Grounding brush assembly

Abstract

[Grounding Brush Assembly] The grounding brush assembly comprises 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) integral with the support (32), characterized in that the support (32) and the conductive fibers (31) each extend helically, the support (32) being provided with a first end (32a) and a second end (32b) which define the circumferential dimension of said support (32) and which are axially offset from each other. Reference: Figure 2

Description

Title of the invention: Grounding brush assembly technical field

[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 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] During the operation of the electric machine, the sweeping of the conductive fibers of the brush on the external surface of the rotating shaft causes wear and an increase in friction torque.

[0008] A known solution to limit these effects is to reduce the thickness of the conductive fibers of the brush. However, this is at the expense of the electrical performance of the brush assembly.

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

[0010] The invention provides for this purpose an assembly of grounding brushes comprising a grounding brush provided with a plurality of conductive fibers and a support within which the conductive fibers are mounted. The assembly further comprises a brush mounting plate which is integral with the brush support.

[0011] The support and the conductive fibers of the brush each extend helically, the support being provided with a first end and a second end opposite to the first end, which first end and second end delimit the circumferential dimension of said support and are axially offset from each other.

[0012] Such an earthing assembly is designed to be mounted radially between a rotating shaft and an electric motor housing, the brush surrounding the rotating shaft with its conductive fibers in contact with the external cylindrical surface of the rotating shaft. The support gives the brush its general shape, resulting in a helical shape.

[0013] Thus, during the operation of the electric machine, the external cylindrical surface of the rotating shaft will be swept by the brush over an axially larger area than if the same brush extended entirely in the same plane (i.e., if the brush were straight), while the instantaneous contact area between the brush and the shaft will be substantially the same as if the brush were straight.

[0014] Thus, shaft wear is reduced while the electrical performance of the brush assembly is maintained. Furthermore, when the shaft is lubricated with oil, the brush acts like a worm gear to drain any excess oil and thus limit the frictional torque that such an excess could cause. The direction of the helical winding can, in particular, be adapted to the direction of rotation of the shaft in order to drain the oil in a predetermined direction, for example, away from a bearing near which the brush assembly is mounted.

[0015] According to another feature, the mounting plate comprises a radial portion and at least one centering portion extending at least axially from the radial portion, offset radially outwards from the support and provided with an outer surface defining the outer diameter of the mounting plate, and in which the radial portion of the mounting plate delimits a through opening, the brush support extending through the opening.

[0016] In addition, the radial portion of the mounting plate is annular and extends radially between an inner edge delimiting the opening and an outer edge from which the centering portion extends, the brush support being at least partially radially supported against the inner edge.

[0017] In addition, the radial portion of the mounting plate is provided with a first lateral face and a second lateral face opposite to the first lateral face and which delimit the thickness of said radial portion, the first end of the brush support being axially supported against the first lateral face and / or the second end of the brush support being axially supported against the second lateral face.

[0018] Advantageously, the radial portion of the mounting plate locally has a projection extending radially inside the opening, the first end and / or the second end being axially supported against the locking projection.

[0019] Moreover, considering the circumferential direction, the length of the projection of the radial portion of the mounting plate is greater than the gap between the first end and the second end of the brush support.

[0020] According to another feature, the mounting plate includes a plurality of retaining elements for the brush support.

[0021] In addition, the retaining elements are, for a first part of them, provided on the first lateral face of the radial portion of the mounting plate and for a second part of them, provided on the second lateral face of the radial portion of the mounting plate.

[0022] For example, the retaining members include centering tabs each having an axial branch and a radial branch extending radially and inwards from the axial branch, the support being axially supported against at least some of the radial branches of the centering tabs and radially supported against at least some of the axial branches of the centering tabs.

[0023] The invention further 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 described above 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] Other purposes, advantages and features will become apparent from the following description, given for illustrative purposes only and with reference to the accompanying drawings on which:

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

[0026] [Fig.2] and

[0027] [Fig.3] are perspective views of an assembly of grounding brushes 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 cross-sectional view along the VV axis of [Fig.4],

[0030] [Fig.6] is a detail view of [Fig.5], and

[0031] [Fig.7] is a cross-sectional view along axis VII-VII of [Fig.4]. Detailed description of the invention

[0032] 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.

[0033] 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.

[0034] 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.

[0035] With reference to figures 2 to 7, an assembly 20 of grounding brushes according to an example of an embodiment of the invention will now be described.

[0036] The grounding brush assembly 20 has a general annular shape and thus delimits a through opening 55 forming a passage for the rotating shaft 14. The assembly 20 includes a grounding brush 30 and a brush mounting plate 40 configured to radially center said brush 30.

[0037] As can be seen in particular in Figures 2 and 3, the brush 30 has a helical shape, in the circumferential direction. The brush 30 also extends here through the opening 55 and protrudes axially on each side of the opening 55. Alternatively, the brush 30 could extend entirely on one side or the other of the opening 55. Alternatively, the brush 30 could extend within the opening 55 and protrude only on one side of the opening 55.

[0038] 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.

[0039] The brush 30 further includes 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.

[0040] As can be seen in Figures 2 and 3, the support 32 is fixed to the mounting plate 40 such that it extends helically, in the circumferential direction, between a first end 32a and a second end 32b opposite the first end 32a. The first and second ends 32a, 32b define the circumferential dimension of said support. The first end 32a and the second end 32b are thus axially offset from each other. Furthermore, here the support 32 extends through the opening 55, so that its ends 32a and 32b are located axially on either side of the opening 55. Alternatively, the support 32 could extend entirely on one side or the other of the opening 55. Alternatively, the support 32 could extend into the opening 55 and protrude only on one side of the opening 55.

[0041] The support 32 can be made by cutting and stamping. The support 32 is made of an electrically conductive material, such as, for example, aluminum, stainless steel, bronze, copper, or other material. Alternatively, the support 32 can be made of an electrically non-conductive material with a conductive coating or a conductive paint.

[0042] As more clearly illustrated in [Fig. 6], the support 32 comprises an axial mounting portion 34 and two opposing lateral flanks 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 flanks 36, 38. The conductive fibers 31 are axially supported on both sides against the inner faces of the lateral flanks 36, 38.

[0043] 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.

[0044] The conductive fibers 31 can be bent around a connecting wire (not shown) of the support 32. The free distal end of the conductive fibers 31 is intended to come into radial contact with the outer surface 14a of the rotating shaft 14 of the motor 10. The proximal end of the conductive fibers 31 is in radial contact with the mounting portion 34 of the support.

[0045] Similar to the support 32, the conductive fibers 31 also extend helically. The lateral flank 36 of the support 32 extends from one end of the mounting portion 34, and the lateral flank 38 extends from the opposite end. The lateral flanks 36 and 38 extend substantially parallel to each other inward from the mounting portion 34. Alternatively, the lateral flanks 36 and 38 could extend obliquely inward from the mounting portion 34. The lateral flanks 36 and 38 are symmetrical to each other with respect to a median radial plane of support 32. The mounting portion 34 extends axially here. Alternatively, the mounting portion 34 could extend obliquely.

[0046] As previously stated, the brush 30 is in the form of an open ring, as can be seen in particular in Figures 2 to 4. This allows the brush to adapt to different diameters of the motor shaft. The ends of the brush 30 are not fixed to each other.

[0047] The mounting plate 40 includes an annular radial portion 42 extending radially between an internal annular edge 51, or edge of small diameter, and an external annular edge 52, or edge of large diameter, opposite the internal annular edge 51.

[0048] The internal annular edge 51 delimits the central opening 55.

[0049] The radial portion 42 extends axially between a first lateral face 53 ([Fig.3]) and a second lateral face 54 ([Fig.2]), opposite the first lateral face 53. The lateral faces 53, 54 delimit the thickness of the radial portion 42.

[0050] The radial portion 42 has a radially enlarged portion forming a locking projection 56 on the inner side of the radial portion 42, i.e. on the side where the central opening 55 is located. The locking projection 56 extends radially to a free end 57. The locking projection 56 extends in the circumferential direction between a first end 56a and a second end 56b, opposite the first end 56a.

[0051] The mounting plate 40 further includes a plurality of brush retaining elements provided here on the radial portion 42. These retaining elements take the form of centering tabs 44 extending from the radial portion 42. Alternatively, the retaining elements could be welds between the support 32 and the mounting plate 40.

[0052] The tabs 44 are partly formed on the first lateral face 53 and partly formed on the second lateral face 54. More precisely, the plurality of centering tabs 44 comprises first centering tabs 441 extending from the first lateral face 53 and second centering tabs 442 extending from the second lateral face 54. The tabs 441 and 442 therefore extend in opposite axial directions.

[0053] The first tabs 441 and the second tabs 442 are further arranged alternately in the circumferential direction, that is to say that each second tab 442 is located, in the circumferential direction, between two successive first tabs 441.

[0054] Each centering tab 44 is provided with an axial branch 44a extending axially from the radial portion 42 and a radial branch 44b extending radially and inwards from the axial branch 44a, such that the centering tab 44 has an L-shaped profile. As can be seen in Figures 5 to 7, and further Specifically on [Fig.6], the axial branch 44a has an internal face 58, oriented radially inwards and which is flush with the internal edge 51, that is to say that the internal face 58 extends axially by prolonging the internal edge 51. The radial branch 44b extends opposite the opening 55.

[0055] Generally, the tabs 44 and the radial portion 42 are configured to retain the brush 30 axially and radially.

[0056] Indeed, the brush 30 is arranged on the mounting plate 40 so that the support 32, and more specifically its mounting portion 34, is radially supported against the inner edge 51 of the radial portion 42 as well as against at least some of the inner faces 58 of the axial branches 44a.

[0057] In addition, the brush 30 is arranged on the mounting plate 40 so that at least one of the ends 32a and 32b of the support 32 is axially supported against the locking protrusion 56, while the rest of the support 32 is supported against at least some of the radial branches 44b of the centering tabs 44.

[0058] More specifically, with the ends 32a and 32b located axially on either side of the radial portion 42, the first end 32a is axially supported against the first lateral face 53 and the second end 32b is axially supported against the second lateral face 54.

[0059] Furthermore, as can be seen in [Fig.6], the lateral side 36 of the support 32 is axially supported against the radial branches 44b of the first tabs 441, while the lateral side 38 is axially supported against the radial branches 44b of the second tabs 442.

[0060] Furthermore, in the circumferential direction, the length of the axial branch 44a of the first tabs 441 gradually decreases from one tab 441 to the next, while the length of the axial branch 44a of the second tabs 442 gradually increases from one second tab 442 to the next. In other words, in the circumferential direction, the distance between the radial branch 44b of the first tabs 441 and the radial portion 42 gradually decreases from one tab 441 to the next, while the distance between the radial branch 44b of the second tabs 442 and the radial portion 42 gradually increases from one second tab 442 to the next.

[0061] Thus, the tabs 44 and the radial portion 42 define between themselves a mounting path extending along a helical path in which the support 32 is received by being guided. More precisely, the path is axially delimited on one side by the radial branches 44b of the first tabs 441 and axially on the opposite side by the radial branches 44b of the second tabs 442, while it is radially delimited by the inner edge 51 and the axial branches 44a of the tabs 44. In guiding the support 32, the path gives its helical shape to the support 32 and therefore to the brush 30.

[0062] It will be noted that among the first tabs 441 and among the second tabs 442 there is a tab 441a and a tab 442a respectively whose length of the axial branch 44a is substantially equal to the thickness of the radial branch 44b which extends it, so that this radial branch 44b has an internal face, oriented towards the opening 55, which is axially aligned with the corresponding lateral face 53 or 54.

[0063] It will be noted that, in the circumferential direction, the length of the locking projection 56, i.e. the distance between its ends 56a and 56b, is greater than the gap between the ends 32a and 32b of the support 32. Thus, if the gap between the ends 32a and 32b increases, for example to adapt to the diameter of the rotating shaft 14, the ends 32a and 32b slide on the locking projection 56 and remain axially supported against it.

[0064] According to other features, the tabs 44 are spaced from each other circumferentially, here at regular intervals. Alternatively, irregular circumferential spacing could be provided. The number of first tabs 441 is equal to the number of second tabs 442. In the illustrated embodiment, there are six tabs 44: three first tabs 441 and three second tabs 442.

[0065] Alternatively, it is possible to provide a greater or lesser 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.

[0066] The tabs 44 extend here only over a circumferential portion of the radial portion 42. In other words, the radial portion 42 has a circumferential portion devoid of tabs 44, which portion includes entirely the locking projection 56.

[0067] 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 (Figures 2 to 4) 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.

[0068] 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, that is, from its outer annular edge 52. The legs 46 are partially offset radially outwards relative to the tabs 44. The legs 46 are identical here. The legs 46 define the outer diameter of the mounting plate 40. Each leg 46 extends obliquely here. Alternatively, the legs 46 could to extend axially. Each leg 46 is in the form of a portion of a cylinder. The bore of each leg 46 is radially spaced from the support 32 by a non-zero radial distance. The outer surfaces of the legs 46 define the outer diameter of the mounting plate 40. The legs 46 allow the mounting plate to be centered after installation in the bore of the housing of the associated electric motor.

[0069] As clearly shown in Figures 2 to 4, the tabs 46 are spaced circumferentially from one another, here at regular intervals. Alternatively, irregular circumferential spacing could be provided. Each tab 44 is located circumferentially between two immediately successive tabs 46. Each tab 44 is spaced circumferentially from the two immediately adjacent tabs 46. Each tab 46 has a circumferential dimension greater than that of the tabs 44.

[0070] 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.

[0071] During the operation of the electric machine, the electrical charges which accumulate on the shaft are dissipated towards the housing 4 through the conductive fibers 20, the support 22 of the brush, and the mounting plate 40 of the assembly.

[0072] The helical shape of the brush 30 allows it to sweep the external cylindrical surface of the rotating shaft 14 over a relatively large area without affecting the instantaneous contact area between the brush 30, and more specifically the conductive fibers 31, and the shaft 14. Thus, wear on the shaft 14 is limited while the electrical performance of the brush assembly 20 is maintained. Furthermore, when the shaft 14 is lubricated with oil, the brush 30 acts like a worm gear to drain any excess oil and thus limit the frictional torque that such an excess could cause. The direction of the helical winding in which the support 32 and the brush 30 wind can in particular be adapted to the direction of rotation of the shaft 14 in order to drain the oil in a predetermined direction, for example to move it away from the bearing 16 near which the brush assembly 20 is mounted.

[0073] The assembly 20 is mounted so that the centering lugs 46 of the mounting plate are located axially on the bearing side.

[0074] 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

Demands

1. Grounding brush assembly (20) comprising 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), characterized in that the support (32) and the conductive fibers (31) of the brush each extend helically, the support (32) being having a first end (32a) and a second end (32b) opposite the first end (32a) and which delimit the circumferential dimension of said support (32), the first end (32a) and the second end (32b) being axially offset from each other.

2. Assembly according to claim 1, wherein the mounting plate (40) comprises a radial portion (42) and at least one centering portion (46) extending at least axially from the radial portion (42), offset radially outwards from the support (32) and provided with an outer surface defining the outer diameter of the mounting plate (18), and wherein the radial portion (42) of the mounting plate (40) delimits a through opening (55), the support (32) of the brush (30) extending through the opening (55).

3. Assembly according to claim 2, wherein the radial portion (42) of the mounting plate (40) is annular and extends radially between an inner edge (51) delimiting the opening (55) and an outer edge (52) from which the centering portion (46) extends, the support (32) of the brush (30) being at least partially radially supported against the inner edge (51).

4. Assembly according to claim 2 or 3, wherein the radial portion (42) of the mounting plate (40) is provided with a first lateral face (53) and a second lateral face (54) opposite the first lateral face (53) and which delimit the thickness of said radial portion (42), the first end (32a) of the support (32) of the brush (30) being axially supported against the first lateral face (53) and / or the second end (32b) of the support (32) of the brush (30) being axially supported against the second lateral face (54).

5. Assembly according to claim 4, wherein the radial portion (42) of the mounting plate (40) locally has a projection of locking (56) extending radially inside the opening (55), the first end (32a) and / or the second end (32b) being axially supported against the locking projection (56).

6. Assembly according to claim 5, wherein, considering the circumferential direction, the length of the locking projection (56) of the radial portion (42) of the mounting plate (40) is greater than the gap between the first end (32a) and the second end (32b) of the support (32) of the brush (30).

7. Assembly according to any one of the preceding claims, wherein the mounting plate (40) comprises a plurality of retaining elements (44) for the support (32) of the brush (30).

8. Assembly according to claim 7 dependent on any one of claims 4 to 6, wherein the retaining members (44) are for a first part of them provided on the first lateral face (53) of the radial portion (42) of the mounting plate (40) and for a second part of them provided on the second lateral face (54) of the radial portion (42) of the mounting plate (40).

9. Assembly according to any one of claims 7 or 8, wherein the retaining members comprise centering tabs (44) each having an axial branch (44a) and a radial branch (44b) extending radially and inwards from the axial branch (44a), the support (32) being axially supported against at least some of the radial branches (44b) of the centering tabs (44) and radially supported against at least some of the axial branches (44a) of the centering tabs (44).

10. Electric motor comprising a housing (12), a shaft (14), at least one bearing (16) mounted radially between the housing (12) and the shaft (14), and at least one grounding brush assembly (20) according to any one of the preceding claims mounted radially between the housing (12) and the shaft (14), the conductive fibers (31) of the brush (30) of said assembly (20) being in contact with the shaft.

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