Patent ID: 8301342

Claim:
An electric power steering apparatus that generates a steering assist force by a motor, comprising: a main power supply for supplying an electric power to the motor; an auxiliary power supply capable of supplying the electric power to the motor; a charge-discharge circuit that charges the auxiliary power supply by using the main power supply and that selectively configures a first output mode in which only the main power supply is used to supply the electric power to the motor or a second output mode in which the main power supply and the auxiliary power supply are used to supply the electric power to the motor; and a control circuit that selects the output mode of the charge-discharge circuit according to the electric power required for steering assist and that selects the second output mode when the electric power required for steering assist in the first output mode becomes equal to or higher than a first threshold value or selects the first output mode when the electric power required for steering assist in the second output mode becomes equal to or lower than a second threshold value that is lower than the first threshold value.