Tractor and trailer combination

To allow a semi-trailer (9) to be towed by a drawbar tractor (T), a connector device is used to couple the tractor to the trailer. The connector is provided for lifting the trailer, and is arranged so that (i) a single point of articulation is defined between the tractor and trailer, and (ii) no vertical load is transmitted to the tractor from the trailer. The connector includes a sleeve (5) fixedly mounted on the tractor towing plate, an hydraulic ram (4) slidable in the sleeve, a freely rotating castor wheel (3) at the lower end of the ram and a bolt (7) mounted on the ram piston rod (6) for cooperation with the ball socket (10) of the trailer.

This invention relates to tractor and trailer combinations. 
Drawbar tractors are known and are used for towing trailers through drawbar 
connections. These tractors are ballasted to ensure sufficient grip with 
the ground and apply only pulling forces to the trailers they tow. 
Consequently, the trailers used with drawbar tractors must have enough 
ground engaging wheels to be self supporting when being towed. At least 
one pair of the trailer wheels must be steerable and parking brakes are 
generally required to prevent trailer motion when disconnected from a 
tractor. Due to these requirements trailers for drawbar tractors tend to 
be rather expensive. 
Semi-trailers, i.e. trailers having only one pair of fixed wheels normally 
mounted at the rear end of the trailer, are also known. With trailers of 
this type the front end of the trailer rests on the ground when it is 
detached from a tractor, so no parking brakes are required. In addition 
there are no steerable wheels, so semi-trailers are comparatively 
inexpensive to manufacture. However, for towing a semi-trailer a tractor 
is needed which is capable of lifting the front end of the trailer and 
supporting a substantial part of the trailer load. As a result 
conventional drawbar tractors cannot be used for towing semi-trailers as 
they are not designed to accept vertically imposed loads. 
There are in existence many load handling systems e.g. at airports and the 
like, which are based on drawbar tractor drive units. In the majority of 
cases it would be prohibitively expensive to replace all the drive units, 
which means that advantage cannot be taken of the cheaper semi-trailers. 
There is known a dolly converter which allows a semi-trailer to be towed by 
a drawbar tractor. The dolly converter comprises a pair of wheels, a tow 
plate on which the front end of the trailer rests to pivot about the plate 
axis, and a drawbar which is coupled to the tractor by a second pivotal 
connection. The major disadvantage of the dolly converter is that there 
are two essential points of articulation, which has the result that it is 
very difficult to manoeuvre in reverse and there is a tendency for the 
dolly converter to jack-knife when travelling down steep slopes, such as 
ramps, especially when the trailer is heavily laden. These drawbacks make 
dolly converters of limited practical use. 
The present invention aims at eliminating the aforementioned drawbacks and 
accordingly provides a tractor and trailer combination, comprising a 
drawbar tractor, a semi-trailer, and a connector interconnecting the 
tractor and trailer, the connector including means for lifting the 
trailer, and ground engaging wheel means arranged to support vertical 
loads imposed on the connector by the trailer, whereby no vertical load is 
transmitted to the tractor, and said connector defines one single point of 
articulation between the tractor and trailer. 
The connector is preferably coupled to the trailer in a manner permitting 
some pitching movement between the trailer and connector. A ball and 
socket connection or other universal joint of similar effect may 
interconnect the trailer and connector. The lifting means may be operated 
manually, but is preferably power driven, e.g. electrically or 
hydraulically. 
In one embodiment of the invention the connector includes a load bearing, 
freely rotating castoring wheel supporting a vertical hydraulic ram 
surmounted by a universal coupling. The connector includes a frame 
including means for attaching the frame rigidly to the tractor chassis. 
The hydraulic ram is extended and retracted for raising and lowering the 
trailer by means of an hydraulic power take off from the tractor, and is 
fully controllable by the driver seated in the normal driving position. 
According to another embodiment, the connector comprises a frame, a load 
bearing, freely rotatable castoring wheel supported by the frame and 
having a vertical axle, an arm pivoted on said axle and carrying a hook 
for engaging the trailer, means for lifting and lowering the hook, and 
parallel link arms pivoted to the frame for connecting the connector to 
the tractor chassis in a manner permitting vertical movement of the 
connector frame with respect to the tractor.

Referring to FIGS. 1 and 2 there is shown a ballasted drawbar tractor T, a 
connector having a frame 1 rigidly fixed to the tractor chassis back plate 
2, and a semi-trailer 9 to be coupled to the tractor by the connector. The 
connector frame includes a sleeve 5 in which the cylinder 4 of an 
hydraulic ram is slidably mounted. A freely rotatable load bearing 
castoring wheel 3 is affixed to the lower end of cylinder 4. The piston 
rod 6 of the hydraulic ram carries a ball 7 for cooperation with a ball 
socket 10 provided at the front end of the trailer. The hydraulic ram is 
coupled to the tractor engine power take off through a pipeline 8 and a 
control device operable by a lever 11 conveniently mounted on the tractor 
for operation by the driver without leaving his seat. 
In use, the connector will normally remain fixed to the tractor although it 
can be dismounted if required. With the ball 7 fully lowered the tractor 
is reversed to position the ball 7 beneath the socket 10 of the parked 
trailer. The driver then operates the control lever 11 to extend the ram 
and locate the ball 7 into the trailer socket 10. Extension of the ram is 
continued until the trailer legs 12 are lifted free of the ground. When 
raised in this way the tractor and trailer combination can be driven 
easily in either direction. There is only one point of articulation 
provided by the ball and socket universal joint 7, 10 which also allows 
some pitching and rolling movement between the tractor and trailer. 
Furthermore, all the trailer imposed vertical load is supported solely by 
the castor wheel 3 of the connector so that the tractor is free from 
vertical loads. 
Vertical movement between the connector and tractor is permitted by virtue 
of the sliding connection between the cylinder 4 and the sleeve 5. In the 
modified embodiment of FIG. 3, such vertical movement is obtained through 
an arrangement of parallel arms 13 each pivoted at its opposite ends to 
the cylinder 4 and a mounting plate 1 attached to the tractor chassis 2. 
The alternative connector shown in FIGS. 4 to 7 has a frame 15, a freely 
rotating castor wheel 16 carried on the lower end of a vertical axle 17 
journalled in the frame 15, a mounting plate 18 fixedly mounted on the 
back plate of a drawbar tractor chassis, and pivoted parallel link arms 19 
interconnecting the frame 15 and mounting plate 18 to permit vertical 
movement between the frame and tractor T. Journalled on the upper end of 
the axle 17 is an arm 20. At its free end the arm 20 carries a vertically 
reciprocable slide 21 which is driven by an hydraulic motor, e.g. a ram, 
mounted within the arm 20. The motor is connected to the tractor engine 
power take off in similar manner to the ram of FIGS. 1 to 3, in order to 
be operable by the tractor driver. A hook 22 is pivoted on a part 21a and 
includes a locking element 23. The part 21a can pivot about a longitudinal 
horizontal axis X with respect to the slide 21. 
The low bed trailer 24 includes a chassis with a pair of wheels 25 at the 
rear end and a transverse supporting foot 26 carried by pillars 27 at the 
front end. Extending between two pillars at the centre of the trailer is a 
horizontal lifting bar 28. 
In use, with the connector mounting plate 18 fixedly attached to the 
tractor chassis back plate and with the slide 21 in its lowermost 
position, the tractor is reversed to position the hook 22 below the 
lifting bar 28 of the trailer 24. The hydraulic motor in arm 20 is then 
operated to raise the slide 21 and engage hook 22 with the bar 28. The 
hook is caused to turn about its pivot to locate the locking element 23 
against the top of trailer 24 in order to prevent the trailer bouncing off 
the hook whilst being towed. Continued upward displacement of the slide 
causes the hook to lift the trailer foot 26 free of the ground to the 
position shown in FIG. 7. 
The tractor and trailer combination can now be driven. The only point of 
articulation between them is at the axis of the vertical axle 17, which 
means that reversing is easy. In addition, all vertical loads imposed by 
the trailer 24 are supported by the wheel 16 of the connector so the 
tractor is only subject to pulling and pushing forces. The hook and bar 
connection between the trailer and connector allows for some rolling and 
pitching but no yawing movement between them. The rolling movement is 
possible due to the pivotal connection between the hook carrying part 21a 
and the slide 21.