Electric motor

1. 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.

2. The motor of claim 1 , wherein the stator core comprises a yoke and a plurality of teeth extending inwardly from the yoke, the yoke and the teeth meet the following equation:

0.35 <Wt/Ws< 0.5

wherein Ws represents the height of the teeth measured along the radial direction of the stator and Wt represents the width of the teeth.

3. The motor of claim 1 , wherein the stator core comprises a yoke and a plurality of teeth extending inwardly from the yoke, the yoke and the teeth meet the following equation:

1 <Wy/Wt< 1.3,

wherein Wy represents the width of the yoke and Wt represents the width of the teeth.

4. The motor of claim 1 , wherein the stator core comprises a plurality of teeth on which the windings are wound, and a skew angle ⊖ of the boundary line between two adjacent magnetic poles defined as a circumferential offset of two end points of the boundary line is in a range of (⊖r, 20⊖r),

wherein ⊖r, in electrical degrees, is defined as,

⊖ r= 180×(number of magnetic poles in the rotor)/(smallest integer of which both the number of magnetic poles in the rotor and the number of teeth in the stator).

5. The motor of claim 1 , wherein the plurality of boundary lines between adjacent magnetic poles in the ring magnet do not radially overlap the plurality of grooves in the rotor core.

6. The motor of claim 1 , wherein at an end plane extending through an end of the rotor core and a corresponding end of the magnet, an angle β formed between a line extending through the center of the rotor and the start charging point of each magnetic pole and another line extending through the center of the rotor and the middle of the corresponding groove is in a range of 10˜20 mechanical degrees.

7. The motor of claim 1 , wherein the stator comprises an end cap fixed to the housing, and the housing comprises an open end and a flange bent inwardly from the open end of the housing and abutting against the end cap, inwardly and axially, thereby fixing the end cap to the housing, the flange having a length along the circumferential direction of the housing being greater than half of that of the housing.

8. The motor of claim 7 , wherein the length of the flange along the circumferential direction of the housing is greater than 80 percent of that of the housing.

9. The motor of claim 7 , wherein:

the open end of the housing defines a plurality of locking cutouts; and

the end cap comprises a plurality of lugs protruding outwardly from a periphery thereof and being locked in respective locking cutouts, thereby preventing the end cap from rotating relative to the housing.