EP0303413A1

EP0303413A1 - Narrow aisle lift truck

Info

Publication number: EP0303413A1
Application number: EP88307271A
Authority: EP
Inventors: Frederick Leslie Brown
Original assignee: Translift Material Handling Ltd
Current assignee: Translift Material Handling Ltd
Priority date: 1987-08-13
Filing date: 1988-08-05
Publication date: 1989-02-15
Also published as: GB8719175D0; GB2208500A; GB8818637D0; GB2208500B

Abstract

A narrow aisle forklift truck (Figure 1) has a pivot between the mast and body and means for turning the mast relative to the body so as to steer the truck. The mast has a load extensor/retractor (28) between the forks (26) and the mast (24). This enables insertion and extraction in particularly narrow aisles relative to the dimensions of the truck and its load.

Description

This invention relates to lift trucks for use in narrow aisles of warehouses and the like, for extracting loads from stacks at the sides of such aisles and inserting them into such stacks. The truck of the invention is of the kind comprising a truck body, a pivoted mast, and a load carrier which can be elevated on the mast.
U.S.Patent 3335879 shows a lift truck having a frame with front non-steerable wheels and rear steered wheels, and with a mast mounted on the front of the frame via an upright spindle so that the mast, together with the usual fork-carrying carriage for the load which is mounted on the mast can be pivoted, that is swung so that the load is at the side of the frame. This is for the purpose of lifting an elongate load extending generally transversely of the truck, and swinging it to lie laterally of the truck pointing in a fore-and-aft direction, for conveyance especially along aisles narrower than the length of the load. This arrangement does not lend itself to insertion and extraction of loads from stacks at the side of narrow aisles.
U.S.Patent 309638 shows a forklift truck having a body with a pair of steered rear wheels and a pair of front located outrigger wheels. There is also a further pair of driven or traction wheels located underneath a mast which is (also in this case) pivoted to the body and has the usual carriage and forks. This is intended to be used for inserting or removing a load to or from a stack by an appropriate pivoting and positioning so that the mast is taken to the face of the stack. However in so doing, the vehicle becomes unstable and is only prevented from toppling over by the outriggers which are therefore subject to considerable load. Moreover, the vehicle needs six wheels.
According to the invention a narrow aisle lift truck comprises a wheeled body and a wheeled mast carrier connected together by a pivot for relative angular movement about a generally vertical axis between the respective sets of wheels, and a carriage on the mast with load carrying means, characterised in that means are provided for extending and retracting said load carrying means relative to the mast, and in that the truck is arranged to be steered by causing relative movement of the body and mast carrier about the pivot.
This enables a load to be inserted or extracted by a combination of positioning of the body and mast carrier with extension or retraction of the said means. Hence it is unnecessary to take the mast up to the face of the stack. The result is found to be that the truck according to the invention requires a smaller clearance in the aisle, and can either be made wider, to carry wider loads with even greater stability, or enables better use of warehouse space by using narrower aisles. The outriggers are unnecessary and the construction is considerably simplified.
One embodiment of the invention is now mare particularly described with reference to the accompany drawings wherein:

Figure 1 is a perspective view of a truck;
Figure 2 is a diagrammatic plan view showing the truck manoeuvreing in a confined space.

Referring first to Figure 1, the truck comprises a body 10 here shown as provided with a driving seat 12 and a steering wheel 14. Wheels 16 are driven wheels located under the vehicle. Those wheels are on a common axis.
A main frame member 18 carries a king pin pivoting the mast structure 20 which has forwardly projecting feet 22 carrying a pair of wheels 24 on a second common axis. The mast is located rearwardly of the wheels 24 in the interest of stability. The mast may have a plurality of telescopic extensions in conventional manner. The mast mounts a carriage 24 which is arranged to be hoisted and lowered on the mast by the usual chains, cylinders and the like. Carriage 24 is provided with load elevating means which in the illustrated form are forks 26.
Interposed between forks 26 and the part of the carriage 24 which slides on the mast is an extensor/retractor 28 which in the illustrated version comprises lazy tongues or pantagraph linkage extensible and retractable for example by a hydraulic cylinder not shown.
The parts 18 20 are, as stated, pivoted together about a vertical axis. They may be angularly adjusted by any convenient means. A simple method is the use of a pair of angling rams or hydraulic cylinders each pivoted at one end to the part 20, for example one on either side of the vertical pivot axis, and pivoted at the other end to the part 18 or the body 10, and coupled in a hydraulic circuit so that one is extended by pressurisation as the other one is exhausted and contracted.
An alternative method uses a gear system to turn the mast carrier about its pivot relative to the body.
The steering wheel 14 is arranged to cause drive of the gear system, or movement of valves controlling flow of hydraulic fluid, in appropriate directions according to the direction of turning of the wheel 14.
Figure 2 shows the truck manoeuvreing to place the load into the gap 40 between the existing loads 42,44 on one side of the aisle. As shown the load has a length D and the truck a maximum width W. The aisle then requires to be of the width D plus W, if the maximum angle of mast carrier to truck body is (as preferred) 90 deg. This aisle width (D plus W) may in practice be as much as 1 meter less than would be needed (all other things being equal) with prior art load carriers to perform the same functions. It will also be appreciated that the preferred embodiment is capable of inserting or extracting loads from either side of the aisle, unlike some prior art constructions which could only work to one side and hence needed to travel in a particular direction along an aisle in order to gain access to a particular side.
Preferably the forks occupy a width N which is less than the gap G between the feet of the mast carrier. This can allow the forks to descend to ground level to enable a load to be picked off the floor in appropriate circumstances. It is desirable that the length of said side members be less than that of the forks or equivalent, in order to minimise the extension movement needed by the linkage 28 or its equivalent.
In a modification, not shown, the mast carrier 22 comprises a first part which extends upwardly adjacent the king pin and carries the mast structure, and a second part which is generally U - shaped in plan and carries the wheels 24. These two parts are pivoted together about an axis which extends fore-and-aft when the truck is moving in a straight line. The effect is to allow the said second part to rock, without affecting stability, if a wheel encounters uneven ground or an obstacle.

Claims

1. A narrow aisle lift truck comprising a wheeled body and a wheeled mast carrier connected together by a pivot for relative angular movement about a generally vertical axis between the respective sets of wheels, and a carriage on the mast with load carrying means, characterised in that means are provided for extending and retracting said load carrying means relative to the mast, and in that the truck is arranged to be steered by causing relative movement of the body and mast carrier about said pivot.

2. A truck as claimed in Claim 1 wherein the said means for extending and retracting the load carrying means is a linkage.

3. A truck as claimed in Claim 1 wherein the wheeled mast carrier comprises side members having their wheels at their free ends and which project from the pivot for a distance less than that of the load carrying means.

4. A truck as claimed in Claim 3 wherein said side members are spaced apart by a gap wider than the load carrying means.

5. A truck as claimed in any preceding claim wherein the steering means comprise rams between the carrier and body.

6. A truck as claimed in any of Claims 1-4 wherein the steering means comprise a gear system to turn the mast carrier relative to the body.

7. A narrow aisle lift truck substantially as hereinbefore described with reference to and as shown in the accompanying drawings.