Double-Row Needle Roller Thrust Bearings
for Car Air Conditioners and Automatic Transmissions
In order to set new standards for longer service life, lower torque, and lower noise, NTN Corporation has developed a series of double-row needle roller thrust bearings. By using two rows of needle rollers in each retainer pocket and by optimizing the roller shape, NTN has successfully minimized roller slippage, extending service life and reducing noise.
In order to improve fuel economy, there has been a trend in recent years toward reducing the amount and viscosity levels of lubricants used in automotive applications, resulting in more severe bearing lubrication conditions. While longer service life is desired, under these circumstances, roller slippage can reduce the service life of needle roller thrust bearings for automotive applications such as air conditioning compressors and automatic transmissions.
1) Automotive air conditioner compressors
In order to improve system performance, automotive air conditioning compressors use minimal amounts of low-viscosity lubricants, resulting in conditions which can reduce the service life of conventional needle roller thrust bearings. To make matters worse, even lower viscosity lubricants will be used in A/C compressors in the near future to provide better overall fuel economy.
Furthermore, as refrigerants switch from Freon to more environmentally-friendly alternatives such as CO2, high-pressure refrigerant compression will become prevalent, adding yet another factor reducing bearing service life.
NTN's new double-row thrust needle roller bearings for automotive air conditioning compressors use optimized roller shape and light-weight plastic retainers with double rows of needles to suppress roller slippage, reduce torque, increase service life, and minimize noise.
Performance comparison with single-row bearings
(Under NTN test conditions simulating use in automotive air conditioning compressors)
- Service life: 12 times improvement over baseline
- Rotating drag torque: 50% reduction from baseline
2) Automotive automatic transmissions
Because needle roller thrust bearings have small cross sectional areas and high load capacities, they are used extensively in automotive automatic transmissions. However, lowering the viscosity levels of automatic transmission fluid to reduce shift shock and improve fuel economy can result in more severe bearing lubrication conditions which can further reduce service life of conventional needle roller thrust bearings.
NTN's new needle roller thrust bearings for automatic transmissions feature double rows to suppress roller slippage while using optimized roller shape to provide increased service life and reduce drag torque and noise. In addition, NTN's new manufacturing technique called "full-circumference tight seal staking" produces a retainer with a new and improved shape, significantly increasing retainer strength.
Performance comparison with single-row bearings
(Under NTN test conditions simulating automotive automatic transmission applications)
- Service life: 300% improvement over baseline
- Rotating drag torque: 40% reduction from baseline levels
- Retainer strength: 1.6 times better than conventional design
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For automotive air conditioning compressors | For automotive automatic transmissions | New retainer for automatic transmission bearings |
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