Grounding brush assembly

Abstract

[Grounding Brush Assembly] This grounding brush assembly (10) comprises a grounding brush (16) and a mounting plate (18) for the brush (16), said brush (16) being provided with a plurality of conductive fibers (20) and a support (22) within which the conductive fibers (20) are housed, the mounting plate (18) being integral with the support (22) and provided with a radially extending main body (32), an axially extending centering portion (36), and retaining tabs (34) for axially maintaining said support (22), the assembly also comprising bearing portions (40) consisting of radial deformations of the centering portion (36), in order to axially maintain the support (22). Figure for the abbreviation: Fig 1.

Description

Title of the invention: Grounding brush assembly Technical field of the invention

[0001] The present invention relates to the field of grounding devices for controlling shaft current generated in electric motors or machines, and in particular grounding brush assemblies. Prior art

[0002] In an electric motor or machine, at least one roller bearing is mounted between the housing of the motor or electric machine and the rotating shaft in order to support this shaft.

[0003] During operation when the shaft is rotating, an electrical potential difference may appear between it and the housing of the motor or electrical machine, which generates an electric current between the inner ring of the bearing which is attached to the rotating shaft, and the outer ring attached to the housing.

[0004] The electric current passing through the components of the rolling bearing can damage these components, in particular the rolling elements and the raceways formed on the inner and outer rings. Electrical discharges can also generate vibrations.

[0005] To overcome these drawbacks, it is known to ground or earth the rotating shaft using a grounding brush or broom having conductive fibers. The grounding brush is generally mounted in the bore of the electric motor housing such that the free ends of the fibers are in radial contact with the outer surface of the rotating shaft.

[0006] Thanks to the conductivity of the fibers, the brush is maintained at the same electrical potential as the electric motor housing. The inner and outer rings of the bearing are also at the same electrical potential, which reduces, or even eliminates, problematic electrical discharges through the bearing.

[0007] A grounding brush assembly is known from US patent 2021 / 0021180. This assembly comprises a grounding brush with a support and a plurality of conductive fibers mounted in the support, and an annular mounting plate with a plurality of radial and axial retaining tabs for the grounding brush support, and an outer annular flange radially surrounding the brush and the tabs. The tabs are formed by plastic deformation of the mounting plate.

[0008] Such an assembly of grounding brushes has a relatively large radial dimension. For electric motor applications with reduced radial compactness, this assembly could not be installed.

[0009] The present invention aims to remedy this drawback. Summary of the invention

[0010] The invention relates to an assembly of grounding brushes for an electric motor equipped with a rotating shaft, a fixed housing, and a bearing.

[0011] The assembly includes a grounding brush provided with a plurality of conductive fibers and a support within which the conductive fibers are mounted. The assembly also includes a brush mounting plate which is integral with the brush support.

[0012] The mounting plate comprises: a main body formed by a radial portion, the brush support being axially supported against said main body; and a centering portion extending at least axially from the main body, extending axially on the same side as the brush support, offset radially outwards relative to the support, and provided with an outer surface defining the outer diameter of the mounting plate in order to allow centering of the mounting plate after mounting in a bore of the housing of an associated electric motor.

[0013] According to a general feature of the invention, the mounting plate comprises a plurality of retaining tabs for the support, and a plurality of bearing portions for the support.

[0014] According to the invention, said retaining tabs extend radially inwards from the centering portion of the assembly. Each retaining tab bears axially against the brush support on the side axially opposite the main body, the support thus being axially retained by the main body on one side and by the retaining tabs on the other side.

[0015] Said support portions consist of radial deformations extending from the centering portion, radially towards the interior of the assembly. The support portions bear radially on an upper axial surface of the brush support.

[0016] In one embodiment, the centering portion may be annular. Alternatively, the centering portion may comprise a plurality of axial portions spaced from each other in the circumferential direction.

[0017] In one embodiment, the retaining tabs and the support portions are distributed alternately in the circumferential direction.

[0018] According to one embodiment, the support portions consist of local radial deformations, each formed along an angular sector less than or equal to 5°, and preferably less than or equal to 1°.

[0019] According to an alternative embodiment, the support portions consist of radial deformations extended in the circumferential direction, each formed according to an angular sector between 5° and 40°, and preferably between 15° and 30°.

[0020] The invention also relates to an electric machine or motor comprising a housing, a shaft, an assembly of grounding brushes as defined above mounted radially at least in part between the housing and the shaft, the conductive fibers of said assembly being in contact with the shaft. Brief description of the figures

[0021] The present invention will be better understood upon study of the detailed description of embodiments, taken by way of non-limiting examples and illustrated by the accompanying drawings in which:

[0022] [Fig-1] is an axial cross-sectional view of an assembly of grounding brushes mounted radially partly between a rotating shaft and an electric motor housing according to a first embodiment of the invention;

[0023] [Fig.2] is a perspective view of the grounding brush assembly of [Fig.1];

[0024] [Fig.3] is a front view of the grounding brush assembly of [Fig.1];

[0025] [Fig.4] is a cross-sectional view of the whole of [Fig.3] along axis II;

[0026] [Fig.5] is a cross-sectional view of the whole of [Fig.3] along axis II-II;

[0027] [Fig.6] is a cross-sectional view of the entire [Fig.3] along axis III-III; and

[0028] [Fig.7] is an axial cross-sectional view of a mounted grounding brush assembly radially in part between a rotating shaft and an electric motor housing according to a second embodiment of the invention. Detailed description of the invention

[0029] Figure 1 shows, in axial section, a portion of an electric motor or machine 2 comprising a fixed housing 4, a rotating shaft 6, with axis XX, radially supported by a bearing 8. The bearing 8 is, for example, a ball bearing. Alternatively, other rolling elements, such as rollers, may be provided. In another embodiment, a plain bearing may also be provided.

[0030] The motor 2 includes a grounding brush assembly 10 mounted radially in part between the bore 12 of the housing and the external cylindrical surface 14 of the shaft. The assembly 10 is, for example, press-fitted into the bore 12 of the housing.

[0031] In the following description, the adjectives "axial" and "radial" and the adverbs "axially" and "radially" are defined with respect to the central axis X. Thus, an axial portion or part is parallel to the axis X, while a radial portion or part is perpendicular to this axis and surrounds it. Furthermore, a radial portion is provided with a an "interior" surface oriented towards the X axis, and an "exterior" surface oriented in the opposite direction to this axis.

[0032] As more clearly illustrated in Figures 2 to 6, the grounding brush assembly 10 has a generally annular shape. The assembly 10 comprises a grounding brush 16 and a mounting plate 18 for the brush 16.

[0033] The grounding brush 16 comprises a plurality of conductive fibers 20 and a support 22, the conductive fibers being housed inside the support 22 of the brush 16. The conductive fibers 20 are, for example, made of carbon, stainless steel, conductive plastics such as acrylic fibers, or nylon. The plurality of conductive fibers 20 are in the form of an open ring. In the illustrated example, the conductive fibers 20 are bent around a connecting wire 24. The free distal end of the conductive fibers 20 is intended to come into radial contact with the external surface 14 of the shaft 6.

[0034] To ensure the mounting and retention of the conductive fibers 20, the support 22 comprises a cylindrical portion 26 defining an upper axial surface for the support 22, a first lateral rim 28 extending from the cylindrical portion 26 on one side, and a second lateral rim 30 extending from the cylindrical portion 26 on the other. The first rim 28 is located axially towards the outside of the assembly, while the second rim 30 is located axially towards the bearing 8, said rims 28 and 30 being axially opposed with respect to the cylindrical portion 26 and the fibers 20.

[0035] The mounting plate 18 is integral with the support 22. The mounting plate 18 comprises a main body 32 formed by a radial portion which is axially supported against the first rim 28 of the support, and an axial centering portion 36.

[0036] The centering portion 36 of the mounting plate 18 extends axially from the main body 32, in a direction opposite to the bearing 8. According to the embodiment illustrated in Figures 1 to 6, the centering portion 36 consists of an annular cylindrical portion. Alternatively, it could be provided that the centering portion comprises a plurality of axial portions spaced from each other in the circumferential direction.

[0037] The centering portion 36 is provided with an outer surface 38 defining the outer diameter of the mounting plate 18 in order to allow the centering of said mounting plate after mounting in the bore 12 of the housing 4 of the associated electric motor 2. The centering portion 36 is preferably press-fitted into the bore 12 of the housing 4 in order to create a diametrical interference to ensure mechanical retention of the mounting plate 18 in said housing 4.

[0038] According to the invention, the mounting plate comprises a plurality of axial retaining tabs 34 for the brush 16

[0039] The retaining tabs 34 extend radially inwards from the centering portion 36 of the mounting plate 18. Each of the tabs 34 consists of an essentially radial portion, bent inwards from the axial portion 36. The tabs 34 are spaced from each other in the circumferential direction.

[0040] Each retaining tab 34 extends from the centering portion 36 of the mounting plate 18 so that the retaining tab 34 makes axial contact with the lateral edge 30 of the support 22. On the axially opposite side, the other lateral edge 28 of the support 22 is held axially against the radial portion 32 of the mounting plate 18 by the tabs 34. The support 22 is thus held axially by the retaining tabs 34.

[0041] In the example shown, the mounting plate 18 comprises four retaining tabs 34 spaced evenly around its circumference. Alternatively, the mounting plate comprises a different number of retaining tabs 34.

[0042] The centering portion 36 extends axially from the main body 32, extends axially on the same side as the support 22 held by the tabs 34, and is radially offset outwards relative to said support 22.

[0043] The cylindrical portion 26 of the support 22 is radially spaced from the centering portion 36, and the second lateral rim 30 is in axial contact with said tabs. The cylindrical portion 26 extends the large-diameter edge of the first lateral rim 28. The cylindrical portion 26 extends axially here.

[0044] The second lateral rim 30 of the support 22 extends radially inwards from the cylindrical portion 26. The second lateral rim 30 extends the cylindrical portion 26 on the side opposite the first lateral rim 28. The cylindrical portion 26 and the first and second lateral rims 28, 30 are annular in shape and define a channel open radially on the inner side, inside which one end of the conductive fibers 20 is located. The first and second lateral rims 28, 30 axially enclose the conductive fibers 20. The conductive fibers 20 are axially supported on both sides against the first and second lateral rims 28, 30.

[0045] In the illustrated embodiment, the conductive fibers 20 come radially to rest against the cylindrical portion 26, the first and second lateral edges 28, 30 extending obliquely inwards from the cylindrical portion 26. Alternatively, the first and second lateral edges 28, 30 could extend radially.

[0046] The mounting plate 18 and the grounding brush 16 comprise an electrically conductive material, such as, for example, aluminium, stainless steel, bronze, copper or other material.

[0047] According to another aspect of the invention, the mounting plate 18 also includes a plurality of support portions 40 for axially holding the brush support 22.

[0048] According to the first embodiment of the invention illustrated in Figures 2 to 6, the support portions 40 consist of localized radial deformations extending from the centering portion 36, radially towards the interior of the assembly 10.

[0049] The support portions 40 are each formed according to an angular sector less than or equal to 5°, and preferably less than or equal to 1°.

[0050] In the illustrated example, the deformations are essentially conical in shape, with an inner wall 42 inclined towards the inside of the assembly 10. According to other, unillustrated variants, the support portions may have other shapes such as spheres, cylinders, parallelepipeds, etc., without departing from the scope of the present invention. In practice, the deformations 40 can be produced by stamping, for example. The material of the centering portion 36 is deformed radially inwards by a punch exerting a radial force from the upper surface 38 of said centering portion 36.

[0051] Each of the support portions 40 bears radially on an upper axial surface of the cylindrical portion 26 of the brush support 22. More specifically, the inclined inner wall 42 of each support portion 40 comes into direct radial contact with the cylindrical surface 26 via a bearing surface 44.

[0052] The support 22 is thus held radially in position by the plurality of support points 44 in direct contact with the outer surface of the cylindrical portion 26 of said support 22. This radial holding of the support 22 comes in combination with its axial holding between the tabs 34 and the main body 32, ensuring that said support 22 is held in position with the mounting plate 18. The mounting plate 18 being itself fitted into a bore 12 of the housing 4, the fibers 20 mounted in the support 22 are thus positioned relative to the bearing 8, the housing 4, and the rotating shaft 6 in order to ensure a function of passing electric current.

[0053] In the example shown, the mounting plate 18 comprises four bearing portions 40 spaced regularly in the circumferential direction. Alternatively, the mounting plate comprises a different number of bearing portions 40.

[0054] In the example shown, the retaining tabs 34 and the support portions 40 are distributed alternately in the circumferential direction. Alternatively, the tabs and the support portions can be positioned according to other distributions, for example two or more support portions between two successive tabs circumferentially, or two or more tabs between two successive support portions.

[0055] Thanks to the invention, the grounding brush assembly 10 can be configured to have a reduced radial compactness compared to an assembly of the prior art, in US-A1-2021 / 0021180 for example.

[0056] Furthermore, the support portions 40 improve the rigidity of the mounting plate 18. The centering portion 36 is press-fitted into a housing 4, and the risk of deformation of the centering portion 36, the main body 32, or the connecting portion between the two, is significant. The deformations of the support portions 40 provide inclined walls 42 which help to stiffen the assembly.

[0057] A second embodiment of the invention is illustrated in [Fig.7], which differs from the previous embodiment in the dimension of the support portions.

[0058] The mounting plate 18 includes a plurality of bearing portions 50 for axially retaining the brush support 22. The bearing portions 50 consist of extended radial deformations extending from the centering portion 36, radially towards the interior of the assembly 10.

[0059] The support portions 50 are each formed according to an angular sector equal to 20° in the illustrated example. This angular sector could be smaller or larger, between 5° and 40°.

[0060] The deformations of the support portions 50 each have inner walls 52 inclined towards the inside of the assembly 10. Each of the support portions 50 bears radially on an upper axial surface of the cylindrical portion 26 of the brush support 22. More precisely, the inclined inner walls 52 come into direct radial contact with the cylindrical surface 26 via a bearing surface 54.

[0061] Furthermore, the technical characteristics of the different embodiments can be combined, in whole or in part. Thus, the grounding brush assembly can be adapted in terms of cost, performance, and ease of implementation.

Claims

Demands

1. Grounding brush assembly (10) for an electric motor (2) having a shaft (6) rotating about an axis (X), a fixed housing (4) and a bearing (8), and comprising a grounding brush (16) having a plurality of conductive fibers (20) and a support (22) inside which the conductive fibers are mounted, and a brush mounting plate (18) which is integral with the brush support (22), the mounting plate (18) comprising - a main body (32) formed by a radial portion, the brush support (22) being axially supported against said main body (32), - a centering portion (36) extending at least axially from the main body (32), extending axially on the same side as the brush support (22), offset radially outwards relative to the support (22),and provided with an outer surface (38) defining the outer diameter of the mounting plate (18) to allow centering of the mounting plate (18) after mounting in a bore (12) of the housing (4) of an associated electric motor (2), characterized in that the mounting plate also comprises: - a plurality of retaining tabs (34) for the support, said tabs (34) extending radially inward from the centering portion (36) of the assembly (10), each tab (34) bearing axially against the brush support (22) on the side axially opposite to the main body (32), the support (22) thus being axially retained by the main body (32) on one side and by the retaining tabs (34) on the other side, and - a plurality of bearing portions (40; 50) for the support (22), said bearing portions (40; 50) consisting in radial deformations extending from the centering portion (36),radially towards the interior of the assembly (10), said support portions (40; 50) bearing radially on an upper axial surface (26) of the brush support (22).

2. Assembly (10) according to claim 1, wherein the centering portion (18) is annular.

3. Assembly (10) according to claim 1, wherein the centering portion (18) comprises a plurality of axial portions spaced from each other in the circumferential direction.

4. Assembly (10) according to any one of the preceding claims, wherein the retaining tabs (34) and the support portions (40; 50) are distributed alternately in the circumferential direction.

5. Assembly (10) according to any one of the preceding claims, wherein the support portions (40) consist of local radial deformations, each formed along an angular sector less than or equal to 5°, and preferably less than or equal to 1°.

6. Assembly (10) according to any one of claims 1 to 4, wherein the support portions (50) consist of radial deformations extended in the circumferential direction, each formed along an angular sector between 5° and 40°, and preferably between 15° and 30°.

7. Electric motor (2) comprising a housing (4), a shaft (6), an assembly (10) of grounding brush according to any one of the preceding claims mounted radially at least in part between the housing (4) and the shaft (6), the conductive fibers (20) of said assembly being in contact with the shaft (6).

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