Background Art According to this invention there is already provided a conventional ball and socket type of coupling. The articulation of this coupling does not permit enough vertical movement, therefore limiting the type of terrain that a draught vehicle can tow a trailer especially over steep inclines, gullies or other terrain commonly found in off-road conditions.

Disclosure of the Invention In the coupling of this invention the ball is mounted on a member which is fixed to a pivotal torque element, which is resiliently yieldable under torque and may be arranged in such a manner as to permit relative vertical movement of the ball on the pivoting axes of the torque element.

The torque element may consist of an outer tubular metal member having an angular cross-section and an inner elongated metal member of angular cross- section. A resiliently deformable material such as polyurethane or rubber may be used to mount the inner angular cross-sectioned member within the outer tubular member. The inner member may be positioned within the outer member in such a manner as to allow adequate clearance within the outer member as the outer member moves deforming the resilient material which resists such a movement.

The coupling may include two spaced plates, the plates may be positioned apart from each other with the ends of the inner elongated member protruding through a receiving means in each of the plates. The plates may be secured at right angles to an attachment plate by means of welding or any other suitable method. The attachment plate may be secured to the towbar of the draughting vehicle by means of bolts or any other suitable method.

In operation the socket part of the coupling which is attached to the drawbar of the trailer, pivots on the ball in a vertical axes, as this vertical movement increases, the socket part of the coupling may engage the neck of the ball. This may in turn apply a torque to the neck of the ball, this torque may be transferred to the torque element of the coupling, which is resiliently yieldable under torque and may permit relative vertical movement of the ball on the pivoting axes of the torque element, thus extending the angle of vertical travel on the trailers drawbar. Therefore enabling the trailer to be towed over rough terrain, by example, through ditches and over mounds.

It is noted that the outer tubular member and the inner elongated member may be of any suitable angular cross-sectional shape. It is further noted that the attachment plate may in an alternative arrangement include an angular cross- sectional member that is arranged in such a manner as to engage a receiving member on the towbar of the draughting vehicle.

Brief Description of Drawings THE INVENTION is now described with reference to the accompanying drawings, in which: Figure 1A shows a three-dimensional view of the coupling disassembled in two main parts and in accordance with the invention.

Referring to figure 1A, reference numeral-1 indicates the coupling ball which is mounted to the member-2 of which is secured to the outer tubular metal member-3 of the torque element by means of welding or any other suitable method. The inner elongated metal member-4 is held in position by means of the resiliently deformable material-5 such as polyurethane, rubber or any other type of material that would be suitable for this application. The inner elongated member-4 protrudes through the outer tubular member-3 on either end.

The protruding sections of the inner member-4 slot into the receiving means-7 of the two spaced plates-6. The receiving means-7 hold the inner elongated member-4 in place, it is noted that the inner elongated member-4 may be secured in the receiving means-7 of the two spaced plates-6 by welding or any other suitable method. The two spaced plates-6 may be secured to the attachment plate-8 by means of welding or any other suitable method and the attachment plate-8 may be secured to the draughting vehicles towbar by means of bolts or any other suitable method.

In operation as the vertical angle of the drawbar of the trailer increases the socket part of the coupling engages the neck of the ball-1. This in turn applies a force on the member-2 which is secured to the outer tubular metal member-3, this force causes the outer tubular metal member-3 to turn, permitting relative vertical movement of the ball-1 on the pivoting axes of the torque element. When the outer tubular member-3 turns the resilient material-5 is compressed and as the force on the outer tubular member-3 subsides the outer tubular member-3 returns to its original position.

Figure 2A shows a three-dimensional view of the coupling in accordance with the invention.

Figure 3A shows a sectional side view of the coupling on the line x-x of figure 2A.

Figure 4A shows a sectional side view of the coupling with the alternative towbar mounting arrangement on line x-x of figure 2A.