Method for a hydraulic drive, control unit, computer program, and machine-readable storage medium

Description

Technical area

[0001] The present invention relates to a method for a hydraulic drive, a control unit, a computer program and a computer-readable storage medium. State of the art

[0002] Common flow-controlled hydraulic drives are typically implemented with hydrostatic pumps with hydraulic-mechanical control of a variable that determines the displacement. The latter depends on the design. In the case of an axial piston machine with a swashplate design, for example, it is the swivel angle of the swashplate. This conventional control of the swivel angle, based on angle detection by a sensor, offers the advantage of high displacement and thus quantity accuracy compared to a pressure-controlled pump. However, this eliminates a simple pressure control option, meaning that flow control or swivel angle control combined with pressure control in conventional hydraulic-mechanical swivel angle-controlled pumps can only be achieved through a complex expansion of the control system.

[0003] For example, hydraulic drives are known from DE 10 2015 207 258 A1, DE 10 2013 213 896 A1 and DE 10 2013 217 708 A1 in which a target pressure is determined to control a torque and the drive is controlled according to the pressure.

[0004] DE 10 2019 210 003 A1 discloses a method for converting a specified swivel angle into a pressure, more precisely, into a desired pressure trajectory, and controlling a hydraulic machine based on the pressure. All of these disclosures have in common that control is not based on a specified volume flow, but rather solely on the desired swivel angle or pressure as the controlled variable.

[0005] The disclosed hydraulic machines are pressure-controlled, but cannot deliver a constant flow rate. Specifying the differential pressure or the fixed swivel angle results in the output flow rate of the hydraulic pump changing under the influence of external forces / loads or environmental conditions (e.g., temperature). The described change in the output flow rate may not be desirable in all situations, for example, when a constant flow rate is to be provided to a consumer. Ein Similar prior art is disclosed in DE102012020632. This discloses a volume flow control, but not a pressure control.

[0006] The present invention is therefore based on the object of creating a method with a hydraulic drive having a hydraulic machine configured with an adjustable displacement volume and electronically controllable in accordance with a consumer load, with which the hydraulic machine can be controlled both according to a requested volume flow and according to another operating variable of the hydraulic machine. Further objects are to create a control unit configured to carry out this method, to create a computer program that causes a processor with hardware to execute steps of the method, and finally to create a machine-readable storage medium with the computer program stored thereon.

[0007] The first object is achieved by a method having the features of claim 1.

[0008] The further objects are achieved by claim 10, claim 12 and claim 13. Advantageous developments of the respective invention are the subject of the respective dependent claims.

[0009] The present invention relates to a method provided with a hydraulic drive. This has at least one hydraulic machine with an adjustable displacement volume, which is intended to supply pressure medium to at least one hydraulic consumer. Oriented to the consumer's load—in particular, the load pressure—the hydraulic machine is electronically controllable. A control circuit or controller of the hydraulic machine is thus not "classically" hydraulically mechanically designed, but is based solely on electronic signal processing within the control loop. The applicant classifies such hydraulic machines as "electronified" and can be connected to the at least one consumer in an open or closed circuit. The method comprises the following steps: Detecting an actual speed and a target volume flow of the hydraulic machine; and calculating a target displacement volume of the hydraulic machine or a mechanical target equivalent thereof, in particular a swivel angle, depending on the actual speed and the target volume flow.

[0010] Depending on the target displacement volume or mechanical target equivalent, as well as depending on at least one parameter of the drive or depending on at least one measured variable of the drive, one of the following steps is carried out: Regulating the displacement volume according to the target displacement volume or mechanical target equivalent and limiting an operating variable of the hydraulic machine depending on the at least one parameter or; controlling the displacement volume according to the target displacement volume or mechanical target equivalent and regulating an operating variable of the hydraulic machine depending on the at least one measured variable.

[0011] The at least one parameter is, for example, a limiting parameter that defines a maximum pressure or differential pressure, a maximum torque or maximum power of the hydraulic pump, or the like. According to the invention, the at least one measured variable of the drive is the pressure or differential pressure of the hydraulic pump.

[0012] In the method, the target volume flow is thus specified, which is converted into the target displacement volume or its target equivalent using the current speed. One or more characteristic parameters of the drive are adopted and one or more measured variables are recorded. According to the invention, the control of the hydraulic machine has two alternative modes. In the first, the displacement volume or equivalent is controlled as a function of the target displacement volume or target equivalent, and the operating variable of the hydraulic machine is limited as a function of the at least one parameter, in particular to protect the drive from overload. In the other mode, the displacement volume or equivalent is controlled according to the target displacement volume or target equivalent, and the operating variable of the hydraulic machine is controlled as a function of the at least one measured variable.

[0013] One control variable of a hydraulic machine is its adjustable displacement. The corresponding actuator is, for example, a swash plate or inclined axis of the hydraulic machine with an adjustable swivel angle, where the swivel angle is the mechanical equivalent of the displacement. Since it is not possible to control two operating variables—the displacement and the other operating variable—with just one actuator, the operating variable is limited when the displacement is controlled. Conversely, the displacement is controlled when the operating variable is controlled.

[0014] In a further development of the method, the target displacement volume or target equivalent is converted into a target control current for controlling the hydraulic machine as a function of the at least one measured variable.

[0015] In the second mode mentioned above, the displacement volume and thus the volume flow are controlled with a subordinate control based on the operating variable. This allows control based on the operating variable to be implemented at a constant volume flow.

[0016] At least one of the drive's parameters is, for example, a key figure that specifies a limit on the operating size. If the parameter is exceeded or undershot, the control of the displacement volume is overridden or overridden.

[0017] The measured variable can be recorded using a suitable sensor unit, or it can be transmitted from a secondary, subordinate, or higher-level control unit. In the case of the actual speed, this can be done, for example, by a control unit of a prime mover that drives the hydraulic machine.

[0018] Alternatively, a value of the hydraulic machine underlying the displacement volume, i.e., the mechanical equivalent of the displacement volume, can be used for the displacement volume. This value depends particularly on the design of the hydraulic machine. In the case of an axial piston machine with an adjustable swash plate or axis, this is, for example, a swivel angle of the swash plate or axis. In the following, the displacement volume can be replaced by the swivel angle, and vice versa.

[0019] According to a further feature of the invention, the target displacement volume is converted into the operating variable of the hydraulic machine, and the operating variable is limited when the displacement volume is controlled. The operating variable is controlled when the displacement volume is controlled.

[0020] The desired displacement volume is converted into a setpoint value for the operating variable. If the operating variable is controlled, the setpoint value is the reference variable of the control system. The at least one measured variable is the feedback, and the actuating current of the hydraulic machine is the controlled variable of the control system. Thus, the control system converts the setpoint value of the operating variable into the actuating current based on the at least one measured variable.

[0021] Converting the displacement volume into the operating variable, especially the pressure, has the advantage that no sensor is required to measure the displacement volume. The only sensor required is to record at least one measured variable. By eliminating the displacement volume sensor, costs can be saved.

[0022] According to a further feature of the invention, the operating variable is a pressure provided by the hydraulic machine and the control is a pressure control which regulates the pressure of the hydraulic machine as a function of a target pressure and the measured variable.

[0023] The target displacement volume is converted into the target pressure. The target pressure then serves as the reference variable for the pressure control. In this case, at least one measured variable is, for example, the actual pressure of the hydraulic machine. The pressure control thus converts a target pressure, dependent on the actual pressure, into the control current as feedback. Thus, a subordinate pressure control for the hydraulic machine is implemented.

[0024] For example, the target displacement volume is converted into a target pressure trajectory, which maps a temporal relationship between the displacement volume and the pressure. Time derivatives of the target trajectory can also be determined to refine the control.

[0025] The hydraulic machine can be operated with pressure control, while a constant flow rate is provided by the displacement volume control. Thus, volume control or angle control is realized with a pressure-controlled hydraulic machine. A pressure sensor is installed as standard in common hydraulic drives. Using the actual pressure as the measured variable eliminates additional costs for the hydraulic drive's sensor technology. Furthermore, pressure limits can be easily maintained by converting the displacement volume into pressure.

[0026] The operating variable of a hydraulic machine does not necessarily have to be pressure. Rather, it can also be torque, power, or current.

[0027] According to a further feature of the invention, the calculation of the target displacement volume based on the target flow rate and the actual speed comprises the following steps: First, calculating a theoretical flow rate from the target flow rate, the actual speed, and a maximum pump displacement, and calculating a displacement volume using the calculated flow rate, the current pump speed, and the maximum pump displacement.

[0028] The target flow rate, which results, for example, from a movement request to at least one hydraulic consumer, must be provided by the hydraulic pump. However, the flow rate is not regulated or controlled directly, but rather as a function of the calculated target displacement. This conversion converts the target flow rate into a variable that can be easily controlled or regulated, since the corresponding control variable is available via the swivel angle of the hydraulic machine.

[0029] According to a further feature of the invention, a total deviation from the theoretical flow rate is calculated. This total deviation results from one or more factors that affect the flow rate. Major influences include, in particular, pressure, speed, and / or swivel angle.

[0030] In a preferred further development, the total deviation is therefore determined as the sum of a high-pressure-dependent volume flow deviation, a speed-dependent volume flow deviation and a swivel angle-dependent volume flow deviation.

[0031] According to a further feature of the invention, a modified target volume flow is calculated from the theoretical volume flow and the total deviation, and the modified target volume flow is converted into the modified displacement volume.

[0032] By calculating the total deviation from the theoretical volume flow, a modified volume flow can be calculated. The modified volume flow is the sum of the theoretical volume flow and the total deviation. By converting the modified volume flow into the modified displacement volume, the displacement volume can be determined more accurately than is possible by converting the theoretical volume flow into the displacement volume. By calculating the displacement volume as accurately as possible depending on the disruptive influences, the displacement volume can be controlled as precisely as possible. The calculated displacement volume is the input variable for the closed-loop or open-loop control depending on the displacement volume. Deviations between the calculated displacement volume and the actual displacement volume therefore result in less precise control of the hydraulic machine.

[0033] According to a further feature of the invention, the calculated target displacement volume is corrected using a detected measured variable. If high accuracy is required, the previously calculated target displacement volume is corrected by a displacement volume control. For this purpose, a measured variable is detected. Based on this detected measured variable, the displacement volume is corrected or controlled. The measured variable can be, for example, the swivel angle of the hydraulic machine. If the swivel angle is detected and fed back to the displacement volume control as the measured variable, the correction of the displacement volume is a swivel angle control.

[0034] Displacement volume control has a cost disadvantage compared to a hydraulic drive without it, as a sensor is required to record the measured variable, in this case, for example, the swivel angle. However, displacement volume control enables more precise control of the hydraulic machine. Displacement volume control compensates for disturbances such as load jumps and / or (model) inaccuracies better than without it. This enables more precise delivery of the desired flow rate.

[0035] The displacement volume control also allows additional functions to be implemented in the hydraulic drive.

[0036] According to a further feature of the invention, an inner control loop regulates the hydraulic machine depending on its operating size, and an outer control loop regulates the displacement volume. The two control loops form a cascade control system.

[0037] The outer control loop controls the displacement volume. The controlled or corrected displacement volume is the input variable for controlling the operating variable. This is preferably the pressure control. The pressure control converts the corrected displacement volume into the target pressure and controls the pressure depending on the target pressure and the at least one measured variable. The at least one measured variable is preferably the actual pressure.

[0038] The cascaded control allows specifications and restrictions for the volume flow, the swivel angle and the pressure to be met simultaneously.

[0039] According to a further feature of the invention, switching occurs between an operating mode with pressure control and another operating mode with displacement control. In some applications, it is desirable to be able to switch between the operating mode with pressure control and the further operating mode with displacement control. The displacement control makes it possible to control according to pressure in one operating mode and according to the displacement or swivel angle of the hydraulic machine in the other operating mode.

[0040] According to a further feature of the invention, the displacement volume control compensates for hysteresis effects of the hydraulic machine. The displacement volume control continuously corrects the target displacement volume, which is input to the hydraulic machine's control system. This compensates for the hydraulic machine's hysteresis effects.

[0041] According to a further feature of the invention, the displacement volume control is overridden in the event of a limitation of the operating variable. In the event of a limitation of the operating variable, for example, in the event of pressure cutoff, the displacement volume control is overridden to prevent the displacement volume control from being wound up.

[0042] According to a further feature of the invention, the swivel angle of the hydraulic machine is limited based on further specifications, in particular further parameters. The method can thus, for example, implement a swivel angle limitation based on these specifications (e.g., an HMI input / setting and / or a function for implementing an operating strategy).

[0043] The object of the invention is further achieved by a control unit which carries out a method according to the invention which is designed according to at least one aspect of the preceding description.

[0044] The control unit preferably has three sections: As a first section, a calculation unit for calculating the desired displacement volume from the desired volume flow, in particular taking into account at least one of the influences.

[0045] The second section is a displacement controller, particularly a swivel angle controller, which calculates the deviation between the displacement calculated by the calculation unit and the measured displacement. However, the displacement controller is optional. The third section is a pump controller, alternatively referred to as a pump driver, which converts the target displacement calculated / specified by the calculation unit and, if applicable, the displacement controller into a control current for the hydraulic machine.

[0046] The calculation unit converts the specified target flow rate into the target displacement volume, taking into account at least one influence. The (optional) displacement volume controller corrects the calculated displacement volume by comparing the calculated target displacement volume with the measured variable, preferably the detected swivel angle, and correcting any control deviation. The pump controller converts the target displacement volume calculated by the calculation unit, or possibly corrected by the displacement volume controller, into the control current for controlling the hydraulic machine.

[0047] The calculation unit is positioned upstream of the optional displacement volume controller, enabling control that delivers the requested flow rate (as accurately as possible). When calculating the displacement volume from the flow rate specification, disturbances such as leakage can be taken into account, and the target displacement volume can be corrected accordingly. The amount of the flow rate deviation to be compensated can be calculated, for example, based on the current pump speed, pump angle, and system pressure.

[0048] The present invention is implemented, for example, by external control hardware, such as a control unit or an ECU, and an electrically connected control device for the hydraulic machine. The control device is preferably an electrically directly controlled pressure control valve, in particular a pressure reducing valve, via which, for example, a piston chamber of an actuating cylinder can be pressurized with actuating pressure medium, to which the aforementioned swash plate is hinged.

[0049] The object of the invention is further achieved by a computer program which is capable of carrying out a method according to at least one aspect of the preceding description.

[0050] The object of the invention is finally achieved by a machine-readable storage medium on which the computer program is stored.

[0051] In the following, an embodiment of a method according to the invention and a control unit according to the invention are explained in more detail with reference to the following figures. They show: Figur 1 a schematic representation of an electronic control unit according to the invention for a hydraulic drive, in particular for its hydraulic machine; and Fig. 2 a schematic representation of a calculation unit of the electronic control unit according to Figur 1 .

[0052] Fig. 1 shows a schematic representation of an electronic control unit 1 according to the invention for a hydraulic drive, in particular for a hydraulic machine 2 of the drive. The displacement volume Vg of the hydraulic machine 2 can be adjusted by means of electrical control. In the exemplary embodiment shown, it is designed as an axial piston machine in swash plate design with a pivoting swash plate. The displacement volume is adjusted by adjusting its mechanical equivalent, the pivot angle alpha of the swash plate. The description below therefore refers to the pivot angle alpha. In the exemplary embodiment, the swash plate is articulated by an adjusting cylinder (not shown) which can be pressurized with pressure medium via a directly electrically controllable pressure reducing valve, which, depending on the application, effects adjustment, a constant pivot angle, or resetting.The actuating or control current i_des is determined by the control unit 1 as a function of a target volume flow Q_desln. The target volume flow Q_desln is the volume flow that the hydraulic machine 2 must provide to the at least one hydraulic consumer of the drive, which it supplies with pressure medium, so that a movement request directed to the consumer can be fulfilled.

[0053] According to Figur 1 The control unit 1 has three sections. A first section is a calculation unit 4, a second section is an (optional) displacement volume controller 6, and a third section is a pump controller 8. The calculation unit 4 calculates a target displacement volume from the detected, determined, or otherwise specified target volume flow Q_desln. Knowing the kinematics of the swash plate of the hydraulic machine 2, it calculates the mechanical equivalent of the target displacement volume, the aforementioned target swivel angle alpha_des. An actual speed n_pmp and an actual pressure p_pmp of the hydraulic machine 2 are transmitted to the calculation unit 4 from corresponding sensors 10. The calculation unit 4 transfers the calculated target swivel angle alpha_des to the optional displacement volume controller 6.

[0054] The displacement volume controller 6 corrects the target swivel angle alpha_des to the corrected target swivel angle alpha_descorr. For this purpose, a measured variable detected by sensor 10 is input to the displacement volume controller 6. In the exemplary embodiment, this measured variable is the current swivel angle alpha_pmp of the hydraulic machine 2. To correct the target swivel angle alpha_des, the displacement volume controller 6 thus regulates the deviation between the calculated target swivel angle alpha_des and the detected, current swivel angle alpha_pmp. The target swivel angle alpha_des is a reference variable of the displacement volume control, and the detected swivel angle alpha_pmp is the feedback variable of this control. The displacement volume controller 6 subsequently transfers the corrected target swivel angle alpha_descorr as an input variable to the pump controller 8.

[0055] Without the previously described displacement volume controller 6, which, as mentioned, is optional, the displacement volume / swivel angle alpha is merely controlled. The reason for using the displacement volume controller 6 is that, in some applications, controlling the swivel angle alone is not sufficiently precise. The target swivel angle alpha_des input to the displacement volume controller 6 can either be determined from control signals or calculated in the calculation unit 4. The signal of the incoming target swivel angle alpha_des can be filtered first, if necessary. Deviations from the detected swivel angle alpha_pmp are corrected by the displacement volume controller 6, which is preferably designed as a PID controller.

[0056] An included anti-windup function prevents the displacement volume controller 6 from winding up and thus impairing the pump control by the displacement volume controller 6 and can contain various scenarios for automatic activation. For example, activation is possible in the event of a pressure cut-off. In this case, the start of the pressure cut-off, i.e. when a swiveling back of the hydraulic machine 2 is controlled because, for example, a parameter limit of the hydraulic machine 2 has been reached, and the exit from the pressure cut-off (re-swivelling of the hydraulic machine 2 to the target swivel angle) can each be detected, and a respective permissible deviation from the target swivel angle can be parameterized for both cases. The (de)activation of the anti-windup can be set separately via the permissible deviations and the detection of the swiveling back and out of the hydraulic machine 2.

[0057] The anti-windup function can also be activated by a significant deviation between the target swivel angle alpha_des and the measured swivel angle alpha_pmp. The magnitude of the deviation can be adjusted using a parameter.

[0058] The thus corrected target swivel angle alpha_descorr is an input variable of the pump controller 8. The latter's task is to convert the corrected target swivel angle alpha_descorr (or, in the case without a displacement volume controller 6, the target swivel angle alpha_des) into a target current i_des for controlling the hydraulic machine 2. For this purpose, the pump controller 8 converts the corrected target swivel angle alpha_descorr into a corresponding operating variable that is easily detectable. The pressure p of the hydraulic machine 2 is suitable for this purpose, as it changes sufficiently proportionally to the change in the swivel angle. The current pressure p is recorded as a measured variable p_pmp via the sensor unit 10 and fed back to the pump controller 8 to regulate the pressure p, provided the displacement volume / swivel angle alpha is controlled.

[0059] However, if the swivel angle alpha is controlled, the operating variable - the pressure p - is not continuously controlled, but only limited or "cut off" when necessary.

[0060] The pump controller 8 converts the target pressure, calculated internally from the corrected target swivel angle alpha_descorr, into the target current i_des, which is used to control the pressure reducing valve of the hydraulic machine 2 described above. The resulting application of pressure medium to the adjusting cylinder leads to the adjustment of the swash plate, as a result of the swivel angle alpha and thus the displacement volume.

[0061] Fig. 2 shows a schematic representation of the calculation unit 4. The calculation unit 4 calculates the target displacement volume from the target volume flow Q_desIn. For this purpose, the calculation unit 4 has a number of inputs. The target volume flow O_desIn results, as mentioned above, from the volume flow requirement of the hydraulic consumer(s) to be supplied with pressure medium. The pump speed n_pmp and the pressure p_pmp are detected by the sensors 10. From the target volume flow Q_desIn and the pump speed n_pmp, a theoretical target volume flow Q_desTheo is calculated (formula (1)). Using the pressure difference Δp across the hydraulic machine 2 - the so-called system pressure - a high-pressure-dependent volume flow deviation ΔQ_Δp is calculated (formula (2)). A speed-dependent volume flow deviation ΔQ_n is calculated using the pump speed n_pmp (formula (3)). Further volume flow deviations are calculated (4).The calculation of further flow rate deviations can be carried out using characteristic curves or measurements or based on empirical values. An example of one of the further flow rate deviations could be a swivel angle-dependent flow rate change (formula (4)).

[0062] The total deviation ΔQ is calculated as the sum of the product formed by the speed-dependent volume flow deviation ΔQ_n and the swivel angle-dependent volume flow deviation ΔQ_alpha, and the high-pressure-dependent volume flow deviation ΔQ_Δp. The corrected target volume flow Q_desOut is calculated from the sum of the theoretical target volume flow Q_desTheo and the total deviations ΔQ. This Q_desOut is converted by the calculation unit 4 into the target displacement volume or the target swivel angle alpha_des (formula (7)). This is output by the calculation unit 4 to the displacement volume controller 6 or, if this is not provided, to the pump controller 8, and acts as an input variable for both.

[0063] The conversion of the target volume flow Q_desln into the mechanical equivalent of the target displacement volume, the target swivel angle alpha_des, is described in detail below.

[0064] The specified target flow rate is converted into the target displacement volume, taking into account any unavoidable flow rate deviation that may be caused by external influences or varying operating points. For this purpose, the current pump speed and system pressure are recorded by sensors.

[0065] To calculate the target displacement volume from the target volume flow, a theoretical volume flow must first be calculated from the target volume flow specification Q_desIn without taking possible deviations into account. The calculation of the theoretical volume flow Q_desTheo can be calculated using the current pump speed n_pmp and a maximum pump delivery volume Vg_pmpMax be implemented as follows: Q _ desTheo = Q _ desIn * n _ pmp * Vg _ pmpMax

[0066] The extent of the volume flow deviations depends on various factors, including the following: Change in system pressure Change in pump speed Change in pump swivel angle Change in flow rate requirement of consumers downstream of the hydraulic pump Change in temperature Change in air pressure

[0067] To achieve the desired flow rate that deviates from the theoretical flow rate, the influences listed above must be taken into account and corrected. Depending on the required control accuracy, computational effort, and data availability, various mathematical or data-based approaches for compensation can be selected. For some influencing factors, for example, the following approaches can be used: A high-pressure-dependent flow rate deviation dQ_Δp is calculated using a specific pressure compensation factor Fac_Δp, the current system differential pressure Δp and a specific offset for pressure compensation Off_Δp calculated: ΔQ _ Δp = Fac _ Δp * Δp + Off _ Δp

[0068] This influence provides the core of the volume flow compensation, with further compensation options described below.

[0069] A speed-dependent volume flow deviation ΔQ_n is calculated using a specific factor for speed compensation Fac_n, the current pump speed n_pmp and a specific offset for speed compensation Off_n calculated: ΔQ _ n = Fac _ n * n _ pmp + Off _ n

[0070] A swivel angle-dependent volume flow deviation ΔQ_alpha is calculated using the theoretical volume flow Q_desTheo (1) and a specific factor for swivel angle compensation Fac_alpha calculated: ΔQ _ alpha = arctan Q _ desTheo * Fac _ alpha / π / 2

[0071] This function enables a smooth transition from a compensation of 0 l / min at a swivel angle of 0° to a compensation curve that does not pass through the zero point. About the swivel angle compensation factor Fac_alpha the transition time of the compensation from 0 l / min to the characteristic curve can be shortened or extended.

[0072] From the individual volume flow deviations (2), (3) and (4) a total deviation ΔQ can be calculated as follows: ΔQ = ΔQ _ Δp + ΔQ _ n * ΔQ _ alpha

[0073] From the total deviation (5) and the theoretical volume flow (1) a modified target volume flow Q_desOut be calculated, the portion of which emanating from the hydraulic pump then corresponds to the required target volume flow: Q _ desOut = Q _ desTheo + ΔQ

[0074] The modified target volume flow Q_desOut can be determined using the current pump speed n_pmp and a maximum pump delivery volume Vg_pmpMax into a modified pump target swivel angle alpha_des be converted: alpha _ des = Q _ desOut / n _ pmp * Vg _ pmpMax

[0075] The factors and offsets described above for the mathematical description of the respective deviations can be determined by various methods, such as a measurement on a test vehicle, a measurement on the test bench or an estimation based on empirical values.

[0076] The accuracy of the compensation for the flow rate deviating from the target flow rate can be further increased by using nonlinear models for pressure-, speed-, or swivel angle-dependent compensation. Furthermore, the accuracy of the system behavior with respect to the setpoint specification can be further improved by taking into account the leakage of the hydraulic motor or multiple hydraulic motors.

[0077] The basic functional principle of a second embodiment is identical to the first embodiment. The difference, however, is that the optional displacement volume controller 6 of the first embodiment is Figur 1 is missing (shown in dashed lines). This means that the calculated displacement volume is transferred from the calculation unit 4 to the pump controller 8 without correction. The displacement volume calculated by the calculation unit 4 is thus the reference variable of the pump controller 8.

[0078] The hydraulic drive can be used, for example, in a winch or travel drive.

Claims

1. Method for operating a hydraulic drive having at least one hydraulic machine (2) with an adjustable displacement volume which, in order to supply pressure medium to at least one hydraulic consumer, can be electronically regulated in a manner oriented to the load thereof, having the steps of: - capturing an actual speed (n_pmp) and a target volume flow (Q_desln) of the hydraulic machine (2) in each case; - calculating a target displacement volume of the hydraulic machine (2) or a mechanical target equivalent (alpha_des) thereof on the basis of the actual speed (n_pmp) and the target volume flow (Q_desln); and, on the basis of the target displacement volume or mechanical target equivalent (alpha_des) and at least one parameter of the hydraulic drive or at least one measurement variable (alpha_pmp, p_pmp) of the hydraulic drive, either: - regulating the displacement volume or equivalent (alpha) according to the target displacement volume or mechanical target equivalent (alpha_des) and limiting an operating variable of the hydraulic machine (2) on the basis of the at least one parameter, or - controlling the displacement volume or equivalent (alpha) according to the target displacement volume or mechanical target equivalent (alpha_des) and regulating an operating variable (p) of the hydraulic machine (2) on the basis of the at least one measurement variable (p_pmp), wherein the operating variable is a pressure (p) of the hydraulic machine (2) or a differential pressure (Δp) over the hydraulic machine (2).

2. Method according to Claim 1, wherein the target displacement volume or mechanical target equivalent (alpha_des) is converted into a target value (p_des) of the operating variable (p).

3. Method according to one of Claims 1 to 2, wherein the calculation of the target displacement volume or mechanical target equivalent (alpha_des) on the basis of the target volume flow (Q_desln) and the actual speed (n_pmp) comprises steps of - calculating a theoretical volume flow (Q_desTheo) on the basis of the target volume flow (Q_desln), the actual speed (n_pmp) and a maximum pump delivery volume (Vg_pmpMax); - calculating a total deviation (ΔQ) from the theoretical volume flow (Q_desTheo) on the basis of at least one influencing variable (p, Δp, n_pmp, alpha, Q_V, T, p_L) acting on the volume flow (Q); - calculating a modified target volume flow (Q_desOut) on the basis of the theoretical volume flow (Q_desTheo) and the total deviation (ΔQ); and - calculating a modified target displacement volume or modified target equivalent (alpha_descorr) on the basis of the modified target volume flow (Q_desOut), the actual speed (n_pmp) and the maximum pump delivery volume (Vg_pmpMax).

4. Method according to Claim 3, wherein the influencing variables include at least one from the pressure (p), a differential pressure (Δp), the speed (n_pmp), the displacement volume or equivalent (alpha), a requested volume flow requirement (Q_V) of the at least one consumer, a temperature of the pressure medium (T) or an air pressure (p_L).

5. Method at least according to Claim 3, wherein the target displacement volume or its mechanical target equivalent (alpha_des) or the modified target displacement volume or the modified target equivalent (alpha_descorr) is corrected on the basis of a captured measurement variable (alpha_pmp).

6. Method according to Claim 5, wherein the operating variable (p) can be regulated via an internal control loop and the displacement volume or its equivalent (alpha) can be regulated via an external control loop, wherein the two control loops form cascade regulation.

7. Method according to one of the preceding claims, wherein there is a switch between an operating mode with the regulation of the operating variable (p) and a further operating mode with the regulation of the displacement volume or equivalent (alpha).

8. Method according to one of the preceding claims, wherein a hysteresis effect of the hydraulic machine (2) is compensated for by regulating the displacement volume or equivalent (alpha).

9. Method according to one of the preceding claims, wherein the regulation of the displacement volume or equivalent (alpha) is overridden or can be at least overridden when limiting the operating variable (p).

10. Control unit (1) which is configured to carry out a method according to one of the preceding claims, at least having a calculation unit (4) for calculating the target displacement volume or target equivalent (alpha_des) on the basis of the target volume flow (Q_desln) and the actual speed (n_pmp), and having a pump regulator (8) for controlling the hydraulic machine (2) on the basis of the calculated target displacement volume or target equivalent (alpha_des).

11. Control unit (1) according to Claim 10, having a displacement volume, equivalent or pivot angle regulator (6) for correcting the calculated target displacement volume, target equivalent or target pivot angle (alpha_des) on the basis of the captured displacement volume, equivalent or pivot angle (alpha_pmp).

12. Computer program for prompting a processor with hardware to carry out the steps according to Claim 1.

13. Machine-readable storage medium with a computer program according to Claim 12 stored thereon.