TECHNICAL REPORT

Development of Next Generation Low Friction Torque TaperedRoller Bearing (LFT-IV)
D. OKAMOTO A. SUZUKI T. AIDA

K. NAITOWe JTEKT have been developing low friction torque bearings from the viewpoint of environmental issues such as
global warming. In particular, we are more advanced than competitor companies regarding the development of low
friction tapered roller bearings (TRB), which at JTEKT are called our "LFT series". Furthermore, we have engaged
in the development of the new TRB, known as the "LFT-IV", and have achieved a 50 percent reduction in friction
torque compared with the previous product ("LFT-II") by utilizing CAE tools.
Key Words: low friction torque, tapered roller bearing, cage, resin, CFD, LFT-IV①Rolling viscosity resistance

1. Introduction
In response to environmental issues such as global
warming, needs such as reduced friction loss, higher
efficiency and lower energy consumption are growing
stronger year after year. Particularly in regards toautomobiles, the CO 2 emission regulations of eachcountry are becoming stricter every year and there
are expectations of low friction technology for rolling
bearings. JTEKT has been engaging in ongoing initiatives
to advance the low torque specifications of tapered roller
bearings (LFT series) contributing to the downsizing
and weight reduction of units with compact and high1)
load capacity designs. As a result, the LFT-III wasdeveloped in 2006, which provided 50% less torque2)
loss than the standard bearing (40% less than LFT-II ).
However, in order to meet market requirements, which
grow tougher year after year, JTEKT has developed a newproduct (LFT-IV) with even less friction loss, achieving
a reduction of up to 50% compared with the LFT-II. This
report discusses the results of this development.

2. Development Aims

Lubricant flow

失②Agitating resistance③Sliding resistance between the innerring back face rib and roller end faceFig. 1 Elements of tapered roller bearing torque①Rolling viscosity resistance②Agitating resistance③Sliding resistance between
the inner ring back face riband roller end faceFig. 2 Factors contributing to friction torque and theircontribution ratio

Three main factors leading to friction loss in a taperedroller bearing are ①rolling viscosity resistance, ②lubricant agitating resistance and ③sliding resistance
between the inner ring back face rib and roller end face3)(Fig. 1) . Figure 2 shows the contribution ratio of each.
Factor 3 has been reduced in the LFT-I, factor 1 in theLFT-II and factors 1 and 2 in the LFT-III (Table 1).

JTEKT ENGINEERING JOURNAL English Edition No. 1014E (2017)69

−Development of Next Generation Low Friction Torque Tapered Roller Bearing (LFT-IV)−

Table 1 Low friction torque tapered roller bearings
Applied/not applied＊２
AppliedReduction＊１technology
factor LFT-Ⅰ LFT-Ⅱ LFT-Ⅲ LFT-Ⅳ
Optimization ofroughness and proﬁle③○←←←
for large rib androller end face
Raceway crowning①−○◎←
Optimization of①②−−○←
internal geometry
Inﬂow control of②----○◎lubricating oil＊１ ①Rolling viscosity resistance②Agitating resistance of lubricant③Sliding resistance between the inner ring backface rib and roller end face
＊２ ○：Applied ◎ Further improved

For the LFT-III, in order to reduce lubricant agitating
resistance (factor 2), the amount of lubricant whichflows into the bearing (lubricant inflow) from the cage issuppressed. In order to suppress the amount of lubricant
inflow further, it is necessary to reduce the clearances
between the inner ring and cage and the outer ringand the cage at the small end of the cage, as these are
the locations where lubricant enters. However, if theclearance becomes too small, there is a risk that lubricant
becomes blocked off entirely considering temperaturechange and dimensional variance, therefore it is necessary
to reduce flow while maintaining clearance to a certain
extent. For this development project, JTEKT investigatedwhether or not it was possible to achieve both a clearance
which did not become blocked and suppress lubricant
inflow by changing the shape of the small end face of thecage and altering the flow of lubricant near the inlet. Also,
resin with a high degree of freedom in regards to shape
was adopted as material for the cage.

3. Shape Optimization Utilizing CAE
In recent years, systems and equipment have become
increasingly high-function, therefore the components usedin them are becoming more sophisticated and complex.
This means products with even higher reliability thanin the past are being sought by consumers. Meanwhile,
there is a need to shorten the time taken for design andevaluation, therefore utilization of CAE technology
early on in the development process is essential. For
this development project, CAE technology was used tooptimize the cage shape.
The concept for the newly developed LFT-IV wasto reduce the amount of lubricant inflow through being
innovative with the shape of the cage’s small end face.
To achieve this, it is important to understand the dynamic
characteristics of the lubricant when it flows into thebearing. However, it is difficult to obtain sufficient
data with experiments alone, therefore by using fluid
analysis technology to make the flow visible and quantify
characteristics, it became possible to evaluate changes incharacteristics due to shape improvement cost-effectively
and with better speed.
The analysis conditions are shown in Table 2. Aparameter study was conducted for the dimensions shownin Fig. 3 and the shape for which lubricant inflow isminimum was found. Figure 4 shows the results of a fluid
analysis on the clearance between the outer ring and cage.

Table 2 Simulation conditions
ItemConditions

Rotational speed

5 000 min−1

LubricantGear oilTemperature

80℃
Uncompressed, constanttemperature, turbulent, steady

OtherOuter ring
ABCCageRoller

EDF

Inner ring

Fig. 3 Parameter study of tapered roller bearing

70

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

−Development of Next Generation Low Friction Torque Tapered Roller Bearing (LFT-IV)−

Fast

Flow velocity

Cage

Flow rate

large
Outer ring

small

small
small

CB

Slowlarge

large

Fig. 4 Simulated results of velocity vector and flow rate

The results of this analysis showed the following typesof shapes would be advantageous in reducing the amountof lubricant inflow.
•Regarding the positional relationship of the inner ringand cage, the cage end face is towards the inside•Regarding the positional relationship of the outer ringand cage, the cage end face is towards the outside•An incision is made in the side of the cage so that thecross-section looks like a less-than sign (<)•Reciprocal interaction was recognized with thedimension parameters. Also, there is a max./min.
value and if these are exceeded or not reached, theeffectiveness will be diminished.
Based on the above knowledge, the final shape for thecage small end was determined (Fig. 5).

LFT-III

LFT-IV

Fig. 6 Simulated results of dynamic oil flow

4. LFT-IV Performance
4. 1 Oil Flow Rate to the Bearing

Fig. 5 Optimized shape of LFT-IV by utilizing oil flow
simulation

In order to confirm the effect of controlling lubricant
inflow, we created a model simulating a oil flow rate
testing machine (details discussed later), and analyzed
the behavior of lubricant oil for gas-liquid two-phaseflow. The results of this analysis are shown in Fig. 6.
With the LFT-IV, there is less lubricant inside the bearing,
therefore it is obvious that the amount of lubricant inflow
is limited. Our analysis showed that oil flow rate is−1
reduced by approximately 95% (3 000 min ).

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

The amount of oil flow through to the bearing wasmeasured on the LFT-IV, which featured an optimizeddesign cage based on fluid analysis. The result wascompared with the model’s predecessor, the LFT-III.
Table 3 shows the test conditions, while Fig. 7 shows
the testing equipment and Fig. 8 shows the results of theamount of oil flow rate measurement. When rotational−1speed is between 1 000 and 4 000 min , the reduction
ratio of the oil flow rate is between 87 and 92% less for
the LFT-IV in comparison with the LFT-III (Fig. 8), while−1
at 3 000 min , the test result is a reduction of 91%, whichis in good agreement with the fluid analysis result of 95%,
therefore it can be said that it is possible to accurately
predict oil flow rate using fluid analysis.
Table 3 Test conditions
Rotational speed
LubricantTemperature

1 000〜4 000 min−1
Gear oil50℃

Oil Supply method Circulating lublication71

−Development of Next Generation Low Friction Torque Tapered Roller Bearing (LFT-IV)−

1.4

Load cell
Air bearing

Rotational torque (Nm)Load

Oil supply

Lubricant

LFT-II

1.2▲56％

LFT-III

1.0

LFT-IV

0.8

▲46％
?46％

0.6

ً32％
▲32％

▲16％

0.4
0.2
0.001 000

2 000

3 000

4 000

5 000−1

Rotational speed (min )Fig. 9 Results of torque measurement

Test bearing
Arbor

Turntable

4. 3 Effectiveness on an Actual Vehicle
Fig. 7 Testing equipment

15Oil flow rate (l/min)

LFT-III
LFT-IV
105
Reduction ratio
87%

Reduction ratio
89%

Reduction ratio
91%

Reduction ratio
92%

00

1 000

2 000

3 000

4 000

5 000

−1

Rotational speed (min )Fig. 8 Results of measurement of penetrated lubricant

Next, in order to verify effectiveness on an actualvehicle, we assembled the LFT-IV on a rear differentialfor a passenger vehicle and measured the amount oftorque necessary to rotate the pinion shaft. The testconditions are shown in Table 4, while the testing
equipment is shown in Fig. 10. After running in the test
bearing, it was assembled on the pinion shaft support
portion with a preload of 3 kN. We measured the torque ofthe pinion shaft in isolation, making sure the pinion gearand ring gear did not mesh. Also, we used another motor
to rotate the ring gear at a speed which correspondedwith the rotational speed of the pinion, thus making thelubricant flow inside the differential the same as that ofan actual vehicle. Figure 11 shows the results of thisrotational torque measurement. By adopting the LFT-IV,
loss can be reduced by around 50% compared with theconventional type (LFT-II).
Table 4 Test conditions

4. 2 Bearing Individual Torque
We confirmed the effect on reducing rotational torquefor the LFT-IV (test conditions and testing equipment
were identical to when oil flow rate was measured). The
results of measuring the bearing’s individual rotational
torque are shown in Fig. 9. Results confirm that, for theLFT-IV, rotational torque has been reduced by up to 50%
compared with the conventional type (LFT-II) and up to30% compared with the LFT-III. Therefore, the LFT-IV
has the ability to suppress the amount of lubricant thatoil flow rate to the bearing, and achieves low torque by
reducing the agitating resistance of lubricant.

−1

Rotational speed

2 000 minLoad

No-load (preload 3.0 kN)

LubricantGear oilTemperature

50℃

Differential carrier
Drive pinion

Ring
gear
drive
motor

Tested bearing
Piniongear
drive motor

Torquemeter

No meshing of the pinion gearand ring gear

Fig. 10 Testing equipment

72

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

−Development of Next Generation Low Friction Torque Tapered Roller Bearing (LFT-IV)−

Rotational torque (Nm)

3.0
2.5
2.0
1.5
1.0
0.5
0.0

LFT-II

LFT-III

LFT-IV

Fig. 11 Results of pinion torque measurement

5. Conclusion
For the LFT-IV, by using resin for the cage materialand controlling lubricant flow at the small end face ofthe cage, the amount of lubricant which oil flow rate
to the bearing was reduced, resulting in a reduction ofbearing friction torque of up to 50% compared to theconventional type (LFT-II) and up to 30% compared tothe LFT-III. During development, a parameter study using
fluid analysis was conducted to efficiently determine theoptimal shape of the cage.
If the LFT-IV is used as a support bearing for thepinion shaft of a differential, where a particularly large
amount of highly viscous lubricant is used, an evengreater effect is had on reducing friction loss. JTEKT willcontinue to develop highly efficient products, which willserve an increasingly important role for their contribution
to alleviating environmental issues.
*1 LFT is a registered trademark of JTEKT Corporation.

References
1)

2)

3)

Y. asai, H. Ohshima: Development of Low Friction
Tapered Roller Bearings, Koyo Engineering Journal, No.
143 (1993) 23. (in Japanese)
H. Ooshima: Low Friction Torque Bearings forDifferential Pinion, JTEKT ENGINEERING JOURNAL,
No. 1009E (2012) 37.
H. Matsuyama: High Efficiency and Tribology in RollingBearings, JTEKT ENGINEERING JOURNAL, No.
1009E (2012) 108.

D. OKAMOTO*

A. SUZUKI***

T. AIDA**

K. NAITO*****

New Business Promotion Dept.
Experiment & Analysis Dept., Bearing Operations
Headquarters*** Automotive Bearing Development Dept., Bearing
Operations Headquarters

JTEKT ENGINEERING JOURNAL English Edition No. 1014E (2017)73