EP4253754A1 - Method for operating a variable-speed pump - Google Patents

Abstract

The invention relates to a method for operating a variable-speed variable pump (120), in which a conveyor mechanism (122) which can be adjusted in a displacement volume per working cycle is driven by means of a variable-speed drive (121), comprising determining a load torque on the variable-speed variable pump (120), Depending on an operating state, specifying a setpoint (V_Pu,Soll) for a parameter determining the displacement volume per working cycle so that a drive torque of the variable-speed drive (121) is at most a peak drive torque (M< sub>an,max</sub>) of the drive (121) or a continuous drive torque (M_an,0) of the drive (121).

Description

The present invention relates to a method for operating a variable-speed variable pump, in which a conveyor mechanism that can be adjusted in a displacement volume per working cycle is driven by means of a variable-speed drive, and to an electro-hydraulic system.

State of the art

Pumps on which the invention is based have a conveyor mechanism with a variable displacement volume per working cycle (so-called hydraulic displacement machine, e.g. axial piston machine), which is driven by a variable speed drive. When operating such pumps, the volume flow and/or the delivery pressure (i.e. pressure difference between inlet and outlet) are usually regulated by appropriately adjusting the displacement volume of the conveyor and the speed, i.e. such pumps have two degrees of freedom in the control.

From the EP 2 192 309 B1 For example, a method is known in which such a pump is operated by regulating a pressure or a quantity of pressure medium by controlling the volume setting of the pump. A speed deviation of the drive is taken into account.

Disclosure of the invention

According to the invention, a method and an electro-hydraulic system with the features of the independent patent claims are proposed. Advantageous refinements are the subject of the subclaims and the following description.

The invention is concerned with the operation of a variable-speed variable pump, in particular an axial piston pump with, for example, proportional adjustment, in which a conveyor mechanism that can be adjusted in a displacement volume per working cycle is driven by means of a variable-speed drive, such as an electric motor. To adjust the conveyor system, a so-called swivel plate can be provided in such a variable pump. Based on the load torque (in particular load pressure or differential pressure) on the pump as well as load characteristics of the drive motor (e.g. peak and continuous drive torque, max. overload time (=duration of the max. torque)), an appropriate setpoint for the displacement volume is generated to limit the drive torque. The invention thus creates a decoupling of the drive torque of the drive from the load pressure of the driven conveyor by adjusting the displacement volume with the aim of optimal engine utilization.

The current or drive torque of electric drives is usually thermally limited and depends on the duration of the load. However, hydrostatic motor-pump units often have to provide high load pressures over a relatively long period of time. A suitable adjustment of the displacement volume decouples pressure and drive torque. The invention prevents the drive from being overloaded. Within the scope of the invention, the displacement volume is specified so that it can always be applied by the electric drive. The invention is particularly applicable to pumps that are equipped with an adjusting device for specifically influencing their displacement volume based on control specifications. In particular, two operating states, static and dynamic, with different displacement volume specifications can be distinguished

The dependence on the operating state is expediently taken into account by a dependence on a temporal change in the load torque on the variable-speed variable pump. This is an easy-to-implement option for characterizing the operating state.

According to a preferred embodiment, the load torque and the peak drive torque of the drive become a first manipulated variable in accordance with a first filter function with a time delay, in particular a PDT1 function, and the load torque and the continuous drive torque of the drive in accordance with a second filter function with a time delay, in particular a PDT1 function, a second manipulated variable is determined, the setpoint for the parameter determining the displacement volume per working cycle being specified based on the smaller of the first and second manipulated variables. This makes it possible to implement an operating state or load gradient dependency with a predeterminable time course, in particular in such a way that a timely change from the peak drive torque to the continuous drive torque takes place almost automatically before the motor is damaged. For this purpose, the first filter function preferably has a smaller time delay than the second filter function, preferably zero.

Preferably, in a dynamic operating state, the setpoint for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive is greater than the continuous drive torque and corresponds at most to the peak drive torque of the drive. In this way, the displacement volume is controlled or regulated in such a way that dynamic operating states are realized using the corner power or peak power of the electric drive.

In particular, in the dynamic operating state, the setpoint for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive corresponds at most to the peak drive torque of the drive for a permissible overload time. This means that peak performance can be maintained for as long as possible. It can additionally be provided to adapt the overload time using a determined (in particular measured (e.g. using a temperature sensor) or estimated) thermal drive utilization. This means that thermal damage to the drive can be avoided.

According to a further advantageous embodiment, in a static operating state, the setpoint for the parameter determining the displacement volume per working cycle is specified so that the drive torque of the variable-speed drive corresponds at most to the continuous drive torque of the drive. This ensures long-term or continuous operation; Stationary operating states are achieved using the nominal power of the electric drive.

A computing unit according to the invention, for example a control and/or regulating unit for a variable-speed variable pump with a variable-speed drive, is set up, in particular in terms of programming, to carry out a method according to the invention.

The invention furthermore relates to an electro-hydraulic drive system such as an electro-hydraulic axle comprising a variable-speed variable pump with a variable-speed drive and a computing unit according to the invention.

The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous because this causes particularly low costs, especially if an executing control device is used for additional tasks and is therefore present anyway. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard drives, flash memories, EEPROMs, DVDs, etc. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and refinements of the invention result from the description and the accompanying drawing.

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 alone, without departing from the scope of the present invention.

The invention is shown schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing.

Character description

• Figure 1 shows a circuit diagram of a hydraulic system, a drive motor and a controller with a device for adjusting the speed and a conveyor with a device for adjusting the delivery volume.
• Figure 2 shows a signal flow diagram of a control scheme according to a preferred embodiment of the invention.
• Figure 3 shows exemplary curves of operating variables pressure, drive torque and delivery volume when using a control scheme according to a preferred embodiment of the invention.

Detailed description of the drawing

In Figure 1 an electro-hydraulic system 100, as may be the basis for the invention, is shown schematically. The electrohydraulic system 100 has an actuator designed as a hydraulic cylinder 110 with a piston 111 movable along an x-axis, which is actuated by a variable-speed variable pump 120. A hydraulic circuit 130 with, for example, oil as a medium or operating medium is arranged between the variable-speed variable pump 120 and the hydraulic cylinder 110.

The variable-speed variable pump 120 has a variable-speed drive designed as an electric motor 121 and a conveyor mechanism 122 and is designed, for example, as an axial piston pump in a swashplate design. By adjusting the angle of the swivel plate, i.e. the so-called swivel angle, the displacement volume of the conveyor can be changed per work cycle.

A control and/or regulating unit 140 is set up in terms of programming to carry out a preferred embodiment of a method according to the invention. In the example shown, it has several modules 141, 142, 143, here a control module 141, a speed control module 142 and a displacement volume control module 143. However, it should be made clear that the individual modules do not have to be installed in a unit and do not have to be implemented in a programmatic manner. In particular, a displacement volume control module 143 is often designed, for example, as an analog swivel angle controller.

A speed setpoint n _target and an actual speed value n _{ist are} supplied to the speed control module 142, from which a setpoint M _An for a drive torque is determined according to conventional regulation or control methods, for example using P and/or I and/or D transfer functions. The speed setpoint can, for example, be a controlled specification from a user or control value of a higher-level pressure/force/position/speed controller for the hydraulic circuit or the output machine (e.g. cylinder or hydraulic motor).

The displacement volume control module 143 is supplied with a displacement volume setpoint V _PU,soll and an actual displacement volume value V _PU,ist , from which a manipulated variable for the conveyor system is determined using conventional methods.

In order to detect the pressure p ₁ , p ₂ in front of and behind the conveyor, two pressure sensors are provided in the present case.

The control module 141 receives the pressure values p ₁ , p ₂ and the (setpoint or actual) value M _An (in electrical machines, the time constant is significantly shorter compared to hydraulics, so that the setpoint and actual value are always viewed as the same when viewed in this way can be supplied for the drive torque, from which the setpoint for the displacement volume is determined. The drive torque can preferably be used here in order to take into account a portion of the friction in the total torque (which is present in addition to the external load, which is not negligible). As shown below, it is particularly taken into account in the form of additional load pressure.

Hydrostatic pumps provide a volume flow that is essentially proportional to the product of the speed and the pump size characterized by the displacement volume. The flow occurs from one work connection to the other depending on the direction of rotation. If different pressures p ₁ , p ₂ prevail at the working connections, a drive machine must provide a corresponding torque. The required torque is proportional to the product of the pressure difference and the pump size characterized by the displacement volume.

By means of an adjustment device for the displacement volume of the pump and a suitable operating strategy, the area of application of the motor-pump unit can be significantly expanded compared to a system with a constant pump, in that a high volume flow can be provided at low load pressures, while the drive motor cannot be used at high load pressures is overloaded. The present invention takes into account both the limitation of the continuous torque M ₀ and the peak torque M _max and allows the time-limited utilization of the maximum power of the drive motor/converter.

A pressure difference on the pump drive requires/generates a proportional torque M _L,P on the pump shaft according to: $$M_{L,p}=\frac{v_{\mathit{Pu},\mathit{Is}}}{2\cdot \pi }\cdot \left(p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\right)$$

A speed approximately generates (minus leakage volume flows) a volume flow according to: $$Q_{\mathit{Pu}}=v_{\mathit{Pu},\mathit{Is}}\cdot n$$

wobei J_MoPu das Trägheitsmoment der Einheit ist, ϕ̈ die Drehwinkelbeschleunigung und M_R,ges das Gesamt-Reibmoment am Triebwerk.Overall, the torque balance on the engine of the motor-pump unit is: $${\mathrm{J}}_{\mathrm{MoPu}}\cdot \ddot{\varphi }=M_{\mathit{at}}-M_{L,p}-M_{R,\mathit{total}}$$

where J _MoPu is the moment of inertia of the unit, ϕ̈ is the rotational angular acceleration and M _R,ges is the total frictional moment on the engine.

um die Kontrolle über die Antriebsdrehzahl zu behalten und ein ungewolltes Absinken derselben zu verhindern.When limiting the engine torque M _an to a limit value M _an,max, the following must therefore apply as a minimum requirement: $$M_{L,p}\le M_{\mathit{at},\mathit{Max}}$$

to maintain control over the drive speed and prevent it from dropping unintentionally.

This condition can be met by appropriately adjusting the displacement volume as follows: $$\frac{v_{\mathit{Pu},\mathit{Should},\mathit{Great}}}{v_{\mathit{Pu},\mathit{Max}}}\le \frac{2\cdot \pi }{v_{\mathit{Pu},\mathit{Max}}}\cdot \frac{M_{\mathit{at},\mathit{Max}}}{\left|p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\right|+\left|{\widehat{p}}_{R,\mathit{total},scH\mathrm{ä}\mathit{tz}}\right|}$$

This already takes into account that devices for adjusting the displacement volume of a pump (such as a swivel angle adjustment) often expect a target signal, which is related to the maximum displacement volume V _PU,max , and the actual displacement volume is also given as a relational size. The real (total) friction on the engine can be taken into account as an estimated additional pressure difference p̂ _R,tot , which is derived from the drive torque and the delivery volume.

welche in Abhängigkeit vom jeweils anstehenden Lastdruck die Pumpenverstellung so ausführt, dass das Spitzenmoment des Motors nicht durch das Abtriebsmoment überschritten wird.An alternative form can be given for Equation 5a if the relative quantity α is introduced for the relative displacement volume. This results in the requirement: $${\alpha }_{\mathit{Should},\mathit{Great}}\le \frac{2\cdot \pi }{v_{\mathit{Pu},\mathit{Max}}}\cdot \frac{M_{\mathit{at},\mathit{Max}}}{\left|p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\right|+\left|{\widehat{p}}_{R,\mathit{total},scH\mathrm{ä}\mathit{tz}}\right|}$$

which, depending on the load pressure, adjusts the pump in such a way that the peak torque of the motor is not exceeded by the output torque.

In an analogous manner, a setpoint for the (relative) displacement volume can be derived, which ensures compliance with the (lower) continuous torque M _an,0 of the drive motor: $${\alpha }_{\mathit{Should},\mathit{Length\; of\; time}}\le \frac{2\cdot \pi }{v_{\mathit{Pu},\mathit{Max}}}\cdot \frac{M_{\mathit{at},0}}{\left|p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\right|+\left|{\widehat{p}}_{R,\mathit{total},scH\mathrm{ä}\mathit{tz}}\right|}$$

Since M _an,0 ≤ M _{an, max} , a direct application of the torque limitation rules as in Eq. 5b and 6 formulate the displacement volume must always be reduced to such an extent that the continuous torque is not exceeded. This would prevent the basic power of the drive motor from being used.

In order to (short-term) utilize the maximum power of the drive, the values from Eq. 5b and 6 resulting setpoint values for the swivel angle are advantageously filtered in order to influence them over time in such a way that the engine utilization is suitably optimized.

This advantageously results in the regulation for specifying a pump displacement volume for torque limitation in general form: $${\alpha }_{\mathit{Should},\mathit{Length\; of\; time}}\le \frac{2\cdot \pi }{v_{\mathrm{Pu},\mathrm{Max}}}\cdot \mathrm{MIN}\left[\begin{array}{c}\mathrm{<figure-callout\; id="0"\; label="f\; K\; redM"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">f</figure-callout>}\left(\frac{K_{\mathit{redM}}}{}\right)\left(\frac{{\mathit{}0}_{}\cdot M_{\mathit{at},0}}{\left|p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\right|+\left|{\widehat{p}}_{R,\mathit{total},scH\mathrm{ä}\mathit{tz}}\right|},\omega \right)\\ G\left(\frac{K_{\mathit{redMmax}}\cdot M_{\mathit{at},\mathit{Max}}}{\left|p_1-{\mathrm{<figure-callout\; id="2"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_2\right|+\left|{\widehat{p}}_{R,\mathit{total},scH\mathrm{ä}\mathit{tz}}\right|},\omega \right)\end{array}\right]$$

The correction values designated K _redM ∗ take into account the fact that the torque limit values in a real drive system can deviate from the nominal values.

Technically advantageously, a filter or a filter function g ( M _an,max , Δ p , ω ) can be designed in such a way that a dynamic delay of the adjusting device is compensated for in order to implement the limitation to the maximum torque without delay and thus the functionality even in the event of dynamic load changes to guarantee. A PDT1 transfer function can advantageously be used as a filter function.

Furthermore, a filter or a filter function f (M _an,0 , Δ p, ω ) can be technically advantageously designed in such a way that as the load increases, the reduction in the displacement volume is delayed in a defined time in order to be able to optimally use the peak power of the drive. However, when the load drops, the displacement volume is adjusted back with as little delay as possible in order to be able to achieve a high volume flow for load reduction. A PDT1 transfer function can advantageously be used as a filter function.

In order to maintain an application-related volume flow in particular, a change in the displacement volume _is expediently taken into account in the speed specification n target. The product of speed and displacement is proportional to the requested or necessary volume flow.

The signal flow plan of a preferred implementation of such a filter concept is in Figure 2 shown and labeled 200 in total.

On the input side (left), the difference between the pressure values p ₁ and p ₂ is first formed and fed to an amount formation 201. Likewise, the amount 202 of the estimated additional pressure difference p̂ = p̂ _{R,tot,estimate} is added to form the total relevant differential pressure Δp. This is offset in a division element 203 or 204 with the maximum drive torque M _an,max or the continuous drive torque M _an,0 and then in a Elements 205, 206 are offset against the mentioned correction values and the maximum volume in order to obtain the relational volume control values.

$$f:G\left(s\right)=\frac{T_{N,\mathit{Dauer}}\cdot s+1}{T_{P,\mathit{Dauer}}\cdot s+1}$$

These are fed to a filter function 207, 208, which represents a PDT transmission behavior in particular according to the following equation. The corresponding transfer functions are: $$G:G\left(s\right)=\frac{T_{N,\mathit{Great}}\cdot s+1}{T_{P,\mathit{Great}}\cdot s+1}$$

$$f:G\left(s\right)=\frac{T_{N,\mathit{Length\; of\; time}}\cdot s+1}{T_{P,\mathit{Length\; of\; time}}\cdot s+1}$$

The resulting output values or manipulated variables α _{S, peak} and α _{S, duration} are fed to a minimum value element 209, which selects the respective smaller displacement volume as the actual manipulated variable α _target .

• Vorhaltzeit: $$T_{N,\mathit{Spitze}}=T_{\mathit{Stell}}$$
  
• Verzögerungszeit: $$T_{P,\mathit{Spitze}}=0$$
  
• Vorhaltzeit: $$T_{N,\mathit{Dauer}}=T_{\mathit{Maxmoment}}\cdot \left(1-\frac{1}{e}\right)\cdot \mathit{SGN}\left({\dot{\propto }}_{S,\mathit{Dauer},\mathit{stat}}\right)$$
  
• Verzögerungszeit: $$T_{P,\mathit{Dauer}}=T_{\mathit{Maxmoment}}\cdot \left(1-\frac{1}{e}\right)$$
  

An advantageous parameterization of the filter parameters is as follows:

• Lead time: $$T_{N,\mathit{Great}}=T_{\mathit{Place}}$$
  
• Delay Time: $$T_{P,\mathit{Great}}=0$$
  
• Lead time: $$T_{N,\mathit{Length\; of\; time}}=T_{\mathit{Max\; moment}}\cdot \left(1-\frac{1}{e}\right)\cdot \mathit{SGN}\left({\dot{\propto }}_{S,\mathit{Length\; of\; time},\mathit{stat}}\right)$$
  
• Delay Time: $$T_{P,\mathit{Length\; of\; time}}=T_{\mathit{Max\; moment}}\cdot \left(1-\frac{1}{e}\right)$$
  

Therein T _Stell corresponds to the parameter of a simplified model of the dynamics of the pump adjustment. T _{maximum torque} is the time for which the drive should be able to generate its peak torque. This is to be seen as an essential operating parameter of the adjustment strategy presented and must be smaller than the actual time after which the drive reaches its thermal overload. Furthermore, e is Euler's number.

To further improve the method, the estimate of the frictional torque can be adapted to the current operating conditions using a suitable estimator. A possible device would be an integral controller for the static engine torque or other estimating devices that are common in control technology, such as observers.

To further improve the method, the effective limit value for the continuous torque can be adapted to the existing operating conditions using the measured or estimated thermal drive utilization by adapting the correction factor K _redM0 . In a similar way, the permitted overload time T _Maxmoment , which is used in the signal filter, can be adapted to the existing operating conditions.

An exemplary course of operating variables when using a preferred embodiment of the invention is shown in Figure 3 shown.

There, in the upper diagram, the pressure difference 301 on the conveyor and a drive torque 302 on the electric drive are plotted in exemplary units against the time t, also in exemplary units. In particular, starting from a time of 0 to a time of approximately 0.85, the pressure difference and thus the load is increased from 0 to approximately 100%.

In the diagram below, the displacement volume in percent is plotted against time t for different control variables. These include α _{should, duration, stat} 303, α _should , _{peak, dyn} 304, α _{should, duration, dyn} 305, α _should , _{peak, stat} 306. Furthermore, the actual swivel angle α _lst 307 resulting from an exemplary actuating dynamic is plotted .

The two conditions for the limitation to the maximum torque or the continuous torque result in the two static swivel angle setpoints α _{target, duration, stat} 303 and α _{target, peak, stat} 306 with the increasing pressure difference shown. After filtering through the corresponding signal filters 207 and 208, they are The setpoint values α _{target, duration, dyn} 305 and α _{target, peak, dyn} 304 are valid for the swivel angle control. The minimum value element 209 supplies the control device 143 for the swivel angle with the smaller value of α _{target, duration, dyn} 305 and α _{target, peak, dyn} 304 at the respective time as the valid target value. With a usual configuration of the control device 143 for the swivel angle as a proportional controller, there is a time delay of the actual swivel angle value compared to the setpoint, which is shown, for example, by the actual value curve α _lst 307.

With an advantageous parameterization of the filter times, the filter 207 for the peak torque limitation compensates for the actuating dynamics of the control device 143 so that the actual value α _is 307 exactly follows the static setpoint α _{setpoint, peak, stat} 306, so that the peak torque is not exceeded despite the limited control dynamics of the swivel angle controller.

Furthermore, the filter 208 for the permanent torque limitation is designed with a direction-dependent signal component, so that when the load torque increases, the effective setpoint α _{target, duration, dyn} 305 lags behind the filter input α target _{, duration, stat} 303 by the desired time-limited maximum load of the electric drive machine to be able to use it, while when the load torque is reduced, the effective setpoint α _{target, duration, dyn} 305 leads the filter input α _{target, duration, stat} 303. With an advantageous parameterization of the filter times, as shown above, the filter 208 for the continuous torque limitation compensates for the control dynamics of the control device 143 so that the actual value α _lst 307 exactly follows the static setpoint α _{target, duration, stat} 303, so that when the load decreases The full performance of the motor-pump unit is available without delay and in compliance with the torque limitation despite the limited control dynamics of the swivel angle controller.

Claims (18)

Method for operating a variable-speed variable pump (120), in which a conveyor mechanism (122) which can be adjusted in a displacement volume per working cycle by means of a variable-speed drive (121) which has a peak drive torque (M _An,max ) and a continuous drive torque (M _{An ,0} ), is driven, comprising: determining a load torque (Δp) on the variable-speed variable pump (120), depending on an operating state, specifying a setpoint (V _Pu,Soll ) for a parameter determining the displacement volume per working cycle to an adjusting device (143) of the conveyor so that a drive torque of the variable-speed drive (121) is either more than the continuous drive torque (M _an,0 ) and at most the peak drive torque (M _an,max ) of the drive (121), or at most the Continuous drive torque (M _an,0 ) of the drive (121) corresponds. Method according to claim 1, wherein the dependence on the operating state is taken into account by a dependence on a temporal change in the load torque (Δp) on the variable-speed variable pump (120). Method according to claim 1 or 2, wherein a first manipulated variable is formed from the load torque (Δp) and the peak drive torque (M _An,max ) of the drive (121) in accordance with a first filter function (207) with a time delay ( _TP,peak ). (α _S,peak ) and from the load torque (Δp) and the continuous drive torque (M _An,0 ) of the drive (121) in accordance with a second filter function (208) with a time delay ( _TP,duration ) a second manipulated variable ( α _S,Duration ) is determined, whereby the setpoint (V _Pu,Soll ) for the parameter determining the displacement volume per work cycle is specified based on the smaller of the first and second manipulated variables. Method according to claim 3, wherein the first filter function (207) has a smaller time delay ( _{TP, peak} ) than the second filter function (208), preferably zero. Method according to claim 3 or 4, wherein the first filter function (207) and/or the second filter function (208) is a PDT1 transfer function with a lead time (T _{N, peak} , T _{N, duration} ) and a delay time (T _{P, peak} , T _P,Duration ), where the lead time (T _{N, peak} , T _{N, duration} ) is specified in particular depending on an actuating dynamic of the adjusting device (143) of the conveyor system. Method according to one of the preceding claims, wherein in a dynamic operating state the setpoint (V _Pu,Soll ) for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive (121) is more than the continuous drive torque (M _{An .0} ) of the drive (121) and at most corresponds to the peak drive torque of the drive (121). Method according to claim 6, wherein in the dynamic operating state the setpoint (V _Pu,Soll ) for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive (121) is more than the continuous drive torque for a maximum of a permissible overload time (M _An,0 ) of the drive (121) and at most corresponds to the peak drive torque of the drive (121). Method according to claim 7, wherein the overload time is adjusted using a determined thermal drive load, and preferably with reference to claim 3, wherein the time delay ( _{TP, duration} ) of the second filter function (208) is predetermined as a function of the overload time. Method according to one of the preceding claims, wherein in a static operating state the setpoint (V _Pu,Soll ) for the parameter determining the displacement volume per working cycle is specified such that the drive torque of the variable-speed drive (121) is at most the continuous drive torque of the drive (121 ) corresponds. Method according to one of the preceding claims, wherein determining the load torque on the variable-speed variable pump (120) comprises determining a pressure difference (Δp) between an inlet and an outlet of the conveyor (122). Method according to one of the preceding claims, wherein determining the load torque on the variable speed variable pump (120) comprises determining a friction as an additional pressure difference ( p̂ ). Method according to one of the preceding claims, wherein the peak drive torque (M _an,max ) of the drive (121) and / or the continuous drive torque (M _an,0 ) of the drive (121) as a product with a correction factor ( K _redMmax , K _redM0 ) are taken into account. Method according to claim 12, wherein the correction factor ( K _redMmax , K _redM0 ) is adjusted using a determined thermal drive utilization. Method according to one of the preceding claims, additionally comprising: specifying a target value (n _Soll ) for the speed of the variable-speed drive (121) depending on the target value (V _Pu,Soll ) or an actual value (V _Pu,Sst ) for the displacement volume determining parameter for each work cycle. Computing unit (140), which is set up to carry out a method according to one of the preceding claims. Electro-hydraulic system (100) comprising a variable-speed variable pump (120) with a variable-speed drive (121) and a computing unit (140) according to claim 15. Computer program which causes the computing unit (140) of the electro-hydraulic system (100) according to claim 16 to carry out a method according to one of claims 1 to 15 when it is executed on the computing unit (140). Machine-readable storage medium with a computer program stored thereon according to claim 17.

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