Brushless motor

1. A brushless motor comprising:

a stator comprising a stator core with teeth protruding inwardly and windings wound on the teeth, and

a rotor comprising a shaft, a rotor core fixed to the shaft, and a ring magnet fixed to the circumferential outer surface of the rotor core, the magnet comprising a plurality of magnetic poles radially magnetized so that north poles and south poles are arranged alternately in the circumferential direction,

wherein boundary lines between magnetic poles are skewed by an angle α relative to an axis (Z) of the shaft, and a plurality of grooves formed in the circumferential outer surface of the rotor core, each groove extending axially from one end of the rotor core to the other end of the rotor core;

wherein the boundary lines between adjacent magnetic poles do not radially overlap the grooves.

2. The brushless motor of claim 1 , wherein the angle α is in the range of 15 ˜30 degrees.

3. The brushless motor of claim 1 , wherein a skew angle ⊖ of the boundary lines between magnetic poles measured at an end plane extending through one end of the magnet, is in the range of ⊖r to 2⊖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 number of magnetic poles in the stator are factors).

4. The brushless motor of claim 1 , wherein the number of magnetic poles is 4 and the number of teeth is 6.

5. The brushless motor of claim 1 , wherein the number of the grooves is equal to the number of magnetic poles of the rotor, and wherein in a radial plane midway between the axial ends of the rotor core, each groove and a centerline of the corresponding magnetic pole radially overlap.

6. A bladeless fan comprising the brushless motor of claim 1 .

7. The bladeless fan of claim 6 , wherein the fan comprises a base with an inner chamber and a ring nozzle mounted on the base, the nozzle comprises an inner passage communicating with the chamber of the base, the motor being disposed within the chamber, an impeller being mounted to the shaft of the motor and arranged to move air from outside of the base into the chamber and through the inner passage of the nozzle.

8. The bladeless fan of claim 7 , wherein the nozzle further comprises a ring outlet communicating with the inner passage, and a Coanda surface formed at the outlet of the nozzle.

9. The brushless motor of claim 1 , wherein entire radial inner surfaces of the teeth of the stator core are arranged on an imaginary circle concentric with the shaft.

10. The brushless motor of claim 1 , wherein a bottom surface of each groove is a concave surface.

11. A brushless motor comprising:

a stator comprising a stator core with teeth protruding inwardly and windings wound on the teeth, and

a rotor comprising a shaft, a rotor core fixed to the shaft, and a ring magnet fixed to the circumferential outer surface of the rotor core, the magnet comprising a plurality of magnetic poles radially magnetized so that north poles and south poles are arranged alternately in the circumferential direction,

wherein boundary lines between magnetic poles are skewed by an angle α relative to an axis (Z) of the shaft, and a plurality of grooves formed in the circumferential outer surface of the rotor core, each groove extending axially from one end of the rotor core to the other end of the rotor core;

wherein the number of the grooves is equal to the number of magnetic poles of the rotor, and a start charging point of each magnetic pole is offset from a corresponding end of a corresponding groove.

12. The brushless motor of claim 11 , 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 middle of the corresponding groove and the center of the rotor is in the range of 10˜30 mechanical degrees.

13. A bladeless fan comprising the brushless motor of claim 11 .

14. The bladeless fan of claim 13 , wherein the fan comprises a base with an inner chamber and a ring nozzle mounted on the base, the nozzle comprises an inner passage communicating with the chamber of the base, the motor being disposed within the chamber, an impeller being mounted to the shaft of the motor and arranged to move air from outside of the base into the chamber and through the inner passage of the nozzle.

15. The bladeless fan of claim 14 , wherein the nozzle further comprises a ring outlet communicating with the inner passage, and a Coanda surface formed at the outlet of the nozzle.