The present invention relates to a dishwasher comprising a tub, a sump located between said tub, and a filter provided between said tub, and a filter provided between said tub and said sump. The present invention also relates to a method for cleaning a filter provided between a tub and a sump of a dishwasher.

Known dishwashers comprise a washing tub in which usually one or two horizontal shelves are provided to hold the dishes to be washed, wherein within the tub a plurality of spraying nozzles or spraying rotors are provided to direct a washing liquid towards the dishes. The washing liquid, i.e. water and detergent, collects in a sump that is located below the tub, and which is separated from the tub by a filter, which usually comprises a shallow funnel-shaped filter element, sometimes referred to as flatfilter, and which at its lowest section merges into a dirt trap comprising a course filter and a microfilter from which spent washing liquid a smaller dirt particles are drained from the dishwasher into a waste water disposal line.

In order to achieve an efficient operation of the dishwasher, the filter elements have to be cleaned from soil particles so as to prevent clogging of the filters.

To this effect, there was suggested in DE 102 44 243 A1 a domestic dishwashing machine having a funnel shaped flat filter, in the centre of which there is provided a sieve element that is surrounded by an annular recess acting as a soil and dirt collector. In order to clean the central sieve element from soil particles there is provided a nozzle arrangement within the sieve element by means of which water can be sprayed from the inside of the sieve element onto the surface of the sieve element so as to remove soil particles that have collected on the sieve element.

From EP 0 774 230 B1 there is known a dishwasher which also comprises a shallow funnel-shaped filtering plate at the bottom of the tub, which filtering plate merges into a cylindrical filter element, which acts as collector for soil and dirt particles washed off the dishes. Inside the cylindrical filter element there is provided an atomizing spraying nozzle by means of which water can be sprayed onto the cylindrical filter so as to remove soil that has collected on the vertical walls of the filter.

Furthermore, in EP 0 374 009 B1 there is suggested a dishwashing machine wherein the washing liquid within the washing tub, after having passed the dishes to be washed, passes a shallow filter element provided at the bottom of the tub and' is circulated by means of a circulation pump to spraying nozzles provided within the tub. At the same time water is collected in an inlet collector of a drain pump and, during the normal washing cycle is passed through a microfilter back into the tub. During draining the tub at the end of the washing cycle the drain pump is operated in an opposite direction so that water is withdrawn from the tub and, due to the opposite flow direction, through the microfilter so as to clean that the microfilter.

Although the prior art thus was aware of the problems associated with soiled or even clogged filters, up to now no effective measures have been suggested to clean also the shallow filter elements provided between the tub and the sump of particles that have accumulated during the normal washing cycle.

Therefore it is an object of the invention to provide for a dishwasher having a tub, a sump located between the tub, and a filter provided between the tub and the sump, in which dishwasher clogging of the filter is prevented.

In accordance with a first aspect of the present invention, this object is achieved by a method as it is defined in claim 1. In particular, the present invention thus provides for a method for cleaning a filter provided between a tub and a sump of a dishwasher, in which method the sump temporarily is flooded to a level above the filter so as to lift off matter that has accumulated on the filter, whereupon the sump is drained, i.e. water is pumped out of the sump either to be recirculated to the spraying nozzles or to be withdrawn to waste, so that the water level in the sump area is lowered to a level below the filter, so as to flush away matter which prior to flooding the sump had accumulated on the filter. By flooding the sump in this manner it is possible to lift off matter from the entire filter elements, that is particularly also from any shallow filter elements that are provided at the bottom of the tub at the interface between tub and sump.

In a preferred embodiment of such method the said temporary flooding of the sump is effected by withdrawing washing liquid from the sump and passing said washing liquid back into the sump. Thus, rather than flooding the sump with fresh water, the flooding of the sump is effected by using the washing liquid that already is present in the tub and during a regular washing cycle is circulated through the tub and the sub.

In particular, the washing liquid employed for the temporary flooding of the sump can be diverted from a liquid circulation cycle by which washing liquid which has been passed into the tub and which has accumulated in the sump is reintroduced into the tub via a plurality of spraying nozzles. Thus, rather than passing the washing liquid to the spraying nozzles, part or all of the washing liquid is used to raise the water level within the sump so as to lift off matter such as food residues or other soiling that have accumulated on the filter elements and particularly on the shallow funnel-shaped flatfilter provided at the interface between tub and sump.

Preferably, during flooding of the sump no washing liquid is passed to the spraying nozzles so that the entire washing liquid that is drained from the sump by a circulation pump which supplies the spraying nozzles within the tub is reintroduced into the sump, so as to achieve a high reverse flow into the sump so as to provide for a quick and effective cleaning of the filter.

The temporary flooding of the sump can be integrated into the regular washing cycle by effecting the flooding periodically at fixed time intervals.

In preferred embodiments the degree of soiling of the filter is detected and, based upon such detection, the temporary flooding of the sump is effected. ,

In accordance with a second aspect of the present invention, the above mentioned object is solved by a dishwasher as it is defined in claim 8. In particular, the present invention provides for a dishwasher comprising a tub, a sump located below the tub, and a filter provided between the tub and the sump, wherein the dishwasher further comprises means for temporarily flooding the sump, so as to lift-off and remove matter that has accumulated on the filter.

While, as already mentioned above, the flooding of the sump could also be effected by introducing fresh water into the sump, it is preferred to achieve the flooding of the sump by means of the regular washing liquid which already is present in the tub and is circulated through the tub and the sump during the regular washing cycles. To this end the dishwasher preferably comprises a plurality of spraying nozzles provided within the tub, a fluid circulation assembly comprising a pump, means for passing liquid from within the sump to the pump and from the pump to the spraying nozzles. For flooding of the sump there are provided means for passing liquid' from the pump back into the sump as well as switching means for selectively directing the flow from the pump either to the spraying nozzles or into the sump.

While in such embodiments the switching means can be adapted to direct the entire flow from the pump to either only the spraying nozzles or to only the sump so as to provide for a large reverse flow into the sump for flooding the same, the switching means could also be adapted to divide the flow from the pump into a first portion that is passed to the spraying nozzles and a second portion that is passed to the sump. Although in the latter variant, the upward flow through the holes of the filter provided at the bottom of the tub during flooding of the sump is decreased, the simultaneous operation of one or more of the spray arms provided within the tub creates a flow which diverts the upward flow through the holes of the filter to a more horizontal direction towards the drain of the sump, where any dirt particles present in the washing liquid are trapped and from which the washing liquid is sucked into either the inlet of the circulation pump to be recirculated to the spraying nozzles or, during flooding of the sump, to the sump, or is drained by a drain pump to a waste disposal line.

Whereas flooding of the sump preferably is achieved by means of the circulation pump which is used for circulating washing liquid collected in the sump to the spraying nozzles provided within the tub, alternatively a separate feed pump can be provided to pass liquid into the sump for temporary flooding thereof. Although such a separate feed pump adds to the complexity of the system, it at the same time provides for more flexibility in operating the dishwasher.

Further, while a separate feed pump could be supplied by a separate drain at the sump, which drain is provided in addition to the drain that feeds the circulation pump, in order to cause as little as possible redesign versus known dishwasher systems, the feed pump preferably is connected to the inlet of the circulation pump.

Alternatively, if such separate feed pump is connected to the outlet of the circulation pump, rapid flooding of the sump could be achieved also with a separate feed pump of small capacity.

As already mentioned above, the flooding of the sump can be effected either periodically or, preferably, in dependency of the degree of soiling of the filter. The degree of soiling of the filter can be detected by means of sensors which detect a decrease in flow rate through the filter as it is caused by soiling or clogging. This can be achieved, for example, by the provision of a sensor which measured the water level within the sump, which will decrease when the filter element between the tub and the sump is clogged and hence less water is able to flow into the sump. The water level could be detected, for example, by optical sensors or by pressure sensors, in particular, by an analogue pressure sensor. Alternatively clogging of the filter could also be detected by means of a sensor which detects the water flow or the pressure downstream the circulation pump. Furthermore, clogging of the filter could be determined by detecting operation parameters of the circulation pump, such as speed, rotational frequency, power input, current drain etc.

In further embodiments of the present invention, the removal of dirt particles or other soiling from the shallow filter element between the tub and the sump as it is achieved in accordance with the present invention by the uplifting motion of the water level within the sump can be assisted by supplying the washing liquid for flooding the sump through a plurality of nozzles that are located below the filter and which preferably are positioned directly underneath the filter, so as to inject the washing liquid with a higher momentum into the sump in a plurality of liquid jets which impinge on the lower side of the filter element.

These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show an embodiment in accordance with the present invention.

The drawings show the lower section of a dishwasher according to a preferred embodiment of the invention, wherein:

• Fig. 1 shows the dishwasher during a regular washing cycle wherein washing liquid that is drained from the sump is fed to spraying nozzles provided within the tub; and,
• Fig. 2 shows the dishwasher of Fig. 1 during flooding the sump for cleaning the filter.

Fig. 1 shows the lower part of a dishwasher in accordance with the present invention in the region of the sump 10 that is provided below the tub 12, which in the usual manner can be provided with slideable baskets for holding dishes to be cleaned an in which a number of rotating spray arms is mounted to feed washing liquid into the tub and onto the dishes to be cleaned. In order to feed washing liquid to the spray arms, a liquid circulation pump 14 is connected with its inlet or sucking side to a drain 16 provided in a lower section of the sump 10. The bottom of tub 12 is generally funnel-shaped so that washing liquid which has been sprayed onto the dishes and drops down therefrom or flows downward along the walls of the tub is guided towards the central region of the bottom of the tub which merges into sump 10. At the interface between sump 10 and tub 12 there is provided a flat filter element 18 in the shape of a shallow funnel. In its central portion, funnel-shaped filter element 18 merges into a cylindrical dirt trap 20 which comprises a course filter 22 and a microfilter 24 and from which spent washing can be drained to a waste water disposal line, as will be further explained below.

During a washing operation water is supplied into the sump through a fresh water inlet 26 which is connected to a water supply. Upon activation of the circulation pump 14 water is sucked from sump 10 via inlet 16 into pump 14 and is passed into a first supply line 28 which feeds a lower spray arm within tub 12 as well as into a second supply line 30 which feeds an upper spray arm provided within tub 12. Water dripping down from the dishes again collects at the bottom of the tub, flows towards the centre of the tub along the slanted surfaces of the bottom 32 of the tub as well as along and through the slanted surfaces of the filter element 18 and into sump 10, either by flowing through the holes of filter element 18 or by flowing along the upper side of filter element 18 and downwards into dirt trap 20. While some of the dirt particles that are washed-off from dishes in tub 12 are guided with the water flow directly into dirt trap 20, further dirt particles 34 will collect on the upper side of filter element 18, which during a regular cleaning operation will be above the water level within the sump which in Fig. 1 is indicated at 36.

The step of cleaning filter element 18 in accordance with the teachings of the present invention is explained by reference to Fig. 2, which is an illustration of the dishwasher shown in Fig. 1 in which a switching element 38 which in Fig. 1 is shown in a first position, in which the switching element 38 blocks the inlet of a line 40 which is provided between pump 14 and supply lines 28 and 30, is displaced into a second position (Fig. 2) so as to block supply lines 28 and 30 and to divert the entire flow leaving circulation pump 14 into line 40 which directs the washing liquid back into sump 10. In doing so the water level within the sump 10 raises to a level 42 which is above filter element 18 so as to lift-off dirt particles 34 from filter 18 so that these dirt particles can be drained into dirt trap 20 when the sump is drained by switching the switching element 38 into the position shown in Fig. 1. The dirt particles 34 that are passed into the dirt trap 20 either can be collected therefrom after termination of a cleaning cycle or they can be drained and removed from the system at the end of a cleaning cycle by activating a drain pump (not shown) which is connected to a drain pipe 44 connected at the bottom section of sump 10.

As will be appreciated by those skilled in the art, switching element 38 could also be adapted to assume, in addition to the two positions shown in Fig. 1 and 2, one or more intermediate positions, so as to divide the exit flow from pump 14 into a first portion which feeds the upper and lower spray arms through supply lines 28 and 30 as well as into a second portion which feeds return line 40. Activation of the switching element 38 can be effected by the controller that controls also the further elements of the dishwasher such as the water supply system and the heating system for heating the washing liquid, wherein the switch 38 can be activated either at fixed intervals within the cleaning cycle, or at variable time intervals in dependency of a soiling detection of filter 18.

Furthermore, while Figs. 1 and 2 show an embodiment which, apart from an adaptation of the control scheme, requires only minimum hardware redesign in order to be implemented in known dishwasher systems, namely merely the provision of return line 40 and of switching element 38, it should be appreciated that the flooding of sump 10 could also be effected by a separate feed pump (not shown) and/or with the assistance of spraying nozzles that are positioned underneath filter element 18 so as to direct water jets onto filter element 18 so as to lift-off dirt particles or other soiling which adheres to the filter.

While a single embodiment in accordance with the present invention has been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as are encompassed by the scope of the appended claims.