Patent ID: 7596441

Claim:
A power steering device comprising: a hydraulic power cylinder configured to assist a steering force of a steering mechanism linked to steered road wheels; a pump configured to supply hydraulic pressure to a selected one of two hydraulic cylinder chambers defined in the power cylinder; an electric motor configured to drive the pump; a driving power source configured to supply electric power to the motor; and a power steering control system electrically connected to at least the motor and the driving power source, and configured to control a driving state of the motor and a power source voltage of the driving power source; the power steering control system including: a motor control circuit configured to generate a motor driving signal, whose command signal value is determined based on a steering assist force applied through the power cylinder to the steered road wheels; a booster circuit configured to boost the power source voltage of the driving power source; a motor angular acceleration detection circuit configured to detect or estimate a motor angular acceleration; and a booster-circuit control circuit configured to control, responsively to the motor angular acceleration, switching between operating and non-operating states of the booster circuit, wherein the motor includes a brushless motor having an angular position sensor configured to detect an angular position of a brushless-motor rotor, and the motor angular acceleration detection circuit estimates the motor angular acceleration based on a sensor signal from the angular position sensor, and wherein the booster-circuit control circuit is configured to switch on the booster circuit, when the estimated motor angular acceleration becomes greater than or equal to a motor-angular-acceleration threshold value.