FIELD OF THE INVENTION AND PRIOR ART

This invention relates to a power unit of the type varying its length according to the preamble of claim 1.

The purpose of a power unit of this kind is to achieve that the total, maximum extension of the power unit will rise to at least twice as much as the extension in the contracted initial position of the power unit. Such a power unit can for instance be used in trans¬ ferring load between two load vehicles, e.g. a lorry and a railway wagon, or between a load vehicle and e.g. a pallet. Since the load carrier of these vehicles often are approximatively equally wide and it is desi¬ rable to be able to move" the load from one load carrier to another load carrier in one step, so that the load in every situation comes so far into the other load room as desired, the power unit must be able to be extended to a length, which is at least two times greater than its length in the contracted state. The expression at least two times does here refer to a length which exceeds the double one with at least the length which the shortest possible distance, which is formed as a result of that the two load vehicles mostly cannot be placed completely against each other, between the two load rooms constitutes.

A number of power units for the purpose mentioned above are already known. Among these a power unit according to US patent 3 521 939 can be considered to be the basis of the present invention. This and also other known power units do all have only one transmission and they possess through the location of the transmission

as a consequence of this fact the disadvantage that the force-lever ratio for the member to which the wheels are attached is getting very unfavourable. For that reason this member has to be made very strong and rigid, which lead to that it becomes heavy, unhandy and volu¬ minous as well as rather costly. The power unit tends through this location also to become rather high, seen in the direction of the normal of the load surface, which leads to its becoming ungainly and room demanding and by that also difficult to locate.

SUMMARY OF THE INVENTION

The object of the invention is to provide a power unit of the type varying its length, which reduces the above mentioned disadvantageous of the power units already known and which renders an easy transport of objects from a first place to a place located at a distance from the first place which is greater than the length of the power unit in the contracted state possible, the transport being mostly carried out generally in the horizontal plane, but also other planes are pos¬ sible. This object is obtained according to the inven¬ tion by that the first member at least partly has the character of a housing for the power unit, said hou¬ sing having an elongated shape in cross section, the power device being disposed generally in the central region of the first member, the transmissions being two in number, and said two transmissions being gene¬ rally symmetrical in a mirror image relation to each other with respect to a plane comprising the longi¬ tudinal axis of the power device and being perpendicular to the greater dimension of the cross-sectional shape of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a specific description of an embodiment of the invention chosen as an example. In the drawings:

Fig 1 is a partly simplified view cut in the symmetry plane S-S of the power unit in accordance with the invention,

fig 2 illustrates the same power unit as is illustra-

•*• ted in fig 1 in a partly sectioned- view from the N- direction (fig 1 ) ,

fig 3 is a detailed cross section view of said power unit along III-III, illustrating the mutual holding and guiding of the different members,

fig 4 is a detailed cross section view of the power unit along the- cut IV-IV illustrating among other things the location of the chain transmission, and

fig 5 is a view of the same sort as fig 2, but of the power unit in a more extended state .

In fig 1 , 2 and 5 the power unit has been shrinked in the direction of the arrow I by omitting a part of the central region of the power unit (see dashed line) .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In fig 1 the first member, which generally constitutes an outer housing of the power unit, is indicated with 1. This member is at its one outer end provided with a first attaching means 4, by means of which the power unit can be attached to an object, for example a lorry platform. A second member which is indicated with 2

is encased of the first one and a third member indicated with 3 and has an elongated extension in the direction to the right in the figure. The second member is at its outer end provided with a second attaching means 5 for attaching of the power unit to preferably a trans¬ mitting means of a* transferring device _* The second and the third member are movable in the direction of the arrow I with respect to the first, generally fixed localized member and with respect to each other.

The power unit has a power device which consists of the components described hereafter. The second member includes a longitudinal screw 6 extending in the direc¬ tion of the arrow I generally between the two outer ends of the power unit. This screw is borne by two bearings 7, which are fixed at the two ends of the first member, rotatable -about its longitudinal axis but not displaceable in the directi n of said axis. The screw 6 is through a coupling 8 at the one outer end of the power unit connected to a motor 9, prefe¬ rably a hydraulic one, which is intended to set the screw in rotation. The coupling is of such type, that, in order to prevent damages of the power unit, it will slip if the-torque of the screw 6 gets to high. A nut 10 is in engagement with the thread of the screw 6 and is on the rotation of the screw moved forwards and backwards along the screw. In doing so, the nut 10 is prevented to rotate, since it at opposite sides is firmly connected to a connecting plate 11 , which in its turn is connected to a portion of the third member. The rotation of the screw 6 and the displacement of the nut caused by that accordingly lead to a similar displacement of the third member.

In the following it is referred to fig 2 as well as fig 3. The third member has two portions, here called frames 12, which are located on both sides of the symmetry plane S-S. A rotatable chain wheel 13 is fixedly disposed on each frame 12 at the two opposite ends thereof, in such manner that the pin bolt 14 of the- chain wheels, the geometrical center axis of which is parallel to the N-direction, is secured to the frame. Each of the two wheel pairs carries a chain loop 15, which during the rotation of the wheels 13 moves generally parallel to the displacement direc¬ tion of the third member (arrow I). In this embodiment example a transmission including a chain has been chosen, but the loop 12 can also consist of a band, a belt or other flexible tractive force transmitting means Thus, this chain loop 15 engages with the chain wheels 13 for example because the chain wheels are having teeth or the like σr because the chain wheels, as indicated in the drawings, has peripherical grooves, in which the chains are received and guided against lateral movement. Each chain loop has an inner 16 and an outer 17 chain part. The chain loop is through a first connecting member 18 at a first point 19 firmly connected to the first member and through a second connecting member 20 at a second point 21 firmly connec¬ ted to the second member (see especially fig 3). On displacing the third member with respect to the first member the distance L, the second member will accordingly be displaced the distance 2 L with respect to the first member (see also fig 5).

By referring to fig 3 the advantageous constitution and disposition of the three main members of the power unit in accordance with the preferred embodiment will be explained. The first member has an elongated cross- sectional shape and is generally forming a housing for the power unit. The center region 22 of this hou¬ sing encases the power device with the geometrical

center axis of the screw 6 extending in the symmetry plane S-S of the power unit. The first member has por¬ tions 23 which are gripping around and holding the third member, which in this way, through the surfaces of the these portions, is displaceably supported by the first member. Similarly the third member is provided with portions 24, 25, 27 and surfaces for displaceably supporting and guiding the second member. The housing formed by the first member is provided with an opening 26 emerging in the direction opposite the N-direction, this opening being closed by an elongated portion 27 of the third member. This portion 27 and the portion 25 of the third member are holding the second member against displacements in the latter direction. At the same time the portion 24 of the third member is holding the second member against displacements in the direction of the normal of the symmetry plane S-S. Through the curved portion 23 of the first and the curved portion 28 of the third*member the third member is held against displacements in the direction of the normal of the symmetry plane S-S as well as in the direction opposite the N-direction At the same time the third member is by this very advantageous design of the invention held indirectly by itself, as a result of that it, being held by the first member, holds the second member, which by means of this in its turn together with the first member holds portions 25 of the third member.

This design of the different members leads to their joint defining of a number of rooms. With the symmetry plane S-S as starting-point the power unit is provided with the following rooms in the direction of the nor¬ mal of this plane: The central region 22 of the first member and the second member are forming a room 29 elongated in the displacement direction (I) and gene-

rally housing the power device. The portion 30 of the second member and the portion 31 of the third member define a room 32 elongated in the same direction and housing the inner chain part 16 of the chain loop 15. In fig 3 the connecting member 20, which connects the inner chain part 16 to a second member, is visible, said connecting member being also situated in this room 32. The portions 27, 31, 33 and 34 of the third member encase a room 35 extending between the two chain wheels 13 and generally constituting an empty space. Finally the portions 28 and 34 of the third member and the outer portion 22 of the first member encase a room 36 elongated also in a direction of the arrow I, through which room the outer chain part 17 of the chain loop 15 passes.

Fig 4- illustrates that only one room, which is encased by the first member and the portion 27 of the third member, exists at the cross section IV-IV; this is also necessary in order to make the housing of the two chain wheels 13 in the way mentioned above possible (with the center axis of the pin bolt 14 parallel to the N-direction). The pin bolt 14 is secured to the earlier mentioned frames 12. In this figure it is also clearly visible how the connecting plate 11 is fixed on one hand by the bolt 37 to the nut 10 and on the other hand by the bolts 38 to portions of the third member (see also fig 1 and fig 2).

Hereunder the function and the advantages of the inven¬ tion according to the preferred embodiment are described, Fig 5 illustrates how the power unit from its almost completely contracted state (fig 2) is displaced in the direction of the arrow I. The third member, to which the chain wheels 13 are attached, has by the rotating of the screw 6 been displaced the distance L with respect to the first, fixedly attached member. In doing so a part of the opening 26 has been exposed,

and the internal members of the power unit, a.o. the power device, have become visible. The connecting mem¬ ber 20 between the inner chain part 16 and the second member has at the same time been displaced the distance L with respect to the third member. As a result of this the point 21, accordingly the second member, has been displaced the distance 2 L with respect to the first member.

In using the power unit it can for instance be fixed on a bearer, as a lorry chassis or platform, so that it is situated in a recess or a groove in the bearer, so that the portion 27 of the third member extends beneath unrecessed parts of the bearer. Over the power unit a lifting device, for example of the pressure fluid type can be disposed so as to act between the two members,, e.g. two plates, of the transmitting means. The lower part of the transmitting means which through- the attachment means 5 is attached to the second member 2 rests upon portions of said groove in the bearer. The two members of the transmitting means are only connected vertically displaceable between themselves. When the lorry is loaded and driven close to for instance a railway wagon for further transport of the load, the upper member of the transmitting means is lifted by means of the lifting device in relation to the lower member first of all vertically upwards until the load rests solely upon this member. It should be added that it is of advantage to dispose a plurality of power units and transmitting means in grooves in the bearer parallel with respect to each other, in order to make the carrying and transmitting of the load to take place in a stable and safe way. When the load is resting upon the upper member of the transmitting means the screw 6 is rotated through the starting of the hydraulic motor 9. This causes the nut 10 to push the third member in the direction of the arrow I, simultaneously as

the third member by the action of the chain transmissions is displacing the second member with respect to itself in the same direction and the same distance (see fig 5). The load is now resting upon the upper member of the transmitting means indirectly connected through the lower member to the second member, and displaced so far into the railway wagon as required. By conversion of the number of rotation of the screw 6 caused by the hydraulic motor 9, the distance which the load is moved can be measured easily, instantaneously and very exactly during the whole operating process. In already known power units pressure cylinders are often employed as power devices, which causes a length mea¬ surement not at all so exact as this. The railway wagon is preferably provided with transversal beams between which vacant spaces are located, into which vacant spaces the power unit and the lower member of the trans¬ mitting means can run and into which "the upper part of the transmitting means can be lowered by means of the lifting device in order to lay the load down in the railway wagon. After this the screw 6 is rotated in the direction opposite to the previous mentioned one, and the power unit is contracted to its starting position.

Some members of the power unit are exposed during the transfer of the load (see fig 5), since the opening 26 -in the first member is not any longer closed by the portion 27 of the displaced third member. This can possibly be advantageous, if it is desired to get access to certain members inside the power unit, but if one wishes to protect the internal members of the power unit by holding the opening 26 closed all the time, an appropriate design of the first member can naturally easily be made.

Since there are two chain transmissions and they are located in the way described above, important advan¬ tages in comparison with the already known construc¬ tions are obtained. Thanks to that the pin bolt 14 of the chain wheels has been located with its geomet¬ rical center axis parallel to the N-direction and that the chain transmissions are disposed on both sides of the power device, it was possible to make the power unit very thin in said direction. This leads to that the housing of the power unit requires much less room in the vertical direction (the N-direction), which is very advantageous. The'disposition of the chain transmissions according to above does also lead to, and this is of great importance, that the torsion loads upon the frame 12 of the third member bearing the chain wheels 13 are getting considerably lower than for already known constructions. The fact that two instead of one chain transmission are used, reduces said loads, but the most important thing is the locating of the chain transmissions symmetrically to the S-S plane and in generally one and the same normal plane to the S-S plane.

The disposition for displaceably supporting and bearing the different members by means of each other can be performed in other manners than that here described, but it must be pointed out that the illustrated dis¬ position is very appropriately constructed. The different members are held stable, the internal members of the unit are protected by the first member constituting the housing and the different members can be mutually displaced in the direction of the arrow I, completely rectilinearly by forming support for each other from all directions.

Through the embodiment of the invention described above the object of the invention is obtained in a satisfying manner. But it is a matter of course that the inven¬ tion is not limited to this embodiment example, but

several modifications of the invention, for adaption to different application branches, will be possible. For instance it is possible to use other power devices than of the screw-nut-type, such as a piston-cylinder mechanism.