AU2010246497B2

AU2010246497B2 - A docking system for a roll back trailer

Info

Publication number: AU2010246497B2
Application number: AU2010246497A
Authority: AU
Inventors: Gregory Brown
Original assignee: Freighter Group Property Pty Ltd
Current assignee: Freighter Group Property Pty Ltd
Priority date: 2009-12-11
Filing date: 2010-11-29
Publication date: 2013-11-07
Anticipated expiration: 2030-11-29
Also published as: NZ589580A; AU2010246497A1

Abstract

A docking system, for a roll back trailer, includes: 5 a) a frame member and a double acting actuator mounted or mountable on the frame member; and b) an engagement member with which the actuator is releasably engageable. The actuator is extendable and retractable along the line of movement of the van or 10 body between the forward and rearward positions such that engagement of the actuator with the engagement member is able to be made and retained during the final stage of movement towards the forward position, retained while in the forward position and retained during the initial stage of movement away from the forward position, to move the van or body towards and away from the forward position, 15 respectively, during the final stage and the initial stage. The system is operable with bearing members to respectively raise the van or body to lift the rollers out of contact with the rails and to lower the van or body to bring the rollers back into rolling contact with the rails. 874593 sped fo AU & NZ co N*

Description

P/00/01 1 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: A DOCKING SYSTEM FOR A ROLL BACK TRAILER Applicant: Transtech Research Pty Ltd The following statement is a full description of this invention, including the best method of performing it known to me: 1 6007 SYC 2 A DOCKING SYSTEM FOR A ROLL BACK TRAILER The present invention relates to a docking system for a roll back trailer. 5 Roll back trailers of the type to which the present invention relates have a horizontally disposed chassis along which a cargo or produce storage van or body is horizontally moveable on rollers running on chassis rails. The arrangement is such that the body is moveable between a forward position which it occupies during travel on the trailer, and a rearward position for loading and unloading of the body. Examples of that type 10 of roll back trailer are the Reefer lead trailer and the Hi-CUBE Reefer lead trailer manufactured in Ballarat, Victoria by the Maxi-CUBE Division of MaxiTRANS Industries Limited. Another example is the FREIGHTER Roll Back lead trailer manufactured by the Freighter Division of that company. 15 These Maxi-CUBE and Freighter lead trailers have a roll back system that uses a rack external to the chassis and a horizontal hydraulic drive motor powered by an electro hydraulic power pack. Each of those Maxi-CUBE trailers has a refrigerated van body with a refrigerator plant which automatically charges the battery of the power pack, although the present invention also extends to vehicles of the type described which, 20 like the Freighter lead trailer, are not refrigerated. The hydraulic output from a power pack of those lead trailers is operable to move the van body between the forward and rearward positions, along the rack, by means of a pinion mounted on the van body and engaged with the rack. The van body has rollers spaced along each side, with rollers nearer to the leading end of the body as the body moves towards the forward 25 position running on the upper flange of chassis rails. The other rollers are mounted on brackets which depend below the other end of the van body to enable the other rollers to run on the lower flange of the chassis rails. The Maxi-CUBE lead trailers are suitable for transporting heat sensitive produce such 30 as dairy and meat products, other chilled and frozen foods, as well as non-food heat sensitive products. However, like the Freighter lead trailer, they also can transport other produce and cargo. 874593 .po (or AU & NZ 3 The trailers of the type to which the invention relates usually are used as the lead trailer of a B-double combination. That is, the lead trailer usually is coupled to a prime mover by one fifth wheel coupling, with a second trailer coupled to the lead trailer by another fifth wheel coupling. For that combination, the lead trailer needs to be in its 5 forward position to enable coupling of the second trailer between the lower chassis rails. However, the lead trailer usually is able to be loaded and unloaded at its rear end. For this, the second trailer is uncoupled to enable access at the rear end after the body of the lead trailer is moved along the rails to its rearward position. The arrangement is such that, after uncoupling of the second trailer, the prime mover 10 lead trailer combination is able to be reversed up to a loading dock and, with the van body of the lead trailer in its rearward position, the body is able to be loaded or unloaded. Trailers of the type to which the present invention relates suffer from a significant 15 disadvantage if the rollers remain in contact with their rails during transportation. This results from rocking of the van body, both laterally of and parallel to the rails, and from the van body lifting slightly from the rails during travel of the trailer over rough surfaces. As a consequence, depressions form in the upper surface of the flanges of the rails at locations at which each roller bears against its rail in the forward position 20 of the van body. The depressions result from wear due to frictional engagement of the rollers with the rails and brinelling resulting from the weight of a lead van body and from severe impact loading of the rail caused by vertical movement of the van body relative to the rails. With time, the depressions increase in depth until the electro hydraulic drive pack is unable to pull the loaded van body from its forward position. 25 This is due to the need for the rollers to ride up out of the depressions against the downward load of the van body and its contents. When this occurs, there is a risk of costly failure of the drive pack, while there also is a need for the worn rails to be replaced. In each case there is consequential significant and costly down-time for the user of the trailer. 30 The present invention is directed to providing a docking system, for a roll back trailer of the type described above, which enables avoidance of depressions forming in the upper surface of the rails of the flanges of the trailer during travel. 874593 speci for AU & NZ 4 The present invention provides a docking system for a roll back trailer of the type described. The system is operable over a minor part of the distance the van or body (hereinafter abbreviated to "van body") is moveable between the forward and rearward positions, to control movement of the van body over a final stage of 5 movement to, and an initial stage of movement from, the forward position. The system includes a frame member, and a double acting piston and cylinder device mounted or mountable on the frame member. The system further includes an engagement member with which the piston and cylinder device is releasably engageable. The frame member is mounted or mountable on a structural member of 10 one the van body and the trailer chassis, so that the piston and cylinder device is extendable and retractable along the line of movement of the van body between the forward and rearward positions. The engagement member is mounted or mountable on a structural member of the other one of the van body and the trailer chassis. The relative positions of the frame member and the engagement member is such that 15 engagement and disengagement, respectively, of the piston and cylinder device with the engagement member is able to be made and retained during the final stage of movement of the van body towards the forward position, retained while the van body is in the forward position and retained during the initial stage of movement of the van body away from the forward position. During the final stage and the initial stage, the 20 piston and cylinder device is operable to move the van body towards and away from the forward position, respectively. The present invention also includes a roll back trailer of the type described which has such a docking system. 25 The system further includes a respective plurality of bearing pads mounted or mountable on, or the system is operable with a respective plurality of bearing pads defined by, the van body and the trailer chassis. The arrangement is such that a bearing surface of each pad for the van body faces downwardly while a bearing 30 surface on each pad for the chassis faces upwardly. The respective bearing pads are positioned such that, with movement of the van body by the piston and cylinder device, each pad on the van body is able to ride up onto and along or along, and down from, a respective pad on the chassis, by sliding contact between respective bearing surfaces, depending on whether the van body is moving towards or away 874593 spoo for AU & NZ 5 from the forward position. The bearing pads enable the van body to be raised slightly to lift its rollers out of contact with the chassis rails as the van body moves to, and while the body is retained in, the forward position. Similarly, the van body is able to be lowered to bring its rollers back into rolling contact with the flanges of the rails as 5 the van body moves from the forward position. The piston and cylinder device could be pneumatically operated. However, as a practical matter it most preferably is hydraulically operated, as this enables use of a more compact arrangement able to be powered by the electro-hydraulic power pack 10 of the trailer. Hydraulic operation is assumed in the following and, for brevity, the piston and cylinder device will be referred to as a hydraulic actuator. The hydraulic actuator may retract to pull the van body over the final stage of movement to the forward position. In that case the actuator will extend to push the 15 van body over the initial part of the movement away from the forward position. For this, the frame member may be mounted or mountable on the van body, with the engagement member on the chassis and the hydraulic actuator extending forwardly from its mounting on the frame member to enable the leading end of the actuator to engage the engagement member in movement toward the forward position. This 20 arrangement is preferred, although other arrangements are possible. Thus, the frame member may be on the chassis with the engagement member on the van body, and the hydraulic actuator extending from its mounting on the frame member away from a forward position, to enable the engagement member to engage with the trailing end of the actuator in movement of the van body to the forward position. 25 Alternatively, the hydraulic actuator may extend to push the van body over the final stage of movement to the forward position, and pull the van body over the initial stage away from that position. In one arrangement for this, the frame member may be on the chassis, with the actuator extending towards the forward position from its 30 mounting on the frame member, and with the engagement member on the van body. In another arrangement, the frame member may be on the van body, with the actuator extending from its mounting away from the forward position, and with the engagement member on the chassis. 874593 spec for AU & NZ 6 The bearing pads may have bearing surfaces which are inclined at a small angle to the horizontal, such as at an angle from 50 to 100. However, it is preferable and found to be sufficient for each bearing surface to be substantially horizontal, but for at least each pad on the chassis to have a bevelled end at which it first is engaged by another 5 bearing pad. The bevelled ends may be at a larger angle, such as from about 150 to 250. In each case, the arrangement is to lift the van body and space its rollers from the flanges of the rails in movement of the van body to the forward position, and to lower the body so the rollers again bear against the flanges of the rails in movement of the body from that position. 10 In a first arrangement, at least the bearing pads mounted or mountable on the chassis may simply comprise a bearing plate which is connected or connectable to the chassis and which defines the bearing surface. 15 In a second arrangement, the bearing pads may have a base plate connected or connectable to the chassis and an upper bearing block which defines the bearing surface. The bearing plate of the first arrangement, or the base plate of the second arrangement may be of a suitable metal, such as steel, with the bearing block of a non-metallic material which defines the bearing surface and has physical properties 20 enabling the block to accommodate the loading applied by the van body and its contents. Where used, the bearing block preferably is of an engineering plastic material, such as Nylon. The bearing block may be mechanically inter-engaged with the base plate, or securely bonded to the base plate. Alternatively, the bearing pads mounted or mountable on the chassis may simply comprise such a bearing block 25 supported or supportable on an upwardly facing surface of the chassis. For at least some of the bearing pads mounted or mountable on the rear of the chassis, the docking system of the invention may include a respective retainer pad also mounted or mountable on the chassis. Each retainer pad is intended to be 30 spaced above its bearing pad by a distance sufficient to enable a respective bearing pad mounted on the van body to be received there between. The retainer pads may be of a similar form to the bearing pads of the second arrangement, but have a bearing face opposed to the bearing face of its bearing pad. The retainer pads are able to bear against an upper surface of a bearing pad mounted on the van body, to 874593 spec for AU & NZ 7 restrain the van body from lifting so as to separate that bearing pad from one mounted on the chassis, during travel of the trailer with the van body in the forward position. 5 The bearing pads mounted or mountable on the van body may simply comprise a metal plate, such as of steel, connected or connectable to the van body, either directly or indirectly. However, the bearing pads for the van body may comprise or include bearing block similar to that of the bearing pads of or for this chassis. Also, those bearing pads of or for the van body against which a retainer pad is to be able to bear, 0 may have an upper bearing block against which the retainer pad is to bear. While other arrangements are possible, the hydraulic actuator preferably is one able to be mounted or mountable on the frame member at, or adjacent to, a closed end of its cylinder. Thus the piston may be able to extend from the housing, away from the 15 mounting at that end. However, with this or other arrangements, the end of the actuator piston rod remote from the mounting preferably is guided during extension and retraction by a guide way defined by the frame member. The guide way may be a slot which has a main extent in the direction of movement of the van body between the forward and rearward positions. The guideway may be defined in a single plate of ?0 the frame member, or in each of substantially parallel plates between which the actuator is positioned. The actuator may have a projection, such as a transverse pin, which locates in the guideway for guiding extension and retraction of the actuator. In one form, the guideway has a lateral portion, with respect to the guideway, in which the projection of the actuator is able to be biased to hold the actuator in an extended, 25 or retracted condition, against hydraulic pressure acting against that condition. Initial contact between the actuator and the engagement member, in achieving engagement with the engagement member, may be such as to move the projection from the lateral portion of the guideway, and enable hydraulic pressure to commence extension or traction of the actuator. Prior to the projection being moved fully out of the lateral 30 guideway portion, the projection or another part of the actuator may be positioned to secure the actuator in releasable engagement with the engagement member. Thus, when the projection moves free of the lateral portion the actuator is able to retract, or to extend, to move the van body relative to the chassis to the forward position. During this movement, the projection of the actuator is able to move along the main extent of 874593 spoca for AU & NZ 8 the guideway. With reversal of operation of the actuator, the projection is able to move back along the main extent of the guideway, as the van body moves away from the forward position relative to the chassis, until the actuator is able to disengage from the engagement member and re-locate in the lateral portion of the guideway. 5 The actuator may be secured to the frame member by a coupling at which the actuator can pivot relative to the frame member. Where this is the case, the projection of the actuator may be able to enter a downwardly extending slot portion of the guideway under the influence of gravity acting on the actuator. Alternatively, the 10 slot portion may extend upwardly, with the actuator resiliently biased, by a spring or other resilient member, to enter the slot portion against gravity. In each case, the engagement member may have an inclined cam or guide surface along which the actuator rides to move the projection out of or into the slot portion of the guideway. The cam or guide surface may lead to a downwardly or upwardly open bight into 15 which the end of the actuator piston rod is received, to secure the frame member to the engagement member for movement of the van body to the forward position. For movement away from that position, the actuator may pivot, under the influence of gravity or the resilient bias, to move the projection respectively out of a downwardly or out of an upwardly opening bight. 20 In order that the invention may more readily be understood, description now is directed to the accompanying Figures, in which: Figure 1 is a side elevation of a semi-trailer incorporating a docking system according to the invention; 25 Figure 2 shows in side elevation a main part of the system in Figure 1; Figure 3 is a perspective view of the system part of Figure 2, taken from one end; Figure 4 is similar to Figure 3, but taken from the other end; Figure 5 is a perspective view of a first component of the system part of Figure 30 2; Figure 6 is similar to Figure 5, but taken from the other side of the first component; Figure 7 is a perspective view of a second component of the system part of Figure 2; 874593 apec, for AU & NZ 9 Figure 8 is a perspective view of further components of the system part of Figure 2; Figure 9 is a perspective view of one section of the trailer of Figure 1, showing additional components of the docking system; 5 Figure 10 shows in larger detail one of the additional components of Figure 9; and Figure 11 is a perspective view of another section of the trailer of Figure 1, showing more components of the docking system which are cooperable with the components of Figures 9 and 10. 10 The roll back semi-trailer 10 shown in Figure 1 of the drawings has a chassis 12 supported on wheels 14 and on retractable support legs 16. The trailer 10 also has a van body 18 carried on the chassis 12. The trailer 10 is able to be mounted behind a prime mover (not shown) by a king pin 20 depending from chassis 12 engaging with a 15 fifth wheel of the prime mover to provide a fifth-wheel coupling. Also, the trailer 10 carries a fifth wheel 24 enabling a second semi-trailer (not shown) to be hitched to and towed by trailer 10. The van body 18 is shown in a forward position, relative to the forward direction of 20 travel for trailer 10. The body 18 occupies the forward position during travel, but is able to move between that position and a rearward position shown in broken outline. To be moveable to the rearward position, any second trailer first must be uncoupled from fifth wheel 24 and the trailer 10 moved away from the second trailer, since body 18 is located over the fifth wheel 24 when in the rearward position. Movement 25 between the forward and rearward positions is enabled by a roller or roller set 26 at each side of body 18 adjacent to its forward end, and a roller or roller set 27 at each side of body 18 adjacent to its rearward end. The rollers 26 ride on the upper flange 29a of each of a laterally spaced pair of rails 28, while rollers 27 ride on a lower flange 29 of rails 28. 30 The van body 18 can be driven in its movement between the forward and rearward positions by a number of different arrangements. A preferred arrangement (not shown) has an electro-hydraulic drive which has a hydraulic motor by which drive is 874593 spec for AU & NZ 10 imparted to a pinion wheel mounted on body 18 and engaged with a rack secured along the chassis 12, between the upper rails 28. The semi-trailer 10 also includes a docking system for adjusting movement and 5 positioning of van body 18 in a final stage of its movement to the forward position, and in an initial stage of the movement of body 18 towards the rearward position, away from the forward position. As shown in Figures 2 to 8, the docking system includes a frame member 32 mounted at one side of body 18, adjacent to the roller 27 at that side, a hydraulic actuator 34 mounted in frame member 32, and an engagement 0 member 36 mounted on chassis 12. The member 36 is at a location enabling engagement between actuator 34 and member 36 which enables body 18 to be adjusted in the final stage of the movement to, and the initial stage of its movement from, the forward position for body 18. 15 The docking system also includes co-operable pairs of bearing pads spaced along the trailer 10. The bearing pads include pads 38 spaced along chassis 12, and pads 40 spaced along body 18. The location of bearing pads 40 on body 18 is such that each of them is able to co-operate with a respective one of bearing pads 38 when the body 18 is in the forward position, and during the final stage of movement to and the initial 20 stage of movement from that position. The main part of the docking system is shown in Figure 2 and includes the frame member 32, the hydraulic member 34 and the engagement member 36. As can be appreciated more readily from Figures 3 to 6, frame member 32 includes a horizontal 25 top plate 42 by which member 32 is able to be mounted, such as by bolts or welding, to the underside of a structural frame forming part the base or floor 44 of van body 18. The frame member 32 is positioned so that a vertical plate 46, which depends from and is integral with top plate 42, is located to one side of chassis 12. A stub axle 27a of one of rollers 27 is journalled in plate 46 to position that roller 27 to run on the 30 adjacent lower flange 29 of rail 28. Forwardly, of roller 27 in the direction of movement of van body 18 to the forward position, frame member 32 has a laterally spaced pair of guide plates 48. A guide slot 50 is provided in each plate 48, with each slot 50 having its main extent along the line of movement of van body 18 between the 874593 spec for AU & NZ 11 forward and rearward positions. At its end nearer to the forward position, each slot 50 has a downwardly extending lateral part 50a. The hydraulic actuator 34 is associated with frame member 32. The actuator 34 has 5 a cylinder 52 through one end of which a piston rod 53 is extendable and retractable. At its closed end, cylinder 52 has an extension tab 52a by which the actuator 34 is pivotably mounted by pin 53 to boss 54 of plate 46 of frame member 32. From boss 54, the actuator 34 extends along the line of movement of van body 18, with the outer end of rod having a lateral pin 55 which has a respective end located in the guide slot 10 50 of each guide plate 48. Thus, extension or retraction of actuator 34 moves pin 55 along the guide slots 50. When actuator 34 is extended sufficiently, pin 55 is able to move into part 50a of slot 50 by actuator 34 pivoting under gravity on pin 53. The engagement member 36, as best seen in Figure 7, has inner and outer side 15 plates 56 and 57, respectively. The plates 56 and 57 are spaced by, and integral with, a base plate 58. The member 36 is secured against a side face of structural member 60 of chassis 12, by bolts (not shown) through openings 56a of inner plate 56. The positioning of member 36 along member 60 is such that member 36 is closely adjacent to the leading end of guide plates 48 of frame member 32 when van ?0 body 18 is moved towards its forward position (to the left in Figure 2) by the above mentioned hydraulic motor. Starting with van body 18 in the rearward position, the actuator 34 is extended with pin 55 in guideway part 50a, but with hydraulic pressure supplied through coupling 25 52b. Thus, the actuator 34 is seeking to retract, but is prevented from doing so as pin 55 is held captive in guideway part 50a. When van body 18 has been loaded, the above-mentioned hydraulic motor provides drive to the pinion wheel to move van body 18 along rail 28 to the forward position. This movement is continued until actuator 34 engages with engagement member 36, after which the hydraulic motor is 30 able to be supplemented by actuator 34. Engagement of actuator 34 with member 36 is initiated by the leading end of piston rod 53 of actuator 34 engaging with an inclined cam or guide surface 57a of plate 57 of member 36. The leading end of piston rod 53 is lifted as it rides up surface 57a 874593 spec for AU & NZ 12 until, just prior to pin 55 being lifted from part 50a of guideway 50, the leading end of rod 53 enters and is held captive, during retraction of piston rod 53 relative to cylinder 52, in a downwardly opening bight 57b defined by plate 57 of engagement member 36. However, the actuator 34 then is able to retract, moving cylinder 52 along piston 5 rod 53 towards engagement member 36. This retraction of actuator 34 also draws frame member 32 relative to engagement member 36 towards the forward position. When this occurs, the van body 18 also is drawn towards the forward position, with each guide plate 48 of frame member 32 moving so each is spaced from a respective main face of plate 57 of engagement member 36. Simultaneously, guide slots 50 are 0 moved relative to the pin 55, at the leading end of rod 53 of actuator 34, until pin 55 is located at or towards the trailing end of slots 50. The stroke length for actuator 34 permitted by guide slots 50 sets the length of the final stage of movement of van body 18 over which the docking system is operable. 15 The reverse procedure is put into operation when it is required to move van body 18 to the rearward position. This proceeds over an initial stage of that movement, until actuator 34 disengages from engagement member 36, by supply of hydraulic pressure via coupling 52b (and release of pressure via coupling 52a), thereby causing actuator 34 to extend. Thus, actuator 34 extends to push frame member 32 away 20 from member 36, until pin 55 is located at the end of slots 50 nearer to the forward end of trailer 10, and pin 55 is able to fall into the part 50a of each guide slot 50. In movement of van body 18 to or towards the forward position, each bearing pad 40 is caused to move over and bear down against a respective bearing pad 38. In the 25 case of the pads 38, 40 shown in Figure 2, this is achieved by pad 40 being secured on and moveable with frame member 32, and by pad 38 having a bevel or taper 38a at its end first engaged by pad 40 as frame member 32 approaches engagement member 36. This bevel or taper 38a causes pad 40 to ride up onto pad 36, with pad 40 lifted by an amount sufficient to lift van body 18 and raise its roller 27 out of contact 30 with the lower flange of rail 28. The same occurs with the pads 38 and 40 on the opposite side of van body 18. Also the same occurs with the pads 38 shown in Figures 9 and 10 as spaced across the top surface of chassis 12, and corresponding pads 40 on the van body 18, as shown in Figure 11. The pads 38 of Figure 9 and 10 are spaced to either side of cover plate 60 above king pin 20 nearer the forward end 874593 spc for AU & NZ 13 of chassis 12. The pads 40 are located below van body 18, nearer to the forward end of body 18. The positioning of pads 38 and 40 is such that all of pads 40 move simultaneously so each rides up onto and bears down on its pad 38. While the pad 40 shown in Figure 2 is mounted on frame member 32, the other pads 40 are 5 mounted on the chassis 12. The pads 38 preferably are made of a suitable engineering plastic material, such as Nylon. They are able to be secured into position by bolts passing through holes 38b. In the case of the pads 38 shown in Figure 2 to 4 and 8, the bolts secure the pads 10 against a side surface of chassis 12. In the case of the pads 38 shown in Figures 9 and 10, each has two bearing blocks 38c bolted through holes 38b to a metal bracing member secured to an upper surface of chassis 12. The bearing pad 40 shown in Figure 2 to 4 simply comprises a metal plate secured to 15 frame member 32. Each pad 40 shown in Figure 11 is similar to its bearing pad 38 shown in Figure 9 and 10, but secured to a bottom surface of van body 18. The bearing pads 38 and 40 on the opposite side of trailer 10 and laterally in line with the pads shown in Figures 2 to 4 may be similar to the pads 38 and 40 shown in 20 Figure 9 and 10 and in Figure 11, respectively. At least for the pads 38 and 40 at the end of van body 18 shown in Figures 2 to 4, and those on the opposite side of van body 18 at that end, the adjusting system includes a retaining pad 66 secured to a bracket 66a mounted on chassis 12. The pad 66 is 25 spaced from pad 38 by a distance neatly accommodating pad 40. The pad 66 therefore is able to serve to prevent lifting of van body 18 so as to lift pad 40 out of contact with pad 38. The docking system illustrated is able to be of a simple robust and easily repaired 30 form. Its operation is able to be integrated with the usual movement of the van body between the forward and rearward positions. No additional action needs to be taken by a driver, and yet a major problem of rail wear by rollers at the forward position is able to be avoided. 874593 spc fo AU & NZ

Claims

1. A docking system, for a roll back trailer having a horizontally disposed chassis along which a storage van or body is horizontally moveable on rollers running on 5 chassis rails; wherein the docking system is operable, over a minor part of the distance the van or body is moveable between forward and rearward positions, to control movement of the van or body over a final stage of movement to and an initial stage of movement from the forward position; wherein the system includes: 10 a) a frame member and a double acting piston and cylinder actuator mounted or mountable on the frame member; and b) an engagement member with which the actuator is releasably engageable; the frame member is mounted or mountable on a structural member of one of: 15 (i) the van or body, and (ii) the trailer chassis, so that the actuator is extendable and retractable along the line of movement of the 20 van or body between the forward and rearward positions, and the engagement member is mounted or mountable on the other one of: (i) the van or body, and (ii) the trailer chassis; 25 with the relative positions of the frame member and the engagement member such that engagement of the actuator with the engagement member is able to be made and retained during the final stage of movement of the van or body towards the forward position, retained while the van body is in the forward position and retained 30 during the initial stage of movement of the van or body away from the forward position, whereby the actuator is operable to move the van or body towards and away from the forward position, respectively, during the final stage and the initial stage; and 15 wherein either the system is operable with a respective plurality of bearing members defined by the van body and the trailer chassis, or the system includes a respective plurality of bearing members mounted or mountable on the van body and the trailer chassis, such that a bearing surface of each bearing member of or for the van or body 5 faces downwardly and a bearing surface of each bearing member of or for the chassis faces upwardly, with the bearing members positioned such that, with movement of the van or body by the actuator, each bearing member of or for the van or body is able to ride up onto and along, or along and down from, a respective bearing member of or for the chassis, depending on whether the van or body is moving towards or away 10 from the forward position, to respectively raise the van or body to lift the rollers out of contact with the rails and to lower the van or body to bring the rollers back into rolling contact with the rails.

2. The system of claim 1, wherein the actuator is a hydraulically operated piston 15 and cylinder device.

3. The system of claim 1 or claim 2, wherein the actuator is retractable for pulling the van or body over the final stage of movement to the forward position, and extendable to push the van or body over the initial part of movement away from the 20 forward position.

4. The system of claim 3, wherein the frame member is mounted or mountable on the van or body, with the engagement member mounted or mountable on the chassis, with the actuator extending forwardly from its mounting on the frame member to 25 enable a leading end of the actuator to engage the engagement member in movement toward the forward position.

5. The system of any one of claims 1 to 4, wherein the bearing members comprise bearing pads mounted or mountable on the van or body and on the chassis, 30 with each pad having a substantially horizontal bearing surface, with at least each pad mounted or mountable on the chassis having a bevelled end at which it is first engageable by a pad mounted or mountable on the van or body. 16

6. The system of claim 5, wherein at least each bearing pad mounted or mountable on the chassis has a non-metallic block which is secured on a base and which defines the bearing surface, with the block secured to a metallic base of the bearing pad, or directly secured or securable to the chassis. 5

7. The system of claim 5, wherein at least each bearing pad mounted or mountable on the chassis comprises a metallic block which defines the bearing surface. 10

8. The system of any one of claims 5 to 7, wherein the system further includes, for at least some of the bearing pads mounted or mountable on the chassis, a respective retainer pad also mounted or mountable on the chassis to restrain the van body from lifting during travel of the trailer with the van or body in the forward position. 15

9. The system of any one of claims 1 to 8, wherein, at or adjacent to a closed end of the cylinder, the actuator is pivotably mounted on the frame member, with the piston having a piston rod projecting from the other end of the cylinder; the frame member defines an elongate guideway that has a main extent in the direction of the line of movement of the van or body, with a projection of the piston rod engaged with 20 the guideway throughout extension and retraction of the actuator; the guideway has a downwardly extending portion remote from the cylinder into which the projection is able to be biased to hold the piston rod in an extended condition in movement of the frame member towards the engagement member; and wherein the engagement member has a cam or guide surface engageable with the extended piston rod to lift 25 the projection from the downwardly extending portion of the guideway for engagement of the piston rod with the engagement member whereby the actuator is able to retract and thereby move the frame member relative to the engagement member and move the van or body to the forward position. 30

10. The system of claim 9, wherein the projection is biased into the downwardly extending portion of the guideway under gravity and the cam or guide surface is adapted to lift the projection into a bight defined by the engagement member and in which the projection is held by the retracted actuator. 17

11. A roll back trailer having a horizontally disposed chassis along which a storage van or body is horizontally moveable on rollers running on chassis rails; wherein the trailer includes a docking system operable, over a minor part of the distance the van or body is moveable between forward and rearward positions, to control movement of 5 the van or body over a final stage of movement to and an initial stage of movement from the forward position; wherein the system includes: a) a frame member and a double acting piston and cylinder actuator mounted on the frame member; and 10 b) an engagement member with which the actuator is releasably engageable; the frame member is mounted on a structural member of one of: 15 (i) the van or body, and (ii) the trailer chassis, so that the actuator is extendable and retractable in the direction of the line of movement of the van or body between the forward and rearward positions, and the 20 engagement member is mounted on the other one of: (i) the van or body, and (ii) the trailer chassis; 25 with the relative positions of the frame member and the engagement member such that engagement of the actuator with the engagement member is able to be made and retained during the final stage of movement of the van or body towards the forward position, retained while the van body is in the forward position and retained during the initial stage of movement of the van or body away from the forward 30 position, whereby the actuator is operable to move the van or body towards and away from the forward position, respectively, during the final stage and the initial stage; and wherein either the system includes a respective plurality of bearing members mounted on the van body and the trailer chassis, such that a bearing surface of each bearing member of the van or body faces downwardly and a bearing surface of each 18 bearing member of the chassis faces upwardly, with the bearing members positioned such that, with movement of the van or body by the actuator, each bearing member of the van or body is able to ride up onto and along, or along and down from, a respective bearing member of the chassis, depending on whether the van or body is 5 moving towards or away from the forward position, to respectively raise the van or body to lift the rollers out of contact with the rails and to lower the van or body to bring the rollers back into rolling contact with the rails.

12. The trailer of claim 11, wherein the actuator is a hydraulically operated piston 10 and cylinder device.

13. The trailer of claim 11 or claim 12, wherein the actuator is retractable for pulling the van or body over the final stage of movement to the forward position, and extendable to push the van or body over the initial part of movement away from the 15 forward position.

14. The trailer of claim 13, wherein the frame member is mounted on the van or body, with the engagement member mounted on the chassis, with the actuator extending forwardly from its mounting on the frame member to enable a leading end 20 of the actuator to engage the engagement member in movement toward the forward position.

15. The trailer of any one of claims 11 to 14, wherein the bearing members comprise bearing pads mounted on the van or body and on the chassis, with each 25 pad having a substantially horizontal bearing surface, with at least each pad mounted on the chassis having a bevelled end at which it is first engageable by a pad mounted on the van or body.

16. The trailer of claim 15, wherein at least each bearing pad mounted on the 30 chassis has a non-metallic block which is secured on a base and which defines the bearing surface, with the block secured to a metallic base of the bearing pad, or directly secured or securable to the chassis. 19

17. The trailer of claim 15, wherein at least each bearing pad mounted on the chassis comprises a metallic block which defines the bearing surface.

18. The trailer of any one of claims 15 or claim 17, wherein the system further 5 includes, for at least some of the bearing pads mounted or mountable on the chassis, a respective retainer pad also mounted or mountable on the chassis to restrain the van body from lifting during travel of the trailer with the van or body in the forward position. 10

19. The trailer of any one of claims 11 to 18, wherein, at or adjacent to a closed end of the cylinder, the actuator is pivotably mounted on the frame member, with the piston having a piston rod projecting from the other end of the cylinder; the frame member defines an elongate guideway that has a main extent in the direction of the line of movement of the van or body, with a projection of the piston rod engaged with 15 the guideway throughout extension and retraction of the actuator; the guideway has a lateral portion remote from the cylinder into which the projection is able to be biased to hold the piston rod in an extended condition in movement of the frame member towards the engagement member; and wherein the engagement member has a cam or guide surface engageable with the extended piston rod to move the projection from 20 the lateral portion of the guideway for engagement of the piston rod with the engagement member whereby the actuator is able to retract and thereby move the frame member relative to the engagement member and move the van or body to the forward position. 25

20. The trailer of claim 19, wherein the projection is biased into the lateral portion of the guideway under gravity and the cam or guide surface is adapted to lift the projection into a bight defined by the engagement member and in which the projection is held by the retracted actuator.