Control apparatus for vehicle steering system

摘要

A control apparatus for a power-assisted steering system, comprising a power cylinder having pressure acting chambers respectively communicating with the control ports of a pressure control valve having inlet and outlet ports respectively communicable with the delivery and suction ports of a pump, and first and second flow control valves each having an inlet port and a discharge port communicating with the suction port of the pump, each flow control valve including a control pressure acting chamber communicating with a pressure acting chamber of the power cylinder to develop a differential pressure variable with a differential pressure between the pressure acting chambers of the cylinder, and a valve member movable in response to the differential pressure acting thereon and urged to provide communication between the inlet and discharge ports of each flow control valve, the inlet port of the first flow control valve being in constant communication with the delivery port of the pump and the inlet port of the pressure control valve, the inlet port of the second flow control valve being in constant communication with the outlet port of the pressure control valve, the valve member of each flow control valve being operative to block the communication between the inlet and discharge ports of the valve when the differential pressure is higher than a predetermined value, the second flow control valve further comprising a bypass providing constant communication between the outlet port of the pressure control valve and the suction port of the pump independently of the valve member.