Patent ID: 8547043

Claim:
A motor control device for detecting a short-circuit fault and a disconnection fault of a power relay, the motor control device comprising: a drive circuit supplying a driving electric power to a motor according to a supply voltage from a power supply; the power relay disposed on a power line, which couples the power supply and the drive circuit, wherein the power relay includes a first switching element disposed on the power line so that a polarity of a parasitic diode thereof is oriented toward the power supply, and a second switching element disposed on the power line on a drive circuit side of the first switching element so that a polarity of a parasitic diode thereof is oriented toward the drive circuit, and wherein the power relay interrupts and permits a current, which flows along the power line, according to operation of the first switching element and second switching element; a capacitor having one terminal connected to the power line between the second switching element and drive circuit; a voltage detector disposed on the power line between the first switching element and the second switching element, and detecting a voltage of the first switching element on a second switching element side; a charger charging the capacitor by applying a charge voltage to the capacitor; and a control section controlling the drive circuit to control drive of the motor, controlling operation of the power relay to interrupt and permit the current, which flows along the power line, and controlling operation of the charger to charge the capacitor, wherein the control section executes a first step for detecting a short-circuit fault of one of the first switching element and second switching element according to the voltage detected by the voltage detector in a case where the control section controls both of the first switching element and second switching element to turn off after the control section controls the charger to charge the capacitor, wherein, when the control section does not detect the short-circuit fault of both of the first switching element and second switching element in the first step, the control section executes a second step for detecting a disconnection fault of the second switching element according to the voltage detected by the voltage detector in a case where the control section controls the first switching element to turn off, and controls the second switching element to turn on, and wherein, when the control section does not detect the disconnection fault of the second switching element in the second step, the control section executes a third step for detecting a disconnection fault of the first switching element according to the voltage detected by the voltage detector in a case where the control section controls the first switching element to turn on, and controls the second switching element to turn off.