Washing process for an automatic dishwasher

Abstract: Washing process for an automatic dishwasher having a tub (6) with a lower spray arm (10) and an upper spray arm (11) supplied by a pump (8) with water wich can be heated by a resistance (15) to perform, during the washing process, at least an operative cycle in which said spray arms are supplied alternately to spray the crockery. The operative cycle consists of a first phase (t1 - t2) in which only the lower spray arm (10) is supplied, and a second phase (t3 - t4) in which only the upper spray arm (11) is supplied. The heating resistance (15) is only energized when the lower spray arm (10) is supplied.

Description: The present invention relates to an improved washing and/or rinsing process to be performed in an automatic dishwashing machine of the type comprising a wash tub in which are provided at least a lower and at least an upper baskets for supporting crockery to be washed. As is known, each basket is associated with a relevant rotary spray arm which is fed with water by a circulating pump. As described in EP-A-0 237 994, for instance, the spray arms are preferably supplied alternately, rather than concurrently, in order to reduce the dimensioning of the motor and the hydraulic circuit of the circulating pump, and also to reduce the noise produced by the water jets impinging on the crockery. To this aim, the spray arms are connected to the delivery section of the circulating pump through respective supply conduits which are associated with a monostable flow distributing valve; this latter is indirectly controlled by the programmer of the machine to perform washing processes during which the spray arms are ciclically operated alternately. In particular, the flow distributing valve is controlled by repeatedly discontinuing, with different idle times, the energization of the motor driving the circulating pump. Although this solution is particularly advantageous and precise in operation, the number of commutations occurring during every washing phase may in the long run shorten the life of the motor. In addition, when the water heating resistance, that is positioned on the bottom of the wash tub, is energized during the operative phases in which only the upper spray arm is supplied, the resistance may easily get overheated and therefore damaged, giving off bad odours. In fact, during these phases the heating resistance, located relatively far from the upper spray arm, is only insufficiently sprinkled by the water which is in suspension in the wash tub. This drawback, which however for dimensional reasons does not arise when the lower spray arm is operated, may be overcome by increasing the amount of water fed into the tub, but this is in contrast with the current energy saving trends. As an alternative, the heating resistance may be associated with special means capable of collecting the water circulated in the tub so as to keep the resistance wet. This solution is only partially effective and in any case undesirably complicates the structure of the bottom part of the wash tub, therefore affecting the correct positioning of the various parts and the manufacturing costs of the machine on an industrial scale. Dishwashers are also known in which the heating resistance is arranged in correspondence of the delivery or suction side of the circulating pump, so as to be permanently immersed in water when it is energized. This solution, however, involves remarkable complications in the structure and assembling of the machine. Furthermore, to prevent parts made of plastics and adjacent to the resistance from being damaged it is necessary to provide temperature and/or level sensing devices capable of controlling the actual operating temperature of the heating resistance; this provision further complicates the structure of the whole dishwasher. Moreover, with such a solution it is obviously impossible to use the same heating resistance to perform, as is traditional, a final drying phase of the crockery by operating the heating resistance under "dry" conditions. It is the main scope of the present invention to provide a washing process which can be readily carried out with good performances in an automatic dishwasher of a substantially known type. Another scope of the present invention is to provide a washing process of the kind mentioned above, which enables the dishwasher to be generally undersized, while keeping a high degree of reliability. A further scope of the present invention is to provide a washing process of the kind mentioned above, which enables problems concerning overheating of the water heating elements to be substantially overcome without the need to arrange the dishwasher with special constructional features. According to the invention, these scopes are attained in a washing process for an automatic dishwasher embodying the features recited in the appended claims. The characteristics and advantages of the invention will be more apparent from the following description, given only by way of non-limiting example, with reference to the accompanying drawings, in which: Figure 1 diagrammatically shows the main hydraulic components of an automatic dishwasher able to perform the washing process according to the invention; Figures 2 to 4 are curves respectively representing the time relationships in the actuation of some operational components of the dishwasher during the progress of the washing process according to the invention. With reference to Figure 1, the washing process according to the invention is to be carried out in an automatic dishwasher of per se known type, without the need to provide it with substantial structural modifications. In particular, the dishwasher mainly comprises a wash tub 6 provided at the bottom with a sump 7 for collecting the water which in known manner is filled into the machine and can be heated by heating means 15, e.g. including a common electric resistance located at the bottom of the tub. The suction side and the delivery side 9 of a circulating pump 8 are arranged to respectively draw water from the sump 7 and deliver it to at least two rotary spray arms 10 and 11. These latters are arranged in the tub 6 at different levels, in correspondence of relevant baskets 16 and 17 for supporting the articles to be washed. More particularly, the delivery side of pump 8 is connected with the lower spray arm 10 via a conduit 13 extending upwards to a short distance, and with the upper spray arm 11 via a conduit 14 extending upwards to a substantially higher level than the conduit 13. The conduits 13 and 14 are in turn connected to the delivery side 9 of the circulating pump through flow distributing means diagrammatically indicated at 12 in Figure 1. In a per se known manner, the flow distributing means 12 is able to be at least indirectly controlled by the programmer of the dishwasher in order to selectively communicate the delivery side 9 of pump 8 with either conduit 13 and 14. The flow distributing means 12 is preferably, although not exclusively, arranged as disclosed in the aforementioned EP-A-0 237 994, to which reference is made for better comprehension thereof. In particular, the flow distributing means 12 comprises a monostable ball valve through which the lower spray arm 10 or the upper spray arm 11 can be supplied selectively by temporarily stopping operation of the pump 8 for a time period respectively shorter or longer than a predetermined interval. The programmer of the automatic dishwasher, not shown, may be of any appropriate kind and in a per se known manner controls operation of substantially all operative components of the machine; for instance, it may be an electronic programmer, readily settable by a person skilled in the art according to the various requirements. In a way which is also per se known, the dishwasher may be arranged to carry out an automatic washing process including an actual washing cycle, possibly preceded by a prewashing cycle and preferably followed by at least a rinsing cycle. With reference also to Figures 2 to 4, a washing cycle is hereinafter described forming part of the washing process according to the invention. In particular, Figure 2 diagrammatically shows the changes versus time of the temperature T of the operative fluid of the dishwasher, while Figures 3 and 4 diagrammatically illustrate the operational periods of the lower spray arm 10 and the upper spray arm 11, respectively. At time t0 the programmer determines the wash tub 6 to be fed with a predetermined amount of water at a temperature T1 (Figure 2), for instance 20° C, and detergent as well. After termination of the water-fill phase, e.g. lasting about 1 to 3 min, at time t1 the circulating pump 8 is actuated with the flow distributing means 12 arranged to connect the delivery side 9 of the pump to conduit 13. As shown in Figure 3, at time t1 only the lower spray arm 10 is thus supplied, and according to an aspect of the invention these working conditions last substantially, e.g. a period of about 20 min, until time t2, at which the articles supported by the lower basket 16 are suitably cleaned. According to another aspect of the invention, the programmer determines energization of the heating means 15, in order to heat the water collected in the sump 7, only during the phase t1 - t2 in which the lower spray arm 10 is in operation. Therefore, the temperature of the water raises gradually as shown in Figure 2, up to a predetermined value T2, e.g. approximately 65° C, which may be thermostatically controlled in a per se known way. Preferably, both the lower spray arm 10 and the heating resistance 15 are operated continuously and concurrently during phase t1 - t2. As an alternative, however, the spray arm 10 and the heating resistance 15 may be operated discontinuously and/or during different intervals during phase t1 - t2. At any rate, attention is directed to the fact that, according to the invention, during this phase the upper spray arm 11 keeps being inoperative and the heating resistance is energized only when the lower spray arm 10 is supplied. Hence, during phase t1 - t2 substantially the whole amount of water delivered by the circulating pump 8 supplies the lower spray arm 10, which is substantially adjacent to the water collecting sump 7. As a consequence, the water sprayed by the spray arm 10 onto the associated basket 16 falls back into the sump 7 quickly, in this way ensuring the heating resistance 15 to be properly wetted continuously when it is energized, although the water level in the sump 7 decreases substantially when the circulating pump 8 is in operation. This not only ensures high reliability of the resistance 15 and the adjacent components, but also enables the heating power of the resistance to be used in the best way. In other words, the resistance 15 can effectively heat the water collected in the sump 7 rapidly, correspondingly shortening the time required for washing the crockery. Of course, also bad odours given off when the resistance 15 is overheated are eliminated, and the resistance may have a simple and cheap structure. In addition, it was also experimentally found that during the phase t1 - t2, in which only the lower spray arm 10 is supplied, the hot moisture developed within the wash tub 6 affects the crockery supported by the upper basket 17, too. This moisture, made of water added with detergent, produces on the crockery supported by the upper basket an emollient effect which advantageously promotes detachment of the dirt particles from the crockery, whose washing can thus be easily and rapidly completed. Hence, according to still another aspect of the invention, at time t3 the programmer of the machines determines the flow distributor 12 to switch to the position in which it communicates the delivery side 9 of the circulating pump with the upper spray arm 11 only. When, as is preferable, the flow distributor 12 is arranged as described in the aforementioned EP-A-0 237 994, this switching action can easily be determined by, temporarily stopping operation of the pump 8 for a time period longer than a predetermined interval, for instance 2 sec. Thus, time t3 can in this case occur at least two seconds after occurrence of time t2, that is to say, with a delay which however is negligible compared with the duration of the whole washing cycle. Starting from time t3, the upper spray arm 11 is supplied, until time t4, for a relatively short time period (10 to 15 min, for example) which is shorter than the preceding phase t1 - t2 and during which the heating resistance 15 is de-energized. During phase t3 - t4 the lower spray arm 10 is inoperative, so that all the water delivered by the circulating pump 8 is conveyed to the upper spray arm 11 which, thanks to the emollient effect referred to before and to the fact that the water temperature keeps having a substantially constant value T2 (Figure 2), effectively cleans the crockery supported by basket 17. During phase t3 - t4, in fact, even though the resistance 15 is de-energized the previously heated water contained in the tub 6 cools down to a negligible extent, thanks not only to the good thermal insulation provided in modern dishwashers, but also to the short duration of the phase itself. The upper spray arm 11 is preferably actuated continuously during phase t3 - t4, but of course it could even be operated intermittently. In any case, it should be pointed out that during both phases t1 - t2 and t3 - t4 the dishwasher needs a reduced amount of water to ensure correct priming conditions of the circulating pump 8 and an effective mechanical action on the crockery supported by the baskets 16 and 17 by the water jets issuing from the spray arms 10 and 11, respectively. The washing cycle terminates in a traditional manner, with a drain phase t4 - t5 during which the temperature of the water keeps decreasing as illustrated in Figure 2. As already stated, the washing process according to the invention may include also a hot prewashing cycle and/or a hot rinsing cycle, respectively preceding and following the above-described washing cycle. In this case the progress of each cycle is substantially similar to the one described with reference to Figures 2 to 4. The only differences consist of the fact that the water temperature at the beginning of the washing cycle and/or at the beginning of the rinsing cycle may be higher if the wash tub and the relevant components associated therewith have been formerly heated; moreover, in a traditional way the water will be added with detergent during the prewashing and washing cycles, whereas it will be added with rinse-aid during the rinsing cycle. At any rate, the washing process according to the invention consists of at least an operative cycle t0 - t5 substantially including, besides a traditional water-fill phase t0 - t1 and a traditional final drain phase t4 - t5, a washing cycle t1 - t4 substantially consisting of a first phase t1 - t2 in which the water is heated and only the lower spray arm is supplied, and a second phase t3 - t4 during which the resistance 15 is de-energized and only the upper spray arm 11 is supplied. As already stated, the interval t2 - t3 is negligible and may even be skipped if a different flow distributor 12, for instance of the electro-mechanical type, is employed. Besides the advantages mentioned above, the washing process according to the invention enables the crockery to be properly cleaned with a reduced water consumption and without the need to repeatedly switch the main operative components of the machine (i.e. circulating pump 8 and heating resistance 15) on and off, these components thus being reliable in the long run. In addition, the total duration of the washing process according to the invention, in order to obtain the same performances, is shorter with respect to a traditional washing process in which the spray arms are cyclically operated alternately, and substantially equal to the duration of a traditional washing process in which the spray arms are operated concurrently (with relevant drawbacks which are overcome with the invention). Obviously, the washing process described above may undergo a number of modifications without departing from the scope of the invention. For example, the washing process may embrace also a traditional final drying cycle, including a short phase in which the heating resistance 15 is energized under "dry" conditions. Moreover, in order to clean the mechanical filter usually provided in the dishwasher, a further and negligible short phase (e.g. lasting about 15 sec) in which the lower spray arm 10 is operated may be provided after termination of at least one of the operative cycles included in the washing process. Anyway, it will be apparent to those skilled in the art that the washing process according to the invention can easily be performed in a known automatic dishwasher with substantially no need of special structural features; in fact, it will only be necessary to set up the programmer of the machine so as to carry out the various operative phases with the progress and times provided for by the invention.

Claims: Washing process for an automatic dishwasher having a wash tub in which are provided at least a lower spray arm and at least an upper spray arm able to be supplied by a circulating pump with water which is contained in said tub and can be heated by heating means to perform, during said washing process, at least an operative cycle in which said spray arms are alternately supplied to spray the crockery, characterized in that said operative cycle substantially consists of a first phase (t1 - t2) in which only said lower spray arm (10) is supplied, and a second phase (t3 - t4) in which only said upper spray arm (11) is supplied, said heating means (15) being only energized when the lower spray arm is supplied. Washing process according to claim 1, characterized in that said second phase (t3 - t4) has a shorter duration than said first phase (t1 - t2). Washing process according to claim 1, characterized in that said heating means (15) are energized discontinuously during said first phase (t1 - t2). Washing process according to claim 1, characterized in that said lower spray arm (10) is supplied discontinuously during said first phase (t1 - t2). Washing process according to claim 1, characterized in that said upper spray arm (11) is supplied dicontinuously during said second phase (t3 - t4).

Inventors: MILOCCO CLAUDIO, MILOCCO, CLAUDIO
Applicants: ZANUSSI ELETTRODOMESTICI, ZANUSSI ELETTRODOMESTICI S.P.A.
Application year: 1991
Main classification: A47L15
IPC codes: A47L15