GB2364992A

GB2364992A - Lifting structure for an industrial truck

Info

Publication number: GB2364992A
Application number: GB0018116A
Authority: GB
Inventors: Barry Michael Warner
Original assignee: Lansing Linde Ltd
Current assignee: Linde Material Handling UK Ltd
Priority date: 2000-07-24
Filing date: 2000-07-24
Publication date: 2002-02-13
Anticipated expiration: 2020-07-24
Also published as: DE10133585B4; DE10133585A1; GB2364992B; GB0018116D0

Abstract

A lifting structure for an industrial truck has a vertically non-movable upright mast (1) and at least one travelling mast (3) which can be raised along the upright mast (1). A load-receiving arrangement (4) is fastened directly or indirectly on the travelling mast (3) such that the weight of a load received by the load-receiving arrangement (4), with the travelling mast (3) raised, produces a bending moment (9) which acts on the upright mast (1). A compensation arrangement is provided which can be used to produce a counter-moment which acts on the upright mast (1) and is directed counter to the bending moment (9). The compensation arrangement may comprise at least one hydraulic compensation cylinder (6) which has a compensation-cylinder tube (14) and a compensation-cylinder piston (15) which can be extended out of the compensation-cylinder tube (14), the compensation-cylinder tube (14) and the compensation-cylinder piston (15) acting on opposite ends of the upright mast (1). Preferably, the compensation cylinder (6) is integral with and below the lifting cylinder (5).

Description

<Desc/Clms Page number 1> Lifting structure for an industrial truck The invention relates to a lifting structure for an industrial truck, having a vertically non-movable upright mast and at least one travelling mast which can be raised along the upright mast, a load-receiving arrangement being fastened on the travelling mast directly or indirectly such that the weight of a load received by the load-receiving arrangement, with the travelling mast raised, produces a bending moment which acts on the upright mast. The invention also relates to an industrial truck having a lifting structure as defined above.

Lifting structures of the above generic type are usually used in industrial trucks, e.g. fork stackers. In this case, the upright mast of the lifting framework is connected to a frame of the industrial truck. In one possible embodiment, the upright mast is fastened rigidly on the frame. Also known are industrial trucks in which the upright mast can be displaced in the horizontal direction or inclined in relation to the frame.

The travelling mast is guided on the upright mast by means of rollers and can be extended upwards. It is possible to arrange on the travelling mast a further telescopically extensible mast which, in turn, is guided on the first travelling mast by means of rollers. A load-receiving means is guided on the travelling mast, or in the case of more than one travelling mast on the travelling mast which can be extended furthest. This load-receiving arrangement is often designed as a lifting fork by means of which, for example, pallets can be received and transported. The force necessary for extending the or each

travelling mast and for raising the load-receiving arrangement and the load is usually produced by at least one hydraulic lifting cylinder.

The centre of gravity of the raised load-receiving arrangement and of the load is located, in the case of the configuration described, in front of the lifting structure. This results in the weights of the load-receiving arrangement and of the load producing a moment which acts on the lifting structure and by means of which the components of the lifting structure are elastically deformed. In particular when a heavy load is raised by the load-receiving arrangement, the lifting structure tilts forwards to a considerable extent as a result of the elastic deformation.

In order for it to be possible to compensate for this undesired deformation of the lifting structure, the prior art includes lifting structures which are mounted in an articulated manner on a frame of the industrial truck and can be actively tilted rearwards. However, such an arrangement involves high outlay in design terms since, in addition to a bearing for the lifting structure, it is also necessary to provide hydraulic tilting cylinders and a control arrangement for the tilting cylinders.

An object of the present invention is to provide a lifting structure in which a straightforward arrangement can be used to compensate for elastic deformation of the lifting structure as a result of the loading weight.

According to the invention the above defined lifting structure is provided with a compensation arrangement which can be used to produce a counter-moment which acts on the upright mast and is directed counter to

the bending moment. The counter-moment produced by the compensation arrangement reduces or prevents elastic deformation of the upright mast since the counter-moment and the bending moment compensate for one another. This can be achieved, in particular, in that the magnitude of the counter-moment is produced in dependence on the weight of the load. The counter-moment is thus directly proportional to the bending moment.

Preferably for the purpose of raising the travelling mast there is provided at least one hydraulic lifting cylinder which has a lifting-cylinder tube and a lifting-cylinder piston which can be extended out of the lifting-cylinder tube, these being connected, on the one hand, to the upright mast and, on the other hand, to the travelling mast.

It is also preferred that the compensation arrangement comprises at least one hydraulic compensation cylinder which has a compensation-cylinder tube and a compensation-cylinder piston which can be extended out of the compensation-cylinder tube, the compensation-cylinder tube and the compensation-cylinder piston acting on opposite ends of the upright mast. The compensation cylinder is preferably arranged parallel to the upright mast. In accordance with a preferred configuration, the compensation-cylinder tube is fastened at the top end of the upright mast, while the compensation-cylinder piston is connected to the bottom end of the upright mast. However, it is also possible for these to be arranged the other way around, in which case the compensation-cylinder piston acts on the top end, and the compensation-cylinder tube acts on the bottom end, of the upright mast. Since the compensation cylinder is offset in relation to the centre of gravity of the

surface area of the upright mast, the upright mast may be subjected to a moment by a compressive force produced by the compensation cylinder. If the compensation cylinder is offset in relation to the upright mast in the direction of the load-receiving arrangement, said moment constitutes a counter-moment in relation to the bending moment produced by the loading weight.

Particular advantages are achieved if a pressure chamber of the lifting cylinder is connected hydraulically to a pressure chamber of the compensation cylinder. The compensation cylinder is thus always subjected to the hydraulic pressure which prevails in the lifting cylinder and, in turn, depends directly on the loading weight. This means that the counter-moment is directly dependent on the loading weight.

A particularly straightforward configuration is achieved if the lifting-cylinder tube and the compensation-cylinder tube are connected rigidly to one another. The hydraulic connection between the lifting cylinder and the compensation cylinder can then be produced without the use of external connecting lines. The lifting-cylinder tube and the compensation-cylinder tube may be fastened jointly on the lifting structure.

An expedient configuration of the invention is provided if the lifting-cylinder tube is fastened with the compensation-cylinder tube at the top end of the upright mast.

The lifting-cylinder piston can be extended upwards out of the lifting-cylinder tube and is connected to the travelling mast. This corresponds to the

conventional configuration for lifting structures when a lifting cylinder is fastened on the upright mast.

It is also expedient if the compensation-cylinder piston can be extended downwards out of the compensation-cylinder tube and is supported at the bottom end of the upright mast. In this embodiment, the compensation-cylinder piston is preferably arranged coaxially with the lifting-cylinder piston and projects downwards out of the structural unit formed by the lifting-cylinder tube and the compensation-cylinder tube. The bottom end of the compensation-cylinder piston is supported on a component belonging to the upright mast or to the frame of the industrial truck and thus produces a compressive force which acts between the bottom end of the upright mast and the top end of the upright mast and is transmitted by way of the lifting-cylinder tube and the compensation-cylinder tube.

The compensation-cylinder piston preferably has a larger cross-sectional surface area than the lifting-cylinder piston. The force produced by the compensation cylinder is thus larger than the force produced by the lifting cylinder. This produces a force distribution within the cylinder arrangement which ensures that at least some of the force produced by the compensation cylinder is introduced as counter-moment into the upright mast.

The invention also provides an industrial truck having a lifting structure as defined above.

Further advantages and details of the invention will be explained in more detail with reference to the exemplary embodiment illustrated in the accompanying schematic drawings, in which:

Figure 1 shows a schematic illustration of a lifting structure according to the invention, and Figure 2 shows an embodiment of the compensation arrangement.

Referring to the drawings, Figure 1 shows a schematic illustration of a lifting structure according to the invention with an upright mast 1 which is fastened on a frame 2 of an industrial truck. A travelling mast 3 is guided such that it can be displaced in the vertical direction on the upright mast 1 by means of rollers (not illustrated). A load-receiving arrangement 4 designed as a lifting fork may likewise be displaced along the travelling mast 3 by means of rollers, the position of the load-receiving arrangement 4 being adjusted by means of a load chain (not illustrated).

In the case of the lifting structure illustrated, a hydraulic lifting cylinder 5 is arranged on the load side of the upright mast 1, and a compensation cylinder 6 is located, according to the invention, coaxially beneath the lifting cylinder 5. A cylinder tube of the lifting cylinder 5 and a cylinder tube of the compensation cylinder 6 together form a component 7. This component 7 is connected to the upright mast 1 at the top end. A piston 8 of the lifting cylinder 5 can be extended upwards out of the component 7 and is connected fixedly to the travelling mast 3. A piston 15 of the compensation cylinder 6 can be extended downwards out of the component 7 and is supported on the frame 2 of the industrial truck. It is likewise possible for the compensation-cylinder piston 15 to be supported on a part of the upright mast 1 which projects in the forward direction.

Figure 2 shows an embodiment of the compensation

arrangement. The upright mast 1 is illustrated, and it is likewise possible to see parts of the travelling mast 3, which is arranged essentially behind the upright mast 1. If a load is raised by the load-receiving arrangement (not illustrated in this figure), said load subjects the upright mast 1 to a moment 9 in the direction indicated by the arrow.

The hydraulic lifting cylinder 5 comprises a lifting-cylinder tube 10 and a lifting-cylinder piston 11 which can be extended upwards. The lifting-cylinder tube 10 is fastened at the top end of the upright mast 1 by means of a fastening arrangement 12 such that at least an upwardly directed compressive force can be transmitted from the lifting-cylinder tube 10 to the upright mast 1. The lifting-cylinder piston 11 is connected to the travelling mast 3 by means of a fastening arrangement 13, with the result that said travelling mast can be raised by virtue of the lifting-cylinder piston 11 being extended out of the lifting-cylinder tube 10.

A cylinder tube 14 of the compensation cylinder 6 is screwed on at the bottom end of the lifting-cylinder tube 10. The compensation-cylinder tube 14 and the lifting-cylinder tube 10 thus form a structural unit. The compensation-cylinder piston 15 can be extended downwards out of the compensation-cylinder tube 14 and is supported on the frame 2 of the industrial truck or on a component which is connected rigidly to the upright mast 1.

The lifting cylinder 5 and the compensation cylinder 6 have a joint pressure chamber 16, which is supplied with hydraulic oil via a connection stub 18 and a channel 17 arranged in the compensation-cylinder piston 15. Subjecting the pressure chamber 16 to the

action of pressure results in the following force distribution: The lifting force which acts on the lifting-cylinder piston 11 is depicted by F. With the load-receiving means raised, the lifting force F corresponds to the sum of the weights of the load, of the load-receiving arrangement 4, of the travelling mast 3 and of the other raised components. The magnitude of the hydraulic pressure in the pressure chamber 16 thus depends directly on the loading weight.

The force F+FO acts on the compensation-cylinder piston 15, the force component Fo being produced on account of the surface area of the compensation-cylinder piston 15 being larger than that of the lifting-cylinder piston 11. The reaction force of the force component Fo is transmitted, via the hydraulic fluid located in the pressure chamber 16, to the compensation-cylinder tube 14 and, from the latter, to the lifting-cylinder tube 10, which absorbs the force FO on the fastening arrangement 12. The compressive force FO thus acting between the frame 2 and the fastening arrangement 12 causes a moment which is directed counter to the moment 9 and counteracts the elastic deformation of the upright mast 1 as a result of the loading weight.

If desired there may be more than one travelling mast mounted in extensible manner on the upright fixed mast. In this case, the load-receiving arrangement 4 is mounted on the travelling mast which can be extended furthest.

Claims

Claims: 1. Lifting structure for an industrial truck, having a vertically non-movable upright mast and at least one travelling mast which can be raised along the upright mast, a load-receiving arrangement being fastened on the travelling mast directly or indirectly such that the weight of a load received by the load-receiving arrangement, with the travelling mast raised, produces a bending moment which acts on the upright mast, wherein there is provided a compensation arrangement which can be used to produce a counter-moment which acts on the upright mast and is directed counter to the bending moment.
2. Lifting structure according to Claim 1, wherein for the purpose of raising the travelling mast there is provided at least one hydraulic lifting cylinder which has a lifting-cylinder tube and a lifting-cylinder piston which can be extended out of the lifting-cylinder tube, these being connected, on the one hand, to the upright mast and, on the other hand, to the travelling mast.
3. Lifting structure according to Claim 1 or Claim 2, wherein the compensation arrangement comprises at least one hydraulic compensation cylinder which has a compensation-cylinder tube and a compensation-cylinder piston which can be extended out of the compensation-cylinder tube, the compensation-cylinder tube and the compensation-cylinder piston acting on opposite ends of the upright mast.
4. Lifting structure according to Claim 3, wherein a pressure chamber of the lifting cylinder is

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connected hydraulically to a pressure chamber of the compensation cylinder.
5. Lifting structure according to Claim 3 or Claim 4, wherein the lifting-cylinder tube and the compensation-cylinder tube are connected rigidly to one another.
6. Lifting structure according to any one of Claims 3 to 5, wherein the lifting-cylinder tube is fastened with the compensation-cylinder tube at the top end of the upright mast.
7. Lifting structure according to any one of Claims 2 to 6, wherein the lifting-cylinder piston can be extended upwards out of the lifting-cylinder tube and is connected to the travelling mast.
8. Lifting structure according to any one of Claims 3 to 7, wherein the compensation-cylinder piston can be extended downwards out of the compensation-cylinder tube and is supported at the bottom end of the upright mast.
9. Lifting structure according to any one of Claims 3 to 8, wherein the compensation-cylinder piston has a larger cross-sectional surface area than the lifting-cylinder piston.
10. A lifting structure for an industrial truck substantially as hereinbefore described with reference to and as shown in the accompanying drawings.
11. An industrial truck having a lifting structure as claimed in any one of the preceding claims.