Assembly for electric machine

Abstract

The invention relates to an assembly (1) for an electric machine, comprising: - a casing (20) which is made of conductive material and is connected to a reference potential; - a rotor (10) having an axis of rotation (A1); - an electrically conductive connecting element (100) which is in electrical contact with the casing and with an electrically conductive part of the rotor. According to the invention, the connecting element extends along the axis of rotation.

Description

Description Title of the invention: Assembly for an electrical machine Technical field of the invention

[0001] The present invention relates generally to the field of electrical machines.

[0002] It relates more specifically to an assembly for an electrical machine.

[0003] The invention finds a particularly advantageous application in the production of electrical machines for motor vehicle engines. State of the art

[0004] An electric machine typically consists of a stator and a rotor housed within a casing. During operation, the rotor accumulates an electrical charge, much like a capacitor. When the accumulated charge becomes excessive, the rotor discharges, generating electrical arcs along the paths of least resistance, namely at the ball bearings or gears mechanically connected to the rotor's output shaft. These electrical arcs cause microscopic wear on the ball bearings or gears, which, over time, increases rotor friction and degrades the electric motor's performance.

[0005] One solution for controlling rotor discharge is to electrically connect the housing and the rotor output shaft using a conductive junction element. The housing is connected to a reference potential. The rotor can thus be "grounded".

[0006] For example, US2016 / 010750 describes an annular disc made of conductive felt that is positioned around the rotor output shaft and is in contact with the housing. However, felt is a fragile and expensive material, which limits its industrial application.

[0007] In addition, the tangential speed at the periphery of the rotor output shaft (which typically rotates at over 20,000 rpm) is high, resulting in significant wear of the connecting element.

[0008] Finally, the connecting element requires the use of a longer and therefore more fragile output shaft. Presentation of the invention

[0009] In this context, the present invention proposes an assembly for an electrical machine comprising: - a casing made of conductive material which is connected to a reference potential; - a rotor with an axis of rotation; - an electrically conductive connecting element which is in electrical contact with the housing and with an electrically conductive part of the rotor, the connecting element extending along the axis of rotation.

[0010] Thus, thanks to the invention, the connecting element is positioned where the tangential speed of the rotor is lowest. For example, for a rotor whose output shaft typically measures 30 mm in diameter, positioning the connecting element approximately three millimeters from the axis of rotation, instead of at the periphery of the output shaft, reduces the tangential speed in the contact area with the connecting element by a factor of ten.

[0011] Consequently, wear on the connecting element is greatly reduced.

[0012] Furthermore, it is not necessary to dedicate a specific portion of the output shaft length to contact with the connecting element. In other words, the electrical machine assembly according to the invention allows for a reduction in the output shaft length compared to the prior art rotor, thus improving compactness and robustness.

[0013] Other advantageous and non-limiting features of the device according to the invention, taken individually or in all technically possible combinations, are as follows: - the joining element is centered on the axis of rotation; - the joining element is cylindrical in shape, preferably of revolution around the axis of rotation; - at least one of the rotor and the casing includes a recessed relief in which the connecting element is partially inserted; - said recessed relief comprises a deep portion, a part of the joining element being inserted into the deep portion, the deep portion being designed to fit together, with a slight play, with said part; - said recessed relief includes a flush portion opening outwards towards the outside of said at least one among the rotor and the casing, the flush portion being flared outwards towards the outside of said at least one among the rotor and the casing; - the connecting element comprises a cylindrical body of revolution and, on the side of the housing, a head wider than the diameter of the body; - at least one of the rotor and the casing includes a carbon brush arranged to be in contact with the connecting element; - said coal delimits said relief in hollow; - the connecting element is free to rotate around the axis of rotation relative to the rotor and the housing; - a contact surface between the joining element and at least one of the rotor and the housing is less than 5 mm, and preferably less than 3 mm, from the axis of rotation ; - the assembly also includes an annular deflector arranged around the joining element so as to block at least partially the passage of dust or particles.

[0014] Of course, the various features, variants, and embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0015] The description that follows, with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0016] Regarding the attached drawings:

[0017] [Fig.1] is a schematic cross-sectional view of a first embodiment of an assembly for an electrical machine according to the invention;

[0018] [Fig.2] is a detail view of zone II of [Fig.1], the whole being equipped with a deflector;

[0019] [Fig.3] is a schematic cross-sectional view of a second embodiment of an assembly for an electrical machine according to the invention.

[0020] An assembly 1 for an electric machine according to the invention is shown in [Fig. 1]. Assembly 1 comprises a rotor 10 and a housing 20.

[0021] Assembly 1 is intended to be part of an electrical machine such as an electric motor for a motor vehicle. The electrical machine further includes a stator (not shown).

[0022] Typically, the rotor 10 is disc-shaped or cylindrical, centered around a rotational axis A1. The rotor 10 includes magnetic elements 13, for example, electromagnets or permanent magnets. The stator is a flattened ring and, on its face facing the rotor 10, has teeth around which windings of electrically conductive wire are wound. When these windings are energized, they generate a rotating magnetic field that drives the magnetic elements 13, thus setting the rotor 10 in motion around the rotational axis A1.

[0023] To transmit this rotational motion to the outside of the electric machine, the rotor 10 includes an output shaft 11 which also rotates around the axis of rotation A1. It further comprises teeth 12, as shown in [Fig. 1]. The rotor 10, and in particular the output shaft 11, is made of an electrically conductive material. The output shaft 11 is, for example, made of aluminum or steel.

[0024] The rotor 10 and the stator are mounted in the housing 20 which ensures the retention of these the latter as well as their protection against external aggressions (shocks, dust, etc.). The stator is fixed relative to the housing 20 while the rotor 10 is held so as to be free to rotate around its axis of rotation Al relative to the housing 20, for example by means of ball bearings.

[0025] The casing 20, or at least a portion thereof, is made of an electrically conductive material. This portion of the casing 20 thus comprises a metallic material such as aluminum. This portion of the casing 20 is electrically connected to a reference potential, which forms the vehicle's ground.

[0026] As shown in [Fig. 1], assembly 1 also includes an electrically conductive connecting element 100. The connecting element 100 is in electrical contact with both the housing 20 and the rotor 10, here with the output shaft 11 of the rotor 10. The connecting element 100 thus enables the rotor 10 to be "grounded" by connecting it to the reference potential of the housing 20.

[0027] Preferably, the connecting element 100 is made of a material with low electrical resistivity. Here, the connecting element 100 is made of a metallic material, and more particularly of copper. The electrical charges accumulated by the rotor 10 during its rotation are thus efficiently conducted to the housing 20. Furthermore, the connecting element 100 according to the invention is therefore inexpensive and robust. The connecting element 100 can also be made of aluminum.

[0028] As shown in [Fig. 1], the connecting element 100 extends along the rotation axis Al. This means that the connecting element 100 has a principal dimension substantially parallel to the rotation axis Al and that the connecting element 100 is traversed by the rotation axis Al. Conversely, it also means that the connecting element 100 has transverse dimensions that are smaller than the principal dimension and that are substantially orthogonal to the rotation axis Al.

[0029] Here, the connecting element 100 extending along the axis of rotation Al is characterized in particular by the fact that the latter is generally long-sloping with two ends 120, 130 opposite and aligned on the axis of rotation Al, as shown in figures 1 and 3. A first end 120 is in contact with the rotor 10 while a second end 130 is in contact with the housing 20.

[0030] As shown in [Fig.1], the junction element 100 is more specifically centered on the rotation axis Al. In general, this means that the junction element 100 has a geometric and inertial center positioned on the rotation axis AL. Here, the junction element 100 more precisely has a mean fiber (or neutral fiber) which is substantially coincident with the rotation axis Al.

[0031] The joining element 100, as shown in figures 1 to 3, is cylindrical here and its generatrices are substantially parallel to the axis of rotation Al. The joining element 100 extends more specifically along a cylindrical surface of revolution. The junction element 100 thus presents an axis of symmetry which is here, because the junction element 100 is centered on the axis of rotation Al, coincides with the axis of rotation Al.

[0032] As an example, the cylindrical connecting element 100 has a diameter between 1 mm and 4 mm and a height, i.e., a length along the axis of rotation Al, between 15 mm and 30 mm. The length and diameter of the connecting element 100 can be adjusted to provide the desired bending strength or stiffness. The stiffness of the connecting element 100 can also be adjusted by means of heat treatment.

[0033] The arrangement of the connecting element 100 relative to the rotor 10 and the housing 20 is illustrated in detail in figures 1 to 3.

[0034] As shown in [Fig. 1], the connecting element 100 is partially inserted into the rotor 10 (on the side of the first end 120) and into the housing 20 (on the side of the second end 130). The cylindrical surface of revolution of the connecting element 100 thus provides a sufficiently large contact area to ensure electrical conduction. Remarkably, because the connecting element 100 is inserted into the rotor 10 along the axis of rotation A1, the tangential velocity in the contact zone between the connecting element 100 and the rotor 10 remains relatively low, for example, compared to the tangential velocity at the periphery of the output shaft 11. The connecting element 100 is therefore subject to little wear due to the rotation of the rotor 10.

[0035] Here, the contact surface between the connecting element 100 and the rotor 10 is less than 5 mm, and preferably less than 3 mm, from the axis of rotation Al. Similarly, the contact surface between the connecting element 100 and the housing 20 is less than 5 mm, and preferably less than 3 mm, from the axis of rotation Al.

[0036] To position the connecting element 100 in the rotor 10 and the housing 20, the rotor 10 includes a first recessed relief 30 and the housing 20 includes a second recessed relief 40. Each recessed relief 30, 40 has a shape adapted to receive the connecting element 100. Each recessed relief 30, 40 is also centered on the axis of rotation Al. The first recessed relief 30 is located inside the output shaft 11 of the rotor 10. The length of the insertion of the connecting element 100 in the recessed reliefs 30, 40 is, for example, between 5 mm and 12 mm.

[0037] As shown in [Fig. 2], the first recessed relief 30 provided inside the output shaft 11 of the rotor 10 comprises a flush portion 31 and a deep portion 32, aligned along the axis of rotation A1 and contiguous. The flush portion 31 opens onto the exterior of the rotor 10 towards the housing 20. The flush portion 31 of the first recessed relief 30 is therefore located opposite the housing 20. The deep portion 32, on the other hand, is located opposite the housing 20 with respect to the flush portion 31, at the bottom of the first recessed relief 30. From the housing 20, the first recessed relief 30 is here made up of the outcropping portion 31 and then the deep portion 32.

[0038] Similarly, as shown in [Fig. 2], the second recessed relief 40 provided inside the housing 20 also comprises a flush portion 41 and a deep portion 42, aligned along the axis of rotation A1 and contiguous. The flush portion 41 opens onto the exterior of the housing 20 towards the rotor 10 and is therefore located opposite the rotor 10. The deep portion 42, on the other hand, is located opposite the rotor 10 with respect to the flush portion 41, at the bottom of the second recessed relief 40. From the rotor 10, the second relief 40 is thus composed of the flush portion 41 and then the deep portion 42.

[0039] Each flush portion 31, 41 and each deep portion 32, 42 is designed to house a part of the joining element 100. Said part being for example between 20% and 50% of the length of the joining element 100. Here, the deep portions 32, 42 are however specifically adapted, within a clearance, to the shape of the joining element 100 while the flush portions 31, 41 are flared to tolerate a bending of the joining element 100.

[0040] Here, each deep portion 32, 42 has in particular a cylindrical internal surface of revolution whose diameter is equal, up to a clearance, to that of the joining element 100. The deep portions 32, 42 and the joining element thus have a fit-type interlocking with clearance, i.e. in which the fit is positive so that the joining element 100 can pivot freely in the recessed reliefs around the axis of rotation Al.

[0041] In practice, variations in the straightness of the junction element 100 due to its manufacture generate several contact zones between the latter and the deep portions 32, 42, which allows electricity to pass efficiently while ensuring low friction resistance.

[0042] Here, each flush portion 31, 41 has an increasing diameter, along the axis of rotation Al, from the deep portions 32, 42 towards the outside of the rotor 10 or the housing 20. Their diameter can for example increase from a diameter equal to that of the joining element 100 (and therefore of the deep portions 32, 42) to a diameter 5% to 10% greater than that of the joining element 100.

[0043] As an example, the flush portions 31 and 41 may have an internal surface extending along a frustoconical surface that forms an angle with the axis of rotation Al of between 5 and 15 degrees. As another example, the diameter of the flush portions 31 and 41 may increase parabolically as shown in Figures 2 and 3.

[0044] The flush portions 31, 41 are thus slightly wider than the joining element 100 to allow for a mechanical tolerance, i.e., a slight deflection, when the rotation axis Al of the rotor 10 moves slightly and briefly relative to the Carter 20, for example when the motor vehicle is subjected to a jolt.

[0045] The recessed reliefs 30, 40 can be through, such as the second recessed relief 40 illustrated in [Fig.1], or blind, such as the first recessed relief 30 illustrated in [Fig.3].

[0046] It could be envisaged that the recessed reliefs would be made directly in the casing and in the rotor output shaft.

[0047] But here, on the contrary, they are provided in intermediate parts called "Carbons." Advantageously, the rotor 10 comprises a first carbon brush 15. The first carbon brush 15 is engaged in a suitable recess in the rotor shaft 11. The housing 20 more specifically comprises a metallic housing block 21, which is connected to the reference potential (the housing block 21 here corresponds to the electrically conductive sub-part of the housing 20), and a second carbon brush 25. The housing block 21 forms a recess that delimits a well 22, the bottom of which defines an opening in which the second carbon brush 25 is engaged. The carbon brushes 15 and 25 are thus press-fitted into the output shaft 11 and into the housing block 21, thereby securing them.

[0048] Carbon brushes 15 and 25 are characterized by their high electrical conductivity and mechanical strength, as well as their low adhesion and even self-lubricating properties. Here, carbon brushes 15 and 25 are made of graphite.

[0049] The first hollow relief 30 is planned in the first coal 15 while the second hollow relief 40 is then planned in the second coal 25. In other words, coals 15, 25 delimit the hollow reliefs 30, 40.

[0050] Thus, the connecting element 100 is in contact with the brushes 15 and 25, which are themselves in contact with the output shaft 11 of the rotor 10 and the housing block 21 of the housing 20. The contact between the connecting element 100 and the brushes 15 and 25 is direct, both mechanically and electrically. This ensures greater wear resistance than if the connecting element 100 were in direct contact with the metal of the rotor 10 or the housing block 21, thanks in particular to the non-stick properties of the brushes 15 and 25. Since the brushes 15 and 25 are very good electrical conductors, they have very little influence on the flow of electricity. Preferably, the connecting element 100 is in contact exclusively with the brushes 15 and 25.

[0051] Coals 15, 25 can, for example, have external cylindrical shapes, for example with a diameter between 10 mm and 15 mm, or parallelepiped shapes.

[0052] The connecting element 100 is preferably free to rotate both relative to the housing 20 and relative to the rotor 10. This allows it to rotate freely, at a speed lower than the rotational speed of the rotor 10, and consequently to limit overall wear on the contacts with the housing 20 and the rotor 10. In practice, the rotational speed of the connecting element 100 stabilizes at around half the rotor rotation speed 10, the wear of the junction element 100 is therefore distributed in a substantially equal manner at the level of the two brushes 15, 25.

[0053] In a first embodiment, shown in figures 1 and 2, the connecting element 100 is fixed in translation along the axis of rotation Al. The advantage of this embodiment is to improve the electrical contact between the rotor 10 and the housing 20.

[0054] As shown in [Fig. 1], in this first embodiment, the connecting element 100 specifically comprises a body 110 and a head 140 on the side of the second end 130 of the connecting element 100 (the end facing the housing 20). The body 110, which is cylindrical in revolution, represents more than 90%, and in particular more than 95%, of the length of the connecting element 100 along the axis of rotation Al. The head 140 is wider than the body 110. This means that one of its dimensions transverse to the axis of rotation Al is greater than the diameter of the body 110. It forms a sort of nail head. The connecting element 100 thus has an overall nail shape. Furthermore, in this first embodiment, the second recessed relief 40 is through-hole.

[0055] As shown in [Fig.2], the head 140 comes to rest on one side of the second brush 25 opposite the rotor 10, which holds the connecting element 100 along the axis of rotation Al on one side.

[0056] As shown in [Fig. 1], assembly 1 also includes a plug 60 embedded or screwed into the housing block 21. The head 140 is then sandwiched between the plug 60 and the second carbon brush 25, which allows the connecting element 100 to be locked along the axis of rotation A1. Here, a metal washer 50 is interposed between the head 140 and the second carbon brush 25 to facilitate tightening the head 140 onto the second carbon brush 25.

[0057] Preferably, the contact between the plug 60 and the connecting element 100 is made by means of a pin 61 arranged on the plug 60. As shown in [Fig. 2], the pin 61 has, for example, a conical pyramid shape along the axis of rotation Al, which leaves the connecting element 100 free to rotate. The pin 61 can be made of a harder material than the connecting element 100 so as to deform the head 140. Conversely, the pin 61 can be softer so as to undergo the deformation.

[0058] Assembly 1 may also include at least one spring 70, provided between the cap 60 and the second carbon brush 25, to improve the retention of the second carbon brush 25 relative to the housing 20.

[0059] In a second embodiment, represented in [Fig.3], the joining element 100 is left mobile in translation along the axis of rotation Al.

[0060] For this reason, unlike the first embodiment, the joining element 100 does not does not include an enlarged end. Thus, in this second embodiment, the joining element 100 is essentially cylindrical.

[0061] As suggested by [Fig.3], the connecting element 100 can move in translation along the axis of rotation Al between the plug 60 and a bottom 33 of the first recessed relief 30, which thus form stops for the connecting element 100.

[0062] In this second embodiment, the connecting element 100 is less mechanically constrained, in the sense that it has more degrees of freedom than in the first embodiment, and is thus more able to resist a momentary displacement of the axis of rotation Al relative to the housing 20.

[0063] Regardless of the embodiment, assembly 1 may also include a deflector 70 arranged around the periphery of the connecting element 100, as shown in [Fig. 2]. The deflector 70 prevents dust or particles produced by the friction of the connecting element 100 in the recessed areas 30, 40. Thanks to the deflector 70, such dust or particles will not contaminate the oil mist contained in the housing 20, which is used for lubrication.

[0064] As shown in [Fig. 2], the deflector 70 comprises two rings 71, 71', each with a base 72, 72' which is in contact with one of the carbons 15, 25, and a lip 73, 73' extending along the axis of rotation Al. The rings 71, 71' are made of semi-rigid materials, for example, silicone or polyamide. The bases 72, 72' are, for example, bonded to the carbons 15, 25.

[0065] The lip 73, 73' of each ring 71, 71' extends beyond the lip 73, 73' of the other ring 71, 71' (in other words, they are nested within each other). The connecting element 100 is thus completely surrounded by the deflector 70, from the housing 20 to the rotor 10. Each ring 71, 71' terminates in a fold 74, 74' directed towards the lip 73, 73' of the other ring 71, 71'. Dust or particles are thus trapped, in particular, at the junction between the lips 73, 73' and the folds 74, 74'.

[0066] The present invention is in no way limited to the embodiments described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

[0067] For example, the connecting element can be cylindrical while having a non-circular transverse cross-section. The connecting element can also have an axis of symmetry along the axis of rotation without being cylindrical. Similarly, the recessed reliefs may not be cylindrical. The connecting element can also be fixed relative to the housing or the rotor, and therefore only movable within one of the two recessed reliefs. The recessed reliefs themselves can be formed directly into the metal constituting the housing and the rotor. It is therefore not necessary to The use of carbon brushes is employed. The first recessed feature can be located elsewhere than on the rotor output shaft, for example, on the opposite side. Finally, the connecting element can be in contact with the rotor or housing without being inserted into them, for example, by means of a flat contact at one of its bases. The connecting element can then be held against the rotor or housing by a metal spring.

Claims

Demands

1. Assembly (1) for an electrical machine comprising: - a casing (20) made of conductive material which is connected to a reference potential; - a rotor (10) having an axis of rotation (Al); - an electrically conductive connecting element (100) which is in electrical contact with the housing (20) and with an electrically conductive part of the rotor (10); characterized in that the connecting element (100) extends along the axis of rotation (Al).

2. Assembly (1) according to claim 1, wherein the joining element (100) is centered on the axis of rotation (Al).

3. Assembly (1) according to claim 1 or 2, wherein the joining element (100) is cylindrical in shape, preferably of revolution about the axis of rotation (Al).

4. Assembly (1) according to any one of claims 1 to 3, wherein at least one of the rotor (10) and the housing (20) comprises a recessed relief (30, 40) in which the connecting element (100) is partially inserted.

5. Assembly (1) according to claim 4, wherein said recessed relief (30, 40) comprises a deep portion (32, 42), a part of the joining element (100) being inserted into the deep portion (32, 42), the deep portion (32, 42) being designed to fit together, with a clearance, with said part of the joining element (100).

6. Assembly (1) according to claim 5, wherein said recessed relief (30, 40) comprises a flush portion (31, 41) opening outwards from said at least one of the rotor (10) and the housing (20), the flush portion (31, 41) being flared outwards from said at least one of the rotor (10) and the housing (20).

7. Assembly (1) according to any one of claims 1 to 6, wherein the connecting element (100) comprises a cylindrical body (110) of revolution and, on the side of the housing (20), a head (140) wider than the diameter of the body (110).

8. Assembly (1) according to any one of claims 1 to 7, wherein at least one of the rotor (10) and the housing (20) comprises a carbon brush (15, 25) arranged to be in contact with the connecting element (100).

9. Assembly (1) according to any one of claims 1 to 8, wherein the joining element (100) is free to rotate about the axis of rotation (Al) relative to the rotor (10) and the casing (20).

10. Assembly (1) according to any one of claims 1 to 9, further comprising an annular deflector (70) arranged around the joining element (100) so as to block at least part of the passage of dust or particles.

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