GB2266700A - Load lifting carriage for an industrial lift truck - Google Patents

Abstract

A load lifting carriage of the kind mounted for sliding movement up and down a mast of an industrial lift truck, comprises a rear part (16) mounted on the mast assembly (10), and a front part (17) pivotally connected to the rear part to tilt about a horizontal axis and carrying a load-supporting fork (12). First actuating means (26 Fig. 3 not shown) operable longitudinally are provided for moving the front part together with the load support thereon relative to the rear part about the horizontal axis. Second actuating means (30) are provided for tilting the front part and the load support thereon relative to the rear part about the horizontal axis. The horizontal axis is coincident with the longitudinal axis of the first actuating means. In an embodiment in which the carriage has a pair of load supporting forks (12), the forks may be interconnected by crossed links (50, 51 Fig. 6 not shown) and means are provided for expanding and contracting the crossed links and thereby altering the spread of the forks. <IMAGE>

Description

INDUSTRIAL LIFT TRUCKS AND LOAD LIFTING CARRIAGES THEREFOR This invention relates to industrial lift trucks and to load lifting carriages therefor.

In British Patent Specification No. 1200675 there is described an industrial lift truck having a mast assembly, and a load lifting carriage mounted for sliding movement up and down the mast, the carriage comprising a rear part mounted on the mast assembly, a front part pivotally connected to the rear part to tilt about the axis of a pair of horizontal pivot bars and carrying a load support such as a load-supporting fork, a first operating jack for sliding the front part together with the load support thereon relative to the rear part along the axis of the pivot bars, and a second operating jack to effect tilting of the front part and the load support thereon relative to the rear part about the axis of the pivot shaft. The load carriage is thus of the kind which is capable of sideshifting and/or tilting movements relative to the mast assembly as required during operation of the truck.

According to one aspect of the invention there is provided a load lifting carriage for an industrial lift truck of the kind having a mast assembly, and a load lifting carriage mounted for sliding movement up and down the mast, the carriage comprising a rear part mounted on the mast assembly, a front part pivotally connected to the rear part to tilt about a horizontal axis and carrying a load support such as a load-supporting fork, first actuating means operable longitudinally for moving the front part together with the load support thereon relative to the rear part along said horizontal axis, and at least one second actuating means to effect tilting of the front part and the load support thereon relative to the rear part about said horizontal axis, wherein the horizontal axis about which the front part of the carriage pivots relative to the rear part is coincident with the longitudinal axis of the first actuating means for moving the front part laterally relative to the rear part during a sideshifting movement.

In one embodiment of the invention the first actuating means is a hydraulic or pneumatic jack of which the cylinder and piston are respectively connected to one or other of the two parts of the carriage.

Preferably the jack comprises a cylinder mounted on the rear part of the carriage, and a piston rod with a piston mid-way along its length projecting from both ends of the cylinder, the front part of the carriage being suspended from the projecting ends of the piston rod.

The front part of the carriage is preferably a framework having uprights which are rigidly attached to the projecting ends of the piston rod, the piston rod sliding and pivoting within bearings internally of the cylinder of the jack. In the case of the jack being a hydraulic jack, the bearings are preferably immersed in the operating fluid of the jack.

In another embodiment the first actuating means may be an electrically operated linear actuator having two members one of which is movable longitudinally relative to the other by electrically operated drive means, the stationary and movable members of the linear actuator being respectively connected to the rear and front parts of the carriage. In such an arrangement the front part of the carriage is preferably a framework having uprights which are rigidly attached to the movable member of the linear actuator, said movable member being mounted to move longitudinally and pivot relatively to the stationary member of the linear actuator and the rear part of the carriage.

Similarly, the or each second actuating means may conveniently be a hydraulic or pneumatic jack having its cylinder mounted in fixed relation on the rear part of the carriage and its piston projecting forwardly for engagement with the back surface of the front part of the carriage, whereby extension of the jack or jacks effects upward tilting of the front part of the carriage and the load support thereon relative to the rear part of the carriage.

Alternatively, the or each second actuating means may be an electrically operated linear actuator having two members one of which is movable longitudinally relative to the other by electrically operated drive means, the stationary member of the linear actuator being mounted in fixed relation on the rear part of the carriage, and the movable member of the linear actuator projecting forwardly for engagement with the back surface of the front part of the carriage, whereby operation of the linear actuator in a forward direction effects upward tilting of the front part of the carriage and the load support thereon relative to the rear part of the carriage about the horizontal axis.

Preferably a friction reducing contact surface is provided between the end of the movable member of the or each second actuating means and the back surface of the front part of the carriage. The friction reducing surface may be provided by a strip of plastics material, e.g. nylon, extending horizontally along at least the central position of the back surface of the front part of the carriage. In an alternative arrangement the end of the movable member of the or each second actuating means is capped with a suitable friction reducing material.

According to the another aspect of the invention there is provided a load lifting carriage for an industrial lift truck of the king having a mast assembly, and a load lifting carriage mounted for sliding movement up and down the mast, the carriage having a pair of load-supporting forks spaced apart on the carriage, and means for increasing and decreasing the distance between the forks, thereby altering the spread of the forks, wherein the forks are interconnected by crossed links and the means for altering the spread of the forks comprises means for expanding and contracting the crossed links.

Preferably the means for altering the spread of the forks is a double-acting hydraulic or pneumatic jack.

It is also preferred that the jack operates vertically to expand and contract the crossed links.

The forks are preferably interconnected by two pairs of crossed links, each pair of links being attached at their outer ends to one of the forks and interconnected at their inner ends by the vertically operating jack. Preferably the cylinder and piston of the jack are respectively connected to the upper and lower inner ends of the two pairs of crossed links.

Preferably the crossed links are attached at their outer ends to the forks at points at or adjacent the top and bottom of the respective fork.

The invention also provides an industrial lift truck having a mast assembly and load lifting carriage as defined above mounted for sliding movement up and down the mast.

By way of example, specific embodiments in accordance with the invention will be described with reference to the accompanying diagrammatic drawings in which: - Figure 1 is a side elevation of an industrial lift truck having a load lifting carriage and load supporting forks; Figure 2 shows the load lifting carriage of the truck of Figure 1 in side elevation and in enlarged section along line 2-2 in Figure 3; Figure 3 is a front view of the load lifting carriage showing the carriage side-shifted in one direction in full lines, and in the other direction in chain-dot lines; Figures 4 and 5 illustrate the load lifting carriage pivoted into downward and upward tilt positions relative to the horizontal;; Figure 6 illustrates a modified embodiment in which the load lifting carriage has means for altering the spread of the load-supporting forks, the carriage being shown centrally aligned on the mast, and the forks being shown horizontal and in their maximum spread position; Figure 7 is a similar view to Figure 6, showing the forks in their minimum spread position; Figure 8 is a section along line 8-8 in Figure 6; and Figure 9 is a section along line 9-9 in Figure 6.

The subject of this example is an industrial truck of the kind shown in Figure 1 and having a mast assembly 10 and a load lifting carriage 11 mounted for relative sliding movement up and down the mast. Load supporting forks 12 are carried on the load lifting carriage. This invention is only concerned with the construction and operation of the load lifting carriage and the load supporting forks and thus the following description will be limited thereto.

With reference to Figures 1 to 5 of the drawings, the mast assembly 10 has a fixed outer mast 13 and an extensible inner mast 14 capable of sliding up and down the outer mast, although the load lifting carriage could also be used on a single mast or a triple mast. The load lifting carriage 11 also has sets of rollers 15 mounted in conventional manner for engagement with the inwardly facing channels of the vertical uprights of the inner mast. The carriage 11 is split into two parts, a rear part 16 carrying the rollers 15 and a front part 17 capable of sideshifting and tilting movements relative to the rear part.

The rear part 16 of the carriage 11 comprises two uprights 18 held rigidly spaced apart by a support tube 19 adjacent their top ends and a transverse member 20 at their bottom ends. The rollers 15 are mounted on the outwardly facing surfaces of the uprights 18.

The front part 17 of the carriage likewise comprises a framework made up of two uprights 21 and two transerse members 22, 23 welded thereto for carrying the forks 12. Extending horizontally between the uprights 21 adjacent their top ends is a double-acting hydraulic jack 26 comprising a cylinder 24 and a piston rod 25 carrying a piston 37 mid-way along the piston rod. The cylinder 24 is mounted within the support tube 19 of the rear part of the carriage 11. The piston rod 25 projects from each end of the cylinder 24 through sealed bearings 36 and is rigidly attached to the uprights 21 of the front part. Each projecting end of the piston rod 25 fits into a support boss 38 carried by the respective upright 21 and is bolted thereto by a bolt 39.

Hydraulic fluid is fed to each side of the piston 37 through a respective connection member 28 which passes through the support tube 19 and which is screwed into an aperture in the cylinder wall. The bearings 36 are thereby immersed in the hydraulic fluid which ensures that they remain lubricated and thus resistant to wear.

Movement of the piston 37 along the cylinder 24 in one direction or the other effects a sideshift movement of the front part 17 of the carriage 11 laterally relative to the rear part 16 in that direction.

If desired, the mounting of the cylinder and the piston rod of the jack 26 could be reversed so that the cylinder is the movable member and the piston rod carrying the piston remains stationary during a sideshifting movement. For this purpose, the piston rod would be mounted on the rear part of the carriage, and the cylinder would carry the front part.

It will also be appreciated that the longitudinal axis of the jack 26 is the same as, i.e. coincident with, the pivot axis of the front part 17 of the carriage 11 relative to the rear part 16. For pivoting the front part 17, there are provided two hydraulically operated tilt jacks 30 mounted on the transverse member 20 of the rear part 16 of the carriage, and extending forwardly for acting on the back surface 31 of the lower transverse member 23 of the front part 17. Each tilt jack 30 has a cylinder 32 fixed in an aperture in the member 20 and a piston rod 33 which in its fully withdrawn position (Figure 4) allows the forks 12 to extend downwardly under their own weight or under the weight of a load supported thereon.Full extension of the jacks 30 moves the forks 12 through a level position into an upwardly tilted position (Figure 5), the front part 17 of the carriage 11 pivoting with the piston rod 25 of the sideshifting jack 26 about the axis of the jack 26. In this embodiment the tilt movement is through an angle of -3 to +30. For preventing over tilt with the tilt jacks 30 contracted, there is provided a hooked bar 34 projecting rearwardly from the upper transverse member 22 of the front part of the carriage, for interengagement with a corresponding hook 35 formed on the front edge of the adjacent upright 18 of the rear part 16 of the carriage.The length of the bar 34 is sufficient to remain in hooked engagement with the hook 35 within the full range of sideshifting movements of the front part of the carriage on either side of its normal central position relative to the mast assembly, e.g. 100 mm in each direction.

Mounted horizontally on the back surface 31 of the lower transverse member 23 of the front part 17 of the carriage 11, for movement therewith, is a slide strip 40 of suitable plastics material, e.g. nylon, with which the ends of the piston rods 33 make contact. This slide strip 40 reduces friction during the sideshifting movements of the front part 17 of the carriage. The slide strip 40 is also attached to at least the central portion of the member 23 and has a length sufficient to remain in contact with both piston rods 33 within the range of sideshifting movement of the front part of the carriage.

Alternatively, the ends of the piston rods 33 may be capped with a similar material. In either case, there is no positive connection between the tilt jacks and the front part 17 of the carriage 11. The front part 17 is thus free to pivot if necessary, independently away from the tilt jacks 30 within the movement permitted by the rear part 16 perhaps to clear an obstruction which might be hit by the front part of the carriage or the forks.

It will be appreciated that in the above embodiment, the jack 26 comprises a first actuator for effecting the lateral sideshifting movements of the front part 17 of the carriage 11 relative to the rear part 16 along the axis of the jack. Similarly, the tilt jacks 30 comprise a pair of second actuators for effecting the required pivotal movements of the front part 17 of the carriage about the same axis, i.e. the longitudinal horizontal axis of the jack 26.

However, in another embodiment, the sideshifting jack 26 may be a pneumatically operated jack instead of a hydraulic jack. In this case, the bearings 36 may conveniently be air bearings. Additionally or alternatively, the tilt jacks 30 may be operated pneumatically instead of hydraulically.

In a further embodiment, any one of the actuating means may be an electrically operated linear actuator which has two members one of which is movable longitudinally relative to the other by electrically operated drive means, e.g. an electric motor. In the case of the first actuating means being a linear actuator, the two members of the linear actuator, in effect, operate as a direct replacement for the cylinder and piston rod of the jack 26, the stationary member of the linear actuator being mounted horizontally on the rear part 16 of the carriage 11, and the front part 17 of the carriage being suspended from the movable member of the linear actuator.

Operation of the linear actuator will thereby laterally sideshift the front part 17 of the carriage and the load supporting forks 12 carried thereon relative to the rear part 16 in the desired direction.

Similarly, the tilt jacks 30 may be replaced by electrically operated linear actuators with the stationary member of each actuator mounted in fixed relation on the transverse member 20 of the rear part 16 of the carriage, and the movable member of the actuators projecting forwardly for engagement with the slide strip 40 on the back surface of the member 23 of the front part 17 of the carriage. Thereby operation of the actuators by electrically operated drive means, e.g. an electric motor, in a forward direction will effect upward tilting of the front part of the carriage and the load support thereon relative to the rear part of the carriage about the horizontal axis of the first actuating means, which may itself be a hydraulic or pneumatic jack or an electrically operated linear actuator.Operation of the tilt actuators in the reverse direction will allow the front part of the carriage and the load support thereon to return, under their own weight, into a level position or a downward tilting position as desired.

One advantage of each embodiment of load lifting carriage described above, compared with known designs of carriage having a sideshifting jack, is that it gives better visibility to the driver of the truck.

This is because the sideshifting jack 26 or other equivalent horizontally operable actuating means, e.g.

an electrically operated linear actuator, is positioned higher than in conventional arrangements and, in the embodiment illustrated, is above at least the lower edge of the upper transverse member 22 of the front part 17 of the carriage.

Another advantage is that the carriage projects a smaller distance forwardly of the mast assembly than is usual in other similar conventional arrangements.

This dimensional advantage assists manoeuvrability of the truck in that it reduces the turning circle which is an important consideration in conditions of restricted space. It is also a direct result from pivoting the front part of the carriage about the axis of the actuating means which effects sideshifting of the carriage.

In the embodiment described above, the spread of the forks 12, i.e. the distance separating the forks, is manually adjustable by moving the forks away from each other or towards each other along the transverse members 22, 23 of the front part of the carriage 11.

Conventionally there are provided on the upper transverse member 22, means for positively locating each fork 12 in a variety of different positions.

Referring to Figures 6 to 9, there is shown a modified embodiment in which the front part 17 of the carriage 11 comprises a framework of two uprights 21 and two transverse members 22, 23 welded together. If desired, an equivalent framework may comprise a single plate. Linkage means are also provided for adjusting the spread of the forks 12. The forks 12 are interconnected by two pairs of crossed links 50, 51 which are themselves interconnected by a double-acting hydraulic or pneumatic jack 52.

The outer ends of each pair of crossed links 50, 51 have an upper pivotal connection 53 of the link 50 to the respective fork 12 and a lower pivotal connection of the link 51 to the same fork. The lower pivotal connection comprises a pin 54 and slot 55 to allow vertical movement of the lower end of the link 51 relative to the fork 12 during expansion or contraction of the crossed links.

At the inner ends of the links 50, 51 the upper end of the rear link 51 is pivotally attached by a pin 56 to a bracket 59 bolted to the front part 17 of the carriage 11, and the lower end of the front link 50 is pivotally connected to a yoke 57 mounted on the protruding end of the piston rod 58 of the jack 52. At the upper end of the piston rod 58 is a piston. The cylinder of the jack 52 is mounted vertically on the front part 17 of the carriage 11, and is provided with fluid connecting means 62, 63.

In operation of the jack 52, downward movement of the piston within the cylinder 61 lowers the yoke 57 and thereby causes contraction of both pairs of crossed links 50, 51 (Figure 7) and thus movement of the forks 12 closer together on the carriage 11.

Similarly upward movement of the piston acts to expand both pairs of links 50, 51 and thus increases the spread of the forks 12 (Figure 6).

A vertical guide slot 64 is provided for receiving a square block 65 (Figure 9) forming the part of the yoke 57 which is carried on the piston rod 58. The guide slot 64 thereby prevents the yoke 57 from being able to rotate which would tend to bend the links 50.

Each rear link 51 also carries a block 66 on its back surface at a height compatible with the upper transverse member 22 of the front part 17 of the carriage 11. The blocks 66 thus serve to reinforce the links 50, 51 by abutting against the upper transverse member 22, should the links be subjected to rearward pressure from a load supported on the forks 12. The blocks 66 thereby use the upper member 22 of the front part of the carriage as a stop to prevent over deflection of the links 50, 51 which could otherwise cause permanent deformation.

An advantage of the crossed links 50, 51 is that they apply an even lateral force against both the top and bottom of each fork 12 and thus assist a smooth sliding movement of the forks 12 on the carriage 11 in each direction.

It will also be appreciated from Figure 8 that the whole crossed link mechanism including the jack 52 is mounted on the front part 17 of the carriage 11 within the thickness of the forks 12, and thus the mechanism does not increase the respective longitudinal dimension of the truck.

In a similar manner to the sideshifting jack 26 and the tilt jacks 30, the jack 52 for altering the spread of the forks could be replaced by a linear actuator.

Claims (20)

1. A load lifting carriage for an industrial lift truck of the kind having a mast assembly, and a load lifting carriage mounted for sliding movement up and down the mast, the carriage comprising a rear part mounted on the mast assembly, a front part pivotally connected to the rear part to tilt about a horizontal axis and carrying a load support such as a load-supporting fork, first actuating means operable longitudinally for moving the front part together with the load support thereon relative to the rear part along said horizontal axis, and at least one second actuating means to effect tilting of the front part and the load support thereon relative to the rear part about said horizontal axis, wherein the horizontal axis about which the front part of the carriage pivots relative to the rear part is coincident with the longitudinal axis of the first actuating means for moving the front part laterally relative to the rear part during a sideshifting movement.

2. A load lifting carriage as claimed in Claim 1, wherein the first actuating means is a hydraulic or pneumatic jack of which the cylinder and piston are respectively connected to one or other of the two parts of the carriage.

3. A load lifting carriage as claimed in Claim 2, wherein the jack comprises a cylinder mounted on the rear part of the carriage, and a piston rod with a piston mid-way along its length projecting from both ends of the cylinder, the front part of the carriage being suspended from the projecting ends of the piston rod.

4. A load lifting carriage as claimed in Claim 3, wherein the front part of the carriage is a framework having uprights which are rigidly attached to the projecting ends of the piston rod, the piston rod sliding and pivoting within bearings internally of the cylinder of the jack.

5. A load lifting carriage as claimed in Claim 4, wherein the jack is a hydraulic jack and the bearings are immersed in the operating fluid of the jack.

6. A load lifting carriage as claimed in Claim 1, wherein the first actuating means is an electrically operated linear actuator having two members one of which is movable longitudinally relative to the other by electrically operated drive means, the stationary and movable members of the linear actuator being respectively connected to the rear and front parts of the carriage.

7. A load lifting carriage as claimed in Claim 6, wherein the front part of the carriage is a framework having uprights which are rigidly attached to the movable member of the linear actuator, said movable member being mounted to move longitudinally and pivot relatively to the stationary member of the linear actuator and the rear part of the carriage.

8. A load lifting carriage as claimed in any one of the preceding claims, wherein the or each second actuating means is a hydraulic or pneumatic jack having its cylinder mounted in fixed relation on the rear part of the carriage and its piston projecting forwardly for engagement with the back surface of the front part of the carriage, whereby extension of the jack or jacks effects upward tilting of the front part of the carriage and the load support thereon relative to the rear part of the carriage about the horizontal axis.

9. A load lifting carriage as claimed in any one of Claims 1 to 7, wherein the or each second actuating means is an electrically operated linear actuator having two members one of which is movable longitudinally relative to the other by electrically operated drive means, the stationary member of the linear actuator being mounted in fixed relation on the rear part of the carriage, and the movable member of the linear actuator projecting forwardly for engagement with the back surface of the front part of the carriage, whereby operation of the linear actuator in a forward direction effects upward tilting of the front part of the carriage and the load support thereon relative to the rear part of the carriage about the horizontal axis.

10. A load lifting carriage as claimed in Claim 8 or Claim 9, wherein a friction reducing contact surface is provided between the end of the movable member of the or each second actuating means and the back surface of the front part of the carriage.

11. A load lifting carriage as claimed in Claim 10, wherein the friction reducing surface is provided by a strip of plastics material extending horizontally along at least the central portion of the back surface of the front part of the carriage.

12. A load lifting carriage for an industrial lift truck of the kind having a mast assembly, and a load lifting carriage mounted for sliding movement up and down the mast, the carriage having a pair of load-supporting forks spaced apart on the carriage, and means for increasing and decreasing the distance between the forks, thereby altering the spread of the forks, wherein the forks are interconnected by crossed links and the means for altering the spread of the forks comprises means for expanding and contracting the crossed links.

13. A load lifting carriage as claimed in Claim 12, wherein the means for altering the spread of the forks is a double-acting hydraulic or pneumatic jack.

14. A load lifting carriage as claimed in Claim 13, wherein the jack operates vertically to expand and contract the crossed links.

15. A load lifting carriage as claimed in Claim 14, wherein the forks are interconnected by two pairs of crossed links, each pair of links being attached at their outer ends to one of the forks and interconnected at their inner ends by the vertically operating jack.

16. A load lifting carriage as claimed in Claim 15, wherein the cylinder and piston of the jack are respectively connected to the upper and lower inner ends of the two pairs of crossed links.

17. A load lifting carriage as claimed in any one of the Claims 14 to 16, including guide means for preventing the piston of the jack from tending to rotate relative to the cylinder of the jack.

18. A load lifting carriage as claimed in any one of the preceding claims, wherein the crossed links are attached at their outer ends to the forks at points at or adjacent the top and bottom of the respective fork.

19. A load lifting carriage substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

20. An industrial truck having a mast assembly and a load lifting carriage as claimed in any one of the preceding claims mounted for sliding movement up and down the mast.