Electric machine comprising a rolling bearing and a rotor assembly comprising a groove

Abstract

The invention relates to an electric machine (1) comprising a rolling bearing (5) and a rotor assembly (10) carried by the rolling bearing (5) so as to be rotatable about an axis of rotation (X), the rolling bearing (5) comprising an inner ring (7) which is in contact with a contact surface (40) formed on the rotor assembly (10), the rotor assembly (10) comprising a groove (30) and an electrical conductor (15) accommodated in the groove (30), the groove comprising a first groove portion (31) opening onto the contact surface (40), characterized in that the first groove portion (31) is not parallel to the axis of rotation (X); the invention being particularly suitable for an electric machine (1) having a wound rotor and a slip ring.

Description

Description Title of the invention: Electric machine comprising a roller bearing and a rotor assembly having a groove. Technical field

[0001] The present invention relates to an electrical machine. Technological background

[0002] Figure 1 schematically represents, in axial half-section, a known electrical machine 1. The electrical machine 1 comprises a rotor assembly, generally designated as 110. The rotor assembly 110 is supported by rolling bearings 4, 5, such as ball bearings, so as to rotate about an axis of rotation X. The axial half-section of Figure 1 lies in a plane that includes the axis of rotation X.

[0003] The rotor assembly 110 includes a shaft 111 on which coil supports 20 are mounted. Each coil support 20 supports a coil 21. Only one coil support 20 and one coil 21 are shown in [Fig. 1]. The coils 21 and their coil supports 20 are arranged within the internal volume 3 of a housing 2 of the electric machine 1. The stator of the electric machine 1, not shown in [Fig. 1], is arranged around the rotor assembly 110, for example within the internal volume 3.

[0004] The rotor assembly 110 further includes a rotating commutator 13 which comprises one or more slip rings 14. To carry electric current from a slip ring 14 to a coil 21, an electrical conductor 15 electrically connects the slip ring 14 to a terminal piece 16, and the coil 21 is electrically connected at 22 to the terminal piece 16. The electrical machine 1 shown is therefore of the wound rotor and rotating commutator type.

[0005] With reference to [Fig. 1], it is understood that in order to electrically connect the slip ring 14 to the coil 21, the electrical conductor 15 must necessarily pass under the bearing 5. For this, with reference to [Fig. 2], a known solution consists of providing the shaft 111 with straight grooves 30 which extend parallel to the axis of rotation X, and of housing a conductor 15 in each of these grooves 30. The grooves 30 pass under the inner ring 7 of the bearing 5.

[0006] This solution makes the manufacture of the shaft 111 very simple, since the grooves 30 can be easily made by machining the shaft 111. However, as indicated by the reference marks Q in [Fig. 2], the contact between the inner ring 7 and the shaft 111 is interrupted by the grooves 30. In other words, since the grooves 30 are hollow, the inner ring 7 is not supported by the shaft 111 over its entire periphery. As a result: the inner ring 7 tends to become oval; the rolling elements 5A of the bearing housing 5 pass several times per revolution (as many times per revolution as there are grooves 30) over a region of the inner ring 7 that is not supported by the shaft 111; and the inner ring 7 tends to oscillate radially relative to the outer ring 6. These different phenomena create vibrations in the electrical machine 1 and in particular in the shaft 111.

[0007] This is particularly undesirable when the electric motor 1 is part of the powertrain of an electric vehicle, because the vibrations are then transmitted to the vehicle's body and passenger compartment, where they generate a low-frequency noise sometimes referred to as "rumbling." From the perspective of someone inside the passenger compartment, this low-frequency noise is unexpected coming from the propulsion of an electric vehicle and can even be unpleasant. Furthermore, because this noise is low-frequency, it is difficult to attenuate with soundproofing panels or other mechanical noise reduction methods. Summary of the invention

[0008] The invention aims to remedy at least partially the aforementioned drawbacks.

[0009] The invention relates to an electrical machine. According to the invention, the electrical machine comprises a roller bearing and a rotor assembly supported by the roller bearing so as to be rotatable about an axis of rotation. the bearing housing comprising an inner ring which is in contact with a contact surface formed on the rotor assembly, the rotor assembly comprising a groove and an electrical conductor housed in the groove, the groove including a first portion of the groove opening onto the contact surface, and The first groove section is not parallel to the axis of rotation. This configuration of the first groove section tends to ensure that even at a position where the contact surface is interrupted by the first groove section, the inner ring of the bearing is partially supported by the rotor assembly. This tends to reduce the phenomena described above, which generate vibrations in the electric motor and low-frequency noise in the vehicle's passenger compartment.

[0010] According to one possible feature of the invention, the first portion of the groove describes a curve that is not contained in a plane. Such a curve can also be described as a skew curve.

[0011] According to one possible feature of the invention, the contact surface describes a cylinder of revolution, and the first portion of the groove describes a circular helix with a non-zero helix angle [3]. This allows the first portion of the groove to be machined very simply, using a milling cutter that advances at a constant speed parallel to the axis of rotation, while the rotor assembly rotates at a constant speed around the axis of rotation. The desired helix angle [3] is obtained by appropriately selecting the feed rate of the milling cutter and the rotational speed of the rotor assembly.

[0012] According to a possible feature of the invention, the helix angle [3], a width e of the first portion of the groove in a plane perpendicular to the axis of rotation, and a length Lr of the contact surface parallel to the axis of rotation, satisfy the following relationship: Lr.tan([3) > e. When this relationship is satisfied, the inner ring is supported over a sufficient part of the contact surface, which appreciably reduces the phenomena described above that generate vibrations in the electrical machine and low-frequency noise in the vehicle's passenger compartment.

[0013] According to one possible feature of the invention, the rotor assembly comprises a first shoulder and a second shoulder spaced apart along the axis of rotation, the contact surface being formed between the first shoulder and the second shoulder. The second shoulder can, in particular, prevent the inner ring from translating relative to the axis of rotation.

[0014] According to one possible feature of the invention, the rotor assembly comprises a cylindrical portion with a diameter greater than the cylinder of revolution described by the contact surface. This cylindrical portion is delimited by a second shoulder and a third shoulder distinct from the first shoulder. The groove includes a second groove portion that extends the first groove portion into the cylindrical portion. The cylindrical portion with the second groove portion allows the electrical conductor to be easily routed to an electrical connection, for example, an electrical connection to a coil.

[0015] According to one possible feature of the invention, the second portion of the groove is parallel to the axis of rotation. The second portion of the groove is then particularly easy to machine.

[0016] According to one possible feature of the invention, the rotor assembly comprises a coil and a slip ring, with the electrical conductor connecting the coil to the slip ring, and the roller bearing located between the coil and the slip ring along the axis of rotation. The electrical machine can then be described as a wound-rotor, rotating-commutator electric machine. Electric machines of this type offer certain advantages over permanent-magnet electric machines, including lower material costs, particularly because permanent magnets increasingly need to contain rare earth elements to achieve the desired performance level.

[0017] According to one possible feature of the invention, the rotor assembly comprises N so-called grooves and N so-called electrical conductors, each housed in a so-called groove, N being an integer at least equal to 2, the N so-called grooves being mirror images of each other by rotation about the axis of rotation. Preferably, the N so-called grooves are arranged at regular intervals around the axis of rotation. Each of the grooves can then be used to route an electrical conductor that electrically connects a slip ring to a coil (or a group of coils).

[0018] The invention also relates to an electric vehicle comprising a powertrain that includes an electric machine as described above. The term "electric vehicle" encompasses battery electric vehicles and hybrid electric vehicles. Brief description of the figures

[0019] The following description, with reference to the accompanying drawings, given by way of non-limiting examples, will clearly explain the nature of the invention and how it can be implemented. Regarding the accompanying figures:

[0020] [Fig. 1], already described above, represents a schematic axial half-section view of a known electrical machine,

[0021] [Fig.2], already described above, represents the front view of the rotor assembly of the electric machine,

[0022] [Fig.3] partially represents, in top view, the rotor assembly of an electrical machine according to one embodiment of the invention,

[0023] [Fig.4] partially represents the rotor assembly in perspective,

[0024] [Fig.5] represents a partial schematic view of the rotor assembly, in cross-section along VV on [Fig.4],

[0025] [Fig. 6] partially represents, in top view, the rotor assembly of an electrical machine according to another embodiment of the invention,

[0026] [Fig. 7] partially represents, in top view, the rotor assembly of an electric machine according to yet another embodiment of the invention. Description of method(s) of implementation

[0027] In the figures, and unless otherwise specified, identical elements will bear the same reference symbols. It should be noted that the figures are schematic and not drawn to scale.

[0028] Figures 3, 4, and 5 represent a rotor assembly 10 according to an embodiment of the invention. The rotor assembly 10 is intended to be used in the electric machine 1 in place of the rotor assembly 110 described above with reference to Figures 1 and 2. Consequently, elements identical or similar to those already described with reference to Figures 1 and 2 bear the same reference numerals and are not described again unless necessary.

[0029] In Figures 3, 4, and 5, reference numeral 40 designates a contact surface formed on the rotor assembly 10. The inner ring 7 of the bearing housing 5 (not shown in [Fig. 3] and [Fig. 4]) is intended to be in contact with the contact surface 40. As can be seen in [Fig. 4], the contact surface 40 describes a cylinder of revolution and is formed between a first shoulder 51 and a second shoulder 52, which are spaced apart along the axis of rotation X. The second shoulder 52 can, in particular, prevent the inner ring 7 from translating relative to the axis of rotation X.

[0030] In the embodiment of figures 3, 4 and 5, the groove 30 comprises a first portion of groove 31 and a second portion of groove 32. The first portion of groove 31 opens onto the contact surface 40. The second portion of groove 32 extends the first portion of groove 31 as will be detailed below.

[0031] In general, and unlike the rotor assembly 110 described above, the first portion of the groove 31 is not parallel to the axis of rotation X. Therefore, as indicated by the reference mark W in [Fig. 5], it can be ensured that even at a position where the contact surface 40 is interrupted by the first portion of the groove 31, the inner ring 7 of the bearing 5 is partially supported by the rotor assembly 10. This tends to reduce the phenomena described above which generate vibrations in the electric machine 1 and low-frequency noise in the vehicle's passenger compartment.

[0032] Various geometries are possible for the first portion of groove 31. In very simple execution variants, the first portion of groove 31 is straight so as to extend in a plane which makes a non-zero angle with the axis of rotation X. However, it is preferable that the first portion of groove 31 describes a skew curve, in other words a curve which is not contained in a plane.

[0033] Preferably, and as shown in [Fig. 3] and [Fig. 4], the left-hand curve is a circular helix; in other words, the first portion of the groove 31 describes a circular helix on the contact surface 40, the latter describing a cylinder of revolution as already mentioned above. The helix angle of the circular helix is ​​denoted by [3 (see [Fig. 3]), where [3 is non-zero, i.e., [3 ≥ 0°. This allows the first portion of the groove 31 to be machined very simply, using a milling cutter that advances at a constant speed parallel to the axis of rotation X while the rotor assembly 10 rotates at a constant speed around the axis of rotation X. The desired helix angle [3] is obtained by appropriately choosing the feed rate of the milling cutter and the rotational speed of the rotor assembly 10.

[0034] Referring to [Fig. 3], the first portion of the groove 31 has a width e in a plane perpendicular to the axis of rotation X. The length of the contact surface 40 parallel to the axis of rotation X, which here is equal to the distance between the shoulders 51 and 52, is denoted by Lr. In [Fig. 3], the value of the width e has been deliberately exaggerated to show that if the width e becomes excessively large for given values ​​of [3] and Lr, the inner ring 7 may only be supported on an excessively small portion of the contact surface 40 where the contact surface 40 is interrupted by the first portion of the groove 31. It is therefore necessary that the width e remain below a certain limit value, which is a function of [3] and Lr, so that the inner ring 7 is supported on a sufficient portion of the contact surface 40.

[0035] In particular, according to preferred embodiment variants, the quantities e, [3 and Lr satisfy the following relation: Lr.tan([3) > e. When this relation is satisfied, the inner ring 7 is supported on a sufficient part of the contact surface 40, which appreciably reduces the phenomena described above which generate vibrations in the electrical machine 1 and low-frequency noise in the vehicle's passenger compartment.

[0036] Figures 4 and 5 show that, similarly to Figure 2, the electrical conductor 15 is housed in the groove 30 and in particular in the first portion of the groove 31. Preferably, the electrical conductor 15 can be surrounded by an insulating material 70 present in the first portion of the groove 31.

[0037] With reference to [Fig. 3] and [Fig. 4], the rotor assembly 10 comprises a cylindrical portion 60 with a diameter larger than the cylinder of revolution described by the contact surface 40. The cylindrical portion 60 is adjacent to the contact surface 40; in other words, the cylindrical portion 60 is delimited on one side by the second shoulder 52, and on the other side by a third shoulder 53 distinct from the first shoulder 51. Furthermore, the second groove portion 32 extends the first groove portion 31 into the cylindrical portion 60. The second groove portion 32 opens onto the outer surface of the cylindrical portion 60. Thus, and as shown in [Fig. 3], it is easy to route the electrical conductor 15 to the end piece 16 (see [Fig. 1]), the connection between the electrical conductor 15 and the end piece 16 being made in the second groove portion 32.

[0038] It is preferable for the second groove portion 32 to be straight, as shown in Figures 3 and 4. Indeed, if the second groove portion 32 were not straight, it would be difficult to machine after machining the first groove portion 31 due to the presence of the second shoulder 52. Even more preferably, the second groove portion 32 is straight and parallel to the axis of rotation X. In this case, after machining the first groove portion 31, it is sufficient to stop the rotation of the rotor assembly 10 and advance the cutter until the desired dimensions of the second groove portion 32 are obtained. The second groove portion 32 is then particularly easy to machine.

[0039] Thanks to the rotor assembly 10, it is possible to pass the electrical conductor 15 under the inner ring 7 of the bearing 5, and thus to connect a coil 21 (see [Fig. 1]) to a slip ring 14 (see [Fig. 4], [Fig. 5]), while appreciably reducing the phenomena described above which generate vibrations in the electric machine 1 and low-frequency noise in the vehicle's passenger compartment, even if the bearing 7 is located between the coil 21 and the slip ring 14 along the axis of rotation X. An electric machine 1 comprising the rotor assembly 10 is therefore particularly suitable for constructing the powertrain of an electric vehicle.

[0040] The cylindrical portion 60 and the second portion of the groove 32 are optional and can be omitted if desired, for example if it is desired to route the electrical conductor 15 in a channel formed in an internal volume of the rotor assembly 10 and extending the first portion of the groove 31. This possibility has been represented on [Fig.6].

[0041] Up to this point, reference has been made only to a first portion of a groove 31 for routing an electrical conductor 15 under the inner ring 7. However, the invention is not limited to this scenario. More generally, the rotor assembly 10 can comprise N grooves 30, each having a first portion of a groove 31 and optionally a second portion of a groove 32, and N electrical conductors 15, each housed in a groove 30, where N is an integer at least equal to 2. In this case, each of the grooves 30 can be used to route an electrical conductor 15 that electrically connects a slip ring 14 to a coil 21 (or to a group of coils 21).

[0042] To simplify the manufacture and assembly of the electrical machine 1, it is preferable that the N grooves 30 be images of each other by rotation around the axis of rotation X, and it is more preferable that the N grooves 30 be arranged at regular intervals around the axis of rotation X.

[0043] The integer N can be equal to 2 or 3. The case where N = 2 has been shown for illustration in [Fig. 4]. In this figure, the locations where the second groove 30 opens onto the contact surface 40 and onto the outer surface of the cylindrical portion 60 are shown in dashed lines. The two grooves 30 are images of each other under a rotation of 180° around the axis of rotation X, and are therefore symmetrical to each other with respect to the axis of rotation X.

Claims

Demands

1. An electrical machine (1) comprising a bearing (5) and a rotor assembly (10) supported by the bearing (5) so as to be rotatable about an axis of rotation (X), the bearing housing (5) comprising an inner ring (7) which is in contact with a contact surface (40) formed on the rotor assembly (10), the rotor assembly (10) comprising a groove (30) and an electrical conductor (15) housed in the groove (30), the groove including a first portion of groove (31) opening onto the contact surface (40), characterized in that the first portion of groove (31) is not parallel to the axis of rotation (X).

2. Electric machine (1) according to claim 1, wherein the first portion of groove (31) describes a curve which is not contained in a plane.

3. Electric machine (1) according to claim 2, wherein the contact surface (40) describes a cylinder of revolution and the first portion of groove (31) describes a circular helix having a non-zero helix angle [3].

4. Electric machine (1) according to claim 3, wherein the helix angle [3, a width e of the first portion of groove (31) in a plane perpendicular to the axis of rotation (X), and a length Lr of the contact surface parallel to the axis of rotation (X), satisfy the following relation: Lr.tan(f ) > e.

5. Electric machine (1) according to any one of claims 3 to 4, wherein the rotor assembly (10) comprises a first shoulder (51) and a second shoulder (52) which are spaced apart along the axis of rotation (X), the contact surface (40) being formed between the first shoulder (51) and the second shoulder (52).

6. Electric machine (1) according to claim 5, in which the rotor assembly (10) comprises a cylindrical portion (60) of diameter greater than the cylinder of revolution described by the contact surface (40), the cylindrical portion (60) being delimited by the second shoulder (52) and by a third shoulder (53) distinct from the first shoulder (51), and the groove (30) including a second portion of groove (32) which extends the first portion of groove (31) into the cylindrical portion (60).

7. Electric machine (1) according to claim 6, wherein the second portion of groove (32) is parallel to the axis of rotation (X).

8. Electric machine (1) according to any one of claims 1 to 7, wherein the rotor assembly (10) comprises a coil (21) and a slip ring (14), the electrical conductor (15) connecting the coil (21) to the slip ring (14), and the bearing (5) being located between the coil (21) and the slip ring (14) along the axis of rotation (X).

9. Electric machine (1) according to any one of claims 1 to 8, wherein the rotor assembly comprises N said grooves (30) and N said electrical conductors (15) each housed in a said groove (30), N being an integer at least equal to 2, the N said grooves (30) being images of each other by rotation about the axis of rotation (X), preferably wherein the N said grooves (30) are arranged at regular intervals around the axis of rotation (X).

10. Electric vehicle comprising a powertrain which includes an electric machine (1) according to any one of claims 1 to 9.

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