A study on vibration at the field weakening control of DC brushless motor for EPS (electric power steering)

A permanent magnet DC brushless motor is the most suitable for high torque electric power steering (EPS). Unlike brush motors, these motors can be driven up to high revolution speeds by using the field weakening control that reduces the magnetic flux. However, a motor vibration is caused by this field weakening control. Therefore, we need to develop a low vibration motor at the field weakening control. The authors focused on this issue, and investigated a mechanism of the motor vibration caused by the field weakening control. As a result, the authors clarified the mechanism of the motor vibration caused by a magnetostriction of a stator core and developed a formula for calculating the motor vibration at the field weakening control. In addition, this mechanism and formula were verified by the experiment that used an actual motor. It was shown that the authors obtained a new finding by the process of this research.