DE102022211201A1 - Improved determination of the idle current consumption of drain pumps - Google Patents

Abstract

The invention relates to a method for determining an idle current consumption of a drainage pump, for example in the form of a drain pump of a water-conducting household appliance, wherein the drainage pump is controlled by a control unit in such a way that the drainage pump is operated at a first speed during a first time interval, wherein a first current required for operation at the first speed is determined, wherein the drainage pump is operated at a second speed during a second time interval, wherein the first speed and the second speed are lower than a zero delivery speed of the drainage pump and the second speed is designed to be greater than the first speed, wherein and a second current of the drainage pump required for operation at the second speed is determined, wherein based on the determined first current and second current, an idle current consumption for any speed of the drainage pump is determined; or wherein a temperature of the drainage pump is measured, wherein based on the determined first current and the measured temperature, an idle current consumption for any speed of the drainage pump is determined. Furthermore, the invention relates to a household appliance.

Description

The present invention relates to a method for determining an idle current consumption of a drainage pump, for example in the form of a drain pump of a water-conducting household appliance, in which the drainage pump is controlled by a control unit in such a way that the drainage pump is operated at a first speed during a first time interval. The invention also relates to a household appliance.

When controlling drain pumps, there is usually a linear relationship between the flow rate and the electrical current consumption of the pump motor depending on the speed of the pump motor or the drain pump. The flow rate can therefore be described in the form of a straight line equation. The starting value of this straight line equation or the intersection of this line with the Y axis represents the current consumption that is required even without flow rate. The starting value consists of a hydraulic component for building up pressure and the internal torque of the pump motor. The internal torque, which consists of friction and electrical losses, depends on changing influences, in particular the pump motor temperature. The exact pump motor temperature and the internal torque are usually not known, so the starting value of the flow rate/current consumption line is also unknown and it is not possible to determine the flow rate of the drain pump precisely.

If the pump is operated in idle mode, ie without water, at a constant motor temperature, the result is 1 a non-linear relationship between the no-load current IL and the speed n. In idle operation, the drain pump is not filled with water, so only the current is needed to overcome the internal torque. The torque caused by the air flow around the impeller of the drain pump is negligible. In the 1 Curves of the no-load current IL as a function of a speed n are shown for different temperatures of the pump motor, which illustrate the significant influence of the temperature. In particular, fluid friction of the rotor (magnetic body), which floats in oil in the rotor housing of the drain pump, has the greatest influence on the no-load current IL. This influence results from the temperature dependence of the viscosity of the oil, which is directly related to the pump motor temperature.

It is therefore the object of the present invention to provide a method in which an idle current consumption of a drainage pump or drain pump is determined taking into account the pump motor temperature.

This object is achieved by a method having the features of claim 1 and by a household appliance having the features of claim 9.

According to one aspect of the present invention, a method is provided for determining an idle current consumption of a drainage pump. The drainage pump can also be referred to as a drain pump. The drainage pump can be designed, for example, in the form of a drain pump of a water-conducting household appliance. In addition, the drain pump can be designed as a so-called free-flow pump or as a centrifugal pump.

In one step, the drainage pump is controlled by a control unit such that the drainage pump is operated at a first speed during a first time interval. During the first time interval, a first current required for operation at the first speed is determined.

Furthermore, the drainage pump is operated at a second speed during a second time interval. The first speed and the second speed are designed to be lower than a zero delivery speed of the drainage pump. The first speed and the second speed are different. Preferably, the second speed is higher than the first speed.

During the second time interval, a second current of the drainage pump required for operation at the second speed is determined. Based on the determined first current and second current, an idle current consumption is determined for any speed of the drainage pump.

The first time interval and the second time interval can be the same length or different lengths.

As an alternative to operating the drainage pump at the second speed during the second time interval and determining the second current, a temperature of the drainage pump is measured and an idle current consumption is determined for any speed of the drainage pump based on the determined first current and the measured temperature. The determination of the idle current consumption can thus be accelerated because the measurement of the second current during the second time interval is omitted.

According to a further aspect of the invention, a household appliance is provided which has a control unit and at least its drainage pump. The drainage pump can be controlled by the control unit. The household appliance is advantageously set up to carry out the method according to the invention.

The household appliance can be designed, for example, as a water-conducting household appliance, which can be designed as a washing machine, a dryer, a washer-dryer, a dishwasher and the like. The method can be used to carry out an in-situ calibration when the drainage pump is put into operation, which results in a precise setting of the flow rate. This makes it possible to implement a particularly accurate remaining duration display for a cleaning program of the household appliance, which does not fluctuate with varying temperatures of the drainage pump.

The method according to the invention can be used to derive the idle current consumption for any desired speed of the drainage pump. In principle, the selection of a washing program and the ambient conditions n are not known for the operation of the drainage pump. Thus, the thermal stress on the drainage pump during activation is also not known. The method can advantageously be carried out when the drainage pump is started up or shortly beforehand in order to take the temperature of the drainage pump or a motor of the drainage pump into account when determining the idle current consumption. Thus, the idle current can be determined for any desired target speed or several target speeds, for example in the form of an idle operating curve, which includes the influence of the motor temperature when the pump starts.

By taking the engine temperature into account when calculating the idle current consumption, the control of the drainage pump can be thermally decoupled, which results in the control of the drainage pump being independent of the engine temperature. In particular, a set target flow rate of the drainage pump can be set to be constant over a wide temperature range, since the hydraulic operating point remains the same.

The thermal stress on the drainage pump can be optimally taken into account when determining the idle current consumption if the drainage pump is controlled by the control unit to set the first speed and/or the second speed during a washing program and/or at the end of a washing program. The thermal influence of a washing program on the drainage pump varies with the set washing program and can also fluctuate depending on external influences and the varying operating conditions of the household appliance. The method allows a calibration to be carried out immediately before the drainage pump is operated, which takes into account the thermal influences on the operating parameters of the drainage pump motor.

According to a further embodiment, a current consumption for pressure build-up by the drainage pump at the first speed and/or the second speed, designed as a second-order function dependent on a speed, is determined. With this proportion of pump power or pump motor current, the drainage pump builds up pressure in the conveying medium, but with this proportion of the current consumption, no conveying flow is generated. This part of the current consumption of the drainage pump is not influenced by temperature and describes the current consumption of the drainage pump when the drainage pump is filled with the conveying medium, minus a current consumption when the drainage pump is empty. By taking into account the pressure build-up by the overflow pump, for example in a waste water hose of the household appliance, the accuracy of the determined idle current consumption can be further increased.

Taking the pressure build-up into account when controlling the drainage pump can be implemented particularly easily from a technical perspective if it is designed as a second-order function of the current consumption for pressure build-up and has two constant approximation parameters of the pressure build-up d1 and d2, which are determined based on the first current and the second current.

According to a further embodiment, an idle operating current is approximated as a second degree equation dependent on the speed with constant approximation parameters of the idle operation a and b and calculated for any speed. Advantageously, the approximation parameters a and b each depend linearly on a temperature and are based on a difference between the second current and the first current minus a pressure component. The approximation parameters of the idle operation of the drainage pump can thus be calculated using the determined current difference from the first current and the second current. In particular, the approximation parameters of the idle operation of the drainage pump can each depend linearly on the current difference.

Corresponding straight line equations for calculating the approximation parameters based on the determined current difference can be determined for a pump type during initial commissioning at different temperatures. In particular, the constant components of the straight line equation for the approximation parameters can be determined and stored in the memory of the control unit.

According to a further embodiment, the idle current consumption for any speed is determined as a sum of an idle operating current and a current consumption for pressure build-up. This measure allows all relevant current components of the drainage pump to be added together in order to achieve a particularly precise determination of the idle current consumption. The idle current consumption can be used to regulate a delivery rate or a volume flow of the drainage pump that can be regulated independently of thermal influences on the drainage pump.

Any target speed of the drainage pump can be set particularly quickly if the approximation parameters of the pressure build-up and the approximation parameters of the idle operation are determined by the control unit after the first time interval and the second time interval and are stored at least temporarily in a memory of the control unit. The stored approximation parameters can be used by a pump model or by a mathematical algorithm to determine the required speed for setting a desired delivery rate or volume flow.

According to a further embodiment, the approximation parameters of the idle operation are stored in the form of a temperature-dependent equation or in the form of a table for different temperatures in the memory of the control unit. This allows the measurement of the pump motor temperature to be used to determine the required approximation parameters of the idle operation. The respective temperature dependence of the approximation parameters can, for example, be determined in advance and can preferably be used without restriction for a series of drainage pumps or a specific type of drainage pump.

The pump motor temperature can advantageously be determined by a motor-side sensor or indirectly by measuring an ambient temperature, for example in a suds container or sump of the household appliance.

The sensor can preferably be coupled to the control unit in a data-conducting manner.

The advantages and features explained above in connection with the device also apply analogously to the method and vice versa. Individual features or aspects of the present invention can be combined with one another and have the advantages explained in this context.

• 1 ein Leerbetriebsstrom-Drehzahl-Diagramm zum Veranschaulichen einer Temperaturabhängigkeit eines Leerbetriebsstroms einer Entwässerungspumpe.
• 2 eine Frontansicht eines Haushaltsgeräts gemäß einer Ausführungsform.
• 3 ein schematisches Diagramm zum Veranschaulichen einer Stromaufnahme der Ablaufpumoe zum Druckaufbau in einem Fördermedium.
• 4 ein Diagramm zum Veranschaulichen eines quadratischen Approximationsparameters einer Annäherungskurve zweiten Grades für den Verlauf des Leerbetriebsstroms aus 1.
• 5 ein Diagramm zum Veranschaulichen eines linearen Approximationsparameters einer Annäherungskurve zweiten Grades für den Verlauf des Leerbetriebsstroms aus 1.
• 6 ein Diagramm, welches ein Verfahren zur Bestimmung eines Leerlaufstroms für jede beliebige Drehzahl veranschaulicht.
• 7 ein Diagramm zum Veranschaulichen eines erfindungsgemäßen Verfahrens gemäß einer ersten Ausführungsform.
• 8 ein Diagramm zum Veranschaulichen einer Temperaturabhängigkeit von Approximationsparametern einer Annäherungskurve zweiten Grades für den Verlauf des Leerbetriebsstroms aus 1.
• 9 ein Diagramm zum Veranschaulichen eines erfindungsgemäßen Verfahrens gemäß einer zweiten Ausführungsform.

In the following, the invention is explained in detail using advantageous embodiments with reference to the attached figures.

• 1 an idle operating current-speed diagram to illustrate a temperature dependence of an idle operating current of a drainage pump.
• 2 a front view of a household appliance according to an embodiment.
• 3 a schematic diagram illustrating the current consumption of the drain pump for building up pressure in a pumped medium.
• 4 a diagram illustrating a quadratic approximation parameter of a second degree approximation curve for the course of the no-load current from 1 .
• 5 a diagram illustrating a linear approximation parameter of a second degree approximation curve for the no-load current curve from 1 .
• 6 a diagram illustrating a method for determining an idle current for any speed.
• 7 a diagram illustrating a method according to the invention according to a first embodiment.
• 8th a diagram illustrating a temperature dependence of approximation parameters of a second degree approximation curve for the course of the no-load current from 1 .
• 9 a diagram illustrating a method according to the invention according to a second embodiment.

In the figures, like or corresponding elements are designated by like reference numerals. Factors such as numerical values, shapes, components, locations of components, and the manner in which the components are connected are merely illustrative and not limiting. In the For reasons of clarity and to improve recognizability, some drawings use different scales.

The figures serve in particular to illustrate a method for determining an idle current consumption IL of a drainage pump 110 of a household appliance 100.

The 2 shows a front view of a household appliance 100 according to an embodiment. The household appliance 100 has a control unit 120 which is set up to control a drainage pump 110. The drainage pump 110 is designed as a free-flow pump and can convey a quantity of liquid collected in a lye container 130 or sump into a drain 200. The drain 200 has a height relative to the lye pump 110 which functions as the delivery head H of the drainage pump 110.

In the 3 is a schematic diagram to illustrate a current consumption Ip of the drainage pump 110 for building up pressure in a conveying medium. The Y-axis describes the current consumption Ip of the drainage pump 110 and the X-axis the speed of the drainage pump 110. The diagram can be based, for example, on measurements from 1 at a constant pump motor temperature with a filled drainage pump 110 and a closed drainage hose. The drainage pump 110 can thus build up pressure, but no further current is required to generate the flow rate. It is clear that the current consumption Ip for generating pressure is not temperature dependent. The course of the current curve in 3 thus shows a quadratic current consumption Ip, which agrees with the so-called hydraulic affinity law p~n ² .

In the 7 a flow chart is shown to illustrate a method 10 according to the invention in accordance with a first embodiment. The method 10 is used to determine an idle current consumption I0 of a drainage pump 110 for any set speed n of the drainage pump 110.

The measurement of the current consumption or the motor currents of a drive motor (not shown) of the drainage pump 110, which drives a pump impeller (not shown) directly or indirectly via a clutch, is carried out, for example, by an internal sensor system of the control unit 120 and/or by additional sensors 141. For example, voltmeters for indirect current measurement, Hall sensors and the like can be used to determine the motor currents I required to maintain the respective speeds n.

In a step 11, the drainage pump 110 is controlled by the control unit 120 such that the drainage pump 110 is operated at a first speed n1 during a first time interval t1. During the first time interval t1, a first current I(n1) required for operation at the first speed n is determined.

Furthermore, the drainage pump 110 is operated during a second time interval t2 at a second speed n2 12. The first speed n1 and the second speed n2 are designed to be lower than a zero delivery speed of the drainage pump 110. Furthermore, the second speed n2 is designed to be greater than the first speed n1. In the exemplary embodiment shown, the first time interval t1 is equal to the second time interval t2.

During the second time interval t2, a second current I(n2) of the drainage pump 110 required for operation at the second speed n2 is determined. Based on the determined first current I(n1) and second current I(n2), an idle current consumption I0 is determined for any speed n of the drainage pump 110 13. The drainage pump 110 can then be controlled by the control unit 120 based on the determined idle current consumption I0 to set a target delivery rate 14.

The idle current consumption or the idle current I0 corresponds to a starting value of a flow rate-current line. This corresponds to a drainage pump 110 filled with water, which is however not delivering water. Such a case occurs, for example, with a closed drain hose.

The method 10 can be carried out when the drainage pump 110 is started. Two different speeds n1, n2 are set. The speeds n1, n2 are set so low that only the water level in the drain hose rises and is not yet pumped. The drainage pump 110 can therefore only build up pressure. These speeds n1, n2 are therefore lower than the so-called zero pumping speed. An analysis of the data of the 1 shows that there is a regularity between the temperature dependence of the curves and the difference in motor currents, for example at 1400 rpm and 1000 rpm. This temperature dependence can be described mathematically. For this purpose, the curves are 1 approximated as quadratic functions IL = a*n ² + b*n.

$$\text{b}=\text{c}3*\text{T}+\text{c}4\text{ bzw}.\text{ b}=\text{f}\left(\text{c}3;\text{c}4\right);\left(\text{c}3;\text{c}4\right)=\text{f}\left(\mathrm{\Delta }\text{I}\right)$$

There is a linear relationship between the approximation parameters a, b and the current difference (I(n2=1400)-I(n1=1000)) for all measured pump motor temperatures. These relationships are shown in the 4 and the 5 illustrated. The 4 a diagram illustrating a quadratic approximation parameter a of a second degree approximation curve for the course of the no-load current IL from 1 . In the 4 The temperature T is plotted on the X-axis and the resulting quadratic approximation parameter a is plotted on the Y-axis. Analogously, the 5 a diagram illustrating a linear approximation parameter b of a second degree approximation curve for the course of the no-load current IL from 1 . In the 5 The temperature T is plotted on the X-axis and the resulting linear approximation parameter b is plotted on the Y-axis. The following straight line equations can thus be set up for the approximation parameters a,b. $$\text{a}=\text{c}1*\text{T}+\text{c}2\text{or}.\text{a}=\text{e}\left(\text{c}1;\text{c}2\right);\left(\text{c}1;\text{c}2\right)=\text{e}\left(\mathrm{\Delta }\text{I}\right)$$

$$\text{b}=\text{c}3*\text{T}+\text{c}4\text{or}.\text{b}=\text{e}\left(\text{c}3;\text{c}4\right);\left(\text{c}3;\text{c}4\right)=\text{e}\left(\mathrm{\Delta }\text{I}\right)$$

The 4 and 5 The relationships shown can be approximated as a straight line and the approximation parameters c1(a), c2(a), c3(b) and c4(b) are stored in the control unit 120 for the method 10. For this purpose, the control unit 120 can have a memory unit (not shown).

The constant approximation parameters d1 (for the quadratic part) and d2 (for the linear part) of the pressure parabola are also determined from 3 for the method 10 in the control unit 120. This allows the pressure parabola to be simulated using a second degree equation Ip = d1*n ² + d2*n.

At one of the two set speeds n1, n2, the pressure parabola, which is constant with respect to the temperature T, and the corresponding no-load curve IL is calculated from the difference between the two measured values for the current I(n1) and I(n2). 1 added to a no-load current consumption I0, so that the resulting curve I0 (sum) enables the determination of the no-load current I0(n) at any speed n. The 6 shows a diagram which illustrates the method 10 for determining the no-load current I0 for any speed n and visualizes the respective components for the no-load current IL and the current for pressure build-up Ip. 6 the set speeds n of the drainage pump 110 on the X-axis and the motor currents I of the drainage pump 110 resulting from the set speeds n on the Y-axis.

For method 10, the following calculation steps can be used as part of a calibration by the control unit 120:

$$\text{b}=\text{c}3*\text{T}+\text{c}4\text{ bzw}.\text{ b}=\text{f}\left(\text{c}3;\text{c}4\right);\left(\text{c}3;\text{c}4\right)=\text{f}\left(\mathrm{\Delta }\text{I}\right)$$

$$\text{Ip}=\text{f}\left(\text{d}1;\text{d}2\right);\left(\text{d}1;\text{d}2\right)=\text{const}.$$

The following relationships apply to the constant approximation parameters a, b of the idle operation and the constant approximation parameters d1, d2 of the pressure build-up: $$\text{a}=\text{c}1*\text{T}+\text{c}2\text{or}.\text{a}=\text{e}\left(\text{c}1;\text{c}2\right);\left(\text{c}1;\text{c}2\right)=\text{e}\left(\mathrm{\Delta }\text{I}\right)$$

$$\text{b}=\text{c}3*\text{T}+\text{c}4\text{or}.\text{b}=\text{e}\left(\text{c}3;\text{c}4\right);\left(\text{c}3;\text{c}4\right)=\text{e}\left(\mathrm{\Delta }\text{I}\right)$$

$$\text{IP}=\text{e}\left(\text{d}1;\text{d}2\right);\left(\text{d}1;\text{d}2\right)=\text{const}.$$

$$\text{I}2=\text{I}\left(\text{n}2\right)-\left(\text{d}1*\text{n}{2}^2+\text{d}2*\text{n}2\right)$$

In a further step, the current components Ip(n1), Ip(n2) for the pressure build-up are subtracted from the measured first current I(n1) and second current I(n2). $$\text{I}1=\text{I}\left(\text{n}1\right)-\left(\text{d}1*\text{n}{1}^2+\text{d}2*\text{n}1\right)$$

$$\text{I}2=\text{I}\left(\text{n}2\right)-\left(\text{d}1*\text{n}{2}^2+\text{d}2*\text{n}2\right)$$

In a subsequent step, the difference between the first current and the second current minus the current component Ip for pressure build-up can be determined: $$\mathrm{\Delta }\text{I}=\text{I}2-\text{I}1$$

$$\text{b}=\text{c}3*\mathrm{\Delta }\text{I}+\text{c}4$$

With this difference ΔI, the constant approximation parameters a, b of the idle operation can be determined according to the 4 and 5 be calculated: $$\text{a}=\text{c}1*\mathrm{\Delta }\text{I}+\text{c}2$$

$$\text{b}=\text{c}3*\mathrm{\Delta }\text{I}+\text{c}4$$

The approximation parameters a, b can alternatively or additionally be determined within the framework of a linear and/or quadratic regression.

$$\text{IL}\left(\text{n}\right)=\left(\text{a}*{\text{n}}^2+\text{b}*\text{n}\right)-\left(\text{a}*\text{n}{1}^2+\text{b}*\text{n}1\right)$$

$$\text{I}0\left(\text{n}\right)=\text{I}\left(\text{n}1\right)+\text{Ip}\left(\text{n}\right)+\text{IL}\left(\text{n}\right)$$

In a further step, the idle current consumption I0 is determined for any target speed n, for example 3000 rpm. This is done by summing up the current component Ip for the pressure build-up and the current component IL for idle operation: $$\text{IP}\left(\text{n}\right)=\left(\text{d}1*{\text{n}}^2+\text{d}2*\text{n}\right)-\left(\text{d}1*\text{n}{1}^2+\text{d}2*\text{n}1\right)$$

$$\text{IL}\left(\text{n}\right)=\left(\text{a}*{\text{n}}^2+\text{b}*\text{n}\right)-\left(\text{a}*\text{n}{1}^2+\text{b}*\text{n}1\right)$$

$$\text{I}0\left(\text{n}\right)=\text{I}\left(\text{n}1\right)+\text{IP}\left(\text{n}\right)+\text{IL}\left(\text{n}\right)$$

As an alternative to the first speed n1, the second speed n2 can also be used. In the 6 the individual components I0, Ip, IL of the sum described above are illustrated. The curves summarized using the curly brackets describe the temperature dependence of these current components I0 and IL. The offset or the absolute part I(n1) of the total current consumption I0 is shown in the 6 not shown for the sake of clarity.

Thus, for any target speed n (or several target speeds n), the corresponding no-load current I0(n) can be determined, which includes the influence of the pump motor temperature T when the pump starts (see 6 ).

In the 9 a diagram is shown to illustrate a method 10 according to the invention according to a second embodiment. As an alternative to operating the drainage pump 110 at the second speed n2 during the second time interval t2 and determining the second current I(n2), a temperature T of the drainage pump 110 is measured 15 and, based on the determined first current I(n1) and the measured temperature T, an idle current consumption I0 is determined for any speed n of the drainage pump 110 16. For this embodiment, a temperature sensor 140 ( 2 ) is provided, which is read out by the control unit 120. In a subsequent step, the control unit 120 can control the drainage pump 110 based on the calibration carried out 14.

The 8th shows a diagram to illustrate a temperature dependence of the constant approximation parameters a, b of a second degree approximation curve for the course of the no-load current IL from 1 If a sufficiently accurate pump motor temperature measurement exists, the curve of the no-load current consumption I0 can be determined directly from this pump motor temperature T. In the 8th the temperature T of the drainage pump 110 forms the X-axis and the resulting values of the approximation parameters a, b form the Y-axis.

For example, the 8th The value table shown as an example can be stored in the memory of the control unit 120 in order to assign the constant approximation parameters a, b to the measured pump motor temperature T. Alternatively, the assignment of the constant approximation parameters a, b can be carried out depending on the pump motor temperature T using a formula or a model.

List of reference symbols

10

Proceedings

100

Household appliance

110

Free-flow pump / drainage pump

120

Control unit

130

Lye container

140

Temperature sensor

200

Drain

IP

Current share for pressure build-up

IL

Power share for idle operation

I0

No-load current / no-load current consumption

T

Pump motor temperature

n

number of revolutions

I(n1)

first stream

In 2)

second stream

t

Time interval

Claims (10)

Method (10) for determining an idle current consumption (I0) of a drainage pump (110), for example in the form of a drain pump of a water-conducting household appliance (100), wherein the drainage pump (110) is controlled by a control unit (120) such that the drainage pump (110) is operated at a first speed (n1) during a first time interval (t1), wherein a first current (I(n1)) required for operation at the first speed (n1) is determined, wherein the drainage pump (110) is operated at a second speed (n2) during a second time interval (t2), wherein the first speed (n1) and the second speed (n2) are lower than a zero delivery speed of the drainage pump (110) and the second speed (n2) and the first speed (n1) differ, and wherein a second current (I(n2)) required for operation at the second speed (n2) of the drainage pump (110) is determined, wherein based on the determined first current (I(n1)) and second current (I(n2)) an idle current consumption (I0) is determined for any speed (n) of the drainage pump (110), or wherein a temperature (T) of the drainage pump (110) is measured, wherein based on the determined first current (I(n1)) and the measured temperature (T) an idle current consumption (I0) is determined for any speed (n) of the drainage pump (110). Procedure according to Claim 1 , wherein the second speed (n2) is greater than the first speed (n1). Procedure according to Claim 1 or 2 , wherein the drainage pump (110) is controlled during a washing program and/or at the end of a washing program by the control unit (120) to set the first speed (n1) and/or the second speed (n2) and/or a measurement of the temperature (T) of the drainage pump (110) is carried out. Method according to one of the preceding claims, wherein a current consumption (Ip), designed as a second-order function dependent on a rotational speed (n), for pressure build-up by the drainage pump (110) is determined at the first rotational speed (n1) and/or the second rotational speed (n2). Procedure according to Claim 4 , wherein the second order function of the current consumption (Ip) for pressure build-up has two constant approximation parameters (d1, d2) of the pressure build-up, which are determined based on the first current (I(n1)) and the second current (I(n2)). Method according to one of the preceding claims, wherein an idle operating current (IL) is approximated as a second degree equation dependent on the rotational speed (n) with constant approximation parameters (a, b) of the idle operation and is calculated for any rotational speed (n), wherein the approximation parameters (a, b) each depend linearly on a temperature (T) of the drainage pump (110) and are determined based on a difference (ΔI) of the second current (I(n2)) and the first current (I(n1)) minus a pressure component (Ip). Method according to one of the Claims 4 until 6 , where the no-load current consumption (I0) for any speed (n) is determined as a sum of an no-load current (IL) and a current consumption (Ip) for pressure build-up. Method according to one of the Claims 4 until 7 , wherein the approximation parameters (d1, d2) of the pressure build-up and the approximation parameters (a, b) of the idle operation are determined after the first time interval (t1) and the second time interval (t2) by the control unit (120) and are stored at least temporarily in a memory of the control unit (120). Procedure according to Claim 8 , wherein the approximation parameters (a, b) of the idle operation are stored in the memory of the control unit (120) in the form of a temperature-dependent equation or in the form of a table for different temperatures (T) of the drainage pump (110). Household appliance (100) comprising a control unit (120) and at least its drainage pump (110) which is controlled by the control unit (120), wherein the household appliance (100) is adapted to carry out the method (10) according to one of the preceding claims.

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