Electric machine rotor sleeve

1. A rotor sleeve for a rotor of an electric machine, the rotor sleeve defining a rotational axis and comprising:

a plurality of first layers of carbon fibre reinforced polymer, each first layer comprising fibres oriented between 89° and 90° to the rotational axis;

at least one second layer of fibres comprising one or more of glass fibre, aramid, ultra-high molecular weight polyethylene, nylon or poly(p-phenylene-2,6-benzobisoxaole) (PBO) within a matrix material, wherein:

the at least one second layer is provided between two layers of the plurality of first layers,

the fibres of the plurality of first fibers have a higher modulus of elasticity than the fibres of the at least one second layer, and

the fibres of the at least one second layer are oriented between 50° and 75° relative to the rotational axis.

2. The rotor sleeve according to claim 1 , wherein the fibres of each first layer are oriented between 89.2° and 89.9° to the rotational axis.

3. The rotor sleeve according to claim 2 , wherein the fibres of each first layer are oriented approximately 89.5° to the rotational axis.

4. The rotor sleeve according to claim 1 , wherein each first layer defines a radial thickness of no more than 2 mm.

5. The rotor sleeve according to claim 1 , wherein the sleeve comprises between 5 and 20% low modulus of elasticity fibre reinforced composite.

6. The rotor sleeve according to claim 1 , wherein the fibres of the at least one second layer are oriented approximately 60° relative to the rotational axis.

7. The rotor sleeve according to claim 1 , wherein the fibres of the at least one second layer comprise first fibres oriented 50° to 75° relative to the rotational axis in a clockwise direction interwoven with second fibres oriented 50° to 75° relative to the rotational axis in an anti-clockwise direction.

8. The rotor sleeve according to claim 1 , wherein the fibers of the plurality of first layers and the at least one second layer are provided within a matrix material comprising one or more of epoxy, cyanate ester or phenolic resin.

9. A method of manufacturing a sleeved rotor of an electric machine, the method comprising:

providing a first layer of carbon fibre filaments aligned substantially 90° relative to a rotational axis;

providing a second layer of fibre filaments comprising one or more of glass fibre, aramid, ultra-high molecular weight polyethylene, nylon or poly(p-phenylene-2,6-benzobisoxaole) (PBO) within a matrix material, the fibers having a lower modulus of elasticity than the carbon fibre filaments wound around the first layer of carbon fibre filaments; and

providing a third layer of carbon fibre filaments around the second layer of fibre filaments aligned substantially 90° to the rotational axis; wherein

the fibres of the first layer and the third layer have a higher modulus of elasticity than the fibres of the second layer, and

the fibres of the second layer are oriented between 50° and 75° relative to the rotational axis.

10. The method according to claim 9 , wherein the fibres of the second layer comprise first fibres oriented 50° to 75° relative to the rotational axis in a clockwise direction interwoven with second fibres oriented 50° to 75° relative to the rotational axis in an anti-clockwise direction.

11. The method according to claim 9 , wherein the rotor comprises one or more permanent magnets, and the method comprises sliding the sleeve over the outer diameter over the one or more permanent magnets.

12. The method according to claim 9 , wherein the method comprises, in a first step, winding the first, second and third layers of filaments around a mandrel, followed by curing of the filaments to form a composite ring.

13. The method according to claim 12 , wherein the method comprises, in a second step subsequent to the first step, urging the ring over a conical stressing device to increase an inner diameter of the ring and produce a pre-stress on the ring, and sliding the sleeve over the outer diameter of the rotor.

14. An electric machine comprising a rotor fitted with the rotor sleeve according to claim 1 .

15. The electric machine according to claim 14 , wherein the electric machine is configured to operate as one or both of a generator and a motor.

16. The electric machine according to claim 14 , wherein the electric machine comprises a permanent magnet electric machine comprising one or more surface permanent magnets provided at an outer diameter of the rotor.