GB2043585A - Mobile crane - Google Patents

Abstract

A mobile crane comprises a luffing jib (17) mounted on an upper chassis (16) and the upper chassis (16) is mounted by a rotatable connection (15), which allows sewing, on an intermediate frame (12) instead of being mounted directly on a carriage (10) as is conventional. The frame (12) is longitudinally slidable by means of guides (13) on the carriage (10) between a forward travelling position as shown in the drawing, in which the weight of the crane as a whole is uniformly distributed over the various wheels (11) of the carriage (10) to give a minimum axle loading while travelling, and one of a number of rearward lifting positions in which the centre of gravity S2 of the upper chassis and the parts which it carries is rearwardly displaced for load counterbalancing purposes. Fixing elements (14) detachably lock the intermediate frame (12) in its various positions on the carriage (10) and can be automatically disengaged when a drive (not shown) to slide the frame (12) along the carriage (10) is actuated. <IMAGE>

Description

SPECIFICATION Mobile crane This invention relates to mobile cranes, particularly cranes for lifting heavy loads, comprising an upper chassis which is rotatably mounted on a wheeled carriage and supports a luffing jib.

In such mobile cranes which usually have several wheel axles to distribute their weight and keep within permissible axle and wheel loads, two competing basic requirements usually have to be fulfilled. Firstly, it is necessary to provide a reasonably uniform weight distribution for travelling by road or rail in order that the required axle and wheel loadings shall be kept as uniform as practicable.

Secondly for lifting heavy loads an optimum utilization of weight and centre of gravity must be present, in order that the desired lifting capacity shall be attained with satisfactory stability of the crane.

These basic requirements can usually only be satisfied by additional measures and devices.

For this purpose counter-weights or parts thereof may be shifted in a manner dependent upon lifting requirements on the upper chassis or may be transferred from one end to the other of the carriage.

Both measures however have the disadvantage that shifting the centre of gravity of the crane as a whole is possible only to a limited extent and that a considerable amount of space is required on the upper chassis and/or on the carriage for the weight movement to take place. It is in essence also possible, for optimising the weight distribution, to remove parts of the counter-weight, jib and/or the upper chassis when travelling and to install additional axles and transport wheels. For this purpose, however, a considerable amount of rigging and dismantling work and additional transport equipment is required, and this leads to considerable expenditure on machine components and handling operations.

The object of the present invention is to provide a mobile crane of the type initially described by which, with the use of easily and rapidly handled, simple means, a substantially uniform weight distribution can be attained for travelling and also a satisfactory utilization of the weight and centre of gravity can be achieved during lifting operations.

To this end, according to this invention, in a mobile crane comprising an upper chassis which is rotatably mounted on a wheeled carriage and supports a luffing jib, the upper chassis is also longitudinally displaceable on the carriage between one or more lifting positions and a travelling position in which the weight of the crane is more uniformly distributed amongst the wheels than in the lifting position or positions, and means are provided for releasably locking the upper chassis in its travelling position and its lifting position or positions.

The invention is thus based upon the concept of providing an optimization of the adaptation of weight and centre of gravity in the load-lifting and travelling conditions by longitudinal displacement of the entire mass of the upper chassis of the crane together with the components mounted thereon. As a result, the hitherto necessary, highly labourintensive and time-consuming manipulation of parts of the upper chassis in order to shift the centre of gravity can be eliminated, since the upper chassis as a whole is displaced and is adapted, in respect of its position relative to the lower chassis, to the required operating conditions. Apart from the longitudinal displaceability of the upper chassis all the crane parts, such as the counter-weight, can thus remain permanently connected to each other in an unchanged manner.The longitudinal displacement itself can be effected very simply and also rapidly and accurately.

Especially favourable conditions are obtained if the upper chassis is rotatably mounted on an intermediate frame and the intermediate frame is longitudinally slidable on the lower chassis by means of sliding guides. By the clear separation between the rotating and longitudinal displacement elements, it is possible to construct the rotating mounting of the upper chassis in the manner usual in mobile cranes of the type described. The only main structure added is the intermediate frame which is only longitudinally slidable on the carriage.

This frame constitutes a kind of intermediate chassis for the rotating mounting. By such a construction, it is in certain circumstances possible to convert existing mobile cranes into cranes in accordance with the invention with an acceptable expenditure.

In one preferred example, releasable locking of the intermediate frame in the lifting and travelling positions is carried out by interengaging or frictionlocking fixing elements. When locked, these elements connect together with the carriage and the intermediate frame in a horizontal longitudinal direction and preferably also in a vertical direction.

Whereas the compressive forces that occur in the crane during lifting are transmitted via the intermediate frame and the slide guides directly into the carriage, transference of tensile forces that occur to the carriage is effected via the intermediate frame and the fixing elements. The fixing elements ensure that the intermediate frame and thus the upper chassis together with the parts which it carries are immovably secured in the lifting and travelling positions, so that no unintended longitudinal displacements can occur. It is also possible to shift the vertical connecting function from the fixing elements to the slide guides. This can be done, for example, by providing on the carriage and on the intermediate frame parts that engage around one another. These parts prevent the intermediate frame and the carriage from separating in the vertical direction.

A controlled drive is preferably provided for moving the intermediate frame with the upper chassis, the jib and counter weight between the lifting and travelling position. This drive can, for example, be in the form of hydraulic cylinders.

Conditions especially favourable for handling may be achieved by providing an interlock between the fixing elements for locking the intermediate frame in the end positions and the controlled drive. This interlock may, for example, be of such a form that when the drive is actuated for the purpose of moving the intermediate frame together with the upper chassis longitudinally, unlocking of the fixing elements is automatically effected. On the other hand, the interlock may also be such that actuation of the drive is possible only when the fixing elements have been released.

For optimum utilization of the weight and location of the centre of gravity of the crane during lifting, the centre of gravity of the upper chassis and parts carried thereby are displaced to a greater or lesser extent backwards in the lifting position with respect to the centre of gravity of the carriage. In principle it is sufficient to provide a single lifting position for all loading conditions. Instead, however, it is also possible to provide a number of selectable lifting positions, in which the upper chassis can be locked.

These positions are spaced longitudinally apart from each other, and are for different loading states, so that smaller longitudinal spacings or displacement distances for the intermediate frame and upper chassis are used, for example, for ranges of comparatively low loadings as compared with ranges of comparatively higher loadings. With this there is the advantage, amongst others, that a mobile crane which isto be only lightly loaded although it is basically designed for a higher lifting capacity, can be moved more rapidly from the travelling into the lifting position and vice versa on account of the small displacement necessary.Another result also is that a more uniform axle and wheel load distribution, adapted to the lower load state, can be achieved as compared with the case in which only one lifting position adapted to the maximum loading state is available.

Since the mobile crane is normally unloaded when travelling, only one travelling position, dependent upon the particular crane construction, is in general necessary. In this position, with advantage, the centre of gravity of the upper chassis and the parts which are longitudinally movable therewith and the centre of gravity of the carriage lie approximately vertically one above the other. To provide a good travelling and manoeuvring capability of the crane and for optimum utilization of the maximum permissible axle and wheel loadings, it is important that all the axles and travelling wheels shall be loaded as uniformly as possible in the travelling position.

The invention thus makes possible, by the longitudinal displaceability of the upper chassis, a displace ment of the centre of gravity of the entire upper chassis, counter-weight and jib in such a manner that in the travelling and lifting positions, optimum weight and centre of gravity relationships are present. This is of special importance particularly in compact mobile cranes that are utilized to the extreme limits in regard to lifting. The weight distribution required in each case determines the longitudinal distance between the lifting and travell ing positions, that is the distance of travel of the upper chassis relative to the carriage. The extremely easily and rapidly handled mobile crane in accord ance with this invention is of comparatively simple construction.Furthermore, as already mentioned, existing mobile cranes with a rotational connection between the upper chassis and the carriage can be converted into cranes in accordance with the invention.

An example of a mobile crane in accordance with the invention is illustrated diagrammatically in the accompanying drawings in which: Figure 1 is a diagrammatic side view of the crane with its upper chassis in the travelling position; and, Figure 2 is a similar view but with the upper chassis rearwardly displaced on the carriage into a lifting position.

As shown in Figures 1 and 2, the mobile crane, which in this example has a multi-axle carriage 10, has travelling wheels 11. An intermediate frame 12 is mounted on the carriage 10 and is longitudinally displaceable between lifting and travelling positions.

For this purpose the carriage 10 is provided, instead of with a seating for a rotational connection as in conventional cranes, with seatings forming linear sliding guides 13, on which the intermediate frame 12 isslidably mounted. Furthermore, fixing elements 13 are provided, which ensure detachable locking of the intermediate frame 12 to the carriage in the lifting and travelling positions, so that the intermediate frame 12 cannot move longitudinally in an uncontrolled manner. Also, the fixing elements 14 prevent, at least in the lifting and travelling positions, lifting the intermediate frame 12 from the carriage 10.Correspondingly, weight-induced compressive forces are transferred from the intermediate frame 12 via the sliding guides 13 to the carriage 10, whereas tensile forces resulting from tilting moments are transmitted from the intermediate frame 12 via the fixing elements 14 to the carriage 10.

An upper chassis 16 is rotatably mounted on the intermediate frame 12 together with the parts which the chassis 16 carries such as crane counter-weight, and a jib 17. The connection between the frame 12 and the chassis 16 is exclusively rotatable and consists of a conventional rotational connection 15.

The upper chassis 16 is thus rotatable by means of the rotational connection 15. The upper chassis 16 is thus rotatable by means of the rotational connection 15 about a vertical axis A. In the present example, this axis is displaced forwards in the travelling position of the crane illustrated in Figure 1 by a distancexwith respect to a vertical plane B passing through the centre of gravity S1 of the symmetrically constructed carriage 10. In this travelling position the common centre of gravity S2 of the upper chassis 16 and the parts which it carries is likewise situated in the aforementioned vertical plane B.

Since the intermediate frame 12 can be displaced in the longitudinal direction C, the vertical axis A can be displaced rearwardly from the travelling position shown in Figure 1 into the lifting position shown in Figure 2. in the lifting position, the vertical axis A in the present example lies in the vertical plane B, so that it passes through the centre of gravity S1 of the carriage 10. In contrast, the centre of gravity S2 of the upper chassis 16 and the parts carried thereby is displaced longitudinally towards the rear by the same distance x with respect to the vertical plane B.

As a result of this a favourable axle and wheel load distribution is obtained in the lifting position while a load is being lifted.

Ajib 17, which is illustrated in Figures 1 and 2 in its lowered position, can be raised in the direction of an arrow D by a luffing connecting 18 on the upper, rearward part of the upper chassis 16. On the free, forward end of the jib 17 which is preferably telescopically extensible, there is a guide sheave 19, over which a lifting rope 20 runs. A lifting hook 21 is attached to the end of the rope 20.

The example illustrated in Figures 1 and 2 has a symmetrical carriage 10. The invention can also be realised in a mobile crane with an asymmetric carriage. In every case it is important that the centres of gravity of the carriage and of the upper chassis together with parts situated thereon shall be disposed in positions such that uniform weight distribution to the wheels shalal be obtained for travelling. It is furthermore important for lifting purposes that the centre of gravity of the upper chassis together with the parts situated thereon shall be displaced towards the rear with respect to the centre of gravity of the carriage in the lifting position, to an extent sufficient for weight compensation. For this purpose a drive, which is preferably hydraulic but is not shown, is provided.This makes possible a sufficient longitudinal displacement between the intermediate frame 12 and the carriage 10. The fixing elements 14 which lock the intermediate frame 12 in the longitudinal direction in the lifting and travelling positions can be coupled to the drive and, for example, can be automatically disengaged when this drive is actuated. Furthermore, an interlock system is preferably provided, which makes possible the execution of the remaining crane functions, such as slewing of the upper chassis 16 and luffing ofthejib 17,onlywhen the intermediatefromae 12 is in the lifting position. If it is desired, a number of lifting positions for lifting loads of differing magnitudes and different lifting radii may also be provided.

An extremely advantageous facility is thus offered by this invention for a surprising simple and rapid adaptation of the weight and centre of gravity which can be handled in an optimum manner and which is most desirable in mobile cranes for fulfilling differing basic requirements for travelling and lifting states.

Claims (10)

1. A mobile crane comprising an upper chassis which is rotatably mounted on a wheeled carriage and supports a luffing jib, wherein the upper chassis is also longitudinally displaceable on the carriage between one or more lifting positions and a travelling position in which the weight of the crane is more uniformly distributed amongst the wheels than in the lifting position or positions, and means are provided for releasably locking the upper chassis in its travelling position and its lifting position or position.

2. A crane according to Claim 1, in which the upper chassis is rotatably mounted on an intermediate frame by a rotational connection and the intermediate frame is longitudinallyslidably mounted on the carriage by sliding guides.

3. A crane according to Claim 2, in which the releasable locking means comprise interengaging or friction-locking fixing elements which releasably lock the upper chassis in the lifting and travelling positions.

4. A crane according to Claim 3, in which the fixing elements are operative to lock together the carriage and the intermediate frame in the longitudinal direction of movement and in a vertical direction.

5. A crane according to any one of Claims 2 to 4, in which there is a controlled drive for displacing the intermediate frame together with the upper chassis between the travelling and lifting positions.

6. A crane according to Claim 5, in which there is an interlock between the fixing elements and the controlled drive, whereby actuation of the drive releases the fixing elements or whereby the drive can only be actuated after the fixing elements have been released.

7. A crane according to any one of the preceding Claims, in which the centre of gravity of the upper chassis and the parts carried thereby is displaced rearwards behind the centre of gravity of the carriage when the upper chassis is in the lifting position.

8. A crane according to Claim 7, in which the upper chassis has a plurality of selectable lifting positions at mutual longitudinal spacings relative to the carriage.

9. A crane according to any one of the preceding Claims, in which the centre of gravity of the upper chassis and the parts carried thereby and the centre of gravity of the carriage are substantially vertically one above the other when the upper chassis is in the travelling position.

10. A crane according to Claim 1, substantially as described with reference to the accompanying drawings.