TECHNICAL REPORT

Development of Anti-Creep Ball Bearing for Outer Ring
Y. ISHII T. JINBO

In ball bearings receiving heavy radial load, there have been problems in the past where, for example, thebearing housing became worn due to creep caused by continuous strain in the outer ring of the ball bearing. The
conventional countermeasure against this creep phenomenon is to increase outer ring thickness. However, thiscountermeasure comes with the setbacks of increased weight and larger outer ring diameter. JTEKT has therefore
developed an anti-creep ball bearing which was designed without increasing the outer ring thickness.
Key Words: creep, ball bearing, wear, strain

the past, and countermeasures are being sought to address
this issue.
One form of creep often seen as a problem from theperspective of ease of assembly, is the creep which forms
between the outer ring and housing which serves as theclearance fit. Outer ring creep is categorized into three
types as shown in Table 1 depending on the mechanism
occurrence.
If creep occurs, wear will progress between the bearing
and housing, causing misalignment and inclination of theshaft to increase, which will in turn result in problems
such as abnormal noise. In support bearings for CVT
pulleys, which are subjected to a large radial load, and1. Introduction
Various types of transmissions are used in automobiles,
from the conventional manual transmission (MT)and automatic transmission (AT) to transmissionsfor HV/FCV, and these are all constantly undergoing
improvement. Many bearings are used in thesetransmissions to support the gear, and in recent years thepercentage of ball bearings with thin outer ring being
adopted is increasing due to the market needs requiringbearings to be low torque, compact and lightweight.
Due to these circumstances, bearing creep has becomeviewed as problematic, whereas it hardly ever had been in

Table 1 Types of outer ring creep①②③

Creep type

Creep caused by strain

Creep caused by dragCreep caused by run-out

Creep direction

Bearing rotational direction

Bearing rotational direction

Opposite to bearing rotation

Creep speed

Slow

Fast

Slow
If the outer ring is the clearance
fit, creep will occur due to thedifference in perimeter lengthof the outer ring outer diameterand housing inner diameter
which is created through runout radial load

Outer ring circumferential strain
Cause of creep
caused by large unidirectional
occurrence
radial load

Housing

Bearing
Friction torquerotational ＞ between the outertorquering and housing
Easily occurs when no load or
light load

Unidirectionalradial load

Run-out load
Outer ring end
face mark

Schematic
Inner ringrotational direction

Outer ring
creep direction

Increase outer ring thickness,
Countermeasureanti-rotation pin

Inner ringrotational direction

Outer ring
creep direction

Creep amountO-ring, resin winder, increased interference with housing, antirotation pin

JTEKT ENGINEERING JOURNAL English Edition No. 1014E (2017)59

−Development of Anti-Creep Ball Bearing for Outer Ring−

Creep occurs
regardlessof if there isclearance or not

Direction of rolling Direction ofouter ring
Rolling element travel
creep travel
element load
Unidirectional load
Rollingelement
Inner ring rotational
direction
Outerring

Based on the abovementioned occurrence mechanism,it was deemed that reducing the strain which occurredon the outer ring would be effective as a countermeasurea g a i n st c re e p c a u se d b y o u t e r ri n g st ra i n. The
conventional creep countermeasure of making the outerring thicker was believed to reduce outer ring strain andbe effective in suppressing creep as the shortest distancefrom the contact point of the outer ring raceway androlling element to the contact point of the outer ringouter diameter face and housing inner diameter face isextended.
First, in order to confirm the relationship between outerring thickness and creep amount, we performed a CAE
analysis. The results are shown in Fig. 2. This analysis
confirmed that, by making the outer ring thicker, thestrain is reduced and creep can be suppressed.
As such, we conceived the concept of creating a space(groove contour) in the center of the outer ring outside
diameter face in order to extend the shortest distance
between the contact point of the outer ring outer diameter
face and the housing inner diameter face, thereby
reducing the strain which occurs on the outer ring in acircumferential direction and suppressing creep caused byouter ring strain (Fig. 3) like what can be achieved fromthe thickening of the outer ring.

00.1

Rolling
element loadbａb

GrooveHousing

SeizedportionOccurrence of strain in circumferential direction

Fig. 1 Mechanism of creep occurrence due to outer ring strain

60

0.3

0.4

0.5

0.6

Fig. 2 Results of CAE analysis of outer ring thickness andcreep amountGroove width
Outer ring creep
direction

0.2

Outer ring thickness, ball dia. comparison

Developed bearing(conceptual drawing)

Relationship of distance to housing
contact portion and outer ring strain(conceptual drawing)
Outer ring strain

Ball bearings used for inner ring rotation, if subjected
to a radial load in one direction, are more likely to havestrain occur on the outer ring than if the outer ring was
subjected to load from a rolling element (rolling elementload). When the bearing is rotating, the strain will occur
consecutively on the outer ring due to the balls passing by.
Moreover, there is a large surface pressure being
created when directly subjected to rolling element
load therefore seizure due to frictional force will occur
whereby the outer ring outer diameter surface and housing
inner diameter surface come into contact. At the boundaryof this seized portion, the outer ring will become distorted
as though it is being crushed in the circumferential
direction due to strain in the circumferential direction on
the outer ring towards the front of the direction in which
the ball is travelling. Towards the back of the directionin which the ball is travelling, the outer ring will distortwhen it returns to its original state after being crushed.
Every time the balls pass through the area being
subjected to load, the abovementioned distortion caused
by outer ring strain occurs consecutively causing the outerring to gradually shift the same direction as the ball istravelling relative to the housing. This is the mechanism
by which creep occurs due to outer ring strain (Fig. 1).

3.1 Concept of the Developed Bearing

Groove depth

2. Mechanism of Creep Occurrence
Caused by Outer Ring Strain

3. Outline of the Developed Bearing

Creep amountthin ball bearings used for HV transaxles to achieve
weight reduction, creep easily occurs due to outer ringstrain, therefore there is concern problems caused byhousing wear will emerge.
In order to prevent creep caused by outer ring strain, itis effective to thicken the outer ring, however this comeswith the setbacks of being difficult to mount and heavier
due to an increase in the outer diameter.
As such, instead of making the outer ring thicker,
JTEKT has developed an anti-creep ball bearing which
succeeds in suppressing creep and reducing housing wear.

Reduced outerring straina b
Distance between the baseof the outer ring raceway andthe housing contact portion

Fig. 3 Concept of developed bearing

JTEKT ENGINEERING JOURNAL English Edition No. 1014E (2017)

−Development of Anti-Creep Ball Bearing for Outer Ring−3.2 Design of the Outer Ring Groove
Increasing the groove width shown in Fig. 3 would
be effective in suppressing creep, however this would
increase stress at the groove base, therefore the design ofthe groove contour must be a balanced one. We conducted
another CAE analysis using groove width and depth
as parameters in order to find the amount of creep thatoccurs due to outer ring strain and the amount of stressthat occurs at the groove base. The results were used todetermine groove contour.
A CAE analysis was conducted to compare the creep
amounts of the current bearing (standard bearing) anda bearing with a thicker outer ring versus the developedbearing. The analysis conditions are shown in Table 2
and the results are shown in Fig. 4. The bearing housing
model used in the CAE analysis was identical to thehousing of the device for measuring creep amount(Fig. 5). Results showed that the developed bearing,as was the case with the thicker outer ring bearing,
suppressed creep amount caused by outer ring strain byaround 50% compared with the current bearing.
Moreover, a CAE analysis using a housing model
equivalent to that on an actual unit was performed on abearing with a thicker outer ring as a countermeasure
to outer ring creep. This analysis showed that creep had
not occurred. This suggested that if the creep amount on
the developed bearing found through evaluation of thebearing in isolation was less than that of the bearing withthe thicker outer ring, creep could be prevented on theactual unit.

4. Performance of the Developed Bearing
4.1 Method of Confirming Creep AmountFigure 5 shows the measuring device used to findcreep amount. In order to clarify the effectiveness of theanti-creep ball bearing for outer ring, the housing was
made from steel - a material in which creep easily occurs.
Moreover, in order to verify the behavior of the outer ring,the outer ring end face was marked (Fig. 6) and filmedusing a video camera. The amount of creep per unit time
was found by conducting an image analysis on the filmed
video.
Radial load

Housing
Axial load
Acrylic plate(transparent)Video camera
Support bearing Test bearing

Fig. 5 Device for measuring outer ring creep amount
Creep amountMark

Table 2 CAE analysis conditions of creep amountCurrentbearing
Outer ring outerdia, mm
Outer ring
thickness, mm
Radial load, kN

BearingwithDeveloped
thickerbearingouter ring

u70

u72.4

u70

3.2

4.4

3.2

4

Creep amount, %

1.2
150%
reduction

0.855%
reduction

0.6
0.4
0.2
0

Current bearing

Bearing withthicker outer ring

Developed
bearing

Fig. 6 Method for measuring outer ring creep amount4.1.1 Creep amount under a pure radial loadcondition
The effect on suppressing creep under a pure radialload condition was confirmed. The creep amountmeasurement conditions are shown in Table 3 and theresults are shown in Fig. 7. It can be seen that, for thecurrent bearing, the bearing with a thicker outer ring andthe developed bearing alike, creep amount increases as
the radial load increases and is virtually proportional toradial load. Furthermore, compared to the current bearing,
creep amount was reduced by 40% on the bearing witha thicker outer ring and 55% on the developed bearing,
meaning that the developed bearing had less creep thanthe bearing with a thicker outer ring.

Fig. 4 Results of CAE analysis of creep amount

JTEKT ENGINEERING JOURNAL English Edition No. 1014E (2017)61−Development of Anti-Creep Ball Bearing for Outer Ring−

4.2 Housing Wear Amount

Table 3 Test conditions
Radial load, kN

1，2，4

Rotational speed, min−1Lubrication

Creep amount, %6Current
bearing
Bearing withthicker outer ring
Developedbearing5432

10 000Oil application

40% reduction

55% reduction

1001

2

3

456

Radial load, kN

Fig. 7 Relationship of radial load and creep amount

Using housing made from aluminum alloy, the samematerial as that used on an actual unit, we made acomparison of the housing wear amount on the developed
bearing and that of the current bearing. In order topromote the occurrence of creep, the housing was shaped
to be highly rigid and the radial load was set higher thanthe operating conditions on an actual unit (equivalent tothe basic static load rating). The conditions of the wear
test are shown in Table 5 and the results are shown inFig. 9. Figure 10 provides a representative example ofpost-test housing wear contour. The developed bearing
had 50% less housing wear than the current bearing. Thisresult confirms that housing wear caused by outer ring
creep has been suppressed on the developed bearing.

Table 5 Test conditions

4.1.2 Creep amount under a combined loadcondition

Radial load, kN

3.6

Axial load, kN

1.8

Rotational speed, min−1

10 000Lubrication

Oil application

05 000
Immersion

Current bearing
Developed bearing
50%
reduction

50

100

150

200

Test duration, hours

Fig. 9 Measurement results of housing wear

1.2

Outer ring contact portion

140%
reduction

0.8
0.6

Current bearing

0.4
0.2
0

Current bearing

Outer ring
contact portion

Developed bearing

Fig. 8 Measurement results of creep amount under combinedload conditions

Housing contour

Outer ring
contact portion

Measuredlocation

Wear amount

Creep amount, %11.9

Wear amount

Table 4 Test conditions

Housing wear amountThe effect on suppressing creep under a combined loadcondition, consisting of both radial and axial load, wasconfirmed. The creep amount measurement conditions
are shown in Table 4 and the results are shown in Fig. 8.
The results demonstrated that the developed bearing also
succeeded in suppressing creep by 40% compared to thecurrent bearing under a combined load condition.

Radial load, kN
Rotational speed,−1minLubrication

Developed bearing

Fig. 10 Contour of housing wear

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JTEKT ENGINEERING JOURNAL English Edition No. 1014E (2017)

−Development of Anti-Creep Ball Bearing for Outer Ring−

5. Confirmation of Setbacks
A high-load endurance test was performed on thedeveloped bearing to confirm the raceway peeling life
and outer ring fatigue strength. The result showed thatthe actual life was more than ten times greater than thecalculated life, which is also the case with the current
bearing. It was also confirmed that there were no issues
regarding outer ring strength due to the absence ofabnormalities such as cracks in the outer ring.

6. Conclusion
JTEKT has developed an anti-creep ball bearing forouter ring able to suppress creep caused by outer ringstrain without increasing the outer diameter by making
a groove in the outer ring outer diameter face, thus
ultimately reducing the amount of housing wear.
It was confirmed that the anti-creep ball bearing
for outer ring was effective in reducing housing wear
compared to the current bearing and there were nosetbacks in regards to bearing life and outer ring strength.
The adoption of the anti-creep ball bearing for outerring can reduce both the size and weight of the bearing
and, through its popularization, JTEKT wishes tocontribute to the realization of vehicles with enhanced
fuel economy and energy-saving benefits.

Y. ISHII****JTEKT ENGINEERING JOURNAL English Edition No. 1014E (2017)

T. JINBO**Automotive Bearing Development Dept., BearingOperations Headquarters
Experiment & Analysis Dept., Bearing Operations
Headquarters

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