GB2232139A

GB2232139A - Anti-jack-knife device

Info

Publication number: GB2232139A
Application number: GB8807767A
Authority: GB
Inventors: James Steel
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-03-31
Filing date: 1988-03-31
Publication date: 1990-12-05
Anticipated expiration: 2008-03-31
Also published as: GB2232139B; GB8807767D0

Abstract

An anti-jack-knife device for an articulated vehicle comprising a pair of piston and cylinder assemblies (24). These are symmetrically arranged on each side of the axis of articulation and are connected between the front and rear parts of the articulated vehicle. The front and rear parts of the cylinder 36 either side of the piston, may be connected via a flow restricting device 41. For straight travel the piston-cylinder devices may be locked, but controlled to become operate in response to vehicle speed exceeding a predetermined threshold. <IMAGE>

Description

ANTI-JACK-KNIFE DEVICE The present invention relates to an anti-jackknife device for articulated vehicles in particular towed vehicles such as caravans, horseboxes and also trailers behind lorry cabs i.e. articulated lorries.

The tendency for articulated vehicles to "jackknife" can occur when the front member of the vehicle brakes more sharply than the rear section (or towed part) with the result that the rear section tends to overtake the front. This is particularly dangerous in the case of caravans and articulated freight lorries in wet road conditions.

Another instance where jack-knifing can occur in the case of caravans and trailers is when swaying of the trailer takes place. This may be as a result of being overtaken by a large vehicle or due to crosswinds. Often, the swaying builds up and the driver may loose control.

It is an object of the present invention to provide a device which can reduce or minimise the risk of jack-knifing and of a vehicle swaying excessively.

According to the invention, an anti-jack-knife device for an articulated vehicle comprises an hydraulic piston and cylinder assembly connected between part of the articulated vehicle and a member which is rotationally fixed relative to the other part of the vehicle in the sense of articulation.

Preferably, the piston and cylinder assembly is offset from the axis of articulation and is preferably connected between the rear part of the vehicle and a member attached to the front part of the vehicle. In the present application, the term articulated vehicle is intended to cover not only such vehicles as articulated lorries, but also a car towing a trailer, caravan, horsebox, etc.

In the case of a single piston and cylinder being used, the portions of the cylinder on each side of the piston are preferably interconnected, preferably through a flow restrictor of some sort. Preferably, a control valve is provided which is operable to restrict progressively the flow of hydraulic fluid, thereby enabling the piston to be effectively "locked". Even in the "locked" position a small leakage is preferably provided.

The invention may therefore be considered to provide an hydraulic circuit in which the fluid is made to move as articulation of the vehicle occurs. Any restriction to the flow of fluid will therefore tend to oppose articulation and conveniently, the control valve could be operated at a vehicle speed threshold to begin a progressive restriction up to a maximum at a relatively high speed such as 3D mph or more. The valve could be manually operated or may operate automatically e.g. by a wind-operated flap, and may act against a resilient or biasing force such as a spring.

In a preferred embodiment, two piston and cylinder assemblies are employed. These may be symmetrically located on each side of the axis of articulation. They may each include an hydraulic connection as described above. More preferably, however, the cylinders are connected hydraulically "front-to-front" and "back-toback". This arrangement then effectively constitutes a single hydraulic circuit and only one flow control valve need be provided, though, of course, more than one can be present if required.

The invention may be used with existing tow-bar arrangements e.g. by connecting a cross-member to the tow bar bracket. The piston and cylinder assembly or assemblies can then be connected between the bracket and the trailer.

The invention may be carried into practice in various ways and one embodiment will now be described by way of example with reference to the accompanying drawings in which the single figure is an exploded schematic view of an anti-jack-knife device in accordance with the invention. The device illustrated is to be used with an existing tow-bar arrangement.

The existing tow bar arrangement comprises a tow bar mount 11 and a ball coupling 12 held together by bolts 13. In order to attach the anti-jack-knife device, an intermediate plate 14 is inserted between the mount 11 and the coupling 12.

The plate 14 has a series of eyelets 15 while a corresponding series of eyelets 16 are formed on a stub shaft member 17. A hinge pin 18 passes through the eyelets 15, 16 and is locked in place by a locking pin 19. A stub shaft 21 extends from the member 17 and is received in a bearing bush 22 mounted on a transverse angle iron or bracket 23.

The stub shaft is capable of sufficient fore and aft movement to allow the over-run brakes of the caravan or trailer to operate.

An hydraulic piston and cylinder assembly 24 extends rearwardly from each end of the bracket 23. The two assemblies 24 are identical and so only one will be described. The end of the piston 25 of the assembly 24 is attached to the bracket 23 by means of a bolt 26 passing through corresponding holes in the bracket 23, in an end piece 27 of the piston 25, and in a lower support flange 28. The bolt 26 is locked in place by a locking pin 29 and the assembly 24 is capable of a swinging movement about the bolt.

A plate 30 is bolted to the A-frame on each side of the trailer at the required height by means of a series of bolt holes 31. The position of each plate 30 is arranged so that the piston 25 is at a position approximately half way along its travel. The plate 29 includes a hole 32 which receives a spigot 33. The spigot 33 is held in place by a locking pin 34 which passes through a hole at one end of the spigot 33. A U-bracket 35 is attached to the other end of the spigot 33 and the end of the cylinder 36 of the assembly 24 is located in the U-bracket 35 by means of a pin 37 which passes through corresponding holes in the U-Bracket 35 and the cylinder 36, thereby allowing limited pivotal movement of the cylinder relative to the plate 30 about the pin 37 and the spigot 33.

An hydraulic linkage 38-38 is provided between the front ends of the two pistons 36 and a similar linkage 39-39 is provided between the rear ends of the piston 36. Thus, an hydraulic circuit is formed linking the two pistons 36. A flow restricting valve 41 is located in the line 38-38 which is controlled manually from the vehicle by means of a control line 42.

The operation of the device is as follows. The trailer is attached to the towing vehicle by means of the ball coupling 12 in the normal way and also by means of the pins 34 and the spigots 33. As the coupled vehicle articulates the pistons 25 move into and out of the cylinders 36 and the hydraulic fluid flows in the lines 38-38 and 39-39. Any relative pitching between the two parts of the vehicle would be accommodated by the hinge pin 18 while any relative rolling and longitudinal movement would be accommodated by the stub shaft 21.

As speed increases, the valve 41 is operated to restrict hydraulic flow, thereby increasing the opposition to articulation provided by the piston and cylinder assemblies 24. At a desired speed, such as 30 mph, the valve may be closed completely so that the hydraulic circuit becomes rigid. Nevertheless, a small leakage is provided to allow for small movements.

Claims

1. An anti-jack-knife device for an articulated vehicle comprising a hydraulic piston and cylinder assembly connected between part of the articulated vehicle and a member which is rotationally fixed relative to the other part of the vehicle in the sense of articulation.

2. A device as claimed in Claim 1 in which the piston and cylinder assembly is offset from the axis of articulation.

3. A device as claimed in Claim 1 or Claim 2 in which the piston and cylinder assembly is connected between the rear part of the vehicle and a member attached to the front part of the vehicle.

4. A device as claimed in any preceding claim in which the portions of the cylinder on each side of the piston are interconnected by way of a flow restrictor.

5. A device as claimed in Claim 4 in which the flow restrictor is a control valve operable to restrict progressively the flow of hydraulic fluid, thereby enabling the piston to be locked.

6. A device as claimed in Claim 5 in which, even in the locked position, a small leakage is provided.

7. A device as claimed in Claim 5 or Claim 6 in which the control valve is operable at a vehicle speed threshold to begin a progressive restriction up to a maximum at a predetermined speed.

8. A device as claimed in any preceding claim including two piston and cylinder assemblies.

9. A device as claimed in Claim 8 in which the two piston and cylinder assemblies are symmetrically located on each side of the axis of articulation.

10. A device as claimed in Claim 8 or Claim 9 in which there is a hydraulic connection between the front parts of each of the two cylinders and a hydraulic connection between the back parts of the two cylinders.

11. An anti-jack-knife device constructed and arranged substantially as herein specifically described with reference to and as shown in the accompanying drawing.