Method for reducing power losses in an electrohydraulic system

Abstract

The invention relates to a method for reducing power losses in an electrohydraulic system comprising an electric drive (3) with at least one electric drive component and at least one hydraulic machine (8, 10) coupled to the electric drive and driven by it according to a rotational speed, wherein the electrohydraulic system has several power losses which depend on the rotational speed and / or an operating point of the electrohydraulic system and / or on other detected quantities, wherein the several power losses include at least one power loss of the at least one electric drive component and at least one power loss of the at least one hydraulic machine, each of which depends on the rotational speed;wherein a target speed (58) is determined for the speed as a function of the operating point of the electro-hydraulic system (130), wherein the target speed is determined such that it optimizes a function to be optimized which includes a sum of the several power losses.;

Description

[0001] The present invention relates to a method for reducing power losses in an electrohydraulic system, as well as a computing unit and a computer program for carrying it out, and an electrohydraulic system. Background of the invention

[0002] Machines, such as mobile construction equipment like excavators, loaders, or bulldozers, typically have a hydraulic system that moves the machine's components, such as the excavator's arm sections. This system incorporates one or more hydraulic pumps to supply pressure. These pumps can be driven by an electric motor via a shaft. If multiple pumps are connected to the same shaft, they can all be driven by the electric motor.

[0003] DE102013006137A1 discloses a method for controlling a pressure medium supply for at least one hydraulic actuator driven by a variable-speed pump. The method optimizes the speed setpoint using an objective function that includes minimizing power loss. Disclosure of the invention

[0004] According to the invention, a method for reducing power losses in an electrohydraulic system, a computing unit and a computer program for its implementation, and an electrohydraulic system with the features of the independent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.

[0005] The invention employs a method of determining a target speed of the hydraulic machine or the electric drive in an electrohydraulic system, in which a hydraulic machine (hydraulic pump) is driven by an electric drive, as a function of an operating state of the electrohydraulic system. This is achieved by optimizing a function to be optimized, which includes a sum of power losses of the electrohydraulic system, wherein at least speed-dependent power losses are provided for electric drive components and the hydraulic machine. The power losses depend on parameters that characterize the state of the electrohydraulic system, namely the speed and / or an operating point of the electrohydraulic system and / or other measured parameters.This makes it possible to reduce the total power loss depending on the respective state of the electro-hydraulic system, especially compared to using a target speed that was determined independently of the operating point and / or other parameters.

[0006] The operating point characterizes the state and / or properties of the electrohydraulic system, at least partially. The operating point is characterized or defined in particular by one or more of the following quantities (or parameters): at least one target pressure of the at least one hydraulic machine, at least one target flow rate of the at least one hydraulic machine, at least one target torque of the at least one hydraulic machine, at least one target swashplate angle (or at least one target displacement) of the at least one hydraulic machine, a target noise level of the electrohydraulic system, at least one actual pressure of the at least one hydraulic machine, at least one actual flow rate of the at least one hydraulic machine, at least one actual torque of the at least one hydraulic machine, at least one actual swashplate angle (or at least one target displacement) of the at least one hydraulic machine.The target values ​​are at least one actual displacement of the at least one hydraulic machine and one actual noise level of the electro-hydraulic system (where other or additional quantities are also conceivable). The target values ​​can be considered together as the target operating point or as quantities that characterize the target operating point. The actual values ​​can also be considered together as the actual operating point or as quantities that characterize the actual operating point. The target values ​​are typically values ​​specified for a control system. The actual values ​​can be measured or recorded using sensors. Likewise, or additionally, the actual values ​​can be derived from target values ​​and / or measured actual values ​​and / or calculated and / or estimated, e.g., using suitable formulas and / or one or more suitable models.It may happen that some of the quantities cannot be included in the operating point at the same time; for example, it is typically not possible to specify a target pressure and a target volume flow rate for a single hydraulic machine (in which case, for example, the target pressure and the actual pressure are included in the quantities that characterize the operating point).

[0007] Other recorded quantities may include quantities measured with sensors, e.g., measured temperatures or pressures of the pressure medium, and / or calculated or estimated quantities, e.g., using a model.

[0008] In one embodiment, the sum of several power losses is calculated as a weighted sum of the power losses, in which one or more of the power losses are weighted by a respective weighting factor. In particular, the weighting factors each depend on at least one parameter, where the at least one parameter is selected from the group that includes the target speed, a quantity that characterizes the operating point, and at least one other measured quantity. This enables the optimization of power losses taking into account constraints implemented by the weighting factors.

[0009] In a further embodiment, the at least one parameter or at least one other measured quantity includes at least one temperature of the at least one drive component, wherein the weighting factors include at least one drive weighting factor for the at least one power loss of the at least one drive component, which depends on the at least one temperature. In particular, the at least one drive weighting factor increases when the at least one temperature exceeds at least one predetermined temperature threshold and / or is above the at least one predetermined temperature threshold. The increase from the temperature threshold can be continuous, e.g., according to a monotonically or strictly monotonically increasing function, and / or in one or more steps. The steepness of the increase can be, for example,The temperature threshold can be determined, for example based on data sheets of the electric machine and / or through tests, in such a way that a critical temperature of the electric machine, at which a reduction in power becomes necessary, is not reached if possible. The level of at least one predetermined temperature threshold, as well as the slope or step size with which the weighting factor increases, can be appropriately selected (taking into account the dynamics of the electric drive and its heat generation and dissipation) to prevent overheating.

[0010] In one embodiment, the electrohydraulic system comprises at least one further component in which power loss occurs, the sum of which includes at least one power loss for the at least one further component. The at least one further component can, for example, include at least one cooling device. The at least one cooling device can be, for instance, one or more components such as a fan for the electric drive, a cooling circuit pump (in particular for the electric drive), a cooler for hydraulic fluid, or the like.

[0011] The electro-hydraulic system can, in particular, have two hydraulic circuits, each supplied with hydraulic fluid by a hydraulic machine, wherein the two circuits can be hydraulically connected by a summing device, in particular a summing valve. In this case, in one embodiment, at least one further component can include at least the summing device. The function to be optimized accordingly includes a summand (power loss of the summing device) for the summing device (summing valve). Power loss occurs at the summing device because the hydraulic pressure in the two circuits differs, and consequently a pressure drop occurs, resulting in the conversion of hydraulic energy into heat.

[0012] In one embodiment, the summing device has a state according to which the circuits are either interconnected or disconnected, wherein the state of the summing device is a free parameter of the function to be optimized, which is further varied with respect to this state. In this embodiment, for example, the interconnection of the circuits can depend on the state of the summing device in which the function to be optimized is optimal. That is, the circuits are interconnected when the optimum of the function to be optimized (e.g., the minimum of a cost function) corresponds to the interconnected state, and disconnected when the optimum of the function to be optimized corresponds to the disconnected state.The summation loss power term can optionally be additionally weighted with a (summation) weighting factor, which depends on whether there is a requirement to connect the circuits (e.g., to meet high power requirements in one circuit) (e.g., equal to one if such a requirement does not exist, and less than 1 if such a requirement exists).

[0013] A computing unit according to the invention, e.g. a control unit of an electro-hydraulic system of a mobile working machine, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0014] Implementing 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, as this incurs particularly low costs, especially if an executing control unit is already available for other tasks. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical storage media, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading a program via computer networks (Internet, intranet, etc.) is also possible.

[0015] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0016] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0017] The invention is schematically illustrated in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Character description

[0018] Figur 1 The image shows an example of a construction machine, namely a mobile excavator. Figur 2 shows an exemplary electro-hydraulic system with two circuits, such as that used in the excavator of the Figur 1 can be used. Figur 3 shows a control loop for controlling an electric machine and a hydraulic pump. Figur 4 shows a flowchart according to one embodiment of the method for reducing the thermal load of an electric drive in an electrohydraulic system. Detailed description of the drawing

[0019] Figur 1 Figure 3 shows an example of a work machine, namely a mobile excavator 30. The excavator 30 comprises a chassis 32 and a rotatable superstructure 34 mounted on it. Wheels 36 are mounted on the chassis. Rotation of the superstructure relative to the chassis is enabled by a slewing mechanism 38. This rotation can be driven, for example, by an electric drive or electric slewing mechanism drive. A boom or excavator arm 40 is attached to the superstructure 34, at the end of which is a bucket 42. The boom, arm, and bucket are moved or driven, for example, by an electro-hydraulic system 44, i.e., a hydraulic system driven by an electric motor, by means of hydraulic cylinders 46. A battery 48 (but could also be any other electrical energy source such as a fuel cell system or a cable) supplies the electric drive of the slewing mechanism and the electro-hydraulic system with electrical energy.

[0020] Figur 2 shows an exemplary hydraulic or electro-hydraulic system with two circuits, such as that used in the excavator of the Figur 1 The two circuits can either be operated separately or connected to each other via a summing valve (i.e., a summing device).

[0021] An electric battery 2 is shown, which supplies electrical energy to an electric drive 3 of the electro-hydraulic system for driving hydraulic pumps and to an electric rotary drive for driving a rotary mechanism (not shown). The battery 2 can be considered part of the electro-hydraulic system. Alternatively, an external battery could also be used. A different power supply could also be provided instead of a battery. The electric drive 3 of the hydraulic system comprises an inverter 4 (e.g., a DC / AC converter) and an electric motor 6 as its electrical drive components. The electric rotary drive comprises an inverter 5 (e.g., a DC / AC converter) and an electric rotary motor 7 as its electrical components.

[0022] The electric machine 6 is coupled via a shaft to a first hydraulic pump 8 (or hydraulic machine) and a second hydraulic pump 10. A first output channel 14 of the first hydraulic pump 8 is connected to a first hydraulic circuit to supply it with hydraulic fluid (typically hydraulic oil). A second output channel 16 of the second hydraulic pump 10 is connected to a second hydraulic circuit to supply it with hydraulic fluid. Additional hydraulic pumps 12 or auxiliary pumps, for example, are driven via the shaft. These serve, for instance, to provide control pressure for actuating hydraulically or electro-hydraulically operated valves.

[0023] For example, a summing valve 18 is provided with which the two circuits can be hydraulically connected (for example, to meet a high performance requirement in one of the circuits).

[0024] The first circuit connects two hydraulic cylinders 20 as hydraulic consumers (e.g., the movement of the excavator's boom). Figur 1 The hydraulic cylinders 20 are supplied with hydraulic fluid. The flow to and from the hydraulic cylinders 20 is controlled by means of a first valve arrangement 24, which is hydraulically connected to the first output channel 14, to the summing valve 18 and to a reservoir for hydraulic fluid.

[0025] The second circuit supplies two hydraulic cylinders 22, 23 as hydraulic consumers (which, for example, control the movement of a middle arm element and the bucket of the excavator). Figur 1 The hydraulic cylinders 22, 23 are supplied with hydraulic fluid. The flow to and from the hydraulic cylinders 22, 23 is controlled by means of second valve arrangements 26, 27, which are hydraulically connected to the second output channel 14, to the summing valve 18 and to the hydraulic fluid tank.

[0026] The valve arrangements comprise adjustable or adjustable passages, represented as adjustable orifice plates, so that the flow of hydraulic fluid to and from the hydraulic consumers can be controlled by adjusting them. The orifice plates (passages) can be formed, for example, in valves, and in particular directional control valves, where different switching positions, such as different positions of a spool or piston in a directional control valve, correspond to different cross-sectional areas of the orifice plates; that is, the orifice plates or their cross-sections can be adjusted by adjusting the (directional control) valves. The exact design of the valve arrangements, which depends on the specific application, e.g., the machine in which the electrohydraulic system is used, need not be explained here and is generally known to those skilled in the art. Ultimately, the settings of the valve arrangements correspond to specific hydraulic performance requirements, e.g.,a required pressure and / or flow rate that must be met by the hydraulic pumps 8, 10 or the electric drive (inverter 4, electric machine 6).

[0027] Figur 3 Figure 1 shows a control loop for controlling an electric drive 64 and a hydraulic pump 72. At least one pressure 52 and a target flow rate 54 are given, corresponding approximately to a power demand of the consumers. Based on an operating strategy, or by a module 56 that implements the operating strategy, both a target speed 58 and a setpoint 60 for the hydraulic pump are determined. 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 swashplate angle of the hydraulic pump 72 from the setpoint 60 for the hydraulic pump. The leakage 74 of the hydraulic pump can be taken into account. Overall, an effective flow rate 76 is obtained, which should be equal to the target flow rate within the framework of the control system. The power or torque 78 of the hydraulic pump is supplied by the electric motor.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 unit (computing unit) of the electrohydraulic system.

[0028] It applies n · V g = Q soll + Q Leck , i.e., two adjustable parameters, namely the rotational speed n and the repression V g , can be selected to achieve a desired target volume flow rate Q soll to obtain, whereby the leakage volume flow Q Leck This should be taken into account. Due to the constraint imposed by the above equation, there is therefore one degree of freedom or one free parameter (within technical limits).

[0029] Choosing the parameters speed and displacement according to the operating strategy can take into account power losses occurring 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.

[0030] In simplified terms, for a given power input, the power losses of the electric motor and inverter are lower at higher speeds, meaning they operate more efficiently at higher speeds. Conversely, the power loss of the hydraulic pump (at constant pressure) is lower with a larger displacement or lower speed, meaning it operates more efficiently at lower speeds. More generally, power losses are not solely dependent on speed.

[0031] The power loss P V,EM The electric machine's performance depends particularly on its rotational speed. n, the torque M,a DC voltage at the inverter U dc and a temperature T EM The power loss of the electric machine can therefore be seen as a function of these parameters (also called electric machine temperature; measured at a suitable point, e.g. at the windings and / or at the iron core). P V , EM = P V , EM n M U dc T EM .

[0032] The power loss P V,Inv The inverter's output depends particularly on the speed. n, the torque M, the DC voltage at the inverter U dc and a temperature T Inv of the inverter (also referred to as inverter temperature; measured at a suitable point, e.g. on a heat sink and / or a semiconductor of the inverter), the power loss of the inverter can therefore be seen as a function of these parameters, i.e. P V,Inv = P V,Inv ( n, M, U dc , T Inv ).

[0033] The power loss P V,Pmp The hydraulic pump is particularly dependent on a pressure difference Δ p via the hydraulic pump, the volume flow Q delivered by the hydraulic pump, the rotational speed n, and the repression V g The power loss of the hydraulic pump can therefore be seen as a function of these parameters, i.e. P V,Pmp = P V,Pmp (Δ p, Q, n, V g Here, the adjustment effort could also be taken into account in the calculation of the power loss. In particular, depending on how far the speed-swivel angle pairing is to be shifted (starting from the current value), a different additional loss component will result (estimated via the size of the actuating and return cylinders, the adjustment rate, and the pressure).

[0034] The parameters on which the power losses or power loss terms depend, or can depend, can include, in addition to rotational speed, parameters that characterize the operating point and other measured or recorded parameters (e.g., temperatures). In general, each of the power losses can depend (independently of the others) on the rotational speed and / or at least one parameter that characterizes the operating point and / or at least one other measured or recorded parameter. Besides the aforementioned power losses, power losses can also occur at other components of the electrohydraulic system and be considered in the cost function, where these power losses can depend on the parameters mentioned above. For example, power losses can occur at a summing valve when hydraulic circuits are interconnected or at a cooling device for hydraulic fluid.

[0035] To minimize the total power loss, the rotational speed or displacement can be determined in an optimization, e.g. using a suitable optimization method, such that the following cost function is obtained. K 1 is minimized: K 1 = P V , EM n M U dc T EM + P V , Inv n M U dc T Inv + P V , Pmp Δ p , Q , n , V g

[0036] The cost function includes power loss terms for the power loss of the electric machine (electric machine power loss term), for the power loss of the inverter (inverter power loss term), and for the power loss of the hydraulic pump (pump power loss term). The electric machine power loss term and the inverter power loss term can each be considered drive power loss terms. More generally, with potentially other power losses, the following applies: K 1 = Σ i P V,i , with i ∈ { EM, Inv, Pmp, ...}.

[0037] In this process, the rotational speed can be optimized. nThe free parameter can be varied so that the cost function is minimized. The displacement V g This results from the equation given above for a given target volume flow rate. Q soll The torque of the electric drive is derived from the rotational speed. V g and from the pressure difference Δ p via the hydraulic pump and preferably taking into account a frictional torque of the pump, which can be determined from a characteristic map considering a swivel angle and a rotational speed of the pump. Alternatively, the displacement could be varied, with the rotational speed being considered the dependent variable due to the equation given above.

[0038] Because power losses depend on factors other than rotational speed, minimizing them based on these other factors can lead to different solutions for the rotational speed. This is especially true even if the operating point or the target operating point is the same. For example, if the target values ​​that characterize the operating point are identical, but different external loads result in different actual values ​​or different temperatures are present.

[0039] To solve the described minimization problem, a suitable method can be used (e.g., fmincon in Matlab). For example, the rotational speed can be varied as a free parameter in steps between a minimum and a maximum speed (which are technically predetermined by the electric drive, for instance) with a specific step size. The cost function can be evaluated for each step, and then the step at which the cost function is minimal can be determined. Furthermore, an iterative method is conceivable in this example, in which the step size is reduced in iterations.

[0040] For a system with two hydraulic pumps driven jointly by an electric drive, which supply two circuits connectable via a summing valve with hydraulic fluid (as e.g. in Figur 2 (as shown), the power losses of the drive and both hydraulic pumps and, on the other hand, possible summation losses (in the interconnected state), i.e., a power loss of the summing valve (additional pressure drop when supplying the circuit with the lower load pressure), can be taken into account as additional summands in the cost function.

[0041] The switching state, or state, of the summing valve (or summing device) then represents a second free parameter in the cost function. This parameter can assume two different states: closed, meaning the circuits are not connected, or open, meaning the circuits are connected (where the degree of opening or opening cross-section results from the pressures in the two circuits). When minimizing the cost function, the speed should be varied across both switching states. For example, the minimum value should be determined for both switching states (connected and disconnected), and the switching state with the smaller minimum (at the corresponding speed) should be selected. The decision as to whether or not to perform summation (connected or disconnected) is then made primarily to minimize the cost function.

[0042] Optionally, the individual power losses can be weighted differently, with the weighting depending on one or more parameters. For example, the electrical drive components of the electric drive, i.e., the electric motor and / or the inverter, can heat up considerably, especially at lower speeds, due to the higher electrical currents involved. This necessitates a reduction in power output (so-called derating) to prevent overheating of the drive components and potential damage. Since the hydraulic pump is circulated with hydraulic fluid, which also dissipates heat, excessive heating of the hydraulic pump does not normally occur.Accordingly, it can be provided that the power losses of the electric machine and the inverter are weighted against the power losses of the hydraulic pump depending on the temperature of the electric machine or the inverter, respectively, and particularly more heavily at high temperatures compared to the power losses of the hydraulic pump. For example, the following cost function is used. K 2. Formed, which is optimized or minimized: K 2 = X EM T EM ⋅ P V , EM n M U dc T EM + X Inv T Inv ⋅ P V , Inv n M U dc T Inv + P V , Pmp Δ p , Q , n , V g

[0043] This involves X EM = X EM ( T EM ) and X Inv = X Inv ( T Inv ) weighting factors with which power loss P V,EM of the electric machine and the power loss P V,Inv of the inverter in the cost function depending on the respective temperature T EM or T Inv They can be weighted differently. Generally, other losses can also be included in the total here: K 2 = Σ i X i · P V,i , which also includes the case where individual (not all) weighting factors can be constant at 1.

[0044] In particular, the functional dependence of the weighting factor can be X EM the electric machine (also known as the electric machine weighting factor) from the temperature T EM The electric machine is chosen such that it is equal to one up to a temperature threshold or electric machine temperature threshold and increases to values ​​greater than one when the temperature threshold is exceeded or from the temperature threshold onwards (e.g. to values ​​in the range of 1 to 2 or in the range of 1 to 5).

[0045] Similarly, the functional dependence of the weighting factor can be determined in particular. X Inv of the inverter (also known as inverter weighting factor) from the temperature T Inv The inverter is selected such that it is equal to one up to a temperature threshold or inverter temperature threshold (which may be different from the electric machine temperature threshold) and increases to values ​​greater than one when the temperature threshold is exceeded or from the temperature threshold onwards (e.g. to values ​​in the range of 1 to 2 or in the range of 1 to 5).

[0046] In both cases, the increase from the respective temperature threshold can be continuous, e.g., according to a monotonically or strictly monotonically increasing function, and / or in one or more steps. The steepness of the respective increase can be determined, for example, based on data sheets of the inverter or the electric machine and / or by testing to ensure that a critical temperature or maximum permissible operating temperature of the inverter or the electric machine, at which a reduction in power becomes necessary, is not reached.

[0047] Are the temperatures T EM the electric machine below the electric machine temperature threshold and the temperature T Inv If the inverter temperature is below the inverter temperature threshold, both weighting factors are equal to one, thus minimizing the total power loss. If at least one of the temperatures is above the corresponding temperature threshold, the respective power loss is weighted more heavily compared to the power loss of the hydraulic pump, resulting in an operating point (speed or displacement) with lower power loss from the electric motor and / or the inverter. Therefore, a higher total power loss than the minimum possible is accepted to prevent overheating of the electric motor and / or the inverter. Due to a flat optimum (of the total loss function), the total power loss increases only minimally in most cases. This means that the loss components are largely just shifted (e.g., from the electric drive to the pump).

[0048] If a thermal overload of the electric machine and / or inverter is imminent, the power losses of the electric machine and / or inverter can be weighted more heavily in the cost function, thus achieving an overall lower thermal load on the electrical components. For example, the rotational speed will also be adjusted to higher speeds. For an electro-hydraulic system with two circuits that can be connected via a summing device, the minimization process may also result in a different decision regarding whether or not to activate the summation. For instance, if one circuit demands additional hydraulic power, the summation may still not occur because the electric machine and / or inverter temperature in the other circuit is high.Conversely, in the event of a thermal overload (high electric machine temperature and / or inverter temperature) of the electric drive of a circuit, thermal relief can be achieved by summation, i.e., the circuits are connected together, even though this would not be necessary solely due to the required hydraulic power.

[0049] In addition to weighting with temperature-dependent weighting factors, more generally, at least one of the power losses (here, power loss of the electric machine, power loss of the inverter, power loss of the hydraulic pump) can be weighted with a weighting factor that depends on at least one specific parameter. With such parameter-dependent weighting factors, desired constraints can be implemented so that the optimization determines the target speed that minimizes the power loss while considering the constraint(s). In the example above, the constraint is preventing excessively high temperatures of individual components.In another example, if certain rotational speeds associated with high noise levels or high wear are to be avoided, weight factors could be used that depend on the rotational speed and are larger relative to other speed ranges at certain rotational speeds and possibly in small areas around these certain rotational speeds.

[0050] The determination of the free parameter (rotational speed or displacement) or, more generally, the free parameters (e.g., in the case of interconnectable circuits) within the framework of minimization or optimization can be carried out within the context of a control system for the electrohydraulic system, which is implemented by an electronic control unit, e.g., by executing a corresponding computer program or corresponding computer program modules. It is also conceivable that pre-calculated values, perhaps stored in the form of a characteristic map, could be used. Referring to Figur 3 Minimization or optimization can be achieved, for example, within the framework of the operating strategy or through Module 56, which implements the operating strategy. It should be noted that even if Figur 3 Since the present invention describes only one circle and the module 56 only controls the speed and swivel angle of this one circle, it can also be used with several modules, or with modules that can each control several speeds and swivel angles.

[0051] Furthermore, it should be noted that a weighting factor can also be added for the pump. This could, for example, be determined based on the other weighting factors.

[0052] Cost functions were discussed above. K 1 , KThe sum or weighted sum of individual power losses is chosen, and a minimization is performed. Clearly, a formulation as a maximization problem would also be conceivable. Accordingly, and more generally, an optimization is carried out, where the function to be optimized includes a sum of power losses, which can be weighted with weighting factors. In total, speed-dependent power losses of the electrical drive components and the hydraulic machine(s) are taken into account. In particular, in the optimization, a change in speed is always automatically linked to a change in displacement and torque. These multidimensional dependencies of the power losses are considered in the (model-based) optimization.

[0053] If weighting with weighting factors is used, these can depend on certain parameters (e.g., temperatures). For example, at least one power loss (in the example above, the power losses of the electric machine and the inverter) is weighted or taken into account depending on at least one temperature of at least one electrical drive component (electric machine temperature, inverter temperature) of the electric drive, so that the power loss in the electric drive is reduced if necessary, i.e., at a correspondingly high temperature, to prevent further heating and possible overheating.The target speed and, if applicable, the set state (target state) of the summing valve are thus determined at a given operating point such that the at least one power loss of the at least one electrical drive component is reduced when the at least one temperature is high, for example, above at least one temperature threshold. The at least one temperature threshold is specifically chosen to be lower than a maximum permissible operating temperature of the corresponding at least one electrical drive component.

[0054] Figur 4 shows a flowchart according to one embodiment of the method for reducing the thermal load of an electric drive in an electrohydraulic system.

[0055] In step 110, a target flow rate and, optionally, at least one pressure are specified, corresponding, for example, to the power requirements of hydraulic consumers. Other parameters that characterize the operating point can also be recorded or specified here.

[0056] In optional step 120, at least one parameter (on which weighting factors may depend) is recorded. For example, at least one temperature of at least one drive component of the electric drive is recorded (e.g., values ​​measured by temperature sensors are received).

[0057] In step 130, a target rotational speed is determined by optimizing a function to be optimized, and from this (corresponding to the target volume flow rate or, more generally, the operating point) a displacement (or a swivel angle) is determined. This is done, for example, as described above, within the framework of an operating strategy. The function to be optimized includes or is itself a sum of the power losses. This sum can be calculated as a weighted sum, with weighting factors provided for individual power losses, which depend in particular on the at least one parameter recorded in step 120 (e.g., the at least one temperature).

[0058] In step 140, the electric drive is regulated or controlled according to the specified speed and the at least one hydraulic pump (or hydraulic machine) is controlled according to the specified displacement.

[0059] Steps 120 (if available), 130, and 140 can be performed continuously, allowing the rotational speed to change even without altering the setpoint (target values, e.g., target flow rate, pressure; or operating point). In the optional step 150, the operating point can be adjusted, for example, if actual values ​​that characterize the operating point change (e.g., due to a change in the load on the hydraulic consumers) and / or in response to a changed operator setting. The process can then continue with step 110 using the adjusted operating point.

Claims

1. Method for reducing power losses in an electrohydraulic system which has an electric drive (3) comprising at least one electric drive component and at least one hydraulic machine (8, 10) which is coupled to the electric drive and driven by it in accordance with a speed, wherein the electrohydraulic system has several power losses which are dependent on the speed and / or an operating point of the electrohydraulic system and / or other detected variables, wherein the several power losses include at least one power loss of the at least one electric drive component and at least one power loss of the at least one hydraulic machine, each of which are dependent on the speed; wherein a target speed (58) is determined for the speed depending on the operating point of the electrohydraulic system (130), wherein the target speed is determined such that it optimizes a function to be optimized which includes a sum of the several power losses, wherein the sum of the several power losses is formed as the weighted sum of the power losses, in which one or more of the power losses are weighted with respective weighting factors.

2. Method according to any of the preceding claims, wherein the operating point is characterized by one or more of the following variables: at least one target pressure of the at least one hydraulic machine, at least one target volume flow of the at least one hydraulic machine, a target noise level of the electrohydraulic system, at least one actual pressure of the at least one hydraulic machine, at least one actual volume flow of the at least one hydraulic machine, an actual noise level of the electrohydraulic system.

3. Method according to either of the preceding claims, wherein the electrohydraulic system has at least one further component at which power loss occurs; wherein the sum includes at least one power loss for the at least one further component; wherein the at least one further component in particular includes at least one cooling device.

4. Method according to Claim 3, wherein the electrohydraulic system has two hydraulic circuits and at least two hydraulic machines (8, 10), wherein each hydraulic circuit is supplied with pressure medium by one of the at least two hydraulic machines (8, 10); wherein the two circuits can be hydraulically interconnected by a summing device, in particular a summing valve (18); wherein the at least one further component includes the summing device.

5. Method according to Claim 4, wherein the summing device has a state in accordance with which the circuits are interconnected or not interconnected; wherein the state of the summing device is a free parameter of the function to be optimized, wherein this is additionally varied with respect to the state; wherein in particular the circuits are interconnected depending on the state of the summing device in which the function to be optimized is optimal.

6. Method according to any of the preceding claims, wherein the at least one electric drive component includes an electric machine (6) and / or an inverter (4).

7. Method according to any of the preceding claims, wherein the weighting factors are each dependent on at least one parameter; wherein the at least one parameter includes one or more of: the target speed, a variable which characterizes the operating point, at least one other detected variable.

8. Method according to Claim 7, wherein the at least one parameter or the at least one other detected variable includes at least one temperature of the at least one drive component; and wherein the weighting factors include at least one drive weighting factor for the at least one power loss of the at least one drive component, which drive weighting factor is dependent on the at least one temperature.

9. Method according to Claim 8, wherein the at least one drive weighting factor increases when the at least one temperature exceeds at least one predetermined temperature threshold and / or is above the at least one predetermined temperature threshold; and / or wherein the at least one drive weighting factor is independent of the at least one temperature and / or constant, in particular equal to one, when the at least one temperature is below the at least one predetermined temperature threshold; and / or wherein a weighting factor of the power loss of the hydraulic machine is independent of the at least one temperature and / or constant and / or equal to one.

10. Method according to any of the preceding claims, wherein the operating point is adjusted (150).

11. Computing unit comprising a processor, which is configured such that it executes the method according to any of the preceding claims.

12. Electrohydraulic system which has an electric drive (3) comprising at least one electric drive component (4, 6) and at least one hydraulic machine (8, 10) which is coupled to the electric drive and is driven by it in accordance with a speed, wherein the at least one electric drive component (4, 6) and the at least one hydraulic machine each have at least one power loss which is dependent on the speed; further having a computing unit according to Claim 11.

13. Computer program comprising instructions which, when the program is executed by a computer, cause the computer to execute the method according to Claims 1 to 10.

14. Computer-readable data carrier on which the computer program according to Claim 13 is stored.

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