Prediction of Spur Gear Mechanical Power Losses Using a Transient Elastohydrodynamic Lubrication Model

Abstract

A model to predict load-dependent (mechanical) power losses of spur gear pairs is proposed based on an elastohydrodynamic lubrication (EHL) model. The EHL model includes gear-specific time variations of all key contact parameters such as the rolling and sliding velocities, radii of curvature, and normal load such that a single continuous analysis of a tooth contact from its root to tip can be performed under any lubrication condition ranging from full-film to mixed EHL or boundary lubrication conditions. Predicted transient pressure and film thickness distributions are used to determine the instantaneous rolling and sliding shear within the lubricant, from which the gear mesh mechanical power losses are determined. Correction factors are introduced for the power losses to account for the thermal effects. The accuracy of the proposed model is assessed through comparisons to published spur gear efficiency experiments. The contribution of the rolling action to the total power loss is quantified to show that the rolling losses are indeed not negligible.