WO2010071484A1

WO2010071484A1 - Method and system for supplying energy to one or more work machines

Info

Publication number: WO2010071484A1
Application number: PCT/SE2008/000707
Authority: WO
Inventors: Patrik WAHLSTRÖM; Jan Karlsson
Original assignee: Volvo Construction Equipment Ab
Priority date: 2008-12-15
Filing date: 2008-12-15
Publication date: 2010-06-24

Abstract

The invention relates to a method for supplying energy to one or more work machines (10a, 10b, 10c), each work machine (10a, 10b, 10c) being provided with at least one energy storage unit (30a, 30b, 30c) arranged on the work machine (10a, 10b, 10c) for supplying energy to the work machine (10a, 10b, 10c), each work machine (10a, 10b, 10c) being associated with a control station (100), and each work machine (10a, 10b, 10c) being provided with a device for transmitting signals to the control station (100), comprising the steps of: (i) monitoring the charging level of the respective energy storage unit (30a, 30b, 30c) by transmitting signals containing information about the current charging level (SOCa, SOCb, SOCc) of the respective energy storage unit (30a, 30b, 30c) from each work machine (10a, 10b, 10c) to the control station (100); and (ii) accomplishing an upgrading of the respective energy storage unit (30a, 30b, 30c) provided that information received by the control station (100) indicates that the charging level (SOCa, SOCb, SOCc) is below a predetermined threshold value.

Description

Method and System for Supplying Energy to One or More Work Machines

TECHNICAL FIELD

The invention relates to a method for supplying energy to one or more work machines and a system for supplying energy to one or more work machines.

BACKGROUND OF THE INVENTION

Work machines or working machines are often operating in a restricted area. The term "work machine" comprises different types of material handling vehicles like construction machines, such as for example wheel loaders, dump trucks and (articulated) haulers, excavators, trucks and the like. A work machine is normally provided with a bucket, container or other type of work implement for carrying/transporting a load. Further terms frequently used for work machines are "earth-moving machinery", "off-road work machines" and "construction equipment".

In connection with transportation of heavy loads, e.g. in contracting work, work machines are frequently used. A work machine may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines and similar environments.

A work machine is often used in a repeated work cycle. The term "work cycle" comprises a route of the work machine (i.e. the work cycle travel path) and a movement of a work implement, such as a bucket (lifting/lowering operation). The work cycle is repeated in the same geographical area. During the performance of the work cycle, the work machine often encounters different gradients of the ground (uphill and downhill), and turns (cornering).

It is known in the art to provide vehicles with a hybrid drive as an energy source for propulsion and for auxiliary devices in the vehicle, exhibiting at least two power sources. It is known for instance to add an electric power source to a conventional combustion engine. The electric power source can be at least one of a battery, a fuel cell, a super capacitor. Typically, the electric power source is embodied to store electric energy, for instance during regenerative braking where kinetic energy of the vehicle is transformed to electric energy and stored e.g. in a battery or a super capacitor.

It is also known to employ electrically driven vehicles which can operate free of emissions. Such vehicles can be hybrid vehicles in an electric operational mode in which a combustion engine is inoperative, or purely electrically electrical vehicles without a combustion engine. A problem connected to electric and hybrid vehicles is the limited range of electric power sources compared to a fuel tank supplying energy to a combustion engine.

In US 2004/0225435 A1 a system for vehicles is disclosed in which an assistance vehicles couples to a dump truck on or at bases of ascending paths, wherein power is supplied as auxiliary power from the assistant vehicle to a propulsion motor of the dump truck, while the assistance vehicle moves synchronous uphill with the dump truck. The drive train of the dump truck itself is designed to have sufficient performance for horizontal paths enabling size and weight reduction of the dump truck. When a multitude of dump trucks is operating, an adequate number of assistance vehicles are required.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for supplying energy to one or more work machines. Another object is to provide a system for supplying energy to one or more work machines.

The objects are achieved by the features of the independent claims. The other claims and the description disclose advantageous embodiments of the invention. A method for supplying energy to one or more work machines is proposed, each work machine being provided with at least one energy storage unit arranged on the work machine for supplying energy to the work machine, each work machine being associated with a control station, and each work machine being provided with a means for transmitting signals to the control station, comprising the steps of: (i) monitoring the charging level of the respective energy storage unit by transmitting signals containing information about the current charging level of the respective energy storage unit from each work machine to the control station; and (ii) accomplishing an upgrading of the respective energy storage unit provided that information received by the control station indicates that the charging level is below a predetermined threshold value.

Upgrading the energy storage unit can be e.g. charging the energy storage unit at an upgrading station, such as a service station, charging the energy storage unit at an actual location of the work machine on the working site, replacing the energy storage unit at an upgrading station, e.g. a service station, replacing the energy storage unit at the actual operation site of the work machine, and the like.

Preferably, the work machines are operating in a restricted working site, e.g. in off- road premises. The local energy storage unit can preferentially be an electrochemical storage device such as a battery or a super capacitor. However, the energy storage unit can also be a storage unit for hydride material for a work machine driven with hydrogen as fuel, or other fuel types.

Advantageously, a purely electric driven vehicle can be operated with virtually unlimited range. For a work machine operating or moving on a restricted area such as a construction field or a mining area, the inoperative time due to charging the local energy storage unit can be reduced. The purely electric operational mode allows for operating the work machine free of emissions and with reduced noise.

By controlling the charging level of the local energy storage units.the frequency of charging cycles can be reduced compared to - in case of electrochemical storage devices - charging cycles with a generator on board of the work machine. Aging of the electrochemical storage device can be reduced. A complex charge management when charging the energy storage device can be avoided.

According to a favourable method step of the invention, upgrading the energy storage unit can be performed by charging the energy storage unit to a charging level above the threshold value. The threshold value is preferably a value which allows a safe long-term serviceability for the energy storage unit. Charging of the energy storage unit can be chosen dependent on various parameters, such as available cheap energy for charging, a short distance for reaching a charging station and the like.

According to a further favourable method step of the invention, upgrading the energy storage unit can be performed by replacing the current energy storage unit by a corresponding energy storage unit having a charging level above the threshold value. The threshold value is preferably a value which allows safe long- term serviceability for the energy storage. Replacing on the current energy storage can be chosen dependent on various parameters, such as availability of a charged energy storage with appropriate size and capacity and the like.

According to a further favourable method step of the invention, upgrading the energy storage unit can be performed at a designated upgrading station. The location of the upgrading station can be chosen to optimize operation parameters of the one or more work machines for an individual work machine or for the fleet of work machines. Favourably, the upgrading station can estimate the gain of a specific form of upgrading and chose an optimal form of upgrading the electric energy storage.

According to a further favourable method step of the invention, upgrading the energy storage unit can be performed at the current position of the work machine. Preferably, a vehicle provided with one or more energy storage units and/or charging equipment for replacing or charging the current energy storage unit can be sent to the work machine. The method can be applied flexibly depending on operation parameters of individual work machines within a working site and/or a fleet of work machines particularly operating in a working site. According to a favourable development of the invention, a control station can consider at least one operation parameter in addition to the charging level of the at least one local energy storage unit of the one or more work machines. If a multitude of work machines is monitored, an optimization of the usage of the multitude of work machines can be performed instead of an optimization of only one work machine. The control station can e.g. comprise the upgrading station.

According to a further favourable development of the invention, the control station can select the energy supply mode causing on a minimum time delay in operation of the one or more work machines compared to other energy supply modes.

According to a further favourable development of the invention, the control station can decide on the energy supply mode based on the assumed energy request among a multitude of work machines monitored by the control station. The available energy in the local energy storage units carried by the work machines and furnishing of energy storage units stored in one or more upgrading stations can be optimized.

According to a further favourable development of the invention, the control station can broadcast the decision to the one or more work machines and can trigger a reaction of the one or more work machines. For instance, if the control station decides on charging of the local energy storage unit at a central upgrading station, the work machine can move to the central upgrading station knowing that the work machine, e.g. a vehicle, will be inoperative for some time during charging of the local energy storage unit. If the control station decides on replacing the local energy storage unit at a central upgrading station, the work machine can move to the central upgrading station and the depleted local energy storage unit can be replaced by another. If the control station decides on replacing the local energy storage unit at a handover location, the work machine can move to the handover location and the depleted local energy storage unit can be replaced by another. In this case, an energy storage unit can be dumped at the handover location by another work machine passing by the handover location carrying a spare energy storage unit or by a service vehicle driving to the handover location. According to a further favourable development of the invention, in the case it is decided to replace the at least one local energy storage unit at the actual position of the respective work machine, the control station can trigger the work machine to move to a handover location and/or triggers delivery of at least one energy storage unit to a handover location. The delivery can be performed by a service vehicle or another work machine. The handover location can be the actual position of the work machine or another appropriate location. Optionally, the handover location can be selected by estimating an available range of the work machine when operated with a depleting local energy storage unit. This allows to optimizing the usage of the available energy in the local energy storage unit without unwanted breaks in operation of the work machine.

The handover location can also be the actual position of the respective work machine at the time the control station decides to replace the local energy storage unit. For instance, the work machine can operate locally, e.g. perform digging or perform earth moving tasks, on that actual position while a service vehicle approaches the work machine bringing with it the new energy storage unit.

According to a further favourable development of the invention, a service vehicle can be sent to the handover location carrying at least one energy storage unit for replacing the local energy storage unit. The service vehicle can transport a multitude of energy storage units and move around while distributing the energy storage units to work machines in need of a charged energy storage unit. The service vehicle can be controlled to deliver the energy storage units in a predefined sequence according to an optimization of usage of the local energy storage units.

Preferably, a work machine can be temporarily employed as the service vehicle. This is advantageous if a work machine has originated from an upgrading station and was triggered to take one or more energy storage units in order to bring these to one or more handover locations on its way to its normal place of action. Of course, an energy storage unit for a work machine operating at a distant place of actions can be transported via a multitude of work machines or service vehicles to an appropriate handover location for the distantly operating work machine. According to another aspect of the invention, a system for supplying energy to one or more work machines is proposed, each work machine being provided with at least one energy storage unit arranged on the work machine for supplying energy to the work machine, the system comprising a control station and means adapted to be arranged on each work machine for transmitting signals to the control station. The control station comprises a means for receiving signals containing information about the current charging level of the respective energy storage unit from each work machine and monitoring the charging level of the respective energy storage unit, and the system further comprises a means for accomplishing an upgrading of the respective energy storage unit provided that information received by the control station indicates that the charging level is below a predetermined threshold value.

Favourably, the system can monitor a multitude of work machines in a way that the local energy storage units can be replaced in time in a way that can improve the performance of the single work machine as well as the multitude of work machines. The system allows the work machines to employ e.g. electric motors in a more environmental friendly way in terms of. noise and emissions compared to a hybrid vehicle in which the combustion engine charges the energy storage unit, i.e. a battery or a super capacitor.

According to a favourable development of the invention, a storage space for one or more energy storage units can be provided. The system can be managed in a way that energy can reliably be provided to the one or more work machines as required. The energy storage units can be prepared ready to use for replacing a depleted local energy storage unit of one or more work machines.

According to a further favourable development of the invention, a loading unit for loading the energy storage units can be provided. Favourably, the charging of the energy storage unit.can be performed in a cost efficient way. For instance, a cheaper and more efficient source of electric energy can be employed for upgrading, i.e. charging, a battery or a super capacitor than a generator which is driven by a combustion engine. According to a further favourable development of the invention, the control station can be assigned to a vehicle fleet moving inside a defined area. Favourably, a fleet of construction equipment can be managed by the control station, thus optimizing the energy consumption of the work machine fleet and the work result , of the work machines.

According to a further favourable development of the invention, at least one service vehicle can be provided for transporting one or more energy storage units to one or more handover locations. The handover locations can be fixed locations in a defined area, such as a construction area, a city area or the like. The handover locations can also be moving locations which can be appointed depending on demand of a work machine or on the decision of the control station.

According to a further favourable development of the invention, one or more upgrading stations can be provided for upgrading, e.g. charging, the at least one energy storage units. The one or more upgrading stations can be installed in a way to have good access to energy which has to be supplied to the one or more work machines and/or to be accessible in a convenient way for the one or more work machines.

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. 1 a preferred embodiment of a system comprising a control station and a multitude of work machines according to the invention;

Fig. 2 . a preferred embodiment of a system comprising a control station and a multitude of work machines which can be supplied by a service vehicle according to the invention; and Fig. 3 a flow chart illustrating preferred method steps according to the invention.

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.

Fig. 1 depicts schematically a preferred example embodiment of a system comprising a control station 100 and a multitude of work machines 10a, 10b, 10c assigned to the control station 100 according to the invention. By way of example, the work machines 10a, 10b, 10c are electrically driven vehicles or hybrid vehicles which are equipped with local energy storage units 30a, 30b, 30c embodied e.g. as batteries. The work machines 10a, 10b, 10c are operating in a construction site, for example, and can be moving around or operate more or less locally at their respective location 60a, 60b, 60c, e.g. for performing digging operations, hauling and the like. The work machines 10a, 10b, 10c can be members of a vehicle fleet 12.

Each work machine 10a, 10b, 10c is equipped with a device 50a, 50b, 50c for transmitting a state of charge SOCa, SOCb, SOCc to the control station 100. Optionally, more information can be transmitted which indicates the actual states of condition of the energy storage units 30a, 30b, 30c. The transmission is indicated by double sided arrows drawn with broken lines.

In the illustration, work machine 10a is equipped with a nearly full local energy storage unit 30a, while work machine 10b has a local energy storage 30b which is nearly depleted and the local energy storage unit 30c of work machine 10c has an intermediate state of charge SOCc. The control station 100 comprises a storage space 20 for 1 to n storage units 30 which can be upgraded, i.e. charged, by a loading unit 40. The storage units 30 are preferably stored fully charged so that a depleted local energy storage unit 30a, 30b, 30c can be replaced when necessary.

The control station 100 comprises also a unit 90 for monitoring the amount of energy which is disposable by the respective local energy storage units 30a, 30b, 30c of the work machines 10a, 10b, 10c. Preferably, the control station 100 can decide on a mode of energy supply, i.e. how energy is best to be supplied to the one or more work machines 10a, 10b, 10c. The decision can be made in an adequate computer system coupled to the control station 100.

The control station 100 comprises a communication unit 50 for communicating with the one or more work machines 10a, 10b, 10c. Preferably, the communication can be bidirectional. Besides the state of charge SOCa, SOCb, SOCc, information concerning the work machine 10a, 10b, 10c can be provided either by transmitting such data between one or more of the work machines 10a, 10b, 10c and the control station 100 and/or by identifying each work machine 10a, 10b, 10c once at the control station 100 on resuming operation in the construction area.

The control station 100 can also serve as an upgrading station 110 where local energy storage units 30a, 30b, 30c of the work machines 10a, 10b, 10c can be upgraded, i.e. recharged. There can be a multitude of upgrading stations 110 distributed in the area.

Referring now to Fig. 2, another preferred embodiment of a system comprising a control station 100 and a multitude of work machines 10a, 10b, 10c is illustrated. As the embodiment of Fig. 1 is similar to the embodiment of Fig. 1 it is referred to the description of Fig. 1 for more details in order to avoid unnecessary repetitions. Additionally or alternatively to the embodiment depicted in Fig. 1 , one or more service vehicles 80 can carry charged 1 to n energy storage units 30 to one or more handover locations 70 and/or to positions 60a, 60b, 60c of the work machines 10a, 10b, 10c. It is also possible that a work machine 10a, 10b dumps an energy storage unit 30 at a handover location 70 and a work machine 10c picks it up at the handover location 70 and dumps the depleted local energy storage unit 30c at the handover location 70. It can be picked up later and transported to an upgrading station 110.

In both embodiments of Fig. 1 and Fig. 2, the control station 100 monitors an actual charging level SOCa, SOCb, SOCb of the local energy storage units 30a, 30b, 30c coupled to the work machines 10a, 10b, 10c. The work machines 10a, 10b, 10c may transmit their actual location 60a, 60b, 60c to the control station 100. More information like kind of work machine, e.g. digging machine, articulated hauler, dump truck and the like, kind of work to be done, e.g. digging, hauling, moving earth and the like, can also be supplied to the control station 100. Based on the information the control station 100 the control station 100 can estimate how long the actual amount of energy in the local energy storage units 30a, 30b, 30c will suffice to sustain operation of each of the work machines 10a, 10b, 10c.

The control station 100 will select an energy supply mode depending on the actual charging level SOCa, SOCb, SOCc of the at least one local energy storage unit 30a, 30b, 30c and eventually further information related to one or more of the work machines 10a, 10b, 10c. Preferably, the mode will be selected to fulfil an optimization criterion, such as causing on a minimum time delay in operation of the one or more work machines 10a, 10b, 10c compared to other energy supply modes.

The modes of energy supply are either filling the at least one local energy storage unit 30a, 30b, 30c coupled to the at least one work machine 10a, 10b, 10c at an upgrading station 110, replacing the at least one local energy storage unit 30a, 30b, 30c at an upgrading station 110 and furnish the at least one work machine 10a, 10b, 10c with at least one local energy storage unit 30a, 30b, 30c with a high charging level SOCa, SOCb, SOCc; replacing the at least one local energy storage unit 30a, 30b, 30c at an actual position of the respective work machine 10a, 10b, 10c coupled to the at least one local energy storage unit 30a, 30b, 30c. The control station 100 can decide on the energy supply mode based on the assumed energy request among a multitude of work machines 10a, 10b, 10c monitored by the control station 100. An optimization criterion could be in this case to optimize the overall performance of all work machines 10a, 10b, 10c. In such a case it may be acceptable that one work machine, e.g. 10b, has a longer operation stop phase, when in sum all work machines 10a, 10b, 10c show an optimized performance.

The control station 100 broadcasts the decision on the mode to the work machine 10a or 10b or 10c concerned or to all work machines 10a, 10b, 10c. Consequently, if the control station 100 decides that the local energy storage device 30b of the work machine 10b has to be recharged at the control station 100 (or another upgrading station 110) the work machine 10b is triggered to move towards the appropriate upgrading station 110. The control station 100 can decide how much energy the work machine 10b can still use before moving to the indicated upgrading station 110.

Also, the control station 100 can decide that it is more beneficial to replace the local energy storage device 30b instead of recharging it on board. In such a case the control station 100 can indicate an appropriate handover location 70 to pick up a fully charged energy storage unit 30, which can be at an appropriate location in the area or at the control station 100 or at a meeting place of a service vehicle 80 carrying charged energy storage units 30 and the work machine 10b requiring replacement of the depleted local energy storage unit 30b.

Further, the control station 100 can decide that it is more beneficial to replace the local energy storage device 30b instead of recharging it on board. In such a case the control station 100 can indicate an appropriate handover location 70 to pick up a fully charged energy storage unit 30, which can be at an appropriate location in the area or at the control station 100.

Fig. 3 illustrates a flow chart with preferred method steps according to the invention. For all work machines 10a, 10b, 10c (step 200) of the vehicle fleet 12 (Fig. 1 , Fig. 2) the state of charge SOCa, SOCb, SOCc is monitored. Additional data related to the work machines 10a, 10b, 10c can be taken into account in step 202. In step 204 the state of charge SOCa, SOCb, SOCc of each work machine 10a, 10b, 10c is compared to a predetermined threshold value Hm of the state of charge SOCa, SOCb, SOCc.

If the state of charge SOCa, SOCb, SOCc is above the predetermined threshold value ("n" in the flow chart), the procedure end in step 214. If the state of charge SOCa, SOCb, SOCc is equal or below the predetermined threshold value ("y" in the flow chart), the control station 100 estimates the range in which the work machine 10a, 10b, 10c can still operate (step 206). An actual energy requirement of the other work machines 10a, 10b, 10c can also be estimated (step 208) and considered in the selection of the appropriate mode of energy supply (step 210).

In step 212 it is checked if the states of charge SOCa, SOCb, SOCc and/or the relevant information of all work machines 10a, 10b, 10c have been considered. If the answer is yes ("y" in the flow chart) the routine ends in step 214. If the answer is no ("n" in the flow chart), the procedure jumps back to step 202 and collects state of charge and/or work machine data of the residual work machines 10a, 10b, 10c until all work machines 10a, 10b, 10c have been considered.

The monitoring of the work machines 10a, 10b, 10c can be performed continuously or periodically, depending on the actual circumstances.

Claims

C L A I M S

1. A method for supplying energy to one or more work machines (1 Oa, 10b, 10c), each work machine being provided with at least one energy storage unit (30a, 30b, 30c) arranged on the work machine (10a, 10b, 10c) for supplying energy to the work machine (10a, 10b, 10c), each work machine (10a, 10b, 10c) being associated with a control station (100), and each work machine (10a, 10b, 10c) being provided with a device for transmitting signals to the control station (100), comprising the steps of: (i) monitoring the charging level of the respective energy storage unit

(30a, 30b, 30c) by transmitting signals containing information about the current charging level (SOCa, SOCb, SOCc) of the respective energy storage unit (30a, 30b, 30c) from each work machine (10a, 10b, 10c) to the control station (100); and (ii) accomplishing an upgrading of the respective energy storage unit

(30a, 30b, 30c) provided that information received by the control station (100) indicates that the charging level (SOCa, SOCb, SOCc) is below a predetermined threshold value.

2. The method according to claim 1 , performing the step of upgrading the energy storage unit (30a, 30b, 30c) by charging the energy storage unit (30a, 30b, 30c) to a charging level (SOCa, SOCb, SOCc) above the threshold value.

3. The method according to claim 1 , performing the step of upgrading the energy storage unit (30a, 30b, 30c) by replacing the current energy storage unit (30b) by a corresponding energy storage unit (30) having a charging level (SOCa, SOCb, SOCc) above the threshold value.

4. The method according to claim 2 or 3, performing the step of upgrading the energy storage unit (30a, 30b, 30c) at a designated upgrading station (110).

5. The method according to claim 2 or 3, performing the step of upgrading the energy storage unit (30a, 30b, 30c) at the current position (60a, 60b, 60c) of the work machine (10a, 10b, 10c).

6. The method according to claim 5, performing the step of sending a vehicle (80, 30a, 30c) provided with one or more energy storage units (30) and/or charging equipment for replacing or charging the current energy storage unit (30b).

7. The method according to any preceding claim, performing the step of considering at least one operation parameter in addition to the charging level (SOCa, SOCb₁ SOCc) of the at least one local energy storage unit (30a, 30b, 30c) of the one or more work machines (10a, 10b, 10c).

8. The method according to any preceding claim, performing the step of selecting the energy supply mode causing on a minimum time delay in operation of the one or more work machines (10a, 10b, 10c) compared to other energy supply modes.

9. The method according to any preceding claim, performing the step of deciding on the energy supply mode based on the assumed energy request among a multitude of work machines (10a, 10b, 10c) monitored by the control station (100).

10. The method according to any preceding claim, performing the step of broadcasting the decision to the one or more work machines (10a, 10b, 10c) and triggering a reaction of the one or more work machines (10a, 10b, 10c).

11. The method according to any preceding claim, when deciding to replace the at least one local energy storage unit (30a, 30b, 30c) at the actual position (60a, 60b, 60c) of the respective work machines (10a, 10b, 10c), performing the step of triggering the work machine (10b) to move to a handover location (70) and/or triggering delivery of at least one energy storage unit (30) to the handover location (70).

12. The method according to claim 11 , performing the step of selecting the handover location (70) by estimating an available range of the work machine (10a, 10b, 10c) operated with a depleted local energy storage unit (30a, 30b, 30c).

13. The method according to claim 11 or 12, wherein the handover location (70) is the actual position (60b) of the respective work machine (1 Ob) when the control station (100) decides to replace the local energy storage unit (30b).

14. The method according to anyone of the claims 11 to 13, performing the step of sending a service vehicle (80) to the handover location (70) carrying at least one energy storage unit (30) for replacing the local energy storage unit

(30b).

15. The method according to claim 14, performing the step of temporarily employing one or more work machines (10a, 10c) as the service vehicle (80).

16. A system for supplying energy to one or more work machines (10a, 10b, 10c), each work machine being provided with at least one energy storage unit (30a, 30b, 30c) arranged on the work machine for supplying energy to the work machine, the system comprising a control station (100) and means adapted to be arranged on each work machine for transmitting signals to the control station (100), characterized in that the control station comprises a device (90) for receiving signals containing information about the current charging level (SOCa, SOCb, SOCc) of the respective energy storage unit (30a, 30b, 30c) from each work machine (10a, 10b, 10c) and monitoring the charging level (SOCa, SOCb, SOCc) of the respective energy storage unit (30a, 30b, 30c), and the system further comprises a device for accomplishing an upgrading of the respective energy storage unit (30a, 30b, 30c) provided that information received by the control station (100) indicates that the charging level (SOCa, SOCb, SOCc) is below a predetermined threshold value.

17. The system according to claim 16, wherein a storage space (20) for one or more energy storage units (30) is provided.

18. The system according to claim 16 or 17, wherein a loading unit (40) for loading the energy storage units (30) is provided.

19. The system according to one of the claims 16 to 18, wherein the control station (100) is assigned to a vehicle fleet (12) moving inside a defined area.

20. The system according to one of the claims 16 to 19, wherein at least one service vehicle (80) is provided for transporting one or more energy storage units (30) to one or more handover locations (70).

21. The system according to one of the claims 16 to 20, wherein one or more upgrading stations (110) are provided for upgrading the at least one energy storage units (30).

22. A method for supplying energy to one or more work machines, each work machine being provided with at least one energy storage unit arranged on the work machine for supplying energy to the work machine, each work machine being associated with a control station, and each work machine being provided with a device for transmitting signals to the control station, comprising the steps of:

(i) monitoring the charging level of the respective energy storage unit by transmitting signals containing information about the current charging level of the respective energy storage unit from each work machine to the control station; and

(ii) accomplishing an upgrading of the respective energy storage unit provided that information received by the control station (100) indicates that the charging level is below a predetermined threshold value.

23. The method according to claim 22, performing the step of upgrading the energy storage unit by charging the energy storage unit to a charging level above the threshold value.

24. The method according to claim 22, performing the step of upgrading the energy storage unit by replacing the current energy storage unit by a corresponding energy storage unit having a charging level above the threshold value.

25. The method according to claim 22, performing the step of upgrading the energy storage unit at a designated upgrading station.

26. The method according to claim 22, performing the step of upgrading the energy storage unit at the current position of the work machine.

27. The method according to claim 26, performing the step of sending a vehicle provided with one or more energy storage units and/or charging equipment for replacing or charging the current energy storage unit.

28. The method according to claim 22, performing the step of considering at least one operation parameter in addition to the charging level of the at least one local energy storage unit of the one or more work machines.

29. The method according to claim 22, performing the step of selecting the energy supply mode causing on a minimum time delay in operation of the one or more work machines compared to other energy supply modes.

30. The method according to claim 22, performing the step of deciding on the energy supply mode based on the assumed energy request among a multitude of work machines monitored by the control station.

31. The method according to claim 22, performing the step of broadcasting the decision to the one or more work machines and triggering a reaction of the one or more work machines.

32. The method according to claim 22, when deciding to replace the at least one local energy storage unit at the actual position of the respective work machines, performing the step of triggering the work machine to move to a handover location and/or triggering delivery of at least one energy storage unit to the handover location.

33. The method according to claim 32, performing the step of selecting the handover location by estimating an available range of the work machine operated with a depleted local energy storage unit.

34. The method according to claim 32 or 33, wherein the handover location is the actual position of the respective work machine when the control station decides to replace the local energy storage unit.

35. The method according to claim 32, performing the step of sending a service vehicle to the handover location carrying at least one energy storage unit for replacing the local energy storage unit.

36. The method according to claim 35, performing the step of temporarily employing one or more work machines as the service vehicle.

37. A system for supplying energy to one or more work machines, each work machine being provided with at least one energy storage unit arranged on the work machine for supplying energy to the work machine, the system comprising a control station and means adapted to be arranged on each work machine for transmitting signals to the control station, characterized in. that the control station comprises a device for receiving signals . containing information about the current charging level of the respective energy storage unit from each work machine and monitoring the charging level of the respective energy storage unit, and the system further comprises a device for accomplishing an upgrading of the respective energy storage unit provided that information received by the control station indicates that the charging level is below a predetermined threshold value.

38. The system according to claim 37, wherein a storage space for one or more energy storage units is provided.

39. The system according to claim 37 or 38, wherein a loading unit for loading the energy storage units is provided.

40. The system according to claim 37, wherein the control station is assigned to a vehicle fleet moving inside a defined area.

41. The system according to claim 37, wherein at least one service vehicle is provided for transporting one or more energy storage units to one or more handover locations.

42. The system according to claim 37, wherein one or more upgrading stations are provided for upgrading the at least one energy storage units.