Method for controlling a hydraulic drive system and hydraulic drive system

Abstract

The invention provides a method for controlling a hydraulic drive system having at least two hydraulic machines (2a, 2b).SOLUTION: For each of the hydraulic machines 2a, 2b, a setpoint value for a delivery quantity of the hydraulic machine is detected, wherein the delivery quantity is dependent on the displacement volume, and wherein manipulated values for the displacement volumes of the two hydraulic machines 2a, 2b are implemented in such a way that a ratio of the manipulated values to one another is equal to a corresponding ratio of the setpoint values, and in such a way that at least one condition is satisfied, the at least one condition includes a condition that the sum of the driving amount requests of the hydraulic machines 2a and 2b corresponding to the operation values is equal to or smaller than the driving amount maximum value, and the hydraulic machines 2a and 2b are controlled using the determined operation values.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a hydraulic drive system, a computing unit, a computer program for implementing the method, and a hydraulic drive system. [Background technology]

[0002] Background of the Invention Work machines, particularly mobile work machines such as excavators, may have hydraulic drive systems for inducing movement of work machine elements using hydraulic cylinders or hydraulic motors (hydraulic consumers). Such hydraulic drive systems may include multiple hydraulic pumps driven by a single engine (e.g., an internal combustion engine or an electric motor), which supply hydraulic fluid to each of the hydraulic consumers in multiple hydraulic circuits. In this case, for example, if two hydraulic pumps are used, it may be envisaged to hydraulically couple the individual power control devices of the two hydraulic pumps, which influence the power distribution between the two hydraulic pumps. Summary of the Invention [Problem to be solved by the invention]

[0003] Disclosure of the Invention According to the invention, a method for controlling a hydraulic drive system, a computing unit and a computer program for implementing the method, and a hydraulic drive system are proposed having the features set forth in the independent claims. Preferred embodiments are the subject of the dependent claims and the following description. [Means for solving the problem]

[0004] The present invention relates to a means for controlling a hydraulic drive system having at least two hydraulic machines, comprising: determining, for each of the hydraulic machines, a set value for the hydraulic machine's pumping volume, the pumping volume being a function of the displacement; determining manipulated values ​​for the displacement volumes of the at least two hydraulic machines, the determination being carried out so that the ratios of the manipulated values ​​are equal to the corresponding ratios of the set values ​​and so that at least one condition is met, the at least one condition including that the sum of the drive demands of the hydraulic machines corresponding to the manipulated values ​​is less than or equal to a maximum drive value; and controlling the hydraulic machines using the manipulated values.

[0005] By setting the ratio of the operating values ​​to be equal to the ratio of the set values, when combining and moving a number of components driven by a number of hydraulic consumers supplied with pressure medium by a number of different hydraulic machines, the relative speeds of these components are maintained equal, i.e. the corresponding spatial curves of the elements (e.g. excavator shovels) located at the free ends of the components remain unchanged and are only executed at speeds that are changed so that at least one condition is observed.

[0006] When determining the manipulated variable for the displacement, a corresponding mathematical formula or control element (within the framework of a control scheme) that maps input quantities (including setpoints) to the manipulated variable can be used. Alternatively or additionally, an iterative method, etc., can be used. For example, an estimated or provisional manipulated variable can first be determined so that the resulting value of the pumping quantity, which is a function of the manipulated variable, is equal to the corresponding setpoint (i.e., for the same hydraulic machine). It is checked whether at least one condition is met for the provisional manipulated variable. If at least one condition is met, the provisional manipulated variable is determined as the manipulated variable (to be used in the control). On the other hand, if at least one condition is not met, the provisional manipulated variable is multiplied by a common scaling factor, which is determined so that at least one condition is met. If only a condition regarding the sum of the drive demands is to be met, the scaling factor can be selected, for example, as the quotient of the drive maximum value divided by the sum of the drive demands. By using a common scaling factor, the ratio between the manipulated variables remains unchanged. Furthermore, in the iterative process, friction or friction torque and / or leakage, which are generally dependent on the operating variable, can also be taken into account. In this case, for example, in one iteration, an average or maximum value for the friction torque and / or leakage is first assumed, and an estimated operating variable is determined based on this. In subsequent iterations, the friction torque and / or leakage present for the estimated operating variable is used to correct the estimated operating variable.

[0007] The term "connected" or "connection", unless otherwise stated, is to be understood in the sense of "hydraulicly connected", i.e. in the sense of hydraulic connections, e.g. hydraulic lines or passages, which allow a volumetric flow or flow of pressure medium to pass between the elements connected via the hydraulic connections, and in which the hydraulic connections may be provided with optional control elements, e.g. valves or the like, which influence the volumetric flow of pressure medium or which can influence the volumetric flow of pressure medium in a controllable manner.

[0008] According to one embodiment, the actuation value is determined so that the deviation between the setpoint and the value of the pumping rate that results from the actuation value, particularly when the rotational speed is known, is as small as possible or equal to zero. In other words, the actuation value is determined so that the setpoint is achieved as far as possible. That is, the setpoint is a target value for the pumping rate that should be achieved if or as far as possible.

[0009] In one embodiment, the at least one condition includes that the operating value of each of the hydraulic machines is less than or equal to the maximum displacement value of the respective hydraulic machine, or, if the displacement can be set to zero, that the operating value of each of the hydraulic machines is less than or equal to the maximum displacement value of the respective hydraulic machine and greater than or equal to the minimum displacement value of the respective hydraulic machine. These conditions make it possible to take into account the technical situation of the hydraulic machines, in particular without abandoning the proportional distribution of the drive amounts, i.e., the proportional distribution of the drive amounts according to the ratio between the set values. The maximum (or minimum) displacement value may be determined, for example, as a function of a technically maximally (minimally) adjustable limit value for the displacement, for example as a function of the maximum swivel angle, and in particular may be equal to the maximally (minimally) adjustable limit value for the displacement, or may be determined at a small distance (for example less than 5%) from this limit value (for example, in order to provide a control reserve when the displacement is controlled to a predetermined operating value by controlling the respective hydraulic machine and this predetermined operating value is adjusted).

[0010] According to one embodiment, the pumping rates for each of the hydraulic machines are the volumetric flow pumped by the respective hydraulic machine or the displacement or swivel angle of the respective hydraulic machine, which correspond to the speed of the hydraulic consumer to which the hydraulic machine supplies pressure medium.

[0011] According to one embodiment, the drive quantity is the power provided by the engine or the torque provided by the engine. For a given engine speed, power and torque are substantially equivalent, since power is equal to the speed times the torque. Optionally, friction can be additionally taken into account in this case, so that the power output by the engine or the torque output by the engine gives the power actually provided for the hydraulic machine or the torque actually provided for the hydraulic machine. The maximum value of the drive quantity is the corresponding maximum power or maximum torque, both of which depend inter alia on the speed.

[0012] According to one embodiment, for each hydraulic machine, a pressure measurement value is detected at the pressure outlet of the respective hydraulic machine or at a pressure line connected to the pressure outlet, and for each hydraulic machine, a drive quantity request is determined from the detected pressure measurement value for the respective hydraulic machine and the operating value. The drive quantity request is in particular a torque request or a power request, depending on the drive quantity. In the case of a torque request, the torque request is substantially proportional to the product of the displacement and the pressure measurement value. In the case of a power request, the power request is substantially proportional to the product of the rotational speed, the displacement and the pressure measurement value or to the product of the pumped volumetric flow rate and the pressure measurement value. The expression "substantially" is to be understood here as meaning that leakage, friction, etc. are not taken into account.

[0013] According to one embodiment, the method comprises, after detecting the setpoints and before determining the operating values, adjusting at least one of the setpoints, the determining of the operating values ​​being performed using at least one reduced setpoint, by adjusting the setpoints it is possible to take into account conditions that may exist individually for each hydraulic machine and / or for each circuit to which pressure medium is supplied.

[0014] According to one embodiment, for each hydraulic machine, a pressure measurement value at the pressure outlet of the respective hydraulic machine or at a pressure line connected to the pressure outlet is detected. If the pressure measurement value of a hydraulic machine exceeds a threshold value corresponding to the hydraulic machine, the setpoint for the respective hydraulic machine is adjusted by reducing it in absolute terms. The threshold value is defined, for example, as a predetermined distance (e.g., expressed as an absolute value, e.g., in bar, or as a relative value, e.g., as a percentage) below the pressure value to which a possibly present pressure limiting valve in the pressure line or another suitable location responds, i.e., the pressure value at which the pressure limiting valve begins to divert pressure medium toward the tank to avoid excessive pressure and possible associated damage. According to the proposed embodiment, this response of the pressure limiting valve and the resulting diversion of pressure medium by the pressure limiting valve, which leads to power losses, can be largely avoided. Furthermore, the pressure limiting valve can also be omitted.

[0015] According to one embodiment, for hydraulic machines that do not allow zero setting, if the setting value is below the minimum setting value for the respective hydraulic machine, the setting value for the respective hydraulic machine is adjusted by increasing it above or equal to the minimum setting value. According to this embodiment, a certain volume flow rate can be maintained even by a hydraulic machine with a zero setting value, for example to maintain standby pressure in the circuit supplied with pressure medium by the respective hydraulic machine. If the setting value is increased, it can be increased, for example, to the minimum setting value or to a value above the minimum setting value by a predetermined distance (for example, less than 5% or less than 10%).

[0016] The computing unit according to the invention, for example a control device for a mobile working machine, is particularly designed in terms of program technology to carry out the method according to the invention.

[0017] The hydraulic drive system according to the present invention comprises at least two hydraulic machines, which are commonly driven by an engine and pump a hydraulic medium to at least one consumer connected to each hydraulic machine, each hydraulic machine having an operable displacement and controllable by a manipulated variable, whereby the displacement of each hydraulic machine is adjusted or controlled to the respective manipulated variable, and the engine provides a drive quantity for driving the hydraulic machines. The hydraulic drive system further comprises a calculation unit according to the present invention.

[0018] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with program code for performing all method steps, since this entails particularly low costs, especially if the control device performing the implementation is already existing since it is also used for other tasks. 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. Downloading the program via a computer network (Internet, intranet, etc.) is also possible.

[0019] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0020] It is obvious that the features mentioned above and those to be further described below can be used not only in the respective presented combinations but also in other combinations or alone, without departing from the scope of the invention.

[0021] The invention is illustrated diagrammatically in the drawing by way of an embodiment and is explained in more detail below with reference to the drawing. [Brief explanation of the drawings]

[0022] [Figure 1] 1 shows the structure of an exemplary hydraulic drive system to which the control method according to the invention can be applied; [Figure 2] 1 is a flowchart according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Detailed Description of the Drawings 1 shows, in a highly simplified manner, the structure of an exemplary hydraulic drive system to which the control method according to the invention can be applied, such as is provided in a work machine, in particular a mobile work machine, for example an excavator.

[0024] The drive system includes two hydraulic pumps or machines, i.e., a first operable hydraulic machine 2a and a second operable hydraulic machine 2b, which are commonly driven by a single engine 4. For example, the engine 4 is connected to the first and second hydraulic machines via a shaft to drive them. Optionally, one or more transmissions, in particular variable speed transmissions, can be provided between the engine and / or one or both hydraulic machines, which allows different rotational speeds depending on the respective transmission ratios. The hydraulic machines 2a, 2b are each configured to pump a pressure medium (i.e., hydraulic fluid, in particular hydraulic oil) from, for example, a tank to respective hydraulic lines (first hydraulic line 6a, second hydraulic line 6b) connected to outlets or pressure outlets of the hydraulic machines. Both hydraulic machines 2a, 2b are operable, i.e. their displacement (i.e. the volume of pressure medium pumped per revolution, also called suction or pumping volume) can be varied or manipulated, for example as a function of the swivel angle. The hydraulic machines 2a, 2b may be axial piston mechanisms, in particular swash plate mechanisms. The engine 4 may be, for example, an internal combustion engine, in particular a diesel engine, or an electric motor or motor.

[0025] The displacements of the hydraulic machines 2a, 2b can be adjusted between a minimum displacement value and a maximum displacement value, respectively. If the hydraulic machines are not zero-settable, the minimum displacement value is in particular equal to zero. If the hydraulic machines are zero-settable, i.e., if for a given direction of rotation the hydraulic machine pumps pressure medium in different directions depending on whether the displacement is greater or less than zero, the minimum displacement value is less than zero and the maximum displacement value is greater than zero (if appropriately defined, for example, for a given direction of rotation the pressure medium is pumped from the tank to the pressure outlet if the displacement is greater than zero).

[0026] The hydraulic machines 2a, 2b are controlled using respective manipulated variables, and the displacement is adjusted and / or controlled depending on these manipulated variables. The manipulated variable is, for example, the value of the displacement to be adjusted or a setpoint value of the displacement. In particular, the hydraulic machines 2a, 2b are hydraulically operated with electromagnetic pilot control. That is, the displacement adjustment is performed hydraulically by at least one operating cylinder, the flow of pressure medium to which is controlled by an electrically or electromagnetically operable control valve. This displacement adjustment or control valve is controlled, for example, by an electrical signal, e.g., by a current with a predetermined current intensity (dependent on the manipulated variable) or, in the case of PWM control, by a current with a predetermined duty cycle, or by a control command (e.g., via a CAN interface). Correspondingly, an electrical signal or a control command is determined from the manipulated variable (setpoint value) for the displacement, for adjusting or controlling the hydraulic machine to the displacement corresponding to the manipulated variable within the framework of open-loop or closed-loop control. This open-loop or closed-loop control may be performed by the electronic control unit of the hydraulic drive system or by individual control units of each hydraulic machine, in which case only the operating values ​​(e.g., the target displacement value) are transmitted from the electronic control unit of the hydraulic drive system to the control units of each hydraulic machine.

[0027] For example, in particular for controlling the displacement, displacement sensors (or swivel angle sensors) are provided, where a first displacement sensor 10a measures or determines the displacement (or swivel angle) of the first hydraulic machine 2a and a second displacement sensor 10b measures or determines the displacement (or swivel angle) of the second hydraulic machine 2b.

[0028] Further, pressure sensors may be provided, the first pressure sensor 8a measuring the pressure (outlet pressure) of the pressure medium at the pressure outlet of the first hydraulic machine 2a (or in the first hydraulic line 6a), and the second pressure sensor 8b measuring the pressure (outlet pressure) of the pressure medium at the pressure outlet of the second hydraulic machine 2b (or in the second hydraulic line 6b).

[0029] The pressure outlet of the first hydraulic machine 2a is connected (by a first hydraulic line 6a) to a first valve device 12a, which controls the flow of pressure medium to and from one or more (first) hydraulic consumers 14a. Here, a hydraulic cylinder is shown, for example, as the first hydraulic consumer 14a. The pressure outlet of the second hydraulic machine 2b is connected (by a second hydraulic line 6b) to a second valve device 12b, which controls the flow of pressure medium to and from one or more (second) hydraulic consumers 14b. Here, a hydraulic motor is shown, for example, as the second hydraulic consumer 14b. If a hydraulic drive system is provided on the excavator, for example, the hydraulic cylinder can cause a pivoting movement of the excavator arm, and the hydraulic motor can cause a rotational movement of the superstructure relative to the chassis. Alternatively or additionally to the illustrated hydraulic consumers, each of the valve devices 12a, 12b can be connected to another or another hydraulic consumer, thereby controlling the inflow and outflow of pressure medium to / from the other or another hydraulic consumer. That is, typically, each valve device 12a, 12b is connected to at least one first hydraulic consumer 14a or one second hydraulic consumer 14b (e.g., at least one hydraulic cylinder and / or hydraulic motor), thereby controlling the inflow and outflow of pressure medium to / from the at least one first hydraulic consumer 14a or one second hydraulic consumer 14b. The valve devices include, for example, one or more valves, in particular control valves or directional control valves, each of which is at least partially controllable to control the inflow and outflow of pressure medium. The desired movement of the hydraulic consumer and the current load of the hydraulic consumer result in a demand for the outlet pressure and / or volumetric flow rate (also referred to as the pumping volume) of the corresponding hydraulic machine. For example, a desired speed of movement of a hydraulic cylinder or a desired number of revolutions of a hydraulic motor results in a predetermined volumetric flow rate of pressure medium.

[0030] An electronic control unit 16 (computing unit) may be provided, which is configured to control the hydraulic machines 2a, 2b, i.e., to control their displacements (or swivel angles) in an open-loop or closed-loop manner. For this purpose, the control unit 16 may detect sensor data from the first and second pressure sensors 8a, 8b and / or the first and second displacement sensors 10a, 10b. Furthermore, the control unit 16 may be configured to control the engine 4 (e.g., to control the engine 4 using a target speed) and / or to detect the engine speed. From the engine speed, the speeds of the hydraulic machines 2a, 2b can be determined (the speeds of the hydraulic machines 2a, 2b are equal to the engine speed or, independently of each other, are equal to the engine speed multiplied by the respective transmission ratios). Alternatively or additionally, the hydraulic machines may be provided with speed sensors. The control device 16 may be configured to control the valve devices and thus the hydraulic consumers, for example, on the basis of control signals detected by a control device 18 (e.g., a joystick) and transmitted to the control device. Respective control and / or signal lines (for transmitting control signals or measurement data) are exemplarily shown with dashed lines in the drawings. The electronic control device 16 is particularly configured to implement the method according to the invention for controlling a hydraulic drive system.

[0031] The control signals detected by the control device 18 and transmitted to the electronic control device 16 can be regarded as a setpoint (or target setting) for the pumping rate of each of the hydraulic machines 2 a, 2 b, either by itself or in a further processed (e.g. filtered) form, which setpoint (or target setting) is in particular the volumetric flow rate of the pressure medium to be pumped by the respective hydraulic machine and / or, for example, the outlet pressure required to enable the corresponding movement of one or more consumers supplied with pressure medium by the hydraulic machine. Generally speaking, the setpoint for the pumping rate can be derived from the control signals. Alternatively or additionally, it is also possible, at least in part, to automatically set the setpoint for the pumping rate by an automatic control function for the consumer or the like. The pumping rate can be regarded as a quantity that depends on the displacement of the respective hydraulic machine and thus on the corresponding operating value, or as a function thereof.

[0032] The engine 4 provides a so-called drive quantity, in particular torque (e.g. measured in Nm) and / or power (e.g. measured in kW). The upper limit of the drive quantity that can be provided by the engine 4 is limited by a drive quantity maximum value (e.g. maximum torque or maximum power), which is typically rotational speed dependent. The provided drive quantity is converted (in distributed form) by a hydraulic machine into a hydraulic power or quantity, e.g. pressure and / or volumetric flow rate.

[0033] Each of the hydraulic machines 2a, 2b receives a certain proportion of the drive force, referred to as the drive force demand. The proportion of the drive force received is substantially (i.e., ignoring, in particular, leakage and friction) determined by the pumping pressure (i.e., the pressure difference between the outlet pressure and the pressure at the tank connection), the displacement, and, if power is used as the drive force, the rotational speed. That is, for a given outlet pressure of the hydraulic machine (determined, for example, by the respective load pressure and measurable, for example, by the pressure sensors 8a, 8b) and a given rotational speed (which is controlled to a predetermined value, for example, in an internal combustion engine) when power is used as the drive force, the proportion of the drive force received is substantially determined by the manipulated variable. That is, the drive force demand of the hydraulic machine is determined by the manipulated variable used for control, i.e., the drive force demand corresponds to the respective manipulated variable.

[0034] Generally, hydraulic drive systems have limitations that make it impossible to simultaneously achieve all setpoints. The maximum drive value mentioned above is one such limitation. In order to prevent unexpected behavior of the hydraulic consumer, the invention provides for determining the operating value such that, on the one hand, the ratio between the setpoints (which can be considered as the operator's expectations for the consumer's behavior) is respected, and, on the other hand, at least one condition is respected. A corresponding method is shown in FIG. 2.

[0035] 1 shows two hydraulic machines 2a, 2b by way of example, which are commonly driven by an engine 4. In general, there can be three or more hydraulic machines commonly driven by one engine, each of which supplies pressure medium to a corresponding hydraulic consumer (in particular via a valve arrangement).

[0036] FIG. 2 shows a flow chart of a method for controlling a hydraulic drive system according to an embodiment of the present invention. The method relates to a hydraulic drive system having at least two hydraulic machines, which are commonly driven by an engine and pump a hydraulic medium to at least one consumer connected to each hydraulic machine. Each of the hydraulic machines has an operable displacement and is controllable using a manipulated variable, whereby the displacement of each hydraulic machine is adjusted or controlled to the respective manipulated variable. The engine provides a drive force for driving the hydraulic machines. Such a hydraulic drive system is shown in FIG. 1, to which reference is made for the definition of terms used below and for the features of the hydraulic drive system.

[0037] In step 110, for each hydraulic machine, a setpoint for the pumping rate of the hydraulic machine is detected or determined. The pumping rate is a function of the displacement, for example the pumped volume flow rate or the displacement. The setpoint is detected in particular by means of a control device (or a user interface) or determined from a control signal transmitted from the control device. Processing of the original control signal or further processing, for example filtering, can be performed. Adjustment of the setpoint can also be performed.

[0038] In step 120, for each hydraulic machine, a manipulated variable for the hydraulic machine's displacement is determined. This determination is performed so that the ratios of the manipulated variables are equal to the corresponding ratios of the setpoints and so that at least one condition is met. The at least one condition includes that the sum of the hydraulic machine's drive demands corresponding to the manipulated variables is less than or equal to a drive maximum value. The at least one condition may include further conditions, such as not exceeding the hydraulic machine's maximum displacement value.

[0039] According to this process, even if the setpoint cannot be achieved due to compliance with at least one condition, the ratio of the manipulated variables will still be equal to the corresponding ratio of the setpoints. It should be noted that both the value of the pumping volume and the value of the drive demand correspond to the respective manipulated variable (relative to the displacement). If torque is used as the drive quantity, the drive demand is determined by the manipulated variable, i.e., the displacement, and the outlet pressure, which is detected, for example, by a pressure sensor. More precisely, the pressure difference across the hydraulic machine, i.e., the pressure difference between the outlet pressure and the suction (tank) pressure, is important. In this case, the latter pressure typically has a known value, which is relatively low, e.g., a few bar, while the outlet pressure exceeds 100 bar. If power is used as the drive quantity, the drive demand is additionally determined by the rotational speed.

[0040] In step 130, the operating values ​​determined in step 120 are used to control the hydraulic machine.

[0041] The method sequence is in particular repeated continuously, so that changes (eg setpoint, load pressure, etc.) that may be the result of control using manipulated variables are also taken into account continuously.

Claims

1. 1. A method for controlling a hydraulic drive system comprising at least two hydraulic machines (2a, 2b), comprising: the at least two hydraulic machines (2a, 2b) are commonly driven by one engine (4) and pump a pressure medium to at least one consumer (14a, 14b) connected to each of the hydraulic machines; each of the at least two hydraulic machines (2a, 2b) has an operable displacement and is controllable using an operating value, whereby the displacement of each of the hydraulic machines is adjusted or controlled to the respective operating value; the engine (4) provides a driving force for driving the at least two hydraulic machines (2a, 2b); The method comprises: - detecting (110) for each of the at least two hydraulic machines (2a, 2b) a set value for a pumping rate of the at least two hydraulic machines, the pumping rate being a function of the displacement (110); determining (120) manipulated values ​​for the displacements of the at least two hydraulic machines (2a, 2b), the determining being performed so that a ratio between the manipulated values ​​is equal to a corresponding ratio between the setpoints and at least one condition is satisfied, the at least one condition including that a sum of drive demands corresponding to the manipulated values ​​of the hydraulic machines (2a, 2b) is less than or equal to a drive maximum value; controlling (130) the at least two hydraulic machines (2a, 2b) using the determined operating values; A method comprising:

2. the operating value is determined in such a way that the deviation between the setpoint and the value of the pumping rate obtained from the operating value, in particular when the rotational speed is known, is below a threshold value or is equal to zero; The method of claim 1.

3. The at least one condition is: the operating value of each of the at least two hydraulic machines (2a, 2b) being equal to or less than a maximum displacement value of the respective hydraulic machine, or When the displacement can be set to zero, the operation value of each of the at least two hydraulic machines (2a, 2b) is equal to or less than a maximum displacement value of the respective hydraulic machine and equal to or greater than a minimum displacement value of the respective hydraulic machine.

3. The method according to claim 1 or 2.

4. the pumping rate for each of the at least two hydraulic machines (2a, 2b) is the volume flow rate pumped by the respective hydraulic machine or the displacement or swivel angle of the respective hydraulic machine; 4. The method according to any one of claims 1 to 3.

5. The driving force is a power output provided by the engine (4) or a torque provided by the engine (4).

5. The method according to any one of claims 1 to 4.

6. for each of the at least two hydraulic machines (2a, 2b), a pressure measurement value is detected at a pressure outlet of the respective hydraulic machine or at a pressure line (6a, 6b) connected to the pressure outlet; a drive request is determined for each of the at least two hydraulic machines (2a, 2b) from the pressure measurements detected for the respective hydraulic machine and from the operating value; 6. The method according to any one of claims 1 to 5.

7. The method comprises: further comprising adjusting at least one of the set points after detecting the set points and before determining the operating value; determining the operating value is performed using at least one reduced set point; 7. The method according to any one of claims 1 to 6.

8. for each of the at least two hydraulic machines (2a, 2b), a pressure measurement value is detected at a pressure outlet of the respective hydraulic machine or at a pressure line (6a, 6b) connected to the pressure outlet; If the pressure measurement value of the hydraulic machine exceeds a threshold value corresponding to the hydraulic machine, the setpoint value for each hydraulic machine is adjusted by being reduced in absolute value. The method of claim 7.

9. For hydraulic machines (2a, 2b) that are not zero-settable, if the set value is below a minimum set value for the respective hydraulic machine, the set value for the respective hydraulic machine is adjusted by increasing it above or equal to the minimum set value.

9. The method according to claim 7 or 8.

10. A computing unit (16) comprising a processor configured to perform the method according to any one of claims 1 to 9.

11. A hydraulic drive system, comprising: The hydraulic drive system comprises at least two hydraulic machines (2a, 2b), the at least two hydraulic machines (2a, 2b) are commonly driven by one engine (4) and pump a pressure medium to at least one consumer (14a, 14b) connected to each of the hydraulic machines; each of the at least two hydraulic machines (2a, 2b) has an operable displacement and is controllable using an operating value, whereby the displacement of each of the hydraulic machines is adjusted or controlled to the respective operating value; the engine (4) provides a driving force for driving the at least two hydraulic machines; The hydraulic drive system further comprises a calculation unit (16) according to claim 10. Hydraulic drive system.

12. A computer program comprising instructions for causing a computer to carry out the method of any one of claims 1 to 9 when the program is executed by the computer.

13. 13. A computer readable data carrier on which a computer program according to claim 12 is stored.

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