EP4389678A1

EP4389678A1 - Hydraulic cylinder assembly, and a crane comprising such assembly

Info

Publication number: EP4389678A1
Application number: EP22215252.2A
Authority: EP
Inventors: José María Badía Sánchez
Original assignee: Hiab AB
Current assignee: Hiab AB
Priority date: 2022-12-21
Filing date: 2022-12-21
Publication date: 2024-06-26

Abstract

A hydraulic cylinder assembly (2) comprising an elongated cylinder housing (4) having a first end (6) and a second end (8), and a movable hydraulic piston (10) arranged within the cylinder housing (4) and configured to move along a longitudinal axis A of the cylinder housing (4) in response to supply and return of hydraulic fluid applied to the cylinder housing, a piston cylinder (12) is attached to the hydraulic piston (10) and configured to move within the cylinder housing (4) together with the piston (10). The hydraulic cylinder assembly (2) further comprises a displacement sensor system, comprising a magnetostrictive detector unit (28) and a magnet (30), arranged to monitor the displacement of the piston (10) relative to the cylinder housing (4). The magnetostrictive detector unit (28) is mounted at a first end (13) of the piston cylinder (12) in connection to a detection rod (14), and said magnet (30) is mounted in a fixed position at a detection rod sleeve (16) by a magnet holder (32). The detector unit (28) is configured to monitor its displacement to said magnet (30) and to generate a displacement signal (34) in relation thereto, and to apply said displacement signal (34) to a displacement signal cable (36).

Description

Technical field

The present disclosure relates to a hydraulic cylinder assembly applied in telescopic boom systems for loader cranes and in particular for use in boom systems in applications with a so-called jib, which is a detachable additional telescopic boom system for loader cranes (sometimes referred to as a 3rd, or in some cases also 4th, crane boom in the context of loader cranes).
Generally, this disclosure relates to cranes arranged to be mounted to a vehicle such as a truck. These cranes conventionally comprise a crane base arranged to be mounted to the vehicle, a column which is rotatably mounted to the crane base so as to be rotatable in relation to the crane base about an essentially vertical axis of rotation and an actuator for rotating the column in relation to the crane base. Stabilizers are further included in the crane assembly and attached to an outrigger beam connected to the crane base. Crane booms, like for example a first and a second boom, are attached to the column to achieve a desired reach of the crane. Often the second boom is, although it is referred to as a boom, a telescopic boom system.

Background

Loader cranes may be equipped with one or more additional detachable telescopic boom systems, "jibs", to extend the reach of the crane. The jib is mounted to the tip of the "original" loader crane, a second jib may further also be mounted to the tip of the first jib (its final boom extension) in some cases. The tip of the "original" loader crane is typically part of a telescopic boom system, having several extension booms, that may be telescopically extended or retracted in response to the crane operation commands. The tip of the "original" crane is located at the final part of the final extension boom. The jib has got a lifting capacity based on its actuators and structural design. This capacity of the jib is however sometimes reduced when the last telescopic crane boom system is not fully retracted. This situation occurs when the last telescopic crane boom is weak compared to the maximum capacity of the jib.
One solution to know the position status of the last extension boom of the telescopic boom system that the jib is mounted to is by adding a digital (on/off) sensor on the last extension boom, to monitor if it is fully retracted or not.
There are also solutions where a sensor system gives feedback regarding the position of the last crane and enables a variable jib capacity reduction based upon the determined position.
In a solution known in the art for detecting the position of the hydraulic piston of the hydraulic cylinder, is based on integrating a so-called MTS sensor (magnetostrictive position sensor) in the hydraulic cylinder. The sensor hardware is placed on a rear side of the cylinder at a stationary cylinder housing and with a sensor rod extending in a hollow cylinder piston rod and magnet placed on the cylinder piston. By detecting the position of the magnet along the sensor rod the position of the piston and/or piston rod may be monitored.
CN212803832U discloses an automatic hydraulic cylinder and a hoist which comprises a cylinder body and a piston movably arranged in the cylinder body. The piston is fixedly connected with a piston rod and the end head of the piston rod is provided with a magnetic displacement sensor which is fixedly connected with a detection rod. Moreover, a magnetic ring is arranged at the end of the fixed rod. Also, the magnetic ring is sleeved with a detection rod and relative displacement between the piston and the cylinder body is detected through relative movement of the detection rod and the magnetic ring. CN104895862A discloses a hydraulic oil cylinder with a displacement sensor. A magnetostrictive linear displacement sensor is arranged in a sensor seat hole and a sensor rod is inserted in a hollow cavity of the piston rod coaxially. A control system controls the piston rod of the hydraulic cylinder to perform the telescopic movement, the magnetic ring is stationary in the gland at the outer end of the guide sleeve and the magnetic linear displacement sensor and the sensor rod are extended and contracted together with the piston rod.
CN101929484A discloses a built-in piston cylinder for a stroke detecting device. The device comprises an output cable, a displacement sensor head, a displacement sensing rod, a piston, a piston rod, a cylinder body, and a cylinder cover. Further, the displacement sensor head and the displacement sensing rod are arranged inside the outward end of the piston rod. Moreover, the magnet ring is installed in the connecting tube at the other end and extends into the plunger inside and the displacement sensor bar passes the magnet ring and extends into the connecting tube.
Currently applied systems have several important drawbacks. For the digital (on/off) solution, it is only monitoring if the final telescopic crane extension boom is retracted or not, which results in that the jib capacity percentage is reduced by a constant factor as soon as the final crane boom starts moving out. Another drawback is that the on/off sensor must be properly adjusted and attached so it is not sending the wrong status/position of the crane boom extension to the crane logic.
In addition, possible misuse or accidents might occur as the sensor is placed visible and accessible to the crane user, the position of one part of the sensor could be easily damaged by accident or moved to mislead the system and get full jib capacity at any given crane boom extension position.
The solutions in prior art applying an MTS sensor arranged within the hydraulic cylinder is not suited for the jib application as it would require advanced cable routing from the rear of the hydraulic cylinder to the tip as the circuitry of the MTS sensor is connected to a control unit of the jib. More particularly, a control unit, arranged at the jib, is connected via cables to the sensor unit of the last crane extension boom, and the distance in between is varying with the extension of this extension boom.
There is hence a need for an improved solution for a variable jib boom capacity reduction.
The object of the present invention is to achieve an improved hydraulic cylinder assembly provided with capabilities of detecting cylinder extension, and particularly to achieve a crane provided with a jib, having an improved jib capacity reduction, that is more robust and reliable than the presently applied solutions, and that also provides a higher capacity.

Summary

The above-mentioned objects are achieved by the present invention according to the independent claims.
Preferred embodiments are set forth in the dependent claims.
According to a first aspect of the present invention, the placement of the magnetic detector unit at the first end of the hydraulic cylinder is advantageous as it enables a constant distance between the magnetic detector unit and its connection to the control unit of the second telescopic boom system. This results in that no cable guiding solution managing the cables during a relative movement between the magnetic detector unit and the second telescopic boom system is needed.
Thus, from the outside of the hydraulic cylinder, only the sensor connector and the short cable connecting it to the second telescopic boom system will be visible in the region where the additional telescopic boom system is mounted to a final extension boom of another telescopic boom system of the crane. The solution according to the present invention is hence well-protected from foreseeable misuse and is also a robust solution not affected by potential collisions with external elements, because the magnetic detector unit moves at the same time that the last crane extension moves.
According to a second aspect, the present invention is applied on a crane provided with a second telescopic boom system pivotably connected to a first telescopic boom system. The hydraulic cylinder assembly according to the present invention, allows for a fine-tuned capacity reduction or even a stepless capacity reduction of the second telescopic boom system capacity.
The variation of the capacity of second telescopic boom system is made in dependence of a measure value related to the extension of the final telescopic boom of the first telescopic boom system. If fully retracted, the measured value is 0, and the second telescopic boom system can work with maximal capacity. The capacity will then be decreased in the dependence of the measured extension value according to a predetermined capacity reduction algorithm of a set of capacity reduction algorithms.

Brief description of the drawings

Figure 1 schematically illustrates a vehicle provided with a crane where the present invention may be applied.
Figure 2 is a side view of a crane provided with a first telescopic boom system.
Figures 3 and 4 are side views of a first telescopic boom system and a second telescopic boom system.
Figure 5 is a perspective view of a hydraulic cylinder assembly according to the present invention.
Figure 6 is a perspective view also showing the interior of a hydraulic cylinder assembly according to the present invention.
Figure 7 is a perspective view also showing the interior of a first end of a hydraulic cylinder assembly according to an embodiment of the present invention.
Figure 8 is a perspective view also showing the interior of a second end of a hydraulic cylinder assembly according an embodiment of the present invention.
Figure 9 is a perspective view also showing the interior of a first end of a hydraulic cylinder assembly according to an embodiment of the present invention.
Figure 10 is a perspective view also showing the interior of a second end of a hydraulic cylinder assembly according an embodiment of the present invention.
Figures 11 and 12 are schematic illustrations of cross-sectional views along the longitudinal axis of the hydraulic cylinder assembly according to the present invention.
Figure 13 is a perspective view of a valve applied in the hydraulic cylinder assembly according to an embodiment of the present invention.
Figure 14 is a perspective view also showing the interior of a valve applied in the hydraulic cylinder assembly according to an embodiment of the present invention.

Detailed description

The hydraulic cylinder assembly and the crane will now be described in detail with references to the appended figures. Throughout the figures the same, or similar, items have the same reference signs. Moreover, the items and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
Figure 1 schematically illustrates a vehicle 1 provided with a crane 24. As illustrated, the crane may be arranged between the driver's cabin and a load carrying part. Alternatively it may be placed at the rear side of the vehicle.
Figure 2 illustrates a part of the basic structure of a crane which the invention can be applied to. With reference to the illustration in figure 2, a boom 3 is arranged to the column 5 and an actuator is arranged to be able to move the boom around a first axle 7 with reference to the column 5. A first telescopic boom system 50 is arranged to the boom 3 and another actuator is arranged to be able move the first telescopic boom system 50 around a second axle 11 with reference to the boom 3.
Cranes like this may further have a second telescopic boom system 58 that is mounted to the first telescopic boom system 50. See the illustrations in figures 3 and 4 where the first and second telescopic boom systems 50, 58 are illustrated in various positions in relation to each other. A further actuator is then arranged to be able move the second telescopic boom system around a third axle, herein denoted telescopic boom pivot axle 62, with reference to the first telescopic boom system 50. This second telescopic boom system 58 may also, as discussed above, be referred to as a "jib". A "jib" may be defined as an additional detachable telescopic boom system that may be mounted to a crane, or another jib that in turn may be mounted to a crane. In figures 3 and 4, the crane is provided with a hoisting wire connected to a hook.
With references to figures 1-4, the present invention relates to a crane 24 comprising a first telescopic boom system 50 that comprises a main section 52 and a set of boom sections 54 carried by the main section, the boom sections being telescopically mounted inside one another according to their cross sectional size.
The first telescopic boom system 50 further comprises a set of hydraulic cylinder assemblies 56 each comprising a cylinder housing, a movable piston inside the housing, wherein each hydraulic cylinder assembly is arranged to displace a boom section, relative to a neighbouring, partly enclosing, boom section 26, to which the cylinder housing is mounted to, in response to the supply and return of hydraulic fluid to the cylinder housing.
The set of boom sections 54 comprises a final boom section 18 with an end 20 representing a tip of the first telescopic boom system 50, and the set of hydraulic cylinder assemblies 56 comprises a corresponding final hydraulic cylinder assembly arranged to displace the final boom section 18 relative to its neighbouring, and partly enclosing, boom section.
The crane 24 also comprises a second telescopic boom system 58 movably attached to the tip of the first telescopic boom system 50 via the telescopic boom pivot axle 62.
The second telescopic boom system 58 comprises a control unit 60 configured to control operation of the second telescopic boom system. The control unit 60 is schematically indicated in figures 3 and 4, and is arranged within the second telescopic boom system. It comprises circuitry having the necessary processing capabilities to perform its intended tasks.
The functionality and operation of the second telescopic boom system 58 will be described in detail below, but first another aspect of the present invention will be described in detail with references to figures 5-12, especially with references to figures 11 and 12, that show simplified and schematic cross-sectional views along the longitudinal axis A of a hydraulic cylinder assembly 2.
According to the present invention a hydraulic cylinder assembly 2 is provided. The hydraulic cylinder assembly 2 is shown in its entirety in figures 5 and 6, where figure 6 shows part of the interior of the assembly. Figures 7 and 9 show perspective views of the first end of the cylinder assembly, and figures 8 and 10 show perspective views of the second end of the cylinder assembly.
The hydraulic cylinder assembly 2 comprises an elongated cylinder housing 4 having a first end 6 and a second end 8, and a movable hydraulic piston 10 arranged within the cylinder housing 4 and configured to move along the longitudinal axis A of the cylinder housing 4 in response to supply and return of hydraulic fluid applied to the cylinder housing. The hydraulic system of for example a crane, structured to supply hydraulic fluid to the cylinder housing comprises e.g. various hydraulic lines, valves, and one or more hydraulic pump(s), which have been excluded in the schematic illustrations for sake of simplicity.
A piston cylinder 12 is attached to the hydraulic piston 10 and configured to move within the cylinder housing 4 together with the piston 10, the piston cylinder 12 has a first end 13 and a second end 15 oriented as the first end 6 and the second end 8 of the cylinder housing 4. In figure 11, the piston 10 is close to the second end 8 of the cylinder housing, and in figure 12, the piston is moved to the left. The movement within the cylinder housing is designated by a double-arrow in figure 12.
A rod assembly is arranged within the cylinder housing 4 along the longitudinal axis A. The rod assembly comprises a detection rod 14 and a detection rod sleeve 16. The detection rod 14 is arranged within the detection rod sleeve 16 and is configured to move in relation to said sleeve 16. The detection rod sleeve 16 is fixed to the cylinder housing at the second end 8, and the detection rod 14 is fixed to the first end of the piston cylinder 12, and is thus configured to move together with said hydraulic piston 10.
The hydraulic cylinder assembly 2 is structured to be mounted to a final boom section 18 with an end 20 representing a tip of a first telescopic boom system 50 of a crane 24, and to a neighbouring, partly enclosing, boom section 26 (see figure 3), such that the first end 13 of the piston cylinder 12 is fixedly mounted to the final boom section, and the cylinder housing is fixedly mounted to the neighbouring boom section 26.
The hydraulic cylinder assembly 2 is arranged to displace the final boom section 18 relative to its neighbouring boom section 26.
The hydraulic cylinder assembly 2 further comprises a displacement sensor system, comprising a magnetostrictive detector unit 28 and a magnet 30, arranged to monitor the displacement of the piston 10 relative to the cylinder housing 4, or more specifically the second end 8 of the hydraulic cylinder housing 4. The magnetostrictive detector unit 28 is mounted at the first end 13 of the piston cylinder 12 in connection to the detection rod 14, and the magnet 30 is mounted in a fixed position at the detection rod sleeve 16 by a magnet holder 32. Preferably, the magnet 30 is mounted near the end of the detection rod sleeve 16 closest to the first end 13 of the piston cylinder 12.
The detector unit 28 is configured to monitor its displacement to the magnet 30 and to generate a displacement signal 34 in relation thereto, and to apply the displacement signal 34 to a displacement signal cable 36. The displacement between the detector unit 28 to the magnet 30 is thus a measure of the extension of the hydraulic cylinder, i.e. the distance between the first end 13 of the piston cylinder 12, and the second end 8 of the cylinder housing 4, that may easily be calculated based upon the information in the displacement signal 34.
In the following, a short overview will be described regarding how the measurements are performed by the magnetostrictive detector unit 28.
Generally, magnetostrictive linear position sensors measure the distance between a position magnet, herein magnet 30, and a head end of a sensing rod, herein detection rod 14. They provide highly accurate and reliable position control signals and are suited for demanding industrial (automation) environments.
When a ferromagnetic material - such as iron, nickel, or cobalt - is subjected to an external magnetic field, the magnetic domains within the material align, creating internal stresses that cause the material's shape or dimensions to change. This phenomenon is referred to as magnetostriction.
In magnetostrictive sensors, a wire, a rod or a bar, is referred to as a waveguide. It is typically made from an iron alloy and is mounted to a stationary part of the machine. The magnetic field is provided by a magnet, referred to as a position magnet, which is attached to the moving part being measured. Short pulses of current (1-3 µs) are applied to a conductor attached to the waveguide, i.e. in this case, to the detection rod 14.
The time between the initial current pulse and the detection of the pulse indicates the location of the position magnet, and therefore, the position of the moving part being measured. The interrogation rate, or update rate, can range from one time per second to over 4000 times per second, with the maximum update rate determined by the length of the waveguide.
According to an embodiment, the hydraulic cylinder assembly 2, comprises a body valve 38 arranged at second end 8 of the cylinder housing 4 at the longitudinal axis A. The valve is shown in figures 13 and 14. The body valve 38 comprises a fastening member 40 configured to attach the detection rod sleeve 16 to the valve 38. The fastening member 40 is e.g. a fixation pin arranged through openings in the valve and in corresponding openings of the detection rod sleeve 16, see figure 10. The valve is provided with radially directed channels 42 allowing supply and return of hydraulic fluid to a piston side chamber of the cylinder housing (the side of the piston that is opposite of the site with the piston rod). The body valve provides two specific tasks: the detection rod sleeve 16 is fixed to the body valve with the fastening member, e.g. the fixation pin, and the body valve is provided with hydraulic channels allowing hydraulic oil to get into the piston side chamber of the cylinder housing in a radial direction. For example, during a retraction operation, hydraulic oil present on the piston side will escape through the channels.
In a further embodiment, the displacement sensor system is arranged completely within the hydraulic cylinder assembly 2, and wherein only the displacement signal cable 36 of the displacement sensor system extends outside the hydraulic cylinder assembly. Thus, the magnetic detector unit 26 moves together with the first end 13 of the piston cylinder 12 and then also the signal cable 36, which is advantageous, as this movable end is fixedly mounted to the end of the final boom section 18 pivotably attached to the second telescopic boom system 58, and particularly connecting the signal cable 36 to the control unit 60 without any cable guiding solution managing the cable during the relative movement between the magnetic detector unit 26 unit and the control unit 60.
In another embodiment, the magnet holder 32 is mounted in a fixed position at an end of the detection rod sleeve 16 opposite the end of the detection rod sleeve where it is fixed to the second end 8 of the cylinder housing. Furthermore, the magnet holder 32 is an elongated jacket having a circumferential and circular cylindrical shape enclosing the end of the detection rod sleeve 16.
According to still another embodiment, the hydraulic piston 10 is provided with an inner surface facing the outer surface of the detection rod sleeve, and that the inner surface has recesses 44 (see figures 8 and 10) adapted to the magnet holder 32 such that the hydraulic piston 10 does not interfere with the magnet holder when being displaced in the proximity of the magnet holder. Particularly, the magnet is held in a position by the magnet holder arranged at the end of the rod sleeve, and when the cylinder piston is in the position close to the magnet the recesses are provided at the inner surface of the piston, the surface faced against the rod sleeve, in order not for the piston to interfere with the rod sleeve.
The hydraulic cylinder assembly also comprises a first attachment member and a second attachment member structured to mount the hydraulic cylinder assembly to the final boom section 18. The first attachment member is structured to fixedly mount the first end 13 of the piston cylinder 12 to the final boom section 18, and the second attachment member is structured to fixedly mount the cylinder housing 4 to the neighbouring boom section 26.
Now again with references to figures 1-4, and the above description in relation thereto, the final hydraulic cylinder assembly is the hydraulic cylinder assembly 2 as described above in relation to figures 5-14.
The control unit 60, arranged at the second telescopic boom system, is configured to receive the displacement signal 34, being generated by the magnetostrictive detector unit 28, via the displacement signal cable 36.
The cable 36 exits the hydraulic cylinder assembly 2 at the first end 13 of the piston cylinder 12, i.e. at the part that is attached to the second telescopic boom system 56. This is advantageous as stated above, as no complicated cable guiding solutions are required managing the cables during the relative movement between the sensor unit and the jib, i.e. a constant linear distance is provided between the jib and the first end 13 of the piston cylinder 12 when the final crane extension is extending or retracting.
The control unit is further configured to determine a maximum allowable working capacity of the second telescopic boom system 58 in dependence of the monitored displacement of the final boom section 18 relative to its neighbouring, and partly enclosing, boom section measured by the displacement sensor system.
According to an embodiment, the maximum allowable working capacity is determined by applying a predetermined capacity reduction algorithm of a set of capacity reduction algorithms. Preferably, one capacity reduction algorithm is a linear algorithm where the capacity reduction is linearly dependent on a measured final boom extension value such that if the extension value is increased, the capacity reduction is increased, i.e. a maximal extension will result in a minimal capacity of the jib.
In a further embodiment, the set of capacity reduction algorithms includes algorithms comprising exponential, stepwise, or other more complex, relationships between a final boom extension value and the capacity reduction, and combinations of those relationships.
The present invention is not limited to the above-described preferred embodiments. Various alternatives, and modifications may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.

Claims

A hydraulic cylinder assembly (2) comprising:
- an elongated cylinder housing (4) having a first end (6) and a second end (8);

- a movable hydraulic piston (10) arranged within the cylinder housing (4) and configured to move along a longitudinal axis A of the cylinder housing (4) in response to supply and return of hydraulic fluid applied to the cylinder housing, a piston cylinder (12) is attached to the hydraulic piston (10) and configured to move within the cylinder housing (4) together with the piston (10), the piston cylinder (12) has a first end (13) and a second end (15) oriented as the first end (6) and the second end (8) of the cylinder housing (4), and

- a rod assembly arranged within the cylinder housing (4) along said longitudinal axis A, the rod assembly comprises a detection rod (14) and a detection rod sleeve (16), wherein the detection rod (14) is arranged within said detection rod sleeve (16) and is configured to move in relation to said sleeve (16), wherein the detection rod sleeve (16) is fixed to the cylinder housing (4) at said second end (8), and the detection rod (14) is fixed to the first end of the piston cylinder (12), and is thus configured to move together with said hydraulic piston (10),
said hydraulic cylinder assembly (2) is structured to be mounted to a final boom section (18) with an end (20) representing a tip of a first telescopic boom system (50) of a crane (24), and to a neighbouring, partly enclosing, boom section (26), such that said first end (13) of the piston cylinder (12) is fixedly mounted to the final boom section, and said cylinder housing is fixedly mounted to the neighbouring boom section (26), and wherein the hydraulic cylinder assembly (2) is arranged to displace the final boom section (18) relative to its neighbouring boom section (26), characterized in that the hydraulic cylinder assembly (2) further comprises a displacement sensor system, comprising a magnetostrictive detector unit (28) and a magnet (30), arranged to monitor the displacement of the piston (10) relative to the cylinder housing (4), wherein the magnetostrictive detector unit (28) is mounted at the first end (13) of the piston cylinder (12) in connection to said detection rod (14), and said magnet (30) is mounted in a fixed position at said detection rod sleeve (16) by a magnet holder (32), wherein said detector unit (28) is configured to monitor its displacement to said magnet (30) and to generate a displacement signal (34) in relation thereto, and to apply said displacement signal (34) to a displacement signal cable (36).
The hydraulic cylinder assembly (2) according to claim 1, comprising a body valve (38) arranged at second end (8) of the cylinder housing (4) at the longitudinal axis A, wherein the body valve (38) comprises a fastening member (40) configured to attach said detection rod sleeve (16) to said valve (38), and that the valve is provided with radially directed channels (42) allowing hydraulic fluid to reach said hydraulic piston (10).
The hydraulic cylinder assembly (2) according to claim 1 or 2, wherein the displacement sensor system is arranged completely within the hydraulic cylinder assembly (2), and wherein only the displacement signal cable (36) of the displacement sensor system extends outside the hydraulic cylinder assembly.
The hydraulic cylinder assembly (2) according to any of claims 1-3, wherein said magnet holder (32) is mounted in a fixed position at an end of said detection rod sleeve (16) opposite the end of the detection rod sleeve where it is fixed to the second end (8) of the cylinder housing, and wherein said magnet holder (32) is an elongated jacket having a circumferential shape enclosing said end of the detection rod sleeve (16).
The hydraulic cylinder assembly (2) according to any of claims 1-4, wherein said hydraulic piston (10) is provided with an inner surface facing the outer surface of the detection rod sleeve, and wherein said inner surface has recesses (44) adapted to the magnet holder (32) such that said hydraulic piston (10) does not interfere with said magnet holder when being displaced in the proximity of the magnet holder.
The hydraulic cylinder assembly (2) according to any of claims 1-5, wherein said hydraulic cylinder assembly comprises a first attachment member and a second attachment member structured to mount the hydraulic cylinder assembly to the final boom section (18), and wherein said first attachment member is structured to fixedly mount said first end (13) of the piston cylinder (12) to the final boom section (18), and said second attachment member is structured to fixedly mount said cylinder housing (4) to the neighbouring boom section (26).
A crane (24) comprising a first telescopic boom system (50), the first telescopic boom system (50) comprising:
- a main section (52) and a set of boom sections (54) carried by the main section, the boom sections being telescopically mounted inside one another according to their cross sectional sizes;

- a set of hydraulic cylinder assemblies (56) each comprising a cylinder housing, a movable piston inside the housing, wherein each hydraulic cylinder assembly is arranged to displace a boom section, relative to a neighbouring, partly enclosing, boom section, to which the cylinder housing assembly is mounted to, in response to the supply and return of hydraulic fluid to the cylinder housing, wherein:

- the set of boom sections (54) comprises a final boom section (18) with an end (20) representing a tip of the first telescopic boom system (50), and the set of hydraulic cylinder assemblies (56) comprises a corresponding final hydraulic cylinder assembly arranged to displace the final boom section (18) relative to its neighbouring, and partly enclosing, boom section,

wherein the crane (24) also comprises a second telescopic boom system (58) movably attached to said tip of the first telescopic boom system (50), the second telescopic boom system (58) comprises a control unit (60) configured to control operation of the second telescopic boom system,

characterized in that said final hydraulic cylinder assembly is a hydraulic cylinder assembly (2) according to any of claims 1-6, wherein said control unit (60) is configured to receive the displacement signal (34) via said displacement signal cable (36), and to determine a maximum allowable working capacity of the second telescopic boom system (58) in dependence of the monitored displacement of the final boom section (18) relative to its neighbouring, and partly enclosing, boom section measured by said displacement sensor system.
The crane (24) according to claim 7, wherein said maximum allowable working capacity is determined by applying a predetermined capacity reduction algorithm of a set of capacity reduction algorithms.
The crane (24) according to claim 7 or 8, wherein one capacity reduction algorithm is a linear algorithm where the capacity reduction is linearly dependent on a measured final boom extension value such that if the extension value is increased, the capacity reduction is increased.
The crane (24) according to claim 7 or 8, wherein the set of capacity reduction algorithms includes algorithms comprising exponential, stepwise, or other more complex, relationships between a final boom extension value and the capacity reduction, and combinations of those relationships.