IES72485B2

IES72485B2 - Extendable fork for forklift trucks

Info

Publication number: IES72485B2
Authority: IE
Inventors: Robert Moffett; Carol Moffett; James Mcadam; Paul Quinn; Gerry Mchugh; Gerry Harte; Andy Wylie; Martin Mcvicar; Tommy Cadden
Original assignee: Moffett Res & Dev Ltd
Priority date: 1996-05-31
Filing date: 1996-05-31
Publication date: 1997-04-23
Also published as: GB9624126D0; GB2313590A; IE960814A1

Abstract

An extendable fork 1 for a forklift truck comprising a fixed inner fork part 2 and a movable outer fork part 12 slidably mounted thereon, actuating means operable to slide the outer fork part on the inner fork part, and one or more wheels or rollers 10 to facilitate the sliding of the outer fork part on the inner fork part. Preferably, the outer fork part acts as a sleeve for reception of the inner fork part. The actuating means may comprise a hydraulic ram demountably secured in a longitudinally extending slot in the inner fork part. The ram may include a cylinder 8 and a piston rod 14, the cylinder being integrally formed with the inner fork part and the piston rod extending outwardly from the cylinder with its free end connected to the movable outer fork part. A pair of vertically spaced apart mounting hooks 4 may be provided on an upright portion 3 of the inner fork part for engagement with a fork carrier of the forklift truck and an upwardly projecting pallet stop may be included at the inner end of the outer fork part.

Description

Extendable Fork tor Forklift Trucks This 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 G3 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.

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 S?24 eg - 2 part on a fork carrier of a forklift truck, and actuating means operable to slide the outer fork part on the inner fork part, the actuating means comprising a ram mounted between the fixed inner fork part and the movable outer 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. 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 another embodiment, each fork part has rollers for engagement with the other fork part.

In a preferred embodiment, the rollers are mounted on the fixed inner fork part.

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

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

The invention will be more clearly understood by the following description of an embodiment 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; - 3 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 detailed perspective view illustrating an outer end of an inner fork part; Fig. 5 is an elevational view of an alternative construction of inner fork part; Fig. δ is an end elevational view of the inner fork part of Fig. 5; and Fig. 7 is a plan view of the inner fork part of Fig. 5» Referring to the drawings, 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 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 am 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. ~ 4 ~ 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 and thus advantageously the depth of the fork can be minimised.

Referring now to Figs. 5 to Ί, an alternative construction of inner fork part is shown indicated generally by the reference numeral 20. The inner fork part 20 is of L-~ shaped 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

1. 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 5 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, the actuating means comprising a ram mounted between the fixed 10 inner fork part and the movable outer 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.

2. An extendable fork as claimed in claim 1 wherein each 15 fork part has rollers for engagement with the other fork part.

3. An extendable fork as claimed in claim 1 wherein the rollers are mounted on the fixed inner fork part.

4. An extendable fork as claimed in claim 3 wherein a 20 pair of rollers are mounted spaced-apart at an outer end of the fixed inner fork part, and preferably the outer fork part forms a sleeve for reception of the inner fork part within the outer fork part.

5. An extendable fork for a forklift truck substantially , 25 as hereinbefore described with reference to the ' accompanying drawings.