GB2329368A

GB2329368A - Towing Hitch

Info

Publication number: GB2329368A
Application number: GB9813518A
Authority: GB
Inventors: Frederick David Friend
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-06-24
Filing date: 1998-06-24
Publication date: 1999-03-24
Also published as: GB9713197D0; GB9813518D0

Abstract

A hitch for coupling a towed vehicle (10) to a towing vehicle (9) comprises a drawbar (1) pivotally mounted on the towed vehicle (10) for releasable engagement with a pick-up point on the towing vehicle (9). The piston of a first piston and cylinder mechanism (5) mounted on the towed vehicle (10) engages in a socket (3) on the towing vehicle (9), and a second piston and cylinder mechanism (2) acts between a bracket (14) on the towed vehicle (10) and the drawbar (1).

Description

HITCHES Field of the Invention This invention relates to hitches for connecting a towed vehicle to a towing vehicle, the term "towed vehicle" being interpreted broadly as including wheeled machines and implements generally as well as trailers. The invention has particular application to the coupling of a trailer to an agricultural tractor, but is not limited thereto.

Background to the Invention Tractor-trailer combinations often suffer from a pitching motion when travelling on all but the smoothest of road surfaces.

Stresses to both the driver and the tractor-trailer combination can be high, often dictating a much slower rate of travel than would otherwise be desirable.

If, for example, a farmer is towing a load of sugar beet or like produce, he may have to drive at a speed of 15 m.p.h. when a speed of 25 m.p.h. would otherwise be possible. Equally, accidents can occur when a tractor-trailer combination is driven at speeds such that a pitching motion results.

It is accordingly an object of the present invention to provide an improved form of hitch.

Summarv of the Invention According to the present invention there is provided a hitch for coupling a towed vehicle to a towing vehicle comprising a drawbar pivotally mounted on the towed vehicle for releasable engagement with a first attachment point on the towing vehicle, a first piston and cylinder mechanism mounted on the towed vehicle and having means for releasable engagement with a second attachment point on the towing vehicle, and a second piston and cylinder mechanism acting between a fixed point on the towed vehicle and a point on the drawbar intermediate the two ends thereof.

The first and second piston and cylinder mechanisms are preferably hydraulic piston and cylinder mechanisms charged by the braking system of the towing vehicle.

Each of the hydraulic piston and cylinder mechanisms is preferably a single-acting piston and cylinder mechanism, the piston of the first piston and cylinder mechanism being biased forwardly relative to the towed vehicle into engagement with a socket forming the second attachment point on the towing vehicle.

The piston of the second piston and cylinder mechanism is preferably biased generally downwardly relative to the fixed point on the towed vehicle in order to respond to the weight of the front of the towed vehicle.

Brief Description of the Drawings Figure 1 is a diagrammatic view showing a hitch between an agricultural tractor and a trailer, Figure 2 is a flow diagram showing the hydraulic circuit of the hitch, and Figure 3 is a detail view of the hitch.

Description of the Preferred Embodiment The drawings show a hitch between an agricultural tractor 9 and a trailer 10. A drawbar 1 is pivotally mounted on a bracket 11 underneath the front of the trailer and the forward end of the drawbar 1 is coupled to the standard pick-up formation 12 on the tractor 9 which is provided with a self-centering pivoting socket element 3 which has a locating formation. This element 3 is pinned or otherwise attached to the standard top link attachment point 13 of the tractor 9.

A mounting bracket 14 is welded or otherwise attached to the front of the trailer 10 and has a pivot mounting 4 for the cylinder of a hydraulic piston and cylinder mechanism 5. The piston of the piston and cylinder mechanism 5 is movable against the action of an internal spring into a position in which a locating formation at the free end of the piston engages within the socket 3. A strut or support 8 extends upwardly from the drawbar 1, so as to hold or maintain the piston and cylinder mechanism 5 in a position such that, when the piston is extended, it will engage in the socket 3.

A second piston and cylinder mechanism 2 extends between the bracket 14 and the drawbar 1. This piston and cylinder mechanism 2 is connected to an accumulator 6 and also to piston and cylinder mechanism 5 via valves and restrictors as shown in the flow diagram of Figure 2. The hydraulic circuit is charged with hydraulic fluid from the tractor-trailer brake line 15 via a drawbar ride height control valve 7, which has a latching and manual override mechanism 16 mounted on the side of the trailer 10.

The above arrangement is such that, when the system is charged with hydraulic fluid, the weight of the front of the trailer 10 acting on the drawbar 1 causes a pressure rise in cylinder 2, causing a forward thrust from cylinder 5 which, by transferring weight to the front wheels of the tractor 9, tends to counter any pitching forces from the drawbar 1. In addition, restrictor 17 limits the retracting speed of piston and cylinder mechanism 5 and so damps any pitching oscillations. The accumulator 6 absorbs shock loads imposed on the drawbar 1 by the trailer 10 and enhances the pitch-restraining effect of the system.

The invention thus provides a simple and effective means whereby a tractor-trailer combination can be driven with improved safety at speeds in excess of those which are currently practical and also greatly reduces the dynamic forces on the rear axle and pick-up hitch of the tractor 9.

With the trailer 10 uncoupled from the tractor 9, both cylinders 2 and 5 will be retracted. Cylinder 5 will rest on the support 8 and the pressure in the hydraulic circuit will be zero.

The procedure for coupling the tractor 9 to the trailer 10 will be as follows: The operator will first attach the self-centering pivoting socket element 3 to the tractor top link point 13 with two pins. He will then couple the trailer 10 in the normal way with the standard pick-up hitch before connecting the trailer braking line and other services which are required, as normal. Before driving off, he will apply the foot brakes of the tractor which, via the tractor brake line, will extend the free end of the piston of cylinder 5 into the locating formation of socket 3.

Continued pressure on the brake pedals will cause a further rise in hydraulic pressure and thus extend the piston of cylinder 2 until the drawbar ride height control lever is relocked, with control valve 7 isolating the trailer brake line from the hitch system. The tractor-trailer combination is now ready to be used in the normal way, with no more restriction on the tractor-trailer tuming circle or articulation than would be the case with a standard hitch.

All pitching forces caused by uneven road surfaces are controlled by the cylinder 5 and restrictor 17 (Figure 2).

Furthermore, as the trailer is loaded, the increase in pressure generated by cylinder 2 causes cylinder 5 to apply more force to the socket element 3, Figures 1 and 3, and so transfer more weight to the front wheels of the tractor from the rear wheels of the tractor.

This improves stability and also tends to counter pitching forces.

Again, as the trailer is loaded, the system pressure rises above the pre-charge pressure of the accumulator 6, and the accumulator 6 thus cushions the forces acting on the drawbar 1 from the mass of the load in the trailer 10.

The ride height control valve 7 (as its name implies) also has the function of maintaining the height of the front of the trailer, within preset limits, by allowing hydraulic fluid into the system (during braking) and out of the system, according to whether the trailer is loaded or unloaded.

When the operator wishes to uncouple the tractor from the trailer (whether or not it is loaded), he first manually unlocks and moves the drawbar ride height control lever 16 to the down position.

This allows the hydraulic fluid to flow back to the tractor via the brake line and so allows the accumulator 6 to discharge and the cylinder 2 to retract under the weight of the trailer 10. Then, as the pressure falls away, cylinder 5 retracts due to its intemal spring.

When cylinder 5 has fully retracted and the free end of the piston has come well clear of the socket element 3 and cylinder 5 is resting on strut 8, the operator uncouples the brake line and other services, and unhitches the trailer 10 in the normal way. Socket element 3 can, of course, remain on the tractor 9, provided that the tractor 9 is not going to be used with mounted implements. If it is, the socket element 3 will be removed.

Claims

Claims:

1. A hitch for coupling a towed vehicle to a towing vehicle comprising a drawbar pivotally mounted on the towed vehicle for releasable engagement with a first attachment point on the towing vehicle, a first piston and cylinder mechanism mounted on the towed vehicle and having means for releasable engagement with a second attachment point on the towing vehicle, and a second piston and cylinder mechanism acting between a fixed point on the towed vehicle and a point on the drawbar intermediate the ends thereof.

2. A hitch as claimed in Claim 1, in which the first and second piston and cylinder mechanisms are hydraulic piston and cylinder mechanisms charged by the braking system of the towing vehicle.

3. A hitch as claimed in Claim 2, in which each of the hydraulic piston and cylinder mechanisms is a single-acting piston and cylinder mechanism.

4. A hitch as claimed in any one of the preceding claims, in which the piston of the first piston and cylinder mechanism is biased forwardly relative to the towed vehicle into engagement with a socket forming the second attachment point on the towing vehicle.

5. A hitch as claimed in any one of the preceding claims, in which the piston of the second piston and cylinder mechanism is biased generally downwardly relative to the fixed point on the towed vehicle in order to respond to the weight of the towed vehicle.

6. A vehicle hitch substantially as hereinbefore described with reference to and as shown in the accompanying drawings.