GB2030933A - Construction kits for trailers - Google Patents

Abstract

A kit comprises parts for a multipurpose trailer to be towed behind a motor car or a small commercial vehicle. The kit includes chassis members 52, 53 such that trailers may be constructed in which the distance between the towing hitch 54 and the trailer wheels 49 may be varied. The kit also includes a plurality of load receiving means e.g. 46 or 64, 65 for selective attachment to the chassis members so that at least two trailers, such as a boat trailer and a camp box trailer, may be constructed. <IMAGE>

Description

SPECIFICATION Improvements relating to trailers This invention relates to trailers and in particular trailers intended to be towed behind a motor car or a small commercial vehicle, such trailers being for use for such purposes as transporting boats, livestock, motor vehicles or camping equipment.

Such trailers are fitted with either a single pair of wheels or with two pairs of close coupled wheels. In either case the wheel axles will be located at the approximate centre of mass-of the load. These designs are tobe distinguished from the large and costly trailers produced for commercial purposes and which incorporate a steerable axle or a "fifth wheel" towing attachment. In the latter cases balance problems are relatively insignificant, the load being disposed between the various axles or between the axles and the fifth wheel.

Known trailers of the type with which the present invention is concerned are generally intended to fulfil only a single function as, for example, goods box trailers.

According to the present invention there is provided a kit of parts for a multi-purpose trailer, the kit comprising at least one pair of wheels, chassis members including means for attaching an assembled trailer to a towing vehicle and a plurality of load receiving means for attachment to the chassis members, the chassis members being such that trailers may be constructed in which the distance between said attachment means and the at least one pair of wheels may be varied.

The chassis members may be such that a plurality of chassis may be constructed having different lengths. Alternatively or additionally said distance may be varied by providing an axle, the position of which is capable of being adjusted longitudinally of the chassis.

The present invention also provides a trailer formed from a kit of parts of the invention.

Also provided by the present invention is a method of making a trailer from a kit of parts of the invention, the method comprising combining chassis members to form a chassis, locating the or each pair of wheels on the chassis and locating a selected load receiving means on the chassis.

Adjustable axle trailers are known in connection with boat trailers in which a friction or clamping arrangement between the axle and the central spine or towbar of the trailer permits boats having different lengths to be accommodated on a single chassis without upsetting trailer balance or creating any unnecessary chassis protrusion ahead of or behind the load. However, such a trailer is designed only to carry boats and, by contrast with the present invention, is a single purpose trailer in that it serves a single main function not withstanding that it can be used to carry various boats of different sizes and weights.

By contrast the term "multi-purpose trailer", as used herein, is a trailer designed to fulfil two or more roles. Accordingly the superstructurès are designed in such a way as to be readily interchangeable.

A trailer formed from a kit of parts in accordance with the present invention is intended to be towed behind, but is detachable from, a motor vehicle.

The motor vehicle will provide the main locomotive power four both. In the sense in which the term will be used here, a trailer will comprise at least one pair of wheels, an adequate method of wheel suspension, mudguards, a chassis, a towhitch,any legally required lighting arrangements and identification marks and a load receiving superstructure to which a load may be added.

A towhitch is a device used to connect the trailer to the towing vehicle. Most commonly, for the sizes of trailer under consideration, this will connect with a standard 50 mm diameter ball fitting on the towing vehicle.

As used herein the term "chassis" means at least one substantially transverse load bearing member which will serve to locate the wheel suspension arrangements and hence the wheels relatively with one another and at least one substantially longitudinal load bearing member which will serve to locate the wheels relative to the towhitch.

Any substantially transverse load bearing member serving to space a pair of wheels will be referred to alternatively as an axle. Any single purely longitudinal part of the various substantially longitudinal members comprised in a chassis will be referred to, alternatively, as a spine or towbar.

As used herein the term trailer width will refer to the maximum overall width of a trailer including any contribution from an overhanging load. It will not generally be necessary to provide a separate adjustment facility in this regard in order to achieve a satisfactory multi-purpose trailer design.

In all cases it will be desirable to minimise the overall length of any trailer, commensurate with the dimensions of the load to be transported, thereby minimising obstruction to other road users and retaining maximum manoeuverability. This can be achieved by adjusting the location of any transverse axle relative to the towhitch provided that the proportionate change in load length is not too great. However, where the proportionate change in load length is considerable it will be seen that there will be a hazardous protrusion of any fixed length chassis either ahead of or behind the shortest load to be accommodated. There would thus be severe limitations on the usefulness of any multi-purpose trailer design incorporating a chassis of fixed length. However, a multi-purpose trailer will be more costly to produce than will a corresponding single purpose arrangement.

In consequence, the broadest possible specification will be drawn and hence a variable length chassis will be required.

The degree of variation in terms of chassis length allowed by any particular design will depend upon a judicious selection amongst various factors which will limit an otherwise desirable broad general specification in terms of sizes and weights to be carried. Amongst the factors to be considered will be constraints arising as a result of the necessity to cut expensive structural materials as economically as possible, the stress-raising properties of any joints or connections to be made in load bearing members, various legal requirements which may differ between countries and the dimensions and cost of the structural materials to be employed. The last factor will generally be defined by the most stressful condition arising. Clearly, it would be both inconvenient and uneconomic to draw the broadest possible specification in terms of, say, load capacity without regard to other factors.

For trailers in the large commercial field variable length chassis have been proposed in order to limit the unloaded size of very long trailers. More stringent limitations are imposed on the designer working in the area of the small multi-purpose trailer, as here. In the large commercial area the designer might reasonably expect any required adjustments to be carried out by trained operatives considerable forces could be applied as necessary to achieve the required transformation, the cost of the equipment wou Id be a much less limiting factor and balance would be less important.

As mentioned above, it is possible to achieve a variation in the distance between the towhitch and the wheels by means of variation of the chassis length or adjustment of the axle position, or both. It is preferred that the chassis length be variable. However, in some instances it might be desirable to retain the adjustable axle facility in a variable length chassis, multi-purpose trailer. Such a facility may be desirable, for example, to aid fine balancing or for convenience in storage or transport. Although more costly to produce, the variable length chassis trailer is more convenient in use as a boat trailer than such a trailer in which only the axle position may be adjusted, since the latter requires a relatively unsatisfactory trial and error method to achieve balance.

By means of adjustment of axle position above, the length of the load to be accommodated may be allowed to vary in a ratio of approximate two to one, greatly increasing the usefulness of a given trailer chassis. However, for a multipurpose design, the load lengths might be expected to vary in the range three to one and upwards. Thus a balanced multi-functional design or minimum overall length would normally require variability of the length of the chassis.

There are five ways of achieving the desired variability in terms of chassis length: by providing interchangeable main chassis members, by providing interposable or foldabie elements in main chassis members and by providing telescopable or relatively slidable main chassis members. A sub-species of the first design will be an arrangment based on a standard axle and supplied with a permanently attached towbar or with permanently attached primarily longitudinal structural members, the lengths of which were made variable at the manufacturing stage only.

Such a design would have production and cost advantages over conventional designs by virtue of greater standa rdisation (standard single purpose arrangements use different chassis designs for different purposes). By way of example, the five approaches identified will be compared with one another and with a conventional adjustable axle boat trailer.

Embodiments of the present invention will now be described, by way of examples only, and with reference to the accompanying drawings, in which: Figure 1 shows, in outline, the chassis fora typical small adjustable boat trailer, Figure 1A representing the chassis in its fully extended condition and Figure 1 B the same chassis with the axle adjusted into a forward location. The towhitch 1, axle 2 and wheels 3 are shown in a conventional manner. The towbar 4 may be adjusted relative to the axle 2 and to lightweight drag links 5, these drag links 5 serving only to stiffen the attachment between the towbar4 and the axle 2.

Where a correct trailer balance is achieved, the centre of mass of the applied load will be located slightly ahead of the wheel centres. The centre of mass of a boat will typically be located aft of centre. Thus it will be seen that the situation represented in Figure 1, whereby the longitudinal dimension between the wheel centres and the towitch in Figure 1 B is half that of Figure 1 A, represents an optimistic appraisal of the available range of adjustment using this design. A similar proportionate change has been introduced into the succeeding Figures 2 to 7 inclusive, which refer to variable length chassis designs. It will be seen that a similar limitation will not apply to these designs.

As such they are capable of accepting a greater range of load lengths and would be suitable for application in a multi-purpose role.

Figures 2 and 3 show two different variable length chassis designs making use of interchangeable longitudinal chassis elements.

The items shown as 1, 2, 3 and 5 have already been described. Parts 5 will be unnecessary in connection with the design of Figure 3. A long towbar 4A is shown installed in the arrangement of Figure 2A, to be replaced by a shorter element 4B in the Figure 2B. Also interchangeable, but now only substantially longitudinal chassis members 4A and 4B perform similariy in the case of the design of Figure 3.

Adjustability in terms of axle location may be incorporated into the designs of Figures 2 and 3 if required. In certain circumstances it might be convenient to incorporate parts such as 4A and 4B into the design of any removable load receiving superstructure. Whilst recognising this practical alternative, such integration will not be illustrated here in the interests of clarity.

Figures 4 and 5 outline two alternative variable length chassis designs in these cases making use of interposed or foldable towbar elements to control chassis length. Items 1, 2, 3 and 5 have already been identified. In these cases items 6 and 7 represent separate basic chassis elements and 8 an interposed part. The parts 6, 7 and 8 are connected through the joints 9. Any generally useful multi-purpose trailer design will provide members 8 in lengths appropriate to the various projected applications. It will be seen that the parts 8 represent the simplest possible embodiment of a range of practical alternatives and that the parts 7 and 8 might be combined reducing the number of joints 9 required.It should also be noted that an interposed chassis member, such as 8 could be of a folding construction which would again achieve the required control and in which case the design of the joints 9 would be different.

Figures 6 and 7 exemplify two alternative variable length chassis designs using telescopic or relatively sliding spinal elements. Items 1, 2, 3 and 5 are in common with the foregoing. Items 10 represent outer telescoping members and items 11 the inner parts,. In either case reliable joints 13 will be required to connect the parts 10 and 11.

Without loss of generality these designs could incorporate two or more telescopic pairs arranged either in parallel or in series. Furthermore it will be seen that the parts 10 and 11 will not necessarily penetrate one another axially, they might equally overlap, in which case a sliding joint 13 would be required.

All the examples cited relate to trailer designs having only a single pair of wheels, whilst many small trailers make use of four wheels mounted in close coupled pairs. It will be apparent that the design problems arising in the latter cases will be similar and that the fundamentals laid down here will be appropriate.

Some observations follow concerning the relative merits of the various chassis designs exemplified in Figures 2 to 7 inclusive: designs such as those of Figures 3, 5 and 7 incorporate fewer separate parts than do the parallel alternatives 2, 4 and 6, by virtue of the stiffening parts 5. However, the members 5 will be of a relatively light construction and the total cost of a chassis incorporating such elements will probably be less than alternatives. It would also be possible to dispense with parts 5 in some cases, for example, in smaller sizes. The designs of Figures 2 and 3 will generally be rather less convenient in use than others in that they would require interchanging or replicating the towhitches 1. A similar comment applies in regard to the designs of Figures 4 and 5 where the parts 7 and 8 are integrated.The designs of Figures 6 and 7, whilst more costly, would be more convenient in use, requiring no separate elements. A foldable design as exemplified by Figures 4 or 5 will generally prove more expensive than will an alternative interposable arrangement. A sliding configuration according to Figures 6 or 7 will generally be cheaper but less adequate structurally than will a corresponding telescopic design. In all cases involving the use of joints or connections in main structural members, great care should be taken to ensure that adequate safety fetures are retained in the fatigue environment. It will generally be found that a sufficiently broad range of applications for the multi-purpose trailer will result from only a limited range of chassis lengths.It will usually be found sufficient to provide only three interchangeable chassis members in connection with the designs of 2 or 3, two different interposed chassis members for the arrangement of Figures 4 and 5 or only a single telescoping or sliding element for the designs of Figures 6 or 7.

The adjustable trailer design of Figure 1 will require detachable connections at the intersections between the spine and the axle and between the spine and the drag links. U-shaped bolts are used at these locations in the boat trailer field, the only known current application. Identical attachment methods would be appropriate to the designs of Figures 2 or 3 and could be used in connection with the arrangements of Figures 4 to 7 inclusive where disassembly or adjustabiiity was required. Otherwise permanent attachment would be satisfactory in the latter cases. Since, at most, a relatively limited degree of adjustability would be required in connection with variable length chassis, more satisfactory joint designs become practical, in particular, devices yielding positive locking would be preferable. The requirements of any such design are reliable, tamper proof operation.Although stresses on the joints will generally be low, design features inducing enhanced stresses would be avoided.

Many different designs would meet the specified objectives. For example, see Figure 8, which arrangement would be appropriate to the designs of Figures 2, 4 or 6, or, with minor modification, to those of Figures 3, 5 or 7. Here 14, identifies an axle member, 1 5 a drag link and 16 a spinal part. Drilled brackets 17, welded to 1 4 and 1 8 and 19, welded to 16, together with setscrews 20 permit limited adjustment of 14 and 1 5 relative to 1 6. Where neither adjustability nor disassembly was required permanent attachment, for example by welding, would become practical.

Joints in the length of main structural chassis elements, as for example those identified at 9, in Figures 4 and 5 or at 13 in Figures 6 and 7, represent a new design problem arising out of the introduction of a variable length chassis. As such they deserve attention here. Certain essential elements can be identified: these joints, being located in zones of high stress, must be strong and stress-raising must be minimised. Any failure in a main chassis member would be disastrous. This positive locking is to be required to guard against the possibility of misuse. The joint should be easy to adjust. Thus, with locking devices removed, no great skill or force should be required to change the chassis length despite weathering. The joint should be tamper proof to the extent that it would resist children and deter vandals.Hence locking devices designed for convenient removal are to be avoided, arrangements requiring tools are to be preferred, special tools or keys would be best.

Some important, but less critical, design features would be: there should be no slacking or noise from a correctly assembled joint, so that it should be possible to take up looseness or replace worn parts. Surface finishes should not be damaged as a result of adjustment The chassis designs of Figures 4 and 5 differ from those of Figures 6 and 7 only in that one member must pass through or slide relative to the other in the latter cases. This difference need limit only the detailed design of appropriate joints, there need be no fundamental differences in the approach.

Three solutions to the design problem are advanced; externally fitted locking pieces, penetration iocks and designs relying on friction.

There are many possible designs depending on fitted locking pieces, latches, keys or wedges. This category would include, for example bayonet fittings and screwed fittings. The most basic design represented here would probably be a common through bolted flange coupling. Such designs would share the common advantage that it would be unnecessary to cut holes through mating structural parts. Figure 9 shows an example of this type of joint the specific arrangement being appropriate to the designs of Figures 4 or 5. Part numbers 21 and 22 indicate two tubular members to be connected. Flanges 23 and 24 integral with or attached to 21 and 22 respectively fit adjacent to one another when the coupling is made. An external muff or collar 25, pivotted at 26 for convenience in assembly, clamps the parts in engagement and is tightened by means of the machine screw 27.Stresses resulting from the applied bending moments will be distributed as a result of the fitted tongue 28 engaging with the member 21. Slackness resulting from wear will be taken up by means of small tapers designed into the parts 23, 24 and 25. A flexible surface coating of packing sleeve 29 will help to reduce surface damage and seizure.

The second type of joint to be considered is that characterised by the penetration of a locking piece through one or both of the engaging members. In any adequate joint of this kind, steps will be taken to reduce stress-raising effects. For example, the arrangement of Figure 10 shows an embodiment appropriate to any of the chassis designs of Figures 4 to 7 inclusive. In the case of a design such as Figure 6 there may be a considerable length of engagement between the telescoping parts, a close fit along the whole length being both impractical and undesirable. In the case of Figure 10, 30 and 31 represent telescoping members, through which pass bolts 32 to engage with nuts 33 and washers 34 by way of holes 35 and 36 to lock the parts in the required position.Stressraising resulting from the holes is minimised by drilling on a neutral axis and by strengthening members iocally by the addition of plates 37 welded to 31 and welded tubular inserts 38 passing through 30. The clearance between mating parts is reduced locally and undue slack avoided vertically by means of interposed packings 39 and horizontally by protuberances 40 in the transverse tubes 38. The packings 39 would best be made from a dissimilar material to avoid seizure. They may be attached to the part 31 by adhesives, by brazing or by rivetting in regions of low stress. Thus Figure 10 exemplifies a range of possible designs requiring a locking piece to penetrate one or both engaging parts and making use of localised plastic, elastomeric or metallic inserts or surface coatings to remove excessive clearance between telescoping parts.

The third class of joint would rely primarily on the force of friction to maintain chassis integrity, to which extent such joints will be seen to be fundamentally inferior to the alternatives. By way of example, Figure 11 outlines one such arrangement, the detail being appropriate to the design of Figure 7. Here part numbers 41 and 42 telescope with one another, parts 42 being rigidly attached to neighbouring structural members.

Slots 43 permit sufficient dispiacement of the parts 42 to permit adequate clamping whilst remaining within their elastic limit. Large clamping forces are induced through machine screws 44 and lugs 45, the latter being integral with parts 42. Preferably, as here, at least two separate clamping devices 42 will be employed in any design relying mainly on friction. Flexible collars on surface treatment to the parts 42 will protect the surface finish of 41.

The problems associated with the attachment of various demountable load receiving superstructures will now be considered. Similar considerations will apply for any case involving a variable length chassis for example the designs of Figures 2 to 7 inclusive. It may be considered advantageous to incorporate any separable spinal or other essentially longitudinal chassis members into the removable superstructures. Appropriate designs would be those outlined in Figures 2 to 5 inclusive when observations pertinent to the more difficult problem associated with the telescopic and sliding designs of Figures 6 and 7 orto the folding designs represented in Figures 4 and 5 would require detaiied revision. The following notes refer to the case where the superstructure is separate.

Attachments will be required only to locate superstructures and hence loads relative to the chassis since separating forces will not appear under any conditions worthy of consideration. The exception will be any forward attachment, which should be relatively robust to guard against any possibility of failure due to a badly loaded trailer.

It will be important to locate any loading configuration accurately relative to an axle in order to achieve a satisfacotry trailer balance. This would best be achieved by the use of attachments located towards the ends of the axle where the spacing will be maximum, where stresses will be relatively low and holes may be cut into the main member.

The length of any load receiving superstructure will be variable with the application. Also it may be thought desirable to retain the advantages of the adjustable axle. However, it would be unwise to rely on skilful adjustments being made in the latter case. Some designs require telescoping spinal members and the stresses in towbars can be high. For these reasons it would be difficult to provide fixed attachment locations on the spine.

There are several possible solutions to these problems, for example, the superstructure might be retained by means of a pair of setscrews engaging with captive nuts near the ends of the axle together with a single U-shaped bolt well forward on the towbar.

Attention will now be given to the various required lighting and marking requirements for trailers.

The regulations in some countries require an identification plate to be displayed in such a way as to be readable from the side of the vehicle. For unusually long trailers sidelights or reflectors are sometimes required. Since outwardly there is little to distinguish a multi-purpose trailer from others, any such requirements may readily be accommodated.

With the above exceptions, only specified lights, registration marks and warning symbols need be displayed, these to be visible from the rear. All such may be conveniently grouped on a single removable board. This is already common practice in connection with both trailers, where a lighting board is commonlycarried on brackets attached to the transom of the boat. It would obviously be convenient to follow a similar practice in connection with the multi-purpose trailer, in the interests of economy. The lighting board might be carried on adjustable brackets attached to the chassis, or on fittings integral with the load or superstruture as most convenient in a particular instance. The first alternative has the advantage of convenience but does have some disadvantages: electrical parts would be mounted low and in an exposed position.Mounting brackets, being subject to fatigue, will be relatively costly. Further, in some countries at least, the allowable rearward overhang of any load carried will be limited by the mounting bracket adjustment provided. This last would be particularly true of sailing dinghies and it would limit the general usefulness of the trailer correspondingly.

Most commonly the electrical powerfora trailer is provided through a standard seven pin plug and socket from the towing vehicle. A multipurpose trailer will require cables of various lengths dependent on the superstructure and load, any excess cable being safely stowed.

Two extreme possibilities emerge; the provision of interchangeable cables appropriate to various applications or the provision of a cable long enough to meet the most demanding requirement, together with suitable arrangements for cable control. The latter requires the provision of suitable cable clips whilst the former, possibly neater arrangement, several cables and additional plugs and sockets.

Excess cable may be stowed inconspicuously behind the lighting board or alongside chassis or superstructural parts as most convenient Note that the maximum excess of cable will usually appear in connection with a goods box superstructure, that normally being the shortest configuration. In this case, and for example, cable could be stowed on clips mounted on the forward end of the box.

There emerges from the foregoing a range of possible designs for a multi-purpose trailer incorporating a variable length chassis. For example, Figure 12 shows a typical small goods box 46 mounted on a telescopic chassis. Here 47 identifies an axle, to which are attached suspension units 48, wheels 49, mudguards 50, drag links 51 and an outer telescoping member 52. 53 identifies the inner telescoping member which carries a towhitch 54. A sliding joint, as required by the design exemplified will be located at 55. The goods box 46 will be attached to the axle by two setscrews 56, not shown in this view, and to the spine by a U-bolt 57. Frictional clamps 58 complete the chassis.The lighting board 59, together with cable 60, sufficient for the longest load to be carried and a plug 61 will be attached to the box by means of integral screws 62, not shown here, and wing nuts 63. The telescoping members are shown in the fully retracted position appropriate to the superstructure fitted.

Also by way of example, Figure 13 shows the same basic chassis in a position of maximum extension together with, as an example, and in an overhead exploded position relatively, supports and attachments appropriate to a small boat. The parts 46 to 63 inclusive have already been identified. In addition, 64 indicates a simple form of bilge support, 65 a single keel support and 66 its clamp. The lighting board would be carried on the boat transom.

It will be seen that superstructures designed to accommodate various loads could be mounted on the basic chassis described, for example, the motorcycle platform of Figure 14. Here 67 represents a channel member intended to support the motorcycle wheels, 68 a locating arm which pivots for convenient storage and which may be locked in position for road use by means of the setscrew 69. Other numbered parts have already been described. Where a motorcycle is to be carried, it will be found necessary to extend the chassis to a position intermediate between the cases illustrated in Figures 12 and 1 3.

Claims (14)

1. A kit of parts for a multi-purpose trailer, the kit comprising at least one pair of wheels, chassis members including means for attaching an assembled trailer to a towing vehicle and a plurality of load receiving means for attachment to the chassis members, the chassis members being such that trailers may be constructed in which the distance between said attachment means and the at least one pair of wheels may be varied.

2. A kit of parts according to claim 1 wherein the chassis members are such that a plurality of chassis may be constructed having different lengths.

3. A kit of parts according to claim 1 or claim 2 wherein the chassis members include an axle, the position of attachment of the axle to the remainder of the chassis being adjustable longitudinally of the chassis.

4. A kit of parts according to any of claims 1 to 3 and including a plurality of interchangeable chassis members.

5. A kit of parts according to any of claims 1 to 3 wherein the chassis members include members which may optionally be included in the chassis to increase the length thereof.

6. A kit of parts according to any of claims 1 to 3 wherein the chassis members include at least one member which is foldable to reduce its length and thereby the length of the chassis.

7. A kit of parts according to any of claims 1 to 3 wherein the chassis members include members adapted to telescope relative to each other to vary the length of the chassis.

8. A kit of parts according to any of claims 1 to 3 wherein the chassis members include members adapted to slide relative to each other to vary thb length of the chassis.

9. A kit of parts according to any of the preceding claims wherein the chassis members are connected together by frictional connection means.

10. A kit of parts according to any of claims 1 to 8 wherein the chassis members are connected together by positive locking means.

11. A kit of parts according to claim 10 wherein the positive locking means include parts which penetrate the chassis members.

12. A kit of parts according to claim 10 in which the positive locking means do not penetrate the chassis members.

13. A trailer formed from a kit of parts in accordance with any of the preceding claims.

14. A method of making a trailer from a kit of parts in accordance with any of claims 1 to 1 2 comprising combining chassis members to form a chassis, locating the or each pair of wheels on the chassis and locating a selected load receiving means on the chassis.

1 5. A method according to claim 14 wherein the selected chassis members are connected together to form a chassis of fixed length.