GB1575911A

GB1575911A - Extendable fork for fork lift trucks

Info

Publication number: GB1575911A
Application number: GB2756076A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-09-14
Filing date: 1977-09-14
Publication date: 1980-10-01

Description

(54) EXTENDABLE FORK FOR FORK LIFT TRUCKS (71) I, GEORGE EDWARD HERBERT SON, of 13, Holm Lane, Oxton, Birkenhead, Wirral, Merseyside; a British subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to an extendable fork for fork lift trucks.

At the present time many varieties of fork lift trucks are available having a pair of forks either projecting from the front of the vehicle or, in the case of a side loader, having a pair of forks housed within the width of the vehicle and extendable to project from one side of the vehicle. With a side loader fork lift truck, the length of the forks must not exceed the overall width of the vehicle by more than a minimal amount otherwise manoeuvrability of the vehicle is reduced and its usefulness is therefore impaired. Consequently because the forks cannot exceed a predetermined length, the forks sometimes cannot be used for particularly wide loads, or loads which are situated away from the side or rear of the vehicle without preparatory manoeuvring of the load into a suitable position for loading onto the forks which results in extra time-consuming work.

It is the aim of the present invention to seek to provide an extendable fork for fork lift trucks so as to overcome the disadvantages of forks restricted to a maximum length.

According to the present invention there is provided a fork for fork lift trucks, comprising a fork member having a guide channel for receiving and guiding an extension member, said extension member being formed as an insert member and being displaceable with respect to said fork member by displacement means so as to extend beyond the end of said fork member by a selectively variable amount not exceeding a predetermined limit, wherein removable guides are provided, said removable guides being of substantially the same length as the extension member.

The fork member is of a conventional shape and size and made of conventional materials, e.g. forged steel. The fork member may have lateral guide grooves either formed in the fork member itself, in which case the extension member would have removable replaceable guide rails, or the fork member may have guide grooves provided in removable and replaceable slides, which may, for example, be made of brass or other suitable bearing material, and the extension member would have guide rails formed thereon. Conversely, the fork member may have guide rails provided in the channel, in which case the extension member would have guide grooves provided in removable replaceable slides, or the fork member may have guide rails formed on removable replaceable inserts, with lateral guide groovs formed in the extension member.The extension member is preferably dimensioned and shaped so that when fully retracted into the channel of the fork member it lies flush on all sides so that the fork member has the apeparance of a conventional fork.

The displacement means for the extension member may comprise either hydraulic means or mechanical screw means driven respectively either from a main hydraulic pump, if the forks are normally hydraulically opearted, or via a chain or belt drive, if the forksPare mechanically operated.

When in use, the extension members would only be displaceable by approximately one third of their length so that the overall length of the fork would be increased by approximately 25 to 30 /O of the normal length of the fork. Thus, the forks with this additional extension could be used for carrying wider loads or for lifting loads situated further from the sides of the vehicle being unloaded, whilst not detracting from the convenience and manoeuvrability of a truck with normal sized forks.

The extensions to the forks are not intended to carry the full weight of the load being lifted but are mainly intended to provide an additional stability for loads where the centre of gravity of the load is very near the end of the fork members and thus would, in the absence of the extensions, be very unstable and would be likely to sway or topple. Under normal circumstances such a load would probably be dragged sufficiently near to the edge of the vehicle being unloaded for the fork to get right underneath or might even have to be unloaded by a crane, for example.

The extendable forks of the present invention therefore provide a conventional fork lift truck with an additional scope of use and therefore avoids the necessity of using cranes for unloading, or of manhandling or dragging a load to a suitable position for loading on the forks of a fork lift truck. Thus, the forks would provide a labour saving and cost saving modification for conventional fork lift trucks.

Although the forks have been described in connection with a side loader fork lift truck, they could of course be used for any type of fork lift truck, if desired.

The present invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a plan view of an etxendable fork of the present invention with the extension member extended; Fig. 2 is a side elevation of the fork of t. s Fig. 1; Fig. 2a is a side view, .of a leg of the fork member; Fig. 3 is a section on the line A-A of Fig. 2a; Fig. 4 is a section on the' 'line B-B of Fig.

2a; Fig.' 5 is a section on the ine C-C. of Fig.

2a; Figs. 6a, b, c show end, elevation, side elevation and plan of, an extension member; Fig. 7 shows end elevation,. side elevation and plan of a fork upright: - - Figs. 8a, and - b, show a front elevation and side elevation of the joint between the fork legs and the fork upright; Figs. 9 shows the section X-X of. Fig. 2; Fig. 10 shows the- 'section Y-Y of Fig. 2; and Fig. 11 shows, schematically, a hydraulic system for extending and retracting the fork extensions.

In Figs. 1 and 2 an assembled fork is shown with its extension member 15 in an extended position. The fork comprises two fork legs 4 and 5 secured to a fork upright 1 (see also Figs. 8a and 8b) between which fork legs 4 and 5 the extension member 15 is displaceably supported on slide assemblies secured to the fork legs 4 and 5. Figure 2a shows the left-hand fork leg 4 with a groove 4a for receiving a slide 13 (see Fig.

1) which may be secured therein by means of bolts (not shown). A corresponding slide 14 is similarly secured (see Fig. 9) in a channel provided in the right-hand fork leg 5. Additional slide members 11 and 12 are supported on the slides 13, 14, or on the respective legs 4 and 5.

The extension member 15 and the associated slide assemblies are located in the forward end of the fork and the space between the forks remaining, i.e. between the rear end of the slides and the extension member, and the fork upright is substantially occupied by the displacement means for the extension member. The displacement means comprises a hydraulic cylinder 16 supported on two mountings 18 secured between the fork legs 4 and 5 (see Fig. 10).

The hydraulic cylinder 16, as in conventional practice, has a piston rod which extends axially from the forward end of the cylinder and is connected to the inner end face of the extension member 15 and is locked in place by means of a lock nut 17. The hydraulic cylinder 16- is connectable, in a known manner, with the hydraulic system of the fork lift truck on which the forks are fitted. In the case of a fork lift truck where the drive of the fork is carried out mechanically by means of a chain, or belt drive, the hydraulic cylinder would be replaced by a mechanical screw or the like.

The extension member 15 is shown in detail in Figs. 6a, .b and c, from which it can be seen that it is generally the shape of a fork but it is only approximately twothirds of the overall length of the fork and it is generally dimensioned and shaped so that when the extension member 15 is fully retracted it lies within the space between the fork legs 4 and 5 so that it is flush with the upper and forward surfaces thereof.

Below the extension member -15 the space between the fork legs 4 and 5. is closed by a plate 6, which also serves to provide a morse rigid structure and it lies flush with the bottom surfaces of the fork- .legs to provide a neat appearance. Further plates 7 and 8 are provided below the space containing the displacement cylinder 16, and at the heel of the fork legs, respectively. A cover plate 23 is also provided which is secured above the space containing the cylinder 16, which cover plate 23 also lies flush with the surface of the fork legs 4 and 5 and serves to protect the displacement mechanism from damage during use.

The fork legs 4 and 5 are connected to the upright 1 (shown in Fig. 7) by bolts 9 and 25 and the joint is then strengthened by welding and dressing flush to provide a permanent connection. Alternatively, it is possible to form the fork legs 4 and 5 and upright 1 in one piece.

In Fig. 11 a schematic diagram illustrates the manner in which the extendable forks can be operated hydraulically using a single control and connected into the existing drive system of the vehicle. The forks, as is conventional with the majority of fork lift trucks, are removable and replaceable and are merely attached by means of suitable hooks 2 and 3 the upper one of which would be permanently attached to the fork upright 1 whilst the lower one would be removable or disengageable to enable the forks to be detached from the vehicle as and when necessary.

The forks would normally be made of forged steel whereas the slides 11, 12, 13 and 14 would be made of brass and would be replaceable as they wear out, whilst the remaining components, other than the hydraulic system, would be made from mild steel or other suitable material.

WHAT I CLAIM IS: 1. A fork for fork lift trucks, comprising a fork member having a guide channel for receiving and guiding an extension member, said extension member being formed as an insert member and being displaceable with respect to said fork member by displacement means so as to extend beyond the end of said fork member by a selectively variable amount not exceeding a predetermined limit, wherein removable guides are provided, said removable guides being of substantially the same length as the extension member.

2. A fork as claimed in claim 1 wherein the fork member comprises two fork legs each secured at their rear to an upright member and the extension member is supported betwen the front ends of the two fork legs.

3. A fork as claimed in claim 1 or 2 wherein the removable guides are secured to the inner surface of the guide channel and the extension member has grooves formed in the sides thereof for receiving the guides.

4. A fork as claimed in claim 1 or 2 wherein said removable guides are secured to said extension member, and grooves are provided in each inner surface of said guide channel, for receiving the guides.

5. A fork as claimed in any preceding claim wherein the displacement means com- prises a hydraulic cylinder having a displacement rod connected to the rear end of the extension member.

6. A fork as claimed in any of claims 1 to 3 wherein the displacement means is a mechanical screw drive.

7. A fork as claimed in any preceding claim wherein the displacement means is protected by means of cover plates provided above and below.

8. A fork substantially as hereinbefore described with reference to and illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. mechanism from damage during use. The fork legs 4 and 5 are connected to the upright 1 (shown in Fig. 7) by bolts 9 and 25 and the joint is then strengthened by welding and dressing flush to provide a permanent connection. Alternatively, it is possible to form the fork legs 4 and 5 and upright 1 in one piece. In Fig. 11 a schematic diagram illustrates the manner in which the extendable forks can be operated hydraulically using a single control and connected into the existing drive system of the vehicle. The forks, as is conventional with the majority of fork lift trucks, are removable and replaceable and are merely attached by means of suitable hooks 2 and 3 the upper one of which would be permanently attached to the fork upright 1 whilst the lower one would be removable or disengageable to enable the forks to be detached from the vehicle as and when necessary. The forks would normally be made of forged steel whereas the slides 11, 12, 13 and 14 would be made of brass and would be replaceable as they wear out, whilst the remaining components, other than the hydraulic system, would be made from mild steel or other suitable material. WHAT I CLAIM IS:

1. A fork for fork lift trucks, comprising a fork member having a guide channel for receiving and guiding an extension member, said extension member being formed as an insert member and being displaceable with respect to said fork member by displacement means so as to extend beyond the end of said fork member by a selectively variable amount not exceeding a predetermined limit, wherein removable guides are provided, said removable guides being of substantially the same length as the extension member.