Method for controlling an electric drive of a hydraulic pump in a hydraulic system
The method addresses inefficiencies in hydraulic systems by using separate controllers to manage manipulated variables, ensuring smooth transitions and preventing component damage through anti-windup, thereby enhancing energy efficiency and system stability.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2025-10-29
- Publication Date
- 2026-05-15
AI Technical Summary
Existing hydraulic systems with fixed displacement pumps driven by electric motors face inefficiencies in controlling flow rate and pressure, leading to potential limitations being overlooked by either speed or pressure controllers, which can result in energy inefficiencies and component damage.
A method for controlling an electric drive of a hydraulic pump using separate controllers to determine and manage first and second values for manipulated variables, such as torque or speed, with additional limit values to ensure smooth transitions and prevent windup, while considering system limitations.
Ensures energy-efficient operation by preventing limitations from being overlooked, maintaining minimum pressures and speeds, and avoiding component damage through smooth transitions and anti-windup mechanisms.
Smart Images
Figure EP2025081231_15052026_PF_FP_ABST
Abstract
Description
[0001] R.414981 DE
[0002] Method for controlling an electric drive of a hydraulic pump in a hydraulic system
[0003] The present invention relates to a method for controlling an electric drive of a hydraulic pump in a hydraulic system, as well as a computing unit and a computer program for its implementation and a hydraulic system.
[0004] Background of the invention
[0005] Machines, especially mobile construction equipment (e.g., excavators), can have a working hydraulic system, i.e., a hydraulic system, to effect the movement of elements (e.g., boom sections) by means of hydraulic actuators (e.g., hydraulic cylinders and / or hydraulic motors). One way to make the use of the working hydraulic system more efficient is to provide a demand-based flow rate, for example, by using a variable displacement pump, i.e., a hydraulic pump with a variable displacement, which, however, are typically relatively expensive compared to fixed displacement pumps. In hydraulic systems that have a fixed displacement pump driven by an electric motor, the speed of the fixed displacement pump or the electric motor can be varied to vary the delivered flow rate.To supply hydraulic systems used in mobile applications to control work equipment with the desired flow rate, various control concepts are possible. For example, in flow-rate-based systems such as EFM (Electro-hydraulic Flow Matching), flow rate or speed control is used. In systems whose control is based on pressure or pressure differential, such as LS and LUDV systems (LS: Load-Sensing, LUDV: Load-Pressure-Independent Flow Distribution), pressure control is employed.
[0006] Disclosure of the invention
[0007] According to the invention, a method for controlling an electric drive of a hydraulic pump in a hydraulic system, as well as a computing unit and a
[0008] Page 1 of 20 R.414981 DE
[0009] A computer program for its execution and a hydraulic system with the features of the independent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description.
[0010] Within the scope of the invention, in a hydraulic system with a pump driven by an electric drive controlled by a manipulated variable, a first value and a second value for the manipulated variable are determined by a pressure regulator and a speed controller. Furthermore, a third value is determined from the first and second values. Several limit values for the manipulated variable are determined by means of respective controllers, wherein the controllers regulate one or more limit values of the hydraulic system to one or more limit setpoints. Finally, a control value for the manipulated variable is determined from the third value and the one or more limit values.This enables a sequential control system between the pressure and speed controllers, which additionally takes into account limitations imposed by individual components, dependent on the operating state or mode, or resulting from the system design. By having these limitations addressed by separate controllers, rather than directly within the speed or pressure controllers themselves, a situation is prevented where a limitation is overlooked when the other controller (speed or pressure controller), which does not address the limitation, is active.
[0011] The control variable is, in particular, a torque or a speed of the electric drive.
[0012] According to one embodiment, the third value is determined as the minimum of the first and second values, or the third value is determined by a function that, in particular, selects the minimum of the first and second values as the third value after a time interval has elapsed since a change in the minimum of the first and second values has occurred, or the third value is determined as the average of the first and second values. Selecting the minimum ensures energy-efficient operation. When using the function, the time interval can, for example, be fixed or determined by limiting the rate of change of the third value. This, as well as averaging, results in...
[0013] Page 2 of 20 R.414981 DE, in particular smooth transitions are achieved. On average, the first and second values can be weighted differently and variably. For example, a time-dependent weighting can be applied, whereby, for instance, from a point in time when the first or second value falls below the other, the smaller of the two values is weighted more heavily over time, in particular until its weight is equal to 1 and the weight of the other is equal to 0, or until a change in the situation occurs in which the smaller value is determined. A weighting that depends on the distance between the larger of the two values (i.e., first and second value) is also possible; for example, the smaller of the two values can be weighted more heavily as the distance increases.
[0014] According to one embodiment, the manipulated value is determined as greater than or equal to at least one first constraint value of the one or more constraint values, and / or as less than or equal to at least one second constraint value of the one or more constraint values. In particular, the manipulated value is determined as the maximum of the third value and the at least one first constraint value, and / or as the minimum of the third value and the at least one second constraint value. The at least one first constraint value represents a lower constraint on the manipulated variable. The at least one second constraint value represents an upper constraint on the manipulated variable.The phrase "greater than or equal to at least one first constraint value" means, in the case of multiple first constraint values, that the setpoint is greater than or equal to each first constraint value. The phrase "less than or equal to at least one second constraint value" means, in the case of multiple second constraint values, that the setpoint is less than or equal to each second constraint value. The "at least one first constraint value" or the "at least one second constraint value" can include all constraint values of the one or more constraint values.
[0015] Examples of a lower limit include a minimum rotational speed that should not be undercut to ensure adequate pump lubrication, or a minimum pressure that should not be undercut to maintain a certain pressure level, e.g., idle pressure, in the hydraulic system. An example of an upper limit is a maximum power output from the electric motor, which depends particularly on the temperature of the electric drive.
[0016] Page 3 of 20 R.414981 DE can be specified, e.g. to avoid overheating of the electric drive and a related severe reduction in the power output of the electric drive (so-called derating).
[0017] It is assumed that there is a positive relationship between the manipulated variable and limiting variables, as well as with the pump pressure and speed, i.e., the latter also increase with (in absolute value) increasing manipulated variable.
[0018] According to one implementation, the setpoint is determined as the maximum of the third value and one or more limit values. A downward limit is thus implemented.
[0019] According to one embodiment, the one or more limiting parameters include the pump pressure, with the corresponding limiting setpoint being a minimum pump pressure, and / or the one or more limiting parameters include the pump speed, with the corresponding limiting setpoint being a minimum speed. Limiting the pressure according to the minimum pump pressure ensures that a certain minimum pressure is maintained in the hydraulic system, for example, to guarantee that the hydraulic consumers respond with minimal delay when transitioning from a situation where the consumers are not activated to a situation where they are activated (due to specific user requirements).By limiting the speed according to the minimum rotational speed, a certain volume flow through the pump can be maintained, for example to ensure sufficient lubrication or cooling of the pump.
[0020] The pressure regulator and / or the speed regulator and / or the regulator(s) used to determine the limit values can each independently incorporate a proportional component and / or an integral component, and may also include a differential component. If an integral component is present, because the respective regulator cannot see which value is actually used as the control input (due to the determination of the third value from the first and second values, or the control input from the third value and the limit values), a so-called windup can occur, i.e., an uncontrolled increase of the integral component, which can lead, for example, to discontinuous control behavior. The following configurations address this issue.
[0021] Page 4 of 20 R.414981 DE shows how this problem can be resolved. The anti-windup function can, for example, be implemented by correcting the control deviation for the integral component by the difference mentioned in the specifications (multiplied by a suitable factor).
[0022] According to one embodiment, the pressure regulator has an integral component, wherein a difference between the first value and the third value is determined and the difference is used in an anti-windup function of the integral component of the pressure regulator, and / or the speed controller has an integral component, wherein a difference between the second value and the third value is determined and the difference is used in an anti-windup function of the integral component of the speed controller.
[0023] According to one embodiment, the pressure regulator has an integral component, wherein a difference between the third value and the control value is determined and the difference is used in an anti-windup function of the integral component of the pressure regulator, and / or the speed controller has an integral component, wherein a difference between the third value and the control value is determined and the difference is used in an anti-windup function of the integral component of the speed controller.
[0024] According to one embodiment, the pressure regulator has an integral component, wherein a first difference between the first value and the third value is determined, a second difference between the third value and the control value is determined, and the minimum of the first and the second difference is used in an anti-windup function of the integral component of the pressure regulator, and / or the speed controller has an integral component, wherein a third difference between the second value and the third value is determined, a fourth difference between the third value and the control value is determined, and the minimum of the third and the fourth difference is used in an anti-windup function of the integral component of the speed controller.
[0025] According to one embodiment, for each of the one or more constraint values, the respective controller has an integral component, whereby a difference between the respective constraint value and the manipulated value is determined and the difference is used in an anti-windup function of the integral component of the respective controller.
[0026] Page 5 of 20 R.414981 DE
[0027] A computing unit according to the invention, e.g., a control unit of a hydraulic system of a mobile working machine or an inverter control of an electric drive by which a pump of a hydraulic system is driven, is configured, particularly by means of programming, to carry out a method according to the invention. A hydraulic system with a computing unit according to the invention is also the subject of the invention.
[0028] 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.
[0029] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.
[0030] 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.
[0031] The invention is schematically illustrated in the drawing using exemplary embodiments and is described in detail below with reference to the drawing.
[0032] Character description
[0033] Figure 1 shows a hydraulic system with a constant-displacement pump driven by an electric machine, which can be operated using the method according to the invention.
[0034] Page 6 of 20 R.414981 DE
[0035] Figure 2 shows a flowchart according to an exemplary embodiment of the invention.
[0036] Figure 3 shows a control structure according to an exemplary embodiment of the invention.
[0037] Figure 4 schematically represents a possible signal flow for determining the setpoint for the pump pressure to be regulated.
[0038] Detailed description of the drawing
[0039] Figure 1 shows an electro-hydraulic system with a constant displacement pump 2 driven by an electric drive (i.e., a hydraulic pump with constant displacement V). g or constant swallowing volume, where displacement denotes the volume conveyed per revolution), which can be operated with the method according to the invention.
[0040] The constant-displacement pump 2 (hereinafter also referred to simply as the pump) has two hydraulic connections. One of the connections, referred to as the tank-side connection, is connected to a tank for hydraulic fluid (hydraulic fluid, in particular hydraulic oil), and the other connection, referred to as the outlet-side connection, is connected via a hydraulic line 12 to a valve assembly 8 (e.g., a modular valve block), which is not shown in detail. This valve assembly controls the flow of hydraulic fluid to and from at least one hydraulic consumer 10 (here, for example, a hydraulic cylinder). The valve assembly 8, i.e., the valves or valve spools it comprises, is controlled by a control unit 20, e.g., based on user inputs that are detected by an operating device (e.g., a joystick; not shown) and transmitted to the control unit 20.Optionally, a volume flow rate and / or pressure rate (i.e., a volume flow rate setpoint and / or a pump pressure setpoint) can also be determined by the control unit 20 based on user input.
[0041] A pressure sensor (i.e., a sensor that measures the pressure of the hydraulic fluid), designated as a load pressure sensor 14, can be provided on the hydraulic line between the valve assembly 8 and the hydraulic consumer 10, with which the load pressure of the
[0042] Page 7 of 20 R.414981 DE The hydraulic consumer or the maximum load pressure in the case of multiple hydraulic consumers can be detected or measured. In a system with direct flow rate control, a load pressure sensor can be omitted, in which case, for example, the control unit 20 can determine a flow rate and / or (maximum) pressure setpoint.
[0043] A pressure sensor, or pump pressure sensor 16, is provided on the output side of the constant-pressure pump 2, i.e., at the output port of the constant-pressure pump or on the hydraulic line 12 between the constant-pressure pump 2 and the valve block 8. The pump pressure sensor 16 measures the pump pressure, which here is considered to be the output pressure of the hydraulic fluid present at the output port of the constant-pressure pump or on the hydraulic line between the constant-pressure pump and the valve assembly. Alternatively, the pump pressure sensor 16 can be provided directly on the constant-pressure pump 2, for example, if it has a dedicated port where the pump pressure is provided as a hydraulic signal.
[0044] The electric drive comprises an electric machine 4 and an inverter 6 (power converter, in particular an inverter), which supplies the electric machine 4 and its phase windings with alternating current voltages. The inverter 6 is connected, for example, via a DC link to an electrical energy source, such as a battery. The electric machine 4 is mechanically coupled to the constant-speed pump 2, for example, by means of a shaft, and a gearbox with a specific gear ratio may also be provided. The rotational speed of the constant-speed pump 2 is therefore equal to the rotational speed of the electric machine 4, or, taking the gear ratio into account, corresponds to the rotational speed of the electric machine 4; that is, the ratio of the two rotational speeds is equal to 1 or equal to the gear ratio.
[0045] An inverter control unit 22 is provided, which is configured to control the inverter 6 according to a manipulated variable, wherein the manipulated variable is, in particular, the torque to be applied by the electric machine 4 (which is caused by alternating currents generated in the inverter). Values for the manipulated variable, referred to as manipulated values, can be transmitted to the inverter control unit 22 by a higher-level control unit, such as the control unit 20, which determines the manipulated values, or can be determined, in whole or in part, by the inverter control unit 22 itself. A [missing information - likely a specific device or component] can be used to determine the manipulated values to be used.
[0046] Page 8 of 20 R.414981 DE
[0047] The control is carried out according to a method according to the invention, which is implemented in the inverter control 22 and / or the control unit 20.
[0048] Figure 2 shows a flowchart according to an exemplary embodiment of the invention, i.e., a method for controlling an electric drive of a hydraulic pump in a hydraulic system that has at least one hydraulic consumer, as shown, for example, in Figure 1. The at least one hydraulic consumer is supplied with hydraulic fluid by the pump based on consumer demands. The electric drive is controlled by a manipulated variable or by values of the manipulated variable referred to as control values. The manipulated variable can be, for example, the torque to be applied by the electric motor or the speed of the electric motor, or equivalently, the speed of the pump (provided there is a fixed transmission ratio).
[0049] In an optional step 100, consumer requirements can be determined, and based on these, a target pump pressure and a target pump speed can be calculated. The consumer requirements are determined, for example, from user input (e.g., via a joystick) and / or from measured values of parameters (e.g., load pressure) of the hydraulic system. The user input indicates, for instance, a desired movement speed of a hydraulic cylinder (e.g., corresponding to a joystick deflection), from which a flow rate of hydraulic fluid to the hydraulic cylinder can be calculated to achieve this speed. Accordingly, a total required flow rate that should be delivered by the pump to effect the desired consumer movements, and from this, a required pump speed, which is used as the target pump speed, can be determined, taking leakage into account as well.From a measured load pressure, for example, a required pump pressure, which is used as the target pump pressure, can be determined. A (positive) pressure differential is added to the measured load pressure (see Figure 4) to ensure a sufficient pressure difference across the inlet orifices to the consumers. In addition to or as an alternative to these examples of determining the target pump pressure and target pump speed according to consumer requirements, other methods and / or treatment steps (e.g., filtration, etc.) are also possible. Alternatively, the target pump pressure and target pump speed can be specified by a higher-level control system.
[0050] Page 9 of 20 R.414981 DE
[0051] In step 110, a value for the manipulated variable, referred to as the first value, is determined by means of a pressure regulator, which regulates the pump pressure of the pump to the target pump pressure, which is determined by the consumer requirements.
[0052] Similarly, in 120, a value for the manipulated variable, referred to as the second value, is determined by means of a speed controller, which regulates the speed of the pump to a target pump speed determined by the consumer requirements.
[0053] It should be noted that steps 110 and 120 can be performed in any order and simultaneously.
[0054] In step 130, a third value for the manipulated variable is determined from the first and second values, in particular as a smaller of the first and second values for the manipulated variable or by a function that smooths transitions when this minimum (from the first and second values) changes.
[0055] In step 140, one or more limit values for the manipulated variable are determined by means of respective controllers (in particular, a controller or limit controller is provided for each limit value), by which one or more limit variables of the hydraulic system are controlled to one or more limit setpoints. The limit setpoints can be fixed values independently of each other or be variable, whereby in the latter case the respective limit setpoint is, for example, determined by measured operating parameters (e.g., a temperature) of the hydraulic system or a component of the hydraulic system, or by an operating mode (which is, for example, selected automatically or by user input).
[0056] It should be noted that steps 130 and 140 can be performed in any order and simultaneously.
[0057] In step 150, a control value for the manipulated variable is determined from the third value and the one or more restriction values, in particular as the maximum of these values.
[0058] Page 10 of 20 R.414981 DE
[0059] Examples of limiting parameters are the pump speed (or pump rotational speed), where the limiting value is a minimum speed, and the pump pressure, where the limiting value is a minimum pressure (minimum pump pressure). The inventive method, in which limiting values are determined by separate controllers (independent of the pressure controller and the speed controller), is advantageous because corresponding limits are always observed, even if they are not visible from the perspective of the pressure controller and / or the speed controller. For example, a minimum pressure could be implemented in the pressure controller by limiting the target pump pressure to the minimum pressure; however, this limit would not be visible in the speed controller, so that if a low flow rate is requested, and the third value in step 130 is selected to be equal to the second value (from the speed controller), the minimum pressure can be undercut.
[0060] The examples mentioned concern lower limits. Alternatively or additionally, upper limits are conceivable. For example, the temperature of the electric drive, e.g., an inverter temperature, could be measured and limited by a (limiting) controller with a maximum temperature as the limit setpoint. In this case, step 150 could additionally include a minimum selection with respect to this limit value. Instead of temperature, in another example, the output power (speed of the electric machine times applied torque or speed of the pump times pump pressure times displacement volume) could be a limiting variable, where the limit setpoint is a maximum power dependent on the temperature of the electric drive, which is selected to be lower at higher temperatures. An upper limit of the pump pressure and / or the pump speed can also be implemented in the pressure controller or...This can be implemented in the speed controller by limiting the target pump pressure or the target pump speed, since in step 130 a minimum selection is typically made or a similar determination (using a function) of the third value is carried out.
[0061] In step 160, the electric drive is controlled with the setpoint. For example, in an inverter controller, control signals are determined for the inverter that correspond to the setpoint or with which the setpoint is achieved. The inverter controller can perform a control procedure or a regulation procedure for this purpose.
[0062] Page 11 of 20 R.414981 DE
[0063] It should be noted that the first, second, and third values for the manipulated variable, as well as the one or more limit values for the manipulated variable, are values based on which the manipulated variable is determined, and in particular, selected. That is, the first, second, and third values for the manipulated variable, as well as the one or more limit values for the manipulated variable, are not directly the values used to control the electric drive; rather, the manipulated variable used to control the electric drive is determined or selected from these values.
[0064] Figure 3 shows a control structure according to an exemplary embodiment of the invention. Functional block 34 includes functional elements for preparing the setpoints for the subsequent individual controllers arranged in parallel. Such setpoint preparation can include, for example, elements for filtering signals, but also for modifying signals. For example, a speed signal can be determined as a setpoint from a required volume flow signal.
[0065] Typically, for variable pump operation, an operator specifies a desired flow rate, which must be converted into a speed signal. This can be done either using a simple equation that primarily defines the relationship between speed and flow rate via the pump's displacement or volumetric volume, or by evaluating a pre-recorded pump characteristic curve. The latter method can be more accurate, as it can also take into account the pump's leakage oil flow, which depends on the current speed and pressure. Alternatively, the joystick signal-flow rate relationship can also be determined using a learned model or adaptively.
[0066] Another modification can be the determination of the setpoint for the pressure to be regulated. For LS and LUDV systems, a defined value is added to the measured LS pressure (i.e., the measured load pressure) by which the pump pressure should be higher than the LS pressure in order to achieve the desired constant pressure differential. The individual input signals 32 to the function module 34 can thus be, for example, the setpoints for the volume flow rate (or even directly the speed), for the pressure, for the minimum speed and for a minimum pressure, as well as the specified LS pressure differential and also the current value of the LS pressure.
[0067] Page 12 of 20 R.414981 DE
[0068] Function module 76 is used to process primarily measured signals 74 of the current actual values of the system states to be controlled. This can, for example, involve filtering the measured values. Examples of input signals 74 here are the pump pressure and the speed of the pump or electric motor. Function modules 40, 50, 96, and 98 are the actual controllers. Function module 40 contains the controller (pressure controller) for regulating the pump pressure. Here, input signal 36 is the setpoint of the desired pressure, and input signal 38 represents the actual value of the measured pump pressure. Within module 40, a (first) value 42 for the manipulated variable is determined from the two input signals 36 and 38. The other controllers operate similarly. Within the function module 50 (speed controller) the input variables 44 (target speed) and 46 (actual speed) are used to determine a second value 52 for the manipulated variable.
[0069] A controller 96 (minimum speed controller) receives the setpoint 78 for the minimum speed and the actual value 80 for the current speed as inputs and calculates a manipulated variable value 82 from these. Using inputs 88 (setpoint for minimum pressure) and 90 (actual value of the current pump pressure), the controller 98 can calculate a manipulated variable value 102 to maintain a minimum pressure. The manipulated variable values 82 and 102 are also referred to as limit values. Controllers 96 and 98 are therefore also called limit controllers.
[0070] All four controllers operate simultaneously, generating individual values for the manipulated variable. Function modules 54 and 58 determine the manipulated variable value, designated as setpoint 60, from these individual values. This setpoint is then forwarded as the actual control signal to the inverter or the inverter's subordinate control system (e.g., torque control). Function module 54 determines a third manipulated variable value, 56, from the first value, 42, and the second value, 52. Function module 54 could, for example, be a simple minimum function that selects the minimum value from the values 42 and 52 (the first and second values). However, a function is also conceivable that, at least when the minimum value remains unchanged over a certain period or undergoes only relatively minor changes, e.g.,The maximum deviation is + / - 10% or + / - 5%, and the minimum of 42 and 52 is also selected, but these two quantities are blended more harmoniously, e.g., transitions are made continuous and / or the rate of change (of the third value) is limited. A minimal selection at this point is appropriate because...
[0071] Page 13 of 20 R.414981 DE The upper limiting value for the manipulated variable should be the minimum of the values 42 and 52 in order to limit the pressure and / or the speed (or the volume flow rate) towards larger (positive) values. This allows, for example, compliance with the specified maximum pressure when setting a volume flow rate.
[0072] To limit the speed and / or pump pressure towards smaller (positive) values, function module 58 can be implemented as a maximum function, which selects the maximum of the individual values 56, 82, and 102 for the manipulated variable as the setpoint 60. It is also conceivable that a function within module 58 determines the third value, again essentially aiming for the maximum, which can lead to a smoother transition between the individual values for the manipulated variable in the control signals. By selecting the maximum value as setpoint 60, a predefined minimum speed of the drive and / or a predefined minimum pressure of the pump can be achieved.
[0073] To achieve a smooth and robust transition between individual control units when changing from one manipulated variable value to another, for example, via submodule 54, it is possible to modify the integral (I) components of the controllers 40 and 50 (and / or 96 and 98) in such a way that they do not increase uncontrollably or become too close to the current values of the states. For example, if controller 50 is not active because submodule 54 selects the first manipulated variable value 42, the second manipulated variable value 52 has no direct influence on the variable being controlled. This can lead to a control deviation within this controller and cause the integral component to increase. Consequently, a transition might occur much later, or not at all, when controller 40 should actually become active again.
[0074] To prevent an increase in the integral component, it is proposed that the third value 54 for the manipulated variable, after function module 54, is fed back to the controller 50 as signal 72 via a differential element 70, minus the second value 52 for the manipulated variable. If the controller 50 is active (i.e., the second value is selected by function module 54), the values 52 and 56 for the manipulated variable are equal, and the value zero is passed to the controller 50 as signal 72. If the controller 50 is inactive, the second value 52 for the manipulated variable is greater than the third value 56 for the manipulated variable, and a
[0075] Page 14 of 20 R.414981 DE A negative value is passed as signal 72 to the controller 50. This signal 72 can be used within the controller 50 for anti-windup of the integral component. The same applies to the feedback of signal 68 via the differential element 66 for the controller 40.
[0076] However, if controller 98 (minimum pressure control) or controller 96 (minimum speed control) is active, the additional signals 64 and 100 (third value 56 minus control value 60) can be made available to controller 40 and controller 50, respectively. Signals 64 and 100 are determined by a differential element 62, which subtracts control value 60 from the third value 56 for the manipulated variable. If the third value 56 is active for the manipulated variable, the feedback values, i.e., signals 64 and 100, are zero. If one of the values 82 or 102 (limit values) is selected for the manipulated variable, the third value 56 for the manipulated variable is less than control value 60, and signals 64 and 100 have a negative value. Within controllers 40 and 50, signals 64 and 68 or 72 and 100 can each be linked to a minimum element and the result made available to the anti-windup.In order to implement an anti-wind dup in the controllers 96 and 98 as well, the same feedback methodology can be implemented with the signals 86 and 94 obtained from differential elements 84 and 92.
[0077] Figure 4 schematically illustrates a possible signal flow for determining the setpoint for the pump pressure to be regulated. As already described, this partial functionality can be part of the function module 34 of Figure 3 for preparing the setpoints for the control operations to be performed. A summing element 116 calculates the sum 118 of the measured (and optionally filtered) load cell pressure value 112 with the specified value 114 of the desired pressure difference. The signal 118 thus determined is compared with the setpoint for a specified absolute value 120 of the pump pressure, i.e., a specification for the maximum pump pressure (maximum pressure specification), by element 122 and output as signal 124. Signal 124 corresponds to the pump pressure setpoint, which is transmitted to the controller 40 of Figure 3 (as input signal 36). This implementation allows, for example, a maximum pressure limit to be realized even with load cell control.
[0078] Page 15 of 20
Claims
R.414981 DE 1. Method for controlling an electric drive (4, 6) of a hydraulic pump (2) in a hydraulic system having at least one hydraulic consumer (10), wherein the electric drive is controlled by a manipulated variable and wherein the at least one hydraulic consumer (10) is supplied with hydraulic fluid by the pump (2) based on consumer requirements, comprising: Determining (110) a first value (42) for the manipulated variable by means of a pressure regulator (40) which regulates a pump pressure (38) of the pump to a setpoint pump pressure (36) which is determined by the consumer requirements; Determining (120) a second value (52) for the manipulated variable by means of a speed controller (50)), which regulates a speed (46) of the pump to a target pump speed (44) which is determined by the consumer requirements; Determine (130) a third value (56) for the manipulated variable from the first and the second value; Determine (140) one or more limit values (82, 102) for the manipulated variable by means of respective controllers (96, 98) by which one or more limit variables (80, 90) of the hydraulic system are controlled to one or more limit setpoints (78, 88); Determining (150) a control value (60) for the control variable from the third value and the one or more constraint values; and - Controlling (160) the electric drive with the setpoint (60).
2. Method according to claim 1, wherein when determining the third value (56): the third value (56) is determined as the minimum of the first value (42) and the second value (52), or the third value (56) is determined by means of a function which, in particular, after a period of time after a change in the minimum of the first value (42) and the second value (52) has occurred, selects the minimum of the first and the second value as the third value, or the third value (56) is determined as an average of the first and the second value (52). Page 16 of 20 R.414981 DE 3. A method according to any of the preceding claims, wherein when determining the setpoint (60), the setpoint (60) is determined as greater than or equal to the at least one first limit value of one or more limit values (82, 102) and / or as less than or equal to the at least one second limit value of one or more limit values (82, 102) for at least one second limit value; wherein, in particular, the setpoint (60) is determined as the maximum of the third value (56) and the at least one first limit value and / or as the minimum of the third value (56) and the at least one second limit value.
4. Method according to one of the preceding claims, wherein when determining the setpoint (60) the setpoint (60) is determined as the maximum of the third value (56) and the one or more restriction values (82, 102).
5. A method according to any of the preceding claims, wherein the one or more limiting parameters include the pump pressure, wherein the corresponding limiting setpoint is a minimum pump pressure; and / or wherein the one or more limiting parameters include the speed of the pump, wherein the corresponding limiting setpoint is a minimum speed.
6. Method according to one of the preceding claims, wherein the manipulated variable is a torque or a speed of the electric drive (4, 6).
7. A method according to any one of the preceding claims, wherein the pressure regulator (40) has an integral component, wherein a difference (68) between the first value (42) and the third value (56) is determined and the difference is used in an anti-windup function of the integral component of the pressure regulator (40); and / or wherein the speed controller (50) has an integral component, wherein a difference (72) between the second value (52) and the third value (56) is determined and the difference is used in an anti-windup function of the integral component of the speed controller (50). Page 17 of 20 R.414981 DE 8. A method according to any one of the preceding claims, wherein the pressure regulator (40) has an integral component, wherein a difference (64) between the third value (56) and the control value (60) is determined and the difference is used in an anti-windup function of the integral component of the pressure regulator; and / or wherein the speed controller (50) has an integral component, wherein a difference (100) between the third value (56) and the control value (60) is determined and the difference is used in an anti-windup function of the integral component of the speed controller.
9. A method according to any one of claims 1 to 6, wherein the pressure regulator (40) has an integral component, wherein a first difference (68) between the first value (42) and the third value (56) is determined, a second difference (64) between the third value (56) and the control value (60) is determined, and the minimum of the first and the second difference is used in an anti-windup function of the integral component of the pressure regulator (40); and / or wherein the speed controller (50) has an integral component, wherein a third difference (72) between the second value (52) and the third value (56) is determined, a fourth difference (100) between the third value (56) and the control value (60) is determined, and the minimum of the third and the fourth difference is used in an anti-windup function of the integral component of the speed controller (50).
10. Method according to one of the preceding claims, wherein for each of the one or more restriction values (82, 102) the respective controller (96, 98) has an integral component, wherein a difference (86, 94) between the respective restriction value (82, 102) and the actuated value (60) is determined and the difference is used in an anti-windup function of the integral component of the respective controller.
11. Computing unit comprising a processor configured to perform the method according to any of the preceding claims.
12. Hydraulic system comprising a hydraulic pump (2) with an electric drive (4, 6) and a hydraulic consumer (10), wherein the electric drive is controlled by a manipulation variable and wherein the at least one hydraulic Page 18 of 20 R.414981 DE Consumer (10) is supplied with pressure medium by the pump (2) based on consumer requirements, and a computing unit according to claim 11.
13. Computer program comprising instructions which, when the program is executed by the computing unit of the hydraulic system according to claim 12, cause it 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. Page 19 of 20