Pole-piece bonding
We describe a method of manufacturing a housing for the stator of an axial flux permanent magnet machine, in particular a Yokeless and Segmented Armature motor, 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 comprises: fabricating a radial wall for said stator housing to be located in said gap between said rotor and said stator by: providing a membrane of fibre-reinforced polymer material; pressing a set of said stator bars into said membrane of fibre-reinforced polymer whilst said polymer is mouldable, wherein said reinforcement inhibits said stator bars from pushing through said membrane; solidifying said polymer to hold said set of stator bars in their respective positions; and manufacturing said housing using said radial wall.
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:
providing a membrane of polymer material;
pressing at least ends or shoes of said set of said stator bars into said membrane of polymer whilst said polymer is mouldable, wherein at least a said end or shoe of a said stator bar is formed from a porous magnetic material;
solidifying said polymer to hold said ends or shoes of said set of stator bars in their respective positions; and
manufacturing said housing using said radial wall;
wherein said polymer of said membrane bonds with said porous magnetic material during said pressing to bond said set of stator bars to said polymer.
2. A method as claimed in claim 1 wherein substantially a complete face of said end or shoe of a stator bar bonds with said membrane.
3. A method as claimed in claim 1 wherein said end or shoe of a stator bar comprises a face with a step or flange around the edge; wherein said membrane has a set of apertures into which said faces of said ends or shoes of said stator bars fit, and wherein said step or flange presses into and bonds with said polymer membrane.
4. A method as claimed in claim 1 wherein, during said bonding, material diffuses between said polymer membrane and said porous magnetic material to bond said membrane with said porous magnetic material.
5. A method as claimed in claim 1 wherein said membrane is a fibre-reinforced polymer material; and wherein during said pressing of said stator bars into said membrane of fibre-reinforced polymer whilst said polymer is mouldable said reinforcement inhibits said stator bars from pushing through said membrane.
6. A method as claimed in claim 1 wherein said porous magnetic material comprises soft magnetic composite (SMC).
7. A method as claimed in claim 1 wherein said porous magnetic material comprises laminated magnetic material.
8. A method as claimed in claim 1 further comprising treating a surf ace of at least an end or shoe of a said stator bar to improve the porosity of said end or shoe.
9. A method as claimed in claim 1 further comprising heating said stator bars to make said polymer of said membrane mouldable.
10. A method as claimed in claim 1 wherein an in-plane Young's modulus of said membrane is less than 50 GPa and more preferably less than20 GPa.
11. A method as recited in claim 1 , wherein said membrane has a thickness of less than 1 mm, preferably less than or equal to 0.5 mm.
12. A method as recited in claim 1 wherein said membrane polymer comprises one or more of PPS, PPA, PEEK, ABS and PA.
13. A method as claimed in claim 1 wherein said membrane comprises a first, fibre-reinforced thermoplastic polymer, the method further comprising strengthening said membrane of fibre-reinforced polymer by:
placing said membrane of fibre-reinforced polymer into a mould of an injection moulding machine; and
injection moulding a set of reinforcing features onto said membrane using a second thermoplastic polymer miscible when molten with said first thermoplastic polymer.
14. A method as claimed in claim 13 wherein said second thermoplastic polymer is fibre-reinforced with glass fibre, carbon fibre, or aramid fibre.
15. A method as claimed in claim 13 , 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.
16. A method as claimed in claim 13 further comprising heating said membrane of fibre-reinforced polymer prior to said injection moulding.
17. A method as claimed in claim 13 wherein said radial walls with said reinforcing features hold said stator bars in position during operation of said machine.
18. A method as claimed in claim 13 , wherein a said reinforcing feature has a height of at least 3 mm above a plane of said membrane of fibre-reinforced polymer.
19. A method as claimed in claim 1 further comprising providing a supplementary layer of polymer between said stator bars and said membrane prior to said pressing and solidifying.
20. 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, and wherein said housing defines a chamber for coolant for said coils of said stator.
21. 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.
22. A stator assembly for 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 stator assembly comprising a stator housing containing said stator, said stator housing having a radial wall comprising a membrane of fibre-reinforced polymer to be located in said gap between said rotor and said stator, wherein at least an end or shoe of a said stator bar is formed from soft magnetic composite (SMC), and wherein said polymer of said membrane of fibre-reinforced polymer is bonded with said SMC to bond said set of stator bars to said membrane of fibre-reinforced polymer.