EP1464268B1 - Process for detecting the charge of the strainer arrangement of a dishwasher - Google Patents

Description

The invention relates to a method for detecting the loading of a screening system of a dishwasher.

During the rinsing process in the dishwasher particle-containing impurities are rinsed with the rinsing liquid into the sump. In order to retain the solid components of the impurities from the rinsing liquid, a sieve system is provided in the circulation circuit of the dishwasher, on which the solid components are deposited. The screen system is generally arranged on the suction side of the circulation pump.

Increasing loading of the screen system with the dirt particles filtered out of the flushing liquid worsens the flowability of the screens and the pressure loss in the circulation loop increases. The consequence is an increasing static height difference in the liquid levels before and after the sieves. The sieve system reaches its loading limit when the pressure loss is so high that the circulating volume flow can no longer flow completely through the sieves and there is a strong lack of flushing liquid on the suction side of the circulating pump. This can cause the liquid level after the sieves to drop so much that the circulating pump absorbs more air, which among other things a reduction Hydraulic performance and negative impact on the cleaning result.

Furthermore, in dishwashers with level control on the suction side of a circulating pump as in DE 41 40 949 C2 The lack of fluid on the suction side will cause overfilling of the equipment. If the liquid level falls below a minimum operating level, which is preferably above the suction opening of the circulating pump, a filling process is triggered until either a predetermined level is reached or until safety devices end the filling process. If the sieve system is at its loading limit, hardly any water penetrates to the suction side of the downstream circulating pump and water is accordingly continuously added.

For detecting soiled sieves in household dishwashers with washing container including drain pan and sieve combination incorporated herein disclosed DE 44 00 877 C2 a method in which, while the circulation pump is running, a dynamic level is established within the screen in the drain pan. A height difference is determined from the level outside the screen and the level within the screen. The height difference value is limited and a measured value exceedance of the limited height difference is used as a criterion for contamination of the sieve.

With this method, a sieve contamination can be reliably detected. However, to determine the level of water in the dishwasher, measuring devices before and after the sieve assembly are necessary, which causes additional costs. In addition, especially the Measuring device in front of the sieve susceptible to failure, since the rinsing liquid is loaded in front of the screen assembly with impurities that can be deposited on the measuring device and affect the accuracy or even the functioning of the device. In order to prevent false readings, the determination of the dynamic height difference therefore takes place during the last intermediate rinse cycle or in the final rinse cycle.

It is an object of the invention to provide a method for detecting the screen loading, which at least partially overcomes or at least reduces the aforementioned disadvantages of the prior art.

This object is achieved by a method having the features of patent claim 1. Advantageous embodiments and further developments emerge from the claims dependent on claim 1.

In the method for detecting the loading of a sieve system of a dishwasher (in particular a domestic dishwasher, hereinafter also referred to as dishwasher), a circulation circuit with a sieve and a circulating pump for circulating the rinsing liquid. The first value of a process variable assigned to a level of the rinsing liquid and at least one second value of the process variable assigned to a level of the rinsing liquid or at least one first level of the rinsing liquid corresponding to a first value of a process variable and at least one, a second one Value of the process variable corresponding to the second level of the rinsing liquid determined at least one load characteristic and used as a measure of the Siebbeladung. The process variable is in Clear relationship with the rotational speed of the circulation pump, in particular a Umwälzpumpendrehzahl, a Umwälzpumpenförderdruck, an electrical capacity of the circulating pump, a mechanical capacity of the circulation pump, a volume of the washing liquid or a volume flow of the washing liquid or a flow rate of the washing liquid.

In the method according to claim 1, the effect is exploited that the level of the rinsing liquid upstream of the screen system (hereinafter referred to as level before the screen system) or on the upstream side of the screen system or upstream and downstream of the screen system (hereinafter Also referred to as level after the screen system) or on the downstream side of the screen system or downstream, has a different height, which is dependent on the pressure loss of the screen system. The pressure loss of the screens is a function of screen loading and flow rate across the screens. With increasing flow velocity, which can be increased, for example, via the speed of the sieve system downstream circulation pump or another in unambiguous relation with the speed process variable, the level of the washing liquid decreases in the flow direction after the sieves and the level on the upstream side of the sieves increases accordingly both unloaded and loaded screen system.

Furthermore, with increasing deposition of contaminants on the screen system, the pressure loss in comparison to the unloaded screen system increases at the same rotational speed of the circulating pump or another process variable which is clearly related to the rotational speed. This is also the reason Liquid level at the same speed, for example, after the loaded sieves or downstream less than after the unloaded sieves. In addition, the liquid level decreases with increasing circulation pump speed after loaded sieves more or faster than after unloaded sieves. It follows in the opposite sense that for adjusting the level of the rinsing liquid between two predetermined levels on the downstream side of the screen system respectively different speeds or speed increases or decreases for the loaded and the unloaded screen system are required.

A loading characteristic value which is determined from the first and second values of a process variable assigned to one level of the rinsing fluid and which is unambiguously related to the rotational speed of the circulating pump can therefore be used as a measure of the sieve load. The loading characteristic value can be determined, for example, by determining the first and second values of the process variable at the same level or, preferably, different levels, respectively, and setting these and possibly at least one reference value in a mathematical relationship to one another.

Since, in addition, the liquid level at each identical rotational speed after a loaded screening system is lower than after an unloaded screening system, a loading characteristic value which comprises at least one first level of the rinsing liquid and at least one corresponding to a first value of a process variable unambiguously associated with the rotational speed can also be used. a second value of the second level of the rinsing liquid corresponding to the speed in unambiguously related process variable is determined, advantageously as a measure of the Siebbeladung be used. In this case, when using a suitable measuring device, the screen loading can be derived from a loading characteristic value which has been determined from a first and second value of a process variable corresponding level of the rinsing liquid. This value can then, for example, be compared to a corresponding reference value for a maximally loaded or unloaded screening system.

A great advantage of the method according to claim 1 over the prior art is that for detecting the Siebbeladung only on one side of the screen system, a measuring devices in the dishwasher is necessary. As a result, on the one hand, the costs for a second measuring device can be saved. Furthermore, no additional opening in the drain pan or in the washing tub is to be installed, which represents an additional leak and is therefore costly to seal. In addition, the process can be carried out without interference at any desired time of the rinsing process, if the level of the rinsing liquid is determined by the sieve system, that is to say in the cleaned rinsing liquid.

The loading limit of the screening system is reliably detected by the method according to the invention. As a result, an optimal cleaning result is always guaranteed. In downstream circulation pump is a lack of flushing liquid on the suction side of the circulation pump and the associated disadvantages, such as reduced hydraulic power of the pump, increased noise or foaming excluded.

Furthermore, the method according to claim 1 allows in a simple manner and at any time of the rinsing process, an accurate determination of the current degree of contamination of the screening system. As a result, even incomplete cleaning or backwashing processes can be detected. Incomplete cleaning of the sieve system can have a negative effect on the rinsing result, as both caustic and dirt particles are carried off into the next rinsing process. Furthermore, the screen system achieves the loading limit more quickly if incomplete cleaning is carried out. If incomplete cleaning processes are detected, the necessary measures can be taken in good time, for example renewed backwashing. This leads to a more economical rinsing operation and improved cleaning performance.

According to a preferred aspect of the present invention, the at least one loading characteristic value is calculated as a difference between the at least one first value of the process variable or the level and the at least one second value of the process variable or the level or at least one reference value of the process variable or the level and determines the at least one first value of the process variable or the level and / or the at least one second value of the process variable or the level. Particularly preferably, the difference or the difference of the first and second values of the process variables or levels is used as a measure of the Siebbeladung. It may furthermore be advantageous to use a difference from at least one reference value, for example a maximum or minimum first and / or second value for the process variable or the level, and form the at least one first value and / or the at least one second value, and Use this difference as a measure of the Siebbeladung or load characteristic.

According to a further, particularly preferred aspect of the present invention, the at least one load characteristic value is calculated as a quotient of the at least one first value of the process variable or the level and the at least one second value of the process variable or the level or as a quotient of the at least one first value of the process variable or the level and the at least one second value of the process variable or the level and at least one reference value of the process variable or the level or as a quotient of the at least one first value of the process variable or the level and / or at least one second value of the process variable or of the level and at least one mathematical function comprising the at least one first value of the process variable or the level and / or the at least one second value of the process variable or the level, in particular at least one sum and / or at least a difference and / or at least one Q uotient and / or at least one product determined. In addition, the at least one load characteristic may preferably comprise, as a quotient of mathematical functions, the at least one first value of the process variable or level and / or the at least one second value of the process variable or level, in particular at least one sum and / or at least one difference and / or at least one quotient and / or at least one product.

Preferably, the at least one first value and the at least one second value of the process variable or the level are set in direct relation to one another, ie divided by one another, or via a suitable reference value, for example a maximum or minimum first and / or second value for the process variable , or the sum of the first and second values is normalized accordingly. In this way, a loading characteristic can be determined which can be used advantageously as a measure of the Siebbeladung. In addition, all further calculation types or relationships between the respective first and second values of the process variable or level and possibly a reference value for the determination of a load characteristic value suitable as a measure for a screen load are accordingly possible.

According to a particularly preferred aspect of the present invention, at least one first value of a process variable and at least one second value of the process variable assigned to a lower (or also second) level of the rinsing liquid is at least one load characteristic value from at least one level of the rinsing liquid determined and used as a measure of the Siebbeladung, wherein the upper and the lower level of the rinsing liquid always on one side of the screen system; So both levels are before the screen system or both levels after the screen system or adjust.

In an advantageous embodiment, a minimum value of the process variable is limited by a maximum upper level of the rinsing liquid downstream of the sieve system (or downstream) or a minimum lower level of the rinsing liquid upstream of the sieve system (or inflow side).

It is particularly advantageous if the minimum value of the process variable is determined by the operating level of the dishwasher. The working level is usually set at the factory and chosen so that an optimum cleaning result is achieved by the amount of rinsing liquid circulated in the dishwasher. If the working level is exceeded, that is to say a lower rotational speed of the circulating pump or a process variable which is unambiguously associated therewith, there is a risk that the pressure in the lines is insufficient to ensure a distribution of the rinsing liquid in the washing container required for a good cleaning result.

In particular, it is advantageous if a maximum value of the process variable is limited by a minimum lower level of the rinsing liquid downstream of the sieve system or a maximum upper level of the rinsing liquid upstream of the sieve system. The minimum lower level after the sieving system or the maximum upper level in front of the sieve system should be selected so that sufficient rinsing liquid can still flow through the sieve system in order to feed all the necessary lines in the circulating circuit. This ensures that the determination of the Siebbeladung can be performed at any time of the rinsing process, without a Spülflüssigkeitsmangel occurs after the screen system. In a circulation system connected downstream of the sieve system, this also ensures optimum operation of the pump. If the pump no longer draws enough rinsing liquid but instead partly air, the result of the determination of the sieve loading would also be falsified.

In a particularly advantageous embodiment, the level of the rinsing liquid is determined in a drain pan of the washing container, which is located at the bottom of the washing and in which the screening system is introduced.

Preferably, the level (s) of the rinsing liquid is determined by the sieve system. This has the advantage that the impurities are filtered out of the rinsing liquid and thus can not influence the measuring device. If the levels in front of the sieve are to be determined, then the measuring device can be installed in the drain pan in front of the sieve or in the rinsing tank.

The upper level of the rinsing liquid, to which the at least one first value of the process variable is assigned, and the lower level of the rinsing liquid to which the at least one second value of the process variable is assigned, or the first level of the rinsing liquid corresponding to a first value of a process variable , a second value of the process variable corresponding second level of the rinsing liquid are preferably determined with at least one level measuring device. The determination of the upper and lower levels in front of the screening system or after the screening system can be carried out optionally with two or with only one sensor device. As a level measuring device, for example, an electrical sensor with a pair of electrodes or an optical level sensor with associated switching device or a pressure sensor can be used.

It is particularly advantageous if a measuring device for adjusting the working level in the dishwasher is used as the level measuring device. This saves the installation of another measuring device.

As a result, a further leakage point is avoided and it can be saved an additional seal.

It can also be advantageous if a measuring device for determining the static pressure of the rinsing liquid column before or after the screening system, in particular an analogue pressure sensor, is used as the level measuring device. The use of an analog pressure sensor allows a precise statement about the height of the liquid column or the level, for example in the drain pan and thus also the determination of the load characteristic of only one, a value of a process variable corresponding level. When using such a pressure sensor, for example, a level of the rinsing liquid can be monitored by the sieve system. The loading characteristic value can then be described, for example, as a minimum or maximum level of the rinsing fluid that can be achieved by increasing or decreasing the rotational speed of the circulating pump or another process variable that is clearly related to the rotational speed by a predetermined amount or within a predetermined time window. The load characteristic value or the minimum lower level can be determined, for example, during a startup process of the circulation pump.

In a particularly advantageous embodiment, the upper level of the rinsing liquid to which the at least one first value of the process variable is assigned and the lower level of the rinsing liquid to which the at least one second value of the process variable is assigned are determined by switching points of the level measuring device. This has the advantage that only one measuring device is necessary. Furthermore, there is no large volume difference of the rinsing liquid and thus no large pump capacity performance necessary to set the necessary for the determination of Siebbeladung level difference.

For detecting the loading of the screening system, it is particularly advantageous if the determined loading characteristic value is compared with one or more loading reference values. For this purpose, for example, at least two times during a rinsing process or several successive rinsing operations, the load characteristic can be determined. If these load characteristics are compared with each other, then it is possible to make a statement about the time course of the screen load.

It is particularly advantageous if the loading reference value is from the first value of the process variable assigned to the upper level of the rinsing fluid and the second value of the process variable assigned to the lower level of the rinsing fluid or the loading characteristic value from the first level of the first level corresponding to a first value of the rinsing fluid Rinsing liquid and, corresponding to a second value of the process variable second level of the rinsing liquid at unloaded sieve corresponds. The determined load characteristics can then be compared to this load reference value and it can be determined how far the screen load has progressed. This is advantageous if, for example, incomplete cleaning of the screen should be detected.

It is particularly advantageous if the loading reference value corresponds to the loading characteristic value from the first value of the process variable assigned to the upper level of the rinsing liquid and the second value of the process variable or the load characteristic value assigned to the lower level of the rinsing liquid from the first level of the rinsing liquid corresponding to a first value of a process variable and the second level of rinsing liquid corresponding to a second value of the process variable at a maximum sieve load. The maximum screen load can be any boundary load that can be assigned to incomplete screen cleaning up to completely clogged screen different conditions.

In a particularly advantageous embodiment of the method according to the invention, the loading reference value for the unloaded screening system or the loaded screening system is determined during the first start-up of the dishwasher, preferably at the factory, or predetermined at the factory.

In an expedient embodiment, a screen cleaning process is triggered upon reaching the maximum Siebbeladung. To remove the contamination on the screen system, the cleaning process may then include, for example, tangential flushing or backwashing the screen system.

It is particularly advantageous if a display is triggered when the maximum screen load is reached. This can be advantageous, among other things, if the screen system is so heavily polluted that it must be removed from the machine and mechanically cleaned.

The method according to the invention is advantageously carried out during the operation of the dishwasher, preferably during the filling of the dishwasher with liquid. Will the screen system at the beginning of each Flushing tested, always an optimal operation of the dishwasher is guaranteed. It may also be advantageous to test the sieve system at the end of a rinsing process and, if appropriate, to clean it off so that the contaminants do not cake together or rinse on the sieve between the rinsing operations.

The invention will be further elucidated on the basis of exemplary embodiments and with reference to the accompanying drawings.

• FIG 1 eine Prinzipskizze der Betriebsverhältnisse in einem Spülbehälter mit Ablaufwanne bei beladenem Siebsystem und niedriger Umwälzpumpendrehzahl,
• FIG 2 eine Prinzipskizze der Betriebsverhältnisse in einem Spülbehälter mit Ablaufwanne bei beladenem Siebsystem und hoher Umwälzpumpendrehzahl,
• FIG 3 ein Diagramm das die Abhängigkeit des Wasservolumens in der Geschirrspülmaschine von der Drehzahl der Umwälzpumpe darstellt,
• FIG 4 ein Diagramm das die Abhängigkeit des Spülflüssigkeitsniveaus in der Ablaufwanne nach dem Siebsystem von der Drehzahl der Umwälzpumpe darstellt,
• FIG 5 ein Diagramm das die Abhängigkeit der Siebbeladung von der Drehzahldifferenz der Umwälzpumpe darstellt,
• FIG 6 ein weiteres Diagramm das die Abhängigkeit des Spülflüssigkeitsniveaus in der Ablaufwanne nach dem Siebsystem von der Drehzahl der Umwälzpumpe darstellt.

Shown schematically in each case:

• FIG. 1 a schematic diagram of the operating conditions in a washing container with drain pan with loaded screen system and low circulation pump speed,
• FIG. 2 a schematic diagram of the operating conditions in a washing container with drain pan with loaded sieve system and high circulation pump speed,
• FIG. 3 a diagram showing the dependence of the water volume in the dishwasher on the speed of the circulating pump,
• FIG. 4 a diagram showing the dependence of the Spülflüssigkeitsniveaus in the drain pan after the screen system of the speed of the circulation pump,
• FIG. 5 a diagram illustrating the dependence of the Siebbeladung of the speed difference of the circulation pump,
• FIG. 6 another diagram illustrating the dependence of the Spülflüssigkeitsniveaus in the drain pan after the screen system of the speed of the circulating pump.

Corresponding parts and sizes are in the 1 to 6 provided with the same reference numerals.

FIG. 1 illustrates the basic operating conditions in a washing container with drain pan with loaded screen system and low circulation pump speed. At the bottom of a washing compartment 1 partially shown a drain pan 2 is attached. The opening of the drain pan 2 in the washing container 1 is covered by a sieve plate 3 of a removable sieve system. The sieve system consists of the sieve plate 3 and a sieve 4, which is placed centrally on the Sieblatte 3 and protrudes into the drain pan 2. The sieve 4 is opened on the side facing away from the washing container 1 and extends to the intake manifold of a drain pump 5. The sieve system is usually constructed of several sieves with different opening widths. In this case, for example, the area of the sieve plate 3, which covers the sieve 4 larger openings than the adjacent areas, so that the dirt particles can get into the sieve 4 and are discharged from there by means of the drain pump 5. On the drain pan 2 of the intake manifold of the circulation pump 6 is mounted laterally above the bottom.

The rinsing liquid, usually water, flows through an inlet, not shown here, into the rinsing container 1 and from there into the drain pan 2 until a working level is reached in the drain pan 2, which via a level measuring device likewise not shown here the sieve 4 and the outer wall of the drain pan 2 is determined. If now the rinsing liquid is circulated by the circulating pump 6, depending on the flow velocity before and after the sieve end 4, a different level of the rinsing liquid is created. The flow rate of the rinsing liquid can be adjusted, for example, via the rotational speed of the circulating pump 6. FIG. 1 shows the liquid levels before and after the sieve 4 at low pump speed n *. The liquid level on the suction side of the circulation pump 6, which is referred to below as the upper level 7 is lower than the liquid level within the screen 4.

FIG. 2 The liquid level on the suction side of the circulation pump 6, hereinafter referred to as the lower level 8, is significantly lower than the liquid level 7 at low speed n * ( FIG. 1 ). This can be explained by the fact that with increased flow velocity the pressure loss of the sieve system 3, 4 is greater and thus more rinsing liquid must be dammed up in front of the sieve system 3, 4 in order to build up the necessary liquid pressure for overcoming the sieve system 3, 4. From the, the upper level 7 ( FIG. 1 ) associated with circulating pump speed n * and, the lower level 8 ( FIG. 2 For example, a rotational speed difference Δn = n-n *, which is necessary in order to change the fluid level between the upper level 7 and the lower level 8 and can advantageously be used as a loading characteristic value for monitoring or determining the screen loading , In addition to the difference However, Δn may also be a ratio n / n * of the two speeds n and n * necessary to change the liquid level between the upper level 7 and the lower level 8, or another mathematical relationship claimed in the present application the speed values n and n * are used as a load characteristic value for monitoring or determining the screen load.

FIG. 3 shows the volume of water in the dishwasher as a function of the speed of the circulation pump. The speed n of the circulating pump is plotted on the x-axis and the volume of water V on the y-axis. The curves K1 to K3 shown as solid lines are assigned to an unloaded screening system. The curves K4 to K6 shown as dashed lines represent the behavior of a loaded sieve system. The lower level 8 and the upper level 7 of the rinsing liquid is determined in the drain pan 2 after the sieve system or sieve 4 (see. 1 and 2 ).

The dependence of the volume of water on the circulating pump speed illustrated in the diagram can be determined independently of the level measuring device used. Especially for the in FIG. 3 The diagram shown was a measuring device for determining the working level in the drain pan, as it is also used in practice, provided. The lower level 8 and the upper level 7 of the washing liquid are determined by the switching hysteresis of the level measuring device. The upper level 7 corresponds to the switching point (SP) of the level measuring device. Upon reaching this level, a liquid addition is interrupted in the washing in practice. The lower level 8 corresponds to the switch-back point (RSP) of the level gauge. If this level is exceeded, in practice, a liquid addition is triggered in the washing and that until such time as the switching point (SP) or, the upper level 7 is reached. The curves K3 and K6 in the diagram illustrate the water demand at a constant upper level (SP) and the curves K2 and K5 at a constant lower level (RSP).

The curve K1 in the diagram represents the theoretical dependence of the water volume in the dishwasher on the circulation pump speed for an unloaded sieve. In practice, however, the rinsing liquid is passed through the dishwasher and through a sieve system with several sieves. When considering this overall system, the unloaded screen system produces the parallel curves K2 and K3 as a function of the circulation pump speed for the switching point and the switch-back point of the level-measuring device. If the speed of the circulation pump is increased, the level of the rinsing fluid drops after the sieving system. In order to keep the level at the switching point or the switch-back point constant more rinsing liquid must be brought into the circulation circuit and the volume of water in the dishwasher increases. The volume difference ΔV between the two solid lines corresponds to the volume difference in the drain pan between the switching point and the switch-back point. The curves K2 and K3 are shifted parallel to this volume difference.

The curve K4 in the diagram represents the theoretical dependence of the water volume in the dishwasher on the circulation pump speed for a loaded sieve. It can be clearly seen that when the sieve is loaded, the Water volume increases much faster with increasing speed than with unloaded sieve. The two curves K5 and K6 show the actual dependence of the water volume in the dishwasher on the circulating pump speed when the sieve system is loaded. Again, K5 and K6 illustrate the water demand at a constant upper level (SP) and a constant lower level (RSP). The volume of water increases with loaded sieve system with increasing speed much more than with unloaded sieve system. The volume difference ΔV between the curves K5 and K6 again corresponds to the volume difference in the drain pan between the switching point and the switch-back point.

If for example the speed of the circulation pump starting n from a high speed _{1, 2} n lowered until the volume of water in the dishwasher is reduced at a constant level by .DELTA.V, so laden sieve a reduction is to the rotational speed n ₂ * sufficient unladen sieve the speed must be reduced to the lower value n ₁ *. The required speed difference Δn ₂ is therefore smaller than Δn ₁ for the unloaded screen and the speed range shown throughout the diagram for the loaded screen. From this context, the loading of the sieve system can be derived.

FIG. 4 shows the Spülflüssigkeitsniveau after the screen system as a function of the speed of the circulation pump. The speed n of the circulating pump is plotted on the x-axis, and the flushing liquid level N is plotted on the y-axis. The curves K1 to K3 shown as solid lines are assigned to the unloaded screen system. The dashed curves K4 to K6 illustrate the behavior with loaded sieve system. The lower level N _RSP and the upper level N _{SP of} the rinsing liquid is determined in the drain pan after the screening system by the switching points of the level measuring device (see. FIG. 3 ).

The curves K1 to K3 and K4 to K6 illustrate the change in the Spülflüssigkeitsniveaus with a constant volume of water held in the dishwasher. K2 and K5 refer to the same value for the constant volume of water. The value here corresponds to the volume of water necessary for reaching the lower level N _RSP at a given speed. For K4 and K6, the same, constant volume of water is also used. The volume of water in this case corresponds to the volume which is necessary at the given speed for reaching the upper level N _SP . The level difference ΔN between the curves K2 and K3 or K5 and K6 corresponds to the height difference in the drain pan between the switching point and the switch-back point of the level measuring device.

The curves K1 and K4 represent the theoretical dependence of the liquid level on the circulating pump speed for an unloaded screen and a loaded screen. Considering the overall system, the curves K2 and K3 are given with unloaded screen system and the curves K5 and K6 with the screen system loaded.

If, for example, the rotational speed of the circulating pump is lowered starting from a high rotational speed n ₁ (unloaded sieve) or n ₂ (laden sieve) until the level in the drain pan has dropped by the value ΔN between the upper and lower levels predetermined by the switching points of the level measuring device is sufficient with laden Straighten a reduction by a smaller amount of speed to the speed n ₂ *. When the sieve is unloaded, the speed must be reduced by a larger number of revolutions to the lower value n ₁ *. The necessary speed difference Δn ₂ is therefore smaller for the loaded wire than Δn ₁ , for the unloaded wire (in the entire speed range shown). This results in the same dependence of the Siebbeladung of the speed difference as in FIG. 3 ,

In FIG. 5 is the Siebbeladung x plotted against the speed difference of the circulation pump .DELTA.n for the change in the liquid level between the switching point and the switch-back point. The graph illustrates that the higher the necessary speed difference for the change in liquid level between the upper and lower levels, the lower the screen load.

For determining the loading of the sieve system, the necessary speed difference amounts can now be determined as a load characteristic value and compared with each other or with a loading reference value at different times of one rinsing operation or several successive rinsing operations. If a speed difference, which corresponds to an arbitrary limit loading, is specified as the loading reference value, then, for example, a screen cleaning process can be triggered when this loading reference value is reached. If a loading reference value of the speed difference corresponds to the unloaded screen system and another loading reference value corresponds to the speed difference at maximum loading, the degree of contamination, for example, can be evaluated.

Furthermore, one could also directly from the in FIG. 3 and FIG. 4 shown relationship between water volume V and circulating pump speed n or Spülflüssigkeitsniveau N and circulating pump speed n derive the load of the screen system. This could for example be FIG. 3 the amount of the slope of the curves K2 or K3 and K5 or K6 are determined in the set speed range and compared with each other. The same applies to FIG. 4 , The gradients for the unloaded and the loaded sieve arise at FIG. 3 from the quotient of volume difference ΔV by load characteristic value or speed difference Δn ₁ , or Δn ₂ and at FIG. 4 from the quotient of the level difference ΔN by load characteristic value or speed difference Δn ₁ , or Δn ₂ . The determined quotient is in both cases for the loaded sieve in terms of amount higher than for the unloaded sieve. By comparing the determined values with each other or with one or more reference values, it is possible to detect existing pollution or the degree of contamination.

In addition to the speed difference or level difference as a load characteristic, the necessary time for adjusting the fluid level between the lower level (RSP) and the upper level (SP) at a constant high speed increase or decrease can preferably also be determined and used for the evaluation of the screen load. This results in a similar dependence as in the determination of the speed difference. When the sieve system is loaded, the level difference is overcome faster than when the sieve system is unloaded.

The level measuring device in the drain pan 2 after the sieve system 3, 4, in particular sieve 4, for example, can be designed as an analog pressure sensor with which the liquid level in the drain pan 2 can be accurately determined after the sieve 4. One possibility with the use of an analog pressure sensor is to determine an upper level 7 corresponding to a first speed value n * and a lower level 8 corresponding to a second speed value n and to determine the load characteristic value as a difference or a quotient of these levels, for example.

FIG. 6 illustrates the dependence of the Spülflüssigkeitsniveaus N in the drain pan after the sieve system or Siebstutzen 4 of the rotational speed n of the circulation pump 6. By way of example here from the previously described curves K1 to K6 for the unloaded sieve curve K2 and for the loaded sieve curve K5 picked out in each case the same volume of water in the work container.

FIG. 6 shows that when the sieve is loaded (curve K5), the level N ₂ corresponding to the predetermined, first value n * of the speed is already lower than the level N _{1 of} the unloaded sieve (curve K2) at the same speed n *, so that in use of the analog pressure sensor can already be detected by measuring the two levels N ₁ and N ₂ at the speed n * the loading of the screen system.

For example, when the unloaded sieve, the rotational speed n of a predetermined first value n *, which may be equal to 0 in extreme cases, ie at standstill of the circulating pump 6, increased to a predetermined second value n, then the level N lowers after the sieve 4 from a first level N ₁ by the amount ΔN ₁ to a second level N ₁ *. When the sieve is loaded, as the speed increases from the predetermined, first value n * by the amount Δn to the predetermined second value n, the rinsing fluid level decreases from a first level N ₂ by the amount ΔN ₂ to a second level N ₂ *. When the sieve is loaded, the level of the rinsing liquid is reduced by a greater amount than in the case of a loaded sieve, ie the loading characteristic value ΔN ₂ is greater than the loading characteristic value ΔN ₁ . By comparing load characteristics with each other or with a corresponding load reference value for an unloaded or maximum loaded screen system, the screen load can thus be monitored or determined. Instead of a predetermined speed amount Δn in this embodiment of the invention, a time interval, in particular between several seconds and a split second, preferably 1/2 s, be predetermined in which the level change or the current level are determined, wherein in this time interval in each case one constantly fast speed increase or decrease takes place. In practice, for example, for determining the Siebbeladung the circulation pump stopped for a few seconds, the speed can therefore be set to 0, and then restarted. While the arrival time of the circulation pump, the liquid level in the drain pan is continuously monitored for at least half a second, for example with the analog pressure sensor. The minimum level after the downcomer 4, which is measured in this time window or time interval is then proportional to the loading level of the screen system.

LIST OF REFERENCE NUMBERS

1

rinse tank

2

drain pan

3

sieve plate

4

Siebstutzen

5

drain pump

6

circulating pump

7

upper level

8th

lower level

K1 to K6

curves

Claims (19)

1. Method for detecting the loading of a filter system (3, 4) of a dishwasher which comprises a circulating circle with a filter system (3, 4) and a circulating pump (6) for circulating the washing liquid, characterised in that in the method at least one loading characteristic (Δn, ΔN) is ascertained from at least one first value (n*) of a process parameter assigned to a level (7, N_SP) of the washing liquid and at least one second value (n) of the process parameter assigned to a level (8, N_RSP) of the washing liquid or from at least one first level (N₁) of the washing liquid corresponding to a first value (n₁) of a process parameter and at least one second level (N₂) of the washing liquid corresponding to a second value (n₂) of the process parameter and used as a measure of the filter loading, wherein the process parameter is unambiguously connected to the speed (n) of the circulating pump (6), in particular is a circulating pump speed, a circulating pump conveying pressure, an electric conveying capacity of the circulating pump (6), a mechanical conveying capacity of the circulating pump (6), a volume of the washing liquid or a volumetric flow of the washing liquid or a flow rate of the washing liquid.
2. Method according to claim 1, in which the at least one loading characteristic is ascertained as a difference (Δn, ΔN) from the at least one first value (n*) of the process parameter or of the level (7, N_SP) and the at least one second value (n) of the process parameter or of the level (8, N_RSP) or from at least one reference value of the process parameter or of the level and the at least one first value (n₁) of the process parameter or of the level (N_L) and/or the at least one second value (n₂) of the process parameter or of the level (N₂).
3. Method according to claim 1 or claim 2, in which the at least one loading characteristic is ascertained as a quotient of the at least one first value (n₁) of the process parameter or of the level (N₁) and the at least one second value (n₂) of the process parameter or of the level (N₂) or the at least one first value (n₁) of the process parameter or of the level (N₁) and the at least one second value (n₂) of the process parameter or of the level (N₂) and at least one reference value of the process parameter or of the level or the at least one first value (n₁) of the process parameter or of the level (N₁) and/or the at least one second value (n₂) of the process parameter or of the level (N₂) and at least one mathematical function comprising the at least one first value (n₁) of the process parameter or of the level (N₁) and/or the at least one second value (n₂) of the process parameter or of the level (N₂), in particular at least one sum and/or at least one difference and/or at least one quotient and/or at least one product, or mathematical functions comprising the at least one first value (n1) of the process parameter or of the level (N₁) and/or the at least one second value (n₂) of the process parameter or of the level (N₂), in particular at least one sum and/or at least one difference and/or at least one quotient and/or at least one product.
4. Method according to one or more of the preceding claims, in which at least one loading characteristic is ascertained from at least one first value (n*) of a process parameter assigned to an upper level (7, N_SP) of
   the washing liquid and at least one second value (n) of the process parameter assigned to a lower level (8, N_RSP) of the washing liquid and used as a measure of the filter loading.
5. Method according to claim 4, in which a minimum value of the process parameter is limited by a maximum upper level of the washing liquid after the filter system (3, 4) or a minimum lower level of the washing liquid before the filter system (3, 4).
6. Method according to claim 5, in which the minimum value process parameter is determined by the operating level of the dishwasher.
7. Method according to one or more of claims 4 to 6, in which a maximum value of the process parameter is limited by a minimum lower level of the washing liquid after the filter system (3, 4) or a maximum upper level of the washing liquid before the filter system (3, 4).
8. Method according to one or more of the preceding claims, in which the level (N) of the washing liquid is determined in a discharge tank (2) of the washing container (1).
9. Method according to claim 8, in which the level (N) of the washing liquid is determined after the filter system (3, 4).
10. Method according to one or more of the preceding claims, in which the upper level (7, N_SP) of the washing liquid, to which is assigned the at least one first value (n*) of the process parameter, and the lower level (8, N_RSP) of the washing liquid, to which is assigned the at least one second value (n) of the process parameter, or the first level (N₁) of the washing liquid corresponding to a first value (n₁) of a process parameter and the second level (N₂) of the washing liquid corresponding to a second value (n₂) of the process parameter are determined using at least one level measuring device.
11. Method according to claim 10, in which a measuring device for adjusting the operating level in the dishwasher is used as the level measuring device.
12. Method according to claim 10 or 11, in which a measuring device for determining the static pressure of the washing liquid column before or after the filter system (3, 4), in particular an analog pressure sensor, is used as the level measuring device.
13. Method according to one or more of claims 10 to 12, in which the upper level (7, N_SP) of the washing liquid, to which is assigned the at least one first value (n*) of the process parameter, and the lower level (8, N_RSP) of the washing liquid, to which is assigned the at least one second value (n) of the process parameter, are determined by the switching points of the level measuring device.
14. Method according to one or more of the preceding claims, in which the at least one ascertained loading characteristic (An, ΔN) is compared to one or more loading reference value(s).
15. Method according to claim 14, in which the loading reference value corresponds to the loading characteristic from the first value (n*) of the process parameter assigned to the upper level (7, N_SP) of the washing liquid and/or the second value (n) of the process parameter assigned to the lower level (8, N_RSP) of the washing liquid or to the loading characteristic from the first level (N₁) of the washing liquid corresponding to a first value (n₁) of a process parameter and/or the second level (N₂) of the washing liquid corresponding to a second value (n₂) of the process parameter in the case of unloaded filter system (3, 4) and/or in the case of maximum filter loading.
16. Method according to one or more of the preceding claims, in which the loading reference value for the unloaded or the maximum loaded filter during first start-up of the dishwasher is ascertained, preferably at the factory, or is preset at the factory.
17. Method according to one or more of the preceding claims, in which on reaching the maximum filter loading, a filter cleaning process is triggered.
18. Method according to one or more of the preceding claims, in which on reaching the maximum filter loading, a display is triggered.
19. Method according to one or more of the preceding claims, which is carried out during operation of the dishwasher, preferably during filling of the dishwasher with liquid.

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