Process for manufacturing a rotor for an electric motor

Abstract

The invention relates to a process for manufacturing a rotor (4) for an electric motor (2), comprising: - a step (E1) of manufacturing a sub-assembly 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 electrical wire, each coil being intended to have an electrical current flowing through it in order 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) in order to supply electrical power to the coils; then - a step (E2) of impregnating the coils with a resin, in particular a thermosetting polymer resin; then - a step (E3) of exposing the sub-assembly to a heat source (15) in order to cure the resin; then - a step (E4) of laser cleaning the at least one ring.

Description

[0001] Method of manufacturing a rotor for an electric motor

[0002] Technical field of the invention

[0003] 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.

[0004] State of the prior art

[0005] So-called "electric" or "hybrid" motor vehicles comprise an electric motor capable of driving the vehicle's drive wheels. There are different types of electric motors, including so-called "wound rotor" electric motors. Such electric motors comprise a rotor provided with a plurality of poles, each pole comprising a coil formed by a winding of an electric wire. The rotor is supplied with electrical energy via rings cooperating with brushes, so as to circulate an electric current in each coil. The circulation of the electric current induces a magnetic field which interacts with a stator of the electric motor so as to rotate the rotor. The advantage of a wound rotor electric motor is that it does not require any permanent magnets. These electric motors are simpler to manufacture and in particular do not require rare earths, which are difficult to source.

[0006] The rotor is exposed to very significant temperature variations, vibrations and centrifugal forces. These constraints can lead to displacement of the electrical wires of the coils 7 within the rotor, which then causes malfunctions of the electric motor. In order 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 then consists of depositing the resin in the liquid state on the coils of the rotor so that it fills the empty spaces around the electrical wires, then hardening the resin by exposing the rotor to a heat source such as a heating resistor.

[0007] The resin also helps seal the rotor, which then allows cooling and lubricating fluid, such as oil, to be channeled into the rotor to cool and lubricate it. The resin also improves the electrical insulation of each coil.

[0008] However, it has been found that the resulting electric motors still have residual friction and malfunctions. The efficiency of these electric motors is therefore not optimal.

[0009] Presentation of the invention

[0010] The aim of the invention is to provide a method of manufacturing a rotor and a method of manufacturing an electric motor which overcomes the above drawbacks and improves the manufacturing methods known from the prior art.

[0011] More specifically, a first object of the invention is to provide a method of manufacturing a rotor and a method of manufacturing an electric motor making it possible to obtain an electric motor with optimal efficiency.

[0012] Summary of the invention

[0013] The invention relates to a method of manufacturing a rotor for an electric motor, comprising:

[0014] - a step of manufacturing a subassembly 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 be traversed by 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

[0015] - a step of impregnating said coils with a resin, in particular a thermosetting polymer resin, then

[0016] - a step of exposing said subassembly to a heat source to harden said resin, then

[0017] - a step of laser stripping of at least one ring.

[0018] The laser stripping step may be performed with a laser beam generating means generating a laser beam having a wavelength of approximately 532 nm.

[0019] The 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 performed by rotating the at least one ring around said axis of rotation.

[0020] The 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.

[0021] The laser stripping step may comprise a step of evaluating an oxidation state of the at least one ring, the evaluation step being carried out after the step of exposing the rotor to a heat source, and the manufacturing method may comprise a step of parameterizing the laser stripping step as a function of the oxidation state of the at least one ring. Said step of evaluating an oxidation state may comprise a step of acquiring at least one image of the at least one ring by means of an optical sensor, then a step of analyzing a color of the at least one ring.

[0022] The manufacturing process may include a debris suction step in parallel with the laser stripping step.

[0023] The stripping step can be carried out with a means for generating a laser beam positioned at a distance from the at least one ring of between 20 cm and 80 cm inclusive.

[0024] The at least one ring may comprise at least two coaxial rings assembled side by side on the same central shaft of the rotor.

[0025] The invention also relates to a method of manufacturing an electric motor for a motor vehicle, comprising

[0026] - the implementation of the manufacturing process of a rotor as defined previously, then

[0027] - the assembly of a stator around the rotor, and

[0028] - the assembly of at least one brush cooperating with at least one ring of the rotor.

[0029] Presentation of figures

[0030] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of a particular embodiment made without limitation in relation to the attached figures among which: Figure 1 is a schematic view of a motor vehicle comprising an electric motor.

[0031] Figure 2 is a perspective view of the electric motor of Figure 1. Figure 3 is a block diagram of a method of manufacturing an electric motor according to one embodiment of the invention.

[0032] Figure 4 is a side view of a portion of the electric motor of Figure 1 during a process of impregnating the coils of the electric motor with a resin.

[0033] Figure 5 is a microscope photograph of the surface of a rotor ring of the motor of Figure 1 after a step of exposing the rotor to a heat source to cure a resin.

[0034] Figure 6 is a schematic sectional view of a laser stripping step of the ring of Figure 5.

[0035] Figure 7 is a side view of the laser etching step of the ring of Figure 5.

[0036] Detailed description

[0037] 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 drive wheels 3 of the vehicle. 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.

[0038] Referring to Figure 2, the rotor 4 comprises a plurality of poles 6. Each pole 6 comprises a coil 7 formed by the winding of an electric wire, for example made of copper. The circulation 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 circulation 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 poles and South poles. According to the embodiment presented, the rotor 4 comprises eight poles. Alternatively, the number of poles could be equal to any other number.

[0039] The rotor 4 also comprises a central shaft 8 intended to be coupled to a transmission system for driving the drive wheels 3. For this purpose, the central shaft 8 is provided with splines 9.

[0040] 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 come into 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 energy source 12 of the vehicle such as a battery, via the brushes 11A, 11B.

[0041] The two rings 10A each comprise a tubular shape centered on an axis of rotation 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, 10B are assembled side by side on the central axis 8. According to an alternative embodiment of the invention, the central shaft 8 could be equipped with a different number of conductive rings.

[0042] 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 protuberances. Each coil then comprises a winding of an electric wire around a radial protuberance.

[0043] The rotor 4 is intended to rotate on 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 rotation speed of the rotor can reach, for example, 15,000 revolutions per minute. The rotor 4 also comprises an electrically insulating resin and filling empty spaces 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 into all the empty spaces of the rotor 4 up to the immersion height of the rotor. Then, the resin is hardened by exposing the rotor to a heat source.

[0044] With reference to the block diagram of Figure 3, a method of manufacturing the electric motor 2 according to one embodiment of the invention is now described.

[0045] In a first step E1, a subassembly is manufactured comprising in particular the central shaft 8 provided 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 protuberance of a core of the rotor 4, then the central shaft 8 can be inserted into a central opening of the core itself equipped with the coils. Then the rings 10A, 10B can be assembled to the central shaft 8. The rings 10A, 10B can, for example, be force-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.

[0046] In a second step E2, illustrated schematically in Figure 4, the coils 7 are impregnated with the resin. For this purpose, the subassembly manufactured during the first step E1 is partially immersed in a bath 13 comprising resin 14 in the liquid state. The rotor 4 is then rotated around its axis of rotation X, so as to gradually immerse the entire outer periphery of the rotor 4.

[0047] Then, in a third step E3, also illustrated in FIG. 4, the rotor 4 is exposed to a heat source 15 to harden said resin. The heat source 15 may be, for example, a heating resistor, possibly integrated into an oven in which the rotor 4 is positioned. The third step E3 may possibly be carried out in parallel with the second step E2, or at least be started after the end of the second step E2. By exposing said subassembly to a heat source, an oxidation phenomenon occurs on the outer surface of the rings 10A, 10B. The rings 10A, 10B then comprise an irregular oxide layer 16 on their outer surface.

[0048] Figure 5 shows a microscope 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 11A, 11B and the rings 10A, 10B, and consequently friction during rotation of the rotor 4, and premature wear of the brushes.

[0049] Then, the manufacturing method advantageously comprises a step E4 of laser stripping the rings 10A, 10B. This method is carried out with the rings 10A, 10B already assembled to the central shaft 8 of the rotor 4.

[0050] As illustrated in Figure 6, this step is carried out by means of a stripping device 17 equipped with a means for generating a laser beam 18. The means for generating a laser beam 18 is connected to an electrical energy source 19 and to a control means 20 adapted to control the activation state of the means for generating a laser beam 18. The control means 20 may 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. In addition, the stripping device 17 also comprises a means 21 for suctioning debris resulting from the stripping process.

[0051] Laser stripping has many advantages compared to other stripping methods known from the state of the art. In particular, this method removes little material from the treated ring. Consequently, it is not necessary to provide a significant excess thickness for each ring, and the quantity of debris to be removed is moderate. Laser stripping does not require any direct mechanical contact with the ring since the latter is supported by the central shaft 8. This avoids any unnecessary handling of each ring and avoids damaging or soiling them. In addition, the stripping method is rapid. In particular, the stripping method requires at most about twenty seconds per treated ring. The stripping method does not require significant maintenance of the means for generating a laser beam 18. The stripping method is therefore easy to implement and has very good repeatability over time.

[0052] The stripping step can be carried out successively for each ring 10A, 10B using the same stripping device 17. Alternatively, the stripping step can be carried out in parallel for each ring 10A, 10B using a separate stripping device 17 for each ring. As a note, in Figures 6 and 7, the stripping step of the ring 10A is shown, the stripping of the ring 10B being carried out in the same way. The means for generating a laser beam 18 can be positioned at a distance D1 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 is therefore quite easily integrated into a rotor manufacturing workshop.

[0053] The means for generating a laser beam 18 is advantageously configured to emit a so-called “green” laser, i.e. a laser whose wavelength is approximately 532 nm. It has been observed that such a wavelength makes it possible to obtain a laser beam which is less reflected by the treated ring 10A, 10B. This makes it possible to better manage the absorption of the laser beam by the oxide layers. Alternatively, a laser whose wavelength is 1064 nm could also be considered.

[0054] Figure 7 illustrates a side view of the ring 10A during the stripping process. The laser beam generating means 18 is adapted to generate an incident laser beam FL over the entire height of the ring along the rotation axis X. In other words, the laser spot obtained extends over the entire height of the ring 10A along the rotation axis X. Thus, the outer surface of the ring 10A is completely treated by making a complete revolution of the ring around the rotation axis X. The treated ring can optionally make several revolutions around the rotation axis X, so as to perfect the stripping. An advantage of rotating the ring 10A during its laser stripping is that the laser beam generating means 18 can remain stationary.

[0055] In Figure 7, the zones Z1 correspond to the zones of the ring 10A that are not etched, and therefore covered with the oxide layer 16. The zone Z2 corresponds to a zone of the etched ring. The zone Z2 is devoid of an oxide layer and comprises an excellent surface condition, thus minimizing the friction of the brush 11A with the ring 10A. Advantageously, the laser etching step comprises a first sub-step E41 of evaluating an oxidation state of the ring 10A. The evaluation sub-step E41 is carried out just after the third step E3. This sub-step E41 may comprise a sub-step E411 of acquiring at least one image of the ring 10A by means of an optical sensor 22, then a sub-step E412 of analyzing a color of the ring 10A. Sub-step E41 can advantageously be executed automatically by the control means 20 connected to the optical sensor 22.

[0056] Then, the laser stripping step comprises a sub-step E42 of parameterizing the laser stripping step as a function of the oxidation state of the ring obtained at the end of the sub-step E41. This parameterization step consists in particular of adapting the operational operating parameters of the means for generating a laser beam 18 (frequency of the laser beam, pulse duration, energy distribution, etc.). The laser beam is then collimated on the oxide layer 16 which detaches from the ring 10A.

[0057] Advantageously, the manufacturing method further comprises a step E5 of suctioning debris from the oxide layer 16. Step E5 is carried out in parallel with the laser stripping step E4. The small amount of debris generated by the laser stripping is thus suctioned and evacuated. This prevents this debris from polluting the rotor 4.

[0058] At the end of steps E4 and E5, a rotor 4 is available 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 during a sixth step E6, and the brushes 11 A, 11 B are assembled so that they establish electrical contact with the rings 10A, 10B, to transmit an electric current delivered by 12 to the coils 7 of the rotor. Steps E6 and E7 can be interchanged.

[0059] Finally, an electric motor 2 is obtained whose rotor 4 is impregnated with hardened resin. The coils 7 of the rotor 4 are thus well maintained and well electrically insulated. In addition, the rings 10A and 10B have an excellent surface condition obtained thanks to the laser stripping step E4. The brushes 11 A, 11 B can slide in contact with the rings 10A, 10B without generating significant friction. The efficiency of the electric motor 2 is thus optimal.

Claims

CLAIMS 1. 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 be traversed by 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 (11 A, 11 B) 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 stripping of the at least one ring.

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

3. Manufacturing method according to one of the preceding claims, characterized in that the 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 by rotating the at least one ring around said axis of rotation.

4. Manufacturing method according to one of the preceding claims, characterized in that the 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 means for generating a laser beam (18) generating a laser beam (FL) extending over the entire height of the ring along said axis of rotation.

5. Manufacturing method according to one of the preceding claims, characterized in that the laser stripping step (E4) comprises a step (E41) of evaluating an oxidation state of the 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) of parameterizing the laser stripping step as a function of the oxidation state of the at least one ring.

6. 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 the at least one ring by means of an optical sensor (22), then a step (E412) of analyzing a color of the at least one ring (10A, 10B).

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

8. Manufacturing method according to 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 the at least one ring of between 20 cm and 80 cm inclusive.

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

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