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This paper investigates and describes the fatigue mechanism in bearings for automotive alternators. We have analyzed the peculiar microstructure change found in these bearings. We have also investigated the effects of grease properties, vibration, and elastic deformation of the outer ring. By analyzing the bearings used in actual engine tests and grease tests for fundamental characteristics, we were able to conclude that the fatigue causes were two-fold: load amplification caused by resonance and high bending stresses caused by elastic deformation of the outer ring. As a practical result, we were able to adopt a newly formulated grease which decreased the vibration level and the peak rolling element load. This led to the development of longer life bearings for automotive alternators.

Lubricant contamination is a frequent hazard to bearing life in automotive transmissions. The “Sealed Clean” bearing concept uses dynamic, rubber seals to exclude significant contamination from transmission bearings. However there is often insufficient space in a roller bearing application to accommodate seals. HTF steel specifications and processing were developed for such applications. Debris within a rotating bearing will create indentations in the raceway. Contact stress is concentrated at the indentation edges and fatigue damage is accelerated. A indentation's diameter and edge radius determine the stress concentration between the ball and raceway. The HTF steel specification and tightly controlled heat treatment processing have been developed to provide long life despite the contamination hazard. Testing confirms the effectiveness of the new material.