Electric motor
An electric motor has a rotor ( 20 ), a housing ( 10 ) and a ring magnet ( 12 ) fixed onto an inner surface of the housing. The housing ( 10 ) has a cross section in a polygon, preferably tetragonal, shape that comprises a plurality of side portions ( 10 a˜ 10 d ) and a plurality of curved corner portions ( 11 a˜ 11 d ), each of which connects two adjacent side portions. The thickness of the ring magnet at portions corresponding to the corner portions of the housing is larger than the thickness of the ring magnet at portions corresponding to the side portions of the housing. An air gap ( 123 ) is formed between a peripheral surface of the rotor and an inner surface of the ring magnet, the thickness of the air gap at portions corresponding to the corner portions of the housing being smaller than that of the air gap at portions corresponding to the side portions of the housing. The motor has a polygon housing which is convenient to install and has good space utilization.
1. An electric motor comprising a stator and a rotor rotatably mounted confronting the stator, wherein the stator comprises:
a housing having a cross section in a polygon shape that comprises a plurality of side portions and a plurality of curved corner portions, each of which connects two adjacent side portions,
a ring magnet fixed onto an inner surface of the housing, the thickness of the ring magnet at portions corresponding to the corner portions of the housing being greater than the thickness of the ring magnet at portions corresponding to the side portions of the housing,
an air gap being formed between a peripheral surface of the rotor and an inner surface of the ring magnet, the thickness of the air gap at portions corresponding to the corner portions of the housing being smaller than that of the air gap at portions corresponding to the side portions of the housing;
wherein gaps are formed between the ring magnet and the corner portions of the housing.
2. The electric motor of claim 1 , wherein the thickness of the air gap is smallest at portions corresponding to the thickest portions of the ring magnet, and is largest at portions corresponding to the thinnest portions of the ring magnet.
3. The electric motor of claim 1 , wherein gaps are formed between the side portions of the housing and the ring magnet.
4. The electric motor of claim 1 , wherein each of the corner portions has an even thickness, and curves around a center which is offset from the rotational center of the rotor.
5. The electric motor of claim 1 , wherein the radius of curvature of the inner surface of the corner portions is larger than the radius of curvature of the outer surface of the ring magnet at portions corresponding to the corner portions.
6. The electric motor of claim 1 , wherein the ratio of the radius of curvature of the inner surface of the corner portions to the radius of curvature of the inner surface of the ring magnet is between 1.1 and 1.8.
7. The electric motor of claim 1 , wherein the housing has an even thickness.
8. The electric motor of claim 1 , wherein the thickness of the housing at the corner portions is larger than the thickness of the housing at the side portions.
9. The electric motor of claim 1 , wherein the housing has a tetragonal cross section.