Abstract:
This invention relates to a lattice piece for a large mobile crane, comprising four corner posts and null bars and diagonal bars connecting the same. In accordance with the invention, the lattice piece each is divided in two such that one part of the null and diagonal bars each is foldably hinged at two corner posts connected with each other. Furthermore, the invention relates to a method for erecting such lattice piece.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to a lattice piece for a large mobile crane and a method of erecting such lattice piece. 
   Large mobile cranes are transported to the respective sites of operation on public roads. Here, the rules of public road traffic are applicable, in Germany for instance the German Road Traffic Regulations. The maximum admissible weights and also dimensions are specified, for instance. In other countries, similar regulations are applicable. 
   These regulations lead to the fact that the dimensions of the parts to be transported are limited. As a result, the total size of the mobile crane and therefore also the maximum achievable load capacity and the outreach (load moment) thereof also are limited. 
   Different approaches for increasing the load capacity have already been formulated. In DE 20 2005 017 362 U1, for instance, it has already been proposed to couple two cranes. From WO 2005/030632 A1 it is known to use two booms on one crane in parallel. In these two proposals, the two booms provided here are connected with each other. 
   In accordance with another proposal, lateral reinforcements were mounted on both sides of the booms and adjusted by means of a dual derrick (as proposed in DE 100 02 917 A1). 
   In EP 1 015 374 B1 it is described already to create lattice pieces which are dimensioned slightly smaller than the dimensions of a container, in order to simplify the transport of the lattice pieces. Here, differently profiled corner posts were used. The transport of the lattice pieces was effected analogous to the transport of a container with corresponding connections, as they are known for containers. 
   Since the booms constructed of the lattice pieces should be slewable on a common axis, all solutions have in common that the width of the assembled booms always was larger than the height. Thus, the known booms have less load capacity in the luffing plane than vertical to the luffing plane. In the case of long and heavy main booms, the maximum length to be erected also is limited by the cross-sectional values of the boom in the luffing plane. 
   With large radii, the “buckling bar boom” also is greatly loaded by its own weight in the direction of the luffing plane, i.e. high cross-sectional values of the boom provide for high load capacity values. 
   SUMMARY OF THE INVENTION 
   It is the object of the present invention to create lattice pieces which can be used in a large mobile crane, wherein extremely high loads can be lifted to large altitudes, with the individual lattice pieces nevertheless remaining suitable for road transport. 
   In accordance with the invention, this object is solved by a lattice piece with the features described herein. 
   Accordingly, a lattice piece for a large mobile crane, which consists of four corner posts and of diagonal bars connecting the same, is divided in two such that one part of the diagonal bars each is foldably hinged at two corner posts connected with each other. The lattice pieces of the invention can be transported in this disassembled form. In this way, large lattice pieces can be created with a profile which has a cross-section of e.g. 8×6 m and a length of 11 m. The lattice pieces of the present invention can be assembled to form a correspondingly powerful boom. The lattice pieces of the invention can be transported with so-called flat containers. The same have dimensions which are uniform all over the world. 
   While the length of the lattice pieces can be chosen such that the length can be maintained during transport, disassembly of the lattice pieces in two parts preferably is chosen such that disassembly is effected both in the width and in the height of the lattice pieces. The lattice pieces should be designed such that assembly and disassembly of the respective lattice piece can be performed economically. This means that assembly and disassembly of the lattice piece must be effected within a reasonable period, with as little auxiliary devices as possible and in consideration of safety during assembly and disassembly. 
   Advantageous aspects of the invention can be taken from the description herein. 
   Accordingly, null bars additionally can be foldably hinged at two corner posts connected with each other. These null bars serve to increase stability. They are, however, not absolutely necessary. In accordance with another preferred aspect of the invention, a rigid connection can instead be used between the individual lattice pieces. 
   Furthermore, the lattice pieces advantageously can have corner posts made of profiles which have fork-finger connections at their ends. At each corner post, four null bars and four diagonal bars can be hinged. 
   At least part of the null bars and/or of the diagonal bars can be telescopable. 
   During assembly, both the null bars and the diagonal bars can each be fixable at the corner posts or at each other via bolt connections. 
   Advantageously, the profile of the corner posts is fabricated of two angular sheets welded to each other in the form of a box, to each of which the fork-finger connections are welded. Advantageously, the connection between the corner posts and the diagonal and null bars is rigid. 
   Advantageously, positioning devices can be provided for positioning the diagonal bars and/or null bars in the disassembled condition. Thus, the transport units are safely kept connected. In the assembled lattice piece and in crane operation, the positioning devices also can remain on or in the lattice piece. 
   A further advantageous aspect of the invention consists in that in each lattice element an additional spatial diagonal is provided. 
   A preferred method for erecting a lattice piece of the invention consists of the following steps:
         placing the two lattice piece parts beside each other;   swivelling out corresponding diagonal bars and bolting with the corner posts of the opposed lattice piece parts,   lifting the upper disk obtained by connecting the lattice piece parts and thereby extending four telescopable diagonal bars and bolting the diagonal bars in their extended position;   bolting the null bars swivelled into the end position while lifting.       

   Particularly advantageously, the null bars can roll along the corner posts via rollers disposed on their free ends during erection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features, details and advantages of the invention can be taken from the embodiments illustrated in the drawing, in which: 
       FIG. 1 : shows a perspective view of a lattice piece of the invention in the assembled form, 
       FIG. 2 : shows a side view of a lattice piece of  FIG. 1  in the folded form, 
       FIG. 3 : shows a side view of a lattice piece of  FIG. 1 , 
       FIG. 4 : shows a top view of a lattice piece of  FIG. 1 , 
       FIG. 5 : shows a front view of a lattice piece of  FIG. 1 , 
       FIG. 6 : shows a partial section through a part of a lattice piece, and 
       FIGS. 7   a )- c ): show a schematic representation of the process of erection of a lattice piece of the invention in various intermediate stages. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIG. 1 , a lattice piece  10  of the invention is shown in perspective. This lattice piece consists of four corner posts  12 , which are connected with each other via diagonal bars  14  and  16  and null bars  18  and  20 , respectively. A lattice piece  10 , as shown in  FIGS. 1 to 5 , for instance has a length L of 11 m, a width B of 8 m and a height H of 6 m. 
   To be able to transport this lattice piece on the road, it is divided in two. There are formed two lattice piece halves, which each comprise two corner posts  12 . Proceeding from the assembled lattice piece as shown in  FIG. 1 , these lattice piece parts are formed in that corresponding bolt connections on the diagonal bars  16  and on the null bars  18  are released on at least one side each. The respectively divided lattice pieces  10  then are transferred into a folded position, as shown in  FIG. 2 . For this purpose, the null bars  20  are folded in and the diagonal bars  14 , which are telescopable, are telescoped in. The correspondingly folded or extended condition is shown in  FIG. 3  by the distinction between continuous lines and dash-dotted lines. As shown in  FIG. 3 , the diagonal bars  14  each are hinged at swivel points  22  and  24  of the corner posts  12 . In the extended position, as shown in  FIG. 3  in a continuous line, the diagonal bars  14  are bolted in their extended position via bolts  26 . The null bars  20  each are hinged at a corner post  12  via swivel points  28 . The opposite free end can be bolted with the opposite corner post  12 . 
   In  FIG. 4 , a top view is shown. Here, the corner posts  12  are connected with each other via the diagonal bars  16  and the null bars  18 . The diagonal bars  16  can be swivelled about swivel points  28 , whereas the null bars  18  can be swivelled about swivel points  30  and  32 , respectively. The position swivelled in each is represented in  FIG. 4  by dash-dotted lines. In the illustrated extended position, the free ends of the diagonal bars  16  and null bars  18 , respectively, each are bolted with the opposite bolting point on the corner post  12 . As shown in  FIG. 5 , no spatial diagonal bars are provided. Only the adjacent corner posts  12  each are connected with each other. This is enabled by creating rigid connections between the corner posts  12  and the diagonals  16  and  14 , respectively, and the null bars  18  and  20 , respectively. 
   Between the lattice pieces, very high forces must be transmitted. Thus, the fork-finger connections  34  provided on the corner pieces  12  are subjected to very high loads. To facilitate the handling of the bolts, multishear fork-finger connections  34  can be used, as shown for instance in  FIG. 4  or  FIG. 1 . Here, comparatively smaller bolts can be used. 
   The corner posts  12  can be fabricated of any kind of profile. Advantageously, the profile is made of two angular and welded sheets  36 ,  38 , in accordance with the embodiments as shown in  FIG. 6 . The profile of square cross-section has a side length of about 800×800 mm. To the corner piece, guide sheets  40  with corresponding reinforcements  42  can be welded for receiving the null bars or diagonal bars. Bolt connections here are designated with reference numeral  44 . 
   The profiles of the diagonal bars  14 ,  16  and of the null bars  18 ,  20  can be as desired. For instance, they consist of a welded pipe construction or a welded construction of straight or bent sheets. In any case, however, the profiles are protected against buckling. 
   With reference to  FIG. 7 , the procedure for assembly of the lattice piece of the invention is shown schematically and by way of example. 
     FIG. 7   a  shows how a first transport unit  46  is removed by means of a non-illustrated auxiliary crane from a likewise non-illustrated flat container, on which the first transport unit was transported, and is put down by a second transport unit  48  at a distance B. This second transport unit  48  previously likewise was picked up from a flat container by means of the auxiliary crane and put down at the position shown in  FIG. 7   a.    
   As shown in  FIG. 7   b , the lower diagonal bars  16  first were swivelled out and bolted, whereby the distance B of 8 m is obtained. For correspondingly unfolding, the diagonal bars  16  and the null bars  18  are suspended on an auxiliary crane. After the lower diagonals  16  and the lower null bars  18  were swivelled out and bolted, the upper diagonals  16  and the upper null bars  18 , i.e. the diagonals  16  and the null bars  18  of the upper disk, are swivelled out and bolted with the corner posts  12  by means of bolts  50 . 
   As shown in  FIG. 7   c , the upper disk then is lifted to the top in the direction of arrow a by means of a non-illustrated auxiliary crane. As a result, the four telescopable diagonal bars  14 , which are shown in  FIG. 7   c  not in a side view, but in a front view, are extended, so that the height of 6 m is obtained. In the corresponding end position, the diagonal bars are bolted with each other via bolts  26 . While erecting the lattice piece  10  by means of the auxiliary crane, the null bars  20 , which for simplification are not shown in  FIG. 7   c , run over rollers  52  (cf.  FIG. 3 ) along the corner posts  12  into their assembly position. As shown in the slightly modified embodiment of  FIG. 3 , the null bars  20  can enclose the corner posts  12  in a fork-like manner. In this position, the null bars  20  can be bolted with the corner posts  12 . In accordance with the embodiment of  FIG. 1  and  FIG. 5 , the null bars  20  are bolted with corresponding tabs welded to the corner posts. What is not shown here are rollers, which act similar to the way described in  FIG. 3 . 
   For again folding the boom  10  now from its erected position, as it is shown for instance in  FIG. 3 , the null bars  20  are slightly pressed to the inside after removing the bolts, until a lever arm is obtained on the roller  52 , so that when lowering the upper disk, the null bar  20  runs further along the corner post  12  under its own weight. During disassembly, the bolts  26  of course are withdrawn, so that the telescopable diagonal bars  24  can be pushed together. 
   Similar to the lattice pieces  10  shown here, the hinged piece or the head piece (not shown here) can be designed to be foldable.