Elastohydrodynamic Lubrication in Extended Parameter Ranges — Part I: Speed Effect

Elastohydrodynamic Lubrication (EHL) has been given great attention in the last 40 years. Conventional theories by Dowson and Higginson for line contacts and Hamrock and Dowson for point contacts have been among the most important contributions and widely used in industries. However, commonly used film thickness formulae, developed more than 25–40 years ago when the computational power was very limited, were originally from curve-fitting based on limited numbers of numerical solutions obtained in relatively narrow parameter ranges. Actual operating conditions in typical engineering applications, such as gears, bearings, cams and traction drives, sometimes fall far outside those parameter ranges, and prediction through extrapolation is often difficult to give satisfactory results. As the computer technology and numerical simulation methods have been advancing greatly, one can now analyze cases in extended parameter ranges that cover various practical applications under severe conditions. This paper is Part I of a recent study, focusing on the speed effect on the EHL film thickness. In a relatively narrow speed range, the present results agree well with those from the conventional theory. In the extended speed and load ranges, however, the relationship between the film thickness and the rolling speed may no longer obey the simple power law described by the conventional theory. It appears to be a complicated function of speed, load and contact ellipticity. Commonly used formulae may often overestimate the film thickness especially when the load is heavy and the speed is not high.