Elastohydrodynamic Lubrication in Extended Parameter Ranges — Part II: Load Effect

Abstract

The elastohydrodynamic lubrication (EHL) analysis has been extended to wide parameter ranges in order to satisfy the needs in design optimization of heavy-duty mechanical components, such as gears, bearings, cams and traction drives, especially when operated under severe conditions. Following the first part of the present study that investigates the effect of speed on the EHL film thickness, this paper is focused on the effect of load in an extended load parameter range that covers six orders of magnitude. Obtained results show that, when the load is moderate within a relatively narrow range, the present results agree well with the conventional EHL theory. If the load is light and the speed is high, the film thickness may sometimes go up and down then up again with continuously decreasing load due to the transition from EHL to the pure hydrodynamic lubrication, in which piezo-viscous and elastic deformation effects are negligible. When the load is heavy and the speed is not high, the EHL film may drop quickly as the load increases, and commonly used EHL formulae may sometimes overestimate the film thickness. At a certain constant speed there appears to be a critical load, beyond which the EHL film breaks down. The higher the speed, the heavier the critical load would be. In the extended speed and load ranges the relationship between the film thickness and the load may no longer obey the simple power law described by the conventional theory, but rather a complicated function of speed, load and contact ellipticity. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Cancun, Mexico October 27–30, 2002