Earthing brush assembly

Abstract

The earthing brush assembly (20) comprises an earthing brush (30) provided with a plurality of conductive fibres (31) and with a support (32) inside which the conductive fibres are mounted, and a brush mounting plate (40) which is secured to the support (32) of the brush. The mounting plate comprises a radial portion (42) and at least one centring portion (46) extending the radial portion (42) at least axially, which is offset radially outwards with respect to the support (32) and has an outer surface defining the outside diameter of the mounting plate (18). The mounting plate (40) comprises at least one collar (50) extending at least axially from the radial portion (42) on the side opposite the support (32).

Description

[0001] Description

[0002] Title: Earthing brush assembly

[0003] Technical field of the invention

[0004] The present invention relates to the field of earthing devices for controlling the shaft current generated in electric motors or machines, and in particular earthing brush assemblies.

[0005] Prior art

[0006] In an electric motor or machine, at least one rolling bearing is mounted between the housing of the electric motor or machine and the rotary shaft so as to support this shaft.

[0007] In operation, as the shaft rotates, an electrical potential difference can appear between said shaft and the housing of the electric motor or machine, which produces an electric current between the inner race of the rolling bearing, which is secured to the shaft, and the outer race secured to the housing.

[0008] 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 races. Electrical discharges can also generate vibrations.

[0009] In order to remedy these drawbacks, it is known practice to earth or ground the rotary shaft by using an earthing brush comprising conductive fibres. The earthing brush is generally mounted in the bore of the housing of the electric motor in such a way that the free ends of the fibres are in radial contact with the outer surface of the rotary shaft.

[0010] By virtue of the conductivity of the fibres, the brush is kept at the same electrical potential as the housing of the electric motor. The inner and outer races of the rolling bearing are also at the same electrical potential, which reduces or even eliminates problematic electrical discharges through the rolling bearing.

[0011] For further detail regarding the design of such an earthing brush assembly, reference may, for example, be made to document US-A1- 2021 / 0021180, which describes an assembly comprising an earthing brush provided with a plurality of conductive fibres, a support inside which the conductive fibres are mounted, and an annular mounting plate comprising a plurality of tongues for the radial and axial retention of the support.

[0012] Depending on the relative axial positions of the earthing brush assembly and the bearing, there may be contact, during the operation of the electric machine, between the conductive fibres of the assembly on the one hand, and the rolling elements and / or the inner race of the bearing on the other hand.

[0013] This can damage the bearing.

[0014] The present invention aims to remedy this drawback.

[0015] Summary of the invention

[0016] The invention relates to an earthing brush assembly comprising an earthing brush provided with a plurality of conductive fibres and with a support inside which the conductive fibres are mounted. The assembly also comprises a brush mounting plate which is secured to the support of the brush.

[0017] The mounting plate comprises a radial portion and at least one centring portion extending the radial portion at least axially, which is offset radially outwards with respect to the support and has an outer surface defining the outside diameter of the mounting plate.

[0018] According to a general feature, the mounting plate comprises at least one collar extending at least axially from the radial portion on the side opposite the support.

[0019] With this design, the risk of contact between the conductive fibres of the assembly and the bearing is limited. To be specific, said collar of the mounting plate makes it possible to keep an axial space between the brush and the bearing or the housing.

[0020] Preferably, said collar of the mounting plate extends a small-diameter edge of the radial portion. This simplifies the manufacture of the mounting plate. Alternatively, it remains possible to make provision for said collar to extend another zone of the radial portion.

[0021] According to a particular design, said collar of the mounting plate is made in one piece with the radial portion. This simplifies the manufacture of the mounting plate. Said collar may be formed by locally deforming the material of the radial portion.

[0022] According to another design, said collar may be a part which is distinct from the radial portion of the mounting plate and attached thereto by any appropriate means, for example by adhesive bonding. After attachment, said collar extends at least axially from the radial portion of the mounting plate.

[0023] With such a design, it may be possible to make said collar from a material different to the material of the radial portion of the mounting plate. Said collar may for example be made from a material which is electrically insulating, in other words electrically non-conductive. This makes it possible to prevent the dissipation of electrical charge to the bearing in the event of contact between the latter and said collar. Said collar may for example be made from a synthetic material, from plastic, in particular from PEEK, PBT, PPS, PAI.

[0024] In one embodiment, said collar of the mounting plate is annular, i.e. extends circumferentially over 360°. Alternatively, said collar could extend over an angular sector of less than 360° and thus be open at a point on its circumference.

[0025] In another variant, the mounting plate could comprise at least two collars extending at least axially from the radial portion on the side opposite the support and spaced apart from one another in the circumferential direction.

[0026] 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.

[0027] The mounting plate may comprise a plurality of tongues for retention of the support of the brush, extending from the radial portion. Said centring portion may be offset radially outwards with respect to the retention tongues.

[0028] In one embodiment, the mounting plate comprises a plurality of centring portions spaced apart in the circumferential direction.

[0029] In another embodiment, the mounting plate may comprise an annular centring portion.

[0030] The mounting plate may be made as a single piece.

[0031] The invention further relates to an electric motor comprising a housing, a shaft and at least one earthing brush assembly as defined hereinabove and mounted radially between the housing and the shaft, the conductive fibres of the brush of said assembly being in contact with the shaft.

[0032] Brief description of the figures The present invention will be better understood on studying the detailed description of an embodiment, given by way of non-limiting example and illustrated by the appended drawings, in which:

[0033] [Fig 1] is a view in axial section of an earthing brush assembly mounted radially between a rotary shaft and a housing of an electric motor,

[0034] [Fig 2]

[0035] [Fig 3] are perspective views of an earthing brush assembly according to an exemplary embodiment of the invention,

[0036] [Fig 4] is a face-on view of the earthing brush assembly of Figures 2 and 3, and

[0037] [Fig 5] is a view in section along line V-V in Figure 4.

[0038] Detailed description of the invention

[0039] Figure 1 shows, in axial section, part of an electric motor 10 or machine comprising a fixed housing 12, a rotary shaft 14, of axis X-X, which is supported radially by a rolling bearing 16. The bearing 16 is mounted radially between the housing 12 and the rotary shaft 14. In this instance, the bearing is of the ball bearing type. As an alternative, it is possible to provide other rolling elements, or a plain journal bearing.

[0040] The motor 10 further comprises an earthing brush assembly 20 which is mounted radially between the bore 12a of the housing 12 and the outer cylindrical surface 14a of the rotary shaft 14.

[0041] The earthing brush assembly 20 serves to continuously dissipate the electrical charge that builds up on the shaft 14 of the motor when the motor is in operation, by transferring this charge to the housing 12.

[0042] An earthing brush assembly 20 according to an exemplary embodiment of the invention will now be described with reference to Figures 2 to 5.

[0043] The earthing brush assembly 20 has an annular overall shape. The assembly 20 comprises an earthing brush 30 and a brush mounting plate 40 which is configured to centre said brush 30 radially.

[0044] As will be described in more detail below, the mounting plate 40 is also configured to keep an axial space between the brush 30 and the bearing or the housing.

[0045] The brush 30 comprises a plurality of conductive individual fibres 31 which are intended to come around the rotary shaft of the motor. The conductive fibres 31 may be made from carbon, stainless steel, conductive plastics, such as fibres made from acrylic or nylon.

[0046] The brush 30 further comprises a holding or support member 32, inside which the conductive fibres 31 are mounted. In the exemplary embodiment illustrated, the support 32 is in the form of an open ring. The support 32 may be produced by cutting and pressing. The support 32 is made from an electrically conductive material such as aluminium, stainless steel, bronze, copper or another material. Alternatively, the support 32 may be made from an electrically non-conductive material with a conductive coating or a conductive paint.

[0047] As shown more clearly in Figure 5, the support 32 comprises an axial mounting portion 34 and two opposite lateral flanks 36, 38 extending inwards from the mounting portion 34 and axially gripping the conductive fibres 31. The conductive fibres 31 press axially on each side against the lateral flanks 36, 38. The conductive fibres 31 press axially on each side against the internal faces of the lateral flanks 36, 38.

[0048] The mounting portion 34 and the two lateral flanks 36, 38 delimit a channel which is open radially on the inside and inside which the conductive fibres 31 are partially positioned.

[0049] In the example illustrated, the conductive fibres 31 are bent around a connecting wire 39 of the support 32. The free distal end of the conductive fibres 31 is intended to come into radial contact with the outer surface of the rotary shaft of the motor. The proximal end of the conductive fibres 31 is in radial contact with the mounting portion 34 of the support.

[0050] The lateral flank 36 extends one end of the mounting portion 34, and the lateral flank 38 extends the opposite end of said portion. The lateral flanks 36, 38 extend obliquely inwards from the mounting portion 34. The lateral flanks 36, 38 are symmetrical with each other about a radial midplane of the support 32. The mounting portion 34 here extends axially. Alternatively, the mounting portion 34 could extend obliquely.

[0051] As stated above, the brush 30 is in the form of an open ring, as can be seen in particular in Figures 2 and 3. This allows the brush to adapt to suit different diameters of motor shaft. In general, the ends of the brush are not joined together. As a variant, it is possible to join these ends of the brush 30 together. With reference to Figures 2, 3 and 5, the mounting plate 40 comprises an annular radial portion 42, and a plurality of centring tongues 44 extending from the radial portion 42.

[0052] The radial portion 42 of the mounting plate bears axially against the support 32 of the brush 30. More specifically, the radial portion 42 bears axially against the lateral flank 36 of the support.

[0053] The tongues 44 are spaced apart from one another in the circumferential direction, in this instance evenly. As an alternative, it could be possible to provide an irregular circumferential spacing. In the exemplary embodiment illustrated, there are eight tongues 44. As an alternative, it is possible to provide a greater or smaller number of tongues 44. It is possible to provide two tongues 44, or at least four tongues. Preferably, the number of tongues 44 is at least equal to two.

[0054] Each tongue 44 protrudes axially with respect to the radial portion 42. Each tongue 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 bearing against the radial portion 42 of the mounting plate by the tongues 44. The tongues 44 serve for axially and radially retaining the earthing brush 30. 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 tongues 44. The tongues 44 are in this case identical to one another.

[0055] As shown more clearly in Figure 5, each tongue 44 is provided with an axial portion extending axially from the radial portion 42, locally radially surrounding the support 32 and in radial contact therewith, and with a bentover portion at the free end of the axial portion. The bent-over portion 44b of each tongue serves for axially retaining the support 32 of the earthing brush 30. The bent-over portion 44b of each tongue is in axial contact against the lateral flank 38 of the support.

[0056] The mounting plate 40 of the brush also comprises a plurality of centring tabs 46 extending from the radial portion 42 and spaced apart from one another in the circumferential direction. A cutout 48 (Figure 2) is formed on the radial portion 42 between each pair of immediately successive tabs 46. The tabs 46 are formed by cutting and bending the radial portion 42.

[0057] 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 from the same side as the tongues 44. Each tab 46 locally radially surrounds the support 32 of the brush 30 while remaining separated therefrom. The tabs 46 are partially offset radially outwards with respect to the tongues 44. The tabs 46 are in this case identical to one another. The tabs 46 define the outside diameter of the mounting plate 40. Each tab 46 here extends obliquely. Alternatively, the tabs 46 could extend axially. Each tab 46 is in the form of a portion of a cylinder. The bore in each tab 46 is radially spaced apart 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 provide the centring of the mounting plate once it has been mounted in the bore of the housing of the associated electric motor.

[0058] As illustrated in Figures 2 and 4, the tabs 46 are spaced apart from one another in the circumferential direction, in this instance evenly. As an alternative, it could be possible to provide an irregular circumferential spacing. Each tab 46 is positioned in the circumferential direction between two immediately successive tongues 44. Each tab 46 is spaced apart in the circumferential direction from the two immediately adjacent tongues 44. In this instance, each tab 46 has a circumferential dimension greater than that of the tongues 44.

[0059] As stated above, the mounting plate 40 is also configured to keep an axial space between the brush 30 and the bearing or the housing.

[0060] For this purpose, the mounting plate 40 further comprises a collar 50 axially extending the radial portion 42 axially on the side opposite the tongues 44 and the tabs 46, as can be seen in Figures 3 and 5. The collar 50 axially extends the radial portion 42 on the side opposite the support 32. The collar 50 extends outwards. The collar 50 here extends axially. As an alternative, the collar 50 could extend obliquely, in other words axially and radially. In the exemplary embodiment illustrated, the collar 50 is of annular shape. The collar 50 extends a small-diameter edge of the radial portion 42.

[0061] The radial portion 42 of the mounting plate has an internal face against which the support 32 is mounted, pressing axially thereon, and an external face axially opposite the internal face. The internal and external faces delimit the axial thickness of the radial portion 42. The collar 50 protrudes axially with respect to the external face of the radial portion 42.

[0062] As indicated above, in the exemplary embodiment illustrated, the mounting plate 40 comprises an annular collar 50. As an alternative, the mounting plate 40 could comprise a collar 50 having an angular dimension of less than 360°. In another variant, the mounting plate 40 could comprise a plurality of collars 50 extending circumferentially while remaining spaced apart from one another in the circumferential direction.

[0063] The mounting plate 40 is produced by cutting and pressing. The mounting plate 40 is made from a conductive material such as aluminium, stainless steel, bronze, copper or another material. Alternatively, the mounting plate 40 may be made from an electrically non-conductive material with a conductive coating or a conductive paint. In this instance, the mounting plate is made as a single piece. While the electric machine is in operation, the electric charge that builds up on the shaft is dissipated to the housing 4 through the conductive fibres 20, the support 22 of the brush, and the mounting plate 40 of the assembly.

[0064] By virtue of the collar 50 of the mounting plate, contact between the conductive fibres 20 of the brush and the bearing is prevented. In the exemplary embodiment illustrated, the mounting plate 40 of the earthing brush assembly comprises a plurality of centring tabs 46. Alternatively, the tabs could be replaced by an annular flange forming an annular centring portion.

Claims

Claims1. Earthing brush assembly (20) comprising an earthing brush (30) provided with a plurality of conductive fibres (31) and with a support (32) inside which the conductive fibres are mounted, and a brush mounting plate (40) which is secured to the support (32) of the brush, the mounting plate (40) comprising a radial portion (42) and at least one centring portion (46) extending the radial portion (42) at least axially, which is offset radially outwards with respect to the support (32) and has an outer surface defining the outside diameter of the mounting plate (18), characterized in that the mounting plate (40) comprises at least one collar (50) extending at least axially from the radial portion (42) on the side opposite the support (32).

2. Assembly according to Claim 1, wherein said collar (50) of the mounting plate extends a small-diameter edge of the radial portion (42).

3. Assembly according to Claim 1 or 2, wherein said collar (50) of the mounting plate is made in one piece with the radial portion (42).

4. Assembly according to any one of the preceding claims, wherein said collar (50) of the mounting plate is annular.

5. Assembly according to any one of Claims 1 to 3, wherein the mounting plate (40) comprises at least two collars (50) extending at least axially from the radial portion (42) on the side opposite the support (32) and spaced apart from one another in the circumferential direction.

6. Assembly according to any one of the preceding claims, wherein the brush (30) is mounted axially against the radial portion (42) of the mounting plate.

7. Assembly according to any one of the preceding claims, wherein the mounting plate comprises a plurality of tongues (44) for retention of the support (32) of the brush, extending from the radial portion (42), said centring portion (46) being offset radially outwards with respect to the retention tongues (44).

8. Assembly according to any one of the preceding claims, wherein the mounting plate (40) is made as a single piece.

9. Electric motor comprising a housing (12), a shaft (14) and at least one earthing brush assembly (20) according to any one of the preceding claims, mounted radially between the housing (12) and the shaft (14), the conductive fibres of the brush of said assembly being in contact with the shaft.

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