Single-phase brushless motor

1. A single-phase brushless motor comprising a stator and a rotor rotatable with respect to the stator, the rotor comprising a rotor core having a plurality of permanent magnetic poles, the stator comprising a stator core and a winding wound on the stator core, the stator core comprising an outer annular portion, an inner annular portion, and a plurality of stator pole portions connecting the inner annular portion to the outer annular portion, the winding being wound around the stator pole portions, the rotor being received in the inner annular portion;

wherein the inner annular portion of the stator and the rotor form a substantially uniform air gap therebetween, an inner surface, which faces the rotor, of a part of the inner annular portion between every two adjacent ones of the stator pole portions rather than in the stator pole portions is formed with a recess, and a center of each recess is offset from a middle line between corresponding two adjacent ones of the stator pole portions, and

wherein, when the winding is not energized, a center line of each rotor permanent magnetic pole is offset from a center line of an adjacent one of the stator pole portions, in such a way as to enable the rotor start relative to the stator upon energizing the winding.

2. The single-phase brushless motor of claim 1 , wherein the inner surface of the inner annular portion is located on a circle concentric with the rotor.

3. The single-phase brushless motor of claim 1 , wherein a magnetic bridge is formed at the part of the inner annular portion between every two adjacent ones of the stator pole portions.

4. The single-phase brushless motor of claim 3 , wherein the magnetic bridge comprises a groove formed in an outer surface of the inner annular portion.

5. The single-phase brushless motor of claim 3 , wherein the magnetic bridge comprises an aperture or hole formed in the inner annular portion.

6. The single-phase brushless motor of claim 1 , wherein a number of the recesses is equal to a number of the stator pole portions and equal to a number of the magnetic poles of the rotor, the recesses being uniformly spaced from each other in a circumferential direction of the inner annular portion.

7. The single-phase brushless motor of claim 1 , wherein the stator pole portions are separately formed with respect to one or both of the inner annular portion and the outer annular portion.

8. The single-phase brushless motor of claim 1 , wherein the recesses run through the inner surface of the inner annular portion along an axial direction of the motor.

9. The single-phase brushless motor of claim 1 , wherein the recesses are spacingly disposed in the inner surface of the inner annular portion along an axial direction of the motor.

10. The single-phase brushless motor of claim 1 , wherein the motor has a start up angle which is in a range of 60 to 80 degrees electrical angle.

11. A single-phase brushless motor comprising:

a stator comprising a stator core and a winding wound on the stator core, the stator core comprising an outer annular portion, an inner annular portion, and a plurality of stator pole portions connected between the inner annular portion and the outer annular portion, the winding being wound around the stator pole portions; and

a rotor being received in the inner annular portion and rotatable with respect to the stator, the rotor comprising a plurality of permanent magnetic poles,

wherein the rotor and the inner annular portion of the stator form a substantially uniform air gap therebetween, an inner surface, which faces the rotor, of a part of the inner annular portion between every two adjacent stator pole portions rather than in the stator pole portions is formed with a recess, a center of each recess is offset from a middle line between corresponding two adjacent stator pole portions which results in a center line of each rotor permanent magnetic pole offset from a center line of an adjacent one of the stator pole portions when the motor is not powered on, such that the rotor is capable of being started in two directions.

12. The single-phase brushless motor of claim 11 , wherein an offset angle formed between the center of each recess and the middle line between corresponding two adjacent stator pole portions is in a range of 45 to 135 degrees electrical angle.

13. The single-phase brushless motor of claim 11 , wherein the inner surface of the inner annular portion is located on a circle concentric with the rotor.

14. The single-phase brushless motor of claim 11 , wherein a magnetic bridge is formed in the part of the inner annular portion between every two adjacent stator pole portions.

15. The single-phase brushless motor of claim 14 , wherein the magnetic bridge comprises a groove formed in an outer surface of the inner annular portion.

16. The single-phase brushless motor of claim 14 , wherein the magnetic bridge comprises an aperture or hole formed in the inner annular portion.

17. The single-phase brushless motor of claim 11 , wherein a number of the recesses is equal to a number of the stator pole portions and equal to a number of magnetic poles of the rotor, the recesses being uniformly spaced from each other in a circumferential direction of the inner annular portion.

18. The single-phase brushless motor of claim 11 , wherein the stator pole portions are separately formed with respect to one or both of the inner annular portion and the outer annular portion.

19. The single-phase brushless motor of claim 11 , wherein the rotor further comprises a rotor core and the plurality of permanent magnetic poles is formed by one or more permanent magnets mounted on a radially outer surface of the rotor core.