Steering control apparatus

摘要

A steering control apparatus for a power-assisted vehicle steering system for a vehicle, comprising a steering pressure pump, a power cylinder, a pressure control valve operative to direct fluid under pressure from the pump to the power cylinder to develop in the cylinder a differential fluid pressure to produce a controlled degree of hydraulic steering assistance, and a fluid flow control valve bypassing the pressure control valve between the suction and delivery ports of the pump, wherein the differential fluid pressure to be developed in the power cylinder or the flow rate of the fluid to be discharged through the flow control valve is variable in two or more different basic modes in each of which the differential fluid pressure or the fluid flow rate is further continuously variable so that the vehicle driver is enabled to steer the vehicle with a manual steering effort continuously variable with, for example, the vehicle speed.