Load haulage vehicles which can be loaded and unloaded through open sides may have curtains suspended from slide tracks which can be drawn across the sides for closure purposes. Typically, the curtains are formed from strong plastics sheeting or fabric and are secured in the closure position by means of straps at intervals along the bottom edge region of the curtain. The straps extend between the curtain and a horizontal edge member, or rave, of the vehicle chassis and a buckle and over-centre or toggle mechanism is provided for each strap so that the curtain can be secured and firmly tensioned vertical downwards. With this known arrangement considerable manual effort may be involved in drawing the curtains and manipulating the strap tensioning system, and there is therefore the risk of strain or other injury to personnel.

Open-sided vehicles are also known which are provided with doors, but with these there is the problem of ensuring easy opening and closing without requiring excessive or inconvenient space requirements around the vehicle for movement of the doors.

An object of the present invention is to provide a door arrangement for a load-carrying vehicle body which can be convenient and easy to use without requiring excessive space requirements for movement purposes.

According to the invention therefore there is provided a load-carrying vehicle body with a door arrangement comprising at least one door which can be moved across an open side of the vehicle body, characterised in that the door is foldable upwardly to a retracted position at which the said open side of the vehicle body is free for loading and unloading purposes.

With this arrangement due to the use of a retractable foldable door it is possible to provide for opening and closing of the open side of the vehicle body in a convenient and easy manner, and excessive space around the vehicle and particularly outwardly of the side of the vehicle need not be required to accommodate opening and closing movements. Also, opening and closing can be achieved speedily and by way of example a closure time of the order of say 15 seconds can be possible compare with say 10 minutes for a conventional curtain-sided body.

The door may comprise a plurality of elongate door elements arranged one above another and these may be interconnected by hinge joints whereby the door can be folded by pivoting the elements relative to each other at the joints. Other arrangements are also possible and thus, for example, the elements may be slidably or otherwise interconnected whereby folding is achieved by sliding the elements over each other or otherwise as appropriate.

The said elongate door elements may comprise rigid or semi-rigid panels having flat or substantially flat outer faces. In a closed position of

the door the elements may be disposed relative to each other to define a generally planar door structure or outer door surface and in the open retracted position the elements may be disposed in superimposed or zig-zag or v-or z-shaped disposition.

Preferably, the arrangement is such that in the open retracted position there is an upper element which extends in a level, or horizontal, disposition and a plurality of lower elements which are disposed in one or more upright (upwards and/or downwards) v-shaped conformations beneath such upper element. In particular, there may be three lower elements, two of which define an upward v-shaped conformation connected at its outer extremity to an outer extremity of the upper element, and the third of which depends from an inner extremity of the upward v-shaped conformation to define therewith a downward v-shaped conformation.

In a particularly preferred embodiment, the door elements comprise skeletal structures having spaced apart upright ribs linked by transverse elongate members. With this arrangement a lightweight high strength construction can be achieved which requires relatively low power to move up and down but which can retain its shape and structural integrity over relatively large lengths.

The door may be hinged to an upper edge member of the open side and this may be at a position spaced inwardly of the said open side achieved for example as a consequence of an inset said upper edge

member. To accommodate this inwardly spaced hinge position, an uppermost edge region of the door may be bent or cranked inwardly. A so-called guilwing mode of door movement can thereby be achieved.

Most preferably, the said uppermost edge region is curved inwardly.

The use of a curved profile can contribute significantly to the strength of the door along its length as well as giving a pleasing appearance.

In a preferred embodiment, at least part, and preferably a major part, of the door may be disposed above the said upper edge member of the open side in the said open retracted position of the door.

Movement of the door between the open and closed positions is preferably power-operated or power-assisted and this may be achieved in any suitable manner.

In a particularly preferred embodiment an opening and closing device comprising a member movable through an upright path is provided at at least one end of the door, such member being connected to the door and being connected to a power or drive source to effect movement of the member. Suitably a drive chain or a lift screw engaging a threaded element linked to the door and rotatably driven by an electric motor or hydraulic or pneumatic cylinder or other power source may be used.

Most preferably, additionally or alternatively to the opening and closing device there is provided at least one biassing device which is arranged to act on the door to urge this to the retracted open position

during opening of the door. With this arrangement opening of the door can be achieved with relatively low power consumption. The biassing means may comprise a gas strut or spring or pneumatic or hydraulic cylinder or the like.

Suitably the arrangement may be such that the (or each) opening and closing device acts on a lower part (e. g. the bottom said element or a bottom end region of the door) and the biassing means acts on an upper part (e. g. the top said element or the said top region of the door).

There may be a respective said opening and closing device at each end of the door. In this case, in one embodiment the drive source comprises an electric motor positioned between the ends of the door and having a through drive shaft which is linked at its opposite ends by respective drive transmissions to the respective opening and closing devices. Alternatively there may be only one such device at one end and there may be a suitable guide arrangement at the other end.

In an alternative embodiment, a common drive device, alternative to the above mentioned electric motor, may be provided between the ends of the door linked by drive transmissions to the respective opening and closing devices. This common drive device may comprise an extendable actuator or ram device which may operate in a level or horizontal disposition and which may comprise a hydraulic/pneumatic piston and cylinder device. This may be connected by chain drives to the opening and closing devices.

In another embodiment, the opening and closing device at at least one end of the door comprises an upright extendable actuator or ram device which is connected to the door via a movement-amplifying device which causes the door to move through a greater distance than the extension of the actuator or ram. The ram device may comprise a hydraulic or pneumatic piston and cylinder or any other suitable device. The movement amplifying device may comprise axially linked wheels or sprockets having different diameters and/or numbers of teeth whereby the actuator causes one wheel or sprocket to rotate e. g. via a chain drive and this causes the other wheel or sprocket to rotate through the same angle but through a greater number of teeth and/or circumferential distance and this is communicated to the door e. g. via a further chain drive.

There may be a single said door extending along the entire length of the open side. Advantageously, a door length in excess of say 10 metres, and in particular more than 13 metres is possible, although the invention is not restricted to this and can also be used on much shorter doors.

Alternatively two or more doors may be provided, each extending along part only of the length of the open side.

The vehicle body of the invention may be a body of a wheeled road trailer or a lorry or any other suitable kind of vehicle. The body may be a container body transportable on any suitable kind of vehicle.

The door may be formed from any suitable material and may have its

outer surface finished and/or formed from appropriate materials to provide a surface having required properties such as waterproofing, colour, smoothness, especially having regard to desirability of providing an attractive surface to support printed or otherwise applied advertising material. If desired the door may incorporate thermal insulation.

The vehicle body of the invention may be of the open-sided kind i. e. having a longitudinally extending openable side and may be open-sided at one side only. Alternatively the body may be open-sided at two opposite sides in which case the door arrangement of the invention may be provided at both sides, or at only one of the sides with any other suitable closure arrangement at the other side.

The invention is not restricted to application of the said door arrangement to one or both longitudinal sides. Alternatively or additionally the door arrangement may be applied to a front end and/or a rear end of a vehicle body e. g. in substitution for a usual hinged door arrangement or raller shutter or the like.

The door arrangement may be appropriately constructed to ensure secure closure as for example by provision of locks for securing a bottom edge of the door to a chassis member of the vehicle.

The vehicle body of the invention may be constructed and supported in any suitable manner. Thus the body may be mounted on a chassis and may have front and rear end structures, and a roof structure supported by

uprights. Doors may be provided at a rear end of the body and/or at a front end and, as mentioned, the door arrangement in accordance with the invention may be applied to one or both longitudinal sides and/or one or both ends of the body.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic side perspective view of a road trailer incorporating a door arrangement in accordance with one embodiment of the invention.

Figure 2 is a rear end view of the trailer of Figure 1; Figures 3 & 4 are diagrammatic sectional views on the line A-A of Figure 1 respectively showing closed and open door positions; Figure 5 is a sectional view of a corner post of the trailer to an enlarged scale.

Figure 6 is an enlarged sectional view similar to Figure 4 (but taken from the opposite end), of a detail of an alternative door arrangement; Figure 7 is a sectional view similar to Figure 6 of a further door arrangement shown in open and closed positions; Figure 8 is a schematic side elevation of the door arrangement of Figure 6 in a closed position;

Figure 9 is a diagrammatic plan view showing the disposition of drive motors for the door arrangement of Figure 7; Figure 10 is a view similar to Figure 5 of a corner post used with the door arrangement of Figure 7.

Figure 11 is a view from one side of an alternative drive arrangement; Figure 12 is a view from another side of the arrangement of Figure 11; and Figure 13 is an enlarged sectional view on III-III of Figure 11.

Referring to Figure 1 a road trailer has a rectangular load-carrying body 1 mounted on a chassis 2 having the usual linkage 3 at one end for connection to a tractor unit, and road wheels 4.

The chassis 2 has longitudinal and transverse metal t-beams and, along each side a respective attached channel section side member 5, or 'rave'.

The rectangular load-carrying body 1 is mounted on top of the chassis 2 with the assistance of four rigid, hollow-section upright corner posts 6. There are also central front and rear upright end posts 7. These posts 6,7 support an upright front end wall 8, an upright rear end frame structure 9 incorporating two conventional doors 10 hinged at upright edges to the two adjacent corner posts 6, and a flat horizontal roof 11.

The roof 11 extends the entire length of the body 1 but, as can be

seen from Figures 3 and 4, the roof 11 extends only over a major part of the width of the body 1 and has longitudinal edge members 12 or'cant' rails which are inset slightly relative to the respective sides of the body 1 as defined by the vertical plane containing the corner posts 6.

Each side of the body has an opening 13 defined vertically by the respective roof edge member 12 and the respective chassis rave 5, and defined horizontally by the respective two corner posts 6.

Each of these side openings 13 is provided with a respective door arrangement. Each such door arrangement comprises a door having four elongate metal panels 14,15. One panel 14 has a flat rectangular body part 16 with one flat edge region 17 bent or cranked at right angles to the body part 16. The other panels 15 are all flat rectangular panels.

The panels 14,15 are of a length equal to the longitudinal extent of the side opening 13 i. e. equal to the separation of the corner posts 6.

Typically this length would be 13.4 metres.

The bent panel 14 is fixed to the roof edge member 12 by a hinge joint extending along the roof edge member 12 and along the free edge of the bent region 17 of the panel 14. The other panels 15 are hinged to the bent panel 14 and to each other along their longitudinal free edges. The arrangement is such that the panels 14,15 can be moved relative to each other and to the roof 11 to adopt a closed position, as shown in Figure 3, in which the body part 17 of the bent panel 14 and the other panels 15 are

coplanar and extend vertical between the chassis rave 5 and a position level with the roof 11, the bent region 17 of the panel 14 thereby extending horizontally level with the roof 11.

In this closed position, the side opening 13 of the body 1 is completely closed and if desired the door can be fixed in position using locks (not shown).

The panels 14,15 can also be moved relative to each other and to the roof 11 to adopt an open position, as shown in Figure 4. In this position the bent panel 14 is hinged upwardly so that the bent region 17 extends vertically and the flat body part 16 lies horizontally at a level above the roof 11, and the other panels 15 are folded against each other generally horizontally beneath the flat body part 16.

In the open position the panels 14,15 of the door are above or substantially level with the roof 11 whereby the entire side of the vehicle body 1 is open for loading and unloading purposes.

Movement of the door between the open and closed positions is achieved with a screw drive arrangement at each end of the door incorporated in the respective corner post 6.

As shown in Figure 5, the corner post 6 comprises a vertical box-section member 18 with a slot 19 along its length at the side of the post which faces along the door panels 14,15. Channel members 20,21 are fixed on the outer surface of the post 6 on opposite sides of the slot 19

with the openings of the channel members 20,21 facing towards each other.

In the embodiment of Figure 5, a screw 22 is located within the box- section member and runs the entire length of the corner post. As described hereinafter alternative drive arrangements, particularly drive chains, can be used and indeed may be preferred. A threaded block 23 is engaged with the screw 22 and is of such dimensions as to fit closely yet slidably within the box-section member 18.

A bar 24 is fixed to the block and projects transversely through the slot and between the channel members 20,21. Guide rollers 22a are attached to the bar 24 and fit slidably within the channel members 20,21.

The bar 24 is fixed to the respective bottom corner of the lowermost panel 15.

The screw 22 is drivably connected at its bottom end to a motor (not shown) which may be an electric motor powered by the vehicle electric system via a suitably located switch (not shown), or by a hydraulic or pneumatic drive source.

The screws 22 at opposite ends of the doors may be interconnected mechanically or electrically so as to be rotatable together thereby to lift and lower the door evenly.

With the arrangement described, with the doors in the open position the side openings 13 of the vehicle are wholly free for loading and

unloading purposes. In the closed position the openings 13 are securely covered with doors which present planar surfaces which can be attractively decorated or provided with advertising material or the like if required.

Movement of the doors between the open and closed positions is achieved easily and conveniently using the powered screws 22 or other drive devices. There is therefore little likelihood of strain or injury being caused to personnel.

Due to the manner in which the door folds upwardly during opening, little space is required around and particularly at the side of the vehicle to accommodate movement of the door. Loading and unloading can therefore be achieved in a particularly convenient manner in restricted space.

The alternative door arrangement of Figure 6 is generally similar to that of Figure 4 and the same numerals are used for corresponding parts.

The arrangement of Figure 6, however, differs, from that shown in Figure 4 in that the three lower panels 15 are folded in horizontal Z confirmation in the closed position, rather than the vertical Z conformation shown in Figure 4. That is, the uppermost panel 14 is located with its body part 16 horizontal and the three lower panels are beneath this with the lowermost panel 15 vertical and the two intermediate panels 15 inclined, thereby defining an upwardly directed v-shaped conformation which is substantially symmetrical about a vertical axis and a downwardly direct asymmetrical v- shaped conformation. The three lower panels 15 are substantially wholly

beneath the body part 16 and are substantially level, at their lower extremities with the top edge member 12.

The upwardly directed v-shaped conformation is hinged at its outermost extremity to the outermost extremity of the body part 16 and this conformation is hinged at its innermost extremity to the lowermost vertical panel 15.

This folding arrangement, as shown in Figure 6, is particularly advantageous in that the panels 15 can be moved easily and smoothly to the folded position without imposing any undue bending stresses on the panels likely to cause deformation or deflection or damage.

Also, gas struts 25 are fixed at spaced positions along the length of the top panel 14 extending between pivotal connection points 26 on the body part 16, adjacent to the top part 17, and pivotal connection points 27 on a flange 28 fixed to the roof edge member 12 and projecting horizontally outwardly towards the open side 13 of the vehicle body.

The gas struts 25 extend in upright disposition or substantially vertically in the open position of the door and swing to substantially horizontal or downwardly inclined positions in the closed position of the door.

The gas struts 25 act to bias the door to the open position as the top panel 14 swings upwardly. Thus, the door opens readily and requires relatively little force to be applied by the drive arrangement used to open

the door.

The arrangement of Figures 7 and 8 is generally similar to that of Figure 6 except that the panels 14,15 are constructed using a strong, light-weight skeletal construction made from vertical parallel spaced apart flat ribs 29 linked by transverse parallel horizontal rigid tubes 30 with respective skins (not shown) extending respectively across inner and outer edges 31,32 of the ribs 29.

Referring to Figure 8, each panel 14,15 may be constructed from 13 ribs. The ribs 29 of the top panel 14 are J-shaped (as shown in Figure 7) whereas the ribs 29 of the other panels 15 are straight. Each pair of ribs 29 at each end of each panel are spaced from each other by say approximately 925mm whereas the other intermediate ribs are spaced by say approximately 1125mm.

In the closed position, the vertical extent of the top panel 14 is say approximately 1275mm and the lower panels extend through say approximately 675mm, 725mm and 600mm respectively, from top to bottom. The door is therefore suitable to close a standard long distance road trailer side opening of approximately 13.4 by 3.3 metres.

The top ends of the ribs 29 of the top panel 14 are fixed via fixing flanges 33 to a rectangular section horizontal beam 34 (Figure 7). The bottom ends of these ribs 29 are fixed to a channel section member 35, as are the top and bottom ends of the ribs 29 of the other panels 15. Rigid

end members 36 are provided along the ends of the panels 14,15.

The rectangular section beam 34 at the top end of the top panel 14 is pivotally connected to the roof edge member 12 which is a horizontal rectangular section beam (cant rail) via multiple pivots 37 respectively at the location of each of the ribs 29 and the end members 36. There is a depending right angle bracket 38 welded to the member 12 at each pivot 37 with a lower outwardly extending horizontal arm 39. A respective gas strut 40 is fixed between each arm 39 and a position adjacent the curved transition of the rib 29.

It will be noted that the top panel 14 of Figure 7 differs from that of Figure 6 in that the profile is relatively larger and more robust. The top part 17 is thicker than the body part 16 with both Figure 6 and Figure 7 but the curvature of the Figure 7 profile gives further strength.

As shown in Figure 8, the panels 15 are hinged to each other and to the panel 14 by respective elongate hinges 35a in the region of the ribs 29 and the end members 36, between the members 35.

As shown in Figure 8, the hinges 35a are short hinges. Alternatively, it is possible to use, between each pair of adjacent panels 14,15 or 15,15, a single continuous hinge structure extending along substantially the entire length of the elements. This may comprise two elongate aluminium mouldings linked by an elongate flexible plastics (poiyurethane) strip.

Alternatively the mouldings may be linked by interfitting elongate shaped

channel portions which slide one within the other to permit pivoting, possibly with an elongate rubber or plastics cover flap. Such continuous hinges advantageously provide weather seals along the junction between the panels. With these continuous hinges it may be necessary or desirable to provide load bearing pivots at least in the region of the end members 36.

The gap between the top members 34 and 12 may be covered with a flexible cover strip for weatherproofing.

Figure 7 shows the panel 14 in the open position, and also in the closed position with the strut 40 extended and contracted.

The door arrangement of Figures 6 and 7 differs from that of Figures 1-5 with regard to the drive arrangement.

With the arrangement of Figures 6 and 7, an electric motor is fixed centrally behind the cant rail 12 as indicated in Figure 9.

The motor 41 is a direct drive DC electric motor which has a shaft 42 which extends through the motor so as to project from each end. A respective gear box 43 is drivably connected to each shaft end so as to convert rotation of the shaft 41 about a horizontal axis parallel to the cant rail 12 to rotation of a cog 44 about a horizontal axis at right angles to the cant rail 12. The cogs are arranged to rotate at the same speed in opposite directions.

With the arrangement of Figures 6 and 7, the respective corner posts 6, at opposite ends of the door arrangement, as shown in Figure 10 each

consists of a box section member 45 with a vertical parallel-sided opening 46 at the inner side of the post 6 which faces towards the opposite corner post 6 at the same side of the trailer body.

Within the opening 46 there is fixed a vertical box section guide rail 47 with a parallel-sided guide opening 48 facing towards the opposite corner post 6.

The guide rail 47 terminates top and bottom at positions spaced respectively below and above the top and bottom of the box section member 45.

At the top of the member 45, above the end of the guide rail 47 there is rotatably mounted on bearings 49 a horizontal shaft 50 carrying a sprocket 51, within the member 45 which overlaps the guide rail 47. If desired there may be a similar shaft and sprocket (not shown) at the bottom of the member 45 below the bottom end of the rail 47.

The top shaft 50 extends through an opening 52 in that side of the member 45 which faces inwardly of the trailer body, into a rectangular shallow trough-shaped box structure 53 with a side opening 54 on that side of the box structure 53 which faces towards the opposite corner post 6 at that side of the vehicle body.

The shaft 50 is mounted within the box structure 53 on bearings 55 and has at its free end a sprocket 56 which is aligned with the opening 54.

The above described construction of the corner post 6 and box

structure 53 is the same, in mirror image, at the opposite end of that side of the vehicle body. Drive is transmitted from the respective motor 41 at that side by means of endless chains 57 running between the sprockets 44 on the gear boxes 43 and the sprockets 56 within the extension box structures 53. Within each corner post member 45 there is an endless chain 58 running round the top sprocket 51, and any corresponding bottom sprocket, through the guide rail 47. The run of this chain within the guide rail 47 is connected to the bottom panel 15 of the door arrangement by means of a link member (not shown) within the opening in the guide rail, generally in like manner to the arrangement of Figure 5.

In use, the door can be moved to the closed position by actuating the motor 41 to rotate in a direction which causes the chain runs in the guide rails 47 to move downwardly at the same speed at opposite ends of the door.

When required, the door can be moved to the open position by actuating the motor 41 to rotate in the opposite direction so that the chain runs move upwardly at the same speed in the guide rails 47.

Appropriate electric controls are provided (not shown) for operating the motor 41.

As the door moves upwardly, the gas struts 40 swing up from their horizontal or downwardly inclined positions so as to be inclined upwardly.

The gas struts 40 then operate to assist lifting of the top panel 14 whereby

the door can now be moved to the fully open position with relatively little power. The motor 41 supplies drive through the chain 58 to the bottom panel 15 of the door, whereas the gas struts 25, or 40 act on the top panel 14. This ensures that relatively little motor power is required after initial opening of the door. The lower panels 15 are initially moved upwards by the motor 41 and then the gas struts 25, or 40 take over to apply the main opening force.

With the embodiment of Figure 7, the relatively light weight skeletal construction of the door panels 14,15 also helps reduce power requirements.

The electric motors 41 do not therefore need to be of especially high power and by way of example a 300rpm 1. 1 kw motor has been found to be satisfactory with the door arrangement of Figure 7.

Notwithstanding the light weight of the panels 14,15 of the arrangement of Figure 7, the skeletal structure gives great strength, as also does the curved J-shaped profile of the top panel 14. It is therefore possible to ensure adequate strength along the entire length of the door opening sufficient to prevent bending, distortion or structural failure whilst at the same time ensuring easy opening and closing movement.

One door arrangement on one side of the vehicle body has been described in relation to Figures 6 and 7 but there may be two opposite door arrangements as described in relation to Figures 1-5.

Figures 11-13 show a further, particularly preferred drive arrangement for the door arrangement of Figures 6 and 7.

The corner posts 6 at opposite ends of the door arrangement each consists of an elongate metal post which is of right angle cross-section having two main side walls (a front side wall 62 and an outer side wall 63) with an inturned rear lip 64 at the rear edge of the outer side wall 63.

Within the confines of the post 6 there are fixed two square box-section metal members 65,66 which are enclose except for gaps 67, 68 along the entire length of one side.

These members 65,66 are fixed respectively to the inner face of the front side wall 62 adjacent its free inner edge, and to the inner face of the outer side wall 63 adjacent its rear edge. The gaps 67,68 face in the same inner direction away from the outer side wall 63. These members 65,66 terminate at positions spaced from the top and bottom ends of the post 6.

Also within the confines of the post 6 there are two box-section channel members 69,70 which may be formed from any suitable material and are of the same length and level with the members 65,66. One member 69 is fixed in the inner corner between the front and outer side walls 62,63, aligned with the box-section member 65. The other member 70 is fixed, by a bridge piece 71, to the member 65, and is aligned with the other member 66.

A pneumatic or hydraulic actuator 72 is fixed longitudinally within the

post 6 by attachment of its cylinder 73 to a lower part of the post 6. Its piston 74 extends upwardly and is connected at its upper free end to a curved bracket 75 described hereinafter. Pipes 76 connect the cylinder 73 to a source of pressurised fluid (not shown). The piston and cylinder is disposed between the members 66,70.

At the top of the post 6, in the space above the top ends of the members 65,66,69,70 there are rotatably mounted three sprockets 77, 78,79 above the members 66,70 and the piston and cylinder 72. There is also a single larger sprocket 80 above the other members 65,69 and this is mounted rotatably on an axle 81 which is common to a top sprocket 77.

There is a corresponding arrangement of three sprockets 82 and one larger sprocket 83 at the bottom of the post 6 beneath the bottom ends of the members 65,66,69,70.

A first drive chain 84 runs around the top three sprockets 77-79 and the bottom three sprockets 82 through the channel member 70 and the box-section member 66. Within the box-section member 66 the chain 84 has an interposed guide element 85 carrying wheels 86 which run on the inner surfaces of the member 66.

The curved bracket 75 on the top of the piston 74 extends through the gap 68 in the member 66 and is fixed to the guide element 85.

It will be appreciated that movement of the piston 74 causes movement of the guide element 85 and consequent movement of the chain

84 and drive of the sprockets 77-79,82.

A second guide chain (not shown) runs around the top and bottom large sprockets 80,83 through the channel member 69 and the box-section member 65. Within the box-section member 65 the chain has an interposed guide element 87 carrying wheels 88 which run on the inner surfaces of the member 65, like the element 85.

A link 89, which may be a projecting rigid tongue or any other suitable structure, is fixed to the element 87 and projects through the gap 67 in the member 65.

In use the link 89 is fixed to a bottom panel of the door.

In use, feed of pressurised fluid to the cylinder 73 causes the piston 74 to extend upwardly and thereby to move the first drive chain 84. This causes the top large sprocket 80 to rotate by virtue of its axial connection to the top sprocket 77, whereby the second chain is moved. The link 89 is therefore moved along the gap 67.

The large sprocket 80 rotates through the same angle as the connected sprocket 77 but is of larger diameter and has more teeth.

Accordingly, full extension of the piston 74 through a minor part of the length of the post 6 causes the link 89 to move through a much larger distance, along substantially the entire length of the member 65.

Movement of the piston 74 in the opposite direction i. e. into the cylinder causes the door to move in the opposite direction.

This arrangement, provides powerful, controlled lifting device with a compact, elongate construction which can be readily accommodated without undue intrusion into loading, or load carrying areas.

It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

Thus, for example, additionally or alternatively to the gas struts 25 or 40 other spring or biassing devices may be used. Also, although it is desirable for the powered drive to be applied to the bottom panel 15 and the gas struts or other biassing means to act on the top panel, other arrangements are also possible. In particular, the drive may be applied to two or more lower panels.

As described, the door panels 14,15 extend throughout the full length and height of a standard 13.6 metre trailer body (the actual door length being say 13.4 metres and the height say 3.3 metres). However, the invention may also be used on bodies (whether trailer or integral driven vehicle bodies) which are shorter and lower, as desired. Thus, the door arrangement may be used as a substitute for curtain side closures on long distance load haulage trailers or on load carrying vans or lorries or for any other suitable use. The materials used in the construction of the door panels will depend on the desired use and thus for example may incorporate thermal insulation material for chilled load transport.

As an alternative to the two rams of Figures 12 and 13 there may be a single ram operating horizontally between the ends of the door behind the cant rail 12, in like manner to the electric motor arrangement of Figure 9.

This arrangement may involve corner posts of like form to those shown in Figure 10, i. e. having a continuous vertical-running chain 58 passing round a top sprocket 51 on a shaft 50 bearing a smaller sprocket 56. The sprocket 56 is linked by a continuous horizontal-running chain to a sprocket mounted in the middle of the cant rail 12. The opposite corner post at the opposite end of the door has a like arrangement and the two sprockets in the middle of the cant rail 12 mesh with each other whereby the two horizontal chains run in opposite directions and the two vertical chains run in the same direction. At one side portion of the cant rail, the single horizontal driving ram is mounted and this engages a slider interposed in the respective horizontal chain. Extension and contraction of the ram causes the respective chain to move around its sprockets thereby driving the other horizontal chain and the two vertical chains. The ram may have a stroke of say 1100mm and the ratio of teeth on the sprocket 56 to the sprocket 51 is selected to give an appropriate amplification of movement for the required vertical travel of the vertical chains and hence the door. This arrangement is particularly convenient and simple and, since it uses only one ram (on the respective vehicle side) balanced movement of the two vertical chains is readily attainable.