Rotary dynamo electric machine with protection against demagnetization of low flux portion of permanent magnet poles
AssigneeLucas Industries Limited
InventorJohn G. W. West
Life of this patent
Estimating the term…
Abstract
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.
Claims23
A permanent magnet dynamo electric machine of the kind wherein the rotor is always intended to rotate in the same direction relative to the stator, and wherein each permanent magnet pole is provided on that face which is presented to the air gap defined between the permanent magnet poles and the wound poles with a shield of material of high saturation flux density, said shield extending circumferentially of the machine from the edge, or from adjacent the edge, of the weak tip of the pole towards the strong tip and covering not less than 20% and not more than 75% of that area of said face of the pole which is swept by the wound poles during relative rotation of the permanent magnet poles and the wound poles, said shield at its weak end, covering the whole axial dimension of said swept area and terminating, in the circumferential direction, short of the edge of the strong tip of the pole, wherein said shield is set in a recess in the pole face so that the radial thickness of the machine air gap is substantially constant, and wherein the thickness of the shield is in the range of 5-15% of the overall radial dimension of the combined pole and shield.
A reversible, permanent magnet, dynamo electric machine wherein each permanent magnet pole is provided on that face which is presented to the air gap defined between the permanent magnet poles and the wound poles with first and second shields of material of high saturation flux density, said first shield extending circumferentially of the machine generally from the edge of one of the circumferential tips of the pole towards the axial centerline of the pole, and the second shield extending circumferentially of the machine generally from the edge of the other circumferential tip of the pole towards the axial centerline of the pole, both of said first and second shields covering, substantially at its weak end, the whole axial dimension of that area of the pole which is swept by the wound poles during relative rotation of the permanent magnet poles and the wound poles, said shields being magnetically separate, wherein said first and second shields are each set in respective recesses in said pole face so that the radial thickness of the machine air gap is substantially constant, and wherein the thickness of each shield is in the range 5-15% of the overall radial dimension of the combined pole and shield.
Dependencies are inferred from the claim text.