Hydraulic drive system and method for operating a hydraulic drive system

Abstract

The invention relates to a hydraulic drive system of a work machine having a rotatable machine component (2) driven by the drive system, comprising a primary side with an adjustable primary-side hydraulic machine (10) that is or can be mechanically coupled to a motor (20), and at least one primary-side hydraulic consumer (12) that is hydraulically connected to a pressure connection (16) of the primary-side hydraulic machine; a secondary side with an adjustable secondary-side hydraulic machine (30) that is mechanically coupled to the rotatable machine component (2); a controllably adjustable throttle element (40), via which the primary side and the secondary side are hydraulically connected and which is adjustable between a minimum and a maximum opening cross-section;and an electronic control unit (50) configured to control the throttle element (40), to determine whether a braking operating state exists in which a braking torque is applied by the secondary-side hydraulic machine (30), and, if the braking operating state exists, to adjust the throttle element (40) so that a power to be applied by the motor (20) to drive the primary-side hydraulic machine (10) in order to correspond to a primary-side pressure request of the at least one primary-side consumer (12) is not increased.;

Description

[0001] The present invention relates to a hydraulic drive system and a method for operating a hydraulic drive system as well as a control unit and a computer program for carrying out the method. Background of the invention

[0002] Machines, e.g. mobile work machines such as excavators, loaders or crawlers, can have a hydraulic drive system with which components of the respective machine, such as arm elements and / or a slewing gear of an excavator, are driven. A primary-side hydraulic machine is provided in the hydraulic system for supplying pressure medium. In order to drive a rotary component, another, secondary-side hydraulic machine can be provided, which is hydraulically connected to the primary-side hydraulic machine. The rotary component can be, for example, a slewing gear or a drive of a travel drive, such as a chain drive, of the work machine. In general, it can be provided that the secondary-side hydraulic machine applies an accelerating or a braking torque, depending on the operating situation. Disclosure of the invention

[0003] According to the invention, a hydraulic drive system and a method for operating a hydraulic drive system, as well as a control unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the subclaims and the following description.

[0004] The invention makes use of the measure of providing, in a hydraulic drive system having a primary side with an adjustable primary-side hydraulic machine and at least one primary-side hydraulic consumer, and a secondary side with an adjustable secondary-side hydraulic machine coupled to a rotatable machine component, a controllably adjustable throttle element via which the primary side and the secondary side are hydraulically connected, and an electronic control unit for controlling the throttle element.The electronic control unit is configured to determine whether a braking operating state exists in which a braking torque is applied by the secondary-side hydraulic machine. If the braking operating state exists, it adjusts the throttle element so that the power required by a motor to drive the primary-side hydraulic machine in order to meet (or satisfy) a primary-side pressure demand of the at least one primary-side consumer is not increased. This measure achieves greater energy efficiency of the hydraulic drive system.

[0005] The term “pressure request” refers to a pressure value that is to be achieved at least, i.e. a pressure value that is sufficient in each case to achieve a desired movement of one or more primary-side machine elements (or primary-side machine components) that are coupled to the at least one primary-side consumer, or a desired movement of the rotatable machine component coupled to the secondary-side hydraulic machine. The primary-side pressure request is a pressure request of the at least one primary-side consumer. The secondary-side pressure request is a pressure request of the secondary-side hydraulic machine. The “primary-side pressure” corresponds to the pressure at a pressure connection of the primary-side hydraulic machine. The “secondary-side pressure” corresponds to the pressure at a pressure connection of the secondary-side hydraulic machine.The term “hydraulically connected” means that a volume flow of pressure medium is possible between the respective elements, e.g. via a hydraulic line or a hydraulic channel, whereby valves or similar devices can be provided to control the volume flow.

[0006] According to one embodiment, the electronic control unit is configured, when the braking operating state is present and a secondary-side pressure requirement of the secondary-side hydraulic machine is greater than a primary-side pressure requirement of the at least one primary-side consumer, to adjust the throttle element such that a secondary-side pressure corresponds to the secondary-side pressure requirement. This avoids the primary-side pressure having to be raised to the level of the secondary-side pressure requirement by the primary-side hydraulic machine. A passage cross-section of the throttle element is adjusted such that the pressure drop across the throttle element corresponds to or is equal to the pressure difference between the secondary-side and primary-side pressure requirements. The pressure drop is caused by the volume flow through the throttle element or its passage cross-section, which occurs due to the pressure difference.Accordingly, it is ensured that the primary-side pressure, which corresponds to the output pressure of the primary-side hydraulic machine, remains at the level of the primary-side pressure requirement.

[0007] The wording "that a secondary-side pressure corresponds to the secondary-side pressure requirement" means in particular that the secondary-side pressure is (or should be) equal to the secondary-side pressure requirement or that the secondary-side pressure is equal to the secondary-side pressure requirement within the framework of a control system (i.e., is equal to the secondary-side pressure requirement except for control deviations).

[0008] According to one embodiment, the throttle element is continuously adjustable between a minimum and a maximum opening cross-section. This continuous adjustability allows the opening cross-section to be continuously changed, thus precisely meeting the respective pressure requirements.

[0009] According to one embodiment, the electronic control unit is further configured to set a target pressure of a pressure control of the primary-side hydraulic machine equal to the primary-side pressure requirement when the braking operating state is present, when the secondary-side pressure requirement is greater than the primary-side pressure requirement. This also enables the primary-side pressure, which corresponds to the output pressure of the primary-side hydraulic machine, to remain at the level of the primary-side pressure requirement.

[0010] According to one embodiment, the electronic control unit is further configured to perform pressure control of the primary-side hydraulic machine so that a primary-side pressure corresponds to the target pressure. Alternatively, the pressure control can be performed by another computing unit, wherein the electronic control unit transmits the target pressure it determines to the other computing unit in order to set it.

[0011] According to one embodiment, the electronic control unit is further configured to set the target pressure equal to the primary-side pressure requirement when the braking operating state is present and the secondary-side pressure requirement is not greater than the primary-side pressure requirement. This case can occur if only a low braking torque is generated by the secondary-side hydraulic machine.

[0012] According to one embodiment, the electronic control unit is further configured to set the target pressure equal to the greater of the primary-side pressure requirement and the secondary-side pressure requirement when the braking operating state is not present. Thus, both the primary-side and the secondary-side pressure requirement can be met.

[0013] According to one embodiment, the electronic control unit is further configured to adjust the throttle valve to the maximum opening cross-section when the braking operating state is not present. This is expedient because, in the event that an accelerating torque is generated by the secondary-side hydraulic machine, an unimpeded volume flow from the primary side to the secondary side is possible.

[0014] According to one embodiment, the electronic control unit is further configured to adjust the throttle element depending on a pressure difference between the secondary-side and primary-side pressure demands when the braking operating state is present, when a secondary-side pressure demand of the secondary-side hydraulic machine is greater than the primary-side pressure demand of the at least one primary-side consumer. This is expedient because the volume flow through a hydraulic passage is typically a function of the pressure difference across the passage and the opening cross-section.

[0015] According to one embodiment, the hydraulic drive system further comprises a secondary-side pressure sensor configured to measure the secondary-side pressure and transmit it to the electronic control unit, and / or a primary-side pressure sensor configured to measure the primary-side 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, the electronic control unit is further configured, when the braking operating state is present and a volume flow delivered by the secondary-side hydraulic machine is equal to or greater than a primary-side volume flow requirement of the at least one primary-side hydraulic consumer, to adjust the primary-side hydraulic machine so that it delivers no volume flow, or, if the primary-side hydraulic machine can be set to zero and the motor is an electric machine, to adjust it so that a torque is exerted on the motor by the primary-side hydraulic machine. Accordingly, if more pressure medium is delivered on the secondary side than is required on the primary side during the braking operating state, the drive power of the motor can be largely reduced or, if the motor is an electric machine, energy can be recuperated by the motor. In this case, i.e.If more pressure medium is delivered on the secondary side during braking operation than is required on the primary side, the throttle element can also be adjusted so that the primary and secondary side pressure requirements are met.

[0017] According to one embodiment, a hydraulic accumulator is provided on the secondary side, which is hydraulically connected to the pressure connection of the secondary-side hydraulic machine. The accumulator enables the hydraulic storage of energy generated, for example, during braking.

[0018] A method according to the invention for operating a hydraulic drive system of a work machine having a rotatable machine component driven by the hydraulic drive system relates to a hydraulic drive system having a primary side with an adjustable primary-side hydraulic machine which is or can be mechanically coupled to a motor, and at least one primary-side hydraulic consumer which is hydraulically connected on the primary side to a pressure connection of the primary-side hydraulic machine, a secondary side with an adjustable secondary-side hydraulic machine which is mechanically coupled to the rotatable machine component, and a controllably adjustable throttle element via which the primary side and the secondary side are hydraulically connected and which is adjustable between a minimum and a maximum opening cross-section.In the method, it is determined whether a braking operating state in which a braking torque is applied by the secondary-side hydraulic machine exists, and if the braking operating state exists, if a secondary-side pressure requirement of the secondary-side hydraulic machine is greater than a primary-side pressure requirement of the at least one primary-side consumer, the throttle element is adjusted so that a secondary-side pressure corresponds to the secondary-side pressure requirement.

[0019] A control unit according to the invention, e.g. a control device of a hydraulic drive system of a mobile work machine, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0020] Implementing a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is also advantageous, as this entails particularly low costs, particularly if an executing control unit is also used for other tasks and is therefore already present. Suitable data storage devices for providing the computer program include, in particular, magnetic, optical, and electrical storage devices, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

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

[0022] 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 or on their own, without departing from the scope of the present invention.

[0023] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Character description Fig. 1 shows a hydraulic drive system of a work machine according to an embodiment of the invention. Fig. 2 shows a flowchart according to an embodiment of the invention. Detailed description of the drawing

[0024] Fig. 1 shows a hydraulic drive system of a work machine according to one embodiment of the invention. The work machine has a rotatable machine component 2, e.g., a part of a slewing gear of an excavator or a travel drive of the work machine, and at least one further primary-side, movable machine element (not shown), e.g., a boom element of an excavator. The rotatable machine component 2 and the at least one primary-side machine element are driven by the hydraulic drive system.

[0025] The hydraulic drive system has a primary side and a secondary side. On the primary side, a primary-side hydraulic machine 10 and at least one primary-side hydraulic consumer 12 (e.g., at least one hydraulic cylinder and / or at least one hydraulic motor) are provided, which is (mechanically) coupled to the at least one further machine element in order to drive it (i.e., to cause its movement). The primary-side hydraulic machine 10 is (mechanically) coupled to a (drive) motor 20, which drives the primary-side hydraulic machine with a (drive) power. The power to be applied by the motor depends on the pressure difference (e.g., the difference between the output-side pump pressure, i.e., the primary-side pressure, and the input-side tank pressure) across the primary-side hydraulic machine 10 and on the delivered volume flow. In particular, the power to be applied is proportional to a constant of proportionality, into which, for example,An efficiency factor is included, the product of pressure difference and volume flow. The engine 20 is, for example, an internal combustion engine, such as a diesel engine, or an electric motor.

[0026] The at least one primary-side hydraulic consumer 12 is hydraulically connected to a pressure port 16 of the primary-side hydraulic machine 10 via a valve arrangement 14. The valve arrangement 14 has one or more valves (not shown) that can be adjusted to control the inflow of pressure medium to the at least one primary-side hydraulic consumer 12 and the outflow of pressure medium from the at least one primary-side hydraulic consumer 12. A tank port 18 of the primary-side hydraulic machine 10 is connected to a tank in which pressure medium is provided.

[0027] On the secondary side, a secondary hydraulic machine 30 with a pressure connection 36 is provided. The secondary hydraulic machine 30 is mechanically coupled to the rotatable machine component 2 (e.g., via a shaft and / or a gear), so that rotations of the secondary hydraulic machine 30 correspond to rotations of the machine component 2. A tank connection 38 of the secondary hydraulic machine 30 is connected to a tank in which pressure medium is provided. Optionally, a hydraulic pressure medium accumulator b can also be provided on the secondary side, which is hydraulically connected to the pressure connection of the secondary hydraulic machine 30.

[0028] The primary-side hydraulic machine 10 and the secondary-side hydraulic machine are adjustable (and independently of one another, in particular, adjustable to zero), i.e., they have an adjustable displacement or an adjustable displacement volume, where the term "displacement" refers to the volume of pressure medium delivered per revolution. For example, the primary-side hydraulic machine 10 or the secondary-side hydraulic machine 30 is an axial piston machine, e.g., with a swashplate design or a bent-axis design, where the displacement corresponds to an adjustable pivot angle. The pressure medium (i.e., hydraulic fluid) is, for example, hydraulic oil.

[0029] The primary side and the secondary side are hydraulically connected or hydraulically coupled by a throttle element 40. The throttle element 40 is adjustable, i.e., a passage cross-section or a cross-sectional area of a passage through the throttle element (between the primary side and the secondary side) for pressure medium is variable. This adjustment 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 port 16 of the primary-side hydraulic machine 10 and hydraulically connected on the secondary side to the pressure port 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, wherein a passage with an adjustable cross-section is formed between the primary-side connection and the secondary-side connection of the throttle element. The throttle element can, for example, be a 2-2 directional control valve having a passage that is continuously adjustable between an open position (maximum cross-sectional area of the passage) and a closed position (minimum cross-sectional area, which is in particular equal to zero, of the passage). The adjustment is performed electromagnetically or electromagnetically pilot-controlled, and the open position can be the normal position (e.g., the 2-2 directional control valve is preloaded into the open position).

[0030] The electronic control unit 50 may also be configured to adjust the displacement of the primary-side and / or secondary-side hydraulic machine.

[0031] Overall, a hydrostatic system is formed, wherein the rotational speed of the rotatable machine component 2 is controllable on the secondary side, e.g., by adjusting the displacement of the secondary-side hydraulic machine 30. If an accelerating torque is to be generated for the machine component 2 on the secondary side (by the secondary-side hydraulic machine 30), the secondary-side hydraulic machine 30 acts as a hydraulic motor. If, on the other hand, a braking torque is to be generated for the machine component 2, the secondary-side hydraulic machine 30 acts as a hydraulic pump, i.e., the secondary-side hydraulic machine 30 delivers pressure medium from the tank connection to the pressure connection. The torque is proportional to the product of displacement and pressure difference between the pressure connection and the tank connection. The primary-side hydraulic machine 10 typically acts as a hydraulic pump, but can, in certain operating situations, e.g.,If the at least one primary-side hydraulic consumer 12 requires no or only a small volume flow of pressure medium and the secondary-side hydraulic machine 30 simultaneously acts as a hydraulic pump, it can also act as a hydraulic motor; in particular, if the motor 20 is an electric machine, electrical energy can be recuperated.

[0032] The primary-side hydraulic machine 10 is, for example, pressure-controlled, so that the primary-side pressure of the pressure medium, which is detected, for example, by a primary-side pressure sensor 52, corresponds to a primary-side target pressure, i.e. is regulated to this or (within the scope of pressure regulation) is equal to this. This pressure regulation can be carried out, for example, by the electronic control unit 50 or by another computing unit, wherein in the latter case it can be provided that the electronic control unit 50 determines the primary-side target pressure and transmits it to this computing unit. If the secondary-side hydraulic machine 30 acts as a hydraulic motor (i.e., if an accelerating torque is to be generated by it), the primary-side target pressure is approximately equal to the larger of a primary-side pressure request and a secondary-side pressure request.In this situation, the throttle element 40 is adjusted in particular so that it has the maximum passage cross-section.

[0033] The term "pressure requirement" refers to a minimum pressure value that must be achieved. The primary-side pressure requirement is a pressure requirement of the at least one primary-side consumer 12, which is determined, for example, by loads acting on the at least one other machine element. The secondary-side pressure requirement is a pressure requirement of the secondary-side hydraulic machine 30, which is determined by the torque to be applied by the secondary-side hydraulic machine 30 (e.g., assuming maximum displacement).

[0034] 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 output 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 output pressure of the primary-side hydraulic machine 10.

[0035] In a situation in which the secondary-side hydraulic machine 30 acts as a hydraulic pump (i.e., when a braking torque is to be generated by it), it may happen that the secondary-side pressure requirement to apply the required braking torque exceeds the primary-side pressure requirement (of the at least one primary-side consumer 12), so that if no throttle element is provided or the throttle element 40 remains in the maximum passage cross-section, the pressure of the pressure medium on the primary side must be raised by the primary-side hydraulic machine 20 to the pressure level of the secondary-side pressure requirement. The control behavior of the at least one primary-side consumer 12 is not affected by this, since the volume flow to them is throttled in the valve arrangement, for example, by pressure compensators, which, however, causes energy losses.

[0036] In order to avoid this effect, whereby the primary-side hydraulic machine 20 requires additional power to reach the pressure level of the secondary-side pressure requirement, it is provided to adjust the throttle element 40, i.e. to adjust or reduce its passage cross-section such that the primary-side pressure is equal to the primary-side pressure requirement of the at least one primary-side consumer 12 and, at the same time, the secondary-side pressure is equal to or greater than the secondary-side pressure requirement. The throttle element 40 is therefore adjusted such that the pressure drop in the volume flow of pressure medium from the secondary side to the primary side caused by the throttle element is equal to the pressure difference between the secondary-side and primary-side pressure requirements. In this case, the target pressure of the pressure control of the primary-side hydraulic machine can be selected to correspond to or be equal to the primary-side pressure requirement.

[0037] To achieve this, for example, a secondary-side pressure sensor 54 can be provided, which detects the secondary-side pressure of the pressure medium. Control can then take place, e.g. by the electronic control unit 50, wherein the throttle element 40 is adjusted such that the secondary-side pressure detected by the secondary-side pressure sensor 54 is adjusted to the secondary-side pressure requirement (control or sensor lines are shown in the figure as dashed lines). The manipulated variable here is, for example, a control variable (e.g. electrical current intensity or duty cycle of a PWM signal) with which the throttle element 40 is adjusted. An additional pilot control is also conceivable here, wherein by means of a flow characteristic map of the throttle element (e.g.given by a flow equation of a throttle point or orifice) from an assumed given volume flow (from the speed and displacement of the secondary-side hydraulic machine) and the pressure difference between the secondary-side and primary-side pressure requirements, a corresponding passage cross-section or a corresponding adjustment is determined.

[0038] Fig. 2 shows a flowchart according to an embodiment of the invention. Fig. The method shown in Figure 2 can be used, for example, for a hydraulic drive system as in Fig. 1, wherein the steps of the method can be implemented in particular by the electronic control unit, which executes a suitable computer program or suitable computer program modules for this purpose.

[0039] It is assumed that the pressure of the primary hydraulic machine is controlled according to a predefined target pressure.

[0040] In step 100, a primary-side pressure demand of the at least one primary-side hydraulic consumer and a secondary-side pressure demand of the secondary-side hydraulic machine are detected. The secondary-side pressure demand can, for example, correspond to a pressure that must be present at the maximum displacement of the secondary-side hydraulic machine at a minimum in order to generate a desired torque.

[0041] In step 110, a check is performed to determine whether a braking torque is being applied on the secondary side by the secondary-side hydraulic machine. Whether a braking torque is present on the secondary side can be determined, for example, from control signals and / or measured values (e.g., a difference between a target speed and an actual speed, or from the direction of rotation, displacement). If this is not the case, i.e., if no braking torque is being applied on the secondary side by the secondary-side hydraulic machine, in step 115, the target pressure (used on the primary side in pressure control) can be set equal to the larger of the primary-side pressure request and the secondary-side pressure request.In addition, in step 115, the throttle element can be adjusted so that it has the largest opening cross-section, which may correspond to the neutral position of the throttle element (in the above-mentioned case of an electromagnetically or electromagnetically pilot-controlled adjustable 2-2 way valve, no current is applied to the adjustment mechanism of the valve).

[0042] If a braking torque is applied on the secondary side by the secondary-side hydraulic machine, an operating state (of the hydraulic drive system) referred to as the braking operating state exists, in which a braking torque is applied by the secondary-side hydraulic machine. In step 110, it is determined whether the braking operating state exists. Otherwise, an operating state exists in which no braking torque is applied by the secondary-side hydraulic machine.

[0043] If the braking operating state exists, a check can be made in step 120 to determine whether the secondary-side pressure demand is greater than the primary-side pressure demand. If this is not the case, i.e., if the secondary-side pressure demand is not greater than the primary-side pressure demand, the target pressure (used on the primary side in pressure control) can be set equal to the primary-side pressure demand in step 125. Additionally, in step 125, the throttle element can be adjusted so that it has the largest opening cross-section. The desired torque of the secondary-side hydraulic machine can be achieved by appropriately adjusting the displacement.

[0044] If the secondary-side pressure requirement is greater than the primary-side pressure requirement, the target pressure (which is used on the primary side in the pressure control) can be set equal to the primary-side pressure requirement in step 130. Furthermore, in step 140, the throttle element, i.e. its opening cross-section, is adjusted such that a secondary-side pressure of the pressure medium (which is detected, for example, with a pressure sensor) corresponds to the secondary-side pressure requirement and, in particular, is essentially (i.e. within the scope of a control deviation of a control) equal to the secondary-side pressure requirement. For this purpose, a control can be carried out, for example, as described above. Accordingly, in the case of a braking operating state, the primary-side hydraulic machine can be controlled or regulated with a target pressure regardless of whether the secondary-side pressure requirement is greater or lesser than the primary-side pressure requirement.which is equal to the primary-side pressure requirement. An increase in the target pressure if the secondary-side pressure requirement is higher than the primary-side pressure requirement, and a corresponding increase in the power and / or torque demand on the engine, is not necessary.

[0045] In more general terms, the throttle element is adjusted so that the power required by the motor to drive the primary-side hydraulic machine so that the primary-side pressure requirement is met or satisfied is not increased when the braking operating state exists. This can be done as a function of the secondary-side and primary-side pressure requirements, as described in the steps mentioned above. Alternatively or additionally, if the volume flow of pressure medium delivered on the secondary side during the braking operating state is greater than the volume flow required by the primary-side consumers on the primary side, the displacement (e.g. swivel angle) of the primary-side hydraulic machine can also be reduced. The speed can also be reduced, particularly if an electric machine is used as the motor.If the primary side hydraulic machine is adjustable to zero, a negative displacement can also be set (i.e. pressure medium is pumped from the primary side to the tank), so that the primary side hydraulic machine exerts a torque on the motor, whereby in the case of an electric machine, electrical energy can be recovered.

Claims

[1] Hydraulic drive system of a work machine having a rotatable machine component (2) driven by the hydraulic drive system, comprising a primary side with an adjustable primary-side hydraulic machine (10) which is mechanically coupled or can be coupled to a motor (20), and with at least one primary-side hydraulic consumer (12) which is hydraulically connected on the primary side to a pressure connection (16) of the primary-side hydraulic machine; a secondary side with an adjustable secondary side hydraulic machine (30) which is mechanically coupled to the rotatable machine component (2); a controllably adjustable throttle element (40) via which the primary side and the secondary side are hydraulically connected and which is adjustable between a minimum and a maximum opening cross-section; and an electronic control unit (50) which is arranged to to control the throttle element (40), to determine whether a braking operating state in which a braking torque is applied by the secondary-side hydraulic machine (30) exists, and when the braking operating state is present, to adjust the throttle element (40) so that a power to be applied by the motor (20) to drive the primary-side hydraulic machine (10) in order to correspond to a primary-side pressure requirement of the at least one primary-side consumer (12) is not increased. [2] Hydraulic drive system according to claim 1, wherein the electronic control unit is configured to adjust the throttle element (40) in such a way that a secondary-side pressure corresponds to the secondary-side pressure requirement when the braking operating state is present and the secondary-side pressure requirement of the secondary-side hydraulic machine (30) is greater than the primary-side pressure requirement of the at least one primary-side consumer (12). [3] Hydraulic drive system according to claim 2, wherein the electronic control unit (50) is further configured to set (130) a target pressure of a pressure control of the primary-side hydraulic machine (10) equal to the primary-side pressure requirement when the braking operating state is present, if the secondary-side pressure requirement is greater than the primary-side pressure requirement; and wherein the electronic control unit (50) is in particular configured to carry out the pressure control of the primary-side hydraulic machine (10) so that a primary-side pressure corresponds to the target pressure. [4] Hydraulic drive system according to claim 2 or 3, wherein the electronic control unit (50) is further configured to set the target pressure equal to the primary side pressure requirement (125) when the braking operating state is present and the secondary side pressure requirement is not greater than the primary side pressure requirement. [5] Hydraulic drive system according to one of claims 3 to 4, wherein the electronic control unit (50) is further configured to set the target pressure equal to the larger of the primary-side pressure request and the secondary-side pressure request (115) when the braking operating state is not present. [6] Hydraulic drive system according to one of the preceding claims, wherein the throttle element (40) is continuously adjustable between a minimum and a maximum opening cross-section. [7] Hydraulic drive system according to claim 6, wherein the electronic control unit (50) is further configured to adjust the throttle valve (40) to the maximum opening cross-section when the braking operating state is not present. [8] Hydraulic drive system according to one of the preceding claims, wherein the electronic control unit (50) is further configured to adjust the throttle element depending on a pressure difference between the secondary-side and the primary-side pressure requirement when the braking operating state is present, if a secondary-side pressure requirement of the secondary-side hydraulic machine (30) is greater than the primary-side pressure requirement of the at least one primary-side consumer (12). [9] Hydraulic drive system according to one of the preceding claims, further comprising a secondary-side pressure sensor (52) configured to measure the secondary-side pressure and transmit it to the electronic control unit (50); and / or a primary-side pressure sensor (54) configured to measure the primary-side pressure and transmit it to the electronic control unit (50). [10] Hydraulic drive system according to one of the preceding claims, wherein the electronic control unit (50) is further configured, in the presence of the braking operating state, when a volume flow delivered by the secondary-side hydraulic machine (3) is equal to or greater than a primary-side volume flow requirement of the at least one primary-side hydraulic consumer (12), to adjust the primary-side hydraulic machine (10) such that it does not deliver any volume flow, or, if the primary-side hydraulic machine (10) is adjustable to zero and the motor (20) is an electric machine, to adjust it such that a torque is exerted on the motor (20) by the primary-side hydraulic machine (10). [11] Method for operating a hydraulic drive system of a work machine having a rotatable machine component (2) driven by the hydraulic drive system, wherein the hydraulic drive system a primary side with an adjustable primary-side hydraulic machine (10) which is mechanically coupled or can be coupled to a motor (20), and with at least one primary-side hydraulic consumer (12) which is hydraulically connected on the primary side to a pressure connection (16) of the primary-side hydraulic machine, a secondary side with an adjustable secondary-side hydraulic machine (30) which is mechanically coupled to a rotatable machine component (2), and a controllably adjustable throttle element (40) via which the primary side and the secondary side are hydraulically connected and which is adjustable between a minimum and a maximum opening cross-section; wherein it is determined (110) whether a braking operating state in which a braking torque is applied by the secondary-side hydraulic machine (30) exists; and wherein, when the braking operating state is present, the throttle element (40) is adjusted so that a power to be applied by the motor (20) for driving the primary-side hydraulic machine (10) in order to correspond to a primary-side pressure requirement of the at least one primary-side consumer (12) is not increased. [12] Method according to claim 11, wherein, in the presence of the braking operating state, if a secondary-side pressure requirement of the secondary-side hydraulic machine (30) is greater than a primary-side pressure requirement of the at least one primary-side consumer (12), the throttle element (40) is adjusted (140) so that a secondary-side pressure corresponds to the secondary-side pressure requirement; wherein, in particular, in the presence of the braking operating state, if the secondary-side pressure requirement is greater than the primary-side pressure requirement, a target pressure of a pressure control of the primary-side hydraulic machine (10) is set equal to the primary-side pressure requirement. [13] Control unit (50) comprising a processor configured to carry out the method according to claim 11 or 12. [14] A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to claim 11 or 12. [15] A computer-readable data carrier on which the computer program according to claim 14 is stored.

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