Grounding brush and associated assembly

Abstract

[Grounding brush and associated assembly] The grounding brush 30 is provided with a plurality of conductive fibers 31, a support 32 within which the conductive fibers are mounted, and a ring 33 around which the conductive fibers are arranged within the support. The support 32 comprises a mounting portion 34 and two lateral flanges 36, 38 extending from the mounting portion and axially clamping the conductive fibers 31. The ring 33 is made at least in part of an elastically deformable material. Reference: Figure 4

Description

Title of the invention: Grounding brush and associated 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. State of the 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 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] For more details on the design of such an assembly of grounding brushes, reference may be made, for example, to US-A1-2021 / 0021180, which describes an assembly having a grounding brush comprising a plurality of conductive fibers, a support inside which the conductive fibers are mounted, and a steel ring mounted inside the support and around which the conductive fibers are folded, and an annular mounting plate comprising a plurality of radial and axial retaining tabs for the brush support.

[0008] With this type of design, losses of the conductive fibers can occur by the support or breaks in these fibers, which creates pollution inside the motor or associated electrical machine.

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

[0010] The invention relates to a grounding brush comprising a plurality of conductive fibers and a support within which the conductive fibers are mounted. The support comprises a mounting portion and two lateral sides extending from the mounting portion and axially clamping the conductive fibers.

[0011] The grounding brush also includes a ring around which the conductive fibers are arranged inside the support.

[0012] The support comprises a mounting portion and two lateral sides extending the mounting portion and axially clamping the conductive fibers.

[0013] According to a general characteristic, the ring is made at least partly of elastically deformable material.

[0014] Thus, the ring is able, by the material used, to deform under the action of an external stress, and to return by elasticity to its initial position in the event of cessation of the stress.

[0015] With such a brush design, the risk of loss or breakage of the fibers that exists for a conventional brush with a steel ring is limited, given the brush manufacturing process with crimping of the sides of the support against the fibers.

[0016] Indeed, depending on the force exerted on the fibers by the sides of the support during this crimping operation, the ring can deform and limit the pressure exerted on the fibers by these sides. The ring thus acts as a means of dampening the pressure exerted by the sides of the support on the conductive fibers, given its capacity to deform.

[0017] The mounting portion and the lateral sides of the support define a channel that is radially open on the inner side and within which the conductive fibers are partially located. The ring is located at least partially inside the channel.

[0018] Preferably, the ring is made entirely of elastically deformable material. Alternatively, it is possible to make the ring partly of elastically deformable material and partly of rigid material.

[0019] The ring may have a circular or square profile in cross-section.

[0020] Advantageously, the ring can have an elongated radial profile in cross-section. In this case, the contact area between the ring and the conductive fibers is increased, which further limits the risk of fiber displacement and loss. When the ring has an elongated radial profile in cross-section, this- It can, for example, be rectangular.

[0021] In order to increase the contact area between the conductive fibers and the ring, the latter can extend radially inwards relative to the lateral sides of the support.

[0022] Advantageously, the ring has a coefficient of friction of at least 0.2, and preferably at least 0.25. Thus, the adhesion between the conductive fibers and the ring is promoted.

[0023] In one embodiment, the ring has a corrugated shape in the circumferential direction. This further increases the deformability of the ring in the axial direction.

[0024] In one embodiment, the support is made of rigid material.

[0025] The invention also relates to an assembly of grounding brushes comprising a grounding brush as defined above, and a brush mounting plate which is integral with the brush support.

[0026] The mounting plate and the support can be made as one piece.

[0027] Alternatively, the mounting plate and the support may be two separate parts. In this case, the mounting plate may comprise a main body and a plurality of axial and radial retaining tabs for the support of said brush extending from said main body, the retaining tabs bearing radially against the mounting portion of the support and axially against one of the lateral sides of said support.

[0028] The brush ring also helps to limit the risk of fiber loss or breakage during the assembly of the mounting plate and the support. Indeed, the tabs of the disassembly plate are formed by local cuts in the main body and folding against the support, which exerts pressure on the support and the fibers. The brush ring can then deform and limit the pressure exerted on the fibers.

[0029] The mounting plate can be made in one piece.

[0030] The invention further relates to an electric motor comprising a housing, a shaft, and at least one grounding brush assembly as defined above and mounted radially between the housing and the shaft, the conductive fibers of the brush assembly being in contact with the shaft. Alternatively, the conductive fibers of the brush could be in contact with the housing. Brief description of the figures

[0031] The present invention will be better understood upon study of the detailed description of an embodiment, taken by way of non-limiting example and illustrated by the accompanying drawings in which:

[0032] [Fig. 1] is an axial cross-sectional view of a grounding brush assembly mounted radially between a rotating shaft and an electric motor housing,

[0033] [Fig.2] is a perspective view of an assembly of grounding brushes according to a first embodiment of the invention,

[0034] [Fig.3] is a front view of the grounding brush assembly of [Fig.2],

[0035] [Fig.4] is a cross-sectional view along axis IV-IV of [Fig.3],

[0036] [Fig.5] is a cross-sectional view of an assembly of grounding brushes according to a second example of an implementation of the invention,

[0037] [Fig.6] is a cross-sectional view of a grounding brush assembly according to a third embodiment of the invention, and

[0038] [Fig.7] is a side view of a ring of a grounding brush assembly according to a fourth embodiment of the invention. Detailed description of the invention

[0039] Figure 1 shows, in axial section, a portion of a motor 10 or electrical machine comprising a fixed housing 12, a rotating shaft 14, with axis XX, radially supported by a roller bearing 16. The bearing 16 is mounted radially between the housing 12 and the rotating shaft 14. The bearing is of the ball type. Alternatively, other rolling elements, or even a plain bearing, may be used.

[0040] The motor 10 further includes a radially mounted grounding brush assembly 20 between the bore 12a of the housing 12 and the external cylindrical surface 14a of the rotating shaft 14.

[0041] The grounding brush assembly 20 allows for the continuous dissipation of electrical charges which accumulate on the shaft 14 of the motor during motor operation by transferring them to the housing 12.

[0042] With reference to figures 2 to 4, an assembly 20 of grounding brushes according to a first embodiment of the invention will now be described.

[0043] The grounding brush assembly 20 has a generally annular shape. The assembly 20 comprises a grounding brush 30 and a brush mounting plate 40 configured to radially center said brush 30.

[0044] 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.

[0045] The brush 30 further comprises a retaining 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 is made of a rigid material. The support 32 can be produced by cutting and stamping. The support 32 is made of an electrically conductive material, such as, for example, aluminium, stainless steel, bronze, copper or other material. Alternatively, support 32 can be made of electrically non-conductive material with a conductive coating or conductive paint.

[0046] As will be described in more detail later, the brush 30 also includes a ring 33 around which the conductive fibers 31 are arranged inside the support 32. The ring 33 fulfills a support function for the conductive fibers 31.

[0047] As more clearly illustrated in [Fig. 4], the support 32 comprises an axial mounting portion 34 and two opposing lateral sides 36, 38 extending inwards from the mounting portion 34 and axially enclosing the conductive fibers 31. The conductive fibers 31 are axially supported on both sides against the lateral sides 36, 38. The conductive fibers 31 are axially supported on both sides against the inner faces of the lateral sides 36, 38.

[0048] The mounting portion 34 and the two lateral sides 36, 38 define a channel open radially on the inner side and within which the conducting fibers 31 are partly located.

[0049] 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 portion of the conductive fibers 31 located radially opposite the free distal end is in radial contact with the mounting portion 34 of the support.

[0050] The side flange 36 extends from one end of the mounting portion 34, and the side flange 38 extends from the opposite end. The side flanges 36 and 38 extend obliquely inward from the mounting portion 34. The side flanges 36 and 38 are symmetrical with respect to a median radial plane of the support 32. Alternatively, only one of the side flanges 36 and 38 could extend obliquely inward. In another embodiment, both side flanges 36 and 38 could extend radially. The mounting portion 34 extends axially in this case. Alternatively, the mounting portion 34 could extend obliquely.

[0051] As previously stated, the brush 30 includes the ring 33 which is mounted inside the support 32 and around which the conductive fibers 31 are arranged. The conductive fibers 31 are bent around the ring 33. The ring 33 is mounted inside the channel delimited by the mounting portion 34 and by the lateral sides 36, 38 of the support.

[0052] The ring 33 remains axially distant from the lateral sides 36, 38 of the support, and radially distant from the mounting portion 34. The conductive fibers 31 are arranged axially on either side of the ring 33 inside the support 32. The conductive fibers 31 are also arranged radially on either side of said ring.

[0053] The ring 33 is open here at a point on its circumference. The ring 33 is provided of first and second opposite ends and delimiting the ring in the circumferential direction.

[0054] The ring 33 is made of an elastically deformable material. By way of example, the ring 33 may be made of a synthetic material such as SEBS, silicone, latex, butyl, EPDM, nitrile, thermoplastic elastomer, etc.

[0055] In the illustrated embodiment, the ring 33 has a circular profile in cross-section. Alternatively, the ring 33 may have other profiles, for example a polygonal profile, in particular a square one as illustrated in [Fig. 5] or a rectangular profile as illustrated in [Fig. 6].

[0056] In the two embodiments illustrated in Figures 4 and 5, the ring 33 is entirely housed inside the support 32. In the embodiment illustrated in [Fig. 6], the ring 33 extends radially inward from the lateral sides 36, 38 of the support. The ring 33 therefore extends both inside and outside the support 32.

[0057] In another embodiment, the ring 33 may have a series of undulations in the circumferential direction, as illustrated in [Fig. 7]. The ring 33 is here of the axially elastic type. The undulations are distributed around the circumference of the ring 33. The ring thus takes the form of a corrugated elastic washer.

[0058] Referring again to Figures 2 and 3, and as previously stated, the brush 30 is in the form of an open ring. 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 is possible to fix these ends of the brush 30 to each other. In this case, the ring 33 is not open at any point on its circumference, and its two ends are in contact with each other. Alternatively, the ring 33 could be annular.

[0059] The mounting plate 40 includes an annular radial portion 42, and a plurality of centering tabs 44 extending from the radial portion 42.

[0060] 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 side 36 of the support.

[0061] The tabs 44 are spaced circumferentially from one another, here at regular intervals. Alternatively, irregular circumferential spacing may be provided. In the illustrated embodiment, there are eight tabs 44. Alternatively, a greater or lesser number of tabs 44 may be provided. Two tabs 44 may be provided, or at least four. Preferably, the number of tabs 44 is at least two.

[0062] Each tab 44 extends axially beyond the radial portion 42. Each tab 44 locally surrounds the support 32 of the brush 30 radially and is in radial contact with the mounting portion 34 of said support. The support 32 is held axially against the radial portion 42 of the mounting plate by the tabs 44. The tabs 44 provide axial and radial retention for the grounding brush 30. The lateral side 36 of the support bears against the radial portion 42 of the mounting plate, and the lateral side 38 bears against the tabs 44. The tabs 44 are identical.

[0063] As more clearly illustrated in [Fig. 4], each tab 44 has an axial portion extending axially from the radial portion 42, locally surrounding the support 32 radially and in radial contact with it, and a folded portion at the free end of the axial portion. The folded portion 44b of each tab axially retains the support 32 of the grounding brush 30. The folded portion 44b of each tab is in axial contact against the lateral side 38 of the support.

[0064] The brush mounting plate 40 also includes a plurality of centering lugs 46 extending from the radial portion 42 and spaced circumferentially from one another. A notch 48 ([Fig. 2]) is formed on the radial portion 42 between each pair of immediately successive lugs 46. The lugs 46 are formed by cutting and bending the radial portion 42.

[0065] Each leg 46 extends axially from the radial portion 42. The legs 46 extend obliquely from a large diameter edge of the radial portion 42. The legs 46 extend axially on the same side as the tabs 44.

[0066] Each tab 46 locally surrounds the support 32 of the brush 30 radially while remaining at a distance from it. The tabs 46 are partially offset radially outwards relative to the tabs 44. The tabs 46 are identical to each other. The tabs 46 define the outer diameter of the mounting plate 40. Each tab 46 extends obliquely. Alternatively, the tabs 46 could extend axially. Each tab 46 is in the form of a portion of a cylinder. The outer surfaces of the tabs 46 define the outer diameter of the mounting plate 40. The tabs 46 allow the mounting plate to be centered after installation in the bore of the housing of the associated electric motor.

[0067] As illustrated in Figures 2 and 4, the tabs 46 are spaced circumferentially from one another, here at regular intervals. Alternatively, irregular circumferential spacing could be provided. Each tab 46 is located circumferentially between two immediately successive tabs 44. Each tab 46 is spaced circumferentially from the two immediately adjacent tabs 44. Each tab 46 here has a circumferential dimension higher rent than that of tabs 44.

[0068] 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 materials. Alternatively, the mounting plate 40 can be made of an electrically non-conductive material with a conductive coating or conductive paint. The mounting plate is made here in one piece.

[0069] During the operation of the electric machine, the electrical charges which accumulate on the shaft are dissipated towards the housing 12 through the conductive fibers 31, the support 32 of the brush, and the mounting plate 40 of the assembly.

[0070] In the illustrated embodiment, the mounting plate 40 of the grounding brush assembly comprises a plurality of centering lugs 46. Alternatively, the lugs could be replaced by an annular flange forming an annular centering portion.

Claims

Claims

1. Grounding brush (30) comprising a plurality of conductive fibers (31) and a support (32) inside which the conductive fibers are mounted and provided with a mounting portion (34) and two lateral flanks (36, 38) extending the mounting portion and axially enclosing the conductive fibers (31), the brush further comprising a ring (33) around which the conductive fibers are arranged inside the support, characterized in that the ring (33) is made at least partly of elastically deformable material.

2. Brush according to claim 1, in which the ring (33) is made entirely of elastically deformable material.

3. Brush according to claim 1 or 2, in which the ring (33) has a circular or square profile in cross section.

4. Brush according to claim 1 or 2, in which the ring (33) has in cross section a profile elongated in the radial direction, in particular rectangular.

5. A brush according to any preceding claim, wherein the ring (33) projects radially inwardly relative to the lateral flanks (36, 38) of the support.

6. Brush according to any one of the preceding claims, in which the ring (33) has a coefficient of friction at least equal to 0.2, and preferably at least equal to 0.

25.

7. A brush according to any preceding claim, wherein the ring (33) has a circumferentially wavy shape.

8. A grounding brush assembly (20) comprising a grounding brush (30) according to any preceding claim, and a brush mounting plate (40) which is integral with the brush holder (32).

9. An assembly according to claim 8, wherein the mounting plate (40) comprises a main body (42) and a plurality of axial and radial retaining tabs (44) for the support (32) of said brush (30) extending from said main body (42), the retaining tabs (44) being radially in abutment against the mounting portion (34) of the support and axially in abutment against one of the lateral flanks (36, 38) of said support.

10. An electric motor comprising a housing (12), a shaft (14) and at least one grounding brush assembly (20) according to claim 9 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 or with the housing.

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