| 摘要 |
<p>A power steering system includes a bypass valve (40) for bypassing fluid from a main fluid conduit (34) connected between an engine-driven, power steering pump (26) and an actuatable, open-center, steering control valve (12) which is actuated upon turning of a vehicle steering wheel. When the steering control valve is actuated, the demand for fluid through the steering control valve to a power steering motor increases. The fluid pressure in the main conduit (34) varies as a function of the demand for fluid to the steering control valve. The bypass valve (40) is urged toward an open condition by a fluid pressure signal. The bypass valve is urged toward a closed condition by a spring and by a fluid pressure (74) which varies as a function of the demand for fluid to the steering control valve and as a function of vehicle operating parameter, such as vehicle speed. The fluid pressure which urges the bypass valve toward a closed condition is controlled by (i) a pressure responsive pilot valve (50) which is responsive to the fluid pressure in the main conduit and (ii) a solenoid operated valve (250) which is responsive to vehicle speed.</p> |
