| 摘要 |
PROBLEM TO BE SOLVED: To provide an electric power steering device that achieves protection of a Zener diode without damaging steering performance, by hour integrating the lost electric power of the Zener diode for FET protection, even if the power source voltage is lowered, while by gradually limiting duties as an integrated loss increases.SOLUTION: With respect to an electric power steering device in which a steering assist command value is calculated based on a steering torque and a vehicle speed to generate PWM signals, while by PWM-driving a motor via an FET bridge circuit with Zener diode mounted thereon for assist-controlling the steering system, when a difference between an ignition voltage and an inverter applied voltage is found to be equal to or more than a prescribed voltage, there are provided: a lost electric power calculation section that calculates the lost electric power; an integrated loss calculation section that computes the integrated electric power lost; a tolerant loss calculation section that calculates a tolerant loss based on the temperature; a minimum value selecting section that selects a minimum value of the difference of loss between the tolerant loss and integrated loss; and a limiting value calculation section that calculates a limiting value of the PWM signals based on the minimum value of the difference of loss and the tolerant loss. |
