GB2373712A

GB2373712A - Frangible fixing for traffic light

Info

Publication number: GB2373712A
Application number: GB0107825A
Authority: GB
Inventors: Smith Philip Andrew Forrest; Miles Steven Wills; Keith Manston; David Antony Martin
Original assignee: Siemens PLC
Current assignee: Siemens PLC
Priority date: 2001-03-29
Filing date: 2001-03-29
Publication date: 2002-10-02
Anticipated expiration: 2021-03-29
Also published as: GB2373712B; GB0107825D0

Abstract

A fixing for street furniture, eg a traffic light, includes three bushes 17,18,19 mounted on a common axis 22. Relative rotation between the bushes, after a desired position has been selected, is prevented by projections 37 on bush 19 engaging recesses 24 on bush 17. The projections are narrower than the separations between the recesses whereby in the event of an impact, eg from a vehicle, the projections are broken and relative rotation is permitted. Repair hence necessitates replacing only the bush 19. A projection 39 on bush 19 engages arcuate recess 32 in bush 18 to allow arcuate adjustment of the fitting (see Figure 2).

Description

Sacrificial Location Mechanism

This invention relates to a sacrificial location mechanism, particularly, but not exclusively for use on street or highway furniture.

Street furniture is a term used to encompass items that are often placed in public places. Typically they are placed by municipal or transport infrastructure authorities. Such items include signs for directing traffic, traffic lights and barriers. In the case of items, which are placed near roads, it is necessary that they be designed with safety in mind. In particular, thought has to be given to what would happen in the event of a collision between a vehicle and indeed a rider or occupant of the vehicle with the item. Unfortunately, even a minor collision can result in damage to the street furniture that necessitates its complete replacement. Such replacement is often expensive and time consuming.

The prior art figure shows a typical traffic signal arrangement in which a light cluster formed of light-box modules is mounted via brackets to a pole. The lower bracket is provided with a lug which engages a track attached to the light cluster. This enables alignment movement prior to

tightening of the fixing bolts. The angle of tilt relative to the pole is achieved by applying forward or rearward pressure to an upper end of the light box and then tightening the bolts. Such alignment is required in order that the lights have the correct alignment to be viewed by roadusers. Unfortunately, this in effect"shortens"the light cluster in a vertical plane causing stress to the fixings and to the light cluster itself.

The stress applied to the light cluster tends to cause the modules to separate, at least partially. The alignment is also further adjusted by rotation of the light relative to the bracket about an axis of the fixing bolts. When the alignment is judged to be correct the bolts are tightened. The torque that the bolts are tightened to is difficult to judge.

It has to be sufficient that there is no subsequent movement due to wind or vibration or other environmental factors and yet permit some movement when struck by, for instance, a passing lorry. This requirement is further complicated by the range of temperatures that the bolts encounter with the passage of the seasons. Thermal expansion may cause a fixing which is firm in the winter months to become inadequately loose in the summer months.

The natural temptation is, of course, for service personnel to over tighten the bolts and when struck the light cluster is damaged through failure of the light to pivot about the bolts.

The invention arose from a desire by the inventors to alleviate, at least partially, the problems caused by prior art fixings.

According to the invention there is provided a fixing for fixing first and second parts of an assembly which fixing comprising a first bush for location at the first part of the assembly, a second bush for location at the second part of the assembly and a third bush for location at a position intermediate therebetween which bushes, in use, being colocated on an axially extending fastener for retaining the assembly together, and a set of mutually engaging members provided on the bushes to prevent relative rotation therebetween which members being at least in part frangible to enable breakage when subjected to a predetermined load to permit relative motion therebetween.

By providing, a set of engaging members being frangible when subjected to a pre-determined load the fixing can provide secure

retention of the assembly until an excessive load is encountered. When such a load is encountered at least part of the frangible mutually engaging members break disengaging the arrangement and permitting the assembly members to move.

Preferably, the mutually engaging members are a set of at least one complimentary projection and recess provided on the bushes which projection engaging the recess to prevent relative rotation of the bushes.

Whilst, one projection and complimentary recess may suffice in some arrangements, preferably a plurality of recesses is provided. By providing a number of recesses, the arrangement will permit the "locking"of the relative angular positions of the bushes, and hence the relative positions of the assembly parts, at more than one location. In the preferred embodiment, a plurality of projections are provided to engage the recesses.

In the preferred embodiment, the projections are formed on one of the bushes and the complimentary recesses form on another although it may be desirable in some arrangements to provide recesses and projections

on more than one of the bushes to permit engagement with complimentary recesses and projections on another of the bushes.

It is preferred, that the frangible part of the mutually engaging members is formed on one bush to engage with the other part on another bush.

This is preferred since, in the event of a collision or impact only one of the bushes requires replacement.

In the preferred arrangement more than one set of mutually engaging members are provided to prevent relative rotation of any of the bushes.

In the specific embodiment, there is provided on the first bush a first recess, on the second bush there is provided a plurality of recesses, on the third bush, a first projection for engaging the first recess to prevent relative rotation of the of the first and the third bush and a second set of projections for engaging the plurality of recesses on the second bush for preventing relative rotation of the second and the third bush. In this embodiment the second set of projections is rendered frangible and in the event of a collision, or other overload situation, it is these projections that fail first thus, releasing the arrangement.

The manner in which the frangible nature is achieved may be through the use of different materials, one relatively weaker than the other, the relative dimensions of the members, the formation of weaknesses by, for example, moulding in weaknesses or later operations. In the preferred embodiment, the dimensions of the projections are chosen to be, in terms of breadth, less than the breadth of walls defining the complimentary recesses.

Many materials may be used for the bushes but the preferred material is glass-reinforced nylon because of its moulding capabilities, permitting the formation of the projections and recesses, and its strength.

Bearing surfaces are preferably provided to reduce the frictional contact area between the bushes to ensure relative rotational movement therebetween in the event of the breaking of the mutually engaging members.

A specific embodiment of the invention will now be described by way of example only, with reference to the drawings in which: Figure 1 is a prior art figure;

Figure 2 shows a fixing in accordance with the invention being used to fix a traffic light cluster to a pole ; Figure 3 is shows a fixing prior to assembly; and Figure 4 shows an end view the fixing in assembled form.

With reference to figure 2, a pair of fixings 1 and 2 for attaching a traffic signal light box 3 to a metal post 4 is shown. The lighting box 3 comprises a set of light-box modules 3a to 3c which interconnect by mean of lugs and recesses generally indicated at 5 and 6. The modular approach confers the advantage of the enablement of the formation of a number of different light box configurations from these basic modules.

The material primarily used in the construction of the modules is a plastics material chosen for its moulding properties.

The metal pole 4 is formed as a tube of steel coated dipped in an anticorrosion paint and the lower end is provided with a bar 7. The bar 7 keys the post 4 into a concrete filled hole 10 when the traffic light is erected. Fixings in the form of anchor bolts, two of which, 8 and 9 can be seen, secure the footplate to a concrete base 10.

Two"L"shaped steel brackets 11 and 12 hold the light box 3 via the fixings 1 and 2 to the post 4. The brackets are held to the post by bolts 13 which pass through slotted holes in the brackets to permit some latitude for adjustment of the vertical position before the bolts are tightened and to cater for tilting of the light box 3 relative to the post 4.

The fixings are attached to the other arm of the brackets 11 and 12 by bolts 14 and 15.

The fixing 1 is shown in disassembled form in Figure 3a and 3b and it comprises three bushes moulded from glass reinforced nylon; a first bush 17, a second bush 18 and a third bush 19. The first bush 17 is generally circular in plan-form having a raised cylindrical land 20 the sidewalls of which are blended into an end wall which provides a generally flat bearing surface 21. In the figure, a lower portion of the first bush 17 extends in a direction away from an axis 22 of the fixing 1 to form a circumferentially extending waist 23. The waist 23 is provided with integrally moulded recesses 24 as is more clearly shown in the enlarged proportion of the figure. The recesses have a width x which is smaller than the width y of the defining walls. As will be later described, these recesses 24 are designed to accept projections or teeth

to prevent relative rotation of the bushes ; the teeth and the recesses being mutually engaging members.

The bush 17 is also provided with integrally moulded circumferentially spaced apart fixing lugs 25 which, by means of through bolts, enable it to be fixed to the light box 3, and a threaded insert 26.

The second bush 18 is a generally rectangular box shape an end view of which is apparent in figure 3c and a side view is apparent in figure 3b.

The major sides 27 are wedge-like in configuration extending and narrowing from a first end face 28 to a second end face 29. The upper line of the face 27 (upper in the sense of the figure) is a generally straight line 30. The lower defining line has two distinct portions, a first portion extending for just under half of the length being an arcuate bearing surface 31 and a second portion extending for just over half of the length being a generally straight line 32 and thus forming an arm.

As is most clearly shown in the view of the end face 28 a rebate 32 is formed in the end face 28 and extends in an arcuate manner corresponding to the arcuate lower line 31 in spaced apart relationship

thereto. The arcuate nature of the rebate 32 is shown in broken outline in figure 3b. As will be later described this rebate accepts a projection formed on the third bush 19.

A further recess is provided in the moulding process in order to accept a fixing bolt. This bolt recess 33 is shown in broken outline and it defines a"U"shaped channel open at the uppermost face as depicted in the drawing. The lower defining wall is arcuate to correspond in curvature to the lower arcuate surface 31. A slot is provided through the wall and into the rebate 32 over the arcuate length of the channel.

This slot takes the shank of a fixing bolt 45 of the type having a socket head as shall be later described and permits the bolt 45 to traverse the arcuate length of the slot.

The arm of the bush 18 is moulded to render it solid over its length (apart from through holes 34 provided to accept fixing bolts 14,15 to

attach the arm to the bracket 12, 11). The third bush 19 is moulded from glass-reinforced nylon to provide a generally cylindrical configuration with an upper end closed and a

lower end open. At a lower end of the sidewall is formed a circumferential wasted portion 35 that extends radially outwards. On a downwardly directed face 36 of the wasted portion a number of projections or teeth 37 are provided. These are configured to fit with the before mentioned recesses in the first bush 17.

An upper face 38 of the bush 19 is arcuate in a direction extending out of the plane of the paper. This matches the curvature of the lower line 31 of the second bush 18. A location lug 39 extends from the upper face in an axial direction away from the face 38. The location lug 39 also extends in a direction into the plane of the paper and is provided with an upper bearing face 40 which is arcuate having the same a matching curvature to that of the lower line 31 of the bush 18 to form a flattened arcuate crest. A hole 41 is provided in the crest to permit the passage of the fixing bolt 45.

A lower surface 42 of the end-wall of the bush 19 is shown in broken outline and it can be seen to have a downwardly directed boss 43. The boss 43 is centrally located about the axial through-hole. The flattened lower surface formed by the boss 43 is raised beyond the rest of the lower surface profile to provide a bearing surface when the fixing is assembled. It is necessary to reduce the contact area between the bushes in this way to ensure that relative rotational movement can take place therebetween in the event of an impact.

The fixing is assembled in the following manner. The bushes 17,19 and 18 are located and held together and the bolt 45 inserted through the assembly. The bolt 45 is then driven by an allen key to engage with the threaded insert 26. The bolt 45 is not fully tightened until the alignment is judged to be satisfactory.

The upper-most fixing differs to that of the lower one in that the intermediate bush 19 is provided without the projections 37. This means that rotational movement about the bolt 45 is permitted which assists the alignment and locking process that will now be described with respect to figure 2.

The brackets 11 and 12 are located and fixed to the post 4 using the bolts 13 and 14. The light-box 3 together with fixings is offered up to the brackets 11 and 12 and retained in place by the use of bolts 14 and

15 and corresponding nuts which are held captive in hexagonal recesses formed in the lower surface of the arm. A certain amount of play is available to permit the lifting of the light-box 3 to disengage the projections and recesses in the lower fixing. The light-box may then be rotated about an axis 46 to the required angular position before being lowered to engage the projections 37 into locking engagement with the recesses 24. The light-box 3 may then be tilted in the vertical plane by pushing the bottom to or away form the post. This results in the bolt 45 moving alone the arcuate surface of the retaining bolt recess 33. The movement is further facilitated by the matching arcuate surfaces 38 and 31.

When the alignment is satisfactory the bolt 45 is tightened to the required torque and the assembly is complete. One of the fixings is shown in the assembled form in figure 4 In the event of an impact, the sacrificial nature of the fixing will ensure that in most cases only the third bush 19 in the intermediate position will require replacement. The projections 37 prevent relative rotational movement until a force caused by a collision exceeds their physical

limits. The projections then snap to release the bushes 20 and 19. The light-box is then free to rotate under the impact forces saving further damage to other components.

The traffic light may then be repaired by replacement of the third bush alone.

The way in which the arrangement avoids imparting stresses to the light ..,., ng stresses t the light box when the inclination is varied is explained with reference to Figure 2. Variation of the line of sight 8 is achieved by pushing one end (bottom or top) of the light box 3 in or outwards relative to the post 4.

The arcuate faces 31 of the upper 1 and lower 2 fixing arrangement permit movement in the manner of the curved arrows. This movement enables the light modules 3a to 3c to remain in alignment. In prior art arrangements a bending moment would be applied to the box 3 which would tend to flex, opening up the joints between the modules.

Claims

Claims 1. A fixing, for fixing first and second parts of an assembly, which fixing comprising a first bush for location at the first part of the assembly, a second bush for location at the second part of the assembly and a third bush for location at a position intermediate therebetween, which bushes, in use, being co-located on an axially extending fastener for retaining the assembly together, and a set of mutually engaging members provided on the bushes to prevent relative rotation therebetween which members being, at least in part, frangible to enable breakage when subjected to a pre-determined load to permit relative motion therebetween.
2. A fixing as claimed in claim 1 wherein the mutually engaging members are a set of at least one projection and at least one recess provided on the bushes which projection and recess, in use, engaging to prevent relative rotation of the bushes.
3. A fixing as claimed in claim 2 wherein the at least one projection is formed on one of the bushes and the recess is formed on one of the other bushes.
4. A fixing as claimed in any one of claims 1 to 3 wherein one of the mutually engaging members is frangible.
5. A fixing as claimed in any preceding claim further comprising at least a second set of mutually engaging members.
6. A fixing as claimed in claim 5 wherein the first set of mutually

4A "LIL d engaging members is provided on the first and third bushes and the second set of mutually engaging members is provided on the second and third bushes.
7. A fixing as claimed in any preceding claim wherein the or at least one of the sets of mutually engaging members permits movement having a component in a direction substantially normal to the axis of rotation of the bushes.
8. A fixing as claimed in claim 7 wherein the second set of mutually engaging members comprises a projection provided on one of the second and third bushes for engaging a longitudinal recess provided on the other of the second bush and third bushes to permit relative

longitudinal movement therebetween whilst preventing relative rotational movement therebetween.
9. A fixing as claimed in claim 8 wherein the projection and recess are provided with arcuate bearing surfaces to permit arcuate relative movement of the bushes.
10. A fixing as claimed in any preceding claim wherein the bushes are glass-reinforced plastics material.
11. A fixing as claimed in claim 10 wherein the bushes are formed of glass-reinforced nylon.
12. A fixing as claimed in claims 10 or 11 wherein the projections and recesses are integrally formed.
13. A fixing as claimed in any preceding claim wherein the recesses of the mutually engaging members have a breadth which is smaller than their separation.
14. A fixing for fixing first and second parts of an assembly substantially as hereinbefore described with reference to and as illustrated by figures 2,3 or 4 of the drawings.
15. A fixing for fixing first and second parts of an assembly together comprising a first member coupled to the first part and a second member coupled to the second part which members including mutually engaging formations to prevent relative rotation therebetween which formations comprising a projection and a recess the recess permitting a range of movement in a direction at an angle to the axis of rotation.
16. A fixing as claimed in claim 15 wherein the mutually engaging formations permit arcuate movement.
17. A modular light signal apparatus comprising a plurality of light modules held together to form a light box; respective first and second fixings attached to respective ends on the light box to fix the light-box to an object wherein at least one of the fixings permits user selective arcuate movement of that end of the light-box relative to the object.
18. Apparatus as claimed in claim 17 wherein the at least one fixing comprises a fixing as claimed in any one of claims 1 to 16.
19. A modular light signal apparatus substantially as hereinbefore described with reference to and as illustrated by the drawings.