GB2146616A - Lifting jack - Google Patents

Abstract

A mobile electrohydraulic lifting jack has a vertical column 71 supporting a guide trolley 72 having four wheels of which the two lower run on the front and the two upper on the rear side of the column, which comprises two vertical channel sections, the webs of which are parallel with the central plane 10 of the jack and extend at a distance therefrom while their flanges are aligned in pairs. The trolley is raised and lowered by an electrically-powered hydraulic piston-and-cylinder device 28 via cables 44, 46, 51, 52 passing over sprockets 38, 39 arranged in the central plane 10, the cables carrying a lug 52 which extends between plates 54, 56 at the front of the column. <IMAGE>

Description

SPECIFICATION Lifting jack The invention relates to a lifting jack according to the preamble to the Main Claim.

Such a lifting jack is known from Belgian Patent 709415 of 16th January 1968.

In this field, the electrohydraulic principle has the advantage that the loads can be set in motion smoothly and that operation is quiet.

In the last 15 years, however, no one has succeeded in constructing lifting jacks which are sufficiently light and which can nevertheless be used for heavy loads. These lifting jacks must be light because they are mobile and it must as far as possible be feasible for them to be handled by one man. Nevertheless, they must be capable of raising and lowering heavy loads safely, from the ground to at least 2 m, so that people can work under the raised load. Loads are between 3 and 15 tons with a static maximum of around 5 tons. 5-ton lifting jacks are needed, for instance, for buses, for heavy goods vehicle bodies, for containers, etc. 15-ton lifting jacks are used for lifting railway locomotives and so on.

Climbing jacks, e.g. according to German Patent No. 1 286276 have become well established on the market. It is true that they are light but they are loud.

Since with such jacks an air-bellows driven carriage travels up and down and is of a specific length, the effective lifting height is substantially less than the height of the column. It is however frequently decisive, in fact both for the design and also for the application, whether the column is 10 cm longer or shorter. Where lifting jacks are concerned, it is important also to remember that they run synchronously upwards or downwards when several of them are being moved. Otherwise, the lorry or suchlike will end up in a slanting position. With regard to the facility for controlling such synchronous travel, however, compressed air is by no means equivalent to hydraulics, because hydraulic systems can be controlled more finely, more smoothly and more effectively. British Patent No.

100 3025, Figures 1 and 2, show for example how the co-operation of four lifting jacks might be envisaged.

Also very widely used are lifting jacks which use spindles with an electric drive, e.g. according to German Utility Model 1 800 434. However, these constructions have quite a number of disadvantages: the spindle may only be subjected to tension, as it otherwise buckles. This means that the spindle must be suspended at its top end. Therefore, any load will always ne initiated at the least favourable point on the column. Furthermore, the upper end of the spindle must be suspended by a cardan joint, so that it can be positioned accurately in the direction of pull. Cardan or universal joints which have to withstand loads of the above-mentioned order are however expensive and susceptible to breakdown.

Above all, the spindle is worn by the spindle nut more quickly in its bottom zone than in its upper, because lifting occurs more in the lower zone. Then the spindle has to be thrown away although it might partially be still usable. For safety reasons, spindle lifting jacks require two spindle nuts. When one breaks, the other must still hold. The electric motor and the gear mechanism represent a considerable mass in vibration and therefore the spindle drive still lags behind even after the electric motor has been switched off. Electric motors of spindle drive systems must always be over-dimensioned several times in order to achieve synchronous running. They are simply made so powerful that any friction which occurs is negligible and it is then assumed that after a certain connection time, the guide trolley will be at a certain place.And yet it is not even sufficient purely to use motors with an over-dimensioned output. Instead, the motors must also be selected for equality of operating characteristics. The spindles are protected by rubber bellows. Since these lifting jacks are also used by untrained personnel in rough workshop conditions, creases due to damage are often discovered too late. It is true that the patent literature discloses paper inventions in which the electric motor and gear mechanism are provided low down on the lifting jack. For various reasons, however, the only lifting jacks which have enjoyed established use are those where the electric motor and the gear mechanism are arranged high up on the column. This does however mean that the overall height is increased and the lifting jacks becomes top heavy. The height of lift is reduced in relation to the overall height.

The apparatus according to Belgian Patent No. 709 415 has the following properties which lead to unsuitability in practice: (a) The chain 11 is looped at a different angle in relation to the front strand of the chain 11, independently of the height of lift.

(b) The front strand of the chain 11 pulls the wheel 10 farther forwards the higher the lift. Therefore, no purely axial forces arise. This means that the piston is tilted in the lifting cylinder 8 and the seal is destroyed.

(c) Because the main beam 13 is located relatively far forwards, it is not possible to move with optimum proximity up to the column 1.

(d) The front wheels 21 run on the front of the channel section of the column 1. This surface is very narrow and can only be made wide by making the side flanges of the column 1 very thick.

(e) In terms of optimum rigidity, the channel section is exactly upside down. In order to make it sufficiently rigid in its "soft" direction, sufficiently thick material has to be used.

(f) The rear strand of the chain 11 is fixed to the projection 12. Since the tractive forces of the chain 11 are initiated there, the column 1 must, in the area underneath it, withstand both the flexion forces and also the chain forces. To cope with this, the column must be made even thicker.

(g) In principle, the column is open where the work is performed and closed in fact from the point where it could be maintained.

(h) There are no standard sections from which the column 1 could be produced.

Therefore, the column lisa non-standard unit, with all the concomitant disadvantages.

The object of the invention is to indicate a lifting jack of the type mentioned at the outset, which uses little material and which is therefore both lightweight and also inexpensive and nevertheless safe, which is capable of practical use and which offers a comparatively considerable height of lift.

According to the invention, this problem is resolved by the features disclosed in the characterising part of the Main Claim.

As a result of the features according to Claim 2, the channel sections are in practice braced at about half their height, which may result in an even lighter construction, but on the other hand this also provides a secure supportforthe lifting cylinder.

By reason of the features according to Claim 3, the chain remains slender when viewed in the direction of the central plane. Consequently, the lifting cylinder can remain substantially in the space between the channel sections.

The features according to Claim 4 may be conducive to safety and at the same time provide additional rigidity, indeed first and foremost against laterai buckling or buckling in the direction of the central plane.

The invention will now be described hereinafter with reference to a preferred and practically viable embodiment shown in the accompanying scale drawings, in which: Figure 1 is the front view of a lifting jack with the guide trolley fully raised; Figure 2 is a plan view of Figure 1, and Figure 3 is a view according to the arrow A in Figure 1.

The lifting jack is designed to be virtually entirely symmetrical in relation to the central plane 10.

In operation, it stands on two front plates 11 and one rear plate 12. In this position, its front wheeis 13 disappear into the longitudinal associated supporting spar 14. Transverse spars 16 extending at an angle of 45" connect the supporting spars 14to a base 17. At the rear of the base 17 is a horizontal journal 18 on which is mounted a chassis 19 with a draw bar 21. Fixed to the base 17 is a bracket 22 on which is a hydraulic unit 23 in which there are pumps and controllable valves. The pumps are driven by an electric motor 24 which is flanged onto the hydraulic unit 23. Fixed on the base 17 is a sleeve 24 into which fits the bottom end zone 27 of a double acting hydraulic ram 28.The hydraulic ram 28 stands upright on the base frame which is constituted substantially by the supporting spars 14, the transverse spars 16 and the base 17. At its upper end zone, the hydraulic ram 28 has two horizontal journals 29 which extend at a right-angle to the central plane 19. The end of each journal 29 is fixed to the spine 31 of a channel section 32. The channel section 32 is to specification DIN 126 for channel steel No. 160 and is of material St 37 Standard or St 52. Further details of dimensions can be ascertained from the overall height of the lifting jack according to Figure 1. The overall height is 2,270 mm. At the bottom, the channel sections 32 are rigidly fixed to the base 17. Their spines 31 merge into free flanges 33,34. The ends of the journals 29 are connected to the spines 31.The upper ends of the channel sections 32 are connected rigidly to one another by a transverse yoke 36 which is not shown in Figure 2 because this drawing is actually a cross-section.

Emerging from the top of the hydraulic ram 28 is a piston rod 37. At its top end it carries two independently rotatable idler sprockets 38,39.

According to Figure 3, these have a pitch circle 41.

A single chain 42 is looped around the idler sprocket 38 and a single chain 43 is looped around the idler sprocket 39. The rear strands 44,46 extend as far as the top end of the hydraulic ram 28 where they are attached jointly to a two-part pull rod 47 which is located behind the hydraulic ram 28 and the bottom end of which is rigidly connected to the base 27. The upper part 48 of the pull rod 47 is screwed into the bottom part, secured by a lock nut and its screwthreading serves for adjustment of the chains 42,43 and also for screwing back any stretch which might occur during operation. The centre line 49 of the rear strand 44,46 emerges tangentially into the pitch circle 41 and is also the centre line of the pull rod 47.

The centre line 49 is parallel with the common centre line 50 of the hydraulic ram 28 and of its piston rod 37 and the middle of the idler sprockets 38,39, as can be seen particularly clearly in Figure 3.

The front strands 51, 52 extend parallel with the centre line 49 and thus also parallel with the centre line 50. Their bottom ends are, in the central plane 10, secured to a lug 53 which emerges at the front through a narrow slit extending between two cover plates 54, 56 which are omitted from Figure 1. The cover plates 54,56 are secured to the front of the free flanges 33,34 in the manner which is shown in Figure 2.

The lug 53 shows the manner of connection to a guide trolley 57 which, according to Figure 3, has obliquely extending plates 58, 59 which engage over the column in the manner illustrated. At the top, the plates 58, 59 are rigidly connected to an L-shaped profile 61 at the rear of the column. In the corner zone created by the L-shaped profile 61 there are two idler wheels 62,63, the periphery of which runs on the free flanges 33 while the rims 64, 66 run on the outer face of the bridges 31.

In the lower part (Figures 2 and 3) of the plates 58, 59, simiiar idler wheels 66,67 are provided to run on the outer face of the cover plate 54,56, under which lie the free flanges 33,34. The idler wheel 62 is located exactly opposite the idler wheel 66, just as the idler wheel 63 is exactly opposite the idler wheel 67. The rims 68,69 of the idler wheels 66,67 likewise run on the outside face of the spines 61.

On the front and top end faces, where according to Figure 3 these do not intersect the column 71, they are rigidly connected to each other by an obliquely positioned transverse plate 72 of rectangular plan.

This and also the bottom zone of the plates 58, 59 merge into a lifting fork 73.

Welded on the outside and front to the spines 31 are flat profile sections 74,76 which have a rearwardly directed tooth system which, for reasons of safety, co-operates with a detent system 77 which is not of interest here.

Claims (5)

1. Mobile electrohydraulic lifting jack with a horizontal base frame with a vertical column rising from the base frame, with a guide trolley having fourwheels and movable vertically and parallel with the central plane of the lifting jack, of which wheels the two lower run on the front and the two upper on the rear side of the column, with a lifting fork mounted on the guide trolley, with a vertical lifting cylinder having one end in the column, standing on the base frame and through the upper end of which a piston rod emerges, carrying at its free end a chain sprocket with a horizontal axis, with a drag chain, one end of which is articulated on the guide trolley, said chain passing over the top of the sprocket and having its other end attached to a fixed point on the lifting jack, with an electric motor and with a pump device adapted to be driven by the electric motor, characterised by the following features: (a) The column comprises two vertical channel sections, the spines of which are parallel with the central plane and extend at a distance therefrom while their free flanges are aligned and orientated at each other in pairs.

(b) At their top end the channel sections are connected rigidly to each other by a transverse yoke.

(c) At the 3 o'clock and 9 o'clock positions, the pitch circle of the sprocket merges into the central line through the relevant strand of the drag chain and both strands extend parallel with the central axis of the column.

(d) The wheels of the guide trolley have treads, for which the outer surface of the relevant column channel section serves as a guide surface, the wheels being supported on the outside of the flanges at the corner zone between the respective spine and the free flanges.

2. Apparatus according to Claim 1, characterised in that the spines of the channel sections have at the level of the end zone of the lifting cylinder in each case a fixing device which extends horizontally, is capable of being subjected to a traction loading and which engages both the spine and also the lifting cylinder.

3. Apparatus according to Claim 1, characterised in that the drag chain is a sprocket chain which runs over an idler sprocket.

4. Apparatus according to Claim 1, characterised in that the front plane of the drag chain is located behind the front free flanges of the channel sections and in that the front free flanges support the outer marginal zone of in each case a cover plate, the cover plates leaving between them and in the central plane a slot through which an articulation emerges, connecting the drag chain to the lifting fork.

5. Mobile electrohydraulic lifting jack substantially as herein described with reference to the accompanying drawings.