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A rotary electric machine is disclosed having stator windings and a rotor incorporating permanent magnets distributed about the axis of the rotor to create a magnetic field having circumferentially alternating north and south poles. In the invention, the principal structural member is an external sl

A rotary electric machine is disclosed having stator windings and a rotor incorporating permanent magnets distributed about the axis of the rotor to create a magnetic field having circumferentially alternating north and south poles. In the invention, the principal structural member is an external sleeve, this providing resistance to bending and to centrifugally induced stresses due to rotation. The direction of polarization of the permanent magnets 214 is such that the parts of the magnetic circuits that lie within the outer circumference of the rotor pass predominantly through the bodies of the permanent magnets 214, thereby avoiding the need for a central ferromagnetic core to complete the magnetic circuit of the magnets.

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What is claimed is: 1. A rotary electric machine comprising: a plurality of stator windings; and a rotor incorporating one or more permanent magnets to create a magnetic field having circumferentially alternating north and south poles and incorporating a torque transmitting section formed as a holl

What is claimed is: 1. A rotary electric machine comprising: a plurality of stator windings; and a rotor incorporating one or more permanent magnets to create a magnetic field having circumferentially alternating north and south poles and incorporating a torque transmitting section formed as a hollow tube of low magnetic permeability material, wherein the permanent magnets are arranged radially within and are radially retained by the hollow tube, wherein a part of a magnetic circuit that lies within the hollow tube passes predominantly through the permanent magnets, and wherein the torque transmitting section performs the function of at least a portion of a shaft of the rotary electric machine. 2. The rotary electric machine as claimed in claim 1, wherein the torque transmitting section of the rotor is formed of a ceramic material. 3. The rotary electric machine as claimed in claim 2, wherein the ceramic material comprises a high fracture toughness material of the zirconia or silicon nitride types. 4. The rotary electric machine as claimed in claim 1, wherein the one or more permanent magnets comprise a plurality of magnets provided within the hollow tube, each magnet extending tangentially between each adjacent pair of opposite poles of the rotor. 5. The rotary electric machine as claimed in claim 4, wherein a central mass-balancing core of a material having the same density as the permanent magnets is arranged radially inwardly of the magnets. 6. The rotary electric machine as claimed in claim 1, wherein a system of segmented magnets extends between each adjacent pair of opposite poles of the rotor, the segmented magnets being partly cylindrical and being polarized along an angle with a tangential component. 7. The rotary electric machine as claimed in claim 1, wherein the density profile of the rotor is substantially the same in all planes containing the axis of rotation of the rotor and in all planes normal to the axis of the rotor. 8. The rotary electric machine as claimed in claim 1, wherein the permanent magnets are formed of Neodymium-Boron-Iron or Samarium-Cobalt. 9. The rotary electric machine as claimed in claim 1, wherein the one or more permanent magnets constitute a single magnet arranged within the hollow tube, the single magnet having a shape of a diametrically magnetized cylinder. 10. The rotary electric machine as claimed in claim 9, wherein the single magnet has a shape of a diametrically magnetized cylinder with an axially extending cylindrical bore. 11. The rotary electric machine of claim 1, in which the rotary electric machine of claim 1 lacks a shaft at a core of the rotor, and the torque transmitting section performs the function of the portion of the shaft at the core of the rotor. 12. A rotary electric machine comprising: a plurality of stator windings; and a rotor incorporating one or more permanent magnets to create a magnetic field having circumferentially alternating north and south poles, the rotor including, a hollow tube of low magnetic permeability material surrounding the rotor, wherein the permanent magnets are arranged radially within and are radially retained by the hollow tube, wherein a part of a magnetic circuit within the hollow tube passes predominantly through the permanent magnets, and wherein the hollow tube performs the function of at least a portion of a shaft of the rotary electric machine. 13. The rotary electric machine as claimed in claim 12, wherein the rotor includes a core formed at least in part with non-ferromagnetic material. 14. The rotary electric machine of claim 13, in which the rotary electric machine of claim 11 lacks a shaft at the core of the rotor, and the hollow tube performs the function of the portion of the shaft at the core of the rotor. 15. The rotary electric machine as claimed in claim 12, wherein at least the hollow tube of the rotor is formed of a ceramic material. 16. The rotary electric machine as claimed in claim 15, wherein the ceramic material comprises a high fracture toughness material of the zirconia or silicon nitride types. 17. The rotary electric machine as claimed in claim 12, wherein the one or more permanent magnets constitute a system of segmented magnets, the system of segmented magnets extending tangentially between each adjacent pair of opposite poles of the rotor. 18. The rotary electric machine as claimed in claim 17, wherein a central mass-balancing core of a material having the same density as the permanent magnets is arranged radially inward of the magnets. 19. The rotary electric machine as claimed in claim 12, wherein a system of segmented magnets extends between each adjacent pair of opposite poles of the rotor, the segmented magnets being partly cylindrical and being polarized along an angle with a tangential component. 20. The rotary electric machine as claimed in claim 12, wherein the density profile of the rotor is substantially the same in all planes containing the axis of rotation of the rotor and in all planes normal to the axis of the rotor. 21. The rotary electric machine as claimed in claim 12, wherein the permanent magnet are formed of Neodymium-Boron-Iron or Samarium-Cobalt. 22. The rotary electric machine as claimed in claim 12, wherein the one or more permanent magnets constitute a single magnet arranged within the hollow tube, the single magnet having a shape of a diametrically magnetized cylinder. 23. The rotary electric machine as claimed in claim 22, wherein the single magnet has a shape of a diametrically magnetized cylinder with an axially extending cylindrical bore.