Power steering system

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 torque sensor and a vehicle speed sensor (15) 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 (It) in accordance with steering torque detected by the steering torque sensor and a current instruction value (Iv) in accordance with a vehicle speed detected by the vehicle speed sensor (15),
• 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),
• changing the standby current instruction value (Is) on the basis of the vehicle speed.

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 (I1) in accordance with a steering angle supplied from the steering angle sensor (14), a current instruction value (I2) in accordance with a steering angular velocity and current instruction values (I5, I6) 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.

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 torque sensor, 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 (It) in accordance with steering torque detected by the steering torque sensor and a current instruction value (Iv) in accordance with a vehicle speed detected by the vehicle speed sensor (15),
• 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.