Rotary dynamo electric machine with protection against demagnetization of low flux portion of permanent magnet poles

摘要

A permanent magnet dynamo electric machine is provided with a shield of high saturation flux density at the weaker or lower flux tip or edge of a permanent magnet pole face to prevent both circumferential and axial demagnetization of that portion of the pole face. The shield resides in a recess in the pole face so as to maintain a constant width air gap between the rotor and stator and has a thickness in the range of 5-15% of the overall thickness of the shield and pole combined. The shield and its pole face extend axially at least over the entire axial dimension of the area swept by the rotor.