A wear model for EHL contacts in gerotor type hydraulic motors

Abstract

The heart of gerotor motors is a gear-set. The gear-set consists of an inner gear which is rotating and orbiting in contact with an outer gear. Wear in these contacts is investigated experimentally and with a numerical implementation of an Archard based wear model in combination with a load sharing concept. The model utilizes the symmetry of the motor and is based on a three-scale approach to estimate the wear on the gears. The global model calculates contact forces, relative surface velocities and contact radii in the contacts between inner and outer gear. The calculations performed on the local scale are used to collect information about the influence of the surface roughness on lubricant film thickness. The wear depth is calculated on a semi-local scale, involving only one tooth on the outer gear. In partial elastohydrodynamic lubrication, load is carried by the part of the conjunction where there is direct contact between the mating surfaces and by the lubricant pressure. In the wear model, wear only occurs as a direct consequence of contact between the mating surfaces. Experimental results are compared with the model predictions for equivalent running conditions. The wear predicted by the model agrees with the experimental results. For this reason, it is concluded that wear in the gerotor motor is dominated by the wear mechanisms which are considered in the tribological model.