Patent Publication Number: US-10786137-B2

Title: Determining whether process water has been added to a sump of an appliance for washing and rinsing goods during interruption of appliance operation

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/EP2015/077675 filed Nov. 25, 2015, which application is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The invention relates to a method performed by an appliance for washing and rinsing goods of detecting process water added to a sump of the appliance during interruption of operation of the appliance, upon recommence of appliance operation, and an appliance performing the method. 
     BACKGROUND 
     In a washing appliance such as a dishwasher, it happens that operation of the dishwasher is unexpectedly interrupted. That is, the dishwasher is running a washing programme, when for instance a user opens a door to the compartment of the dishwasher, or a power failure occurs. 
     During such an interruption of normal operation of the dishwasher, water is sometimes added to a sump of the dishwasher. As an example, if the user opens the door to the compartment, he or she may discover that a bowl has been turned over in a rack of the dishwasher, whereupon the user turns the bowl over and thus adds a bowl full of water to the sump of the dishwasher, before closing the door and resuming the current washing programme. 
     This may affect performance of the dishwasher when the washing programme is resumed, or even result in an overflow situation. To this end, sensors are required for monitoring water levels in a compartment of the dishwasher, such as e.g. flow sensors, pressure sensors, pressure switches, float switches, etc. These sensors add to the complexity, and thus the cost, of the dishwasher. 
     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 whether process water has been added to a sump of an appliance for washing and rinsing goods during interruption of operation of the appliance. 
     This is attained in a first aspect of the invention by a method performed by an appliance for washing and rinsing goods of detecting process water added to a sump of the appliance during interruption of operation of the appliance, upon recommence of appliance operation. The method comprises increasing operating speed of a circulation pump of the appliance to a target speed, measuring a parameter indicating circulation pump pressure or process water flow rate through the circulation pump, and determining that process water has been added to the sump of the appliance during the interruption in case the measured pressure or flow rate is maintained at a sufficient level after the speed of the circulation pump has reached the target speed. 
     This is attained in a second aspect of the invention by an appliance for washing and rinsing goods being configured to detect process water added to a sump of the appliance during interruption of operation of the appliance, upon recommence of appliance operation. The appliance comprises a circulation pump, a sensing arrangement arranged to measure a parameter indicating circulation pump pressure or process water flow rate through the circulation pump, a controller arranged to control operating speed of the circulation pump. The controller is further arranged to increase the operating speed of a circulation pump of the appliance to a target speed, and determine that process water has been added to the sump of the appliance during the interruption in case the measured pressure or flow rate is maintained at a sufficient level after the speed of the circulation pump has reached the target speed. 
     Advantageously, upon resuming a washing programme that was running before operation of the appliance, in the following being exemplified in the form of a dishwasher, was interrupted, the speed of the circulation pump is increased in to a predetermined target speed. 
     Typically, the target speed is a speed at which it is known that the circulation pump pressure or process water flow rate through the circulation pump would fall to an insufficient level, i.e. a level where the flow from the pump exceeds the flow to the pump and the pump thus draws air, if the amount of process water in the sump is at a desired level. It should be noted that this level typically will vary depending on the washing programme that the dishwasher is running, and on the type of dishwasher. 
     If during the increase of the circulation pump speed, it is measured that the circulation pump pressure or process water flow rate through the circulation pump remains at a sufficient level, i.e. a level where the flow from the pump does not exceed the flow to the pump, it can advantageously be concluded that process water has been added to the sump of the dishwasher during the interruption. 
     In contrast, in case the measured pressure or flow rate reaches an insufficient level, it is advantageously determined that no process water has been added to the sump of the dishwasher during the interruption. 
     In an embodiment, in case process water has been added during the interruption, the sump is drained on process water until the measured pressure or flow rate reaches an insufficient level, wherein the amount of process water advantageously has been restored at a desired level and the draining is stopped. 
     In a further embodiment, the drained process water is relocated to a storage tank of the dishwasher for subsequent reuse. 
     In yet an embodiment, insufficient circulation pump pressure or process water flow rate through the circulation pump is measured indirectly by measuring operating current of a motor driving the circulation pump. This may be measured by measuring the voltage of a known shunt resistor in the motor and calculating the current by using 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 pressure or flow rate sensor to measure the pump pressure or flow of process water through the pump. With the measured operating current, it can be determined whether the pressure or flow is insufficient, or whether it has been restored to a sufficient level. 
     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 can 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 which can be controlled according to embodiments of the present invention; 
         FIG. 4 a    illustrates operating current of the circulation pump as a function of increased pump speed when a washing programme resumes after having been interrupted, but where process water has been added to the sump according to an embodiment of the invention. 
         FIG. 4 b    shows a flowchart illustrating an embodiment of a method according to the invention of determining whether process water has been added to a sump of the dishwasher during the interruption of the washing programme; 
         FIG. 5  illustrates operating current of the circulation pump as a function of increased pump speed when a washing programme resumes after having been interrupted, but where no process water has been added to the sump according to an embodiment of the invention; and 
         FIG. 6  illustrates a flowchart of a further embodiment of the method according to the invention. 
     
    
    
     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. 
     A sensing arrangement  25  may be arranged at the circulation pump  21  for measuring flow rate of the process water  18  passing through the circulation pump  21 , or the pressure of the circulation pump  21 . The sensing arrangement may be embodied in the form of a pressure or flow rate transducer. Alternatively, 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. From the measured current, it is determined whether the pressure/flow rate is sufficient or not. The current is thus a parameter indicating pressure of flow rate. 
       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 . 
     Now, where the process water  18  flowing to the circulation pump  21  is in contact with vacuum or any gas, for instance via an evaporator, a lower flow of process water to the pump  21  than from the pump will eventually cause a pressure loss due to vacuum or gas inside the pump  21 . 
       FIGS. 4 a  and  b    illustrate an embodiment of the invention where operation of the dishwasher is unexpectedly interrupted. That, is, the dishwasher  1  is running a washing programme, when for instance a user opens the door  4  to the compartment  2  of the dishwasher  1  or e.g. a power failure occurs. 
       FIG. 4 a    illustrates operating current of the circulation pump  21  as a function of increased pump speed when the washing programme resumes after having been interrupted, but where process water has been added to the sump according to an embodiment of the invention. 
       FIG. 4 b    shows a flowchart illustrating an embodiment of a method according to the invention of determining whether process water has been added to the sump  17  of the dishwasher  1  during the interruption of the washing programme. 
     If the user opens the door  4  to the compartment  2 , he or she may discover that a bowl has been turned over in the upper rack  7  of the dishwasher  1 , whereupon the user turns the bowl over and thus adds a bowl full of water to the sump  17  of the dishwasher  1 , before closing the door  4  and resuming the current washing programme. 
     In order to appropriately run the various washing programmes in a dishwasher, it is generally desirable that the amount of process water in the compartment  2  is known in order for the controller  1  to determine whether additional fresh water should be added via water inlet  15  and water supply valve  16 , or if the dishwasher  1  should be drained on process water  18  to comply with requirements of the currently selected washing programme, or whether any adjustment should be made to the washing programme. 
     It should be noted that while the process water  18  may be drained via the process water outlet  20  and the drain pump  29  to leave the compartment  2  for further transport to a sewer system, it is also envisaged in an embodiment of the invention that the drained process water  18  advantageously is relocated to a storage tank (not shown) of the dishwasher  1 , either inside or outside the compartment  2  for subsequent reuse. 
     Upon resuming the washing programme that currently was running before the user opened the door  4 , the speed of the circulation pump is increased in step S 101  to a predetermined target speed, at which speed it is known that the circulation pump pressure or process water flow rate through the circulation pump  21  would fall to an insufficient level if the amount of process water  18  in the sump  17  is at a desired level. It should be noted that this level typically will vary depending on the washing programme that the dishwasher is running, and on the type of dishwasher. 
     If during the increase of the circulation pump speed the circulation pump pressure or process water flow rate through the circulation pump  21  remains at a sufficient level as measured in step S 102 , it can be concluded in step S 103  that process water  18  has been added to the sump  17  of the dishwasher  1  during the interruption. 
     Hence, the controller  11  increases the speed of the circulation pump  21  in step S 101  and measures in step S 102 , via the sensing arrangement  25 , the circulation pump pressure or process water flow rate through the circulation pump  21 . The controller  11  thereafter determines in step S 103 , whether the measured circulation pump pressure or process water flow rate through the circulation pump  21  is at a sufficient level. If so, process water  18  is considered to have been added to the sump  17  during the interruption. If not, the controller  11  concludes that no process water  18  has been added to the sump  17  during the interruption. 
     The pressure/flow rate may be measured by reading a pressure or flow rate transducer, or as is performed in an embodiment of the invention, by measuring the operating voltage of a known shunt resistor in the motor  22  of the circulation pump  21  and calculating the operating current. From the measured current, it is determined whether the pressure/flow rate is sufficient or not. 
     Measured current can be directly translated into circulation pump torque; 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 through the circulation pump. When the operating current decreases to a particular level, it can thus be deducted that the process water flow from the pump exceeds the flow of process water to the pump, thereby indicating an insufficient pressure or flow rate. Hence, it is possible to determine pressure or flow rate by determining a difference in measured current, such as a difference, or change, from a nominal measured current value. 
     As is illustrated in  FIG. 4 a   , the operating current will increase linearly with the increasing pump speed to the target speed v T  (and a corresponding current I T ) since a steady flow of process water passes through the circulation pump  21  in an example where process water  18  indeed has been added to the sump  17  by the user during the interruption of the washing programme. 
       FIG. 5  illustrates operating current of the circulation pump  21  as a function of increased pump speed when the washing programme resumes after having been unexpectedly interrupted, but where no process water has been added to the sump according to an embodiment of the invention. 
     With further reference to the flowchart of  FIG. 4 a   , upon the controller  11  resuming the washing programme that currently was running before the user opened the door  4 , the speed of the circulation pump is increased in step S 101 . 
     If during the increase of the circulation pump speed the circulation pump pressure or process water flow rate, indirectly measured by measuring the operating current of the circulation pump  21  in step S 102 , falls to an insufficient level (represented by current IL) where the flow from the pump exceeds the flow to the pump, it can be concluded in step S 103  that no process water  18  has been added to the sump  17  of the appliance  1  during the interruption. Hence, the circulation pump  21  will start to draw air, and the torque—and corresponding pump operating current—will consequently decrease. 
       FIG. 6  illustrates a flowchart of a further embodiment of the method according to the invention. 
     If in step S 103 , the controller  11  concludes that process water  18  has been added to the sump  17  of the dishwasher  1 , it drains the sump  17  on process water  18  until a desired amount of water is contained in the sump  17 . As previously discussed, the process water may be drained to a sewer system or to a storage tank for subsequent reuse. 
     While draining the sump  17 , the controller again measures in step S 105  circulation pump pressure or process water flow rate through the circulation pump  21 , wherein in case the measured pressure or flow rate reaches an insufficient level, the circulation pump  21  again draws air, and the amount of process water has been restored at a desired level. The draining is thus stopped, and normal dishwasher operation may advantageously be resumed. 
     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.