GB2347132A

GB2347132A - Lift truck

Info

Publication number: GB2347132A
Application number: GB9904455A
Authority: GB
Inventors: Frederick Leslie Brown
Original assignee: Translift Engineering Ltd
Current assignee: Translift Engineering Ltd
Priority date: 1999-02-27
Filing date: 1999-02-27
Publication date: 2000-08-30
Also published as: GB9904455D0

Abstract

A fork lift truck in which the ratio of the mass of the truck, M, to the working length, L2, is greater than 3.6 kg per mm, where the working length is defined as the distance between the back of the truck and a load stop 32. This is achieved by the provision of a counterbalance weight 20, which also acts as a chassis, supporting wheels 12, (14, Fig. 2) and a mast (16, Fig. 2). The counterbalance weight may be cast, or alternatively may be made from several sheets of metal. In the preferred embodiments the front most portion of the front wheels 12 are positioned to the rear of the load stop 32. Preferably, the centre of gravity, CG, of the truck lies less than 600 mm above the ground; the ratio of mass, M, to body length, Z, is greater than 3.6 kg per mm and the ratio of mass moment arm length, G, to rear overhang length, F, is less than 0.25.

Description

LIFT TRUCK The present invention relates to lift trucks such as forklift trucks.

Known lift trucks are capable of carrying loads supported on forks, a spike or the like mounted on a mast. The mast is capable of lifting say the forks to different heights to place or pick up the load from say a racking storage system or the bed of a lorry or off the ground etc.

The centre of gravity of the load tends to be in front of the front wheels of the lift truck and hence a counterbalance must be provided to prevent the lift truck tipping forward about its front wheels.

Typically known lift trucks are provided with a chassis which supports front and rear wheels of the lift truck in their relative positions and also mounts the lift mast. A counterbalance weight is then mounted on the chassis at the rear of the truck. The chassis may be fabricated from sheet steel typically 12 mm thick. Such known types of lift truck tend to be relatively long and when used in the aisles of a warehouse to retrieve or deposit loads from a rack storage system, the aisles have to be made relatively wide so as to accommodate turning of the lift truck through 90 degrees within the aisle.

A known solution to providing a lift truck for use in relatively narrow aisles is to provide a lift truck A (see figure 1) with a shorter working length (L) having stabilising legs B with wheels C that project beyond the front of the load stop D on the forks.

However such lift trucks, when picking up loads directly off the ground are limited to loads having a width which is narrower than the distance between the innermost portions of the stabilising legs B. Furthermore when positioning several loads in a row along the ground gaps have to be left between adjacent loads in order to allow access for the stabilising legs B thus wasting storage space. Such lift trucks are thus incapable of picking up relatively wide loads directly off the ground and when used with a rack system, space is wasted at the bottom of the rack system since the stabilising wheels have to pass under the racking arrangement. To minimise wasted space the wheels are made relatively small and the legs are made relatively narrow.

To overcome the inability of such lift trucks to pick up relatively wide loads from the ground a reach mechanism can be provided which moves either the forks, or the forks and mast forwards relative to the wheels of the lift truck such that the load stop D sits in front of the front stabilising wheels C. The load is picked up whilst the lift truck is stationary and the reach mechanism moves to its retracted position following which the lift truck itself can transport the load to its destination. However the lift capacity for lifting loads off the ground when the reach system is deployed is reduced when compared to lifting relatively narrow loads or lifting goods off a rack storage system, (when lifting can be achieved with the reach mechanism in the retracted position) and provision has to be made in the counterbalance weight to counterbalance the weight of the reach mechanism itself which can be positioned towards the front of the lift truck. Also the lift truck is limited to use in dry conditions on relatively flat surfaces since the relatively small stabilising wheels cannot cope with uneven surfaces and wet conditions typically found out of doors.

Thus according to the present invention there is provided a lift truck having a mass M and a working length L2, L2 being defined as the distance from a load stop on lifting forks, a spike, or the like, to the back of the lift truck, in which the M/Lz ratio is greater than 3.6 kg per millimetre.

Preferably the M/L2 ratio is greater than 3.7 kg per millimetre and preferably greater than 3.75 kg per millimetre.

According to a further aspect of the present invention there is provided a lift truck including a counterbalance weight which acts as a chassis for the lift truck.

According to a further aspect of the present invention there is provided a lift truck including front and rear ground engaging means such as wheels and a counterbalance weight which supports the ground engaging means in their relative positions.

According to a further aspect of the present invention there is provided a lift truck including a lift mast and a counterbalance weight which supports the lift mast.

In one form, the counterbalance weight is made from at least one casting and in another form the counterbalance weight is a laminated counter balance weight made from a plurality of sheets of metal.

Preferably the counterbalance weight when made from sheet metal includes at least one profiled plate preferably of steel having a thickness of greater than 19 mm, preferably greater than 39 mm, preferably greater than 99 mm and preferably greater than 149 mm.

Preferably there are more than 2 laminations, preferably more than 3 laminations and preferably more than 4 laminations.

Preferably the total thickness of the laminations is greater than 200 mm preferably greater than 300 mm, preferably greater than 400 mm, and preferably greater than 500 mm.

Preferably the laminations are substantially horizontally orientated.

According to a further aspect of the present invention there is provided a lift truck having a mass M and a body length Z, Z being defined as the distance between the front and rear most portions of the body, the ratio of M/Z being greater than 3.6 kg per millimetre, preferably greater than 3.7 kg per millimetre, preferably greater than 3.75 kg per millimetre.

According to a further aspect of the present invention there is provided a lift truck having a mass moment arm length G defined as the horizontal distance between an overload pivot point and the centre of gravity of the lift truck and a rear overhang length F defined as the horizontal distance between the overload pivot point and the rear of the lift truck, the ratio of G/F being less than 0.25 preferably less than 0.2.

According to a further aspect of the present invention there is provided a lift truck having a mass M, the centre of gravity of the mass being less than 600 mm above the ground, and preferably less than 550 mm above the ground.

Preferably the working length L2is less than 1500 mm and preferably less than 1350 mm.

Preferably the lift truck is counter balance lift truck, a counter balance lift truck being defined as a lift truck having the front most portion of the body, such as the front most portion of the front wheels or the front most portions of the front wheel guards, being substantially in line with or behind a load stop on lifting forks, a spike, or the like.

The invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a schematic view of a known lift truck including stabilising legs; Figure 2 is an isometric view of a lift truck according to the present invention; Figure 3 is an isometric view of part of the lift truck of figure 2; Figure 4 is a schematic side elevation of the lift truck of figure 2; and Figure 5 is a view similar to figure 3 of a second embodiment of a lift truck according to the present invention.

With reference to figures 2-4 there is shown a lift truck 10 having front ground engaging means in the form of driven wheels 12 and rear ground engaging means in the form of steerable tandem wheels 14 (though in further embodiments the front wheels could be idle and the rear wheels could be driven). A lift mast 16 is mounted on the front of the lift truck and allows the forks 18 to be lifted up and down. A counterbalance weight 20 (shown cross hatched in figure 4) supports a vertical pivot 22 on which are mounted the rear tandem wheels 14 to enable the lift truck 10 to be steered.

The counterbalance weight 20 includes a main body portion 21 having a rear wheel recess 26 and forwardly projecting arms 24. Each arm 24 supports an appropriate front wheel 12.

Body portion 21 when viewed from above has curved edges 28 to improve the manoeuvrability of the lift truck within an aisle.

The lift mast 16 is pivotally mounted for rotation about a horizontal axis about pivots 30 (only one shown). Typically the mast might be able to pivot by a relatively small angle rearward when a load is carried to encourage the load to rest against a load stop 32 (see figure 4). In this case the load stop 32 is formed by the vertically orientated portions 34 of the forks 18.

In this case the body portion 21 and arms 24 of the counterbalance weight 20 are all formed as a single casting. However in further embodiments the counterbalance weight can be formed from two or more castings. Alternatively the counterbalance weight can be formed from one or more castings and one or more profiled sheets of material such as sheet steel.

It is apparent that the counterbalance weight 20 is additionally providing the function of a chassis since it supports the front and rear wheels in their relative positions.

Furthermore the forces associated with a load to be carried are transmitted through the counterbalance weight itself. For example a sufficiently large downward force applied to the forks 18 would cause the counterbalance weight to hog and any load situated between the front and rear wheels such as the operators weight will cause the counterbalance weight to sag.

An industy-recognized dimension of lift trucks is L, (see figure 4) which is the dimension between the load stop 32 and the rear of the lift truck. This dimension (herein also referred to as the working length of the lift truck) is a primary dimension in defining the narrowness of an aisle within which the lift truck can work. A reduction in L2 allows the lift truck to work within a narrower aisle but such a reduction also reduces the counterbalance weight moment and thus reduces the lift capacity of the lift truck. The applicant is the first to realise that by providing a lift truck with a mass M to L2 ratio of greater than 3.6 kg M per millimetre L, it is possible to provide a lift truck having improved manoeuvrability within an aisle whilst maintaining the lift capacity or to improve the lift capacity of a lift truck having the same L2 as compared with heretofore known lift trucks.

Any particular lift truck has a body length Z, herein defined as the distance between the front most and rear most portions of the body (see figure 1 and figure 4). The body length Z may be greater than the working length L2 (see figure 1), or Z may be less than L2 (see figure 4).

The applicant is the first to realise the benefits of providing a lift truck having a mass M to body length Z ratio (M/Z) of greater than 3.6 kg per millimetre.

It can be seen from figure 4 that lift truck 10 is a counter balance lift truck, that is to say a lift truck having a the front most portion of the body substantially in line with or behind the load stop, ie Z is substantially equal to or less than L2.

When considering figure 4, by applying a sufficiently high load to the forks 18 the lift truck 10 will ultimately start to pivot about the point of contact 36 of the wheel 12 with the ground 37. Point of contact 36 is herein defined as the overload pivot point. The horizontal distance between the overload pivot point and the centre of gravity CG of the lift truck is herein defined as the mass moment arm length G. The horizontal distance between the overload pivot point and the rear most portion of the truck is herein defined as the rear overhang length F (dimensions G and F are not shown to scale in figure 4).

The applicant is the first to realise the benefits of providing a lift truck having a mass moment arm length G to rear overhang length F of less than 0.25 ie G/F is less than 0.25.

The arrangement described allows the centre of gravity of the lift truck to be positioned close to the ground (see dimension H, not shown to scale in figure 4). In this case H equals 500 mm though in further embodiments H could be less than 500 mm, less than 550 mm or less than 600 mm depending on the particular arrangement.

The lift truck 10 has the following dimensions: M =5 tonnes L2 = 1300 mm Z = 1230 mm G =198mm F = 1030 mm H = 500 mm M/L2 = 3.8 kg/mm M/Z = 4.06 kg/mm G/F = 0. 192 Turning to figure 5 there is shown a second embodiment of a lift truck 110 according to the present invention in which the counter balance weight 120 is the same shape as the counter balance weight 20 of lift truck 10 but is fabricated from laminations R1-R6 of sheet steel. The laminations are of various thickness and are cut to an appropriate plan profile prior to being welded together to from the unitary counter balance weight 120. Further embodiments of a laminated counter balance weight might typically include laminations of 20 mm thick, and/or 40 mm thick, and/or 100 mm, and/or 150 mm thick.

Claims

Claims 1. A lift truck having a mass M and working length L, L being defined as the distance from a load stop on lifting forks, a spike, or the like, to the back of the lift truck, in which the M/L2. ratio is greater than 3. 6 kg per millimetre.
2. A lift truck according to claim 1 in which the M/Lz ratio is greater than 3. 7 kg per millimetre.
3. A lift truck according to claim 1 in which the M/L2 ratio is greater than 3. 75 kg per millimetre.
4. A lift truck according to any preceding claim, the iift truck including a counterbalance weight which acts as a chassis for the lift ; A
5. A lift truck according to any preceding claim including front and rear ground engaging means, such as wheels, and a counterbalance weight which supports the ground engaging means in their relative positions.
6. A lift truck according to any preceding claim, the lift truck including a lift mast and a counterbalance weight which supports the lift mast.
7. A lift truck according to any one of claims 4 to 6 in which the counterbalance weight is made from at least one castings.
8. A lift truck according to any one of claims 4 to 6 in which the counterbalance is a laminated counterbalance weight made from a plurality of sheets of metal.
9. A lift truck according to claim 8 in which as least one of the plurality of sheets has thickness greater than 19 mm.
10. A lift truck according to claim 8 or 9 in which at least one of the plurality of sheets has a thickness greater than 39 mm.
11. A lift truck according to any one of claims 8 to 10 in which at least one of the plurality of sheets has a thickness of greater than 99 mm.
12. A lift truck according to any one of claims 7 to 11 in which the least one of the plurality of the sheets has a thickness greater than 149 mm.
13. A lift truck according to any one of claims 8 to 12 in which there are more than two laminations.
14. A lift truck according any one of claims 8 to 13 in which there are more than three laminations.
15. A lift truck according to any one of claims 8 to 14 in which there are more than four laminations.
16. A lift truck according to any one of claims 8 to 15 in which the total thickness of the laminations is greater than 200 mm.?'
17. A lift truck according to any one of claims 8 to 16 in which the total thickness of the laminations is greater than 300 mm.
18. A lift truck according to any one of claims 8 to 17 in which the total thickness of the laminations is greater than 400 mm.
19. A lift truck according to any one of claims 8 to 18 in which the total thickness of the laminations is greater than 500 mm.
20. A lift truck according to any one of claims 8 to 19 in which the laminations are substantially horizontally orientated.
21. A lift truck according to any preceding claim having a body length Z, Z being defined as the distance between the front and rear most portions of the body, the ratio of MIZ being greater than 3. 6 kg per millimetre.
22. A lift truck according to claim 21 in which the ratio of M/Z is greater than 3. 7 kg per millimetre.
23. A lift truck according to claim 21 in which the ratio of M/Z is greater than 3. 75 kg per millimetre
24. A lift truck according to any preceding claim, the lift truck having a mass moment arm length G defined as the horizontal distance between an overload pivot point and the centre of gravity of the lift truck, and a rear overhang length F defined as the horizontal distance between the overload pivot point and the rear of the lift truck, the ratio of G/F being less than 0.25.
25. A lift truck according to claim 24 in which the ratio G/F is less than 0. 2.
26. A lift truck according to any preceding claim in which the centre of gravity of the mass M is less than 600 mm above the ground.
27. A lift truck according to claim 26 in which the centre of gravity of the mass M is less than 550 mrn above the ground.
28. A lift truck according to any preceding claim in which the working length L) is less than 1500 mm.
29. A lift truck according to claim 28 in which the working length L2 is less than 1350 mm.
30. A lift truck according to any preceding claim in which the lift truck is a counterbalance lift truck, the counterbalance lift truck being defined as a lift truck having the front most portion of the body, such as the front most portion of the front wheels or the front most portion of the front wheel guards, being substantially in line with or behind a load stop on lifting forks, a spike, or the like.
31. A lift truck including a counterbalance weight which acts as a chassis of the lift truck.
32. A lift truck including front and rear ground engaging means, such as wheels and a counterbalance weight which supports the ground engaging means in their relative positions.
33. A lift truck including a lift mast and a counterbalance weight, the counterbalance weight acting to support the lift mast.
34. A lift truck having a mass M and body length Z, Z being defined as the distance between the front and rear most portions of the body, the ratio of M/Z being greater than 3. 6 kg per millimetre.
35. A lift truck having a mass moment arm length G defined as the horizontal distance between an overload pivot point and the centre of gravity of the lift truck, and a rear overhang length F defined as the horizontal distance between the overload pivot point and the rear of the lift truck, the ratio of G/F being less than 0.25.
36. A lift truck having a mass M, the centre of gravity of the mass being less than 600 mm above the ground.