Patent ID: 7730993

Claim:
A power steering device comprising: a hydraulic power cylinder configured to assist a steering force of a steering mechanism linked to steerable road wheels; a pump configured to supply a hydraulic pressure to respective pressure chambers of the hydraulic power cylinder; an electric motor configured to drive the pump; a torque sensor configured to detect a steering torque of the steering mechanism; an operating load state detecting circuit configured to detect an operating load state of the pump based on a viscosity resistance characteristic of a working oil; and an electric motor control circuit configured to output a drive signal to the motor on the basis of a torque signal from the torque sensor and the operating load state of the pump, wherein the operating load state detecting circuit detects the operating load state of the pump on a basis of an actual number of revolutions per unit time of the electric motor, wherein the operating load state detecting circuit comprises a revolution state detecting circuit configured to detect a revolution state of the electric motor and the operating load of the pump is estimated on the basis of the revolution state of the electric motor, and wherein the revolution state detecting circuit detects the revolution state of the electric motor by detecting a number of revolutions per unit time of the electric motor when a constant voltage is caused to flow into the electric motor, and wherein the operating load state detecting circuit estimates a temperature of the working oil on the basis of the revolution state of the electric motor and the electric motor control circuit outputs the drive signal to the electric motor on the basis of the temperature of the working oil and the steering torque.