Cooling of electric motors

1. A rotor for an electric motor, the rotor configured to rotate about a longitudinal axis in use, the rotor comprising:

one or more permanent magnets or windings; and

a layer of material disposed over the permanent magnets or windings, wherein the layer of material extends circumferentially around the magnets or windings so as to radially confine the magnets or windings when the rotor is rotated;

wherein the layer of material comprises one or more grooves or channels for directing fluid along the rotor,

wherein the rotor has a length between a first longitudinal end and a second longitudinal end, wherein the first longitudinal end is opposite to the second longitudinal end, and each groove or channel extends along a fluid path from the first longitudinal end of the rotor to the second longitudinal end of the rotor to direct fluid along the entire length of the rotor,

wherein the fluid path of each groove or channel consists of a single path formed by a leading portion, a central portion and a trailing portion,

wherein the leading portion extends from the first longitudinal end to the central portion and around the rotor in a first circumferential direction,

wherein the central portion interconnects the leading and trailing portions, and has a direction substantially parallel to the longitudinal axis,

wherein the trailing portion extends from the central portion to the second longitudinal end and around the rotor in the first circumferential direction, such that the leading and trailing portions both extend in the same circumferential direction around the rotor and fluid will be urged into and along each groove or channel regardless of which direction the rotor is rotated.

2. The rotor of claim 1 , wherein the layer of material comprises a banding wound around the rotor.

3. The rotor of claim 1 , wherein one or more grooves are provided in a radially outermost surface of the layer of material.

4. The rotor of claim 1 , wherein a path formed by the leading portion has a direction having a component in a longitudinal direction of the rotor and a component in a circumferential direction of the rotor.

5. The rotor of claim 1 , wherein a path formed by the trailing portion has a direction having a component in the longitudinal direction of the rotor and a component in the circumferential direction of the rotor.

6. The rotor of claim 1 , wherein the leading portion extends around the rotor only in the first circumferential direction as a function of distance from the first longitudinal end of the rotor towards the central portion, and the trailing portion extends around the rotor only in the first circumferential direction as a function of distance from the central portion to the second longitudinal end of the rotor.

7. An electric motor comprising:

the rotor of claim 1 ,

wherein the electric motor further comprises a stator.

8. The electric motor of claim 7 , wherein there is a gap between the stator and the rotor; and

wherein each groove opens into the gap, such that when the rotor rotates in use, fluid is urged into the gap.

9. A method of manufacturing the rotor of claim 1 , the method comprising:

disposing the one or more permanent magnets or windings on the rotor;

providing the layer of material over the permanent magnets or windings; and

forming one or more grooves or channels in the layer of material before or after the layer of material has been provided on the rotor.

10. A rotor for an electric motor, the rotor configured to rotate about a longitudinal axis in use, the rotor comprising:

one or more grooves or channels, each configured to direct fluid along a fluid path that extends along the entire length of the rotor in a substantially longitudinal direction;

wherein each groove or channel extends from a first longitudinal end of the rotor to a second longitudinal end of the rotor, wherein the first longitudinal end is opposite to the second longitudinal end; and

wherein a leading portion of each groove or channel extends from the first longitudinal end and around the rotor in a first circumferential direction so as to urge fluid into the groove or channel as the rotor rotates in a first rotational direction,

wherein a trailing portion of each groove or channel extends to the second longitudinal end and around the rotor in the first circumferential direction so as to urge fluid into the groove or channel as the rotor rotates in a second rotational direction.

11. The rotor of claim 10 , wherein each groove or channel comprises a central portion which is fluidly connected to the leading portion;

wherein the leading portion is directed away from a longitudinal axis of the rotor such that there is a non-zero angle between a path formed by the leading portion and the longitudinal axis of the rotor;

wherein a path formed by the central portion is substantially parallel to the longitudinal axis of the rotor; and

wherein the trailing portion is directed away from the longitudinal axis of the rotor such that there is a non-zero angle between a path formed by the trailing portion and the longitudinal axis of the rotor.