HYDRAULIC SYSTEM FOR AN AGRICULTURAL MACHINE

Description

[0001] The present invention relates to a hydraulic system according to the preamble of claim 1. Furthermore, the present invention relates to an agricultural machine, in particular a self-propelled harvesting machine, according to the preamble of claim 14.

[0002] A hydraulic system of the type mentioned above is known from EP 2 636 907 B1. This patent describes a hydraulic system for an agricultural machine, such as a combine harvester, which, among other things, serves to drive a hydraulic motor for a fan. The hydraulic motor is supplied with hydraulic fluid by means of a variable displacement pump. Furthermore, the variable displacement pump supplies the working hydraulics of the agricultural machine. During operation of the agricultural machine, temporary situations may arise in which the hydraulic fluid supply provided by the variable displacement pump is insufficient to adequately supply all the driven components of the hydraulic system with hydraulic fluid. EP 2 636 907 B1 proposes that, in the event of an operationally induced pressure drop in the hydraulic system, the fan's power output be temporarily reduced.When self-propelled harvesters enter the headland, a header attachment is raised, resulting in a sudden increase in hydraulic fluid demand. To compensate for this temporarily increased demand, the hydraulic motor's fan's displacement is temporarily reduced, thus temporarily providing more hydraulic fluid to the working hydraulics. The associated reduction and subsequent increase in fan speed is often perceived as audibly disruptive by the operator. Furthermore, such a reduction in fan speed is only feasible for a very short period, as the fan's cooling capacity would otherwise be insufficient for the machine's safe operation.The duration of the temporary reduction in fan speed achieved by controlling the hydraulic motor is limited by the prevailing ambient conditions during operation. Particularly during typical harvest periods, the influence of ambient temperatures on the required cooling capacity is significant, meaning that compensating for an operationally induced pressure drop in the hydraulic system is only partially possible.

[0003] Publication EP2613060A1 discloses a hydraulic system for a working machine with three or four hydraulic pumps.

[0004] Based on the aforementioned prior art, the object of the present invention is therefore to further develop a hydraulic system of the type mentioned at the outset, which is characterized by improved compensation of an operationally induced pressure drop in the hydraulic system, which in particular does not come at the expense of the fan drive.

[0005] This problem is solved according to the invention by the features of independent claim 1, wherein advantageous further developments of the transmission arrangement according to the invention are the subject of the corresponding dependent claims 2 to 13. According to claim 1, a hydraulic system for an agricultural machine, in particular a self-propelled harvester, is proposed, wherein the hydraulic system comprises a variable displacement pump which is designed and configured to supply a hydraulic system of the machine and a hydraulic motor connected to a fan with a hydraulic fluid at substantially constant pressure.According to the invention, the hydraulic system comprises an auxiliary pump controlled by a valve arrangement having a first switching position and a second switching position, wherein the auxiliary pump is fluidly connected to a heat exchanger of the hydraulic system via a supply line in the first switching position of the valve arrangement and that the auxiliary pump is fluidly connected to the hydraulic motor via a pressure line in the second switching position of the valve arrangement.

[0006] The invention is based on the idea of ​​integrating a switchable auxiliary pump into the hydraulic system instead of a more powerful variable displacement pump. This auxiliary pump can be switched on as needed via the valve arrangement, or is switched on automatically when an operationally induced pressure drop occurs in the hydraulic system. Compared to the prior art cited above, this avoids the problem that compensating for the pressure drop comes at the expense of fan operation, thus preventing the associated effects on the working components of the machine that require cooling. Furthermore, a variable displacement pump adapted to or designed for the power demand regularly required during operation can be used, i.e., essentially without considering operationally induced load peaks. The auxiliary pump is switched on via the valve arrangement to compensate for these peak loads.Accordingly, the variable displacement pump can be smaller, so that it is better utilized by driving the fan and operating the working hydraulics and thus has a better efficiency than a larger variable displacement pump.

[0007] An operationally induced pressure drop in the hydraulic system can occur during the automatic activation of the working hydraulics, for example when reaching or passing through a headland.

[0008] The heat exchanger of the hydraulic system has the task of cooling the pressure fluid flowing back from the working hydraulics and the hydraulic motor of the fan.

[0009] In particular, the hydraulic system is designed as a constant pressure system.

[0010] The auxiliary pump is preferably designed as a constant-displacement pump. The auxiliary pump can also be designed as a variable-displacement pump. Designing the auxiliary pump as a constant-displacement pump has the advantage that the flow rate supplied by the variable-displacement pump of the hydraulic system can be reduced for the duration of the auxiliary pump's activation. In particular, the flow rate supplied by the variable-displacement pump can be reduced by essentially the amount supplied by the auxiliary pump, which is preferably designed as a constant-displacement pump.

[0011] Another advantage of the smaller variable displacement pump is that it can be operated at a higher drive speed than the drive speed provided by a drive motor, especially an internal combustion engine, of the agricultural machinery.

[0012] An operationally induced pressure drop in the hydraulic system can still occur in a drive motor designed as an internal combustion engine due to engine pressure during ongoing harvesting operations as well as during road travel.

[0013] The agricultural machine is preferably a self-propelled harvesting machine, in particular a combine harvester or a forage harvester. According to a further development, the pressure line is branched into a first branch leading to the working hydraulics and a second branch leading to the hydraulic motor. Branching the pressure line has the advantage that, in the second switching position of the valve arrangement, both the working hydraulics and the hydraulic motor are supplied with hydraulic fluid by the auxiliary pump in addition to the variable displacement pump. The use of an auxiliary pump designed as a constant displacement pump enables a large power spread across the entire speed range of the machine's drive motor in the second switching position of the valve arrangement, in which the auxiliary pump works together with the variable displacement pump.

[0014] According to the invention, the heat exchanger is connected to a cooling pump for supplying the hydraulic fluid. The cooling pump, preferably a constant-displacement pump, maintains a continuous flow rate to supply the heat exchanger, ensuring the cooling of the returning hydraulic fluid regardless of the valve assembly's switching position. In the first switching position of the valve assembly, the cooling pump can be assisted by the auxiliary pump.

[0015] According to further training, the working hydraulics can include a hydraulic steering system and / or a lifting device. The working hydraulics can also include other hydraulic consumers.

[0016] In particular, a control device can be associated with the valve arrangement, which is configured to control the valve arrangement depending on at least one detected operating parameter of the hydraulic system and / or the working hydraulics supplied by the hydraulic system and / or the fan supplied by the hydraulic system. The control device is responsible for determining the occurrence of operationally induced load peaks and controlling the valve arrangement accordingly. The control device can be connected to at least one sensor arrangement of the hydraulic system and / or the working hydraulics, in particular the lifting device and the steering system, in order to receive signals from the at least one sensor arrangement for evaluating the operating parameters to be detected.

[0017] According to a preferred embodiment, the control device is designed to control the valve arrangement depending on the power of the variable displacement pump and depending on a specific drive speed of the fan.

[0018] In particular, the control device can be configured to control the variable displacement pump.

[0019] The control device can include a storage unit in which at least one characteristic curve or characteristic curve field for the performance of the variable displacement pump and at least one characteristic curve for the performance of the fan is stored, as well as a computing unit which evaluates the at least one characteristic curve or at least one characteristic curve field of the variable displacement pump and the fan for controlling the valve arrangement.

[0020] In particular, the control device can be configured to determine a differential value for the output power of the variable displacement pump and the speed-dependent power consumption of the fan using at least one characteristic curve for the performance of the variable displacement pump and the performance of the fan, and to compare this value with limit values ​​stored in the storage unit. If a first limit value is not met, the auxiliary pump is operated by controlling the valve arrangement in the first switching position to supply the heat exchanger. If a second limit value is exceeded, the auxiliary pump is operated in the second switching position to drive the fan and the working hydraulics. The first limit value can represent a power reserve available to the working hydraulics, which results from the difference between the output power of the variable displacement pump and the power drawn by the fan.The second limit value can represent a lower limit of the power reserve, at which point the valve assembly is activated to switch from the first to the second switching position and engage the auxiliary pump. If the first limit value is exceeded again, the valve assembly is activated once more to return to the first switching position. This design has the advantage that the variable displacement pump requires a smaller power reserve. The variable displacement pump can therefore be utilized more efficiently and operate within a range of high efficiency. Peak loads occurring in the hydraulic system are mitigated by the activation of the auxiliary pump.

[0021] According to a preferred embodiment, the control device can be configured to control the valve arrangement depending on whether a threshold value for a steering angle is passed.

[0022] Preferably, the control device can be configured to actuate the valve arrangement depending on a threshold value for the actuation current of a steering valve of the hydraulic steering system. In particular, the machine can include a control unit configured for automatic steering. The control unit can be configured to actuate the hydraulic steering system. While necessary compensatory steering movements when driving in a field to be cultivated require a low actuation current, steering movements such as turning at the headland require a higher actuation current for the steering valve. The actuation current value generated by the steering system's control unit can preferably be transmitted from the machine to the control device for evaluation in essentially real time via a bus system, for example, a CAN bus system.

[0023] According to a preferred embodiment, the control device can be configured to actuate the valve arrangement depending on a threshold value for the actuation current of a control valve of the lifting device. In particular, the machine can include a control unit configured for the automatic actuation of the lifting device. The automatic actuation of the lifting device, for example upon reaching a headland, serves to raise the implement, which results in a higher demand for hydraulic fluid than a compensating movement when guiding the implement above a traversed or cultivated area during a work process, especially a harvesting process. The control unit of the lifting device can also transmit the value it generates for the actuation current to the control device for evaluation, preferably via a bus system, for example a CAN bus system, of the machine, essentially in real time.

[0024] Preferably, further operating parameters can include sensor-determined temperatures of cooling media that are cooled directly or indirectly by the hydraulic system. A radiator pump is provided for direct cooling of a cooling medium, in this case, the hydraulic fluid circulating in the hydraulic system. The radiator pump is an integral part of the hydraulic system. A fan is provided for indirect cooling, cooling a radiator assembly. The radiator assembly can include an intercooler and / or an engine coolant radiator. Other cooling media used can include the air from an intercooler or the engine oil and / or the coolant of an internal combustion engine, which are indirectly cooled by the hydraulic system's fan.

[0025] According to a further aspect of the invention, the variable displacement pump and at least the auxiliary pump can be driven or powered by a common drive shaft. Furthermore, the cooling pump can also be driven or powered by the common drive shaft. An advantage of this arrangement is its space efficiency. Alternatively, the variable displacement pump and at least the auxiliary pump can be driven or powered by two separate drive shafts. The cooling pump can be driven by a common drive shaft of the auxiliary pump or by a separate drive shaft that drives only the cooling pump.

[0026] In particular, the valve arrangement can include a directional control valve and a check valve, with the directional control valve being located upstream of the heat exchanger and the check valve upstream of the working hydraulics and the fan. The pressure line connecting the variable displacement pump to the fan and the working hydraulics includes a pressure accumulator which, in the event of an operationally induced load peak, bridges the period during which the valve arrangement is actuated to activate the auxiliary pump for driving the fan and the working hydraulics and to cover the auxiliary pump's response time.

[0027] The problem according to the invention is further solved by an agricultural machine, in particular a self-propelled harvester, comprising a working hydraulic system, a hydraulic motor driven by a fan, and a hydraulic system designed and configured to supply the working hydraulic system and the hydraulic motor with a pressure medium, according to independent claim 14. Reference may be made to the advantages of the hydraulic system according to the invention.

[0028] The present invention is explained in more detail below with reference to an embodiment illustrated in the drawings.

[0029] They show: Fig. 1 schematically shows an agricultural machine in side view; Fig. 2 is an example of a simplified circuit diagram of a hydraulic system of the agricultural machine; Fig. 3 is an example of the circuit diagram according to Fig. 2with a valve arrangement in a second switching position; Fig. 4 an exemplary course of a characteristic curve of a fan of the working machine; and Fig. 5 an exemplary course of a performance characteristic curve of the variable displacement pump and a course of a performance characteristic curve of variable displacement pump and switched-on auxiliary pump.

[0030] In Fig. 1Figure 1 schematically depicts an agricultural machine 1 in side view. Specifically, the agricultural machine 1 is designed as a self-propelled harvesting machine, here and preferably as a combine harvester. The machine 1 has an attachment 2, in the illustrated embodiment a header for a combine harvester, which is height-adjustable by means of a hydraulically operated lifting device 3. The lifting device 3 is part of the working hydraulics 7 of the machine 1. Furthermore, the working hydraulics 7 may include a hydraulic steering system 6, which serves to actuate a steering axle 8 of the machine 1.

[0031] A drive motor 4, generally designed as an internal combustion engine, is provided to power the working machine 1. The drive motor 4 is equipped with a cooling device 5, which serves to cool the cooling media used, the air from a charge air cooler, or the engine oil and / or the cooling water of the internal combustion engine drive motor 4. The cooling device 5 includes a hydraulically driven fan 15. Reference numeral 9 designates a hydraulic system for the working machine 1.

[0032] The representation according to Fig. 2Figure 1 shows an exemplary simplified circuit diagram of the hydraulic system 9 of the agricultural machine 1. The hydraulic system 9 comprises a variable displacement pump 10. In particular, the hydraulic system 9 is designed as a constant pressure system. The variable displacement pump 10 is designed and configured to supply the working hydraulics 7 of the machine 1 and the hydraulic motor 14, which is driven by the fan 15 of the cooling device 5, with a hydraulic fluid that is essentially at constant pressure. For this purpose, the variable displacement pump 10 draws the hydraulic fluid from a hydraulic fluid reservoir T through a suction line 20.

[0033] A pressure line 11, which branches into a first line branch 12 leading to the working hydraulics 7 and a second line branch 13 leading to the hydraulic motor 14, connects the variable displacement pump 10 to the working hydraulics 7 and the fan 15 in order to supply them with a pressure medium that is essentially under constant pressure. A pressure relief valve 16 is provided in line branch 12, which serves to protect the working hydraulics 7.

[0034] The hydraulic fluid flows from the working hydraulics 7 and the hydraulic motor 14 through a common return line 17 to a heat exchanger 18 for cooling. A filter 19 is connected downstream of the heat exchanger 18, through which the hydraulic fluid is passed before it enters the hydraulic fluid reservoir T. The filter 19 is primarily intended to remove impurities from the hydraulic fluid that may be introduced by the working hydraulics 7.

[0035] Furthermore, the hydraulic system 9 includes a cooling pump 22. The cooling pump 22 is connected to the heat exchanger 18 by a supply line 23. The cooling pump 22 draws hydraulic fluid from the hydraulic fluid reservoir T through a suction line 21 and supplies it to the heat exchanger 18 to cool the hydraulic fluid returning from the working hydraulics 7 and the hydraulic motor 14.

[0036] Additionally, the hydraulic system 9 includes a booster pump 24. The booster pump 24 is connected to a valve assembly 27 via a supply line 25. The valve assembly 27 has at least two switching positions: a first switching position and a second switching position. Depending on the at least two switching positions of the valve assembly 27, the booster pump 24 is either connected via a supply line 26 to the supply line 23 leading to the heat exchanger 18, or to the pressure line 11 or the line branches 12 and 13.

[0037] The valve arrangement 27 comprises a directional control valve 28, in particular a 2 / 2-way valve, which, in the first switching position of the valve arrangement 27 shown, connects the auxiliary pump 24 to the supply line 26. According to this first switching position, the cooling pump 22 and the auxiliary pump 24 jointly supply hydraulic fluid to the heat exchanger 18. A check valve 29 is arranged between the supply line 25 and the second branch 13 of the pressure line 11 leading to the hydraulic motor 14, and this check valve blocks flow towards the auxiliary pump 24. In the first switching position of the valve arrangement 27 shown, the hydraulic fluid supplied by the auxiliary pump 24 flows out via the directional control valve 28 and passes through the supply line 26 into the supply line 23 and from there on to the heat exchanger 18.

[0038] In the first switching position of the valve arrangement 27 according to the illustrated embodiment, the supply of the working hydraulics 7 and the hydraulic motor 14 for driving the fan 15 is provided exclusively by the variable displacement pump 10.

[0039] The pressure line 11, which connects the variable displacement pump 10 to the fan 15 via the branch line 13 and to the working hydraulics 7 via the branch line 12, includes a pressure accumulator 30 that provides hydraulic fluid. The pressure accumulator 30 serves to cushion a pressure drop in the hydraulic system 9.

[0040] Fig. 3 shows an example of the circuit diagram according to Fig. 2with the valve arrangement 27 in the second switching position. In the second switching position, the fluid-conducting connection between the supply line 25 and the supply line 26 is interrupted. The hydraulic fluid supplied by the switching pump 24 flows via the check valve 29 into the two line branches 12, 13. This serves to compensate for an operationally induced pressure drop in the hydraulic system 9, which can occur as a reaction to the activation of the working hydraulics 7. Such a situation occurs, among other things, when the lifting device 3, as part of the working hydraulics 7, is automatically activated to raise the implement 2 using the lifting device 3, for example, when reaching the headland. Activating the lifting device 3 to raise the implement 2 leads to an increased demand for hydraulic fluid. In addition, a steering movement is initiated when reaching or passing through the headland in order to achieve the smallest possible turning radius.This additionally activates the hydraulic steering system 6 as a consumer, increasing the demand for hydraulic fluid and thus the power requirement of the variable displacement pump 10. Depending on the prevailing operating and environmental conditions, the associated power requirement can exceed the maximum power of the variable displacement pump 10, leading to the operationally induced pressure drop in the hydraulic system 9. In particular, high ambient temperatures lead to an increased power requirement of the fan 15, so that the pressure drop cannot be compensated for by the pressure accumulator 30 alone. The automatic activation of the auxiliary pump 24 by controlling the valve arrangement 27 makes it possible to compensate for this pressure drop in the hydraulic system 9.

[0041] A control device 31 is associated with the valve arrangement 27. The control device 31 is configured to control the valve arrangement 27 depending on at least one detected operating parameter of the hydraulic system 9 and / or the working hydraulics 7 supplied by the hydraulic system 9 and / or the fan 15 supplied by the hydraulic system 9. The control device 31 comprises a storage unit 32 and a processing unit 33. Furthermore, the control device 31 is connected to at least one sensor arrangement 34 of the hydraulic system 9 and / or the working hydraulics 7. Signals received from the at least one sensor arrangement 34 are evaluated by the processing unit 33 to determine operating parameters.

[0042] Operating parameters include the power consumption of the variable displacement pump 10 and the drive speed of the fan 15. An operating parameter of the hydraulic steering system 6 is the control current of a steering valve of the hydraulic steering system 6. An operating parameter of the lifting device 3 is the control current of a control valve of the lifting device 3. A further operating parameter is the sensor-determined temperature of cooling media that are cooled directly or indirectly by the hydraulic system 9.

[0043] The storage unit 32 of the control device 31 can store at least one characteristic curve 36 or a characteristic curve array for the performance of the variable displacement pump 10 and at least one characteristic curve 35 for the performance of the fan 15. The processing unit 33 is configured to evaluate the at least one characteristic curve 35, 36, or the at least one characteristic curve array in order to control the valve arrangement 27.

[0044] The control device 31 is configured to determine a differential value for the output power of the variable displacement pump 10 and the speed-dependent power consumption of the fan 15 using at least one characteristic curve 35 for the power of the variable displacement pump 10 and for the power of the fan 15. The differential value is compared with limit values ​​stored in the storage unit 32. If a first limit value G1 is not reached, the auxiliary pump 24 is operated by the control of the valve arrangement 27 in the first switching position to supply the heat exchanger 18. If a second limit value G2 is exceeded, the valve arrangement is operated in the second switching position to drive the fan 15 and the working hydraulics 7 by the auxiliary pump 24.The first limit value G1 can represent a power reserve available to the working hydraulics 7, which results from the difference between the output power of the variable displacement pump 10 and the power drawn by the fan 15. The second limit value G2 can represent a lower limit of the power reserve, upon reaching which the valve assembly 27 is actuated to switch from the first to the second switching position and activate the auxiliary pump 24 to operate the fan 15. If the first limit value G1 is again undershot, the valve assembly 27 is actuated again to switch back to the first switching position.

[0045] The control of the valve arrangement 27, based on the characteristic curves 35, 36, is described below using the Figs. 4 and 5 explained in more detail. Fig. 4 shows an exemplary progression of the characteristic curve 35 of the fan 15 of the working machine 1 and the representation in Fig. 5shows as an example a course of the performance characteristic curve 36 of the variable displacement pump 10 and a course of a performance characteristic curve 37 of variable displacement pump 10 and the additional pump 24 of the hydraulic system 9 which is switched on in the second switching position.

[0046] The power consumption of fan 15 is shown as a function of speed and increases disproportionately with increasing fan speed. The characteristic curve 35 of fan 15 depends, among other things, on the geometry of fan 15, the air resistance of a cooling assembly and its surroundings, as well as the air density, which in turn depends on the ambient temperature and humidity. The cooling assembly can include an intercooler and / or an engine coolant radiator. An air conditioning evaporator can also be a component of the cooling assembly.

[0047] The pumping capacity of the variable displacement pump 10 depends on the drive motor speed of the drive motor 4, which in turn is subject to fluctuations depending on the operating conditions of the machine 1, particularly during field and road operation. In both operating conditions, a motor load, i.e., a drop in the drive motor speed, can occur, which can result in the variable displacement pump 10 not providing sufficient pumping capacity for the operation of the fan 15 and / or other hydraulic consumers.

[0048] The control of the valve arrangement 27 can also be based on the control current of the steering valve as an operating parameter of the hydraulic steering system 6 and / or the control current of the control valve of the lifting device 3 as an operating parameter of the lifting device 3.

[0049] Preferably, the control device 31 can be configured to control the valve arrangement 27 depending on a threshold value for the control current of the steering valve of the hydraulic steering system 6. In particular, the machine 1 can include a control unit configured for automatic steering of the machine 1. The control unit can be configured for automatic control of the hydraulic steering system 6. While necessary compensatory steering movements when driving on a field to be cultivated require a low control current, steering movements such as turning at the headland require a higher control current for the steering valve. The value for the control current generated by the control unit can preferably be transmitted from the machine 1 to the control device 31 for evaluation in essentially real time via a bus system, for example, a CAN bus system.This makes it possible to switch from the first switching position to the second switching position by controlling the valve arrangement 27 as needed. This can happen so quickly that the dimensioning of the pressure accumulator 30 is sufficient to bridge the period until the activation of the auxiliary pump 24 affects the available combined pumping capacity of the variable displacement pump 10 and the auxiliary pump 24.

[0050] According to a preferred embodiment, the control device 31 can be configured to actuate the valve arrangement 27 depending on the threshold value for the actuation current of the control valve of the lifting device 3. In particular, the working machine 1 can include a control unit configured for the automatic actuation of the lifting device 3. The automatic actuation of the lifting device 3, for example upon reaching a headland, serves to raise the implement 2, which results in a higher demand for hydraulic fluid than a compensating movement when guiding the implement 2 above a traversed or cultivated area during a work process, in particular a harvesting process. Reference symbol list 1 work machine 34 Sensor arrangement 2 attachment 35 Characteristic curve of 15 3 Lifting device 36 characteristic curve of 10 4 drive motor 37 Characteristic curve of 10 and 24 5 Cooling device 6 Steering system G1 First limit value 7 Working hydraulics G2 Second limit 8 steering axle T Pressure medium reservoir 9 hydraulic system 10 Variable displacement pump 11 Pressure line 12 Line branch 13 Line branch 14 hydraulic motor 15 fan 16 Pressure relief valve 17 Return line 18 Heat exchanger 19 filter 20 Suction line 21 Suction line 22 Coolant pump 23 Supply line 24 Switch-on pump 25 supply line 26 Supply line 27 Valve arrangement 28 Directional control valve 29 non-return valve 30 Pressure accumulator 31 Control device 32 Storage unit 33 computing unit

Claims

1. Hydraulic system (9) for an agricultural work machine (1), in particular a self-propelled harvester, wherein the hydraulic system (9) comprises a variable displacement pump (10) which is designed and configured to supply a pressure medium which is substantially under constant pressure to working hydraulics (7) of the work machine (1) and a hydraulic motor (14) drive-connected to a fan (15), wherein the hydraulic system (9) comprises an auxiliary pump (24) actuated by a valve arrangement (27) having a first switching position and a second switching position, wherein the auxiliary pump (24) is connected in a fluid-conducting manner to a heat exchanger (18) of the hydraulic system (9) by a supply line (26) in the first switching position of the valve arrangement (27) and wherein the auxiliary pump (24) is connected in a fluid-conducting manner to the hydraulic motor (14) by a pressure line (11) in the second switching position of the valve arrangement (27), characterized in that the heat exchanger (18) is connected to a radiator pump (22) for being supplied with pressure medium.

2. Hydraulic system (9) according to Claim 1, characterized in that the pressure line (11) is branched into a first line branch (12) leading to the working hydraulics (7) and a second line branch (13) leading to the hydraulic motor (14).

3. Hydraulic system (9) according to either of the preceding claims, characterized in that the working hydraulics (7) comprise a hydraulic steering system (7) and / or a lifting device (3).

4. Hydraulic system (9) according to any of the preceding claims, characterized in that a control device (31) is assigned to the valve arrangement (27) and is designed to actuate the valve arrangement (27) depending on at least one detected operating parameter of the hydraulic system (9) and / or the working hydraulics (7) supplied by the hydraulic system (9) and / or the fan (15) supplied by the hydraulic system (9).

5. Hydraulic system (9) according to Claim 4, characterized in that the control device (31) is designed to actuate the valve arrangement (27) depending on the power of the variable displacement pump (10) and depending on a determined drive speed of the fan (15).

6. Hydraulic system (9) according to Claim 4 or 5, characterized in that the control device (31) comprises a memory unit (32), in which at least one characteristic curve (36) or a family of characteristic curves for the power of the variable displacement pump (10) and at least one characteristic curve (35) for the power of the fan (15) are stored, and a computing unit (33), which evaluates the at least one characteristic curve (35, 36) or the at least one family of characteristic curves for actuating the valve arrangement (27).

7. Hydraulic system (9) according to Claim 6, characterized in that the control device (31) is designed to determine a differential value for the output power of the variable displacement pump (10) and the speed-dependent power consumption of the fan (15) by means of the at least one characteristic curve (35, 36) for the power of the variable displacement pump (10) and for the power of the fan (15), and to compare the differential value with limit values (G1, G2) stored in the memory unit (32) and to operate the auxiliary pump (24) in the first switching position for supplying the heat exchanger (18) by actuating the valve arrangement (27) when a first limit value (G1) is exceeded and in the second switching position for driving the fan (15) and the working hydraulics (7) when a second limit value (G2) is undershot.

8. Hydraulic system (9) according to any of Claims 4 to 7, characterized in that the control device (31) is designed to actuate the valve arrangement (27) depending on a threshold value for a steering angle being passed.

9. Hydraulic system (9) according to any of Claims 4 to 8, characterized in that the control device (31) is designed to actuate the valve arrangement depending on a threshold value for an actuation current of a steering valve of the hydraulic steering system (6).

10. Hydraulic system (9) according to any of Claims 4 to 9, characterized in that the control device (31) is designed to actuate the valve arrangement (27) depending on a threshold value for an actuation current of a control valve of the lifting device (3).

11. Hydraulic system (9) according to any of Claims 4 to 10, characterized in that further operating parameters are sensorially determined temperatures of cooling media which are indirectly or directly cooled by the hydraulic system (9).

12. Hydraulic system (9) according to any of the preceding claims, characterized in that the valve arrangement (27) comprises a directional control valve (28) and a check valve (29), wherein the directional control valve (28) is connected upstream of the heat exchanger (18) and the check valve (29) of the working hydraulics (7) and the fan (15).

13. Agricultural work machine (1), in particular self-propelled harvester, which comprises working hydraulics (7), a hydraulic motor (14) drive-connected to a fan (15), and a hydraulic system (9) which is designed and configured to supply a pressure medium to the working hydraulics (7) and the hydraulic motor (14), characterized in that the hydraulic system (9) is designed according to any of the preceding claims.