GB2254542A - Dishwashing machine with self-cleaning recirculation filter - Google Patents

Abstract

A dishwashing machine comprises a washing tub 1, 2 with a self-cleaning recirculation filter 5 having a frustoconical portion 6 provided with a central aperture 13 connecting the interior of the tub to the intake of a discharge pump 8, and a cylindrical portion 9 which from the aperture extends downwardly. An arm assembly 4 directs towards the filter first and second jets 16, 17 of liquid which are turned towards the central aperture and tangential to the frustoconical portion and the cylindrical portion respectively. The central aperture is disposed at a higher level D relative to the peripheral edge 15 of the frustoconical portion and relative to the maximum dynamic level B of the liquid upstream of the recirculation filter. <IMAGE>

Description

DISHWASHING MACHINE WITH SELF-CLEANING RECIRCULATION FILTER The present invention relates to a dishwashing machine provided with a filter referred to as a 'recirculation filter' which is capable of being automatically cleaned during operation of the machine.

A dishwashing machine of that type is known for example from GB-B-2204482 and comprises a washing tub having a recirculation filter which is disposed in the flow path of the water which is drawn in by a circulation pump for feeding at least one rotary arm assembly disposed above the actual filter. The filter comprises a portion which is substantially shaped in the form of an inverted truncated cone with a central aperture which directly communicates the interior of the tub with the intake of a discharge pump. A further substantially cylindrical portion of the filter extends downwardly from the central opening of the inverted frustoconical portion.The two portions of the filter are concentric with respect to the axis of rotation of the arm assembly which directs towards the filter a jet of water which is substantially tangential to the cylindrical portion and which is capable of automatically cleaning it.

The arm assembly also directs towards the filter a further jet of water which is tangential to the inverted frustoconical portion and thus extends in a correspondingly downwardly inclined fashion in the direction of the central aperture. In particular the further jet is capable of moving downwardly towards the central aperture and thus towards the hydraulic discharge circuit the particles of dirt which are retained by the frustoconical portion of the filter. As a result, in operation of the machine all the particles of dirt which are of a specific weight greater than that of the operating liquid are automatically removed from the entire recirculation filter.

That construction is particularly advantageous but it does not eliminate the problem of the particles of dirt which, being of a specific weight which is close to or less than that of the operating liquid, remain in suspension in that liquid, thus reducing the general levels of performance of the dishwashing machine. In actual fact, during the washing and/or rinsing phases, the recirculation filter is substantially submerged by the water which collects on the bottom of the washing tub, in particular in the discharge circuit, comprising of the region of the tub upstream of the filter.Therefore the major part of the lighter particles of dirt which are retained by the recirculation filter and urged towards the central aperture by the inclined jet of water (which is substantially submerged) have a tendency to float; in consequence, instead of being trapped in the region of relative calm enclosed by the cylindrical portion of the filter, the light particles of dirt return into suspension in the operating liquid.

In addition, during a washing and/or rinsing phase and/or at the end of the phase, there may be at least one pause in operation of the circulating pump; that is normally the case whenever the dishwashing machine is designed as described for example in EP-A-0237994 for alternately supplying two spraying arm assemblies. As is known, during such a pause, there is a rapid rise in the level of liquid which collects on the bottom of the washing tub, with the particles of dirt which have been previously deposited in the interior of the cylindrical portion of the filter being consequentially stirred up.

The particles of dirt which are stirred up in that way tend thus to go back into suspension in the liquid, affecting the general levels of performance of the machine.

The main aim of the present invention is that of providing a dishwashing machine provided with a selfcleaning recirculation filter capable of providing for optimum filtration of substantially all the dirt removed from the crockery.

Another aim of the present invention is that of providing a dishwashing machine of the above-identified type in which any interruptions in operation do not substantially affect the efficiency of the self-cleaning filter.

In accordance with the present invention there is provided a dishwashing machine comprising a washing tub provided with a self-cleaning recirculation filter disposed in the path of flow of the liquid which is drawn in by a circulating pump for feeding at least one rotary spray arm assembly disposed above the filter, the filter comprising a substantially frustoconical portion provided with a central aperture directly connecting the interior of the tub to the intake of a discharge pump, and a substantially cylindrical portion which is connected to said aperture and which extends downwardly from the frustoconical portion, said arm assembly being capable of directing towards the filter at least first and second jets of liquid which are turned towards said central aperture and which are substantially tangential to the surface of said frustoconical portion and said cylindrical portion respectively, wherein said central aperture is disposed at a higher level with respect to the peripheral edge of the frustoconical portion and with respect to the maximum dynamic level of the liquid upstream of the recirculation filter.

The features and advantages of the present invention will be clearly apparent from the following description given solely by way of non-limiting example.

The description refers to the accompanying Figure which is a diagrammatic partial view of the main components of the dishwashing machine according tot he invention, in a preferred embodiment.

The dishwashing machine primarily comprises a washing tub 1 (of which only part is shown), the bottom of which is defined by a bowl 2 for collecting the washing and rinsing liquid. The collecting bowl 2 communicates with the intake (not shown) of a circulating pump 3 for feeding a least one rotary arm assembly 4 for spraying in known manner the crockery to be washed.

The washing tub 1 also accommodates, below the arm assembly 4, a fine-mesh recirculation filter 5 which is disposed in the path of flow of the water which, after having been sprayed over the crockery, is collected in the bowl 2 in order to be drawn in again by the circulation pump 3. The filter 5 comprises a substantially frustoconical portion 6 provided with a central aperture 13 for directly communicating the interior of the tub 1 with the intake 7 of a discharge pump 8. The filter 5 also comprises a substantially cylindrical portion 9 which is connected to the central aperture 13 of the frustoconical portion 6 and extends downwardly to a wall 12 connected to the intake of the discharge pump 8.

The intake of the discharge pump 8 can also communicate with the bottom of the bowl 2 by way of a siphon element 14 which permits emptying thereof during the discharge phases.

Preferably, as described for example in abovementioned GB-B-2204482, the cylindrical portion 9 of the recirculation filter removably accommodates a coarse-mesh pump-protection filter (not shown for the sake of simplicity). In any case the recirculation filter 5 is substantially concentric with respect to the axis of rotation of the arm assembly 4 and is rendered selfcleaning by virtue of two jets of water 16 and 17 which issue from respective additional nozzles 18,19 on the arm assembly 4. In particular the jets 16 and 17 are substantially tangential to the surface of the frustoconical portion 6 and the cylindrical portion 9 respectively of the recirculation filter.

In accordance with a feature of the invention the frustoconical portion 6 of the filter is disposed as shown in the drawing, that is to say with the central aperture 13 higher than the peripheral edge as indicated at 15. More precisely, the central aperture 13 of the filter is disposed at a higher level than the maximum dynamic level A of the water upstream of the filter; the peripheral edge 15 however may also be disposed at a lower level than the above-mentioned dynamic level A. It should be recalled that the term 'dynamic level' means the level reached by the water which collects on the bottom of the tub 1, 2 during a washing phase; as is known, that dynamic level is generally greater in the region upstream of the recirculation filter.

During the washing operation therefore the jet of water 16 is directed upwardly and advantageously extends in the air, rather than being submerged in water, at least in its final portion adjacent to the central aperture 13 of the filter. In addition, contrary to the known constructions, the recirculation filter 5 according to the invention subdivides the bottom of the tub 1,2 into three separate regions in which the water attains respective levels during the washing phases. The abovementioned dynamic level A is reached, upstream of the filter 5, in the region adjacent to the peripheral edge 15 of the frustoconical portion 6.Within the cylindrical portion 9, upstream of the recirculation filter, the water reaches a level B which is generally lower than the level A, as has also been verified experimentally; in substance in fact the interior of the cylindrical portion 9 receives only the water of the cleaning jets 16 and 17. On the bottom of the collecting bowl 2, downstream of the filter (that is to say in the region adjacent to the intake of the circulation pump 3), the water reaches a level C which is lower than the levels A and B.

In consequence the particles of dirt which are retained by the frustoconical portion 6 of the filter are urged by the jet 16 towards the central aperture 13 in a particularly effective manner, in spite of the unfavourable angle of inclination. In actual fact, under the worst operating conditions, the jet 16 is immersed in water only in its initial portion in which the pressure is greatest. In addition, not being substantially submerged by the washing liquid, not only the heavier particles of dirt but also those of a lower specific weight relative to the liquid are effectively urged towards the central aperture 13 by the jet 16.Accordingly substantially all the particles of dirt which are retained by the frustoconical portion 6 of the filter drop under the effect of gravity through the aperture 13 into the interior of the cylindrical portion 9 where they are trapped in order to be removed during a subsequent discharge phase. It will be noted that, even if the nozzle 18 is partially immersed in water, the rotary movement of the arm assembly 4 which is normally fairly slow is practically unaffected.

In per se known manner, the particles of dirt which are retained by the cylindrical portion 9 are also removed by virtue of the jet of water 17, whereby substantially all the filter 5 is automatically cleaned in the course of operation of the machine.

It is known in this respect that the jet of water 17 is also particularly effective since the level B of the water within the cylindrical portion 9 is relatively low in relation to the known constructions.

That gives rise to another important advantage: since the degree of blockage of the cylindrical portion 9 of the filter depends on the hydraulic pressure applied by the liquid contained therein, and thus the level B, the degree of blockage is correspondingly reduced. To sum up, the dishwashing machine according to the invention is provided with a self-cleaning filter system 5 which is particularly simple and effective for efficiently filtering - and progressively, during operation of the machine - all the dirt removed from the crockery. That also makes it possible, with equal levels of performance, to use a frustoconical portion 6 of larger mesh size than the known constructions.

In accordance with another feature of the invention, in the case in which the dishwashing machine is of the type which provides for discontinuous operation of the circulating pump 3 during a washing and/or rinsing phase, the central aperture 13 of the frustoconical portion 6 of the filter is disposed at a level which is even higher that the 'static' level of the water. That static level which is higher than the dynamic level A and indicated at D in the drawing is the level which is reached by the water in the tub 1,2 when the circulating pump 3 is de-activated during a washing and/or rinsing phase. Advantageously therefore the particles of dirt in suspension in the liquid contained with the cylindrical portion 9 of the filter are prevented from being capable of overflowing into the region upstream of the frustoconical portion 6 where they would have to be freshly filtered.

It will be appreciated that the dishwashing machine described may be the subject of numerous modifications which fall within the scope of the invention.

Claims (3)

1. A dishwashing machine comprising a washing tub provided with a self-cleaning recirculation filter disposed in the path of flow of the liquid which is drawn in by a circulating pump for feeding at least one rotary spray arm assembly disposed above the filter, the filter comprising a substantially frustoconical portion provided with a central aperture directly connecting the interior of the tub to the intake of a discharge pump, and a substantially cylindrical portion which is connected to said aperture and which extends downwardly from the frustoconical portion, said arm assembly being capable of directing towards the filter at least first and second jets of liquid which are turned towards said central aperture and which are substantially tangential to the surface of said frustoconical portion and said cylindrical portion respectively, wherein said central aperture is disposed at a higher level with respect to the peripheral edge of the frustoconical portion and with respect to the maximum dynamic level of the liquid upstream of the recirculation filter.

2. A dishwashing machine according to claim 1 wherein the liquid which collects on the bottom of said washing tub attains said dynamic level and a higher static level when the circulating pump is in operation and inactive respectively, wherein said central aperture of the frustoconical portion of the recirculation filter is disposed at a higher level than said static level.

3. A dishwashing machine constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.