WO2000052354A1

WO2000052354A1 - Jackknife resistant apparatus

Info

Publication number: WO2000052354A1
Application number: PCT/GB1999/000565
Authority: WO
Inventors: Robert Preston
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-03-03
Filing date: 1999-03-03
Publication date: 2000-09-08
Anticipated expiration: 2001-09-03

Abstract

A jackknife resistant device comprises a piston (14) cylinder (12) arrangement and a pressure/flow rate sensitive restrictor means (20) operable to control flow to or from the variable volume in a piston/cylinder combination. The restrictor means operates so that, when the movement of the piston relative to the cylinder is within normal limits encountered during normal driving conditions, the restrictor is open, but when the extent or rate of movement exceeds a preset limit, indicative of a potential jackknife situation, the restrictor closes under the influence of the flow rate and/or pressure, to make the coupling rigid.

Description

Jackknife Resistant Apparatus

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 90° 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.

British Published AODlication 2 232 129A discloses an anti-jackknife arrangement which uses a pair of piston and cylinder assemblies symmetrically disposed to either side of the articulation axis. The cylinders are connected hydraulically front to front and back to back and a manually-operated control valve is provided to allow a user to close the valve and make the coupling rigid. There is also mention of an automatic arrangement in which the valve is progressively closed as the vehicle speed increases, e.g. by means of a wind-operated flap. British Published Application No. 2 181 398A discloses an arrangement in which a drawbar is pivotally mounted on a tractor and provided with a damping arrangement comprising a pair of hydraulic rams connected front to back with a flow circuit of non-return valves and an adjustable flow restrictor which controls the extent of hydraulic damping applied between the drawbar and the trailer.

British Published Application No. 2 076 766A discloses a hydraulic device for restricting articulation of a trailer and the towing vehicle, which comprises a telescopic ram which is connected to a reservoir via a remotely operated solenoid valve which can be open for damped movement or closed to make the ram rigid.

British Published Application No. 2 000 904A discloses a complicated system for hitching a trailer onto a towing vehicle. The system incorporates hydraulic rams and a fluid circuit including a hydraulic pump one or more remotely operated valves and one or more flow restrictors. The system may be operated to provide hydraulic damping during normal forward movement, but to make the coupling rigid for reverse movement .

British Patent No. 1,556,259 discloses an arrangement in which a pair of hydraulic rams are disposed between the towing vehicle and a trailer. The rams each comprise a piston located within a cylinder with non-captive piston rods. A pressure fluid circuit is provided with a pressure reservoir.

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 jackknifing 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 if the angular speed exceeds a preset limit (apart from a small bypass flow for control purposes) . I do this by providing a hydraulic piston and cylinder or a similar type of arrangement to define a variable volume chamber with an inlet/outlet with which is associated a pressure sensitive valve which closes to prevent relative movement if the flow through or pressure in said inlet/outlet exceeds a preset amount, to make the hydraulic piston/cylinder combination substantially rigid. This is in marked contrast to certain of the above arrangements which use a manual or remotely operated valve to make the coupling rigid when required. Clearly the manual arrangement requires the action or intervention of the driver, which is not realistic or safe in a jackknife situation. The remotely controlled valves also require complex electronic control circuits. Others of the arrangements incorporate pressure relief valves which open to allow movement when the fluid pressure rises, which in a jackknife situation means that the coupling will be capable of pivoting when under pressure, which is the opposite of what the present invention provides.

Accordingly, in one aspect, this invention provides apparatus for being coupled between the articulated portions of a vehicle to control the relative articulation movement thereof, comprising a hydraulic device including a piston means slidably mounted within a cylinder means to define at least one variable volume chamber, means for coupling in use said cylinder means and piston means to respective ones of said articulated portions, said variable volume chamber containing hydraulic fluid and having inlet/outlet means and flow restrictor means controlling the fluid flow to and/or from said variable volume chamber, and for closing to substantially prevent flow in a given direction through said inlet/outlet means if the flow rate through and/or the pressure gradient across said inlet/outlet means exceeds a preset threshold.

Preferably said hydraulic device comprises a piston means slidably mounted within a cylinder means to define a variable volume chamber to either side of said piston means, each of said variable volume chambers containing hydraulic fluid.

Said inlet/outlet means may comprise a flow passage in said piston means interconnecting said variable volume chambers, or it may comprise a flow passage connecting opposite end regions of said cylinder means.

The piston cylinder combination may be a conventional linearly acting piston within a cylinder, or it may comprise a piston vane element or the like moving angularly within a chamber constituting a cylinder, in a sealed manner similar to that of a fluid vane motor.

The apparatus preferably further includes bleed flow means for allowing a bleed flow to or from said variable volume chamber at least when said pressure-sensitive valve means is closed.

Advantageously said flow restrictor means comprises a shuttle control member disposed within a flow control passage and biassed towards an open position in which said passage is open for the flow of fluid, and being movable against said bias, in response to pressures and/or the flow rates upstream thereof above a threshold, to a closed position in which the flow through said flow control passage is nil or relatively low.

Said shuttle control member may be biassed towards an intermediate open position, and may be moved from said intermediate open position in opposite directions to two opposed closed positions in response to pressures and/or flow rates above the respective thresholds in respective directions .

In one arrangement said apparatus may further include, in series with said flow restrictor valve means, an adjustable throttle means, for adjustably throttling the fluid flow presented to said valve means in accordance with an external variable .

Said adjustable throttle means may include means for directly or indirectly sensing the road speed of the articulated vehicle and for progressively restricting the flow presented to the value means as the road speed decreases .

In another aspect this invention provides a method for controlling the relative movement of two articulated portions of a vehicle, to reduce or prevent the possibility of said portions jackknifing, said method comprising providing a hydraulic device including a piston means slidably mounted within a cylinder means to define at least one variable volume chamber, and coupling said cylinder means and piston means to respective ones of said articulated portions, said variable volume chamber containing hydraulic fluid and having inlet/outlet means and pressure-sensitive valve means controlling the fluid flow to and/or from said variable volume chamber, and for closing to substantially prevent flow in a given direction through said inlet/outlet means if the flow rate through and/or the pressure gradient across said inlet/outlet means exceeds a preset threshold.

Where the apparatus is linearly movable, it is preferably mounted in use in a position spaced the yaw axis of articulation of said vehicle, to exert control over yaw movement .

The apparatus is also preferably suitably spaced vertically from the pitch articulation axis, to exert control over pitch movement.

The coupling should also not be exposed to relative linear movement between the articulated portions, such as is found for example in automatic braking arrangements 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 subject in use to relative linear movement to the other articulated portion.

In preferred embodiments, the rate of flow allowed through said inlet/outlet means 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 view through a first embodiment of an anti-jackknife coupling in accordance with this invention;

Figure 2 is a schematic section view taken on lines II: II 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 ;

Figure 5 is a view looking aft onto the anti-jackknife bracket secured to the draw bar of the trailer, and

Figure 6 is a schematic view of a second embodiment of anti-jackknife coupling in accordance with this invention. Referring to 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 to define respective inversely varying volume chambers to either side of the piston 14. In this example, the piston is formed with a group of six flow passages 18 which pass from one side of the piston to the other. The flow passages may co-operate with and 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 shuttle chamber by means of leaf springs 24 acting in opposite senses. A bypass bleed passage 26 is also disposed elsewhere in the piston 14 for allowing bleed flow from one side of the piston to the other. The function provided by the flow passages 18 and the bleed passage 26 could be achieved by tubes connecting two ports at the end of the cylinder and an associated shuttle device or the like. Equally, the piston could transfer fluid to or from a separate reservoir via a shuttle valve control device on an inlet/outlet thereof, instead of having the piston defining two chambers.

The chambers to either side of the piston are filled with a hydraulic fluid such as hydraulic oil. In use, the dynamic characteristics of this strut 10 are that, at low rates of movement of the piston, the flow of hydraulic fluid through the flow passages 18 is not sufficient to overcome the bias applied to the valve shuttle member 20 by either of the leaf springs 24, and so the piston 20 may move within the cylinder. However, at a certain rate of movement of the piston relative to the cylinder, the pressure built up to one side of the piston (and/or the effect of the flow through the passages 18) will be sufficient to drive the shuttle valve member 20 to a limit position in which it blocks the flow passages. At 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 is bi-directional in that it 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 two axis pivotal couplings 28 to an attachment point on a tow plate 30 rigidly secured to the rear of the towing vehicle and to a similar two axis pivotal coupling 28 on a bracket 29 rigidly secured to the towed vehicle. In this example, the attachment points on the tow plate 30 and the bracket 29 are displaced from the longitudinal towing axis both laterally and vertically on the same amounts so that the effective 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 and/or flow rate causes the shuttle to close thus substantially locking the device, to a rigid condition.

Referring now to Figure 6, in this embodiment the piston 40 is located in a cylinder 42 defining two variable volume chambers 44,46 filled with hydraulic fluid with the piston 40 having a bleed passage 45 as previously. However in this embodiment the variable volume chambers are connected by a pipe 44 connecting opposite ends of the cylinder 42, and a pressure/flow rate sensitive shuttle device 46 operating on similar principles to the device described in the previous embodiment controls flow along the pipe 42. In addition, a variable flow restrictor or throttle 48 is connected in series with the shuttle device 46. This throttle 48 is remotely controlled in accordance with the speed of the vehicle e.g. from a signal from the speedometer 50. At low speed, the throttle 48 is set with its smaller opening. As the speed increases, the throttle is opened in proportion to the road speed of the towing vehicle, and thus increasing the sensitivity of the shuttle device 44 to changes in pressure, thereby permitting less relative movement between the two parts of the articulated vehicle as the speed increases.

Both these embodiments comprise a device which includes a piston cylinder arrangement and a pressure/flow rate sensitive restrictor means operable to control flow to or from the variable volume in a piston/cylinder combination. The restrictor means operates so that, when the movement of the piston relative to the cylinder is within normal limits encountered during normal driving conditions, the restrictor is open, but when the extent or rate of movement exceeds a preset limit, indicative of a potential jackknife situation, the restrictor closes under the influence of the flow rate and/or pressure, to make the coupling rigid.

Claims

1. Apparatus for being coupled between the articulated portions of a vehicle to control the relative articulation movement thereof, comprising a hydraulic device including a piston means slidably mounted within a cylinder means to define at least one variable volume chamber, means for coupling in use said cylinder means and piston means to respective ones of said articulated portions, said variable volume chamber containing hydraulic fluid and having inlet/outlet means and flow restrictor means controlling the fluid flow to and/or from said variable volume chamber, and for closing to substantially prevent flow in a given direction through said inlet/outlet means if the flow rate through and/or the pressure gradient across said inlet/outlet means exceeds a preset threshold.

2. Apparatus according to Claim 1, wherein said hydraulic device comprises a piston means slidably mounted within a cylinder means to define a variable volume chamber to either side of said piston means, each of said variable volume chambers containing hydraulic fluid.

3. Apparatus according to Claim 2, wherein said inlet/outlet means comprises a flow passage in said piston means interconnecting said variable volume chambers.

4. Apparatus according to Claim 2, wherein said inlet/outlet means comprises a flow passage connecting opposite end regions of said cylinder means.

5. Apparatus according to any preceding Claim, wherein said piston means moves linearly within said cylinder means to vary the volume of the or each chamber.

6. Apparatus according to any of Claims 1 to 5 , wherein said piston means is angularly moveable within said cylinder means to vary the volume of the or each chamber.

7. Apparatus according to any of the preceding Claims, further including bleed flow means for allowing a bleed flow to or from said variable volume chamber at least when said pressure-sensitive valve means is closed.

8. Apparatus according to any of the preceding Claims, wherein said flow restrictor means comprises a shuttle control member disposed within a flow control passage and biassed towards an open position in which said passage is open for the flow of fluid, and being movable against said bias, in response to pressure and/or the flow rate upstream thereof above a threshold, to a closed position in which the flow through said flow control passage is nil or relatively low.

9. Apparatus according to Claim 8, wherein said shuttle control member is biassed towards an intermediate open position, and may be moved from said intermediate open position in opposite directions to two opposed closed positions in response to pressure and/or flow rate above the respective thresholds in respective opposite directions.

10. Apparatus according to any of the preceding Claims, which further includes in series with said pressure- sensitive valve means an adjustable throttle means for adjustably throttling the fluid flow presented to said valve means in accordance with an external variable .

11. Apparatus according to Claim 10, wherein said adjustable throttle means includes means for directly or indirectly sensing the road speed of the articulated vehicle and for progressively restricting the flow presented to the value means as the road speed decreases.

12. A method for controlling the relative movement of two articulated portions of a vehicle, to reduce or prevent the possibility of said portions jackknifing, said method comprising providing a hydraulic device including a piston means slidably mounted within a cylinder means to define at least one variable volume chamber, and coupling said cylinder means and piston means to respective ones of said articulated portions, said variable volume chamber containing hydraulic fluid and having inlet/outlet means and pressure-sensitive valve means controlling the fluid flow to and/or from said variable volume chamber, and for closing to substantially prevent flow in a given direction through said inlet/outlet means if the flow rate through and/or the pressure gradient across said inlet/outlet means exceeds a preset threshold.