A digital computer model to simulate the starting and low speed running characteristics of an Hydrostatic Transmissions Ltd hydraulic motor has been developed. The inelasticity of the oil columns connected to, and within, the motor cause extremely high instantaneous rates of change of pressure. This produces numerical stability problems if normal integration methods are employed and a 'pseudo-analytical' method has been developed to overcome this. A rigorous evaluation of the technique shows that it can be applied to a wide range of hydraulic simulations. The hydraulic motor is of the radial piston-eccentric type with the piston forces transmitted to the eccentric by a fully floating pentagon. A detailed analysis of the torque developed by the motor is derived with the motor internal friction described by the three coefficients of friction between piston-cylinder wall, piston-pentagon and pentagon-eccentric. The evaluation of these coefficients is from empirically derived MON torque efficiencies measured at different motor speeds and pressures. It has been shown conclusively by experimental means that the tor developed when the motor shaft is held stationary is dependent not only on the motor pressure level and angle of rotation, but c significantly, on the rate at which the pressure is raised to the measuring level. A simple theoretical model is used to explain the reasons for this effect and it is deduced that in general motor with significant internal friction will exhibit this effect. The overall model of the motor and system is compared to experience results and is shown to exhibit the sort of characteristics exp. The levels of motor pressure, torque and speed predicted by the are, in the first instance, less than those measured and this is shown to be due to the oversimplification of certain parts of the model.
|Date of Award||1976|