Method of forming irregular shaped coils of an electric machine

1. A method of fabricating a coil for mounting on a tooth of a stator or a rotor of an electric machine, the method comprising:

winding a wire about a mandrel in a spiral pattern to form the coil having an internal cavity extending from a first end to a second end and having a first shape corresponding to the shape of the mandrel;

removing the coil having the first shape from the mandrel;

applying a mechanical force on the coil to change the shape of the coil from the first shape to a second shape, wherein the second shape corresponds to the shape of the tooth, wherein applying the mechanical force on the coil includes selectively increasing a size of the cavity at one of the first end or the second end; and

mounting the coil of the second shape on the tooth.

2. The method of claim 1 , wherein the wire is formed of a plurality of strands of an electrical conductor.

3. The method of claim 1 , wherein the wire is formed by twisting together an electrical conductor or made in the form of a Litz wire.

4. The method of claim 1 , wherein the wire has a circular cross-sectional shape.

5. The method of claim 1 , wherein the wire has one of a square or a rectangular cross-sectional shape.

6. The method of claim 1 , wherein the first shape is a cylindrical shape or any shape with a substantially constant perimeter.

7. The method of claim 1 , wherein the second shape is a trapezoidal shape.

8. The method of claim 1 , wherein applying the mechanical force on the coil includes changing a shape of the internal cavity.

9. The method of claim 8 , wherein changing the shape of the internal cavity includes changing a cross-sectional shape of the internal cavity along a plane perpendicular to a central axis of the internal cavity from a circular shape to a rectangular shape.

10. The method of claim 9 , wherein a width and a length of the rectangular shape both vary from the first end to the second end.

11. The method of claim 9 , wherein a perimeter of the rectangular shape is substantially a constant from the first end to the second end and an area of the rectangular shape varies from the first end to the second end.

12. The method of claim 11 , wherein the area of the rectangular shape increases from the first end to the second end.

13. The method of claim 8 , wherein changing the shape of the internal cavity includes changing a 3-dimensional shape of the inner cavity from a cylindrical shape to a trapezoidal shape.

14. The method of claim 1 , wherein applying the mechanical force on the coil includes inserting a second mandrel into the internal cavity of the coil to change a shape of the first end of the internal cavity compared to the shape of the second end of the internal cavity.

15. The method of claim 1 , wherein applying the mechanical force on the coil includes applying a first mechanical force to increase a dimension of the internal cavity at one of the first end or the second end and a second mechanical force to decrease a dimension of the internal cavity at the other of the first end or the second end.

16. The method of claim 15 , wherein the first mechanical force acts towards a central axis of the internal cavity and the second mechanical force acts away from the central axis.

17. The method of claim 1 , wherein applying the mechanical force on the coil includes stretching the wire of the coil that defines at least one of the first end or the second end of the internal cavity.

18. The method of claim 1 , wherein the wire is made of copper.