Patent attributes
An electric power steering device for a vehicle includes a plurality of assist systems electromagnetically driving an electric motor. When a first or second assist system malfunctions, a malfunction state assist amount calculation part calculates an assist amount while decreasing a limit value at the vehicle stopping, to an amount smaller than a limit value at the vehicle moving. When a malfunction such as a disconnection or a fixing of the switching elements occurs in the first or second assist systems on the basis of a judgment result of a malfunction judgment function, an assist amount switching part supplies an assist amount received from the malfunction state assist amount calculation part to first and second motor drive control parts. When a malfunction occurs in one of the first and second assist systems, one of the first and second motor drive control parts drives the motor by using the assist amount.
