Patent ID: 8467938

Claim:
An electric power steering apparatus that generates a steering assist force by a motor, comprising: a motor drive circuit for driving the motor; a current detector for detecting an actual current supplied from the motor drive circuit to the motor; a battery for supplying a drive voltage to the motor drive circuit; an auxiliary power supply connected in series to the battery and capable of supplying a drive voltage to the motor drive circuit; a discharge circuit including switching devices for alternately opening and closing a first electrical conduction path for supplying the motor drive circuit with a drive voltage from the battery alone and a second electrical conduction path for supplying the motor drive circuit with a drive voltage from a series connection of the battery and the auxiliary power supply; and a control circuit that controls the motor drive circuit for driving the motor to generate the steering assist force, the control circuit determining a command value of a drive voltage to be supplied to the motor drive circuit based on the actual current and a target current and controlling the amount of discharge from the auxiliary power supply according to a difference between the command value and its previous value if the command value exceeds the previous value having a lower limit equivalent to a limit value representing the limit of the power supply from the battery.