| 摘要 |
PROBLEM TO BE SOLVED: To provide a motor power steering system equipped with a booster circuit operating to minimize switching loss. SOLUTION: A motor control section, i.e., a microcomputer, calculates a command value for feedback control from the difference of a target current value being set based on the steering torque and the vehicle speed and the detection value of motor current, and then calculates the duty ratio Dc of a PWM signal for turning on/off the switching element of a motor drive circuit from that command value. When the duty ratio Dc thus calculated is not higher than 100%, a booster circuit does not operate (S246) and a battery voltage is supplied to the motor drive circuit, but when it exceeds 100%, the microcomputer delivers a PWM signal for turning on/off the switching element (LO-MOS) of the booster circuit at a duty ratio corresponding to the excess amount (S244). Consequently, the battery voltage is boosted depending on the excess amount and fed to the motor drive circuit. |
