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 that is detachably connected to a main jib head of the main jib by means of 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 may be a component of an angling plate in the form of a combi-angling plate.

Claims

1. A mobile crane comprising a main jib which is mounted in a luffable manner thereon and can be raised by means of a luffing cylinder, and comprising: a main jib extension that is releasably connected to a main jib head of the main jib by upper and lower bolts, wherein the main jib extension, proceeding from a basic position after release of the upper or lower bolts, can be angled relative to the main jib about a luffing axis by an angling drive, wherein the angling drive engages a foot of the main jib extension, and a maximum angling angle is limited by an adjustable angling plate and the angling plate engages the foot of the main jib extension and the main jib head, and wherein the mobile crane further includes a combi-angling plate comprising the angling drive, wherein the angling drive engages the main jib head on the one hand and engages the main jib extension on the other hand, and wherein the combi-angling plate comprises a sliding plate, a guiding plate and the angling drive, the angling drive drivingly engages the sliding plate on the one hand and the guiding plate on the other hand and the sliding plate can be displaced relative to the guiding plate by the angling drive, and wherein the angling drive is releasably fastened to the sliding plate, wherein the sliding plate is pivotably mounted on the main jib head, the guiding plate is pivotably mounted on the main jib extension, the sliding plate is guided in the guiding plate and a maximum displacement of the sliding plate in the guiding plate can be limited by a stop bolt.

2. The mobile crane as claimed in claim 1, wherein the main jib extension, proceeding from a basic position after release of the upper bolts, can be angled about a luffing axis in the region of a bottom chord of the main jib extension by the angling drive, and the angling drive engages in the region of the top chord of the main jib extension.

3. The mobile crane as claimed in claim 2, wherein the angling drive is designed such that the main jib extension can be raised and lowered so as to pivot about the luffing axis against the effect of the gravitational force of the main jib extension.

4. The mobile crane as claimed in claim 3, wherein the luffing axis is formed in the region of the lower bolts.

5. The mobile crane as claimed in claim 4, wherein the angling drive is designed as a hydraulic cylinder having a housing and rod.

6. The mobile crane as claimed in claim 1, wherein the angling drive is designed such that the main jib extension can be raised and lowered so as to pivot about the luffing axis against the effect of the gravitational force of the main jib extension.

7. The mobile crane as claimed in claim 1, wherein the luffing axis is formed in the region of the lower bolts.

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

9. A method for angling a main jib extension relative to a main jib of a mobile crane, wherein the main jib is mounted in a luffable manner on the mobile crane and can be raised by a luffing cylinder with the main jib extension being releasably connected to a main jib head of the main jib by upper and lower bolts, wherein an angling drive engages a foot of the main jib extension and a maximum angling angle is limited by an adjustable angling plate and the angling plate engages the foot of the main jib extension and the main jib head, said method comprising: raising the main jib extension from a basic position relative to the main jib about a luffing axis as far as until the upper or lower bolts are relieved using the angling drive, wherein the mobile crane further comprises a combi-angling plate comprising the angling drive, and wherein the angling drive engages the main jib head on the one hand and engages the main jib extension on the other hand, and wherein the combi-angling plate comprises a sliding plate, a guiding plate and the angling drive, the angling drive drivingly engages the sliding plate on the one hand and the guiding plate on the other hand, and wherein the sliding plate can be displaced relative to the guiding plate by the angling drive, and wherein the angling drive is releasably fastened to the sliding plate, wherein the sliding plate is pivotably mounted on the main jib head, wherein the guiding plate is pivotably mounted on the main jib extension, wherein the sliding plate is guided in the guiding plate and a maximum displacement of the sliding plate in the guiding plate can be limited by a stop bolt; removing the upper or lower bolts; inserting at least one combi-angling plate between the main jib head and a top chord or bottom chord of the main jib extension, wherein said inserting may be previously performed; lowering the main jib extension using the angling drive for as long as until the maximum angular position is reached or a head of the main jib extension comes to rest on a ground; drivingly separating the angling drive from the combi-angling plate; and raising the main jib if the maximum angular position is not yet reached in order to angle the main jib extension until the desired angling angle is achieved.

10. The method as claimed in claim 9, wherein said raising the main jib extension from a basic position comprises raising the main jib extension relative to the main jib about a luffing axis as far as until the upper bolts are relieved, and wherein said removing the upper or lower bolts comprises removing the upper bolts, and wherein said inserting at least one combi-angling plate comprises inserting at least one combi-angling plate between the main jib head and a top chord of the main jib extension.

11. The method as claimed in claim 10, wherein the main jib extension, proceeding from a basic position after release of the upper bolts, can be angled about a luffing axis in the region of a bottom chord of the main jib extension by the angling drive, and the angling drive engages in the region of the top chord of the main jib extension.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 2 shows a detailed view of FIG. 1 from the region where the main jib extension is coupled to 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 side view of FIG. 4a;

(6) FIG. 5 shows a sectional view of FIG. 4b taken along section line B-B;

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

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

(9) FIG. 7b shows a side view of FIG. 7a;

(10) FIG. 8 shows the main jib of FIG. 1 with the main jib extension in a 40 position;

(11) FIG. 9a shows a detailed view of a combi-angling plate in the position shown in FIG. 8;

(12) FIG. 9b shows a side view of FIG. 9a;

(13) FIG. 10 shows an exploded view of a combi-angling plate in an alternative embodiment;

(14) FIG. 11a shows a detailed view of an assembled combi-angling plate shown in FIG. 10; and

(15) FIG. 11b shows a side view of FIG. 11a.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(16) 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 comprising a basic box 2b and corresponding telescopic sections 2c. A main jib head 2a is provided at the free end of the innermost telescopic section 2c. The main jib 2 is a component of telescopic crane, not illustrated, and typically can be raised by means of a hydraulic luffing cylinder 7 which is supported on a superstructure 8 of the telescopic crane. In FIG. 1, the superstructure 8 is indicated only by a frame part thereof. In FIG. 1, the main jib extension 1 and the main jib 2 are shown in a so-called stored position in which the main jib extension 1 with its longitudinal direction v and the main jib 2 with its longitudinal direction h are oriented substantially horizontally. Therefore, a so-called luffing angle a of the main jib 2 relative to the superstructure 8 is 0 in the stored position. The raising of the main jib 2 relative to the superstructure 8 is described by the luffing angle a. The main jib extension 1 is releasably fastened to the main jib head 2a by means of a bolt connection. The main jib extension 1 can be used temporarily or continuously with the telescopic crane in order to achieve an even greater total length of the jib which goes beyond the largest jib length of the main jib 2.

(17) This main jib extension 1 is divided into a basic jib 1a which is designed as a lattice mast and typically has a truss pipe construction, and a tip 1b which adjoins said basic jib and is 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 2 and the longitudinal direction v of the main jib extension 2 are aligned with one another or extend in parallel with one another. A corresponding angling angle b is therefore 0. The main jib extension 1 can be luffed with respect to the main jib 2 about a luffing axis w which is formed by a lower rolling head spindle. In this basic position, the main jib extension 1 is spaced apart from a ground 3 having first to third ground levels 3a to 3c and is thus supported on the main jib head 2a by the main jib 2 via the bolt connections in corresponding bolting locations A, B, C and D (see FIG. 2).

(18) Basically, such main jib extensions 1 are constructed as modular systems from individual main elements and can be assembled depending upon the requirement of the length or load-bearing capacity thereof. The individual main elements have dimensions allowing transportation and in most cases are not also carried with the telescopic crane but instead are transported separately. If the axle loads of the telescopic crane and the installation size of the main jib extension 1 allow, the main jib extension 1 can also be carried if required. This would then be located in a transport position laterally next to and in parallel with the main jib 2. The individual main elements are connected to one another by means of bolt connections to form the desired main jib extension 1. The attachment to the main jib head 2a can be effected using main elements or as a preassembled unit or units.

(19) FIG. 2 shows a detailed view of FIG. 1 from the region where the main jib extension 1 is coupled to the main jib 2. The main jib extension 1 which typically has a rectangular cross-section is fastened to the main jib 2 by means of four bolt connections, which are arranged in the corner regions of the main jib extension 4, at bolting points A, B, C and D. The lower right bolt connection at the bolting point C is concealed by the main jib 2 but is identical to the bolt connection at the bolting point D. Each of the four bolt connections is designed as a so-called double-shear bolt connection which is correspondingly constructed substantially from a fork plate 4a, a plate 4b and a bolt 4c. The fork plate 4a with its two opposite bores for the bolt 4c is fastened in each case in the four bolting points A to D to the foot is of the main jib extension 1 and in extension of the main jib extension 1. In this case, the bores in the fork plate 4a are oriented vertically when the main jib extension 1 is horizontal. The plate 4b is fastened to the main jib head 2a by means of a spindle 4d. When the main jib head 2a is oriented horizontally, the spindle 4d is oriented 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, each plate 4b is also rotatable about the horizontal spindle 4d. The plate 4b also has a bore which is aligned with the bores of the fork plate 4a. A bolt 4c is inserted into the bores of 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.

(20) 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 withdraw the two upper bolts 4c at the bolting points A and B in the region of a top chord 1d of the main jib extension 1 so that the main jib extension 1 can be angled relative to the main jib 2 about the lower spindle 4d in the region of the lower bolting points C and D in the region of a bottom chord 1e of the main jib extension 1 about the angling angle b. The lower spindle 4d thus forms the luffing axis w. Instead of the spindle 4d, the bolts 4c could also be used if they were aligned horizontally. The angling angle b is typically in the range of 0 to 40. In order to limit the angling angle b or to be able to set it to the typical angling angle values of 20 and 40, two so-called angling plates 5 are provided, one of which is designed as an active combi-angling plate 6. The angling plate 5 and the combi-angling plate 6 extend in the region of the longitudinal sides of the top chord 1d of the main jib extension 1 and in parallel with one another.

(21) The passive angling plate 5, by means of which a displacement path and therefore the angling angle b can be manually limited by means of a stop surface 5a, consists substantially of a sliding plate 5b having a long hole-shaped guiding opening 5c, at which a guiding plate 5d can be guided in the longitudinal direction c along a sliding plate 5b. The sliding plate 5b is designed as an elongated flat profile having the stop opening 5c and extends substantially in parallel with the longitudinal direction v of the main jib extension 1. At an end facing the main jib head 2a, the sliding plate 5b has a bore, via which the sliding plate 5b is releasably fastened to the main jib head 2a at the bolting point E by means of a bolt 5e. The bolt 5e is oriented with its longitudinal extension in parallel with the spindle 4d. Slid onto the sliding plate 5b is the guiding plate 5d which for this purpose has a closed rectangular cross-section with a guiding opening 5f (see FIG. 5), into which the sliding plate 5b is inserted and displaceably guided. The guiding plate 5d per se is releasably fastened to the basic jib 1a of the main jib extension 1 at an end facing the main jib head 2a by means of a further bolt 5i in a bolting point G. The bolt 5i is oriented with its longitudinal extension in parallel with the spindle 4d. In this case, the bolt 5i is also guided through the stop opening 5c of the sliding plate 5b. In order to limit a displacement of the guiding plate 5d on the sliding plate 5b, two stop bores 5g which are continuous and spaced apart from one another in the longitudinal direction of the guiding plate 5d are arranged in the side parts of the guiding plate 5d. A first one of the two stop bores 5g serves to limit the angling angle b to 20 and a second one of the stop bores serves to limit the angling angle to 40. The stop bores 5g for 40 are accordingly arranged closer to the main jib head 2a in order to permit a larger displacement path. Depending upon the desired angling angle b, the respective stop bore 5g has a stop bolt 5h inserted therein which then extends through the two opposite stop bores 5g and the stop opening 5c located therebetween. In FIG. 2, the stop bolt 5h is inserted into the second one of the two stop bores 5g which limits the angling angle b to 40. The stop bolt 5h is guided next to the bolt 5i in the stop opening 5c. The bolt 5i would only come into contact with the opposite stop surface 5a of the stop opening 5c if no stop bolt 5h is inserted. The second one of the two stop openings 5g is free.

(22) The active combi-angling plate 6 is comparable in terms of the structure of the manual part with the above-described passive angling plate 5 and correspondingly has a stop surface 6a, a sliding plate 6b, a stop opening 6c, a guiding plate 6d, a bolt 6e, a guiding opening 6f, a stop bore 6g, a stop bolt 6h which corresponds to the stop bolt 5h and is also defined as a bolt 6p, and a bolt 6i. In the exemplified embodiment, the stop bolt 6h and the bolt 6p are the same and are provided with different terms and reference signs only in relation to their insertion location. Two bolts can also be provided next to one another but the function of the active combi-angling plate 6 does not provide a simultaneous use of the stop bolt 6h and bolt 6p which means that only one bolt can be provided for this purpose. The bolt 6e is releasably fastened to the main jib head 2a in a bolting point F and the bolt 6i is releasably fastened thereto at a bolting point H. The stop bolt 6h is not inserted in the basic position with the angling angle b of 0.

(23) Compared with the passive angling plate 5, the active combi-angling plate 6 is supplemented by a drive 6j in order to be able to actively displace the guiding plate 6d relative to the sliding plate 6b. For this purpose, the sliding plate 6d is provided, at its end opposite the main jib head 2a, with an angle bracket 6m, at which the angling drive 6j consisting of two hydraulic cylinders extending mutually in parallel and having housings 6k and a rod 6l are connected on the housing side. The hydraulic cylinders extend in the c longitudinal direction of the angling plate 5 or combi-angling plate 6. In order to connect the angling drive 6j or the hydraulic cylinders extending mutually in parallel and having its rods 6l to the sliding plate 6b of the combi-angling plate 6, the sliding plate 6 is extended with respect to the passive angling plate 5 by a rod part 6n in order to form an abutment for the angling drive 6j. Arranged at the end of the rod part 6n opposite the main jib head 2a is a bore 6o (see FIG. 3) in order to fasten a coupling part 6q via a further bolt 6p, the rods 6l of the hydraulic cylinders or angling drives 6j being mounted at said coupling part. The hydraulic cylinders can be connected e.g. to existing hydraulic circuits. Basically, the hydraulic circuit of a cylinder used for horizontally pivoting an entrained main jib extension out of a transport position is suitable for this purpose.

(24) The angling drive 6j is dimensioned such that only the empty weight of the main jib extension 1 can be angled down or up.

(25) FIG. 3 shows an exploded view of a combi-angling plate of FIG. 2. It can be seen that the coupling part 6q has a total of three bores in order to receive the bolt 6p and the ends of the rods 6l of the angling drive 6j and therefore to divert the force between the sliding plate 6b and the guiding plate 6d. FIG. 3 also illustrates the stop bolt 6h.

(26) FIG. 4a illustrates a detailed view of a combi-angling plate 6 in the position shown in FIG. 1. It can be seen that the angling drive 6j is extended, i.e. the rod 6l is moved out of the housing 6k by the distance of an extension path d. This extension path d corresponds to the basic position, illustrated in FIG. 1, between the main jib extension 1 and the main jib 2. The angling drive 6j can be extended even further in order to reduce the spaced interval between the bolting points G, H and E, F. This then results in the upper bolts 4c at the bolting points A, B being relieved. Moreover, the angling drive 6j is coupled to the sliding plate 6b because the bolt 6p is inserted.

(27) FIG. 4b shows a side view of FIG. 4a with the extension path d indicated.

(28) FIG. 5 illustrates a sectional view of FIG. 4b taken along section line B-B. It can be seen that the guiding plate 6d has a rectangular cross-section having a central guiding opening 6f, in which the sliding plate 6b with its stop opening 6c is guided.

(29) The angling of the main jib extension 1, which is located in the basic position shown in FIG. 1, to a 40 position will be explained hereinafter with reference to FIGS. 1 to 9, in particular FIGS. 6 to 9. In a first step, the angling plate 5 and the combi-angling plate 6 are fastened to the main jib head 2a in the bolting points E and F by means of the bolts 5e and 6e. Then, the angling drive 6j is actuated and the rods 6l of the hydraulic cylinders are extended until the sliding plate 6b is withdrawn relative to the guiding plate 6d in the direction of the main jib extension 1 by means of the coupling part 6q so that the spaced interval between the bolting points G, H and E, F is reduced and the main jib extension 1 pivots slightly upwards via the spindles 4d of the bolting points C, D, which spindles are arranged in the region of the bottom chord 1d. As a result, the main jib extension 1 is raised slightly so that the upper bolts 4c on the top chord 1d of the main jib extension 1 are relieved in the bolting points A, B. The now relieved bolts 4c are then removed. The main jib extension 1 is now supported on the main jib 2 by means of the two lower bolts 4c in combination with the combi-angling plate 6. The two lower bolts 4c or the spindle 4d which is also a rolling head spindle thus form the luffing axis w for the purpose of angling the main jib extension 1.

(30) In a next step, the angling drive 6j is again actuated and the rods 6l of the hydraulic cylinders are slowly retracted. As a result, the sliding plate 6b is slid relative to the guiding plate 6d in the direction of the main jib 2 via the coupling part 6q so that the spaced interval between the bolting points G, H and E, F is increased and the main jib extension 1 pivots about the angling angle b via the spindle 4d of the bolting points C, D arranged in the region of the bottom chord 1d. By reason of this angling movement, the head 1f of the main jib extension 1 is lowered in the direction of the ground 3 until it contacts the ground 3. The angling drive 6j is then retracted slightly further, whereby the bolt 6p in the bore 6o is relieved and is then transferred as a stop bolt 6h to the stop bore 6g. This has the advantage that, during the setting-up procedure, it is not forgotten to decouple the angling drive 6j and the angling drive is no longer involved in the main flow of forces when a load is being lifted. The desired maximum displacement path is also set at the angling plate 5 previously or at the latest at the present time in order to permit or limit the angling of the main jib extension 1 to the 20 position or 40 position.

(31) FIG. 6, showing the main jib extension 1 of FIG. 1 in a 15 position, shows the previously described position in which the lowered head 1f is supported on the ground 3. The luffing angle a of the main jib 2 is still 0.

(32) FIG. 7a shows a detailed view of the combi-angling plate 6 in the 15 position shown in FIG. 6. It is shown that the rods 6l of the hydraulic cylinder are completely retracted and the coupling part 6q is still connected to the rod part 6n of the sliding plate 6b by means of the bolt 6p. Now, because the tip 1f is resting on the ground 3 the bolt 6p is withdrawn and therefore the angling drive 6j is released from the combi-angling plate 6 which therefore also becomes a passive angling plate.

(33) FIG. 7b shows a side view of FIG. 7a.

(34) In a further step, by luffing the main jib 2 about the luffing angle a the main jib extension 1 is angled further and the tip 1f of the main jib extension 1 slides therethrough across the ground 3 in the direction of the main jib 2. By means of the luffing action, the main jib extension 1 is angled further for as long as until the angling plate 5 and the combi-angling plate 6 limit the angling in a preselected position. At the point in time the angling movement is limited in the 40 position by the angling plate 5 and the combi-angling plate 6, the tip 1f is still just about in contact with the ground 3. During further luffing of the main jib 2, the main jib extension 1 lifts from the ground 3 in the 40 position. This position, in which the main jib extension 1 is located in a 40 position with respect to the main jib 2, is illustrated in FIG. 8. For reasons of clarity, the tip 1b of the main jib extension 1 is not shown therein.

(35) FIG. 9a illustrates a detailed view of a combi-angling plate 6 in the position shown in FIG. 8. The stop bolt 6h is inserted in the stop bore 6g which faces the main jib head 2a in order thus to limit the maximum displacement possibility of the guide plate 6d on the sliding plate 6b. The stop bolt 6h lies against the stop surface 6a at the end of the stop opening 6c. Since the stop bolt 6h is inserted into the stop bore 6g which is closer to the main jib head 2a, the angling angle b is limited to 40. Moreover, the angling drive 6j is still decoupled because the bolt 6p is not inserted.

(36) FIG. 9b shows a side view of FIG. 9a.

(37) Back-fitting or angling-up the main jib extension 1 is performed in the reverse sequence.

(38) FIG. 10 illustrates an exploded view of a combi-angling plate 6 in an alternative embodiment which is currently preferred. The active combi-angling plate 6 is comparable in design to the previously described active combi-angling plate 6 and correspondingly has a sliding plate 6b, a guiding plate 6d and an angling drive 6j.

(39) The substantial difference in this alternative sliding plate 6b compared with the previously described sliding plate 6b is that this sliding plate 6b is not flat profile-shaped over its entire length but instead is formed, at least in the region of the stop opening 6c and the bore 6o, from two flat profile-shaped sliding plate parts 6b, 6b which extend in parallel and spaced apart from one another in order to receive therebetween the angling drive 6j which is designed as a hydraulic cylinder. The sliding plate 6b also has, in addition to the stop opening 6c, a bore 6o in the region of its centre in order to releasably connect the rod 6l of the angling drive 6j to the sliding plate 6b by means of the bolt 6p. This bore 6o is also used as a stop surface 6a for the stop bolt 6h or bolt 6p in the 20 position. The further bolt which is shown in FIG. 10 but does not have a reference sign does not have any function. The associated bore can be used for storing bolts which are not being used at that time.

(40) The guiding plate 6d shown in FIG. 10 is comparable to the previously described guiding plate, wherein the guiding opening 6f is correspondingly wider in order to receive the wider sliding plate 6b. Instead of two stop bores 6g in the guiding plate 6d, only one long hole-shaped stop opening 6g is provided. In order to achieve the desired angling of the main jib extension in the 20 and 40 position, the sliding plate 6b has not only a stop opening 6c but also the additional bore 6o. The illustrated bolt 6p, 6h can be used either to connect the angling drive 6j to the sliding plate 6b or to limit the displacement of the guiding plate 6d along the sliding plate 6b.

(41) FIG. 10 also illustrates the angling drive 6j in the form of an individual hydraulic cylinder having a housing 6k and rod 6l. At the free end of the rod 6l, the hydraulic cylinder can be connected to the bore 6o of the sliding plate 6b by means of the bolt 6p as required. At the opposite end, the housing 6k of the hydraulic cylinder is connected together with the guiding plate 6d in the stop point H on a plate of the foot 1c of the main jib extension 1 to the bolt 6i. In contrast to the view in FIG. 2, the plate will be arranged further removed from the main jib head 2a because the flow of forces through the combi-angling plate 6 shown in FIG. 10 differs from the combi-angling plate 6 in FIG. 2.

(42) FIG. 11a shows a detailed view of an assembled combi-angling plate 6 shown in FIG. 10. It can be seen that the angling drive 6j is arranged in the sliding plate 6b between the two sliding plate parts 6b and 6b. The sliding plate parts 6b and 6b are correspondingly guided in the guiding opening 6f of the guiding plate 6d. In accordance with the interleaved design, the sliding plate 6b can be displaced relative to the guiding plate 6d by means of the coupled angling drive 6j or, when the angling drive 6 is decoupled, by means of the empty weight of the main jib extension 1.

(43) FIG. 11b shows a side view of FIG. 11a.

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

(45) Furthermore, the exemplified embodiment relates to the use of an angling plate 5 and a combi-angling plate 6. Instead of providing one angling plate 5 and one combi-angling plate 6, it is also possible to provide two combi-angling plates 6 which are each arranged in the edge region of the top chord 1d of the main jib extension 1. This embodiment comprising two combi-angling plates 6 without an angling plate 5 is preferred. The use of a single combi-angling plate 6 which is arranged centrally in relation to the width of the top chord 1d of the main jib extension 1 is also feasible. Furthermore, the combi-angling plate 6 has been described up to this point as a tension member. An embodiment as a compression member is also feasible as is the arrangement in the bottom chord region. It is also feasible that the luffing axis w is then arranged 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.