Self-preparing earth bracket

Abstract

A self-preparing earth bracket 7 for mounting to a railway vehicle is provided. The earth bracket has a connector 8 configured for electrical connection thereto of a terminal of an earthing cable. The

Description

Field of the Invention The present invention relates to a self-preparing earth bracket for mounting to a railway vehicle. Background During production of railway vehicles it is common that earth tabs are added, typically to the underframe of a vehicle, so that direct electrical connection (metallic contact) can be created between earthing cables and the car body. Conventionally, these tabs are welded in position to create permanent electrically conductive attachment points for the earthing cables. However, occasionally the tabs are missed off during assembly or are welded in the wrong position. At other times, wiring or equipment alterations mean that the earth position on the vehicle has to be changed. In such a situation, a conventional solution is for manufacturing personnel to remove paint or other protective film from the position where the new / additional tab is to be fixed, and then weld the tab in place. However, this procedure can require removal of underframe equipment to create suitable access, as well as a need for additional production steps, such as making the area safe by setting up weld screens etc. Such steps increase manufacturing times and costs. The present invention has been devised in light of the above considerations. Summary of the Invention In a first aspect, the present invention provides a self-preparing earth bracket for mounting to a railway vehicle, the earth bracket having: a connector configured for electrical connection thereto of a terminal of an earthing cable, and a fastening fixture configured for mechanical fastening to a mounting point on the railway vehicle, the mounting point having a coated surface; wherein the fastening fixture includes a coat stripping arrangement which is configured such that on mechanical fastening of the fastening fixture to the mounting point the coat stripping arrangement strips the coat from the surface of the mounting point to achieve an electrical connection between the earth bracket and the railway vehicle at the fastening fixture. Thus advantageously, the earth bracket avoids a need for welding by enabling mechanical fastening of the bracket to the vehicle, which fastening also removes the coat (typically paint or other protective film) from the surface of the mounting point. The bracket can thus be installed as and when required with little disruption to other manufacturing processes. In a second aspect, the present invention provides a railway vehicle including: a mounting point, and the self-preparing earth bracket according to the first aspect, wherein the fastening fixture is fastened to the mounting point such that a coated surface (e.g. paint or other protective film) of the mounting point is stripped therefrom by the coat stripping arrangement to achieve an electrical connection between the earth bracket and the railway vehicle at the fastening fixture. In the second aspect, an earthing cable may also be electrically connected to the connector of the earth bracket. In a third aspect, the present invention provides a method of mounting an earth bracket to a mounting point on a railway vehicle, the mounting point having a coated surface, the method including: providing the self-preparing earth bracket according to the first aspect; and mechanical fastening the fastening fixture of the earth bracket to the mounting point such that the coat stripping arrangement of the fastening fixture strips the coat from the surface of the mounting point to achieve an electrical connection between the earth bracket and the railway vehicle at the fastening fixture. The invention includes the combination of the aspects and following optional features, except where such a combination is clearly impermissible or expressly avoided. The connector may comprise a first channel (e.g. an aperture or slot) for receiving a first bolt, whereby a first nut threaded onto the first bolt tightens the terminal of the earthing cable to the earth bracket at the connector. The fastening fixture may comprise a second channel (e.g. an aperture or slot) for receiving a second bolt, whereby a second nut threaded onto the second bolt urges the coat stripping arrangement against the mounting point to strip the coat from the surface of the mounting point while simultaneously tightening the earth bracket to the mounting point at the fastening fixture. In general, it is important that the earth bracket remains tightly secured to the mounting point during vehicle operation, and in particular is able to resist becoming loose in a demanding vibration environment. Accordingly, a third nut can be threaded onto the second bolt to tighten against the second nut. In this case, one of the second and third nuts can have a convex portion which nests in a concave portion of the other of the second and third nuts when the nuts are tightened together. One of the convex and concave portions can then be eccentrically located relative to the other convex and concave portions, and the convex and concave portions can be shaped such that, on tightening the nuts together, a wedging force is exerted on the second nut that locks it in position. Such combinations of nuts are known commercially as Hardlocks™ and are available in the UK from Staytite Ltd. Conveniently, the mounting point on the railway vehicle can be a T-slot. Such slots may be formed, for example, on the bottom side of an underframe of the railway vehicle, e.g. running along the length direction of the vehicle. By using a T-slot as the mounting point, it is possible to avoid undesirable interventions which might otherwise be needed to form a suitable mounting point, such as drilling a hole into an existing part of the vehicle. A T-slot has a main slot portion and a neck portion. The aforementioned second bolt can thus have a head which is shaped and sized to allow it to pass through the neck portion to be received in the main slot portion, and then rotated through 90° to trap it in the main slot portion. The coat stripping arrangement may comprise one or more toothed surfaces which bite through the coated surface of the mounting point when urged thereagainst on mechanical fastening of the fastening fixture to the mounting point such that the teeth electrically connect with the railway vehicle at the mounting point. The teeth may take various forms. For example, a toothed surface may comprise parallel sharp-edged ridges which scrape the coat from the mounting point surface as they are driven across the surface perpendicularly to the direction of the ridges. In another example, the toothed surface may comprise an array of point teeth (e.g. diamond points of a knurled surface) which score through the coat as they are driven across the surface. Particularly when the mounting point on the railway vehicle is a T-slot, the earth bracket may have two toothed surfaces on opposite outwardly facing walls of the fastening fixture such that the toothed surfaces strip the coat from opposing sides of the neck portion of the T-slot. In this case, the aforementioned second channel can conveniently extend between the toothed surfaces. Thus when the second bolt is received in the second channel with a head of the second bolt trapped in the main slot portion of the T-slot, a length of the second bolt can then extend between the toothed surfaces through the neck portion of the T-slot. Preferably, the opposite outwardly facing walls of the fastening fixture are angled relative to each other (e.g. in the range 15° to 25°) such that they form a wedge which urges the toothed surfaces against the sides of the neck portion as the fastening fixture is secured at the T-slot. Conveniently, the earth bracket may be substantially L-shaped, the connector being formed on a first arm of the L, and the fastening fixture being formed on a second arm of the L. For example, the first arm may be a relatively long arm, and the second arm a relatively short arm. Conveniently, the earth bracket may be formed of aluminium alloy, such alloy being corrosion resistant and electrically conductive (as well as light, strong and cost effective). The earth bracket may be plated or anodised, e.g. for additional corrosion protection while maintaining electrical conductivity. The earth bracket may be formed by casting or machining. Summary of the Figures Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which: Figure 1 shows a transverse cross-section through an underframe 1 of a railway vehicle car body; Figure 2 shows a perspective view of a special bolt which can be used to mount equipment to a T-slot of an underframe; Figure 3 shows a perspective view of a self-preparing earth bracket; Figure 4 shows a cross-sectional view through a T-slot, a special bolt and a fastening fixture; Figure 5 shows a perspective view of the T-slot and the special bolt of Figure 4 with the fastening fixture in wireframe; Figure 6 shows a perspective view from above of the T-slot, the special bolt and the fastening fixture of Figure 4 with the rest of the underframe removed; Figure 7 shows a cross-sectional view on plane A of Figure 3; and Figures 8A and 8B show schematically close-up views of three successive teeth ridges in region B from Figure 7 for respectively two configurations of the teeth. Detailed Description of the Invention Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference. Figure 1 shows a transverse cross-section through an underframe 1 of a railway vehicle car body. The underframe is formed by friction stir welding together a number of aluminium alloy extrusions along the length of the frame. The resulting underframe has top 2 and bottom 3 panels with braces 4 extending therebetween, and plural T-slots 5 running the length of the vehicle which project from the bottom side of the frame. Each T-slot has a main slot portion 5a and a narrower neck portion 5b for providing access to the main slot portion. After manufacture, the entire bottom side of the underframe, including the T-slots, is coated with protective film or paint. Figure 2 shows a perspective view of a special bolt 6 which can be used to mount equipment at any position along the T-slots 5. The bolt has a head 6a and a thread 6b extending therefrom. The head has a rectangular cross-section which is shaped and sized so that when it is rotated with the long direction of the rectangle parallel to the slot extension direction the head can pass through the neck portion 5b of a T-slot into the main slot portion 5a, and when rotated with the long direction of the rectangle perpendicular to the slot extension direction the head is prevented from leaving the main slot portion. Figure 3 shows a perspective view of a self-preparing earth bracket 7 for mounting to the railway vehicle at T-slots 5 which advantageously avoids a need to weld an earth tab to the underframe 1. The bracket is substantially L-shaped. A connector in the form of a hole 8 is formed in a first one 7a of the arms of the L-shape. In use the hole receives a bolt, whereby a nut threaded onto the bolt can be used to tighten a terminal of an earthing cable to the earth bracket so that the cable is electrically connected to the bracket. The second arm 7b of the L-shape carries a fastening fixture 9 for mechanical fastening the bracket to the T-slot. In particular, the fastening fixture provides a further hole 10 which penetrates through the second arm and receives the thread 6b of the special bolt 6 when the head 6a of the bolt is held in the T-slot. The lateral dimension of the main body of the second arm is such that it cannot enter the T-slot’s neck portion 5b. However, the fastening fixture also provides a narrower projection 11 from the top side of the second arm which does slot through the neck portion, albeit while making close contact with the sides of the neck portion. This projection is shaped as a wedge and has toothed surfaces 12 at opposite outwardly facing walls which are configured to strip the protective coat from the sides of the neck portion, as described in more detail below. A transverse slot 15 in the projection 11 is sized to receive the special bolt’s head 6a. A nut system, also described in more detail below, threaded onto the special bolt’s thread 6b keeps the bracket securely fastened to the T-slot. Figures 4 to 6 show the bracket 7 secured to the T-slot 5 so that the first arm 7a providing the hole 8 projects downwards from the underframe 1. More particularly, Figure 4 shows a cross-sectional view through the T-slot 5, the special bolt 6 and the fastening fixture 9; Figure 5 shows a perspective view of the T-slot 5 and the special bolt 6 with the fastening fixture in wireframe; and Figure 6 shows a perspective view from above of the T-slot 5, the special bolt 6 and the fastening fixture 9 with the rest of the underframe 1 removed. The nut system which threads onto the thread 6b is formed by a Hardlock™ arrangement in which a proximal nut 13 closest to the fastening fixture 9 has a convex portion which nests in a corresponding concave portion of a distal nut 14. In use, the proximal nut is firstly tightened onto the thread 6b to secure the bracket to the T-slot 5, and then the distal nut is tightened onto the proximal nut to lock it in place. The concave portion of the distal nut is coaxial to the thread 6b, while the convex portion of the proximal nut is eccentrically arranged. This, along with complimentary wedging surfaces at the perimeters of the convex and concave portions, causes a wedging force to be exerted on the proximal nut 13 that urges it upwards against the thread 6b and prevents it become loose in the demanding vibrational environment that the railway vehicle experiences in operation. The T-slot’s neck portion 5b has parallel-sided walls. In contrast, and referring to Figure 7 which shows a cross-section through the first arm 7a of the bracket 7 on plane A of Figure 3, at least a portion of the side walls of the projection 11 which carry the toothed surfaces 12 are angled relative to each other (in this case at about 19°) such that this portion of the projection enters the neck portion 5b as a wedge which urges the toothed surfaces 12 more tightly against the sides of the neck portion as the proximal nut 13 is progressively tightened onto the thread 6b. More particularly, for ease of initial location a leading portion 11a of the projection is sized to pass through the neck portion 5b without interfering with the sides of the neck portion. A trailing portion 11b of the projection then provides the angled side walls carrying the toothed surfaces, the angled side walls progressively driving the toothed surfaces into closer engagement with the sides of the neck portion as the projection is forced deeper into the T-slot 5. With further tightening of the nut 13, eventually abutment surfaces 16 on the first arm 7a to either side of the projection reach the T-slot and prevent further progression of the projection into the slot. The teeth of the toothed surfaces are parallel, sharp-edged ridges extending along the length direction of the T-slot. The projection 11 thus forms a coat stripping arrangement in which the teeth scrape off the film or paint on the walls of the neck portion as they are driven across their direction of extension into tighter engagement with these walls. The intimate contact between the fastening fixture 9 and the metal of the T-slot 5 thus-produced is a self-preparing electrical connection between the bracket 7 and the underframe 1 which is robust enough to serve as a reliable earthing path for the earthing cable connected at the hole 8. Conveniently, the bracket 7 can be formed of aluminium alloy for corrosion resistance, electrical conductivity, lightness, strength and cost effectiveness. If necessary, the bracket can be plated or anodised for additional corrosion protection, as long as adequate electrical conductivity is maintained. The bracket can be formed by casting or machining. In variants of the bracket 7, the teeth, instead of being parallel, sharp-edged ridges, can be an array of point teeth (e.g. diamond points of a knurled surface) which score through the film or paint as they are driven across the walls of the neck portion 5b. Such stripping of the surface coat from the neck portion can also produce an intimate contact between the fastening fixture 9 and the metal of the T-slot that may serve as a reliable earthing path. Experimental Visual inspections performed after self-preparing earth brackets like the one described above were removed from T-slots suggested that they are reliably capable of stripping paint and film coats from the neck portions of the slots. Figures 8A and 8B show schematically, for two of these brackets, respective close-up views of three successive ridges of the teeth in the region B of one of the angled side walls from Figure 7. Each tooth has a leading side 17a and a trailing side 17b, the leading side making an elevation angle a to the plane N normal to the insertion direction D of the projection 11 into the T-slot 5. In Figure 8A a is shown at about 16°, and in Figure 8B it is shown at 0°. The visual inspections indicated that best paint stripping results were obtained with an angle a in the range from 0° to 25°. Therefore, as a proof of concept, another self-preparing earth bracket (with teeth formed by parallel, sharp-edged ridges) was secured to a T-slot of a railway vehicle underframe and used as an earth for MIG welding equipment, the conventional earth clamp of the equipment being attached to the downwardly projecting first arm 7a of the bracket. A weld was then created on the car body of the vehicle at a location approximately 2 m distant from the bracket, the positive side of the welding circuit being the weld torch, and the negative side of the circuit being completed by the attachment of the earth clamp to the bracket. A resistance check showed that the earthing via the bracket was sufficient. The welding equipment operator completed the weld satisfactorily, with no increase in temperature at the earth clamp and bracket suggesting the earthing resistance stayed low for the entire process. *** The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations. Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / -10%.

Claims

1. A self-preparing earth bracket (7) for mounting to a railway vehicle, the earth bracket having: a connector configured for electrical connection thereto of a terminal of an earthing cable, and a fastening fixture (9) configured for mechanical fastening to a mounting point on the railway vehicle, the mounting point having a coated surface;wherein the fastening fixture (9) includes a coat stripping arrangement which is configured such that on mechanical fastening of the fastening fixture to the mounting point the coat stripping arrangement strips the coat from the surface of the mounting point to achieve an electrical connection between the earth bracket (7) and the railway vehicle at the fastening fixture.

2. The earth bracket according to claim 1, wherein the connector comprises a first channel (8) for receiving a first bolt, whereby a first nut threaded onto the first bolt tightens the terminal of the earthing cable to the earth bracket at the connector.

3. The earth bracket according to claim 1 or 2, wherein the fastening fixture comprises a second channel (10) for receiving a second bolt, whereby a second nut (13) threaded onto the second bolt urges the coat stripping arrangement against the mounting point to strip the coat from the surface of the mounting point while simultaneously tightening the earth bracket to the mounting point at the fastening fixture.

4. The earth bracket according to any one of the previous claims, wherein the mounting point on the railway vehicle is a T-slot (5).

5. The earth bracket according to any one of the previous claims, wherein the coat stripping arrangement comprises one or more toothed surfaces (12) which bite through the coated surface of the mounting point when urged thereagainst on mechanical fastening of the fastening fixture (9) to the mounting point such that the teeth electrically connect with the railway vehicle at the mounting point.

6. The earth bracket according to claim 5 as dependent on claim 4, and having two toothed surfaces (12) on opposite outwardly facing walls of the fastening fixture (9) such that the toothed surfaces strip the coat from opposing sides of a neck portion (5b) of the T-slot (5).

7. The earth bracket according to claim 6, wherein the opposite outwardly facing walls are angled relative to each other such that they form a wedge which urge the toothed surfaces (12) against the sides of the neck portion (5b).

8. The earth bracket according to any one of the previous claims, which is substantially L-shaped, the connector being formed on a first arm (7a) of the L, and the fastening fixture (9) being formed on a second arm (7b) of the L.

9. The earth bracket according to any one of the previous claims, which is formed of aluminium alloy.

10. A railway vehicle including:a mounting point, and5 the self-preparing earth bracket (7) according to any one of the previous claims, wherein thefastening fixture (9) is fastened to the mounting point such that a coated surface of the mounting point is stripped therefrom by the coat stripping arrangement to achieve an electrical connection between the earth bracket and the railway vehicle at the fastening fixture.

11. The railway vehicle according to claim 10, wherein an earthing cable is electrically connected to 10 the connector of the earth bracket.

12. A method of mounting an earth bracket to a mounting point on a railway vehicle, the mounting point having a coated surface, the method including:providing the self-preparing earth bracket (7) according to any one of claims 1 to 9; andmechanical fastening the fastening fixture (9) of the earth bracket to the mounting point such that15 the coat stripping arrangement of the fastening fixture strips the coat from the surface of the mounting point to achieve an electrical connection between the earth bracket and the railway vehicle at the fastening fixture.AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS:-10Claims:

1. A self-preparing earth bracket (7) for mounting to a railway vehicle, the earth bracket having: a connector configured for electrical connection thereto of a terminal of an earthing cable, and a fastening fixture (9) configured for mechanical fastening to a mounting point on the railway vehicle, the mounting point having a coated surface;wherein the fastening fixture (9) includes a coat stripping arrangement which is configured such that on mechanical fastening of the fastening fixture to the mounting point the coat stripping arrangement strips the coat from the surface of the mounting point to achieve an electrical connection between the earth bracket (7) and the railway vehicle at the fastening fixture; andwherein the fastening fixture comprises a second channel (10) for receiving a second bolt, whereby a second nut (13) threaded onto the second bolt urges the coat stripping arrangement against the mounting point to strip the coat from the surface of the mounting point while simultaneously tightening the earth bracket to the mounting point at the fastening fixture.

2. The earth bracket according to claim 1, wherein the connector comprises a first channel (8) for receiving a first bolt, whereby a first nut threaded onto the first bolt tightens the terminal of the earthing cable to the earth bracket at the connector.

3. The earth bracket according to any one of the previous claims, wherein the mounting point on the railway vehicle is a T-slot (5).

4. The earth bracket according to any one of the previous claims, wherein the coat stripping arrangement comprises one or more toothed surfaces (12) which bite through the coated surface of the mounting point when urged thereagainst on mechanical fastening of the fastening fixture (9) to the mounting point such that the teeth electrically connect with the railway vehicle at the mounting point.

5. The earth bracket according to claim 4 as dependent on claim 3, and having two toothed surfaces (12) on opposite outwardly facing walls of the fastening fixture (9) such that the toothed surfaces strip the coat from opposing sides of a neck portion (5b) of the T-slot (5).

6. The earth bracket according to claim 5, wherein the opposite outwardly facing walls are angled relative to each other such that they form a wedge which urge the toothed surfaces (12) against the sides of the neck portion (5b).

7. The earth bracket according to any one of the previous claims, which is substantially L-shaped, the connector being formed on a first arm (7a) of the L, and the fastening fixture (9) being formed on a second arm (7b) of the L.

8. The earth bracket according to any one of the previous claims, which is formed of aluminium alloy.

9. A railway vehicle including:a mounting point, andthe self-preparing earth bracket (7) according to any one of the previous claims, wherein the fastening fixture (9) is fastened to the mounting point such that a coated surface of the mounting point is5 stripped therefrom by the coat stripping arrangement to achieve an electrical connection between the earth bracket and the railway vehicle at the fastening fixture.

10. The railway vehicle according to claim 9, wherein an earthing cable is electrically connected to the connector of the earth bracket.

11. A method of mounting an earth bracket to a mounting point on a railway vehicle, the mounting10 point having a coated surface, the method including:providing the self-preparing earth bracket (7) according to any one of claims 1 to 8; andmechanical fastening the fastening fixture (9) of the earth bracket to the mounting point such that the coat stripping arrangement of the fastening fixture strips the coat from the surface of the mounting point to achieve an electrical connection between the earth bracket and the railway vehicle at the15 fastening fixture.

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