
Make the cage riding clearance
between the cage and the ringsmall and reduce oil inflow into
the bearing
Countermeasure ②
Flick out oil by centrifugal force
and outward oil flow created by
the tapered cage back face

Countermeasure ③
Promote discharge of oil inside
the bearing through pumping
action by centrifugal force

Oil quantity controlling cage

Fig. 22 Oil quantity controlling cage

1.0
Torque loss ratio

model. Also, in the case of equivalent axial load capacity,
the O.D. can be reduced by 15% compared to the current
deep groove ball bearing (Fig. 21). Moreover, regarding
the issues of shortened bearing life due to contaminatedoil and increased torque loss due to oil agitation, we
improved cage shape to control the amount of oil thatpenetrates the bearing, thus reducing the contaminantspassing through the bearing and reducing oil agitation
resistance (Fig. 22). This reduced torque loss by up
to 48% compared to a deep groove ball bearing withequivalent load capacity (Fig. 23).
In regards to bearings for planetary gears also, JTEKT
has engaged in technical development to reduce the size
and weight of the unit. The planetary gear mechanism
has a speed variation function for a section to switch
power between the engine and the motor and for motor
efficiency enhancement. Inside the planetary gear
mechanism, a radial needle roller and cage assembly anda planetary shaft are used. There is a need for size/weight
reduction of the bearing to reduce the overall weight of
the unit. However, bearing size reduction would lead todecreased load capacity, and then, the issue of insufficientbearing life. At JTEKT, we have addressed such issue by
developing a long-life bearing with our original special
heat treatment performed on the planetary shaft. However,recently we also developed a super-long life bearing
featuring surface modification technology (Fig. 24).

[Conditions]
Oil amount: Up to 10mm below
the bearing axis

0.8

Rotational speed: 10 000 min1
Temperature: 50℃
Load: Radial 2 kN
Axial 1 kN

48% reduced

0.6
0.4
0.2
0.0

Conventional product Developed product(deep groove ball bearing) (equivalent axial load capacity)

Fig. 23 Torque comparison results

Carrier[Special heat treatment/surface modification]
Bearing raceway surface (high hardness)

Planetary
shaft
Radial needle roller andcage assembly
Planetary gear[Special heat treatment]
Staked shaft end(low hardness)

Fig. 24 Super-long life bearing for planetary gear
Fig. 20 High axial load-compatible ball bearing20

15% OD

u35

u72

u35

u85

17

Developed product
Conventional product(deep groove ball bearing) (equivalent axial load capacity)

Fig. 21 Example of downsizing

30

By applying special heat treatment, we enhanced thehardness of the raceway surface and optimized the amountof retained austenite, thus successfully extending bearing
life. Moreover, with the aim of reducing the size andweight of the planetary gear mechanism, we maintained
the low hardness of the end portion of the planetary shaft
to deal with fixing it to the planetary carrier by staking.
Additionally, through surface modification of the raceway
surface, we further improved the hardness of raceway
surface, and suppressed crack growth by forming highresidual compressive stress layer in the surface layer.
As a result, super long life, equivalent to five times thatof the conventional model, has been achieved (Fig. 25).
This enabled study to reduce bearing width by up to 40%
and to reduce the number of pinions in the planetary

JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)Technological Trends and Outlook of Automotive Bearing

mechanism to contribute to reduction of unit size andweight (Fig. 26).

Load: 0.3C + moment load
Rotational speed: 6 000 min1
Lubricant temperature: 100℃
6
5.0 times

L10 life ratio

5

1.5 times

4
3
2
1
0

Conventional Long-life
product
product

Developed
product

Fig. 25 Comparison of bearing basic rating lives

Conventional productMax. 40%width reduction
Developed model
Example of calculation using the same
bearing bore/outside diameters＊

Fig. 26 Image of bearing downsizing

produced by the engine. However, there was a limit
to response speed depending on engine RPM andtemperature. To overcome this issue, VVT mechanisms
using motor drive are increasing instead of hydraulicdrive. Motor drive makes optimal control of valve timing
possible due to improved response speed as well as
control even at low temperature and low rotational speedof the engine, which makes high output and high fueleconomy possible.
Movable mechanisms adopt a motor reduction gearwith a large reduction ratio.
Figure 28 shows the principle of the wave reduction
gear mechanism using thin section ball bearings (Fig. 27)
as a typical example. The inner ring, pressed onto theelliptical shaft, is deformed into an elliptical shape,
and the position of outer ring deformation varies as
the elliptical shaft rotates since the outer ring is also
deformed via balls due to the inner ring deformation.
Compared to the inner ring, which requires only simple
deformation analysis, the outer ring requires cyclic
bending fatigue strength verification. However, at JTEKT,
we perform CAE (Fig. 29) and experimental verifications
to offer bearings with even higher reliability.
Engine downsizing, a known approach to improving
the fuel efficiency of engine-driven vehicles, requires asupercharging system. Recently, in order to improve fuelefficiency even further, electric superchargers have been
added to conventional turbochargers utilizing exhaust to
sophisticate supercharging systems with improved turbo
efficiency through solving turbo lag, etc. This electric

2. 3 Response to Engines
In the markets of newly emerging countries, thepercentages of engine-driven vehicles and engineequipped vehicles such as PHV/HV are high, andincreasing engine efficiency is still a major issue. One
feasible solution is a variable valve timing mechanism
elaborately controlling engine gas intake.
Conventional variable valve timing (VVT) mechanisms
featured hydraulic control utilizing hydraulic pressure

Fig. 27 Thin section ball bearing for wave reduction gear

Gear engagement point
Flex gear(elliptical deformation）
Major axis

Internal gear
(perfect circle)

Minor axis

Elliptical camshaft

Gear engagement point
Because the number of teeth on the internal gear and that on the flex gear differ, the phase becomes
displaced when the elliptical camshaft rotates (reduced speed)

Fig. 28 Principle of wave reduction gear

JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)31Technological Trends and Outlook of Automotive Bearing

Inner ring

Outer ring

1/4 model

1/4 model

Raceway
Raceway
Maximum stress amplitude
Raceway shoulder’s vicinity

Maximum stress Shoulder chamfer’s vicinity

Fig. 29 CAE analysis examples

supercharger uses two ball bearings supporting the
motor shaft. These ball bearings use grease lubrication.
However, due to operating in extremely harsh conditions,
namely ultra-high-speed and rapidly accelerated/decelerated rotation, conventional bearings faced theissue of seizure in a short time as a result of improper
lubrication.
The ball bearing for electric superchargers developedby JTEKT recently (Fig. 30) has 1.5 times longer life
than the conventional model by an internal design suited
to high-speed rotation, and improved cage and seal lip
shape, as well as adopting JTEKT’s original grease forhigh-speed rotation (Fig. 31).
In order to improve engine efficiency, we have engaged
in not only the electrification discussed here, but also
replacement of the sliding bearings used for the cam
shaft, balancer shaft and turbocharger by rolling bearings.
With this, we anticipate not merely torque reduction, butalso the secondary effects of pump reduction, oil hole/groove elimination, etc. although pumps and oil holes/
grooves have been considered necessary for sliding
bearings to produce hydraulic pressure. JTEKT willcontinue proactively engaging in efforts to achieve higher
engine efficiency.

3. Bearings for Chassis
The hub unit (Fig. 32) is a unit bearing located in a
vehicle’s wheels to support the wheel, while supporting
vehicle weight. Even amidst the electric motorization
trend, wheel bearings are essential and there is astrong demand to reduce hub unit torque loss not only
to improve fuel consumption, but also to improve
electrical consumption. A hub unit comprises a bearing,which has a function to smoothly rotate tires, and aseal, which prevents muddy water splashed up by thetires from entering the bearing. Two types of torqueloss exist; namely, bearing rolling resistance and seal
sliding resistance. JTEKT has halved hub unit torqueby developing low friction torque grease and a low
friction torque seal (Fig. 33) as measures to reduce these
individual resistances causing torque loss.

Outboard seal
Inboard seal
Cage・Special material forhigh speed rotation+ special shape

Internal design
・Internal heat generation
minimization design
Grease・Grease for super highspeed rotation

Seal
・Design with enhanced
labyrinth<Axle unit>

1.5 times or larger

Developed product
0.5

1

1.5

Life ratio

Fig. 31 Durability test result

32

2

1
Torque ratio

Rotational speed: 100 000 min1
Temperature: 120℃
Load: Preload of 110 N

0Bearing

Fig. 32 Hub unit

Fig. 30 Bearing for electric supercharger

Conventional product<Hub unit>

0.8

Seal torque

0.6
0.4
0.2
0

Bearing torque
Conventional
product

Developed
product

Fig. 33 Hub unit torque

JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)Technological Trends and Outlook of Automotive BearingFirst, in the development of low friction torque grease,bearing rolling resistance can be broadly divided into baseoil viscous resistance, bearing rolling/sliding resistance,
and agitation resistance of the grease itself. JTEKT
achieved torque reduction by implementing measures forthese three loss types.
①In regards to base oil viscous resistance, the kinematic
viscosity of the base oil is the controlling factor.
Therefore, we reduced kinematic viscosity to thebare minimum with consideration to securing oil film
thickness even when the bearing is subjected to highsurface pressure.
②As for bearing rolling/sliding resistance, we focused on
the coefficient of friction of the interface, and revised
the molecular structure of the base oil in order toreduce the coefficient of friction. Moreover, because
there is correlation between the coefficient of friction
and oil film thickness, we added to the grease anadditive able to thicken oil film even at low speeds at
which rolling/sliding resistance is large.
③Grease agitation resistance can be lowered byincreasing grease consistency (softening). However,if grease fluidity increases, there is a conflicting
issue such as grease leakage from the seal. As such,
we adopted a special thickener able to lower grease
shearing resistance without increasing consistency.
Next, in the development of a low friction torque seal,
there is a need to reduce sliding resistance in order toreduce torque. However, in addition to this, there is aneed to curb rust on the sliding surface of the outboard
seal which is problematic in extremely cold regions
and areas without adequate infrastructure. When rust isformed on the seal sliding surface, bearing life will be
shortened because it will cause lip wear, which allows
muddy water entry into the bearing. To address these twoissues, we performed fluid analysis aiming to improvethe environment of water exposure around the sealing lip(Fig. 34), and quantified water flow direction and flow
volume, which we had been unable to confirm previously.
Consequently, with consideration also to the surrounding
structure of seal, we achieved 75% torque reduction
and significant extension of bearing life in muddy water
environment compared to the current model by improving
five points (Fig. 35) on the outboard seal alone.

Water flow
Outer ring

Water injection

Hub shaft

Ball
Water amount on theouter side of the lip, g

Air
Seal

1.8

Conventional
product

1.4
1

In the current model, the space on the outer side of the lip is saturated with muddy water
quickly but in the developed model, muddy water doesn’t reach the lip even if time elapses

0.6
0.2
0.2

Developed product
0

1

2

3

Time, sec

3 lipsDeveloped product[Seal internal portion]
Prevents muddy water from reaching the lip⇒Addition of a gutter structure[Slinger portion]
Prevents abnormal wear of the lip by curbing rust generation⇒Addition of a stainless slinger

Outer ring
(fixed)[Lip portion]
Reduce sliding resistance by reducing the number of lips (currently 3 lips)⇒2 lips

Rolling element

Hub shaft(rotating)[Grease lip portion]
Reduce lip reactive force by reducing the influence of interference⇒ (secure larger space by fitting the seal on the outer ring outside surface)
Revise the lip shape to thinner and longer one

Torque reduction[Seal opening]
Reduces the amount of muddy water that penetrates inside the seal
⇒Strengthen labyrinth

Conventional productImprove the environmentof water exposure

Fig. 34 Results of fluid analysis

Fig. 35 Development points of seal on the hub unit outboard side

JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)33

Technological Trends and Outlook of Automotive Bearing

4. Future Outlook

34

Fig. 36 Appearance of non-recirculating type ball screw
Efficiency, %The above sections have discussed development
trends for various torque reduction technologies as wellas downsizing/weight reduction technologies primarily
focusing on JTEKT’s response to electric motorization.
At the same time as electric motorization, however,
we believe that autonomous driving will also have amajor impact on our bearing products. In regards toautonomous driving, there are outstanding issues suchas establishment of infrastructure and legislation, which
are the premise of popularization. However, technicalprogress is remarkable, and currently SAE Level 2
vehicles (partial automation where vehicle operation isled by a human driver) have been put to practical use. At
the fully autonomous level, safety is of utmost priority,and sophisticated vehicle control technology is essential.
Due to the fact that grasping road condition information isimportant in improving vehicle control accuracy, JTEKT
is aiming to develop a road condition detection systemleveraging the hub unit. By swiftly acquiring informationfrom the hub unit, which is the closest to the road surface
among all JTEKT products, we believe we can utilize
such information for improving vehicle line traceability,
braking control, and so forth.
Moreover, as a technology for the brake portion
that can contribute to autonomous driving, we are also
pushing ahead with ball screw development. For HVs,
etc. electric brake boosters cooperatively controlled withenergy regeneration (EHB: Electro Hydraulic Brake),etc. are being introduced to the market. However, in thenear future, it is expected that electric calipers suitable
for EVs, etc., which render hydraulic power source
unnecessary (EMB: Electro Mechanical Brake), will also
be released on the market. Ball screws are a promisingitem as a mechanism to convert motor rotary motion intolinear motion and can contribute to reduction of motor
size, etc.
JTEKT focused on the fact that the stroke is short when
the EMB operates, and is developing a non-recirculatingtype ball screw with limited functions. We eliminatedthe ball circulating mechanisms such as tubes required inregular ball screws and arranged several springs internally(Fig. 36). As a result, we have succeeded in maintaining
high efficiency without inhibiting ball rolling motion
and in securing sufficient durability in maintenance-freegrease lubrication conditions (Fig. 37). In EVs, etc., theEMB will be used as a brake-by-wire system connectedwith an electric cable alone, so it is easy to secure battery
mounting space and passenger space. We believe thiswill greatly contribute to the realization of autonomous
driving.

Systemrequirements

0

OKLong life(The test was censored at three times the target life.)

L
Target life

2×L

3×L
No. of cycles

Fig. 37 Durability test result

5. Conclusion
In this once-in-a-century time of major change, thenature of automobiles is drastically changing. This
report has introduced responses to electric motorization
and autonomous driving as forms of that change. Highrotational speed ball bearings, anti-creep ball bearings,
etc. which are technologies responding to electricmotorization, can all contribute to energy reduction,and thus preservation of the global environment,
while sensing hub units, a technology responding toautonomous driving, can help to make human life moreconvenient. Moving forward, there will be a greater needfor even more sophisticated mechanisms and systems
such as those in FCVs, fully-autonomous vehicles, etc.,
which are called ultimate eco-friendly automobiles.
JTEKT will deepen our unique tribological technologies
and focus on developing not only low friction torqueand size/weight reduction technologies, but also various
sensing technologies and system products using actuators,
etc. The change of automobiles in this age of revolution
will make people’s lives safer, more convenient, andmore affluent. As a bearing manufacturer, JTEKT will
steadily respond to such change and support realization ofprosperous life.
* LFT is a registered trademark of JTEKT Corporation.

JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)Technological Trends and Outlook of Automotive Bearing

References
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ABeam Consulting: EV·Jidouunten wo koete “nihonryuu” de katsu, 2030nen no aratana kyousou-jiku towa ,Nikkei BP (2018) (in Japanese).

K. YOKOTA**JTEKT ENGINEERING JOURNAL English Edition No. 1017E (2020)

Executive Managing Officer

35