Electric motor

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.