Electronic constant speed control for a hydrostatic transmission

Abstract

An electronic constant speed control for a hydrostatic transmission having a variable displacement hydraulic pump with a displacement controlling member movable to various positions at either side of a neutral position and having an input shaft connectable to a prime mover and a hydraulic motor having an output shaft, an electric controller for positioning siad displacement controlling member, a command potentiometer for establishing a set constant speed signal representing a desired constant speed between zero and maximum speed in either direction of rotation for said output shaft, a speed detecting device for establishing a pump input shaft speed signal, a circuit for generating a position control signal representing the required position of the displacement controlling member for the set speed which is responsive to the constant speed and pump input shaft speed signals, a speed detecting device for establishing an output shaft speed signal, a circuit for comparing the output shaft speed signal with said set constant speed signal and integrating any error therebetween and generating a speed error control signal, and a summing circuit for summing said position and speed error control signals to provide a control signal to said electric controller.