EP1352605A1

EP1352605A1 - Dishwasher with means for short-cycle operation and relevant operating cycle

Info

Publication number: EP1352605A1
Application number: EP02425201A
Authority: EP
Inventors: Ezio Gobbi
Original assignee: Bonferraro SpA
Current assignee: Bonferraro SpA
Priority date: 2002-04-02
Filing date: 2002-04-02
Publication date: 2003-10-15

Abstract

A dishwasher including a plurality of conventional elements such as a water softening unit, a collecting sump formed on the tank bottom, a pressure switch (P) for controlling the water level, a drain pump (D), a wash pump (W), a heating member to heat the water in the sump and a sensor to detect the temperature thereof, as well as a microprocessor to manage the machine operation, and also an additional water heating unit (Q, H) suitable to operate in parallel with the above-listed elements, as well as suitable valve means (VD, VS) to control the water flow to (M) and from (K) said unit and relevant detecting and measuring means (F, T) to allow to manage the operation thereof. In this way it is possible to achieve the water heating in an independent and parallel manner with respect to the normal operation of the machine, thus transforming the operating cycle from a sequence of steps rigidly in series to a plurality of steps some of which are carried out in parallel so as to significantly reduce the overall length of the cycle.

Description

The present invention relates to dishwashing machines, and in particular to a dishwasher for domestic use provided with means to shorten the times of the operating cycle.
It is known that in order to achieve an effective cleaning of the dishes it is necessary for the washing water to reach a temperature of 55°-65°C, typically through heating by one or more electrical resistors. The water heating times make up for a great part of the length of the operating cycle, in particular if the heating is intentionally slow to allow enzymatic detergents to work better at low temperatures.
There are also dishwashers intended to be connected to the hot water hydraulic network, but this is a significant limitation and reduces the overall energetic efficiency anyway since the water is heated in another place and then supplied to the dishwasher with an unavoidable loss of heat along the path.
Therefore the preferred arrangement is that of heating the water directly in the dishwasher at the beginning of the washing cycle, and then again during the cycle in order to keep the water at the required temperature. However, the initial heating step contributes to the prolonging of the overall length of the cycle which sometimes the user might wish to shorten in order to have the clean dishes available sooner and/or to be able to carry out sooner the washing of another load of dishes.
Some types of dishwasher allow to shorten the length of the washing cycle by carrying out a pre-heating cycle prior to the loading of the dishes. In other words, when the dishwasher is still empty, the water is loaded and initially heated by activating the washing pump and sprinkling the water through the sprinklers until the desired temperature is reached. When the dishwasher indicates to the user that the water has reached the set temperature, then he can load the dishes and start the real washing cycle.
However, this kind of "idle" running has two types of drawback respectively relating to consumptions and user's comfort. First of all, the circulation of hot water throughout the dishwasher implies the heating of all the parts of the dishwasher, which results in a certain consumption of water and electric power as well as a certain duration of the pre-heating cycle. Moreover, when the user opens the dishwasher to load the dishes he receives a wave of heat and runs the risk of burning himself with the hot water spread over all the surfaces. On the other hand, waiting till the tank cools down before loading the dishes involves a partial loss of the advantage provided by the pre-heating and an unavoidable decrease in the energetic efficiency.
In order to overcome these drawbacks application EP-1004266 discloses a dishwasher including valve means suitable to interrupt the water delivery from the pump to the sprinklers as well as a recirculation duct connecting the pump to the collecting sump. In this way during the pre-heating it is possible to circulate the water only between the pump and the sump, thus preventing its dispersion throughout the machine.
This arrangement of the dishwasher allows to carry out the pre-heating cycle in a shorter time and with a lower consumption of water and electric power. Furthermore, by restricting to the tank bottom the spread of hot water, the user does not run any risk of burn and a greater "thermal inertia" of the machine is achieved, which reduces the decrease in temperature of the water in case the user does not immediately start the washing cycle.
However, also this solution is not free from drawbacks in that it still implies a waiting time for the user, moreover it can be used only to shorten the pre-heating time but not for the times of the subsequent heatings, typically for the second rinse carried out with hot water.
Therefore the object of the present invention is to provide a dishwasher suitable to overcome the above-mentioned drawbacks and a relevant operating cycle which takes advantage of the features of this dishwasher.
This object is achieved by means of a dishwasher provided with an additional water heating unit, capable of operating in parallel with the other components of the machine, as well as with suitable valve means for controlling the flow of water to and from said unit. Other advantageous features are disclosed in the dependent claims.
The main advantage of the dishwasher according to the present invention is exactly that of being able to heat the water in an independent and parallel process with respect to the normal operation of the machine. In other words, the pre-heating can be carried out even while the user is loading the dishwasher, the heating for the second rinse can be carried out while the machine is performing the washing and/or the first rinse and so on.
Therefore it is clear that transforming the operating cycle from a sequence of steps rigidly in series to a plurality of steps some of which are carried out in parallel allows to significantly reduce the overall length of the cycle, indicatively of about 30%.
A second significant advantage of this dishwasher is that it can still operate in standard mode, in that the user may decide to set it so as to bypass the additional components and carry out a conventional cycle with a slow heating directly in the tank.
A further advantage of this type of machine stems from the fact that in case of consecutive operating cycles there is a partial overlapping of one cycle with another, whereby the overall length of two consecutive cycles is shorter than the sum of the lengths of two single cycles.
These and other advantages and characteristics of the dishwasher according to the present invention will be clear to those skilled in the art from the following detailed description of an embodiment thereof, with reference to the annexed drawings wherein:
Fig.1 is a diagrammatic view showing the essential elements of the present dishwasher and their respective connections; and
Fig.2 is an enlarged sectional view showing in detail the structure of a wall of said dishwasher.
With reference to Fig.1, there is seen that a dishwasher according to the invention conventionally includes a plurality of known elements: an electrovalve VN controlling the entrance of water from the network, a collecting sump formed on the tank bottom which receives the water through a supply duct L, the level being controlled by a pressure switch P, a drain pump D to drain water from the sump and a wash pump W which receives the water from the sump and through respective ducts feeds it to the top and bottom sprinklers.
Upstream from duct L there is also provided a unit for softening the water, by means of decalcifying resins located in a container R, which includes a chamber A for the collection of water intended for the regeneration of said resins by means of a sodium chloride solution which is formed in the salt container S, which is connected to container R through an electrovalve VR.
It is obvious that also other elements not illustrated in the figure are provided, such as heating members in the sump and/or on the connecting duct between the sump and the wash pump W, temperature sensors, a microprocessor to control the operation of the machine and so on.
The novel aspect of the dishwasher according to the present invention consists of a plurality of additional elements which allow to achieve the shortening of the length of the operating cycle as previously mentioned. In brief, said elements consist of a parallel water heating unit and of suitable valve means controlling the water flow to and from said unit, as well as relevant detecting and measuring means to manage the operation thereof.
More specifically, the core of the heating unit is an accumulator Q provided with an inlet E, to which there is connected a supply duct M, which carries the water to the top of accumulator Q, as well as with two bottom outlets which enter a connecting duct K to the sump. A first outlet G is free and receives the water coming from an overflow X located at the same height as the mouth of inlet E, whereas the second outlet is controlled by an electrovalve VS. Accumulator Q is also provided with a temperature sensor T, a breather Y connected to the tank to let off air and vapour, and a plurality of substantially horizontal ribs U arranged at different heights and horizontal positions.
A heating member H (e.g. PTF resistor, heating cable) is applied to accumulator Q, preferably on the side facing the tank. In particular, in the preferred embodiment illustrated in Fig.2, accumulator Q is located in a side wall of the machine between the outer casing O and the heating member H, which is separated from tank I by a soundproofing panel Z. In this figure there are also seen a couple of said ribs U whose purpose is to limit the convective movements of the water to restricted areas, in order to prevent situations of excessive temperature stratification in the accumulator which could lead to differences of even 10°C between the top and bottom thereof.
The supply of water to said parallel unit is controlled by a deviating electrovalve VD, arranged between the softening unit and the sump, which can direct the flow directly to the sump through duct L or to accumulator Q through duct M. There is also provided a meter F, preferably just downstream from electrovalve VN, suitable to measure the amount of water entering the machine.
In the light of the description above, first of all it is clear that the dishwasher can operate in standard mode simply by keeping valve VD set on duct L, so as to bypass accumulator Q. On the contrary, if the user sets the short-cycle function, the dishwasher uses the additional elements to decrease the cycle length as explained in the following non-limiting example of a normal cycle at 65°C without pre-wash.
When the dishwasher is given the order "prepare machine" the operating cycle starts with a first resin wash step, to remove therefrom the sodium chloride solution used for the regeneration in order to prevent the introduction into the tank of water with a high saline concentration. To this purpose, valve VN is opened and water flowing through inlet C fills chamber A until it overflows and goes out through outlet J into container R. Coming out of container R, the water finds valve VD set on duct L and enters the sump from where it is instantly drained by the drain pump D.
The following step is the loading and pre-heating of the water which still passes through chamber A, outlet J and container R but then finds valve VD set on duct M and fills accumulator Q through inlet E. The amount of water loaded in the machine is controlled through meter F, and the water possibly in excess enters the tank through overflow X, outlet G and duct K. In order to prevent overheating of the heating member H, there is also checked the presence of water in accumulator Q by checking that the pressure switch P does not detect the filling of the sump which would imply a leak through valve VS.
Thereafter, the microprocessor orders the activation of heater H only upon receipt of the confirmation of the amount of water measured by meter F and of the non-activation of the pressure switch P. It should be noted that if meter F does not indicate the correct amount (or it fails) and/or the pressure switch P detects the presence of water in the sump when there should not be any, then an alarm signal is triggered to inform the user that the machine can not operate in short-cycle mode, but it can still operate in standard mode.
The heater H operates until sensor T detects the reaching of the desired temperature (e.g. 50°C), and its position between the accumulator and the tank not only causes the heating of the water inside accumulator Q but also of the whole side wall of the tank so as to decrease the heating time in the subsequent washing step.
These first two steps globally require about 22 minutes, and they can be carried out even if the dishwasher door is open whereby in the meantime the user can load the dishes.
Upon closure of the door, the real washing cycle may start with a loading step of the water into the tank, by opening valve VS, a further heating to 65°C and the simultaneous activation of the wash pump W. In this step the water which is already at about 50°C quickly reaches the 65°C temperature and therefore a decrease of about 10 minutes of the required time is achieved with respect to the standard cycle in which cold water (e.g. at 15°C) is introduced in the tank. Moreover at the same time, i.e. in parallel with the washing step, the loading of water in the accumulator and its heating to 50°C is carried out again.
As a consequence, when the hot water is drained at the end of the washing and up comes the first rinse which is conventionally carried out with cold water, in this case the water is loaded in the tank through the accumulator by simultaneously opening valves VN and VS so as to obtain a rinse with lukewarm water. More specifically, the water reaches duct K through both valve VS and overflow X plus outlet G since the incoming flow rate from the network is greater than the outgoing flow rate from the accumulator. Furthermore, valve VN is closed some seconds later with respect to valve VS in order to assure the filling of the accumulator for the following heating.
The machine operates then in parallel again and, while the first rinse is being carried out, the water in the accumulator is restored to 50°C in a few minutes starting from the temperature of 35-38°C to which it has dropped due to the mixing with the cold water coming from the network.
Therefore the water in the accumulator is already almost at the required temperature when the water of the first rinse is drained and up comes the second rinse with hot water which is loaded in the tank from the accumulator, always by opening valve VS. The further heating to 68°C is thus performed quickly and a decrease of about 12 minutes of the required time is achieved with respect to the standard cycle in which cold water is introduced in the tank. This decrease is even greater than in the first washing step since also the first rinse with lukewarm water contributes to maintaining the internal machine temperature higher and therefore to shortening the following heating time.
After this second rinse, the operating cycle provides the resin regeneration step, by opening valve VR so that the water flows down from chamber A through outlet B into the salt container S and from there the sodium chloride solution passes to container R. It should be noted that the water flowing out from the latter finds valve VD set on duct L for the introduction in the sump and the drain so as to prevent the contamination of the accumulation circuit with water having a high saline concentration.
Once the water drain is over, the cycle is completed by the drying step which can be used, together with the two previous steps, to prepare the machine for a subsequent operating cycle if the user so wishes.
In fact if the machine is set to operate in consecutive cycles, during the second rinse there is already carried out another loading of the water in the accumulator, and the subsequent heating to 50°C takes place during said rinse, the regeneration and the drying. Finally, the initial resin washing step for the following cycle is carried out during the drying, whereby at the end of the present cycle the user can take out the dry dishes and load other dishes to be washed and start immediately the dishwasher which is already ready for the washing step.
Therefore it is clear that in the above-described operating cycle 3 partial heatings of the water (4 in the case of consecutive cycles) are carried out while the machine is performing other steps of the cycle, thus achieving a significant decrease of the overall length of the cycle.
It is clear that the above-described and illustrated embodiment of the dishwasher according to the invention is just an example susceptible of various modifications. In particular, the shape and position of accumulator Q may be changed and the water heating may be performed by a heater of different kind or placed in a different position with respect to the illustrated heater H, or by more than one heater.
Similarly, meter F may be arranged at other positions (e.g. downstream from the softening unit) and its function of controlling the accumulator filling may be achieved also through other means such as an indicator of the level inside the accumulator itself.
Finally, the use of a short cycle could be a factory setting and the user might be provided with a specific control to exclude it only when this is deemed necessary.

Claims

A dishwasher including an electrovalve (VN) controlling the entrance of water from the network, a water softening unit, a collecting sump formed on the tank bottom which receives the water from said softening unit through a supply duct (L), a sensor for controlling the water level in said sump, a drain pump (D), a wash pump (W), at least one heating member suitable to heat the water and a sensor suitable to detect the temperature thereof, as well as a microprocessor to manage the machine operation, characterized in that it further includes an additional water heating unit suitable to operate in parallel with said above-listed elements, as well as suitable valve means controlling the water flow to and from said unit and relevant detecting and measuring means which allow said microprocessor to manage the operation thereof.
A dishwasher according to claim 1, characterized in that it includes control means which allow the user to engage or disengage said additional heating unit.
A dishwasher according to claim 1 or 2, characterized in that the valve means controlling the water flow consist of an electrovalve (VS) arranged on a connecting duct (K) between the additional unit and the sump, and a deviating electrovalve (VD), arranged between the softening unit and the sump, which can direct the water flow directly to the sump through the supply duct (L) or to the additional unit through a relevant supply duct (M).
A dishwasher according to claim 3, characterized in that the additional unit includes an accumulator (Q) provided with a breather (Y) connected to the tank, with a temperature sensor (T), with an inlet (E), to which there is connected the supply duct (M), as well as with two bottom outlets which enter the connecting duct (K) to the sump, a first outlet (G) being free and receiving the water coming from an overflow (X) and a second outlet being controlled by an electrovalve (VS).
A dishwasher according to claim 4, characterized in that inside the accumulator (Q) there are provided a plurality of substantially horizontal ribs (U) arranged at different heights and horizontal positions.
A dishwasher according to one or more of the preceding claims, characterized in that a heating member (H) is applied to the accumulator (Q) on the side facing the tank.
A dishwasher according to one or more of the preceding claims,
characterized in that the accumulator (Q) is located in a side wall of the machine between the outer casing (O) and the heating member (H).
A dishwasher according to one or more of the preceding claims, characterized in that it further includes means suitable to check the filling of the accumulator (Q) prior to the activation of the relevant heating member (H).
A dishwasher according to claim 8, characterized in that said checking means include a meter (F), preferably located just downstream from the water entrance electrovalve (VN), and a pressure switch (P) suitable to detect the level of water in the sump.
An operating cycle for a dishwasher according to one or more of the preceding claims, characterized in that it includes the following steps:

a) loading a pre-established amount of water for washing the decalcifying resins of the softening unit, and draining said water through the supply duct (L) to the sump from where it is drained by the drain pump (D);

b) switching the deviating electrovalve (VD) from the sump supply duct (L) to the supply duct (M) of the additional heating unit;

c) loading the water in the additional unit and partially heating it, upon checking of the actual filling of the circuit;

d) loading in the tank hot water coming from the additional unit by opening the electrovalve (VS) arranged on the connecting duct (K) between the additional unit and the sump;

e) activating the wash pump (W) and further heating to the pre-established temperature to carry out the washing step;

e') simultaneously loading for the second time the water in the additional unit and partially heating it, upon checking of the actual filling of the circuit;

f) draining the wash water;

g) loading in the tank the water for the first rinse by simultaneously opening said electrovalve (VS) and the network water entrance electrovalve (VN);

h) activating only the wash pump (W) to carry out the first rinse;

h') simultaneously restoring the temperature of the water contained in the circuit of the additional unit;

i) draining the first rinse water;

j) loading in the tank hot water coming from the additional unit;

k) activating the wash pump (W) and further heating to the pre-established temperature to carry out the second rinse;

l) draining the second rinse water;

m) switching the deviating electrovalve (VD) from the supply duct (M) of the additional heating unit to the sump supply duct (L);

n) loading a pre-established amount of water for the regeneration of the decalcifying resins, upon opening of the relevant electrovalve (VR), and draining said water through the supply duct (L) to the sump from where it is drained by the drain pump (D);

o) drying;

where the first three steps a), b), c) can be carried out even if the dishwasher door is open.
An operating cycle according to claim 10, characterized in that it further includes, in case of consecutive cycles setting, the steps of:

k') loading for the third time the water in the additional unit and partially heating it, upon checking of the actual filling of the circuit, simultaneously with said steps k)-o);

o') loading a pre-established amount of water for washing the decalcifying resins of the softening unit, and draining said water through the supply duct (L) to the sump from where it is drained by the drain pump (D), simultaneously with said drying step o).