TECHNICAL REPORT

Development of Isolated Needle Bearing
J. BRUBAKER

Automotive drivetrains are complex mechanical systems that generate a wide range of noise & vibration.
Automakers are continuously working to improve or suppress the noise & vibration in order to meet the needs ofthe market for a quiet and comfortable car. JTEKT has developed & produced a small isolator which attaches to aroller thrust bearing for controlling the noise produced by the bearing or transmitted through it by the drivetrain.
The developed product reduces noise on average by 10 dB and minimized the potential of increased weight. This
report presents a revolutionary product which reduces application noise and vibration by the addition of an isolator
to a conventional bearing.
Key Words: noise & vibration, NV, isolator, thrust needle roller bearing, automatic transmission, compact

1. Introduction
Passenger comfort is an ever increasing priority in theautomotive market. The modern automobile is a complex
assembly including mechanical systems which generatevarious levels of noise & vibration (NV).
NV must be regulated to ensure the quietness of theautomobile system.
Rolling bearings are a component used in the drivetrain
which not only increase efficiency but also contribute &influence NV. JTEKT has taken the initiative concerning
NV within thrust needle roller bearings used in automatictransmissions (written in following as "AT", Fig. 1).
The following introduces the innovative newtechnology of the compact bearing isolator (Fig. 2),
which dampens bearing vibration and enables systemlevel NV reduction.

Fig. 1 Thrust needle roller bearing isolator for Automatictransmission

2. Baseline
An evaluation was carried out to assess the influence ofthrust needle roller bearings to passenger comfort of AT
equipped automobiles.
Fig. 2 Developed isolator & bearing assembly

2. 1 Test Piece
To understand the current situation, two thrust needle
roller bearings were obtained from ATs with and without
acceptable NV.

2. 2 Test Equipment/Test Conditions
The test equipment in Fig. 3, installed in an anechoicroom, is used for the bearing-only NV evaluation. The
test conditions are shown in Table 1.

JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

The test equipment was developed specially to measureand analyze the characteristics of NV created by thrustroller bearings at differing speeds and loads.
NV characteristics were analyzed through audible
sounds and vibration signals using a microphone and anaccelerometer, respectively.
The accelerometer is mounted onto the top plate, whereonly the vibration of the test bearing is transmitted.

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−Development of Isolated Needle Bearing−

2. 3 Test Results

Table 1 Test condition

Results for the bearing-only test and general inspection
are compiled in Table 2. The results of these two tests
confirmed that there were no differences in the bearings.
Since the bearings did not produce a vibrationdifference, attention was focused on the transfer ofvibration within the AT, with the development objectiveof reducing vibration transfer across the bearing.

3. Product Development
An NV characteristic improvement plan wasestablished and confirmed.
The development results are shown below.

3. 1 Layout Proposal
The placement of a material with superior damping
characteristics in between the bearing and housing wasproposed as the basic layout to reduce vibration transfer.
A high-polymeric material was placed on the location
shown in Fig. 4, to act as the component which blocks or
isolates the vibration transfer pathway.
The high-polymeric material must have an optimum
structure able to preserve the durability of the roller
bearing and must provide cost effectiveness, productivity,and compactness, while exhibiting the maximum damping
properties.

Dynamic Load Rating (C)13.8 kN

Test Load

1.62 kN

Rotational Speed

1 000 min−1

Lubrication

ATF drop

Table 2 Test result
Noisy AT

Quiet AT

Bearing only
NV testresult84-86 db

84-86 db

Bearing
Inspection
resultOKOK

AT：Automatic transmission

Polymer Isolator

Fig. 4 Original concept layout
90

TEST BEARINGDecibels, dB85

ISOLATOR

807570TESTBEARINGdB METERBearing
only1mm2mm

3mm

Isolator thickness, mm

Fig. 5 Isolator thickness effect
ACCELEROMETER
25.6 kHz max

LOAD
Dispersion of NV in groove

backupisolator

Fig. 3 NV test equipment
Bearing

Fig. 6 Groove function

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JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

−Development of Isolated Needle Bearing−

3. 2 Isolator Optimization
3. 2. 1 Isolator Material
A reinforced polyamide (with an excellent AT
performance history) was selected as the isolator material.

Outer

3. 2. 2 Isolator Thickness
The test results shown in Fig. 5 demonstrate theinfluence of isolator thickness on NV. The applicationof a reinforced polyamide isolator was verified to have aremarkable reduction in NV. It was also confirmed that
NV has a tendency to drop with an increase in isolatorthickness.

Inner

Parallel

Type-A

Parallel
Sweep

Parallel
Sweep
Open

Type-B

Type-C

Fig. 7 Groove style90

3. 2. 3 Innovation
85
Decibels, dB

Next, methods to further reduce NV while maintaining
or reducing isolator thickness were examined.
As shown in Fig. 6, grooves were cut in the backup
side of the isolator, forming a structure to disperse thevibration.
The groove styles are arranged in three types, shown inFig. 7.
The A type features grooves perpendicular to therolling direction of the roller; the B type features grooves
at an angle to the rolling direction; the C type features
angled grooves which increase in width from the inside tooutside diameters.
Samples of each were used in tests under the conditionsof both the test equipment in Fig. 3 and in Table 1. Thetest results are shown in Fig. 8.
The C type produced the best results, verifying thatgroove angle combined with increasing groove width was
the most effective.

8075

70
Bearing
only

3mm
Nogroove

3mm
Type-A

3mm
Type-B

Fig. 8 Groove effectType-C3. 3 Final Isolator Specifications

2mm

Fig. 9 Final result
40

Weight, gSince the grooves dramatically improved the NVperformance, the thickness of the isolator was reduced
to minimize the weight and packaging impact on the ATsystem (Fig. 10).
Similarly with the comparison of NV for the conditionsin Table 1 and the test equipment in Fig. 3, the results
shown in Fig. 11 confirm the vibration dispersion effectsof the grooves were more effective than increasing thethickness of the isolator.
The improvements of NV characteristics are shownover the entire frequency range in Fig. 12.

35

The developed compact bearing isolator was successful
in meeting the needs of the market concerning comfort,
cost & packaging and is now in volume production.

JTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)

Isolator
Bearing30254. Conclusion

3mmType-C

3mm No groove

2mm Type-CFig. 10 Weight benefit

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−Development of Isolated Needle Bearing−

The Greenville Technical Center will use its abundant
knowledge and experience to propose this & otherinnovations, continuing to provide solutions with valuable
technology which exceeds customer's expectations.

90-9.7 dB（-11.3%）

Decibels, dB

85807570

Bearing
only

3mmNo groove

2mm Type-C

Fig. 11 NV benefit
1.2Bearing only
1Bearing with Isolator

g‘s

0.8
0.6
0.4
0.2
001 600

3 200

4 800

6 400

8 000

9 600

11 20012 800

HzFig. 12 FFT comparison data

J. BRUBAKER**48

KOYO BEARINGS NORTH AMERICA LLC
Greenville Technical CenterJTEKT ENGINEERING JOURNAL English Edition No. 1011E (2014)