November 27, 2020

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NSK develops automobile transmission bearing with solid lubricant film

NSK develops automobile transmission bearing with solid lubricant film
Photo courtesy of NSK.

Japan’s NSK Ltd. announced that it has developed a bearing with solid lubricant film for various transmissions, such as automobile automatic transmissions (AT) and continuously variable transmissions (CVT).

This product contributes to higher automobile reliability by reducing wear due to creep, a phenomenon where the outer ring of the bearing starts to shift in transmission cases. NSK is targeting JPY 2 billion (USD 19.4 million) in global annual sales of this product in 2020.

In recent years, demand for more compact, lightweight transmissions have become stricter, with the need to improve automobile fuel efficiency, resulting in thinner transmission housings and bearings. Due to this thinness, with time, the housing can slightly deform, leaving a gap between the housing and bearing, which in turn can cause the outer ring of the bearing to lose its shape. This leads to creep, a phenomenon where the outer ring starts to very gradually rotate when it should not. Creep eventually causes housing wear.

Housing wear due to creep amplifies transmission vibration, resulting in improper rotation and creating wear debris, which adversely affects the functionality of parts within the transmission, thereby reducing automobile reliability and comfort.

Preventing creep generally involves mechanically attaching the bearing to the housing, installing an O-ring, and thickening the outer ring. These measures, however, are costly, require parts to be larger, and make it more difficult to assemble the bearings. To solve these issues, NSK set out to develop a product that would not cause housing wear even if some creep occurred.

This product includes a low-friction, solid lubrication film coating on the outside surface of the outer ring, lowering the friction coefficient to reduce housing wear even if the fixed outer ring starts to creep. Since simply coating the outside surface of the outer ring can prevent wear, there is no need to increase bearing size or change the construction of the bearing periphery, thus maintaining ease of assembly.

The solid lubricant film consists of a processed substrate on the surface of the bearing base material and a bonded film coating on the substrate (resin binder, solid lubricants, friction and wear adjusters).

This product eliminates the need to make bearing dimensions larger, prevents T/M housing wear due to creep, and contributes to better automobile fuel efficiency and reliability.

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