Variable assist power steering system with varying power assist with vehicle speed

摘要

A control valve includes valve elements relatively displaceable in response to a steering torque to define therebetween two parallel fluid flow paths connected between a fluid source and a fluid reservoir to produce pressure difference in a power cylinder. The control valve comprises a bypass path including a first externally controlled variable flow orifice and a variable flow orifice variable with steering torque and a first externally controlled variable flow orifice valve which are connected in series, a second externally controlled variable flow orifice valve, and a second variable flow orifice variable with steering torque. The bypass path is arranged in parallel with a portion of the two parallel fluid paths, the second externally controlled variable flow orifice valve is arranged in parallel with another portion of the parallel fluid paths, and the second variable flow orifice is arranged in series in the remaining portion of the parallel fluid paths.