EP0460250B1

EP0460250B1 - Dishwashing machine with improved washing water dosage

Info

Publication number: EP0460250B1
Application number: EP19900110587
Authority: EP
Inventors: Dino Bongini; Mario Samoncini
Original assignee: Merloni Elettrodomestici SpA
Current assignee: Whirlpool EMEA SpA
Priority date: 1990-06-05
Filing date: 1990-06-05
Publication date: 1995-08-23
Anticipated expiration: 2010-06-05
Also published as: DE69021871D1; EP0460250A1; DE69021871T2; ES2076991T3

Description

The present invention refers to a dishwashing machine having a high precision in the dosage of the washing water.
As known, dishwashing machines are usually supplied with the water necessary to the washing operations, by enabling the opening of an electric valve arranged on the supply pipe connected to the water main. The supplied water is collected in a sump which is arranged under the washing chamber and whose mouth is defined in the lower wall of the washing chamber. Such a sump is connected to the suction pipe of a washing pump which supplies the spraying arms fitted in the washing chamber.
Usually, the sump has a volume smaller than the volume of water required for the operation of the machine and the level of the water charged in the machine rises over the lower wall of the washing chamber. The water inlet is interrupted when the water reaches a predefined level which is detected by means of appropriate sensor means, for instance a pressure switch with a sensor arranged in the sump.
In other types of machines the water inlet is done with the washing pump not operating, while in other types of machines the washing pump is enabled during such inlet, by presetting in a suitably way the sensor means.
In both cases, the water level at the end of the inlet reaches the washing chamber and so the water surface has an area substantially equal to the section of such chamber.
Due to this fact it is possible that great errors occur in the determination of the quantity of water charged.
In fact, using for instance as sensor means a pressure switch with good sensitivity, the detecting tollerance can be of some millimeters with variations of the quantity of charged water in the order of about one liter for each charging.
An error of this kind has a great importance, in consideration of the fact that each complete washing cycle needs usually five water charges.
In designing dishwashing machine, the precision in the determination of the quantity of charged water has a great importance because, in order to save both water and energy, the discrepancy between said quantity and the theoric quantity required for the correct operation of the machine must be as little as possible.
It is known from EP-A-248 339 a method for controlling the supply of water to a washing machine wherein the sump shows a complicated hydraulic structure, comprising a collecting well, communicating with a control chamber, where the pressure sensitive means are located, via an overflow wall on one side and with the intake of the circulation pump on the other side, via communication means having a calibrated section.
The main object of the present invention is to solve the above said problem realizing a dishwashing machine which has a high precision in the dosage of the washing water.
In order to achieve the above said object, it is an aim of the present invention to realize a dishwashing machine which, the water level detecting means sensitivity being the same and, as a consequence, the costs of such detecting means being equal, allows a more precise dosage of the water charged in the machine in respect of the machines of known type.
A further aim of the invention is to realize a dishwashing machine which shows reduced water and energy consumption. This object and the said and other aims which could be better understood later, are obtained by a dishwashing machine, and a method for the dosage of the washing water in a dishwashing machine, comprising the characterizing feature of the annexed claims 1 and 5.
Further characteristics and advantages of the invention will appear better from the description of a preferred, not exclusive, embodiment of the dishwashing machine according to the invention, shown as an indicative and not limitative example in the accompanying drawings, where:

figure 1 shows a lower portion of the dishwashing machine according to the invention,in a cross section on a vertical plane;
figure 2 shows an inside plan of the lower wall;
figure 3 shows a simplified scheme of the circuit controlling the electric supply valve of the machine; and
figure 4 shows an enlarged section of figure 2 along the IV-IV axis.

With reference to the cited figures, the dish-washing machine according to the invention, indicated as a whole with reference number 1, comprises a water collecting sump 2, which is arranged under the lower wall 3 of the washing chamber 4, and which presents a mouth defined in such lower wall.
Sump 2 presents, in known way, ports 5 and 6 connected respectively to the suction pipes of a washing pump 7, which supplies one or more spraying arms (8) fitted in the washing chamber 4, and of a drainage pump, of known type and not shown for simplicity.
According to the invention, sump 2 is realized so to have a working volume at least equal to the difference between the total volume of water required for the correct operation of the machine and the total volume of water that is kept in circulation, outside the sump, by washing pump 7 when working. Furthermore, in corrispondence of the level 9 reached in the sump by a volume of water equal to such difference, the sump shows, in a horizontal plane tangent to the water surface, a passage section notably smaller than the section of the washing chamber 4.
According to the type of machine, said passage section has an area which is preferably comprised between 1/6 and 1/4 of the section of the washing chamber 4.
The water level inside the sump 2 is detected by means of a pressure switch 10 of known type, which has a sensor 11 arranged inside the sump 2, below the level 9.
Sensor 11 is realized so to keep in its own zone 11a a quantity of air which undergoes a compression proportional to the level of the overlaying water. Zone 11a is connected by a pipe 12 with the body of the pressure switch which transforms the pneumatic signal into an electric command.
Inside the sump 2 there is also arranged in a known way a filter 13. In figure 3 it is shown in a very schematic and simplified way an electric circuit 14 which feeds the control device 15 of the supply electric valve 16 of the machine arranged on the supply pipe 17 connected to the water main. More in detail, circuit 14 provides in series first interruption means 18 of the electric supply and second interruption means 19 controlled respectively by the pressure switch 10 and by a timer which controls the various stages of the washing cycle of the machine. First interruption means 18 and second interruption means 19 are arranged in series and could be, for instance, on-off or chance-over switches.
The water inlet in the dishwashing machine according to the invention is as follows.
At the start of the machine operation, timer 20 closes the switch 19 and pressure switch 10 does not act on switch 18, closed itself at this stage. In this way electric supply valve 16 is open and supply pipe 17 charges water in the machine, which collects in the sump 2. During the water inlet, it is enabled washing pump 7 which, sucking from the sump 2, conveys water to spraying arms 8.
The water inlet continues until the water in the sump reaches a level corresponding to the preset value of the pressure switch 10. With the sizing of the sump according to the invention, the water level corresponding to the preset of the pressure switch lays under the lower wall 3 of the washing chamber 4. In this way, possible tolerances in the preset value of the pressure switch can cause only very small variations of the charged water quantity because the passage section of the sump in the zone occuped by the water surface, near the correct level, is small and in any case notably smaller than the section of the washing chamber 4.
The achieving of the correct level cause the opening of the switch 18 and so the closure of the electric supply valve 16 which interrupts the water inlet.
It has been practically ascertained that the dishwashing machine according to the invention fulfils very well the extablished aim, because, due to the fact that the correct water level is reached in a zone of the machine which has a water passage section highly reduced in respect of the section of the washing chamber, by using a pressure switch with a sensitivity equal to the ones employed in the traditional dishwashing machines where such level lays over the lower wall, it is obtained a more precise dosage of the charged water.
A further advantage is that the inlet of a water quantity compensates in an automatic way for the operating tolerance of the washing pump and the spraying arms, and the water pipes geometric variations due to manufacturing spreads and circuit modifications, because the water dosage is done with the washing pump operating. Also for this reason, the final dosage depends on the easiness for water to fall in the sump, which is influenced by the crockery presence, that is to say the dosage is self-regulated in function of the crockery load.
Not last is the advantage that there is realized a dosage where, in case of an eventual partial obstruction of the filters or accidental water leaks, more water is charged granting in any way a correct washing.

Claims

Dishwashing machine having high precision in the washing dosage, comprising a water collecting sump (2) arranged under the lower wall (3) of a washing chamber (4) and with a mouth defined in said lower wall (3), said sump (2) having at least a first port (5) communicating with the suction pipe of a pump (7) connected by its delivery side to at least one ware spraying arm (8) arranged inside said washing chamber (4), water level sensor means (10,11,12) being provided with said sump (2), the sensitive element (11) of said water level sensor means (10,11,12) being arranged directly inside said sump, characterized in that
- the working volume of said sump (2) is at least equal to the difference between the total volume of water required for the operation of the machine and the volume of water kept in circulation outside said sump (2) when the pump (7) is working, and

- in correspondence of the level (9) reached in said sump (2) by a water quantity equal to said difference, said sump (2) shows, in a horizontal plane tangent to the water surface, a passage section (9) which is substantially comprised between 1/6 and 1/4 of the washing chamber (4) section.
Dishwashing machine, according to claim 1, characterised by the fact that it comprises an electric valve (16) controlling the water inlet in said sump (2), said valve being supplied by an electric circuit having in series at least first electric supply interruption means (18) and second electric supply interruption means (19).
Dishwashing machine, according to claim 2, characterised by the fact that said first electric supply interruption means (18) are controlled by a timer (20) and said second electric supply interruption means (19) are controlled by said water level sensor means (10,11,12).
Dishwashing machine, according to claim 2, characterised by the fact that said first electric supply interruption means (18) and/or said second electric supply interruption means (19) are represented by on-off or change-over switches.
Method for the dosage of the washing water in a dishwashing machine comprising a water collecting sump (2) arranged under the lower wall (3) of a washing chamber (4) and with a mouth defined in said lower wall (3), said sump (2) having at least a first port (5) communicating with the suction pipe of a pump (7) connected by its delivery side to at least one ware spraying arm (8) arranged inside said washing chamber (4), water level sensor means (10,11,12) being provided with said sump (2), the method comprising the steps of
- supplying washing water in said collecting sump (2), and

- enabling, during said supply, said washing pump (7) for sucking in said sump (2) and feeding said spraying arm (8), so as that a quantity of water is kept in circulation outside said sump (2) while said pump (7) is working, said method being characterized in that it comprises the step of interrupting the water supply when into said sump (2) the water reaches a level (9) corresponding to the difference between the total volume of water required for the operation of the machine and the volume of water kept in circulation outside said sump (2), at said level (9) in the sump (2) the water surface showing an area which is substantially comprised between 1/6 and 1/4 of the washing chamber (4) section.