Electric motor unit

An electric motor unit comprising:

• a motor shaft;
• a rotor fixed to the motor shaft;
• a stator for rotating the rotor;
• a pair of bearings for rotatably supporting both end portions of the motor shaft;
• a housing to which the stator and the bearings are fixed;
• a ring-shaped first permanent magnet with its inner peripheral surface coaxially fixed to the motor shaft and having one pole on its outer peripheral surface;
• a second permanent magnet disposed coaxially with the first permanent magnet in the housing and disposed within the housing so as to be slidable along the axis of the motor shaft, having its inner peripheral surface opposed to the outer peripheral surface of the first permanent magnet, and having on its inner peripheral surface a pole different from the pole on the outer peripheral surface of the first permanent magnet so that the first permanent magnet is attracted by the second permanent magnet in the radial direction of the motor shaft;
• and
• means for adjusting the axial position of the second permanent magnet including a ring holder fixedly mounted with the second permanent magnet and slidably fitted in the motor housing, a screw member screwed in the motor housing to move the ring holder along the axis of the motor shaft, and an elastic member to press the ring holder against the screw member.