Device for compressing a fluid, driven by an electric machine with a rotor shaft having a non-magnetic shrink ring

1. A compression device of a fluid which is driven by an electric machine, the electric machine comprising a rotor including a rotor shaft and a stator, a compressor shaft on which is mounted at least one impeller wheel, the rotor being fastened to the compressor shaft, a cylindrical magnet mounted on at least a part of the rotor shaft, means comprising a shrink ring of non-magnetic material which compresses the magnet and axially holds the magnet on the rotor shaft to combat magnetic leakage, the rotor shaft including a bore for receiving one end of the compressor shaft, and at least one ring-shaped non-magnetic stop on one side of the magnet which is located between a shoulder of the rotor shaft and the magnet.

2. The compression device according to claim 1 , wherein the rotor has an outer diameter less than a diameter of an inlet to one of the at least one impeller wheel.

3. The compression device according to claim 1 , wherein the shrink ring comprises either titanium or carbon.

4. The compression device according to claim 1 , wherein the rotor includes a portion having a diameter less than an end which is fastened to the compressor shaft, and the magnet is mounted on the portion having the diameter less than the end.

5. The compression device according to claim 1 , wherein the rotor includes a flat surface which contacts a flat surface of an end of at least one of the at least one impeller wheel.

6. The compression device according to claim 1 , wherein the rotor includes a cylindrical portion inserted into at least one of the at least one impeller wheel.

7. The compression device according to claim 6 , wherein the cylindrical portion of the rotor has an axial length that is 1.5 times a diameter of the compressor shaft.

8. The compression device according to claim 6 , comprising a tubular sleeve mounted on the compressor shaft which is located between one end of one of the at least one impeller wheel and the cylindrical portion of the rotor.

9. The compression device according claim 1 , wherein the rotor is fastened to the compressor shaft by a screw thread.

10. The compression device according to claim 1 , wherein the compression device is a turbocharger comprising a turbine and a compressor.

11. The compression device according to claim 10 , wherein the electric machine is located at a gas inlet of the turbocharger.

12. A method for manufacturing a compression device comprising a rotor of an electric machine including a rotor shaft including a bore for receiving one end of a compressor shaft and a stator of the electric machine, a compressor shaft and at least one impeller wheel which is driven by the electric machine, the method comprising:

a) mounting the at least one impeller wheel on the compressor shaft;

b) mounting a cylindrical magnet on at least a part of the rotor shaft;

c) attaching the cylindrical magnet to the rotor shaft by a non-magnetic shrink ring which axially holds and compresses the cylindrical magnet on the rotor shaft and combats magnetic rotor leakage;

d) inserting a ring-shaped non-magnetic stop on a side of the cylindrical magnet which is located between a shoulder of the rotor shaft and the cylindrical magnet; and

e) inserting one end of the compressor shaft into a bore of the rotor shaft, and fastening the compressor shaft to the rotor shaft to hold the non-magnetic stop against the shoulder.

13. The method of manufacturing according to claim 12 , comprising inserting the compressor shaft into the bore of the rotor shaft so that the rotor abuts the at least one impeller wheel by contact with flat surfaces.

14. The manufacturing method according to claim 12 , comprising inserting the compressor shaft into the bore of the rotor shaft while a cylindrical portion of the rotor is inserted into the at least one impeller wheel.

15. The manufacturing method according to claim 12 , comprising screwing the rotor shaft into to an end of the shaft of the compressor.