Modelling of a radial-pistod hydraulic motor

The paper is concerned with the theoretical modelling of the torque-producing mechanism in a radial-piston, eccentric-type, hydraulic mvtor for low-speed operation. The major difficulty in such an malysis 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-jlm ejects 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 i s 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 lhese coefficient values in &he model. Such a model is inoatuable for establishing critical areas in the mechanism and for predicting the effect of component design changes on the rnotor,gerformance. * NOTATION A connecting-rod bearing contact angle piston area slipper area A, A s b slipper land width d0 slipper feed restrictor diameter ec difference between slipper and eccentric radii f c slipper friction coefficient piston friction coefficient connecting-rod bearing friction coefficient fP f h F piston pressure forc