Fluid-operated control apparatus for power-assisted steering system of

Abstract

A control apparatus for a power-assisted vehicle steering system, comprising a power cylinder having two pressure-acting chambers, a control valve having inlet and outlet ports respectively communicable with a pump and a fluid reservoir and selectively with the inlet and outlet ports, a pressure compensating valve having an inlet port communicating with the pressure-acting chambers, outlet and control ports and a valve member for varying the degree of communication between the inlet and outlet ports, the fluid pressure in the inlet port being variable with the fluid pressure from the pump and urging the valve member to move in one direction and a spring urging the valve member to move in the other direction to maintain constant the differential pressure between the inlet and outlet ports, and a pressure reducing valve having an inlet port communicating with the outlet port of the compensating valve, a discharge port communicating with the reservoir and the control port of the compensating valve and a valve member to vary the degree of communication between the inlet and discharge ports of the reducing valve, the fluid pressure in the discharge port being directed to the control port and developing therein the fluid pressure urging the valve member of the compensating valve for movement in the said other direction, the valve member of the reducing valve being responsive to a signal variable with vehicle speed.