Single-phase motor

1. A single phase motor, comprising:

a rotor including magnetic poles; and

a stator comprising a stator core and a winding wound on the stator core, the stator core comprising a plurality of stator teeth each comprising a tooth body extending along a radial direction of the rotor and a tooth end formed at an end of the tooth body, the tooth end comprising first and second arcuate regions facing the rotor,

wherein, when the winding is not energized, a first magnetic coupling between said first arcuate region and a selected magnetic pole of said rotor is greater than a second magnetic coupling between said second arcuate region and the selected magnetic pole, said first arcuate region being offset from a selected tooth body in such a way as to enable movement of said rotor to initiate in either of two opposite directions relative to said selected tooth body upon energizing the winding, and

wherein each two adjacent tooth ends of the stator are completely disconnected from each other, and only an empty slot is between the each two adjacent tooth ends.

2. The single phase motor of claim 1 , wherein each magnetic pole has an edge region facing the stator, a distance between the edge region and a central axis of the rotor decreases from a central portion of the edge region to end portions of the edge region.

3. The single phase motor of claim 2 , wherein the edge region of each magnetic pole is symmetrical about a middle radial line of the magnetic pole.

4. The single phase motor of claim 2 , wherein the first arcuate region is coaxial with the rotor, and a width of an air gap formed between the edge region of the magnetic pole and the first arcuate region increase from the central portion of the edge region to the end portions of the edge region.

5. The single phase motor of claim 4 , wherein a width of the air gap at the end portion of the edge region and a width of the air gap at the central portion of the edge region have a ratio ranging from 5:1 to 1.5 to 1.

6. The single phase motor of claim 1 , wherein:

the rotor defines a central axis;

an inner surface of the first arcuate region facing the rotor has a first radius uniform about the central axis; and

an inner surface of the second arcuate region facing the rotor has a second radius about the central axis greater than the first radius.

7. The single phase motor of claim 1 , wherein the first arcuate region is made of a first soft ferromagnetic material, and the second arcuate region is made of a second soft ferromagnetic material different from the first soft ferromagnetic material, the second soft ferromagnetic material having a lower magnetic permeability than the first soft ferromagnetic material.

8. The single phase motor of claim 1 , wherein, when the winding is not energized, a middle radial line of the selected magnetic pole is angularly offset from a middle radial line of the selected tooth body by a start up angle ranging from 45 to 135 degrees electrical angle.

9. The single phase motor of claim 1 , wherein a ratio of a circumferential width of the empty slot to a minimum air gap between the magnetic poles of the rotor and the stator core ranges from zero to four.

10. The single phase motor of claim 1 , wherein the second arcuate region defines a recess, each magnetic pole has a circumferential outer surface facing the stator, and the size of an air gap formed between the second arcuate region and the circumferential outer surface of the magnetic pole is greater than the size of the air gap formed between the first arcuate region and the circumferential outer surface of the magnetic pole.

11. The single phase motor of claim 1 , wherein the stator core comprises a first stator portion and a second stator portion, the stator teeth extending inwardly from the second stator portion, the tooth ends cooperatively forming the first stator portion.

12. The single phase motor of claim 11 , wherein the second stator portion is ring-shaped.

13. The single phase motor of claim 1 , wherein:

the rotor defines a central axis;

the first arcuate region has a first radius uniform about the central axis; and

the second arcuate region has a second radius uniform about the central axis, the second radius being equal to the first radius.

14. The single phase motor of claim 13 , wherein the second arcuate region defines a hole covered by an inner surface of the second arcuate region.

15. A single phase motor, comprising:

a rotor including magnetic poles; and

a stator comprising a stator core and a winding wound on the stator core, the stator core comprising a plurality of stator teeth each comprising a tooth body and a tooth end formed at an end of the tooth body, the tooth end comprising first and second arcuate regions both made of magnetic material and facing the rotor, wherein each two adjacent tooth ends of the stator are completely disconnected from each other, and only an empty slot is between the each two adjacent tooth ends,

wherein, when the winding is not energized, a first magnetic coupling between said first arcuate region and a selected magnetic pole of said rotor is greater than a second magnetic coupling between said second arcuate region and the selected magnetic pole, said first arcuate region being offset from a selected tooth body in such a way as to enable movement of said rotor to initiate in either of two opposite directions relative to said selected tooth body upon energizing the winding.

16. The single phase motor of claim 15 , wherein:

the rotor defines a central axis;

an inner surface of the first arcuate region facing the rotor has a first radius uniform about the central axis; and

an inner surface of the second arcuate region facing the rotor has a second radius about the central axis greater than the first radius.

17. The single phase motor of claim 15 , wherein a ratio of a circumferential width of the empty slot to a width of an air gap formed between the edge regions of the magnetic poles of the rotor and the first arcuate regions of the stator range is less than four.