GB2168021A

GB2168021A - Adjustable trailer towing linkages

Info

Publication number: GB2168021A
Application number: GB08431212A
Authority: GB
Inventors: Alan Cartwright
Original assignee: CARTWRIGHT FREIGHT SYSTEMS LIM
Current assignee: CARTWRIGHT FREIGHT SYSTEMS LIM
Priority date: 1984-12-11
Filing date: 1984-12-11
Publication date: 1986-06-11
Also published as: GB8431212D0; GB2168021B

Abstract

A rear trailer body is connected to a front load-carrying towing vehicle body by means of an adjustable towing linkage. The towing linkage comprises a tow bar (12) arranged telescopically within a tube (11). The bar (12) and the tube (11) are interconnected by a first hydraulic piston and cylinder assembly (16), and this assembly (16) is linked hydraulically to a second piston and cylinder assembly (23). As the rear trailer body pivots relative to the front towing vehicle body, the second assembly (23) is actuated, for example, by movement of a cam follower (25) along a cam track (19) and this actuates the first assembly (16) to move the bar (12) in and out of the tube (11). <IMAGE>

Description

SPECIFICATION Adjustable linkages This invention relates to adjustable linkages for use with road vehicles particularly for linking rear, load-carrying trailer bodies to front, driven, loadcarrying bodies.

With road vehicles having linked front and rear load-carrying bodies there are regulations governing the maximum overall length of the combination. In order to increase the load-carrying capacity without exceeding the maximum length it is known to use an adjustable linkage between the front and rear bodies. The linkage is retracted when the vehicle is travelling along a straight or generally straight course thereby to give a minimum separation between the bodies. When the vehicle is manoeuvred around a corner the linkage is extended to give sufficient space between the bodies for turning purposes. The size of the trailer body is selected such that the maximum permissible vehicle length is attained when the linkage is in its retracted state.Accordingly, it will be appreciated that it is possible to use a larger trailer body than is the case with a non-adjustable linkage which has to be long enough to permit turning and therefore gives a much larger separation between the bodies during normal travelling conditions.

One known adjustable linkage utilises a chain drive which is driven from the usual steering pivot of the front axle of the rear trailer body. The linkage is automatically mechanically extended and retracted in correspondence with rotation of the axle about the pivot. This arrangement is however inevitably relatively complicated and expensive, especially bearing in mind that the chain drive and extension/retraction mechanism have to be sufficiently robust to withstand the large forces which are applied in use through the linkage. Moreover it can be difficult to construct the mechanism to give a desired possibly non-linear mode of extension retraction as the axle rotates about the pivot.

A further known adjustable linkage utilises a hydraulic actuator operated from a battery-powered hydraulic drive unit. This arrangement can be of a simpler nature but it requires the provision of a battery and appropriate switching circuitry which may be inconvenient and may give rise to the risk of system failure e.g. due to battery discharge. Difficulty may also be encountered in achieving promptly a desired mode of extension/retraction especially if the switching is to be effected manually.

An object of the present invention is to provide a simple, inexpensive and reliable adjustable linkage with which a desired mode of extension and retraction can be readily automatically effected.

According to the invention therefore there is provided an adjustable linkage for interposition between first and second vehicle body structures, said linkage comprising a first member for connection to the first body structure, a second member for connection to the second body structure, a first hydraulic piston and cylinder assembly arranged between the first and second members so as to be capable of varying the separation thereof, a second hydraulic piston and cylinder assembly hydraulically connected to the first assembly, and a drive link between the second body structure and the second hydraulic assembly arranged to cause the hydraulic pressure transmitted between the said assemblies, and consequently the separation of the said members, to vary with turning of the vehicle body structures relative to each other.

With this arrangement, due to the use of hydraulic assemblies which are automatically operated in correspondence with turning of the vehicle body structures, a simple, inexpensive and reliable construction can be achieved.

Moreover, by appropriate selection of the nature of the drive link, a desired mode of variation of the separation of the said members can be readily achieved. In this respect, in a particularly preferred embodiment, the drive link comprises a cam arrangement for example a cam follower which runs along a cam track, whereby a desired mode of movement of the members can be achieved by appropriate shaping of the track. The cam track may be a passage defined between two plates and the cam follower may be a roller held captive between the plates within the passage.

Preferably the hydraulic assemblies are interconnected in an essentially closed system i.e. such that the two sides of one cylinder are respectively connected to the two sides of the other cylinder.

With regard to the said members these may be telescopically moveble relative to each other. Thus, one of the members (particularly the first member) may comprise a bar or rod movable longitudinally within a tubular part of the other member. The tubular part may be mounted centrally of an A-frame structure. The piston of the first hydraulic assembly may be connected to the rod or bar to effect movement of this into and out of the tubular part.

The second body structure is preferably a rear trailer body and the first body structure is preferably a driven front load-carrying body.

The invention will now be described further by way of example only and with reference to the accompanying drawings in which: Figure l is a diagrammatic side view of a road vehicle fitted with one form of a linkage according to the invention; Figure 2 is a partially sectioned plan view of the linkage; and Figure 3 is a diagrammatic enlarged sectional view of part of the arrangement of Figure 2.

As shown in Figure 1, a road vehicle has a front driven load-carrying body 1 linked to a rear loadcarrying trailer body 2 having front and back axle assemblies 3, 4.

As shown in Figures 2 and 3 the front axle assembly 3 has thereon a platform 5 and king pin 6 which support a front end part 7 of the trailer body 2 and permit rotation of the axle assembly 3 relative to the trailer body 2 about a vertical axis. An A-frame 8 is rigidly fixed to the axle 3 so that the apex of the frame projects forwardly of the trailer body 2. The frame 8 has two side members 9, a cross-strut 10 and an upper tube 11 which is welded on top of the members 9 and strut 10. The tube 11 extends horizontally centrally of the frame 8. A rigid tow bar 12 extends longitudinally within the tube 11 and projects at one end 13 beyond the front end of the tube 11. An eye 14 is provided in this projecting end 13 of the bar 12. The bar 12 is located within the tube 11 by supports 15 which permit free sliding of the bar 12.

A first hydraulic piston and cylinder assembly 16 is fixed to the frame 8. The cylinder is aligned with the axis of the tube 11 and the piston is rigidly fixed to the end of the bar 12 opposite to the eye 14.

The platform 5 comprises two superimposed disc-shaped plates 17, 18 and the confronting faces are provided with corresponding tracks therein which toyether define a shaped passage 19 which is open along one side 20 between the plates 17, 18. The passage 19 is symmetrical about a vertical plane through the axis of the tube 11 which plane also contains the pivot axis of the axle assembly 3.

The passage 19 has two curved inner portions 21 which extend away from and generlly transversely to the plane of symmetry, and two curved outer portions 22 inclined towards this plane.

A second hydraulic piston and cylinder assembly 23 is fixed to the trailer body 2 adjacent the platform 5 and the piston 24 projects between the plates 17, 18 at the open side 20 of the passage 19 and terminates in a roller end 25 which is slidably retained within the passage 19. Opposite ends of the cylinder of the assembly 23 are connected hydraulically respectively to the opposite ends of the cylinder of the assembly 16. The hydraulic system is closed except possibly for a top-up reservoir (not shown) to replace leaked hydraulic fluid.

In use the eye 14 is connected to a rear pivot point at the back end of the front vehicle body 1.

When the two bodies 1, 2 are in alignment the arrangement is as shown in Figure 2 i.e. the roller end 25 lies on the central point of the passage 19, the longitudinal axis of the assembly 23 lies on the vertical plane of symmetry of the passage 19, the piston of the assembly 23 is at a forward position, and the piston of the assembly 16 is at a rearward position.

If the vehicle turns round a sharp corner the platform 5 rotates relative to the roller end 25 of the piston 24 of the assembly 23 and this causes the piston to be moved rearwardly within its cylinder.

It will be seen that the shape of the passageway 19 is such that the movement of the piston does not occur linearly. The movement is small initially but becomes greater with further rotation of the platform 5.

As the piston 24 is moved rearwardly in the assembly 23, hydraulic fluid is transferred between the assemblies 16,23 and the piston of the assembly 16 moves forwardly thereby to extend the bar 12 (to the position shown in broken lines 26). The separation of the front and rear bodies 1, 2 of the vehicle is thereby increased to give adequate clearance for turning purposes.

If the vehicle bodies 1, 2 are now straightened the reverse procedure to that described above takes place and the bar 12 is retracted to the position shown in Figure 2. The bodies 1, 2 are now at the minimum separation suitable for normal travelling.

It will be appreciated that the weight of the rear trailer body 2 is towed by the front body 1 via the hydraulic assemblies 16, 23. Should the hydraulic system fail the adjustable linkage fails safe in that the bar 12 moves to its extended position but cannot be drawn out of the tube 11 due to the restraining action of stops 27 on the bar 12 which engage the support 15.

The arrangement so far described is simple and inexpensive to manufacture and install, it is reliable in operation and responds automatically to provide requisite extension or retraction of the linkage in dependence on the relative pivotal dispositions of the bodies 1, 2.

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.

Claims

1. An adjustable linkage for interposition between first and second vehicle body structures, said linikage comprising a first member for connection to the first body structure, a second member for connection to the second body structure, a first hydraulic piston and cylinder assembly arranged between the first and second members so as to be capable of varying the separation thereof, a second hydraulic piston and cylinder assembly hydraulically connected to the first assembly, and a drive link between the second body structure and the second hydraulic assembly arranged to cause the hydraulic pressure transmitted between the said assemblies, and consequently the separation of the said members, to vary with turning of the vehicle body structures relative to each other.

2. A linkage according to claim 1, wherein the drive link comprises a cam arrangement.

3. A linkage according to claim 2, wherein the cam arrangement comprises a cam follower which runs along a cam track.

4. A linkage according to claim 3, wherein the cam track comprises a passage defined between two plates and the cam follower is a roller held captive between the plates within the passage.

5. A linkage according to any one of claims 1 to 5, wherein the hydraulic assemblies are interconnected in an essentially closed system so that the two sides of one cylinder are respectively connected to the two sides of the other cylinder

6. A linkage according to any one of claims 1 to 5, wherein the said members are telescopically movable relative to each other.

7. A linkage according to claim 6, wherein one member comprises a bar or a rod movable longitudinally within a tubular part of the other member.

8. A linkage according to claim 7, wherein the tubular part is mounted centrally of an Aframe structure.

9. A linkage according to claim 7 or 8, wherein the piston of the first hydraulic assembly is connected to the rod or bar to effect movement of this into and out of the tubular part.

10. A linkage according to any one of claims 1 to 9, wherein the second body structure is a rear trailer body and the first body structure is a driven front load-carrying body.

11. An adjustable linkage according to claim 1, substantially as hereinbefore described with refer ence to and as illustrated in the accompanying drawings.