WO1982002860A1

WO1982002860A1 - Loading platform attachment

Info

Publication number: WO1982002860A1
Application number: PCT/SE1982/000055
Authority: WO
Inventors: Gunnar Svensson; Stefan Lindfors
Original assignee: Gunnar Svensson; Stefan Lindfors
Priority date: 1981-02-25
Filing date: 1982-02-24
Publication date: 1982-09-02
Also published as: SE426301B; SE8101225L; EP0083592A1

Abstract

A loading platform attachment is designed for small trucks (21) with fixed loading platform. The loading platform attachment is built up from an underframe (3), a tipping platform (1) which is hinge-connected with the underframe at the tipping edge of the tipping platform and at one side or end of the underframe, and a tipping arrangement (2) arranged to raise the tipping platform relative to the underframe around the said tipping shaft (4). The loading platform attachment forms a separate unit which can be changed over between an application position in which the loading platform attachment's underframe rests against the fixed loading platform (22) with the tipping platform either in the lowered state or raised state, and a storage position in which the loading platform attachment is removed from the truck.

Description

Title:

Loading platform attachment

Technical field:

The present invention relates to a loading platform attachment for small trucks with fixed loading platforms.

Technical problem:

The majority of small trucks which are employed for small-scale transport operations have only a fixed loading platform which thus lacks facilities for tipping the load transported. This however is a considerable disadvantage in for example municipal authority activities such as park administration, for farmers, small businesses and the like which for the transportation of say bulk material such as sand, soil or the like either have to hire a larger lorry with tipping platform for certain occasional transport operations or to have unloading carried out manually by means of for example of shovels. Manual unloading is however extremely labour-intensive and time consuming and hence - like the hire of larger lorries - is costly.

The aim of the present invention is to provide a loading platform attachment by means of which the disadvantages mentioned above are eliminated.

The solution:

The said aim is achieved by means of loading platform attachment which is characterised in that the loading platform attachment is constructed from an underframe, a tipping platform which by means of a tipping shaft is hinge-connected with the underframe at the tipping edge of the tipping platform and at one side or end of the underframe, also a tipping arrangement designed to raise the tipping platform relative to the underframe around the said tipping shaft, besides which the loading platform attachment forms a separate unit which can be changed over between an application position in which the loading platform attachment rests with its underframe against the fixed loading platform with the tipping platform either in the lowered or raised position, and a storage position in which the loading platform attachment is removed from the truck. Brief description of drawings :

In the following the invention will be described in greater detail with the aid of two embodiments by reference to appended drawings on which Fig. 1 illustrates the loading platform attachment in accordance with the invention in an initial embodiment viewed from the side in the application position in the lowered state, Fig. 2 illustrates the loading platform attachment as in Fig. 1 in the raised position and Fig. 3 illustrates the same loading platform attachment from underneath in the lowered position. Fig. 4 illustrates the loading platform attachment in accordance with the first example in the raised position, the dash-dotted lines also illustrating the complete truck on which the attachment is located, Fig's . 5 and 6 illustrate the change over of the loading platform attachment between the application position and the lowered position. Figs. 7, 8 and 9 show the loading platform attachment in accordance with a second embodiment in three different positions .

Best mode of carrying out the invention:

As shown on the drawings the loading platform attachment in accordance with the invention forms a separate unit which is essentially built up from a tipping platform 1, a tipping arrangement 2 and an underframe 3. The tipping platform is hinge-connected with the underframe 3 by means of a tipping shaft 4 which is located at one end of the underframe and at the tipping end 5 of the tipping platform, at which the tipping edge 6 of the tipping platform is located. More particularly the tipping shaft 4 is located somewhat inside the tipping edge 6. The tipping shaft 4 is designed for example in the form of one or two hinge links which hinge connect the tipping platform 1. with the underframe 3. The tipping arrangement 2 in the example shown comprises two expandable force arrangements 7 in the form of two hydraulic piston cylinders which are connected in hinge fashion between a lower fixing point 8 in the underframe 3 and an upper fixing point 9 in the tipping platform 1. The expandable force arrangements 7 are located at the sides of both side flaps 10 of the tipping platform 1, by means of which the loading platform attachment and particularly the overall height of the underframe can be kept low. To obtain the requisite stroke length and a favourable geometry of forces the upper fixing point 9 is located at as high a leval as possible, so that the side flaps in the example shown are provided with an upper edge portion 11 which is elevated at the upper fixing point.

In the example illustrated the tipping arrangment is of the hydraulic type and has an hydraulic arrangement 12. appertaining to the loading platform attachment and which consists of a hydraulic fluid pump 13 with hydraulic fluid reservoir 14 and an electric drive motors )15 for driving the hydraulic fluid pump . Hydraulic fluid pipelines 16 lead to each of the force devices 7. On one side of the underframe 3 actuating devices are provided for activation of the lifting arrangment 2. In the example illustrated the actuating device comprises an electrical switch 17 for starting and stopping the electric drive motor 15 for the hydraulic pump and a. changeover device 18 for changing over between the lifting movement and lowering movement. This changeover device 18 activates hydraulic valves, not shown, for controlling the hydraulic fluid in a known manner so that the hydraulic fluid is controlled to give alternatively expansion or compression of the hydraulic piston cylinders 7. In the example shown these are double-acting and hence have double pipelines 16 to each of the piston cylinders 7.

The tipping platform 1 is more particularly designed, apart from the above mentioned side flaps 10, also with a platform base 19 which as shown by fig. 3 is provided with reinforcing edges 20 which extend partly transversely and partly lengthwise to the tipping platform. Together with a front flap 34 and a rear flap 22 the side flaps 10 form the border to the loading space of the tipping platform 1. The rear flap is mounted in hinge fashion by means of two pivot pins in guides in the side flaps and is provided with locks , not shown, by means of which the rear flap can be kept in the locked position. These locks are designed to be released so as to permit the rear flap to swing outwards so as to open the tipping platform in order to tilt the platform. Both the side flaps and the front flap have reinforcing edges which are situated in such a way that maximum strength for the structure is obtained. The upper edge portion 11 which runs along the side flaps and the front flap is , in connection with the upper fixing point 9 of the force arrangements 7, designed in such a way that the upper fixing points are partially enclosed and hence well protected. The loading platform attachment can be designed with advantage from a material which is as light as possible, e.g. plastic, which can be reinforced by for example glass fibres. The tipping platform and the underframe can be made from plastic. Alternatively, the tipping platform can be made from plastic whilst the underframe 3 is made from a metallic material such as steel, light metal such as aluminium or the like. The underframe can be designed as a square frame of box profile, the hydraulic arrangement 12 being attached to the inside of the frame, e.g. orientated towards one corner of it. By way of example, it has been shown that a loading platform attachment in accordance with the invention can have a weight less that 200 kg for smaller trucks .

Figs . 1, 2 and 4 illustrate the loading platform attachment in accordance with the invention in the apphcation position, i.e. placed on a small truck 21 which is indicated by dash-dotted lines . The truck 21 is of such a type that in its original design it has a fixed loading platform 22, the side flaps 23 of which are similarly indicated by dot-dashed lines. The loading platform attachment is thus placed in the usual loading area, of the truck, i. e. on the fixed loading platform and between its two side flaps, so that from the formal point of view the loading platform attachment can be regarded as a load, and hence no particular inspection requirements or the like are imposed upon it, and any truck 21 of the type concerned here can thus be subsequently provided with a loading platform attachment in accordance with the invention. Hence here it rests with the underframe 3 directly on the base of the fixed loading platform 22 and normally rests extremely stably as a result of its own weight which however is relatively low because of the light construction and suitably chosen materral composition for the loading platform attachment. The attachment is placed in such a way that its tipping edge 6 is located somewhat beyond the rear end 24 of the vehicle. This position is ensured by means of a guide device 25 which in the example shown comprises an angle element which is permanently attached to the underframe below the tipping shaft 4.

By means of suitably chosen dimensions in accordance with various standard dimensions on the part of the fixed loading plat forms in use it is thus possible in accordance with the invention to convert a truck with fixed loading platform to a truck with tipping platform without noticeably reducing the maximum possible load volume or load weight. As a result of the shallow height of the underframe the base of the tipping platform is raised only slightly as compared with the base of the fixed platform. Sideways and towards the front only a small clearance is required between the flaps of the loading platform attachment and the flaps of the fixed platform to ensure satisfactory functioning. Instead of loading bulk material or other tippable material directly into the loading area of the fixed platform, loading takes place on the tipping platform . in its loading area between these flaps . During this the tipping platform 1 is naturally in the lowered position as shown in Fig. 1. To drive the tipping arrangement 2 a connection is required merely to the conventional starting battery of the truck 21 by means of a single connecting lead, which is not shown. This can comprise a twin electrical conductor connected to the drive motor 15 having a contact: device which is detachably connectible to a socket at an appropriate point on the vehicle, either by way of a direct connection to the battery or via a specially arranged socket.

After transportation of the material to be tipped to the desired location, the tipping arrangment 2 is actuated by changing over the electrical switch 17 which by way of example is a press button, as a result of which hydraulic fluid under pressure is supplied to the hydrauhc piston cylinder 7 whilst the switch 17 is actuated, whereby the tipping platform 1 is rotated around the tipping shaft and the rear flap 22 is swung out after its locks are released, following which the material to be tipped is tipped off. Various tipping positions can. naturally be selected by ceasing to actuate the switch in the desired position for the tipping platform. When actuation ceases , the hydrauhc fluid pipelines 16 are blocked by the said hydrauhc valves so that hydrauhc fluid cannot flow back to the hydrauhc fluid reservoir 14, so that the tipping platform is retained in the desired position. After tipping has terminated the tipping platform 1 is lowered by changing over the actuating device 18 so that hydrauhc fluid flows back to the hydrauhc reservoir. With double-acting hydrauhc piston cylinders lowering takes place not only because of the dead weight of the tipping platform , but also the lowering movement is accelerated in that the hydrauhc motor is actuated also during the lowering movement so as to create hydrauhc fluid pressure which is controlled in such a way that the hydrauhc piston cylinders are compressed.

As indicated above, the loading platform attachment in accordance with the invention is designed to be capable of being switched over from its apphcation position on the truck 21 to a storage position" where the loading platform attachment has been removed from the truck. Figs . 5 and 6 illustrate an example of an arrangement for changing over the attachment between the apphcation and storage positions. This arrangement 26 comprises a bridge-like rack with supporting legs 27 which extends on either side of the truck 21 and thus exhibits a mutual space which must exceed its width and a cross member 28 which is designed to extend between the supporting legs 27 at such a height above the vehicle that the loading platform attachment can be raised towards the cross member. Furthermore four supporting elements 29, 30 are provided which are attached pair-wise in two upper fixing points 31 on the cross member 28 and which extend pair-wise from this down to each of the upper edge portions of the side flaps and which have hook-like fixing elements 32, 33 at their ends . The two fixing points 31 are situated at a mutual spacing which corresponds essentially with the width of the tipping platform. The supporting elements 29, 30 are appropriately wires, chains or the like the length of which is so adapted that the loading platform attachment can be carried by the rack 26 at a height above the truck 21.

In accordance with the invention the loading platform attachment's own force arrangements 7 are employed to provide the requisite lifting force so as to r-emove the attachment from the truck. In the diagrams the usual flaps of the vehicle which belong to the fixed loading platform have been removed for the sake of clarity . However they do not need to be removed in actual practice to lift off the attachment, which is done as follows. The truck 21 is reversed under the rack 26 in accordance with the invention so that the loading platform attachment is located essentially straight underneath the cross member 28. Then the tipping platform 1 is raised to a suitably selected intermediate position, e.g. the intermediate position illustfated in Fig. 5. Then the supporting elements 29, 30 are attached between fixing points 31 on one side of the cross-member 28 and on the other side to the hook-like fixing elements 32, 33 in the side flaps of the tipping platform. The supporting elements 29 are then essentially mutually parallel, whilst the supporting elements 30 are similarly mutually in parallel. Then the tipping arrangment 2 is actuated for lowering in the usual manner by means of its actuating device 17, 18, which is possible in the example shown because the hydrauhc piston cylinders 7 are double-acting. As a result the hydrauhc piston cylinders are drawn together so that the underframe 3 is drawn up towards the lower face of the tipping platform whereby the latter is tilted somewhat to a more horizontal position as shown in Fig. 6. In this connection the length of the supporting elements is so chosen that the attachment becomes correctly balanced with respect to the rack, so that this tilting can take place, and the attachment makes contact with the fixed loading platform on the truck. If no double-acting hydrauhc piston cylinders are available, it can be sufficient if the hydraulic arrangment is changed over in such a way that the hydrauhc fluid valve involved is opened and the hydrauhc piston cylinders are enabled to be drawn together because the tipping platform is so balanced that by virtue of its own weight it tends to change over to a more horizontal position. Then, if necessay it is easy to swing the attachment muanually in such a way that it ceases to make contact with the truck, which can then drive away from the rack.

The change over from the lowered position to the apphcation position takes place in accordance with the same principle, but in the reverse order. The truck 21 is reversed in under the rack, after which the underframe 3 is pressed down against the fixed loading platform by actuating the tipping arrangement so that the supporting elements 29, 30 become slackened and can easily be unhooked from their fixing elements 32, 33. Then the tipping platform can be swung downwards by actuation of the tipping arrangement so that the tipping platform adopts the lowered position, after which the loading platform attachment is ready for use. Apart from the obvious advantage of being able to add a tipping function to a small truck, other advantages are also obtainable from a removable loading platform attachment in accordance with the invention. The truck can easily be restored for use in applications where fixed loading platforms are preferable, e.g. when placing a caravan attachment on the platform. The loading platform attachment has a service life which exceeds that of the truck and it can be retained when replacing the truck. In the case of a vehicle inventory consisting of severaly vehicles it can be sufficient to procure one or a few attachments which can easuy be transferred between vehicles.

Figs . 7, 8 and 9 illustrate the loading platform attachment by way of a second embodiment where the same notation numbers, with an added hundred, are provided for corresponding components in comparison, with the first embodiment. Fig. 7 illustrates the loading platform attachment in the transportation position, i.e. the tipping platform 101 is in the lowered position. The loading platform attachment has the same main components as the attachment in the first embodiment, i.e. tipping platform 101, a tipping arrangement 102 and an underframe 103. The essential difference is that the attachment in accordance with the second embodiment can be changed over, with the tipping platform 101 in a forward position with the tipping platform lowered, which thus represents a transportation position, and a rear position which comprises the tipping position. This capability of displacement on the part of the tipping platform has been provided to facilitate tipping so that the material being tipped lands beyond the rear edge 24 of the fixed loading platform 22, in combination with the fact that the tipping platform 101 in the transportation position can be located inside the rear edge of the fixed platform. This is achieved in that the tipping shaft 104 of tipping platform 101 is displaceably mounted in the underframe 103 in two guides 35, which by way of example comprise two slots or troughs in the two outer frame girders 38 of the underframe. Here the tipping shaft 104 can be designed as two sideways axle journals which are located at a distance from the underside 39 of the tipping platform 101, each by means of its bracket 40. Since the tipping shaft 104 is located at a distance from the underside of the tipping platform , a shght backward movement of the tipping edge 106 occurs during the tilting of the tipping platform , which to some extent can contribute towards the tipping edge ending up beyond the rear edge 24 of the fixed platform 22.

However, in the embodiment shown in Figs . 7, 8 and 9 the mainly backward displacement of the tipping platform 101 takes place as a result of a direct backward movement of the tipping shaft 104, which occurs due to the action of the force arrangement 102. In this example this is gripped between the underframe 103 and the underside 39 of the tipping platform 101. Here the piston cylinders 107 of the tipping arrangement 102, which can be one, two or more in number, are essentially located in the initital position illustrated in Fig. 7. One end 108 of each piston cylinder 107, i. e. one end of the cylinder portion, is hinge-connected with some girder in the underframe 103, whilst the other end 109, i. e. the outer end of piston rod 40, of the the piston cylinder is hinge-connected with the tipping platform 101. However the outer end 109 of the piston rod is not directly linked with the tipping platform in the example shown, this occuring via an intermediate swivel arm mechanism consisting of two swivel arms 41, 42. These are hinge-connected with each other at one end at the outer end 109 of the piston rod 40, whust the swivel arms 41 , 42 are hinge-connected at their opposite ends 43, 44 with the underside 39 and the underframe 103 respectively of the tipping platform 101. On the underframe 103 the hinge point at the end 44 of swivel arm 42 is designed as a pivot pin or the like which is displaceably mounted in a guide 45 in the form of a slot, trough in for example the two outer frame girders 38.

To provide lifting force for the tipping platform 101 the loading platform attachment in accordance with the second embodiment has an auxiliary arrangement, the layout of which is best illustrated by Figs . 8 and 9. This arrangement comprises at least two supporting elements 36 in the form of support rolls, sideways directed shde pins or the like, each located on its bracket 46 which is firmly attached to the underside of the tipping platform 101 or at the lower edge of its side flaps 110. Furthermore this arrangement includes a guide way 37 firmly attached to the underframe 103 in the form for example of an angle iron or the like which is firmly attached to both side members 38 of the underframe. This guide way 37 is directed obliquely upwards to the rear and is so located in relation to the supporting element 6 that it starts the tipping movment of the tipping platform 101, as will be described in detail later. The supporting element 36 also provides the function of giving support for the tipping platform 101 against the underframe 103 during its displacement movement between the forward and the rear position.

During transportation and during the garaging of the vehicle the attachment is in the transportation position illustrated in Fig. 7 with the tipping platform 101 in its forward, lowered position. Thus the tipping shaft 104 is in the forward extreme position of the guides 35, so that the tipping edge 106 of the .tipping platform 101, and thus the platform as a whole, is located inside the rear edge 24 of the fixed loading platform 22. This has been achieved in that the piston cylinders 107 which are double-acting have been provided with medium under pressure so that they are in the contracted position, so that also the link arm mechanism is fully folded. The hinge position 44 of the swivel arm 42 is located at the forward end of the guide 45 and the supporting element 36 is in front of the obliquelypositioned guide path 37. When the medium under pressure is supplied to the piston cylinders 7 so that they expand, a backwarddirected force is applied against the swivel arm mechanism 41, 42 at the outer end 109 of the piston rod 40. Since the tipping shaft 104 is displaceably mounted in the guides .35, and since the tipping platform 101 is in any case cabable of movement relative to the underframe by means of the supporting element 36 and because the swivel arm mechanism 41, 42 is permitted to move relative to the underframe 103 as a result of the hinge point 44 being capable of movement in the guides 45, the tipping platform 101 is thus moved backwards. Since, as soon as the displacement movement is started, the supporting element 36 moves up the oblique guide paths 37, this also causes the tipping movement to start. This results in the swivel arms 41, 42 gradually straightening and the piston cylinders 107 swinging upwards somewhat, as illustrated in Fig. 8. In this position such an angle is reached between the two swivel arms 41, 42 and the piston cylinders 107 that a satisfactory force component is obtained in an upward direction, i. e. for raising the loading platform. At the same time the tipping shaft 104, also the hinge point 44 of swivel arm 42, has reached its rear extreme position in the respective guides 35, 45, with the result that the rear extreme position is adopted by the tipping platform and the complete tipping movement is carried out. Thus the tipping platform 101 with its tipping edge 106 is located at the rear of and beyond the rear edge 24 of the fixed loading platform 22, so that tipping can take place without the load landing up on the fixed loading platform . The raised tipping position is illustrated in Fig. 9. If the piston cylinders 107 have an adequate stroke length, it is possible for the tipping platform 101 to be raised even further until the two swivel arms 41, 42 are in line with each other.

Lowering takes place in fundamentally the same manner, but in reverse order, the piston cylinders being changed over to contract, with the result that the tipping platform is first lowered to the position shown in Fig. 8, after which the tipping platform is pulled to its forward position whilst finally it is lowered whilst the supporting elements 36 move along the guide paths 37. In actual practice however the supporting elements do not need to make contact with the guide path 37 during this change over movement from the tipping position from the rear position to the forward position. It is perhaps feasible that the displacement movement from the rear position to the forward position takes place first, prior to the folding movement taking place, or else simultaneously with the latter, dependent on the frictional conditions between the tipping shaft 104 and the guides 35, also the hinge position 44 and the guides 45.

The invention is not restricted to the embodiments described above and illustrated on the drawings, but can be varied in a number of ways within the framework of the claims which follow. For example the loading platform attachment can be provided with some form of fixing arrangement so as to further safeguard its position on the vehicle. This can comprise a locking arrangement, which for example is adjustable and which can lock the underframe in the correct position between the side flaps of the fixed loading platform. Such an arrangement can be provided at two or four locations at the side of the underframe and be directed sideways and outwards from the underframe. If another type of fixing arrangement is se- lected, it is also feasible as such that the usual flaps on the fixed loading platform can be omitted. Another way of ensuring reliable locking is to dimension the underframe in such a way that it rests with a good fit between the fixed flaps on a fixed loading platform having conventional dimensions. Different dimensions can be employed for both the underframe and the tipping platform to suit different vehicle dimensions . The attachment can also be so designed that tipping takes place around a tipping shaft located along one side of the underframe and the tipping platform.

The second embodiment can be modified whilst retaining its principal changeover function between a forward and a rear position. Here the swivel arm mechanism can be replaced by a single swivel arm, the outer end of the piston rod being controlled in a guide. Here however a longer stroke length on the part of the piston cylinders is required. Furthermore the attachment in accordance with the second embodiment can be provided with a control device, in the form for example of an angle element or the like, which projects to the rear from the underframe and which like the first embodiment rests against the rear edge of the fixed loading platform and governs the position of the attachment relative to the fixed loading platform. As such it is also feasible to employ a tipping arrangement other than that shown here, e.g. an electric drive motor with a set of gears.

Claims

Claims :

1. Loading platform attachement for small trucks (21) with fixed loading platform (22) CHARACTERISED in that the loading platform attachment is built up from an underframe (3/103) , a tipping platform (1/101) which by means of a tipping shaft (4/104) is hinge-connected with the underframe at the tipping edge (6/106) of the tipping platform and one side or end of the underframe, and a tipping arrangement (2/102) designed to raise the tipping platform relative to the underframe around the said tipping shaft, in addition to which the loading platform attachement forms a separate unit which can be changed over between an apphcation position in which the loading platform attachement underframe rests against the fixed loading platform (22/122) with the tipping platform in either the lowered or raised position , and a storage position in which the loading platform attachment is removed from the truck.

2. Loading platform attachment as in claim 1 , CHARACTERISED in that the tipping arrangement (2) comprises firstly two expandable piston cylinders (7) driven by pressure means , one located on each side of the tipping platform (1) and attached to the underframe (3) by means of a lower fixing point (8) and at the tipping platform by means of an upper fixing point (9) , and secondly a pump for pressure medium (13) with pressure medium reservoir (14) and drive motor (15) , and where the pressure medium pump is connected with the piston cylinders by means of pressure medium pipelines (16) .

3. Loading platform attachment as in claim 2, CHARACTERISED in that the upper fixing point (9) of the piston cylinders (7) is located at a portion of the upper edge (11) of both side flaps (10) of the tipping platform (1) .

4. Loading platform attachment as in claim 1 , CHARACTERISED in that the underframe (3) is designed as a framework to which the pressure medium pump (13) with pressure medium reservoir and drive motor are permanently attached.

5. Loading platform attachment in accordance with any of the preceding claims CHARACTERISED in that the underframe (3) has a guide device (25) for determining the position of the attachment in relation to the fixed platform (22) so that the tipping edge (6) of the tipping platform (1) is located beyond the rear end (24) of the truck (21) .

6. Loading platform attachment in accordance with any of the preceding claims CHARACTERISED in that the attachment has an arrangement for the said changeover between the apphcation position and the storage position , which arrangement comprises a rack (27) and four supporting elements (29, 30) attached to the rack, whereby the ends of the supporting elements are fastened to the tipping platform (1) , after which the underframe (3) is drawn towards the tipping platform.

7. Loading platform attachment in accordance with claims 2 and 6, in which the piston cylinders (7) are double-acting, CHARACTERISED in that the piston cylinders (7) are actuated to lower the tipping platform (1) with the result that the underframe is instead drawn towards the tipping platform.

8. Loading platform attachment in accordance with claim 1, CHARACTERISED in that the tipping platform (101) , due to the action of the tipping arrangement (102) is arranged to be displaced relative to the underframe (103) between a forward position which represents the transportation position and a rear position which comprises the tipping position.

9. Loading platform attachment as in claim 8, CHARACTERISED in that the tipping arrangement (102) comprises one or more expandable piston cylinders (107) , which are hinge-connected at one end with the underframe (103) and hinge-connected at their other end (109) with the tipping platform (101) so that the said piston cylinders during their expansion with the tipping platform lowered provide a backward-directed force for moving the tipping platform backwards and an upward-directed force for enabling the tipping movement of the tipping platform.

10. Loading platform attachment as in claim 9, CHARACTERISED in that the tipping shaft (104) of the tipping platform (101) is moveable along at least two guides (35) in the underframe (103) , that the tipping platform has at least two supporting elements (36) which are located at a distance from the tipping shaft and that the underframe has a sloping guide path (37) directed upwards and rearwards for the said supporting elements, by means of which the tipping platform even in the event of a mainly backward- directed force during displacement to the rear starts to rise, resulting in such a change in position on the part of the said piston cylinders (107) that these provide a force towards the tipping platform for the continued tipping movement.