METHOD FOR SELF-CLEANING OF A STRAINER SYSTEM INCLUDED IN AN APPARATUS FOR WASHING ARTICLES, PREFERABLY A DISHWASHER AND APPARATUS FOR CARRYING OUT SAID METHOD

Abstract: A washing-apparatus, preferably a dish-washer, has a con­ tainer (1) with baskets (2,3) for the articles to be washed up or cleaned, a flushing system with a circulation pump (8), spray arms (4,5), a strainer system with a fine strainer (15) and a coarse strainer (19), and a discharge pump (17). The function of the dish-washer is controlled by a control means (24). After a pre-wash-up, washing-up liquid is drained off to such an extent that the water level is lower than the upper surface (151) of the fine strainer (15). With this reduced water level the fine strainer is cleaned by running the flushing system during a predeter­ mined time interval. Dirt flushed away from the strainer suface is collected in the central part of the strainer system and is discharged after completion of the flushing together with the residual water quantity.

Description: The invention relates to a method for self-cleaning of a strainer system included in an apparatus for washing articles, preferably a dish-washer, according to the introductory part of claim 1. The invention also relates to an apparatus according to the introductory part of claim 6 adapted for carrying out the afore-mentioned method. During, for example, the pre-wash-up step in a dish-washer, normally large quantities of dirt are removed from the articles to be washed up. The dirt accompanies the water flowing down to the bottom of the container of the dish-washer. To prevent resoiling of the articles, the flushing system is provided with a strainer, the upper surface of which is slightly inclined towards the centre of the strainer. The dirt flushed to the bottom by the water adheres to the surface of the strainer due to the powerful suction force of the circulation pump. This soiling is particularly pronounced on the upper surface of the strainer. In known dish-washers a pre-wash-up is terminated by ceasing of the flushing (by stopping the circulation pump), whereafter the dish-water is pumped out with the aid of a discharge pump. Part of the dirt deposited on the surface of the fine strainer is discharged with the dish-water whereas part of the dirt remains on the strainer surface. During a subsequent wash-up step, for example the main wash-up succeeding the pre-wash-up, this remaining dirt will soil the dish-water and cause resoiling of the articles being washed up. This resoiling requires a relatively large number of rinsings after the main wash-up, for example three such rinsings. The consumption of water for a complete wash-up procedure is therefore relatively great. This is a considerable disadvantage since both the water costs and the cost of heating the water are relatively high. Proposals have been made to introduce extra rinsings after the pre-wash-up to rinse away, as far as possible, the dirt removed during the pre-wash-up, thus reducing the resoiling during the main wash-up. However, no reduction of the total number of necessary rinsings and hence of the total water consumption can be obtained in this way. Further, an obvious method of reducing the water consumption would be to reduce the volume of water used during each rinsing. However, it has proved to be difficult to reduce the water consumption in this way, since a volume of water reduced below a certain limit results in the circulation pump sucking air, which leads to a deteriorated flushing action and an increased noise level. Similarly, it has proved to be impossible to reduce the water consumption by reducing the number of rinsings without simultaneously deteriorating the desired good result of the washing-up. From DE-A-26 57 764 a dish-washer of the kind described above is previously known, in which, during the pumping out of washing-up liquid after a wash-up step, the circulation pump is kept running while the liquid is continuously pumped out at least until the liquid level has dropped to below the upper strainer surface of the fine strainer. This is done for the purpose of obtaining a rinsing of the fine strainer. However, tests performed have shown that, in a typical dish-washer, no significant improvement is achieved in this way. No real cleaning of the strainer surface is obtained until, during the pumping out, the liquid surface has dropped to such an extent that the strainer surface is exposed. The remaining quantity of liquid is then so small that the further pumping out is performed very rapidly, and no significant cleaning of the filter surface is ever performed. From EP-A-222 306 a dish-washer of the kind referred to in this specification is known, in which the spray arm has nozzles on its underside which provide a flow of water in the washing-up liquid with a component parallel to the surface of the fine strainer. In dish-washers of this kind, the liquid level during the wash-up steps is so high that the liquid surface lies above the strainer surface. The proposed method therefore only provides a certain amount of flow in the washing-up liquid along the strainer surface and only incomplete cleaning of the strainer. The circulation pump working during the wash-up steps has a high capacity and generates a powerful suction force. This causes particles of dirt to adhere to the surface of the strainer, which further prevents an efficient cleaning of the strainer. The invention aims to provide a method for cleaning the strainer system of a washing-apparatus of the above-mentioned kind, by means of which, during an early stage of the wash-up procedure, a very large part of the dirt removed from the articles to be washed is discharged from the washing-apparatus, whereby the resoiling of the articles during subsequent wash-up steps is greatly reduced and hence also the number of required rinsings and, in turn, the total water consumption during the whole wash-up procedure. The invention also aims to provide a device for carrying out this method and, in the same way and hence without deterioration of the wash-up result, for considerably reducing the volume of water required for the wash-up procedure. To achieve this aim the invention suggests a method according to the introductory part of claim 1, which is characterized by the features of the characterizing part of claim 1. Further developments of the method according to the invention are characterized by the features of the claims 2 to 5. A washing-apparatus for carrying out the afore-mentioned method is, according to the invention. characterized by the features of the characterizing portion of claim 6. Further developments of this apparatus are characterized by the features of the additional claims 7 to 11. The invention will now be described in greater detail with reference to the accompanying drawings showing - by way of example - in Figure 1 a dish-washer of the kind to which the invention relates, Figure 2 in more detail the strainer system of the dish-washer of Figure 1, Figure 3 the strainer system of the dish-washer and the level of the water surface when flushing with a reduced water quantity according to the invention, Figure 4 in the form of a function diagram, the function of a dish-washer for carrying out the method according to the invention. Figure 1 shows a dish-washer of the kind to which the present invention relates. It comprises a container 1 with withdrawable baskets 2 and 3 for the articles to be washed up. A typical use of a machine of this kind is as household dish-washer, whereby the articles to be washed up normally consist of plates, glasses, cutlery, pots, etc. Below the upper basket 2 an upper spray arm 4 is arranged, which is supplied with flushing water through the pipe 11 during the washing operation. The dish-water is sprayed out through a number of spray nozzles 41 on the arm, at least some of these spray nozzles being inclined horizontally in order to impart rotation to the spray arm during the flushing. The spray arm is journalled to be easily movable on a stub tube 12 serving as a hub, through which stub tube the flushing water from the pipe 11 flows out into the spray arm through openings 14. In similar manner, the spray arm 5 mounted below the lower basket 3 is mounted to be easily movable on a stub tube 10 serving as a hub, the arm being supplied with dish-water during the flushing through openings 13, and the dish-water flowing out through a number of spray nozzles 51 on the arm. The dish-water sprayed out through the nozzles of the spray arms during the flushing runs down into the lower part of the container and is collected in a sump 6. The flushing system includes a circulation pump 8. This pump sucks dish-water from the sump 6 through a pipe 7 and recirculates the dish-water via the pipes 9 and 11 to the two spray arms. To prevent resoiling of the items being washed up, the flushing system is provided with a strainer 15. The strainer 15 has an upper strainer surface slightly inclined towards the centre of the strainer as well as a stub tube 152 arranged centrally in the strainer and extending down to the bottom of the sump 6. Both the upper strainer surface 151 and the stub tube 152 are constructed as strainers, for example made of sheet metal and provided with a large number of fine holes. In the bottom of the sump 6 and straight below the stub tube 152 of the fine strainer, a waste pipe 16 is arranged through which the dish-water can be drained off with the aid of a discharge pump 17 and an outlet pipe 18. To prevent coarser particles from causing clogging of the discharge pump 17 or the waste pipe 16, a coarse strainer 19 is arranged at the outlet from the dish-washer. Dish-water is supplied to the machine through a supply pipe 20, a controlled movement downwards into the container 1 being imparted to the dish-water by a shield 23. For control of the water supply a solenoid valve 21 is arranged in the supply pipe. The function of the dish-washer is controlled and monitored by a control means 24. In conventional manner, this may consist either of a conventional, rotary electromechanical control means, or of a microprocessor or the like which is provided with suitable input and output means. To start the washing up, select the desired program, etc., a number of schematically shown operating members 25,26,27 are arranged. A typical water level during any of the wash-up steps is shown by the horizontal line A in Figure 1. The control means 24 controls the wash-up procedure in a plurality of consecutive wash-up steps, for example pre-wash-up, main wash-up and three rinsings. Before the pre-wash-up step a flushing step may possibly be provided. Between the pre-wash-up step and the main wash-up step an intermediate rinsing step may be provided, and after the last rinsing a drying step may be provided during which the washed-up articles are dried with the aid of heating elements activated by the control means and built into the dish-washer. In addition, the heating elements may be used for heating the admitted dish-water to the desired temperature at the beginning of each wash-up step. Figure 2 shows in more detail the strainer system of the dish-washer as well as the lower spray arm 5. The flushing water is supplied to the spray arm through the stub tube 10 and the openings 13 provided therein. The spray arm rests on a flange 102 on the stub tube 10 and is readily movable around the stub tube. The spray arm has, for example, the three spray nozzles 51a,51b and 51c, arranged on the upper side, as well as an additional nozzle 51d on the underside. The Figure shows the fine strainer 15 with its upper strainer surface 151, and the stub tube 152. These two elements may be made of sheet metal and are provided with a large number of relatively fine holes 153,154. In the left-hand part of the sump 6 a stub tube 71 is provided for connection of the pipe or hose 7 to the circulation pump 8. Similarly, in its central part the sump has a stub tube 161 for connection of the pipe or hose 16 leading to the discharge pump 17. The coarse strainer 19, which is to capture such larger objects that may cause clogging of the pump, is designed as a coarse-meshed metal or plastic strainer with holes 191 and is suspended from a flange in the stub tube 152 of the fine strainer. An embodiment of the invention will now be described with reference to Figures 1 to 4. The function diagram in Figure 4 illustrates an example of a method according to the invention. It is shown there how the circulation pump 8 (CP), the discharge pump 17 (DP) and the inlet valve 21 (IV) are activated during different time intervals during the period from the end of the pre-wash-up (t = t1) to the beginning of the main wash-up (t = t5). The time during which one of these members is activated is indicated in Figure 4 by heavy line segments. During the pre-wash-up, the circulation pump 8 is activated and circulates dish-water through the flushing system. The dish-water has the level designated A in Figure 1 and Figure 2. At t = t1, the pre-wash-up is terminated by the circulation pump 8 being stopped. According to a preferred embodiment of the invention, the wash-up procedure now takes a pause between t = t1 and t = t2, during which time both the circulation pump 8 and the discharge pump 17 remain inoperative. This time interval may, for example, amount to 40 seconds. During this pause the major part of the dirt, which as a result of the powerful sucking action of the circulation pump 8, has adhered to the surface of the fine strainer 15, particularly to its upper surface 151,, will loosen from the filter and float upwards to the water surface. When the above-mentioned pause is terminated, the control means 24 starts both the circulation pump 8 and the discharge pump 17 at t = t2. Dish-water is pumped away under simultaneous flushing. During this pumping away, part of the dirt present in the dish-washer tends to float towards the drainage point and is transported away. The pumping out is performed during the interval t = t2 to t = t3, and the duration of this interval is so chosen in relation to the drainage rate that the water level at the end of this interval lies lower than the upper strainer surface 151 of the fine strainer 15. This water level is designated B in Figure 3. This water level may, for example, correspond to a residual water quantity of 40% of the original water quantity. At some time during this pumping-out interval, therefore, the strainer surface 151 will become exposed, and after that the water stream flowing towards the drainage point provides rinsing away of dirt from the strainer surface 15. The particles of dirt which are rinsed away accompany the water stream down into the stub tube 152 and are transported away by the discharge pump. At t = t3, i.e. when the desired water level B in Figure 3 has been reached, the discharge pump 17 is stopped while the flushing is continued during a period of, for example, 40 seconds. During this prolonged interval the upper surface of the fine strainer is all the time exposed to the powerful water stream flowing towards the drainage point, and there is ample time for the water stream to effectively rinse away practically all of the dirt particles present on the strainer surface. These particles are rinsed down into the stub tube 152 where they are collected. At t = t4, the circulation pump 8 is stopped and the discharge pump 17 started. The residual water quantity, together with dirt particles present in the stub tube 152, are then transported away. The pumping out continues for such a long time that all the dish-water, together with residual dirt particles, has been safely discharged. At t = t5 the discharge pump 17 is stopped and the next wash-up step can be started. Typically, this constitutes the so-called main wash-up, which is started by the inlet valve 20 being opened, at t = t5, and being held open for such an adaptable time interval that the water quantity in the container reaches the desired level. The filling of water is terminated at t = t6, whereafter the flushing system is started and the main wash-up is carried out. Compared with prior art wash-up procedures, a considerable reduction of the amount of dirt remaining in the dish-washer after the pre-wash-up step, or the like, is obtained by the invention. This is achieved by the use of dish-water already present in the dish-washer and previously used. No additional supply of dish-water whatsoever is thus required to achieve this effect. The greatly reduced amount of dirt means that the water which is used during a subsequent wash-up step, typically the main wash up, will be much cleaner than what has previously been the case. This in turn means that the so-called resoiling of the articles being washed up is greatly reduced and hence also the need of a subsequent rinsing step. It has proved that with a wash-up method according to the invention, the number of rinsings following the main wash-up step can be reduced from three to two. Further, it has proved that the water quantity used during each wash-up step can be reduced, typically by about 20%. Taken together these effects of the invention permit the total water consumption for a wash-up procedure to be reduced by, for example, 35%. It has further been found that this considerable reduction of the water consumption can be obtained without any deterioration of the wash-up result whatsoever. The cleaning method according to the invention provides the greatest effect if it is performed after the pre-wash-up step or a corresponding wash-up step, since it is at this stage that a considerable quantity of loose dirt is rinsed away from the articles being washed up. It is self-evident, however, that the cleaning method can be carried out, as an alternative or as a complement, after the main wash-up step. Figures 2 and 3 show how the lower spray arm 5 is provided on its underside with a spray nozzle 51d, through which water is flushed downwards. The flushing from this spray nozzle provides an additional improvement of the cleaning of the upper surface of the fine strainer. If desired, in order to further enhance the flushing effect on the strainer, the underside of the spray arm 5 can, of course, be provided with more spray nozzles than the only one shown. In the embodiment described above, the drainage of the dish-water has taken place with the aid of a discharge pump. In those cases where a level difference need not be overcome, the dish-water may, of course, be drained off by being discharged, via a solenoid valve or the like, downwards to a floor drain or the like. In the foregoing description the designation "dish-water" has been used for the liquid used during the washing-up, which liquid normally consists of water or an aqueous solution of a detergent. Also other washing-up liquids can, of course, be used, for example in those cases where a dish-washer is utilized for cleaning in industry.

Claims: Method for self-cleaning of a strainer system (15) included in an apparatus, preferably a dish-washer, for washing up or cleaning articles placed within a container (1) of said apparatus, the strainer system (15) being arranged in the lower part of said container and having a first strainer surface (151) arranged at a higher level than the lowermost part of the container, the apparatus comprising a flushing system (4,5,7-12) adapted to suck a washing-up or cleaning liquid through the strainer system from the lower part (6) of the container and to spray this liquid into the container through spray nozzles (41,51), and with the apparatus further comprising drainage means (16-18) for drainage of washing-up liquid from the lowermost part of the container, the wash-up procedure being carried out in a plurality of consecutive wash-up steps, characterized in that, after one of said wash-up steps, such a quantity of washing-up or cleaning liquid is tapped off that said first strainer surface (151) is exposed and that thereafter the drainage is interrupted and washing-up or cleaning liquid is circulated through the flushing system at a substantially constant amount of liquid in the apparatus. Method according to claim 1, characterized in that prior to the drainage, the circulation of washing-up liquid is interrupted during a pre-determined time interval (t1-t2) to enable particles present in the strainer system to be released from the surface of the strainer. Method according to any of the preceding claims, characterized in that the washing-up liquid is circulated through the flushing system while the washing-up liquid is being drained off. Method according to any of the preceding claims, characterized in that, after the interruption of the drainage, the washing-up liquid is circulated through the flushing system during a predetermined time interval (t3-t4). Method according to any of the preceding claims, characterized in that the partial drainage and the cleaning of the strainer system are carried out between the first wash-up step in one wash-up procedure and the immediately succeeding wash-up step. Apparatus, preferably a dish-washer, with a container (1) for articles to be washed up, a strainer system (15) arranged in the lower part of the container and having a first strainer surface (151) arranged at a higher level than the lowermost part of the container (1), with a flushing system (4,5,7-12) adapted to suck a washing-up or cleaning liquid through the strainer system from the lower part (6) of the container and to spray this liquid into the container through spray nozzles (41,51), with drainage means (16-18) for drainage of washing-up or cleaning liquid from the lowermost part of the container, and with control means (24) adapted to automatically control the flushing system (4,5,7-12) and the drainage means (16-18) during the wash-up procedure, which procedure is adapted to performed in a plurality of consecutive wash-up steps, characterized in that the control means are adapted, after one of said wash-up steps, to control the drainage means for drainage of such a large quantity of washing-up liquid present in the container that said first strainer surface (151) is exposed and, thereafter, to interrupt the drainage and activate the flushing system for cleaning of the strainer system by circulation of the residual amount of washing-up or cleaning liquid in the flushing system. Apparatus according to claim 6, characterized in that the control means (24) are adapted, before the drainage, to interrupt the circulation of washing-up liquid during a predetermined time interval (t1-t2) to enable particles present in the strainer system to be released from the surface of the strainer. Apparatus according to any of claim 6 or 7, characterized in that the control means (24) are adapted to activate the flushing system for circulation of the washing-up liquid through the flushing system during the drainage of the washing-up liquid. Apparatus according to any of claims 6-8, characterized in that the control means (24) are adapted, after interruption of the drainage, to activate the flushing system for circulation of the washing-up liquid through the flushing system during a predetermined time interval (t3-t4). Apparatus according to any of claims 6-9, characterized in that the control means (24) are adapted to activate the partial drainage and cleaning of the strainer system between the first wash-up step in a wash-up procedure and the immediately succeeding wash-up step. Apparatus according to any of claims 6-10 in which the flushing system comprises a movable spray arm (5), which is arranged immediately above the bottom of the container and is provided with spray nozzles (51a-51c) on its upper side for flushing of articles to be washed up which are located above the spray arm, characterized in that the spray arm has spray nozzles (51d) on its underside as well for flushing of the upper surface (151) of the strainer (15).

Inventors: MARTINSSON, CHRISTER, NORDQVIST, BARBRO
Applicants: ABB CYLINDA AB
Application year: 1988
Main classification: A47L15
IPC codes: A47L15