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 assembly further comprises a spacer washer 50 supported by the mounting plate 40 and arranged axially on the side opposite the brush 30 relative to said mounting plate. 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 for the support.

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

[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] According to a general characteristic, the assembly further comprises a spacer washer supported by the mounting plate and arranged axially on the side opposite the brush relative to said mounting plate.

[0013] With this design, the risk of contact between the conductive fibers of the assembly and the bearing is limited. Indeed, the spacer washer makes it possible to maintain an axial spacing between the mounting plate of the assembly and the bearing or the housing.

[0014] Advantageously, the spacer washer extends axially projecting relative to the mounting plate. This further limits the risk of contact between the conductive fibers of the assembly and the bearing.

[0015] Preferably, the spacer washer is made of electrically insulating material, i.e. electrically non-conductive. This makes it possible to avoid the dissipation of electrical charges towards the bearing in the event of contact between the latter and the assembly.

[0016] According to a particular design, the spacer washer is annular. Alternatively, the spacer washer may be open at a point on its circumference.

[0017] The mounting plate may comprise a radial portion against which the brush and the spacer washer are mounted axially in abutment on either side.

[0018] The mounting plate may include at least one mounting portion extending at least axially from the radial portion and on which the spacer washer is mounted. Said mounting portion may extend a small diameter edge of the radial portion of the mounting plate.

[0019] In a particular embodiment, the mounting plate includes a plurality of brush holder retaining tabs extending from the radial portion.

[0020] In one embodiment, the mounting plate comprises 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.

[0021] The mounting plate can be made in one piece.

[0022] Preferably, the spacer washer is flush with or remains radially recessed relative to the outer surface of the centering portion. This makes it easier to mount the assembly inside the associated casing.

[0023] The invention also relates to an electric motor comprising a casing, a 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. Brief description of the figures

[0024] 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:

[0025] [Fig-1] is an axial sectional view of a grounding brush assembly mounted radially between a rotating shaft and an electric motor housing,

[0026] [Fig.2]

[0027] [Fig.3] are perspective views of a grounding brush assembly according to an exemplary embodiment of the invention,

[0028] [Fig.4] is a front view of the grounding brush assembly of Figures 2 and 3,

[0029] [Fig.5] is a sectional view along the VV axis of [Fig.4], and

[0030] [Fig.6] is a sectional view along the VLVI axis of [Fig.4]. Detailed description of the invention

[0031] In [Fig.l] 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 here is of the ball type. Alternatively, it is possible to provide other rolling elements, or even a plain bearing.

[0032] 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.

[0033] 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.

[0034] With reference to Figures 2 to 6, a grounding brush assembly 20 according to an exemplary embodiment of the invention will now be described.

[0035] 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.

[0036] As will be described in more detail hereinafter, the assembly 20 also includes a spacer washer 50 supported by the mounting plate 40.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] As indicated previously, the brush 30 is in the form of an open ring, as seen in particular in FIGS. 2 and 3. This allows the brush to adapt to different diameters of the motor shaft. In general, the ex 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.

[0044] 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.

[0045] The radial portion 42 of the mounting plate is axially supported against the support 32 of the brush 30. More precisely, the radial portion 42 is axially supported against the lateral flank 36 of the support.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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 extend axially on the same side as the tabs 44.

[0051] 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.

[0052] 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.

[0053] Referring again to Figures 5 and 6, the mounting plate 40 further comprises a mounting portion 52 axially extending the radial portion 42 axially on the side opposite the tabs 44 and the legs 46. The mounting portion 52 here extends axially and is annular in shape. The mounting portion 52 extends a small diameter edge of the radial portion 42.

[0054] 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 a conductive paint. The mounting plate 40 is made here in a single piece.

[0055] As indicated previously, the assembly 20 comprises the spacer washer 50 supported by the mounting plate 40. The washer 50 is a separate part from the mounting plate 40. The washer 50 is disposed axially on the side opposite the brush 30 relative to the radial portion 42 of the mounting plate.

[0056] The washer 50 is mounted on the mounting portion 52 of the mounting plate. The washer 50 is centered on the mounting portion 52. The washer 50 is mounted axially bearing against the radial portion 42 of the mounting plate axially on the side opposite the brush 30. The brush 30 and the washer 50 are mounted axially bearing on either side of the radial portion 42. The washer 50 extends partly axially outwardly relative to the mounting portion 52 of the mounting plate. In the illustrated embodiment, the washer 50 is annular in shape. Alternatively, the washer 50 could be open at a point on its circumference.

[0057] The washer 50 comprises a cylindrical axial outer surface 50a, a cylindrical bore 50b radially opposite the outer surface 50a, and two opposite radial end faces 50c, 50d axially delimiting the bore and the outer surface. The end face 50c of the washer is mounted axially bearing against the radial portion 42 of the mounting plate. The end face 50d is axially offset outwardly relative to the free end of the mounting portion 52 of the mounting plate. The bore 50b of the washer is mounted radially bearing against the outer surface of the radial portion 42 of the mounting plate. The outer surface 50a is radially offset inwardly relative to the large diameter free edges of the tabs 46 of the plate.

[0058] The washer 50 is advantageously made of electrically insulating material. The washer 50 may for example be made of synthetic material, plastic material, in particular PEEK, PBT, PPS, PAI.

[0059] 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.

[0060] Thanks to the washer 50, contact between the conductive fibers 31 of the brush and the bearing is avoided.

[0061] 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.

Claims

Claims

1. A grounding brush assembly (20) comprising a grounding brush (30) provided with a plurality of conductive fibers (31) and a holder (32) within which the conductive fibers are mounted, and a brush mounting plate (40) which is integral with the brush holder (32), characterized in that the assembly further comprises a spacer washer (50) supported by the mounting plate (40) and disposed axially on the side opposite the brush (30) relative to said mounting plate.

2. An assembly according to claim 1, wherein the spacer washer (50) extends axially outward from the mounting plate (40).

3. An assembly according to claim 1 or 2, wherein the spacer washer (50) is made of electrically insulating material.

4. An assembly of any preceding claim, wherein the spacer washer (50) is annular.

5. An assembly according to any one of the preceding claims, in which the mounting plate (40) comprises a radial portion (42) against which the brush (30) and the spacer washer (50) are mounted axially in abutment on either side.

6. An assembly according to claim 5, wherein the mounting plate comprises at least one mounting portion (52) extending at least axially from the radial portion (42) and on which the spacer washer (50) is mounted.

7. An assembly according to claim 5 or 6, wherein the mounting plate comprises a plurality of tabs (44) for retaining the brush support (32) extending from the radial portion (42).

8. An assembly according to any one of claims 5 to 7, wherein the mounting plate comprises at least one centering portion (46) extending at least axially the radial portion (42), offset radially outwards relative to the support (32) and provided with an outer surface defining the outer diameter of the mounting plate (18).

9. An assembly according to claim 8, wherein the spacer washer (50) is flush with or radially recessed relative to the outer surface of the centering portion (46).

10. An electric motor comprising a housing (12), a shaft (14) 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.

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