WASHING MACHINE WITH A CONTROL SYSTEM FOR CONTROLLING THE SUPPLY OF WATER

Abstract: A washing machine comprising a control system for controll­ ing the amount of water in a collecting well (5) adapted to be filled via a supply conduit (6) provided with a supply valve (13) which is opened during a water supply phase. A circulation pump (9) for circulating the water collected in the collecting well is operated during the supply phase. The collecting well (5) communicates with a control chamber (14) via an overflow wall (12) provided with a calibrated opening (10) communicating with the intake (8) of the pump. A pressure switch (16) or the like causes the supply valve to close when the water overflows from the collecting well (5) into the control chamber (14) at a rate at least equal to the flow rate through the calibrated opening (10).

Description: The present invention relates to a washing machine, in particular to a dishwashing machine, provided with an improved water supply control system. Known from patent FR-B-1,385,971 is a device for controlling the level of a liquid supplied to a tub; this device com­ prises a first chamber adapted to receive water from the supply mains and communicating via an overflow wall with a second chamber cooperating with a pressure switch adapted to control a solenoid valve for the supply of the water from the water mains. The first chamber also communicates with the tub through the intake conduit of a discharge pump. In operation, the mains water flows into the tub under control and into the first chamber to fill the latter up to the level of the overflow wall, whereupon it over­ flows into the second chamber, so that the pressure switch is abruptly actuated to close the supply solenoid valve. This control device is in fact of simple construction and reliable in operation, its employ in a washing machine, particularly in a dishwasher, is still insatisfactory, how­ ever, because it is designed to function with the respective machine in the inoperative state, i.e. when the circulation pump is not operating. This means that the control device, contrary to what would be desirable, is not capable of stopping the water supply to the tub as soon as the minimum water level required for proper operation of the circulation pump has been attained. In particular, the described control device does not take into account the various parameters such as the charge of dishes and the like, the amount of water in circulation, the characteristics of the pump and of the piping within the machine, which together determine the optimum charging level. In contrast thereto, the increasing concern about the con­ servation of resources makes it fundamentally important to reduce the amount of water supplied to a washing machine for each operating cycle to the absolute minimum required for effective operation. It has therefore been proposed, as described in patent application EP-A-0118719, to provide a dishwashing machine with a water supply control system of the dynamic type capable of taking into account all of the above mentioned parameters. In particular, this control system comprises a water supply valve controlled by a program control unit so as to open during a water supply phase during which the circulation pump of the machine is also in operation. A transducer generates an output signal proportional to the outlet pressure of the pump. The output signal of the transducer is applied to control means responsive to variations of the output signal for closing the valve when the magnitude of these variations drops below a predetermined value. While this control system is highly accurate in operation, it requires relatively complicated control and actuating components (particularly electronic components) which it would be desirable to eliminate. It is therefore an object of the present invention to provide a washing machine equipped with a water supply control system of simple and reliable operation, which should be capable of accurately establishing the minimum water level required for optimum operation of a circulation pump provided in the washing machine. According to the invention this object is attained in a washing machine having a control system for controlling the supply of water to a collecting well adapted to be filled through a supply conduit provided with at least one con­ trollable supply valve adapted to be opened during at least one supply phase. The machine comprises a pump for circul­ ating the water collected in the collecting well adapted to ba actuated at least during the last part of the supply phase, and is characterized in that the collecting well communicates with a control chamber via at least one overflow wall having a predetermined overflow level. Additionally provided are flow connection means of calib­ rated cross-sectional area communicating on one side with the inlet of the circulation pump and on the other side with the control chamber. Pressure-sensitive means are adapted to cause the supply valve to be closed when the water overflows from the collecting well to the control chamber at a rate at least equalling the flow through said flow connection means. The characteristics and advantages of the invention will become more clearly evident from the following description, given by way of example with reference to the accompanying drawings, wherein: fig. 1 shows a diagammatic illustration of a part of a washing machine in a preferred embodiment of the invention, and figs. 2 and 3 show the variations over time of the pressure P in respective zones of the water supply and circ­ ulation circuit of the machine of fig. 1 during the water supply phase. With reference to fig. 1, the washing machine according to the invention is preferably a dishwasher comprising a washing tub 4 (only partially shown), the bottom of which is provided with a well 5 for collecting the liquid the level of which is to be controlled. Well 5 is adapted to be filled with mains water through a supply conduit 6 provided with a supply valve 13 which is controlled in the known manner by the program control unit of the machine (not shown) with the assistance of a pressure switch 16 or the like. Collecting well 5 can be emptied in conventional manner via a pump 7 and a discharge pipe 17. A circulation pump 9 has its intake 8 disposed within collecting well 5 and an outlet 18 connected to at least one rotatable sprinkler arm 11 for spraying the dishes and the like (not shown) with the liquid collected in well 5. The machine is further provided with a liquid level control system substantially comprising at least one overflow wall 12 whereover collecting well 5 communicates with a control chamber 14 associated to pressure switch 16 and acting as a pressure sensing dome. Overflow wall 12 defines a chamber 15 having a considerably smaller cross-sectional area than well 5 and extending upwards to an overflow level design­ ated at A in fig. 1, this overflow level substantially corresponding and being preferably somewhat lower than the minimum dynamic level (i.e. with circulation pump 9 in oper­ ation) to be presumably attained by the water in well 5 for ensuring proper operation of pump 9. Overflow level A is thus obviously determined at the design stage, taking into account the characteristics of the entire water supply and circulation system of the machine. Adjacent its bottom portion overflow wall 12 is formed with at least one calibrated opening 10 communicating with intake 8 of circulation pump 9 and being preferable dis­ posed at a location whereat it is substantially subjected to the action of the intake flow of pump 9. The cross-­ sectional area of calibrated opening 10 is smaller than that of the free space above overflow wall 12. In a per se known manner, for instance as described in the cited patent application EP-A-0118719, the program control unit of the machine is adapted to actuate circulation pump 9 at least during the last part of the phase in which supply valve 13 is open for admitting water to collecting well 5. In operation, the program control unit of the machine initiates the water supply phase by causing valve 13 to open for supplying water to tub 4. The water thus supplied via conduit 6 collects at the bottom of well 5, so that its level steadily rises in well 5 and in chamber 15 commun­ icating therewith via opening 10. In control chamber 14, the water rises only to a certain level, as this chamber is closed on top for the actuation of pressure switch 16 as already explained. At a certain instant t0, preferably shortly before the water in collecting well 5 and chamber 15 has risen to level A, the program control unit of the machine initiates the oper­ ation of circulation pump 9. As shown in fig. 2, the oper­ ation of circulation pump 9 causes the hydraulic pressure at outlet 18 to rise gradually until an instant t1, when the air entering inlet 8 together with the water abruptly causes pump 9 to run empty for a period t1-t2. Considering now the pressure within control chamber 14, i.e. the pressure acting on pressure switch 16 as depicted in fig. 3, one observes a decrease of this pressure during the interval t0-t1 irrespective of the fact that supply valve 13 is open, because the operation of circulation pump 9 causes the water level in well 5 and chamber 15 to drop. In particular, there is a considerable drop of the water level in chamber 15 due to the action of the intake flow of pump 9 on calibrated opening 10. In this context it is noted that this suction effect and the rise and fall of the water level in chamber 15 together determine the magnitude of the pressure within control chamber 14. During the dry-running period t1-t2 of circulation pump 9 the suction effect of the pump is practically zero, causing the water level in well 5 to rise suddenly, with a result­ ant overflow over wall 12 into chamber 15 and a correspond­ ing pressure rise in control chamber 14. As will be noted by comparing figs. 2 and 3, the pressure variation at outlet 18 of pump 9 during this period is in effect amplifed in control chamber 14 and may temporarily exceed a value C to which pressure switch 16 is calibrated for closing supply valve 13. Subsequently there occurs in a per se known manner another suction period of circulation pump 9 up to an instant t4 followed, for the same reasons as explained above, by another dry-running period of pump 9 up to an instant t5, when another suction period is initiated. In a corresponding manner, the pressure at outlet 18 of circulation pump 9 increases during the period t2-t4, abruptly drops during the period t4-t5, and then starts to rise again. During these periods the water level in collecting well 5 and particularly in chamber 15 varies in response to the operating conditions of pump 9 as described above. As a result, the pressure in control chamber 14 acting on pressure switch 16 drops during the period t2-t4, rises abruptly to a value above C during the period t4-t5, and then tends to diminish again. It is noted that during all this time supply valve 13 stays open, except for the substantially negligible transitory periods during which the pressure in control chamber 14 exceeds the value C before it drops again to a value B to which pressure switch 16 is calibrated for opening supply valve 13 again. As can be seen in fig. 3, these transitory periods begin immediately before the instants t2 and t5, respectively, and end at instants t3 and t6, respectively. As a whole the water level in collecting well 5 tends to rise in a substantially continuous manner (neglecting the above explained variations), so that the suction effect of circulation pump 9 is gradually improved. After instant t5 the suction effect of pump 9 approaches the optimum operation conditions, with a gradually improv­ ing proportion of water and air taken in by the pump. Corresponding thereto, after instant t5 the pressure at the outlet 18 of circulation pump continues to rise as shown in fig. 2, while the pressure within control chamber 14 drops at a decreasing rate, because the water collected in well 5 starts to flow over wall 12 into chamber 15 at a gradually increasing rate which tends to exceed the flow rate through calibrated opening 10. These conditions per­ sist up to an instant t7, when a dynamic equilibrium is attained between collecting well 5 and chamber 15, that is, when the level of the water collected in tub 4 of the dish­ washer is stabilized at a value at least equal to the value A indicated in fig. 1. As shown in fig. 3, during this phase the pressure within control chamber 14 at a given instant tends to reverse the previous tendency to decrease for subsequently rising ab­ ruptly above the value C substantially at the instant t7 when the dynamic equilibrium is attained. As a result, at the instant t7 pressure switch 16 causes supply valve 13 to be definitely closed, because the pressure acting on it remains at a substantially constant value above the value C. The further operation of the dishwashing machine then proceeds in the conventional manner. It is noted that the amount of water admitted to the washing tub 4 for attaining the optimum level in collect­ ing well 5 is automatically controlled by taking into account the amount of waetr in circulation through tub 4, which may be variable in accordance with the character­ istics of the water circulation circuit of the machine and with the amount of dishes and the like to be washed at any given instance. In accordance with the object of the invention, the dish­ washing machine is thus provided with an extremely simple, compact and reliable control system adapted to determine the admission of an amount of water which is effectively the absolute minimum for ensuring optimum operating con­ ditions for circulation pump 9 and the associated water circulation system. Further, as opening 10 always main­ tains communication of control chamber 14 and chamber 15 with collecting well 5, the described control system is capable of continuously monitoring the water level in collecting well 5. Thus in the case for instance of a mal­ function of pump 9 caused for instance by an excessive formation of foam or by obturation of a recirculation filter (not shown) provided in the machine, the control system is capable of responding to a resultant pressure drop in control chamber 14 below the value B and of automatically initiate corrective action (as by opening supply valve 13) so as to re-establish the optimum liquid level for the operation of pump 9. In this context is is to be noted that calibrated opening 10 may be replaced by any equivalent communication arrange­ ment, such as for instance a flow conduit formed and acting as a syphon possible arranged to pass over overflow wall 12. In any case the communication means such as opening 10 is self-cleaning during operation of circulation pump 9, while during the discharge phase by means of discharge pump 7 it permits control chamber 14 and chamber 15 to be simultan­ eously emptied. An important functional advantage of the dishwashing machine according to the invention consists in the above mentioned "amplification" of the pressure in chambers 14 and 15 corresponding to the variations of the water level in collecting well 5, which ensures rapid and accurate response of pressure switch 16, even if the latter is of low sensitivity with a wide tolerance. This permits the employ of a pressure switch of an elementary type, or even a pressure-sensitive device of a per se knon type, compris­ ing a diaphragm or the like subjected to the action of the pressure within control chamber 14 for directly actuating the closure element of supply valve 13. In the latter case it is obviously possible to avoid the employ of a supply valve 13 of an electromechanical type. The described washing machine may of course undergo various modifications within the scope of the invention. By suitably dimensioning the various operative components it is for instance possible to avoid that the pressure peaks appearing in control chamber 14 at instants t2 and t5 (fig. 3) exceed the value C to which the pressure switch responds. It is also understood that the machine according to the invention may also be a laundry washing machine with recirculation of the laundering liquid, of the type for instance as described in the patent application EP-A-0146719.

Claims: 1. A washing machine having a control system for controlling thesupply of water to a collecting well adapted to be filled via a supply conduit provided with at least one controllable supply valve adapted to be opened during at least one supply phase, said machine comprising a circulation pump for circulating the water collected in said collecting well and adapted to be oper­ ated during at least the last part of the supply phase, characterized in that said collecting well (5) communicates with a control chamber (14) via at least one overflow wall (12) having a predetermined overflow level (A), flow communication means (10) of a calibrated section communic­ ating with the intake (8) of said circulation pump (9) on one side, and with said control chamber (14) on the other, pressure-sensitive means (16) being adapted to cause said supply valve (13) to close when the water overflows from said collecting well (5) to said control chamber (14) at a rate at least equal to the flow rate through said flow communication means (10). 2. A washing machine according to claim 1, character­ ized in that said flow communication means comprise at least one calibrated opening (10) formed adjacent the bottom portion of said overflow wall (12). 3. A washing machine according to claim 1, character­ ized in that said overflow wall (12) defines a chamber (15) having a smaller cross-section that said collecting well (5) and adapted to connect said collecting well (5) to said control chamber (14).

Inventors: BATTEL, MARIO, MILOCCO, CLAUDIO
Applicants: INDUSTRIE ZANUSSI S.P.A.
Application year: 1987
Main classification: A47L15
IPC codes: A47L15