This invention relates to a forklift truck, particularly of a type suitable for carrying on trucks or trailers.

Demountable forklift trucks are well known, being widely used in delivery of building materials and farm produce.

Generally the forklift mast is mounted on horizontally opposed channels with rollers. When lifting a load the mast is extended forwardly to provide the maximum counterbalance. When the load is raised the mast is retracted over and above the wheels for travelling. There are a number of disadvantages in this type of construction.

First, it is complex and therefore expensive. Secondly, it is of considerable weight and thirdly, because of the fixed length chassis, expensive modifications are required to the rear of the carrying vehicle so that at least part of the forklift is within the vehicle body length when travelling.

It is an object of the invention to provide a construction of forklift truck which mitigates at least some of these disadvantages.

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According to the present invention there is provided a forklift truck comprising front and rear chassis sections connected together by at least three tubular members which can slide telescopically within one another to vary the overall length of the chassis.

The invention has the advantage that the overall length of the chassis may be contracted to a minimum when it is desired to carry the forklift on another vehicle, yet extended to a maximum to provide stability when carrying a load. Further, -the telescopic construction is relatively simple and may be manufactured at relatively low cost, yet provides a forklift of light weight relative to its lifting capacity.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a first embodiment of forklift truck with a three-part telescopic connection between front and rear chassis sections, in its extended position,

Figure 2 shows the truck of figure 1 in its closed position,

Figure 3 shows the hydraulic mechanism associated with the telescopic connection of figures 1 and 2 ,

Figure 4 is a side view, partially in cross-section, of a second embodiment of forklift truck in its extended position,

Figure 5 shows the truck of figure 4 in its closed position and ready to be raised to a transport position on a carrying vehicle,

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Figure 6 shows the mechanical construction of the mast of the forklift truck of figure 4,

Figure 7 shows brackets welded or bolted to the underrun guard of a carrying vehicle, and

Figure 8 shows the forklift truck of figure 5 in an elevated position for transport.

Referring first to figures 1 and 2, a forklift truck has front and rear chassis sections 10 and 11 respectively. The front section 10 includes front road wheels 12, a lift mast 13 and forks 14, and the rear section 11 includes steerable wheels 15 and, inside a rear cover 16, the equipment such as engine or batteries to power the forklift.

The front and rear chassis sections 10 and 11 are coupled together by a telescopic connection 17 consisting of three steel tubes 18, 19 and 20, the tube 18 being connected to the front chassis section 10 and the tube 20 being connected to the rear chassis section 11. The tubes 18 to 20 are of rectangular, square or other substantially constant cross-section and can slide within one another in the manner of telescopic rings to vary the overall length of the chassis.

As shown in figure 3, the telescopic connection 17 is extended and contracted by two double acting hydraulic rams 21 and 22. The cylinder 23 of each hydraulic ram is fixed to the centre tube 19, while the piston rod 24 of one ram is fixed to the tube 18 and the piston rod 24a of the other ram is fixed to the tube 20. The full bore sides of the rams are connected by pipes 25 and the annular sides of the rams are connected by pipes 26 so that the rams extend and contract together.

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The rams are operated by the hydraulic system of the forklift truck, and by extending the piston rods 24 and 24a the overall length of the forklift truck chassis can be extended to provide a long wheelbase for stability when working, figure 1. By retracting the piston rods 24 and 24a the front and rear chassis sections can be closed up to reduce the overall length and hence the wheelbase of the forklift truck for storage or carrying on a vehicle, figure 2.

Figures 4 and 5 show a second embodiment of forklift truck according to the invention in its extended and closed positions respectively. In these figures the same reference numerals have been used as in figures 1 to 3 for like parts.

The principle difference from the first embodiment is in the arrangement of the hydraulic rams. In this embodiment the cylinders 23 of the rams are fixed to the front and rear tubes 18 and 20 respectively, while the piston rods 24 and 24a are fixed to the centre tube 19. As before the full bore sides of the rams and the annular sides of the rams are connected by pipes so that the rams extend and contract together. The hydraulic rams are maintained under pressure by a pilot valve or by an accumulator in the hydraulic pipe system.

The maximum extension of the tubes 18 to 20 is defined by stops 27a and 27b welded on the internal surfaces of the tubes 18 and 19 respectively which come to abut against stops 28a and 28b welded on the external surfaces of the tubes 19 and 20. Typically, allowing for the necessary overlap of the tubes 18 to 20 in the extended position, the use of a three-part telescopic connection as shown permits the overall length of the chassis to be extended from its closed

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position by one and a half times the length of the front tube 18.

The tubes 18 to 20 are a relatively loose fit within one another so that when they are fully extended they form a slight arch as shown in figure 4. In this position, when a load is carried on the forks 14, the left hand ends (as viewed in figure 4) of the tubes 19 and 20 become frictionally jammed inside the right hand ends of the tubes 18 and 19, forming a very rigid chassis. Further, the greater the load the greater the tension on the upper surfaces of the tubes 18 to 20, increasing the rigidity of the chassis.

As seen in figures 4 and 5, the forklift truck has a seat 30 and steering wheel 31 which can be swung up out of the way in order to permit the forklift truck to be closed.

The mast 13 of the forklift truck, figure 6 has a fixed section 32 and an upwardly slidable section 33. Upper and lower pulleys 34 and 35 respectively are mounted at the top and bottom of the slidable section 33. The forks 14 are mounted on an upwardly slidable fork carrier in the form of a plate 36 having a shallow T-shaped cross-section with upper and lower flanges 37 and 38 engaging the forks 14. A first chain 39' is connected at its lower end to the plate 36 and at its upper end to the fixed mast section 32 and passes round the upper pulley 34. A second chain 39' ' is connected at its upper end to the fixed mast section 32 and at its lower end to the plate 36 and passes around the lower pulley 35. A double acting hydraulic ram 40 is connected between the fixed and slidable sections 32 and 33 of the mast.

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The ram 40 is operated by the hydraulic system of the forklift truck, and when it is extended the slidable mast section 33 is raised and when it is contracted the slidable mast section 33 is lowered. Raising or lowering of the mast section 33 causes the fork carrier 36 to move twice as far in the same direction.

The forklift truck may be mounted on the rear of a vehicle such as a truck or trailer using the fitment shown in figure 7, in which the horizontal bars 4.1 and 42 represent the cross-bars of an underrun guard commonly fitted at the rear of trucks, trailers and other commercial high-bottom vehicles. A pair of U-shaped brackets 43 are welded or bolted at laterally spaced positions to the lower bar 42, and a further bracket 44 is mounted on the upper bar 41 centrally between the brackets 43. The bracket 44 is rotatable about a horizontal axis A normal to the bar 41 and comprises a tongue 45 and an eccentric cam 46 welded together for co-rotation.

When one wishes to mount the forklift truck on the rear of a truck or other vehicle, the bracket 44 is first rotated until the tongue 45 and cam 46 are pointing upwards, as indicated by dashed lines in figure 7. Then the forklift truck is driven slowly towards the rear of the truck and by manipulation of the height of the mast 13 and the position of the forklift truck the flange 38 of the plate 36 is eased into the U-shaped brackets 43. Now the bracket 44 is rotated 180 degrees to the position shown in solid lines in figure 7, whereupon the cam 46 engages and pushes down on the edge of the upper flange 37 of the plate 36 to force the lower flange 38 properly down into engagement with the brackets 43. At the same time the tongue 45 engages behind the flange 37. Now the

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forklift truck is locked onto the rear underrun guard, which is the position shown in figure 5.

Now, by attempting to lower the sliding section 33 of the mast 13, the forklift truck is raised off the ground into a position for transport, as shown in figure 8.

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