Abstract:
A cover system for a trailer of a freight transport vehicle having a cargo space, the cover system having a pair of track brackets, tracks, generally U-shaped bow portions mounted to the trucks so that there is displacement of the bow portions as each member of the pair of trucks is displaced along the length of the members of the track and a flexible canopy supported by the bow members for covering or uncovering the cargo space.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part of U.S. application Ser. No. 11/412,104 filed on Apr. 27, 2006 which claims priority from U.S. Provisional Application No. 60/675,893 filed on Apr. 29, 2005 the contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to covers, in particular but not exclusively to covers for freight transport vehicles. 
       SUMMARY OF THE INVENTION 
       [0003]    In certain modes of freight transport, it is desirable to have a load supporting deck structure of some kind, and a movable superstructure. The deck structure is used to support lading of some kind, perhaps steel coils, auto parts, or some other object. The movable superstructure is used to protect the lading from the elements (wind, snow, sleet, rain, dirt, and undesirable exposure to direct sunlight, for example), yet, by being movable, permits the loading of large objects either from above or from the side, in a manner that would not otherwise be possible with a fixed superstructure. 
         [0004]    In some instances, it may be possible to achieve this end with a superstructure of rigid panels, or an arch-like section, where several rigid sections can telescope on inside another, thus giving better access to the deck for loading. However, in one type of covering superstructure, such as has been used on highway trailers, for example, the superstructure is made up of a number of rigid frames, such as may typically roll or slide upon a pair of rails along either longitudinal edge of the trailer bed, used in co-operation with a flexible covering, in the nature of a tarpaulin. When the arches, or frames (typically referred to as “bows”) are in place, the tarpaulin extends over them to provide a canopy which covers the lading. 
         [0005]    Two patents that show the general layout and description of the principles and operation of flexible tarpaulins for highway trailers are U.S. Pat. No. 5,152,575 of DeMonte et al., issued Oct. 6, 1992; and U.S. Pat. No. 5,538,313 of Henning, issued Jul. 23, 1996, and U.S. Pat. No. 6,511,117 of Henning, issued Jan. 28, 2003. 
         [0006]    Movable tarpaulin systems may come in a relatively flat top style, as shown in the two Henning patents (supra), or in a centrally peaked style, as shown in Demonte. Demonte shows a number of variations between a fully deployed tarpaulin system and a retracted system. Most commonly, the bows and their tarpaulin covering are moved to an accordion style position near the front of the truck bed. Whereas DeMonte shows only single bows, Henning shows, in both patents, doubled bows at both the foremost and rearmost positions, and single bows arrayed therebetween. 
         [0007]    A movable cover not only permits access to the load, but, in addition, may be a lighter structure. This is particularly so when the frame elements are made of aluminium rather than steel. This is also desirable in terms of maintaining a lower centre of gravity than might otherwise be the case. 
         [0008]    In highway use, a number of features may be noted. First, it is desirable that the tarpaulin covering be of a relatively heavy duty material, and that, in use, the tarpaulin be drawn relatively tightly over the bows. Within reason, the tighter the tarpaulin covering is stretched over the bows, the longer the service life of the covering. That is, if the cover is allowed to flap excessively in the wind, wear of both the cover and the underlying bow assemblies may tend to be more rapid than if the elements of the system are held more tightly in place. 
         [0009]    In attempting to achieve this desired structural relationship, existing highway trailer systems tend to use fabricated bow structures, where the method of fabrication is the painstaking welding together of piece parts. A typical welded bow may tend to require a large number of welds by a highly trained welder. This is particularly so when the bows are fabricated of aluminium, and generally speaking, a greater level of skill is required reliably to weld aluminium than other metals, such as steel. The process tends to be slow, it tends to require a large number of welds, and tends to be highly labour intensive. It has been observed that the top corner fittings at each side of the double bows may tend to be particularly troublesome. Although some attempts have been made to cast the top corner fittings, this has not necessarily been as successful as might have been desired. That is, casting may sometimes have a tendency to be brittle. Alternatively, such parts can be machined from solid, but this may tend to result in expensive parts that may simply not be commercially viable. 
         [0010]    Not only is such a form of construction highly reliant on the skill of the individual welder, but, further, notwithstanding the use of jigs, it is improbable that any two bows will be the same. Repeatability may tend to be poor. The process may be prone to generate a relatively high proportion of scrapped assemblies. Each manufacturing inconsistency may tend to yield a point of higher stress concentration in the fabric cover, or may yield a protrusion or other imperfection tending toward premature wear of components. Alternatively, a badly made weld, may be a crack initiation site, and hence may tend to be the cause of premature failure. 
         [0011]    Further still, the all welded styles of construction complicates distribution and repair. The built up bows are large and cumbersome to distribute and if a bow is damaged, the remedy is to re-supply an entire fabricated replacement bow, or to require a custom repair at the location of the trailer upon which the covering structure is mounted. Shipment of a fully built-up fabricated bow tends to be cumbersome, and prone to damage. Repair on site tends to require a qualified welder of aluminium. 
         [0012]    It is therefore an object of the present invention to obviate or mitigate the above disadvantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein: 
           [0014]      FIG. 1  is a perspective view of a tractor and trailer combination; 
           [0015]      FIG. 2  is a rear perspective view of a headboard used on the trailer of  FIG. 1 ; 
           [0016]      FIG. 3  is a section on the line III-III of  FIG. 2 ; 
           [0017]      FIG. 4  is a perspective view of a bow used on the trailer of  FIG. 1 ; 
           [0018]      FIG. 5  is a section on the line V-V of  FIG. 1 ; 
           [0019]      FIG. 6  is a perspective view of a bracket used in the trailer of  FIG. 1 ; 
           [0020]      FIG. 7  is an end view of a track used in the trailer of  FIG. 1 ; 
           [0021]      FIG. 8  is a perspective view of a body of a carriage used on the trailer of  FIG. 1 ; 
           [0022]      FIG. 9  is a top perspective view of an assembled carriage using the body of  FIG. 8 ; 
           [0023]      FIG. 10  is a section on the line X-X of  FIG. 4 ; 
           [0024]      FIG. 11  is a perspective view of the a corner of the bow shown in  FIG. 4 ; 
           [0025]      FIG. 12  is a side view of a bracket used in the corner of  FIG. 11 ; 
           [0026]      FIG. 13  is a side elevation of a plate used in the corner of  FIG. 11 ; 
           [0027]      FIG. 14  is a section on the line XIV-XIV of  FIG. 11 ; 
           [0028]      FIG. 15  is a perspective view of a rear bow; 
           [0029]      FIG. 16  is a perspective view of a bracket used in the rear bow of  FIG. 15 ; 
           [0030]      FIG. 17  is an end view of an alternative embodiment of a corner of the bow shown in  FIG. 4 ; 
           [0031]      FIG. 18  is a perspective view of an alternative embodiment of corner of a rear bow as shown in  FIG. 15 ; 
           [0032]      FIG. 19  is a side view of a rear portion of the trailer shown in  FIG. 1 ; and 
           [0033]      FIG. 20  is a section on the line XX-XX of  FIG. 19  on an enlarged scale. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Referring therefore to  FIG. 13  a tractor  10  is connected through a conventional fifth wheel to a trailer  12 , both of which are supported on respective axial assemblies  14 . The trailer  12  includes a trailer bed  16  that is formed in a conventional manner with a structural steel frame and decking. The trailer bed is typically between 45 and 60 feet long and designed to carry a variety of goods. 
         [0035]    The bed  16  is covered by a canopy structure  18  that is secured to the bed  16 . The canopy  18  includes a headboard  20 , a rear bow structure  22  and intermediate bow structures  24  spaced between the headboard  20  and the rear bow  22 . Sections of flexible covering  26  extend between the bows to provide a continuous weather proof canopy over the bed  16 . 
         [0036]    The bows  22 ,  24  are slidable relative to the trailer bed  16  as will be described more fully below, to allow the canopy  18  to be retracted and expose the trailer bed  16 . To protect goods supported on the bed  16  during transit, the canopy  18  may be deployed providing a secure weather tight canopy for the goods. 
         [0037]    The headboard  20  is shown in more detail in  FIG. 2  and includes upper and lower plates  26 ,  28  with vertical frame members  30  extending between the plates. Panels  32  are secured to the frame members with a door  34  provided to permit access to the interior of the canopy from the forward end of the trailer. The plate  26  is secured with bolts  36  to the trailer bed  16  to provide a rigid structure. 
         [0038]    The outer frame members  30  are provided with wing extensions  40  to facilitate sealing of bow  24  to the headboard  20 . The extension  40  is best seen in  FIG. 3  and includes a right angled extrusion  42  having flanges  44 ,  46 . The extrusion  42  is secured to the structural member  30  with bolts  48 . The flange  46  terminates in a re-entrant channel  50  that receives the undercut head  52  of a seal  54 . The seal  54  has a pair of legs  56  with inwardly directed sealing ribs  58 . The seal  54  is formed from a flexible rubber or plastics material and extends around each frame member  30  and across the upper panel  28 . The legs  56  are spaced apart to receive a flange  58  projecting from the adjacent intermediate bow  24  that can best be seen in  FIG. 4 . Over centre clamps (not shown) secure the bow  24  to the headboard. 
         [0039]    The bow  24  has a pair of vertical jambs  60  interconnected by a header  62 . The jambs  60  and header  62  are interconnected by respective corner assemblies  64  and the lower ends of each of the jambs are supported on respective trucks  66 . As will be described in more detail below, the trucks  66  support the intermediate bows to permit longitudinal movement relative to the trailer bed  16 . 
         [0040]    The connection of the trucks  66  to the trailer bed  16  can best be seen in  FIG. 5 . Track brackets  70  are located between a rub rail  68  and the outwardly directed face of the bed  16  so as to be outboard of stake pockets  72  that are typically installed along the length of the trailer. The rub rail  68  is an elongate strip secured to the bed  16  and spaced outwardly from it. The brackets  70 , shown in  FIG. 6 , are formed as an elongate inverted “L” in section having a vertical leg  74  that is cranked as indicated at  76  intermediate its ends. An enlarged head  78  is formed on the other leg  80  to present an upstanding shoulder  81  on the upper surface. The lower end of leg  74  is formed with a pair of slotted holes  82 . 
         [0041]    Brackets  70  are located at spaced intervals along both sides of the bed  16  to support discrete lengths of aluminium track  84  typically eight feet long. The sections of track  84  are located end to end so as to extend along the entire length of the bed  16 . 
         [0042]    The track  84  can best be seen in  FIG. 7  and has a channel  86  defined by a rear wall  88  and vertically spaced side walls  90 , 92 . A laterally directed channel  94  is provided at the intersection of the rear wall  88  and the side wall  90  and has a downwardly extending lip  96 . The channel  94  is dimensioned to receive the head  78  of the track bracket with the shoulder  81  co-operating with the lip  96  to inhibit lateral movement between the bracket and track member. The channel opening defined between the lip  96  and the opposite walls of the channel  94  is sufficient to receive the head  80  and thereby permit the track to be hooked onto the bracket  70 . 
         [0043]    The track  84  also includes a downwardly directed channel  98  whose base is formed by the side wall  92 . The channel  98  has a pair of side walls  100 ,  102  with the side wall  102  being formed with a pair of slots  104 ,  106  at its terminal portion. The slots have overhanging lips  108 ,  110  respectively to partially enclose the slots  104 ,  106 . 
         [0044]    The side wall  92  is also formed with a re-entrant groove  112  directed toward the opposite side wall  90 . The groove  112  is relatively wide compared to its depth and is dimensioned to receive a bearing strip  114  shown in  FIG. 5 . The bearing string  114  is extruded from a low friction coefficient plastics material, such as ultra high molecular weight plastic, and provided in sections of convenient length. 
         [0045]    Referring again therefore to  FIG. 5 , it will be seen that individual lengths of track  84  are located on respective brackets  70  with the head  78  located in the channel  94 . The track  84  is secured in location by bolts  116  whose head is located within the groove  104  and secured by the overhanging lips  108 . The bolt passes through the slots  82  provided in the leg  74  of the bracket  70  and are secured by nuts. Accordingly, the track  84  is secured to the brackets with the lip  96  and bolt  116  inhibiting relative movement between the bracket  70  and the track  84  and the rub rail is gripped between the rack  84  and bracket  70 . The brackets and tracks are able to slide vertically relative to the bed  16 . 
         [0046]    The individual pieces of the track  84  are aligned along the length of the bed  16  so that the slot  112  is continuous from one end to the other. Sections of the plastic bearing strip  114  may then be inserted in the slot  112  to provide a continuous bearing surface over the individual segments of track. The individual lengths of bearing strip  114  are arranged to be staggered relative to the sections of track so that the joints between the individual lengths of track is bridged by the strip  114 . 
         [0047]    To inhibit ingress of water and debris, a seal assembly generally indicated at  150  is secured to the slot  106  on the track. The seal assembly has an “L” shaped plastic deflector  152  that projects beneath the trucks  66 . A pair of flexible seals  154 ,  156  project to opposite sides of the “L” shaped member  152  and seal between the track and deck and overlie the trucks  66  respectively. 
         [0048]    Track  84  supports the trucks  66  of the intermediate bows  24 . The trucks  66  include a carriage body  120 , shown in isolation in  FIG. 8 , that has a planar upper portion  122  and a curved lower portion  124 . A flange  126  projects outwardly from the planar portion  122  to overlie the curved portion  124 . A pair of support wheels  128  are mounted at spaced locations on the planar portion  122  and are received within the channel  86  of the track  84 . A pair of guide wheels  130  are mounted on the flange  126  and received within the channel  98 . Each of the wheels  128 ,  130  is mounted on a respective spindle  132 ,  134  and secured with a nut  136 . The support wheels  128  bear on the plastic bearing strip  114  to provide a smooth movement along the track  84  and the spaced locations of the guide wheels  130  inhibit yawing of the intermediate bow as it moves along the track. The orientation of the channel  98  also ensures that debris and contaminants do not collect to impair rolling of the wheels  130 . 
         [0049]    The carriage body  120  supports the vertical jambs  60  through the use of a pair of support brackets  160 ,  162 . The support brackets  160 ,  162  are bolted to the upper planar section  122  of the body  120  and have inturned flanges  164 ,  166  at the inner edges. Locking blocks  168  extend along the flanges  164 ,  168  and are secured by lock screws  170  and are threaded onto the upper portions of the flanges  164 ,  166 . A pair of slots  167  are formed in the planar section  122  between the flanges  164 ,  166 . 
         [0050]    The jambs  60  are each made from lengths of extruded aluminium, the profile of which is shown in  FIG. 10 . 
         [0051]    The jamb  60 , shown in  FIG. 10 , has a pair of major walls  174  and a pair of lateral interconnecting webs  172  to define a central rectangular core  176 . The terminal portions of each of the walls  172  merges with a “L” shaped arm  178  with orthogonal fingers  177 ,  179 . The fingers  177  of the “L” shaped arms  178  in combination with the walls  172  define a re-entrant slot  180  along each major face of the jamb  60 . Similarly, the walls  172 ,  174  co-operate with the fingers  179  of arms  178  to define re-entrant lateral slots  182 . 
         [0052]    The lateral slots  182  are dimensioned to receive the block  168  with the flanges  164  abutting the outer faces of the arms  178 . The bolts  166  can then secure the block within the slot  168 . The fingers  178  out board of the web  172  pass through slots  167  formed in the planar portion  122  of the body  120  so that the jamb  60  is received on the body  120 . It is then clamped between the flanges  164 ,  166  and respective ones of the blocks  168 . 
         [0053]    The header  62  is formed from the same profile extrusion as the jambs  60  and connected to the jambs  60  through the corner assemblies  64 . The details of the corner assembly  64  are best seen in  FIGS. 11 and 12  and includes a corner bracket  200  and a pair of corner plates  202 . The corner bracket  200  has a central body  204  with oppositely directed end faces  206 . The end faces  206  are interconnected by inner and outer curved webs  208 ,  210  with a radial web  212  extending between them. The curved webs  208 ,  210  extend through 90° so that the faces  206  are orthogonal to one another. 
         [0054]    A pair of tongues  214 ,  216  extend from each of the faces  206  and are offset from the outer surfaces of the webs  204 ,  208  so that a shoulder is defined at the outer edges of the face  206 . The tongues  214 ,  216  are spaced apart sufficiently to be a sliding fit over the bases of the walls  172  in the slots  180  and the width of the corner bracket  202  corresponds with the width of the core  176 . Holes  220  are provided in each of the tongues  214 ,  216  to permit complementary holes to be drilled in the walls  172  and for the suitable fasteners, such as those known as “Rev-nut” to be inserted. A bolt  218  passes through the “Rev-nut” if preferred to secure the corner bracket  200  to the header  62  and jamb  60  respectively. 
         [0055]    It will be appreciated that by virtue of the constant width of the corner bracket, the brackets may be obtained from a continuous extrusion having the profile of the corner bracket. 
         [0056]    The corner plates  202  are illustrated on  FIG. 13  and have a central body portion  230  corresponding in profile to the body portion  204  of the corner bracket. Tongues  232  project outwardly from orthogonal faces of the body  230  to be received within the slots  168 . The plates  202  are secured in that the slots  168  by set screws  234  to form a rigid corner assembly. 
         [0057]    When assembled, the bow  24  has an outer surface defined by one of the slots  180  of the jamb and header. The slots  180  are used to locate a tarp holder  240  that in turn is used to secure the flexible covering  26  to the bows. The tarp holder  240  is formed by a plastic extrusion shown in greater detail in  FIG. 14 . The tarp holder extrusion is formed from an aluminium material and has a generally planar base  242  with oppositely directed faces  243 ,  245  and a central partition  244 . Upstanding retaining walls  246  extend from wall  243  of the base  242  to either side of the partition  244  with a gap  248  provided between opposite ends of the retaining walls  246 . The partition  244  and the retaining walls  246  define a pair of circular voids  250  interconnected at the gap  248 . The voids  250  receive a beaded edge of the flexible covering  26  as will be described more fully below. 
         [0058]    The base  242  has a width corresponding to the width of the slot  180  on the jamb  60  and header  62  so that it may be slid into the slot  180  and retained by the ears  178 . The tarp holder extrusion  240  is thus able to extend along the linear extent of the jambs  60  and header  62  to provide a continuous fixture for retaining the tarpaulins. 
         [0059]    To accommodate the corner assemblies  64 , the extrusion  240  is bent through 90° on a radius corresponding to the outer radius of the corner bracket  200 . The corner tarp holder thus smoothly merges with the linear runs on the jamb  60  and header  62  to provide continuity to the voids  250  and gap  248  and is secured in place by set screws  252 . 
         [0060]    Similarly, at the lower end of the jamb  60 , a foot extrusion  260  is formed to conform to the outer profile of the body  120 . The foot extrusion  260  is secured to the body through the set screws  262  in the outer flanges of the base  242  and again provides a continuity of the voids  250  and gap  248 . 
         [0061]    With the tarp holder  240  corner extrusion and foot extrusion  260  is secured over the peripheral surface of the bow  22 , a continuous void is formed to receive the covering  26 . Each of the coverings  26  is of known construction and includes a membrane  270  and an enlarged beaded portion  272  at each edge. The beaded portion  272  conforms to the diameter of the void  250  with the membrane  270  passing through the gap  248 . The edges of the covering  26  may therefore be slid along the tarp holder  240  from one end to the other to secure the tarpaulin to the bow  22 . 
         [0062]    The rear bow  22  is formed in a similar manner to the intermediate bow  24  and therefore like components will be identified with like reference numerals with a suffix ‘a’ added for clarity. 
         [0063]    The rear bow  22  has two pairs of jambs  60   a  and two headers  62   a  connected by corner assemblies  64   a.  The lower end of the jambs  60   a  are supported on trucks  66   a  with a body  120   a  formed from the same extrusion as body  120  but of greater overall length. The trucks  66   a  include two pairs of support wheels  128   a  and two pairs of guide wheels  130   a.    
         [0064]    The jambs  60   a  and header  62   a  are formed from the same extrusion as the jambs  60  and header  62   a.  Their connection to the upper planar portion  122   a  of the body  120   a  is similar to that described above with the planar portion having two pairs of slots  167   a  to provide a tongue or tine that can slide into the grooves  182   a  of the jambs  60   a.  The support brackets  160   a,    162   a  are bolted to the upper portion  128   a  and secured respective ones of the jamb  60   a  through locking blocks and lock screws as described above. On the rear bow  22  however the support brackets  160   a,    162   a  are located on the inner surfaces of the jambs only to avoid excessive length of the body  120   a.    
         [0065]    The corner assembly  64   a  similarly utilizes a corner bracket  200   a  that spans each of the jambs  60   a  at the respective corner assemblies  64   a.  The corner block  200   a  is formed from the same extrusion as the corner block  200  but of greater length to accommodate the spacing between the jambs  60   a.    
         [0066]    To accommodate the tongs  214   a,    216   a,  the arms  178  are removed at the terminal portion of the inner surface of the jamb  60   a  and header  62   a  to allow the tongues to fit smoothly onto the wall  172 . This notching is provided at the edges of each jamb at the intersection with the corners  64   a.    
         [0067]    To enhance the rigidity of the rear bow, bracing members  280  are located between the jambs  60   a  mid way between the corner assembly  64   a  and the truck  66   a.  The bracing members  280  as best seen in  FIG. 16  are formed from an extrusion and has a pair of spaced parallel feet  282  with inclined cross members  282 ,  284  extending between the feet  282 . Each of the feet  282  has a pair of holes  288  that accommodate a machine screw to co-operate with a T-block positioned within the lateral grooves  182 . The brace  280  may then be positioned along the length of the jamb and secured in position by tightening of the bolt. 
         [0068]    It will be noted from the above description that the major elements of the canopy are formed from extrusions which are assembled to one another without resorting to welding. The jambs and headers are formed from lengths of common aluminium extrusion and the corner assemblies, which themselves are sections of an extrusion and secured to the jambs and headers by mechanical fastenings. This enables the jambs and headers to be supplied disassembled and assembled in situ using common tools. 
         [0069]    Similarly, the track is supplied in manageable lengths, typically eight feet, to facilitate distribution and the arrangement of brackets and bearing strips provides for a continuous bearing surface allowing the track to extend the length of the truck although made from individual sections. The track brackets permit the track to float and thereby accommodate flexure in the bed  16  of the track under different load conditions whilst properly supporting the track and ensuring the continuous bearing surface for the support rollers. 
         [0070]    The bodies  120  of the trucks  66  are similarly cut from extrusions and through the use of the support brackets provide a secure bolted connection to the jambs  60 . The outer surfaces of the jamb also permit the tarp holder  260  to be secured in a continuous manner about the periphery and thereby maintain control over the flexible covering  26 . 
         [0071]    To assembly the canopy  18 , the intermediate and rear bows are first assembled from the individual lengths of extrusion provided. Connections are made to the trucks and to the corner connections to provide completed bows without the necessity of welding. The track brackets are located on the rub strip and the tracks secured to the brackets, again by mechanical interconnection. The tracks are aligned and individual lengths of bearing strip inserted into the groove so that the joints between sections of the track are bridged. The headboard is assembled and bolted to the leading edge of the deck and the bows then slid onto the track with the support rollers and guide rollers engaged in their respective channels. Thereafter, the flexible coverings can be fed through the voids  250  from one truck  66  to the other. It will be noted on the rear bow that the tarp holder is only applied to the rear most jamb and header allowing the flexible coverings to extend to the rear most edge of the bow. 
         [0072]    The deflector is secured to the underside of the track with the respective seals inserted. Again, the deflector is provided in discrete lengths and the joints between the deflector and the seals are themselves staggered to provide an overlapping labyrinth seal. 
         [0073]    With the bows and covering assembled, the bows may be moved along the track to uncover or cover the deck. The provision of the guide wheels inhibits yawing motion of the bows in the event that a force is applied from one side thereby facilitating smooth operation of the bows. In order to cover the bed  16 , the bows are moved rearwardly until limited by the extent of the covering  26 . Tension is applied to the covering by a ratchet mechanism operating on the rear bow to ensure that it is held in situ relative to the bed. 
         [0074]    It will be appreciated therefore that the canopy may be supplied in a disassembled form and readily assembled without the necessity for welding. The provision of extrusion at each corner provides a significant durability and strength. 
         [0075]    An alternative embodiment of corner bracket is shown in  FIGS. 17 and 18  in which like reference numerals will be used to denote like components with a suffix “a” added for clarity. Referring therefore to  FIG. 17 , a corner bracket  200   a  is defined by inner and outer curved webs  208   a,    210   a.  The curved webs  208   a,    210   a  extend through slightly less than 90° to give a slight slope to the header to facilitate drainage of the tarpaulin. Typically the webs  208   a,    210   a  extend through 88°, which has been found to provide the requisite slope. 
         [0076]    The curved webs  208   a,    210   a  terminate at end faces  206   a.  A boss  300  projects from each of the end faces  206   a  comprising a pair of tongues  214   a,    216   a  and enlarged cross pieces  302 ,  304 . The cross pieces  302 ,  304  enhance the rigidity of the tongues  214   a,    216   a  to inhibit flexure of the tongues within the jamb and header. 
         [0077]    The corner bracket  200   a  is a constant width in a manner similar to the corner bracket  200  of  FIG. 12  and therefore can be cut from a continuous extrusion of aluminium alloy having the cross section of the corner bracket. When compared with the embodiment of  FIG. 12 , it would be noted that the radius of curvature of the curved webs  210   a,    208   a  is increased and the number of radial webs  212   a  is similarly increased. The increased radius and increased webs has been found to reduce the stress concentrations at the corner brackets which, in combination with the rigid boss assembly used for connection to the headers and jambs enhances the service life of the bows. 
         [0078]    A similar arrangement is utilized for the corner bracket of the rear bow as shown in  FIG. 18 . In this embodiment, the same extrusions that used for the corner bracket of  FIG. 17  is utilized to provide the elongated body  204   b.  Two pairs of bosses  300   b  are provided on each limb of the bracket by removing the portion of the extrusion between the bosses. Each of the bosses  300  includes cross pieces  302   b,    304   b  as described above with respect to  FIG. 17  and are dimensioned to receive the jambs and headers associated with the rear bow  22   b.  Again therefore, the rear bow benefits from the enhanced rigidity offered by the bosses  300   b  and utilizes the same extrusion as the balance of the corner brackets. 
         [0079]    In order to secure the rear bows in situ during transport, an upstanding post assembly  310  is secured to the rear end of the deck  16  inboard of the rear bow  22 . This arrangement is shown in  FIGS. 19 and 20  and consists of a socket  312  secured to the deck and a post  314  projecting upwardly from the socket. The post assembly  310  has forces applied to it through tensioning strap  316  acting between the post  314  and the rear bow  22   b  to tension the flexible covering  26 . The arrangement of post assembly shown in  FIGS. 19 and 20  is particularly beneficial in opposing such loads. 
         [0080]    As may be seen in  FIG. 19 , the socket  312  is of generally rectangular cross section and has an outstanding bead  320  projecting from the external surface  322  of one side. The side  322  is oriented to be perpendicular to the longitudinal axis of the deck  16  so that the bead  320  is on a rearwardly projecting surface. The post  314  is formed from an extrusion having an outer surface  330  that is complimentary to the inner surface of the socket  310 . Lateral outer surfaces are provided with recesses  332  that accommodate deflection of the section during the extrusion process. The inner surface of  334  of the extrusion is formed with a bead  336  at the mid point of each side. 
         [0081]    The post assembly is formed by inserting the post into the sockets which may then be used to apply a tensioning force to the rear bow. The provision of the beads on both the socket and the inner surfaces of the post provide enhanced bending strength for those loads. It will be noted that the post and socket may each be made from a section of extrusion to further facilitate the manufacture and assembly. 
         [0082]    The embodiment of  FIGS. 17 and 18  provide a robust construction of bow that may be easily assembled without resorting to welding. The enlarged bosses provide the increased retention necessary to withstand the vibrations inherent in use on vehicles and the improved bending resistance of the post assembly shown in  FIGS. 19 and 20  provides enhanced security for the rear bow without significant additional weight. 
         [0083]    Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto. The entire disclosures of all references recited above are incorporated herein by reference.