Electrical machine
An axial flux electrical machine is provided. The machine includes a plurality of rotors, each sandwiched between a respective pair of stator parts. The plurality of rotors, together with their respective stators, are axially-stacked to form a multistage machine. Heat exchangers are provided adjacent each stator to provide cooling. Each rotor disc is a composite rotor disc in which permanent magnets are embedded. The magnets are embedded in apertures through each disc so that surfaces of the magnets are flush with surfaces of the respective rotor disc.
1. An axial-flux electrical machine comprising a rotor-stator module of the machine, the rotor-stator module including a stator having first and second axially spaced stator portions, and carrying windings of an electrical conductor thereon, a rotatable member which extends at least between the stator portions, along the axis of rotation of the machine, and which is rotatable with respect to the stator portions, and a rotor mounted on the rotatable member, the rotor being located adjacent and between the stator portions, and including a series of circumferentially-distributed magnets thereon wherein the rotor-stator module includes a first cooling structure in contact with the first stator portion, the first cooling structure including channels therein for conveying a coolant fluid therethrough, and a second cooling structure in contact with the second stator portion, the second cooling structure defining channels therein for conveying coolant fluid therethrough.
2. An electrical machine according to claim 1 , wherein the machine includes a plurality of such rotor-stator modules arranged to form a series of modules located coaxially along the axis of rotation of the machine, the series having a first module and a last module, and the rotatable member extending through the series of modules along the axis of rotation, wherein each module, except the first module, is arranged such that the first cooling structure thereof is in contact with the second stator portion of the previous module in the series, and wherein the second cooling structure is provided on the last module of the series, in contact with the second stator portion of that last module.
3. An electrical machine according to claim 1 , wherein each cooling structure is provided by a heat exchanger comprising an outer part having a substantially flat annular disc portion from which an inner wall, a first plurality of fins, and an outer wall project, an inner part having a substantially flat annular disc portion from which an inner wall, a second plurality of fins, and an outer wall project, wherein the inner part is located inside, and in contact with, the outer part, such that the outer wall of the inner part is radially inward of the outer wall of the outer part, and the inner wall of the inner part is radially outward of the inner wall of the outer part, and such that the first and second plurality of fins interdigitate so as to form a series of circumferential channels which provide the channels of the cooling structure.
4. An electrical machine according to claim 1 , wherein, in use, a flux travels in a loop substantially axially through adjacent, circumferentially-distributed, magnets of the rotor and substantially circumferentially through each of the stator portions.
5. An electrical machine according to claim 4 , wherein the magnets are arranged in pairs, and the flux travels in a respective loop through each pair of magnets, travelling through each magnet of the pair in a different respective direction.
6. An electrical machine according to claim 1 , wherein the rotor includes a series of circumferentially-distributed magnets thereon, wherein each magnet extends through an aperture in the rotor.
7. An electrical machine according to claim 6 , wherein the aperture is such that material of the rotor surrounds the magnet so as to act to locate each magnet in radial and circumferential directions.
8. An electrical machine according to claim 6 , wherein each magnet projects beyond the surrounding material of the rotor on at least one side of the rotor.
9. An electrical machine according to claim 1 , wherein each magnet is fixed on the rotor by an adhesive material provided by each magnet and material of the rotor.
10. An electrical machine according to claim 1 , wherein the rotor is of a magnetically or electrically insulating material.
11. An electrical machine according to claim 1 , wherein the rotor is a heat insulating material.
12. An electrical machine according to claim 1 , wherein the rotor is formed from a composite material that is a glass-fibre-and-resin-based cross-laminated material.
13. An electrical machine according to claim 1 , wherein the cooling structure defines plural coolant-conveying channels at substantially the same axial position and arranged such that coolant is conveyed thereby at a plurality of different radial positions.