Internal bypass grounding brush assembly with axial brushes

Abstract

Internally bypassed grounding brush assembly with axial brushes. Grounding brush assembly for an electrical machine, comprising a rotating shaft with a bore, an outer housing, one or more bearings rotatingally coupling the shaft to the housing, and a fixed shaft extending through the bore of the rotating shaft and electrically grounded. A conductive base element has a bore dimensioned to receive a portion of the fixed shaft, a centerline, and an outer circumferential surface. One or more conductive brushes are coupled to the base element and comprise conductive fibers extending radially outward from the outer surface of the base element and axially along the centerline.Each conductive fiber has an inner radial end coupled to the base element and an outer radial end that can interact with the inner circumferential surface of the rotating shaft such that at least one conductive path extends from the rotating shaft, through the brush and the base element, and to the stationary shaft. Reference: Figure 1.

Description

Title of the invention: Internal bypass grounding brush assembly with axial brushes Cross-reference

[0001] This application claims priority from Italian patent application no. 102024000016084 filed on July 11, 2024, the content of which is fully incorporated herein by reference. Technical field of the invention

[0002] The present invention relates to grounding devices for bearings, and more particularly to grounding brush assemblies intended to divert a current away from bearings.

[0003] In electrical machines, such as an electric motor, a generator, etc., the machine typically comprises a shaft that can rotate about a central axis, an outer casing, and at least one bearing connecting the shaft to the casing. Such bearings generally comprise an inner ring mounted on the rotating shaft, an outer ring disposed around the inner ring and integral with the casing, and a plurality of rolling elements arranged between the inner and outer rings. During operation, an electrical charge can accumulate on the shaft, which can generate an electric current that flows 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. Prior art

[0004] To prevent damage to the bearings, a grounding brush assembly is known, which establishes a conductive path between the shaft and the housing to divert current away from the bearing(s). Such a grounding brush assembly typically comprises a mount or bracket attached to the housing and a brush fixed to the mount / bracket and comprising a plurality of conductive fibers extending radially inward from the bracket and in contact with the outer surface of the shaft, or a sleeve or other component mounted on the shaft. Alternatively, the bracket may be mounted on the shaft and have a plurality of fibers oriented radially outward interacting with an inner circumferential surface of the housing. Summary of the invention

[0005] According to one aspect, the present invention relates to a grounding brush assembly for an electrical machine, the electrical machine comprising a rotating shaft capable of rotating about a central axis and having a circumferential surface The internal structure defines a hollow bore, an outer housing, at least one bearing that rotationally couples the shaft to the housing, and a fixed shaft extending through the bore of the rotating shaft and being electrically grounded. The grounding brush assembly comprises a conductive base element having a bore dimensioned to receive a portion of the fixed shaft, a centerline capable of being aligned coaxially with the central axis, and an outer circumferential surface. At least one conductive brush is coupled to the base element and comprises a plurality of conductive fibers extending radially outward from the outer circumferential surface of the base element and spaced axially along the centerline.Each conductive fiber has an inner radial end coupled to the base element and an outer radial end capable of interacting with the inner circumferential surface of the rotating shaft in such a way that at least one electrically conductive path extends from the rotating shaft, through the brush and the base element, and to the stationary shaft.

[0006] Preferably, the conductive base element comprises a generally cylindrical body having an outer surface constituting the outer circumferential surface of the base element, an inner circumferential surface defining the bore of the base element, a first axial end, and a second opposing axial end. The cylindrical body of the base element preferably has at least one axial groove extending radially inward from the outer circumferential surface of the cylindrical body and axially between the first and second axial ends, the inner radial end of each of the plurality of conductive fibers of the conductive brush(s) being disposed inside the axial groove(s), and the plurality of conductive fibers being spaced along the axial groove(s).In addition, the axial groove(s) preferably comprise a plurality of axial grooves spaced circumferentially around the center line, each of the plurality of axial grooves extending radially inwards from the outer circumferential surface of the cylindrical body and axially between the first and second axial ends of the cylindrical body, and the conductive brush(s) comprise a plurality of conductive brushes, each of the plurality of conductive brushes being disposed within a groove separate from the plurality of axial grooves of the cylindrical body.

[0007] Preferably, the conductive brush(s) comprise a retaining element disposed inside the axial groove(s) of the cylindrical body and having a base wall and two spaced lateral walls extending from the base wall so as to define an axial channel, the plurality of conductive fibers of the conductive brush(s) being disposed between the two lateral walls and undergoing their action so as to retain the fibers inside the axial channel.

[0008] Furthermore, the grounding brush assembly preferably also includes at least one centering bearing having an inner ring that can be disposed on the fixed shaft and an outer ring capable of interacting with the inner circumferential surface of the rotating shaft, the centering bearing(s) being able to be disposed against the conductive base element or axially spaced relative to it and being configured to center the rotating shaft around the fixed shaft. Brief description of the figures

[0009] The preceding summary, as well as the detailed description of preferred embodiments of the present invention, will be better understood when read in conjunction with the accompanying drawings. To illustrate the invention, the drawings, which are schematic, show currently preferred embodiments. It should be understood, however, that the present invention is not limited to the specific arrangements and instruments illustrated. In the drawings:

[0010] Fig. 1 is an axial cross-sectional view of an electrical machine comprising a grounding brush assembly according to the present invention;

[0011] Fig. 2 is a perspective view of the earthing brush assembly;

[0012] Figure 3 is an exploded perspective view of the earthing brush assembly; and

[0013] Fig. 4 is an end view of the grounding brush assembly; Detailed description of the invention

[0014] Certain terms are used in the following description for convenience only and are not exhaustive. The terms “inside,” “inward,” and “outside,” “outward,” refer to directions toward and away from, respectively, a designated midline or geometric center of a described element, the specific meaning being clear from the context of the description. Furthermore, as used herein, the terms “connected” and “coupled” are each intended to include direct connections between two elements without any interposed elements between them and indirect connections between elements in which one or more other elements are interposed between them. The terminology includes the terms specifically mentioned above, their derivatives, and terms of similar scope.

[0015] Referring now to the detailed drawings, with the same numbers used to indicate the same elements throughout, [Fig. 1] to 4 represent a grounding brush assembly 10 for an electrical machine 1. The electrical machine 1 comprises a rotating shaft 2 capable of rotating about a central axis Ac and having an inner circumferential surface 2a defining a hollow bore 3, an outer housing 4, at least one bearing 5 coupling the shaft 2 to the housing 4 in a rotational manner, and a fixed shaft 6 extending through the bore 3 of the rotating shaft 2 and electrically grounded. The grounding brush assembly 10 basically comprises a conductive base element 12 and at least one conductive brush 14 coupled to the base element 12, and preferably includes at least one centering bearing 18 configured to center the rotating shaft 2 around the fixed shaft 6.

[0016] More specifically, the conducting base member 12 has a bore 13 dimensioned to receive a part of the fixed shaft 6, a center line Lc capable of being aligned coaxially with the central axis Ac and an external circumferential surface 12a. The conductive brush(s) 14 comprise a plurality of conductive fibers 20 extending radially outwards from the outer surface 12a of the base member 12 and axially along the center line Lc, each conductive fiber 20 being able to interact with the inner circumferential surface 2a of the rotating shaft 2. More specifically, each conductive fiber 20 has an inner radial end 20a coupled to the conductive base member 12, preferably by mutual contact with a brush retaining element 40 as described below, and an outer radial end 20b being able to interact with the inner circumferential surface 2a of the rotating shaft 2.

[0017] Accordingly, at least one electrically conductive path extends from the rotating shaft 2, through the conductive brush(s) 14 and the conductive base element 12, to the stationary shaft 6. With this grounding brush assembly 10, any charge accumulating on the rotating shaft 2 flows as electric current through the assembly 10 and to the stationary shaft 6 rather than through the bearing(s) 5 of the electric machine 1. Thus, damage to the rolling elements and raceways (neither of which are shown) of the bearing(s) 5 is avoided. Having described the basic elements and functions above, these and other components of this grounding brush assembly 10 are described in more detail below.

[0018] Referring to [Fig. 2] to 4, the base member 12 comprises a generally cylindrical body 22 having an outer surface 23A constituting the outer circumferential surface 12a, an inner circumferential surface 23B defining the bore 13 of the base member 12, a first axial end 22a, and a second opposing axial end 22b. Preferably, the grounding brush assembly 10 is mounted on the fixed shaft 6 by a friction fit between the inner surface 23B of the cylindrical body 22 and the outer circumferential surface (not shown) of the shaft 6. The cylindrical body 22 is made of an electrically conductive material, such as steel, aluminum, a conductive polymer, or any other suitable conductive material.Preferably, the cylindrical body 22 of the base member 12 has at least one axial groove 24 formed in the outer surface 23A of the cylindrical body 22 and extending axially between the first and second axial ends. 22a, 22b respectively. With this structure, the inner end 20a of each of the plurality of conductive fibers 20 of the conductive brush(s) 14 is disposed inside the axial groove(s) 24 and the plurality of fibers 20 are axially spaced along the groove 24.

[0019] Ideally, the cylindrical body 22 of the conductive base member 12 comprises a plurality of axial grooves 24, each extending axially between the first and second axial ends 22a, 22b of the cylindrical body 22 and circumferentially spaced around the center line Lc. Similarly, the conductive brush(s) 14 comprise a plurality of conductive brushes 14, each of the plurality of conductive brushes 14 being arranged within a separate groove in the plurality of axial grooves 24 of the cylindrical body 22.

[0020] Furthermore, the grounding brush assembly 10 preferably includes at least one retaining ring clip 30 interacting with one of the first and second axial ends 22a, 22b of the cylindrical body 22 of the base member 12. The retaining clip 30 is configured to retain the conductive brush(s) 14 arranged inside the axial groove(s) 24 of the cylindrical body 22 and, preferably, retains the entire preferred plurality of conductive brush(s) 14 inside each associated axial groove 24.Preferably, the cylindrical body 22 has an annular groove 26 located in the vicinity of one of the first and second axial ends 22a, 22b, and ideally two annular grooves 26, each formed at a distinct end among the axial ends 22a, 22b. In addition, the retaining clip 30 is preferably formed as a C-clip disposed inside the annular groove 26, and preferably comprises two C-clips, each disposed inside a distinct groove among the two preferred annular grooves 26, and each can be disposed against an axial end of each brush 14.

[0021] With reference to [Fig. 3] and 4, each conductive brush 14 preferably comprises a retaining element 40 having a base wall 42 and two spaced lateral walls 44, 46 extending from the base wall 42 so as to define an axial channel 41. The plurality of conductive fibers 20 is arranged between the two lateral walls 44, 46 and is acted upon by them so as to retain the conductive fibers 20 inside the axial channel 41. Preferably, the retaining element 40 is formed 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 may be formed of steel, aluminum, a conductive polymer, etc.

[0022] Although the grounding brush assembly 10 preferably comprises one or more conductive brushes 14, each having a plurality of conductive fibers 20, each brush 14 may alternatively be formed from a solid conductive element (not represented) coupled to the conducting base member 12 and having an external radial end capable of interacting with the inner surface 2a of the rotating shaft 2. For example, the solid conducting member can be formed as a rectangular strip of a suitable conducting material positioned so as to extend radially from the conducting body 12 and axially along the center line Lc of the body 12.

[0023] As illustrated in [Fig. 1] and mentioned above, the grounding brush assembly 10 preferably comprises at least one centering bearing 18 having an inner ring 50 disposed on the fixed shaft 6 and an outer ring 52 capable of interacting with an inner circumferential surface 2a of the rotating shaft 2, and preferably comprises a plurality of rolling elements 56 disposed between the inner and outer rings 50, 52. The centering bearing(s) 18 are disposed against the conductive base member 12 or axially spaced relative to it, and function to couple the rotating shaft 2 with the fixed shaft 6 so as to stiffen and prevent vibrations of the fixed shaft 6, and do not primarily serve to support any load between the two shafts 2, 6.

[0024] With the grounding brush assembly 10 of the present invention, the conductive fibers 20 come into contact with the inner surface 2a of the rotating shaft 2, which has a linear speed (i.e. tangent to the surface 2a) whose modulus is less than the modulus of the linear speed at the outer surface 2b of the shaft 2. As such, both the friction and the wear of the conductive fibers 20 are reduced compared to known grounding brush assemblies having conductive fibers in contact with an outer shaft surface.

[0025] Non-limiting representative examples of the present invention have been described in detail above with reference to the accompanying drawings. This detailed description is intended merely to instruct a person skilled in the art in further details for the practice of preferred aspects of the present invention and is not intended to limit the scope of the invention.

[0026] Furthermore, the combinations of features and steps disclosed in the detailed description above may not be essential for carrying out the invention in the broadest sense and are instead indicated simply to describe particular representative examples of the invention. In addition, various features of the representative examples described above, as well as the various independent and dependent claims below, may be combined in a manner not specifically and explicitly stated in order to provide further useful embodiments of the present invention.

[0027] All features disclosed in the description and / or claims are intended to be disclosed separately and independently of each other for the purposes of the original written disclosure, as well as for the purposes of limiting the subject matter claimed, regardless of the feature compositions in the embodiments and / or claims. Furthermore, all value ranges or entity group indications are intended to disclose any possible intermediate value or intermediate entity for the purposes of the original written disclosure, as well as for the purpose of limiting the claimed subject matter. The invention is not limited to the embodiments described above and may vary within the scope of the following claims.

Claims

Demands

1. Grounding brush assembly for an electrical machine, the electrical machine comprising a rotating shaft capable of rotating about a central axis and having an inner circumferential surface defining a hollow bore, an outer housing, at least one bearing coupling the shaft to the housing in a rotational manner, and a fixed shaft extending through the bore of the rotating shaft and electrically grounded, the grounding brush assembly comprising: a conductive base element having a bore dimensioned to receive a portion of the fixed shaft, a center line capable of being aligned coaxially with the central axis and an outer circumferential surface;and at least one conductive brush coupled to the base member and comprising a plurality of conductive fibers extending radially outwards from the circumferential outer surface of the base member and spaced axially along the center line, each conductive fiber having an inner radial end coupled to the base member and an outer radial end capable of interacting with the inner circumferential surface of the rotating shaft such that at least one electrically conductive path extends from the rotating shaft, through the brush and the base member, and to the stationary shaft.

2. Grounding brush assembly according to claim 1, the conductive base member comprising a generally cylindrical body having an outer surface constituting the outer circumferential surface of the base member, an inner circumferential surface defining the bore of the base member, a first axial end and a second opposite axial end.

3. Grounding brush assembly according to claim 2, the cylindrical body of the base member having at least one axial groove extending radially inwards from the outer circumferential surface of the cylindrical body and axially between the first and second axial ends, the inner radial end of each of the plurality of conductive fibers of the conductive brush(s) being disposed inside the groove(s) axial and the plurality of conductive fibers being spaced along the axial groove(s).

4. Grounding brush assembly according to claim 3: the axial groove(s) of the cylindrical body of the base member comprising a plurality of axial grooves spaced circumferentially around the center line, each of the plurality of axial grooves extending radially inwards from the outer circumferential surface of the cylindrical body and axially between the first and second axial ends of the cylindrical body, and the conductive brush(s) comprising a plurality of conductive brushes, each of the plurality of conductive brushes being disposed inside a groove separate from the plurality of axial grooves of the cylindrical body.

5. Grounding brush assembly according to claim 3, the conductive brush(s) comprising a retaining element disposed inside the axial groove(s) of the cylindrical body and having a base wall and two spaced lateral walls extending from the base wall so as to define an axial channel, the plurality of conductive fibers of the conductive brush(s) being disposed between the two lateral walls and subjected to their action so as to retain the fibers inside the axial channel.

6. Grounding brush assembly according to claim 3, the conductive base element further comprising at least one annular retaining attachment interacting with one of the first and second axial ends of the cylindrical body of the base element and configured to retain the conductive brush(s) disposed inside the axial groove(s) of the cylindrical body.

7. Grounding brush assembly according to claim 6, the cylindrical body having an annular groove located in the vicinity of one of the first and second axial ends of the cylindrical body and the retaining clip being a C-shaped clip disposed inside the annular groove and able to be disposed against an axial end of the conductive brush(s).

8. Grounding brush assembly according to claim 1, further comprising at least one centering bearing having an inner ring that can be disposed on the fixed shaft and an outer ring capable of interacting with the circumferential surface inside the rotating shaft, the centering bearing(s) can be arranged against the conducting base element or spaced axially from it and are configured to center the rotating shaft around the fixed shaft.

9. Grounding brush assembly for an electrical machine, the electrical machine comprising a rotating shaft capable of rotating about a central axis and having an inner circumferential surface defining a hollow bore, an outer housing, at least one bearing coupling the shaft to the housing in a rotational manner, and a fixed shaft extending through the bore of the rotating shaft and electrically grounded, the grounding brush assembly comprising: a conductive base element having a center line capable of being aligned coaxially with the central axis and comprising a body generally cylindrical having a first axial end, a second opposite axial end, an outer circumferential surface and an inner circumferential surface defining a bore dimensioned to receive a portion of the fixed shaft;and at least one conductive brush coupled to the base member and comprising a plurality of conductive fibers extending radially outwards from the circumferential outer surface of the base member and spaced axially along the center line, each conductive fiber being able to interact with the inner circumferential surface of the rotating shaft in such a way that at least one electrically conductive path extends from the rotating shaft, through the brush and the base member, and to the stationary shaft.

10. Grounding brush assembly according to claim 9, each of the plurality of conductive fibers of the conductive brush(s) having an inner radial end coupled to the cylindrical body of the base member and an outer radial end capable of interacting with the inner circumferential surface of the rotating shaft.

11. Grounding brush assembly according to claim 10, the cylindrical body of the conductive base member having at least one axial groove extending radially inwards from the outer circumferential surface of the cylindrical body and axially along the center line between the first and second axial ends, the inner end of each of the plurality of conductive fibers of the conductive brush(s) being disposed inside the axial groove(s) and the plurality of conductive fibers being spaced along the axial groove(s).

12. Grounding brush assembly according to claim 11: the axial groove(s) of the cylindrical body of the base member comprising a plurality of axial grooves spaced circumferentially around the center line, each of the plurality of axial grooves extending radially inwards from the outer circumferential surface of the cylindrical body and axially between the first and second axial ends of the cylindrical body, and the conductive brush(s) comprising a plurality of conductive brushes, each of the plurality of conductive brushes being disposed within a groove separate from the plurality of axial grooves of the cylindrical body.

13. Grounding brush assembly according to claim 11, the conductive brush(s) comprising a retaining element disposed inside the axial groove(s) of the cylindrical body and having a base wall and two spaced lateral walls extending from the base wall so as to define an axial channel, the plurality of conductive fibers of the conductive brush(s) being disposed between the two lateral walls and subjected to their action so as to retain the fibers inside the axial channel.

14. Grounding brush assembly according to claim 11, the base member further comprising at least one annular retaining attachment interacting with one of the first and second axial ends of the cylindrical body of the base member and configured to retain the conductive brush(s) disposed inside the axial groove(s) of the cylindrical body.

15. Grounding brush assembly according to claim 14, the cylindrical body having an annular groove located in the vicinity of one of the first and second axial ends of the cylindrical body and the retaining clip being a C-shaped clip disposed inside the annular groove and able to be disposed against an axial end of the conductive brush(s).

16. Grounding brush assembly according to claim 9, further comprising at least one centering bearing having an inner ring disposed on the fixed shaft and an outer ring capable of interacting with the inner circumferential surface of the rotating shaft, the centering bearing(s) being able to be disposed against the conductive base element or axially spaced relative to it.

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