EP2843241A2 - Hydraulic system - Google Patents

Abstract

A hydraulic system has at least two hydraulic circuits (1, 7, 18, 20, 21), to each of which hydraulic pumps (2, 8) are assigned, wherein in the context of a structural unit a drive of a constant-flow pump (16) cooperating with a first hydraulic circuit (1). is connected exclusively to an output of the second hydraulic circuit (7) associated constant-motor (15) and wherein within the first hydraulic circuit (1) hydraulic consumers (2) are arranged. In this case, in the second hydraulic circuit (7) next to the constant motor (15) further consumers (11) may be arranged and the unit should be designed as a pressure booster (14, 19), with the hydraulic power of both hydraulic circuits (1, 7, 18, 20 , 21) are automatically adjustable to an equilibrium.

Description

The invention relates according to the preamble of claim 1, a hydraulic system with at least two hydraulic circuits, which are each associated with hydraulic pumps, wherein in the context of a unit, a drive associated with a first hydraulic circuit constant pump is connected exclusively to an output of the second hydraulic circuit associated hydraulic motor and wherein within the first hydraulic circuit hydraulic consumers are arranged.

Furthermore, the invention according to the preamble of claim 5 also relates to a hydraulic system with a hydrostatic drive system which is arranged in a closed working group and having a hydraulic pump and at least one hydraulic motor, wherein a displacement volume of the hydraulic pump and / or a displacement of the at least one hydraulic motor are variable , wherein the working group via a feed pipe arranged in a feed pump pressure medium is supplied and wherein a limited to the tank leading purge line is provided to limit a maximum load pressure and to replace the pressure medium located in the closed working circuit.

Hydraulic systems may consist of several hydraulic circuits, in which hydraulic circuits different consumers, such as hydraulic motors, actuators, etc. are arranged and these are usually operated with different operating pressures and flow rates. Furthermore, hydraulic circuits can be designed as open or closed circuits. In an open circuit, a hydraulic pump sucks liquid from a tank and displaces it into the connected system, from which the liquid returns to the tank. By contrast, a closed circuit is understood to mean a system which preferably consists of a hydraulic pump and at least one hydraulic motor, the circulation of the hydraulic fluid from the hydraulic pump via the at least one hydraulic motor leading back into the suction port of the hydraulic pump. Hydraulic pumps and hydraulic motors, which are also referred to below as hydrostatic machines, can be a constant or have variable delivery volume or displacement and be designed as gear pumps or motors or as axial pumps or motors. In addition, it is possible to use radial piston or vane pumps as hydraulic pumps. If the delivery or displacement volume is constant, the hydrostatic machines are also referred to as a fixed displacement pump or motor.

A hydraulic system of the type specified in the preamble of claim 1 is known from DE 10 2009 029 840 A1 known. In this case, the first hydraulic circuit is in each case formed as a closed circuit for a hydrostatic drive system in the different design examples. For this purpose, the closed circuit to a hydraulic pump and a hydraulic motor whose displacement or displacement can be changed. As a result, the speed and the direction of rotation of a mechanically connected to the output of the hydraulic motor winch can be changed. Furthermore, a second hydraulic circuit is provided, which is designed as an open circuit and in which promotes a driven by an internal combustion engine variable fluid. The corresponding volume flow is fed to a hydraulic motor arranged downstream of the variable displacement pump, which has a constant displacement volume. An output shaft of this arranged in the second hydraulic circuit hydraulic motor serves as a drive shaft of a constant-displacement pump, which promotes pressure medium in the first hydraulic circuit as a feed pump. This feed is intended to avoid cavitation in the first hydraulic circuit and for subsequent delivery of hydraulic fluid, which escapes due to external leakage from the hydraulic circuit done. A corresponding outgoing from the feed pump feed line leads to the first hydraulic circuit, the corresponding hydraulic fluid via a double check valve.

Furthermore, a hydraulic system of the type specified in the preamble of claim 5 of the DE 10 2010 045 857 A1 known. This document describes a hydrostatic drive serving as a traction drive, in the closed working circuit of which essentially a hydraulic pump with an adjustable delivery volume and two hydraulic motors with a constant displacement volume assigned to each wheel drive are provided. Within a pump unit, the aforementioned adjustable In addition, there is a pump designed as a fixed displacement pump, which is driven together with the adjustable hydraulic pump via a drive shaft. From the feed pump goes from a feed line, which can feed via two provided with check valves fluid paths pressure medium in the closed workgroup. In the area of these fluid paths are also pressure relief valves, via which the pressure in the high-pressure fluid path of the working circuit should be set to 250 bar, for example. Each of these pressure relief valves can thus flow when exceeding this limit value of the pressure pressure medium, which finally derives via a downstream of the feed line provided further pressure relief valve at a pressure of, for example, 30 bar, the pressure medium in the tank.

It is an object of the present invention, in a hydraulic system consisting of at least two hydraulic circuits or a closed hydrostatic working group with a feed pump and a tank leading flushing line to reduce the power loss and to provide an arrangement with low space requirements.

This object is achieved on the basis of the preamble of claim 1, by its characterizing features. Thereafter, additional consumers should be arranged within the second working group in addition to the hydraulic motor, and the unit should be designed as a pressure booster with which the hydraulic power of both hydraulic circuits are automatically adjustable to a balance or a fixed relation to each other.

Thus, the designed as a constant-speed motor hydraulic motor is integrated into the second hydraulic circuit, being supplied in this hydraulic circuit consumers, such as hydraulic actuators, other hydraulic motors, etc., with the pressure medium from a hydraulic pump. The hydraulic motor is preferably designed as a circulation displacement machine and is driven by the pressure medium flow supplied from the second hydraulic circuit. The fixed displacement pump may cooperate with the first hydraulic circuit by conveying pressure medium into it via a line, or it may be arranged directly in the first hydraulic circuit. From a rotor of the Hydraulic motor is a mechanical drive connection, which leads to a conveying element of the fixed displacement pump. The output power of the hydraulic motor P _ab therefore corresponds to the drive power of the constant pump P _on . Incidentally, the following relationship applies $$\frac{{\mathit{p}}_{\mathit{from}}}{{\mathit{p}}_{\mathit{at}}}=\frac{{\mathit{Q}}_{\mathit{at}}}{Q_{\mathit{from}}}=\frac{{\mathit{V}}_{\mathit{at}}}{V_{\mathit{from}}}$$

p_ab

Betriebsdruck in dem zum Hydromotor führenden Leitungsabschnitt des zweiten Hydraulikkreises

p_an

ausgangsseitiger Betriebsdruck der Konstantpumpe

P_ab

Abtriebsleistung des Hydromotors

P_an

Antriebsleistung der Hydropumpe

Q_ab

Förderstrom der Konstantpumpe

Q_an

Schluckstrom der Hydropumpe

V_ab

geometrisches Schluckvolumen des Hydromotors

V_an

geometrisches Fördervolumen der Konstantpumpe

It is

p _from

Operating pressure in the leading to the hydraulic motor line section of the second hydraulic circuit

p _to

output side operating pressure of the constant pump

P _from

Output power of the hydraulic motor

P _on

Drive power of the hydraulic pump

Q _from

Flow rate of the fixed displacement pump

Q _on

Suction flow of the hydraulic pump

V _from

geometric displacement of the hydraulic motor

V _on

geometric delivery volume of the fixed displacement pump

It also follows that the output torque of the hydraulic motor corresponds to the drive torque of the constant pump: $${\mathit{M}}_{\mathit{from}}={\mathit{M}}_{\mathit{at}}$$

während sich die Abtriebsleistung des Konstantmotors ergibt als $$P_{\mathit{ab}}=\frac{\mathrm{\Delta }{p}_{\mathit{ab}}\times Q_{\mathit{ab}}\times {\eta }_{\mathit{ges}}}{600}$$

The drive power P _at the hydraulic pump results from $${\mathit{P}}_{\mathit{at}}=\frac{{\mathit{p}}_{\mathit{at}}\times {\mathit{Q}}_{\mathit{at}}}{600\times {\eta }_{\mathit{ges}}}$$

while the output power of the constant motor results as $$P_{\mathit{from}}=\frac{\mathrm{\Delta }{p}_{\mathit{from}}\times Q_{\mathit{from}}\times {\eta }_{\mathit{ges}}}{600}$$

If the overall efficiency η _ges is not taken into account in each case, and it is assumed that the constant-displacement pump draws liquid from the tank and compresses it, while the hydraulic motor at its pressure medium outlet delivers the liquid to the tank without pressure, this results in the relationship $${\mathit{Q}}_{\mathit{from}}\times {\mathit{p}}_{\mathit{from}}={\mathit{Q}}_{\mathit{at}}\times {\mathit{p}}_{\mathit{at}}$$

Therefore, by means of the assembly, a high pressure occurring in the second hydraulic circuit and a low volume flow can be translated into a low pressure and a high volume flow in the line associated with the first hydraulic circuit.

However, the hydraulic motor and the fixed displacement pump can also be designed so that at a balance, a low pressure and a high volume flow prevail at the inlet of the hydraulic motor, while at the constant pump on the outlet side, a high pressure and a low flow rate can be realized. As a result, the pressure p _at the output of the constant pump breaks, in which a high volume flow demand occurs in this hydraulic circuit, the constant-displacement pump is driven to increase the pressure from the hydraulic motor until the system is in equilibrium with the aforementioned requirements.

The constant pump can be a feed pump for feeding into a closed circuit of a hydrostatic transmission. If necessary, a freewheel can be provided in the mechanical drive connection, which disengages the drive of the constant pump from the output of the constant motor, if in the fixed displacement pump associated with the hydraulic circuit, a relatively large volume flow is promoted, whereas the volume flow is greatly reduced or blocked on the constant motor.

In contrast, after the DE 10 2009 029 840 A1 a variable displacement pump is provided, which is adjusted by a pressure control and thus adjusts a delivery volume and pressure in a line leading to the hydraulic motor line section, said line section would be considered as a second hydraulic circuit in the context of the present invention. However, this line section is used exclusively for supplying the constant pump with pressure medium. A corresponding fixed relationship between the hydraulic power of both hydraulic circuits, especially the volume flow with the help the variable displacement pump is varied, not provided. The previously known device relates to a hydrostatic drive of a feed pump and not arranged between different hydraulic circuits pressure booster.

In a further embodiment of the invention, the second hydraulic circuit to be provided for a working hydraulics of a self-propelled combine harvester, while the first hydraulic circuit is part of a hydrostatic drive for the conveying and separating elements of a header, such as a Maispflückeinrichtung, the self-propelled combine harvester. As already stated, the first hydraulic circuit, via which the harvesting attachment is to be driven at different rotational speeds and in different directions of rotation, can be supplied, if required, with pressure medium via the constant-flow pump designed as a feed pump.

The corresponding feed line is connected via check valves or pressure relief valves to the first hydraulic circuit, so that if necessary can be fed in each case in the operated at low pressure portion of the first hydraulic circuit. A corresponding reversing operation of the drive of the header is required, for example, in a corn header, so that it can be switched to reverse operation in the normal direction of rotation, if in the field of conveying and processing elements, such as the collection organs and / or the picking rollers and / or an inclined conveyor a blockage has occurred through the crop.

Furthermore, the present invention also relates to a hydraulic system with the generic features of claim 5, wherein the object is achieved by the characterizing features of claim 5.

Thereafter, a first hydrostatic machine should be arranged in the purge line. The hydraulic system further comprises a hydraulic circuit of a working or low-pressure hydraulics, with which a second hydrostatic machine promotes pressure medium via a line, which may also be designed as a second feed line, in the first feed line and / or in the working or low-pressure hydraulics. In addition, a drive system of the two hydrostatic machines is designed such that the first and the second hydrostatic machine exclusively drive each other, So no separate drive is available. The unit consisting of the two hydrostatic machines forms a pressure booster. The hydrostatic machines are each operated as a hydraulic motor with a constant displacement or as a hydraulic pump with a constant displacement. By arranged in the purge line first hydrostatic machine according to the invention provided for in the prior art pressure relief valve is replaced.

If the pressure in the closed working circuit of the hydrostatic drive system is high enough, then this working group is flushed out via the flushing line. As a result, a pressure and a volumetric flow are applied to the first hydrostatic machine arranged therein, and the volumetric flow drives the first hydrostatic machine as a hydraulic motor. As a result, the second hydrostatic machine, which is drivingly connected to the hydraulic motor, conveys pressure medium into the working or low-pressure hydraulic system as a constant-displacement hydraulic pump. This condition occurs when an imbalance between the hydraulic powers of the two hydrostatic machines has occurred. If, on the other hand, the pressure in the flushing line and thus the corresponding pressure of the pressure medium flowing out of the closed working group are too low, the first hydrostatic machine becomes a hydraulic pump and delivers pressure medium from the tank into the flushing line, wherein the drive via the second hydrostatic machine, the to the hydraulic pump is done.

This presupposes that a corresponding volume flow with a corresponding pressure is present at this second hydrostatic machine from the working or low-pressure hydraulics. The pressure booster works according to the principle already described in connection with the patent claim 1, according to which a balance of the hydraulic power of both line sections, where the two hydrostatic machines are assigned, is produced via the pressure booster. If the pressure of the hydraulic medium in the purge line and the pressure of the hydraulic medium in the line of the working or low-pressure hydraulics due to the function of the pressure booster, ie its pressure gear ratio, in equilibrium so the whole unit is silent. Normally, by delivering a volume flow by means of the hydraulic pump of the pressure booster in the low-pressure or working circuit, a portion of the energy of the over the purge line be removed recovered pressure medium. Only a small part is converted into heat due to the losses of the pressure booster unit.

In contrast, the closed circuit after the DE 10 2010 045 857 A1 a pressure relief valve, via which pressure medium from the closed working group is discharged into the tank. When flushing warm pressure medium from the working group, the back pressure of the pressure relief valve must be overcome. The energy of the outflowing pressure medium is therefore not utilized, it only leads to the fact that the pressure medium heats up more.

In a further embodiment of the invention, the closed hydraulic circuit to be operated depending on the load conditions with a low pressure section and a high pressure section, wherein the low pressure section via a hydraulically pilot operated 3/3-way valve with the purge line is connectable. Via this directional control valve, a certain quantity of pressure medium is thus diverted into the purge line as a function of the pressure of the closed hydraulic circuit, whereby this pressure medium passes into the pressure booster.

Furthermore, the second feed line can open into the first feed line. It is possible, via the feed pump pressure medium, which is supported in an advantageous manner by the pressure intensifier according to the invention, to promote the working or low-pressure hydraulics. Alternatively, it is possible to supply the low-pressure hydraulics via the feed pump, while pressure medium is fed into the working hydraulics via a separate circuit into which the pressure intensifier can feed. In addition, there are a variety of ways to use the pressure fluid provided by the pressure booster in a hydraulic system.

The invention is not limited to the specified combination of the features of the independent claims 1 and 5 and the claims dependent on these claims. It also results in ways to combine individual features, as far as they emerge from the claims, the advantages of the claims, the following description of the embodiment or at least from the drawings. The Reference of the claims to the drawings by corresponding use of reference numerals is not intended to limit the scope of the claims.

Figur 1

ein Schaltbild eines erfindungsgemäßen Hydrauliksystems mit zwei Hydraulikkreisen, welches beispielsweise für einen Antrieb eines Erntevorsatzes und eine Druckmittelversorgung von Verbrauchern einer Arbeitshydraulik verwendet werden kann,

Figur 2

ein Schaltbild, welches separat eine Anordnung eines Druckverstärkers in zwei Hydraulikkreisen zeigt,

Figur 3

ein Schaltbild eines hydrostatischen Antriebssystems mit einer Speisepumpe sowie einem parallel dazu betriebenen Hydraulikkreis einer Arbeits- oder Niederdruckhydraulik und

Figur 4

ein Schaltbild eines geschlossenen Arbeitskreises für ein hydrostatisches Antriebssystem, wobei eine Speisepumpe mit einem Hydraulikkreis einer Arbeits- oder Niederdruckhydraulik verbunden ist.

For further explanation of the invention reference is made to the drawing, are shown in simplified form in the three embodiments. Show it:

FIG. 1

a circuit diagram of a hydraulic system according to the invention with two hydraulic circuits, which can be used for example for a drive of a header and a pressure medium supply of consumers of a working hydraulics,

FIG. 2

a circuit diagram which shows separately an arrangement of a pressure booster in two hydraulic circuits,

FIG. 3

a diagram of a hydrostatic drive system with a feed pump and a parallel operated hydraulic circuit of a working or low-pressure hydraulic and

FIG. 4

a circuit diagram of a closed working circuit for a hydrostatic drive system, wherein a feed pump is connected to a hydraulic circuit of a working or low-pressure hydraulics.

In the FIG. 1 1 denotes a first hydraulic circuit provided for a hydrostatic drive system. The first hydraulic circuit 1 has a hydraulic pump 2, whose displacement volume is variable via an adjusting element 3. The actuator 3 may be part of a power control. As can be seen from the illustration, the hydraulic pump 2 should be adjustable so that change the flow direction by adjusting the displacement and at a certain pivot angle of the conveying elements, not shown, the flow direction.

From the hydraulic pump 2 go pump lines 4 and 5, of which, depending on the direction of the hydraulic pump 2, a high-pressure line section and form a low pressure line section of the first hydraulic circuit 1. The pump lines 4 and 5 lead to a hydraulic motor 6, which is provided for example for driving a harvesting attachment, not shown, a self-propelled harvester. This harvesting attachment may be a corn picking device, which has, among other things, conveying elements and picking rollers driven by the hydraulic motor 6. In addition, an inclined conveyor of the harvester can be driven by the hydraulic motor.

The hydraulic motor 6 has a constant displacement in the present case. Of course, it is also possible to make the hydraulic motor 6 adjustable, that is to change its displacement by means of the aforementioned power control. In addition, in the first hydraulic circuit 1, which is designed as a closed circuit, several hydraulic motors can be arranged. In this case, the individual hydraulic motors can be used for example as wheel motors for a drive of a working machine. The first hydraulic circuit 1 can also be assigned to a power-split epicyclic gearbox, with the actuating power flowing via the hydrostatic branch.

In addition to this first hydraulic circuit 1, a second hydraulic circuit 7 is provided, which is designed as an open circuit. In this case, a hydraulic pump 8 delivers from a tank 9 liquid via a pressure line 10 to a plurality of hydraulic consumers 11. From these, the pressure medium passes through line sections 12 and 13 back into the tank 9. Furthermore, designed as a pressure booster 14 assembly is provided, the a arranged between the line sections 12 and 13 constant motor 15 and a fixed displacement pump 16 is. In the present case, a drive of the constant displacement pump 16 takes place exclusively via the constant-speed motor 15, for which purpose the corresponding rotors of constant-motor 15 and constant-displacement pump 16 are coupled to one another via a mechanical drive connection 17. It may be a direct drive or a mechanical drive connection 17 with components for speed ratio. Furthermore, it is possible to provide the drive connection 17 with a freewheel, in particular when the constant displacement pump 16 is preceded by a further pump.

The constant displacement pump 16 delivers hydraulic fluid from the tank 9 into a feed line 18, from which the pressure medium can be conveyed via check valves 19 and 20 into the first hydraulic circuit 1. With the built as a structural unit of the fixed displacement pump 16 and the constant-displacement motor 15 pressure booster 14 ensures that between the line sections 12 and 13 on the one hand and the feed line 18 on the other hand, an equilibrium can be established. If the equilibrium exists, ie there is no volume flow requirement in the feed line 18, the rotors of the pressure booster 14 stand still. However, if pressure medium to be promoted via the feed line 18, so a volume flow demand is present, the constant displacement pump 16 is driven until no increase in the volume flow is required.

In the FIG. 2 Once again, the arrangement of a pressure booster 19 in a first hydraulic circuit 21 and a second hydraulic circuit 20 is shown in detail. Within the first hydraulic circuit 21, a first hydrostatic machine 23 is arranged, while within the second hydraulic circuit 20, a second hydrostatic machine 22 is located. The two hydrostatic machines 22 and 23 are designed such that they can be operated in each case as a pump or as a motor and their current direction is reversed.

If in the arrangement after the FIG. 2 a hydraulic fluid in the second hydraulic circuit 20 flows through a consumer 24 or a directional valve associated therewith, it passes through the second hydrostatic machine 22, which operates in this case as a hydraulic motor and enters a tank 25. If between the two hydrostatic machines 22 and 23 a Imbalance of the benefits prevails, the first hydrostatic machine 23 acts as a constant pump and delivers pressure fluid from another tank 26 to a consumer 27. If in the opposite case in the first hydraulic circuit 21, a power requirement occurs, the first hydrostatic machine 23 as a hydraulic motor from that of Consumers driven 27 outflowing pressure medium and continues to drive the second hydrostatic machine 22, which then acts as a pump to. The following conditions prevail between the two hydrostatic machines: $$\frac{{\mathit{p}}_{\mathit{from}}}{{\mathit{p}}_{\mathit{at}}}=\frac{{\mathit{Q}}_{\mathit{at}}}{Q_{\mathit{from}}}=\frac{{\mathit{V}}_{\mathit{at}}}{V_{\mathit{from}}}$$

p_ab

Betriebsdruck in dem Leitungsabschnitt des entsprechenden Hydraulikkreises, der zu der als Hydromotor wirkenden hydrostatischen Maschine führt,

p_an

ausgangsseitiger Betriebsdruck der als Konstantpumpe wirkenden hydrostatischen Maschine

P_ab

Abtriebsleistung des jeweiligen Hydromotors

P_an

Antriebsleistung der jeweiligen Hydropumpe

Q_ab

Förderstrom der jeweiligen Konstantpumpe

Q_an

Schluckstrom der jeweiligen Hydropumpe

V_ab

geometrisches Schluckvolumen des jeweiligen Hydromotors

V_an

geometrisches Fördervolumen der jeweiligen Konstantpumpe

It is

p _from

Operating pressure in the line section of the corresponding hydraulic circuit leading to the hydrostatic machine acting as a hydraulic motor,

p _to

Output-side operating pressure of the hydrostatic machine acting as a fixed displacement pump

P _from

Output power of the respective hydraulic motor

P _on

Drive power of the respective hydraulic pump

Q _from

Flow rate of the respective fixed displacement pump

Q _on

Suction flow of the respective hydraulic pump

V _from

geometric displacement of the respective hydraulic motor

V _on

geometric delivery volume of the respective constant displacement pump

It also follows that the output torque of the hydraulic motor corresponds to the drive torque of the constant pump: $${\mathit{M}}_{\mathit{from}}={\mathit{M}}_{\mathit{at}}$$

während sich die Abtriebsleistung des Konstantmotors ergibt als $$P_{\mathit{ab}}=\frac{\mathrm{\Delta }{p}_{\mathit{ab}}\times Q_{\mathit{ab}}\times {\eta }_{\mathit{ges}}}{600}$$

The drive power P _at the hydraulic pump results from $${\mathit{P}}_{\mathit{at}}=\frac{{\mathit{p}}_{\mathit{at}}\times {\mathit{Q}}_{\mathit{at}}}{600\times {\eta }_{\mathit{ges}}}$$

while the output power of the constant motor results as $$P_{\mathit{from}}=\frac{\mathrm{\Delta }{p}_{\mathit{from}}\times Q_{\mathit{from}}\times {\eta }_{\mathit{ges}}}{600}$$

This results in a coupling of the two hydrostatic machines together and neglecting the respective overall efficiency, the relationship: $${\mathit{Q}}_{\mathit{from}}\times {\mathit{p}}_{\mathit{from}}={\mathit{Q}}_{\mathit{at}}\times {\mathit{p}}_{\mathit{at}}$$

The FIGS. 3 and 4 each show a use of an inventively designed pressure booster in a hydraulic system having a working group for a hydrostatic drive system. The corresponding working group 28 in this case has a hydraulic pump 29 whose delivery volume is variable. In this case, the hydraulic pump 29 is designed such that it can convey in different directions, so that can be achieved with the hydrostatic drive system, a reversal of direction. Furthermore, a hydraulic motor 30 is arranged in the trained as a closed circuit working group 28, the displacement of which is variable. Due to the change in the conveying direction of the hydraulic pump 29 and possibly due to a thrust operation occurring from the wheel drive system of a vehicle, the two branches 31 and 32 of the working group 28 can be operated either as a high-pressure or as a low-pressure line. Between these branches 31 and 32 pressure relief valves 33 and 34 are arranged.

Together with the hydraulic pump 29, a feed pump 35 is driven, sucks the pressure medium from a tank 36 and feeds with a feed pressure of for example 20 to 30 bar via a feed line in each case in the low-pressure branch of the working group 28. This is done via check valves 38 and 39.

Furthermore, each of the two branches 31 and 32 of the working group 28 is connected to a hydraulically piloted 3/3-way valve 40, which promotes in its two working positions in each case from one of the branches 31 or 32 pressure medium in a flushing line 41. This purge line 41 is associated with a pressure booster 42, which consists of a first hydrostatic machine 43 and a second hydrostatic machine 44. The pressure booster 42 corresponds in terms of its structure and its operation in connection with the FIG. 2 explained pressure booster 19, that is, the two hydrostatic machines 43 and 44 can be operated with different directions of flow and operate as a fixed displacement pump or a constant motor.

After FIG. 3 is the second hydrostatic machine 44 via a line 45 with a hydraulic circuit 46 in communication, which is designed as an open circuit. The hydraulic circuit 46 has a variable displacement pump 47, the pressure medium from the tank 36th aspirates and feeds consumers 47 and 48. It is a working hydraulics, such as a self-propelled harvester. The feed line 37, which starts from the feed pump 35, also leads to a low-pressure hydraulic 49th

By means of the pressure booster 42, the first hydraulic machine 43 operates primarily as a constant motor in the purge line 41, the second hydrostatic machine 44 is driven as a fixed displacement pump, which promotes pressure fluid from the tank 36 in the hydraulic circuit 46. This always happens when, via the 3/3-way valve, part of the pressure fluid volume, which is again replaced by the feed pump 35, flows out via the purge line 41. However, it is also conceivable that the two hydrostatic machines 43 and 44 change their function and thus current direction. This is the case, for example, when a value of the pressure falls below the purge line 41 and a pressure in the line 45 is exceeded. Then, the second hydrostatic machine 44 to the motor and the first hydrostatic machine 43 to the constant pump, the pressure medium via the purge line 41 to the 3/3-way valve promotes and this can thus supply the working group 28. For this purpose, the pilot control of the 3/3-way valve must be designed accordingly.

In the embodiment according to the FIG. 4 the consumers are supplied both a low-pressure hydraulic 50 and a working hydraulics 51 with the pressure medium conveyed by the feed pump 35 via the feed line 37. Thus, this branch forms a second hydraulic circuit 53, which is designed as an open circuit. In this case, in contrast to the embodiment according to the FIG. 3 lead from the second hydrostatic machine 44, a second feed line 52 to the first feed line 37, so that increased by this part of the pressure booster 42 in certain working conditions, the volume flow through the feed line 37 in the direction of feeding into the working circuit 28 and the low-pressure hydraulic 50 and the working hydraulics 51 becomes. Also in this case, the volume flows in the purge line 41 and in the second feed line 52 may change such that the two hydrostatic machines 43 and 44 change their function and current direction.

LIST OF REFERENCE NUMBERS

1

First hydraulic circuit

2

hydraulic pump

3

actuator

4

pump line

5

pump line

6

hydraulic motor

7

Second hydraulic circuit

8th

hydraulic pump

9

tank

10

pressure line

11

Hydraulic consumer

12

line section

13

line section

14

Pressure intensifier

15

constant engine

16

fixed displacement pump

17

Mechanical drive connection

18

feeder

19

Pressure intensifier

20

second hydraulic circuit

21

first hydraulic circuit

22

second hydrostatic machine

23

first hydrostatic machine

24

consumer

25

tank

26

tank

27

consumer

28

working Group

29

hydraulic pump

30

hydraulic motor

31

Branch of 28

32

Branch of 28

33

Pressure relief valve

34

Pressure relief valve

35

feed pump

36

tank

37

feeder

38

check valve

39

check valve

40

3/3-way valve

41

flushing line

42

Pressure intensifier

43

First hydraulic machine

44

Second hydraulic machine

45

management

46

hydraulic circuit

47

consumer

48

consumer

49

Air-hydro

50

Air-hydro

51

hydraulics

52

second feed line

53

second hydraulic circuit

Claims (10)

Hydraulic system with at least two hydraulic circuits (1, 7, 18, 20, 21), which are each associated with hydraulic pumps (2, 8), wherein in the context of a structural unit, a drive of a with a first hydraulic circuit (1, 21) cooperating constant displacement pump (16, 23) is connected exclusively to an output of a second hydraulic circuit (7, 20) associated constant-motor (15, 22) and wherein within the first hydraulic circuit (1, 21) hydraulic consumers (2, 24) are arranged, characterized in that in second hydraulic circuit (7, 20) next to the constant motor (15, 22) further consumers (11, 24) are arranged and that the structural unit as a pressure booster (14, 19) is formed, with which the hydraulic power of both hydraulic circuits (1, 7, 18, 20, 21) are automatically adjustable to an equilibrium. Hydraulic system according to claim 1, characterized in that the second hydraulic circuit (7, 20) is provided for a working hydraulics of a self-propelled combine harvester, while the first hydraulic circuit (1, 18, 21) is part of a hydrostatic drive for the conveying and separating elements of a header of the self-propelled combine harvester. Hydraulic system according to claim 2, characterized in that the constant-displacement pump (16, 23) serves as a feed pump which feeds pressure medium into the first hydraulic circuit (1) via a feed line (18) associated with the first hydraulic circuit (1). Hydraulic system according to Patent Claim 1, characterized in that the constant-displacement pump (23) can also work as a motor and the hydraulic motor (22) designed as a constant-velocity motor can act as a pump. Hydraulic system with a hydrostatic drive system which is arranged in a closed working circuit (28) and has a hydraulic pump (29) and at least one hydraulic motor (30), wherein a displacement volume of the hydraulic pump (29) and / or a displacement of the at least one hydraulic motor (30 ) are variable, wherein the working group (28) via a in a first feed line (37) arranged feed pump (35) pressure medium is supplied and wherein a limited to the tank (36) leading purge line (41) is provided for limiting a maximum load pressure and for replacing the pressure medium in the closed working group (28), characterized in that in the purge line ( 41) a first hydrostatic machine (43) is arranged, that the hydraulic system comprises a hydraulic circuit (46) of a working and / or low-pressure hydraulics (47, 48, 49, 50, 51) with which a second hydrostatic machine (44) via a line (45, 52) is connected, that in each case a hydrostatic machine (43 or 44) is operated as a hydraulic motor with constant displacement and a hydrostatic machine (43 or 44) as a hydraulic pump with a constant displacement volume and that the first and the second hydrostatic machine (43 and 44) exclusively drive each other, forming as a unit a pressure booster (42). Hydraulic system according to claim 5, characterized in that the line (52) connected to the second hydrostatic machine (44) is designed as a second feed line and is connected to the first feed line (37). Hydraulic system according to claim 5, characterized in that a displacement volume or a displacement of the two hydrostatic machines (43 and 44) are coordinated such that the hydraulic power of both hydraulic circuits via the pressure booster (42) automatically adjustable to a balance or a fixed relation to each other are. Hydraulic system according to claim 7, characterized in that the first hydrostatic machine (43) in a first operating state, in which a pressure p ₁ in the purge line (41) increases, acts as a constant motor and drives acting as a constant pump second hydrostatic machine (44) until an equilibrium or a predefined relation of the hydraulic powers of purge line (41) and second feed line (52) or line (45) is achieved. Hydraulic system according to claim 7, characterized in that the second hydrostatic machine (44) in a second operating state in which a Pressure p ₂ in the second feed line (52) and the line (45) increases, acts as a constant motor and the acting as a constant pump first hydrostatic machine (43) drives until a balance or a predetermined relation of the hydraulic power of purge line (41) and second feed line (52) is achieved. Hydraulic system according to claim 5, characterized in that the closed working circuit (28) is operated depending on the load conditions with a low pressure section and a high pressure section, wherein the low pressure section via a hydraulically pilot operated 3/3-way valve (40) with the purge line (41) is connectable ,

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