Patent ID: 7843160

Claim:
A motor driving control method for applying three-phase alternating currents as motor drive current from a three-phase bridge circuit to a three-phase brushless motor provided in a vehicle for steering assist, by performing PWM control in a triangle comparison method based on a command value determined in dependence on a steering angle, a vehicle speed, and other driving states and for performing current-feedback control with actual motor drive currents detected by shunt resistances, the motor driving control method comprising: judging whether or not a steering angular velocity is higher than a predetermined reference angular velocity; when the steering angular velocity is lower than the predetermined reference angular velocity, detecting actual motor drive currents by the respective shunt resistances with the peak level of each of three-phase alternating current command waves being limited so that the interval between a pair of intersection points of a peak area of each of the three-phase alternating current command waves with a peak point neighborhood of a triangle wave, which waves are compared in the triangle comparison method, is made to be longer than the sum of a current detection time by the shunt resistances and a dead time for switching; and when the steering angular velocity is higher than the reference angular velocity, inferring an actual motor drive current from a back electromotive voltage and an applying voltage in the three-phase brushless motor instead of detecting the actual motor drive currents by the respective shunt resistances, and mitigating the limitation on the peak level of each of the three-phase alternating current command waves by permitting the interval between the pair of intersection points to become approximately the same length as the dead time.