GB2328666A - Jack-knife resistant apparatus - Google Patents

Abstract

An apparatus for controlling the relative movement of two articulated portions of a vehicle to reduce or prevent jack-knifing comprises a strut 10 having a cylinder 12 with two chambers and a piston 14, in which a group of flow passages 18 pass from one side of the piston to the other. The passages 18 are closable by slidable shuttle members 20 which are biassed to the centre position by leaf springs 24. When the rate of movement between the portions of the vehicle increases, the pressure to one side of the piston builds up and drives the shuttle members 20 to a limit position to block the flow passages 18 and lock the piston, preventing further movement between the portions of the vehicle.

Description

Jackknife Resistant ADDaratus This invention relates to apparatus for resisting or preventing an articulated vehicle from jackknifing, that is moving to a configuration in which the two articulated portions move well beyond the normal allowed range of angular movement to a position of 900 or more. The term articulated vehicle is used broadly to mean any vehicle or combination having two relatively articulated portions, such as car/caravan, car/boat, car/trailer combinations as well as to articulated lorries. It could also extend to motorcycles with hydraulic steering dampers.

Jackknifing of such vehicles is common and in many instances reflects the inherent instability of an articulated combination when travelling at speed.

Jackknifing or fishtailing can be triggered by the bow wave of a passing vehicle sending the articulated vehicle into undamped oscillation.

It is known to provide a friction stay between a car and caravan with the aim of providing friction damping to prevent jackknifing but these systems can only provide limited restraint, and this may not be sufficient in which case the jackknife force overrides the friction restraint.

It is also known to provide a system in which two hydraulic dampers are disposed between the caravan and the car, but these systems do not operate to prevent significant further angular movement when oscillation begins. Furthermore, for articulated lorries it is known to implement a system in which the rotation speeds of the wheels are monitored using the ABS monitors.

The ABS system attempts to avoid jack-knifing by keeping all wheels in sync, but this cannot provide a rapid response which acts directly between the articulated portions.

I have designed an arrangement in which the yawing movement (and possibly pitching if required) is used in a hydraulic device to make the coupling substantially rigid (apart from a small bypass flow for control purposes if the angular speed exceeds a preset limit). I do this by providing a hydraulic piston and cylinder or a similar type of arrangement with a passage through the piston through which fluid mair flow from one side of the piston to the other during normal movements. However the piston also has associated with this passage a pressure sensitive valve which closes the passage if the pressure induced by abnormal movement of the piston exceeds a preset amount. The passage then closes preventing further significant movement, and making the coupling substantially rigid.

Accordingly, in one aspect this invention provides apparatus for controlling the relative movement of two articulated portions of a vehicle, to reduce or prevent the possibility of said portions jackknifing, said apparatus comprising a hydraulic device having two chambers having therein hydraulic fluid, and a piston or valve element movably mounted therein, and said piston or valve element having therein at least one passage element and pressure sensitive valve means associated with said passage element adapted to close said passage if the pressure in one of said chambers exceeds a preset limit.

Although the apparatus may if required be configured as a rotary coupling, with a valve element mounted for sweeping movement in a chamber containing hydraulic fluid, it is preferred for this apparatus to be configured as a linear coupling, comprising a first part defining a cylinder and a second part defining a piston suitably housed within the cylinder, the first part being attached in use to one portion of said articulated vehicle and the second part being attached to the other, the coupling being suitably spaced laterally from the yaw axis of articulation of said vehicle, to exert control over yaw movement.

The linear coupling is also suitably spaced vertically either above or below the pitch articulation axis, to exert control over pitch movement.

The coupling should also not be exposed to relative linear movement between the articular portions, such as is found for example in automatic braking arrangement for trailers or caravans. For this type of arrangement, the linear coupling should be attached to a portion of the trailer, caravan etc. which is not capable in use of linear movement relative to the other articulated portion.

The piston preferably includes in said passage a shuttle control member biassed towards a central position in which the passage is open for the flow of fluid by respective bias means selected to be overcome if the fluid pressure to either side of the piston exceeds a set amount.

Once overcome in either sense the shuttle control member closes said passage. To allow a degree of flow from one side to the other when this passage is closed, this arrangement preferably also includes a by-pass bleed, connecting the spaces to either side of this piston. This may be in the piston itself or a separate tube or pipe connecting associated ports in the cylinder.

The rate of flow allowed through the piston may be selected by appropriately choosing the diameter and number of passages accordingly. Likewise the spring biases may be selected to provide an appropriate cut off pressure.

Indeed, where there are several passages, the spring biases may be different to provide a graduation in the resistance applied by the coupling.

Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description.

The invention may be performed in various ways and, by way of example only, an embodiment thereof will now be described in detail, reference being made to the accompanying drawings in which: Figure 1 is a section viewed through an anti jackknife coupling in accordance with this invention; Figure 2 is a schematic section view taken on lines 2:2 of Figure 1; Figure 3 is a top plan view of the tow bar/draw bar connection between a car and caravan showing the arrangement of this invention; Figure 4 is a view from the rear on a tow plate fitted on the car of Figure 3, and Figure 5 is a view looking aft onto the anti jackknife bracket secured to the draw bar of the trailer.

Referring to this Figure 1, the linear coupling or strut 10 comprises a cylinder 12 and a piston 14, secured to a piston rod 16 which passes through a sliding seal in the end wall of the cylinder. In this example, the piston is formed with a group of 6 flow passages 18 which pass from one side of the piston to the other. The flow passages may be closed by a slidable shuttle member 20 which slides within a chamber 22 in the middle of the piston and is biassed to an intermediate position in a chamber by means of proposed leaf springs 24. A bypass bleed passage 26 is disposed elsewhere in the piston for allowing flow from one side of the piston to the other. This same function could be achieved by a tube connecting 2 ports at the end of the cylinder. The spaces to either side of the piston are filled with a hydraulic fluid such as hydraulic oil. In use, the dynamic characteristics of this strut are that at low rates of movement of the piston are that the flow of hydraulic fluid through the flow passages 18 is not sufficient to overcome the bias applied to the valve shuttle member by the leaf springs and so the piston may move within the cylinder. However, at a certain rate of movement, the pressure builds up to one side of the piston will be sufficient to drive the shuttle valve member to a limit position in which it blocks the flow passages. This point the piston effectively locks, save for the very small amount of fluid which is allowed to escape through the fine bleed passage 26. It should be noted that the piston has this characteristic irrespective of whether it is extending or retracting.

Turning now to Figures 3 to 5, the strut is attached by means of 2 - axis/pivotal couplings to an attachment point on a tow plate 30 on the rear of the towing vehicle and to a similar 2 - axis pivotal coupling on a bracket on the towed vehicle. In this example, the attachment points on the tow plate and the bracket are displaced from the longitudinal towing axis both laterally and vertically on the same amounts so that the variable length of the strut is changed both when there is yaw and when there is pitch.

Depending on the typical, relative movements of these, the displacement of the attachment points in the vertical and lateral senses may be the same.

In use, when fitted to a vehicle, the strut is capable of accommodating the usual ranges and speeds of movement required for routine manoeuvring of the vehicle and the trailer, with the hydraulic fluid flowing through the flow passages -18. If however, there is a sudden movement, the sharp increase in pressure causes the shuttle movement to close thus substantially locking the device.

Claims (6)

Claims

1 Apparatus for controlling the relative movement of two articulated portions of a vehicle, to reduce or prevent the possibility of said portions jackknifing, said apparatus comprising a hydraulic device having two chambers having therein hydraulic fluid, and a piston or valve element movably mounted therein, and said piston or valve element having therein at least one passage element and pressure sensitive valve means associated with said passage element adapted to close said passage if the pressure in one of said chambers exceeds a preset limit.

2 As claimed in claim 1, although the apparatus may if required be configured as a rotary coupling, with a valve element mounted for sweeping movement in a chamber containing hydraulic fluid, it is preferred for this apparatus to be configured as a liner coupling, comprising a first part defining a cylinder and a second part defining a piston suitably housed within the cylinder, the first part being attached in use to one portion of said articulated vehicle and the second part being attached to the other, the coupling being suitably spaced laterally from the yaw axis of articulation of said vehicle, to exert control over yaw movement.

3 As claimed in claim 1 and claim 2, the linear coupling is also suitably spaced vertically either above or below the pitch articulation axis, to exert control over pitch movement.

4 As claimed in claim 2 or claim 3, the coupling should also not be exposed to relative linear movement between the articular portions, such as is found for example in automatic braking arrangement for trailers or caravans. For this type of arrangement the linear coupling should be attached to a portion of the trailer, caravan etc. which is not capable in use of linear movement relative to the other articulated portion.

5 As claimed in any preceding claim, the piston preferably includes in said passage a shuttle control member biassed towards a central position in which the passage is open for the flow of fluid by respective bias means selected to be overcome if the fluid pressure to either side of the piston exceeds a set amount.

Once overcome in either sense the shuttle control member closes Claims said passage. To allow a degree of flow from one side to the other when this passage is closed, this arrangement preferably also includes a by-pass bleed, connecting the spaces to either side of this piston. This may be in the piston itself or a separate tube or pipe connecting associated ports in the cylinder.

6 As claimed in claim 5, the rate of flow allowed through the piston may be selected by appropriately choosing the diameter and and number of passages accordingly. likewise the spring biases may may be selected to provide an appropriate cut off pressure.

Indeed, where there several passages, the spring biases may be different to provide a graduation in the resistance applied by the coupling.