Patent ID: 8169168

Claim:
An electric power steering apparatus for generating a steering assist force by a motor, comprising: a battery for supplying an electric power to the motor; an auxiliary power supply connected in series with the battery and capable of supplying an electric power to the motor; a detector for detecting a failure of the battery; a charge-discharge circuit including a charge circuit for charging the auxiliary power supply by turning on and off a voltage-boosting switching device interposed in an inductance circuit powered by the battery and selectively configuring a first output mode or a second output mode, the first output mode defining a state that the electric power is supplied to the motor by way of a first electrical conduction path through which a voltage of the battery is applied to an electrical conduction path to ground, the second output mode defining a state that the electric power is supplied to the motor by way of a second electrical conduction path through which a voltage of a source including the series-connected battery and auxiliary power supply is applied to the electrical conduction path to ground; and a control circuit for driving the charge-discharge circuit to select either of the first output mode and the second output mode in response to a required steering assist force, the control circuit connecting the first electrical conduction path to the electrical conduction path to ground by continuously holding the switching device in an on-state at the time of detection of a failure of the battery by the detector, the control circuit also driving the charge-discharge circuit to select the second output mode to thereby supply the motor with the electric power only from the auxiliary power supply.