Jtekt Corporation

Yoshihiro Itatsu

Yuji Kariatsumari

Terutaka Tamaizumi

Yoshinobu Shimizu

Hayato Komatsu

Sadanao Baba

An assist command value calculation circuit includes a torque shift control circuit, a phase lag compensation control circuit, a basic assist control circuit, and a phase lead compensation control circuit. A determination circuit determines whether a motor has been continuously under high load or not based on a current command value and a current limit value. The determination circuit determines whether the motor has been continuously under high load or not by comparing the current command value with the current limit value and comparing a basic assist controlled variable with the current limit value, and outputs a phase compensation restriction flag. The phase lag compensation control circuit and the phase lead compensation control circuit restrict phase restriction when the phase compensation restriction flag is ON, and continues phase compensation when the phase compensation restriction flag is OFF.

Electric power steering system

A motor is driven by the &#x3b3;-axis current of a &#x3b3;&#x3b4; coordinate system that is an imaginary rotating coordinate system. A command current value preparation unit sets the &#x3b3;-axis command current value based on the command steering torque and the detected steering torque. The command current value preparation unit includes a command current increase/decrease amount calculation unit and an addition unit. The command current increase/decrease amount calculation unit calculates the current increase/decrease amount for the command current value based on the sign of the command steering torque and the deviation of the detected steering torque from the command steering torque. The current increase/decrease amount calculated by the command current increase/decrease amount calculation unit is added to the immediately preceding value of the command current value by the addition unit. Thus, the command current value in the present calculation cycle is calculated.

Motor control unit and vehicle steering system

When the estimated motor temperature becomes equal to or higher than the first predetermined temperature, an addition angle correction unit temporarily decreases the absolute value of the addition angle output from an addition angle limiter at time intervals. The addition angle correction unit makes the time interval shorter as the estimated motor temperature increases. When the time interval becomes equal to or shorter than the predetermined threshold, that is, when the estimated motor temperature becomes equal to or higher than the second predetermined temperature that is higher than the first predetermined temperature, the addition angle correction unit notifies a command current value changing unit of a current stop command. Thus, the &#x3b3;-axis command current value is changed to 0, and therefore the steering mode is shifted to the manual steer mode.

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Okazaki, Japan

Yoshihiro Itatsu