Method for manufacturing a rotor for an electric motor

Abstract

Method for manufacturing a rotor for an electric motor. Method for manufacturing a rotor (4) for an electric motor (2), comprising: - a step (E1) of manufacturing a subassembly comprising a central shaft (8) provided with at least one ring (10A, 10B), in particular made of copper, and a set of coils (7), each coil comprising a winding of an electric wire, each coil being intended to carry an electric current to form a magnetic pole of the rotor, the at least one ring (10A, 10B) being intended to cooperate with at least one brush (11A, 11B) to supply said coils with electrical energy, then - a step (E2) of impregnating said coils with a resin, in particular a thermosetting polymer resin, then - a step (E3) of exposing said subassembly to a heat source (15) to harden said resin, then - a step (E4) of laser etching the at least one ring. Figure for the abbreviation: figure 2

Description

Title of the invention: Method for manufacturing a rotor for an electric motor Technical field of the invention

[0001] The invention relates to a method for manufacturing a rotor for an electric motor. The invention also relates to a method for manufacturing an electric motor for a vehicle, in particular for a motor vehicle. Prior art

[0002] So-called "electric" or "hybrid" motor vehicles include an electric motor capable of driving the vehicle's drive wheels. There are various types of electric motors, including "wound-rotor" motors. Such electric motors comprise a rotor with a plurality of poles, each pole containing a coil formed by a winding of an electric wire. The rotor is supplied with electrical energy via slip rings cooperating with brushes, so as to circulate an electric current in each coil. The flow of electric current induces a magnetic field that interacts with a stator of the electric motor, causing the rotor to rotate. The advantage of a wound-rotor electric motor is that it does not require a permanent magnet. These electric motors are simpler to manufacture and, in particular, do not require rare earth elements, which are difficult to source.

[0003] The rotor is exposed to significant temperature variations, vibrations, and centrifugal forces. These stresses can cause the electrical wires of the coils 7 to shift within the rotor, which then leads to malfunctions of the electric motor. To ensure the cohesion of the coils 7 within the rotor, it is known to impregnate the coils with a resin, in particular a thermosetting polymer resin. The impregnation process consists of depositing the resin in liquid form onto the rotor coils so that it fills the gaps around the electrical wires, and then curing the resin by exposing the rotor to a heat source such as a heating element.

[0004] The resin also seals the rotor, which then allows a cooling and lubricating fluid, such as oil, to be channeled within the rotor to cool and lubricate it. The resin also improves the electrical insulation of each coil.

[0005] However, it has been observed that the electric motors thus obtained still exhibit residual friction and malfunctions. The efficiency of these electric motors is therefore not optimal. Presentation of the invention

[0006] The object of the invention is to provide a method for manufacturing a rotor and a method for manufacturing an electric motor which remedies the above disadvantages and improves the manufacturing methods known in the prior art.

[0007] More specifically, a first object of the invention is to provide a method for manufacturing a rotor and a method for manufacturing an electric motor enabling the production of an electric motor with optimal efficiency. Summary of the invention

[0008] The invention relates to a method for manufacturing a rotor for an electric motor, comprising: - a manufacturing step of a sub-assembly comprising a central shaft provided with at least one ring, in particular made of copper, and a set of coils, each coil comprising a winding of an electric wire, each coil being intended to carry an electric current to form a magnetic pole of the rotor, the at least one ring being intended to cooperate with at least one brush to supply said coils with electrical energy, then - a step of impregnating said coils with a resin, in particular a thermosetting polymer resin, then - a step of exposing said sub-assembly to a heat source to harden said resin, then - a laser stripping step of at least one ring.

[0009] The laser stripping step can be carried out with a means for generating a laser beam generating a laser beam whose wavelength is approximately 532 nm.

[0010] At least one ring may comprise a tubular shape centered on an axis of rotation of the rotor, and the laser stripping step may be carried out by rotating the at least one ring around said axis of rotation.

[0011] At least one ring may comprise a tubular shape centered on an axis of rotation of the rotor, and the laser stripping step may be carried out with a means for generating a laser beam generating a laser beam extending over the entire height of the ring along said axis of rotation.

[0012] The laser stripping step may include a step of evaluating the oxidation state of at least one ring, the evaluation step being carried out after the step of exposing the rotor to a heat source, and the manufacturing process may include a step of parameterizing the laser stripping step according to the oxidation state of at least one ring.

[0013] Said step of evaluating an oxidation state may include a step of acquiring at least one image of at least one ring by means of a sensor optics, then a step of analyzing a color of at least one ring.

[0014] The manufacturing process may include a debris aspiration step in parallel with the laser stripping step.

[0015] The stripping step can be carried out with a means for generating a laser beam positioned at a distance from at least one ring of between 20 cm and 80 cm inclusive.

[0016] The at least one ring may comprise at least two coaxial rings assembled side-by-side on the same central shaft of the rotor.

[0017] The invention also relates to a method for manufacturing an electric motor for a motor vehicle, comprising - the implementation of the rotor manufacturing process as defined previously, then - the assembly of a stator around the rotor, and - the assembly of at least one brush cooperating with at least one rotor ring. Presentation of the figures

[0018] These objects, features and advantages of the present invention will be described in detail in the following description of a particular embodiment, given by way of non-limiting example, with reference to the accompanying figures, among which:

[0019] Fig. 1 is a schematic view of a motor vehicle comprising an electric motor.

[0020] Fig. 2 is a perspective view of the electric motor of Fig. 1

[0021] Figure 3 is a schematic diagram of a method for manufacturing an electric motor according to one embodiment of the invention.

[0022] Fig. 4 is a side view of part of the electric motor of Fig. 1 during a process of impregnating the coils of the electric motor with a resin.

[0023] Fig. 5 is a microscopic photograph of the surface of a ring of the motor rotor of Fig. 1 after a step of exposing the rotor to a heat source to harden a resin.

[0024] Fig. 6 is a schematic cross-sectional view of a laser stripping step of the ring of Fig. 5.

[0025] The [Fig.7] is a side view of the laser stripping step of the ring of the [Fig.5]. Detailed description

[0026] Figure 1 schematically illustrates a motor vehicle 1 comprising an electric traction and / or propulsion motor 2. The electric motor 2 is capable of driving the vehicle's drive wheels 3. The electric motor 2 is a wound-rotor motor. It comprises a rotor 4 and a stator 5. The stator 5 is arranged around the rotor 4. A radial air gap e is defined between the rotor 4 and the stator 5.

[0027] With reference to [Fig. 2], the rotor 4 comprises a plurality of poles 6. Each pole 6 comprises a coil 7 formed by winding an electric wire, for example, copper. The flow of an electric current in the electric wire induces a magnetic field. Each pole 6 can thus be called a magnetic pole. The direction of the electric current can be defined so that the direction of the magnetic field is reversed between each adjacent pole. The rotor 4 can thus comprise an alternation of North and South poles. According to the embodiment shown, the rotor 4 comprises eight poles. Alternatively, the number of poles could be any other number.

[0028] The rotor 4 also includes a central shaft 8 intended to be coupled to a transmission system to drive the drive wheels 3. For this purpose, the central shaft 8 is provided with splines 9.

[0029] The central shaft 8 is also equipped with two conductive rings 10A, 10B. The two rings 10A, 10B are preferably made of copper. The two rings 10A, 10B are intended to make contact with brushes 11A, 11B to supply the coils 7 with electrical energy. The two rings 10A, 10B are thus electrically connected to an electrical power source 12 of the vehicle, such as a battery, via the brushes 11A, 11B.

[0030] Each of the two rings 10A comprises a tubular shape centered on a rotation axis X of the rotor. The two rings 10A and 10B are therefore coaxial. The two rings may have the same outside diameter. Furthermore, the two rings 10A and 10B are assembled side-by-side on the central shaft 8. According to one embodiment of the invention, the central shaft 8 could be equipped with a different number of conducting rings.

[0031] The coils 7 are mechanically fixed to the central shaft 8, in particular by means of a core. The core may comprise a set of radial protrusions. Each coil then comprises a winding of an electrical wire around a radial protrusion.

[0032] The rotor 4 is intended to rotate about itself around the axis of rotation X. The central shaft 12 extends parallel to the axis of rotation X of the rotor 4 and is centered on the axis of rotation X. When the vehicle 1 is operating, the rotational speed of the rotor can reach, for example, 15,000 revolutions per minute.

[0033] The rotor 4 also includes an electrically insulating resin that fills voids around the coils 7. The resin may, in particular, be a thermosetting polymer resin. As we will see in more detail later, the resin can be applied by immersing the rotor 4 in a bath of liquid resin and rotating the rotor around its axis of rotation. The resin can thus penetrate all the voids in the rotor 4 up to the rotor's immersion depth. Then, the resin is hardened by exposing the rotor to a heat source.

[0034] With reference to the synoptic diagram of [Fig.3], a manufacturing process for the electric motor 2 according to an embodiment of the invention is now described.

[0035] In a first step E1, a subassembly is manufactured comprising, in particular, the central shaft 8 equipped with the rings 10A, 10B and the coils 7 fixed to the central shaft 8. For example, each coil 7 can be formed around a radial protrusion of a rotor core 4, and then the central shaft 8 can be inserted into a central opening in the core itself, which is fitted with the coils. Next, the rings 10A, 10B can be assembled to the central shaft 8. The rings 10A, 10B can, for example, be press-fitted onto a portion of the central shaft 8 provided for this purpose. Alternatively, the rings 10A, 10B could be assembled to the central shaft 8 even before the latter is assembled to the rotor core. The rings 10A, 10B can then be electrically connected to the coils 7.

[0036] In a second step E2, schematically illustrated in [Fig. 4], the coils 7 are impregnated with the resin. For this purpose, the subassembly manufactured in the first step E1 is partially immersed in a bath 13 containing liquid resin 14. The rotor 4 is then rotated about its axis of rotation X, so as to progressively immerse the entire outer circumference of the rotor 4.

[0037] Next, in a third step E3, also illustrated in [Fig. 4], the rotor 4 is exposed to a heat source 15 to harden the resin. The heat source 15 can be, for example, a heating element, possibly integrated into an oven in which the rotor 4 is positioned. The third step E3 can optionally be carried out in parallel with the second step E2, or at least be started after the completion of the second step E2. By exposing the subassembly to a heat source, oxidation occurs on the outer surface of the rings 10A, 10B. The rings 10A, 10B then have an irregular oxide layer 16 on their outer surface.

[0038] Fig. 5 shows a microscopic view of the oxide layer 16 formed on a ring 10A, 10B at the end of the third step E3. The rings 10A, 10B thus have a degraded surface condition, which could lead to imperfect electrical contact between the brushes 1IA, 1IB and the rings 10A, 10B, and consequently friction during the rotation of the rotor 4, and premature wear of the brushes.

[0039] Next, the manufacturing process advantageously includes a step E4 of laser pickling of the rings 10A, 10B. This process is carried out with the rings 10A, 10B already assembled to the central shaft 8 of the rotor 4.

[0040] As illustrated in [Fig. 6], this step is carried out using a stripping device 17 equipped with a laser beam generation means 18. The laser beam generation means 18 is connected to an electrical power source 19 and to a A control means 20 adapted to control the activation state of the laser beam generation means 18. The control means 20 can, in particular, be configured to control the frequency of a laser beam, and / or the pulse duration of the laser beam, and / or the energy distribution of the laser beam, and / or the scanning speed of the laser beam. Furthermore, the stripping device 17 also includes a means 21 for suctioning debris from the stripping process.

[0041] Laser stripping offers numerous advantages compared to other stripping processes known in the prior art. In particular, this process removes very little material from the treated ring. Consequently, it is not necessary to provide a significant extra thickness for each ring, and the amount of debris to be removed is moderate. Laser stripping requires no direct mechanical contact with the ring since it is supported by the central shaft 8. This avoids any unnecessary handling of each ring and prevents damage or soiling. Furthermore, the stripping process is rapid. In particular, the stripping process requires at most about twenty seconds per treated ring. The stripping process does not require significant maintenance of the laser beam generation means 18. The stripping process is therefore easy to implement and has very good repeatability over time.

[0042] The stripping step can be performed successively for each ring 10A, 10B using the same stripping device 17. Alternatively, the stripping step can be performed in parallel for each ring 10A, 10B using a separate stripping device 17 for each ring. Note that Figures 6 and 7 show the stripping step for ring 10A, with the stripping of ring 10B being performed in the same way.

[0043] The laser beam generation means 18 can be positioned at a distance DI from the treated ring of between 20 cm and 80 cm inclusive, for example approximately 40 cm. The stripping device 17 thus occupies a relatively small volume. Such a device can therefore be integrated quite easily into a rotor manufacturing workshop.

[0044] The means for generating a laser beam 18 is advantageously configured to emit a so-called "green" laser, that is, a laser with a wavelength of approximately 532 nm. It has been observed that such a wavelength makes it possible to obtain a laser beam that is less reflected by the treated ring 10A, 10B. This allows for better management of the absorption of the laser beam by the oxide layers. Alternatively, a laser with a wavelength of 1064 nm could also be considered.

[0045] Figure 7 illustrates a side view of the ring 10A during the stripping process. The laser beam generation means 18 is adapted to generate a laser beam FL incident over the entire height of the ring along the axis of rotation X. In other words, the laser spot obtained extends over the entire height of the ring 10A along the axis of X rotation. Thus, the outer surface of the ring 10A is completely treated by rotating the ring once around the X rotation axis. The treated ring can optionally rotate several times around the X rotation axis to further refine the cleaning process. One advantage of rotating the ring 10A during laser cleaning is that the laser beam generation device 18 can remain stationary.

[0046] In [Fig. 7], the Z1 zones correspond to the areas of the ring 10A that have not been cleaned, and are therefore covered with the oxide layer 16. The Z2 zone corresponds to an area of ​​the ring that has been cleaned. The Z2 zone is free of the oxide layer and has an excellent surface finish, thus minimizing the friction of the brush 11A with the ring 10A.

[0047] Advantageously, the laser stripping step includes a first substep E41 for evaluating the oxidation state of the ring 10A. The evaluation substep E41 is carried out immediately after the third step E3. This substep E41 may include a substep E411 for acquiring at least one image of the ring 10A by means of an optical sensor 22, followed by a substep E412 for analyzing the color of the ring 10A. The substep E41 may advantageously be performed automatically by the control means 20 connected to the optical sensor 22.

[0048] Next, the laser stripping step includes a substep E42 for parameterizing the laser stripping step according to the oxidation state of the ring obtained at the end of substep E41. This parameterization step consists in particular of adapting the operating parameters of the means for generating a laser beam 18 (laser beam frequency, pulse duration, energy distribution, etc.). The laser beam is then collimated onto the oxide layer 16 which detaches from the ring 10A.

[0049] Advantageously, the manufacturing process further includes a step E5 for removing debris from the oxide layer 16. Step E5 is carried out in parallel with the laser cleaning step E4. The small amount of debris generated by the laser cleaning is thus removed and evacuated. This prevents the debris from contaminating the rotor 4.

[0050] After steps E4 and E5, a rotor 4 is ready to be assembled with the other components of the electric motor 2. To continue manufacturing the electric motor 2, the stator 5 is assembled around the rotor 4 in a sixth step E6, and the brushes 1IA, 1IB are assembled so that they make electrical contact with the slip rings 10A, 10B, to transmit an electric current supplied by 12 to the rotor coils 7. Steps E6 and E7 can be reversed.

[0051] Finally, an electric motor 2 is obtained whose rotor 4 is impregnated with hardened resin. The coils 7 of the rotor 4 are thus securely held and electrically insulated. In addition, the rings 10A and 10B have an excellent surface finish obtained thanks to the laser etching step E4. The brushes 1IA, 1IB can slide in contact with the rings 10A, 10B without generating significant friction. The efficiency of the electric motor 2 is therefore optimal.

Claims

Demands

1. A method for manufacturing a rotor (4) for an electric motor (2), comprising: - a step (E1) of manufacturing a subassembly comprising a central shaft (8) provided with at least one ring (10A, 10B), in particular made of copper, and a set of coils (7), each coil comprising a winding of an electric wire, each coil being intended to carry an electric current to form a magnetic pole of the rotor, the at least one ring (10A, 10B) being intended to cooperate with at least one brush (11A, 11B) to supply said coils with electrical energy, then - a step (E2) of impregnating said coils with a resin, in particular a thermosetting polymer resin, then - a step (E3) of exposing said subassembly to a heat source (15) to harden said resin, then - a step (E4) of laser etching the at least one ring.

2. A manufacturing method according to the preceding claim, characterized in that the laser pickling step (E4) is carried out with a laser beam generation means (18) generating a laser beam (FL) whose wavelength is approximately 532 nm.

3. A manufacturing method according to any one of the preceding claims, characterized in that at least one ring (10A, 10B) comprises a tubular shape centered on an axis of rotation (X) of the rotor (4), and in that the laser pickling step (E4) is carried out by rotating at least one ring around said axis of rotation.

4. A manufacturing method according to any one of the preceding claims, characterized in that at least one ring (10A, 10B) comprises a tubular shape centered on an axis of rotation (X) of the rotor (4), and in that the laser stripping step (E4) is carried out with a laser beam generation means (18) generating a laser beam (FL) extending over the entire height of the ring along said axis of rotation.

5. A manufacturing method according to any one of the preceding claims, characterized in that the laser pickling step (E4) comprises a step (E41) for evaluating the oxidation state of at least one ring, the evaluation step being carried out after the step (E3) of exposing the rotor to a heat source, and in that it comprises a step (E42) for parameterizing the laser pickling step as a function of the state oxidation of at least one ring.

6. A manufacturing method according to the preceding claim, characterized in that said step (E41) of evaluating an oxidation state comprises a step (E411) of acquiring at least one image of at least one ring by means of an optical sensor (22), and then a step (E412) of analyzing a color of at least one ring (10A, 10B).

7. A manufacturing method according to any one of the preceding claims, characterized in that it comprises a debris aspiration step (E5) in parallel with the laser stripping step (E4).

8. A manufacturing method according to any one of the preceding claims, characterized in that the stripping step (E4) is carried out with a means for generating a laser beam (18) positioned at a distance from at least one ring of between 20 cm and 80 cm inclusive.

9. A manufacturing method according to any one of the preceding claims, characterized in that at least one ring (10A, 10B) comprises at least two coaxial rings assembled side-by-side on the same central shaft (8) of the rotor (4).

10. Method of manufacturing an electric motor (2) for a motor vehicle (1), characterized in that it comprises: - carrying out the method of manufacturing a rotor (4) according to one of the preceding claims, then - assembling a stator (5) around the rotor (4), and - assembling at least one brush (11A, 11B) cooperating with at least one ring (10A, 10B) of the rotor.

Images