R.h. Sheppard Co., Inc.

Kenneth Giurlando

David M Danley

Peter H Sheppard

Jeffrey Tipton

Jeffrey E Tippton

A power steering system for a ground vehicle includes an accumulator that supplies high-pressure fluid through a control valve to a fluid motor that drives the steerable wheels of the vehicle. A normally open control valve between the accumulator and the fluid motor closes prior to the steerable wheels reaching an axle stop to relieve power assist.

Method of relieving power steering assist and a power steering system utilizing the method

A control valve for a hydraulic power steering system includes a pair of flow circuits arranged in parallel. Each flow circuit includes an upstream and downstream flow orifices arranged in series. Each set of orifices defines between the orifices an intermediate pressure zone of the valve. Both orifices close together from a centered condition of the valve and fully close substantially together at a fully closed condition of the valve. The downstream orifice is larger than the upstream orifice when open to minimize the likelihood of cavitation and noise. An equalization passage fluidly connects both intermediate pressure zones to equalize pressure despite variations in orifice size due to manufacturing tolerances. The control valve includes a bypass passage in parallel with the flow circuits. A pressure relief valve in the control valve has a normally closed valving member in the bypass passage that opens the valve in the event of overpressure.

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Lancaster, PA, United States of America

Kenneth Giurlando