An improved ultrasonic method for lubricant-film thickness measurement in cylindrical roller bearings under light radial load

• Oil-film thicknesses in roller bearings under light loads are measured by ultrasound.
• High pulse-repetition frequency is used and brings overlapping measurement regions.
• Ultrasonic reflection coefficients on the non-overlapping regions are studied.
• The measuring accuracy relies on the size of the non-overlapping region.
• The results show a good quantitative agreement with the EHL theory.

Focusing on measuring the oil-film thickness with ultrasonic approaches in roller bearings, a new feasible method is proposed to improve the measuring accuracy. The spatial resolution, which has great influence on the measuring accuracy, is mainly determined by the focus size of the ultrasound transducer. Under the light load conditions, the width of the Hertz contact area is smaller than the focus size, which results in overlapping measurement regions by the high pulse-repetition frequency and then brings about large measurement errors. By introducing reflection coefficients of sound pressure in the non-overlapping areas, the new method improves the measuring accuracy successfully. The experimental results are achieved from the real-time lubricant-film thickness monitoring system for cylindrical roller bearings, which show good agreement with the theoretical solutions.