Patent ID: 6845310

Claim:
A power steering system comprising: a steering valve ( 9 ) for controlling a power cylinder ( 8 ); a variable orifice (a) provided upstream from the steering valve ( 9 ); a solenoid (SOL) for controlling a degree of opening of the variable orifice (a); a controller (C) for controlling a solenoid current instruction value (SI) used for driving the solenoid (SOL); a steering angle sensor ( 14 ), a vehicle speed sensor ( 15 ) and an engine speed sensor which are connected to the controller (C); and a flow control valve (V) for dividing a flow, supplied from a pump (P), into a control flow (QP) supplied to the steering valve (V) in accordance with the degree of opening of the variable orifice (a), and a return flow (QT) circulating back to a tank (T) or the pump (P), the controller (C) determining a basic current instruction value (Id) on the basis of a current instruction value (I 1 ) in accordance with a steering angle supplied from the steering angle sensor ( 14 ), a current instruction value (I 2 ) in accordance with a steering angular velocity and current instruction values (I 5 , I 6 ) in accordance with a vehicle speed, adding a standby current instruction value (Is) to the basic current instruction value (Id), outputting the resultant value of the addition as the solenoid current instruction value (SI), and changing the standby current instruction value (Is) on the basis of the number of revolutions of an engine or strokes of a pump detected by the engine speed sensor.