WO2010077185A1

WO2010077185A1 - Method for operating a crane arrangement, crane arrangement and vehicle comprising a crane arrangement

Info

Publication number: WO2010077185A1
Application number: PCT/SE2008/000747
Authority: WO
Inventors: Jens Gustafsson; Mattias Berglund; Hayder Wokil
Original assignee: Volvo Lastvagnar AB
Current assignee: Volvo Truck Corp
Priority date: 2008-12-29
Filing date: 2008-12-29
Publication date: 2010-07-08
Anticipated expiration: 2011-06-29

Abstract

The invention relates to a method for operating a crane arrangement (200) for a vehicle (100), particularly a truck, wherein a cab mounted crane (10) is arranged on a vehicle frame (120) at a backside (114) of a cab (102), which in a crane working mode is stabilized by a first crane stabilizer unit (20) coupled to a frame (120) of the vehicle (100) and a second crane stabilizer unit (30) in front of the cab (102). A load force caused by payload (150a) handled the crane (10) is selectively distributed between the second crane stabilizer unit (30) and front wheels (110a) arranged on at least one front axle (110) by increasing the load force on the front wheels (110a) with respect to the second crane stabilizer unit (30).

Description

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D E S C R I P T I O N

Method for Operating a Crane Arrangement, Crane Arrangement and Vehicle

Comprising a Crane Arrangement

TECHNICAL FIELD

The invention relates to a method for operating a crane arrangement, a crane arrangement and a vehicle comprising a crane arrangement according to the preambles of the independent claims.

BACKGROUND OF THE INVENTION

It is known in the art that commercial vehicles such as trucks are equipped with special tools such as cranes which haul payloads above the cabin to the front of the vehicle. Such over-cab cranes are often used in building sites with restricted space. In order to stabilize the vehicle during operation of the crane a support leg unit arranged on the frame below the crane and a support leg unit in front of the cab are lowered to the ground.

When the crane is being activated, the middle supporting unit below the crane will be L lowered_, to the ground. In case the crane is working above the cabjjie operator lowers the front supporting leg unit to the ground. When the front leg unit reaches the pressure limit the crane stops prolonging the crane outreach or stops increasing weight of the payload handled by the crane. Today, the force acting on the front stabilisers and the middle supporting unit is controlled by the hydraulic pressure in the crane. When the pressure reaches its upper limit the crane stops functioning. The pressure limit is a value specified by the crane manufacturer. The lifting capacity with crane on the truck is specified by the truck manufacturer and the crane manufacturer in conjunction. Limiting the crane outreach decreases the agility to the vehicle in usually narrow building sites. Limiting the payload limits the usage of the vehicle as loading or off-lading of payload takes longer time. SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for operating a crane arrangement which allows for increasing the crane outreach and/or the lifting capacity of the crane. It is another object of the invention to provide an improved crane arrangement for a vehicle. It is another object of the invention to provide a vehicle with an improved crane outreach and/or lifting capacity of its crane.

The objects are achieved by the features of the independent claims. The other claims and the description disclose advantageous embodiments of the invention.

According to a first aspect of the invention, a method is proposed for operating a crane arrangement for a vehicle, particularly a truck, wherein a crane is arranged close to a backside of a cab, a so called cab mounted crane, which in a working mode is stabilized by a first crane stabilizer unit coupled to a frame of the vehicle and a second crane stabilizer unit in front of the cab. A load force caused by payload handled by the crane is selectively distributed between the second crane stabilizer unit and front wheels arranged on at least one front axle by increasing the load force on the front wheels with respect to the second crane stabilizer unit.

The load force caused by payload handled by the crane in the working mode can be generated by a payload lifted and/or hauled by the crane resulting in a lever arm acting on the mounting parts of the crane to the frame. If the crane is working above the cab, i.e. lifts payload from the vehicle and offloads it in an area in front or sideways of the cab or vice versa, the vehicle frame in the area where the crane is attached to the vehicle frame is one of the weakest points of the frame. Normally, the vehicle frame has to be reinforced in this area which restricts the installation space in this region. However, this region is particularly densely packed with aggregates and components. Favourably, the invention allows to optimize the load force distribution for the complete vehicle between the axles in a way to allow adding more pressure on the front mounted second crane stabilizer unit without the need of reinforcing the chassis frame underneath the cab.

Favourably, the invention allows an improvement of the load handled by the crane. The invention allows to increase the payload lifted by a crane mounted behind the back of the cab which is working above the cab and/or the crane's outreach. At a given outreach of the crane the payload can be increased and/or the outreach of the crane for a given payload can be increased. It is possible to have a smaller crane fitted to the truck and to still maintain the same outreach if the truck runs for load sensitive applications or to increase crane outreach and/or lifting capacity. This is favourable in space constricted working sites where a large outreach of the crane is desired. The crane can operate in front of the vehicle as well as sideways beside the vehicle.

Preferably, a load force caused the crane in the working mode is distributed between the first crane stabilizer unit, the second crane stabilizer unit and the front wheels so that a load force ratio equal to the load force on the second crane stabilizer unit divided by the load force on the front wheels is varied depending on a load force on the second crane stabilizer unit. Favourably, the load ratio can be decreased in favour of the second crane stabilizer unit, i.e. the load force on at least the second crane stabilizer unit can be decreased. Advantageously, according to the invention the load distribution for a complete vehicle between the axles can bejDptimized in_a way to allow adding more pressure on the front mounted crane stabilizer unit without the need of additionally reinforcing the chassis frame underneath the cab.

Favourably, for an air suspended vehicle the pressure in the air bellows can be changed automatically all the time through receiving payload and position data from the crane in purpose to increase the payload lifting capacity and /or increase the outreach for the crane.

In case of a crane operating sideways instead of over the cab in longitudinal direction it is possible to distribute load force between the first and/or second crane stabilizer unit and the wheels in a transversal direction instead of a longitudinal direction.

According to a favourable embodiment of the invention, the load ratio can be varied, particularly decreased, by lifting the second crane stabilizer unit. Consequently, the load force on the front wheels can be increased.

According to a further favourable embodiment of the invention, the load ratio can be varied, particularly decreased, by increasing a load force or force acting on the front wheels, thus advantageously reducing the load force on the second crane stabilizer unit.

According to a further favourable embodiment of the invention, a non-driven rear axle can be lifted, thus advantageously making use of the vehicle as a counterweight for the payload lifted by the crane. Lifting a non-driven rear axle changes the wheel base in a favourable manner and releases load force at the front of the vehicle at a given payload. Thus, the payload and/or the crane outreach can be increased as the second crane stabilizer unit has now free capacity for accepting an increase in load force.

According to a further favourable embodiment of the invention, a bogie axle can be lifted. By lifting the bogie axle when the second crane stabilizer unit mounted at J_.he front of the cab is in touch with the ground, the front overhang of the vehicle_^ can be released from a certain amount of load that can be used by the front second crane stabilizer unit. By lifting the bogie axle the wheel base is changed which in turn decreases the load to the vehicle on the front axle and the front end. This release on the front end of the vehicle can be used to increase the payload and/or the crane outreach until the load limit of the second crane stabilizer unit is reached.

According to a further favourable embodiment of the invention, an air pressure in air bellows in an air suspended vehicle can be varied for supporting the second crane stabilizer unit. Particularly, air from one or more air bellows can be removed at a driven rear axle, thus favourably increasing the stiffness of the frame rails. According to a further favourable embodiment of the invention, a start position can be provided for lifting one or more rear axles by adjusting a suspension of the one or more rear axles to a higher end position. Favourably, the stiffness of the frame rails can be improved thus allowing to increase the payload and/or crane outreach further.

According to a further favourable embodiment of the invention, a load sensor is coupled to second crane stabilizer unit. The sensor can provide an output signal indicating how close the handling is to a stability limit for the second crane stabilizer unit. Favourably, depending on the sensor signal an air suspension of the vehicle can be configured to support the second crane stabilizer unit. If the crane is operating sideways of the vehicle, the air suspension can be varied from side to side of the vehicle. If the crane is operating in front of the vehicle, the air suspension can be varied from the front and rearwards. An optimized load force distribution on the tires can be achieved by changing the wheel base configuration of the vehicle.

According to another aspect of the invention, a crane arrangement for a vehicle is proposed, particularly for a truck, wherein a crane which in a mounted state is arranged close to a backside of a cab, which in a working mode is stabilized by first crane stabilizer unit coupled to a frame of the vehicle and a second crane stabilizer unit in front of the cab. At least one load sensing unit is coupled to the second crane stabilizer unit. The sensor can provide an output signal indicating how close the handling is to a stability limit for the second crane stabilizer unit. Favourably, depending on the sensor signal an air suspension of the vehicle can be configured to support the second crane stabilizer unit. If the crane is operating sideways of the vehicle, the air suspension can be varied from side to side of the vehicle. If the crane is operating in front of the vehicle, the air suspension can be varied from the front and rearwards. An optimized load force distribution on the tires can be achieved by changing the wheel base configuration of the vehicle. According to a further favourable embodiment of the invention, the load sensing unit can be coupled to the second crane stabilizer unit. The load force acting on the second crane stabilizer unit can be determined.

According to a further favourable embodiment of the invention, the load sensing unit can be coupled to a logic unit which triggers distribution of load force between the second crane stabilizer unit and front wheels on at least one front axle so that a load ratio equal to the load force on the second crane stabilizer unit divided by the load force on the front wheels is variable depending on the load force on the second crane stabilizer unit. Favourably, the load force on the front wheels can be increased which provides more load capacity for the second crane stabilizer unit.

According to a further favourable embodiment of the invention, a coupling to a lifting unit can be provided for lifting at least the second crane stabilizer unit and/or lifting a non-driven rear axle and/or lifting a bogie axle. Favourably, the wheel base of the vehicle can be changed in a way to make use of the rear overhang of the vehicle for a better load force distribution between the axles and the second crane stabilizer unit.

According to a further favourable embodiment of the invention, a coupling to an air system can be provided for varying the air suspension depending on the load force on the second crane stabilizer unit. The air suspension can be varied from side to side orjTom the front and rearwards accordingly. Favourably, air from at least one air bellows at a driven rear axle can be removed for improving the stiffness of the frame rails which improves the stability of the vehicle.

According to a further favourable embodiment of the invention, a coupling to a suspension system can be provided for adjusting the suspension of the one or more rear axles to a higher end position. Favourably, the frame rail stiffness can be improved.

According to another aspect of the invention, a vehicle is proposed comprising a crane arrangement according to anyone of the described features. According to a further favourable embodiment of the invention, a logic unit is provided for selectively distributing a load force caused by the crane between the second crane stabilizer unit and front wheels arranged on at least one front axle by increasing the load force on the front wheels with respect to the second crane stabilizer unit. Favourably, the load force can be distributed between a second crane stabilizer unit and front wheels on at least one front axle so that the load ratio equal to the load force on the second crane stabilizer unit divided by the load on the front wheels is variable depending on the load force on the second crane stabilizer unit. The front wheels take away an amount of load force from the second crane stabilizer unit. Thus payload and/or outreach of the crane can be increased compared to a state where the front wheels do not take away a part of the load force from the second crane stabilizer unit.

According to a further favourable embodiment of the invention, a load sensor is provided for determining the load force on the second crane stabilizer unit. The load sensor can provide information about the distance to a stability limit of the vehicle for increasing the payload lifted by the crane and/or the outreach of the crane.

According to another aspect of the invention a computer program is proposed comprising a computer program code adapted to perform a method or for use in a method according to at least one of the method features described above when said program is run on a programmable microcomputer. Favourably, the computer program can be adapted to be downloaded to a control unit or one of its components when run on a computer which is connected to the internet.

Advantageously, a control unit can be provided which selectively distributes the load force on the second crane stabilizer unit for improving the lifting capacity and/or the crane outreach of the crane. Particularly, the control unit can be coupled to an air suspension of the vehicle.

Further a computer program product stored on a computer readable medium is proposed, comprising a program code for use in a method according to one of the method features described above on a computer. The computer program product can easily be coupled to a control unit on the vehicle provided for selectively distributing the load force on the second crane stabilizer unit for improving the lifting capacity and/or the crane outreach of the crane.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above-mentioned and other objects and advantages may best be understood from the following detailed description of the embodiments, but not restricted to the embodiments, wherein is shown schematically:

Fig. 1a, 1b a vehicle with a cab mounted crane according to the prior art with a first and a second crane stabilizer unit (Fig. 1a) and a moment diagram indicating a load force distribution when the second crane stabilizer unit is not supported by front wheels;

Fig. 2 a moment diagram with a second crane stabilizer unit supported by front wheels according to the invention generating a load force gain; Fig. 3a-3c in side views various stages of a first embodiment of the invention comprising lifting of a bogie axle; Fig. 4a-4c in side views various stages of a further embodiment of the invention comprising lifting of a second crane stabilizer unit and a bogie axle; Fig. 5a-5c in side views various stages of a further embodiment of the invention comprising activating a front air suspension and lifting of a bogie axle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention. Figs. 1a depicts a perspective view of a vehicle 100 with a cab mounted crane 10 of a crane arrangement according to the prior art with a first crane stabilizer unit 20 for the crane 10 and a second crane stabilizer unit 30. The crane 10 is located on the frame 120 at the backside 118 of the cab 102 between the cab 102 and a loading platform 104 for carrying payload.

The vehicle 100 may comprise a front axle 110 with front wheels where only the left front wheel 110a is displayed in the drawing, and two rear axles 112 and 114, e.g. comprised by a bogie, with rear wheels of which only the left wheels 112a, and 114a are shown.

The first crane stabilizer unit 20 is coupled to the frame 120 of the vehicle 100. Particularly, the first crane stabilizer unit 20 is arranged below the crane 10 and the second crane stabilizer unit 30 is arranged in front of the cab 102. The frame 120 is reinforced in this region to provide enough strength for crane operations. The first crane stabilizer unit 20 comprises two outrigger legs wherein only the left leg 20a is seen in the drawing.

The second crane stabilizer unit 30 is arranged at the front 116 of the cab 102 and comprises two legs 30a, 30b. Of course, the second crane stabilizer unit 30 can also be equipped with only one leg in the centre of the cab 102.

The first and the second crane stabilizer units 20, 30 are activated and touch the ground for stabilizing the crane 10.

The crane 10 comprises a first arm 18 attached to the frame 120, a second arm 16 and an extendable outrigger arm 12. Arm 12 can be extend by telescopic portions 12a, 12b which can be driven out by an actuator device 14.

As known in the art, the first and second crane stabilizer units 20, 30 are drawn in and lifted off the ground in the vehicle's transport mode. When the vehicle 100 is in the working mode, the crane 10 is activated and the first crane stabilizer unit 20 beneath the crane 10 is activated and its supporting legs 20a are lowered to the ground. When the crane 10 is intended to operate above the cab 102, the operator activates the second crane stabilizer unit 30 at the front of the cab 102, i.e. lowers its one or more legs 30a, 30b to the ground. When the front crane stabilizer unit 30 reaches the pressure limit the crane 10 stops prolonging the crane outreach or lifting more payload. The pressure limit is usually specified by the crane manufacturer.

Fig. 1b displays a moment diagram for such a prior art vehicle indicating a moment Mι_oad, i.e. the torque, acting on the crane 10. The moment Mι__Oad is generated by the payload which imposes a force FL at the end of a crane arm 12 comprising an outreach L when lifted by the crane 10 of the arm 12 causing a load force Fs on the second crane stabilizer unit 30. The horizontal axis of the diagram is presenting the chassis frame distance between the front end indicated by Fs and the crane installation party indicated by F_crane

The first crane stabilizer unit 20 arranged underneath the crane 10 experiences a force Fcrane caused by the crane 10. The second crane stabilizer unit 30 arranged at the front of the vehicle's cab 102 experiences a force F_s. The load case trace LC 1 shows a linear behaviour and varies between a moment M=O at the second crane stabilizer unit 30, indicated by FL, and M=M_Load at the first crane stabilizer unit 20, indicated by F_crane- A maximum allowable moment M_crit indicates the stability criterion for the crane 12 at a given payload (FL). The payload and/or the outreach JL of the crane 10 can be increased as long as the moment at the backside of the cab 102 does not exceed M_Crit- It is possible to enforce the chassis frame towards the rear of the vehicle with a comparably small effort in order to increase a locally acting moment M_cri_t. However, the chassis frame towards the front of the vehicle, particularly under the cab 102, cannot be reinforced with a reasonable effort. The reason is that the frame rail distance narrows towards the front and the space between the frame rails is congested with components such as the engine and the like. Thus, the weakest frame portion is typically located behind the cab 102. If the allowed maximum moment is exceeded, the frame may break there. Accordingly, when the maximum allowable moment M_cri_t is reached, the payload and/or outreach L of the crane 10 must be limited to this value. Referring now to Fig. 2, a moment diagram is depicted which illustrates the advantage of the invention. Whereas in Fig. 1b a selective support of the second stabilizer unit 30 is not applied, now the selective distribution of the force is taken into account. M_ori_t is the moment at the most critical section at the frame, directly in the front of the crane installation. The horizontal axis of the diagram is presenting the chassis frame distance between the front end indicated by F_s at M=O and the crane installation party indicated by F_crane at M= M_Load- The moment M_Load is represented as a normalized parameter in order to illustrate the gain at the location where the moment Meri_t of Fig. 1b is acting on the chassis frame.

Particularly, a load force caused by payload handled by the crane 10 is selectively distributed between the second crane stabilizer unit 30 and front wheels 110a arranged on at least one front axle 110 by increasing the load force on the front wheels 110a with respect to the second crane stabilizer unit 30. As can be seen in the diagram, when the front wheels 110a support the second crane stabilizer unit 30, it carries a part of the load force thus decreasing the actual load force on the second crane stabilizer unit 30.

The result of the selective distribution of the load force can be seen on the load case trace LC2. LC2 has a smaller slope than LC1 between Fs and F_A, corresponding to the acting point of the front wheels 110a, and a larger slope until LC2 reaches Mi_oad- As a consequence, at the intersection between the critical moment M_crj_t, and LCI_,, LC2 a distance between LC1 and LC2 reflects a moment gain MD generated by the support of the front wheels 110a. Thus, the second crane stabilizer unit 30 can now carry an additional load force corresponding to the moment gain M_D.

The distribution of the load force can be adjusted so that the load ratio equal to the load force on the front crane stabilizer unit 30 divided by the load force on the front wheels 110a is varied depending on the load force on the front crane stabilizer unit 30. For instance, the air suspension of the vehicle 100 can be adjusted to increase the pressure on the front wheels 11 Oa, thus decreasing the load ratio in favour of the second crane stabilizer unit 30.

Favourably, for an air suspended vehicle 100 the pressure in the air bellows can be changed automatically all the time through receiving payload and position data from the crane 10 in purpose to increase the payload lifting capacity and /or increase the outreach for the crane 10.

Figs. 3a-3c illustrate various stages of a first embodiment of the invention comprising lifting of a bogie axle 122 of the vehicle 100.

This embodiment is based on establishing a communication between the crane 10 and the vehicle 100 via a control unit 50.

Both the first crane stabilizer unit 20 at the backside 118 of the cab 102 and the second crane stabilizer unit 30 arranged at the front 116 of the cab 102 are fully activated when the crane 10 is intended to carry payload 150, 150a above the cab 102 (Fig. 3a). The second stabilizer 30 can have one or more stabilizer legs 30a. The first crane stabilizer unit 20 may have two stabilizer legs 20a.

A load force acting on the second crane stabilizer unit 30 is measured by a load sensor 60_arranged in the crane stabilizer unit 30. The measured data is transferred from the sensor 60 to the control unit 50 which can control the air suspension of the vehicle 100 (Fig. 3b).

When the front crane stabilizer unit 30 reaches its maximum load force (Fig. 3c) the control unit 50 issues signals 52 to the air suspension of the vehicle 100. The bogie axle 122, comprising a driven axle 112 with wheels 112a and a non driven axle 114 with wheels 114a, will be lifted by a distance d1 from the ground automatically as soon as the front crane stabilizer unit 30 reaches it maximum pressure limit. The rear overhang of the vehicle acts as counterweight and reduces the actual load force on the second crane stabilizer unit 30. Thus the lifting load by the crane 10 and/or to increase the crane outreach when the crane 10 is working above the cab 102 is increased.

Preferably, the following steps are performed in a working mode of the crane 10 (1 a) activating the first and the second crane stabilizer units 20, 30 until both touch the ground;

(1b) measuring the load force on the second crane stabilizer unit 30;

(1c) if the load force reaches an upper limit of the load force;

(1d) lifting the bogie axle 122.

By lifting the bogie axle 122 the wheel base can be changed and that in turn decreases the load force on the front axle 110 and front end of the vehicle 100.

This load force release on the front end of the vehiclelOO can be used to increase the load force on the front crane stabilizer unit 30 through either increasing the payload lifted by the crane 10 or by increase the outreach of the crane arm 12.

Fig. 4a-4c depict various stages of a further embodiment of the invention comprising activating a second crane stabilizer unit 30 late and lifting a bogie axle 122.

The embodiment is based on establishing a communication between the crane 10 and the vehicle 100 via a control unit 50. The first and the second crane stabilizer units 20, 30 are activated, wherein the second crane stabilizer unit 30 is only in "slight" contact with the ground while the cranes' first stabilizer 10 are fully activated and at normal contact with the ground when the crane 10 is in its working mode to operate above the cab 102 (Fig. 4a).

When the second crane stabilizer unit 30 touches the ground, the bogie axle 122 will be lifted (Fig. 4b). Valuable axial load can be added on the second crane stabilizer unit 30. This extra axial load on the front axle and the front wheels 110a increases the crane lifting capacity for and/or increase the crane outreach when the crane 10 is working above the cab 102. In addition, the invention makes it possible to gain even more very valuable extra axial load applicable on the front crane stabilizer unit 30 by using the truck weight as counterweight. This can be achieved by lowering the air controlled rear axels 112, 114 by raising the second crane stabilizer unit 30 by a distance L1 (Fig. 4c).

Preferably, the following steps are performed in a working mode of the crane 10 (2a) activating the first crane stabilizer unit 20 to touch the ground soundly; (2b) activating the second crane stabilizer unit 30 by lowering it just above the ground or only in slight contact the ground;

(2c) measuring the load force on the second crane stabilizer unit 30;

(2d) if the load force indicates that the second crane stabilizer unit 30 is in sound contact with the ground (2e) lifting the bogie axle 122.

Fig. 5a-5c show various stages of a further embodiment of the invention comprising activating a front air suspension of a front axle 110 with front wheels 110a and lifting of a bogie axle 122.

The embodiment is based on establishing a communication between the crane 10 and the vehicle 100 via a control unit 50. The setup is similar to the embodiments in Figs. 3a-3c and Fig. 4a-4c above, but support of the second crane stabilizer unit 30 is provided by lifting the front end of the vehicle 100 built with air controlled front suspension by increasing the pressure in the air bellows for the front axle 110.

Both the first crane stabilizer unit 20 at the backside 118 of the cab 102 and the second crane stabilizer unit 30 arranged at the front 116 of the cab 102 are fully activated when the crane 10 is intended to carry payload 150, 150a above the cab 102 (Fig. 5a). The second stabilizer 30 can have one or more stabilizer legs 30a. The first crane stabilizer unit 20 may have two stabilizer legs 20a.

A load force acting on the second crane stabilizer unit 30 is measured by a load sensor 60 arranged in the crane stabilizer unit 30. The measured data is transferred from the sensor 60 to the control unit 50 which can control the air suspension of the vehicle 100 (Fig. 5b).

When the second stabilizer 30 reaches the maximum axial load the tag axle 114 is started to lift and the air bellows pressure of the air bellows of the front axle 110 is increased (Fig. 5c). The control unit 50 issues signals 52 to the air suspension of the vehicle 100. The bogie axle 122, comprising a driven axle 112 with wheels 112a and the non driven axle 114 with wheels 114a, will be lifted by a distance d1 from the ground automatically as soon as the front crane stabilizer unit 30 reaches it maximum pressure limit. The rear overhang of the vehicle acts as counterweight and reduces the actual load force on the second crane stabilizer unit 30.

Thus the lifting load by the crane 10 and/or to increase the crane outreach when the crane 10 is working above the cab 102 is increased.

By lifting the bogie axle 122 the wheel base can be changed and that in turn decreases the load force on the front axle 110 and front end of the vehicle 100. This load force release on the front end of the vehiclelOO can be used to increase the load force on the front crane stabilizer unit 30 through either increasing the payload lifted by the crane 10 or by increase the outreach of the crane arm 12.

Preferably, the following steps are performed in a working mode of the crane 10

(3a) activating the first and second crane stabilizer units 20, 30 to touch the ground soundly; (3b) measuring the load force on the second crane stabilizer unit 30;

(3c) when the second crane stabilizer unit 30 reaches the maximum load force

(3d) starting lifting the bogie axle 122 and

(3e) increasing the pressure in the air bellows of the front axle 110.

For all embodiments described, the operation conditions can still be improved by increasing the stiffness of the vehicle frame 120 by removing air from air bellows at a driven rear axle 112. By lifting the bogie axle 122 the wheel base can be changed and that in turn decreases the load force on the front axle 110 and front end of the vehicle 100. This load force release on the front end of the vehicIelOO can be used to increase the load force on the front crane stabilizer unit 30 through either increasing the payload lifted by the crane 10 or by increase the outreach of the crane arm 12.

Alternatively or additionally, a better start position for lifting one or more rear axles 112, 114 can be provided by adjusting the suspension of the one or more rear axles 112, 114 to a higher end position.

Claims

C L A I M S

1. A method for operating a crane arrangement (200) for a vehicle (100), particularly a truck, wherein a crane (10) is arranged on a vehicle frame

(120) close to a backside (118) of a cab (102), which in a crane working mode is stabilized by a first crane stabilizer unit (20) coupled to a frame (120) of the vehicle (100) and a second crane stabilizer unit (30) in front of the cab (102), characterized in that a load force caused by payload (150a) handled by the crane (10) is selectively distributed between the second crane stabilizer unit (30) and front wheels (110a) arranged on at least one front axle (110) by increasing the load force on the front wheels (110a) with respect to the second crane stabilizer unit (30).

2. The method according to claim 1 , characterized in that a load ratio equal to the load force on the second crane stabilizer unit (30) divided by the load force on the front wheels (110a) is varied depending on a load force on the second crane stabilizer unit (30).

3. The method according to claim 1 or 2, characterized by decreasing the load ratio by lifting the second crane stabilizer unit (30).

4. Jhe method according to claim 1 or 2, characterized by decreasing thejoad ratio by increasing a pressure or force acting on the front wheels (110a).

5. The method according to any preceding claim, characterized by lifting a non-driven rear axle (114).

6. The method according to any preceding claim, characterized by lifting a bogie axle (122).

7. The method according to any preceding claim, characterized by varying air pressure in air bellows in an air suspended vehicle (100) can be varied for supporting the second crane stabilizer unit (30).

8. The method according to claim 7, characterized by removing air from one or more air bellows at a driven rear axle (112).

9. The method according to any preceding claim, characterized by providing a start position for lifting one or more rear axles (112, 114) by adjusting a suspension of the one or more rear axles (112, 114) to a higher end position.

10. The method according to any preceding claim, characterized in that a load sensor (60) is coupled to the second crane stabilizer unit (30).

11. A crane arrangement (200) for a vehicle (100), particularly a truck, wherein a crane (10) is arranged close to a backside (114) of a cab (102), which crane (10) in a working mode is stabilized by a first crane stabilizer unit (20) coupled to a frame (120) of the vehicle (100) and second crane stabilizer unit (30) in front of the cab (102), characterized by at least one load sensing unit (60) coupled to a second crane stabilizer unit (30) in front of the cab (102) for detecting load force caused by payload (150a) handled by the crane (10).

12. The crane arrangement according to claim 11 , characterized in that the load sensing unit (60) is coupled to the second crane stabilizer unit (30).

13. The crane arrangement according to claim 11 or 12, characterized in that the load sensing unit (60) is coupled to a logic unit (50) which triggers distribution of a load force between the second crane stabilizer unit (30) and front wheels (110a) on at least one front axle (110) so that a load ratio equal to the load force on the second crane stabilizer unit (30) divided by the load force on the front wheels (110a) is variable depending on the load force on the second crane stabilizer unit (30).

14. The crane arrangement according to anyone of the claims 11 to 13, characterized by a coupling to a lifting unit for lifting a second crane stabilizer unit (30) and/or lifting a non-driven rear axle (114) and/or lifting a bogie axle.

15. The crane arrangement according to anyone of the claims 11 to 14, characterized by a coupling to an air system for varying the air suspension depending on the load force on the second crane stabilizer unit for removing air from air bellows at a driven rear axle (112).

16. The crane arrangement according to claim 15, characterized by a coupling to an air system for removing air from air bellows at a driven rear axle (112).

17. The crane arrangement according to anyone of the claims 11 to 16, characterized by a coupling to a suspension system for adjusting the suspension of the one or more rear axles (112, 114) to a higher end position.

18. A vehicle (100) comprising a crane arrangement (10) according to anyone of the claims 11 to 17.

19. The vehicle according to claim 18, characterized in that a logic unit (50) is provided for selectively distributing a load force caused by the crane (10) between the second crane stabilizer unit (30) and front wheels (110a) arranged on at least one front axle (110) by increasing the load force onjhe front wheels (110a) with respect to the second crane stabilizer unit (30).

20. The vehicle according to claim 18 or 19, characterized in that a load sensor (60) is provided for determining a load force on the second crane stabilizer unit (30).

21. Computer program comprising a computer program code adapted to perform a method or for use in a method according to at least one of claims 1 to 10 when said program is run on a programmable microcomputer.

22. Computer program according to claim 21 adapted to be downloaded to a control unit or one of its components when run on a computer which is connected to the internet.

23. Computer program product stored on a computer readable medium, comprising a program code for use in a method according to one of claims 1 to 10 on a computer.