Internal bypass grounding brush assembly with spiral brush

Abstract

Internal bypass grounding brush assembly with spiral brush. Grounding brush assembly for an electrical machine, comprising a rotating shaft with a bore, an outer housing, one or more bearings 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. A conductive base element has a bore dimensioned to receive a portion of the fixed shaft, a centerline, and an outer circumferential surface. A conductive brush is coupled to the base element and comprises conductive fibers extending radially outward from the outer surface of the base element and axially along and circumferentially around 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 spiral brush. Cross reference

[0001] This application claims priority from Italian patent application no. 102024000016087 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. State of the prior art

[0004] To prevent damage to the bearings, a grounding brush assembly is known that 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 rotating shaft and comprise a plurality of fibers oriented radially outward in interaction 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 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 centerline, and an outer circumferential surface. A conductive brush is coupled to the base element and comprises a plurality of conductive fibers extending radially outward from the outer surface of the base element and axially along and circumferentially around 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 conductive path extends from the rotating shaft, through the brush and the base element, and to the stationary shaft.

[0006] Preferably, the conductive brush is formed as a spiral extending circumferentially for at least one turn around the center line of the conductive base member and ideally for a plurality of turns around the center line of the base member. The conductive base member preferably comprises 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.The cylindrical body of the conductive base element preferably has a spiral groove extending radially inwards from the outer surface of the cylindrical body and extending axially between the first and second axial ends and circumferentially around the center line of the cylindrical body, the inner end of each of the plurality of conductive fibers being disposed inside the spiral groove and the plurality of conductive fibers being spaced along the spiral groove.

[0007] Furthermore, the conductive brush preferably comprises a retaining element having a base wall and two spaced lateral walls extending from the base wall and defining a spiral channel, the plurality of conductive fibers being arranged between the two lateral walls and acting upon them so as to retain the fibers within the spiral channel. In addition, the grounding brush assembly preferably further comprises 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 disposed against the conductive base element or axially spaced relative to it. Brief description of the figures

[0008] 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:

[0009] Fig. 1 is an axial cross-sectional view of an electrical machine comprising a grounding brush assembly according to the present invention;

[0010] Fig. 2 is a perspective view of the earthing brush assembly;

[0011] Figure 3 is a side plan view of the grounding brush assembly; and

[0012] Figure 4 is an end view of the earthing brush assembly, cutaway view partial to show details of the conductive fibers. Detailed description of the invention

[0013] 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.

[0014] Referring now to the detailed drawings, with the same numbers used to denote 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 essentially comprises a conductive base element 12 and a conductive brush 14 coupled to the base element 12, and preferably includes at least one centering bearing 18 for centering the rotating shaft 2 about the fixed shaft 6.

[0015] More specifically, the conductive base member 12 has a bore 13 dimensioned to receive a portion of the fixed shaft 6, a center line Lc capable of being aligned coaxially with the central axis Ac, and an outer circumferential surface 12a. The conductive brush 14 comprises a plurality of conductive fibers 20 extending radially outwards from the outer surface 12a of the base member 12 and axially along and circumferentially around the center line Lc. As such, the conductive brush 14 is preferably formed as a spiral extending circumferentially for at least one turn, and preferably multiple turns, around the center line Lc of the base member.In addition, each conductive fiber 20 has an inner radial end 20a coupled to the conductive base element 12, preferably by mutual contact with a brush retaining element 40 as described below, and an outer radial end 20b capable of interacting with the inner circumferential surface 2a of the rotating shaft 2.

[0016] Accordingly, at least one electrically conductive path extends from the rotating shaft 2, through the conductive brush 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 current through the assembly 10 rather than through the bearing(s) 5 of the electrical 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.

[0017] With reference to [Fig. 2] to 4, the base member 12 preferably comprises a generally cylindrical body 22 having an outer surface 23A constituting the outer circumferential surface 12a of the base member 12, 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 and the outer circumferential surface (not shown) of the shaft 6. Furthermore, the cylindrical body 22 is formed of an electrically conductive material, such as steel, aluminum, a conductive polymer, or any other suitable conductive material.With the preferred basic structure, the “spiral” brush 14 extends axially between the first and second axial ends 22a, 22b of the cylindrical body 22 and circumferentially over a plurality of turns around the center line Lc.

[0018] Preferably, the cylindrical body 22 of the base member 12 has a spiral groove 24 extending radially inward from the outer surface 23A of the cylindrical body 22, axially between the first and second axial ends 22a, 22b of the body 12, and circumferentially around the center line Lc. The inner end 20a of each of the plurality of conductive fibers 20 is disposed inside the spiral groove 24, and the plurality of fibers 20 are spaced along the spiral groove 24. Furthermore, the spiral groove 24 has an installation opening 25 at the first axial end 22a of the cylindrical body 22 for the installation of the conductive brush 14, as described below.

[0019] As best illustrated in [Fig. 3], the brush 14 preferably comprises a retaining element 30 having a base wall 32 and two spaced lateral walls 34, 36 extending from the base wall 32 and defining a spiral channel 31. The plurality of conductive fibers 20 is arranged between the two lateral walls 34, 36 and is acted upon by them so as to retain the fibers 20 inside the spiral channel 31. Specifically, the retaining element 30 is inserted into the spiral groove 24 such that the retaining element 30 extends axially along and circumferentially around the center line Lc of the cylindrical body 22.

[0020] Preferably, the retaining element 30 is initially formed as a substantially straight body extending substantially axially. The retaining element 30 then becomes formed as a spiral after insertion into the installation opening 25 of the groove 24 and is pushed through the groove 24 so as to move along and around the center line Lc. Preferably, the retaining element 30 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 made of steel, aluminum, a conductive polymer, etc.In addition, although the conductive brush 14 preferably comprises a plurality of flexible conductive fibers 20, the spiral conductive brush 14 may alternatively be formed of one or more solid conductive elements (none of which are shown) coupled to the conductive base element 12 and having an external radial end that can interact with the inner surface 2a of the rotating shaft 2.

[0021] With reference to [Fig. 3] and 4, the base member 12 further preferably includes a retaining pin 40 interacting with the cylindrical body 22 in the vicinity of the installation opening 25 at the first axial end 22a of the cylindrical body 22 so as to extend axially from the spiral groove 24. The retaining pin 40 is configured to prevent the conductive brush 14 from being dislodged from the spiral groove 24, i.e. by obstructing the opening 25 to prevent the brush 14 from moving outwards through it.

[0022] As 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 interacting with an inner circumferential surface 2a of the rotating shaft 2, and preferably comprises a plurality of rolling elements 54 disposed between the inner and outer rings 50, 52. The centering bearing(s) 18 are disposed against the base member 12 or axially spaced relative to it, and function to couple the rotating shaft 2 with the fixed shaft 6 so as both to stiffen and to prevent vibrations of the fixed shaft 6, and do not primarily serve to support any load between the two shafts 2, 6.

[0023] 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.

[0024] 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.

[0025] 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 additional useful embodiments of the present invention.

[0026] 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 claimed subject matter, regardless of the compositions of the features in the embodiments and / or claims. Furthermore, all ranges of values ​​or indications of entity groups are intended to disclose any possible intermediate value or intermediate entity for the purposes of the original written disclosure, as well as for the purposes of limitation of the claimed object. 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 a conductive brush coupled to the base member and comprising a plurality of conductive fibers extending radially outwards from the outer surface of the base member and axially along and circumferentially around 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 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 brush being formed as a spiral extending circumferentially for at least one turn around the center line of the conductive base member.

3. Grounding brush assembly according to claim 2: the conductive base member having a first axial end and a second opposite axial end; and the conductive brush extending axially between the first and second axial ends of the base member and circumferentially over a plurality of turns around the center line of the base member.

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

5. Grounding brush assembly according to claim 4, the cylindrical body of the conductive base member having a spiral groove extending radially inwards from the outer surface of the cylindrical body and extending axially between the first and second axial ends and circumferentially around the center line of the cylindrical body, the inner end of each of the plurality of conductive fibers being disposed inside the spiral groove and the plurality of conductive fibers being spaced along the spiral groove.

6. Grounding brush assembly according to claim 5, the conductive brush comprising a retaining element having a base wall and two spaced side walls extending from the base wall and defining a spiral chute, the plurality of conductive fibers being arranged between the two side walls and undergoing their action so as to retain the fibers inside the spiral chute.

7. Grounding broom assembly according to claim 6, the retaining element being inserted into the spiral groove such that the retaining element extends axially along and circumferentially around the center line of the cylindrical body.

8. Grounding brush assembly according to claim 5, further comprising at least one retaining pin interacting with the cylindrical body in the vicinity of one of the first and second axial ends of the cylindrical body so as to extend axially from the spiral groove, the pin being configured to prevent the conductive brush from being dislodged from the spiral groove.

9. Grounding brush assembly according to claim 1, 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 disposed against the conductive base element or axially spaced relative to it.

10. 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 generally cylindrical body 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 a conductive brush coupled to the base member and formed as a spiral extending circumferentially for at least one turn around the center line of the conductive base member, the conductive brush comprising a plurality of conductive fibers extending radially outwards from the outer surface of the base member and axially along and circumferentially around 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 conductive path extends from the rotating shaft, through the brush and the base member, and to the stationary shaft.

11. Grounding brush assembly according to claim 10, the conductive brush extending axially between the first and second axial ends of the cylindrical body of the base member and circumferentially over a plurality of turns around the center line of the base member.

12. Grounding brush assembly according to claim 10, the cylindrical body of the conductive base member having a spiral groove extending radially inward from the outer surface of the cylindrical body and extending axially between the first and second axial ends and circumferentially around the center line of the cylindrical body, the end the interior of each of the plurality of conductive fibers being arranged inside the spiral groove and the plurality of conductive fibers being spaced along the spiral groove.

13. Grounding brush assembly according to claim 12, the conductive brush comprising a retaining element having a base wall and two spaced side walls extending from the base wall and defining a spiral chute, the plurality of conductive fibers being arranged between the two side walls and undergoing their action so as to retain the fibers inside the spiral chute.

14. Grounding brush assembly according to claim 13, the retaining element being inserted into the spiral groove such that the retaining element extends axially along and circumferentially around the center line of the cylindrical body.

15. Grounding brush assembly according to claim 12, further comprising at least one retaining pin interacting with the cylindrical body in the vicinity of one of the first and second axial ends of the cylindrical body so as to extend axially from the spiral groove, the pin being configured to prevent the conductive brush from being dislodged from the spiral groove.

16. Grounding brush assembly according to claim 10, 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 disposed against the conductive base element or axially spaced relative to it.

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