Hydraulic fluid supply system with variable pump-displacement arrangement

Abstract

Hydraulic fluid supply system for supplying high pressure hydraulic fluid to power actuators for power steering systems includes a pumping mechanism having independent pumping chambers adapted to discharge fluid to a supply line leading to the power actuator. The supply line contains a variable orifice and a flow control valve responsive to the pressure difference generated by the variable orifice. The pumping chambers include at least first and second pumping chambers connected to first and second feed lines. A switching valve operatively interconnected to the variable orifice and actuated by an electrically operable drive mechanism selectively connects the second feed line to the supply line or to the first feed line. When the drive mechanism shifts the switching valve so that the second feed line leading to the second pumping chamber is switched from the first feed line to communicate with the supply line, a part of the high pressure fluid flowing through the fluid line is returned to the second pumping chamber by bypassing the power actuator thereby disabling the second pumping chamber and reducing the flow rate of the fluid flowing to the power actuator. Disablement of the second pumping chamber during 'drooping' reduces the effective overall displacement capacity of the pumping mechanism thereby saving a considerable amount of power. The system may be electronically controlled depending on various operational conditions of the vehicle and the like.