Modelling of a Radial-Piston Hydraulic Motor

Abstract

The paper is concerned with the theoretical modelling of the torque-producing mechanism in a radial-piston, eccentric-type, hydraulic motor for low-speed operation. The major difficulty in such an analysis is the description of the frictional losses which, at low speeds, principally result from boundary lubrication conditions. The level of friction is also dependent on the distribution of the transferred forces and the amount of distortion in the bearings These forces vary during the pressure cycle, and squeeze-film effects are introduced between the bearing faces during the period of time following the introduction of pressure into the cylinder. The interaction between the frictional effect in the connecting rod bearing and the operation of the hydrostatic slipper is central to the modelling process. Friction coefficients in the bearings are determined that predict similar efficiencies to those obtained from test measurements on a low-speed motor. The evaluation of internal motor parameters is then carried out using these coefficient values in the model. Such a model is invaluable for establishing critical areas in the mechanism and for predicting the effect of component design changes on the motor performance.