Hydraulic crane

Abstract

 A hydraulic crane comprising a control system for controlling different crane functions for the performance of different types of working operations, and an arrangement for regulating the maximum allowed lifting force of the crane (1), said arrangement comprising means (32, 33) for continuos registration of which crane functions that are being controlled via the control system, and a processing unit (33) adapted to identify, based on these registrations, the performed working operation as being of a,certain type among a number of predetermined types of working operations. The processing unit (33) being arranged to determine a, for the time being, maximum allowed lifting force of the crane (1) in dependence on the identified type of working operation. The invention also relates to a method for regulation of the maximum allowed lifting force of a hydraulic crane (1).

Description

FIELD OF THE INVENTION AND PRIOR ART

[0001] The present invention relates to a hydraulic crane, preferably a lorry crane, and a method for regulation of the maximum allowed lifting force of such a crane.

[0002] Hydraulic lorry cranes are used for many different types of working operations, such as:

A) lifting of load between lorry platform and ground, i.e. the unloading from and the loading onto a lorry platform,

B) lifting using a jib, e.g. for lifting a load onto the roof of buildings at building sites,

C) assembly work, comprising for instance lifting and positioning of a transformer and keeping this in place until it has been fixed on the intended place,

D) minor excavation and construction work with hydraulically operated bucket, particularly in narrow spaces where an excavator has problem to get through or causes large damages to the ground, and

E) handling of different types of hydraulic grab tools, e.g. for handling scrap or pallets with building material such as stone or building plates.

[0003] In the lifting of load between a lorry platform and the ground, i.e. working operations of type A as above, it is for instance used a hook together with lifting strings or some simple type of mechanical lifting tool, such as a pallet fork. In this type of working operation, a rotator can further be arranged between the crane boom and the hook. The stress on the crane can here normally be characterized as low to moderate.

[0004] For large lifting heights a so-called jib is used to make possible a longer reach and a more exact position adjustment of the load. When a jib is used, i.e. working operations of type B as above, the crane will generally be subjected to higher stresses due to the long range and the load swingings which are increasing with the range. Furthermore, the lifting frequency can be high, which also results in high stresses on the crane.

[0005] In working operations of type C as above, a hook and lifting strings are normally used. It also occurs that a winch is used in combination with hook and lifting strings, particularly if the load is to be lowered down into a narrow hole or the similar. This type of working operation normally implies a low stress on the crane, since the crane is standing still and holds a static load during the major part of the work.

[0006] Minor excavation and construction works with a hydraulically operated bucket, i.e. working operations of type D as above, often result in very high stresses on the crane. Partly due to the intense working and partly due to the fact that the crane besides being used for lifting excavation masses by means of the bucket also is used for pressing the bucket down into the ground, which results in higher stresses per lifting cycle than during simple lifting work. The bucket is normally fastened to a rotator which makes possible a rotation of the bucket.

[0007] Working operations of type E as above often result in very high stresses on the crane. Partly due to the fact that the working during this type of working operations normally is very intense, and partly due to the fact that the crane, as in excavation and construction work, sometimes is used for exerting a pressing force, for instance for pressing down scrap during scrap handling.

[0008] Lorry cranes normally have one and the same lifting capacity for all the types of working operations, and must therefor be fatigue dimensioned for the hardest type of working. This implies that smaller and middle- sized cranes (3-20 ton meters) normally are dimensioned for working comprising working operations of type D and E, whereas larger cranes (>20 ton meters) normally are dimensioned for jib working, i.e. working comprising working operations of type B. The dimensioning for the hardest type of working will of course result in a non-optimal use of the material during all types of lighter working, since the crane during performance of working operations implying lighter working will be unnecessary expensive and heavy in relation to the lifting capacity required for these working operations. It should also be pointed out that one and the same crane often is used for several different types of working operations, in the extreme case one and the same crane can be used for all the above mentioned types of working operations. As an example, a crane which is normally used for excavation can for instance lift plates at a roadwork by demounting the bucket and instead mounting a hook directly under the rotator. This exchange of implements takes a few minutes. The crane is then suddenly used for performing working operations of type A instead of D, which implies a considerably lighter working. It is also common for lager cranes that the jib (working operations of type B) is demounted, which takes about half an hour, and the crane is used in lighter hook working (working operations of type A).

[0009] The different types of working operations cause different damaging stress per lifting cycle on the welded steel structure of the crane. According to more resent computation standards for the dimensioning of cranes (e.g. prEN13001) the damaging stress per lifting cycle only depends on the difference between the highest and the lowest load during the respective lifting cycle, the so called range of stress. This implies for instance that an excavation cycle (working operation of type D), where the crane presses the bucket down into the ground with a force of 2 kN and thereafter lifts up the bucket build with load with a force of 10 kN, causes the same fatigue damage to the crane as a lifting cycle where a load is lifted in a hook (working operation of type A) with a force of 12 kN. If the static strength so allows, it would in accordance with this example be possible to lift 20% more load with one and the same crane during simple lifting as compared to excavation without jeopardising the fatigue strength. The example above is somewhat simplified since also factors such as e.g. the dead weight of the crane boom system and the positions for the fatigue critical crane sections influence the possible increase in lifting force. However, the example performs the functions of a simple illustration of the basic principle.

[0010] That particularly excavation implies very high stresses on the crane is previously known, and different solutions to the above-mentioned dimensioning problem have been suggested during the years. 1985 the company Hiab AB introduced the expression "hook working", which implied that the crane, if it was not equipped with a set of conduits and hoses for tool functions and only adapted to the four crane functions rotation, lifting, tilting and extension, was given a highest allowed lifting force which was 5-10% higher than if it had been provided with a set of conduits and hoses, since the crane without a set of conduits and hoses only could be used for working operations of type A and C. If the crane was equipped with a set of conduits and hoses it was always given the lower so-called tool capacity with a highest allowed lifting force adapted to working operations of type D and E. This irrespective of whether or not the crane temporarily was used for lighter working embracing working operations of type A and C. This system was very formal since the lifting capacity was completely determined by the design the crane was given during the assembly thereof and no better optimisation was obtained.

[0011] Another system which has been used for reducing the lifting force during tool working (working operations of type D and E) is based on the introduction of a cut-off valve. This system is designed in such a way that the operation of the tool, for instance the bucket, is prevented when the cut-off valve is closed and the allowed and possible lifting force is then simultaneously given an increased value. In this state it is consequently not possible to perform for instance excavations. If the valve is opened, which is carried out manually, the lifting force is reduced in that a pressure-limiting valve with a lower adjusted maximum pressure is connected for the lifting cylinder at the same time as tool working is allowed. In this second state it is consequently possible to perform excavations, but the allowed lifting force is lower than in the first state. A disadvantage with this system is that the activation of the cut-off valve takes place manually, which implies that it is easy to put the system out of operation. It is for instance possible to fill the bucket with the cut-off valve open and thereafter close the valve manually and lift with the higher capacity. Furthermore, the system is relatively expensive and complicated with several valves and additional wire layings, which also occupy place on the limited surface available on a crane base.

OBJECT OF THE INVENTION

[0012] The object of the present invention is to provide a hydraulic crane in which it is possible to regulate the value of the highest allowed lifting force in an effective and appropriate manner.

SUMMARY OF THE INVENTION

[0013] According to the present invention, this object is achieved in that the crane comprises an arrangement for regulating the maximum allowed lifting force of the crane, which arrangement comprises means for the continuos registration of which crane functions that are being controlled via the control system of the crane, and a processing unit adapted to identify, based on these registrations, the performed working operation as being of a certain type among a number of predetermined types of working operations, the processing unit further being adapted to determine a, for the time being, maximum allowed lifting force of the crane independence on the identified type of working operation.

[0014] This solution implies that the maximum allowed lifting force is automatically adjusted depending on how the crane is operated, whereby it will be possible to regulate the allowed lifting force in such a way that the crane can be used optimally during all types of working operations without jeopardising the fatigue strength.

[0015] According to a preferred embodiment of the invention, the control system comprises valve members for controlling the hydraulic flow to the different crane functions, the control system further comprising a number of control devices for regulating the valve members, and the means for registration of which crane functions that are being controlled via the control system being adapted to continuously detect which valve members that are being regulated via the control devices. In this way it will be possible to obtain, in a simple manner, the registration of which crane functions that are being controlled via the control system.

[0016] According to a further preferred embodiment of the invention, the arrangement also comprises a means which registers when the crane lifts up and puts down, respectively, a load, and/or means for registration of the time elapsed since the last registered control of a certain crane function, the arrangement being adapted to use also these registrations in the determination of the, for the time being, maximum allowed lifting force of the crane. In this way several parameters can be used for the determination of the maximum allowed lifting force of the crane, whereby it will be possible to achieve improved adjustment possibilities of the arrangement and an improved adjustment of the lifting force to the present control of the crane functions.

[0017] The invention also relates to a method for regulating the maximum allowed lifting force of a hydraulic crane according to claim 9.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] With reference to the enclosed drawings, a more specific description of embodiment examples of the invention will follow hereinbelow. It is shown in:

Fig 1

a sectional view of a hydraulic crane provided with a bucket,

Fig 2

a sectional view of a hydraulic crane provided with a jib,

Fig 3

a schematic view of an embodiment of the invention,

Fig 4

a schematic view of a control unit with a number of control devices for control of different crane functions, and

Fig 5

a flow chart illustrating a possible process for the determination of the maximum allowed lifting force of the crane.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0019] In this description the expression operating means is used to designate the hydraulic force members which execute the crane movements ordered by the operator of the crane. The expression operating means consequently embraces the hydraulic cylinders 8, 9, 10, 14, 17 and 19 mentioned hereinbelow. The expression control device refers to the devices, for instance operating levers, by means of which the operator regulates the valve members included in the control system which control the flow of hydraulic fluid to the respective operating means. In the described embodiment, said valve members consist of so-called directional-control-valve sections.

[0020] In fig 1 a hydraulic crane 1 attached to a frame 2 is shown, which frame for instance can be connected to a lorry chassis. The frame is provided with adjustable support legs 3 for supporting the crane 1. The crane comprises a column 4, which is rotatable in relation to the frame 2 around an essentially vertical axis. The crane further comprises an inner boom 5 articulately fastened to the column 4, an outer boom 6 articulately fastened to the inner boom 5 and an extension boom 7 displaceable fastened to the outer boom 6. The inner boom 5 is operated by means of a hydraulic lifting cylinder 8, the outer boom 6 by means of a hydraulic outer boom cylinder 9 and the extension boom 7 by means of a hydraulic extension boom cylinder 10. In the shown example a rotator 11 is articulately fastened at the outer and of the extension boom, which rotator in its turn carries a hydraulic grab tool in the form of a bucket 12. Two bucket parts 13 included in the bucket 12 can be operated in relation to each other by means of a hydraulic grab cylinder 14 for opening and closing of the bucket 12. The rotator 11 is rotatable in relation to the extension boom 7 by means of not shown hydraulic operating means.

[0021] In the example shown in fig 1, the crane 1 is equipped for performing excavations, i.e. working operations of type D as above. When the crane 1 is to be used for working operations of type A as above, i.e. proper lifting operations, the rotator 11 and the bucket 12 can be removed and replaced by a lifting hook. It is also possible to keep the rotator 11 and replace the bucket 12 by a lifting hook. In order to perform lifting operations defined as type B by way of introduction, the rotator 11 and the bucket 12 are replaced by a jib 15, see fig 2. The jib 15 comprises a jib boom 16, which is articulately fastened in relation to the extension boom 7 and operated by means of a hydraulic jib boom cylinder 17. The jib can further comprise an extension boom 18 which can be operated by means of a hydraulic extension boom cylinder 19.

[0022] Besides the crane elements shown in fig 1 and 2, the crane 1 can also be provided with a hydraulically controllable winch, which can be used in combination with a lifting hook either with or without jib 15. The crane 1 can also be provided with other types of hydraulic grab tools than a bucket, for instance grab tools for handling scrap or pallets with building material such as stone or building plates.

[0023] The control system for controlling the different crane functions, i.e. lifting/lowering by means of the lifting cylinder 8, tilting by means of the outer boom cylinder 9, extension/retraction by means of the extension boom cylinder 10 etc, comprises a pump 20 which pumps hydraulic fluid from a reservoir 21 to a directional-control-valve block 22. The directional-control-valve block 22 comprises a directional-control-valve section 23 for each of the hydraulic operating means 8, 9, 10, 14, 17, 19, to which hydraulic fluid is supplied in a conventional manner depending on the position of the slide member in the respective valve section 23. The position of the slide members in the directional-control-valve sections 23 is controlled either via a number of control devices in the form of control levers 24, each of which being connected to its own slide member, or by remote control via a control unit 25, see fig 4, comprising a control lever for the respective slide member. In case of remote control, the control signals are transmitted via cable or a wireless connection from the control unit 25 to a microprocessor, which in its turn controls the position of the slide members in the valve sections 23 of the directional-control-valve block 22 depending on the magnitude of the respective control signal from the control unit 25.

[0024] Each separate directional-control-valve section 23 consequently controls the size and the direction of the flow of hydraulic fluid to a specific operating means and thereby controls a specific crane function. For the sake of clarity, only the directional-control-valve section 23 for the lifting cylinder 8 is illustrated in fig 3.

[0025] The directional-control-valve block 22 further comprises a shunt valve 26 pumping excessive hydraulic fluid back to the reservoir 21, and an electrically controlled dump valve 27 which can be caused to return the entire hydraulic flow from the pump directly to the reservoir 21.

[0026] In the shown embodiment, the directional-control-valve block 22 is of load-sensing and pressure-compensating type, which implies that the hydraulic flow supplied to an operating means is at all times proportional to the position of the slide member in the corresponding directional-control-valve section 23, i.e. proportional to the position of the lever 24. The directional-control-valve section 23 comprises a pressure-limiting device 28, a pressure-compensating device 29 and the directional-control-valve 30 proper. Directional-control-valve blocks and directional-control-valve sections of this type are well-known and available on the market. However, also other types of directional-control-valves than the one described here can be used.

[0027] A load holding valve 31 is arranged between the respective operating means and the associated directional-control-valve section 23, which load holding valve makes sure that the load will remain hanging when the hydraulic system runs out of pressure owing to the dump valve 27 being caused to return the entire hydraulic flow from the pump 20 directly to the reservoir 21.

[0028] A sensor 32 is arranged on each of the directional-control-valve sections 23 in order to detect the movements of the valve slide member in the respective directional-control-valve section 23.

[0029] These sensors 32 are connected to a processing unit 33 suitably constituted by a microprocessor. By means of these sensors 32 the processing unit 33 can obtain information that a certain valve slide member is influenced and thereby that a certain function is controlled. In case the valve slide members are regulated via a remote control unit 25, the processing unit 33 can instead be adapted to obtain information about which crane functions that are being controlled by reading the control signals transmitted from the control unit 25.

[0030] The crane further comprises load sensing means in the form of pressure sensors 34 adapted to measure the hydraulic pressure in the respective operating means. The pressure sensors 34 are, just as the sensors 32 in the valve sections 23, connected to the processing unit 33.

[0031] The crane 1 further comprises a so called lifting counter 36 adapted to detect when the crane lifts up and puts down, respectively, a load. The lifting counter 36 detects this by detecting the velocity of the pressure variations in the lifting cylinder 8 of the crane, which pressure variations are measured by the pressure sensor 34 associated with the lifting cylinder 8. During lifting up of a load, the pressure in the lifting cylinder 8 very rapidly increases just at the moment when the load is lifted up from the underlay and becomes free hanging. The same rapid pressure variation occurs when the load is put down and no more is carried by the crane. These pressure variations are much more rapid than the pressure variations caused by the normal natural oscillations which at all times are present in the steel structure of the crane, and hereby the lifting counter 36 can separate "liftings up" and "oscillations". A lifting up and a putting down, respectively, of a load is consequently registered when the velocity of the pressure variation in the lifting cylinder 8 exceeds a certain predetermined value.

[0032] When it comes to loads which are very small for the crane (approximately smaller than 10 % of the maximum capacity of the crane) it might be problematic to register a lifting up and a putting down of a load in the above described way. However, these small loads are in all types of working operations so far below the maximum allowed load that they can be neglected in this connection. However, a more serious complication for the lifting counter is the induced pressure on the piston side of the lifting cylinder that can ensue during lowering movements due to the fact that a certain pressure is required on the piston stem side in order to open the load holding valve. Practical tests have shown that this can give such a rapid pressure variation that it "fools" the lifting counter. However, this problem can be solved in that the lifting counter 36, via the sensors which register the movements of the slide members in the directional-control-valve sections 23, obtains information whether or not a lowering movement of the crane is taking place or not. In this connection, the lifting counter 36 is adapted not to register a lifting up of a load when a rapid pressure variation in the lifting cylinder 8 takes place in connection with a simultaneous registration of a lowering movement.

[0033] The lifting counter 36 is connected to the processing unit 33, to which it transmits information concerning registered liftings up and puttings down of a load.

[0034] In the here described embodiment example, the crane 1 also comprises means 37 for registration of the time elapsed from the last registered control of a certain crane function, i.e. the time elapsed since the last operation of a certain operating device. The time registration means 37 is connected to the processing unit 33 and transmits information to the processing unit concerning said time.

[0035] In fig 3 the lifting counter and the time registration means 37 are shown as separate units, but they can with advantage be integrated with the processing unit 33.

[0036] The order between the operating levers for controlling the different functions of a lorry crane has been standardised for many years. The principal is that the order between the different functions goes from the crane base to the crane tip. Fig 4 schematically shows an example of a conventionally designed operating unit 25 with six operating levers S1-S6 for controlling six different crane functions. A lorry crane which is not provided with any winch normally has such an operating unit provided with six operating levers. In case the crane has a winch, the operating unit normally is provided with seven or nine operating levers. In order to facilitate the clarity this embodiment example relates to a lorry crane without winch.

[0037] Lever S1, i.e. the right lever in the figure, controls the rotation of the column 4. The lever S2 controls the lifting function, i.e. the hydraulic flow to the lifting cylinder 8. The lever S3 controls the tilting function, i.e. the hydraulic flow to the outer boom cylinder 9. The lever S4 controls extension and retraction, i.e. the hydraulic flow to the extension boom cylinder 10. The levers S5 and S6 control different crane functions depending on how the crane is equipped. When a rotator 11 is attached to the extension boom 7, the lever S5 controls the rotation of the rotator 11, i.e. the hydraulic flow to the operating means of the rotator. However, if a jib 15 is fastened to the extension boom 7, the lever S5 is adapted to control the tilting of the jib boom 16, i.e. the hydraulic flow to the jib boom cylinder 17. If a bucket 12 or another hydraulic grab tool is fastened to the rotator 11, the lever S6 controls the grab function of the bucket/grab tool, i.e. the hydraulic flow to the grab cylinder 17. If however a jib 15 is fastened to the extension boom 7, the lever S6 controls the extension function of the jib, i.e. the hydraulic flow to the extension boom cylinder 18 of the jib. It is realised that also other orders of the operating levers for the different crane functions are possible and that also other crane functions than the ones here described can be arranged to be controlled by the operating levers. The shown example is only to be seen as a non-limiting illustration of the basic principle of the invention and constitutes one out of several possible realisations of the invention.

[0038] In the example above, the levers S5 and S6 are adapted to control different crane functions depending on how the crane is equipped. For the processing unit to be able to decide which type of crane function that is controlled when any of these levers are operated, the arrangement for regulating the maximum allowed lifting force has to comprise means for detecting which type of crane element that for the time being is mounted to the extension boom 7. Such a means is included in an overload protection device developed by HIAB AB and present on the market. This overload protection device comprises means for detecting whether or not the sensors (pressure sensor and inclinometer) of the jib are connected. When the overload protection device identifies that these sensors are connected, the operation of any of the levers S5 and S6 is interpreted as a control of a jib function (tilting and extension, respectively) and the overload protection device applies the logic relating to working operations including use of a jib. If the jib is temporarily demounted, for instance when the crane is to be used with hydraulic tools instead of a jib, a specially constructed plug has to be placed in the electric line to the jib. When the overload protection device identifies that this plug has been put in place, the operation of any of the levers S5 and S6 is interpreted as a control of rotator and hydraulic tool, respectively, and the overload protection device applies the logic relating to the working operation including use of a hydraulic tool when the lever S6 is operated.

[0039] With reference to fig 5, a preferred way of processing the different registered parameters for determination of the, for the time being, maximum allowed lifting force of the crane will be described in the following.

[0040] When the control system is activated in the initial stage, the processing unit 33 is adapted to set the maximum allowed lifting force to a value corresponding to the lower value applying to tool working, i.e. for working operations of the type defined as type D and E above.

[0041] If the processing unit 33 gets information that any of the levers S5 and S6 has been operated at the same time as the processing unit 33 has information that a jib 15 is mounted to the extension boom 7, the processing unit 33 is adapted to set the maximum allowed lifting force to a value corresponding to the value applying to jib working, i.e. for working operations of the type defined as type B above. This value of the maximum allowed lifting force is maintained all until the processing unit 33 from the lifting counter 36 obtains information that the crane performs a new lifting up. If the processing unit 33, after a new lifting up has been established, again gets information that any of the levers S5 and S6 has been operated at the same time as the processing unit 33 has information that a jib 15 is still mounted to the extension boom 7, the processing unit 33 is adapted to maintain the previously set value of the maximum allowed lifting force that corresponds to the value applying to working operations of type B, whereupon the described evaluation cycle is run through again.

[0042] If the processing unit 33 gets information that the lever S6 has been operated at the same time as the processing unit 33 does not have information that a jib is mounted to the extension boom 7, the processing unit 33 is adapted to set the maximum allowed lifting force to a value corresponding to the value applying to tool working. If the lever S6 is not again operated within 60 seconds, the processing unit 33 sets the maximum allowed lifting force to a value corresponding to the higher value applying to hook working, i.e. for working operations of the type defined as type A above. The time limit 60 seconds has been chosen bearing in mind that tool working, for instance excavation, is an intense working with working cycles of circa 30 seconds, whereby the processing unit 33 with a time limit of 60 seconds does not run the risk, during the performance of a working cycle including tool working, of erroneously changing the value of the maximum allowed lifting force from the lower value applying to tool working to the higher value applying to hook working. For the operator to be able to "fool" the system during the performance of a working cycle including tool working, the operator has to wait until a time corresponding to two working cycles has elapsed since the last operation of the grab tool. This results in a considerable deterioration of the productivity of the crane, and it is therefor most unlikely that such attempts to "fool" the system occur at any larger extent. The processing unit 33 obtains information about the time elapsed since the last operation of the lever S6 from the time registration means 37.

[0043] When the processing unit 33 has no information that lever S5 and S6 have been manoeuvred within 60 seconds from the starting up of the system, the processing unit 33 sets the maximum allowed lifting force to a value corresponding to the higher value applying to hook working. The same applies if lever S5 and S6 have not been operated after the lifting counter 36 has registered that the crane has performed a new lifting up after a previous registered jib working and, as mentioned above, if the lever S6 is not again operated within 60 seconds after a previous registered tool working.

[0044] The above mentioned values of the maximum allowed lifting force each corresponds to a combination of highest allowed pressure values in the different operating means. These pressure values are stored in a memory 35 included in the processing unit 33. This memory 35 is with advantage a read-write memory so that the stored values easily can be changed if so desired. The processing unit 33 continuously reads the output signals from the pressure sensors 34 and compares the output signal from the respective pressure sensor with the determined value of the maximum allowed pressure in the operating means associated with the pressure sensor 34. If the pressure detected by any of the pressure sensors 34 exceeds the determined maximum allowed pressure in the associated operating means, the processing unit 33 delivers a signal to the dump valve 27 which dumps the flow directly to the reservoir 21, which results in that the hydraulic system runs out of pressure and the load is hold by means of the load holding valve 31. In this situation the system is adapted only to allow moment reducing crane movements.

[0045] The values of the highest allowed pressure in the different operating means for the different types of working operations are determined for the respective crane type by means of stress calculations related to static strength as well as fatigue strength.

[0046] By means of the method according to the invention, the crane can always be used optimally in respect of the strength of the steel structure of the crane and the presently performed type of working operation. The method can be realised by means of minor restructurings of equipment already today included in overload protection devices in certain hydraulic cranes, and can consequently be realised in a simple manner and at a comparatively low cost.

[0047] The invention is of course possible to realise also for cranes having more or fewer crane functions than the six ones described in the example above. The invention is neither limited to the described embodiments as for the rest, a number of modifications thereof are on the contrary possible within the scope of the subsequent claims.

Claims

1. A hydraulic crane comprising a control system for controlling different crane functions for the performance of different types of working operations, and an arrangement for regulation of the maximum allowed lifting force of the crane (1), characterized in that said arrangement comprises means (32, 33) for the continuos registration of which crane functions that are being controlled via the control system, and a processing unit (33) adapted to identify, based on these registrations, the performed working operation as being of a certain type among a number of predetermined types of working operations, said processing unit (33) further being adapted to determine a, for the time being, maximum allowed lifting force of the crane (1) in dependence on the identified type of working operation.

2. A crane according to claim 1, characterized in that the processing unit (33) comprises a memory (35) in which values representing the maximum allowed lifting force of the crane (33) are stored for different types of working operations, the processing unit (33) being adapted to determine the maximum allowed lifting force for the crane by selecting, among the stored values, the values applying to a type of working operation corresponding to the identified one.

3. A crane according to any of the preceding claims, characterized in that the control system comprises valve members (23) for controlling the hydraulic flow to the different crane functions, the control system further comprising a number of operating devices (24;S1-S6) for regulating the valve members (23), and that the means (32, 33) for registration of which crane function that are being controlled via the control system are adapted to continuously detect which valve members (23) that are being operated via the operating devices (24;S1-S6).

4. A crane according to any of the preceding claims, characterized in that the crane (1) comprises load detecting members (34), which are adapted to detect the lifting force exerted by the crane (1), the processing unit (33) being adapted to compare the lifting force detected by the load detecting members (34) with the determined maximum allowed lifting force, and that a dump valve (27) is adapted to prevent load increasing crane movements when the detected lifting force exceeds the maximum allowed lifting force.

5. A crane according to claim 4, characterized in that the load detecting members (34) consist of pressure sensors, which are adapted to measure the pressure in the hydraulic operating means (8, 9, 10, 14, 17, 19) which execute the different crane functions.

6. A crane according to any of the preceding claims, characterized in that the arrangement also comprises a means (36) which registers when the crane (1) lifts up and puts down, respectively, a load, the processing unit (33) being adapted to also use these registrations for the determination of the, for the time being, maximum allowed lifting force of the crane (1).

7. A crane according to claim 6, characterized in that the means (36) for registration of a lifting up and putting down, respectively, of a load is adapted to register a lifting up and a putting down, respectively, by detecting the velocity of the pressure variations in the lifting cylinder (8) of the crane, a lifting up and a putting down, respectively, being registered when the velocity of the pressure variation exceeds a predetermined value.

8. A crane according to any of the preceding claims, characterized in that the arrangement also comprises means (37) for registration of the time that has elapsed since the last registered control of a certain crane function, the processing unit (33) being adapted to also use these registrations in the determination of the, for the time being, maximum allowed lifting force of the crane (1).

9. A method for regulation of the maximum allowed lifting force of a hydraulic crane (1) comprising a control system for controlling different crane functions for the performance of different types of working operations, and an arrangement for regulation of the maximum allowed lifting force of the crane, characterized in that registration of which crane functions that are being controlled via the control system is performed continuously, and that a processing unit (33) identifies, based on these registrations, the performed working operation as being of a certain type among a number of predetermined types of working operations, the processing unit (33) further determining a, for the time being, maximum allowed lifting force of the crane (1) in dependence on the identified type of working operation.

10. A method according to claim 9, characterized in that the processing unit (33) comprises a memory (35) in which values representing the maximum allowed lifting force of the crane are stored for different types of working operations, the processing unit (33) determining the maximum allowed lifting force of the crane (1) by selecting, among the stored values, the values applying for a type of working operation corresponding to the identified one.

11. A method according to any of claims 9-10, characterized in that the hydraulic flow to the different crane functions are controlled via valve members (23), the valve members (23) being regulated by means of a number of operating devices (24;S1-S6) included in the control system, and that it is continuously registered which valve members (23) that are being regulated via the operating devices (24;S1-S6).

12. A method according to any of claims 9-11, characterized in that the lifting force exerted by the crane (1) is detected by means of load detecting members (34), the lifting force detected by the load detecting members (34) being compared with the maximum allowed lifting force determined by the processing unit (33), and that a dump valve (27) prevents load increasing crane movements when the detected lifting force exceeds the maximum allowed lifting force.

13. A method according to any of claims 9-12, characterized in that a means (36) included in the arrangement registers when the crane (1) lifts and puts down, respectively, a load, the processing unit (33) also using these registrations in the determination of the, for the time being, maximum allowed lifting force of the crane.

14. A method according to claim 13, characterized in that the means (36) for registration of a lifting up and a putting down, respectively, of a load registers this by detecting the velocity of the pressure variations in the lifting cylinder (8) of the crane, a lifting up and a putting down, respectively, being registered when the velocity of the pressure variation exceeds a predetermined value.

15. A method according to any of claims 9-14, characterized in that the time that has elapsed since the last control of a certain crane function is registered, the processing unit (33) also using these registrations in-the determination of the, for the time being, maximum allowed lifting force of the crane.

Drawing