Rotor assembly for an electric motor

Abstract

Rotor assembly for an electric motor. Rotor assembly (7) for an electric motor (2) of a vehicle (1), in particular for an electric traction and / or propulsion motor of a motor vehicle, the rotor assembly comprising a rotor (9) having a plurality of poles (10), each pole comprising a winding (11) of an electric wire, the rotor further comprising an electrically insulating varnish filling voids around said windings, characterized in that it comprises a heat-shrinkable sheath (23) enveloping said rotor. Figure for the abbreviation: Figure 4

Description

Title of the invention: Rotor assembly for an electric motor Technical field of the invention

[0001] The invention relates to a rotor assembly for an electric motor of a vehicle, the rotor assembly comprising a rotor having a plurality of poles, each pole comprising a winding of an electric wire. The invention also relates to an electric motor comprising such a rotor assembly. The invention also relates to a vehicle, in particular a motor vehicle, comprising such a rotor assembly and / or such an electric motor. 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" electric motors. Such electric motors comprise a rotor with a plurality of poles, each pole containing a winding of an electric wire. The rotor is supplied with electrical energy so as to cause an electric current to flow through each winding. 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 obtain.

[0003] The rotor is exposed to significant temperature variations, vibrations, and centrifugal forces. These stresses can cause the windings of electrical wire within the rotor to shift, which can then lead to malfunctions in the electric motor. To ensure the cohesion of the electrical wire windings within the rotor, it is known to impregnate the rotor with a varnish. This involves applying a varnish to the rotor, filling the empty spaces within it. The varnish also seals the rotor, which then allows a cooling and lubricating fluid, such as oil, to be channeled into the rotor to cool and lubricate it. The varnish also improves the electrical insulation of each winding.

[0004] The application of this varnish to the rotor is generally carried out by immersing the rotor in a bath of liquid varnish. The varnish is then hardened by exposing the rotor to a heat source. However, this process presents several problems.

[0005] First, the varnish layer applied to the periphery of the rotor is not always uniform. In particular, drops of hardened varnish may form at the rotor surface. The radial air gap of the electric motor, which is defined between the rotor and a stator arranged radially around the rotor, can thus be disrupted, degrading the efficiency of the electric motor. In some cases, drops of hardened varnish can even come into contact with the stator.

[0006] Secondly, the rotor seal provided by the varnish coating is sometimes imperfect. Oil can then leak from the rotor and be directed into the air gap. The oil is sheared in the air gap, which creates friction and therefore a loss of efficiency in the electric motor.

[0007] Third, the varnish adheres poorly to certain parts of the rotor, particularly those parts made of stainless steel. As a result, varnish particles detach and can then contaminate the oil circuit. These particles can, in particular, clog an oil filter and / or an oil pump in a cooling and lubrication system. Presentation of the invention

[0008] The object of the invention is to provide a rotor assembly, a method for manufacturing such a rotor assembly and an electric motor comprising such a rotor assembly improving upon the wound rotor electric motors known in the prior art.

[0009] More specifically, a first object of the invention is to provide an easy-to-manufacture, more reliable, and more efficient wound-rotor electric motor. Summary of the invention

[0010] The invention relates to a rotor assembly for an electric motor of a vehicle, in particular for an electric traction and / or propulsion motor of a motor vehicle, the rotor assembly comprising a rotor having a plurality of poles, each pole comprising a winding of an electric wire, the rotor further comprising an electrically insulating varnish and filling empty spaces around said windings, the rotor assembly further comprising a heat-shrinkable sheath enveloping said rotor.

[0011] According to one embodiment, the rotor comprises a core including a plurality of radial protrusions, each winding being formed around a radial protrusion, the rotor further comprising a plurality of retaining wedges, each retaining wedge being arranged between two adjacent windings, the varnish filling empty spaces between the windings, the radial protrusions and the retaining wedges, the heat-shrinkable sleeve enveloping the windings, the radial protrusions, the retaining wedges and the varnish.

[0012] According to one embodiment, the heat-shrinkable sleeve is made of polytetrafluoroethylene.

[0013] According to one embodiment, the heat-shrink tubing comprises a thickness between 0.1 mm and 0.4 mm inclusive, preferably between 0.2 mm and 0.25 mm inclusive.

[0014] According to one embodiment, the heat-shrinkable sleeve comprises a generally cylindrical shape, an axis of revolution of said generally cylindrical shape being coincident with an axis of rotation of the rotor.

[0015] According to one embodiment, the rotor comprises at least one stainless steel element, in particular at least one stainless steel retaining ring and / or balancing ring, said stainless steel element comprising at least one wall covered by a layer of varnish, said layer of varnish being covered by the heat-shrink sleeve.

[0016] The invention also relates to an electric motor comprising a rotor assembly as defined above, a stator arranged around the rotor assembly, and a radial air gap defined between the stator and the heat-shrink sheath of the rotor assembly.

[0017] The invention also relates to a motor vehicle comprising a rotor assembly as defined above and / or an electric motor as defined above.

[0018] The invention also relates to a method for manufacturing a rotor assembly as defined above, the method comprising: - the supply of a rotor and a heat-shrink sleeve, then - inserting the heat-shrink tubing around the rotor, then - at least partial immersion of the rotor and the heat-shrink tubing in a bath containing a varnish in liquid state, and - exposing the assembly formed by the rotor, at least partially covered with liquid varnish and surrounded by heat-shrink tubing, to a heat source to harden the varnish and to heat-shrink the tubing around the rotor.

[0019] According to one embodiment, the heat-shrinkable sleeve comprises an inner layer intended to be heat-shrinked around the rotor and an outer layer extending outside the inner layer, the manufacturing process further comprising the removal of the outer layer after heat-shrinking the inner layer and curing the varnish.

[0020] According to one embodiment, the heat-shrink tubing further comprises a cutting means, in particular a cutting tab, arranged between the inner and outer layers to facilitate removal of the outer layer. See figures

[0021] 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:

[0022] Fig. 1 is a schematic view of a motor vehicle comprising an electric motor according to an embodiment of the invention.

[0023] Fig. 2 is a perspective view of a rotor of the electric motor of Fig. 1.

[0024] Fig. 3 is a perspective view of a core of the rotor of Fig. 2.

[0025] Fig. 4 is a perspective view of a rotor assembly comprising the rotor of Fig. 2 and a heat-shrinkable sleeve intended to be threaded around the rotor.

[0026] Fig. 5 is a perspective view of the rotor assembly of Fig. 4, with the heat-shrink tubing threaded around the rotor.

[0027] The [Fig.6] is a synoptic diagram of the manufacture of a rotor assembly according to an embodiment of the invention.

[0028] Fig. 7 is a schematic view of a third step of a manufacturing process for the rotor assembly according to an embodiment of the invention.

[0029] Fig. 8 is a schematic view of a fourth and fifth stage of the manufacturing process of the rotor assembly.

[0030] Fig. 9 is a schematic view of a sixth step in the manufacturing process of the rotor assembly. The [Fig. 10] is a schematic view of the rotor assembly at the end of its manufacturing process. Detailed description

[0031] Figure 1 schematically illustrates a motor vehicle 1 according to an embodiment of the invention. The vehicle 1 comprises an electric motor 2 for traction and / or propulsion. The electric motor 2 is capable of driving the vehicle's drive wheels 3. The vehicle 1 also comprises a cooling and lubrication system 4 for the electric motor 2. The system 4 comprises a closed circuit passing through the electric motor 2 in which oil can circulate. The system 4 comprises a pump 5 for circulating the oil in the closed circuit and an oil filter 6 for filtering the oil.

[0032] The electric motor 2 is a wound-rotor motor. It comprises a rotor assembly 7 and a stator 8. The stator 8 is arranged around the rotor assembly 7. A radial air gap e is defined between the rotor assembly 7 and the stator 8. This air gap can have a dimension on the order of a few tenths of a millimeter.

[0033] With reference to [Fig. 2], the rotor assembly 7 comprises a rotor 9 having a plurality of poles 10. Each pole 10 comprises a winding 11 of an electric wire, for example, made of copper. The flow of an electric current in the electric wire induces a magnetic field. Each pole 10 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 9 can thus understanding an alternation of North poles and South poles.

[0034] According to the embodiment presented, the rotor 9 comprises a total of eight poles. Alternatively, the number of poles could be any other number.

[0035] The rotor 9 also includes a central shaft 12 intended to be coupled to a transmission system to drive the drive wheels 3. For this purpose, the central shaft 12 is provided with splines 13. The central shaft 12 is also equipped with conductive rings 14, for example made of copper, intended to make contact with brushes to supply the windings 11 with electrical energy. The conductive rings 14 are thus electrically connected to a power source of the vehicle.

[0036] The rotor 9 is designed to rotate about itself around an axis of rotation X. The central shaft 12 extends parallel to the axis of rotation X of the rotor 9 and is centered on the axis of rotation X. The rotor 9 has a generally cylindrical shape with a circular base, centered on the axis of rotation X. The central shaft 12 passes through the generally cylindrical shape. The rotational speed of the rotor can reach, for example, 15,000 revolutions per minute.

[0037] The rotor 9 also includes two retaining rings 15 on either side of the poles 10 along the axis of rotation X. The retaining rings 15 are designed to hold the windings 11 along the axis of rotation X. The retaining rings 15 include a plurality of holes 31 for the passage of cooling and lubricating oil. The rotor 9 also includes two balancing rings 16 on either side of the two ends of the overall cylindrical shape of the rotor 9 along the axis of rotation X. The balancing rings 16 allow the rotor to be balanced so that it does not vibrate when rotating at high speed. The retaining rings 15 and the balancing rings 16 may be made of stainless steel. Alternatively or in addition, the rotor 9 could include any other component made of stainless steel.

[0038] The rotor 9 comprises a metallic core 17, shown in [Fig. 3]. The core 17 comprises a plurality of radial protrusions 18. Each radial protrusion 18 comprises a prismatic radial portion 19 around which a winding 11 is formed. Each radial protrusion 18 also comprises an end portion 20 that at least partially covers a winding 11. Each end portion 20 forms a radial stop for a winding 11, thus preventing the winding 11 from being ejected by centrifugal force. Each radial protrusion 18 thus has at least roughly a mushroom shape. The combination of a radial protrusion 18 and a winding 11 forms a pole 10. The various radial protrusions 18 are distributed regularly around the axis of rotation X.In this particular case, since the rotor 9 comprises eight poles 10, the radial portions 19 of each radial protrusion form an angle equal to 45° with . The radial portions 19 of the adjacent radial protuberances. The core 17 can be formed by a stack of steel plates along the axis of rotation X, also called a "stack". Each plate can have a thickness on the order of a few tenths of a millimeter.

[0039] The core 17 comprises a plurality of free volumes 21 between each adjacent radial protrusion 18. Not only do the windings 11 take position in these free volumes 21, but also retaining wedges 22 (visible in [Fig. 2]). Each retaining wedge 22 is thus arranged between two adjacent windings. Each retaining wedge 22 may have a generally trapezoidal cross-section in a plane perpendicular to the axis of rotation X. The retaining wedges 22 allow the windings 11 to be held in the correct position when the windings 11 are subjected to centrifugal force.

[0040] Finally, the rotor 9 also includes an electrically insulating varnish that fills gaps around the windings 11. In particular, the varnish fills gaps between the windings 11, the radial protrusions 18, and the retaining wedges 12. The varnish may, in particular, be a thermosetting polymer resin. As will be seen in more detail later, the varnish can be applied by immersing the rotor 9 in a bath of liquid varnish and rotating the rotor about its axis of rotation. The varnish can thus penetrate all the gaps in the rotor 9 up to the rotor's immersion depth.

[0041] According to the invention, the rotor assembly 7 comprises not only the rotor 9 as described above but also a heat-shrink sleeve 23 around the rotor. "Heat-shrink" means that the heat-shrink sleeve 23 is made from a heat-shrinkable sleeve 23' which has undergone heat treatment to shrink around the rotor 9.

[0042] Figures 4 and 5 illustrate the rotor 9 and the heat-shrink tubing 23'. The heat-shrink tubing 23' has a tubular shape with a diameter slightly larger than the diameter of the rotor 9. The diameter of the heat-shrink tubing 23' can be approximately 10% to 15% larger than the diameter of the rotor 9. There is therefore a gap between the heat-shrink tubing 23' and the circumference of the rotor 9 through which liquid varnish can seep during the manufacturing process of the rotor assembly 7.

[0043] The heat-shrink tubing 23 has a tubular shape that extends substantially between the two retaining rings 15. The heat-shrink tubing 23 can extend to the holes 31, or even partially or totally cover the holes 31. At a minimum, the heat-shrink tubing 23 envelops the core 17 of the rotor 9. An axis of revolution of said overall cylindrical shape of the heat-shrink tubing 23 coincides with the axis of rotation X of the rotor 8.

[0044] The heat-shrink tubing 23 conforms to the shape of the underlying rotor 9. The tubing Heat-shrinkable sleeve 23 envelops the rotor 9, and in particular all the varnish contained in the rotor 9. The heat-shrinkable sleeve 23 thus makes it possible to perfect the sealing of the rotor 7 assembly. This prevents oil from being sheared in the air gap, which would have created friction and therefore a loss of efficiency of the electric motor.

[0045] Furthermore, the heat-shrink tubing 23 prevents varnish particles from detaching from the rotor 9 and contaminating the electric motor's cooling and lubrication system 4. This is particularly useful when the rotor 9 contains stainless steel parts, as varnish has difficulty adhering to such parts.

[0046] Advantageously, the manufacturing process for the rotor assembly 7 is adapted so that the outer face of the heat-shrinkable sleeve 23 is free of any layer or drop of varnish. The air gap e between the rotor and the stator thus has a uniform value, unlike wound-rotor motors known in the prior art, for which the air gap e varies according to a local varnish thickness.

[0047] Advantageously, the heat-shrink tubing 23 is made of polytetrafluoroethylene, commonly known as PTFE. Such a material is particularly suitable for the operating conditions of an electric motor for a motor vehicle.

[0048] Preferably, the heat-shrink sleeve 23 has a thickness of between 0.1 mm and 0.4 mm inclusive, and more preferably between 0.2 mm and 0.25 mm inclusive. Thus, the heat-shrink sleeve 23 has a very small radial footprint that does not negatively impact the air gap e between the rotor 9 and the stator 8, while still providing sufficient strength.

[0049] The invention also relates to a method for manufacturing the rotor assembly 7 as defined above. With reference to the diagram shown in [Fig. 6], an embodiment of a method for manufacturing a rotor assembly 7 according to the invention is described.

[0050] In a first step E1, a rotor 9 is provided. The rotor may include a core 17 and a set of windings 11 wound around each radial protrusion 18. However, the rotor 9 does not yet include a varnish. In parallel, in a second step E2, a heat-shrinkable sleeve 23' is provided. In a third step E3, the heat-shrinkable sleeve 23' is threaded around the rotor 9, as illustrated in [Fig. 7].

[0051] Advantageously, the heat-shrinkable sleeve 23' comprises a set of three superimposed layers 24, 25, 26. An inner layer 24 is intended to be heat-shrinked around the rotor 9, and thus to form said heat-shrinkable sleeve 23. An outer layer 26 extends outside the inner layer 24 and is intended to be evacuated so as to provide a rotor assembly 7 free of solidified varnish on its outer periphery. The layer 25 is an intermediate layer between the inner layer 24 and the outer layer 26. The layer 25 includes a cutting means 27 to facilitate the removal of the outer layer 26. In particular, the cutting means 27 may be a cutting tab.

[0052] Alternatively, the heat-shrink tubing 23' could have a different structure. The heat-shrink tubing 23' could comprise only two layers, the outer layer 25 and the outer layer 26 forming a single layer. According to another, much simpler, alternative, the heat-shrink tubing 23' could comprise only the inner layer 24, but in this case, the heat-shrink tubing 23' could be coated with varnish on its outer surface, unless an additional process is implemented to remove the varnish from its outer surface.

[0053] Next, in a fourth step E4, illustrated in [Fig. 8], the rotor 9 equipped with the heat-shrink tubing 23 is partially immersed in a bath 28 containing liquid varnish 29. The rotor 9 is then rotated about its axis of rotation X, so as to progressively immerse the entire outer circumference of the rotor 9. During this rotation, the heat-shrink tubing 23' rotates along with the rotor.

[0054] Next, in a fifth step E5, also illustrated in [Fig. 8], the rotor assembly 7 is heated by means of a heat source 30, for example a heating element. This heat source 30 can be positioned opposite the rotor 9 relative to the bath 28, that is, substantially above the rotor. Heating the rotor assembly 7 both dries the varnish and heat-shrinks the heat-shrink tubing 23'. Preferably, the heat-shrink tubing 23' is exposed to a temperature of 60°C or higher. During its heat shrinking, the 23' heat shrink tubing has its diameter reduced and conforms to the shape of the outer circumference of the rotor 9. The use of heat shrink tubing is therefore also advantageous in that the heat shrinking process does not require an additional means of heating compared to that which was already required to dry the varnish.The fifth step E5 can possibly be carried out in parallel with the fourth step E4, or at least be started after the end of the fourth step E4.

[0055] Next, in step E6, illustrated in [Fig. 9], layer 25 and the outer layer 26 are removed, for example by pulling on the cutting tab. Layers 25 and 26 can then be discarded.

[0056] Finally, as illustrated in [Fig. 10], a rotor assembly 7 is obtained comprising the rotor 9 impregnated with hardened varnish and covered with the heat-shrink tubing 23. The rotor assembly 7 thus obtained exhibits improved oil sealing, reduces the risk of varnish particles being disseminated in the cooling and lubrication circuit 4, and has very well-controlled external dimensions, free of dried varnish droplets, which makes it possible to obtain an air gap e of constant value and therefore optimal operation of the electric motor.

Claims

Claims

1. Rotor assembly (7) for an electric motor (2) of a vehicle (1), in particular for an electric traction and / or propulsion motor of a motor vehicle, the rotor assembly comprising a rotor (9) provided with a plurality of poles (10), each pole comprising a winding (11) of an electric wire, the rotor further comprising an electrically insulating varnish filling empty spaces around said windings, characterized in that it comprises a heat-shrunk sheath (23) enveloping said rotor.

2. Rotor assembly (7) according to the preceding claim, characterized in that the rotor (9) comprises a core (17) comprising a plurality of radial protrusions (18), each winding (11) being formed around a radial protrusion, the rotor further comprising a plurality of holding wedges (22), each holding wedge being arranged between two adjacent windings, the varnish filling empty spaces between the windings, the radial protrusions and the holding wedges, the heat-shrunk sheath (23) enveloping the windings, the radial protrusions, the holding wedges and the varnish.

3. Rotor assembly (7) according to one of the preceding claims, characterized in that the heat-shrunk sheath (23) is made of polytetrafluoroethylene.

4. Rotor assembly (7) according to one of the preceding claims, characterized in that the heat-shrunk sheath (23) comprises a thickness of between 0.1 mm and 0.4 mm inclusive, preferably of between 0.2 mm and 0.25 mm inclusive.

5. Rotor assembly (7) according to one of the preceding claims, characterized in that the heat-shrunk sheath (23) comprises a generally cylindrical shape, an axis of revolution of said generally cylindrical shape being coincident with an axis of rotation (X) of the rotor (9).

6. Rotor assembly (7) according to one of the preceding claims, characterized in that the rotor (9) comprises at least one stainless steel element, in particular at least one retaining ring (15) and / or one balancing ring (16) made of stainless steel, said element comprising at least one wall covered by a layer of varnish, said layer of varnish being covered by the heat-shrunk sheath (23).

7. Electric motor (2), characterized in that it comprises a rotor assembly (7) according to one of the preceding claims, a stator (8) arranged around the rotor assembly, and a radial air gap (e) defined between the stator and the heat-shrunk sheath (23) of the rotor assembly.

8. Motor vehicle (1), characterized in that it comprises a rotor assembly (7) according to one of claims 1 to 6 and / or an electric motor (2) according to claim 7.

9. A method of manufacturing a rotor assembly (7) according to one of claims 1 to 6, characterized in that it comprises: - providing a rotor (9) and a heat-shrinkable sheath (23'), then - inserting the heat-shrinkable sheath around the rotor, then - at least partially immersing the rotor and the heat-shrinkable sheath in a bath (28) comprising a varnish (29) in the liquid state, and - exposing the assembly formed by the rotor covered at least partially with varnish in the liquid state and surrounded by the heat-shrinkable sheath to a heat source (30) to harden the varnish and to heat-shrink the sheath around the rotor.

10. A manufacturing method according to claim 9, characterized in that the heat-shrinkable sheath (23') comprises an inner layer (24) intended to be heat-shrinked around the rotor and an outer layer (26) extending outside the inner layer, and in that the manufacturing method further comprises removing the outer layer after heat-shrinking the inner layer and curing the varnish.

11. Manufacturing method according to the preceding claim, characterized in that the heat-shrinkable sheath (23') further comprises a cutting means (27), in particular a cutting tab, arranged between the internal layer (24) and the external layer (26) to facilitate the removal of the external layer.

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