IMPROVEMENT OF TOTAL EFFICIENCY OF HYDROSTATIC TRANSMISSION BY USING OPTIMIZED CONTROL

Abstract

A basic hydrostatic transmission consists of a variable hydraulic pump and variable hydraulic motor. The most popular strategy is to control the units in sequence. From standstill up to a speed limit set by the maximum pump displacement, the output speed is controlled by the pump. Further increase of the output speed is achieved by decreasing the motor displacement. This way to control of HST is not best thinking of total efficiency. Efficiency of the hydraulic pump and the hydraulic motor are function of pressure, rotating speed and control angle. If it is possible to control independently the hydraulic motor and the hydraulic pump, it can be optimized total efficiency for every operating point (torque and rotating speed of the hydraulic motor). In this study control settings of the hydraulic pump and the hydraulic motor are optimized for each operating point so that the total efficiency should be as good as possible. These optimized efficiencies are compared to efficiencies from traditional control. The entire operating band was studied (rotating speed and torque of the motor) using simulation. Exactly verified simulation models of the HST were used. The base of simulation models was measured data from earlier studies. The results show that efficiency can be improved when the load is low. Power loss decreased maximum about 1.5kW.