Electric machine

1. A stator assembly adapted for use in an external rotor electric motor, said assembly comprising:

a stator core having a hub, a plurality of teeth extending radially outward from the hub, a root tooth diameter and an outer diameter, each tooth of said plurality of teeth having a root, a neck extending from the root and a head opposite the root, said neck having a maximum width, and each adjacent pair of teeth of said plurality of teeth has a pitch measured at the roots of the corresponding teeth; and

a winding wrapped around each tooth of at least three teeth of said plurality of teeth of the stator core;

wherein the outer diameter of the stator core is between about 220 mm and about 300 mm;

wherein a ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is less than about 0.7; and

wherein a ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is greater than about 0.36.

2. A stator assembly as set forth in claim 1 wherein the root tooth diameter of the stator core is between about 100 mm and about 200 mm.

3. A stator assembly as set forth in claim 2 wherein root tooth diameter of the stator core is about 180 mm and the outer diameter of the stator core is about 264 mm.

4. A stator assembly as set forth in claim 2 wherein the ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is about 0.68.

5. A stator assembly as set forth in claim 1 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is greater than about 0.37.

6. A stator assembly as set forth in claim 5 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is greater than about 0.45.

7. A stator assembly as set forth in claim 6 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is about 0.5.

8. A stator assembly as set forth in claim 6 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is about 0.49.

9. A stator assembly as set forth in claim 1 wherein the winding comprises at least one of aluminum and copper.

10. A stator assembly as set forth in claim 9 wherein the winding comprises copper clad aluminum.

11. An electric machine comprising:

a stator core having a hub and a plurality of teeth extending radially outward from the hub, each tooth of said plurality of teeth having a root, a neck extending from the root and a head opposite the root, said neck having a maximum width, each adjacent pair of teeth of said plurality of teeth having a pitch measured at the roots of the corresponding teeth;

a winding wrapped around each tooth of at least three teeth of said plurality of teeth of the stator core;

a rotor body rotatably mounted on the stator core including an annular wall having an interior surface facing said stator core; and

a plurality of magnets positioned on the annular wall of the rotor body for creating a plurality of magnetic dipoles spaced circumferentially around the annular wall creating magnetic flux inside the interior surface of the rotor body wall, each of said plurality of magnets having a maximum residual inductance (Br) of no more than about 12,000 Gauss;

wherein the outer diameter of the stator core is between about 220 mm and about 300 mm;

wherein a ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is less than about 0.7; and

wherein a ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is greater than about 0.36.

12. An electric machine as set forth in claim 11 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is at least about 0.37.

13. An electric machine as set forth in claim 12 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is at least about 0.45.

14. An electric machine as set forth in claim 13 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is about 0.5.

15. An electric machine as set forth in claim 13 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is about 0.49.

16. An electric machine as set forth in claim 11 wherein the stator core is positioned inside the plurality of magnets and the windings are selectively energized to drive the rotor body to rotate relative to the core.

17. An electric machine as set forth in claim 11 wherein the maximum residual inductance (Br) of each of said plurality of magnets is no more than about 8000 Gauss.

18. An electric machine as set forth in claim 17 wherein the maximum residual inductance (Br) of each of said plurality of magnets is no more than about 5000 Gauss.

19. An electric machine comprising:

a stator core having a hub and a plurality of teeth extending radially outward from the hub, the stator core having a root tooth diameter and an outer diameter;

a winding wrapped around each tooth of at least three teeth of said plurality of teeth of the stator core; and

a rotor body rotatably mounted on the stator core including an annular wall having an interior surface facing said stator core;

wherein the outer diameter of the stator core is between about 220 mm and about 300 mm and

wherein a ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is less than about 0.7.

20. An electric machine as set forth in claim 19 wherein the root tooth diameter of the stator core is between about 100 mm and about 200 mm.

21. An electric machine as set forth in claim 20 wherein root tooth diameter of the stator core is about 180 mm and the outer diameter of the stator core is about 264 mm.

22. An electric machine as set forth in claim 19 wherein the ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is about 0.68.

23. An electric machine as set forth in claim 19 further comprising a plurality of magnets positioned on the annular wall of the rotor body, wherein the stator core is positioned inside the plurality of magnets and the windings are selectively energized to drive the rotor body to rotate relative to the core.

24. An electric machine as set forth in claim 19 wherein the thickness of the winding wrapped around each tooth is substantially uniform.

25. An electric machine as set forth in claim 19 wherein the winding comprises at least one of aluminum and copper.

26. An electric machine as set forth in claim 25 wherein the winding comprises copper clad aluminum.

27. An electric machine as set forth in claim 19 further comprising a plurality of magnets positioned on the annular wall of the rotor body for creating a plurality of magnetic dipoles spaced circumferentially around the annular wall creating magnetic flux inside the interior surface of the rotor body wall, each of said plurality of magnets having a maximum residual inductance (Br) of no more than about 12,000 Gauss.

28. An electric machine as set forth in claim 27 wherein the maximum residual inductance (Br) of each of said plurality of magnets is no more than about 8000 Gauss.

29. An electric machine as set forth in claim 28 wherein the maximum residual inductance (Br) of each of said plurality of magnets is no more than about 5000 Gauss.

30. A stator assembly adapted for use in an external rotor electric motor, said assembly comprising:

a stator core having a hub and a plurality of teeth extending radially outward from the hub, the stator core having a root tooth diameter and an outer diameter; and

a winding wrapped around each tooth of at least three teeth of said plurality of teeth of the stator core;

wherein the outer diameter of the stator core is between about 220 mm and about 300 mm; and

wherein a ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is less than about 0.7.

31. A stator assembly as set forth in claim 30 wherein the root tooth diameter of the stator core is between about 100 mm and about 200 mm.

32. A stator assembly as set forth in claim 31 wherein the root tooth diameter of the stator core is about 180 mm and the outer diameter of the stator core is about 264 mm.

33. A stator assembly as set forth in claim 30 wherein the ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is about 0.68.

34. A stator assembly as set forth in claim 30 wherein the winding comprises at least one of aluminum and copper.

35. A stator assembly as set forth in claim 34 wherein the winding comprises copper clad aluminum.

36. A stator assembly adapted for use in an external rotor electric motor having a rotor body rotatably mounted on the stator assembly, said rotor body comprising a plurality of magnets having a maximum residual inductance (Br) or no more than about 12,000 Gauss for creating a plurality of magnetic dipoles spaced circumferentially around the rotor body, said assembly comprising:

a stator core having a hub, a plurality of teeth extending radially outward from the hub, each tooth of said plurality of teeth having a root, a neck extending from the root and a head opposite the root, said neck having a maximum width, each adjacent pair of teeth of said plurality of teeth has a pitch measured at the roots of the corresponding teeth; and

a winding wrapped around each tooth of at least three teeth of said plurality of teeth of the stator core;

wherein the outer diameter of the stator core is between about 220 mm and about 300 mm;

wherein a ratio of the root tooth diameter of the stator core to the outer diameter of the stator core is less than about 0.7; and

wherein a ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is greater than about 0.36.

37. A stator assembly as set forth in claim 36 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is at least about 0.37.

38. A stator assembly as set forth in claim 37 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is at least about 0.45.

39. A stator assembly as set forth in claim 38 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is at least about 0.5.

40. A stator assembly as set forth in claim 39 wherein the ratio of the maximum tooth neck width to the tooth pitch measured at the root of the teeth is about 0.49.

41. A stator assembly as set forth in claim 36 wherein the winding comprises at least one of aluminum and copper.

42. A stator assembly as set forth in claim 41 wherein the winding comprises copper clad aluminum.