Understanding overall efficiency of hydrostatic pumps and motors

摘要

Pump and motor efficiency is a complex subject, to such an extent that most of the available models describing efficiency today rely on experimental data. In spite of that, mathematical models relating efficiency to pressure and angular speed have been proposed throughout the years. In all these models, volumetric and mechanical efficiencies are separately built from flow and torque losses relations. The overall efficiency model is then obtained by multiplying the volumetric and the mechanical efficiency equations. In this paper, we show that the overall efficiency equations must be developed from an energy balance and show that the simple multiplication of mechanical and volumetric efficiencies can potentially lead to inaccurate results. We then obtain a generalised equation relating the overall efficiency to pressure and angular speed for both pumps and motors and show how the resulting model can be fitted to actual experimental data.