Control apparatus for power-assisted steering system

Abstract

In a power-assisted steering system including a steering shaft arranged to be rotated by steering effort applied thereto, a fluid pump driven by a prime mover of the vehicle, a hydraulic cylinder having a power piston mounted for reciprocating movement in the cylinder and operatively connected to driven members of the steering system, and a servo valve interconnecting the fluid pump and the cylinder and being responsive to rotary motion of the steering shaft for selectively directing the flow of fluid under pressure from the pump to one of opposite fluid chambers of the cylinder and permitting the flow of fluid from the other fluid chamber to a fluid reservoir to effect reciprocating movement of the power piston, an electrically operated control valve of the normally closed type is disposed within a bypass passage between the opposite fluid chambers of the cylinder to permit the flow of fluid passing through the bypass passage in its energized condition so as to restrain rapid increase of the pump load during maneuvers of the vehicle. The control valve is arranged to be energized when the power piston approaches to its stroke end.