GB2098582A - Industrial lift trucks and telescopic masts for such trucks - Google Patents

Abstract

A telescopic mast (1) for an industrial lift truck, including a plurality of relatively movable sections (2, 3, 4), a lifting carriage (5) from which extends upwardly at least one chain (72, 73) to a pulley (45, 46) on a movable one of the sections and thence downwardly to an anchorage (35, 36) on a section relatively lower than the section on which the pulley is mounted, a member (53) mounted on and capable of limited vertical movement relative to the carriage, one end of the chain being fixed relative to the said member and the said chain extending downwardly from the member to a pulley (51, 54) mounted on the carriage and thence extending upwardly as aforesaid, and an actuator (6) arranged in a fixed position relative to a fixed, lowermost section of the mast and positioned to produce when the carriage is in its lowermost position upward movement of the said member relative to the carriage. <IMAGE>

Description

SPECIFICATION Industrial lift trucks and telescopic masts for such trucks This invention relates generally to industrial lift trucks and in particular to telescopic masts for them.

In particular the invention concerns a telescopic mast which comprises a plurality of sections each of which includes a pair of uprights, at least one actuator for raising one of the sections relative to a base section, and a lifting carriage from which extends at least one chain upwardly to a pulley on a movable section or one of the movable sections if there is more than one and thence downwardly to an anchorage on a section other than that on which the pulley is disposed. In such an arrangement it is known, if there are, for example, two movable sections and a base section, to move a lower one of those sections upwardly, the other movable section being connected by way of at least one chain to the base section, the chain passing over a pulley on the section which is moved by the actuator.This provision enables both sections to be moved upwards relative to the base section by means of a single actuator or simple pair of actuators effectively connected between the base section and only one of the movable sections. It is also known to provide a chain which extends from the lifting carriage upwardly to a pulley on one of the movable sections and thence downwardly to an anchorage point on either a lower one of the movable sections or the base section, so that the upward movement, whether caused directly by means of an actuator or indirectly by means of chains and pulleys of the section to which this pulley is attached causes upward movement of the lifting carriage.

It is desirable to provide, for telescopic masts for industrial lift trucks, what is known as "partial free-lift" so that the carriage can be raised for a limited distance before the telescopic extension of the mast commences. Several proposals have been made for mechanisms which provide such a partial free lift. One such includes a hydraulic actuator which is provided with a pulley over which extends the respective chain that is anchored to the carriage. The actuator moves the pulley upwardly for a short distance, thereby raising the carriage independently. Usually there are two such chains extending over respective pulleys and an actuator is provided for each pulley.

Such an actuator is then capable of moving the movable section of the mast upwardly relative to the base section after the carriage has been so raised. Since the two ends of the chain or each chain are connected to the carriage and to another section of the mast, the upward movement of the pulley causes upward movement of the carriage for twice the distance which the pulley moves. In a multiple-section mast such an actuator is usually carried on a movable section of the mast and it is necessary to provide flexible hose extending between the sections of the mast.

The present invention is directed to an improved mast which can provide partial free-lift.

In preferred embodiments of the invention partial free-lift is provided in a manner more convenient that the usual arrangements and in particular by means of an actuator which is in a fixed position.

In practice the use of flexible hose extending to an actuator which must move up and down is unnecessary.

In a mast according to the present invention there is provided a member capable of limited vertical movement relative to the lifting carriage, an actuator adapted to move the said member upwardly without restraining further upward movement of the member, and the, or each, chain which extends upwardly from the lifting carriage has an anchorage fixed relative to the said member and extends downwardly from the respective anchorage to a pulley from which it extends upwardly as aforesaid.

Preferably the aforementioned member comprises a bar to which are anchored two chains each of which passes under a respective pulley and thence extends upwardly to a respective pulley on a movable section of the mast. The aforementioned actuator preferably comprises a ram or other actuator having a fixed part and a movable part which is positioned to move the bar either directly or indirectly by means of an intermediate member.

There follows a description of the invention in more detail and by way of example. Reference will be made hereinafter to the accompanying schematic drawings, in which: Figure 1 illustrates one embodiment of a telescopic mast, shown in its retracted position; Figure 2 illustrates the mast after an initial phase of operation; Figure 3 illustrates the mast in an extended position; and Figure 4 illustrates another embodiment of the invention.

The mast which is shown in Figures 1 to 3 of the drawings is intended for incorporation in an industrial lift truck. The mast 1 comprises three telescopic sections 2, 3 and 4 which in Figure 1 are shown in a nested or retracted position. The mast includes a lifting carriage 5, which may include a pair of forks or, alternatively, a turret head from which a pair of forks or other lifting device extends. The main effort for raising the mast to an extended position is provided by an actuator 6 which in this embodiment of the invention comprises at least one and preferably two hydraulic jacks, of which only one is shown.

These jacks may be located behind or outside the mast's uprights. Each jack comprises a cylinder 60 which is fixed relative to the base section 2 of the mast and a piston 61 which is connected to the intermediate section 3 of the mast. In this embodiment of the invention the section 2 is fixed relative to the chassis of the truck and the sections 3 and 4 are relatively movable. Although the section 3 may be disposed, in the nested position of the mast, at the same height as the section 4, the section 4 is arranged to be lifted to a greater height than the section 3 and accordingly the sections 3 and 4 will be termed the lower movable section and the upper movable section respectively.

It is customary for each section of a telescopic mast to consist of two substantially vertical uprights which may be of channel section and which include or are associated with rollers which are disposed between the various sections of the mast so as to provide mutual guidance for the sections of the mast as the movable sections move up or down. Since the particular arrangement of the masts is not of importance to the present invention, the drawing illustrates the mast sections schematically only.

The base section of the mast comprises a horizontal base member 20 from which extend upwardly two uprights 21 and 22, spaced apart along the member 20. The intermediate section 3 of the mast comprises an upright 31 disposed adjacent one upright 21 of the base section and a second upright 32 disposed adjacent the other upright 22 of the base section. The two uprights of the intermediate section are connected at their top ends by a tiebar 33 which extends laterally, the lateral extension 37 being connected to the top end of the aforementioned piston 61. There would normally be upper and lower tiebars (not shown) on all the sections of the mast.

The upper movable section 4 of the mast comprises two uprights 41 and 42, of which the former is disposed adjacent one upright 31 of the intermediate section 3 and of which the other upright 42 is disposed adjacent the other upright 32 of the intermediate section 3. The two uprights of the upper section 4 are connected by a tiebar 43.

In this embodiment of the invention, the uprights of the various sections, including those of the base section 2, are disposed in two groups, there being one upright from each section in each group. The various sections may be disposed in slightly staggered fashion but would normally provide, between the two groups of uprights, a clear space through which the view of an operator is substantially unobstructed.

Connected to an anchorage 23 near the upper end of an upright 21 of the base section is a chain 71 which extends upwardly to a pulley 34 from which the chain extends downwardly to an anchorage point on the section 4. This anchorage point 44 is positioned near the lower end of the upright 41 which is adjacent the respective upright 31 of the section 3. Normally another similar chain, not shown, is connected between the other upright 22 of the base section to the other upright 42 of the upper movable section by way of a pulley mounted on the intermediate section 3.

It is convenient to mention that although it is customary to employ chains and pulleys as described herein, it is possible, though not preferred, to employ other forms of elongate member, such as wire hawser. Furthermore the pulleys may be constituted by sheaves or similar members which provide the action of a pulley; the term pulley is intended to include such equivalents.

Extending upwardly from the carriage 5 are two chains 72 and 73. The chain 72 passes over a pulley 45 which is disposed at the top of the section 4, near the top of one upright 41 of the section 4. From thence this chain 72 extends downwardly to an anchorage 35 on the intermediate section 3 and particularly to an anchorage which is disposed someway below the top of the upright 31 which is adjacent the upright 41 of the upper movable section 4. In like manner the chain 73 passes over a pulley 46 disposed on the section 4 near the top end of the other upright 42 thereof; the chain thence extends downwardly to an anchorage 36 on the upright 32 of the lower movable section 3.

As thus far described the mast is similar to known forms of triple extending telescopic masts.

It has been the practice to secure chains corresponding to the chains 72 and 73 directly to the carriage 5. It has, furthermore, been the practice to mount pulleys 45 and 46 vertically movably with respect to the upper section and to provide such pulleys with actuators which can move the pulleys for a limited distance upwardly with respect to the section 4.

In the present embodiment of the invention the chain 72 extends down to a pulley 51 mounted on the carriage 5 and extends therefrom upwardly for a short distance to an anchorage 52 at one end of a slidable crossbar 53. The chain 73 extends around a pulley 54, mounted on the carriage 5 and extends upwardly from the pulley to an anchorage 55 at the other end of the crossbar 53. The carriage 5 has two lower, spaced apart, end stops 56, each disposed near a respective end of the crossbar 53. The crossbar has parts extending into two vertical guides 57 at the rear of the carriage and spaced apart across the breadth of the carriage 5. The stops 56 limit the downward movement of the crossbar relative to the carriage 5.

Disposed in a fixed position, and in this embodiment of the invention on the base part 20 of the base section 2, is a linear actuator constituted by a ram 25 movable in a cylinder 24.

The head 26 of the ram bears on the underside of the crossbar 53.

The arrangement of the crossbar 53, the chains 72 and 73 and the pulleys 51 and 54 provides partial free-lift for the carriage 5, as is exemplified by Figures 2 and 3.

Figure 2 illustrates the mast 1 after the ram 21 has been actuated to move upwardly for the distance of its stroke. The upward movement of the ram 25 draws up the adjacent end parts of the chains 72 and 73 thereby producing upward movement of the pulleys 51 and 54, and thereby upward movement of the carriage 5, a distance half that moved by the bar 53. Typically this latter distance would be about 30 cm, providing thereby about 1 5 cm of movement of the carriage 5.

Figure 3 illustrates the telescopic extension of the mast 1. For the configuration shown in Figure 3, the piston 61 has advanced out of the cylinder 60 and has raised the lower movable section 3 relative to the base section 2. This movement has raised the pulley 34 (and its counterpart if any) relative to the base section 2. The movement of the pulley 34 has by virtue of the arrangement of the chain 71 produced upward movement of the upper movable section 4 by a distance twice that moved upwards by the pulley 34 and the section 3. Moreover, the upward movement of the section 4 produces upward movement of the pulleys 45 and 46 and accordingly by virtue of the arrangement of the chains 72 and 73 has produced upward movement of the carriage 5 with respect to the upper movable section 4.

The movement of the carriage relative to the section 4 corresponds to twice the movement of the section 4 relative to the section 3 less half the distance of movement of the bar relative to the carriage 5. It will also be understood that when the actuator 61 raises the section 3 so as to produce movement of the section 3 and consequently movement of the section 4, initially the carriage 5 moves upwards at only half pace because the upward movement of the chains 72, 73 along the runs between the pulleys 45 and 51 and the pulleys 46 and 54 respectively is partially offset by the movement of the bar 53 and accordingly the anchorages 52 and 55 relative to the pulleys 51 and 54.After this initial phase however the bar reaches its lower limit stops 56 and thereafter the raising of the carriage 5 by the chains 72 and 73 proceeds as if the chains were fixed to simple anchorages on the carriage 5.

Figure 4 illustrates another embodiment of the invention. In this embodiment there are only two sections, a base section 2 and a movable section 4. In this embodiment of the invention the base section 2 comprises as before a base part 20 and two uprights 21 and 22. The movable section 4 comprises uprights 41 and 42 adjacent the uprights 21 and 22 respectively and the tiebar 43.

Near the top of the section 4 are two pulleys 45 and 46 corresponding to the pulleys 45 and 46 in the first embodiment. A chain 74 extends from an anchorage 23 on the upright 21 over the pulley 45 and down to a pulley 51 on the carriage 5, proceeding from the pulley 51 up to an anchorage 52 on a crossbar 53 arranged in a manner similar to the crossbar 53 in Figure 1. Likewise a chain 75 extends from an anchorage 23a on the upright 22 over a pulley 46 on the section 4 down to the pulley 54 on the carriage 5 and thence up to an anchorage 55 on the crossbar 53. The crossbar 53 is movable in vertical guides 57 in the carriage 5.

The downward movement of the crossbar is limited by the lower end stops 56. A cylinder 60 is disposed on the base part 20 of the section 2 and a piston 61 extends from the cylinder to the section 4. A ram 25 is arranged in a cylinder 24 disposed on the base 20. The ram 25 bears on the underside of the crossbar 53.

The embodiment shown in Figure 4 works in a manner similar to the embodiment shown in Figure 1 except for the omission of the lower movable section. Movement of the ram 25 causes upward movement of the crossbar 53 so as to produce movement of the carriage 5 by half the distance of its stroke. Movement of the piston 61 relative to the cylinder 62 causes upward movement of the movable section 4 relative to the base section 2. Upward movement of the section 4 and the pulleys 45 and 46 that it carries produces initially movement of the carriage at the same rate as the section 4 but thereafter, when the bar 53 reaches its lower stops 56, movement of the carriage 5 at twice the rate of movement of the movable section 4.

In both embodiments of the invention, telescopic retraction of the mast and consequential downward movement of the carriage 5 and any movable section of the mast is caused by relief of the pressure applied to the cylinder 60. The ram 25 may remain in its extended position until the crossbar 53 engages it: thereafter the ram 25 may be lowered by relief of the hydraulic pressure applied to the cylinder 24.

In both embodiments of the invention the cylinders 24 and 60 are in positions which are fixed relative to the base section and accordingly fixed relative to the chassis of the industrial truck.

Accordingly, flexible hose is not required for the cylinders 24 and 60, which may be fed by fixed, rigid piping 80 which has branches 81 and 82 for the cylinders 24 and 60 respectively. For the sake of simplicity control valves are not shown in the hydraulic line 80 or the branches 81 and 82.

Alternatively the guides 57 can be constituted by guide members mounted on the base of the fixed section between the uprights of the upper, movable, section. The bar 53 can then be actuated by an intermediate member moving in these guide members and connected to the ram 25 of the actuator 24 located adjacent these guide members.

Claims (10)

1. A telescopic mast for an industrial lift truck, including a plurality of relatively movable sections, a lifting carriage from which extends upwardly at least one chain to a pulley on a movable one of the sections and thence downwardly to an anchorage on a section relatively lower than the section on which the pulley is mounted, a member mounted on and capable of limited vertical movement relative to the carriage, one end of the chain being fixed relative to the said member and the said chain extending downwardly from the member to a pulley mounted on the carriage and thence extending upwardly as aforesaid, and an actuator arranged in a fixed position relative to a fixed, lowermost section of the mast and positioned to produce when the carriage is in its lowermost position upward movement of the said member relative to the carriage.

2. A mast according to claim 1 in which the actuator comprises a ram which is actuable for upward movement.

3. A mast according to claim 2 in which the ram is arranged to produce lifting action directly or indirectly on an underside part of the said member.

4. A mast according to any foregoing claim in which the member comprises a bar mounted for vertical movement relative to the carriage.

5. A mast according to any foregoing claim in which the sections comprise a fixed section and a movable section, and a lifting jack is disposed to raise the movable section relative to the fixed section.

6. A mast according to any of claims 1 to 4, in which the sections comprise a fixed section, a lower movable section and an upper movable section, and wherein the first-mentioned pulley is disposed on the upper movable section and the aforesaid chain extends from the said anchorage which is disposed on the lower movable section, and wherein the fixed and upper movable sections are linked by at least one chain which extends from an anchorage fixed relative to the fixed section, extends over a pulley disposed on the lower movable section and thence downwardly to an anchorage on the upper movable section.

7. A mast according to claim 6 in which a hydraulic actuator is provided for raising the lower movable section relative to the fixed section.

8. A telescopic mast substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

9. A telescopic mast substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

10. An industrial lift truck having a telescopic mast according to any one of claims 1 to 9.