Hydraulic drive system with two pumps and energy recovery

Abstract

The invention relates to a hydraulic drive system (10, 10´), comprising at least one first actuator (20), a tank (13), a first non-return 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 extends from the tank (13), via the first pump (40), further via a first control point (11), further via the first non-return valve (43) to a second control point (12), wherein at least one first actuator (20) is fluidically connected to the second control point (12), wherein pressure fluid can be led from the first control point (11) to the tank (13) via an adjustable first diaphragm (41), wherein the first diaphragm (41) is loaded in an opening direction with the pressure on the first control point (11). According to the invention, the first diaphragm (41) is acted upon in the closing direction by a fixedly predeterminable control force (44), which is independent of a separate load pressure (23) acting in the at least one first actuator (20).

Description

Technical Field

[0001] The invention relates to a hydraulic drive system. Background Art

[0002] A hydraulic drive system is known from DE 10 2015 216 737 A1. The hydraulic drive system comprises a hydraulic drive having a constant displacement volume. The first pump is a first pump having an adjustable displacement volume and a second pump having an adjustable displacement volume. The delivery flow of the first pump can be directed back into the tank via an adjustable first diaphragm. The first diaphragm is a component of a pressure regulator which regulates the delivery pressure of the first pump as a function of the maximum load pressure of the first actuator. Summary of the invention

[0003] The advantage of the invention is that the hydraulic drive system can be operated at very high pressures, wherein at the same time very high delivery flows can be achieved at relatively low pressures. However, the hydraulic drive system is particularly cost-effective.

[0004] According to the present invention, a hydraulic drive system has at least one first actuator, a tank, a first check valve, and a first and a second pump, wherein the first pump has a constant displacement volume, wherein the second pump has an adjustable displacement volume, wherein a first fluid flow path extends from the tank, via the first pump, further via a first control part, further via the first check valve to a second control part, wherein the at least one first actuator is fluidically connected to the second control part, wherein the first check valve only allows fluid to flow to the second control part, wherein a second fluid flow path leads from the tank via the second pump to the second control part, wherein pressure fluid can flow from The first control point is led to the tank via an adjustable first diaphragm, wherein the first diaphragm is loaded in an opening direction by the pressure on the second control point, characterized in that the first diaphragm is loaded in a closing direction by a control force that can be fixedly predetermined, and the control force is independent of a separate load pressure acting in the at least one first actuator, wherein the first pump and the second pump are or can be placed in a rotational drive connection with each other, wherein their relative rotational direction is fixedly predetermined, wherein the second pump can be adjusted in two opposite directions starting from a position with zero displacement volume, so that the second pump can be operated selectively as a pump or as a motor in the same rotational direction.

[0005] As described above, the first diaphragm is loaded in the closing direction by a fixedly predeterminable control force, which is independent of the individual load pressure acting in the at least one first actuator. The delivery pressure of the first pump is accordingly no longer regulated. On the other hand, when the pressure at the second control point or the delivery pressure of the second pump exceeds the pressure equivalent of the regulating force, it is essentially returned to the tank without pressure. The regulating force is preferably fixedly predetermined and is precisely predetermined in such a way that the hydraulic drive system has a minimum energy consumption under the expected operating conditions.

[0006] The control force is preferably also independent of the individual load pressure in the second actuator described below. The first diaphragm is preferably monotonically adjustable between the fully open position and the fully closed position. The opening cross section of the first diaphragm can be changed stepwise or continuously over the corresponding adjustment stroke. When a plurality of first actuators are provided, these first actuators are preferably connected in parallel to the second control position. Each first actuator can be equipped with a second check valve, which only allows fluid to flow from the second control position toward the relevant first actuator. The first pump can be constructed as an external gear pump. The second pump can be constructed as an axial piston machine in the form of a swash plate structure. The displacement volume of the second pump is preferably continuously adjustable. The first and second fluid flow paths are preferably constructed differently from each other at their end points, namely the tank and the first control position.

[0007] The invention also has advantageous developments and refinements.

[0008] It can be provided that the control force is generated only by the preloaded first spring. The first diaphragm is preferably a component of the pressure-limiting valve. This embodiment is particularly simple and cost-effective.

[0009] It can be provided that the first pump and the second pump are or can be placed in a rotational drive connection with each other, wherein their relative rotational direction is fixedly predetermined, wherein the second pump can be adjusted in two opposite directions starting from a position with zero displacement volume, so that the second pump can be operated selectively as a pump or as a motor when the rotational direction is the same. The first pump and the second pump are preferably permanently coupled to each other in a rotationally fixed manner. Preferably, the first and second pumps are driven by a common motor.

[0010] It can be provided that the drive system has a first operating state, in which the pressure at the second control point is lower than the pressure equivalent of the control force, wherein in the first operating state, a part of the delivery flow of the first pump can be introduced into the tank via the second fluid flow path, so that the second pump is operated in a motor-driven manner, wherein the drive system has a second operating state, in which the pressure at the second control point is higher than the pressure equivalent of the control force, wherein in the second operating state, the delivery flow of the first pump can be introduced into the tank via the first partition, so that the first pump is operated essentially without pressure. In addition to the two operating states mentioned, further operating states can exist, in particular when a second actuator with a priority valve explained below is present.

[0011] A priority valve having a second diaphragm that can be adjusted together and can be adjusted continuously and a third diaphragm that can be adjusted continuously can be provided, wherein the second diaphragm is open in each position of the priority valve, wherein the pressure downstream of the third diaphragm loads the priority valve in the opening direction of the third diaphragm, wherein a second actuator is provided, which is fluidically connected to the first and / or second pump via the second diaphragm, wherein the single load pressure of the second actuator loads the priority valve in the closing direction of the third diaphragm. Thus, even if the delivery flow of the first pump and / or the second pump is insufficient to supply all actuators with pressure fluid, the second actuator is reliably supplied with pressure fluid. Preferably, the priority valve is provided with a second spring, which loads the priority valve in the closing direction of the third diaphragm. The third diaphragm is preferably monotonically adjustable between a fully closed position and a fully open position. The second diaphragm and the third diaphragm are preferably adjustable in opposite directions, that is, when the opening cross section of the third diaphragm increases over the adjustment stroke, the opening cross section of the second diaphragm decreases.

[0012] It can be provided that the third fluid flow path leads from the tank via the first pump and further via the second partition to the second actuator, wherein the third partition is arranged in the first fluid flow path between the first pump and the first non-return valve. This embodiment is particularly advantageous when the second actuator has a low pressure requirement. In an operating state with high pressure at the second control point, the first pump can then be used to supply the second actuator with pressure fluid. This achieves a high supply reliability with low energy losses.

[0013] It can be provided that each first actuator and, if appropriate, the second actuator is respectively assigned an individual load pressure, wherein a first maximum load pressure is determined solely from the individual load pressure of the at least one first actuator, wherein the displacement volume of the second pump can be adjusted as a function of the first maximum load pressure. Energy losses when supplying the first actuators are thereby avoided when the individual load pressure at the second consumer is high.

[0014] It can be provided that the second actuator is fluidically connected to the second control point via a second partition, wherein at least one first actuator is fluidically connected to the second control point via a third partition. This embodiment is particularly energy-efficient when the delivery flow of the first pump is designed to be larger than the delivery flow of the second pump. When a plurality of first actuators are provided, these are preferably connected in parallel to the third partition.

[0015] It can be provided that each first actuator and each second actuator is assigned a separate load pressure, wherein a second maximum load pressure is determined by all the individual load pressures mentioned, wherein the displacement volume of the second pump can be adjusted as a function of the second maximum load pressure. The delivery pressure of the second pump is therefore always high enough to move the loads acting on all actuators.

[0016] It can be provided that the displacement volume of the second pump can be adjusted by means of an electrical control signal, wherein the second pump is connected to a control device, wherein a first pressure sensor is provided, by means of which the pressure at the first control point can be measured, wherein the first pressure sensor is connected to the control device. The regulation of the second pump according to the invention can be realized electronically in a particularly simple manner. A hydraulic regulation which is also possible is relatively more expensive. The control device preferably comprises a digital computer.

[0017] A second pressure sensor can be provided, by means of which the first or second maximum load pressure can be measured, wherein the second pressure sensor is connected to a control device, wherein the control device implements a first regulator, wherein the actual variable of the first regulator is the pressure difference between the first and second pressure sensors, wherein the control variable of the first regulator at least indirectly influences the control signal of the second pump. Thus, in a first operating state, when the actuator consumes less pressure fluid than is delivered by the first pump, the second pump is automatically set, which causes motor-driven operation. The first regulator is preferably a continuous linear regulator, most preferably a PID regulator. The first regulator is preferably implemented digitally, wherein the corresponding digital value is most preferably determined in a predetermined time period. The setpoint variable of the first regulator is preferably fixedly predetermined, wherein the setpoint variable can also be dependent on the operating state of the hydraulic drive system, wherein the change speed is significantly lower than the change speed of the pressure in the hydraulic drive system. Preferably, the difference between the associated actual variable and the associated setpoint variable is input to the first regulator as a control deviation.

[0018] A position sensor can be provided, by means of which the setting of the displacement volume of the second pump can be measured, wherein the position sensor is connected to a control device, wherein the control device implements a second regulator, wherein the regulating variable of the second regulator at least indirectly influences the regulating signal of the second pump, wherein the actual variable of the second regulator is the setting of the displacement volume of the second pump, wherein the regulating variable of the first regulator is the set value of the second regulator. In this way, a particularly dynamic and precise regulation can be achieved. The position sensor is preferably a rotation angle sensor or a pivot angle sensor, by means of which the rotation position of the pivot frame (Schwenkwiege) of the second pump can be measured most preferably. The second regulator is preferably a continuous linear regulator, most preferably a PID regulator. The second regulator is preferably implemented digitally, wherein the corresponding digital value is most preferably determined in a predetermined time period. Preferably, the difference between the associated actual variable and the associated set value is input to the second regulator as a regulation deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention.

[0020] The present invention will be explained in detail below with the aid of the accompanying drawings. It is shown in the drawings:

[0021] Figure 1 A hydraulic drive system according to a first embodiment of the present invention is shown;

[0022] Figure 2 shows a hydraulic drive system according to a second embodiment of the present invention;

[0023] Figure 3a The following diagram is shown in which different pressures of the hydraulic drive system are plotted against time;

[0024] Figure 3b The following diagram is shown in which different volume flows of a hydraulic drive system are plotted over time;

[0025] Figure 4 A circuit diagram of a control device having a first and a second controller is shown. DETAILED DESCRIPTION

[0026] Figure 1A hydraulic drive system 10 according to a first embodiment of the present invention is shown. The hydraulic drive system 10 comprises a first pump 40 having a constant displacement volume, which is designed as an external gear pump, for example. In addition, a second pump 50 having an adjustable displacement volume is provided, which is configured as an axial piston machine in the form of a swash plate structure, for example. The two pumps 40, 50 are driven by a common motor 14, which is configured as a diesel motor, for example. The second pump 50 can also be operated by motor drive, wherein the drive rotation direction is preferably not reversed here. Accordingly, the second pump is preferably designed as a pump that can be adjusted at a displacement volume of zero. In particular, the corresponding pivot frame can be pivoted in two opposite directions starting from a position where the delivery flow or displacement volume is zero.

[0027] exist Figure 1 In the figure, a plurality of tank symbols 13 are indicated, which all represent the same tank. In the tank 13 there is a pressure fluid which is substantially pressure-free. The pressure fluid preferably refers to a liquid and most preferably refers to hydraulic oil.

[0028] Furthermore, in this context, two first actuators 20 are provided, wherein their number can be selected arbitrarily. The first actuator 20 can be a hydraulic cylinder or a hydraulic motor, wherein any hybrid form is conceivable. Furthermore, a second actuator 30 is provided. This second actuator can be a steering cylinder of a vehicle steering system. However, this second actuator can also be a hydraulic motor of a hydraulic fan drive. The second actuator 30 can be omitted, wherein a plurality of second actuators 30 can also be provided.

[0029] Each actuator is respectively assigned a main diaphragm (Hauptblende) 21, 31 and a directional valve 22, 32. They are preferably formed by a common valve, wherein these valves can be adjusted together. The main diaphragm 21, 31 is used to set the movement speed of the respectively associated actuator 20, 30.

[0030] The main partitions 21, 31 can each be assigned a pressure balance (not shown), by means of which the pressure drop across the relevant main partition 21, 31 can be regulated to a predetermined value, so that the corresponding movement speed depends only on the setting of the main partition 21, 31 and not on the corresponding individual load pressure 23, 33. The movement direction of the respectively associated actuator 20, 30 is set by means of the directional valve 22, 32. The directional valve 22, 32 is each equipped with a load pressure tap, to which the pressure on the inlet side of the relevant actuator 20, 30 is applied independently of the movement direction, which pressure on the inlet side is referred to as the individual load pressure within the scope of the present application. In this case, the directional valve 22, 32 has a central locking position, in which the relevant actuator 20, 30 does not move. In this locking position, the load pressure tap is connected to the tank 13 in order to save energy.

[0031] The first fluid flow path extends from the tank 13 via the first pump 40, further via the third diaphragm 72 of the priority valve 70, further via the first control location 11, and further via the first check valve 43 to the second control location 12. The first check valve 43 only allows fluid to flow to the second control location 12. When the second actuator 30 is not present, the priority valve 70 is eliminated, wherein the first pump 40 is as in Figure 2 As in the example, it is directly connected to the first control location 11.

[0032] The second fluid flow path extends from the tank 13 to the second control site 12 via the second pump 50, completely bypassing the first fluid flow path. When the second pump 50 is operated in a motor-driven manner, the pressurized fluid flows from the second control site 12 to the tank 13. In the first fluid flow path, a similar reversal of the flow direction is not possible due to the first check valve 43.

[0033] The first actuator 20 is supplied with pressure fluid in parallel from the second control point 12. In this case, a second non-return valve 24 can be assigned to each actuator, which only allows fluid to flow to the actuator 20. The second non-return valve 24 causes load retention, so that the relevant first actuator 20 cannot be moved against the desired direction of movement if the delivery power of the first pump and / or the second pump 40, 50 is insufficient to maintain the load acting on the relevant actuator 20. The second non-return valve 24 can be partially or completely omitted in order to achieve energy recovery, for example when reducing external loads.

[0034] Furthermore, a first diaphragm 41 is provided, by means of which the pressure fluid can be conducted from the first control point 11 to the tank 13. The first diaphragm 41 is preferably a component of the pressure limiting valve. The first diaphragm is loaded in the closing direction by a fixedly predetermined control force 44, wherein the control force 44 is preferably generated by a prestressed first spring 42. In contrast to the hydraulic drive system according to DE 10 2015 216 737 A1, the control force 44 is independent of the individual load pressures 23, 33 acting on the actuators 20, 30. The control force is preferably selected in such a way that the hydraulic drive system has the lowest possible energy consumption taking into account the expected operating conditions.

[0035] In the opening direction, the first diaphragm 41 is loaded with the pressure on the second control point 12. Therefore, when the pressure on the second control point 12 exceeds the pressure equivalent of the first spring 42, the first diaphragm 41 opens. A continuous, smooth transition is preferably provided between the open position and the closed position of the first diaphragm 41, so that there is sufficient time to adapt the setting of the second pump 50 to the changed position of the first diaphragm 41.

[0036] The optional priority valve 70 comprises a second diaphragm 72 and a third diaphragm 73 which are adjustable together and are continuously adjustable. The second diaphragm 72 is open in each position of the priority valve 70, wherein the pressure 71 downstream of the third diaphragm 73 loads the priority valve 70 in the opening direction of the third diaphragm 73. The priority valve 70 is loaded by a second spring 74 in the closing direction of the third diaphragm 73. The separate load pressure 33 of the second actuator 30 also loads the priority valve 70 in the closing direction of the third diaphragm 73. The third diaphragm 73 is preferably monotonically adjustable between a fully closed position and a fully open position. The second and third diaphragms are preferably adjustable inversely to each other, i.e., when the opening cross section of the third diaphragm 73 becomes larger over the adjustment stroke, the opening cross section of the second diaphragm 72 becomes smaller. The main diaphragm 31 of the second actuator 30 is connected to the first pump 40 via the second diaphragm 72. Accordingly, the second actuator 30 is always supplied with pressure fluid by the first pump 40, regardless of the operating state of the hydraulic drive system 10. The pressure fluid delivered in excess by the first pump 40 either flows to the first actuator 20 or flows back into the tank 13 via the second pump 50. In this case, its hydraulic energy is used to relieve the motor 14 and is therefore not lost.

[0037] The first maximum load pressure 61 is determined from the individual load pressures 23 at the first actuator 20, wherein the individual load pressure 33 at the second actuator 30 is not taken into account. This can be achieved, for example, by means of a directional valve cascade 60, wherein a corresponding directional valve 64 is associated with each first actuator 20. However, other methods known from the prior art for determining the highest load pressure from a plurality of individual load pressures can also be used just as well. If there is only one first actuator 20, the first maximum load pressure 61 is equal to its individual load pressure.

[0038] The pressure at the second control point 12 is measured here by means of a first pressure sensor 53, wherein the first maximum load pressure 61 is measured by means of 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 is preferably adjusted by means of an electrical control signal 54. For this purpose, for example, an electrically actuated 3 / 2-way valve can be provided, by means of which a control cylinder in the second pump 50 is adjusted.

[0039] It is understood that a purely hydraulic pump control can also be used instead of this electronic pump control. However, the reference of the hydraulic drive system 10 can only be realized in a complicated manner using a purely hydraulic control. Figure 3a and 3b The preferred mode of operation is described.

[0040] The second pump can be equipped with a position sensor 52, with which the setting of the relevant displacement volume can be measured. The position sensor 52 is preferably a rotation angle sensor, with the aid of which the rotation position of the pivot bracket 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, wherein the control dynamics are adversely affected thereby.

[0041] Figure 2 A hydraulic drive system 10 ′ according to a second embodiment of the invention is shown. The second embodiment is constructed identically to the first embodiment except for the differences described below, so that reference is made to the Figure 1 Implementation plan. Figure 1 and Figure 2 In the drawings, the same or corresponding parts are provided with the same reference numerals.

[0042] The second embodiment is preferably used when the displacement volume of the first pump is significantly greater than the maximum displacement volume of the second pump. In this case, if the first pump only needs to supply the second actuator, the first pump will be significantly oversized. This operating state is avoided by the second embodiment.

[0043] For this purpose, the priority valve 70 is arranged differently compared to the first embodiment. The second actuator 20 is now fluidically connected to the second control point via a second partition 72. The first actuator 20 is connected in parallel to a third partition 73, via which the first actuator is fluidically connected to the second control point 12. All first actuators 20 and second actuators 30 are now included in the determination of the second maximum load pressure 62. Thus, in contrast to the first embodiment, the directional valve cascade 60 ′ comprises a further directional valve 64 ′, which is associated with the second actuator 30.

[0044] Figure 3a A diagram is shown in which different pressures p of the hydraulic drive system are plotted over time. Figure 3b The following diagram is shown in which different volume flows Q of the hydraulic drive system are plotted against time. Figure 3a and 3b In FIG. 1 , the time t is plotted along the horizontal axis, wherein the two axes are plotted synchronously. The first, third and second operating states 101 , 103 , 102 are separated from one another by vertical dash-dot lines.

[0045] exist Figure 3a In the example, the pressure p is plotted on the vertical axis. For the following explanation, according to Figure 2 The hydraulic drive system is based on the following aspect, wherein no priority valve is arranged in the first fluid flow path. Figure 3a The solid line denoted by 11 in FIG. 1 shows the pressure at the first control point. Figure 3a The dashed line denoted by 12 in FIG. 1 shows the pressure at the second control point. Figure 3a The solid lines denoted by 61 and 62 in FIG. 1 show the maximum load pressure of the corresponding hydraulic drive system. Figure 3a A horizontal dash-dot line denoted by reference numeral 44 is drawn in, which shows the pressure equivalent of the actuating force which is constant over time t.

[0046] According to reference Figure 4 In the described regulation, the pressure at the second control point 12 is higher than the maximum load pressure 61, 62 by the pressure difference 82. Only at very low pressures can the pressure difference predefined as the setpoint variable not be maintained. In the first operating state 101, the pressure at the first control point 12 is lower than the pressure equivalent of the control force 44. The first actuator is completely supplied with pressure fluid by the first pump. The pressure fluid delivered in excess by the first pump is returned to the tank via the second pump. Accordingly, the pressures at the first and second control points are equal, except for the pressure drop at the first nonreturn valve.

[0047] exist Figure 3bIn FIG. 4 , the delivery flow Q is plotted on the vertical axis. The solid line denoted by reference numeral 40 shows the delivery flow of the first pump. This delivery flow is constant over time, since the first pump is typically operated at a substantially constant drive speed with a constant displacement volume. Figure 3b The solid line denoted by reference numeral 50 in FIG. 1 shows the delivery flow of the second pump. Figure 3b The dashed line in FIG. 1 , denoted by reference numeral 104, shows the effective delivery flow, which in particular flows to the first actuator. In the present example, the effective delivery flow should be constant with respect to time.

[0048] In the first operating state 101, approximately half of the volume flow delivered by the first pump 40 flows back into the tank via the second pump 50. The delivery flow of the second pump 50 is Figure 3b Once the pressure on the second control point 12 reaches the pressure equivalent of the regulating force 44, the first diaphragm ( Figure 1 and Figure 2 The first pump is opened by the first diaphragm 41), wherein a continuous opening characteristic is assumed here. This results in a third operating state 103, in which a portion of the volume flow delivered by the first pump flows back into the tank via the first partition. Figure 4 The control described compensates for this by regulating the displacement volume of the first pump. In the present example, the displacement volume varies continuously from a maximum negative value to a maximum positive value. The pressure at the first control point 11 is Figure 3a The pressure curve shown in the third operating state 103 can be regarded as a very rough approximation. The only thing is that the starting pressure and the final pressure are accurately specified. When the first partition is fully opened, the delivery pressure of the first pump is determined only by the flow resistance of the fully opened first partition, which is preferably designed to be very small. Therefore, the first pump operates largely without pressure. The first actuator is completely supplied with pressure fluid by the second pump in the second operating state.

[0049] The first pump and the second pump can also deliver in the same direction, thus generating very high delivery flows. However, the possible delivery pressure is limited by the pressure equivalent of the control force 44. In contrast, the second operating state allows much higher delivery pressures, wherein the maximum delivery flow is given by the maximum delivery flow of the second pump.

[0050] Figure 4The circuit diagram of a control device 51 having a first and a second regulator 80, 90 is shown. The first regulator 80 is preferably a PID regulator, which controls the difference between the maximum load pressure and the pressure at the second control point to a predetermined setpoint variable 83. The maximum load pressure is measured by the second pressure sensor 63, wherein the pressure at the second control point 12 is measured by the first pressure sensor 53. From these two measured values, the actual variable 81 of the first regulator 80 is calculated by difference formation. The control difference 84 input to the first regulator 80 is determined by forming the difference between the setpoint variable 82 and the actual variable 81. The setpoint variable 82 of the first regulator corresponds to the difference between the setpoint variable 82 and the actual variable 81 at the main diaphragm ( Figure 1 and 2 The desired pressure drop at the reference numerals 21, 31).

[0051] The manipulated variable 83 of the first regulator 80 can be used directly as the control signal 54 for the second pump 40. In this case, however, a downstream control with a second regulator 90 is provided in order to improve the control dynamics and the control accuracy.

[0052] The second regulator 90 is preferably a PID regulator. Its control difference 94 is formed by the control variable 83 of the first regulator 80 and the measured value of the position sensor 52 used as the actual variable 91. The control variable 93 of the second regulator 90 forms the control signal 54 of the second pump 40 in this case, wherein other subordinate control loops can also be provided.

[0053] Reference numerals list

[0054] 10 Hydraulic Drive System (First Embodiment)

[0055] 10′ Hydraulic drive system (second embodiment)

[0056] 11First control area

[0057] 12 Second control part

[0058] 13 Storage tank

[0059] 14 Motor

[0060] 20 First actuator

[0061] 21 First main partition

[0062] 22 First directional valve

[0063] 23 Individual load pressure on the first actuator

[0064] 24 Second check valve

[0065] 30 Second actuator

[0066] 31 Second main partition

[0067] 32 Second directional valve

[0068] 33 Separate load pressure on the second actuator

[0069] 40 First Pump

[0070] 41 First partition

[0071] 42 First Spring

[0072] 43 first check valve

[0073] 44 Control

[0074] 50 second pump

[0075] 51 Control device

[0076] 52 Position Sensor

[0077] 53 First pressure sensor

[0078] 54 Adjustment signal

[0079] 60 Directional Valve Cascade (First Implementation)

[0080] 60' reversing valve cascade (second embodiment)

[0081] 61 First maximum load pressure

[0082] 62 Second highest load pressure

[0083] 63 Second pressure sensor

[0084] 64 Directional valve assigned to the first actuator

[0085] 64′ Directional valve assigned to the second actuator

[0086] 70 priority valve

[0087] 71 Pressure downstream of the third diaphragm

[0088] 72 Second partition

[0089] 73 Third partition

[0090] 74 Second Spring

[0091] 80 First Regulator

[0092] 81 Actual parameter of the first regulator

[0093] 82 Rated parameters of the first regulator

[0094] 83 Adjustment parameter of the first regulator

[0095] 84 The regulation difference of the first regulator

[0096] 90 Second Regulator

[0097] 91 Actual parameter of the second regulator

[0098] 92 Rated parameters of the second regulator

[0099] 93 Adjustment parameter of the second regulator

[0100] 94 The regulation difference of the second regulator

[0101] 101 First running state

[0102] 102 Second operating state

[0103] 103 Third operating state

[0104] 104 effectively delivers flow.

Claims

1. A hydraulic drive system (10, 10') having at least a first actuator (20), a tank (13), a first check valve (43) and first and second pumps (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 extends from the tank (13), via the first pump (40), further via a first control point (11), further via the first non-return 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 non-return valve (43) only allows fluid to flow to the second control point (12), wherein a second fluid flow path leads from the tank (13) via the second pump (50) to the second control point (12), wherein pressure fluid can be led from the first control point (11) to the tank (13) via an adjustable first diaphragm (41), wherein the first diaphragm (41) is loaded in an opening direction by the pressure at the second control point (12), The invention is characterized in that the first diaphragm (41) is loaded in the closing direction by a control force (44) which can be fixedly predetermined and which is independent of a separate load pressure (23) acting in the at least one first actuator (20), The first pump and the second pump (40, 50) are or can be placed in a rotational drive connection with each other, wherein their relative rotational direction is fixedly predetermined, wherein the second pump (50) can be adjusted in two opposite directions starting from a position with zero displacement volume, so that the second pump can be operated selectively as a pump or as a motor in the same rotational direction.

2. The hydraulic drive system according to claim 1, in, The control force (44) is generated solely by the preloaded first spring (42).

3. The hydraulic drive system according to claim 1 or 2, wherein: The drive system (10, 10') has a first operating state (101), in which the pressure on the second control part (12) is below the pressure equivalent of the control force (44), wherein, in the first operating state (101), a part of the delivery flow of the first pump (40) can be introduced into the tank (13) via the second fluid flow path, so that the second pump (50) is operated in a motor-driven manner, wherein the drive system (10, 10') has a second operating state (102), in which the pressure on the second control part (12) is above the pressure equivalent of the control force (44), wherein, in the second operating state (102), the delivery flow of the first pump (40) can be introduced into the tank (13) via the first diaphragm (41), so that the first pump (40) operates essentially without pressure.

4. The hydraulic drive system according to claim 1 or 2, in, A priority valve (70) is provided, which has a second diaphragm (72) that can be adjusted together and continuously and a third diaphragm (73) that can be adjusted continuously, wherein the second diaphragm (72) is open in each position of the priority valve (70), wherein a pressure (71) downstream of the third diaphragm (73) loads the priority valve (70) in the opening direction of the third diaphragm (73), wherein a second actuator (30) is provided, which is fluidically connected to the first pump and / or the second pump (40, 50) via the second diaphragm (72), wherein the separate load pressure (33) of the second actuator (30) loads the priority valve (70) in the closing direction of the third diaphragm (73).

5. The hydraulic drive system according to claim 4, A third fluid flow path starts from the tank (13) via the first pump (40) and further leads to the second actuator (30) via the second diaphragm (72), wherein the third diaphragm (73) is arranged between the first pump (40) and the first check valve (43) in the first fluid flow path.

6. The hydraulic drive system according to claim 1 or 2, in, A separate load pressure (23, 33) is assigned to each first actuator (20), wherein a first maximum load pressure (61) is determined solely by the separate load pressure (23) of the at least one first actuator (20), wherein the displacement volume of the second pump (50) can be adjusted as a function of the first maximum load pressure (61).

7. The hydraulic drive system according to claim 4, in, A separate load pressure (23, 33) is assigned to each first actuator (20) and to each second actuator (30), wherein a first maximum load pressure (61) is determined solely by the separate load pressure (23) of the at least one first actuator (20), wherein the displacement volume of the second pump (50) can be adjusted as a function of the first maximum load pressure (61).

8. The hydraulic drive system according to claim 4, The second actuator (30) is fluidly connected to the second control portion (12) via the second diaphragm (72), and the at least one first actuator (20) is fluidly connected to the second control portion (12) via the third diaphragm (73).

9. The hydraulic drive system according to claim 8, in, An individual load pressure (23, 33) is assigned to each first actuator (20) and each second actuator (30), wherein a second maximum load pressure (62) is determined by all the individual load pressures (23, 33), wherein the displacement volume of the second pump (50) can be adjusted as a function of the second maximum load pressure (62).

10. The hydraulic drive system according to claim 1 or 2, in, The displacement volume of the second pump (50) can be adjusted by means of an electrical control 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 second control point (12) can be measured, wherein the first pressure sensor (53) is connected to the control device (51).

11. The hydraulic drive system according to claim 10, in, A priority valve (70) is provided, which has a second diaphragm (72) that can be adjusted together and continuously and a third diaphragm (73) that can be adjusted continuously, wherein the second diaphragm (72) is open in every position of the priority valve (70), wherein a pressure (71) downstream of the third diaphragm (73) acts on the priority valve (70) in the opening direction of the third diaphragm (73), wherein a second actuator (30) is provided, which is fluidically connected to the first pump and / or the second pump (40, 50) via the second diaphragm (72), wherein the separate load pressure (33) of the second actuator (30) acts on the priority valve (70) in the closing direction of the third diaphragm (73), wherein a separate load pressure (23, 33) is assigned to each first actuator (20) and to each second actuator (30), wherein a first maximum load pressure (61) is determined solely by the separate load pressure (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 maximum load pressure (61), wherein a second maximum load pressure (62) is determined by all the individual load pressures (23, 33) mentioned, wherein the displacement volume of the second pump (50) is adjustable as a function of the second maximum load pressure (62), A second pressure sensor (63) is provided, by means of which a first or a second maximum load pressure (61, 62) can be measured, wherein the second pressure sensor (63) is connected to a control device (51), wherein the control device (51) implements a first regulator (80), wherein an actual variable (81) of the first regulator (80) is a pressure difference between the first and the second pressure sensor (53, 63), wherein the control variable (83) of the first regulator (80) at least indirectly influences a control signal (54) of the second pump (50).

12. The hydraulic drive system according to claim 11, A position sensor (52) is provided, by means of which the 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 regulator (90), wherein a manipulated variable (93) of the second regulator (90) at least indirectly influences a manipulated signal (54) of the second pump (50), wherein an actual variable (91) of the second regulator (90) is the setting of the displacement volume of the second pump (50), and wherein the manipulated variable (83) of the first regulator (80) is a setpoint variable (92) of the second regulator (90).

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