EP0772995B1

EP0772995B1 - Dishwashing machine with differenced washing capability

Info

Publication number: EP0772995B1
Application number: EP96117865A
Authority: EP
Inventors: Giuseppe Marchitto; Fabio Roncati
Original assignee: Merloni Elettrodomestici SpA
Current assignee: Whirlpool EMEA SpA
Priority date: 1995-11-10
Filing date: 1996-11-07
Publication date: 2001-05-23
Anticipated expiration: 2016-11-07
Also published as: ITTO950908A0; DE69612941D1; DE69612941T2; EP0772995A1; IT1280477B1; ITTO950908A1; ES2158212T3

Description

The present invention concerns a dishwashing machine with capability of washing a reduced load, also called differentiated washing, and a method for operating a dishwashing machine.
As it is known, dishwashing machines generally consist of a box-like structure defining a washing chamber, wherein an upper basket and a lower basket are housed to load the crockery to be washed.
Below each load basket a sprayer which, rotating around a vertical axis, strikes the crockery positioned in the overlaying basket with several wash-liquid jets.
In dishwashing machines it may be desirable to be able to carry out a differentiated washing cycle if only one basket is used to contain the crockery, i.e. a washing cycle where the machine takes in a reduced water quantity and only the sprayer corresponding to the basket being used is supplied by the wash liquid to reduce water consumption.
The reduced water supply is possible for instance by having the machine control system which changes the control thresholds of a pressure switch if a differentiated washing is selected, so that a lower quantity of water than required for a standard washing cycle will be introduced into the machine washing-tub.
As regards the selective supply of one sprayer alone of the two, a first technical solution is described in the Italian patent no. 1.216.592.
This document describes a dishwashing machine equipped with two independent hydraulic circuits, one for each sprayer, supplied through two washing pumps. Thus, if a differentiated washing cycle is selected, one pump alone will start operating and only one sprayer will be supplied with wash liquid.
However, this solution is rather expensive because the cost for the two pumps is higher than the cost for one pump alone of equivalent power and it is also obvious that the control circuit of the machine will be a more complex one.
A second known technical solution concerning differentiated washing, within the frame of selective water supply is to provide an interception device in one of the two sprayer supply arms for dishwashing machines with one pump only.
According to such a known technology, if a differentiated washing is selected the interception device closes one of the hydraulic circuit arms, so that only one of the two sprayers will be supplied with wash liquid.
However, also such a known technology as it will be further described and commented with reference to Fig. 1 and 3, has some considerable technical problems, specifically for a correct operation of the washing pump and of the intercepting element, even if being a simple and favourable solution for the saving of the washing liquid. Solutions of this type are for instance described in FR-A-2.505.643, EP-A-237.994, FR-A-2.443.231.
It is therefore the main object of the present invention to solve such problems and provide in particular a dishwashing machine equipped with a simple, low-cost efficient and reliable system for the execution of differentiated washing.
According to the present invention said objects are obtained by a dishwashing machine having the characterizing features of the enclosed claim 1 and by a method for operating a dishwashing machine having the characterizing features of the enclosed claim 10. Further advantageous embodiments of the invention are contained in the dependent claim 2-9 and 11-12.
The characteristics and advantages of the present invention will be apparent from the following description and annexed drawings, which are supplied only by way of an explanatory not limiting example, wherein:
Fig. 1 shows schematically the hydraulic circuit of a dishwashing machine with differentiated washing capability according to the known state of the art;

Fig. 2 shows schematically the hydraulic circuit of a dishwashing machine with differentiated washing capability according to the present invention;
Fig. 3 shows schematically a diagram comparing the operating characteristics of a dishwashing machine according to the known state of the art and of a dishwashing machine according to the present invention.

Fig. 1 shows schematically the hydraulic circuit of a dishwashing machine with differentiated washing capability according to the second kind of known technology mentioned at the beginning of this description.
In this figure reference number 2 indicates a washing pump drawing some washing liquid from a collecting sump indicated by number 1, usually available on the bottom of the dishwasher tub. Said pump 2 forces the washing liquid into an hydraulic circuit comprising a first supply arm 3 for a lower sprayer 4 and a second supply arm 5 for an upper sprayer 6.
An interception element indicated by number 7 is provided according to the above known technology, such as for instance a solenoid valve that appears inserted in the supply arm 3 of the lower sprayer 4. Such an interception element 7 is actuated by a control element, not shown in the figure for simplicity's sake, as a function of the selection of a differentiated washing cycle actuated by the user.
As a result, actuation of the interception element 7 and consequently the obstruction of the supply arm 3 prevents feeding the lower sprayer 4, so that the dishwashing machine operates feeding only the sprayer 5 associated with the upper basket (not shown for simplicity's sake), using a reduced water flow.
However, this known technology has some problems related to the washing-pump operation and to the interception element itself.
Operation problems related to the interception element are due to its being subject to a considerable pressure as some calibration and sealing problems arise in time for the device, whose manufacture requires a particular attention (with a consequent cost increase) or has to be submitted to periodical inspections and/or revisions.
Operation drawbacks related to the pump can be explained on the contrary with the aid of Fig. 3, where an example diagram "flow - head" for the various elements comprised in the hydraulic circuit of the dishwasher according to Fig. 1 is shown.
In said diagram of Fig. 3, CP indicates the typical curve of the pump 2, whereas CS and Cl indicate the load curves of the upper supply arm 5-6 and of the lower supply arm 3-4 of the machine hydraulic circuit, respectively. Then CG indicates the global load curve of the entire hydraulic circuit. Since arms 3-4 and 5-6 are parallel, the curve CG is obtained by summing the abscissas Q (flows) of the curves CS and Cl at equaling ordinates H (heads).
In the instance of standard washing, the work point N of the pump 2 is given by the intersection of the curves CP and CG.
Therefore, the pump has to be sized for a nominal function being characterized by the flow Qn and the head Hn.
If a differentiated washing-cycle is selected, the interception element 7 of Fig. 1 closes the arm 3 and the total load curve will then correspond to the one indicated by CS.
The new work point obtained by the intersection of the curves CP and CS will then be the one indicated by M: this means that the pump 2 has to operate at flow values Qm and head Hm, which differ considerably from the nominal parameters, with the risk of several problems such as for instance an overtemperature of the pump motor and an overpressure of the hydraulic circuit.
As said above, it is the object of the present invention to obviate to said problems. Its distinguishing scope is shown schematically in Fig. 2 where the reference numbers of the Fig. 1 have been maintained to indicate technically equivalent elements.
As it can be noticed, according to the present invention an auxiliary hydraulic duct or arm indicated with 8 is provided, preferably containing inside an adjusting element 9 as it will be further described.
The auxiliary hydraulic duct 8 is inserted as a by-pass between a downstream point and an upstream point of the pump 2, such as in particular the collecting sump 1. Such an auxiliary duct 8 is automatically open when selecting a differentiated washing-cycle.
In a preferred but not exclusive embodiment of the present invention, the duct 8 is inserted between a point of the supply arm 3 of the lower sprayer 4 and the sump 1, so as to be activated by the interception element 7'; thus, according to the present invention, the element 7' is practically operating like a flow deviation valve.
The advantage of the suggested proposal will be apparent by reviewing Fig. 3 again. For better understanding let us assume that the load curve of the auxiliary circuit 8 (lacking element 9 further described) is coincides with the load curve Cl of the lower supply arm 3-4. As said above, when a differentiated washing-cycle is selected the duct 8 is connected in parallel with the supply arm 5-6 of the upper sprayer. Under such a condition the global load curve seen from the pump will be the one indicated with CG as in the instance of a standard washing, and the operation point will be again N (intersection between CG and CP).
Thus, with the introduction of the auxiliary duct 8 in the hydraulic circuit we obtain the significant advantage of maintaining the pump operation in the nominal work point, also during the differentiated washing.
In a preferred embodiment of the present invention it is also advantageous to provide a flow adjusting element indicated with 9 incorporated on the duct 8. In its simpler configuration such an adjusting element 9 consists of a simple choke of the auxiliary duct 8.
As a result, through the element or choke 9 it is possible to change the load curve of the auxiliary duct 8 and consequently of the global load circuit.
Referring once more to Fig. 3, the fine curve indicated with CR represents the load curve of the auxiliary circuit 8-9, preset by a proper setting and/or configuration of the element 9 (that will obviously be determined during the design stage of the entire hydraulic circuit for the dishwashing machine).
Therefore, if a differentiated washing is selected the new global load curve becomes the fine curve indicated with C'G' (obtained by the sum of CS and CR) and the new operation point will be R.
As it can be noticed, pump operation is now characterized by the flow Qr, which is lower than the flow Qn of the standard washing cycle and by the head Hr, which is higher than the nominal value Hn.
Through the setting element or choke 9 it is then possible to choose a work point for the differentiated washing-cycle complying simultaneously with the following conditions:
a. optimization of the washing-liquid flow forced by the pump in respect to the liquid supply.
b. optimization of the pump operation point within the tolerance range with respect to the nominal operation point;
c. pressure on the interception element 7 is reduced.
The characteristics and advantages of the dishwashing machine according to the present invention are clear from the above description.
In particular, the invention represents a simple, low-cost reliable system to obtain a differentiated washing-cycle, associated to a reduced washing-liquid consumption, causing no dangerous stress to the most delicate hydraulic elements, such as the washing pump and the interception valve.
The dishwashing machine according to the concept described above is obviously subject to many changes and modifications.
For instance, it is obvious that in-lieu of a simple choke the setting element 9 can be replaced by a real device (such as a flow regulator) suitable to change the hydraulic characteristics of the auxiliary duct 8 according to changing requirements.
It is also obvious that the interception element 7' and the auxiliary duct 8 can be inserted between a point of the supply arm 5 of the upper sprayer 6 and the sump 1, in case the machine has to execute a differentiated washing using the lower basket of the dishwashing machine.
Finally, it is obvious that the interception element 7' and the inlet of the auxiliary duct 8 can be located on the supply arm 3 in a different position in respect to the one shown by way of example in Fig. 2.

Claims

Dishwashing machine of the type with differentiated washing capability, with an hydraulic circuit comprising a washing liquid collecting sump (1), a washing pump (2), at least two liquid spraying elements (4,6), and a supply arm (3,5) for each one of said spraying elements (4,6), where for the washing of the crockery, said pump (2) forces liquid from said sump (1) into said supply arms (3,5) of the hydraulic circuit, said machine also comprising an interception element (7') for the exclusion from the hydraulic circuit of one of the two spraying elements (3,5) when a differentiated washing cycle is selected, characterized in that an auxiliary arm (8) is provided, which is automatically inserted in the hydraulic circuit of the machine when a differentiated washing-cycle is selected, said auxiliary arm (8) connecting a first point of the machine hydraulic circuit downstream said pump (2) with a second point of the machine hydraulic circuit upstream said pump (2).
Dishwashing machine according to Claim 1, characterized in that said second point is said sump (1).
Dishwashing machine according to Claim 1, characterized in that said interception element (7') is arranged in one of said supply arms (3,5), substantially in correspondence with the inlet of said auxiliary arm (8).
Dishwashing machine according to Claim 1, characterized in that said point downstream the pump (2) corresponds substantially to the point where said interception element (7') is arranged.
Dishwashing machine according to at least one of the previous claims, characterized in that said auxiliary arm (8) is inserted in the hydraulic circuit of the machine through the action of said interception element (7).
Dishwashing machine according to at least one of the previous claims, characterized in that said interception element (7') deviates the liquid flow being destined to one of said supply arms (3,5) in to said auxiliary arm (8).
Dishwashing machine according to at least one of the previous claims, characterized in that it provides a setting element (9) for the hydraulic characteristics of said auxiliary arm (8).
Dishwashing machine according to at least one of the previous claims,
characterized in that said interception element (7') is located in the feed line (3) of the lower spraying element (4) of the dishwashing machine.
Dishwashing machine according to at least one of the previous claims, characterized in that said interception element (7') is located in the supply arm (5) of the upper spraying element (6) of the dishwashing machine.
Method for operating a dishwashing machine having at least two liquid spraying elements (4,6), comprising the steps of:

collecting the washing-liquid in a sump (1),

forcing, by means of a pump (2), at least a part of the washing liquid collected in the sump (1) into an hydraulic circuit which comprises a supply arm (3,5) for each one of said spraying elements (4,6),

whereby

in a first mode of operation of the dishwashing machine, said pump (2) forces liquid from said sump (1) into said supply arms (3,5), and

in a second mode of operation of the dishwashing machine, one (3) of said supply arms (3,5) is excluded from the hydraulic circuit, by means of an interception element (7'),

characterized in that, when said second mode of operation is selected, the washing liquid forced by the pump (2) into one of said supply arms (3,5) is deviated along a by-pass path (8) before reaching the relevant spraying element (4,6), said by-pass path (8) ending upstream of said pump (2).
Method according to Claim 10, characterized by the step of changing the global liquid flow in the hydraulic circuit of the machine with respect to the global flow of a standard wash cycle, when said second mode of operation is selected.
Method according to the Claim 10, characterized by the step of reducing of the global liquid flow in the hydraulic circuit of the machine, when said second mode of operation is selected.