Detecting filter clogging

The present invention relates to a method of, and a device for, detecting clogging of a dishwasher filter. The device is arranged to drain the dishwasher on process water, measure operating current of a motor driving a dishwasher drain pump and determine whether the dishwasher filter is clogged based on the measured drain pump motor operating current.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application filed under 35 U.S.C. 371 of International Application No. PCT/EP2012/072204, filed Nov. 8, 2012, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a method of, and a device for, detecting clogging of a dishwasher filter.

BACKGROUND

Dishwashers comprise a filter at a bottom of a washing compartment for filtering soil from process water being recirculated in the dishwasher by means of a circulation pump. This is undertaken in order to prevent dirty process water from being recirculated and sprayed onto goods to be washed. When an excess amount of soil adheres to the filter, the filter becomes clogged and the water will ultimately not pass through the filter. It may thus be desirable to detect filter clogging such that the filter can be cleaned in order for the dishwasher to reach its full washing capability.

International patent application having publication number WO 2005/089621 discloses a dishwasher and a method of controlling the dishwasher, where effects influencing washing performance negatively such as for example filter clogging are identified by detecting current drawn by a circulation pump of the dishwasher. A disadvantage of the approach set forth in WO 2005/089621 is that detection of current drawn by the circulation pump may result in an erroneously taken decision on whether the filter is clogged or not; a reduced load on the circulation pump could just as well be a result of an insufficient amount of process water in the washing compartment of the dishwasher in which case a too small amount of process water will be circulated in the dishwasher resulting in a low process water flow through the circulation pump. Thus, the amount of current drawn by the circulation pump could indicate filter clogging when the problem in fact is that the washing compartment contains an insufficient amount of process water, which is highly undesirable.

SUMMARY

An object of the present invention is to solve, or at least mitigate this problem in the art and provide improved detection of filter clogging.

This objective is attained in a first aspect of the present invention by a device for detecting clogging of a dishwasher filter. The device is arranged to drain the dishwasher on process water, measure operating current of a motor driving a dishwasher drain pump and determine whether the dishwasher filter is clogged based on the measured drain pump motor operating current.

This object is attained in a second aspect of the present invention by a method of detecting clogging of a dishwasher filter. The method comprises the steps of draining the dishwasher on process water and measuring operating current of a motor driving the dishwasher drain pump. Further, the method comprises the step of determining that the dishwasher filter based on the measured drain pump motor operating current.

Thus, load of the drain pump is determined by measuring operating current of the motor driving the drain pump. This may easily be indirectly measured by measuring the voltage of a known shunt resistor in the motor and calculating the current by using Ohm's law. Measured current can be directly translated into drain 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 drain pump. Measuring drain pump motor operating current is in itself advantageous as compared to using a relatively expensive pressure sensor to measure the flow of process water through the pump. With the measured operating current, it can be determined whether the dishwasher filter is clogged. For instance, if the operating current not relatively instantly reaches a certain predetermined level upon washing compartment draining, it can be deducted that the flow of process water through the drain pump is low and that the filter is clogged.

As previously mentioned, as compared to using operating current of a circulation pump of the dishwasher for determine filter clogging, the present invention is advantageous in that in prior art filter clogging detection methods, a reduced load on a circulation pump could just as well be a result of an insufficient amount of process water in the washing compartment of the dishwasher in which case a too small amount of process water will be circulated in the dishwasher resulting in a low process water flow through the circulation pump, which has nothing to do with filter clogging. Thus, prior art filter clogging detection methods may indicate filter clogging when the problem in fact is an insufficient amount of process water in the washing compartment. With the present invention, however, a small amount of process water in the washing compartment would still cause an adequate flow of process water through the drain pump unless the filter is clogged.

In an embodiment of the present invention, which was exemplified in the above, when determining whether the dishwasher filter is clogged, the measured drain pump motor operating current is compared to a first predetermined current threshold value, wherein the filter is considered to be clogged if the measured current is below the first predetermined current threshold value. Hence, if the flow of process water is low, indicating that the filter is clogged, the drain pump load will be reduced. Thus, by appropriately setting a first current threshold value to which the measured drain pump motor operating current is compared, it can be determined whether the filter is clogged or not. In this particular embodiment, if the measured current has not reached the first threshold level relatively instantly, it is determined that the filter is clogged.

In a further embodiment of the present invention, when determining whether the dishwasher filter is clogged, the measured drain pump motor operating current is compared to a second predetermined current threshold value after a predetermined time period has expired from the start of the draining. If the measured current is above the second predetermined current threshold value after the predetermined time period has expired, the filter is considered to be clogged. Hence, if the process water still flows after an appropriately set time period has expired (albeit with a low flow rate), it can be deducted that the filter is be clogged.

In yet another embodiment, when determining whether the dishwasher filter is clogged, a number of measured drain pump motor operating current values are averaged over a predetermined averaging time period. If the resulting average operating current is below a predetermined average current threshold value, the filter is considered to be clogged. Advantageously, this particular embodiment eliminates the risk of making erroneous decisions regarding filter clogging if the water flow through the drain pump for some reason would be uneven and/or fluctuating.

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.

It is noted that the invention relates to all possible combinations of features recited in the claims. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. Those skilled in the art realize that different features of the present invention can be combined to create embodiments other than those described in the following.

DETAILED DESCRIPTION

FIG. 1shows a dishwasher10in which the present invention can be implemented. It should be noted that dishwashers can take on many forms and include many different functionalities. The dishwasher10illustrated inFIG. 1is 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 dishwasher10comprises a washing compartment or tub11housing an upper basket12, a middle basket13and a lower basket14for accommodating goods to be washed. Typically, cutlery is accommodated in the upper basket12, while plates, drinking-glasses, trays, etc. are placed in the middle basket13and the lower basket14.

Detergent in the form of liquid, powder or tablets is dosed in a detergent compartment located on the inside of a door (not shown) of the dishwasher10by a user, which detergent is controllably discharged into the washing compartment11in accordance with a selected washing programme. The operation of the dishwasher10is typically controlled by processing unit40executing appropriate software.

Fresh water is supplied to the washing compartment11via water inlet15and water supply valve16. This fresh water is eventually collected in a so called sump17, where the fresh water is mixed with the discharged detergent resulting in process water18. At the bottom of the washing compartment is a filter19for filtering soil from the process water before the process water leaves the compartment via process water outlet20for subsequent re-entry into the washing compartment11through circulation pump21. Thus, the process water18passes the filter19and is pumped through the circulation pump21, which typically is driven by a brushless direct current (BLDC) motor22, via a conduit23and respective process water valves24,25and sprayed into the washing compartment11via nozzles (not shown) of a respective wash arm26,27,28associated with each basket12,13,14. Thus, the process water18exits the washing compartment11via the filter19and is recirculated via the circulation pump21and sprayed onto the goods to be washed accommodated in the respective basket via nozzles of an upper washing arm26, middle washing arm27and lower washing arm28.

Now, the filter19located in the sump17at the bottom of the washing compartment11is occasionally clogged due to an excess amount of soil in the processing water18, resulting in deteriorated washing capability of the dishwasher10. It is thus desirable to detect such clogging such that a user can clean the filter in order for the dishwasher to reach its full washing capability.

In an embodiment of the present invention, filter clogging is detected by draining the dishwasher10on process water18with a drain pump29driven by a BLDC motor30. It should be noted that it can be envisaged that the drain pump29and the circulation pump21may be driven by one and the same motor. When draining the dishwasher10, the water supply valve16is closed such that fresh water is prevented from entering the dishwasher. Now, when draining the dishwasher, the load of the drain pump29is registered. Practically, this is undertaken by measuring the operating voltage of a known shunt resistor in the motor30of the drain pump29and calculating the operating current. From the measured current, it is determined whether the filter19is clogged or not. For instance, as previously has been discussed, the measured drain pump motor operating current is compared to a predetermined threshold value, and it the measured current has not fallen below the predetermined threshold value within a given time expired from the start of the draining, the filter18is considered to be clogged. Thus, in practice, if the measured current has not fallen to a zero, or near-zero, level within a given number of seconds, water still flow through the drain pump29, which implies that the water flow rate is low and that the filter18thus is clogged. If the filter is not clogged, the process water will flow freely out of drain port31and be drained from the dishwasher31within seconds and as a consequence, the motor30will draw little or no current.

In an embodiment of the present invention, a user of the dishwasher10is given an indication that the filter19is clogged, for example visually via a diode32in the dishwasher housing or audibly via a sound indication. The user may subsequently clean the filter.

The controlling of the dishwasher10with respect to supervising washing programmes selected by a user, controlling circulation and draining of process water18via the circulation pump21and the drain pump29, discharging detergent, effecting rotation of wash arms26,27,28, controlling actuation of water valves16,24,25, etc. as well as detecting whether the filter18is clogged according to different embodiments of the method of the present invention is managed by the processing unit40via drive means such as the two BLDC motors22,30and via further mechanical structures (not shown) for opening the detergent compartment, rotating the washing arms, actuating the water valves, etc. Thus, the processing unit40is communicatively coupled to various hardware elements in the dishwasher10, such as the motor30of the drain pump29. The processing unit40is typically embodied e.g. in the form of one or more microprocessors arranged to execute a computer program42downloaded to a suitable storage medium41associated with the microprocessor, such as a RAM, a Flash memory or a hard disk. The microprocessor40is arranged to at least partly carry out the method according to embodiments of the present invention when the appropriate computer program42comprising computer-executable components is downloaded to the memory41and executed by the microprocessor40. The storage medium41may be a computer program product comprising the computer program42. Alternatively, the computer program42may be transferred to the storage medium41by means of a suitable computer program product, such as a memory stick, or even over a network. The microprocessor40may alternatively be embodied in the form of an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc.

FIG. 2shows a flowchart illustrating a method of detecting clogging of a dishwasher filter according to an embodiment of the present invention. In a first step S101, the processing unit40controls the motor30driving the drain pump29to the drain the dishwasher10on process water18. Thereafter, in step S102, the processing unit40measures operating current of the drain pump motor30. Finally, in step S103, the processor40determines whether the dishwasher filter19is clogged based on the measured drain pump motor30operating current.

In a further embodiment of the present invention, the processing unit40is arranged to control rotational speed of the motor30driving the drain pump29such that the rotational speed is lowered from a nominal value to a rotational speed threshold value when the dishwasher10is drained on process water18. This is advantageous, since the sensitivity of the detection of the filter19clogging is increased. When the motor30for driving the drain pump29is running at nominal speed, say about 3000 rpm, which typically is the rotational speed used for draining the dishwasher during a normal washing cycle, it is less likely that air is detected in the drain pump, which indicates filter clogging. By lowering the rotational speed of the motor30down to about 1800 rpm, changes in drain pump motor operating current are easier to detect, and the processing unit40can determine with higher accuracy whether the filter19is clogged or not.

It should be noted that the filter clogging detection undertaken according to embodiments of the present invention generally is a part of a normal washing cycle of the dishwasher. Typically, the filter clogging detection method according to embodiments of the present invention is applied at the end of a washing cycle when the dishwasher is drained on process water having the advantage that no fresh water must be supplied to the dishwasher for the washing cycle to continue after filter clogging detection. However, the filter clogging detection method according to embodiments of the present invention could be applied during a normal washing cycle if for some reasons indications are given that the filter is clogged. It may even be envisaged that a separate short filter clogging detection program is run to test whether the filter of the dishwasher is clogged.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.