DEVICE FOR COMPRESSING A FLUID DRIVEN BY AN ELECTRIC MACHINE WITH A ROTOR EQUIPPED WITH A SOLID CYLINDRICAL MAGNET

Abstract

The present invention relates to a compression device driven by an electric machine, for which a rotor (4) comprises a cylindrical magnet (5) and a binding ring (6), preferably non-magnetic. According to the invention, cylindrical magnet (5) is solid and cylindrical magnet (5) is fastened to a support piece (7) by means of binding ring (6), support piece (7) being fastened to one end of compression shaft (3).

Claims

1. A fluid compression device driven by an electric machine, the electric machine comprising a rotor and a stator, the rotor comprising a cylindrical magnet and a binding ring, the compression device comprising a compression shaft on which at least one compressor wheel is mounted, and a support piece being fastened to one end of the compression shaft, wherein the cylindrical magnet is a solid piece, and the rotor is fastened to the support piece by means of the binding ring surrounding at least part of the support piece.

2. A compression device as claimed in claim 1, wherein the support piece is fastened to the compression shaft by a threaded connection.

3. A compression device as claimed in claim 1, wherein support piece comprises means for handling the support piece.

4. A compression device as claimed in claim 1, wherein the support piece comprises a cylindrical portion inserted in the compressor wheel.

5. A compression device as claimed in claim 1, wherein the support piece comprises a cylindrical portion for the binding ring.

6. A compression device as claimed in claim 1, wherein the binding ring is made of a non-magnetic material, preferably titanium or carbon.

7. A compression device as claimed in claim 1, wherein the rotor comprises a non-magnetic stop between the cylindrical magnet and the support piece.

8. A compression device as claimed in claim 1, wherein the outside diameter of the rotor is less than or equal to the diameter of the nose of the compressor wheel.

9. A compression device as claimed in claim 1, wherein the compression device is a turbocharger combining a turbine and a compressor, notably for an internal-combustion engine, or a microturbine.

10. A compression device as claimed in claim 9, wherein the electric machine is arranged in the gas intake of the turbocharger.

11. A compression device as claimed in claim 1, wherein the electric machine is a stator grid machine.

12. A method of manufacturing a compression device driven by an electric machine, the electric machine comprising a rotor and a stator, the compression device comprising a compression shaft on which at least one compressor wheel is mounted, wherein the following steps are carried out: a) fastening the solid cylindrical magnet onto the support piece by means of the binding ring that surrounds the cylindrical magnet and at least a portion of the support piece, b) mounting the compressor wheel onto the compression shaft, c) fastening the support piece onto one end of the compression shaft, notably by means of a threaded connection.

13. A method of manufacturing a compression device driven by an electric machine, the electric machine comprising a rotor and a stator, the compression device comprising a compression shaft, on which at least one compressor wheel is mounted, wherein the following steps are carried out: a) mounting the compressor wheel onto the compression shaft, b) fastening the support piece with the rotor onto one end of the compression shaft, notably by means of a threaded connection, step b) comprising the substep as follows: i) fastening the solid cylindrical magnet onto the support piece by means of the binding ring that surrounds the cylindrical magnet and at least a portion of the support piece.

Description

BRIEF DESCRIPTION OF THE SOLE FIGURE

[0035] Other features and advantages of the device and of the method according to the invention will be clear from reading the description hereafter of embodiments, given by way of non limitative example, with reference to the accompanying FIGURE wherein:

[0036] FIG. 1 illustrates a compression device according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention relates to a device for compressing a fluid, notably gas, driven by an electric machine. In other words, the invention relates to the assembly made up of the electric machine and the compression device. Preferably, the compression device is intended to compress air.

[0038] The fluid compression device comprises a shaft, referred to as compression shaft, on which a compressor wheel (also referred to as blade) is mounted.

[0039] The electric machine comprises a rotor and a stator. The rotor is connected to the compression shaft by means of a support piece so as to transmit or draw the torque of the electric machine to the compression shaft and the compressor wheel, and vice versa. The support piece is therefore fastened, on the one hand, to one end of the compression shaft and, on the other hand, to the rotor. The support piece can be made of a magnetic or non-magnetic material.

[0040] The rotor comprises at least: [0041] a cylindrical magnet, the magnet interacts with stator coils so as to generate the rotational motion of the rotor, and [0042] a binding ring (shrink ring), preferably made of a non-magnetic material, titanium or carbon for example, for compressing the magnet and axially retaining the cylindrical magnet of the rotor, and the binding ring can have a substantially cylindrical shape surrounding the cylindrical magnet. Moreover, the non-magnetic material prevents magnetic leakage.

[0043] According to the invention, the cylindrical magnet is a solid piece. In other words, the cylindrical magnet is a solid cylinder without holes, bores or perforations, etc. This solution therefore requires no machining (boring for example) of the cylindrical magnet, which simplifies the manufacture of the compression device and increases the magnetic performances of the magnet (the volume of the magnet is significant). Therefore, the performances of the electric machine can be increased and/or the dimensions of the electric machine can be reduced. Preferably, the rotor according to the invention can radially comprise at most the following elements: cylindrical magnet and binding ring.

[0044] Furthermore, according to the invention, the rotor is fastened to the support piece by means of the binding ring of the rotor. In other words, the cylindrical ring surrounds on the one hand the cylindrical magnet and, on the other hand, a portion of the support piece. Thus, mounting of the magnet onto the support piece is simplified. Assembly of the compression device and of the rotor is simplified thereby and can be carried out industrially.

[0045] According to an embodiment of the invention, the support piece can be fastened to the compression shaft by means of a threaded connection. For example, the end of the compression shaft can comprise a thread and the support piece can comprise a tapped bore.

[0046] For this embodiment, the support piece can comprise means for gripping/handling the support piece in order to rotate the support piece and therefore to achieve fastening by the threaded connection. These gripping/handling means may notably be orifices for inserting tools, sections for forming a handling tip, etc.

[0047] According to an aspect of the invention, the support piece can comprise a cylindrical portion inserted in the compressor wheel. This cylindrical portion surrounds the compression shaft and it is inserted in the bore of the compressor wheel. This cylindrical portion provides long centering of the rotor with respect to the compression shaft, which allows better coaxiality of the compression shaft with the support piece. The outside diameter of the cylindrical portion can be reduced in relation to the outside diameter of the rotor.

[0048] Advantageously, the cylindrical portion surrounding the compression shaft can have an axial length ranging between 2 and 3 times the diameter of the compression shaft, so as to provide optimized long centering.

[0049] According to a first variant of this embodiment, the axial length of the cylindrical portion substantially corresponds to the axial length of the compressor wheel, in order to allow maximum long centering and to stiffen the compressor wheel, in particular for high rotational speeds. This configuration notably allows to stiffen the portion of the shaft below the compressor wheel, which can be a critical point for some bending modes.

[0050] According to an embodiment option of the invention, the support piece can comprise a cylindrical portion intended for positioning of the binding ring. This cylindrical portion can advantageously have an outside diameter equal to the outside diameter of the cylindrical magnet.

[0051] For this embodiment, the length of the ring can be substantially equal to the cumulative length of the cylindrical magnet and the length of the cylindrical portion of the support piece intended for positioning the binding ring.

[0052] According to an aspect of the invention, the rotor can further comprise a non-magnetic stop on at least one side of the magnet (longitudinally). This non-magnetic stop prevents magnetic leakage from the magnet to the support piece and the compression shaft. The non-magnetic stop can also act as a thermal barrier protecting the temperature-sensitive magnet.

[0053] For example, the rotor can comprise a non-magnetic stop between the support piece and the cylindrical magnet. The non-magnetic stop can then have substantially the shape of a disc of diameter equal to the diameter of the cylindrical magnet. Thus, magnetic leakage from the cylindrical magnet to the support piece is prevented.

[0054] According to an embodiment option, the length of the binding ring surrounding the support piece can be greater than 3 mm so as to sufficiently secure the rotor.

[0055] Furthermore, the length of the binding ring surrounding the support piece can be less than the length of the binding ring surrounding the magnet, so as to limit the axial space requirement.

[0056] Preferably, the electric machine can be mounted on the intake side of the compression device.

[0057] According to an embodiment of the invention, the outside diameter of the rotor (here the binding ring) can be less than or equal to the diameter of the compressor wheel nose. The gas flow at the compression device inlet is thus not hindered by the rotor shaft.

[0058] According to an implementation of the invention, the compression device is a turbocharger, notably for an internal-combustion engine of a vehicle. It is then a turbocharger driven by an electric machine. In this case, the compression shaft corresponds to the turbocharger shaft that connects the turbocharger turbine to the turbocharger compressor. The electric machine thus drives both the compressor and the turbine.

[0059] According to a variant of this implementation of the invention, the electric machine can be arranged in the gas (generally air) intake of the turbocharger system. This solution involves a double advantage: the electric machine can be cooled by the intake gas stream, and the intake gas is heated by the electric machine, which may be favourable for some operating modes of the internal-combustion engine.

[0060] Preferably, the electric machine can be a stator grid electric machine, i.e. an electric machine having a stator with stator teeth around which coils are mounted, and these stator teeth have large dimensions to allow passage of the air stream. Such a stator grid machine is notably described in patent applications WO-2013/050,577 and FR-3,048,022.

[0061] FIG. 1 schematically illustrates, by way of non-limitative example, an embodiment of the invention. FIG. 1 is a sectional view of compression device 1 driven by an electric machine. Compression device 1 comprises a compression shaft 3 on which a compressor wheel 2 is mounted. The end of compression shaft 3 is threaded for mounting and securing a support piece 7. Rotor 4 is arranged at the end of support piece 7. Rotor 4 consists of a solid (no bore) cylindrical magnet 5 and a binding ring 6. Rotor 4 further comprises a non-magnetic stop 8 having the shape of a disc. Stop 8 is arranged between cylindrical magnet 5 and support piece 7. Binding ring 6 also surrounds a cylindrical portion 12 of support piece 7 so as to connect rotor 4 and support piece 7. The outside diameter of binding ring 6 is substantially equal to the diameter of the nose of compressor wheel 2. The length of ring 6 is substantially equal to the sum of the length of cylindrical magnet 5 and the length of cylindrical portion 12 of support piece 7. At the other end thereof, support piece 7 has a small-diameter cylindrical portion 11 inserted in compressor wheel 2. Furthermore, support piece 7 comprises blind holes 13 intended for handling support piece 7 for fastening thereof to compression shaft 3, notably by means of operating tools (not shown). On one side, compressor wheel 2 abuts against support piece 7. On the other side, compressor wheel 2 abuts against a guide system 9, for example the inner ring of a bearing whose outer ring 10 is shown.

[0062] Variants of this illustrated embodiment may be considered; for example, cylindrical portion 11 may have the same length as compressor wheel 2, the length of cylindrical portion 11 may be greater than or equal to the length of the compressor wheel, support piece 7 may have no cylindrical portion 11, the rotor may have no non-magnetic stop 8, etc.

[0063] Furthermore, the invention relates to a method of manufacturing a compression device driven by an electric machine, said electric machine comprising a rotor and a stator, and said compression device comprising a compression shaft and a compressor wheel. For this method, the following steps are carried out:

[0064] a) fastening the solid cylindrical magnet onto the support piece by means of a binding ring that surrounds the cylindrical magnet and at least a portion of the support piece;

[0065] b) mounting the compressor wheel onto the compression shaft;

[0066] c) fastening the support piece onto one end of the compression shaft, notably by means of a threaded connection.

[0067] Alternatively, the steps of the method can be as follows:

[0068] a) mounting the compressor wheel onto the compression shaft,

[0069] b) fastening the support piece with the rotor onto one end of the compression shaft, notably by means of a threaded connection, step b) comprising the substep as follows: [0070] i) fastening the solid cylindrical magnet onto the support piece by means of a binding ring that surrounds the cylindrical magnet and at least a portion of the support piece.

[0071] Advantageously, the manufacturing method can be intended for the manufacture of a compression device according to any one of the variants or variant combinations described above. For example, the manufacturing method can be intended for the manufacture of a compression device as described in connection with FIG. 1.

[0072] For the embodiment where fastening of the support piece and the compression shaft is achieved by means of a threaded connection, fastening can be carried out by rotating the support piece, notably using a means for gripping/handling the support piece.

[0073] According to an embodiment, the step of mounting the compressor wheel onto the compression shaft can comprise inserting a cylindrical portion of the support piece into the compressor wheel.

[0074] According to an implementation of the invention, the step of fastening the cylindrical magnet onto the support piece by means of the binding ring can comprise inserting a non-magnetic stop between the cylindrical magnet and the support piece.

[0075] According to an embodiment of the method, the assembly made up of the compression device, or possibly the turbocharger, and the electric machine can be installed in an air loop of an internal-combustion engine.

[0076] Advantageously, the electric machine can be arranged in the air intake pipe, so that the air stream entering the compression device first flows through the electric machine. This solution has a double advantage: the electric machine can be cooled by the intake gas stream and the intake gas is heated by the electric machine, which can be favourable for some operating modes of the internal-combustion engine.

[0077] The manufacturing method may further comprise a step of installing the stator around the rotor.

[0078] Advantageously, the manufacturing method according to the invention can concern the electrification of a compression device or of a conventional turbocharger (equipped with a compressor wheel and a compression shaft, but initially without an electric drive). Therefore, the compressor wheel and the compression shaft can be a wheel and a shaft for which steps a) to c) described above are carried out.

[0079] In this case, the method can comprise an additional step of replacing the compression shaft with a longer compression shaft.

[0080] Besides, the invention is also suited for energy production systems such as microturbines.

[0081] The invention provides the following functional advantages, it allows to: [0082] create a magnetic rotor allowing the shaft to be rotated through the generation of a rotating magnetic field by means of a stator comprising windings (three-phase windings for example), [0083] ensure the mechanical strength of the rotor assembly, notably with respect to the centrifugal forces applied upon rotation, notably by means of the binding ring, [0084] guarantee good electrical performances, in terms of power as well as efficiency, so as to limit internal heating of the rotor (and therefore demagnetization) and to simplify cooling thereof, notably by means of the solid cylindrical magnet, [0085] observe a high level of concentricity between the electric rotor and the turbocharger shaft so as to obtain a complete mechanical system (turbocharger shaft with electric machine rotor) that can be balanced with minimum unbalance, [0086] have a structure compatible with the assembly of the compressor wheel on the turbocharger shaft, [0087] tighten the compressor wheel and preload the roller bearings of the turbocharger, and [0088] be compatible with an electric turbocharger mass production tooling and manufacturing method.