Method for operating a pressure medium supply device of an electrohydraulic system

Abstract

The invention relates to a method for operating a pressure medium supply device (10) of an electrohydraulic system, wherein the pressure medium supply device comprises an electric drive (4) and a hydraulic pump (2) coupled to it, which has an adjustable displacement and delivers the pressure medium, wherein the electric drive is controlled (110) so that the hydraulic pump is driven at a set speed (58, 100), wherein an optimal speed (96) is determined (120) by an operating strategy function (92), which depends on a requested volume flow (54) and / or a requested pressure (52) of the pressure medium delivered by the hydraulic pump, and wherein an adjustment (140) of the set speed (58, 100) according to the optimal speed is carried out when the optimal speed (96) is at least one upper hysteresis value above the set speed or at least one lower hysteresis value below the set speed.where at least one of the upper and lower hysteresis values ​​is not equal to zero.

Description

[0001] The present invention relates to a method for operating 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 operating a pressure medium supply device of an electrohydraulic system, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0004] The proposed method for operating a pressure medium supply device of an electro-hydraulic system, which has an electric drive and a hydraulic pump coupled thereto, uses the measure of controlling the electric drive so that the hydraulic pump is driven at a target speed and of adjusting the target speed according to an optimum speed determined by an operating strategy function if the optimum speed is at least one upper hysteresis value higher than the target speed or at least one lower hysteresis value lower than the target speed, wherein at least one of the upper and lower hysteresis values ​​is not equal to zero. The proposed measure can avoid repeated small changes in the speed of the electric drive and the hydraulic pump at short intervals due to small changes in the optimum speed.This can reduce noise and / or wear.

[0005] The operating strategy function determines, generally speaking, a speed referred to as the optimum speed or optimal speed, so that operation of the pressure medium supply device at the optimum speed is ideal or optimal with regard to a specific intention or goal (e.g., the lowest possible power loss). The operating strategy function therefore determines the optimum speed at any time according to a predetermined operating strategy. By appropriately defining the lower and upper hysteresis values, it is possible to ensure that this operating intention or goal is met as closely as possible, e.g., within the scope of minor deviations.

[0006] The upper and lower hysteresis values ​​are positive values ​​(i.e., greater than or equal to zero), with at least one being unequal to (i.e., greater than) zero. According to one embodiment, both hysteresis values ​​are greater than zero. Alternatively, one of the two hysteresis values ​​is equal to zero (and the other unequal to, i.e., greater than, zero).

[0007] The electric drive, for example, has an inverter and an electric machine, where thermal losses in particular occur.

[0008] According to one embodiment, the target speed is not adjusted or the target speed remains unchanged if the optimum speed is less than the upper hysteresis value above the target speed and less than the lower hysteresis value below the target speed.

[0009] According to one embodiment, when adjusting the target speed, the target speed is adjusted or tracked toward the optimum speed by the respective hysteresis value. In other words, when adjusting the target speed, if the optimum speed is at least, in particular more than, the upper hysteresis value higher than the target speed, the target speed is set equal to the optimum speed minus the upper hysteresis value. If the optimum speed is at least, in particular more than, the lower hysteresis value lower than the target speed, the target speed is set equal to the optimum speed plus the lower hysteresis value. This allows jumps in the target speed to be avoided.

[0010] According to one embodiment, when adjusting the target speed, the target speed is set equal to the optimum speed. This is useful, for example, if the optimum speed already takes into account any additional conditions.

[0011] According to one embodiment, when adjusting the target speed, if the optimum speed is less than or equal to a (first) maximum speed and greater than or equal to a (first) minimum speed, the target speed is set equal to the optimum speed.

[0012] According to one embodiment, when adjusting the target speed, if the optimum speed is greater than the (first) maximum speed, the target speed is set equal to the (first) maximum speed, and if the optimum speed is less than the (first) minimum speed, the target speed is set equal to the (first) minimum speed.

[0013] According to the two above embodiments, the target speed lies in the range determined by the (first) minimum speed and the (first) maximum speed. The (first) minimum speed can be a predetermined idle speed of the hydraulic pump (e.g., to ensure sufficient lubrication) or can be determined based on a maximum displacement of the hydraulic pump and the requested flow rate. The (first) maximum speed can be a reference speed of the electric drive or electric machine.

[0014] According to one embodiment, the upper hysteresis value is smaller than the lower hysteresis value, wherein a ratio of the upper to the lower hysteresis value is preferably in the range from 0 to 0.9, more preferably in the range from 0.1 to 0.9, and / or wherein the upper hysteresis value is equal to zero. These embodiments result in the dynamics with which changes in the optimum speed from the target speed are tracked being greater towards the top than towards the bottom, so that a rapid increase in the pressure medium requirements or a rapid increase in the requested volume flow can be met. In the second case, ie when the upper hysteresis value is equal to zero, the lower hysteresis value is not equal to zero, since at least one of the two is not equal to zero.

[0015] According to one embodiment, the optimal speed is determined such that an operating strategy functional is optimized. The operating strategy functional includes, in particular, at least one power loss term of the electric drive and / or at least one power loss term of the hydraulic pump. The at least one power loss term of the electric drive can include a power loss term of the inverter and / or a power loss term of the electric machine.

[0016] According to an alternative embodiment, the optimal speed can also be the result of a simplified strategy, whereby the optimal speed is determined as a function of (or as a function of) the current operating point or the volume flow and pressure. This simplified strategy can also be an approximation of an optimized strategy, such as the determination using an operating strategy functional, e.g., a metamodel such as a neural network. Regardless of the implementation of an optimized strategy, the determined target speed may fluctuate considerably under certain circumstances and requires intelligent smoothing (calming or harmonization) within the defined range around the determined target value.

[0017] According to one embodiment, the displacement of the hydraulic pump is determined based on the target speed or based on an actual speed of the hydraulic pump, so that the requested volume flow is achieved, taking into account, in particular, any leakage of the hydraulic pump. The hydraulic pump is adjusted according to the determined displacement.

[0018] According to one embodiment, the upper and / or lower hysteresis value is / are dependent on the optimum speed. This embodiment allows different hysteresis values ​​to be provided for different speed ranges.

[0019] According to one embodiment, the upper hysteresis value depends on the optimum speed, so that if the optimum speed is less than a second maximum speed, the sum of the optimum speed and the upper hysteresis value is less than the second maximum speed or equal to the second maximum speed. This ensures that the second maximum speed (which is in particular equal to the (first) maximum speed introduced above) can be achieved in any case. The second maximum speed corresponds (i.e., is, possibly taking a gear ratio into account), for example, to a maximum speed or a reference speed of the electric drive or the electric machine.

[0020] According to one embodiment, the upper hysteresis value is dependent on the optimal speed in a range in which the distance between a third maximum speed (which is in particular equal to the (first) and / or second maximum speed introduced above) and the optimal speed is less than a predetermined upper distance value, and is in particular constant outside of this range. According to one embodiment, the lower hysteresis value is dependent on the optimal speed in a range in which the distance between a third minimum speed (which is in particular equal to the (first) and / or (second) minimum speed introduced above) and the optimal speed is less than a predetermined lower distance value, and is in particular constant outside of this range. This embodiment enables an adaptation of the hysteresis values ​​in the vicinity of the third maximum speed or minimum speed.The (upper) range in which the distance between the third maximum speed and the optimum speed is smaller than the predetermined upper distance value can be specified, for example, as an absolute value (in the form of a speed) or as a relative value, for example as a fraction (approximately 0.2, 0.1 or 0.5) of the maximum speed or of the distance between the (third) maximum speed and the minimum speed. Likewise, the (lower) range in which the distance between the third minimum speed and the optimum speed is smaller than the predetermined upper distance value can be specified, for example, as an absolute value (in the form of a speed) or as a relative value, for example as a fraction (approximately 0.2, 0.1 or 0.5) of the third minimum speed or of the distance between the third maximum speed and the minimum speed.

[0021] According to one embodiment, in the range in which the distance between the third maximum speed and the optimum speed is smaller than the predetermined upper distance value, the upper hysteresis value is dependent on the optimum speed in such a way that the upper hysteresis value becomes smaller as the distance between the third maximum speed and the optimum speed decreases and, in particular, is equal to zero when the third maximum speed is equal to the optimum speed. According to one embodiment, in the range in which the distance between the third minimum speed and the optimum speed is smaller than the predetermined lower distance value, the lower hysteresis value is dependent on the optimum speed in such a way that the lower hysteresis value becomes smaller as the distance between the third minimum speed and the optimum speed decreases and, in particular, is equal to zero when the third minimum speed is equal to the optimum speed.

[0022] For example, in the range in which the distance between the third maximum speed and the optimum speed is smaller than the predetermined upper distance value, the upper hysteresis value can be dependent on the optimum speed in such a way that the upper hysteresis value is less than or equal to the product of a certain upper factor and the distance between the third maximum speed and the optimum speed, where the certain upper factor is greater than or equal to 0 and less than 1. Likewise, for example, in the range in which the distance between the third minimum speed and the optimum speed is smaller than the predetermined lower distance value, the lower hysteresis value can be dependent on the optimum speed in such a way that the lower hysteresis value is less than or equal to the product of a certain lower factor and the distance between the third minimum speed and the optimum speed, where the certain lower factor is greater than or equal to 0 and less than 1.

[0023] A computing unit according to the invention, e.g. a control unit of an electro-hydraulic system or drive system of a mobile work machine, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0024] 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.

[0025] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0026] 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.

[0027] 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 flow chart of the method for operating a pressure medium supply device of an electrohydraulic system according to an embodiment of the invention. Detailed description of the drawing

[0028] Fig. 1 shows an exemplary electro-hydraulic system or drive 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 that measures the speed of the electric machine and / or the hydraulic pump; a displacement sensor that 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 so-called control-engineered observers) (i.e., to partially use "virtual measured values" from "virtual sensors").

[0033] To control the pressure medium supply device 10 or within the scope of such a control, the electronic control can be set up (e.g. by executing corresponding computer programs) to carry out a control process (such as 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.

[0034] Fig. 2 shows a control system for controlling an electric drive 64 and a hydraulic pump 72. A target pressure or a requested pressure 52 and a target volume flow or a requested volume flow 54 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 in accordance with 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 ).

[0039] 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 ).

[0040] 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.

[0041] 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.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 interconnected or at a cooling device for pressure medium can be taken into account.

[0042] 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)

[0043] The cost function includes power loss terms for the electric machine power loss (electric machine power loss term), for the inverter power loss term, and for 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.

[0044] In the optimization, the speed n is 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 rotational speed. Alternatively, the displacement could be varied, whereby the rotational speed can be regarded as the dependent variable based on the equation given above. The optimization can be carried out as part of the operating strategy, for example by the module 56 that implements the operating strategy. For this purpose, an operating strategy function 92 or optimization functionality is provided, which is included, for example, in the module 56 and by which the optimal rotational speed 96 is determined, which is used as the target rotational speed 58 or (for example, if further determination steps are carried out in addition to the optimization) based on which the target rotational speed 58 is determined.

[0045] In the above explanations to Fig. 2, reference was made by way of example to the fact that the power loss should be minimized or that a cost function that includes power loss terms should be minimized. This minimization is carried out using an operating strategy function 92. More generally, in addition to this optimization (here minimization) with regard to power loss, other operating objectives are also conceivable, which can be implemented, for example, as an optimization problem for determining an optimal speed and for which the corresponding optimal speed is determined by an operating strategy function. Even more generally, an operating strategy function can be used to determine an optimal speed that does not include optimization. In these general cases, too, the optimal speed can be used as the target speed, or the target speed 58 can be determined based on the optimal speed.

[0046] A direct use of the optimum speed as the target speed can be problematic, as this can lead to undesirable operating behavior (constant changing of the speed if the optimum speed changes continuously with small changes in the parameters of the operating strategy function (or also the pressure or the target volume flow)) of the pressure medium supply device, which is associated with increased noise generation and / or increased wear. According to the invention, it is therefore provided that the hydraulic pump or the electric drive is not operated directly at the optimum speed, but rather that additional hysteresis values ​​are provided. For this purpose, for example, a hysteresis functionality 94 can be additionally provided in module 56, which implements the operating strategy, which determines the target speed 58 from the optimum speed 96.

[0047] Fig. Figure 3 shows a flowchart of the method for operating a pressure medium supply device of an electrohydraulic system according to one embodiment of the invention. The pressure medium supply device has an electric drive (with an electric motor and an inverter) and an adjustable hydraulic machine or adjustable hydraulic pump. As explained above, the method can be implemented by an electronic controller (processing unit) of the pressure medium supply device of the electrohydraulic system.

[0048] In step 110, the electric drive is controlled so that the hydraulic pump has a (current) target speed of 100. The inverter is thus controlled such that, with a gear ratio of 1 between the electric machine and the hydraulic pump, the electric machine also has the target speed or is adjusted to it, or such that, with a gear ratio not equal to 1 between the electric machine and the hydraulic pump, the speed of the electric machine corresponds to the target speed taking the gear ratio into account. In optional step 115, a displacement of the hydraulic pump is determined so that a requested volume flow of pressure medium is obtained, with particular consideration given to leakage. The hydraulic pump is then adjusted according to the determined displacement. Steps 110 and 115 are carried out continuously and correspond approximately to blocks 62 and 68 of the Fig. 2.

[0049] In step 120, an optimum speed is determined by means of an operating strategy function. The operating strategy function has as variables a target pressure 52 and / or a target volume flow 54 and optionally at least one further variable, ie the optimum speed depends on this variable or on these variables. The operating strategy function can, of course, e.g., as described above in connection with Fig.2 explained may depend on further variables. The operating strategy function can in particular be implemented by means of an operating strategy functional to be optimized, wherein the optimum speed is determined such that this operating strategy functional is optimized. Step 120 is carried out continuously, so that the optimum speed is continuously redetermined or can continuously change (if the variables on which the operating strategy function depends change). The term "continuously" is to be understood here, for example, to mean that the optimum speed is redetermined at time intervals determined by the evaluation (for example by an electronic control or a computing unit) of the operating strategy function. For example, the optimum speed can be redetermined or updated at regularly spaced points in time.

[0050] For the respective current optimum speed, a check is carried out in step 130, which is also carried out continuously, to determine whether the optimum speed is greater than the (current) target speed 100 plus an upper hysteresis value or less than the (current) target speed 100 minus a lower hysteresis, whereby at least one of the two hysteresis values ​​is not equal to zero and it is assumed that the hysteresis values ​​are positive values, i.e. greater than or equal to zero. If neither of these two conditions (optimum speed greater than the target speed plus the upper hysteresis value or less than the target speed minus the lower hysteresis) is met, step 130 is carried out for the next optimum speed, i.e. the target speed is not adjusted or remains unchanged (arrow 135). This means that within the tolerance band (defined by the two hysteresis values) the target speed is not adjusted.

[0051] If, on the other hand, one of these conditions is met, i.e., if the optimum speed is more than the upper hysteresis value above the (current) target speed or more than the lower hysteresis value below the (current) target speed, the target speed is adjusted to 100 in step 140. When adjusting the target speed, optionally taking other conditions into account, the target speed is changed so that it is equal to the optimum speed (for which the check was performed in step 130) or is set equal to it. The target speed can also be changed in such a way that it is pulled along or tracked in the direction of the optimum speed change, in particular at a distance of the respective hysteresis (which was exceeded) from the optimum speed. This prevents the target speed from jumping. Other conditions, if present, can alternatively already be taken into account in the operating strategy function, i.e.In this case, the target speed can always be set equal to the optimum speed during adjustment. After step 140, step 130 is performed again for the next optimum speed.

[0052] An example of a possible further condition is that the target speed should be in a specific first speed range, between a minimum speed and a maximum speed. If the optimum speed is in the specific first speed range, the target speed is set equal to the optimum speed, and if the optimum speed is not in the first speed range, the target speed is set equal to the minimum speed if the optimum speed is below the minimum speed, or equal to the maximum speed if the optimum speed is above the maximum speed. The minimum speed is, for example, indirectly determined by the maximum displacement of the hydraulic pump, i.e.so that the target flow rate is obtained when the minimum speed is set at maximum displacement, again taking any leakage into account (i.e., the following applies: minimum speed times maximum displacement equals target flow rate plus leakage flow rate). The maximum speed corresponds, for example, to a maximum speed or a reference speed of the electric motor.

[0053] The upper and / or lower hysteresis value can also be dependent on the (current) target speed 100. For example, a specific second speed range can be provided, which is in particular a (true) sub-range of the first speed range. If the target speed is in the second speed range, the upper and lower hysteresis values ​​are, for example, constant. If the target speed is above the second speed range, the upper hysteresis value depends on the target speed, for example, in such a way that it decreases towards the maximum speed and becomes zero when the maximum speed is reached (the lower hysteresis value remains, for example, the same value it has in the second speed range).If the target speed is below the second speed range, the lower hysteresis value depends on the target speed, for example in such a way that it decreases towards the minimum speed and becomes zero when the minimum speed is reached (the upper hysteresis value remains, for example, the same as the value it has in the second speed range). In other words, this means that the upper hysteresis value depends on the target speed if the distance between the maximum speed and the target speed is less than a predetermined upper distance value, and is in particular constant outside of this range, or that the lower hysteresis value depends on the target speed in a range in which the distance between the minimum speed and the target speed is less than a predetermined lower distance value, and is in particular constant outside of this range.These designs ensure that the maximum speed and the minimum speed can be achieved.

Claims

[1] Method for operating a pressure medium supply device (10) of an electro-hydraulic system, wherein the pressure medium supply device has an electric drive (4) and a hydraulic pump (2) coupled thereto, which has an adjustable displacement and delivers the pressure medium, wherein the electric drive is controlled (110) so that the hydraulic pump is driven at a desired speed (58, 100); wherein an operating strategy function (92) determines (120) an optimum speed (96) which is dependent on a requested volume flow (54) and / or a requested pressure (52) of the pressure medium delivered by the hydraulic pump; wherein an adjustment (140) of the target speed (58, 100) is carried out in accordance with the optimum speed when the optimum speed (96) is at least one upper hysteresis value higher than the target speed (58, 100) or at least one lower hysteresis value lower than the target speed (58, 100), wherein at least one of the upper and lower hysteresis values is not equal to zero. [2] Method according to claim 1, wherein, if the optimum speed (96) is less than the upper hysteresis value above the target speed (58, 100) and less than the lower hysteresis value below the target speed, the target speed is not adjusted or remains unchanged (135). [3] Method according to one of claims 1 or 2, wherein during the adjustment (140) of the target speed (58, 100), the target speed is adjusted or tracked at a distance of the respective hysteresis value in the direction of the optimum speed (96). [4] Method according to one of claims 1 or 2, wherein when adjusting (140) the target speed (58, 100), the target speed is set equal to the optimum speed (96). [5] Method according to one of the preceding claims, wherein when adjusting (140) the target speed, if the optimum speed (96) is greater than a maximum speed, the target speed is set equal to the maximum speed, and if the optimum speed (96) is less than a minimum speed, the target speed (58, 100) is set equal to the minimum speed. [6] Method according to one of the preceding claims, wherein the upper hysteresis value is smaller than the lower hysteresis value; wherein a ratio of the upper to the lower hysteresis value is preferably in the range from 0 to 0.9, more preferably in the range from 0.1 to 0.9; and / or wherein the upper hysteresis value is zero. [7] Method according to one of the preceding claims, wherein the optimum speed (96) is determined such that an operating strategy functional is optimized; wherein the operating strategy functional includes in particular at least one power loss term of the electric drive and / or at least one power loss term of the hydraulic pump. [8] Method according to one of the preceding claims, wherein the displacement of the hydraulic pump (2) is determined based on the target speed (58, 100) or based on an actual speed of the hydraulic pump, so that the requested volume flow (54) is achieved, wherein in particular a leakage of the hydraulic pump (2) is taken into account; and wherein the hydraulic pump is adjusted according to the determined displacement. [9] Method according to one of the preceding claims, wherein the upper and / or the lower hysteresis value is / are dependent on the target speed (58, 100) and / or on the optimum speed (96). [10] Method according to one of the preceding claims, wherein the upper hysteresis value is dependent on the optimum speed (96), so that if the optimum speed (96) is less than a second maximum speed, the sum of the optimum speed (96) and the upper hysteresis is equal to the second maximum speed or less than the second maximum speed; and / or wherein the lower hysteresis value is dependent on the optimum speed (96), so that if the optimum speed (96) is greater than a second minimum speed, the difference between the optimum speed (96) and the lower hysteresis is equal to the second minimum speed or greater than the second minimum speed. [11] Method according to one of the preceding claims, wherein the upper hysteresis value is dependent on the optimum speed in a range in which the distance between a third maximum speed and the optimum speed (96) is smaller than a predetermined upper distance value, and is in particular constant outside this range; and / or wherein the lower hysteresis value is dependent on the optimum speed (96) in a range in which the distance between a third minimum speed and the optimum speed (96) is smaller than a predetermined lower distance value, and is in particular constant outside this range. [12] Method according to claim 11, wherein, in the range in which the distance between the third maximum speed and the optimum speed (96) is smaller than the predetermined upper distance value, the upper hysteresis value is dependent on the optimum speed (96) such that the upper hysteresis value becomes smaller with decreasing distance between the third maximum speed and the optimum speed (96) and is in particular equal to zero when the third maximum speed is equal to the optimum speed (96); and / or wherein in the range in which the distance between the third minimum speed and the optimum speed (96) is smaller than the predetermined lower distance value, the lower hysteresis value is dependent on the optimum speed (96) such that the lower hysteresis value becomes smaller with decreasing distance between the third maximum speed and the optimum speed (96) and is in particular equal to zero when the third maximum speed is equal to the optimum speed (96). [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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