Mobile crane with lattice boom, lattice boom and method for assembling such a crane

Abstract

Mobile crane (10), in particular crawler crane, with a mobile undercarriage (12), a superstructure (14) rotatably mounted on the undercarriage (12), and a lattice boom (20) pivotally mounted on the superstructure in a vertical luffing plane via a pivot point, the boom comprising a first boom section (21) and a second boom section (22), wherein the first boom section (21) has two parallel first strands (24) of interconnected first lattice sections (26) which are connected to each other at their lower ends via a lower crossbeam (28) and are connected to the pivot point (23) and are connected to each other at their upper ends via an upper crossbeam (30), and wherein the second boom section (22) has a single second strand (34) of interconnected second lattice sections (36) which is connected to the upper crossbeam (30) and is connected at its upper,The second boom section (22) has a head piece (40) at the end opposite the upper crossbeam (30), characterized in that the second boom section (22) is slidably mounted on or in the first boom section (21) and can be detachably locked to it, and that the second boom section (22) has a foot piece (38) at the lower end of the second strand (34) opposite the head piece (40), which is arranged between the lower crossbeam (28) and the upper crossbeam (30) in every position of the second boom section (22) and is preferably connected to at least one, and more preferably to all, first strands (24) via guide means, in particular rollers (39) and / or sliding surfaces.

Description

[0001] The present invention relates to a mobile crane, in particular a crawler crane, with a lattice boom according to the preamble of claim 1, a lattice boom for such a crane and methods for assembling the boom and for assuming a parking position.

[0002] Such cranes, also known as lattice boom cranes, are used, among other things, in the assembly of wind turbines, as they can also be used in difficult or impassable terrain.

[0003] In recent years, wind turbines have gradually become taller. As the number of wind turbines has grown, so has the demand for ever longer lattice booms. Previously, this was achieved through longer main booms. This has resulted in increased space requirements on the ground for assembling and disassembling the lattice boom, as well as increased demands on the crane size and available counterballast to erect the lattice boom.

[0004] The lattice boom is typically held by a luffing cable during luffing. Therefore, when lifting heavy loads with lattice booms (unlike unguyed telescopic booms), the decisive criterion for the tip loads in a steep position is not the deflection of the lattice boom in the luffing plane, but rather the lateral deformation perpendicular to the luffing plane. This problem is further exacerbated by the use of longer lattice booms. As the boom length increases, the permissible wind speed for an upright position without a load (parking position) also decreases.

[0005] To increase the lateral main boom stiffness of lattice boom cranes, various options for widening the boom are known. This can involve either widening the entire boom or only widening a specific, particularly lower, section. A solution using standardized lattice sections, which eliminates the need for special carrier equipment, is known from DE 10 2009 016 033 A1. In this case, two parallel strands of lattice sections are used in the lower section of the boom, which are connected to the pivot section via a lower crossbeam and to a single strand of additional lattice sections via an upper crossbeam. The respective strands can be constructed from identical or different lattice sections, which allows for the use of existing lattice sections.The widened lower section results in a lattice boom with increased lateral rigidity.

[0006] However, such structures require a lot of space on the ground for assembly and disassembly, as well as for luffing up, and also require a correspondingly large counterballast to erect the lattice boom. Such a solution also cannot avoid the aforementioned problem of a reduced maximum permissible wind speed in the parking position with a longer lattice boom.

[0007] Other solutions include a telescopic lattice boom, for example, by storing a smaller telescopic section within a larger section. However, while maintaining standard transport widths, such booms do not represent a solution for the wind turbine requirements described above, as the load-bearing capacity is too low due to a lack of lateral rigidity.

[0008] A mobile crane of this type is already known from WO 2021 / 123236 A1. Another crane of this type is described in US 2019 / 0218075 A1.

[0009] Another solution is known from WO 2019 / 050 404 A1, which discloses a lattice boom crane in which the lattice sections are inserted from below while the crane is in an erected position, similar to the climbing process of a tower crane. The lattice sections are installed vertically, which has the advantage of requiring minimal space, but also the disadvantage that the lattice sections must be installed vertically and vertically. Compared to conventional horizontal installation on the ground, this type of installation involves increased technical complexity and stricter occupational safety requirements.

[0010] Against this background, the present invention is based on the object of providing a mobile crane with a lattice boom that is suitable for use at great heights, such as for the installation of modern wind turbines, while requiring less space for boom assembly and a lower counterweight. Furthermore, the invention aims to increase the permissible wind speed in an upright parking position of the crane compared to a conventional design.

[0011] According to the invention, this object is achieved by a mobile crane having the features of claim 1. Advantageous embodiments of the invention emerge from the subclaims and the following description.

[0012] Accordingly, a mobile crane, in particular a crawler crane, is proposed, comprising a mobile undercarriage, a superstructure rotatably mounted on the undercarriage, and a lattice boom mounted on the superstructure via a pivot piece so that it can be tilted up and down about a horizontal axis or in a vertical luffing plane. The lattice boom comprises a first boom section and a second boom section.

[0013] The first boom section comprises two parallel strands (referred to herein as the first strands) of interconnected first lattice sections, which are connected to each other at their lower ends via a lower cross member and are connected to the pivot section. The latter includes the possibility of the lower cross member being mounted directly to the pivot section, although it is also conceivable for the lower cross member to be connected to the pivot section via one or more additional lattice sections. At their upper ends, opposite the lower cross member, the first strands are connected to each other via an upper cross member.

[0014] The second boom section comprises only a single strand (referred to herein as the second strand) of interconnected second lattice sections, which is connected to the upper crossbeam and has a headpiece at its upper end, opposite the pivot piece. A hoist rope for lifting and lowering a load can be routed over the headpiece.

[0015] The lattice boom, which is divided into different sections, has increased lateral rigidity due to the reinforced or widened first boom section and thus enables a higher load-bearing capacity.

[0016] According to the invention, however, unlike previous solutions, the second boom section is not permanently mounted on the first boom section. Instead, the second boom section is slidably mounted on or within the first boom section and releasably lockable to it. In particular, the second boom section is mounted telescopically within the first boom section.

[0017] Such a structure makes it possible to realize a lattice boom that combines the advantages of increased lateral rigidity of a multi-strand boom, as known, for example, from DE 10 2009 016 033 A1, with the small space requirement of an extendable boom.

[0018] This allows the lattice boom to be mounted on the ground and luffed up with a reduced length in the retracted state, thus requiring less space and less counterballast for the erection process. At the same time, the crane according to the invention can be placed in a parking position with the boom erected but retracted, thus increasing the maximum permissible wind speed for the parking position compared to a design with a rigid boom. Compared to a simple single-leg, telescopic boom, this also offers the advantage of increased load capacity and lateral rigidity, which enables the use of longer booms.

[0019] The first grid sections are preferably smaller or have a smaller cross-sectional area than the second grid sections, for example, as described in DE 10 2009 016 033 A1. The cross-sectional area of ​​a grid section is understood to be the area spanned by the longitudinal struts of the grid sections, i.e., the product of the depth and width of the grid sections. In this case, the first grid sections can advantageously be inserted into the second grid sections for transport. This can significantly reduce the transport volume.

[0020] However, it is also possible to use the same lattice pieces for the first and second strands, i.e., an embodiment in which the first and second lattice pieces have an identical structure. Even a reversed structure is conceivable in principle, in which the second lattice pieces have a smaller cross-sectional area than the first lattice pieces.

[0021] Advantageously, all of the first lattice sections are geometrically identical, i.e. they do not have any geometric differences in terms of their dimensions and / or connection areas. Furthermore, all of the second lattice sections are also advantageously geometrically identical, i.e. they do not have any geometric differences in terms of their dimensions and / or connection areas. As is usual with lattice mast booms, standard elements can therefore be used. In other designs, however, the individual lattice sections can be designed differently. For example, first or second lattice sections installed further down in the boom can have a higher load-bearing capacity than first or second lattice sections installed further up, in particular by using tubes with greater wall thicknesses for the lower lattice sections than for the upper lattice sections. Likewise, additional stiffeners can be provided if necessary.

[0022] In one possible embodiment, the longitudinal axes of the first strands are at the same distance from the longitudinal axis of the second strand. In particular, the first boom section is constructed symmetrically with respect to the luffing plane. This arrangement ensures that the two strands are subjected to essentially equal loading, thus optimally contributing to increasing lateral rigidity.

[0023] Preferably, the smallest distance between the first strands is greater than the width of the second lattice pieces of the second strand, so that the second strand fits between the first strands. Thus, the second strand can be inserted between the first strands.

[0024] The first lattice sections and the second lattice sections advantageously have several, in particular four, parallel longitudinal struts, wherein the longitudinal axis is defined in this case by running parallel to the longitudinal struts and being equidistant from all longitudinal struts. It can therefore also be referred to as the central axis of the lattice sections or the respective strand.

[0025] If more than two parallel first strands are used, the lattice boom advantageously has one or more groups of parallel strands whose longitudinal axes are at the same distance from the longitudinal axis of the second strand.

[0026] Preferably, however, the first boom part comprises exactly two first strands of first lattice pieces, i.e., a double-stranded or double-towered structure. In this case, the longitudinal axes of the first strands and the second strand preferably lie in a common plane, which in particular runs perpendicular to the luffing plane.

[0027] In another possible embodiment, the second strand of the second boom section can be retracted (or telescoped) between the first strands of the first boom section. The first strands have a gap dimensioned to accommodate the second strand. Preferably, the longitudinal axes of the first and second strands lie within a common plane, which is in particular perpendicular to the luffing plane.

[0028] In another possible embodiment, the second boom section is displaceably mounted in the upper cross member, preferably in a recess provided centrally in the upper cross member. The second boom section or second leg is thus guided through the upper cross member and is at least partially, but preferably completely, enclosed by it.

[0029] The upper cross member thus performs several functions. On the one hand, it connects the first strands of the first boom section to each other and to the second boom section, and on the other hand, it serves to guide and movably support the second boom section. In a third function, it can also serve to lock the first and second boom sections together, as described below using an exemplary embodiment.

[0030] According to the solution according to the invention, the second boom section has a foot piece at the lower end of the second leg, opposite the head piece. This foot piece is arranged between the lower cross member and the upper cross member in every position of the second boom section. In the fully retracted position of the second boom section, it is preferably closer to the lower cross member than to the upper cross member, and in the fully extended position, the situation is preferably reversed.

[0031] The base piece is preferably connected to at least one, particularly preferably to all, of the first strands via guide means, in particular rollers and / or sliding surfaces or rails, so that it can roll and / or slide along the first strand(s). These guide means preferably simultaneously serve to stably support and guide the second boom section on / in the first boom section.

[0032] In a further possible embodiment, connecting means are provided on the base section and on the upper cross member, by means of which the second boom section can be firmly locked or connected, in particular bolted, to the first boom section in its fully extended position. The locking or bolting creates a rigid connection between the two boom sections, in particular for positive force transmission during operation. In the locked state, retraction of the second boom section is not possible, and the two boom sections function as a single, extended lattice boom. The connecting means can, in particular, be bolt points for creating a fork-finger connection or means for creating a cantilevered, positive connection.

[0033] The aforementioned connection is preferably established by means of at least one actuator, for example, electric or hydraulic, since this process takes place in the erected boom state. The connection process by means of the at least one actuator is preferably monitored by a crane control system.

[0034] In another possible embodiment, the base piece has rollers and / or sliding surfaces over which it rolls and / or slides along at least one, preferably all, of the first strands. Alternatively or additionally, the upper cross member can have rollers and / or sliding surfaces over which the second strand rolls and / or slides along. Rollers and / or sliding surfaces are preferably provided on both the base piece and the upper cross member, thus ensuring stable and secure mounting of the second boom section.

[0035] In a further possible embodiment, the first boom part comprises a guide frame which is arranged between the upper cross member and the lower cross member, and in particular between the two first strands in the region of the upper cross member. The guide frame is therefore located in particular in front of or below the upper cross member (seen from the superstructure), but is preferably not connected to the upper cross member, but rather to the lattice sections of the first strands. The guide frame has rollers and / or sliding surfaces over which the second strand rolls and / or slides along. An embodiment is preferred in which the rollers and / or sliding surfaces are arranged only on or in the guide frame. In this embodiment, the cross member serves merely as the upper connecting element of the first strands and, if necessary, also for locking the second boom part to the main boom part.The guide frame preferably surrounds the second strand completely or at least partially, ie the second strand preferably runs through the guide frame.

[0036] In another possible embodiment, the foot piece is arranged between the first strands. Alternatively, the foot piece can completely or partially surround or enclose the first strands.

[0037] In a further possible embodiment, it is provided that the base piece is rigid, ie in the extended state the second boom part cannot be moved or pivoted by means of the base piece.

[0038] Alternatively, the base piece can comprise a guide part connected to the first strands via guide means, in particular rollers and / or sliding surfaces, as well as a pivoting part pivotally connected to the guide part and in particular lockable therewith, wherein the second boom part can be tilted relative to the first boom part in the fully extended position by pivoting the unlocked pivoting part in the rocker plane. During assembly and the retracted state, the two parts of the base piece that can be pivoted relative to one another are preferably locked together and therefore cannot be moved relative to one another. After the first and second boom parts have been connected and the two base piece parts have been unlocked, the second boom part can be tilted by means of an adjustable guying system, in particular a cable adjustment.

[0039] It is also conceivable that the base piece is not designed to be pivotable, but rather a special tiltable grid piece or adapter piece is built into the second strand.

[0040] In a further possible embodiment, the displacement of the second boom section relative to the first boom section, i.e. the retraction and extension of the second boom section, is carried out by means of a cable pulley system of the crane. For this purpose, at least one deflection pulley of the cable pulley system is preferably located at the base section and at the upper cross member, over which an extension cable can be guided or is guided. By actuating a winch, the extension cable guided over the deflection pulleys of the cable pulley system is retracted and the second boom section is thereby extended. For this purpose, the extension cable is preferably firmly attached to a fixed point on the head section. A conventional system known from the prior art can be used as the cable pulley system.

[0041] In another possible embodiment, a separate adjustment winch with an extension cable guided over the pulleys of the cable system is provided to operate the cable pulley system. The adjustment winch can be located, for example, on / in the lower crossbeam, the pivot piece, or another location on the superstructure. The extension cable is preferably attached to a fixed point on the headpiece.

[0042] Alternatively, an existing hoist winch with its hoist rope can be used to operate the cable pull system. This could, for example, be a hoist winch with a hoist rope for raising and lowering a hook block suspended from the headpiece, with the end of the hoist rope attached to the designated fixed point on the headpiece or on the hook block.

[0043] To achieve this, the hook block requires a hard stop on the headpiece, which can serve as a counterbearing for the hook block when the second boom section is extended. During extension, the safety shutdown of the hook lifting process, which normally occurs at this point, is deactivated, preferably by a suitably designed crane control system, so that the hook block can be pulled against the stop on the headpiece. It is also conceivable for the hook block to be lockable to the headpiece.

[0044] In another possible embodiment, the first boom section is guyed to the upper crossbeam, preferably via a superstructure guying frame and / or a derrick boom hinged to the superstructure. This guying is preferably adjustable, in particular via a cable adjustment, in order to be able to track or adjust the guy length when the lattice boom is luffing.

[0045] In another possible embodiment, the second boom section is not guyed. This makes the second boom section a flexible beam (similar to a telescopic boom) and thus has limited load-bearing capacity. However, the retraction and extension process is easier, and no separate guying is required, which can be adjusted to the boom length.

[0046] In an alternative possible embodiment, the second boom section is guyed via a guy frame mounted on the upper crossbeam. This increases the load-bearing capacity of the lattice boom in the extended state. Preferably, the additional guy frame is connected to the pivot piece or the lower crossbeam of the first boom section via one or more guy rods, i.e. via a fixed guy. Alternatively or additionally, the guy frame can be connected to the head section of the second boom section via an adjustable cable guy. The guy is adjustable in order to be able to adapt to the extended state of the second boom section and, if applicable, to an optionally provided inclination.

[0047] If the first and second boom sections are firmly connected or bolted to each other at the base and upper crossbeam, this connection represents a firm clamping between the first and second boom sections. The additionally attached rope adjustment creates a statically overdetermined system.

[0048] The advantage of this design is that the load-bearing capacity of the head section can be increased by pre-tensioning the second boom section. The operating principle is familiar, for example, from telescopic cranes. These use guy ropes on the back of the telescopic boom to increase the load-bearing capacity of the telescopic boom by pre-tensioning the bending beam. The pre-tension of the second boom section, appropriate for a particular load case, is preferably monitored and applied in a controlled or regulated manner by the crane control system. An adjustment winch in the linkage of the first boom section, known in the prior art from a lattice boom luffing device, can serve as the winch for the upper rope adjustment.

[0049] Alternatively, the second boom section can be guyed via an uppercarriage guying frame and / or a derrick boom hinged to the superstructure. The guying preferably comprises one or more guy rods and / or an adjustable cable guying system for adapting the guying length to the extended state of the second boom section. Preferably, the first boom section is connected to the superstructure guying frame and / or the derrick boom via a separate guying system. To avoid a statically overdetermined system, it can optionally be provided that the guying of the first boom section can be set to a force-free position, so that the entire boom is guyed only via the guying system connected to the second boom section.

[0050] The first boom part may have further connecting means to enable the second boom part to be locked and firmly connected to the first boom part in a position other than the fully extended position, for example in a fully retracted position, in a half-extended position, etc. For this purpose, the same connecting means are preferably used on the base of the second boom part.

[0051] The lattice pieces can be connected or bolted to each other, preferably using known fork-finger connections.

[0052] Preferably, the lower and upper cross members also have such interlocking fork-and-finger connecting elements at the corresponding positions to allow the first grid sections to be bolted to them. The base section also preferably has corresponding fork-and-finger connecting elements for bolting to a second grid section.

[0053] In one possible embodiment, the upper cross member can have connecting means for establishing a cantilevered, positive-locking connection with the second boom section. These can, in particular, be laterally mounted locking bolts that are preferably linearly movable by means of an actuator and can be moved inward. The base piece can have corresponding bolt receptacles into which the locking bolts can be inserted when the second boom section is fully extended in order to reversibly lock the first and second boom sections together. In principle, several such bolt receptacles could be arranged at different positions along the second strand to define different extension positions.

[0054] The length of the second boom section can essentially correspond to the length of the first boom section. It is also conceivable for the second boom section to be longer than the first boom section, so that the length of the lattice boom can be doubled or more when fully extended. Thus, even with the second boom section fully retracted, the latter would protrude from the first boom section by a certain length, for example, by a second lattice section or more.

[0055] The present invention further relates to a lattice boom for a crane according to the invention. This obviously results in the same advantages and properties as for the crane according to the invention, which is why a repeated description is omitted.

[0056] The present invention further relates to a method for assembling the lattice boom of a crane according to the invention, wherein the second boom part of the lattice boom comprises a base piece as described above. The method according to the invention comprises the following steps: - Mounting the first boom section on the superstructure of the crane, in particular in a substantially horizontal position, - Connecting the base piece to the first boom section, - Mounting the second strand on the base piece, - luffing of the lattice boom, preferably with the second boom section fully retracted, - Extending the second boom part in an erected state of the lattice boom, in particular by means of the cable pull system described above, and locking or connecting the second boom part to the first boom part, in particular by establishing a fixed connection between the base piece and the upper cross member.

[0057] The first boom section can be mounted on the superstructure by first attaching the lower crossbeam to the pivot piece and then assembling the first lattice sections of the first legs one after the other until the desired length of the first boom section is reached. The upper crossbeam can then be attached.

[0058] During the essentially horizontal assembly process of the lattice boom, it can be supported on the ground.

[0059] In one possible embodiment, the mounting of the second strand on the base piece comprises the following steps: - Connecting a second grid piece to the base piece, - Moving the assembled second lattice section including the base piece towards the pivot piece, for example by essentially the length of the second lattice section, in particular by a slightly shorter distance than the length of the second lattice section, - Connecting another second grid piece to the previously mounted second grid piece, - Moving the previously mounted second lattice sections including the base piece towards the pivot piece, for example by essentially the length of the second lattice section, in particular by a slightly shorter distance than the length of the second lattice section, - optionally repeat the two previous steps until the desired length of the second strand is reached, - Connect the headpiece to the last installed second grille piece.

[0060] The second lattice sections are bolted to the previous lattice section and preferably inserted piece by piece from the upper crossbeam into the first boom section. With each second lattice section inserted, the base section of the second boom section is moved one lattice section length toward the pivot piece or lower crossbeam of the first boom section.

[0061] After the second lattice sections have been assembled, the head piece is mounted on the extendable second boom section and preferably the hook block is reeved as known from the prior art.

[0062] The disassembly of the lattice boom according to the invention takes place in the reverse order.

[0063] The present invention further relates to a method for moving a crane according to the invention into a parking position with the lattice boom erected. In the erected state, the locking mechanism between the first and second boom sections is released and the second boom section is retracted toward the connecting piece in order to reduce the overall length of the lattice boom and thereby, in particular, to increase the maximum permissible wind speed. Retraction can be achieved using a cable pull system as described above by unwinding the extension cable.

[0064] Further features, details, and advantages of the invention will become apparent from the following exemplary embodiments explained with reference to the figures. They show: Fig. 1a-b: Side views of the crane according to the invention according to a first embodiment with extended and retracted lattice boom; Fig. 2: the crane according to the invention according to an embodiment in a plan view with the lattice boom retracted and horizontally aligned; Fig. 3a-b: a side view and a top view of the upper cross member of the first boom part according to a first embodiment; Fig. 4a-c: a side view and two top views of the upper cross member of the first boom part according to a second embodiment; Fig. 5: the lattice boom according to the invention according to an embodiment in a plan view with the second boom part retracted; Fig. 6a-c: three embodiments of the base of the second boom part, each in a frontal sectional view along the line AA in Fig. 5; Fig. 7a-b: frontal sectional views of the upper cross member according to an embodiment with and without the second strand mounted therein along the line BB in Fig. 5; Fig. 8a-b: frontal sectional views of the guide frame below the upper cross member according to an embodiment with and without the second strand mounted therein along the line BB in Fig. 5; Fig. 9a-b: a side view and a top view of the base piece of the second boom part according to a first embodiment; Fig. 10a-b: a side view and a top view of the base piece of the second boom part according to a second embodiment; Fig. 11a-b: Side views of the upper cross member according to a first embodiment before and after bolting to the base piece; Fig. 12a-c: Side views of the upper cross member according to a second embodiment before and after bolting to the base piece; Fig. 13: a perspective view of the upper cross member according to an embodiment before bolting to the base piece; Fig. 14: a side view of the headpiece with hook block according to an embodiment; Fig. 15a-b: Side views of the crane according to the invention according to a second embodiment with extended and retracted lattice boom; Fig. 15c: the crane according to Fig. 15b with horizontally aligned lattice boom in a side view; Fig. 16a-b: Side views of the crane according to the invention according to a third embodiment with extended and retracted lattice boom; Fig. 16c: the crane according to Fig. 16b with horizontally aligned lattice boom in a side view; Fig. 17a: a side view of the crane according to the invention according to a fourth embodiment with the lattice boom extended; and Fig. 17b: the crane according to Fig. 17a with horizontally aligned lattice boom and retracted second boom section in a side view.

[0065] The Fig. 1a and Fig. 1b shows a first embodiment of the crane 10 according to the invention in a side view. The crane 10, which is a crawler crane with a lattice boom 20 or a lattice boom crane, has an undercarriage 12 with crawler supports. A superstructure 14 is mounted on the undercarriage 12 so as to be rotatable about a vertical axis.

[0066] The lattice boom 20 is pivotally connected to the superstructure 14 about a horizontal axis, allowing it to be luffed up and down within a vertical luffing plane. The lattice boom 20 according to the invention is not rigid but telescopic in design, and comprises a lower, first boom section 21, which is pivotally connected to the superstructure 14 via a connecting piece 23. The first boom section 21 is guyed by means of an adjustable guying 17 via a derrick boom 16 pivotally mounted on the superstructure 14. The derrick boom 16 is connected to a derrick ballast 18 to provide the necessary counterweight for the main boom 20 and the load to be lifted, in addition to the superstructure ballast mounted on the superstructure 14.

[0067] The lattice boom 20 further comprises an upper, second boom section 22, which is mounted in a displaceable or telescopic manner in the first boom section 21 and can therefore be extended and retracted to change the overall length of the lattice boom 20. At the upper end of the second boom section 22 is a head piece 40, which can be a conventional mast tip. Fig. 1a shows the crane 10 with extended, the Fig. 1b the crane 10 with retracted boom 20.

[0068] The Fig. 2 shows the crane 10 with the lattice boom 20 retracted and horizontally aligned in a plan view, so that the structure of the first and second boom parts 21, 22 is more clearly visible.

[0069] In this exemplary embodiment, the first boom section 21 has a double-tower structure and comprises two first strands 24 of interconnected first lattice pieces 26, which are firmly connected to one another and to the pivot piece 23 via a lower cross member 28. At their upper ends (i.e., opposite the lower cross member 28), the first strands 24 are connected to one another via an upper cross member 30. The first strands 24 run parallel to one another in the longitudinal direction of the boom and are arranged at the same distance from the luffing plane or the centrally extending longitudinal axis of the overall boom 20. The first boom section 21 has a structure symmetrical to the luffing plane.

[0070] The second boom section 22 comprises only a single second strand 34 of interconnected second lattice pieces 36, which is slidably mounted in the upper cross member 30. At the lower end (facing the lower cross member 28), the second strand 34 is connected to a base piece 38, while the second strand 34 has the head piece 40 at the opposite, upper end, over which a hoist rope for lifting and lowering a load is guided.

[0071] The longitudinal axis of the second strand 34 preferably coincides with the luffing plane in plan view, so that the first strands 24 are at the same distance from the longitudinal axis of the second strand 34. All longitudinal axes are parallel to each other and to the extension direction of the lattice boom 20.

[0072] The second boom part 22 or the second strand 34 can be retracted into the space between the two first strands 24 (cf. Fig. 3).

[0073] The first lattice pieces 26 are preferably geometrically identical components that are bolted together to form the strands 24. The second lattice pieces 36 are also preferably geometrically identical components that are bolted together to form the second strand 34. The first lattice parts 26 therefore have, in particular, the same dimensions and connection areas. However, their design can vary considerably. For example, lattice pieces 26, 36 that are installed higher up can have a thinner wall thickness in the tubes used than those that are installed lower down in the boom 20. The first and second lattice elements 26, 36 preferably have a box-shaped structure with a rectangular cross-sectional area and each comprise four parallel longitudinal struts.

[0074] In the Fig. 3 and Fig. 4, the first grid pieces 26 have a smaller cross-sectional area than the second grid pieces 36 (in the Fig. 3 can be seen from the smaller width in plan view), ie smaller lattice pieces 26 are used for the first strands 24 than for the second strand 34. Of course, however, the same lattice pieces could also be used for the first and second strands 24, 34, ie the first and second lattice pieces 26, 36 have an identical structure.

[0075] The Fig. 3a-b and Fig. 4a-b each show the upper cross member 30 without the second boom part 22 in a side view ( Fig. 3a, Fig. 4a) and a top view ( Fig. 3b, Fig. 4b), whereby the first grid pieces 26 connected to the upper cross member 30 are also shown. Fig. 4c shows a sectional view through the upper cross member 30 and the first grid pieces 26, wherein the bolt-shaped connecting means 31 can be seen.

[0076] In the embodiments shown here, the upper cross member 30 has a trapezoidal structure in plan view and a rectangular profile in side view, although other shapes are of course also conceivable.

[0077] In the Fig. In the embodiment shown in Figures 3a-b, the upper cross member 30 has connecting means on the longer side of the trapezoid in the form of fork-finger connecting elements, as are also provided on the end faces of the first grid elements 26. The first grid elements 26 shown are bolted to the upper cross member 30 via these fork-finger connecting elements. The lower cross member 28 also has such fork-finger connecting elements and is bolted to the first grid elements 26 adjacent to the lower cross member 28. The first grid elements 26 are also bolted to one another via such fork-finger connecting elements.

[0078] In the Fig. 3a-b also shows the attachment point on the top side of the upper crossbeam 30 for the guying 17. Furthermore, in the embodiment shown here, the upper crossbeam 30 has, in contrast to the crane 10 of the Fig. 1a-b, another guy frame 70 is provided, over which the second boom section 22 is guyed. This will be discussed in more detail below. The guy frame 70 is attached centrally to the top of the upper cross member 30.

[0079] Furthermore, on the side of the upper cross member 30 facing the articulation piece 23, there are further connecting means 31 for establishing a bolting connection with the base piece 38, which has corresponding connecting means 37 on the side facing the upper cross member 30 (see Fig. 8a-b). By bolting the connecting elements 31, 37 in the fully extended state, the base section 38 and the upper cross member 30, and thus the first and second boom sections 21, 22, are firmly connected to one another and function as a common, rigid lattice boom 20 with an increased overall length.

[0080] In the Fig. In the embodiment shown in Figures 4a-c, the upper cross member 30 has a bore perpendicular to the sliding plane on both the right and left sides, with connecting means 31 located therein. The connecting means 31 are designed here as collinearly arranged locking bolts (see Figure 4a-c). Fig. 4c), which are moved linearly inward for locking with the base piece 38 of the second strand 34, in particular by means of an actuator each. Two or more than two locking bolts 31 can be provided. The base piece 38 of the second strand 34 has the matching connecting means 37 in the form of bores or bolt receptacles, which represent the counterpart to the connecting means 31 (see Fig. 10a). The base piece 38 is positively mounted or bolted in a floating manner by the interaction of the two connecting elements 31 and 37. The locking bolts 31 preferably have a circumferential bevel at the free end to facilitate insertion into the bolt receptacles 37 and to compensate for manufacturing tolerances.

[0081] In the Fig. 4a-c, a guide frame 75 is placed as a separate component below or adjacent to the cross member 30 (see Fig. 8a-b). The guide frame 75 is connected to the upper grid elements 26 of the first rod 24 and arranged between them. The function of this guide frame 75 will be discussed further below.

[0082] The lattice boom 20 is shown in a schematic plan view in the fully retracted state in the Fig. 5. The base piece 38 is located adjacent to the lower cross member 28, while the second strand 34 extends beyond the upper cross member 30—namely, essentially by a second lattice piece 36 (and the head piece 40). Of course, an even longer second strand 34 would also be conceivable. A shorter second strand 34 could also be provided, so that the base piece 38 is spaced from the lower cross member 28 in the fully retracted state.

[0083] The Fig. 6a-c show three different embodiments of the foot piece 38, each in a sectional view along the line AA in Fig. 5, wherein the cross sections of the first lattice pieces 26 of the first strands 24 and of a second lattice piece 36 of the second strand 34 are also shown.

[0084] In the first embodiment of the Fig. 6a, the base piece 38 is located between the first strands 24 and thus has a smaller width than the first boom part 21. This also corresponds to the Fig. 5 shown configuration of the foot piece 38. In the second embodiment of the Fig. 6b, the base piece 38 completely encloses the first grid pieces 26 of the first strands 24 and thus has a greater width than the two first strands 24 together. In the third embodiment of the Fig. 6c, the base piece 38 of the second rod 34 rests on each rod 24 of the first boom section 21 with only one roller 33 each. The rollers 33 of the base piece 38 are arranged at the top and sides, so that the base piece 38 rests on the lattice pieces 26 of the first strands 24 and rolls along them. The axes of rotation of the rollers 33 are particularly collinear.

[0085] In the embodiments shown here, the base piece 38 has rollers 39 on the sides, via which it is connected to the first strands 24 and rolls along them. The rollers 39, which are shown for the different embodiments in the Fig. 9a and Fig. 10a, serve simultaneously to guide and support the second boom part 22 on or in the first boom part 21.

[0086] In each extension position of the second boom part 22, the base piece 38 is located between the lower and upper cross members 28, 38 of the first boom part 21.

[0087] The Fig. 7a and Fig. 7b show an embodiment of the upper cross member 30 in a sectional view along the line BB in Fig. 5, with ( Fig. 7a) and without ( Fig. 7b) second strand 34. The upper cross member 30 has a rectangular shape viewed along the longitudinal axis of the lattice mast and, in the area between the connecting means 31 for the two first strands 24, has a central recess 32 through which the second strand 34 of the second boom part 22 is guided. Rollers 33 are located in the recess 32, which, in this embodiment, are arranged on the upper and lower sides of the recess 32. The second strand 34 is guided in the upper cross member 30 via these rollers 33 and rolls along it.

[0088] The Fig. 8a and Fig. 8b show an embodiment of the already mentioned guide frame 75 according to a preferred embodiment, which is placed as a separate component below the cross member 30 or between the upper and lower cross members 28, 30 (see Fig. 4a-b), each with ( Fig. 8a) and without ( Fig. 8b) second strand 34. The guide frame 75 is connected to the upper lattice elements 26 of the first rod 24, but not to the upper cross member 30. The guide frame 75 has a substantially rectangular shape when viewed along the longitudinal axis of the lattice mast and has a central recess 32 in the area between the connecting means 31 for the two first strands 24, through which the second strand 34 of the second boom part 22 is guided. In the recess 32 there are rollers 33, which in this embodiment are arranged on the upper and lower sides of the recess 32 (see Fig. 4c). The second strand 34 is guided via these rollers 33 in the guide frame 75 in front of or below (seen from the superstructure) the upper cross member 30 and rolls along it. In this exemplary embodiment, the upper cross member 30 does not have its own guide elements. In the exemplary embodiment shown here, two rollers 33 are provided on the inside at each corner of the guide frame 75, the axes of rotation of which are perpendicular to one another. This ensures stable guidance of the second strand 34 within the guide frame 75 (cf. Fig. 8b). Rollers 33 are preferably provided at both ends (seen along the longitudinal axis of the lattice mast) of the guide frame 75 (cf. Fig. 12a).

[0089] The Fig. 9a and Fig. 9b show an embodiment of the foot piece 38 according to Fig. 6a in a side view ( Fig. 9a) and in a top view ( Fig. 9b) together with the lowermost second grid section 36 of the second strand 34. One can see the connecting means by which the base section 38 is bolted to the grid section 36. In addition, Fig. 9b further connecting means 37 can be seen, by means of which it can be bolted to the upper cross member 30.

[0090] The Fig. 10a and Fig. 10b show a further embodiment of the foot piece 38 according to Fig. 6c in a side view ( Fig. 10a) and in a top view ( Fig. 1 0b). In this version, the base piece 38 replaces the first (or "lowest") grid piece of the second rod 34 or it is a combination of both elements. Furthermore, Fig. 10a, the connecting means 37 can be seen, via which it can be bolted to the upper cross member 30 via locking bolts 31. In the exemplary embodiment shown here, the connecting means 37 are designed as bolt receptacles, which have a shape deviating from a circular geometry. In particular, the bolt receptacles 37 have a taper or a section with a decreasing width in the direction of the upper cross member 30, which at the narrowest point preferably has an inner diameter corresponding to the outer diameter of the locking bolts 31 (cf. Fig. 12a-c).

[0091] The first and second lattice sections 26, 36 are, as already described, connected to each other via fork-finger connections. These typically require somewhat more installation space than a round tube, i.e., they protrude radially beyond the contour of the corresponding longitudinal struts. Compared to the telescopic systems known from the prior art, this solution differs in the fork-finger connections between the second lattice sections 36 in the telescopic boom section 22. Therefore, the guide rollers 33 must be designed with a suitable geometry so that the fork-finger connections can be traversed by the rollers 33. This also applies to the rollers 39 of the base section 38.

[0092] In order to counteract this problem, the device according to the invention can be provided with the guide rollers 33, 39 being mounted in pairs as tandem axles, ie double rollers being provided, as is shown by way of example in the Fig. 11a for the rollers 39 of the base piece 38 and the rollers 33 of the upper cross member 30. This allows the fork-finger connections of the first lattice pieces 26 (or, in the case of the upper cross member 30, the fork-finger connections of the second lattice pieces 36) to roll over without the second boom part 22 wobbling or vibrating.

[0093] In a further embodiment, the corner posts of the second grid pieces 36 of the second rod 34 are not designed as round, but as rectangular profiles. These therefore have the property of a guide track. The second rod 34 can thus be pushed through the guide frame 75 via a guide track (see embodiment of the Fig. 4a-c or 8a-b). The rollers 33 or sliding surfaces in the guide frame 75 are therefore not subject to variable geometries, but guide the second rod 34 in a defined manner over the guide surfaces or guideways.

[0094] The second boom part 22 is movably connected or guided to the first boom part 21 at two points: at the base 38 and at the upper cross member 30 (or in the embodiment of the Fig. 4a-c and Fig. 8a-b on the guide frame 75). The second boom section 22 can be retracted and extended into the first boom section 21 via the rollers 33, 39. Alternatively or in addition to the rollers 33, 39, sliding surfaces or slide rails can be provided.

[0095] In the Fig. 11a and Fig. 11b shows an embodiment of the lattice boom 20 according to the invention in the region of the upper cross member 30 in a side view during the extension process of the second boom part 22, namely on the one hand shortly before the maximum extended position is reached ( Fig. 11a) and on the other hand, after this final position has been reached and the two boom parts 21, 22 are bolted together ( Fig. 11b).

[0096] It can be seen how the rollers 39 of the base piece 38 contact the longitudinal struts of the first lattice sections 26 and the base piece 38 rolls along them. The rollers 33 of the upper cross member 30 can also be seen, which contact the longitudinal struts of the second lattice sections 36. Likewise visible are the connecting means 31, 37 of the base piece 38 and the upper cross member 30, which face one another and overlap in the fully extended position so that the bolting can be established. This is preferably done by means of an actuator, for example an electric or hydraulic cylinder, since this connecting process usually takes place with the boom 20 erected at a great height. The bolting process can be carried out and / or monitored by a crane control system.

[0097] In case a guide frame 75, as in the Fig. 4a-c and 8a-b respectively, illustrate the Fig. 12a to 12c show a further embodiment of the lattice boom 20 according to the invention in the area of ​​the upper cross member 30 or the guide frame 75 in a side view during the extension process of the second boom part 22, namely in the view of Fig. 12a shortly before the maximum extended position is reached, in the view of the Fig. 12b when the maximum extension position is reached and in the view of the Fig. 12c after the end position has been reached and the two boom sections 21, 22 have been bolted together. It can be seen how the second strand 34 is contacted and guided by the rollers 33 of the guide frame 75. During extension, the rollers 33 roll along the guideways formed by the rectangular profiles of the second lattice sections 36.

[0098] The connecting elements 31, 37 of the base piece 38 and the upper cross member 30 can also be seen, which overlap or are opposite each other in the fully extended position (cf. Fig. 12b), so that by moving the locking bolts 31 inwards or towards the central axis of the lattice boom 20, a bolt connection can be established (i.e. the locking bolts 31 move into the bolt receptacles 37). This is preferably done by means of actuators, for example electric or hydraulic cylinders, since this connecting process usually takes place with the boom 20 erected at a great height. Once the locking bolts 31 have been pushed into the wider sections of the bolt receptacles 37, i.e. into the sections with a larger diameter, the boom 20 is lowered until the end position is reached. After reaching the end position, the locking bolts 31 are in the precise fitting area, i.e. in the tapered, narrower sections of the bolt receptacles 37 (cf. Fig. 12c). The bolting process can be carried out and / or monitored by a crane control system.

[0099] The Fig. 13 shows in a perspective view the position of the boom 20 according to Fig. 11b. In the embodiment shown here, the upper cross member 30 comprises two parallel, trapezoidal plates, between which frames are arranged, which have the connecting means for mounting the first lattice pieces 26. Of course, the upper cross member 30 can also be formed entirely by plates or sheets or by a continuous lattice structure.

[0100] The extension of the second boom part 22 can be carried out by means of a cable pull system, as shown in the Fig. 13. Here, several deflection pulleys 50 are located both on the base piece 38 and on the upper cross member 30 (or, if provided, on the guide frame 75), over which an extension cable 52 is guided. The latter is preferably firmly attached in the area of ​​the head piece 40, so that the second boom section 22 can be telescoped out by retracting the extension cable 52 via a corresponding winch.

[0101] For example, the cable of a specially installed adjustment winch can be used as the extension cable 52. The adjustment winch can be provided, for example, on / in the lower cross member 28 or on the pivot piece 23.

[0102] Alternatively, an existing hoist winch, preferably the mast nose or head piece 40 with its rope and its anchor point, can be used. For this purpose, the hook block 60 requires the option of a hard stop 62 on the head piece 40, which can serve as a counter bearing for the hook block 60. Such a configuration is shown in the Fig. 14 is shown in a side view. It shows the hook block 60 resting against a stop 62, through which the hoist rope (here functioning as extension rope 52) is guided to a fixed anchor point or fixed point 61.

[0103] In order for such a solution to work with modern cranes 10, in this operating state (hoist rope is guided as extension rope 52 over the deflection rollers 50 of the rope pulley system, second boom section 22 is extended) the safety shutdown of the hook lifting process, which normally applies here, must be switched off when extending by a suitably designed crane control and the hook block 60 can be pulled against the mast nose 40 with its hard stop 62.

[0104] In the Fig. In the embodiment of the crane 10 according to the invention shown in Figures 1a-b, the second boom part 22 is not guyed and thus represents a bending beam (similar to a telescopic boom). Thus, the lattice boom 20 has only a limited load capacity.

[0105] In order to increase the rigidity of the second boom part 22 and thus the maximum load, the second boom part 22 can be guyed, as shown in the Fig. 15a-c for a second embodiment and in the Fig. 16a-c for a third embodiment of the crane 10 according to the invention.

[0106] In the version of the Fig. 15a-c a guy frame 70 is attached to the upper cross member 30 (see also the Fig. 3a-b, Fig. 11a-b and Fig. 13), which is connected to the lower crossbeam 28 or the connecting piece 23 via a fixed guying 72 (for example by means of guy rods). Between the guying frame 70 and the head piece 40, an adjustable guying 74 is provided (in particular by means of a rope adjustment or rope guying, as shown in the Fig. 15a-c) in order to be able to adapt the guy length to the extended state of the second boom part 22.

[0107] Due to the bolting between the base piece 38 and the upper cross member 30, the connection represents a firm clamping between the first and second boom parts 21, 22. The additionally attached rope adjustment 74 creates a statically overdetermined system.

[0108] In the version of the Fig. 16a-b, an adjustable guy wire 74 is mounted between the head piece 40 of the second boom section 22 and the upper end of the derrick boom 16. In order to adapt the guy wire length to the extended state of the second boom section 22, this guy wire is equipped with a rope adjustment 74, as shown in the Fig. 16a-c shown.

[0109] The bolting between the base section 38 and the upper crossbeam 30 provides a secure connection between the first and second boom sections 21, 22. The additional rope adjustment 74 creates a statically overdetermined system. To avoid static overdetermination, in this embodiment, for example, the guying 17 can be de-energized. Thus, only the adjustable guying 74 is loaded, and the system behaves like a conventional, statically determinate crane.

[0110] A preload of the second boom section 22 appropriate for a particular load case is preferably applied in a monitored and regulated or controlled manner by the crane control system. The adjustment winch known from the prior art from a lattice boom rocker in the lower cross member 28 or the connecting piece 30 of the first boom section 21 can serve as the winch for the upper rope adjustment 74.

[0111] As head piece 40, a mast tip with a specially guyed, in particular luffing pivoting part can be provided, as in the Fig. 15a-b shown.

[0112] The Fig. 15c shows the crane 10 with the boom 20 aligned horizontally after assembly.

[0113] To assemble the lattice boom 20, the double-stranded first boom section 21 is first assembled "conventionally" on the ground. In a second step, the base section 38 with its guide system is mounted on / in the first boom section 21. The second lattice sections 36 to be extended are bolted to the previous second lattice section 36 and inserted piece by piece from the upper cross member 30. With each inserted second lattice section 36, the base section 38 is moved by one lattice section 36 toward the pivot piece 23 (or lower cross member 28).

[0114] After the second lattice sections 36 have been installed, the head piece 40 is mounted on the second strand 34 inserted into the first boom section 21. For example, the hook block 60 is reeved as known from the prior art, and the lattice boom 20 is erected. In this case, the second boom section 22 is preferably fully inserted into the first boom section 21. Additional bolting points can be provided on the first boom section 21 to fix or lock the second boom section 22, for example, in the fully retracted position.

[0115] For the fully retracted position, a corresponding stop for the second strand 34 can be provided, for example on the base piece 38 and / or on the upper cross member 30 and / or on one or more first and / or second grid pieces 26, 36.

[0116] Because the lattice boom 20 is retracted during luffing, less space is required on the construction site and less counterweight is required.

[0117] After the lattice boom 20 has been raised to a steep position, the second boom section 22 is extended, for example, using the cable pull system described above. Subsequently, the second boom section 22 is bolted to the first boom section in the fully extended position (connection between the base section 38 and the upper cross member 30).

[0118] The previous explanations regarding the assembly, erection and extension of the lattice boom 20 are of course not only valid with regard to the embodiment of the Fig. 15c, but for all embodiments of the crane 10 according to the invention.

[0119] Due to the possibility of retracting the lattice boom 20, it can be brought into a “storm-proof” state in a very short time, which allows for high wind speeds, without having to attach a suspended ballast and put down the lattice boom 20.

[0120] A further advantage is that the second boom section 22, which is inserted during erection, reduces the required erection moment of the entire boom 20 (the lever arm to the boom head 40 is smaller). This means less counter-torque is required for erection than with a conventional lattice boom, and ballast can be saved. This has the advantage of reducing the number of transports required to relocate the crane 10, which, among other things, results in a cost advantage and a better CO2 footprint.

[0121] In the Fig. 17a-b is a further embodiment of the crane 10 according to the invention in a side view in the erected state with the lattice boom 20 extended ( Fig. 17a) and in horizontal alignment of the retracted boom 20 ( Fig. 17b).

[0122] In this variant, the base piece 38 is designed to be rockable. For this purpose, the base piece 38 comprises two parts, namely a guide part 42 and a pivoting part 44 arranged on this guide part 42 in a pivotable or rockable manner. The corresponding pivot axis is oriented, in particular, horizontally. The guide part 42 can be designed as discussed above with regard to the various embodiments of the rigid base piece 38. In particular, the guide part 42 has the rollers 39 for contacting the first strands 24 and the connecting means 37 for bolting to the upper cross member 30.

[0123] The guide part 42 preferably has a locking device by means of which the pivoting part 44 can be locked or secured relative to the guide part 42 so that it cannot pivot about the pivot axis.

[0124] During assembly of the lattice boom 20 (and during luffing and extending of the boom 20), the pivoting part 44 is locked, thus preventing any luffing movement. Assembly, erection, and extension are carried out analogously to the previously described steps. Once extended and bolted, the pivoting part 44 can now be unlocked and actively luffed using the cable adjustment 74. Blocking or locking the pivoting part 44 is, if at all, essential primarily for assembly.

[0125] The pivoting part 44 preferably has the connecting means for mounting the lowermost second grid section 36. Optionally, the pivoting part 44 can also have rollers for contacting the first strands 24. List of reference symbols: 10 Mobile crane (crawler crane) 12 undercarriage 14 superstructure 16 derrick booms 17 guy wire 18 Ballast 20 lattice booms 21 First boom section 22 Second boom section 23 Linkage piece 24 First strand 26 First lattice piece 28 Lower traverse 30 Upper traverse 31 lanyards 32 recess 33 rolls 34 Second strand 36 Second lattice section 37 lanyards 38 foot piece 39 rolls 40 headpiece 42 Guide part 44 Swivel part 50 pulley 52 extension rope 60 hook block 61 fixed point 62 stop 70 guy stand 72 Fixed guy wire 74 Adjustable guy rope (rope adjustment) 75 guide frames

Claims

[1] Mobile crane (10), in particular a crawler crane, with a mobile undercarriage (12), a superstructure (14) rotatably mounted on the undercarriage (12) and a lattice boom (20) which is pivotally connected to the superstructure via a linkage piece in a vertical luffing plane and which comprises a first boom part (21) and a second boom part (22), wherein the first boom part (21) has two parallel first strands (24) of interconnected first lattice pieces (26) which are interconnected at their lower ends via a lower cross member (28) and are connected to the linkage piece (23) and are interconnected at their upper ends via an upper cross member (30), and wherein the second boom part (22) has a single second strand (34) of interconnected second lattice pieces (36) which is connected to the upper cross member (30) and at its upper,the upper cross member (30) has a head piece (40) opposite end, characterized by that the second boom part (22) is displaceably mounted on or in the first boom part (21) and can be releasably locked thereto and that the second boom part (22) has a foot piece (38) at the lower end of the second strand (34) opposite the head piece (40), which foot piece is arranged between the lower cross member (28) and the upper cross member (30) in every position of the second boom part (22) and is preferably connected to at least one, particularly preferably to all of the first strands (24) via guide means, in particular rollers (39) and / or sliding surfaces. [2] Crane (10) according to claim 1, wherein the longitudinal axes of the first strands (24) have the same distance from the longitudinal axis of the second strand (34), wherein the smallest distance between the first strands (24) is preferably greater than the width of the second lattice pieces (36) of the second strand (34). [3] Crane (10) according to claim 1 or 2, wherein the second strand (34) of the second boom part (22) can be retracted between the first strands (24) of the first boom part (21), wherein the longitudinal axes of the first and second strands (24, 34) preferably lie within a common plane which is in particular perpendicular to the luffing plane. [4] Crane (10) according to one of the preceding claims, wherein the second boom part (22) is displaceably mounted in the upper cross member (30), preferably in a recess (32) provided centrally in the upper cross member (30). [5] Crane (10) according to one of the preceding claims, wherein connecting means (31, 37), in particular for producing a fork-finger connection or a cantilevered positive connection, are provided on the base piece (38) and on the upper cross member (30), via which connecting means the second boom part (22) in its fully extended position can be firmly connected, in particular bolted, to the first boom part (21), wherein the connection is preferably produced by means of an actuator. [6] Crane (10) according to one of the preceding claims, wherein the base piece (38) has rollers (39) and / or sliding surfaces over which it rolls and / or slides along at least one, preferably all, of the first strands (24) and / or wherein the upper cross member (30) has rollers (33) and / or sliding surfaces over which the second strand (34) rolls and / or slides along. [7] Crane (10) according to one of the preceding claims, wherein the first boom part (21) comprises a guide frame (75) which is arranged between the upper cross member (30) and the lower cross member (28) and in particular between the two first strands (24) in the region of the upper cross member (30), wherein the guide frame (75) has rollers (33) and / or sliding surfaces over which the second strand (34) rolls and / or slides along. [8] Crane (10) according to one of the preceding claims, wherein the base piece (38) is arranged between the first strands (24) or completely or partially surrounds the first strands (24). [9] Crane (10) according to one of the preceding claims, wherein the base piece (38) is rigid or wherein the base piece (38) comprises a guide part (42) connected to the first strands (24) via guide means, in particular rollers (39) or sliding surfaces, and a pivoting part (44) pivotably connected to the guide part (42) and in particular lockable therewith, wherein the second boom part (22) is tiltable in the fully extended position by pivoting the unlocked pivoting part (44) in the luffing plane relative to the first boom part (21). [10] Crane (10) according to one of the preceding claims, wherein the lattice boom (20) comprises a cable pull system by means of which the second boom part (22) is displaceable relative to the first boom part (21), wherein the crane (10) is preferably designed according to one of claims 5 to 10 and at least one deflection pulley (50) of the cable pull system is arranged on the base piece (38) and on the upper cross member (30), over which an extension cable (52) can be guided. [11] Crane (10) according to the preceding claim, wherein a separate adjustment winch with an extension cable guided over the deflection pulleys (50) of the cable pull system is provided for actuating the cable pull system, which extension cable is preferably fastened to a fixed point on the head piece (40), or wherein a hoist winch of the crane (10) provided for lifting and lowering a hook block (60) suspended from the head piece (40) by means of a hoist cable can be used for actuating the cable pull system and the hoist cable can be guided over the deflection pulleys (50) of the cable pull system, wherein the hook block (60) can be secured to the head piece (40) and / or the hook block (60) and head piece (40) have a stop (62) against which the hook block (60) can be pressed when the second boom part (22) is extended. [12] Crane (10) according to one of the preceding claims, wherein the first boom part (21) is guyed to the upper cross member (30), preferably via a superstructure guying frame and / or derrick boom (16) hinged to the superstructure (14). [13] Crane (10) according to claim 12, wherein the second boom part (22) is not guyed or wherein the second boom part (22) is guyed via a guy frame (70) mounted on the upper cross member (30), [14] Crane (10) according to claim 12, wherein the second boom part (22) is guyed via a superstructure guying frame and / or a derrick boom (16) or wherein the second boom part (22) is connected via one or more guy rods (72) to the articulation piece (23) of the first boom part (21) and / or via an adjustable rope guying (74) controlled in particular by a crane control system to the head piece (40) of the second boom part (22). [15] Lattice boom (20) for a crane (10) according to one of the preceding claims. [16] Method for assembling the lattice boom (20) of a crane (10) according to one of claims 1 to 14, wherein the second boom part (22) of the lattice boom (20) comprises a base piece (38) which is designed at least according to claim 6, with the following steps: - mounting the first boom part (21) on the superstructure (14) of the crane (10), in particular in a substantially horizontal position, - Connecting the base piece (38) to the first boom part (21), - Mounting the second strand (34) on the base piece (38), - luffing of the lattice boom (20), preferably with the second boom section (22) fully retracted, - extending the second boom part (22), in particular by means of a cable pull system according to claim 11 or 12, and locking the second boom part (22) to the first boom part (21), in particular by establishing a fixed connection between the base piece (38) and the upper cross member (30). [17] Method according to the preceding claim, wherein mounting the second strand (34) on the base piece (38) comprises the following steps: - connecting a second grid piece (36) to the base piece (38), - moving the mounted second lattice piece (36) together with the base piece (38) in the direction of the articulation piece (23), in particular by substantially the length of the second lattice piece (36), - connecting a further second grid piece (36) to the already mounted second grid piece (36), - Moving the mounted second lattice pieces (36) together with the base piece (38) in the direction of the articulation piece (23), in particular by substantially the length of a second lattice piece (36), - optionally repeat the two previous steps until the desired length of the second strand (34) is reached, - Connect the head piece (40) to the last, already mounted second grid piece (36). [18] Method for moving a crane (10) according to one of claims 1 to 14 into a parking position with the lattice boom (20) erected, wherein in the erected state the locking between the first and second boom part (21, 22) is released and the second boom part (22) is retracted in the direction of the link piece (23) in order to reduce the overall length of the lattice boom (20) and thereby in particular to increase the maximum permissible wind speed.

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