Grounding brush assembly

Abstract

[Grounding Brush Assembly] The grounding brush assembly 20 comprises a grounding brush 30 having a plurality of conductive fibers 31 and a support 32 within which the conductive fibers are mounted, and a brush mounting plate 40 which is integral with the brush support 32. The mounting plate comprises a radial portion 42 and at least one centering portion 46 extending at least axially from the radial portion 42, offset radially outward from the support 32 and having an outer surface defining the outer diameter of the mounting plate 18. The mounting plate 40 further comprises at least one spacing portion 50 extending obliquely inward from said centering portion 46 and on the side opposite the radial portion 42. Reference: Figure 5

Description

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

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

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

[0003] In operation when the shaft is rotating, an electrical potential difference may appear between it and the casing of the motor or the electric machine, which generates an electric current between the inner ring of the rolling bearing which is integral with the shaft, and the outer ring integral with the casing.

[0004] Electric current passing through rolling bearing components can damage these components, including rolling elements and raceways 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 comprising 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] Due 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 rolling bearing are also at the same electrical potential, which reduces or even eliminates problematic electrical discharges through the rolling bearing.

[0007] For more details on the design of such a grounding brush assembly, reference may be made, for example, to document US-A1-2021 / 0021180, which describes an assembly comprising a grounding brush provided with a plurality of conductive fibers, a support inside which the conductive fibers are mounted, and an annular mounting plate comprising a plurality of radial and axial retaining tabs of the support and an annular outer flange radially surrounding said brush and the tabs.

[0008] Depending on the relative axial positioning of the grounding brush assembly and the bearing, during operation of the electrical machine, contact may occur between the conductive fibers of the assembly on the one hand and the rolling elements and / or the inner ring of the bearing on the other.

[0009] This can damage the bearing.

[0010] The present invention aims to remedy this drawback. Summary of the invention

[0011] A grounding brush assembly includes a grounding brush having a plurality of conductive fibers and a holder within which the conductive fibers are mounted. The assembly also includes a brush mounting plate that is secured to the brush holder.

[0012] The mounting plate comprises a radial portion and at least one centering portion extending at least axially the radial portion, offset radially outwardly relative to the support and provided with an outer surface defining the outer diameter of the mounting plate.

[0013] According to a general characteristic, the mounting plate further comprises at least one spacing portion extending obliquely inwards from said centering portion and on the side opposite the radial portion.

[0014] With this design, the risk of contact between the conductive fibers of the assembly and the bearing is limited. Indeed, said spacing portion of the mounting plate makes it possible to maintain an axial spacing between the brush and the bearing or the housing.

[0015] The mounting plate may include a plurality of brush holder retaining tabs extending from the radial portion, said centering portion being offset radially outwardly relative to the retaining tabs.

[0016] Preferably, said spacing portion of the mounting plate is axially offset to the side opposite the radial portion relative to the retaining tabs. Thus, the risk of contact between the conductive fibers and the bearing is further limited.

[0017] According to one design, the mounting plate may comprise a plurality of circumferentially spaced centering portions, and a plurality of spacing portions each extending obliquely inwardly from one of said centering portions.

[0018] According to an alternative design, the mounting plate may comprise an annular centering portion. In this case, the mounting plate may comprise a single spacing portion, or a plurality of spacing portions spaced apart from each other in the circumferential direction.

[0019] The brush may be mounted axially against the radial portion of the mounting plate. Alternatively, the brush may be mounted axially against another radial portion of the mounting plate.

[0020] The mounting plate can be made in one piece.

[0021] The invention also relates to an electric motor comprising a casing, a shaft, at least one bearing mounted radially between the casing and the shaft, and at least one grounding brush assembly as defined above and mounted radially between the casing and the shaft, the conductive fibers of the brush of said assembly being in contact with the shaft. The spacing portion(s) of the mounting plate are located axially on the bearing side. Brief description of the figures

[0022] The present invention will be better understood upon studying the detailed description of an embodiment, taken as a non-limiting example and illustrated by the appended drawings in which:

[0023] [Fig-1] is an axial sectional view of a grounding brush assembly mounted radially between a rotating shaft and an electric motor housing,

[0024] [Fig.2]

[0025] [Fig.3] are perspective views of a grounding brush assembly according to an exemplary embodiment of the invention,

[0026] [Fig.4] is a front view of the grounding brush assembly of Figures 2 and 3,

[0027] [Fig.5] is a sectional view along the VV axis of [Fig.4], and

[0028] [Fig.6] is a sectional view along the VLVI axis of [Fig.4]. Detailed description of the invention

[0029] In [Fig. 1] is shown, in axial section, a part of a motor 10 or electric machine comprising a fixed casing 12, a rotating shaft 14, of axis XX, supported radially by a rolling bearing 16. The bearing 16 is mounted radially between the casing 12 and the rotating shaft 14. The bearing is here of the ball type. Alternatively, it is possible to provide other rolling elements, or even a plain bearing.

[0030] The motor 10 further comprises a grounding brush assembly 20 mounted radially between the bore 12a of the housing 12 and the outer cylindrical surface 14a of the rotating shaft 14.

[0031] The grounding brush assembly 20 allows the electrical charges that accumulate on the motor shaft 14 during operation of the motor to be continuously dissipated by transferring them to the housing 12.

[0032] With reference to Figures 2 to 6, a grounding brush assembly 20 according to an exemplary embodiment of the invention will now be described.

[0033] The grounding brush assembly 20 has a generally annular shape. The assembly 20 includes a grounding brush 30 and a mounting plate 40 brush configured to radially center said brush 30.

[0034] As will be described in more detail later, the mounting plate 40 is also configured to maintain an axial spacing between the brush 30 and the bearing or housing.

[0035] The brush 30 comprises a plurality of individual conductive fibers 31 intended to come around the rotating shaft of the motor. The conductive fibers 31 can be made of carbon, stainless steel, conductive plastics, such as acrylic fibers or nylon.

[0036] The brush 30 further comprises a holding member or support 32 inside which the conductive fibers 31 are mounted. In the illustrated embodiment, the support 32 is in the form of an open ring. The support 32 can be made by cutting and stamping. The support 32 is made of electrically conductive material, such as for example aluminum, stainless steel, bronze, copper or other material. Alternatively, the support 32 can be made of electrically non-conductive material with a conductive coating or conductive paint.

[0037] As illustrated more visibly in Figures 5 and 6, the support 32 comprises an axial mounting portion 34 and two opposite lateral flanks 36, 38 extending from the mounting portion 34 inwards and axially enclosing the conductive fibers 31. The conductive fibers 31 are axially supported on either side against the lateral flanks 36, 38. The conductive fibers 31 are axially supported on either side against the internal faces of the lateral flanks 36, 38.

[0038] The mounting portion 34 and the two lateral flanks 36, 38 delimit a channel open radially on the inner side and inside which the conductive fibers 31 are partly located.

[0039] In the illustrated example, the conductive fibers 31 are folded around a connecting wire 39 of the support 32. The free distal end of the conductive fibers 31 is intended to come into radial contact with the outer surface of the rotating shaft of the motor. The proximal end of the conductive fibers 31 is in radial contact with the mounting portion 34 of the support.

[0040] The lateral flank 36 extends one end of the mounting portion 34 and the lateral flank 38 extends the opposite end thereof. The lateral flanks 36, 38 extend obliquely inwardly from the mounting portion 34. The lateral flanks 36, 38 are symmetrical to each other with respect to a median radial plane of the support 32. The mounting portion 34 here extends axially. Alternatively, the mounting portion 34 could extend obliquely.

[0041] As indicated previously, the brush 30 is in the form of an open ring, as seen in particular in Figures 2 and 3. This allows the brush to adapt to different diameters of the motor shaft. Generally, the ends of the brush are not fixed to each other. Alternatively, it remains possible to fix these ends of the brush 30 to each other.

[0042] Referring to Figures 2, 5 and 6, the mounting plate 40 includes an annular radial portion 42, and a plurality of centering tabs 44 extending from the radial portion 42.

[0043] The radial portion 42 of the mounting plate is axially in abutment against the support 32 of the brush 30. More precisely, the radial portion 42 is axially in abutment against the lateral flank 36 of the support.

[0044] The tabs 44 are spaced apart from each other in the circumferential direction, here in a regular manner. Alternatively, it could be possible to provide an irregular circumferential spacing. In the illustrated embodiment, there are eight tabs 44. Alternatively, it is possible to provide a greater or even smaller number of tabs 44. It is possible to provide two tabs 44, or at least four tabs. Preferably, the number of tabs 44 is at least two.

[0045] Each tab 44 extends axially projecting relative to the radial portion 42. Each tab 44 locally radially surrounds the support 32 of the brush 30 and is in radial contact with the mounting portion 34 of said support. The support 32 is held axially in abutment against the radial portion 42 of the mounting plate by the tabs 44. The tabs 44 make it possible to retain the earthing brush 30 axially and radially. The lateral flank 36 of the support bears against the radial portion 42 of the mounting plate and the lateral flank 38 bears against the tabs 44. The tabs 44 are here identical to each other.

[0046] As illustrated more visibly in [Fig. 5], each tab 44 is provided with an axial portion extending axially from the radial portion 42, locally radially surrounding the support 32 and is in radial contact with the latter, and with a folded portion at the free end of the axial portion. The folded portion 44b of each tab makes it possible to axially retain the support 32 of the earthing brush 30. The folded portion 44b of each tab is in axial contact against the lateral flank 38 of the support.

[0047] The brush mounting plate 40 also includes a plurality of centering tabs 46 extending from the radial portion 42 and spaced apart from each other in the circumferential direction. A notch 48 ([Fig.2]) is formed on the radial portion 42 between each immediately successive pair of tabs 46. The tabs 46 are formed by cutting and bending the radial portion 42.

[0048] Each tab 46 axially extends the radial portion 42. The tabs 46 extend obliquely from a large diameter edge of the radial portion 42. The tabs 46 here extend axially on the same side as the tabs 44. The legs 46 extend axially projecting relative to the tabs 44. Alternatively, the legs 46 could extend axially on the side opposite the tabs.

[0049] Each tab 46 locally radially surrounds the support 32 of the brush 30 while remaining at a distance from the latter. The tabs 46 are offset radially outwards in part relative to the tabs 44. The tabs 46 are here identical to each other. The tabs 46 define the outside diameter of the mounting plate 40. Each tab 46 extends here obliquely. Alternatively, the tabs 46 could extend axially. Each tab 46 is in the form of a portion of a cylinder. The bore of each tab 46 is radially spaced from the support 32 by a non-zero radial distance. The outer surfaces of the tabs 46 define the outside diameter of the mounting plate 40. The tabs 46 allow the mounting plate to be centered after mounting in the bore of the casing of the associated electric motor.

[0050] As illustrated in Figures 2 and 4, the tabs 46 are spaced from each other in the circumferential direction, here in a regular manner. Alternatively, it could be possible to provide an irregular circumferential spacing. Each tab 46 is located in the circumferential direction between two immediately successive tabs 44. Each tab 46 is spaced in the circumferential direction from the two immediately adjacent tabs 44. Each tab 46 here has a circumferential dimension greater than that of the tabs 44.

[0051] As previously indicated, the mounting plate 40 is also configured to maintain an axial spacing between the brush 30, and the bearing or housing.

[0052] For this purpose, the mounting plate 40 comprises a plurality of spacer portions 50 each extending obliquely inward from one of the legs 46. In the exemplary embodiment, each leg 46 is extended by a spacer portion 50. Alternatively, only some of the legs 46 could be extended by the spacer portions 50. The spacer portions 50 are spaced apart from each other in the circumferential direction. Like the legs 46, the spacer portions 50 are formed by cutting and folding the radial portion 42. Each spacer portion 50 is in the form of a cylinder portion. The spacer portions 50 are here identical to each other.

[0053] Each spacing portion 50 extends obliquely inwardly the associated tab 46. Each spacing portion 50 extends the associated tab 46 on the side opposite the radial portion 42 of the mounting plate and the support 32. Each spacing portion 50 is axially offset relative to the tabs 44 on the side opposite the radial portion 42 of the mounting plate. Each spacing portion 50 has a circumferential dimension equal to that of the associated tab 46. Alternatively, it could be possible to provide spacing portions 50 having a reduced circumferential dimension compared to that of the legs 46.

[0054] Each spacing portion 50 extends from the large diameter of the associated tab 46. Each spacing portion 50 is here offset radially outwardly relative to the mounting portion 34 of the brush holder. Alternatively, the spacing portions 50 could be offset radially inwardly relative to the mounting portion 34 of the holder.

[0055] The mounting plate 40 is made by cutting and stamping. The mounting plate 40 is made of a conductive material, such as, for example, aluminum, stainless steel, bronze, copper, or other material. Alternatively, the mounting plate 40 may be made of an electrically non-conductive material with a conductive coating or conductive paint. The mounting plate is made here in a single piece.

[0056] During operation of the electric machine, the electrical charges which accumulate on the shaft are dissipated towards the casing 12 through the conductive fibers 31, the support 32 of the brush, and the mounting plate 40 of the assembly.

[0057] The assembly 20 is mounted so that the spacing portions 50 of the mounting plate are located axially on the bearing side. Thanks to the spacing portions 50, contact between the conductive fibers 31 of the brush and the bearing is avoided.

[0058] In the illustrated embodiment, the mounting plate 40 of the grounding brush assembly comprises a plurality of centering tabs 46. Alternatively, the tabs could be replaced by an annular flange forming an annular centering portion.

[0059] With such a design, the mounting plate 40 may include a single annular spacer portion, a single spacer portion extending over an angular sector less than 360°, or a plurality of spacer portions spaced from one another in the circumferential direction.

Claims

Claims

1. A grounding brush assembly (20) comprising a grounding brush (30) provided with a plurality of conductive fibers (31) and a support (32) within which the conductive fibers are mounted, and a brush mounting plate (40) which is integral with the brush support (32), the mounting plate (40) comprising a radial portion (42) and at least one centering portion (46) extending at least axially the radial portion (42), offset radially outwardly relative to the support (32) and provided with an outer surface defining the outer diameter of the mounting plate (18), characterized in that the mounting plate (40) further comprises at least one spacer portion (50) extending obliquely inwardly from said centering portion (46) and on the side opposite the radial portion (42).

2. An assembly according to claim 1, wherein the mounting plate comprises a plurality of brush holder (32) retaining tabs (44) extending from the radial portion (42), said centering portion (46) being offset radially outwardly relative to the retaining tabs (44).

3. An assembly according to claim 2, wherein said spacer portion (50) of the mounting plate is axially offset to the side opposite the radial portion (42) relative to the retaining tabs (44).

4. An assembly according to any preceding claim, wherein the mounting plate (40) comprises a plurality of circumferentially spaced centering portions (46), and a plurality of spacing portions (50) each extending obliquely inwardly from one of said centering portions (46).

5. An assembly according to any one of claims 1 to 3, wherein the mounting plate (40) comprises an annular centering portion.

6. An assembly according to any preceding claim, wherein the brush (30) is mounted axially against the radial portion (42) of the mounting plate.

7. An assembly according to any preceding claim, wherein the mounting plate (40) is made in one piece.

8. An electric motor comprising a housing (12), a shaft (14), at least one bearing (16) mounted radially between the housing and the shaft, and at least a grounding brush assembly (20) according to any preceding claim mounted radially between the housing (12) and the shaft (14), the conductive fibers of the brush of said assembly being in contact with the shaft, said spacer portion (50) of the mounting plate being located axially on the bearing side.

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