Measurement of Oil-Film Thickness and Observation of Oil Distribution in High-Speed Deep-Groove Ball Bearings

High-speed deep-groove ball bearings for the eAxle of electric vehicles must adapt to higher rotational speed conditions, because eAxle motor speed increases to downsize the unit. Therefore, it is necessary to clarify the lubrication process of ball bearings at the high rotational speeds to prevent seizure and wear. The oil-film thickness between outer-ring and ball, and the oil distribution around balls in 6008 deep-groove ball bearings incorporating experimental quartz outer rings were measured under high-speed conditions, with speeds exceeding 20,000 min-1. These measurements were carried out by employing the three-wavelength flash-light optical interferometry method and the UV-LED light-induced fluorescence method. It was found that the oil-film thickness did not increase even when the rolling speeds increased, which is in contrast to the EHL theory under sufficient lubrication condition. Contrary to the EHL theory, these phenomena can be attributed to the oil starvation and lowering effective viscosity of oil containing bubbles resulting from aeration under high-speed conditions.