Motor and compressor

1. A motor comprising:

a rotating shaft;

a single rotor fixed to the rotating shaft; and

first and second stators arranged on opposite axial sides of the rotor with the first and second stators facing each other through air gaps on the opposite axial sides of the rotor,

each of the first and second stators including

a back yoke,

circumferentially arranged teeth located on an air gap side of a respective one of the back yokes, and

coils wound around the teeth,

the back yoke of the first stator having a portion facing an end face of the rotating shaft,

the back yoke of the second stator having a shaft hole with the rotating shaft passing therethrough,

the back yoke of the first stator having a through hole smaller than an outer diameter of the rotating shaft, the rotating shaft not being received in the through hole of the back yoke of the first stator, and

the back yoke of the first stator having a thickness Ty 1 smaller than a thickness Ty 2 of the back yoke of the second stator, with the entire back yokes of the first and second stators having respective generally uniform axial thicknesses Ty 1 and Ty 2 .

2. The motor as claimed in claim 1 , wherein

the through hole of the back yoke of the first stator is centered on an axis passing through a center of the shaft hole of the back yoke of the second stator.

3. The motor as claimed in claim 2 , wherein

an outside radius Ro of the back yoke of the first stator is about the same as an outside radius of the back yoke of the second stator, a radius of the through hole of the back yoke of the first stator is Ri 1 , a radius of the shaft hole of the back yoke of the second stator is Ri 2 , and

( Ro −Ri 1) Ty 1 =( Ro −Ri 2) Ty 2.

4. The motor as claimed in claim 1 , wherein

a magnetic flux passing through magnetic materials of the rotor forms a magnetic circuit axially penetrating the first and second stators.

5. The motor as claimed in claim 1 , further comprising

a bearing freely rotatably supporting the rotating shaft with said bearing being located nearer to the second stator than to the rotor.

6. The motor as claimed in claim 1 , wherein

the rotor includes permanent magnets.

7. The motor as claimed in claim 1 , wherein

the rotor includes permanent magnets arranged in one axial layer and magnetic materials arranged on opposite axial end faces of the permanent magnets, with the magnetic materials being separated per magnetic pole.

8. A compressor equipped with the motor as claimed in claim 1 .

9. The motor as claimed in claim 1 , wherein

the second stator has an overall axial thickness larger than the overall axial thickness of the first stator.

10. The motor as claimed in claim 9 , wherein

the first and second stator teeth having the coils thereon have equal axial thicknesses.

11. The motor as claimed in claim 1 , wherein

the first and second stator teeth having the coils thereon have equal axial thicknesses.

12. The motor as claimed in claim 1 , wherein Rto 1 <Rto 2 and Rti 1 <Rti 2 , where

Rto 1 is a radius of a circle connecting outermost peripheries of the teeth of the first stator,

Rti 1 is a radius of a circle connecting innermost peripheries of the teeth of the first stator,

Rto 2 is a radius of a circle connecting outermost peripheries of the teeth of the second stator, and

Rti 2 is a radius of a circle connecting innermost peripheries of the teeth of the second stator.

13. The motor as claimed in claim 12 , wherein (Rto 1 −Rti 1 ) >(Rto 2 −Rti 2 ).

14. The motor as claimed in claim 12 , wherein Wc 1 >Wc 2 , where

Wc 1 is a radial width of the coils of the first stator, and

Wc 2 is a radial width of the coils of the second stator.

15. The motor as claimed in claim 14 , wherein Lc 1 <Lc 2 , where

Lc 1 is an axial length of the coils of the first stator and

Lc 2 is an axial length of the coils of the second stator.

16. The motor as claimed in claim 15 , wherein Wc 1 ·Lc 1 ≈Wc 2 ·Lc 2 .

17. The motor as claimed in claim 12 , wherein

each of the first and second stators has respective wide portions on air gap side surfaces of tips of the teeth, and

Rho 1 ≧Rto 1 , Rho 2 ≧Rto 2 , Rhi 1 ≦Rti 1 , and Rhi 2 ≦Rti 2 , where

Rho 1 is a radius of a circle connecting outermost peripheries of the wide portions of the first stator,

Rhi 1 is a radius of a circle connecting innermost peripheries of the wide portions of the first stator,

Rho 2 is a radius of a circle connecting outermost peripheries of the wide portions of the second stator, and

Rhi 2 is a radius of a circle connecting innermost peripheries of the wide portions of the second stator.

18. The motor as claimed in claim 12 , wherein Rro 1 <RRo 2 , and Rri 1 <RRi 2 , where

RRo 1 is a radius of a circle connecting outermost peripheries of magnetic materials of the rotor at portions facing the first stator of the rotor,

RRi 1 is a radius of a circle connecting innermost peripheries of the magnetic materials of the rotor at portions facing the first stator,

RRo 2 is a radius of a circle connecting outermost peripheries of the magnetic materials of the rotor at portions facing the second stator, and

RRi 2 is a radius of a circle connecting innermost peripheries of the magnetic materials of the rotor at portions facing the second stator.

19. The motor as claimed in claim 12 , wherein RRo 1 ≈Rto 1 , RRo 2 ≈Rto 2 , RRi 1 ≈Rti 1 , and RRi 2 ≈Rti 2 , where

RRo 1 is a radius of a circle connecting outermost peripheries of magnetic materials of the rotor at portions facing the first stator,

RRi 1 is a radius of a circle connecting innermost peripheries of the magnetic materials of the rotor at portions facing the first stator,

RRo 2 is a radius of a circle connecting outermost peripheries of the magnetic materials of the rotor at portions facing the second stator, and

RRi 2 is a radius of a circle connecting innermost peripheries of the magnetic materials of the rotor at portions facing the second stator.

20. The motor as claimed in claim 12 , wherein RRo ≧Rto 1 , RRo ≧Rto 2 , Rti 1 ≧RRi, and Rti 2 ≧RRi, where

RRo is a radius of a circle connecting outermost peripheries of magnetic materials of the rotor at portions facing the first and second stators, and

RRi is a radius of a circle connecting innermost peripheries of the magnetic materials of the rotor at portions facing the first and second stators.

21. The motor as claimed in claim 1 , wherein the back yoke of the first stator includes axially protruding ribs.

22. A compressor comprising:

a closed container to which a suction pipe and a discharge pipe for a refrigerant are connected:

a compressor mechanism located in the closed container; and

a motor located on one side of the compression mechanism in the closed container and configured to drive the compression mechanism, the motor including

a rotating shaft, the motor being configured to drive the compression mechanism through the rotating shaft,

a single rotor fixed to one end of the rotating shaft, and

first and second stators arranged on opposite axial sides of the rotor with the first and second stators facing each other through air gaps on the opposite axial sides of the rotor, the second stator being located between the compression mechanism and the first stator, each of the first and second stators including

a back yoke,

circumferentially arranged teeth located on an air gap side of a respective one of the back yokes, and

coils wound around the teeth,

the back yoke of each of the first and second stators having two axial end surfaces and an outer peripheral surface, the outer peripheral surface being fixed to an inner surface of the closed container,

the back yoke of the first stator having a portion facing an end face of the rotating shaft,

the back yoke of the second stator having a shaft hole with the rotating shaft passing therethrough,

the back yoke of the first stator having a through hole smaller than an outer diameter of the rotating shaft, the rotating shaft not being received in the through hole of the back yoke of the first stator, and

the back yoke of the first stator having a thickness Ty 1 smaller than a thickness Ty 2 of the back yoke of the second stator, with the entire back yokes of the first and second stators having respective generally uniform axial thicknesses Ty 1 and Ty 2 .

23. The compressor as claimed in claim 22 , wherein

a sectional area of the back yoke of the first stator along a plane including the axis of the back yoke of the first stator is the same as a sectional area of the back yoke of the second stator along the plane.

24. The compressor as claimed in claim 22 , wherein

the through hole of the back yoke of the first stator is centered on an axis passing through a center of the shaft hole of the back yoke of the second stator.

25. The compressor as claimed in claim 22 , wherein

the motor has a bearing located between the compression mechanism and the rotor to support the rotating shaft.

26. The compressor as claimed in claim 22 , wherein

the second stator has an overall axial thickness larger than the overall axial thickness of the first stator.

27. The compressor as claimed in claim 26 , wherein

the first and second stator teeth having the coils thereon have equal axial thicknesses.

28. The compressor as claimed in claim 22 , wherein

the first and second stator teeth having the coils thereon have equal axial thicknesses.

29. A motor comprising:

a rotating shaft;

a single rotor fixed to the rotating shaft; and

first and second stators arranged on opposite axial sides of the rotor with the first and second stators facing each other through air gaps on the opposite axial sides of the rotor,

each of the first and second stators including

a back yoke,

circumferentially arranged teeth located on an air gap side of a respective one of the back yokes, and

coils wound around the teeth,

the back yoke of the first stator having a portion facing an end face of the rotating shaft,

the back yoke of the second stator having a shaft hole with the rotating shaft passing therethrough, and

the back yoke of the first stator having a thickness Ty 1 smaller than a thickness Ty 2 of the back yoke of the second stator,

the second stator having an overall axial thickness larger than an overall axial thickness of the first stator, and

the first and second stator teeth with the coils thereon having equal axial thicknesses.

30. A compressor comprising:

a closed container to which a suction pipe and a discharge pipe for a refrigerant are connected:

a compressor mechanism located in the closed container; and

a motor located on one side of the compression mechanism in the closed container and configured to drive the compression mechanism, the motor including

a rotating shaft, the motor being configured to drive the compression mechanism through the rotating shaft,

a single rotor fixed to one end of the rotating shaft, and

first and second stators arranged on opposite axial sides of the rotor with the first and second stators facing each other through air gaps on the opposite axial sides of the rotor, the second stator being located between the compression mechanism and the first stator, each of the first and second stators including

a back yoke,

circumferentially arranged teeth located on an air gap side of a respective one of the back yokes, and

coils wound around the teeth,

the back yoke of each of the first and second stators having two axial end surfaces and an outer peripheral surface, the outer peripheral surface being fixed to an inner surface of the closed container,

the back yoke of the first stator having a portion facing an end face of the rotating shaft,

the back yoke of the second stator having a shaft hole with the rotating shaft passing therethrough, and

the back yoke of the first stator having a thickness Ty 1 smaller than a thickness Ty 2 of the back yoke of the second stator,

the second stator having an overall axial thickness larger than an overall axial thickness of the first stator, and

the first and second stator teeth with the coils thereon having equal axial thicknesses.