Theoretical and experimental studies on the steady-state performance of low-speed high-torque hydrostatic drives. Part 1: Modelling

Abstract

In this article the steady-state models of an open-circuit and a closed-circuit hydrostatic transmission (HST) drive have been developed to study their performances. A low-speed high-torque multi-stroke cam plate type radial piston motor is considered for both HST drives. Bondgraph simulation technique has been used to model the drives. The multi-bondgraph representation of the HST drives is presented; it takes into account the compression and expansion phases, which occur sequentially in the hydraulic motor. A reduced bondgraph model of the drives has been proposed, where various losses are lumped into suitable resistive elements. The relationships of the loss coefficients with other state variables, obtained from the reduced model, are identified through experimental investigation. The loss coefficients are found to have a non-linear relationship with the load torque and the supply flowrate. Using the characteristics of these loss coefficients, the steady-state performances of the hydrostatic drives are studied in Part 2 of this article (pg. 2675 of this issue).