GB2181398A - Trailer draw-bar control means - Google Patents

Abstract

The invention provides a damping arrangement on a draw-bar pivotally connecting a trailing vehicle and a trailed vehicle combination to dampen slewing and jack-knifing of the trailed vehicle and this is achieved by a pair of identical hydraulic rams symmetrically connected to opposite sides of the draw-bar and hydraulically coupled through a variable flow restrictor. The rams may be single or double acting. Alternatively a single ram may be used with equal volumes either side of a piston each being in hydraulic communication through a restrictor. In a further alternative the rams may be pneumatic or incorporate other spring damping. <IMAGE>

Description

SPECIFICATION Trailer draw-bar control means The invention relates to devices for controlling the orientation of trailing/trailed vehicle constructions, particularly but not exclusively for the prevention of jack knifing and other violent swinging movements of agricultural trailers relative to their trailing tractors. Whilst the invention will be described by reference to tractor-drawn agricultural trailers, it will be understood that the invention is applicable to other trailing/trailed vehicle constructions such as wheeled vehicles drawn by steerable self propelled units.

It is well known that in certain circumstances trailers occasionally divert to one side or other of a desired path, which is generally the path of the towing vehicle, and in some cases the trailer swings from side to side. In extreme cases this may lead to jack knifing with the tail of the trailer leading the nominal front end thereof. Theoretically the turning of the towing vehicle by a given angle should be followed by the turning of the trailer by the same angle, but it is commonly found that the trailer swings through a larger angle and although the additional deviation may be small, the effect of this may be quite significant particularly if the trailer is carrying, for example, a transverse spraying boom.

In order to minimise the above problems we provide, according to the invention, in or for a trailing/trailed vehicle combination having a draw-bar pivotally mounted on the trailing or trailed vehicle for swinging to one or other side of the normal direction of travel of the combination, means for damping the swinging movement of the draw-bar relative to the vehicle to which it is pivotally connected.

The damping means may comprise fluid pressure ram means and preferably comprise a hydraulic ram connected between the drawbar forward of the vehicle to which it is connected and the vehicle itself at each side of the mounting of the draw-bar.

The rams may be in fluid connection with one another through a variable flow restrictor whereby pivoting of the draw-bar causes the extension of one ram and the contraction of the other ram with the displacement of hydraulic fluid through the restrictor which causes damping of the movement of the rams and hence the pivoting of trailed vehicle relative to the trailing vehicle.

Preferably, the draw-bar is pivotally connected to the trailed vehicle.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 shows a two-wheeled trailer in side elevation; Figure 2 shows the trailer in plan; Figure 3 shows, schematically, one hydraulic system for the trailer as shown in Figures 1 and 2; and Figure 4 shows also schematically another hydraulic system for the trailer as shown in Figures 2 and 3.

The trailer shown in Figures 1 and 2 comprises essentially a frame 2 supporting a body 4 and a pair of road wheels 6. The body may be for containing liquid treatment medium to be sprayed on the ground over which the vehicle travels and at the rear the tractor may have a spray boom. A draw-bar 8 is mounted at the front of the trailer by means of a pivot 10 so that it may swing through an angle up to angle X to left and right relative to the normal forward movement of the trailer represented by arrow 12.

The draw-bar is arranged conventionally to be attached to the rear of a tractor or other towing vehicle, which may have the conventional three point hitch, as is well known in the art. The tractor as it is conventional is not shown in the drawings.

If the towing vehicle turns through an angle less than X the bar 8 will turn on its pivot 10 through the same angle, and the normal expectation and desire will be that the trailer would subsequently change its orientation by the same angle without overswinging or over slewing but it is found in practice that sometimes the trailer in these circumstances will turn initially by a greater angle and only perhaps after a significant interval return to the orientation of the tractor, and it may oscilate during the interim.

In this embodiment of the invention however, hydraulic means 14R, 14L are respectively and symmetrically mounted at the respective sides of the frame 2 of the trailer towards the front and the free ends of the piston rods 16 are pivotally mounted to brackets 18 secured at the respective side of the draw-bar 8.

When the tractor turns to the right or left, the draw-bar 8 will turn about its pivot 10 accordingly and one piston rod 16 will enter into the cylinder and ram 14R, 14L so that the overall length of that ram will be reduced whilst the other piston rod 16 will withdraw from the other ram so as to increase the length of that ram. The hydraulic fluid displaced from one ram, or one ram side, is passed through a restrictor, which damps the ram and draw-bar movement to inhibit tractor overswinging, and then is passed to the other ram or ram side or both.

Figure 3 shows in detail one arrangement for the fluid connections between the rams 14R, 14L. Each of the rams is double acting is closed at both ends, and has ports adjacent each end.

Port 18 of crown side of ram 1 4R leads through line 19 to port 20 of rod side of ram 14L and via check valve 22 and adjustable restrictor 24 to reservoir 26.

Similarly port 28 of crown side of ram 1 4L is in direct fluid connection to port 30 of rod end of ram 14R through line 21 as well as to reservoir 26 via check valve 32 and the aforesaid restrictor 24.

The operative directions of the valves 22 and 32 are such as to allow flow of fluid respectively from the crown and rod sides of the pistons of rams 14R and 14L and thence to the restrictor 24. The restrictor of the Fig.

3 embodiment allows flow of fluid only in one direction, and hydraulic fluid lines 36 and 34 are also provided, each with its check valve 38, for the return of fluid respectively to the crown and rod sides of the rams.

The restrictor is variable in setting and is provided with a relief valve 44 and the system is provided with reservoir 26.

The flow arrangement of Fig. 3 will now be described as occuring when the trailer is turned to the right. Each of the pistons 16 will move to the right as shown in Figure 3 and hydraulic fluid will be forced out of the rod side of ram 14L and the crown side of ram 14R through the ports 18, 20 in the direction of junction 40 of the hydraulic circuit.

Because valve 38 in line 34 permits flow only towards junction 40, the fluid is permitted to flow only through valve 22 and, valve 32 being closed to it, through restrictor 24. From restrictor 24 the flow is through line 36 and one way valve 38 to the crown side of ram 14L and the rod side of ram 14R at their ports 28 and 30. As the rams 14R and 14L are identical the fluid displaced from the rams is equal in volume to the fluid supplied to the rams but the speed at which the fluid flows in controlled by the restrictor 24, and the speed of flow controls the rate of pushing of the drawbar, whereby trailer vehicle swing is dampened.

Similarly, when the trailer is turned to the left, the pistons 16 move to the left as shown in Fig. 3, and hydraulic fluid will flow out of the rams through ports 28, 30 and return to the rams via line 34 after having passed through one way valve 38 and restrictor 24.

The valves 22 and 38 and even the pipelines themselves may possibly provide the restriction to the flow of hydraulic fluid and so provide the necessary damping the movement of the pistons of the rams but it is anticipated that the dampening effect provided by the restrictor 24 will be necessary. This is adjustable so that the damping effect may be varied between as wide limits as required, that is to say not too great a restriction to make the rams in effect become rigid limbs which would inhibit steering of the trailer and not too free as to permit significant over steering of the trailer.

Other forms of hydraulic circuit can be employed. Thus, there may be two single acting rams with hydraulic fluid to one side only of the piston, the other side being optionally spring loaded. The fluid sides of the respective rams would be a hydraulic communication through a simple restrictor which is a two way restrictor or through a one way restrictor with associated check valves such as valves 22, 32, 38.

Again, it may be possible to use a single ram of equal swept volume to either side of the piston and the respective side being in hydraulic communication through a restrictor.

The rams although hydraulic, and preferably oil rams may be air or gas operated, and indeed other pneumatic or gas operated damping systems may be used, as may spring damping systems.

Fig. 4 shows a hydraulic circuit which can be used with the ram shown in Fig. 2, and which has the advantage that it is not necessary to use any check valves such as valves 22, 32 and 38 shown in Fig. 3, but instead a two-way restrictor 24 is utilised, and the crown side of ram 14L and rod side of ram 14R are coupled to provide a common outlet to pipe 46, whilst the rod side of ram 14L and crown side of ram 14R are connected to pipe 48. Pipes 46 and 48 are connected to the opposite sides of the prospector 24. It will be understood that when the tractor and trailer pivot one relative to another at pivot point 10, one ram 14 will be expanded and the other ram 14 will be contracted. If it is assumed that the ram 14R is contracted so that piston 16R moves in the direction of arrow 50, piston 14L will also move in the direction of arrow 50. The fluid displaced from the rod side of ram 14L is discharged through pipe 19 and aggregates with the fluid displaced from the rod side of ram 14R so that the aggregated fluid travels through pipe 48 and through the restrictor 24 and then is returned through pipe 46 to the crown side of ram 14L and the rod side of ram 14R, the restrictor controlling the rate at which the rams 14 can expand and contract, and thereby controlling the rate of pivoting of the trailer relative to the tractor to prevent overswing.

The circuit of Fig. 4 can if desired be provided with the relief valve 44 in Fig. 3 and the reservoir 26 if necessary.

The arrangement of Fig. 4 is a particularly suitable and inexpensive embodiment of the invention.

Claims (8)

1. In or for a trailing/trailed vehicle combination having a draw-bar pivotally mounted on the trailing or trailed vehicle for swinging to one or other side of the normal direction of travel of the combination, means for damping the swinging movement of the draw-bar relative to the vehicle to which it is pivotally connected.

2. The draw-bar according to Claim 1, wherein the damping means comprises fluid pressure ram means.

3. The draw-bar according to Claim 2, wherein the fluid pressure ram means comprises a hydraulic ram connected between the draw-bar forward of the vehicle to which it is connected and the vehicle itself at each side of the mounting of the draw-bar.

4. The draw-bar according to claim 3, wherein the rams are in fluid connection with one another through a variable flow restrictor whereby pivoting of the draw-bar causes the extension of one ram and the contraction of the other ram with the displacement of hydraulic fluid through the restrictor which causes damping of the movement of the rams and hence the pivoting of trailed vehicle relative to the trailing vehicle.

5. A draw-bar according to claim 4, wherein the rams are identical double acting rams symmetrically connected to the draw-bar and the crown side of one of said ram is in hydraulic connection with the rod side of the other ram by coupling lines, and from each of said coupling lines a branch line leads through a first one way valve, a one way flow restrictor, a second one-way valve to the other coupling line, the restrictor being common to both branch lines.

6. A draw-bar according to Claim 4, wherein the rams are identical double cutting rams symmetrically connected to the draw-bar and the crown side of each of said rams is in hydraulic connection with the rod side of the other ram by a direct coupling line, and from each of the two coupling lines is a branch line, said branch lines leading to the opposite sides of a twoway flow restrictor.

7. A draw-bar according to any preceding claim, wherein the draw-bar is connected to the trailed vehicle.

8. In or for a trailing/trailed vehicle combination or door-bar substantially as hereinbefore described with reference to the accompanying drawings.