Control arrangement for a hydrostatic system

Abstract

In many hydrostatic systems, the variable displacement pump is controlled by an operator moving a directional control valve to provide pressurized fluid to the displacement changing mechanism thereof which in turn varies the displacement responsive to the degree of pressurized fluid being directed to the displacement changing mechanism. In order to insure that the displacement of the Variable displacement pump is at the desired displacement, various forms of follow-up mechanisms have been required. These follow-up mechanisms are many times complicated and expensive to add to the hydrostatic system. In the subject arrangement, the speed of the pump input shaft and the speed of the motor output shaft is sensed (R,S) and the signals directed to a microprocessor which in turn processes the signals and directs a control signal (P) to a solenoid operated proportional valve. The solenoid operated proportional valve moves in response to the control signal and directs pressurized fluid to the displacement controller of the variable displacement pump to change the displacement thereof. Once the speed of the output shaft is achieved, the microprocessor modifies the control signal to maintain the variable displacement pump at the needed displacement position to maintain the desired speed of the output shaft to a work system. This arrangement provides an accurate control of the displacement of the variable displacement pump without the need of providing complicated follow-up mechanisms and/or servo mechanisms.