GB2109334A - A dock leveller - Google Patents

Abstract

The present invention relates to a dock leveller suitable for operating in a hazardous environment. Essentially, the dock leveller comprises a framework (3, 4) engagable with a loading bay (2). A deck (8) pivotal at its edge 9 on the framework (3, 4) is tiltable by a ram (12) to raise and lower the deck (8) to accommodate varying heights of truck body. The ram (12) is powered by an accumulator (18) in a pre-pressurized closed hydraulic circuit through a one-way valve (32). A linkage mechanism, through a handle (50), operates the valve (32), to raise the deck (8). The deck (8) is lowered by the weight of a man standing thereon, which causes the valve (32) to open. <IMAGE>

Description

SPECIFICATION A dock leveller The present invention relates to a dock leveller of the type generally used, for example, in loading bays, ware houses, sea ports or the like.

There are many types of dock levellers and in general they are either powered hydraulically or mechanically operated. Mechanically operated dock levellers tend to be inefficient in use and tend to require excessive maintenance. Hydraulically powered dock levellers, while being efficient in use and requiring little maintenance, require a supply of pressurized hydraulic fluid. Usually, this fluid is provided by a hydraulic pump driven by an electric motor, mounted within the framework of the dock leveller. Unfortunately, because such dock levellers incorporate an electrical motor, they are unsuitable for use in hazardous enviroments. To overcome this problem in known dock levellers, pressurized hydraulic fluid has been supplied from a remote source.However, this is relatively costly and in many cases leads to pressure drops in the hydraulic lines which ultimately lead to inefficient operation of the dock leveller.

There is therefore a need for a dock leveller which overcomes these problems.

The present invention is directed towards providing such a dock leveller.

According to the invention there is provided a dock leveller comprising a deck having a truck-engaging front edge and a loading bay engaging rear edge, a framework to support the deck, and tilt means to tilt the deck about the rear edge relative to the framework, wherein the tilt means comprises an hydraulic ram powered by a pre-pressurized closed hydraulic circuit.

In one embodiment of the invention the pressure in the closed circuit is sufficient to raise the deck but insufficient to support the deck when supporting an additional load.

Preferably, the pressure in the closed circuit is insufficient to support the deck and a man on the deck.

Advantageously, the hydraulic ram is a single acting ram and the pre-pressurized closed circuit is provided by an hydraulic accumulator.

In another embodiment of the invention hydraulic fluid is delivered to the ram from the accumulator through a valve, the valve comprising valving means to permit fluid flow from the ram to the accumulator only when the pressure in the ram exceeds the pressure in the accumulator.

In a further embodiment of the invention, a truck engaging lip member is pivotally mounted on the front edge of the deck, the lip member being movable from a depending position to an outwardly extended position relative to the deck, and means to releasably retain the lip member in the extended position.

Advantageously, the means to releasably retain the lip member is provided by a lever pivotal on the deck, one end of the lever being engagable with a spud on the lip and spring biased to engage the spud with a ratchet action.

The invention will be more clearly understood from the following description of a preferred embodiment thereof, given by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of a dock leveller according to the invention, Figure 2 is a sectional side view of the dock leveller of Fig. 1, Figure 3 is a sectional view of a detail of the dock leveller of Fig. 1, Figure 4 is a sectional view of the detail of Fig. 3 on the line IV-IV, Figure 5 is a sectional view of another detail of the dock leveller of Fig. 1, and Figures 6(a) to (d) are part diagrammatic view of another detail of the dock leveller of Fig. 1 in different positions.

Referring to the drawings, there is illustrated a dock leveller according to the invention indicated generally by the reference numeral 1 for mounting in a loading bay 2.

The dock leveller 1 comprises a framework having a base portion 3 and upstanding rear portion 4. An angle beam 6 extending across the top of the rear 4 engages the surface of the loading bay 2. A deck 8 having a front truck engaging edge 7 and a rear edge 9 is pivotal at its rear edge 9 on a pivot shaft 10 which is supported on the rear portion 4 of the framework. Tilting means provided by a single acting hydraulic ram 1 2 tilts the deck 8 to raise and lower the front edge 7 to engage varying heights of truck decks by means of a pivotal lip member 1 5. This is described in detail below. The deck 8 is shown in its fully raised position in Fig. 2. The broken lines in Fig. 2 illustrate the deck in its lowest position.

A pre-pressurized closed circuit provided by an accumulator 1 8 powers the ram 1 2. This is also described in detail below.

The base portion 3 of the framework comprises a pair of opposing end members 1 9 of angle iron joined by a pair of channel members 20. The members 1 9 and 20 are welded together. The rear portion 4 of the framework comprises a pair of upstanding side members 21 of angle iron extending between the rear end member 19 and angle beam 6. Intermediate upstanding members 22 of box section also extended between the rear end member 19 and the angle beam 6. The side members 1 9 and upstanding intermediate members 22 are welded together. Re-inforcing webs 23 are welded between the intermediate members 22 and the channel member 20. A ram support member 24 of angle iron is welded to the channel members 20. The ram 1 2 is pivotally mounted on the support member 24 by a pivot mounting 25.A pivot mounting 26 on the underside of the deck 8 is provided to engage the piston rod 27 of the ram 1 3.

The deck 8 comprises a flat plate metal deck 28 supported on a framework having front 29 and rear 30 members of angle section joined by side members 31 also of angle section welded together. Intermediate cross members 1 6 of box section extend between the front and rear members 29 and 30. Tie members 1 7 extend between the re-inforcing cross members and are welded thereto. Two stop members 1 3 of plate metal welded to the front member 29 act as stops to support the deck in its lowest position. The stops 1 3 rest on corresponding stops 100 on the framework. Safety side members 43 extend from each side of the deck to avoid a person's foot being caught between the deck 8 and the loading bay 2.

Hydraulic fluid is delivered from the accumulator 1 8 to the ram 1 2 through a valve 32 mounted on the accumulator 1 8 and a hydraulic hose 33. The accumulator 18 comprises a body 80 which has a neoprene bag 81 pressurized with compressed nitrogen gas.

A valve 82 in the body connected into the nitrogen bag permits charging of the accumulator, see Fig. 5. The nitrogen pressure is such as to be sufficient to raise the deck 8 but insufficient to support the deck when a man is standing on it. This permits the deck 8 to be lowered by a man when standing on the deck.

In this embodiment of the invention the weight of the deck is in the order of 500 kg to 620 kg and it has been found that nitrogen pressure in the order of 90 to 1 30 bar is preferable.

The valve 32 is a one way valve which permits fluid to flow from the ram 1 2 into the accumulator 1 8 when the pressure in the ram exceeds the pressure in the accumulator, thereby allowing the deck to be lowered by the weight of a man standing thereon. An external opening means provided by a linkage mechanism 34 is provided to open the valve to permit fluid flow from the accumulator 1 8 to the ram 12 to rise the deck 8.

The valve 32 comprises a housing 35 with an inlet 36 from the accumulator 1 8 and a valve outlet 37 to the ram 1 2. A valving member provided by a ball 38 is biased by a spring 39 onto a seat 40. The spring 39 is such as to permit the ball 38 to move off the seat 40 when the pressure at the outlet 37 exceeds the pressure at the inlet 36. A plunger 42 slidable in the valve housing 35 is provided to lift the ball 38 off the seat 40 to permit fluid flow from the accumulator 1 8 to the ram 12. The plunger 42 is actuated by the linkage 34 which comprises a plunger actuating member 45 pivotal in the valve housing 35 at 46. An intermediate link 47 connects the member 45 to a cranked pivotal member 48 pivotal on a bracket 49 connected to the rear portion 4 of the framework.

A handle 50 connected to the pivotal member 48 extends through a recessed opening 52 in the deck 8 so that the plunger 42 can be activated from the loading bay 2.

The truck engaging lip member 1 5 is pivotally connected to the deck 8 by a pivot shaft 55 pivotal in tubes 56 mounted along the front edge 14 of the deck 8. The lip 1 5 pivots outwardly from a depending position illustrated in Fig. 6(a) to an extended position illustrated in Fig. 6(c), to engage a truck as will be described below. Means to releasably retain the lip 1 5 in the extended position is provided by a lever 57 which engages a spud 58 on the underside of the lip 1 5 with a ratchet action. The lever 57 is pivotally connected at 59 to a bracket 60 extending from the underside of the deck 8.

The free end of the lever 57 is connected to a biasing spring 63 by a steel cord 64. The spring is anchored to the framework by an anchorage 65. It can be seen from Figs. 2 and 6(a) to (d) that the combined length of the steel cord 64 and the spring 65 is such that when the deck 8 is in its lower positions illustrated in Fig. 4(a), the cord and spring are relaxed, thereby relaxing the biasing on the lever 57. The fulcrum of the lever provided by the pivot point 59 as can be seen in Fig. 6, is so arranged that the lever 57, when the spring biasing is relaxed, will disengage the lip 1 5 under its own weight, see Figs. 6(a) and (b).

The lip 1 5 pivots outwardly under the action of centrifugal force as the deck is being raised and the outward pivoting is assisted by the lever 57 bearing on the underside of the lip 15, see Fig. 6(b). The tension of the spring 63 is such that as the spring is extended the tension is adequate to assist in the outward movement of the lip 1 5.

In use, when it is desired to raise the deck 8 from its lowest horizontal position illustrated by the broken lines in Fig. 2, the handle 50 is raised. This depresses the plunger 42 of the valve 32 thereby opening the ball 38 to permit hydraulic fluid to flow from the accumulator 1 8 to raise the ram 1 2. The deck rises relatively rapidly and the centrifugal force of the deck aided by the lever 57 pivots the truck engaging lip 1 5 outwardly as shown in Figs. 6(b) and (c). When the lip 1 5 has pivoted fully outwardly the lever 57 engages the spud 58 thereby retaining the lip 1 5 in the extended position. It will be noted, see Fig. 6(c), that in this position the lip 1 5 is directed slightly downwardly of the deck 8.

The truck may then be reversed beneath the lip 1 5. A man by standing on the deck 8 then lowers the deck from the position illustrated in Fig. 6(c) so that illustrated in Fig. 6(d) so that the lip 15 rests on a floor 70 of a truck 71, portion of which is illustrated. In this position the lip 1 5 is aligned with the deck 8 and the lever 57 disengages the spud 58. The lever then under its own weight pivots as illustrated in Fig. 6(d). The pressure in the ram and accumulator will then equalise and the ball 38 will close the valve 32.

When it is desired to lower the deck when the loading has been completed, the truck pulls away from the deck 8 and the lip 1 5 pivot downwardly. A man, by standing on the deck, will again lower the deck to its lowest position illustrated by the broken lines in Fig.

2. When in this position, the cord 64 and spring 65 are relaxed.

The deck is then ready for use again.

It will be appreciated that although the framework and deck of the dock leveller have been described as being of particular construction, any other suitable construction could be used. Additionally, it will be appreciated that while a particular construction of accumulator, valve and ram have ben described, any other suitable construction could be used. Indeed, it is envisaged that in certain cases, the pre-pressurized closed circuit could be provided by other means besides an hydraulic accumulator.

It will also be appreciated that other constructions of truck engaging lips and biasing levers and springs could be used.

It will also be appreciated that other means of actuating the valve 32 besides the linkage arrangement just described could be used.

It will be appreciated that because the dock leveller is operated solely by hydraulics and there is no need for electric motors or the like, the dock leveller is ideally suited for use in hazardous environments, for example, in areas where explosions or spontaneous combustion are likely to occur. Additionally, it will be noted that in the event of an accident, such as for example, a truck backing into the dock leveller when it is in the lower position, the truck engaging lip member in the depending position will abut the buffer members thereby preventing the truck reversing further and causing damage.

It will also be appreciated that in certain cases instead of using a single acting ram, a double acting ram could be used.

Claims (14)

CLAIMS:

1. A dock leveller comprising a deck having a truck-engaging front edge and a loading bay engaging rear edge, a framework to support the deck, and tilt means to tilt the deck about the rear edge relative to the framework, wherein the tilt means comprises an hydraulic ram powered by a pre-pressurized closed hydraulic circuit.

2. A dock leveller as claimed in claim 1 in which the pressure in the closed circuit is sufficient to raise the deck, but insufficient to support the deck when supporting an additional load.

3. A dock leveller as claimed in claim 2 in which the pressure in the closed circuit is insufficient to support the deck and a man on the deck.

4. A dock leveller as claimed in any of the preceding claims in which the hydraulic ram is a single acting ram and the pre-pressurized closed circuit is provided by an hydraulic accumulator.

5. A dock leveller as claimed in claim 4 in which hydraulic fluid is delivered to the ram from the accumulator through a valve, the valve comprising valving means to permit squid flow from the ram to the accumulator only when the pressure in the ram exceeds he pressure in the accumulator.

6. A dock leveller as claimed in claim 5 in which the valving means is a one way valve comprising a valving member biased onto a seat in the direction of fluid flow to the ram.

7. A dock leveller as claimed in either claim 5 or 6 in which external opening means is connected to the valving means to open the valve.

8. A dock leveller as claimed in any preceding claim in which the weight of the deck is between 500 and 620 kg and the pressure in the pre-pressurized closed circuit is between 90 and 1 30 bar.

9. A dock leveller as claimed in claim 8 in which the pressure in the pre-pressurized closed circuit is 100 bar.

10. A dock leveller as claimed in any preceding claim in which a truck-engaging lip member is pivotally mounted on the front edge of the deck, the lip member being movable from a depending position to an outwardly extended position relative to the deck, and means to releasably retain the lip member in the extended position.

11. A dock leveller as claimed in claim 10 in which the means to releasably retain the lip member is provided by a lever pivotal on the deck, one end of the lever being engagable with a spud on the lip and spring biased to engage the spud with a ratchet action.

1 2. A dock leveller as claimed in claim 11 in which the lip member pivots outwardly under centrigual force when the deck is tilting, the spud being on the underside of the lip and the lever being on the underside of the deck.

1 3. A dock leveller as claimed in claim 11 or 1 2 in which the lever is pivoted intermediate its ends, the fulcrum being arranged so that the lever disengages the lip member under gravity when the spring biased is relaxed.

14. A dock leveller as claimed in any of claims 11 to 1 3 in which the spring biasing the lever is anchored on the framework below the deck, the free end of the lever being connected to the spring by a flexible member, the combined length of the flexible member and spring being such as to relax the spring when the deck is in its lowest position.

1 5. A dock leveller as claimed in claim 14 in which the outward pivotal movement of the lip member is assisted by the lever.

1 6. A dock leveller substantially as described herein with reference to and as illustrated in the accompanying drawings.