Patent Publication Number: US-11019979-B2

Title: Process water flow detection in circulation pump

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application filed under 35 U.S.C. § 371 of International Application No. PCT/EP2016/053132 filed Feb. 15, 2016, which application is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The invention relates to a method of detecting a change in process water flow of a circulation pump in an appliance for washing and rinsing goods, and an appliance performing the method. 
     BACKGROUND 
     In a washing appliance such as a dishwasher, sensors are required for monitoring water levels in a compartment of the dishwasher, in particular when supplying water to the compartment via a dishwasher inlet to avoid an overflow situation, or simply to just monitor the approximate water level in the dishwasher. 
     Further, even if determination of a water level may not be required, it may still be desirable to detect whether there is process water present in a circulation pump of a dishwasher. In order to determine the presence of process water in the pump in the art, sensors such as e.g. flow sensors, pressure sensors, pressure switches, float switches, etc. are necessary. These sensors add to the complexity, and thus the cost, of the dishwasher. 
     US 2006/219262 discloses a control device and method for detecting and controlling a water fill level in a dishwasher or other similar appliance that includes a pump motor. The control device monitors the pump motor current over time, determines a current change, and compares the current change to a threshold current change that is indicative of the water level. 
     During periods of pump cavitation, the current drawn by the pump motor is measurably lower, while the current drawn by the pump motor increases when the pump is not cavitating. The approach of US 2006/219262 avoids the usage of specialized sensors as discussed hereinabove. 
     However, by monitoring the pump current and determining a change in current I—i.e. a ΔI—as a difference between two instantaneous pump current values I min  and I max  in a cycle, fluctuations in pump current around a nominal value may result in an incorrect decision taken. For instance, if ΔI=I max −I min  exceeds a predetermined threshold value ΔI T , it is concluded that more water should be supplied to the dishwasher, but this may be a result of a temporary fluctuation in pump current which do not indicate a need for activation of water fill. 
     SUMMARY 
     An object of the present invention is to solve, or at least mitigate, this problem in the art, and to provide an improved method of detecting a change in process water flow of a circulation pump in an appliance for washing and rinsing goods. 
     This object is attained in a first aspect of the invention by a method of detecting a change in process water flow of a circulation pump in an appliance for washing and rinsing goods. The method comprises measuring a property indicating torque of the circulation pump, averaging a first set of values of the measured property, thereby creating a first average, and averaging at least a further set of values of the measured property, thereby creating at least one further average. The method further comprises comparing the first average with the at least one further average, and detecting the change in process water flow of the circulation pump based on a difference between the first average and the at least one further average. 
     This object is attained in a second aspect of the invention by an appliance for washing and rinsing goods comprising a circulation pump, a sensing arrangement arranged to measure a property indicating torque of the circulation pump, and a controller. The controller is arranged to average a first set of values of the measured property, thereby creating a first average, average at least a further set of values of the measured property, thereby creating at least one further average, compare the first average with the at least one further average, and to detect change in process water flow of the circulation pump based on a difference between the first average and the at least one further average. 
     Advantageously, by averaging a first set of values of the property indicating torque of the circulation pump, which in an embodiment is circulation pump current indirectly representing pump torque, thereby creating a first average, and comparing the first average to at least one further average created from a further set of values, the effect of temporary fluctuations is eliminated. 
     Thus, in a scenario where the measured property, being e.g. pump current, fluctuates around a nominal value, but where an average of the fluctuating values equals (or is close to) the nominal value, a result of applying the proposed method is that it can be concluded that no change in process water flow of the circulation pump is detected. To the contrary, if there is a sufficient difference between the first average and the at least one further average, a change in process water flow of the pump is indeed detected, and a corresponding action may be taken accordingly, such as supplying water to the appliance in case the flow has decreased. 
     Further advantageous is that individual characteristics of the circulation pump of the appliance, being e.g. a dishwasher or a washing machine, can be eliminated. These characteristics include for instance particular model, production tolerances and change (e.g. demagnetization and/or wear) over time. By using average torque values rather than instant values, the effect of changes in characteristics may be eliminated, or at least mitigated. 
     In an embodiment, the comparing of the first average with the further average comprises calculating a difference between the first average and the at least one further average, and determining whether the difference complies with a predetermined threshold criterion. If so, it is concluded that the further average reflects a decrease in pump torque, and a decrease in process water flow of the circulation pump is advantageously detected. For instance, it may be determined whether a result of a subtraction of the further average from the first average exceeds a predetermined current threshold value. 
     In a further embodiment, the averaging of at least a further set of values of the measured property comprises averaging a plurality of sets of values of the measured property, thereby creating a corresponding plurality of averages. Subsequently, the first average is compared with each of the plurality of averages; and each of the comparisons must indicate change in flow for a flow change to indeed be detected. 
     For instance, each comparison may include calculating a difference between the first average and a respective one of the plurality of averages, and if each calculated difference exceeds a corresponding (or same) threshold value, a decrease in process water flow of the circulation pump is advantageously detected. 
     In yet an embodiment, the torque of the circulation pump is measured by measuring operating current of a motor driving the circulation pump. This may be measured indirectly by measuring the voltage of a known shunt resistor in the motor and calculating the current by applying Ohm&#39;s law. Measured current can be directly translated into circulation pump torque; the higher the torque, the higher the operating current of the motor driving the pump, and a higher pump torque implies a greater flow of process water through the circulation pump. Measuring operating current of the circulation pump motor is in itself advantageous as compared to using a relatively expensive flow rate sensor to measure the flow of process water through the circulation pump. 
     Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is now described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  shows a prior art dishwasher in which the present invention may be implemented; 
         FIG. 2  schematically illustrates a cross-sectional view of the dishwasher of  FIG. 1  taken along section II; 
         FIGS. 3 a  and  b    illustrate two different views of a circulation pump through which a change in process water flow may be determined according to embodiments of the invention; 
         FIG. 4  illustrates fluctuations in circulation pump operating current over time; 
         FIG. 5  shows a flowchart illustrating an embodiment of a method of detecting a change in process water flow of a circulation pump according to the invention; 
         FIG. 6  illustrates a decrease in circulation pump operating current over time; 
         FIG. 7  shows a flowchart illustrating another embodiment of a method of detecting a change in process water flow of a circulation pump according to the invention; 
         FIG. 8  illustrates further decrease in circulation pump operating current over time; 
         FIG. 9  shows a flowchart illustrating a further embodiment of a method of detecting a change in process water flow of a circulation pump according to the invention; and 
         FIG. 10  illustrates a further scenario where circulation pump operating current decreases over time. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description. The washing appliance of the invention will subsequently be exemplified by a dishwasher. 
       FIG. 1  shows a prior art dishwasher  1  in which the present invention can be implemented. It should be noted that dishwashers can take on many forms and include many different functionalities. The dishwasher  1  illustrated in  FIG. 1  is thus used to explain different embodiments of the present invention and should only be seen as an example of a dishwasher in which the present application can be applied. 
     The exemplifying dishwasher  1  comprises a washing compartment or tub  2 , a door  4  configured to close and seal the washing compartment  2 , a spraying system having a lower spray arm  3  and an upper spray arm  5 , a lower rack  6  and an upper rack  7 . Additionally, it may comprise a specific top rack for cutlery (not shown). A controller  11  such as a microprocessor is arranged in the interior of the dishwasher for controlling washing programmes and is communicatively connected to an interface  8  via which a user can select washing programmes. 
     The door  4  of the prior art dishwasher  1  illustrated in  FIG. 1  is further on its inside arranged with a small detergent dispenser  9  having a lid  10  being controllably opened and closed by the controller  11  for dispensing detergent from the dispenser  9  into the tub  2 . 
       FIG. 2  schematically illustrates a cross-sectional view of the dishwasher  1  of  FIG. 1  taken along section II, to further illustrate components included in a dishwasher  1 . Hence, as previously mentioned, the dishwasher  1  comprises a washing compartment or tub  2  housing an upper basket  7  and a lower basket  6  for accommodating goods to be washed such as cutlery, plates, drinking-glasses, trays, etc. 
     Detergent in the form of liquid, powder or tablets is dosed in a detergent compartment located on the inside of a door (not shown in  FIG. 2 ) of the dishwasher  1  by a user, which detergent is controllably discharged into the washing compartment  2  in accordance with a selected washing programme. As previously mentioned, the operation of the dishwasher  1  is typically controlled by the controller  11  executing appropriate software  12  stored in a memory  13 . 
     Fresh water is supplied to the washing compartment  2  via water inlet  15  and water supply valve  16 . This fresh water is eventually collected in a so called sump  17 , where the fresh water is mixed with the discharged detergent resulting in process water  18 . The opening and closing of the water supply vale  16  is typically controlled by the controller  11 . 
     By the expression “process water” as used herein, is meant a liquid containing mainly water that is used in and circulates in a dishwasher. The process water is water that may contain detergent and/or rinse aid in a varying amount. The process water may also contain soil, such as food debris or other types of solid particles, as well as dissolved liquids or compounds. Process water used in a main wash cycle is sometimes referred to as the wash liquid. Process water used in a rinse cycle is sometimes referred to as cold rinse or hot rinse depending on the temperature in the rinse cycle. The pressurized fluid supplied to the detergent dispensing device according to embodiments of the invention thus at least partly contains process water. 
     At the bottom of the washing compartment is a filter  19  for filtering soil from the process water before the process water leaves the compartment via process water outlet  20  for subsequent re-entry into the washing compartment  2  through circulation pump  21 . Thus, the process water  18  passes the filter  19  and is pumped through the circulation pump  21 , which typically is driven by a brushless direct current (BLDC) motor  22 , via a duct  23  and process water valve  24  and sprayed into the washing compartment  2  via nozzles (not shown) of a respective wash arm  3 ,  5  associated with each basket  6 ,  7 . Thus, the process water  18  exits the washing compartment  2  via the filter  19  and is recirculated via the circulation pump  21  and sprayed onto the goods to be washed accommodated in the respective basket via nozzles of the wash arms  3 ,  5 . Further, a controllable heater  14  is typically arranged in the sump  17  for heating the process water  18 . 
     The washing compartment  2  of the dishwasher  1  is drained on process water  18  with a drain pump  29  driven by a BLDC motor  30 . It should be noted that it can be envisaged that the drain pump  29  and the circulation pump  21  may be driven by one and the same motor. 
     In an embodiment of the invention, a sensing arrangement  25  is arranged at the circulation pump  21  for measuring torque of the circulation pump  21 , in the form of e.g. operating current, voltage or power. The sensing arrangement  25  may be implemented in the form of a resistor arranged at the circulation pump motor  22  for measuring operation current of the motor. Practically, this is undertaken by measuring the operating voltage of a known shunt resistor in the motor  22  of the circulation pump  21  and calculating the operating current. 
     Measured pump operating current can directly be translated into circulation pump torque for a given circulation pump speed; the higher the torque, the higher the operating current of the motor  22  driving the pump  21 , and a higher pump torque implies a greater flow of process water  18  through the circulation pump while a lower torque indicates a smaller flow of process water  18  through the circulation pump  21 . 
     It should be noted that a torque sensor (not shown) may be used for directly measuring circulation pump torque instead of indirectly measuring the torque via an electrical property. 
       FIG. 3 a    shows a view of an exemplifying circulation pump  21 . The speed of the circulation pump  21  is typically controlled by the controller  11 .  FIG. 3 a    shows an outlet  40  (referred to as a discharge port) of the circulation pump  21  and an inlet  41 . The casing  42  of the circulation pump  21  is referred to as the volute and can be removed from a main body  43  of the circulation pump  21 . 
       FIG. 3 b    shows a further view of the circulation pump  21  of  FIG. 3 a   , where the volute  42  has been removed from the main body  43  of the circulation pump, thereby revealing the impeller  44  of the circulation pump which under operation pumps the process water that is entering the circulation pump  21  via the inlet  41 . The process water that is pumped by the impeller  44  is subsequently received by the volute  42 , which slows down the flow rate of the process water, and exits the circulation pump  21  via the outlet  40 . 
       FIG. 4  illustrates fluctuations in circulation pump operating current over time, i.e. the operating current being a property indicating torque of the circulation pump  21 . As can be seen, the operating current fluctuates around a nominal pump operating current I nom .  FIG. 4  illustrates seven measured current values from t 1  to t 7 . The measured current at each instant of time t n  will be denoted I(t n ). 
     With reference to the art, in case e.g. ΔI=I(t 1 )−I(t 2 ) exceeds a predetermined threshold value ΔI T , it may be concluded that more water should be supplied to the dishwasher  1 , since the torque of the circulation pump  21  is indicated to having decreased to a level I(t 2 ) where a water fill is required. As will be described in the following with reference to  FIG. 4 , this may be a result of a temporary fluctuation in pump current which in fact do not indicate a need for activation of water fill. 
     In an embodiment of the present invention, where reference further will be made to the flowchart of  FIG. 5 , a property is measured indicating torque of the circulation pump  21  in step S 101 , in this case operating current of the pump. 
     In a second step S 102 , a first set S 1  of measured current values is averaged, thereby creating a first average current value, Ī S1 . This could be undertaken in different ways depending on the particular application, for instance by calculating an arithmetic mean or a moving average. 
     In this particular exemplifying embodiment, an arithmetic mean is calculated as: 
     
       
         
           
             
               
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     In the illustration of  FIG. 4 , it can be concluded that Ī S1 ≈I nom . 
     In a third step S 103 , a second set S 2  of measured current values is averaged, thereby creating a second average current value, Ī S2 : 
     
       
         
           
             
               
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     Again with reference to the illustration of  FIG. 4 , it can be concluded that Ī S2 ≈I nom . 
     In this example, the two sets S 1  and S 2  comprise one overlapping measured current value I(t 4 ). It can be envisaged that further measured current values are common to the two sets S 1  and S 2 , or that no overlap occurs at all. 
     In step S 104 , the first average current Ī S1  is compared to the second average current Ī S2 , and from the comparison it is detected in step S 105  whether a change in process water flow of the circulation pump  21  has occurred based on a difference between the first average Ī S1  and the second average Ī S2 . 
     In this exemplifying embodiment, the first average current Ī S1  and the second average current Ī S2  are substantially equal, and accordingly no change in process water flow is detected. 
       FIG. 6  illustrates another scenario, where initially, for the first set S 1  of measured operating current values consisting of I(t 1 ), I(t 2 ), I(t 3 ) and I(t 4 ), it again can be concluded that Ī S1 ≈I nom . 
     However, for the second set S 2  of measured operating current values consisting of I(t 4 ), I(t 5 ), I(t 6 ) and I(t 7 ), it can be seen that the average current Ī S2  is substantially lower, thereby reflecting a “true” decrease in pump torque (as indicated by the decreasing pump current), and thus process water flow through the circulation pump. 
     Hence, with reference to the flowchart of  FIG. 7 , the operating current I of the circulation pump is measured in step S 101  and a first and second average Ī S1 , Ī S2  is created in steps S 102  and S 103 , respectively. 
     In this particular embodiment, the comparing of the first average Ī S1  with the second average Ī S2  comprises calculating a difference between the first average and the at least one second average as ΔI=Ī S1 −Ī S2 , and determining whether the difference exceeds a predetermined current threshold value ΔI T :
 
Δ I=Ī   S1   − S     S2   ≥ΔI   T .
 
     If so, a decrease in pump torque is detected, and it is concluded in step S 105  that a decrease in process water flow through the circulation pump indeed has occurred. A possible action to be taken by the processor  11  may be to control the valve  15  of the inlet  16  to supply additional water to the dishwasher  1 . 
       FIG. 8  illustrates the scenario of  FIG. 6 , but where a third set S 3  of measured operating current values is taken into account for detecting process water flow change of the circulation pump. 
     Hence, with reference to the flowchart of  FIG. 9 , the operating current I of the circulation pump is measured in step S 101  and a first average Ī S1  is created in step S 102 . 
     Further, in this embodiment, a plurality of sets of current values are averaged in step S 103 , in this example a second set S 2  and a third set S 3 , the third set S 3  consisting of measured current values I(t 7 ), I(t 8 ), I(t 9 ) and I(t 10 ). 
     For the third set S 3  of measured operating current values, it can be seen that the average current Ī S3  is substantially lower as compared to Ī S1  (and even as compared to Ī S2 ), thereby even more strongly reflecting a true decrease in pump torque (as indicated by the decreasing pump current), and thus process water flow through the circulation pump, when compared to the embodiment described with reference to  FIGS. 6 and 7 . 
     In this particular embodiment, the comparing in step S 104  of the first average Ī S1  with the second average Ī S2  comprises calculating a difference between the first average and the second average as ΔI 1 =Ī S1 −Ī S2 , and determining whether the difference exceeds a first predetermined current threshold value ΔI T1 :
 
Δ I   1   =Ī   S1   −Ī   S2   ≥ΔI   T1 .
 
     Further in step S 104 , the first average Ī S1  is compared with the third average Ī S3  by calculating a difference between the first average and the third average as ΔI 2 =Ī S1 −Ī S3 , and determining whether the difference exceeds a second predetermined current threshold value ΔI T2 :
 
Δ I   2   =Ī   S1   −Ī   S3   ≥ΔI   T2 .
 
     If both of theses conditions are fulfilled, a decrease in pump torque is detected, and it is concluded in step S 105  that a decrease in process water flow through the circulation pump indeed has occurred. Again, a possible action to be taken by the processor  11  may be to control the valve  15  of the inlet  16  to supply additional water to the dishwasher  1 . 
     Hence, in this particular example, if both averages Ī S2 , Ī S3  differ from Ī S1  to a certain extent, a change is detected. In practice, averages of even further sets of measured current values may have to fulfil corresponding threshold conditions for a detection of flow rate change to occur. 
     With reference to  FIG. 10 , it should be noted that the average current Ī S3  of the third set S 3  not necessarily must be lower than that of the second set S 2 . 
     In  FIG. 10 , the third average Ī S3  is about the same as the second average Ī S2 , which thus indicates that a true decrease in pump torque has occurred. 
     It may thus suffice in the comparing step S 104  that
 
Δ I   1   =Ī   S1   −Ī   S2   ≥ΔI   T  and Δ I   2   =Ī   S1   −Ī   S3   ≥ΔI   T ,
 
i.e. that both differences in average current ΔI 1 , ΔI 2  exceeds the same predetermined threshold value ΔI T1 , for a decrease in flow should be detected in step S 105 . Again, if both averages Ī S2 , Ī S3  differ from Ī S1  to a certain extent based on the threshold value SIT, a change is detected.
 
     The figures illustrate decrease in process water flow, but an increase in process water flow would be detected analogously, with an increasing average pump current when comparing the first set S 1  with at least one further set S 2 . 
     In practice, the steps of the method performed by the dishwasher  1  according to embodiments of the invention, is caused by the controller  11  embodied in the form of one or more microprocessors or processing units arranged to execute a computer program  12  downloaded to a suitable storage medium  13  associated with the microprocessor, such as a Random Access Memory (RAM), a Flash memory or a hard disk drive. The controller  11  is arranged to cause the dishwasher  1  to carry out at the steps of the method according to embodiments of the present invention when the appropriate computer program  12  comprising computer-executable instructions is downloaded to the storage medium  13  and executed by the controller  11 . The storage medium  13  may also be a computer program product comprising the computer program  12 . Alternatively, the computer program  12  may be transferred to the storage medium  13  by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick. As a further alternative, the computer program  12  may be downloaded to the storage medium  13  over a network. The controller  11  may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc. 
     The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.