EP4365452A1 - Adaptive rotational speed adjustment of free-flow pumps in water-bearing domestic appliances - Google Patents

Abstract

The invention relates to a method for determining a relationship between a volume flow and a speed of a free-flow pump for adaptively adjusting the speed during operation of the free-flow pump, wherein at least two different speeds of the free-flow pump are set via a control unit, a motor current of the free-flow pump is determined for each set speed, based on the set speeds and the determined motor current, a motor current-speed line and a slope of the motor current-speed line and a straight line equation of the motor current-speed line at the intersection of the X-axis depicting the speed are determined, and the determined slope of the motor current-speed line and the straight line equation of the motor current-speed line at the intersection of the X-axis are used as proportionality factors for calculating the volume flow with the aid of a predetermined motor current. The invention further relates to a household appliance.

Description

The present invention relates to a method for determining a relationship between a volume flow and a speed of a free-flow pump for adaptively adjusting the speed during operation of the free-flow pump. The invention also relates to a household appliance.

In water-conducting household appliances, such as washing machines or dishwashers, so-called free-flow pumps are regularly used as wastewater pumps. Such pumps are currently operated at fixed speeds or speed levels. The fixed speeds or speed levels result in different volume flows depending on the connection conditions of the drain hose in the household (pressure loss and discharge head) and, as a result, different pumping times.

The connection conditions of the household appliance in the home determine the system characteristic curve. This results in a volume flow or delivery flow depending on the speed of the free-flow pump. The power or current consumption of the free-flow pump increases with the delivery flow. The motor electronics or the structure of the pump motor only allow a certain maximum current consumption, so this is limited. The maximum possible pump speed therefore depends on the connection conditions in the home.

The fixed speed values also have an impact on the spinning process, as the amount and composition (lye, foam, air content) of the fluid flowing to the pump during spinning vary greatly. Due to the constant speed of the pump, air is sucked in when the inflow quantity is low and the free-flow pump continues to run without pumping. In addition, inaccuracies arise with regard to the remaining time display of the household appliance's washing program.

It is therefore the object of the present invention to provide a method for a water-conducting household appliance which enables a speed-adjusted control of free-flow pumps.

This object is achieved by a method having the features of claim 1, by a control unit having the features of claim 9 and by a household appliance having the features of claim 10.

According to one aspect of the present invention, a method is provided for determining a relationship between a volume flow and a speed of a free-flow pump for adaptively adjusting the speed during operation of the free-flow pump. The method can be carried out, for example, by a control unit coupled to a free-flow pump in a household appliance.

The free-flow pump can be a compact and cavitation-resistant pump. They are particularly suitable for the gentle transport of media containing solids.

In one step, at least two different speeds of the free-flow pump are set via a control unit. After the set speed has settled, a motor current of the free-flow pump is determined for each set speed. This can be implemented via external sensors or via the motor parameters read by the control unit.

Based on the set speeds and the determined motor current, a motor current-speed line and a slope of the motor current-speed line and a straight line equation of the motor current-speed line at the intersection point of the X-axis representing the speed are determined in a further step.

The determined slope of the motor current-speed line and the straight line equation of the motor current-speed line at the intersection point of the X-axis are advantageously used as proportionality factors for calculating the volume flow using a given motor current.

According to a further aspect of the invention, a household appliance is provided which has a control unit and at least one free-flow pump. The free-flow pump can be designed, for example, as a waste water pump which is control unit. The household appliance is designed to carry out at least one method according to the invention.

The process enables adaptive adjustment of the pump speed of a free-flow pump in order to achieve a nominal or maximum flow rate for the largest possible range of connection height and pressure loss of the drain hose in households. The adaptive adjustment of the speeds of the free-flow pump can compensate for variations in the system characteristic curve or take them into account more precisely when displaying the remaining time of a washing program.

The affinity law that applies to the operation of centrifugal pumps cannot usually be used for a mathematical description of the operation of free-flow pumps. Contrary to the affinity law, it was determined that in the case of a drain pump of a water-carrying household appliance, there is a linear relationship between the torque-generating motor current and the speed. This can be explained by the fact that the drain pump is similar to a so-called free-flow pump, which has a large gap between an impeller and a pressure chamber housing so that foreign bodies floating in the medium can pass through the pump unhindered. A linear relationship applies for different delivery heads and pressure losses. As a result, a motor current-speed line can be calculated or determined.

By subtracting a product of the increase with the desired motor current and the straight line equation of the motor current-speed line at the intersection point of the X-axis, the volume flow or delivery flow that occurs at the desired motor current can be determined.

The speed control of the pump according to a target or maximum value for the volume flow enables the predefined sequence of a washing program to be ensured when a nominal value of the volume flow is specified, thus ensuring, for example, the exact remaining time display. When the maximum value is specified, an adaptive shortening of the washing program duration is possible, for example for short programs of the household appliance.

In addition, such control of the operation of the free-flow pump enables further improvements of the pumping process during spinning, for example with the aim of adaptively shortening the spin profile, provided that the household appliance is designed as a washing machine or a washer-dryer.

According to one embodiment, a motor current averaged over a time interval is determined for each speed. Alternatively, a motor current actually measured at a point in time or a corresponding effective value is determined for each speed. On the one hand, the speeds set by the control unit should be as far apart as possible in order to minimize the influence of the measurement deviation and, as a result, to determine the motor current-speed line as precisely as possible. On the other hand, limits arise at high speeds and low zero discharge heads due to the maximum power consumption of the free-flow pump and at low speeds and high zero discharge heads, since no volume flow is established here and the motor current-speed line cannot be determined with sufficient precision.

When using the actual determined value for the speed, the method can be carried out more quickly. The use of averaged values, on the other hand, enables a lower susceptibility to errors and a higher level of accuracy. The method according to the invention can be carried out in an initial step when starting a washing program in order to achieve optimal calibration of the free-flow pump.

The method can be adapted to most applications and installation configurations of the household appliance if the control unit sets at least two different speeds in a speed range between 2400 rpm and 3700 rpm, in particular between 2700 rpm and 3300 rpm. Advantageously, a range of the system delivery head between a floor drain and a hanging height of a drain hose of the household appliance of up to 1.5 m can be mapped if the speeds to be approached are 2700 rpm and 3300 rpm.

According to a further embodiment, a maximum motor current is determined depending on the control unit and/or the free-flow pump and a maximum speed is calculated using the motor current-speed line.

According to a further embodiment, a maximum volume flow is determined by means of the maximum speed and a time for pumping out a predefined amount of water with the maximum volume flow is determined.

By knowing the maximum possible volume flow of the free-flow pump, the remaining time display of a washing program, especially during a spin cycle or a spin phase, can be determined particularly precisely.

Due to the linear relationship between motor current and speed for free-flow pumps, the maximum motor current value can be calculated according to the power consumption of the free-flow pump. However, the relationship does not have to be linear. For this purpose, the slope of the motor current-speed line and the straight line equation of the motor current-speed line at the intersection of the X-axis can be used as proportionality factors for calculating the maximum possible volume flow. The maximum possible motor current depends on the motor design and the design of the motor control (especially the inverter). This sets the household-specific maximum volume flow. In addition, a motor current-volume flow line and/or equation can be determined and the volume flow and the time for pumping out a quantity of water defined according to the washing program can be determined. As a result, the defined quantity of water, for example in the suds container or sump of the household appliance, can be pumped out as quickly as possible in order to minimize the washing time.

According to a further embodiment, an operating point characteristic curve is determined based on the determined volume flow as a function of the motor current. This measure can be used to determine optimal operating conditions for the free-flow pump depending on the installation location and the connection conditions of the household appliance.

According to a further aspect of the invention, a method is provided for determining a relationship between a volume flow and a speed of a free-flow pump for adaptively adjusting the speed during operation of the free-flow pump. The method describes an alternative determination of the volume flow depending on the speed and/or the motor current.

In one step, a pump characteristic curve equation of the free-flow pump is defined as a third-order polynomial depending on a volume flow. In a further step, a system characteristic curve equation of a system in which the free-flow pump is installed is defined as a second-order polynomial depending on a volume flow. Furthermore, the system characteristic curve equation can also be defined as a polynomial of any order.

Then, an intersection point between the pump characteristic curve equation and the system characteristic curve equation is determined for at least two speeds. In a further step, an operating point characteristic curve is determined from the determined intersection points in order to calculate the volume flow using a specified motor current.

The operating point and thus the resulting volume flow results from the intersection between the system characteristic curve and the pump characteristic curve. The pump characteristic curves for different speeds can be measured depending on the pump manufacturer and the pump geometry. If the pump works at the maximum possible delivery head (zero delivery head), no delivery flow occurs. The system characteristic curve is determined according to the connection conditions in the household. It depends on the system delivery head (connection or hanging height of the drain hose) and the pressure loss or flow resistance (for example due to built-in wall siphons or cross-section reductions in the connection area).

The pump characteristics of a pump type are measured for several speeds or defined as equations. In order to be able to determine the pump characteristics continuously for any speed, the approximation parameters of the measured characteristics are transferred to a parameter model. To do this, the characteristic curve approximation parameters are described as a function of the speed using further approximations. The pump characteristics are thus continuously specified using a third-order polynomial equation. The system characteristics can advantageously be approximated by starting up at different speeds when the pump starts. To minimize the number of measuring points required, the system characteristics are assumed to be a second-order polynomial.

To determine the operating point characteristic, the pump and system characteristic are equated. The operating point characteristic can be derived from the resulting zero calculation of the third degree polynomial.

In one embodiment, several intersection points between the pump characteristic curve equation and the system characteristic curve equation for different speeds of the free-flow pump are determined using a numerical method, such as Newton's method. This measure allows the operating point characteristic curve to be calculated quickly and efficiently.

According to a further aspect of the present invention, a control unit for a water-conducting household appliance is provided, wherein the control unit is designed to carry out the method according to one of the preceding claims. The control unit can comprise a computing unit (e.g. a CPU). The control unit can be designed to receive data, process it and output control commands.

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.

Fig. 1

ein schematisches Diagramm zum Veranschaulichen von Betriebspunkten als Schnittpunkte von Anlagenkennlinien und Pumpenkennlinien.

Fig. 2

ein schematisches Diagramm zum Veranschaulichen von Pumpenkennlinien für unterschiedliche Drehzahlen.

Fig. 3

ein schematisches Diagramm zum Veranschaulichen von Motorstrom-Drehzahl-Geraden.

Fig. 4

ein schematisches Diagramm zum Veranschaulichen von Volumenstrom-Motorstrom-Geraden für unterschiedliche Drehzahlen.

Fig. 5

ein schematisches Diagramm zum Veranschaulichen von Anstiegen der Volumenstrom-Motorstrom-Geraden aus Fig. 5.

Fig. 6

ein schematisches Diagramm zum Veranschaulichen von ermittelten Volumenströmen in Abhängigkeit von Drehzahlen basierend auf einem Verfahren gemäß einer ersten Ausführungsform und gemäß einer zweiten Ausführungsform.

Fig. 7

ein schematisches Diagramm zum Vergleichen von ermittelten Volumenströmen in Abhängigkeit von einer Drehzahl basierend auf einem Verfahren gemäß einer ersten Ausführungsform und gemäß einer dritten Ausführungsform.

Fig. 8

eine Frontansicht eines Haushaltsgeräts gemäß einer Ausführungsform.

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

Fig.1

a schematic diagram to illustrate operating points as intersections of system curves and pump curves.

Fig.2

a schematic diagram illustrating pump characteristics for different speeds.

Fig.3

a schematic diagram illustrating motor current-speed curves.

Fig.4

a schematic diagram illustrating volume flow-motor current lines for different speeds.

Fig.5

a schematic diagram to illustrate slopes of the volume flow-motor current line from Fig.5 .

Fig.6

a schematic diagram for illustrating determined volume flows as a function of rotational speeds based on a method according to a first embodiment and according to a second embodiment.

Fig.7

a schematic diagram for comparing determined volume flows as a function of a rotational speed based on a method according to a first embodiment and according to a third embodiment.

Fig.8

a front view of a household appliance according to an embodiment.

In the figures, like or corresponding elements are designated by the same reference numerals. Factors such as numerical values, shapes, components, positions of components and the manner in which the components are connected to one another are merely illustrative and not restrictive. Different scales are used in some of the drawings for reasons of clarity and to improve recognizability.

The Fig.1 shows a schematic diagram to illustrate three example operating points B1, B2, B3. The operating points B1, B2, B3 and thus the resulting volume flows Q result from intersections between system characteristic curves 10 and pump characteristic curve 20. The diagram illustrates the relationship between a delivery head H and the volume flow Q.

The pump characteristic curves 20 for different speeds n1, n2, n3 can be measured depending on the pump manufacturer and pump geometry of a free-flow pump 110 (Fig. 9). If the vortex pump 110 operates at the maximum possible discharge head (zero discharge head), no discharge flow occurs.

The system characteristic curve 10 is determined according to the connection conditions in the household or at the installation location of a household appliance 100. The system characteristic curve 10 depends on the system discharge head H (connection or hanging height of the drain hose) and the pressure loss or flow resistance (for example due to built-in wall siphons or cross-sectional reductions in the connection area).

The pump characteristic curves 20 of a pump type are measured for several speeds n1, n2, n3. In order to be able to determine the pump characteristic curve 20 continuously for any speed, approximation parameters of the measured pump characteristic curve 20 are transferred to a parameter model. For this purpose, the characteristic curve approximation parameters are described as a function of the speed n by the approximations. The pump characteristic curve is thus continuously specified via a third-order polynomial equation in the form of a pump characteristic curve equation 21. In the Fig.2 A diagram illustrates a comparison between the measured or specified pump characteristic curve 20 (dashed line) and the calculated values based on a pump characteristic curve equation 21. There are only deviations at volume flows of less than 20 l/min, which are negligible during operation of the household appliance 100.

Contrary to the affinity law for regular centrifugal pumps, it was determined that in a drain pump 110 of a household appliance 100, such as a washing machine, there is a linear relationship between the torque-generating motor current I and the speed n. This can be explained by the fact that the drain pump 110 resembles a so-called free-flow pump, which has a large gap between the impeller and the pressure chamber housing so that foreign bodies floating in the medium can pass through the drain pump 110. In the Fig.3 This relationship is shown for different operating points B. A linear relationship applies to all different delivery heads H and pressure losses. As a result, motor current-speed lines can be calculated, which are illustrated in the diagram.

The different operating points of the vortex pump 110 lie on a straight line in the volume flow-motor current diagram at a specific speed n. Fig.4 shows a schematic diagram to illustrate volume flow-motor current lines for different speeds n.

The individual measuring points are shown as points. At each measuring point, the operating point of the free-flow pump 110 was adjusted by adjusting the discharge head H and/or by additional pressure loss in the discharge hose. All measuring points of a specific speed n lie on a straight line. All straight lines have a common intersection point with the coordinates S(Xs;Ys). Xs corresponds to an intersection point with the X axis and Ys to an intersection point with the Y axis.

A rise A of the respective volume flow-motor current line is speed-dependent and can be specified using a second degree polynomial equation. The respective rises A of the Fig.4 The volume flow-motor current line shown is in the Fig.5 depending on the speed n.

Subsequently, the relationship between the volume flow Q and the motor current I is formed from the intersection point S(Xs;Ys) of the volume flow-motor current line and the speed-dependent increase A.

The parameterization of these relationships is not generally valid and can advantageously be adapted to the pump type (pump manufacturer, geometric variant).

According to a first embodiment of a method according to the invention, a rise A of the volume flow-motor current line is determined by measurement. For this purpose, at least two different speeds n1, b2 are approached via the pump control or control unit 120. As soon as the motor current I has stabilized, the respective motor current I is determined and the volume flow-motor current line is derived.

The speeds used should be as far apart as possible in order to minimize the influence of the measurement deviation and, as a result, to determine the volume flow-motor current line as accurately as possible. In the example shown, schematic speeds n between 2400 rpm and 3700 rpm are taken into account (see Fig. 6 and Fig. 7 ).

Using the relationships already explained, the volume flow Q can now be calculated for any speed n. To do this, the volume flow Q or delivery flow that occurs at the desired motor current I is determined by subtracting a product of the increase A with the desired motor current I and the straight line equation of the motor current-speed line at the intersection point Xs of the X-axis.
The use of the actual motor current value I _qdelta is just as possible as the use of an averaged value of the motor current I _qMean . The Fig.6 illustrates the calculated volume flows Q depending on the motor current I based on the use of the actual motor current value I _qdelta and the use of the averaged value of the motor current I _qMean . In the previously defined speed range, no relevant difference is present in the diagram. The points represent the calculated values, which have been adjusted by polynomials to illustrate differences.

According to a third embodiment of the method, the operating point B and consequently the volume flow Q are set by equating the system characteristic curve 10 and the pump characteristic curve 20 or corresponding equations. The approximated pump characteristic curve equation 21 is stored as a speed-dependent equation (advantageously as a third-order polynomial). The aim is to approximate the system characteristic curve in the form of a system characteristic curve equation by starting at different speeds n when the pump starts. To minimize the required measuring points, the system characteristic curve equation is assumed to be a second-order polynomial.

To determine the polynomial of the system characteristic curve equation, three measuring points are necessary. To maximize accuracy, the measuring points can be as far apart as possible. To determine the operating point characteristic curve B, the system characteristic curve equation and the pump characteristic curve equation 21 are equated. This results in a zero point problem, which can be solved locally using a numerical method, such as the Newton method, in order to determine a relationship between the volume flow Q and the speed n or motor current I. The Fig.7 shows the comparison of the operating point characteristic curve or the volume flows Q depending on the motor current I based on the use of the actual motor current value I _qdelta (approach 1) and the solution of the zero point problem (approach 2).

In the Fig.8 a front view of a household appliance 100 according to an embodiment is shown. The household appliance 100 has a control unit 120 which is set up to control a drain pump 110. The drain pump 110 is designed as a free-flow pump and can convey a quantity of liquid collected in a drain container 130 or sump into a drain 200. The drain 200 has a height relative to the drain pump 110 which functions as the delivery head H of the drain pump 110.

List of reference symbols

10 -

System characteristic curve

100 -

Household appliance

110 -

Free-flow pump / drain pump

120 -

Control unit

130 -

Lye container

20 -

Pump characteristics

21 -

Pump characteristic equation

200 -

Drain

A -

Rise / Gradient

B -

Operating point

n-

number of revolutions

I-

Motor current

Q-

Volume flow

H -

Head

Claims (10)

Method for determining a relationship between a volume flow (Q) and a speed (n) of a free-flow pump (110) for adaptively adjusting the speed (n) during operation of the free-flow pump (110), wherein - at least two different speeds (n1, n2) of the free-flow pump (110) are set via a control unit (120), - for each set speed (n1, n2) a motor current (I) of the free-flow pump (110) is determined, - based on the set speeds (n1, n2) and the determined motor current (I), a motor current-speed line and a slope (A) of the motor current-speed line and a straight line equation of the motor current-speed line are determined at the intersection point of the X-axis (Xs) depicting the speed (n), - the determined slope (A) of the motor current-speed line and the straight line equation of the motor current-speed line at the intersection point (Xs) of the X-axis are used as proportionality factors for calculating the volume flow (Q) using a given motor current (I). Method according to claim 1, wherein a motor current (I _qMean ) averaged over a time interval is determined for each speed (n), or wherein a motor current (I _qdelta ) measured at a point in time is determined for each speed (n). Method according to claim 1 or 2, wherein the control unit (120) sets at least two different rotational speeds (n1, n2) in a rotational speed range between 2400 rpm and 3700 rpm, in particular between 2700 rpm and 3300 rpm. Method according to one of claims 1 to 3, wherein a maximum motor current (I) is determined depending on the control unit (120) and/or the free-flow pump (110) and a maximum speed (n) is calculated by means of the motor current-speed line. Method according to claim 4, wherein a maximum volume flow (Q) is determined by means of the maximum rotational speed (n) and a time for pumping out a predefined amount of water with the maximum volume flow (Q) is determined. Method according to one of claims 1 to 5, wherein an operating point characteristic curve (B) is determined based on the determined volume flow (Q) as a function of the motor current (I). Method for determining a relationship between a volume flow (Q) and a speed (n) of a free-flow pump (110) for adaptively adjusting the speed (n) during operation of the free-flow pump (110), wherein - a pump characteristic equation (21) of the free-flow pump (110) is defined as a third-order polynomial depending on a volume flow (Q), - a system characteristic equation of a system (100) in which the free-flow pump is installed is defined as a second-order polynomial depending on a volume flow (Q), - for at least two speeds (n1, n2) an intersection point is determined between the pump characteristic equation (21) and the system characteristic equation, - to calculate the volume flow (Q) with the aid of a predetermined motor current (I), an operating point characteristic curve B is determined from the determined intersection points. Method according to claim 7, wherein several intersection points between the pump characteristic equation (21) and the system characteristic equation for different speeds (n) of the free-flow pump (110) are determined by a numerical method, such as Newton's method. Control unit (120) for a water-conducting household appliance (100), wherein the control unit (120) is designed to carry out the method according to one of the preceding claims. Household appliance (100), comprising a control unit (120) and at least its free-flow pump (110) which is controlled by the control unit (120), wherein the household appliance (100) is configured to carry out at least one of the methods according to one of the preceding claims.

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