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Bearings - 2012-01-31

NSK Ltd. announced that it has developed a more compact, lightweight, longer-lasting lipped thrust needle roller bearing for use in automatic transmissions.

Low viscosity transmission oil is commonly used today to improve transmission efficiency, but this creates lubrication challenges. NSK’s new product is designed for outstanding performance in severe lubrication conditions and also helps to improve fuel economy.

Development background  
In recent years, automakers looking to improve fuel economy, reduce gear shift shock and raise power transmission efficiency have increasingly turned to multi-stage automatic transmissions. Low viscosity transmission oil is often employed in these transmissions to reduce agitation resistance, which has a negative impact on transmission efficiency. This type of oil presents lubrication challenges for the thrust needle bearings typically used in transmissions. Meanwhile, demand is rising for more compact, lightweight transmission bearings that can help improve fuel economy in hybrid electric vehicles (HEVs). But when HEVs run on the electric motor alone, the oil pump sometimes stops, which in turn means that the thrust needle bearings in the transmission have to function on lean lubrication. NSK’s new lipped thrust needle roller bearing will help improve fuel economy and reduce CO2 emissions by meeting the need for more compact and lightweight bearings that are more than ready for demanding automotive applications. Product features are summarised below.

Product features
Thickness greater than 2.5 mm, made possible by using a steel material with improved press workability

The new product is made of NSK’s proprietary PCR5 steel material, which features improved toughness achieved by reducing the amount of carbon and silicone and increasing the amount of chrome. This enabled the new product to be press worked despite having a thickness greater than 2.5 mm.

Carbonitriding
NSK’s propriety PCR5 steel—employed in the lipped thrust race—has been carbonitrided for enhanced toughness, surface hardness and fatigue strength.

Effects
1. Service life at least three times longer than a conventional thrust race
2. 20% more compact and lightweight than a conventional thrust race
3. Usable under challenging, low viscosity oil lubrication conditions, such as in HEVs

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