Hydraulic drive system, and operating method of hydraulic drive system

Abstract

To provide a hydraulic drive system, an operating method of a hydraulic drive system, and a machine comprising a control unit and a computer program for implementing the method.SOLUTION: A hydraulic drive system has: a primary side comprising a displaceable primary side hydraulic machine (10) mechanically connected or connectable to an engine (20) and at least one primary side hydraulic load (12) hydraulically connected to a pressure connection portion (16) of the primary side hydraulic machine; a secondary side having a displaceable secondary side hydraulic machine (30) mechanically connected to a rotatable machine component (2); a throttle element (40) displaceable in a controllable manner in which the primary side and the secondary side are hydraulically connected via the throttle element (40) and the throttle element (40) is displaceable between a minimum opening cross-sectional area and a maximum opening cross-sectional area; and an electronic control unit (50).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a hydraulic drive system, a method for operating a hydraulic drive system, a control unit for implementing the method, and a computer program.

[0002] Background of the Invention Machines, such as mobile working machines like excavators, loaders, or bulldozers, can each have a hydraulic drive system for driving components of the respective machine, such as the arm elements and / or the slewing mechanism of an excavator. In this case, a primary hydraulic machine is provided in the hydraulic system for supplying the pressure medium. To drive a rotating component, a further secondary hydraulic machine hydraulically connected to the primary hydraulic machine can be provided. The rotating component can be, for example, the slewing mechanism of a working machine or a drive of a travel drive, such as a chain drive. Generally, it may be assumed that the secondary hydraulic machine applies an accelerating torque or a braking torque depending on the respective operating situation.

[0003] Disclosure of the Invention According to the present invention, a hydraulic drive system having the features described in the independent claims, a method for operating a hydraulic drive system, a control unit for implementing the method, and a computer program are proposed. Preferred embodiments are the subject of the dependent claims and the following description.

[0004] The present invention relates to a measure of providing, in a hydraulic drive system having a primary side comprising a displaceable primary hydraulic machine and at least one primary hydraulic load, and a secondary side comprising a displaceable secondary hydraulic machine connected to a rotatable machine component, a controllably displaceable throttle element for hydraulically connecting the primary side and the secondary side, and an electronic control unit for controlling the throttle element. The electronic control unit determines whether there is a braking operating state in which a braking torque is applied by the secondary hydraulic machine, and when there is a braking operating state, is configured to displace the throttle element so that the output to be applied by the engine for driving the primary hydraulic machine is not increased such that the primary pressure requirement of at least one primary load is met (or satisfied). By this measure, an increase in the energy efficiency of the hydraulic drive system is achieved.

[0005] The term "pressure requirement" as used herein means at least the pressure value to be achieved, i.e., the pressure value sufficient to achieve the desired movement of one or more primary mechanical elements (or primary machine components) connected to at least one primary load, or the desired movement of a rotatable machine component connected to the secondary hydraulic machine. The primary pressure requirement is the pressure requirement of at least one primary load. The secondary pressure requirement is the pressure requirement of the secondary hydraulic machine. "Primary pressure" corresponds to the pressure at the pressure connection of the primary hydraulic machine. "Secondary pressure" corresponds to the pressure at the pressure connection of the secondary hydraulic machine. The expression "hydraulically connected" means that a volume flow of the pressure medium is possible between the respective elements, for example via a hydraulic line or a hydraulic channel, in which case a valve or the like for controlling the volume flow can be provided.

[0006] According to one embodiment, when there is a braking operation state, if the secondary pressure requirement of the secondary hydraulic machine is greater than the primary pressure requirement of at least one primary load device, the throttle element is configured to be displaced so that the secondary pressure corresponds to the secondary pressure requirement. This avoids the situation where the primary pressure has to be increased to the level of the secondary pressure requirement by the primary hydraulic machine. The passage cross-sectional area of the throttle element is displaced so that the pressure drop through the throttle element corresponds to or is equal to the pressure difference between the secondary pressure requirement and the primary pressure requirement. The pressure drop is due to the volume flow rate passing through the throttle element or the passage cross-sectional area of the throttle element, which occurs based on the pressure difference. Accordingly, it is ensured that the primary pressure corresponding to the outlet pressure of the primary hydraulic machine remains at the level of the primary pressure requirement.

[0007] The expression "the secondary pressure corresponds to the secondary pressure requirement" particularly means that the secondary pressure is the same as (or should be the same as) the secondary pressure requirement, or that the secondary pressure is the same as the secondary pressure requirement within the framework of closed-loop control (i.e., the same as the secondary pressure requirement except for the control deviation).

[0008] According to one embodiment, the throttle element is continuously displaceable between a minimum opening cross-sectional area and a maximum opening cross-sectional area. By being continuously displaceable, the opening cross-sectional area can be continuously changed, thereby enabling each pressure requirement to be accurately met.

[0009] According to one embodiment, when there is a braking operation state and the secondary pressure requirement is greater than the primary pressure requirement, the electronic control unit is further configured to set the target pressure of the pressure closed-loop control of the primary hydraulic machine to be the same as the primary pressure requirement. By doing so, it is also possible to ensure that the primary pressure corresponding to the outlet pressure of the primary hydraulic machine remains at the level of the primary pressure requirement.

[0010] According to one embodiment, the electronic control unit is further configured to perform pressure closed-loop control of the primary hydraulic machine such that the pressure on the primary side corresponds to the target pressure. Alternatively, the pressure closed-loop control may be performed by another computing unit. In this case, the electronic control unit transmits the target pressure determined by itself to another computing unit for setting this target pressure.

[0011] According to one embodiment, the electronic control unit is further configured to set the target pressure to be the same as the primary pressure demand when there is a braking operation state and the secondary pressure demand is not greater than the primary pressure demand. This case may occur when only a small braking torque is generated by the secondary hydraulic machine.

[0012] According to one embodiment, the electronic control unit is further configured to set the target pressure to be the same as the greater one of the primary pressure demand and the secondary pressure demand when there is no braking operation state. That is, both the primary pressure demand and the secondary pressure demand can be satisfied.

[0013] According to one embodiment, the electronic control unit is further configured to displace the throttle valve to the maximum opening cross-sectional area when there is no braking operation state. This is advantageous because when an accelerating torque is generated by the secondary hydraulic machine, an unobstructed volume flow rate from the primary side to the secondary side becomes possible.

[0014] According to one embodiment, the electronic control unit is further configured to displace the throttle element depending on the pressure difference between the secondary pressure demand and the primary pressure demand when there is a braking operation state and the secondary pressure demand of at least one secondary hydraulic machine is greater than the primary pressure demand of at least one primary side loader. This is advantageous because the volume flow rate through the hydraulic passage is typically a function of the pressure difference across both ends of the passage and the opening cross-sectional area.

[0015] According to one embodiment, the hydraulic drive system further includes a secondary pressure sensor configured to measure the secondary pressure and transmit it to the electronic control unit, and / or a primary pressure sensor configured to measure the primary pressure and transmit it to the electronic control unit. The corresponding measured values can be used by the electronic control unit to control the throttle element.

[0016] According to one embodiment, when a braking operation state exists, the electronic control unit displaces the primary hydraulic machine so that the primary hydraulic machine does not pump the volume flow rate, or the primary hydraulic machine can be set to zero, when the volume flow rate pumped by the secondary hydraulic machine is greater than or equal to the primary volume flow rate requirement of at least one primary hydraulic load. When the engine is an electric motor, the electronic control unit is further configured to displace the primary hydraulic machine so that torque is applied to the engine by the primary hydraulic machine. Correspondingly, when more pressure medium is pumped on the secondary side than required on the primary side during the braking operation state, it is possible to fully reverse the drive output of the engine, or when the engine is an electric motor, it is possible to regenerate energy by the electric motor. That is, when more pressure medium is pumped on the secondary side than required on the primary side during the braking operation state, it is also possible to displace the throttle element so that the primary pressure requirement and the secondary pressure requirement are met.

[0017] According to one embodiment, on the secondary side, a hydraulic pressure medium reservoir is provided that is hydraulically connected to the pressure connection of the secondary hydraulic machine. The pressure medium reservoir enables, for example, the hydraulic intermediate storage of the energy generated in the braking operation state.

[0018] A method for operating a hydraulic drive system of a machine tool having a rotatable machine component, the rotatable machine component being driven by the hydraulic drive system, the method comprising a displaceable primary hydraulic machine mechanically connected or connectable to the engine, and at least one primary hydraulic actuator connected to the pressure connection of the primary hydraulic machine on the primary side, a primary side comprising a secondary side having a displaceable secondary hydraulic machine mechanically connected to the rotatable machine component, and a controllably displaceable throttle element, the primary side and the secondary side being hydraulically connected via the throttle element, and the throttle element being displaceable between a minimum opening cross-sectional area and a maximum opening cross-sectional area. In this method, it is determined whether there is a braking operating state in which a braking torque is applied by the secondary hydraulic machine, and when the braking operating state exists, if the secondary pressure requirement of the secondary hydraulic machine is greater than the primary pressure requirement of at least one primary actuator, the throttle element is displaced so that the secondary pressure corresponds to the secondary pressure requirement.

[0019] The control unit according to the invention, for example the control device of the hydraulic drive system of a mobile machine tool, is configured in particular in a program-technical manner to carry out the method according to the invention.

[0020] It is also advantageous to implement the method according to the invention in the form of a computer program or a computer program product comprising program code for carrying out all method steps. This is because this means that the control device for carrying out the implementation is also used for further tasks, and thus, if it is already present in any case, it incurs particularly low costs. Suitable data carriers for providing the computer program are in particular magnetic, optical, and electrical memories such as hard disks, flash memories, EEPROMs, DVDs, etc. It is also possible to download the program via a computer network (Internet, intranet, etc.).

[0021] Further advantages and embodiments of the present invention will become apparent from the specification and the accompanying drawings.

[0022] It is obvious that the features described above, and the features to be further described below, can be used not only in the presented combinations but also in other combinations or alone, without departing from the scope of the present invention.

[0023] The present invention is schematically illustrated in the drawings based on embodiments, and will be described in detail below with reference to the drawings.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

[0025] Detailed Description of the Drawings FIG. 1 shows a hydraulic drive system of a working machine according to an embodiment of the present invention. The working machine has a rotatable machine component 2, for example, a part of the rotating mechanism of an excavator or a part of the traveling drive device of the working machine, and at least one further primary movable mechanical element (not shown), for example, the boom element of an excavator. The rotatable machine component 2 and the at least one primary mechanical element are driven by a hydraulic drive system.

[0026] The hydraulic drive system has a primary side and a secondary side. On the primary side, there is a primary hydraulic machine 10 and at least one primary hydraulic load device 12 (for example, at least one hydraulic cylinder and / or at least one hydraulic motor), and the at least one primary hydraulic load device 12 is (mechanically) connected to at least one additional mechanical element in order to drive (i.e., to cause the movement of) the at least one additional mechanical element. The primary hydraulic machine 10 is (mechanically) connected to a (drive) engine 20, and the (drive) engine 20 drives the primary hydraulic machine by a (drive) output. The output to be applied by the engine depends on the pressure difference across the primary hydraulic machine 10 (for example, the pump pressure on the output side, i.e., the difference between the primary pressure and the tank pressure on the input side) and the volume flow rate being pumped. In particular, the output to be applied is the product of the pressure difference and the volume flow rate, excluding, for example, a proportionality constant that includes an efficiency coefficient. The engine 20 is, for example, an internal combustion engine, such as a diesel engine or an electric motor.

[0027] The at least one primary hydraulic load device 12 is hydraulically connected to the pressure connection 16 of the primary hydraulic machine 10 via a valve device 14. The valve device 14 has one or more valves (not shown), and these valves can be displaced in order to control the inflow of the pressure medium to the at least one primary hydraulic load device 12 and the outflow of the pressure medium from the at least one primary hydraulic load device 12. The tank connection 18 of the primary hydraulic machine 10 is connected to a tank from which the pressure medium is provided.

[0028] On the secondary side, a secondary hydraulic machine 30 having a pressure connection portion 36 is provided. The secondary hydraulic machine 30 is mechanically connected to the rotatable machine component 2 (for example, via a shaft and / or a transmission), and thus the rotation of the secondary hydraulic machine 30 corresponds to the rotation of the machine component 2. The tank connection portion 38 of the secondary hydraulic machine 30 is connected to a tank to which a pressure medium is supplied. Optionally, on the secondary side, a hydraulic pressure medium reservoir b hydraulically connected to the pressure connection portion of the secondary hydraulic machine 30 may be further provided.

[0029] The primary hydraulic machine 10 and the secondary hydraulic machine are displaceable (and independently of each other, in particular zero-settable), that is, the primary hydraulic machine 10 and the secondary hydraulic machine have a displaceable displacement volume or a displaceable suction volume, and the expression "displacement volume" means the volume of the pressure medium pumped per revolution. For example, the primary hydraulic machine 10 or the secondary hydraulic machine 30 is an axial piston mechanism of, for example, a swash plate structure type or a swash shaft structure type, and the displacement volume corresponds to a displaceable swivel angle. The pressure medium (i.e., the working fluid) is, for example, hydraulic oil.

[0030] The primary side and the secondary side are hydraulically connected or linked via a throttle element 40. The throttle element 40 is displaceable, i.e., it is possible to change the passage cross-sectional area or the cross-sectional area of the passage of the throttle element (provided between the primary side and the secondary side) for the pressure medium. This displacement of the throttle element 40 can be controlled by an electronic control unit 50. The throttle element 40 is hydraulically connected on the primary side to the pressure connection 16 of the primary-side hydraulic machine 10, and on the secondary side to the pressure connection 36 of the secondary-side hydraulic machine 30. For example, the throttle element 40 has a primary-side connection hydraulically connected to the pressure connection 16 of the primary-side hydraulic machine 10 and a secondary-side connection hydraulically connected to the pressure connection 36 of the secondary-side hydraulic machine 30, and a displaceable passage with respect to the cross-sectional area is formed between the primary-side connection and the secondary-side connection of the throttle element. The throttle element may be, for example, a 2-port 2-position directional control valve, which has a continuously displaceable passage between an open position (the cross-sectional area of the passage is maximum) and a closed position (the cross-sectional area of the passage is minimum, especially equal to zero), and this displacement is carried out electromagnetically or is carried out under electromagnetic pilot control, and the open position may be the normal position (for example, the 2-port 2-position directional control valve is biased to the open position).

[0031] The electronic control unit 50 may, in some cases, be configured to displace the displacement volume of the primary-side and / or secondary-side hydraulic machine.

[0032] As a whole, a hydrostatic system is formed, and the rotational speed of the rotatable machine component 2 can be closed-loop controlled on the secondary side, for example, by displacing the displacement volume of the hydraulic machine 30 on the secondary side. When an accelerating torque for the machine component 2 is to be generated on the secondary side (by the hydraulic machine 30 on the secondary side), the hydraulic machine 30 on the secondary side acts as a hydraulic motor. On the other hand, when a braking torque for the machine component 2 is to be generated, the hydraulic machine 30 on the secondary side acts as a hydraulic pump, that is, the hydraulic machine 30 on the secondary side pumps the pressure medium from the tank connection to the pressure connection. In this case, the torque is proportional to the product of the pressure difference between the pressure connection and the tank connection and the displacement volume. The hydraulic machine 10 on the primary side typically acts as a hydraulic pump and, in a given operating situation, for example, when at least one primary-side hydraulic actuator 12 requires little or no volume flow of the pressure medium and, at the same time, the hydraulic machine 30 on the secondary side acts as a hydraulic pump, it can also act as a hydraulic motor, especially when the engine 20 is an electric motor, electrical energy can be regenerated.

[0033] The hydraulic machine 10 on the primary side is closed-loop controlled, for example, so that the primary-side pressure of the pressure medium detected by the primary-side pressure sensor 52 corresponds to the primary-side target pressure, that is, so as to be closed-loop controlled to the primary-side target pressure or (within the framework of pressure closed-loop control) to be the same as the primary-side target pressure, for example, by pressure closed-loop control. This pressure closed-loop control may be implemented, for example, by an electronic control unit 50 or another computing unit. In the latter case, the electronic control unit 50 determines the primary-side target pressure and transmits it to this computing unit. When the hydraulic machine 30 on the secondary side acts as a hydraulic motor (that is, when an accelerating torque is to be generated by the hydraulic machine 30 on the secondary side), the primary-side target pressure is approximately the same as the greater of the primary-side pressure requirement and the secondary-side pressure requirement. The throttle element 40 is displaced in this situation, in particular, so as to have a maximum passage cross-sectional area.

[0034] In this case, the term "pressure requirement" means at least the pressure value to be achieved. The primary-side pressure requirement is the pressure requirement of at least one primary-side load device 12, and the pressure requirement of this at least one primary-side load device 12 is due to, for example, the load acting on at least one additional mechanical element. The secondary-side pressure requirement is the pressure requirement of the secondary-side hydraulic machine 30, and the pressure requirement of this secondary-side hydraulic machine 30 is due to the torque to be applied by the secondary-side hydraulic machine 30 (for example, when it is assumed that the displacement volume is maximum).

[0035] The primary-side pressure is, in particular, the pressure of the pressure medium at the pressure connection 16 of the primary-side hydraulic machine 10, i.e., the outlet pressure of the primary-side hydraulic machine 10. The secondary-side pressure is, in particular, the pressure of the pressure medium at the pressure connection 36 of the secondary-side hydraulic machine 30, i.e., the outlet pressure of the primary-side hydraulic machine 10.

[0036] In the situation where the secondary-side hydraulic machine 30 acts as a hydraulic pump (i.e., when a braking torque is to be generated by the secondary-side hydraulic machine 30), there may be a situation where the secondary-side pressure requirement for applying the required braking torque exceeds the primary-side pressure requirement (of at least one primary-side load device 12). Therefore, if no throttle element is provided, or if the throttle element 40 remains at its maximum passage cross-sectional area, the pressure of the pressure medium on the primary side must be increased to the pressure level of the secondary-side pressure requirement by the primary-side hydraulic machine 20. The driving behavior of at least one primary-side load device 12 is not impaired thereby, because the volume flow rate to the primary-side load device 12 is throttled in the valve device, for example, by a pressure compensator. However, this causes energy losses.

[0037] To avoid this effect that the primary hydraulic machine 20 requires additional output to achieve the pressure level of the secondary pressure requirement, the primary pressure is made the same as the primary pressure requirement of at least one primary load device 12, and at the same time the secondary pressure is made greater than or equal to the secondary pressure requirement, the throttle element 40 is displaced, that is, the passage cross-sectional area of the throttle element 40 is displaced or reduced. That is, the throttle element 40 is displaced so that the pressure drop caused by the throttle element in the volume flow rate of the pressure medium from the secondary side to the primary side is the same as the pressure difference between the secondary pressure requirement and the primary pressure requirement. In this case, the target pressure of the pressure closed-loop control of the primary hydraulic machine can be selected according to or the same as the primary pressure requirement.

[0038] To achieve this, for example, a secondary pressure sensor 54 for detecting the secondary pressure of the pressure medium can be provided. Then, for example, closed-loop control by an electronic control unit 50 can be implemented, and the throttle element 40 is displaced so that the secondary pressure detected by the secondary pressure sensor 54 is closed-loop controlled to the secondary pressure requirement (the control line or sensor line is shown by a dashed line in the drawing). The manipulated variable is here, for example, the drive amount for displacing the throttle element 40 (for example, the current intensity or duty ratio of the PWM signal). Here, additional pilot control is also considered, and using the flow characteristic map of the throttle element (given, for example, by the flow equation of the throttle point or orifice), from the assumed given volume flow rate (from the rotational speed and displacement volume of the secondary hydraulic machine) and the pressure difference between the secondary pressure requirement and the primary pressure requirement, the corresponding passage cross-sectional area or the corresponding displacement is determined.

[0039] Figure 2 shows a flowchart according to an embodiment of the present invention. The method shown in Figure 2 may be implemented, for example, for a hydraulic drive system as shown in Figure 1, and the steps of the method may be implemented in particular by an electronic control unit that executes an appropriate computer program or an appropriate computer program module therefor.

[0040] It is assumed that the pressure closed-loop control of the primary hydraulic machine is carried out according to a pre-specifiable target pressure.

[0041] In step 100, the primary pressure requirement of at least one primary hydraulic actuator and the secondary pressure requirement of the secondary hydraulic machine are detected. The secondary pressure requirement can, for example, correspond to the pressure that must at least be present in order to generate the desired torque when the displacement volume of the secondary hydraulic machine is at its maximum.

[0042] In step 110, it is checked whether a braking torque is applied by the secondary hydraulic machine on the secondary side. Whether there is a braking torque on the secondary side can be determined, for example, from a control signal and / or a measured value (e.g., the difference between the target rotational speed and the actual rotational speed, or the direction of rotation, displacement volume). If not, i.e., if no braking torque is applied by the secondary hydraulic machine on the secondary side, in step 115, the target pressure (used in the pressure closed-loop control on the primary side) can be set to the same as the greater of the primary pressure requirement and the secondary pressure requirement. Additionally, in step 115, the throttle element can be displaced to have a maximum opening cross-sectional area, which can in some cases correspond to the neutral position of the throttle element (i.e., in the case of the above-described two-port two-position directional control valve that is electromagnetically displaceable or electromagnetically pilot-controlled and displaceable, no current supply to the valve displacement mechanism is carried out).

[0043] When braking torque is applied by the secondary hydraulic machine on the secondary side, there exists an operating state called the braking operation state (of the hydraulic drive system) in which braking torque is applied by the secondary hydraulic machine. That is, in step 110, it is determined whether the braking operation state exists. If not, there exists an operating state in which braking torque is not applied by the secondary hydraulic machine.

[0044] When the braking operation state exists, in step 120, it is possible to check whether the secondary pressure requirement is greater than the primary pressure requirement. If not, that is, if the secondary pressure requirement is not greater than the primary pressure requirement, in step 125, the target pressure (used in the pressure closed-loop control on the primary side) can be set to be the same as the primary pressure requirement. Additionally, in step 125, the throttle element can be displaced to have the maximum opening cross-sectional area. In this case, by appropriately adapting the displacement volume, the desired torque of the secondary hydraulic machine can be achieved.

[0045] When the secondary pressure requirement is greater than the primary pressure requirement, in step 130, the target pressure (used in the pressure closed-loop control on the primary side) can be set to be the same as the primary pressure requirement. Further, in step 140, the opening cross-sectional area of the throttle element, that is, the throttle element, is displaced such that the pressure of the pressure medium on the secondary side (detected by, for example, a pressure sensor) corresponds to the secondary pressure requirement and, in particular, becomes substantially the same as the secondary pressure requirement (i.e., within the control deviation of the closed-loop control). For this purpose, for example, the closed-loop control can be implemented as described above. Correspondingly, in the case of the braking operation state, that is, regardless of whether the secondary pressure requirement is greater than or less than the primary pressure requirement, the primary hydraulic machine can be closed-loop controlled or driven using the target pressure that is the same as the primary pressure requirement. It is not necessary to increase the target pressure when the secondary pressure requirement is greater than the primary pressure requirement and the associated increase in the output requirement and / or torque requirement to the engine.

[0046] More generally, when a braking operation state exists, the throttle element is displaced so that the pressure demand on the primary side is satisfied, or so that the output to be applied by the engine for driving the hydraulic machine on the primary side is not increased to meet the pressure demand on the primary side. This may be carried out depending on the pressure demand on the secondary side and the pressure demand on the primary side, as explained in the above steps. Alternatively or additionally, for example, when the volume flow rate of the pressure medium pumped on the secondary side during the braking operation state is greater than the volume flow rate required by the primary side load device on the primary side, the displacement volume (e.g., swivel angle) of the hydraulic machine on the primary side can be reduced for this purpose. In particular, when an electric motor is used as the engine, the rotational speed can also be reduced. If the hydraulic machine on the primary side can be set to zero, a negative displacement volume can also be set (i.e., the pressure medium is pumped from the primary side to the tank), whereby the hydraulic machine on the primary side can apply torque to the engine and, in the case of an electric motor, it becomes possible to recover electrical energy.

Claims

1. A hydraulic drive system for a working machine having a rotatable machine component (2), wherein the rotatable machine component (2) is driven by the hydraulic drive system, and the hydraulic drive system comprises: a displaceable primary hydraulic machine (10) mechanically connected or connectable to an engine (20); and at least one primary hydraulic load (12) hydraulically connected to a pressure connection (16) of the primary hydraulic machine on the primary side, on the primary side; a secondary side comprising a displaceable secondary hydraulic machine (30) mechanically connected to the rotatable machine component (2); a throttle element (40) displaceable in a controllable manner, wherein the primary side and the secondary side are hydraulically connected via the throttle element (40), and the throttle element (40) is displaceable between a minimum opening cross-sectional area and a maximum opening cross-sectional area, the throttle element (40); an electronic control unit (50); and the electronic control unit (50) is configured to: control the throttle element (40); determine whether there is a braking operating state in which a braking torque is applied by the secondary hydraulic machine (30); when the braking operating state exists, displace the throttle element (40) so that the output to be applied by the engine (20) for driving the primary hydraulic machine (10) does not increase so that the primary pressure requirement of the at least one primary load (12) is met; A hydraulic drive system configured as such.

2. The electronic control unit is configured to: when the braking operating state exists, displace the throttle element (40) so that the secondary pressure corresponds to the secondary pressure requirement when the secondary pressure requirement of the secondary hydraulic machine (30) is greater than the primary pressure requirement of the at least one primary load (12). The hydraulic drive system according to claim 1, configured as such.

3. The electronic control unit (50) is further configured to: when the braking operating state exists and the secondary pressure requirement is greater than the primary pressure requirement, set the target pressure of the pressure closed-loop control of the primary hydraulic machine (10) to be the same as the primary pressure requirement (130); and the electronic control unit (50) is particularly configured to: ​ Implement the pressure closed-loop control of the hydraulic machine (10) on the primary side so that the pressure on the primary side corresponds to the target pressure. The hydraulic drive system according to claim 2, which is configured as described above.

4. The electronic control unit (50) When the braking operation state exists and the pressure requirement on the secondary side is not greater than the pressure requirement on the primary side, set the target pressure to be the same as the pressure requirement on the primary side (125). The hydraulic drive system according to claim 2 or 3, which is further configured as described above.

5. The electronic control unit (50) When the braking operation state does not exist, set the target pressure to be the same as the greater of the pressure requirement on the primary side and the pressure requirement on the secondary side (115). The hydraulic drive system according to claim 3 or 4, which is further configured as described above.

6. The throttle element (40) is continuously displaceable between a minimum opening cross-sectional area and a maximum opening cross-sectional area. The hydraulic drive system according to any one of claims 1 to 5.

7. The electronic control unit (50) When the braking operation state does not exist, displace the throttle valve (40) to the maximum opening cross-sectional area. The hydraulic drive system according to claim 6, which is further configured as described above.

8. The electronic control unit (50) When the braking operation state exists and the pressure requirement on the secondary side of the secondary hydraulic machine (30) is greater than the pressure requirement on the primary side of the at least one primary side load device (12), displace the throttle element depending on the pressure difference between the pressure requirement on the secondary side and the pressure requirement on the primary side. The hydraulic drive system according to any one of claims 1 to 7, which is further configured as described above.

9. The hydraulic drive system A secondary pressure sensor (52) configured to measure the pressure on the secondary side and transmit it to the electronic control unit (50), and / or A primary pressure sensor (54) configured to measure the pressure on the primary side and transmit it to the electronic control unit (50). The hydraulic drive system according to any one of claims 1 to 8, which further includes the above.

10. The electronic control unit (50) when the braking condition exists, the volumetric flow rate pumped by the secondary hydraulic machine (30) is equal to or greater than the primary volumetric flow rate demand of the at least one primary hydraulic load (12); Displacing the primary hydraulic machine (10) so that it does not pump a volume flow, or If the primary hydraulic machine (10) can be set to zero and the engine (20) is an electric motor, the primary hydraulic machine (10) is displaced so that torque is applied to the engine (20) by the primary hydraulic machine (10).

10. The hydraulic drive system of claim 1, further comprising:

11. 1. A method for operating a hydraulic drive system of a work machine having a rotatable mechanical component (2), the rotatable mechanical component (2) being driven by the hydraulic drive system, the hydraulic drive system comprising: a primary side comprising a displaceable primary hydraulic machine (10) mechanically coupled or connectable to an engine (20) and at least one primary hydraulic loader (12) hydraulically connected on the primary side to a pressure connection (16) of the primary hydraulic machine; a secondary side comprising a displaceable secondary hydraulic machine (30) mechanically coupled to said rotatable machine component (2); a throttle element (40) that is displaceable in a controllable manner, via which the primary side and the secondary side are hydraulically connected, and which is displaceable between a minimum opening cross-sectional area and a maximum opening cross-sectional area; having determining (110) whether a braking operating condition exists in which a braking torque is applied by the secondary hydraulic machine (30); When the braking condition exists, the throttle element (40) is displaced such that the power to be applied by the engine (20) to drive the primary hydraulic machine (10) is not increased so that the primary pressure demand of the at least one primary load (12) is met. method.

12. When the braking operation state exists and the secondary pressure requirement of the secondary hydraulic machine (30) is greater than the primary pressure requirement of the at least one primary load device (12), the throttle element (40) is displaced (140) so that the secondary pressure corresponds to the secondary pressure requirement. In particular, when the braking operation state exists and the secondary pressure requirement is greater than the primary pressure requirement, the target pressure of the pressure closed-loop control of the primary hydraulic machine (10) is set to be the same as the primary pressure requirement. The method according to claim 11.

13. A control unit (50) including a processor configured to implement the method according to claim 11 or 12.

14. A computer program including instructions that, when executed by a computer, cause the computer to implement the method according to claim 11 or 12.

15. A computer-readable data carrier storing the computer program according to claim 14.

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