Behavior of EHD Films During Reversal of Entrainment in Cyclically Accelerated/Decelerated Motion

Abstract

Transient elastohydrodynamic lubrication, in which operating parameters such as speed, load or curvature vary over time, occurs in many machine elements including cams, gears and reciprocating devices. It also occurs in rolling-element bearings at the start or stop of motion. This paper presents findings of an experimental study on the behavior of EHD films during reversal of entrainment in reciprocating motion. An optical interferometric technique, which enables interference images to be captured at a rate of 1000 measurements per second, was used to monitor film thickness in the lubricated contact between a transparent flat and a steel ball run in a linear accelerated/decelerated motion. The results show that minimum film thickness does not occur at the position of zero entrainment as predicted theoretically, but with a certain time delay. This delay, as well as the minimum thickness of the film, is highly dependent upon the rate of change of entrainment speed. Comparison of experimental results with an existing theoretical model of minimum film thickness during reversal of entrainment was also carried out. Presented at the 56th Annual Meeting in Orlando, Florida May 20–24, 2001