Rotary tower crane having two trolleys for optional load increase, and coupling arrangement for automatic coupling of two trolleys

Abstract

The invention comprises a rotary tower crane (1), a jib (3), a first trolley (4) and a second trolley (12) which can be moved along the jib (3), wherein: the first trolley (4) has a lower block (6) which is suspended via a load cable (5) and has a load hook; the second trolley (12) is arranged between the first trolley (3) and a tower (2) of the rotary tower crane (1); the second trolley (12) has a second lower block (13), which is characterized by a coupling mechanism (20) for detachably connecting the first trolley (4) to the second trolley (12); and the coupling mechanism (20) is designed to connect the first trolley (4) to the second trolley (12) when the first trolley approaches the second trolley, and to release the connection between the trolleys by lifting the first lower block (6) in the direction of an end stop.

Description

[0001] Description

[0002] title

[0003] Tower crane with two trolleys for optional load capacity increase and coupling arrangement for the automatic coupling of two trolleys

[0004] Technical field

[0005] The invention relates generally to tower cranes, and in particular to a tower crane having two connectable trolleys on its jib. The invention further relates to the possibility of connecting and disconnecting the trolleys from one another and to methods for converting the tower crane between two-strand and four-strand operation.

[0006] Technical background

[0007] Cranes typically have a boom from which a lifting cable extends, and a hook is attached to the cable to hold a load to be lifted. The load can be raised or lowered via the lifting cable. Additionally, by rotating and / or tilting the boom and / or moving a trolley along the boom, the lifting hook and / or the suspended load can be moved in a horizontal plane to allow the load to be moved within a working area.

[0008] In a tower crane, for example, the jib is mounted on a stationary tower so that it can rotate. A trolley travels along the jib. The lifting cable runs from the trolley. By rotating the jib around the tower and moving the trolley along the jib, the load can be transported and positioned within the working area.

[0009] Heavy-duty cranes can be equipped with two trolleys on the jib. For example, publication CN104528542A shows a double trolley of a tower crane. The double trolley of the tower crane comprises a rear trolley, a front trolley, an auxiliary lifting hook, and a main lifting hook. The rear trolley includes a rear trolley frame, a guide wheel, and a pulley block. The front trolley includes a front trolley frame, a guide wheel, and a pulley block. Both trolleys run over the guide wheel on a jib rail and are connected or separated by a trolley connecting rod.

[0010] Furthermore, the document CN102627228A discloses a tower crane and a suspension device for the tower crane. The suspension comprises a load rope that is guided through a first and a second trolley and then connected to a lifting mechanism of the tower crane.

[0011] Cranes with two trolleys can be operated in either a two-strand or a four-strand configuration. In two-strand operation, only one trolley is used, through which the load rope is guided. A first lower block with the load hook is suspended from two strands of the load rope and guided over a pulley.

[0012] To increase the lifting capacity, a four-strand operation can be implemented. For this, the trolleys are connected. The second trolley has a second lower block, which is coupled to the first lower block for four-strand operation. The trolleys are then connected so that the load can be lifted and transported in a four-strand operation. However, the two connected trolleys have a high dead weight, which can result in a particularly high load on the boom at one end in its maximum extension position. This can even reduce the maximum lifting capacity compared to a two-strand operation. This limits the available working range in four-strand operation.

[0013] Currently, converting a crane between two-strand and four-strand operation is a considerable undertaking and requires the involvement of skilled personnel, as it necessitates leaving the cab and entering the boom. This requires numerous safety measures to protect those responsible for the conversion as effectively as possible from operator error and malfunctions.

[0014] The object of the present invention is therefore to provide a way to convert a tower crane with two trolleys between a two-strand operation and a four-strand operation without the need for manual intervention on the boom.

[0015] Disclosure of the invention

[0016] This task is accomplished by an arrangement for switching between a two-strand and a four-strand operation of a tower crane according to claim 1, and by a tower crane and a method for switching between a two-strand and a four-strand operation according to the dependent claims.

[0017] Further details are specified in the dependent claims.

[0018] According to a first aspect, a tower crane is planned, including:

[0019] a boom, in particular arranged on a tower, a first trolley and a second trolley which are movable along the boom, wherein the first trolley has a first lower block suspended by a load rope with a load hook, wherein the second trolley is arranged between the first trolley and a tower of the tower crane, wherein the second trolley has a second lower block,

[0020] a coupling mechanism for detachably connecting the first trolley to the second trolley, wherein the coupling mechanism is designed to connect the two trolleys, in particular automatically, especially by creating a positive locking connection, when the first trolley approaches the second trolley, and to release the connection between the trolleys by lifting the first lower block towards an end stop.Furthermore, the coupling mechanism can comprise a coupling element arranged on the first trolley, which is designed to interact with a retaining element on the second trolley, in particular by latching, in order to mechanically connect the trolleys to each other, wherein a release device is provided which, when the first lower block is fully retracted, in particular up to an end stop, releases the mechanical connection between the coupling element and the retaining element, in particular by deflecting or lifting the coupling element.

[0021] A tower crane with two trolleys mounted on its jib can be operated in either a two-strand or four-strand configuration, depending on the load being transported. In two-strand operation, as is conventional, only one trolley is used to move along the jib to transport the load. A two-strand reeving system for the load rope, which can be lowered or raised, allows a first block attached to the first trolley to be used for lowering or raising the load. Particularly in the area close to the tower, the jib is capable of supporting heavy suspended loads. However, the weight of the suspended load may exceed the lifting capacity of the first trolley and / or load rope. Therefore, for operations close to the tower, the crane can be converted to a four-strand configuration.

[0022] To avoid having to replace the trolley, the jib is to be fitted with a second trolley during crane erection. The second trolley is positioned between the first trolley and the tower and, when activated, enables four-strand operation. The load rope runs through the second trolley, to which a second lower block is attached via a two-strand reeving system. The load rope is guided over pulleys on the trolleys and the pulleys on the lower blocks. In four-strand operation, the lower blocks are coupled together and can be raised and lowered with the shared, now four-strand, reeving system of the load rope. For four-strand operation, it is necessary to mechanically couple the first and second trolleys so that they can be used as a single unit with a common lower block and a common load hook.The trolley drive of the first trolley can therefore be used to move the coupled construction of both trolleys together.

[0023] While the second trolley is held in a parked position on the boom near the tower in two-strand operation, in four-strand operation it is released from the parked position and moved mechanically with the first trolley.

[0024] The trolley arrangement therefore includes a coupling mechanism, which is mechanically releasable and located on the first trolley. This coupling mechanism comprises a coupling element on the first trolley that interacts with a corresponding retaining element on the second trolley to mechanically or positively connect the two trolleys. The coupling element can be a spring-loaded hook element, which, when the first trolley approaches the second trolley, engages or latches with the retaining element, thus coupling or connecting the two trolleys.

[0025] Furthermore, a release device can be coupled to the coupling element, so that when the first lower block is fully retracted to an end stop in the first trolley, the mechanical connection between the coupling element and the holding element is released. This disengages the coupling, and the first trolley can then be moved independently of the second trolley. In particular, by moving the first lower block to the end stop, the release device can raise the coupling element, which is designed as a hook element, to release the latch / lock with the holding element (on the second trolley).

[0026] The two lower blocks of the trolleys are lowered or raised via pulleys using a common load rope. To prevent the lowering of the first lower block from also lowering the second in two-strand operation, a releasable lower block locking mechanism can be provided. This locking mechanism automatically locks the second lower block, typically using a catch hook, when the second block is raised and reaches an upper limit. For this purpose, the catch hook can be located on the second trolley and a lower block retaining element (e.g., a pin / bolt) on the second block. Upon reaching the upper limit on the second trolley, the catch hook engages the lower block retaining element and holds the second block in position, even if the first block is lowered.

[0027] If the second lower block is in a locked position on the second trolley, the load rope continues to pass through the deflection pulleys of the second trolley and the second lower block without affecting the operation of the crane in two-strand operation.

[0028] The lower block locking mechanism can include a decoupling device that deflects or pivots the catch hook during a short movement of the trolleys from the parked position towards the tower, thus releasing the connection between the catch hook and the lower block holding element. After the second lower block has been lowered, it can be coupled to the first lower block in a coupling rack on the ground for four-strand operation.

[0029] To hold the second trolley in the parked position during two-strand operation, a manually or automatically releasable parked position locking mechanism may be provided. When the second trolley is moved into the parked position, the parked position locking mechanism automatically locks the second trolley in the parked position. For this purpose, the parked position locking mechanism may have a detent device comprising a retaining element on the second trolley and a detent hook on the jib to ensure locking in the parked position. The detent hook can be pivoted or deflected manually or automatically to release the detent and move the second trolley together with the first trolley. According to another aspect, a method for switching between two-strand and four-strand operation of the above tower crane is provided, with the steps that:

[0030] the first trolley is moved close to the second trolley, so that the coupling mechanism couples the trolleys,

[0031] the second trolley is released from a parked position

[0032] the load rope is tightened to bring the lower blocks to an end stop,

[0033] the second lower bottle is released by a decoupling device,

[0034] The lower bottles are lowered and coupled together at the bottom.

[0035] To convert the crane from a two-strand to a four-strand operation, it is first assumed that the second trolley is locked in the park position by the parking position locking mechanism on the boom. Furthermore, the second lower block is locked to the second trolley using the lower block locking mechanism. The first trolley can then be moved along the boom on its own with the first lower block attached.

[0036] To convert the crane to a four-strand operation, the first trolley moves inwards towards the tower and locks the coupling mechanism, thus coupling the first trolley to the second trolley. The parking position locking mechanism is then released, allowing the second trolley to move along the boom. Finally, the load rope is tightened so that the first and second lower blocks rest against an end stop at the top.

[0037] The trolleys are then moved inwards towards the tower, causing the decoupling mechanism of the lower block locking system to deflect the catch hook, thus releasing the connection between the catch hook and the lower block retaining element. This releases the second lower block. The load rope is then unwound so that the two lower blocks are no longer resting against the upper end stop. The two lower blocks are then lowered to the ground and connected to each other by bolts using a coupling frame to form a single, connected lower block. The coupled trolleys can now be moved along the boom.

[0038] According to another aspect, a procedure for switching between four-strand and two-strand operation of the above tower crane is provided, with the following steps:

[0039] the second trolley is moved into a parking position and locked, the lower bottles are decoupled at the bottom,

[0040] the load rope is tightened to move the second lower block into an upper end position,

[0041] The lower bottle locking mechanism automatically locks the second lower bottle.

[0042] the first lower bottle is moved to an upper end stop, thereby decoupling the trolleys.

[0043] To switch from a four-strand to a two-strand operation, the trolleys are first moved to the parked position on the boom. The second trolley is then locked to the boom in the parked position by the parking position locking mechanism. Next, the lower blocks are lowered and separated using the coupling frame, specifically by removing the pins. The lower blocks are then pulled upwards by drawing in the load rope. Typically, the second block, which is lighter than the first, moves upwards first, followed by the first. When the second block reaches the upper end stop in the first trolley, it is locked in place by the block locking mechanism and can therefore no longer move downwards when the load rope is lowered.The first lower block is then pulled up to the upper end stop of the first trolley, triggering the release mechanism of the coupling and disconnecting the trolleys. With the coupling mechanism released, the first trolley can now be moved independently towards the boom tip. The first lower block can then be lowered from the hard upper end stop into an operating position.

[0044] This invention makes it possible to couple and uncouple the trolleys of a tower crane without manual intervention on the boom. This eliminates dangerous work at great heights, and the conversion can be carried out directly from the cabin, so no specialist personnel are required.

[0045] Furthermore, the automatic coupling mechanism increases the safety and efficiency of the crane, as no additional safety measures are required to protect personnel from malfunctions or operator errors.

[0046] Brief description of the drawings

[0047] Brief description of the drawings

[0048] The embodiments are explained in more detail below with reference to the accompanying drawings. These show:

[0049] Figure 1 is a schematic representation of a crane;

[0050] Figure 2 shows a cross-sectional view through an arrangement of two trolleys on a section of the boom;

[0051] Figure 3 shows a schematic representation of a coupling mechanism for detachably connecting the first trolley and the second trolley;

[0052] Figure 4 shows a releasable lower bottle locking mechanism for locking the second lower bottle to the second trolley;

[0053] Figure 5 shows a parking position locking mechanism for locking the second trolley in the parking position;

[0054] Figure 6 is a flowchart illustrating a procedure for converting to a four-strand operation; and Figure ? is a flowchart illustrating a procedure for converting the crane to a two-strand operation.

[0055] Description of embodiments

[0056] Fig. 1 shows a tower crane 1 with a tower 2 to which a jib 3 is attached. The jib can be rotated about a pivot axis D that runs inside the tower 2. A first trolley 4 is arranged to move along the jib 3 along its extension.

[0057] The first trolley 4 guides a load rope 5 over pulleys 41 through a lower block pulley 61 to a first lower block 6 with a load hook. A load 7 can be attached to the load hook. The first lower block 6 can then be lowered by lowering the load rope 5.

[0058] The first trolley 4 can be moved along the boom 3 by means of a first carriage 42, so that a horizontal position for a suspended load 7 or the first lower block 6 in the working area can be determined by a rotation position and a boom position of the first trolley 4. The length of the unwound load rope 5 determines the vertical position of the first lower block 6 or the suspended load 7.

[0059] The rotation of the boom 3 about the axis of rotation D and the movement of the trolley 4 can be controlled by suitable crane actuators, e.g., a slewing drive 8 for setting the rotational position and a trolley drive 9 for moving the first trolley 4 or for setting the position of the first trolley 4. The load rope 5 can be unwound or wound up by means of a load rope drive 10, so that the load 7 is raised or lowered.

[0060] The crane actuators can be controlled via a suitable crane control unit 15. Furthermore, the crane 1 can have a second trolley 12, which, like the first trolley 4, can move along the boom 3 by means of a second carriage 122. The load rope 5 is guided in the same way as with the first trolley 4, via pulleys 121 and through a lower block pulley 131 on a second lower block 13, so that the second lower block 13 can also be lowered by unwinding the load rope 5.

[0061] Figure 2 schematically shows the arrangement of two trolleys 4, 12 at a conversion position on the boom 3. Each trolley 4, 12 has the corresponding carriage 42, 122, with two deflection pulleys 41, 121 for deflecting the load rope 5 arranged in each trolley 4, 12. The load rope 5 carries a lower block 6, 13 between the deflection pulleys 41, 121 on a corresponding lower block deflection pulley 61, 131, around which the load rope 5 is guided. When the load rope 5 is lowered, the lower blocks 6, 13 are lowered by their own weight and can be raised by pulling in the load rope 5 towards the corresponding trolley 4, 12. The lower block 6, 13 can be raised until it reaches an end stop on the corresponding trolley.

[0062] The movement of the first trolley 4 can be effected by using the trolley drive 9, which can, for example, use a cable pull to move the first trolley 4 along the boom 3.

[0063] The two trolleys 4 and 12 can be coupled for four-strand operation. To implement the changing operating modes, a coupling mechanism 20 is provided for the detachable coupling of the first trolley 4 and the second trolley 12, a detachable lower block locking mechanism 30 for the automatic locking of the second lower block 13 to the second trolley 12, and a manually or automatically releasable parking position locking mechanism 40 for holding or releasing the second trolley 12 in a parking position on the boom 3.

[0064] Figure 3 shows a schematic view of an exemplary coupling mechanism 20 for connecting the two trolleys 4 and 12. The coupling mechanism 20 comprises a spring-loaded hook element 21, which is pivotable about a pivot axis 22 and is arranged on the first trolley 4 and projects towards the second trolley 12. The hook element 21 is designed with a locking section 24 for engaging with a bolt- or pin-shaped retaining element 27 on the second trolley 12 and is provided with a deflection surface 23. As the second trolley 12 approaches, the deflection surface 23 causes the hook element 21 to be lifted by the retaining element 27 and finally locked into place. During this process, the locking section 24 of the hook element 21 is pulled downwards by a spring element 25, ensuring that the coupling of the trolleys 4 and 12 is secure.For this purpose, the spring element 25 is arranged with a first end on a section of the hook element 21, which is arranged between the pivot axis 22 and the locking section 24.

[0065] A release device is coupled to the hook element 21 via a connecting piece 28. For this purpose, the connecting piece 28 is provided to couple one end of the hook element, opposite the locking section 24 with respect to the pivot axis 22, to a release lever 26. The release lever 26 is pivotably mounted and connected at one end to the connecting piece 28. An end opposite the end of the release lever 26 is positioned at an end stop for the first lower block 6 such that when the first lower block 6 is lifted, the release lever 26 pivots and, via the connecting piece 28, lifts the locking section 24 of the hook element 21 against the spring force of the spring element 25. This releases the coupling of the trolleys 4 and 12, and the first trolley 4 can then move independently of the second trolley.

[0066] The two lower blocks of the trolleys are lowered or raised via pulleys using a common load rope. To prevent lowering the first lower block 6 from also lowering the second lower block 13 in two-strand operation as soon as the first lower block 6 reaches the bottom, a releasable locking mechanism 30 for the lower blocks can be provided.

[0067] As shown in Figure 4, the lower block locking mechanism 30 is located in the second trolley 12 and locks automatically by latching, in particular by means of a catch hook 31, when the second lower block 13 is raised and reaches an upper end stop. For this purpose, the catch hook 31 can be located on the second trolley 12 and a lower block holding element 133 on the second lower block 13. Upon reaching the end stop on the second trolley 12, the catch hook 31 engages with the lower block holding element 133 and prevents the second lower block from lowering, even when the load rope is unwound and the first lower block 6 is lowered.If the second lower block 13 is in a locked position on the second trolley 12, the load rope 5 passes through the deflection pulleys 121 of the second trolley 12 and the lower block deflection pulley 131 of the second lower block 13 without affecting the operation of the crane in two-strand operation.

[0068] The lower block locking mechanism 30 can include a decoupling device that pivots or deflects the catch hook 31 during a short movement of the coupled trolleys 4, 12 from the parked position towards the tower, thus releasing the connection between the catch hook 31 and the lower block retaining element 133. By lowering the second lower block 13, it can be coupled to the first lower block 6 in a coupling rack on the ground for four-strand operation.

[0069] Figure 5 shows a parking position locking mechanism 50. The parking position locking mechanism 50 can be a latching device with a spring-loaded locking element 52 mounted on the boom 3 and a retaining section 51 arranged on the second trolley. The spring-loaded locking element 52 is held at one end at a pivot point 53 and can be subjected to a spring moment there by a torsion spring 55. The opposite end of the locking element 52 is provided with a bolt or pin 54. The retaining section 51 can be provided on the second trolley 12 and can be designed as a half-shell into which the bolt 54 of the locking element 52 slides and engages.When the second trolley 12 moves into the parking position, the locking device automatically engages by positive locking, and the second trolley 12 is held in the parking position by the interaction of the locking bolt 52 with the holding section 51. Furthermore, the parking position locking mechanism 50 can be manually or automatically unlocked by providing a device to lift the locking bolt 52, such as a pull cable or the like, and thus release the locking mechanism.

[0070] A method for converting crane 1 from a two-strand operation to a four-strand operation is described in more detail below with reference to the flow diagram in Figure 6.

[0071] It is initially assumed that the second trolley 12 is locked in the park position by the parking position locking mechanism 50 on the boom 3. Furthermore, the second lower block 13 is locked and held on the second trolley 12 by means of the lower block locking mechanism 30. The first trolley 4 can be moved along the boom 3 on its own with the attached first lower block 6.

[0072] To convert the crane to a four-strand operation, in step S1 the first trolley 4 moves inwards towards the tower and locks the coupling mechanism 20 by moving towards the second trolley 12, so that the first trolley 4 is coupled with the second trolley 12.

[0073] Subsequently, in step S2, the parking position locking mechanism 50 is released manually or automatically, so that the second trolley 12 can now be moved along the boom 3 together with the first trolley 4.

[0074] Subsequently, in step S3, the load rope 5 is tightened so that the first and second lower block 6, 13 rest against a hard end stop at the top, thus providing mechanical relief to the lower block locking mechanism 30.

[0075] Furthermore, in step S4, the trolleys 4 and 12 are moved inwards towards the tower, e.g., by approximately 10 cm. This causes the decoupling device of the lower block locking mechanism 30 to deflect the catch hook, thus releasing the connection between the catch hook 31 and the lower block retaining element 133. This releases the second lower block 13. Subsequently, in step S5, the load rope 5 is unwound so that the two lower blocks 6 and 13 are no longer resting against the upper end stop. The two lower blocks 6 and 13 are then lowered to the ground and, in step S6, connected to each other using a coupling frame, e.g., by bolts, to form a single, connected lower block 6 and 13. The coupled trolleys 4 and 12 can now be moved along the boom 3 in a manner known per se.

[0076] A method for converting crane 1 from a four-strand operation to a two-strand operation is described in more detail below with reference to the flow diagram of Figure 7.

[0077] It is initially assumed that the first and second trolleys 4, 12 are coupled together and located at an arbitrary position on the boom 3. Furthermore, the lower blocks 6, 13 are coupled together.

[0078] To switch from a four-strand operation to a two-strand operation, the trolleys are first moved to the parking position on the boom 3 in step S11. The second trolley 12 is then locked in the parking position by the parking position locking mechanism 50.

[0079] Subsequently, in step S12, the lower bottles 6, 13 are lowered to the bottom and separated from each other using the coupling frame, in particular by removing the bolts.

[0080] In step S13, the load rope 5 is then pulled in, raising the lower blocks 6 and 13. Typically, the second lower block 13, which is lighter than the first lower block 6, moves upwards first, followed by the first lower block 6. When the second lower block 13 reaches the upper end stop in the first trolley, it is locked in place by the lower block locking mechanism 30 and therefore cannot move downwards by lowering the load rope. The first lower block 6 is then pulled to the upper end stop of the first trolley 4, triggering the release mechanism of the coupling mechanism 20 and disconnecting the trolleys 4 and 12.

[0081] Now, with the coupling mechanism released, the first trolley can be moved separately towards the end of the boom.

[0082] Subsequently, in step S14, the first lower bottle 6 can be lowered from the hard upper end stop into an upper operating position.

[0083] The methods described above enable the automatic coupling and uncoupling of a tower crane's trolleys, allowing for flexible adjustment between two-strand and four-strand operation without manual intervention on the jib or trolleys. This results in increased safety, as no work at height is required; increased efficiency, since the conversion can be carried out from the cab; and reduced conversion time, which can increase the crane's productivity. Furthermore, no specialized personnel are required for such a conversion.

Claims

Claims 1. Tower crane (1), comprising: a boom (3), a first trolley (4) and a second trolley (12) which are movable along the boom (3), wherein the first trolley (4) has a first lower block (6) suspended via a load rope (5) with a load hook, wherein the second trolley (12) is arranged between the first trolley (4) and a tower (2) of the tower crane (1), wherein the second trolley (12) has a second lower block (13), characterized by: a coupling mechanism (20) for releasably connecting the first trolley (4) with the second trolley (12), wherein the coupling mechanism (20) is designed to connect the first trolley to the second trolley when the first trolley is moved towards it and to release the connection between the trolleys by lifting the first lower block towards an end stop.

2. Tower crane (1) according to claim 1, the coupling mechanism (20) comprising a coupling element (21) arranged on the first trolley (4), which is configured to interact with a retaining element (27) on the second trolley (12) to mechanically connect the trolleys (4, 12) together, wherein a release device (26) is provided which, when the first lower block (6) is fully retracted to an end stop, releases the mechanical connection between the coupling element (21) and the retaining element (27), in particular by deflecting the coupling element (21).

3. Tower crane (1) according to one of the preceding claims, characterized in that a lower block locking mechanism (30) is provided which automatically locks the second lower block (13), in particular by latching, when it is moved into an upper end position.

4. Tower crane (1) according to claim 3, characterized in that the lower block locking mechanism (30) has a catch hook (31) which is arranged on the second trolley (12) and is designed to latch with a lower block retaining element (133) on the second lower block (13).

5. Tower crane (1) according to one of the preceding claims, characterized in that a parking position locking mechanism (50) is provided which is designed to lock the second trolley (12) in a parking position on the boom (3).

6. Tower crane (1) according to claim 5, characterized in that the parking position locking mechanism (50) has a detent device comprising a retaining element on the boom (3) and a spring-loaded locking bolt on the second trolley, or the parking position locking mechanism (50) has a detent device which has a retaining element (51) on the second trolley (12) and a spring-loaded locking bolt (52) on the boom (3).

7. Method for switching between a two-strand and a four-strand operation of a tower crane (1) according to any one of claims 1 to 6, characterized by the fact that • the first trolley (4) is moved towards the second trolley (12) so that the coupling mechanism (20) couples the trolleys, • the second trolley (12) is released from a parked position, • the load rope (5) is tightened to bring the lower blocks (6, 13) to an end stop (61, 131), • the second lower bottle (13) is released by a decoupling device (32),19 The lower bottles (6, 13) are lowered and coupled together at the bottom.

8. Method for switching between four-strand and two-strand operation of a tower crane (1) according to any one of claims 1 to 6, characterized by the fact that the second trolley (12) is moved into a parking position and locked, the lower blocks (6, 13) are decoupled at the bottom, the load rope (5) is tightened to move the second lower block (13) into an upper end position, the lower cylinder locking mechanism (30) automatically locks the second lower cylinder (13), the first lower block (6) is moved to an upper end stop (61), thereby decoupling the trolleys (4, 12).

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