Patent ID: 9604666
Date: 2017-03-28
CPC Classifications: B62D

Claim:
1. An electric power steering apparatus that calculates a steering assist command value based on a steering torque and a vehicle velocity, generates a Pulse Width Modulation (PWM) signal based on said steering assist command value, PWM-drives a motor through a Field-Effect Transistor (FET) bridge circuit having Zener diodes for protecting FETs, and performs an assist control of a steering system by a PWM-drive control of said motor, comprising: a loss power calculating section that inputs said PWM-signal, an ignition voltage and an inverter applying voltage, calculates a loss power of said Zener diodes when a difference between said ignition voltage and said inverter applying voltage is equal to or more than a predetermined voltage, and outputs said loss power; an integrating loss calculating section to calculate an integrating loss of said loss power; a permissible loss calculating section to calculate a permissible loss of said Zener diodes based on a detected temperature of a temperature sensor for measuring an ambient temperature; a minimum value selecting section to select a minimum value of a loss difference of said permissible loss and said integrating loss; a limit value calculating section to calculate a limit value of said PWM-signal based on said minimum value of said loss difference and said permissible loss; and a rate limiter to limit a rate of said limit value.