Method for determining an optimal rotational speed of a pressure medium supply device of an electrohydraulic system

Abstract

The invention relates to a method for determining an optimal rotational speed of a pressure medium supply device (10) of an electro-hydraulic system, which has an electric drive (4) and a hydraulic pump (2) coupled to it, which delivers pressure medium, wherein the electric drive (4) drives the hydraulic pump (2) according to a rotational speed and wherein the hydraulic pump has an adjustable displacement, wherein a minimum rotational speed value is determined based on a target volume flow rate (54) of the pressure medium requested by the pressure medium supply device (10) (110); wherein several comparative rotational speed values ​​are determined (120) such that a smallest of the several comparative rotational speed values ​​is equal to or greater than the minimum rotational speed value and a largest of the several comparative rotational speed values ​​is equal to or less than a predetermined maximum rotational speed value;wherein for at least some of the several comparative speed values ​​a comparative value corresponding to the respective comparative speed value is calculated using a cost function (190) which includes a sum (180) of at least one speed-dependent power loss term of the electric drive (4) and a speed-dependent power loss term of the hydraulic pump (2); and wherein the comparative speed value which has the smallest comparative value is determined as the optimal speed value (210).;

Description

[0001] The present invention relates to a method for determining an optimal speed of a pressure medium supply device of an electro-hydraulic system, a method for controlling a pressure medium supply device of an electro-hydraulic system as well as a computing unit and a computer program for its execution. Background of the invention

[0002] Machines, e.g. mobile work machines such as excavators, loaders or crawlers, can have a hydraulic system with which elements of the respective machine, such as arm elements of an excavator, are moved. At least one hydraulic pump is provided in the hydraulic system for supplying pressure medium. The hydraulic pump can have an adjustable displacement or an adjustable delivery volume and can be driven by an electric drive, which includes an electric machine and an inverter. In the case of several hydraulic pumps, these can be driven jointly by the electric drive. From user inputs recorded with a user interface, e.g. a joystick, and / or measured values, e.g.measured pressure values, an electronic control system can determine a requirement for the volume flow and / or a requirement for the pressure of the pressure medium delivered by the hydraulic pump, whereby the electric drive and the hydraulic pump are controlled so that these and any other requirements are met as far as possible. Disclosure of the invention

[0003] According to the invention, a method for determining an optimal speed of a pressure medium supply device of an electrohydraulic system, a method for controlling a pressure medium supply device of an electrohydraulic system, as well as a computing unit and a computer program for implementing the same are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0004] The invention utilizes the measure of determining a minimum speed value based on a requested target volume flow of the pressure medium for a pressure medium supply device of an electrohydraulic system, which has an electric drive and a hydraulic pump coupled thereto, determining a plurality of comparison speed values ​​in the interval between the minimum speed value and a predetermined maximum speed value, and calculating corresponding comparison values ​​for at least some of the comparison speed values ​​using a cost function that includes a sum of power loss terms of the electric drive and the hydraulic pump. The optimal speed value is determined as the comparison speed value that has the smallest comparison value (of the cost function).The invention enables the determination of the optimal speed value with relatively little computational effort, so that when load specifications (target volume flow, target pressure, etc.) change, the optimal speed value can be quickly adjusted and efficient operation in terms of the cost function is enabled.

[0005] The maximum speed value is in particular a maximum speed value given for technical reasons or due to other circumstances or boundary conditions, e.g. a reference speed of the hydraulic pump. The maximum speed value is greater than the minimum speed value, provided that the pressure medium supply device is at all capable of providing the target volume flow. In the following it is assumed that this is the case. In the case not considered further here, that this is not possible, i.e. that the maximum speed value is too small to achieve the required target volume flow at maximum displacement, the maximum speed value could, for example, be used as the "optimum speed value" and the pressure medium supply device could be controlled with it and the volume flows made available to the hydraulic consumers could be adjusted, for example by means of a higher-level control system.

[0006] According to one embodiment, when the method is carried out repeatedly, the plurality of comparison speed values ​​are determined in a later execution such that the optimal speed value of an earlier execution, in particular of the immediately preceding execution, lies between the smallest and a largest of the plurality of comparison speed values ​​(of the later execution); wherein a first difference between the largest and the smallest of the plurality of comparison speed values ​​of the later execution is smaller than a second difference between the maximum speed value and the minimum speed value of the later execution. In other words, the interval defined by the smallest and the largest of the plurality of comparison speed values ​​is a true (i.e., non-identical) sub-interval of the interval defined by the minimum speed value and the maximum speed value.By limiting the interval in which the comparison speed values ​​lie, the number of comparison speed values ​​and thus the computational effort is reduced, while the distance between the comparison speed values ​​remains unchanged, or a smaller distance between the comparison speed values ​​can be selected, while the computational effort remains unchanged, whereby intermediate configurations are also conceivable.

[0007] According to one embodiment, an upper distance between the largest of the plurality of comparison speed values ​​of the later implementation and the optimal speed value of the earlier implementation is greater than a lower distance between the smallest of the plurality of comparison speed values ​​of the later implementation and the optimal speed value of the earlier implementation. According to this embodiment, upward speed changes can occur with greater dynamics than downward speed changes, so that a rapid increase in pressure medium requirements can be met efficiently. A ratio of the upper to the lower distance can, for example, be greater than 1.1, greater than 1.3, greater than 1.5, greater than 2, or greater than 3.

[0008] According to one embodiment, the ratio of the first to the second difference is less than 0.8. The ratio of the first to the second difference is, for example, less than 0.8, less than 0.7, less than 0.5, or less than 0.3.

[0009] According to one embodiment, the comparison speed values ​​are evenly spaced from one another. The distance between adjacent comparison speed values ​​can, for example, be a predetermined speed distance value, expressed, for example, in revolutions per minute.

[0010] The distance between adjacent comparison speed values ​​can also be a fraction (e.g., 1 / 5, 1 / 10, 1 / 20, or another fraction) of a specific speed range (or speed interval). The specific speed range can, for example, correspond to the speed range between the minimum speed and the maximum speed or, if applicable, the first difference.

[0011] According to one embodiment, when determining the plurality of comparison speed values, the comparison speed values ​​are selected from a predetermined speed value grid and / or when determining the plurality of comparison speed values, the comparison speed values ​​are selected from a speed value grid that is defined relative to the minimum speed value or, if the method is performed repeatedly, to the optimal speed value of a previous execution, in particular the immediately preceding execution. A predetermined speed value grid results in very little effort in determining the comparison speed values. It may also occur that certain calculated values ​​can be used again in repeated execution without recalculation. A relatively defined speed value grid enables suitable adaptation of the speed value grid.For example, the speed value grid can be selected such that in certain speed ranges the speed values ​​of the speed value grid are closer to each other. For example, if the target volume flow changes only slightly, it can be assumed that the optimal speed value of the later implementation is close to that of the optimal speed value of the previous implementation, so that in its vicinity the speed values ​​of the speed value grid can be selected closer to each other in order to enable a precise determination of the optimal speed value.

[0012] According to one embodiment, upon repeated execution, a distance between the comparison speed values ​​of the current execution and / or a distance (i.e., the first difference) between the largest and the smallest of the comparison speed values ​​of the current execution is / are determined depending on a change in the target volume flow between a previous execution, in particular the immediately previous execution, and the current execution. In particular, the distance between the comparison speed values ​​of the current execution and / or a distance (i.e., the first difference) between the largest and the smallest of the comparison speed values ​​of the current execution can be selected to be relatively small in the case of a small change in the target volume flow (e.g.,A fraction, such as 1 / 2, 1 / 3, 1 / 4, 1 / 5 of the interval between the minimum speed value and the maximum speed value, or smaller, should be selected. For a large change in the target flow rate, the change should be relatively large (e.g., equal to the interval between the minimum speed value and the maximum speed value). The change in the target flow rate can be expressed, for example, as a relative change, whereby a change that exceeds a certain value (e.g., a certain percentage, such as 10%, 20%, 30%, or 50%) is classified as large, and the change otherwise is classified as small.

[0013] According to one embodiment, the power loss term of the hydraulic pump includes a sum of speed-dependent leakage losses and friction losses or is given as such a sum. Alternatively or additionally, the electric drive comprises an electric machine and an inverter, wherein the at least one power loss term of the electric drive includes a power loss term of the electric machine and / or a power loss term of the inverter, and wherein the power loss term of the electric machine and / or power loss term of the inverter is / are dependent on the respective comparison speed value and one or more of: an effective torque, a DC voltage at the inverter, and a temperature of the electric machine or the inverter. According to this embodiment, various dependencies of the power losses are taken into account.

[0014] According to one embodiment, the at least one power loss term of the hydraulic pump includes a leakage power loss term and / or a friction power loss term, and for each of the comparison speed values: a corresponding displacement is determined taking into account an estimated leakage and the respective comparison speed value so that the target flow rate is achieved; an exact leakage flow rate and / or an exact friction torque is determined from the displacement, the respective comparison speed value, and a given pressure difference (across the hydraulic pump); and the leakage power loss term and / or the friction power loss term are determined from the exact leakage flow rate and / or the exact friction torque. By calculating and using exact values ​​for the leakage flow rate and / or the friction torque, a more precise determination of the corresponding power losses is achieved.

[0015] According to one embodiment, when determining the comparison values ​​for each of the comparison speed values: a friction torque of the hydraulic pump is determined based on the respective comparison speed value, an effective torque is determined from the friction torque and a theoretical torque of the hydraulic pump, which is determined by the target volume flow to be delivered at a given pressure difference across the hydraulic pump, a check is carried out to determine whether the electric drive is capable of generating or providing the effective torque, and if the test determines that the electric drive is not capable of generating the effective torque, no comparison value is determined for the respective comparison speed value. During the test, in particular, the respective comparison speed value and / or a DC voltage of the electric drive or at an inverter of the electric drive can be taken into account.This design makes it possible to identify operating points that are not technically feasible and to exclude them from the calculation of corresponding comparison values.

[0016] According to one embodiment, an estimated leakage volume flow, in particular at maximum displacement, is taken into account when determining the minimum speed value. A total volume flow is therefore formed from the target volume flow and the leakage volume flow, and the total volume flow is divided by the maximum displacement (i.e., the maximum possible displacement of the hydraulic pump, maximum swivel angle) to determine the minimum speed value. The estimated leakage volume flow can, for example, be a maximum leakage volume flow that can occur, for example, at maximum displacement; this can also be dependent on the pressure difference across the hydraulic pump. The leakage volume flow estimated in this way can, for example, be taken from data sheets and / or stored characteristic maps.

[0017] A method according to the invention for controlling a pressure medium supply device of an electro-hydraulic system, which has an electric drive and a hydraulic pump coupled to the latter which delivers pressure medium, wherein the electric drive drives the hydraulic pump according to a speed and wherein the hydraulic pump has an adjustable displacement, comprises determining an optimal speed value for a target volume flow to be delivered using a method according to the invention for determining an optimal speed, controlling the electric drive so that the hydraulic pump is driven at the optimal speed value, and adjusting the hydraulic pump so that, with the optimal speed value, the target volume flow is achieved taking into account a leakage volume flow.

[0018] A computing unit according to the invention, e.g. a control unit of a pressure medium supply device of a mobile work machine, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0019] Implementing a method according to the invention in the form of a computer program or computer program product with program code for performing all method steps is also advantageous, as this entails particularly low costs, especially if an executing control unit is also used for additional tasks and is therefore already present. Suitable data storage devices for providing the computer program include, in particular, magnetic, optical, and electrical storage devices, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0020] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0021] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0022] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Character description Fig. 1 shows an example electrohydraulic system. Fig. 2 shows a control system for controlling an electric drive and a hydraulic pump. Fig. 3 shows a flowchart of the method for determining an optimal speed according to an embodiment of the invention. Detailed description of the drawing

[0023] Fig. 1 shows an exemplary electro-hydraulic system comprising a pressure medium supply device 10 and one or more hydraulic consumers 12, which are hydraulically connected to the pressure medium supply device 10 via a valve arrangement 14.

[0024] The pressure medium supply device 10 has a hydraulic pump 2 or hydraulic machine which is adjustable, i.e. which has an adjustable displacement. The term displacement refers to the volume of pressure medium delivered per revolution of the hydraulic pump 2. For example, the hydraulic pump 2 is an axial piston machine, e.g. in a swash plate design or in a bent axis design, wherein the displacement corresponds to an adjustable swivel angle. The hydraulic pump 2 (also referred to as a pump for simplification) delivers pressure medium (hydraulic fluid, typically hydraulic oil) from a tank (which is hydraulically connected to a suction connection of the hydraulic pump) to a working connection or pressure outlet of the hydraulic pump 2. The pressure outlet of the hydraulic pump 2 is connected to the valve arrangement 14, e.g. via a hydraulic line. The valve arrangement 14 is designed to control the inflow and outflow of the pressure medium to and from the tank.by the hydraulic consumers 12, e.g., by means of control valves and / or directional control valves that are suitably controlled. Hydraulic cylinders and a hydraulic motor are shown as examples of hydraulic consumers 12, whereby, in general, at least one hydraulic consumer (e.g., at least one hydraulic cylinder and / or at least one hydraulic motor) can be provided.

[0025] The hydraulic pump 2 is driven by an electric drive 4. The electric drive 4 comprises an electric machine 6 and an inverter 8, which supplies the electric machine 6 or its windings with alternating voltage. The inverter 8 is supplied with direct electrical current or direct electrical voltage, which is provided, for example, by a battery and / or via an intermediate circuit from a power supply network. The hydraulic pump 2 is (mechanically) coupled to the electric machine 6, for example via a shaft and / or a gear, which in particular can have a gear ratio other than one. Accordingly, the speed of the electric machine 6 is equal to the speed of the hydraulic pump 2 or, if a gear with a gear ratio other than one is provided, equal to the product of the gear ratio and the speed of the hydraulic pump 2.

[0026] More generally (not shown), the electrohydraulic system can comprise a plurality of hydraulic pumps, which are driven in particular by the same electric drive. The plurality of hydraulic pumps can, for example, provide pressure medium for a plurality of hydraulic circuits, whereby it can also be provided that different hydraulic circuits can be selectively interconnected, for example by means of a summing valve.

[0027] Furthermore, an electronic control 18 of the electro-hydraulic system is shown (i.e., a computing unit or a control device). The electronic control 18 is configured to control the pressure medium supply device 10, i.e., the electric drive 4 (in particular its inverter 8) and the hydraulic pump 2, e.g., via corresponding electrical control lines shown as dashed lines. Likewise (not shown), sensors can be provided that transmit measured values ​​to the electronic control 18, e.g., via electrical sensor lines. In particular, one or more of the following sensors are provided: a pressure sensor that measures the output-side pressure of the pressure medium delivered by the hydraulic pump 2 (i.e.,the pressure at the pressure outlet of the hydraulic pump or the pressure in the hydraulic line between the hydraulic pump and the valve arrangement); at least one speed sensor which measures the speed of the electric machine and / or the hydraulic pump; a displacement sensor which measures the displacement or the swivel angle of the hydraulic pump. It is also possible to replace one or more of the measured values ​​measured by these sensors with corresponding estimated and / or calculated values ​​(e.g. using measured values ​​from other sensors or a control-related observer) (i.e. to use partially “virtual measured values” from “virtual sensors”). To control the pressure medium supply device 10 or as part of such a control, the electronic control system can be set up (e.g. by executing corresponding computer programs) to carry out a control method (as described, for example, in . Fig. 2) and / or a method according to the invention (e.g. corresponding to the method shown in Fig. 3). The electronic controller 18 may be further configured to control the valve assembly 14.

[0028] Fig. 2 shows a control system for controlling an electric drive 64 and a hydraulic pump 72. A (requested) target pressure 52 or requested pressure and a (requested) target volume flow 54 or requested volume flow are given, approximately corresponding to a power requirement of hydraulic consumers (e.g. hydraulic cylinder and / or hydraulic motor). According to an operating strategy or by a module 56 that implements the operating strategy, both a target speed 58 and a specification 60 for the hydraulic pump are determined from this. A speed control 62 for the electric drive 64 regulates the speed according to the target speed. A pump control 68 sets the displacement 70 or the swivel angle of the hydraulic pump 72 from the specification 60 for the hydraulic pump. The leakage 74 of the hydraulic pump can be taken into account in this process.Overall, an effective volume flow 76 is thus obtained, which, within the scope of the control, should be equal to the target volume flow. The power or torque 78 of the hydraulic pump is generated by the electric machine. The electric drive has a corresponding energy consumption 80. The operating strategy module, i.e., the module 56 that implements the operating strategy, and / or the speed control 62 and / or the pump control 68 can be implemented in particular by at least one computer program or computer program module, which is executed, for example, in an electronic control (processing unit) of the electrohydraulic system.

[0029] The following applies: n · V g = Q soll + Q Leck , ie two adjustable parameters, namely the speed n (of the hydraulic pump) and the displacement V g , can be selected to achieve a desired target volume flow Q soll where the leakage volume flow QLeck should be taken into account. Due to the restriction imposed by the above equation, a degree of freedom or a free parameter (within technical constraints) is present.

[0030] The selection of the speed and displacement parameters according to the operating strategy can take into account power losses that occur in the electric drive, or in the electric machine and inverter, and in the hydraulic pump, in order to ensure, for example, the most efficient operation possible.

[0031] In simple terms, for a given power requirement, the power losses of the electric motor and inverter are lower at higher speeds, meaning their operation is more efficient at higher speeds. While the power losses of the hydraulic pump (at constant pressure) are lower at higher displacement or lower speeds, meaning their operation is more efficient at lower speeds. More generally, power losses are not solely dependent on speed.

[0032] The power loss P V,EM of the electrical machine depends in particular on the speed n, the torque M, a DC voltage at the inverter U dc and a temperature T EM of the electrical machine (also called electrical machine temperature; measured at a suitable location, e.g. on the windings and / or on the iron core), the power loss of the electrical machine can therefore be regarded as a function of these parameters, ie PV,EM = P V,EM (n, M, U dc , T EM ).

[0033] The power loss P V,Inv of the inverter depends in particular on the speed n, the torque M, the DC voltage at the inverter U dc and a temperature T Inv of the inverter (also called inverter temperature; measured at a suitable location, e.g. on a heat sink and / or a semiconductor of the inverter), the power loss of the inverter can therefore be considered as a function of these parameters, ie P V,Inv = P V,Inv (n, M, U dc , T Inv ).

[0034] The power loss P V,Pmp of the hydraulic pump depends in particular on a pressure difference Δp across the hydraulic pump, the volume flow Q delivered by the hydraulic pump, the speed n, and the displacement V g , the power loss of the hydraulic pump can therefore be considered as a function of these parameters, ie P V,Pmp= P V,Pmp (Δp, Q, n, V g ). At least one pressure sensor and / or one speed sensor can be provided to determine the pressure difference Δp across the hydraulic pump or its speed n.

[0035] The variables on which the power losses or power loss terms depend can include, in addition to the speed, variables that characterize the operating point and other measured or recorded variables (e.g. temperatures). In general, each of the power losses can depend (independently of one another) on the speed and / or at least one variable that characterizes the operating point and / or at least one other measured or recorded variable. In addition to the power losses mentioned, power losses can also occur in other components of the electro-hydraulic system and be taken into account in the cost function, whereby the power losses can depend on the aforementioned variables.

[0036] For example, power losses that occur at a summing valve (in the case of several hydraulic pumps and several hydraulic circuits) when hydraulic circuits are connected together or at a cooling device for pressure medium can be taken into account.

[0037] In order to minimize the total power loss, the speed or displacement can be determined in an optimization, e.g. using a suitable optimization method, so that the following cost function K is minimized: K=PV,EM(n,M,Udc,TEM)+PV,Inv(n,M,Udc,TInv)+PV,Pmp(Δp,Q,n,Vg)

[0038] The cost function includes power loss terms for the electric machine power loss (electric machine power loss term), the inverter power loss term, and the hydraulic pump power loss (pump power loss term). The electric machine power loss term and the inverter power loss term can each be considered a drive power loss term. More generally, with any additional power losses, the following applies: K = ∑ i P V,i , with i ∈ {EM, Inv, Pmp, ...}. Also, the different power loss terms P V,i in the cost function K are weighted differently, whereby the weighting can in turn depend on certain parameters (such as one of the temperatures or the speed), so that certain parameter ranges can be avoided by giving them a high weighting.

[0039] In the optimization, the speed n can be varied as a free parameter so that the cost function is minimized. The displacement V g is obtained taking leakage into account using the equation given above for a given target volume flow Q soll from the speed. Alternatively, the displacement could be varied, with the speed being considered the dependent variable based on the equation given above.

[0040] The optimization can be performed within the framework of the operating strategy, for example, by the module 56 that implements the operating strategy. For this purpose, an optimization function 92 or optimization functionality is included in the module 56, which determines the optimal speed using a method according to the invention, which is used as the target speed 58 or (e.g., if further determination steps are performed in addition to the optimization) based on which the target speed 58 is determined.

[0041] Fig. 3 shows a flowchart of the method for determining an optimal speed according to one embodiment of the invention. As explained above, the method can be implemented by an electronic controller (processing unit) of the pressure medium supply device of the electro-hydraulic system, e.g., as part of an operating strategy. It is assumed that a target volume flow is specified that is to be delivered by the hydraulic pump or provided to one or more hydraulic consumers (the target volume flow is determined, e.g., based on input signals that are acquired by a user of the machine in which the electro-hydraulic system is used, using a user interface, such as a joystick).

[0042] The method according to the invention provides a fast method for determining the optimal speed, allowing the optimization to be continuously repeated to ensure optimal operation at the system level at all times. Continuous repetition is useful because the target specifications (or can) continuously change dynamically, or because parameters on which the power loss terms depend can change.

[0043] In step 110, a minimum speed value n min based on the target volume flow Q to be delivered by the hydraulic pump soll of the pressure medium, taking into account in particular an estimated (or well-approximated) leakage, e.g. at maximum displacement.

[0044] For example, the equation n min · V g,max = Q soll + Q Leck,estim evaluated to determine the minimum speed value n min to determine, where Vg,max is the maximum displacement and Q Leck,estim The estimated leakage flow rate, particularly at maximum displacement. In general, leakage can depend on other variables besides displacement, such as the pressure of the pressure medium and the rotational speed, so an approximation or estimate is initially used. For example, the estimated leakage flow rate can correspond to a maximum leakage, a minimum leakage, or an average leakage within a range of possible leaks at maximum displacement.

[0045] It is also conceivable that another suitably determined value for the estimated leakage volume flow Q Leck,estim is used.

[0046] In step 120, several comparison speed values ​​(n0, n1, ...,n M), wherein a smallest comparison speed value of the plurality of comparison speed values ​​is equal to or greater than the minimum speed value. In addition, this determination can be made such that a largest comparison speed value of the plurality of comparison speed values ​​is equal to or less than a maximum or reference speed value of the hydraulic pump. A finite number of comparison speed values ​​is determined. In step 120, one of the comparison speed values ​​is selected, for which the further steps 130 to 170 are carried out, wherein after the further steps 130 to 170 have been carried out, a further one of the comparison speed values ​​is selected, so that an overall loop is formed. In each case, one of the comparison speed values ​​that has not been selected before is selected. The further steps 130 to 170 are carried out accordingly for each of the plurality of comparison speed values.

[0047] When determining the plurality of comparison speed values, the procedure can in particular be such that a speed interval is determined that lies in the maximum interval defined by the minimum speed value and the reference speed value (or another predetermined upper limit), i.e. such that the speed interval is a sub-interval of the maximum interval, also including the case that the speed interval is equal to the maximum interval. The plurality of comparison speed values ​​are then determined as speed values ​​in the speed interval. For example, speed values ​​in the speed interval can be selected as comparison speed values ​​that lie on a predetermined grid, such as a grid with points (i.e. speed values) that are the same distance from one another (i.e. neighboring points of the grid are each the same distance from one another).

[0048] It is possible for all comparison speed values ​​to be determined before performing the further steps 130 to 170. Alternatively, it is also possible for the determination to be carried out partly in parallel with or alternating with these further steps, wherein it is particularly conceivable for further comparison speed values ​​to be determined depending on the result of the further steps 130 to 170.

[0049] In the optional step 130, the respectively selected comparison speed value n i a displacement V g (n i ) or a swivel angle is determined taking into account the estimated leakage so that the target volume flow is achieved.

[0050] The Repression V g (n i ) is determined in such a way that: n i · V g( n i) = Q soll + Q Leck,estim , where again the same value for estimated leakage flow rate Q Leck,estimas can be used in step 110.

[0051] Furthermore, in step 130, an exact leakage volume flow and / or a friction torque M R for the speed value n selected from the respective comparison speed value i certain displacement V g (n i ) can be determined. For this purpose, characteristic maps of the hydraulic pump can be used, which depend on the speed and displacement as well as other variables, e.g., the pressure of the pressure medium at the hydraulic pump. For example, the characteristic maps can be expressed as functions f(p, V g , n), where p is the pressure, V g The displacement and the n speed are used to determine the exact leakage flow rate and friction torque, respectively. The term "friction torque" refers to the torque caused by friction in the hydraulic pump.

[0052] In the optional step 140, it can be checked whether (for the respective selected comparison speed value n i ) the electric drive is capable of delivering an effective torque M eff which is required by the hydraulic pump to supply pressure medium with a given displacement (here the displacement V determined by the selected reference speed value). g (n i )) and a given pressure p. This test takes particular account of the reference speed value and / or a DC voltage at the inverter. Characteristic maps stored, for example, in an electronic control system that implements the method can be used for the test. The effective torque M eff is determined by a theoretical hydraulic pump torque M th , to which further terms may be added. The theoretical hydraulic pump torque M threfers to the torque caused by the pressure of the pressure medium at a given displacement, ie this is proportional to the product of displacement and pressure (M th~ p · V g ). If the friction torque M R calculated as explained above, this can be added (as another term) to the theoretical hydraulic pump torque to obtain the effective torque: M eff = M th + M R If this test shows that the electric drive is not capable of delivering the effective torque M eff is applied for the respective selected comparison speed value n i The further steps 150 to 180 are omitted and, for example, the system returns to step 120 to select the next comparison speed value. Otherwise, ie, if the electric drive is capable of generating the effective torque, the system continues with the further steps 150 to 180.

[0053] In step 150, a hydraulic pump power loss is determined, i.e., a pump power loss term is evaluated. This depends not only on the speed (i.e., the respective speed comparison value) as described above, but also on one or more of the delivered volume flow and the displacement (determined at the respective speed comparison value, as described above). In principle, the hydraulic pump power loss is determined by leakage losses plus friction losses.

[0054] In step 160, a power loss of the electric machine is determined, ie an electric machine power loss term is evaluated.

[0055] In step 170, a power loss of the inverter is determined, ie an inverter power loss term is evaluated.

[0056] In addition to the speed (i.e. the respective speed comparison value), as described above, the power losses of the electrical machine and the inverter are particularly dependent on one or more of: the effective torque, a DC voltage at the inverter and, if applicable, a temperature of the electrical machine or the inverter.

[0057] In step 180, the power losses of the hydraulic pump, the electric motor, and the inverter are added to determine the total power loss. This corresponds to the evaluation of the cost function K introduced above.

[0058] Generally speaking, in steps 130 to 180, which together form a step 190, a respective comparison value (total power loss or, more generally, comparison value corresponding to the cost function) is determined for at least some of the comparison speed values ​​determined in step 120, wherein the comparison value is determined in each case using a function referred to as a cost function, which includes a sum of at least one speed-dependent power loss term of the electric drive and at least one speed-dependent power loss term of the hydraulic pump. If step 140 is provided, the case may arise that a comparison value is not determined for all comparison speed values. More generally, other embodiments are also conceivable in which, depending on certain conditions, a comparison value is not determined for all comparison speed values.

[0059] In step 200, the smallest of the comparison values ​​is determined. In step 210, the comparison speed value having the smallest comparison value is set or determined as the optimal speed value and can be output or transmitted for further processing, for example to a control function of the electric drive and / or the hydraulic pump. In addition, the minimum speed value (determined in step 110) can be output or transmitted for further processing; this can be used in further processing as an optional speed value instead of the optimal speed value, for example, if additional conditions or circumstances are taken into account in further processing, so that if these conditions exist, the use of the optimal speed value is not possible.

[0060] In step 220, in particular, the electric drive is controlled at a target speed based on this optimal speed value (e.g., the target speed, possibly taking into account a gear ratio between the electric machine and the hydraulic pump, is equal to the optimal speed value, or further processing, such as filtering or similar, is provided to obtain the target speed, again possibly taking into account a gear ratio). The displacement of the hydraulic pump is adjusted such that, with the determined optimal speed value, the target volume flow is achieved, taking into account the leakage volume flow, in particular the exact leakage volume flow (as determined in step 130).

Claims

[1] Method for determining an optimum speed of a pressure medium supply device (10) of an electro-hydraulic system, which has an electric drive (4) and a hydraulic pump (2) coupled thereto, which delivers pressure medium, wherein the electric drive (4) drives the hydraulic pump (2) according to a rotational speed and wherein the hydraulic pump has an adjustable displacement, wherein a minimum rotational speed value is determined (110) based on a desired volume flow (54) of the pressure medium requested by the pressure medium supply device (10); wherein a plurality of comparison speed values ​​are determined (120) such that a smallest of the plurality of comparison speed values ​​is equal to or greater than the minimum speed value and a largest of the plurality of comparison speed values ​​is equal to or less than a predetermined maximum speed value; wherein, for at least some of the plurality of comparison speed values, a comparison value corresponding to the respective comparison speed value is calculated (190) by means of a cost function which includes a sum (180) of at least one speed-dependent power loss term of the electric drive (4) and a speed-dependent power loss term of the hydraulic pump (2); and wherein the comparison speed value having the smallest comparison value is determined as the optimal speed value (210). [2] Method according to one of the preceding claims, wherein, upon repeated execution of the method, the plurality of comparison speed values ​​are determined during a later execution such that the optimal speed value of an earlier execution, in particular of the immediately preceding execution, lies between the smallest and a largest of the plurality of comparison speed values; wherein a first difference between the largest and the smallest of the plurality of comparison speed values ​​of the later execution is smaller than a second difference between the maximum speed value and the minimum speed value of the later execution. [3] The method according to claim 2, wherein an upper distance between the largest of the plurality of comparison speed values ​​of the later execution and the optimal speed value of the earlier execution is greater than a lower distance between the smallest of the plurality of comparison speed values ​​of the later execution and the optimal speed value of the earlier execution. [4] The method according to claim 2 or 3, wherein a ratio of the first to the second difference is less than 0.

8. [5] Method according to one of the preceding claims, the comparison speed values ​​are evenly spaced from one another. [6] Method according to one of the preceding claims, wherein, when determining (120) the plurality of comparison speed values, the comparison speed values ​​are selected from a predetermined speed value grid; and / or wherein, when determining (120) the plurality of comparison speed values, the comparison speed values ​​are selected from a speed value grid which is determined relative to the minimum speed value or, when the method is carried out repeatedly, to the optimum speed value of a previous execution, in particular the immediately preceding execution. [7] Method according to one of the preceding claims, wherein, upon repeated implementation, a distance between the comparison speed values ​​of the current implementation and / or a distance between the largest and the smallest of the comparison speed values ​​of the current implementation is / are determined depending on a change in the target volume flow (54) between a previous implementation, in particular the immediately previous implementation, and the current implementation. [8] Method according to one of the preceding claims, wherein the power loss term of the hydraulic pump (2) includes a sum of speed-dependent leakage losses and friction losses or is given as such a sum; and / or wherein the electric drive (4) comprises an electric machine (6) and an inverter (8), wherein the at least one power loss term of the electric drive (4) includes a power loss term of the electric machine (6) and / or a power loss term of the inverter (8); wherein the power loss term of the electric machine (6) and / or the power loss term of the inverter (8) are dependent on the respective comparison speed value and one or more of: an effective torque, a DC voltage at the inverter, and a temperature of the electric machine or the inverter. [9] Method according to one of the preceding claims, wherein the at least one power loss term of the hydraulic pump (2) includes a leakage power loss term and / or a friction power loss term; wherein for each of the comparison speed values: a corresponding displacement is determined taking into account an estimated leakage and the respective comparison speed value (130), so that the target volume flow is achieved, an exact leakage flow rate and / or an exact friction torque is determined from the displacement, the respective reference speed value and a given pressure difference (130), where the leakage power loss term and / or the friction power loss term is / are determined from the exact leakage volume flow and / or the exact friction torque. [10] Method according to one of the preceding claims, wherein in determining the comparison values ​​for each of the comparison speed values: a friction torque of the hydraulic pump is determined based on the respective comparison speed value, an effective torque is determined from the friction torque and a theoretical torque of the hydraulic pump, which is determined by the desired volume flow to be delivered at a given pressure difference across the hydraulic pump, it is checked (140) whether the electric drive is capable of generating or providing the effective torque, and, if the test reveals that the electric drive is not capable of producing the effective torque, no comparison value is determined for the respective comparison speed value; During the test, particular consideration is given to the respective comparison speed value and / or a direct voltage of the electric drive or of an inverter of the electric drive. [11] Method according to one of the preceding claims, wherein an estimated leakage volume flow, in particular at maximum displacement, is taken into account when determining the minimum speed value. [12] Method for controlling a pressure medium supply device (10) of an electro-hydraulic system, which has an electric drive (4) and a hydraulic pump (2) coupled thereto, which delivers pressure medium, wherein the electric drive (4) drives the hydraulic pump (2) according to a speed and wherein the hydraulic pump (2) has an adjustable displacement, wherein an optimal speed value is determined for a desired volume flow to be conveyed using the method according to one of the preceding claims; wherein the electric drive (4) is controlled (220) so that the hydraulic pump is driven at the optimum speed value; and wherein the hydraulic pump (2) is adjusted so that, with the determined optimum speed value, the target volume flow is achieved taking into account a leakage volume flow. [13] Computing unit (18) comprising a processor, configured to carry out the method according to any one of the preceding claims. [14] A computer program comprising instructions which, when executed by a computer, cause the computer to carry out the method according to any one of claims 1 to 12. [15] A computer-readable data carrier on which the computer program according to claim 14 is stored.

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