EP3748168B1 - Hydraulic drive system with two pumps and energy recovery - Google Patents

Description

The invention relates to a hydraulic drive system according to the preamble of claim 1.

From the DE 10 2015 216 737 A1 a hydraulic drive system is known. This includes a first pump with a constant displacement volume and a second pump with an adjustable displacement volume. The flow of the first pump can be returned to the tank via an adjustable first aperture. The first aperture is part of a pressure regulator, which regulates the delivery pressure of the first pump depending on a highest load pressure of the first actuators.

An advantage of the present invention is that the hydraulic drive system can be operated at very high pressures, while at the same time very high delivery flows are possible with a comparatively low pressure. The hydraulic drive system is still particularly cost-effective.

According to the independent claim, it is proposed that the first diaphragm is acted upon in the closing direction by a predeterminable control force, which is independent of an individual load pressure acting in the at least one first actuator. The delivery pressure of the first pump is therefore no longer regulated. Rather, it is returned to the tank essentially without pressure when the pressure at the second control point or the delivery pressure of the second pump exceeds the pressure equivalent of the actuating force. The actuating force is fixed in such a way that the hydraulic drive system has a minimum energy consumption under the expected operating conditions.

The control force is preferably also independent of an individual load pressure in the second actuator discussed below. The first aperture is preferred Monotonically adjustable between a fully open and a fully closed position. The opening cross section of the first aperture can change suddenly or continuously over the corresponding adjustment path. If several first actuators are provided, they are preferably connected in parallel to the second control point. Each first actuator can be assigned a second check valve, which only allows a fluid flow from the second control point to the relevant first actuator. The first pump can be designed as an external gear pump. The second pump can be designed as an axial piston machine with a swash plate design. The displacement volume of the second pump is preferably continuously adjustable. The first and second fluid flow paths are preferably designed differently from one another apart from their end points, namely the tank and the first control point. Advantageous developments and improvements of the invention are specified in the dependent claims.

It can be provided that the control force is generated exclusively by a preloaded first spring. The first orifice is preferably part of a pressure relief valve. This embodiment is particularly simple and inexpensive.

According to the independent claim, it is also provided that the first and the second pump are or can be brought into rotary drive connection with one another, their relative direction of rotation being fixed, the second pump being adjustable in two opposite directions starting from a position with the displacement volume zero so that it can be operated either as a pump or as a motor with the same direction of rotation. The first and second pumps are preferably permanently coupled to one another in a rotationally fixed manner. Preferably the first and second pumps are driven by a common motor.

It can be provided that the drive system has a first operating state in which the pressure at the second control point is below one Pressure equivalent of the control force, wherein in the first operating state a part of the delivery flow of the first pump can be conducted into the tank via the second fluid flow path, so that the second pump is operated by a motor, the drive system having a second operating state in which the pressure at the second Control point is above the pressure equivalent of the control force, wherein in the second operating state the delivery flow of the first pump can be directed into the tank via the first aperture, so that the first pump runs essentially without pressure. In addition to the two operating states mentioned, further operating states can be present, in particular if the second actuator with the priority valve explained below is present.

A priority valve can be provided with a continuously adjustable second aperture and a continuously adjustable third aperture, which are adjustable together, the second aperture being open in every position of the priority valve, with a pressure downstream of the third aperture moving the priority valve in the opening direction of the third Aperture is acted upon, wherein a second actuator is provided, which is fluidly connected to the first and/or the second pump via the second aperture, an individual load pressure of the second actuator acting on the priority valve in the closing direction of the third aperture. This means that the second actuator is reliably supplied with pressurized fluid, even if the delivery flow of the first and/or the second pump is not sufficient to supply all actuators with pressurized fluid. Preferably, the priority valve is assigned a second spring, which acts on the priority valve in the closing direction of the third aperture. The third aperture is preferably monotonically adjustable between a completely closed and a completely open position. The second and third apertures are preferably adjustable in opposite directions, i.e. if the opening cross section of the third aperture becomes larger over the adjustment path, the opening cross section of the second aperture becomes smaller.

It can be provided that a third fluid flow path starts from the tank via the first pump, continues via the second aperture to the second actuator, the third aperture being arranged in the first fluid flow path between the first pump and the first check valve. This embodiment is particularly advantageous if the second actuator has a low pressure requirement. Then, in operating states in which the pressure at the second control point is high, the first pump can be used to supply the second actuator with pressurized fluid. This achieves a high level of security of supply with low energy losses at the same time.

It can be provided that an individual load pressure is assigned to each first actuator and possibly the second actuator, with a first highest load pressure being determined exclusively from the individual load pressures of the at least one first actuator, with the displacement volume of the second pump depending on the first highest Load pressure is adjustable. This avoids energy losses when supplying the first actuators when the individual load pressure on the second consumer is high.

It can be provided that the second actuator is fluidly connected to the second control point via the second aperture, wherein the at least one first actuator is fluidly connected to the second control point via the third aperture. This embodiment is particularly energy efficient if the delivery flow of the first pump is designed to be large compared to the delivery flow of the second pump. If several first actuators are provided, they are preferably connected in parallel to the third aperture.

It can be provided that an individual load pressure is assigned to each first actuator and the second actuator, with a second highest load pressure being determined from all of the individual load pressures mentioned, the displacement volume of the second pump being adjustable depending on the second highest load pressure. This means that the delivery pressure of the second pump is always high enough to move the loads acting on all actuators.

It can be provided that the displacement volume of the second pump is adjustable by means of an electrical control signal, the second pump being connected to a control device, a first pressure sensor being provided, by means of which the pressure at the first control point can be measured, the first pressure sensor being connected to the control device. The control of the second pump on which the invention is based can be implemented electronically in a particularly simple manner. A hydraulic control that is also possible would be much more complex. The control device preferably comprises a digital computer.

A second pressure sensor can be provided, by means of which the first or second highest load pressure can be measured, the second pressure sensor being connected to the control device, the control device implementing a first controller, an actual variable of the first controller being a difference in the pressures first and on the second pressure sensor, wherein a manipulated variable of the first controller at least indirectly influences the control signal of the second pump. This automatically results in a setting of the second pump in the first operating state, which causes motor operation when less pressure fluid is consumed by the actuators than is delivered by the first pump. The first controller is preferably a continuous, linear controller, most preferably a PID controller. The first controller is preferably implemented digitally, with the corresponding digital values most preferably being determined in a predetermined time frame. The setpoint size of the first controller is preferably fixed, and it can also be dependent on the operating state of the hydraulic drive system, the rate of change being significantly lower than the rate of change of the pressures in the hydraulic drive system. The first controller is preferably supplied with a difference between the assigned actual and the assigned target variable as a control deviation.

A position sensor can be provided, by means of which an adjustment of the displacement volume of the second pump can be measured, the position sensor being connected to the control device, the control device implementing a second controller, wherein a manipulated variable of the second controller at least indirectly influences the control signal of the second pump , where an actual variable of the second controller is the setting of the displacement volume of the second pump, where the The manipulated variable of the first controller is a setpoint variable of the second controller. This allows particularly dynamic and precise control to be achieved. The position sensor is preferably a rotation or swivel angle sensor, by means of which a rotational position of a swivel cradle of the second pump can most preferably be measured. The second controller is preferably a continuous, linear controller, most preferably a PID controller. The second controller is preferably implemented digitally, with the corresponding digital values most preferably being determined in a predetermined time frame. The second controller is preferably supplied with a difference between the assigned actual and the assigned target variable as a control deviation.

It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations as long as these combinations do not deviate from the scope of the present invention, as defined by the appended claims.

Fig. 1

ein hydraulisches Antriebssystem gemäß einer ersten Ausführungsform der Erfindung;

Fig. 2

ein hydraulisches Antriebssystem gemäß einer zweiten Ausführungsform der Erfindung;

Fig. 3a

ein Diagramm, in dem verschiedene Drücke des hydraulischen Antriebssystems über die Zeit aufgetragen sind;

Fig. 3b

ein Diagramm, in dem verschiedene Volumenströme des hydraulischen Antriebssystems über die Zeit aufgetragen sind;

Fig. 4

ein Schaltbild der Steuervorrichtung mit dem ersten und dem zweiten Regler.

The invention is explained in more detail below with reference to the accompanying drawings. It shows:

Fig. 1

a hydraulic drive system according to a first embodiment of the invention;

Fig. 2

a hydraulic drive system according to a second embodiment of the invention;

Fig. 3a

a graph plotting various pressures of the hydraulic drive system over time;

Fig. 3b

a diagram in which different volume flows of the hydraulic drive system are plotted over time;

Fig. 4

a circuit diagram of the control device with the first and second controllers.

Fig. 1 shows a hydraulic drive system 10 according to a first embodiment of the invention. The hydraulic drive system 10 includes a first pump 40 with a constant displacement volume, which is designed, for example, as an external gear pump. Furthermore, a second pump 50 with an adjustable displacement volume is provided, which is designed, for example, as an axial piston machine in a swash plate design. Both pumps 40; 50 are driven by a common engine 14, which is designed, for example, as a diesel engine. The second pump 50 can also be operated as a motor, with the drive direction of rotation not being reversed. It is therefore designed as a pump that can be adjusted beyond the zero displacement volume. In particular, the corresponding pivoting cradle can be pivotable in two opposite directions starting from the position in which the delivery flow or the displacement volume is zero.

In Fig. 1 several tank symbols 13 are shown, all of which refer to the same tank. There is pressurized fluid in the tank 13, which is essentially pressureless. The pressurized fluid is preferably a liquid and most preferably hydraulic oil.

Furthermore, two first actuators 20 are provided here, the number of which can be chosen arbitrarily. The first actuators 20 can be hydraulic cylinders or hydraulic motors, with any mixed forms being conceivable. A second actuator 30 is also provided. This can be the steering cylinder of a vehicle steering system. But it can also be the hydraulic motor of a hydraulic fan drive. The second actuator 30 can be omitted, and several second actuators 30 can also be provided.

Each actuator has a main aperture 21; 31 and each a directional control valve 22; 32 assigned. These are preferably each connected by a common valve formed, whereby they are adjustable together. With the main panel 21; 31 is the movement speed of the respectively assigned actuator 20; 30 set. The main panels 21; 31 can each be assigned a pressure compensator (not shown), with which the pressure drop at the relevant main aperture 21; 31 is adjusted to a predetermined value, so that the respective movement speed depends solely on the setting of the main aperture 21; 31 and not from the respective individual load pressure 23; 33 is dependent. With the directional control valve 22; 32 is the direction of movement of the respectively assigned actuator 20; 30 set. The directional control valves 22; 32 are each equipped with a load pressure tap, at which the inlet-side pressure on the relevant actuator 20; 30 is applied, which is referred to as individual load pressure in the context of this application. In the present case the directional control valves 22; 32 a middle locking position in which the relevant actuator 20; 30 not moved. In this blocking position, the load pressure tap is connected to the tank 13 in order to save energy.

A first fluid flow path runs from the tank 13 via the first pump 40, further via a third aperture 72 of a priority valve 70, further via a first control point 11, further via a first check valve 43 to a second control point 12. The first check valve 43 only allows one Fluid flow to the second control point 12. If the second actuator 30 is not present, the priority valve 70 is omitted, with the first pump 40 as in Fig. 2 is connected directly to the first control point 11.

A second fluid flow path runs completely bypassing the first fluid flow path from the tank 13 via the second pump 50 to the second control point 12. When the second pump 50 is operated by a motor, the pressurized fluid flows from the second control point 12 to the tank 13. In the first fluid flow path, a comparable reversal of the flow direction is not possible because of the first check valve 43.

The first actuators 20 are supplied with pressurized fluid in parallel from the second control point 12. Each actuator can be assigned a second check valve 24, which only allows a fluid flow to the actuator 20. The second check valve 24 maintains the load so that the relevant first actuator 20 cannot move against the desired direction of movement when the delivery rate of the first and/or the second pump 40; 50 is not sufficient to hold the load acting on the relevant actuator 20. The second check valves 24 can be partially or completely omitted, for example to enable energy recovery when lowering external loads.

Furthermore, a first aperture 41 is provided, by means of which pressurized fluid can be conducted from the first control point 11 to the tank 13. The first aperture 41 is preferably part of a pressure relief valve. It is acted upon by a predetermined control force 44 in the closing direction, this control force 44 preferably being generated by a preloaded first spring 42. In contrast to the hydraulic drive system according to DE 10 2015 216 737 A1 this control force 44 is independent of the actuators 20; 30 attacking individual load pressures 23; 33. It is preferably selected so that the hydraulic drive system has the lowest possible energy consumption, taking into account the expected operating conditions.

In the opening direction, the first aperture 41 is subjected to the pressure at the second control point 12. Accordingly, the first aperture 41 opens when the pressure at the second control point 12 exceeds the pressure equivalent of the first spring 42. A steady, gentle transition is preferably provided between the open and closed positions of the first aperture 41, so that there is sufficient time to adapt the setting of the second pump 50 to the changed position of the first aperture 41.

The optional priority valve 70 includes a continuously adjustable second aperture 72 and a continuously adjustable third aperture 73, which are adjustable together. The second aperture 72 is open in every position of the priority valve 70, with a pressure 71 downstream of the third aperture 73, the priority valve 70 is acted upon in the opening direction of the third aperture 73. The priority valve 70 is acted upon by a second spring 74 in the closing direction of the third aperture 73. The individual load pressure 33 of the second actuator 30 also acts on the priority valve 70 in the closing direction of the third aperture 73. The third aperture 73 is preferably monotonically adjustable between a completely closed and a completely open position. The second and third apertures are preferably adjustable in opposite directions, ie if the opening cross section of the third aperture 73 becomes larger over the adjustment path, the opening cross section of the second aperture 72 becomes smaller. The main aperture 31 of the second actuator 30 is connected to the first pump 40 via the second aperture 72. Accordingly, the second actuator 30 is always supplied with pressure fluid from the first pump 40, regardless of the operating state in which the hydraulic drive system 10 is. Too much pressurized fluid delivered by the first pump 40 flows either to the first actuators 20 or via the second pump 50 back into the tank 13. In this case, its hydraulic energy is used to relieve the load on the motor 14 and is therefore not lost.

The first maximum load pressure 61 is determined from the individual load pressures 23 on the first actuators 20, with the individual load pressure 33 on the second actuator 30 being ignored. This can be done, for example, by means of a shuttle valve cascade 60, with each first actuator 20 being assigned a corresponding shuttle valve 64. However, other methods known from the prior art can also be used just as well to determine a highest load pressure from several individual load pressures. If only a first actuator 20 is present, the first maximum load pressure 61 is equal to its individual load pressure.

In the present case, the pressure at the second control point 12 is measured with a first pressure sensor 53, with the first highest load pressure 61 being measured with a second pressure sensor 63. The two pressure sensors 53; 63 are connected to a control device 51, which preferably comprises a programmable digital computer. The displacement volume of the second pump 50 becomes preferably adjusted by means of an electrical control signal 54. For this purpose, for example, an electrically operated 3/2-way valve can be provided, by means of which an actuating cylinder in the second pump 50 is adjusted.

It goes without saying that a purely hydraulic pump control can also be used instead of this electronic pump control. The ones with reference to Fig. 3a. and 3b However, the preferred mode of operation of the hydraulic drive system 10 described can only be implemented with great effort using a purely hydraulic control.

A position sensor 52 can be assigned to the second pump, with which the setting of the relevant displacement volume can be measured. The position sensor 52 is preferably a rotation angle sensor, by means of which a rotational position of a pivoting cradle of the second pump 50 can most preferably be measured. The position sensor 52 is also connected to the control device 51. The position sensor 52 can be omitted, whereby the control dynamics are adversely affected.

Fig. 2 shows a hydraulic drive system 10 'according to a second embodiment of the invention. The second embodiment is identical to the first embodiment except for the differences described below, so please refer to the comments in this regard Fig. 1 is referred. In the Fig. 1 and 2 The same or corresponding parts are provided with the same reference numbers.

The second embodiment is preferably used when the displacement volume of the first pump is significantly larger than the maximum displacement volume of the second pump. In this case, the first pump would be significantly oversized if it only had to supply the second actuator. Such an operating state is avoided with the second embodiment.

For this purpose, the priority valve 70 was arranged differently compared to the first embodiment. The second actuator 20 is now fluidic via the second aperture 72 connected to the second control point. The first actuators 20 are connected in parallel to the third aperture 73, whereby they are fluidly connected to the second control point 12 via this. All first actuators 20 and the second actuator 30 are now included in the determination of the second highest load pressure 62. Compared to the first embodiment, the shuttle valve cascade 60' therefore includes a further shuttle valve 64', which is assigned to the second actuator 30.

Fig. 3a shows a diagram in which different pressures p of the hydraulic drive system are plotted over time. Fig. 3b shows a diagram in which different volume flows Q of the hydraulic drive system are plotted over time. In the 3a and 3b The time t is plotted along the horizontal axis, with these two axes plotted synchronously. Vertical dashed lines indicate a first, a third and a second operating state 101; 103; 102 separated from each other.

In Fig. 3a the pressure p is plotted on the vertical axis. For the following explanations, the hydraulic drive system is used in accordance with Fig. 2 based on which no priority valve is arranged in the first fluid flow path. The solid line that is in Fig. 3a marked 11 shows the pressure at the first control point. The dashed line in Fig. 3a marked 12 shows the pressure at the second control point. The solid line that is in Fig. 3a at 61; 62 shows the highest load pressure of the respective hydraulic drive system. Next is in Fig. 3a a horizontal dash-dotted line marked No. 44 is drawn, which shows the pressure equivalent of the actuating force, which is constant over time t.

According to the one with reference to Fig. 4 In the control explained, the pressure at the second control point 12 is higher by the pressure difference 82 than the highest load pressure 61; 62. Only at very low pressures can this pressure difference specified as a target value not be maintained. In the first operating state 101, the pressure at the first control point 12 is smaller than the pressure equivalent of the control force 44. The first actuators are completely supplied with pressurized fluid by the first pump provided. The excess pressure fluid delivered by the first pump is returned to the tank via the second pump. Accordingly, the pressure at the first and second control points is the same, except for the pressure drop at the first check valve.

In Fig. 3b The flow rate Q is plotted on the vertical axis. The solid line, marked No. 40, shows the flow of the first pump. This is constant over time, since the first pump with a constant displacement volume is typically operated at a substantially constant drive speed. The solid line that is in Fig. 3b marked with number 50 shows the flow of the second pump. The dashed line in Fig. 3b marked with No. 104 shows the effective flow, which flows in particular to the first actuators. In this example, this should be constant over time.

In the first operating state 101, approximately half of the volume flow conveyed by the first pump 40 flows back into the tank via the second pump 50. The delivery flow of the second pump 50 is in Fig. 3b accordingly entered negatively. As soon as the pressure at the second control point 12 reaches the pressure equivalent of the actuating force 44, the first orifice (No. 41 in Fig. 1 and 2 ), whereby a constant opening behavior is assumed in this case. This results in a third operating state 103, in which part of the volume flow conveyed by the first pump flows back into the tank via the first orifice. The ones with reference to Fig. 4 The control explained compensates for this by adjusting the displacement volume of the first pump. In the present example, it changes continuously from a maximum negative value to a maximum positive value. The in Fig. 3a The pressure curve shown at the first control point 11 within the third operating state 103 is to be viewed as a very rough approximation. Only the initial and final pressures are specified exactly. When the first aperture is fully open, the delivery pressure of the first pump is determined solely by the flow resistance of the fully opened first aperture, which is preferably designed to be very small. The first pump therefore runs largely without pressure. In the second operating state, the first actuators are completely supplied with pressurized fluid by the second pump.

The first and second pumps can also deliver in the same direction, resulting in a very high delivery flow. However, the possible delivery pressure is limited by the pressure equivalent of the control force 44. The second operating state, in contrast, allows a much higher delivery pressure, with the maximum delivery flow being given by the maximum delivery flow of the second pump.

Fig. 4 shows a circuit diagram of the control device 51 with the first and second controllers 80; 90. The first controller 80 is preferably a PID controller, which regulates the difference between the highest load pressure and the pressure at the second control point to a predetermined target value 83. The highest load pressure is measured with the second pressure sensor 63, with the pressure at the second control point 12 being measured with the first pressure sensor 53. The actual variable 81 of the first controller 80 is calculated from these two measured values by forming the difference. The control difference 84, which is supplied to the first controller 80, is determined by forming the difference between the target variable 82 and the actual variable 81. The setpoint size 82 of the first controller corresponds to that on the main apertures (No. 21; 31 in Fig. 1 and 2 ) desired pressure drop.

The manipulated variable 83 of the first controller 80 could be used directly as a control signal 54 of the second pump 40. In the present case, however, a subordinate control with a second controller 90 is provided in order to improve the control dynamics and the control accuracy.

The second controller 90 is preferably a PID controller. Its control difference 94 is formed from the manipulated variable 83 of the first controller 80 and the measured value of the position sensor 52 used as the actual variable 91. In the present case, the manipulated variable 93 of the second controller 90 forms the control signal 54 of the second pump 40, and further subordinate control loops can be provided.

Reference symbols

10

hydraulic drive system (first embodiment)

10'

hydraulic drive system (second embodiment)

11

first control point

12

second control point

13

tank

14

engine

20

first actuator

21

first main aperture

22

first directional control valve

23

individual load pressure on a first actuator

24

second check valve

30

second actuator

31

second main aperture

32

second directional control valve

33

individual load pressure on a second actuator

40

first pump

41

first aperture

42

first feather

43

first check valve

44

Tax power

50

second pump

51

Control device

52

Position sensor

53

first pressure sensor

54

Control signal

60

Shuttle valve cascade (first embodiment)

60'

Shuttle valve cascade (second embodiment)

61

first highest load pressure

62

second highest load pressure

63

second pressure sensor

64

Shuttle valve, which is assigned to a first actuator

64'

Shuttle valve, which is assigned to the second actuator

70

Priority valve

71

Pressure downstream of the third orifice

72

second aperture

73

third aperture

74

second spring

80

first controller

81

Actual size of the first controller

82

Setpoint size of the first controller

83

Controlling variable of the first controller

84

Control difference of the first controller

90

second controller

91

Actual size of the second controller

92

Setpoint size of the second controller

93

Controlling variable of the second controller

94

Control difference of the second controller

101

first operating state

102

second operating state

103

third operating state

104

effective flow

Claims (11)

1. Hydraulic drive system (10; 10') comprising at least one first actuator (20), a tank (13), a first nonreturn valve (43) and a first and a second pump (40; 50), wherein the first pump (40) has a constant displacement volume, wherein the second pump (50) has an adjustable displacement volume, wherein a first fluid flow path starting from the tank (13) runs via the first pump (40), further via a first control point (11), further via the first nonreturn valve (43), to a second control point (12), wherein the at least one first actuator (20) is fluidically connected to the second control point (12), wherein the first nonreturn valve (43) permits a fluid flow only towards the second control point (12), wherein a second fluid flow path leads from the tank (13) to the second control point (12) via the second pump (40), wherein pressurized fluid can be conducted from the first control point (11) to the tank (13) via an adjustable first orifice (41), wherein the first orifice (41) is loaded in the opening direction by the pressure at the second control point (12), wherein the first and the second pump (40; 50) are or can be brought into a rotational drive connection to each other, wherein their relative direction of rotation is fixedly predefined, wherein the first orifice (41) is loaded in the closing direction by a fixedly predefinable control force (44) which is independent of an individual load pressure (23) acting in the at least one first actuator (20), characterized in that the second pump (50) is adjustable in two opposite directions from a position having a zero displacement volume, so that it can be operated optionally as a pump or as a motor with the same direction of rotation.
2. Hydraulic drive system according to Claim 1, wherein the control force (44) is generated only by a preloaded first spring (42).
3. Hydraulic drive system according to one of the preceding claims, wherein the drive system (10; 10') has a first operating state (101), in which the pressure at the second control point (12) lies below a pressure equivalent of the control force (44), wherein in the first operating state (101) part of the delivery flow from the first pump (40) can be conducted into the tank (13) via the second fluid flow path, so that the second pump (50) is motor-operated, wherein the drive system (10; 10') has a second operating state (101), in which the pressure at the second control point (12) lies above the pressure equivalent of the control force (44), wherein in the second operating state (102) the delivery flow from the first pump (40) can be conducted into the tank (13) via the first orifice (41), so that the first pump (40) runs substantially without pressure.
4. Hydraulic drive system according to one of the preceding claims, wherein a priority valve (70) having a continuously adjustable second orifice (72) and a continuously adjustable third orifice (73) which are jointly adjustable is provided, wherein the second orifice (72) is open in any position of the priority valve (70), wherein a pressure (71) downstream of the third orifice (73) loads the priority valve (70) in the opening direction of the third orifice (73), wherein a second actuator (30) is provided, which is fluidically connected to the first and/or the second pump (40; 50) via the second orifice (72), wherein an individual load pressure (33) of the second actuator (30) loads the priority valve (70) in the closing direction of the third orifice (73).
5. Hydraulic drive system according to Claim 4, wherein a third fluid flow path starting from the tank (13) leads to the second actuator (30) via the first pump (40), further via the second orifice (72), wherein the third orifice (73) is arranged in the first fluid flow path between the first pump (40) and the first nonreturn valve (43).
6. Hydraulic drive system according to one of the preceding claims, wherein each first actuator (20) and possibly the second actuator (30) are each assigned an individual load pressure (23; 33), wherein a first highest load pressure (61) is determined only from the individual load pressures (23) of the at least one first actuator (20), wherein the displacement volume of the second pump (50) is adjustable as a function of the first highest load pressure (61).
7. Hydraulic drive system according to Claim 4, wherein the second actuator (30) is fluidically connected to the second control point (12) via the second orifice (72), wherein the at least one first actuator (20) is fluidically connected to the second control point (12) via the third orifice (73).
8. Hydraulic drive system according to Claim 7, wherein each first actuator (20) and the second actuator (30) are each assigned an individual load pressure (23; 33), wherein a second highest load pressure (62) is determined from all the aforementioned individual load pressures (23; 33), wherein the displacement volume of the second pump (50) is adjustable as a function of the second highest load pressure (62).
9. Hydraulic drive system according to one of the preceding claims, wherein the displacement volume of the second pump (50) is adjustable by means of an electrical manipulated signal (54), wherein the second pump is connected to a control device (51), wherein a first pressure sensor (53) is provided, by means of which the pressure at the first control point (11) can be measured, wherein the first pressure sensor (53) is connected to the control device (51).
10. Hydraulic drive system according to Claim 9, insofar as this depends on Claim 6 or 8, wherein a second pressure sensor (63) is provided, by means of which the first or the second highest load pressure (61; 62) can be measured, wherein the second pressure sensor (63) is connected to the control device (51), wherein the control device (51) implements a first closed-loop controller (80), wherein a current variable (81) of the first closed-loop controller (80) is a difference of the pressures at the first and at the second pressure sensor (53; 63), wherein a manipulated variable (83) of the first closed-loop controller (80) at least indirectly influences the manipulated signal (54) of the second pump (50).
11. Hydraulic drive system according to Claim 9 or 10, wherein a position sensor (52) is provided, by means of which a setting of the displacement volume of the second pump (50) can be measured, wherein the position sensor (52) is connected to the control device (51), wherein the control device (51) implements a second closed-loop controller (90), wherein a manipulated variable (93) of the second closed-loop controller (90) at least indirectly influences the manipulated signal (54) of the second pump (50), wherein a current variable (91) of the second closed-loop controller (90) is the setting of the displacement volume of the second pump (50), wherein the manipulated variable (83) of the first closed-loop controller (80) is a setpoint variable (92) of the second closed-loop controller (90) .

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