Mobile crane and method for angling a main jib extension relative to a main jib of a mobile crane

Abstract

A mobile crane having a main jib that is mounted thereupon for luffing and that can be oriented by means of a luffing cylinder, and a main jib extension which is detachably connected to a main jib head of the main jib by upper and lower bolts, it being possible to angle the main jib extension about a luffing axis relative to the main jib proceeding from a base position following release of the upper or lower bolts and using an angle drive, the angle drive engaging with a foot of the main jib extension, a maximum angling angle being delimited by an adjustable angling plate, and the angling plate engaging with the foot of the main jib extension and the main jib head. The angle drive is a component of an angling plate in the form of a combi-angling plate.

Claims

1. A mobile crane with a main jib luffably mounted thereon and able to be raised via a luffing cylinder, and with a main jib extension releasably connected to a main jib head of the main jib via upper and lower bolts, the main jib extension, starting from a basic position, is able to be angled about a luffing axis relative to the main jib by an angling drive, wherein the angling drive is a component of a combi-angling plate which delimits a maximum angling angle in a mechanically adjustable manner, and wherein the angling drive engages on a foot of the main jib extension and the main jib head and the combi-angling plate comprises a sliding plate, a guiding plate and the angling drive, and wherein the combi-angling plate can be modified in length via the angling drive and the angling drive drivingly engages on the one hand on the sliding plate and on the other hand on the guiding plate, and wherein the sliding plate can be displaced in a length-modifiable manner relative to the guiding plate via the angling drive, wherein the combi-angling plate on the one hand engages on the main jib head and on the other hand on the main jib extension, wherein the sliding plate is displaceably guided in the guiding plate and the angling drive is disposed in the guiding plate.

2. The mobile crane as claimed in claim 1, wherein the angling drive is releasably fastened to the sliding plate.

3. The mobile crane as claimed in claim 2, via a stop bolt, a maximum displacement of the sliding plate relative to the guiding plate can be delimited.

4. The mobile crane as claimed in claim 3, wherein the luffing axis is formed in the region of the top chord of the main jib extension or of the bottom chord of the main jib extension and wherein the combi-angling plate is disposed in the region of the bottom chord of the main jib extension or of the top chord of the main jib extension.

5. The mobile crane as claimed in claim 4, wherein the angling drive is designed such that the main jib extension can be lifted and lowered in a pivoting manner about the luffing axis against the effect of the gravitational force of the main jib extension.

6. The mobile crane as claimed in claim 5, wherein the angling drive is designed as a hydraulic cylinder with a housing and a rod.

7. The mobile crane as claimed in claim 6, wherein two combi-angling plates are disposed in parallel and spaced apart from one another and the two combi-angling plates are preferably disposed in corner regions of the main jib extension.

8. The mobile crane as claimed in claim 7, wherein the combi-angling plate replaces a part of the top chord or of the bottom chord of the main jib extension in the region of the foot of the main jib extension.

9. The mobile crane as claimed in claim 8, wherein the sliding plate is pivotably mounted on the main jib head, the guiding plate is pivotably mounted on the main jib extension and by an insertable stop bolt a maximum displacement of the sliding plate in the guiding plate can be delimited.

10. The mobile crane as claimed in claim 1, via a stop bolt, a maximum displacement of the sliding plate relative to the guiding plate can be delimited.

11. The mobile crane as claimed in claim 1, wherein the luffing axis is formed in the region of the top chord of the main jib extension or of the bottom chord of the main jib extension and wherein the combi-angling plate is disposed in the region of the bottom chord of the main jib extension or of the top chord of the main jib extension.

12. The mobile crane as claimed in claim 1, wherein the angling drive is designed such that the main jib extension can be lifted and lowered in a pivoting manner about the luffing axis against the effect of the gravitational force of the main jib extension.

13. The mobile crane as claimed in claim 1, wherein the angling drive is designed as a hydraulic cylinder with a housing and a rod.

14. The mobile crane as claimed in claim 1, wherein two combi-angling plates are disposed in parallel and spaced apart from one another and the two combi-angling plates are preferably disposed in corner regions of the main jib extension.

15. The mobile crane as claimed in claim 1, wherein the combi-angling plate replaces a part of the top chord or of the bottom chord of the main jib extension in the region of the foot of the main jib extension.

16. The mobile crane as claimed in claim 1, wherein the sliding plate is pivotably mounted on the main jib head, the guiding plate is pivotably mounted on the main jib extension and by an insertable stop bolt a maximum displacement of the sliding plate in the guiding plate can be delimited.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a side view of a main jib extension in a basic position on a main jib;

(2) FIG. 2 is a detailed view of FIG. 1 from the region where the main jib extension is coupled onto the main jib;

(3) FIG. 3 shows an exploded view of a combi-angling plate of FIG. 2;

(4) FIG. 4a shows a detailed view of a combi-angling plate in the position shown in FIG. 1;

(5) FIG. 4b shows a view of FIG. 4a with a sliding plate and guiding plate next to each other;

(6) FIG. 5 shows the main jib of FIG. 1 with the main jib extension in a 15 position;

(7) FIG. 6a shows a detailed view of a combi-angling plate in the position shown in FIG. 5;

(8) FIG. 6b shows a side view of FIG. 6a with a sliding plate and guiding plate next to each other;

(9) FIG. 7 shows the main jib of FIG. 1 with the main jib extension in a 40 position;

(10) FIG. 8a shows a detailed view of a combi-angling plate in the position shown in FIG. 7; and

(11) FIG. 8b shows a side view of FIG. 8a with a sliding plate and guiding plate next to each other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) FIG. 1 illustrates a side view of a main jib extension 1 in a basic position on a main jib 2. The main jib 2 is designed as a telescopic jib with a basic box 2b and corresponding telescopic sections 2c. At the free end of the innermost telescopic section 2c a main jib head 2a is provided. The main jib 2 is a component of a telescopic crane, not illustrated, and is, in a conventional manner, able to be raised via a hydraulic luffing cylinder 7 which is supported on a superstructure 8 of the telescopic crane. The superstructure 8 is indicated in FIG. 1 only by a frame part thereof. FIG. 1 shows the main jib extension 1 and the main jib 2 in a so-called stored position in which the main jib extension 1 is orientated with its longitudinal direction v and the main jib 2 is orientated with its longitudinal direction h substantially horizontally. A so-called luffing angle a of the main jib 2 relative to the superstructure 8 therefore amounts to 0 in the stored position. The luffing angle a describes the raising of the main jib 2 relative to the superstructure 8. The main jib extension 1 is releasable fastened to the main jib head 2a via a bolt connection. The main jib extension 1 can be used temporarily or continuously with the telescopic crane in order to reach an even greater overall jib length exceeding the greatest jib length of the main jib 2.

(13) This main jib extension 1 is divided into a basic jib 1 designed as a girder mast and conventionally being of latticework tubular construction, and a tip 1b adjoining same and designed as a box jib. In FIG. 1, the main jib 2 and the main jib extension 1 are located in a 0 position or basic position in which the longitudinal direction h of the main jib 1 and the longitudinal direction v of the main jib extension 1 are aligned with one another or extend in parallel with one another. A corresponding angling angle b is thus 0. The main jib extension 1 is luffable about a luffing axis w with respect to the main jib 2, said spindle being formed from a lower roller head spindle. In this basic position, the main jib extension 1 is spaced apart from a ground surface 3 with first to third ground levels 3a to 3c and is therefore supported by the main jib 2 via the bolt connections in corresponding bolting points A, B, C and D (see FIG. 2) on the main jib head 2a.

(14) Such main jib extensions 1 are fundamentally constructed as modular design systems from individual main elements and can be fitted together depending on the required length or load capacity thereof. The individual main elements have dimensions suitable for transportation and in most cases are not carried along with the telescopic crane but are transported separately. When the spindle loads of telescopic crane and the construction size of the main jib extension 1 allow, the main jib extension 1 can be carried along if required. This would then be located in a transportation position laterally next to and in parallel with the main jib 2. A connection of the individual main elements to one another to form the desired main jib extension 1 is effected via bolt connections. The attachment to the main jib head 2a can be effected using the main elements or as a premounted unit or units.

(15) FIG. 2 is a detailed view of FIG. 1 from the region where the main jib extension 1 is coupled onto the main jib 2. The main jib extension 1 comprising, in a conventional manner, a rectangular cross-section, is fastened via four bolt connections disposed in the corner regions of the main jib extension 4 to bolting points A, B, C and D on the main jib 2 and possibly an additional bolting point G. The lower right bolt connection at the bolting point C is concealed by the main jib 2 but is designed identically to the bolt connection at bolting point D.

(16) The two lower bolt connections at bolting points C and D are designed as a so-called double shear bolt connection which in a corresponding manner is substantially made up of a fork plate 4a, a plate 4b and a bolt 4c. The fork plate 4a with its two opposing bores for the bolt 4c is fastened at each of the two bolting points C and D to a foot 1c of the main jib extension 1 and as an extension of the bottom chord 1e of the main jib extension 1. In this case the bores in the fork plate 4a are vertically orientated when the main jib extension 1 is horizontal. The plate 4b is fastened to the main jib head 2a via a lower roller head spindle 9a. When the main jib head 2a is orientated horizontally, the lower roller head spindle 9a is orientated horizontally and transversely to the longitudinal direction of the main jib 2 and is rotatably mounted in the main jib head 2a. In a corresponding manner, the plate 4b is in each case also rotatable about the horizontal lower roller head spindle 9a. The plate 4b also comprises a bore which is aligned with the bores in the fork plate 4a when the main jib extension 1 is in the attached position. A bolt 4c is inserted into the bores in the plate 4b and the fork plate 4a in order to fasten the main jib extension 1 to the main jib head 2a in a corresponding manner.

(17) Instead of the lower roller head spindle 9a provided with this construction of the main jib 2, a spindle additionally provided for the attachment of the main jib extension 1 and being orientated and rotatable corresponding to the above-described roller head spindle 9a could also be provided. The plate 4b can also be fastened to the main jib head 2a directly and therefore in a non-rotatable manner. In order to achieve the luffability of the main jib extension 1 relative to the main jib 2, the bore for the bolts 4c in the plate 4b must then be orientated horizontally.

(18) In the region of the top chord 1b, the attachment of the main jib extension 1 at bolting points A and B is effected indirectly via two combi-angling plates 6 extending in parallel with and spaced apart from each other in the region of the corners of the main jib extension 1. The combi-angling plates 6 are connected to the foot 1c of the main jib extension 1 at their end remote from the main jib head 2a via further bolt connections at bolting points E and F. In a so-called 0 position with respect to the angling angle b each of the two combi-angling plates 6 has the function of a rigid rod with in each case a connecting bore 6r at the end facing the main jib 2 and a connecting bore 6s at the end facing the main jib extension. The combi-angling plates 6 extend with their longitudinal directions c substantially in parallel with the longitudinal direction v of the main jib extension 1. The bolt connections at the bolting points A and B are designed as a so-called double shear bolt connection. In this case, a fork plate 4a is located on the main jib head 2a and a plate 4b is formed by one end of the combi-angling plate 6 in the region of the connecting bore 6r. The fork plate 4a comprises two opposing bores for the bolts 4c. In this case the bolts in the fork plate 4a are horizontally orientated when the main jib extension 1 is horizontal. The plate 4b also comprises a bore which is aligned with the bores in the fork plate 4a when the main jib extension 1 is in the attached position. A bolt 4c is inserted into the bores in the plate 4b and the fork plate 4a in order to fasten the main jib extension 1 to the main jib head 2a in a corresponding manner.

(19) At the end opposite the main jib head 2a each of the combi-angling plates 6 is connected to the foot 1c of the main jib extension 1 via a further double shear bolt connection at bolting points E and F. Each of the two bolt connections is characterised by a fork plate 10a which is disposed on the foot 1c of the main jib extension 1 as an extension of the top chord 1d. The fork plate 10a is comparable to the fork plate 4a previously described in relation to the bottom chord 1e but the opposing bores of the fork plate 10a are not orientated vertically but horizontally. A plate 10b engaging into the fork plate 10a and likewise designed as a fork plate is disposed on the end of the combi-angling plate 6 facing the main jib extension 1. In a conventional manner, the fork plate 10a and the plate 10b are connected to one another via a bolt 10c which is horizontally orientated.

(20) Furthermore, FIG. 2 shows that the combi-angling plate 6 consists of a sliding plate 6b and a guiding plate 6d which are pushed one inside the other and can be displaced oppositely to one another. In this case, the angling drive 6j in the sliding plate 6b is disposed between two sliding plate parts 6b and 6b. As described above, the Figure shows the 0 position in which the sliding plate 6b and the guiding plate 6d are locked to one another via a locking bolt 6t and a stop bolt 6h.

(21) Since the combi-angling plates 6 are each integrated into the foot 1c of the main jib extension 1, the bolting points C, D, E and F are located with the lower and upper fork plates 10a in a connecting plane tilted out of a verticalas seen when the main jib extension 1 is orientated horizontallytowards the head if of the main jib extension 1. In other words, the top chords 1d at the foot 1c of the main jib extension 1 are shorter than the bottom chords 1e at the foot 1c of the main jib extension 1 and the upper fork plates 10a are set back with respect to the lower fork plates 10a. The foot 1c, thereby specially formed, of the main jib extension 1 can also be designed as a foot segment which can then be substantially adjoined by further cuboidal segments of the main jib extension 1.

(22) In relation to other functions of the main jib extension 1 apart from the above-described anglabilty it can be advantageous, in addition to the above-described bolting points A to F, to provide a further bolting point G which, in the region of the top chord 1d of the main jib extension 1, is disposed in a vertical plane with the bolting points C and D and on one of the two sides of the main jib extension 1. This additional bolting point G can then, depending on the side, serve as a vertical spindle with one of the bolting points C and D in order to be able to fold a main jib extension 1 into a transportation position in a parallel manner next to the main jib 2.

(23) In order to be able to angle the main jib extension 1 relative to the main jib head 2a or main jib 2, provision is made to pull the two upper locking bolts 6t at the bolting points A and B in the region of the top chord 1d of the main jib extension 1 or at the end facing the main jib head 2a and as an extension of the top chord 1d of the main jib extension 1 disposed combi-angling plates 6 [sic] so that the main jib extension 1 can be angled relative to the main jib 2 about the lower roller head spindle 9a in the region of the lower bolting points C and D in the region of the bottom chord 1e of the main jib extension 1 by the angling angle b. In addition, it may be necessary to pull a bolt 10c in an upper bolting point G on the right side of the main jib extension 1. This bolt 10c is required in order to be able to pivot the main jib extension 1 horizontally into a transportation position. The lower roller head spindle 9a therefore forms the luffing axis w. The angling angle b lies in a conventional manner in the range of 0 to 40. In order to be able to delimit the angling angle b or to be able to adjust angling angles to the conventional values of 20 and 40, the two length-modifiable combi-angling plates 6 are provided.

(24) FIG. 3 shows an exploded view of a combi-angling plate 6. The active combi-angling plate 6 consists substantially of a sliding plate 6b, a guiding plate 6d and an angling drive 6j. The sliding plate 6b, which at its end facing the main jib head 2a comprises the plate 4b with the connecting bore 6r, begins with a flat profile shape at this end and, after approximately one quarter of its length, widens in the shape of a box with two mutually parallel and spaced apart flat-profile-shaped lateral sliding plate parts 6b, 6b. This box-like design is provided to receive the angling drive 6j, designed as a hydraulic cylinder, therebetween. Each of these sliding plate parts 6b, 6b comprises, starting from the main jib head 2a, initially, a locking bore 6m for the 0 position of the main jib extension 1, spaced apart therefrom a bore-like first stop opening 6c for a 20 position of the main jib extension 1, and again spaced apart therefrom a second elongate hole-like stop opening 6c for a 40 position of the main jib extension 1. The stop openings 6c and 6c each comprise, at the side thereof facing the main jib extension 1, a semi-circular stop surface 6a, 6a for a stop bolt 6h. The right locking bore 6c, 6o for the 0 position of the main jib extension 1 also serves as a bore for the releasable fastening of the free end of a rod 6l of the angling drive 6j provided the angling drive 6j is required. The locking bolt 6t illustrated in FIG. 3 in relation to the sliding plate 6b is required only in the 0 position of the main jib extension 1, is removed for the angling to begin and can, after completed slight angling of the main jib extension 1, be inserted, for storage purposes, into the locking bore 6m provided that the guiding plate 6b is no longer located with its stop opening 6 in the region of the locking bore 6m.

(25) In addition to the sliding plate 6b a guiding plate 6d is also illustrated in which the sliding plate 6b is pushed and displaceably guided. In a corresponding manner, the guiding plate 6d is also designed in a box-like manner with a central right-angled guide opening 6f and mutually parallel and mutually spaced first and second guiding plate parts 6d and 6d. An elongate hole-like stop opening 6g is provided in the guiding plate parts 6d and 6d disposed in an opposing relationship. The stop opening 6g comprises, at the ends, opposing stop surfaces 6i, 6i, on which the stop bolts 6h or the locking bolts 6t are in the 0, 20 or 40 position.

(26) Furthermore, FIG. 3 illustrates the angling drive 6j in the form of a single hydraulic cylinder with a housing 6k and a rod 6l. At the free end of the rod 6l is fastened a connection element 6n with a bore in order, if required, to connect the hydraulic cylinder via a stop bolt 6h, if required, to the locking bore 6o of the sliding plate 6b. At the opposite end, the housing 6k of the hydraulic cylinder is connected to the bolt 10c jointly with the guiding plate 6d at the stop point E or F on the plate of the foot 1c of the main jib extension 1. The hydraulic cylinder can be attached e.g. to existing hydraulic circuits. The hydraulic circuit of a drawing cylinder for horizontal pivoting of an entrained main jib extension from a transportation position is fundamentally suited to this purpose.

(27) The angling drive 6j is dimensioned such that only the intrinsic weight of the main jib extension 1 can be angled up or down. Therefore, in the 0 position, the two combi-angling plates 6 form a part of the foot 1c of the main jib extension 1. As a result, the upper and lower bolting points A, B, C, D lie in a plane which extends vertically when the main jib extension 1 is orientated horizontally.

(28) FIG. 4a shows a detailed view of an assembled combi-angling plate 6 according to FIG. 2 in the locked 0 position. In the 0 position, the sliding plates 6b and the guiding plates 6d are fixed relative to the longitudinal direction c via a locking bolt 6t and a stop bolt 5h. The locking bolt 6t and the stop bolt 6h are inserted into the stop opening 6g and the locking bolt 6t lies against the front stop surface 6i and the stop bolt 6h lies against the rear stop surface 6i (see FIG. 3). Already in the 0 position, the stop bolt 6h can already be engaged with the connection element 6n on the rod 6l of the hydraulic cylinder so that the angling drive 6j is already drivingly connected to the combi-angling plate 6.

(29) FIG. 4b illustrates a view according to FIG. 4a, in which the sliding plate 6b and guiding plate 6d have been separated and are therefore illustrated next to one another. This view shows clearly that in the 0 position the right locking bolt 6t and the left stop bolt 6h extend through the stop opening 6g in the guiding plate 6d through the locking bores 6o, 6m.

(30) Angling of the main jib extension 1 located in the basic or 0 position according to FIG. 1 into a 40 position is explained with the aid of FIGS. 1 to 8, in particular FIGS. 5 to 8. In a first step, the angling drive 6j, which is fastened, with its housing 6k, to the fork plate 10b of the main jib extension 1, jointly with the guiding plate 6b via the bolts 10c, is connected to the sliding plate 6b provided that the angling drive 6j is not yet already connected thereto via the stop bolt 6h. For this purpose, the stop bolt 6h is pulled and the retracted angling drive 6j is extended until the bore in the connection element 6n is aligned with the locking bore 6o and the stop opening 6g. The stop bolt 6h is then inserted. This situation is illustrated in FIGS. 4a and 4b. The angling drive 6j is then actuated and the rods 6l of the hydraulic cylinder retracted so little that the sliding plates 6b are pulled relative to the guiding plates 6d in the direction of the main jib extension 1 and the distance between the bolting points A, B and E, F is reduced and the main jib extension 1 pivots slightly upwards over the lower roller head spindles 9a of the bolting points C, D, which are disposed in the region of the bottom chord 1e. In this way, the main jib extension 1 is lifted slightly so that the locking bolts 6t in the combi-angling plates 6 are relieved. The bolt 10c is also relieved at connection point G between the main jib extension 1 and the main jib head 2a which serves for pivoting into or out of the transportation position. This bolt 10c is also removed in the relieved 0 position so that it is not located within the subsequent force flow during load lifting. The now relieved locking bolts 6t and the bolt 10c at connection point G are then removed. The main jib extension 1 is now supported via the two lower bolts 4c in combination with the two combi-angling plates 6 on the main jib 1 and the angling drives 6j. The lower roller head spindle 9a therefore forms the luffing axis w for the angling of the main jib extension 1.

(31) In a next step the angling drives 6j are actuated again and the rods 6l of the hydraulic cylinders are slowly extended. In this way the sliding plates 6b are pushed in the direction of the main jib 2 relative to the guiding plates 6d so that the distance between the bolting points E, F and A, B is increased and the main jib extension 1 pivots over the lower roller head spindle 9e of the bolting points C, D about the angling angle b, said roller head spindle being disposed in the region of the bottom chord 1e. By this angling movement the head 1f of the main jib extension 1 pivots in the direction of the ground surface 3 until it contacts the ground surface 3.

(32) FIG. 5, which illustrates the main jib extension 1 according to FIG. 1 in a 15 position, shows the position described above in which the lowered head 1f is supported on the ground surface 3 but the angling drive 6j is still coupled. The luffing angle a of the main jib 2 continues to be 0.

(33) FIG. 6a shows a detailed view of a combi-angling plate 6 in the 15 position shown in FIG. 5. It shows that the rod 6l of the hydraulic cylinder is extended a long way and the connection element 6n continues to be connected via the stop bolt 6h to the sliding plate 6b.

(34) FIG. 6b illustrates a view according to FIG. 6a, in which the sliding plate 6b and guiding plate 6d have been separated and are therefore illustrated next to one another. This view shows clearly that in the 15 position the right locking bolt 6t is inserted only for storage purposes and has no function and the left stop bolt 6h extends through the stop opening 6g in the guiding plate 6d through the locking bore 6o and couples the angling drive 6j via the connection element 6n thereof.

(35) In a further step the angling drive 6j is now extended a little further, whereby the stop bolts 6h in the locking bores 6o are relieved and then pulled. The decoupled rods 6l of the angling drives 6j are then completely retracted and the stop bolts 6h are inserted through the stop opening 6g in the guiding plate 6d into the stop opening 6c of the sliding plate 6b for the 20 position or into the stop opening 6c of the sliding plate 6b for the 40 position. In the present case, the stop opening 6c of the sliding plate 6b is selected for the 40 position. By luffing-up the main jib 2 about the luffing angle a the main jib extension 1 is now angled further and the tip 1f of the main jib extension 1 slides therethrough over the ground surface 3 in the direction of the main jib 2. By the luffing-up action the main jib extension 1 is further angled until the combi-angling plates 6 delimit the angling in the preselected position. At the time of delimitation of the angling movement in the 40 position by the combi-angling plates 6 the tip 1f still has contact with the ground surface 3. During further luffing-up of the main jib 1, the main jib extension 1 is then lifted from the ground surface 3 in the 40 position. This position, in which the main jib extension 1 is located in a 40 position relative to the main jib 2, is illustrated in FIG. 7. For the sake of clarity, the tip 1b of the main jib extension 1 is not shown therein.

(36) FIG. 8a shows a detailed view of a combi-angling plate 6 in the position shown in FIG. 7. The stop bolt 6h lies in the stop opening 6g on the right stop surface 6i which faces the main jib head 2a. The stop bolt 6h also lies against the left stop surface 6a of the sliding plate 6b. In this way the maximum displaceability of the guiding plate 6d on the sliding plate 6b is delimited. This corresponds to an angling angle of 40.

(37) FIG. 8b illustrates a view according to FIG. 8a, in which the sliding plate 6b and guiding plate 6d have been separated and are therefore illustrated next to one another. This view clearly shows that the angling drive 6j is further decoupled since the connection element 6n is removed from the stop bolt 6h.

(38) Setting back or upwardly angling the main jib extension 1 takes place in the reverse order.

(39) Although in conjunction with the present exemplified embodiment, the main jib 2 is described as a telescopic jib and the main jib extension 1 as a lattice mast jib with a box tip, the invention can also be applied to other embodiments of main jibs 2 and main jib extensions 1. The main jib 2 can also be a lattice mast jib or a combination of a telescopic jib, lattice mast jib and/or box jib. For the main jib extension 1, lattice mast jibs or box jibs or combinations thereof are feasible.

(40) The use of an individual combi-angling plate 6 disposed centrally in relation to the width of the top chord 1d of the main jib extension 1 is feasible. Furthermore, the combi-angling plate 6 has thus far been described as a tension rod. An embodiment as a compression rod is also possible, as is an arrangement in the bottom chord region. It is also feasible for the luffing axis w then to be disposed in the region of the top chord 1d. The foot 1c of the main jib extension 1 is correspondingly chamfered, preferably in the form of an adapter in order to permit angling of the main jib extension 1 about the upper luffing axis w.