Stator-plate overmoulding

1. A method of manufacturing a housing for the stator of an axial flux permanent magnet machine, the machine having a stator comprising a set of coils wound on respective stator bars and disposed circumferentially at intervals about an axis of the machine, and a rotor bearing a set of permanent magnets and mounted for rotation about said axis, and wherein said rotor and stator are spaced apart along said axis to define a gap therebetween in which magnetic flux in the machine is generally in an axial direction, the method comprising:

fabricating a radial wall for said stator housing to be located in said gap between said rotor and said stator by:

placing a resin membrane into a mould of an injection moulding machine;

injection moulding a set of reinforcing features onto said membrane using a thermoplastic polymer bondable when molten with the resin of said membrane; and

manufacturing said housing using said radial wall.

2. A method as claimed in claim 1 further comprising selecting said membrane and said thermoplastic polymer such that an in-plane coefficient of thermal expansion of said membrane is greater than a coefficient of thermal expansion of said thermoplastic polymer when set.

3. A method as claimed in claim 1 wherein said injection moulding comprises:

clamping said membrane in said mould;

heating said membrane;

unclamping said membrane to allow said membrane to thermally expand;

re-clamping said membrane; and

injecting said thermoplastic polymer into said mould.

4. A method as claimed in claim 3 further comprising holding said mould at a temperature of greater than 100° C.

5. A method as claimed in claim 1 further comprising heating said membrane prior to said injection moulding.

6. A method as claimed in claim 1 , wherein said resin membrane comprises a fibre-reinforced polymer, the method further comprising controlling a thickness of said gap by:

pressing a set of said stator bars into said fibre-reinforced polymer membrane whilst said membrane is mouldable; and

solidifying said fibre-reinforced polymer membrane to hold said set of stator bars in their respective positions.

7. A method as recited in claim 6 further comprising providing a supplementary membrane between said stator bars and said fibre-reinforced polymer membrane prior to said pressing and solidifying.

8. A method as recited in claim 6 further comprising heating said stator bars to make said polymer of said membrane mouldable.

9. A method as claimed in claim 6 comprising attaching said stator bars prior to said injection moulding and performing said injection moulding with said membrane horizontal.

10. A method as claimed in claim 1 wherein said resin membrane comprises a first fibre-reinforced thermoplastic polymer, and wherein said thermoplastic polymer comprises a second thermoplastic polymer miscible when molten with said first thermoplastic polymer.

11. A method as claimed in claim 10 wherein said second thermoplastic polymer is fibre-reinforced with glass fibre, carbon fibre, or aramid fibre.

12. A method as claimed in claim 1 wherein an in-plane Young's modulus of said membrane is less than 50 GPa.

13. A method as recited in claim 1 , wherein said membrane has a thickness of less than 1 mm.

14. A method as recited in claim 1 wherein said membrane comprises one or more of PPS, PPA, PEEK, ABS, and PA.

15. A method as claimed in claim 1 , wherein a said reinforcing feature has a height of at least 3 mm above a plane of said membrane.

16. A method as claimed in claim 1 , wherein a said stator bar has a shoe at least at one end, and wherein said set of reinforcing features defines a set of cavities for said shoes of said stator bars.

17. A method as claimed in claim 1 wherein said machine is a yokeless and segmented armature machine having a pair of said rotors, one to either side of said stator, wherein said housing has a pair of said radial walls, one between said stator and each respective rotor, connected by a generally cylindrical wall, wherein said housing defines a chamber for coolant for said coils of said stator, and wherein said radial walls with said reinforcing features hold said stator bars in position during operation of said machine.

18. A method of manufacturing an axial flux permanent magnet machine, the machine having a stator comprising a set of coils wound on respective stator bars and disposed circumferentially at intervals about an axis of the machine, and a rotor bearing a set of permanent magnets and mounted for rotation about said axis, and wherein said rotor and stator are spaced apart along said axis to define a gap therebetween in which magnetic flux in the machine is generally in an axial direction, the method comprising manufacturing a housing for the stator of the machine as recited in claim 1 , and using said housing to hold said set of stator coils in place in the machine.

19. A method as claimed in claim 12 wherein the in-plane Young's modulus of said membrane is less than 20 GPa.

20. A method as recited in claim 13 , wherein said membrane has a thickness of less than or equal to 0.5 mm.