Such trailer hitches are commonplace on the market today. One problem with existing trailer hitches is that there is already inherent free play between the tow ball and tow eye. This free play increases as the trailer hitch is used, partly through normal wear and partly due to sand, earth and other dirt particles entering into the moving parts of the hitch.

The variation in load caused by the said free play between the tow ball and the tow eye on the trailer vehicle is conveyed throughout the vehicle and is perceived as especially disturbing by the driver. Another considerable disadvantage with the said free play is that the entire power train in the traction vehicle, i. e. propeller shaft, universal joints, engine and gearbox will eventually be damaged by the variation in load.

The present invention intends to eliminate these problems and offer a new type of trailer hitch that provides a coupling between the traction vehicle and the trailer vehicle without any free play. This is made possible with a trailer hitch of the aforesaid type exhibiting the characteristics specified in the enclosed claims.

A preferred embodiment of the invention will be described in more detail with reference to the enclosed drawings, where Fig. 1 is a perspective view of the new trailer hitch and Fig. 2 is a vertical cross section of the hitch viewed from one side.

Referring to the drawing, a new trailer hitch is illustrated that exhibits a coupling housing 1, comprising a rear, vertical end piece 2, from which extends an upper, forward protruding coupling yoke piece 3 and a lower, forward protruding coupling yoke piece 4. A tow eye 5 from a trailer and a tow ball 6 arranged inside the tow eye are intended to be contained between these yoke pieces.

Underneath the upper coupling yoke piece 3 and on top of the lower coupling yoke piece 4 are guides 7,8, which are intended to steer the tow ball correctly to couple the trailer to the traction vehicle. Furthermore, the central part of the tow ball 6 has a vertical hole 9 through it, into which a coupling pin 10 is inserted. This arrangement enables the tow ball 6 and the surrounding tow eye 5 to be securely fastened to the traction vehicle.

The coupling pin 10 is intended to be inserted into the tow ball 6 hole 9 and extracted from the same via a suitably driven, e. g. pneumatic or hydraulic, lift cylinder 11 mounted on top of the upper coupling yoke piece 3.

The rear parts of both coupling yoke pieces 3,4 are joined to the end piece 2. In front of this end piece is a vertical wedge 12 arranged between both yoke pieces. The wedge is so designed that the wedging action increases, i. e. the wedge force in the direction of the tow ball increases, as the wedge is pressed down. This downward pressure is achieved with a spring device 13, which acts on the top of the wedge 12.

The wedge 12 is intended to engage an intermediate piece 14, which exhibits partly an upper, forward protruding part 15, which is intended to abut against the top part 16 of the tow ball 6, and partly a lower, forward protruding part 17, which is intended to abut against the bottom part 18 of the tow ball 6. This means that the wedge 12 and the intermediate piece 14, which is steered with guides in the coupling housing, will press the tow ball 6 against the coupling pin 10.

As the tow ball 6 and thereby the tow eye 5 are pressed against the coupling pin 10 in this way, any free play found in the trailer hitch will disappear. Should any wear arise, the wedge 12 will compensate for it automatically as the spring device 13 will press down the wedge.

The top of the wedge 12 is covered by a wedge cover 19 and its bottom interacts with a pneumatic cylinder 20, which is intended to press up the wedge 12 against the action of the spring device 13 to facilitate uncoupling the traction vehicle. The wedge then abuts against a setscrew 21 arranged in the wedge cover 19.

With the assistance of this setscrew 21, the wedge 12 and thereby also the intermediate piece 14 can thus be adjusted so that the tow ball acquires the correct position in relation to the coupling pin 10 so that the pin can move to a locked position.

Once the coupling pin 10 has locked, the pneumatic cylinder 20 will release, whereby the spring 13 will press down the wedge 12 so that the intermediate piece 14 presses against the tow ball 6.

In order to obtain good support of the tow eye 5 against the tow ball 6, the former is equipped with a bearing shell 22, which is thus applied against the tow ball. To prevent sand and dirt entering the interacting parts of the tow ball and tow eye, they are completely enclosed by a rubber gaiter 23.

The invention is, of course, not limited to the submitted and illustrated embodiment but can be modified within the framework of the following claims.