Electrical machine with contra-rotating rotors
An electrical machine comprising: a first stator member ( 16 ) having a field magnet ( 22 ); a second stator member ( 18 ) forming an armature, the second stator member ( 18 ) being spaced from the first stator member ( 16 ); and a pair of contra-rotatable rotors ( 12 a, 12 b ) disposed between the first and second stator members ( 16, 18 ); wherein at least a portion ( 14 ) of each of the rotors ( 12 a, 12 b ) is magnetisable so as to transmit magnetic flux between the field magnet ( 22 ) and the armature.
1. An electrical machine comprising:
a first stator member having a field magnet;
a second stator member forming an armature, the second stator member being spaced from the first stator member; and
a pair of contra-rotatable rotors disposed between the first and second stator members,
wherein at least a portion of each of the rotors is magnetisable,
wherein each rotor comprises a plurality of pole pieces which are magnetisable,
wherein at least one of the rotors is, in use, driven by a prime mover and the rotors transmit magnetic flux from the field magnet to the armature thereby inducing an electromotive force, wherein a magnetic field produced by the plurality of pole pieces extends between the first stator member and the second stator member, such that the plurality of pole pieces of the first and second stator members act as flux linkage poles that transmit the magnetic flux from the field magnet of the first stator to the armature of the second stator member, and
wherein the first and second stator members and the rotors are arranged concentrically.
2. An electrical machine as claimed in claim 1 , wherein the field magnet is an electromagnet or a permanent magnet.
3. An electrical machine as claimed in claim 1 , wherein the first stator member comprises a plurality of field magnets spaced around the first stator member.
4. An electrical machine as claimed in claim 1 , wherein the second stator member comprises a conductor or conductive coil which forms the armature.
5. An electrical machine as claimed in claim 1 , wherein the first and second stator members and the rotors each comprise a plurality of poles.
6. An electrical machine as claimed in claim 5 , wherein the poles extend in an axial direction.
7. An electrical machine as claimed in claim 5 , wherein one or more of the poles are helical.
8. An electrical machine as claimed in claim 1 , wherein at least one of the rotors, the first stator member and the second stator member comprises a plurality of sets of poles.
9. An electrical machine as claimed in claim 1 , wherein the rotors are coupled by a gearbox which causes the rotors to rotate in opposite directions.
10. An electrical machine as claimed in claim 9 , wherein the gearbox provides synchronous rotation of the rotors.
11. An electrical machine as claimed in claim 9 , wherein the gearbox is an epicyclic gearbox.
12. An electrical machine as claimed in claim 10 , wherein the gearbox comprises a fixed idler gear located between the rotors.
13. An electrical machine as claimed in claim 9 , wherein the gearbox comprises an overload clutch to allow non-synchronous movement of the rotors.
14. An electrical machine as claimed in claim 1 , wherein the plurality of pole pieces comprise a material having a magnetic permeability in a range between 500 to 2000.
15. An electrical machine as claimed in claim 1 , wherein the plurality of pole pieces are ferromagnetic.