GB2076766A - Device to Restrict Relative Movement Between a Trailer and a Towing Vehicle - Google Patents

Abstract

A device 20 for restricting relative pivotal movement of a trailer and a towing vehicle comprises a ram 46 carrying a piston 44 movable in a cylinder 34 itself movable in a further cylinder 30. Hydraulic fluid 32 within the device communicates via a pipe 52 and a solenoid valve 56 with a reservoir 50. The valve 56 is maintained open during urban driving to allow damped relative pivotal movement of the trailer and towing vehicle. The valve 56 is closed during motorway driving to substantially prevent relative pivotal movement of the trailer and towing vehicle. <IMAGE>

Description

SPECIFICATION Device to Restrict Relative Movement Between a Trailer and a Towing Vehicle This invention relates to a device for restricting relative movement between a trailer such as a caravan and a vehicle towing it.

Trailers such as caravans are normally connected to the towing vehicle by a single pivotable towing connection. When a caravan is being towed at high speed by a car, there is a danger that the driver may lose control of the car if the caravan should happen to veer about this pivotable connection so that it is no longer aligned with the car. This can for example happen because of slipstream effects when the car and caravan are overtaken by another vehicle, or because of cross winds acting against the higher side of the caravan. Similar problems arise with articulated vehicles.

According to the invention there is provided a device for restricting relative movement between a trailer and a vehicle towing it, which includes means connectable at opposing ends with the trailer and the towing vehicle respectively, which is arranged to resist longitudinal movement of the ends towards or away from each other, whereby when connected between a trailer and a towing vehicle'at a position laterally offset from a pivotable towing connection between the trailer and the towing vehicle, said means tends to resist relative pivoting of the trailer and towing vehicle about the towing connection.

Preferably said means comprises a piston and cylinder connectable one to the trailer and one to the towing vehicle the cylinder containing hydraulic fluid. Preferably the hydraulic fluid can be displaced by the piston from the cylinder to a reservoir. Preferably two cylinders are provided, said piston acting inside one cylinder which itself is arranged to act as a piston inside the other, the two cylinders communicating by means of one or more bleed holes or passages, whereby said one cylinder can telecope inside the other to displace hydraulic fluid into the reservoir.

Three devices according to the invention will now be described by way of example, with reference to the accompanying drawings, wherein: Fig. 1 is a schematic plan view of a car towing a caravan, fitted with either the first or the second device, Fig. 2 is a schematic cross-section through the first device, Fig. 3 is a schematic cross-section through the second device, Fig. 4 is a plan view of a connection between the second device and a towing vehicle, and Fig. 5 is a plan view of the third device.

Referring firstly to Fig. 1, a car 10 towing a caravan 12 has a conventional load bearing ball hitch towing connection 14, mounted on brackets 1 6, 18 respectively at the centre rear of the car and the centre front of the caravan. Normally, when manoeuvring the car and caravan or driving in urban conditions, it is necessary for the caravan to pivot with respect to the car about a vertical axis through the connection 1 4. However, when driving at high speed (for example along a motorway) such pivoting is undesirable because the car 10 is difficult to control when the caravan is blown out of alignment with the car, for example by cross-winds or by the slipstream effect of other vehicles.The device 20 is therefore connected between the rear of the car 10 and the front of the caravan 12, laterally offset from the connection 14, either at the near-side or the offside.

As seen in Fig. 2, the device 20 is arranged between two ball hitch joints comprising a ball 22 attached to a bracket 24 on both of the car and the caravan. These balls 22 mate with ball cups 26 at each end of the device 20, allowing the device 20 to pivot in any direction.

Each ball cup 26 is held onto the corresponding ball 22 by a spring 28 acting between the device 20 and the bracket 24. If the car and caravan should be involved in an accident such as the overturning of the caravan, one or both of these springs will break, allowing the corresponding ball cup 26 to unseat from its ball 22 so that the car is not dragged by the caravan.

The device 20 comprises a first hydraulic cylinder 30 filled with a hydraulic fluid such as oil 32. A second cylinder 34 is of smaller diameter than the cylinder 30, and has an end face 36 which forms a slidable piston inside the cylinder 30, being fitted with a peripheral sealing ring (not shown). The cylinder 34 can thus telescope inside the cylinder 30. The end face 36 is provided with one or more bleed holes 38 between the first and second cylinders, and also with bleedholes 40 communicating between the end space 42 of the cylinder 30 behind the end face 36 and the rest of the cylinder 30.

The second cylinder 34 also has a piston 44, which also has a peripheral sealing ring (not shown) and can telescope into the cylinder 34 under the action of a ram 46.

One ball cup 26 is attached to the cylinder 30 at one end of the device 20, while the other ball cup 26 is attached to the free end of the ram 46.

Because of the telescoping action of the cylinders 30, 34 and the ram 46, there is a wide range of possible longitudinal movement between the two ball hitches.

Slung underneath the first cylinder 30 on mountings 48 is a reservoir 50 for the oil 32. This reservoir 50 communicates with the cylinder 30 by means of a steel pipe 52, in a portion 54 of which is fitted a solenoid valve 56. The solenoid valve 56 is controlled electrically from the dashboard of the car by means of wires 57, and operation of this valve makes or breaks the communication along the pipe 52 between the reservoir 50 and the cylinder 32. From an extension 58 of the pipe 52, before the valve 56, a flexible rubber hose 60 leads to the end space 62 of the second cylinder 34, behind the piston 44. The reservoir has an air breather outlet 64 to allow displacement of air by the oil 32.

In use, for manoeuvring and general urban driving, the solenoid valve 56 will be left open.

This permits the end face 36 and piston 44 to move in their respective cylinders, and allows the car and caravan to pivot relatively about the connection 14. As the ball joints 22 move together and the end face 36 and piston 44 move further into their respective cylinders, the combined volume of the cylinders is reduced and oil 32 is displaced through the pipe 52 to the reservoir 50, oil in the cylinder 34 passing through the bleed hole 38 in the end face 36. At the same time, the end space 42 in the cylinder 30 is filled through the bleed holes 40, while the end space 62 in the cylinder 34 is filled through the flexible hose 60. When the end face 36 and piston 44 are moving outwardiy (i.e. when the ball joints 22 are moving further apart) the oil flows in the reverse direction.

When travelling at high speed along a motorway or other open road, the driver will close the solenoid valve 56 by operating a switch (not shown) on his dashboard. This will prevent the oil 32 from passing into or out of the reservoir 50.

Consequently, the end face 36 and piston 44 are held in substantially fixed positions in their respective cylinders, since any movement would entail a change in volume of the oil 32, which is virtually incompressible. To facilitate this, the diameter of the ram 46 is made comparatively large so as to displace a large volume of oil in the end space 62. As a result, the device 20 substantially prevents any relative pivoting movement between the car and the caravan about the vertical axis through the connection 14.

It will be apparent that by tailoring the diameters of the bleed holes 38, 40 and of the pipes 52, 60, any desired degree of damping can be obtained for the normal condition in which the solenoid valve 56 is open. For example, in normal use it may be arranged that pressures of say 350 to 500 p.s.i. (25 to 35 kg/cm2) act against the bleeding of the oil through the holes 38,40 and pipes 52, 60. With the solenoid valve 56 in the closed position, pressures of up to 1000 p.s.i. (70 kg/cm2) may be experienced. As a safety measure, the solenoid valve 56 may be made of the pressure relief type which allows the passage of oil above a given pressure.Suitably this pressure might be 1000 p.s.i. (70 kg/cm2) so that when this pressure is exceeded (for example if the car or caravan is involved in an accident, or is obliged to swerve suddenly), the valve opens to allow pivoting between the car and the caravan. Such a feature would also come into operation if the dashboard switch were operated to close the solenoid valve when the car and caravan were not aligned with each other; in such a case pressure in the system would prevent the valve from closing compietely until the car and caravan were aligned.

Although it does not matter which ball cup 26 is connected to the car and which to the caravan, it is easier to connect the wires 57 to the car's electrical system if the ball cup 26 on the cylinder 30 is connected to the car. If despite the telescoping action of the cylinders it is found that the length of the cylinder 30 increases the minimum turning circle of the car and caravan combination, this ball cup 26 can be attached to the cylinder 30 further along the body thereof rather than at its end as shown in Fig. 2.

Fig. 3 shows an alternative, simpler device 21 which can be used in place of the device 20 shown in Fig. 2. Like the device 20, it has a first cylinder 30; a second cylinder 34 of smaller diameter, the end face 36 of which forms a slidable piston inside the cylinder 30; and a piston 44 which is slidable in the cylinder 34 under the action of a ram 46. The ends of the cylinders 30, 34 are fitted with air- and oil-tight seals 68. The pistons 44 and 36 both fit in their respective cylinders with a degree of tolerance at 70, so that hydraulic fluid 32 in the cylinders can bleed around them into the end spaces 42, 62, providing a damping action on the sliding of the pistons in the cylinders. Bleed holes 38 are again provided in the end face 36 so that fluid 32 can pass between the cylinders 30, 34, giving more damping.If desired bleed holes could be provided into the end spaces 42, 62 instead of the tolerances at 70.

The cylinder 30 communicates with a reservoir tank 50 for the oil 32 by means of a tube 52.

Unlike the reservoir shown in Fig. 2, inside this reservoir there is a rubber sack 72 for containing the oil 32, which sack expands and contracts in the reservoir tank 50 as the pistons and cylinders telescope into and out of each other, displacing oil through the tube 52. The tank 50 has a breather hole 64 for air as before, but with this arrangement (which could of course be used in the Fig. 2 device) there is no danger of oil being lost through the breather hole.

The arrangement shown in Fig. 3 relies simply on the damping provided at 38 and 70 to resist relative pivoting between the car and caravan, and of course this can be tailored as desired when designing the device by varying the dimensions of the bleed holes 38 and of the tolerances 70, or by using hydraulic oil of a different viscosity. It would however be possible to include a solenoid valve in the tube 52, to enable the user to alter the resistance to pivoting, as in the device of Fig. 2. A pressure relief valve would again be preferred.

In place of the ball hitch connections of Fig. 2, a simple and cheap universal or constant velocity joint is shown in Figs. 3 and 4 for making the connections between the device 21 and the car and caravan. A U-shaped bracket 74 is fixed to each of the ram 46 and the end of the cylinder 30.

The arms of each bracket 74 carry a generally horizontal shear pin 76, about which pivots a lug 78 which is integral with a block 80. The block 80 has a generally vertical bore 82. In use a pin (not shown) will be passed through the bore 82 to pivotably mount the block 80 to a U-shaped bracket on the car or caravan. The device 21 can thus pivot freeiy in any direction relative to the car or caravan, but if an abnormally high load is placed on the shear pin 76 it will shear so that the car will not be dragged by the caravan in the event of an accident. The lugs 78 are deliberately left square and are not rounded off, so as to assist this shearing.

Fig. 5 shows an alternative device. A conventional A-shaped towing bracket 84 projects from the front of the caravan chassis 86.

It has a cup 88 which connects to a conventional ball hitch bracket 90 mounted to the rear of the car by bolts 92. The bracket 90 is provided with a bar 94 extending laterally at either side. At each end portion of the bar 94, laterally offset from the ball hitch, a universal joint 96 of the same type as shown in Fig. 4 pivots about a removable shear pin 98. At each side of the A-shaped bracket 84, a further similar universal joint 100 is mounted on a bracket 101, pivoting about a shear pin 102. On each side, a double-acting telescopic damper 104 is mounted between respective universal joints 96,100. The dampers used are commercially available under the Trade Mark Redmax H from Messrs. Armstrong Shock Absorbers Ltd., and comprise a cylinder containing hydraulic fluid, and a piston, the fluid being allowed to bleed from one side of the piston to the other.It would be possible to use a single acting damper on each side, but their load ratings would have to be increased.

In use, as the A-bracket 84 pivots about the ball hitch bracket 90, one damper 104 will contract and the other will expand, resisting the pivoting movement. For balanced operation and to reduce the danger of accidental shearing, when the device is installed the pins 98 should be in line with the ball hitch. Also, the dampers 104 should be arranged with their two halves 104a, 104b at a midpoint of their telescoping action when the car and caravan are in line. This can be facilitated by an appropriate mask on the inside half 1 04b.

A spring clip 106 (e.g. a Terry clip-Trade Mark) is provided on each side of the A bracket 84 to hold the corresponding damper 104 when the shear pin 98 is removed to disconnect the caravan from the car.

Although particularly reference has been made to cars and caravans, the devices described can be easily adapted for use with other trailers and towing vehicles, e.g. the trailer and tractor unit of an articulated lorry.

Claims (9)

Claims

1. A device for restricting relative movement between a trailer and a vehicle towing it, which includes means connectable at opposing ends with the trailer and the towing vehicle respectively, which is arranged to resist longitudinal movement of the ends towards or away from each other, whereby when connected between a trailer and a towing vehicle at a position laterally offset from a pivotable towing connection between the trailer and the towing vehicle, said means tends to resist relative pivoting of the trailer and towing vehicle about the towing connection.

2. A device according to claim 1 wherein said means comprises a piston and cylinder connectable one to the trailer and one to the towing vehicle the cylinder containing hydraulic fluid.

3. A device according to claim 2 wherein the hydraulic fluid can be displaced by the piston from the cylinder to a reservoir.

4. A device according to claim 2 or claim 3 wherein two cylinders are provided, said piston acting inside one cylinder which itself is arranged to act as a piston inside the other, the two cylinders communicating by means of one or more bleed holes or passages, whereby said one cylinder can telescope inside the other to displace hydraulic fluid into the reservoir.

5. A device according to any one of the preceding claims wherein said means has means for altering the resistance to longitudinal movement of the ends.

6. A device according to any one of the preceding claims, which is arranged to resist said longitudinal movement of the ends both towards and away from each other.

7. A device for restricting relative movement between a trailer and a towing vehicle, substantially as any described herein with reference to the accompanying drawings.

8. A vehicle having a trailer pivotably connected thereto wherein a device according to any one of the preceding claims is connected at one end to the trailer and at the other end to the vehicle, at a position laterally offset from the pivotable connection between the trailer and the vehicle.

9. A vehicle and trailer according to claim 8, having a said device so connected on each side of the pivotable connection.