VARIABLE ASSIST POWER STEERING SYSTEM WITH ELECTRO-HYDRAULIC WORKING PRESSURE AND DIRECTIONAL PRESSURE CONTROL

摘要

A variable assist power steering system for a motor vehicle has an electronically controlled working pressure valve (18) which normally maintains a working pressure at a relief pressure but increases it in response to steering of the vehicle and according to vehicle status, such as vehicle speed. The system also has electronically controlled direction control valves (20, 22) which are actuated to selectively reduce the working pressure to one side or the other of the steering gear piston (24) so as to match a measured handwheel torque with a value which is desired for the vehicle status.