Patent ID: 8886411

Claim:
A power steering system, comprising: a steering mechanism that steers steerable wheels of a vehicle along with a steering operation of a steering wheel; a motor that provides a steering assistance force for the steering mechanism; a control apparatus that drivingly controls the motor; a command signal calculation section disposed in the control apparatus to calculate vector control command signals to drivingly control the motor in accordance with a driving situation of the vehicle; a two-phase to three-phase conversion section disposed in the control apparatus to convert the vector control command signals into three phase command signals which are command signals for respective phases of the motor; a Pulse Width Modulation (PWM) control section disposed in the control apparatus to output a PWM duty signal for each phase of U phase, V phase, and W phase in accordance with the three phase command signals; an inverter disposed in the control apparatus and constituted by a switching circuit drivingly controlled by the PWM duty signal for each phase of the motor; a current detection circuit configured to detect three phase currents flowing into the inverter; a plurality of phase open relays switchable at least any two of the three phases of the motor between a conduction state in which a power supply is enabled to be supplied to the at least any two of the three phases of the motor and an interruption state in which the power supply is disabled to be supplied to the at least any two of the three phases; and an abnormality monitor section configured to output the vector control command signals to supply only a d-axis current in a positive side direction toward the motor, with all of the phase open relays in the interruption state, and to determine an abnormality in at least one of the phase open relays in a case where a current value is detected by the current detection circuit.