Internal shunt grounding brush arrangement with axially extending conductive fibers

Abstract

An earthing brush assembly for an electric machine, comprising a rotatable shaft, an outer housing, one or more bearings coupling the shaft to the housing, and a stationary shaft extending through the rotatable shaft and electrically earthed. The earthing brush assembly includes an inner conductive base element with a bore dimensioned to accommodate a section of the stationary shaft and a radial surface. An outer conductor is capable of engaging the inner circumferential surface of the rotatable shaft and has a radial contact area.A conductive brush is coupled to the base element and comprises several conductive fibers extending axially from the radial surface of the base element and circumferentially around the centerline, each conductive fiber having a first axial end coupled to the base element and an opposite second axial end engaging with the radial surface of the outer conductor to provide a conductive path or paths.

Description

Cross-reference

[0001] This application claims priority over Italian patent application No. 102024000016096, filed on July 11, 2024, the contents of which are hereby incorporated in full by reference. Background of the invention

[0002] The present invention relates to earthing devices for bearings, and more precisely to earthing brush arrangements for dissipating current from bearings.

[0003] In electrical machines, such as an electric motor, generator, etc., the machine typically comprises a shaft rotatable about a central axis, an outer casing, and at least one bearing connecting the shaft to the casing. Such bearings generally include an inner ring fixed to the rotatable shaft, an outer ring arranged around the inner ring and meshing with the casing, and several rolling elements positioned between the inner and outer rings. During operation, electrical charge can accumulate on the shaft, which can generate an electric current flowing from the shaft through the bearing and into the outer casing. These currents can cause damage to the raceways of the inner and outer rings, as well as to the rolling elements.

[0004] To prevent damage to the bearings, it is known to provide a grounding brush arrangement that provides a conductive path between the shaft and the housing to dissipate current from the bearing(s). Such a grounding brush arrangement typically comprises a clamp or holder connected to the housing and a brush attached to the clamp / holder, comprising several conductive fibers extending radially inward from the holder and contacting the outer surface of the shaft or a sleeve or other element mounted on the shaft. Alternatively, the holder may be mounted on the shaft and have several radially outward-facing fibers engaging with an inner circumferential surface of the housing. Summary of the invention

[0005] In one aspect, the present invention is a grounding brush arrangement for an electric machine, wherein the electric machine comprises a rotatable shaft rotatable about a central axis and having an inner circumferential surface defining a hollow bore, an outer housing, at least one bearing rotatably coupling the shaft to the housing, and a stationary shaft extending through the bore of the rotatable shaft and being electrically grounded. The grounding brush arrangement comprises an annular inner conductive base element with a bore dimensioned to accommodate a section of the stationary shaft and a centerline that is alignable coaxially with the central axis.A ring-shaped outer conductor can be engaged with the inner circumferential surface of the rotatable shaft, and a conductive brush is coupled to the conductive base element and comprises several conductive fibers extending axially along and circumferentially around the centerline. Each conductive fiber has a first axial end coupled to the base element and an opposite second axial end engaged with the inner circumferential surface of the rotatable shaft, such that at least one conductive path extends from the rotatable shaft through the outer conductor, the brush, and the base element to the stationary shaft.

[0006] Preferably, the conductive base element comprises an annular hub with an inner circumferential surface providing the bore of the base element, and a radial flange extending radially outward from the hub, the conductive brush being attached to the radial flange of the base element. The outer conductor preferably comprises an axial section that can be engaged with the rotatable shaft to couple the outer conductor to the rotatable shaft, and a radial flange extending radially inward from the axial section, the second axial end of each of the multiple conductive fibers of the conductive brush engaging with the radial flange of the outer conductor.

[0007] The conductive brush preferably further comprises an annular holder with a circumferential channel, wherein the first axial end of each of the multiple conductive fibers is arranged within the circumferential channel, and the radial flange of the conductive base element comprises at least one, and preferably several, retaining tabs, each of which engages with the annular holder of the conductive brush to couple the brush to the base element. Furthermore, the grounding brush arrangement preferably further comprises at least one centering bearing having an inner ring that can be arranged around the stationary shaft and an outer ring that engages with the inner circumferential surface of the rotatable shaft, wherein the at least one centering bearing is arranged on the base element or axially spaced from it. Brief description of the multiple views of the drawings

[0008] The preceding summary and the detailed description of preferred embodiments of the present invention are better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the invention, currently preferred embodiments are shown in the schematic drawings. It is understood, however, that the present invention is not limited to the exact arrangements and devices shown. In the drawings: Fig. Figure 1 is an axial cross-sectional view of an electric machine comprising a grounding brush arrangement according to the present invention; Fig. 2 is an axial cross-sectional view of a first embodiment of the grounding brush arrangement, which is shown installed between an outer rotatable shaft and an inner stationary shaft; Fig. Figure 3 is a perspective view of a basic element and a brush of the first design. Fig. 2; Fig. 4 is a perspective exploded view of the base element and the brush made of Fig. 3; Fig. Figure 5 is an axial cross-sectional view of a second embodiment of the grounding brush arrangement, shown installed between an outer rotatable shaft and an inner stationary shaft; and Fig. Figure 6 is an axial cross-sectional view of a third embodiment of the grounding brush arrangement, which is installed between an outer rotatable shaft and an inner stationary shaft. Detailed description of the invention

[0009] Certain terms are used in the following description for the sake of simplicity only and are not intended to be restrictive. The terms "inner," "inward," and "outward," "outward," refer to directions toward and from a specific center line or geometric center point of a described element, the respective meaning being readily apparent from the context of the description. Furthermore, the terms "connected" and "coupled" in this description are to be understood as encompassing direct connections between two elements without any intervening elements, as well as indirect connections between elements where one or more other elements are intervening. The terminology includes the terms explicitly mentioned above, derivatives thereof, and terms with similar meanings.

[0010] Referring to the drawings in detail, where the same reference numerals denote the same elements, it is in the Fig. Figures 1-6 show an earthing brush arrangement 10 for an electric machine 1. The electric machine 1 comprises a rotatable shaft 2 which rotates about a central axis A. CThe earthing brush arrangement 10 comprises a rotatable shaft 2 and an inner circumferential surface 2a defining a hollow bore 3, an outer housing 4, at least one bearing 5 rotatably coupling the shaft 2 to the housing 4, and a stationary shaft 6 extending through the bore 3 of the rotatable shaft 2 and electrically grounded. The earthing brush arrangement 10 essentially comprises an inner conductive base element 12 arranged around the stationary shaft 6, an outer conductor 14 coupling to the rotatable shaft, and a conductive brush 16 coupled to the base element 12 and engaged with the outer conductor 14. It preferably further comprises at least one centering bearing 18 for centering the rotatable shaft 2 around the stationary shaft 6.

[0011] More precisely, the guiding base element 12 has a bore 13 dimensioned to accommodate a section of the stationary shaft 6 in order to couple the grounding brush assembly 10 to the stationary shaft 6, and a center line L C , which extends through bore 13 and is coaxial with the central axis A C The ring-shaped outer conductor 14 can be brought into engagement with the inner circumferential surface 2a of the rotatable shaft 2 in order to couple the conductor 14 to the shaft 2. The conductive brush 16 is coupled to the base element 12 and comprises several conductive fibers 20, which extend axially from the radial surface 15 of the base element 12 and circumferentially around the center line L. C extend. Each conductive fiber 20 has a first axial end 20a coupled to the base element 12 and an opposite second axial end 20b engaged with the outer conductor 14.

[0012] As such, at least one conductive path extends from the rotating shaft 2 through the outer conductor 14, the brush 16, and the base element 12 to the stationary shaft 6. With the present grounding brush assembly 10, any electrical charge that accumulates on the rotating shaft 2 flows as an electric current through the assembly 10 instead of flowing through the bearing(s) 5 of the electric machine 1. This prevents damage to the rolling elements and raceways (not shown) of the bearing(s) 5. After describing the basic elements and functions, these and other components of the present grounding brush assembly 10 are described in further detail below.

[0013] With reference to the Fig. 4-6 The base element 12 preferably comprises an annular hub 22 and a radial flange 24 extending radially outward from the hub 22. More precisely, the annular hub 22 has an inner circumferential surface 23A, which provides the bore 13 of the base element 12, an opposing outer circumferential surface 23B, a first axial end 22a, and an opposing second axial end 20b. The radial flange 24 extends radially outward from the outer circumferential surface 23B of the hub 22 and has an inner radial end 24a, which is integrally formed with the hub 22, an opposing outer radial end 24b, a first radial surface 25A, which provides a mounting surface 15 for the conductive brush 16, and an opposing second radial surface 25B. Preferably, the radial flange 24 comprises at least one and preferably several retaining tabs 26 that extend circumferentially around the center line L Cof the base element 12, with each tab 26 engaging with the brush 16 to couple or fasten the brush 16 to the base element 12, as further discussed in detail below.

[0014] Furthermore, each retaining tab 26 is preferably provided or formed by a cut and bent section of the radial flange 24, which is preferably bent in engagement with the brush 16, as discussed below. Preferably, the conductive base element 12 further comprises an annular cover section 28 extending axially from the outer radial end 24b of the radial flange 24 to surround a section of the conductive brush 16. Preferably, the base element 12 is formed from an electrically conductive material, such as steel, aluminum, a conductive polymer, or another suitable conductive material, but may alternatively be formed from a non-conductive material that has been coated or treated with an electrically conductive coating.

[0015] With reference to the Fig. 3 and Fig. 4 the conductive brush 16 preferably comprises an annular holder 30 with a circumferential channel 31 ( Fig. 4), wherein each first axial end 20a of the multiple conductive fibers 20 is arranged within the circumferential channel 31. More precisely, the holder 30 preferably comprises an annular base wall 32 with an inner radial end 32a and an outer radial end 32b, an annular inner side wall 34 extending axially from the inner radial end 32a of the base wall 32, and an annular outer side wall 36 extending axially from the outer radial end 32b of the base wall 32 and spaced radially outward from the inner side wall 34. In such a holder structure, the one or more retaining tabs 26 of the radial flange 24 of the base element 12 engage with the outer side wall 36 of the brush holder 30 to couple the brush 16 to the base element 12.

[0016] Furthermore, the multiple conductive fibers 20 are arranged between the inner and outer side walls 34, 36 of the holder 30 and engage with them to hold the conductive fibers 20 within the annular channel 31. Preferably, the holder 30 is made of an electrically conductive material such as steel, aluminum, a conductive polymer, etc., and each conductive fiber 20 is a strand of an electrically conductive material, preferably carbon, but can also be made of steel, aluminum, a conductive polymer, etc. Alternatively, the conductive brush 14 can be formed either as a single, solid annular conductor or as several arc-shaped conductor segments spaced circumferentially apart, in both cases being made of a suitable conductive material such as steel, a conductive polymer, etc.

[0017] With reference to the Fig. 2, Fig. 5 and Fig. 6 The outer conductor 14 preferably comprises an axial section 40, which can be engaged with the rotatable shaft 2, and a radial flange 42, which extends radially inwards from the axial section 40. More precisely, the axial section 40 has an outer circumferential surface 41A, which can be frictionally engaged with the inner circumferential surface 2a of the rotatable shaft 2 in order to couple the outer conductor 14 to the shaft 2, and an opposing inner circumferential surface 41B. The radial flange 42 has a first radial surface 44A, which provides a radial contact surface 17 that can be engaged with the conductive fibers 20 of the conductive brush 16, and an opposing radial surface 44B. The annular conductor 14, which can be connected to the rotatable shaft 2, is rotatable about the central axis A. C , so that the second axial ends 20b of the multiple conductive fibers 20 slide against the radial surface 17 of the conductor 14.

[0018] With reference to the Fig. 5 and Fig. 6 comprises the grounding brush arrangement 10, as discussed above, preferably at least one centering bearing 18 having an inner ring 50 arranged around the stationary shaft 6 and an outer ring 52 engaging with the inner circumferential surface 2a of the rotatable shaft 2. Preferably, each centering bearing 18 comprises several rolling elements 54 arranged between the inner and outer rings 50, 52, but may alternatively be designed as a sliding bearing (not shown). The at least one centering bearing 18 is arranged on or around the conductive base element 12 and the outer conductor 14 and axially spaced from them, as discussed below. In any case, the one or more centering bearings 18 act to couple the rotatable shaft 2 with the stationary shaft 6, to stiffen the stationary shaft 6 and to prevent vibrations from it, and do not primarily serve to bear a load between the two shafts 2, 6.

[0019] With reference to the Fig. In certain embodiments, the guiding base element 12 is generally C-shaped and formed with a radial flange 24 extending radially outwards from the first axial end 22a of the hub 22, and the cover section 28 is spaced radially outwards from the hub 22, as shown in Fig. 2-4 shown. In such an embodiment, the conductive brush 16 is generally enclosed between the hub 22 and the cover section 28. In other embodiments, the base element 12 is generally S-shaped and formed with the radial flange 24 extending radially outward from the second axial end 22b of the hub 22, the hub 22 extending axially from the second radial surface 25B of the flange 24, and the cover section 28 extending axially from the first radial surface 25A, as shown in the Fig. 5 and Fig. 6 is shown.

[0020] Preferably, in a grounding brush arrangement 10 with an S-shaped conductive base element 12, the inner ring 50 of the at least one centering bearing 18 is arranged either around the outer circumferential surface 23B of the hub 22 in order to couple the bearing 18 to the stationary shaft 6, as in Fig. 5 shown, or a section of the hub 22 is arranged within an annular groove 56 extending radially outwards from an inner circumferential surface 51 of the inner ring 50, as shown in Fig. 6 shown. However, if the basic element 12 is C-shaped, as in the Fig. As shown in Figures 2-4, the inner ring 50 of each of the one or more centering bearings 18 is spaced apart from or abuts the base element 12. Furthermore, the axial section 40 of the outer conductor 14 can be axially spaced from the outer ring 52 of the at least one centering bearing 18, as shown in Figures 2-4. Fig. 6 shown, to which the outer ring 52 (not shown) abuts or at least has a partial section 40a which is arranged around at least one section of the outer ring 52, as in Fig. 5 shown.

[0021] Representative, non-limiting examples of the present invention have been described in detail above with reference to the accompanying drawings. This detailed description is intended only to provide a person skilled in the art with further details on the implementation of preferred aspects of the present teaching and is not intended to limit the scope of the invention.

[0022] Furthermore, combinations of features and steps disclosed in the detailed description above may not be necessary to practice the invention in its broadest sense and are instead included merely to provide representative examples of the invention. Moreover, various features of the representative examples described above, as well as the various independent and dependent claims below, can be combined in a manner not specifically and explicitly listed below to provide additional useful embodiments of the present teaching.

[0023] All features disclosed in the description and / or the claims are disclosed independently of one another for the purposes of the original written disclosure and for the purpose of limiting the claimed subject matter, irrespective of the combination of features in the embodiments and / or the claims. Furthermore, all ranges of values ​​or specifications of groups of units are intended to disclose any possible intermediate value or unit for the purposes of the original written disclosure and for the purpose of limiting the claimed subject matter. The invention is not limited to the embodiments described above and may be varied within the scope of the following claims. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] IT 102024000016096

[0001]

Claims

[1] Grounding brush arrangement for an electric machine, wherein the electric machine comprises a rotatable shaft rotatable about a central axis and having an inner circumferential surface defining a hollow bore, an outer housing, at least one bearing rotatably coupling the shaft to the housing, and a stationary shaft extending through the bore of the rotatable shaft and being electrically grounded, wherein the grounding brush arrangement comprises: a ring-shaped inner conducting base element with a bore dimensioned to accommodate a section of the stationary shaft and a centerline that can be aligned coaxially to the central axis; a ring-shaped outer conductor that can be brought into engagement with the inner circumferential surface of the rotatable shaft; and a conductive brush coupled to the conductive base element and comprising several conductive fibers extending axially along and circumferentially around the center line, each conductive fiber having a first axial end coupled to the base element and an opposite second axial end engaged with the outer conductor, such that at least one conductive path extends from the rotatable shaft through the outer conductor, the brush and the base element and to the stationary shaft. [2] Grounding brush arrangement according to claim 1, wherein the conductive base element comprises an annular hub having an inner circumferential surface providing the bore of the base element and a radial flange extending radially outwards from the hub, wherein the conductive brush is attached to the radial flange of the base element. [3] Earthing brush arrangement according to claim 2, wherein the outer conductor comprises an axial section which can be engaged with the rotatable shaft in order to couple the outer conductor with the rotatable shaft, and a radial flange extending radially inwards from the axial section, wherein the second axial end of each of the multiple conductive fibers of the conductive brush engages with the radial flange of the outer conductor. [4] Grounding brush arrangement according to claim 2, wherein: the conductive brush comprises an annular holder with a circumferential channel, wherein the first axial end of each of the multiple conductive fibers is arranged within the circumferential channel; and the radial flange of the conductive base element comprises at least one retaining tab which engages with the annular holder of the conductive brush in order to couple the brush to the base element. [5] Grounding brush arrangement according to claim 4, wherein the holder of the conductive brush comprises an annular base wall with an inner radial end and an outer radial end, an annular inner side wall extending axially from the inner radial end of the base wall, and an annular outer side wall extending axially from the outer radial end of the base wall and spaced radially outwards from the inner side wall, wherein the multiple conductive fibers are arranged between the inner and outer side walls and engage with them to retain the conductive fibers within the annular channel. [6] Grounding brush arrangement according to claim 5, wherein the at least one retaining tab of the radial flange of the base element comprises several retaining tabs spaced circumferentially around the center line of the base element, each retaining tab engaging with the outer side wall of the holder of the conductive brush. [7] Grounding brush arrangement according to claim 4, wherein the conductive base element comprises several retaining tabs spaced circumferentially around the centerline of the base element, each retaining tab being provided by a cut and bent section of the radial flange. [8] Grounding brush arrangement according to claim 2, wherein the radial flange of the conductive base element has an outer radial end and the base element further comprises an annular cover section extending axially from the outer radial end of the radial flange. [9] Earthing brush arrangement according to claim 1, wherein the outer conductor comprises an axial section which can be engaged with the rotatable shaft in order to couple the outer conductor with the rotatable shaft, and a radial flange extending radially inwards from the axial section, wherein the second axial end of each of the multiple conductive fibers of the conductive brush engages with the radial flange of the outer conductor. [10] Grounding brush arrangement according to claim 1, further comprising at least one centering bearing having an inner ring which can be arranged around the stationary shaft and an outer ring which engages with the inner circumferential surface of the rotatable shaft, wherein the at least one centering bearing is arranged on the conductive base element or axially spaced therefrom. [11] Grounding brush arrangement according to claim 10, wherein the conductive base element comprises an annular hub with an inner circumferential surface which provides the bore of the base element and can be arranged around the stationary shaft, wherein the inner ring of the centering bearing is arranged around a section of the annular hub to couple the centering bearing to the stationary shaft. [12] Earthing brush arrangement according to claim 10, wherein the outer conductor comprises an axial section which can be engaged with the rotatable shaft in order to couple the outer conductor with the rotatable shaft, wherein at least a partial section of the axial section is arranged around at least a section of the outer ring of the centering bearing. [13] Grounding brush arrangement for an electric machine, wherein the electric machine comprises a rotatable shaft rotatable about a central axis and having an inner circumferential surface defining a hollow bore, an outer housing, at least one bearing rotatably coupling the shaft to the housing, and a stationary shaft extending through the bore of the rotatable shaft and being electrically grounded, wherein the grounding brush arrangement comprises: an annular inner conducting base element with an annular hub, wherein the hub has a bore dimensioned to accommodate a section of the stationary shaft and a centerline that is coaxial with the central axis, and has a radial flange extending radially outward from the annular hub; an annular outer conductor having an axial section that can be engaged with the inner circumferential surface of the rotatable shaft in order to couple the outer conductor to the rotatable shaft, and a radial flange extending radially inwards from the axial section; and a conductive brush coupled to the conductive base element and comprising several conductive fibers extending axially along and circumferentially around the centerline, each conductive fiber having a first axial end coupled to the radial flange of the base element and an opposite second axial end engaging with the radial flange of the outer conductor, such that at least one conductive path extends from the rotatable shaft through the outer conductor, the brush and the base element and to the stationary shaft. [14] Grounding brush arrangement according to claim 13, wherein: the conductive brush comprises an annular holder with a circumferential channel, wherein the first axial end of each of the multiple conductive fibers is arranged within the circumferential channel; and the radial flange of the conductive base element comprises at least one retaining tab which engages with the annular holder of the conductive brush in order to couple the brush to the base element. [15] Grounding brush arrangement according to claim 14, wherein the holder of the conductive brush comprises an annular base wall with an inner radial end and an outer radial end, an annular inner side wall extending axially from the inner radial end of the base wall, and an annular outer side wall extending axially from the outer radial end of the base wall and spaced radially outward from the inner side wall, wherein the multiple conductive fibers are arranged between the inner and outer side walls and engage with them to retain the conductive fibers in the annular channel. [16] Grounding brush arrangement according to claim 15, wherein the at least one retaining tab of the radial flange of the base element comprises several retaining tabs spaced circumferentially apart around the center line of the base element, each retaining tab engaging with the outer side wall of the holder of the conductive brush. [17] Grounding brush arrangement according to claim 14, wherein the at least one retaining tab of the conductive base element comprises several retaining tabs spaced circumferentially around the centerline of the base element, each retaining tab being provided by a cut and bent section of the radial flange. [18] Grounding brush arrangement according to claim 13, wherein the radial flange of the conductive base element has an outer radial end and the base element further comprises a cover section extending axially from the outer radial end of the radial flange. [19] Grounding brush arrangement according to claim 13, which further comprises at least one centering bearing having an inner ring which can be arranged around the stationary shaft and an outer ring which engages with the inner circumferential surface of the rotatable shaft, wherein the at least one centering bearing is arranged against the conductive base element or axially spaced from it. [20] Grounding brush arrangement according to claim 19, wherein at least one of: The inner ring of the centering bearing is arranged around a section of the annular hub to couple the centering bearing to the stationary shaft; and at least a partial section of the axial section of the outer conductor is arranged around at least a section of the outer ring of the centering bearing.

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