TECHNICAL REPORT

Development of Deep Groove Ball Bearingsfor High-speed Rotation
Y. TANIGUCHI T. UMENO

Motors used in hybrid electric vehicles (HEV), electric vehicles (EV), and the like are required to be small andhigh-output. The downsizing of the motor brings demands for an increase in rotations to preserve motor output,
and the need for higher speed in bearings is also increasing. In response to these needs, we have developed a deep
groove ball bearing for high-speed rotation which adopts a dual-support type resin cage, which we will introduce inthis report.
Key Words: ball bearing, cage, high-speed, dual-support

1. Introduction
As high fuel efficiency needs continue to increase, itis predicted that the demand for HEVs and EVs will also
continue to grow. The drive motors used in HEVs andEVs are required to be compact and lightweight as theymust be installed in limited space. Meanwhile, in orderto make a motor smaller at the same time as maintaining
high output, there is a need to increase rotational speed
therefore a bearing capable of supporting high-speed
rotation is necessary for the support bearings of the motor
also. This paper introduces the development of a deep
groove ball bearing for high-speed rotation.

2. Issues Regarding High-Speed Rotation
The drive motors of HEVs and EVs either use oil orgrease lubrication, however the former is often used forhigh-speed rotation. The cage used in a deep groove ballbearing is normally an iron cage or snap cage, howeverin cases where the bearing is used at high-speed rotation
with oil lubrication, the allowable rotational speed isoften determined by the high-speed limit of the cage. If
an iron cage is used, the contact between the balls andcage pocket intensifies at high-speed rotation due to theeccentric motion of the cage and insufficient lubrication
at the contact points will lead to seizure between the balls
and cage. Figure 1 shows the state of an iron cage after ahigh-speed rotation test.

Seizure occurrence at thebottom of the pocket

Pockets where
seizure occurredFig. 1 State of iron cage after high-speed test

Meanwhile, in the case of a snap cage, the pocket claws
are susceptible to deformation due to the centrifugal force
generated by the single-support type and although thesnap cage has superior high-speed performance compared
to an iron cage, when used under high-speed rotation
conditions, temperature may increase due to strong
contact between the balls and pocket claws as a resultof deformation, which would result in seizure. Figure 2
shows the state of a snap cage after a high-speed rotation
test.

Marks causedby strong contact

Fig. 2 State of snap cage after high-speed test

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JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)

−Development of Deep Groove Ball Bearings for High-speed Rotation−

To make snap cages more suited for high-speed
applications by minimizing deformation caused bycentrifugal force, a conventional measure of making theannular portion of the cage thicker in the axial direction
can be implemented to enhance rigidity. However, even incages with enhanced rigidity, the deformation of the claws
is significantly large at a high-speed rotation whereby*1
the dmn value exceeds 1 500 000 dmn and temperature
increases due to strong contact between the balls andpocket claws, thus resulting in seizure.
Considering this, the only way to increase a snap cage’s
ability to accommodate high-speed would be to change
the shape of the cage to minimize deformation at highspeed rotation.
*1 dmn value: Bearing P.C.D.×rotational speed−1(mm)(min )

3. Features of the Developed Cage

Table 1 Analyzed cages
Standard cage

Highly-rigid cage Developed cage

Table 2 Analysis conditions
Bearing
numberRotational−1speed, min
Temperature,℃

On this occasion, we have developed a dual-support
type cage consisting of two snap cages of identical shapes
combined as a single set (Fig. 3).

6007 (I.D. u35×O.D. u62×Width 14)
MAX. 50 000
120Cage deformation, mm

0.5Standard cage

0.4

Highly-rigid cage

0.3
0.2

(pocket and balls interference limit)

0.1
Developed cage00

10 000Claw fitting shape of a cage

20 00030 00040 00050 000

Rotational speed, min−1

Fig. 4 Analysis results
Fig. 3 Developed cage

The dual-support configuration minimizes any
deformation caused by centrifugal force.
Moreover, even in regards to the shape of the claws
in the combined portion, by forming the claws from theinside, the shape is less susceptible to deformation bycentrifugal force. We performed an FEM analysis of cage
deformation to verify the effects of deformation reductionin the developed cage. Table 1 shows the analyzed cages,
Table 2 shows the analysis conditions and Fig. 4 shows
the analysis results.

The analysis results of Fig. 4 show that, compared
to a standard cage, the highly-rigid cage with a thicker
annular portion in the axial direction has less deformation
however, as mentioned above, its interference limit withthe bearing balls is reached at speeds in excess of 30 000−1min (dmn value: Approx. 1 500 000).
In comparison, the developed cage has even lessdeformation than the highly-rigid cage and does notinterfere with the bearing balls even at speeds of 40 000−1min (dmn value: Approx. 2 000 000).

4. Evaluation
4. 1 Cage⑴Fatigue strength
We conducted an experiment to verify the fatigue
strength of the developed cage. Moreover, for the resin
cage, we also confirmed the fatigue strength of a cageafter it had been dipped in oil as strength decreases due
to deterioration from use in oil lubrication. Table 3

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−Development of Deep Groove Ball Bearings for High-speed Rotation−

New cage/oil-dipped cage

Frequency, Hz
Ambient temperature,℃

New cage250

Oil-dipped cage

200
150

Fatiguestrength(after oildipping)

100
50

Table 3 Test conditions
Sample, cage300

Occurred stress, MPashows the test conditions, Table 4 shows the oil dipping
conditions and Fig. 5 shows the test equipment. The loadon the cage was applied in the tensile direction between
two pin-shaped fixtures by moving the pin-shaped fixture
on the rotating ring side in the rotational direction. Tests
were conducted at various loads until the cage broke andthe number of repetitions was confirmed.

01.E+04

1.E+05

Table 4 Oil dipping conditions
ATF

Temperature, ℃

140Time, h500

1.E+07

Fig. 6 Fatigue strength test results

20±5 (normal temperature)

Oil type

1.E+06

Total repeats, times

10

Breakage of the back portion

Pin-shaped fixture
Pin-shaped fixture (rotating ring side)
Pin rotational direction(fixed ring side)

Fig. 7 Cage after fatigue strength test
Fixed ring

Rotational
direction
Rotating ring

CageFig. 5 Test equipment

Figure 8 shows the results of an analysis to verify
the stress occurring on the developed cage at a speed of−1
40 000 min (dmn value: Approx. 2 000 000) and theseresults reveal that the occurred stress is smaller than thefatigue strength after oil dipping even under such highspeed conditions.

Figure 6 shows the results of a fatigue strength test,
while Fig. 7 is a photo of the cage after a fatigue strength
test has been conducted. Figure 7 shows that the thinnest
annular portion of the cage (the back) is broken, therefore
we can ascertain that the back is the weakest portion. Thestress occurring on the vertical axis shown in Fig. 6 is thestress of the back calculated through FEM analysis fromthe applied load.

Occurred stress, MPa

150
Fatigue strength
100500BackClawsFig. 8 Results of occurred stress analysis⑵Heat shock test
A heat shock test was conducted for the developed
cage in order to confirm how much it was affectedby heat shock. Table 5 shows the test conditions. No
abnormalities such as deformation or splits were observedin the cage after the test was carried out.

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JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)

−Development of Deep Groove Ball Bearings for High-speed Rotation−

Table 5 Test conditions
120͠

−30͠

Test pattern

35 min35 min70 minNumber of cycles

Time needed for temperaturetransfer: 5 mins or less
200

Outer ring temperature, ℃

140Standard bearing

120

Highly-rigid bearing

100

Developed bearing

80
60
40
200010 000

20 00030 00040 000

Rotational speed, min−1Fig. 10 Results of high-speed performance evaluation

4. 2 Bearing⑴High-speed performance
A comparison was made of the temperature increase
in bearings fitted with the existing cages (standard cage,highly-rigid cage) and the developed cage. Table 6 shows
the test conditions, Fig. 9 shows the test equipment andFig. 10 shows the test results. The upward-pointing
arrows in Fig. 10 for rotational speed indicate that anabnormal temperature increase would occur at rotational
speeds any higher than the one given. Abnormal
temperature increase did not occur on the developed cage
−1even at a speed of 40 000 min , proving it had a highspeed performance more than 1.3 times higher than that
−1of the highly-rigid cage (30 000 min .)⑵Durability①High-speed durability
A high-speed durability test was performed for thedeveloped cage. Table 7 shows the test conditions. The
results of the test showed the developed cage satisfied
the test condition of 200 hours. Figure 11 shows theexternal appearance after the test was performed andfrom this it is clear that there was no flaking or seizure
and no abnormalities such as wear on the cage either.

Table 7 Test conditionsBearing number

Table 6 Test conditions

Radial load, N

Radial load, N

6007(I.D. u35×O.D. u62×Width 14)
1 600

Axial load, N

0Bearing number

Oil supply method
Oil type
Oil temperature
Oil amount, ml/min

Oil drip lubrication
ATF
Normal temperature(natural temperature rise)
5

Axial load, N
Rotational speed,min−1
Oil supply method

6007(I.D. u35×O.D. u62×Width 14)
1 600
030 000
Oil drip lubrication

Oil type

ATF

Oil temperature, ℃

140

Oil amount, ml/min

50

Test time, h200

Hydraulic ram
Support bearings

Radial load

Fig. 11 Appearance after high-speed durability test
Sample bearings

Fig. 9 Test equipment

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−Development of Deep Groove Ball Bearings for High-speed Rotation−②High-load durability
A high-load durability test was performed for thedeveloped cage. Table 8 shows the test conditions.
An oil-dipped cage was used. Both of the developedcages tested satisfied the condition of three times thecalculated life (Fig. 12). Figure 13 shows the external
appearance after the test was performed and from thisit is clear that there was no flaking or seizure and noabnormalities such as wear on the cage either.

Table 8 Test conditions
6007(I.D. u35×O.D. u62×Width 14)
Oil-dipped cage
(Conditions: Table 4)
4 900

Bearing number
Cage
Radial load, N
Axial load, N
Rotational speed,
min−1Inclination of shaft

03/1 000

Oil supply method

Oil drip lubrication
ATF

Oil temperature, ℃

80

Oil amount, ml/min

502)

3)

171 (3 times the calculated life)

Suspendn=2

Suspend

50References1)

n=10It was confirmed that the developed cage has a highspeed performance over 1.3 times that of existing cages(standard cage, highly-rigid cage). Moreover, even after
heat shock and durability tests, it was confirmed that thedeveloped cage was free of abnormalities and displayed
satisfactory durability. In line with the future growthof the HEV and EV markets, it is predicted that motors
will become more high-speed. This report introduced adeep groove ball bearing for high-speed rotation however
by continuing to engage in the development of newtechnologies aimed at increasing bearing performance,
JTEKT wishes to contribute to better fuel efficiency ofautomobiles and energy conservation.

10 000Oil type

Test time, h5. Conclusion

100150H. Dodoro, T. Iwata, H. Matsuyama: Tribology
Conference Proceedings, 2017 spring Tokyo (2017) D30.
K. Yokota: Technological Trends and Outlook ofA u t o m o t ive B e a r i n g s , J T E K T E N G I N E E R I N GJOURNAL, No. 1014E (2017) 14.
M. Murakami, Y. Takahashi, D. Okamoto: Efforts
towards a More Efficient Resin Cage for Ball Bearings,
JTEKT ENGINEERING JOURNAL, No. 1011E (2014)
39.

200

Test time, hFig. 12 High-load durability test results

Y. TANIGUCHI*T. UMENO**

Fig. 13 Appearance after high-load durability test
*
**

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Automotive Bearing Development Dept., Bearing
Operations Headquarters
Experiment & Analysis Dept., Bearing Operations
Headquarters

JTEKT ENGINEERING JOURNAL English Edition No. 1015E (2018)