Patent ID: 8796896

Claim:
An electric motor comprising: a stator comprising: a housing having an inner circumferential surface; a stator core fixed to the inner circumferential surface of the housing; and windings wound on the stator core; and a rotor rotatably installed inside the stator and comprising: a shaft defining an axial direction; a rotor core fixed to the shaft and having a plurality of grooves on a circumferential outer surface thereof, spaced from each other, and extending along the axial direction; and a ring magnet fixed on the circumferential outer surface of the rotor core and forming a plurality of permanent magnetic poles in a circumferential direction thereof, wherein: the number of the grooves on the circumferential surface of the rotor core is equal to the number of the permanent magnetic poles on the ring magnet; each of the plurality of permanent magnetic poles has a start charging point offset from a corresponding groove in the circumferential direction; and a boundary line between two adjacent permanent magnetic poles is inclined relative to the axial direction and circumferentially confined between two corresponding adjacent grooves.