Improvement in the washing programmes of clothes washing or dishwashing machines

Abstract: Clothes washing or dishwashing machine provided with a washing vessel, a heating element for heating up the liquor in said vessel, a sensor means for detecting the temperature of said liquor, a control and actuating appratus connected to the various functional parts and sensors of the machine, said apparatus being adapted to trigger and control a plurality of washing programmes which differ from each other at least for the fact that each programme defines the attainment of a highest temperature value of the liquor in the vessel which is anyhow different from the highest temperature value attainable in the other programmes, said machine being also provided with means adapted to automatically cut out the power supply to said heating element for a determined period of time whenever the temperature of the liquor in the vessel reaches at least a pre-determined value below the highest attainable temperature value, wherein said at least a pre-determined value may be a plurality of different temperature values that can be selectively pre-determined for each washing programme.

Description: The present invention refers to a clothes washing or dishwashing machine, in particular of the household type, which is provided with an appropriate electric circuit that, when associated with a timer means, enables a plurality of programmes to be set which differ from each other for their highest attainable temperature, wherein the rising phase of the temperature of the wash liquor can be interrupted selectively for a pre-determined time interval. Clothes washing and dishwashing machines are known in the art the operation of which is controlled by wash cycle programming means, said cycle usually comprising at least a wash liquor heating-up phase, a wash liquor temperature holding phase, wherein said two phases are carried through when the washload holding drum is rotating regularly, and a final series of rinsing and spin-extraction phases (see EP-A-0 501 240). Clothes washing or dishwashing machines are in particular known which are provided with a so-called "thermogradual" system for controlling the temperature of the wash liquor, such a system consisting in allowing one or more temperatures to be reached by energizing the heating element during one or more defined periods through appropriate configurations of the circuits and the programme sequence control switch. It is however widely appreciated that such a solution, although it has actually been able to find a wide application owing to its simple concept, its reliability and its low cost, does not enable optimum temperatures to be attained for any given washing programme selected by the user, since the final temperature reached by the washing liquor depends not only on the time during which the heating element is kept energized and the power input rating of such an element, but also on the initial temperature of the liquor and, more generally, the heat capacity and the heat loss characteristics of the whole lot of elements involved, such characteristics being usually unknown quantities and likely to be subject to variations within quite wide limits. In view of making washing programmes to more strictly comply with the actual requirements of use, it is also a known technique, eg. from the patent specification FR 1.235.659, to enable the length of the washing time to be modified at will through the provision of additional timing means. Such a solution, however, gives only the possibility of modifying the washing time at constant temperature, but does not allow for any additional phases at pre-determined temperatures, differing from the nominal washing temperature, to be carried out within the same programme. The constant search for performance capabilities increasingly adapted to suit evolving consumers' needs requires now to ensure the availability of washing programmes in which the temperature of the washing liquor can be controlled in a more effective manner, considering the varying capacity of removing dirt and stains of different nature and origin as a function of the attained temperature. To this purpose, machines have been developed in which the temperature of the washing liquor is measured directly by specially provided temperature sensors through which the washing programme is controlled and adjusted. However, all such types of machines, which are known in the art under the denomination of "thermostop" machines, share the characteristic that the ultimate, steady-state temperature of the washing liquor is reached with a single temperature-rise ramp. In the description given below, the case of a clothes washing machine is specifically dealt with for mere reasons of simplicity, but it will be appreciated that what is described and claimed therein applies similarly to a dishwashing machine. Since it has been experimentally demonstrated, and it is also a widely known fact, that certain types of stains or fatty soil are removed more effectively at certain temperatures rather than other ones, (in particular, it is a widely diffused prejudice, albeit among consumers and not among those who are skilled in the art, that, all other process conditions being equal, the higher the washing temperature, the better the washing result), it ensues that with a simple "thermostop" type of operation the optimum temperature required to remove certain types of stains, if lower than the highest programmed temperature, is certainly reached, but also almost immediately exceeded. For instance, protein-based, enzyme-removable stains and soil should be handled at temperatures which are below 40°C, whereas other kinds of soil may require washing at temperatures above 60°C for best removal results, and certain types of particularly tenacious stains, such as for instance those originated by substances of some vegetable or sinthetic nature, are most effectively dealt with at temperatures of approx. 90°C. As a result, if the same washing bath, and therefore a single washing temperature, is used according to the known technique, an immediate consequence will be that the effectiveness with which soil is actually removed from certain items in the washload turns out to be unavoidably and definitely impaired. In order to improve such a situation it is a known technique, eg. from the Italian patent application no. PN92A000081 filed by the same applicant, to provide a clothes washing machine provided with a plurality of washing programmes differing from each other for the highest attainable temperature in each one of them. The above cited patent application also discloses the teaching of providing said washing machines with an arrangement adapted to control the duration of the washing phase at the programmed temperature. However, if such a solution is effective in enabling the afore described situation to be improved in the sense that the washing performance can actually be optimized for a particular type of soil, and therefore the dwelling time of the washing bath at the pre-selected temperature can actually be adjusted in accordance with the degree of soil in the washload, the same does not enable the problem to be solved in the more usual and general case of a mixed washload in terms of both types of fabrics and types of soil and stains, in the afore explained sense, contained therein, since it will be readily appreciated that such a kind of washing machine is able to each time handle in an optimum manner only soil of a given type, while just handling poorly, or less satisfactorily, all other types of soil with different properties in the washload. It therefore would be desirable, and it is actually a main purpose of the present invention, to provide a clothes washing machine provided with at least a washing programme which is adapted to handle in an optimum manner, at appropriately differentiated temperatures, all kinds of soil that may be present in a washload, and that may require different washing temperatures for their effective removal, using the most simple and reliable means, the most cost-effective components and most readily available techniques to such a purpose. The invention will be more clearly understood from the description which is given below by way of non-limiting example with reference to the accompanying drawings, in which: Figure 1 is a diagram showing graphically the evolution of the temperature of the washing bath according to a definite washing programme of a washing machine according to the present invention; Figure 2 is a diagram showing an example of the same graphical representation of Fig. 1, but referred to a different washing programme of the same washing machine; Figure 3 is a view of another example of graphical representation of the evolution of the temperature of the washing bath according to a third washing programme performed by the same washing machine according to the present invention. The general term "water" will be used in the following description to indifferently mean both washing liquor and rinse water. However, such a simplification will not affect the intelligibility of the exposure to any extent, owing to the context in which said term is actually used, as anyone skilled in the art will readily appreciate. In order to give the user the possibility of adjusting the duration of the washing action at various temperatures in view of optimizing the effectiveness with which the different types of soil in the washload are going to be dealt with, the present invention substantially relies on creating the possibility of introducing, both during the heating-up phase and the washing phase at the highest pre-set temperature, one or more time intervals which are caused to start when the temperature reaches a pre-determined value and during which the power supply to the heating element is cut off. According to such a mode of operation, the machine goes therefore on with the washing process, in particular keeping its washload-holding drum rotating regularly, while the power supply to the heating element is restored after each one of said time intervals, so that the washing programme can go on regularly until its end. In practice, this enables washing phases at substantially constant temperature to be introduced in the programme, so as to be able to deal in a selective manner with the various types of soil in the washload during a pre-determined period of time, said phases being situated at temperature levels which are of course lower than the level of the highest pre-set temperature and are aimed at handling the type of soil in the washload that is more effectively removed at each one of said temperatures. With reference to a more general case and the illustration appearing in Figure 1, an embodiment of the present invention is explained below along with the related operating principle. Figure 1 illustrates a graphical representation of the evolution of the washing liquor temperature in a 90°C washing programme. Such a temperature evolution can be derived from said diagram for state-of-art machines by completely eliminating the time intervals indicated with the references t b , t c , t d on the abscissa, so that a single temperature rise phase would be obtained forming a single, straight temperature rise ramp from the initial value T 0 through to the final value at 90°C, without any dwelling time at the intermediate values of 40°C and 60°C. According to the present invention, on the contrary, a plurality of intervals of a pre-determined duration t b , t c , t d are planned to occur during the programme in an irregular succession, such intervals being in fact planned to start when the temperature of the washing liquor reaches respective values of 40°C, 60°C and 90°C. During these intervals the heating element provided to heat-up the washing liquor is de-energized, so that the programme, upon reaching said temperature values, undergoes a double effect: on the one hand there is a corresponding extension of the washing time, while this extension of the washing time is on the other hand is obtained by enabling the temperature to dwell exactly at the desired level which has been appropriately selected to cope with the type of soil which is particularly sensitive to and is best removable at precisely that temperature. Figures 2 and 3 illustrate on the contrary the evolution of the temperature of the washing liquor when a 60°C and 40°C washing programme according to the present invention is set, respectively. Such graphical representations are quite readily and easily inferable and understandable by those who are skilled in the art, since they are the respective partializations of the diagram appearing in Figure 1, so that they do not need any further explanation. A whole series of advantageous improvements of the present invention consists in providing the ability of defining, through appropriate control means adapted to be activated directly by the user, both the temperature or the temperatures at which said washing phases at substantially constant temperature are to occur and the duration thereof. Furthermore, the duration of each one of said intervals is adapted to be adjusted either individually for each temperature or in a common manner for all working temperatures reached in said intervals. Finally, in view of conferring the greatest possible extent of flexibility and, at the same time, simplicity to the machine, the duration of said intervals may be adapted to be adjusted either in a continuous manner or at fixed increments corresponding to discrete values. It has been also found experimentally that, in order to further improve the washing performance of the machine, it is appropriate for the drum to be adapted to be driven at rotational speeds differing from the regular one during said washing phases at substantially constant temperature, so that the synergic effect of an intermediate washing action at a particular temperature for a pre-determined period of time, and at a rotating speed of the drum appropriately adjusted to suit that combination of programme, time and temperature, is actually able to ensure the best possible washing results. Even in this case the practical implementation of the corresponding circuits is well within the capability of those skilled in the art, since the same triggering signal coming from the thermostat, apart from de-energizing the heating element, can be used to start an appropriate timing device and, at the same time, send an appropriate control command to the drum driving means. At the end of the interval, said timing device can cause the heating element to be again energized and the formerly interrupted washing programme to be resumed by restoring regular operating conditions of the drum. The methods required to technically obtain such variants are anyway known in the art and can be readily implemented by those skilled in the art.

Claims: Clothes washing or dishwashing machine provided with a washing vessel, at least a drum rotatably arranged in said washing vessel and adapted to hold the washload, a heating element for heating up the liquor in said vessel, at least a sensor means for detecting the temperature of said liquor, a control and actuating apparatus, electric circuits connecting said apparatus with the various functional parts and sensors of the machine, said apparatus being adapted to trigger and control a plurality of washing programmes which differ from each other at least for the fact that each programme defines the attainment of a highest temperature value of the liquor in the vessel which is anyhow different from the highest temperature value attainable in the other programmes, characterized in that externally provided control means are provided which are adapted to include a selectable period of time whenever the temperature of the liquor in the vessel, during the heating-up phase, reaches a pre-determined value below the highest temperature value attainable in the particular washing programme selected, automatically cut off the power supply to said heating element for and to automatically restore the power supply to said heating element at the end of said period of time, said different temperature values, corresponding to the washing program selected, during which the power supply to said heating element is cut off can be pre-determined for each one of said plurality of washing programmes. Washing machine according to claim 1, characterized in that the duration of said selectable periods of time can be adjusted either in a continuous manner or at fixed increments. Washing machine according to any of the preceding claims, characterized in that the number of said periods of time during which said heating element is de-energized depends on the particular washing programme selected. Washing machine according to any of the preceding claims and provided with a 90°C washing programme, characterized in that during said washing programme there are provided three phases during which the heating element is de-energized upon reaching three respective pre-determined temperature values. Washing machine according to any of the preceding claims and provided with a 60°C washing programme, characterized in that during said washing programme there are provided two phases during which the heating element is de-energized upon reaching two respective pre-determined temperature values. Washing machine according to any of the preceding claims and provided with a 40°C washing programme, characterized in that during said washing programme there is provided one phase during which the heating element is de-energized upon reaching a respective pre-determined temperature value. Washing machine according to any of the preceding claims, characterized in that during such at least one period of time during which the heating element is de-energized, the drum is driven so as to rotate in a different manner as compared to the manner in which it rotates during the remaining portion of the washing phase.

Inventors: MORI MAURIZIO, MORI, MAURIZIO
Applicants: ELECTROLUX ZANUSSI ELETTRODOME, ELECTROLUX ZANUSSI S.P.A.
Application year: 1995
Main classification: D06F35
IPC codes: A47L15, D06F35