IE960814A1 - Extendable fork for forklift trucks - Google Patents

Abstract

An extendable fork (1) for a forklift truck has a fixed inner fork part (2) with hooks (4) for mounting the inner fork part (2) on a fork carrier of a forklift truck. A movable outer fork part (12) forms a sleeve which is slidably engaged and receives a horizontal arm (5) of inner fork part (2). A ram (8) is mounted in a central slot (7) of the arm (5) and is operable to slide the outer fork part (12) on the inner fork part (2) for extending the fork (1). Rollers (10) are mounted at an outer end of the arm (5) of the innter fork part (2) to facilitate sliding movement of the movable outer fork part (12) on the arm (5) of the inner fork part (2).<Fig.1>

Description

Extendable Fork for Forklift Trucks invention relates to an extendable fork for a forklift truck.

It is known to provide extendable forks for forklift trucks. Patent Specification US 4,498,837 shows one type of extendable fork having a pair of rams to slide a movable outer fork part on a fixed inner fork part. A pair of rams is used to minimise the depth of the fork while still providing sufficient power to overcome the considerable friction forces exerted between the sliding fork parts when carrying a load. This double ram construction is relatively complicated and therefore expensive to produce. Further, the weight of the double ram construction can adversely affect the stability of a forklift truck, particularly when the forks are fully extended.

Patent Specification GB 1,575,911 discloses an extendable fork with a single ram to extend/retract a movable fork part between bifurcated arms of a fixed inner fork part. However, a relatively large ram is required to slide the fork parts relative to each other when loaded which can lead to problems with weight distribution as previously described and also the depth of the forks tends to be relatively large.

A further problem with the known extendable forks is that it can be difficult to accurately engage and position the outer fork part beneath a pallet in the correct lifting position. This can lead to unnecessary strain being applied to the forks during use with consequent increased risk of damage, breakdown or malfunction of the forks.

' OPEN TO R.A8UC INSPECTKWj ; UNDER j I SECTION 28 AND RUDE 23 I jM. No...........OFAjjfhf j - 2 The present invention is directed towards providing an improved extendable fork which overcomes these problems.

According to the invention, there is provided an extendable fork for a forklift truck of the type comprising a fixed inner fork part and a movable outer fork part slidably mounted on the inner fork part, the inner fork part having means for mounting the inner fork part on a fork carrier of a forklift truck, and actuating means operable to slide the outer fork part on the inner fork part, characterised in that rollers are rotatably mounted on one fork part for rolling engagement with an associated bearing surface on the other fork part to facilitate sliding the outer fork part on the inner fork part. Advantageously, the provision of wheels or rollers greatly decreases the sliding resistance between the two fork parts therefore reducing the power requirement for extending and retracting the fork which can be achieved using a single compact ram enabling the weight and thickness of the fork to be minimised.

In one embodiment of the invention, an upstanding pallet stop is provided at an inner end of the outer fork part, said pallet stop projecting upwardly of a top palletcarrying surface of the outer fork part. This feature advantageously enables the outer fork part to be correctly and accurately positioned in engagement with a pallet.

In another embodiment, each fork part has one or more rollers for engagement with the other fork part.

In a preferred embodiment, the or each roller is mounted on the fixed inner fork part. - 3 In a particularly preferred embodiment, a pair of rollers are mounted spaced-apart at an outer end of the fixed inner fork part.

Preferably, each roller is rotatably mounted within an associated slot at an outer end of the inner fork part, the roller being mounted by a pivot pin within the slot and the roller projecting upwardly of an upper surface of the inner fork part for engagement with the outer fork part.

Conveniently, the outer fork part forms a sleeve for reception of the inner fork part within the outer fork part.

In a particularly preferred embodiment the actuating means is a ram mounted between the fixed inner fork part and the movable outer fork part.

Conveniently, the ram is demountably secured between the inner fork part and the outer fork part.

Preferably, the ram is mounted in a longitudinally extending slot in the fixed inner fork part.

In a particularly preferred embodiment, the fixed inner fork part comprises a pair of spaced-apart substantially parallel bars ridgedly secured together by cross pieces extending between the bars, the bars defining a slot therebetween for reception of the ram.

Preferably each bar is L-shaped having an upright portion and a lower portion extending outwardly at a bottom end of the upright portion, the ram being mounted on the lower portion between the bars and below a top surface of the bars. - 4 In a further embodiment, a pair of vertically spaced-apart mounting hooks are provided on a rear face of the upright portion, the mounting hooks being releasably engageable with a fork carrier of a fork lift truck, the mounting hooks forming cross pieces for interconnecting the bars.

In another embodiment the ram comprises a cylinder with a complimentary piston and piston rod, the cylinder being integrally formed with the fixed inner fork part and the piston rod extending outwardly of the cylinder at an outer end of the fixed inner fork part, a free end of the piston rod being connected to the movable outer fork part.

In a further embodiment, the pallet stop comprises an upstanding plate extending between mounting brackets at each side of the movable outer fork part at an inner end of the outer fork part.

The invention will be more clearly understood by the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which :Fig. 1 is a perspective view of an extendable fork according to the invention; Fig. 2 is a view similar to Fig. 1 with an outer fork part removed; Fig. 3 is a perspective view of the outer fork part; Fig. 4 is a detail perspective view illustrating an outer end of an inner fork part; - 5 Fig. 5 is an exploded view of the extendable fork; Fig. 6 is an elevational view of an alternative construction of inner fork part; Fig. 7 is an end elevational view of the inner fork part of Fig. 6; and Fig. 8 is a plan view of the inner fork part of Fig. 6.

Referring to the drawings, and initially to Figs. 1 to 5 thereof, there is illustrated an extendable fork for a forklift truck, the extendable fork being indicated generally by the reference numeral 1. The fork 1 has a fixed inner fork part 2 of L-shaped construction having an upright 3 with a pair of spaced-apart hooks 4 for mounting the inner fork part 2 on a fork carrier of a forklift truck. A generally horizontal fork arm 5 projects outwardly at the lower end of the upright 3. A central slot 7 is provided in the arm 5 within which a ram 8 is mounted.

Mounted at an outer end of the arm 5 is a pair of spacedapart rollers 10 retained by pivot pins 11 on the arm 5. An outer fork part 12 forms a sleeve which slidably engages and receives the arm 5 of the fixed inner fork part 2. A piston rod 14 of the ram 8 engages an outer end of the movable fork part 2 by means of a pin 15.

The construction of the inner fork part 2 can best be seen in Fig. 5. The inner fork part 2 comprises a pair of spaced-apart substantially parallel bars 16 of L-shaped configuration. Each bar 16 has an upright portion 17 and a substantially horizontal lower portion 18 extending - 6 outwardly at a bottom end of the upright portion 17 . The bars 16 are ridgedly secured together by means of cross pieces comprising a bracket 19 at an outer end of the lower portions 18 and the hooks 4 which are mounted between the upright portions 17. It will be noted that each of the rollers 10 is rotatably housed within an associated slot 40 at an outer end of the inner fork part 2. A pallet stop 42 is provided at an inner end of the outer fork part 12 projecting upwardly of a top palletcarrying surface of the outer fork part 12. The pallet stop 42 comprises an upstanding plate 43 extending between a pair of mounting brackets 44 at each side of the outer fork part 12 at an inner end of the outer fork part 12. The plate 43 and mounting bracket 44 may be integrally formed if desired. It will be noted that the brackets 44 project rearwardly of the outer fork part 12 for nesting engagement with the outer sides of the uprights 17 when the outer fork part 12 is fully retracted on the inner fork part 2. A face cover 45 is secured across front faces of the upright 17 to protect hydraulic lines for the ram 8 which are housed between the upright 17.

In use, the ram 8 is operable to slide the outer fork part 12 on the arm 5 of the inner fork part 2 to extend and retract the fork 1. It will be noted that the rollers 10 facilitate the sliding movement of the movable fork part 12 on the arm 5. Thus advantageously a single actuating ram 8 is required to extend and retract the outer fork part 12. Also, the size of this ram 8 is minimised due to the ease with which the outer fork part 12 slides on the arm 5 due to the rollers 10 and thus advantageously the depth of the fork can be minimised.

The provision of the pallet stop 42 enables the outer fork part 12 to be readily easily positioned correctly in - 7 engagement with a pallet for secure handling of the pallet and proper use of the extendable forks.

Referring now to Figs. 5 to 7, an alternative construction of inner fork part is shown indicated generally by the reference numeral 20. The inner fork part 20 is of Lshaped construction having an upright 23 with hooks 24 for mounting the inner fork part 20 on a fork carrier of a forklift truck. A horizontal fork arm 25 projects outwardly at the lower end of the upright 23. A pair of spaced-apart rollers 26 are retained by pivot pins 27 at an outer end of the arm 25. An outer fork part 12 (not shown) as previously described with reference to Figs. 1 to 4 is slidably engagable with the arm 25. In this case, a single ram for extension and retraction of the outer fork part 12 is formed by a cylinder 30 formed by a bore extending through the arm 25 and an associated piston rod (not shown) which projects outwardly at an outer end 31 of the cylinder 30 to engage the outer fork part 12 as previously described. Passageways 33,34 for delivery of hydraulic oil to each end of the cylinder 30 are provided in the inner fork part 20.

The invention is not limited to the embodiment hereinbefore described which may be varied in both construction and detail.

Claims (16)

1. An extendable fork for a forklift truck, comprising a fixed inner fork part and a movable outer fork part slidably mounted on the inner fork part, the inner fork part having means for mounting the inner fork part on a fork carrier of a forklift truck, and actuating means operable to slide the outer fork part on the inner fork part, characterised in that one or more wheels or rollers are rotatably mounted on one fork part for rolling engagement with an associated bearing surface on the other fork part to facilitate sliding the outer fork part on the inner fork part.

2. An extendable fork as claimed in claim 1 wherein an upstanding pallet stop is provided at an inner end of the outer fork part, said pallet stop projecting upwardly of a top pallet-carrying surface of the outer fork part.

3. An extendable fork as claimed in claim 1 or 2 wherein each fork part has one or more rollers for engagement with the other fork part.

4. An extendable fork as claimed in claim 1 or 2 wherein the or each roller is mounted on the fixed inner fork part.

5. An extendable fork as claimed in claim 4 wherein a pair of rollers are mounted spaced-apart at an outer end of the fixed inner fork part.

6. An extendable fork as claimed in claim 5 wherein each roller is rotatably mounted within an associated slot at an outer end of the inner fork part, the roller - 9 being mounted by a pivot pin within the slot and the roller projecting upwardly of an upper surface of the inner fork part for engagement with the outer fork part.

7. An extendable fork as claimed in any preceding claim wherein the outer fork part forms a sleeve for reception of the inner fork part within the outer fork part.

8. An extendable fork as claimed in any preceding claim wherein the actuating means is a ram mounted between the fixed inner fork part and the movable outer fork part.

9. An extendable fork as claimed in claim 8 wherein the ram is demountably secured between the inner fork part and the outer fork part.

10. An extendable fork as claimed in claim 8 or 9 wherein the ram is mounted in a longitudinally extending slot in the fixed inner fork part.

11. An extendable fork as claimed in any of claims 8 to 10 wherein the fixed inner fork part comprises a pair of spaced-apart substantially parallel bars ridgedly secured together by cross pieces extending between the bars, the bars defining a slot therebetween for reception of the ram.

12. An extendable fork is claimed in claim 11 wherein each bar is L-shaped having an upright portion and a lower portion extending outwardly at a bottom end of the upright portion, the ram being mounted on the lower portion between the bars and below a top surface of the bars. - 10

13. An extendable fork as claimed in claim 12 wherein a pair of vertically spaced-apart mounting hooks are provided on a rear face of the upright portion, the mounting hooks being releasably engagable with a fork 5 carrier of a fork lift truck, the mounting hooks forming cross pieces for interconnecting the bars.

14. An extendable fork as claimed in claim 8 wherein the ram comprises a cylinder with a complementary piston and piston rod, the cylinder being integrally formed 10 with the fixed inner fork part and the piston rod extending outwardly of the cylinder at an outer end of the fixed inner fork part, a free end of the piston rod being connected to the movable outer fork part.

15. 15. An extendable fork as claimed in any of claims 2 to 14 wherein the pallet stop comprises an upstanding plate extending between mounting brackets at each side of the movable outer fork part at an inner end of the outer fork part.

16. 20 16. An extendable fork for a fork lift truck substantially as hereinbefore described with reference to the accompanying drawings.