Abstract: An electronic control system for pressure and flow control of variable displacement pumps consists of a closed loop system of operational amplifiers which provide continuous control of the volume modifying element in the pump. In a variable displacement vane pump application a command flow control signal and a feedback signal representative of the position of the adjustable cam ring in the pump are applied to an integrating amplifier to develop a signal for application to an electro-hydraulic valve in the pressure compensating portion of the pump. A command pressure signal is compared with the control signal to limit the latter to a level, thereby providing pressure control for the pump. Slip compensation is effected in the control system by utilizing a portion of the control signal to provide proportional modification of the command signal.

Abstract: A fluid pressure system includes a source of water pressure 12, a first fluid motor 27 actuated by the pressurized water, a variable displacement hydraulic pump 11, and a second fluid motor 14 actuated by hydraulic fluid from the pump. The pump includes a control device 20 having a control chamber for changing the displacement of the pump. A proportional valve 17 is hydraulically connected to the control chamber for changing the pressure in the control chamber. The proportional valve includes a housing 34, 35 and a diaphragm 36 dividing the housing into first and second chambers 39 and 41. The first chamber is connected to the first fluid motor, and the second chamber is connected to the pump inlet. The pump control chamber is hydraulically connected to the second chamber through a variable orifice, and the size of the orifice is changed in response to the pressure in the first chamber and first fluid motor.