Permanent magnet electric machine including permanent magnets having a sleeve formed from a thermal interface material

1. An electric machine comprising:

a housing;

a stator fixedly mounted relative to the housing; and

a rotor assembly rotatably mounted relative to the stator, the rotor assembly including a plurality of rotor laminations forming a rotor body, one or more permanent magnets provided in the rotor body, and a sleeve formed from a shrinkable tube having a selectively changeable internal dimension extending around the one or more permanent magnets, the sleeve providing a thermal interface between the one or more permanent magnets and the rotor body.

2. The electric machine according to claim 1 , wherein the selectively changeable internal dimension is configured and disposed to shrink when exposed to heat.

3. The electric machine according to claim 2 , wherein the selectively changeable thickness is configured and disposed to expand when exposed to heat.

4. The electric machine according to claim 1 , wherein the shrinkable tube includes an outer surface and an inner surface that define a selectively changeable thickness.

5. The electric machine according to claim 1 , wherein the sleeve is formed from a thermal interface material.

6. A rotor assembly comprising:

a rotor body;

a plurality of rotor laminations forming a rotor body;

one or more permanent magnets provided in the rotor body; and

a sleeve formed from a shrinkable tube having a selectively changeable internal dimension extending around the one or more permanent magnets, the sleeve providing a thermal interface between the one or more permanent magnets and the rotor body.

7. The rotor assembly according to claim 6 , wherein the selectively changeable internal dimension is configured and disposed to shrink when exposed to heat.

8. The rotor assembly according to claim 6 , wherein the shrinkable tube includes an outer surface and an inner surface that define a selectively changeable thickness.

9. The rotor assembly according to claim 8 , wherein the selectively changeable thickness is configured and disposed to expand when exposed to heat.

10. The rotor assembly according to claim 6 , wherein the sleeve is formed from one of at least one of a silicone rubber, epoxy, polyolefin, poly tetra fluoro ethylene (PTFE), fluorinated ethylene propylene (FEP), polyvinylidene fluoride (PVDF) polyvinyl chloride (PVC) and a thermal interface material.

11. The rotor assembly according to claim 10 , wherein the thermal interface material comprises at least one of an aluminum powder, Alumina (Al 2 O 3 ), graphite, boron nitride, and beryllium oxide.

12. A method of forming a rotor assembly, the method comprising:

stacking a plurality of rotor laminations;

aligning a plurality of slots formed in each of the plurality of rotor laminations;

joining the plurality of rotor laminations to form a rotor body;

inserting a permanent magnet into a sleeve formed from a shrinkable tube having a selectively changeable internal dimension; and

guiding the permanent magnet into one of the plurality of slots.

13. The method of claim 12 , further comprising: shrinking the sleeve about the permanent magnet.

14. The method of claim 13 , wherein shrinking the sleeve about the permanent magnet includes exposing the sleeve to a source of heat.

15. The method of claim 14 , wherein exposing the sleeve to a source of heat includes operating the electric motor.

16. The method of claim 12 , wherein shrinking the sleeve about the permanent magnet includes elastically contracting the sleeve.

17. The method of claim 12 , further comprising: expanding a thickness of the sleeve to secure the permanent magnet in the rotor body.

18. The method of claim 12 , wherein inserting the permanent magnet into the sleeve includes providing a thermal interface material about the permanent magnet.