Permanent magnet electric motor

A permanent magnet electric motor comprising a stator and a rotor rotatably mounted confronting the stator, wherein the stator comprises:

• a housing having a polygonal cross section comprising a plurality of side portions and a plurality of curved corner portions, each corner portion connecting two adjacent side portions;
• a permanent magnet fixed to an inner surface of the housing;
• and
• an air gap formed between the rotor and the permanent magnet,
• wherein the permanent magnet is a ring magnet and the thickness of the ring magnet at portions corresponding to said corner portions of the housing is larger than the thickness of the ring magnet at portions corresponding to said side portions of the housing;
• the thickness of said air gap at portions corresponding to said corner portions of the housing is larger than the thickness of said air gap at portions corresponding to said side portions of the housing;
• and
• the thickness of said air gap is largest at portions corresponding to the thickest portions of the ring magnet, and is smallest at portions corresponding to the thinnest portions of the ring magnet.

A permanent magnet electric motor comprising a stator and a rotor rotatably mounted confronting the stator, wherein the stator comprises:

• a housing having a polygonal cross section comprising a plurality of side portions and a plurality of curved corner portions, each corner portion connecting two adjacent side portions;
• a permanent magnet fixed to an inner surface of the housing;
• and
• an air gap formed between the rotor and the permanent magnet,
• wherein the permanent magnet is a ring magnet and the thickness of the ring magnet at portions corresponding to said corner portions of the housing is larger than the thickness of the ring magnet at portions corresponding to said side portions of the housing;
• and
• the ratio of the radius of curvature of the inner surface of said corner portions to the radius of curvature of the inner surface of the ring magnet is between 1.1 and 1.8.