EP3235940A1

EP3235940A1 - Method for the detection of foam in a laundry washing machine and washing cycle using said method

Info

Publication number: EP3235940A1
Application number: EP16166320.8A
Authority: EP
Inventors: Alberto Lucchetta; Martino Bondi
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2016-04-21
Filing date: 2016-04-21
Publication date: 2017-10-25
Anticipated expiration: 2036-04-21
Also published as: CN107385768A; CN107385768B; EP3235940B1

Abstract

The present invention relates to a method for determining the presence of foam in a laundry washing machine (1) comprising a washing tub (3) containing a washing drum (4) and a recirculation pump (21). The method comprises the steps of: performing a steady phase wherein the recirculation pump (21) is deactivated and a recirculation phase wherein the recirculation pump (21) is activated; detecting a first level (L1) of the washing liquid in the washing tub (3) during the steady phase; detecting a second level (L2) of the washing liquid in the washing tub (3) during the recirculation phase; determining the level difference (LD) between the second level (L2) and the first level (L1); comparing the determined level difference (LD) with a threshold value (TV) and if the determined level difference (LD) is below the threshold value (TV) establishing the presence of foam.

Description

The present invention concerns the field of laundry washing techniques.
In particular, the present invention refers to a method for detecting foam in a laundry washing machine during a washing cycle.
Further, the present invention relates to a corresponding laundry washing machine.

BACKGROUND ART

Nowadays the use of laundry washing machines, both "simple" laundry washing machines (i.e. laundry washing machines which can only wash and rinse laundry) and laundry washing-drying machines (i.e. laundry washing machines which can also dry laundry), is widespread.
In the present description the term "laundry washing machine" will refer to both simple laundry washing machines and laundry washing-drying machines.
Laundry washing machines generally comprise an external casing, or cabinet, provided with a washing tub which contains a rotatable perforated washing drum where the laundry is placed. A loading/unloading door ensures access to the washing drum.
Laundry washing machines typically comprise a water inlet circuit and a products supply unit for the introduction of water and washing/rinsing products (i.e. detergent, softener, etc.) into the washing tub.
Known laundry washing machines are also provided with a draining system for draining washing liquid from the washing tub. The draining system typically comprises at least one draining pump, arranged at the bottom of the washing tub, which is operated when necessary during the washing cycle.
Usually the draining system drains the washing liquid out of the laundry washing machine and/or it recirculates the same inside the tub so that the washing liquid is conveyed again on the laundry.
According to the known technique, a complete washing cycle typically includes different phases, or steps, during which the laundry to be washed is subjected to adequate treatments.
A washing cycle usually comprises an initial phase wherein a proper amount of water and detergent is introduced in the washing tub which creates the washing liquid for wetting the laundry.
The washing cycle then typically comprises a main washing phase during which the washing drum is rotated and the washing liquid contained therein is heated, typically by means of an electrical resistor, to a predetermined temperature according to the washing program selected by the user.
Successive steps of the washing cycle may comprise rinsing phases with introduction of clean water and draining steps and a final spinning in which the washing drum is rotated at high speed and the liquid in the washing tub is drained from the machine.
When the washing liquid is moved/agitated by the rotating washing drum a certain amount of foam is typically generated. In particular an high amount of foam can be very negative during the spinning and draining phase of the washing cycle since the foam compromises a correct functioning of the drain pump and it obstructs the draining of the liquid from the machine. The drain pump in presence of foam, then, are noisy.
Foam is typically generated in the washing cycle due to overdosage of detergent by the user or due to foaming agents of the detergent itself that facilitates formation of foam.
Furthermore, excessive foam may cause overflow involving liquid spillage.
Some known methods for operating a laundry washing machine are known, for example as disclosed in WO2015036166 , in which foam is effectively detect and, if necessary, actions for reducing the amount of foam inside the washing tub and/or in the draining region are taken. The detection and reduction of foam is carried out in the balancing phase and/or the spinning phase, i.e. after the main washing phase.
Nevertheless, already during the initial phases and/or the main washing phase a certain amount of foam may be generated. If too much foam is generated at such an early stage of the washing cycle then some phases of the washing cycle cannot be faultlessly performed.
In particular, for the same reason stated above, an high amount of foam can be very negative during the spinning and draining phase of the washing cycle, in particular with reference to the functioning of the pump.
Furthermore, an high amount of foam can be very negative during the main washing itself, since the washing efficiency of the washing liquid is notably reduced with respect normal conditions without foam.
Foam may also cause detergent accumulation on the laundry. The presence of a quantity of residual detergent may cause insufficient rinsing. Insufficient rinsing can leave enough detergent in laundry to affect people with allergies or sensitivity.
A known method for the detection of foam in a laundry washing machine is known from EP 1731656 A2 . Here, a foam sensor is realized integral with a temperature sensor. However, the device known from this document is complex. This negatively affects size and/or manufacturing costs of the laundry washing machine and also reliability of the same.
The object of the present invention is therefore to overcome the drawbacks posed by the known technique.
It is a first object of the invention to provide a laundry washing machine that makes it possible to detect, if necessary, the presence of foam at an early stage of the washing cycle.
It is another first object of the invention to provide a laundry washing machine that makes it possible to reduce residual of detergent on the laundry.
It is another object of the invention to provide a laundry washing machine which detects, if necessary, the presence of foam having reduced complexity and/or size compared to laundry washing machines of known type.
It is a further object of the invention to provide a laundry washing machine which detects, if necessary, the presence of foam and having higher reliability compared to laundry washing machines of known type.

DISCLOSURE OF INVENTION

The applicant has found that by determining the difference of the liquid level in a tub of a laundry washing machine between a phase wherein a recirculation pump if deactivated and a phase wherein the recirculation pump if activated it is possible to establish the presence of foam in the washing tub.
The present invention relates, therefore, to a method for determining the presence of foam in a laundry washing machine during a washing cycle, said laundry washing machine comprising a washing tub containing a washing drum, a recirculation circuit comprising a recirculation pump for draining liquid from the bottom of said washing tub and to re-admit such liquid into an another part of said washing tub, a liquid level sensor for detecting the liquid level in said washing tub, said washing cycle comprising at least one phase of introducing a quantity of water and a quantity of detergent in said washing tub to form a washing liquid, wherein after said at least one phase of introducing a quantity of water and a quantity of detergent said method comprises the steps of:

performing a steady phase wherein said recirculation pump is deactivated and a recirculation phase wherein said recirculation pump is activated:
detecting a first level of said washing liquid in said washing tub during said steady phase;
detecting a second level of said washing liquid in said washing tub during said recirculation phase;
determining the level difference between said second level and said first level;
comparing the determined level difference with a threshold value and if the determined level difference is below said threshold value establishing the presence of foam.

According to a preferred embodiment of the invention, the recirculation phase is performed after the steady phase.
According to another preferred embodiment of the invention, the steady phase is performed after the recirculation phase.
In a preferred embodiment of the invention, during the steady phase and/or the recirculation phase, the washing drum is kept motionless.
According to a preferred embodiment of the invention, the first level is detected in a predetermined first monitoring period.
Preferably, the predetermined first monitoring period corresponds to the time duration of the steady phase.
According to a preferred embodiment of the invention, the second level is detected in a predetermined second monitoring period.
Preferably, the predetermined second monitoring period corresponds to the time duration of the recirculation phase.
In a preferred embodiment of the invention, the first level is the average first level in the predetermined first monitoring period.
In a preferred embodiment of the invention, the second level is the average second level in the predetermined second monitoring period.
According to a preferred embodiment of the invention, the threshold value is between 2 mm and 12 mm, preferably between 4 mm and 10 mm, more preferably equal to 5 mm.
According to a preferred embodiment of the invention, if presence of foam has been established then at least one foam reduction action is taken.
Preferably, the foam reduction action comprises one of the following actions:

the time reduction of the main washing step with respect to the expected time of the main washing step for the washing cycle;
the reduction of the activation time of the heating device with respect to the expected activation time of the same for the main washing step of the selected cycle;
the deactivation of a heating device of said laundry washing machine;
the deactivation of a heating device of said laundry washing machine for a predetermined time;
the variation of the washing drum rhythm with respect to the expected rotation time for the main washing step of the selected cycle;
the introduction of one or more additional rinsing steps with respect to the expected rinsing steps for the selected cycle;
the introduction of a further quantity of water during the main washing step;
the reduction of the activation time of said recirculation pump with respect to the expected activation time for the selected cycle;
the complete deactivation of said recirculation pump.

In a preferred embodiment of the invention, the main washing step comprises:

washing drum rotations;
heating and/or maintaining to a predetermined temperature said washing liquid in said washing tub;
activations of said recirculation pump.

According to a preferred embodiment of the invention, the foam reduction action comprises a drainage step to remove and discharge the washing liquid from the bottom of the washing tub to the outside.
In a preferred embodiment of the invention, clean water is introduced in the washing tub to re-instate a sufficient quantity of washing liquid after the drainage step.
Preferably, the foam reduction action comprises sending a warning alarm for the user, preferably a visual alarm or an acoustic alarm.
In a further aspect thereof the present invention relates to a method for washing laundry during a washing cycle in a laundry washing machine comprising a washing tub containing a washing drum, a recirculation circuit comprising a recirculation pump for draining liquid from the bottom of said washing tub and to re-admit such liquid into an another part of said washing tub, a liquid level sensor for detecting the liquid level in said washing tub, said washing cycle comprising at least one phase of introducing a quantity of water and a quantity of detergent in said washing tub to form a washing liquid and a main washing phase using said washing liquid, wherein said method comprises a method for determining the presence of foam according to any of the preceding claims if it has been established that said recirculation pump is working correctly and/or if it has been established that the level of said washing liquid in said washing tub before said main washing phase washing is above a predetermined minimum level.
In a further aspect thereof the present invention relates to a laundry washing machine, wherein the laundry washing machine is provided for the methods described above.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will be highlighted in greater detail in the following detailed description of preferred embodiments of the invention, provided with reference to the enclosed drawings. In the drawings, corresponding characteristics and/or components are identified by the same reference numbers. In such drawings:

Figure 1 illustrates a perspective view of a laundry washing machine according to a preferred embodiment of the present invention;
Figure 2 illustrates a schematic sectional front view of the laundry washing machine according to the preferred embodiment of the present invention;
Figure 3 illustrates a schematic flow chart diagram of a method for operating a laundry washing machine during a washing cycle according to a preferred embodiment of the present invention;
Figure 4A illustrates a schematic flow chart diagram of a phase of the method of Figure 3;
Figure 4B illustrates an alternative schematic flow chart diagram of a phase of the method of Figure 3;
Figures 5 to 8 show further preferred embodiments of Figure 3.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has proved to be particularly advantageous when applied to laundry washing machines, as described below. It should in any case be underlined that the present invention is not limited to laundry washing machines. On the contrary, the present invention can be conveniently applied to laundry washing-drying machines (i.e. laundry washing machines which can also dry laundry).
In the present description, therefore, the term "laundry washing machine" will refer to both simple laundry washing machines and laundry washing-drying machines.
With reference to Figures 1 and 2 a laundry washing machine 1 according to a preferred embodiment of the invention is described.
The laundry washing machine 1 comprises an external casing or cabinet 2, in which a washing tub 3 is provided that contains a perforated washing drum 4 where the laundry to be treated can be loaded.
The cabinet 2 is provided with a front loading/unloading door 8 which allows access to the washing tub 3 and the washing drum 4.
The washing tub 3 is preferably suspended in a floating manner inside the cabinet 2, advantageously by means of a number of coil springs and shock-absorbers that are not illustrated herein.
The washing drum 4 is advantageously rotated by an electric motor, not visible, which preferably transmits the rotating motion to the shaft of the washing drum 4, advantageously by means of a belt/pulley system, not shown. In a different embodiment of the invention, the motor can be directly associated with the shaft of the washing drum 4.
A water inlet circuit 5 and a products supply unit 6 are arranged in the upper part of the laundry washing machine 1 which are suited to supply water and washing/rinsing products (i.e. detergent, softener, etc.) into the washing tub 3. The water inlet circuit 5 controls the adduction of cold water coming from an external supply line E, hereinafter indicated as mains water supply E.
In a different embodiment, the water inlet circuit may be realized for controlling adduction of hot water coming from a respective hot water external source.
The products supply unit 6 preferably comprises a removable drawer 6 provided with various compartments suited to be filled with washing and/or rinsing products.
In the embodiment herein described, the water is supplied into the washing tub 3 by making it flow through the drawer 6 and through a supply pipe 9.
In a preferred embodiment, the water which reaches the washing tub 3 can selectively contain one of the products contained in the compartments of the drawer 6, or such water can be clean and in this case it may reach the washing tub 3 directly, bypassing the compartments of the drawer 6.
In an alternative embodiment of the invention, a further separate water supply pipe can be provided, which supplies exclusively clean water into the washing tub 3.
The water inlet circuit 5 also preferably comprises a water flow sensor, for example a flow meter, which makes it possible to calculate the quantity of water supplied into the washing tub 3.
Laundry washing machine 1 advantageously comprises a water outlet circuit 25 suitable for withdrawing liquid from the tub 3.
The water outlet circuit 25 preferably comprises a main pipe 17, a draining pump 26 and an outlet pipe 28 ending outside the cabinet 2.
The water outlet circuit 25 preferably further comprises a filtering device 12 arranged between the main pipe 17 and the draining pump 26. The filtering device 12 is adapted to retain all the undesirable bodies (for example buttons that have come off the laundry, coins erroneously introduced into the laundry washing machine, etc.).
This filtering device 12 can preferably be removed, and then cleaned, through a gate 14 placed advantageously on the front wall of the cabinet 2 of the laundry washing machine 1, as illustrated in Figure 1.
In a further embodiment, not illustrated, the filtering device 12 may be provided directly in the tub 3, preferably obtained in a single piece construction with the latter. In this case the filtering device 12 is fluidly connected to the outlet of the tub 3, in such a way that water and washing liquid drained from the tub 3 enters the filtering device 12.
Activation of the drain pump 26 drains the liquid, i.e. dirty water or water mixed with washing and/or rinsing products, from the tub 3 to the outside.
Laundry washing machine 1 advantageously comprises a recirculation circuit 20 adapted to drain liquid from the bottom region of the tub 3 and to re-admit such a liquid into a second region, preferably an upper region, of the tub 3.
The recirculation circuit 20 preferably comprises a recirculation pump 21, a pipe 22 connecting the filtering device 12 to the recirculation pump 21 and a recirculation pipe 23, preferably provided with a terminal nozzle 23a arranged preferably at the upper region of the tub 3. The terminal nozzle 23a is opportunely arranged so that the liquid is sprayed directly into the drum 4 through its holes.
The terminal nozzle 23a, therefore, enhances distribution of liquid over the laundry through the perforated drum 4.
In different embodiments, the recirculation circuit may be preferably realized as an independent circuit from the water outlet circuit.
The liquid from the bottom region of the tub 3 is conveyed towards the upper region of the tub 3 by activation of the recirculation pump 21.
The recirculation circuit 20 is therefore advantageously activated in order to improve wetting of the laundry inside the drum 4.
Preferably, the recirculation circuit is properly realized for transferring a portion of liquid from a bottom region of the tub, preferably from the sump, to an upper region of the tub in order to enhance absorption of the liquid by the laundry. Nevertheless, the recirculation circuit may be properly realized for transferring a portion of liquid from the tub to another region of the tub which allows absorption of the liquid by the laundry. For example, the recirculation pipe may terminate at any vertical position of the tub and/or its terminal nozzle may be opportunely shaped to spray liquid along a direction reaching the laundry inside the washing drum 4.
Advantageously laundry washing machine 1 comprises a device 19 suited to sense (or detect) the liquid level inside the washing tub 3.
The device 19 preferably comprises a pressure sensor which senses the pressure in the washing tub 3, which value is related to the level of liquid contained in the washing tub 3. In another embodiment, not illustrated, laundry washing machine 1 comprises (in addition to or as a replacement of the pressure sensor) a level sensor (for example mechanical, electro-mechanical, optical, etc.) adapted to sense (or detect) the liquid level inside the washing tub 3.
Preferably, the laundry washing machine 1 comprises a heating device 60 adapted to come into contact with the liquid in the washing tub 3 and to heat it. The heating device 60, preferably an electric resistor, is preferably placed in a suitable seat, not illustrated, obtained at the bottom of the washing tub 3 or in a draining region thereof.
In different embodiments, the heating device may be omitted. In a first preferred embodiment, laundry washing machines without heating device may introduce hot water coming from a respective hot water external source. In a second preferred embodiment, laundry washing machines without heating device may perform only washing cycle using cold water coming from the water external source E.
Laundry washing machine 1 advantageously comprises a control unit 22 connected to the various parts of the laundry washing machine 1 in order to ensure its operation. The control unit 22 is preferably connected to the water inlet circuit 5, the water outlet circuit 25 (in particular the drain pump 26), the recirculation circuit 20 (in particular the recirculation pump 21), the electric motor rotating the washing drum 4 and receives information from the various sensors provided on the laundry washing machine 1, like the flow meter of the water inlet circuit 5, the level sensor 19 (or pressure sensor), a temperature sensor, etc.
In particular, the level detected by the level sensor 19 is preferably continuously received by the control unit 22 and advantageously used according to the present invention, as better described below.
Alternatively, the level detected by the level sensor 19 is acquired by the control unit 22, when necessary, at a pre-determined time.
Laundry washing machine 1 advantageously comprises an interface unit 50 connected to control unit 22, accessible to the user and by means of which the user may select and set the washing parameters from time to time, in particular the desired washing program. The washing program selected by the user will correspond to a respective washing cycle performed by the laundry washing machine. Usually, other parameters can optionally be inserted by the user, for example the washing temperature, the spinning speed, the load in terms of weight of the laundry to be washed, etc. The interface unit 50 preferably comprises a display which displays machine working conditions or other information.
Based on the parameters acquired by said interface unit 50, the control unit 22 sets and controls the various parts of the laundry washing machine 1 in order to carry out the desired washing cycle.
According to an advantageous aspect of the present invention, the recirculation pump 21 and the level sensor 19 are utilized to determine the presence and/or amount of foam in the washing tub 3 and/or the draining region thereof.
After introduction of water and detergent in the washing tub 3, the washing cycle preferably performs a foam detection procedure, according to the present invention, comprising a steady phase wherein the recirculation pump is deactivated and a recirculation phase, following the steady phase, wherein the recirculation pump is activated.
Alternatively, the foam detection procedure comprises a recirculation phase wherein the recirculation pump is activated and a steady phase, following the steady phase, wherein the recirculation pump is deactivated.
During the steady phase the level L1 of the liquid is preferably detected by the level sensor 19. During the recirculation phase the level L2 of the liquid is also preferably detected by the level sensor 19. From the detected values L1, L2 of the liquid it is then determined, preferably by the control unit 22, the level difference LD between the liquid level L2 in the recirculation phase, or second liquid level L2, and the liquid level L1 in the steady phase L1, or first liquid level L1, i.e. LD=L2-L1.
Advantageously, it is determined the presence and/or a high amount of foam in the washing tub 3 and/or in the draining region thereof if the determined level difference LD is below a threshold value TV, i.e. LD=L2-L1<TV
If the level difference LD is above, or equal to, the threshold value TV then presence of only water or a low amount of foam is detected.
Tests carried out by the applicant have proved that a small difference between the two liquid levels, i.e. a difference below a threshold value, is indicative of the presence and/or a high amount of foam in the washing tub 3.
This is due to the fact that the recirculation pump 21 in presence of foam does not work properly and is not able to pump liquid and/or foam towards the terminal nozzle 23a and from there above the laundry. Therefore, firstly, the recirculation circuit 20, and in particular its pipes 22, 23, remains empty or substantially empty, and the liquid level detected by the level sensor 19 is the effective liquid presents in the washing tub 3.
Furthermore, being the liquid not sprayed over the laundry there is not absorption by the laundry during the recirculation phase, when the recirculation pump is activated, and therefore the liquid level L2 detected by the level sensor 19 in the recirculation phase does not substantially change with respect to the liquid level L1 detected by the level sensor 19 in the steady phase.
According to an advantageous aspect of the invention, therefore, the presence and/or a high amount of foam in the washing tub 3 is detected by comparing the liquid level in the washing tub 3 while the recirculation pump is deactivated and the liquid level in the washing tub 3 while the recirculation pump is activated. As said above, the recirculation pump may be either deactivated and then activated or activated and then deactivated.
Preferably, the first liquid level L1 and/or the second liquid level L2 is detected while the washing drum 4 is motionless. In such condition, the liquid level inside the washing drum is not affected by oscillation caused by washing drum rotations.
More preferably, the first liquid level L1 is detected at the expiring of a first monitoring period Δt1 while the washing drum 4 is kept motionless and/or the second liquid level L2 is detected at the expiring of a second monitoring period Δt2 while the washing drum 4 is kept motionless.
In a further preferred embodiment, the first liquid level L1 is the average first liquid level AL1 of the liquid in the steady phase calculated during a predetermined first monitoring period Δt1.
Here again, preferably, during the first monitoring period Δt1 the washing drum 4 is kept motionless.
In a further preferred embodiment, nevertheless, the average first liquid level AL1 may be calculated during said predetermined first monitoring period Δt1 while the washing drum 4 is rotating.
The average first liquid level AL1 is preferably calculated as follows: $AL 1 = \frac{1}{Δ t 1} \int_{t 1 i}^{t 1 f} L 1 (t) dt$
wherein t1i is the initial time of the first monitoring period Δt1 and t1f is the final time of the first monitoring period Δt1.
Analogously, in a further preferred embodiment, the second liquid level L2 is the average second liquid level AL2 of the liquid in the recirculation phase calculated during a predetermined second monitoring period Δt2.
Here again, preferably, during the second monitoring period Δt2 the washing drum 4 is kept motionless.
In a further preferred embodiment, nevertheless, the average second liquid level AL2 may be calculated during said predetermined second monitoring period Δt2 while the washing drum 4 is rotating.
The average first liquid level AL2 is preferably calculated as follows: $AL 2 = \frac{1}{Δ t 2} \int_{t 2 i}^{t 2 f} L 2 (t) dt$
wherein t2i is the initial time of the second monitoring period Δt2 and t2f is the final time of the second monitoring period Δt2.
The presence and/or a high amount of foam in the washing tub 3 and/or in the draining region thereof is then determined if the level difference LD using said average values is below a threshold value TV, i.e. LD=AL2-AL1<TV.
In a normal functioning condition of the washing cycle, i.e. substantially without formation of foam in the washing tub 3, the presence of only water or a low amount of foam is determined if the level difference LD is above, or equal to, the threshold value TV, i.e. LD=L2-L1>TV.
In different embodiments, the liquid levels may be differently calculated, for example liquid levels are continuously calculated (instantaneous level). Preferably, the first monitoring period Δt1 is preferably set at as the duration of the steady phase and/or the second monitoring period Δt2 is preferably set at as the duration of the recirculation phase.
In different embodiments the predetermined first monitoring periods Δt1 and Δt2 may have different duration and/or may be differently positioned inside the respective steady phase and recirculation phase.
In further preferred embodiments, the first monitoring period Δt1 and/or the second monitoring period Δt2 are preferably set at a predetermine value, for example 6 sec. In this case the first monitoring period Δt1 is lower than the duration of the steady phase and the second monitoring period Δt2 is lower than the duration of the recirculation phase.
In further preferred embodiments, the first monitoring period Δt1 is preferably set at a predetermine value, for example a fixed value of 6 sec.
In further preferred embodiments, the second monitoring period Δt2 is preferably set at a predetermine value, for example a fixed value of 14 sec.
The threshold value TV for the level difference LD is preferably set at a predetermine value, for example a fixed value of 5 mm.
Preferably, the threshold value is between 2 mm and 12 mm, more preferably between 4 mm and 10 mm.
Preferably, the foam detection procedure is carried out one or more times during the main washing phase of the washing cycle, as will be better described later. Nevertheless, the foam detection procedure may be carried out in any other moment of the washing cycle, obviously after introduction of water and detergent in the washing tub 3, as will be better described later.
According to a further advantageous aspect of the present invention, if presence of foam in the washing tub 3 has been detected, then one or more foam-reducing actions are preferably taken.
Hereinafter, possibly foam-reducing actions that can be preferably performed are described.
A foam-reducing action that can be performed after detection of foam in the washing tub 3 preferably comprises the time reduction of the main washing phase with respect to the expected time of the main washing phase for the washing cycle.
The main washing phase may be defined as the phase of the washing cycle during which the washing drum is rotated and the washing liquid contained therein is heated and/or maintained to a predetermined temperature according to the washing program selected by the user. Furthermore, preferably, during the main washing phase the recirculation pump 21 is opportunely activated and deactivated for transferring a portion of the liquid from the bottom region of the tub 3 to an upper region of the tub 3 so that the liquid is sprayed over the laundry and absorption is facilitated.
The main washing phase precedes successive steps of the washing cycle such as rinsing phases, balances phases, spinning phases etc..
As a consequence of the time reduction of the main washing phase the rotating time of the washing drum 4 is also reduced, thus avoiding excessive movement/agitation of the liquid in the washing tub 3. Dissolution of the foam, therefore, is more rapid.
Another foam-reducing action that can be performed after detection of foam in the washing tub 3 preferably comprises the reduction of the activation time of the heating device with respect to the expected activation time of the same for the main washing phase of the selected cycle. In case, the heating device can be completely deactivated for the remaining time of the main washing phase. Again, dissolution of the foam is more rapid.
Another foam-reducing action that can be performed after detection of foam in the washing tub 3 preferably comprises the variation of the washing drum rhythm, preferably the reduction of the rotation time of the washing drum with respect to the expected rotation time for the main washing phase of the selected cycle.
The reduction of the rotation time of the washing drum avoids excessive movement/agitation of the liquid in the washing tub and therefore dissolution of the foam is more rapid.
Another foam-reducing action that can be performed after detection of foam in the washing tub 3 preferably comprises the introduction of one or more additional rinsing phases with respect to the expected rinsing phases for the selected cycle.
Additional rinsing phases enhances dissolution of the foam and its drainage to the outside.
Another foam-reducing action that can be performed after detection of foam in the washing tub 3 preferably comprises the introduction of a further quantity of water during the main washing phase.
The introduction of additional water decreases the concentration of detergent in the washing tub 3 thus advantageously reducing the possibility of foam generation.
Another foam-reducing action that can be performed after detection of foam in the washing tub 3 preferably comprises a drainage phase to remove and discharge the washing liquid from the bottom of the washing tub to the outside. The discharge of washing liquid decreases the concentration of detergent in the washing tub 3 thus advantageously reducing the possibility of foam generation. In a preferred embodiment, one or more introduction phases of water and/or one or more drainage phases are performed.
In a preferred embodiment, after a drainage phase an amount of clean water is introduced in the washing tub 3 to re-instate a sufficient quantity of washing liquid for the main washing. The introduction of clean water further decreases the concentration of detergent in the washing tub 3.
A further foam-reducing action that can be performed after detection of foam in the washing tub 3 preferably comprises the variation/reduction of the activation time of the recirculation pump 21 with respect to the expected activation time for the selected cycle. This enhances a more rapid dissolution of the foam.
In a further preferred embodiment, the recirculation pump 21 is completely deactivated.
Another action that can be performed after detection of foam in the washing tub 3 preferably comprises sending a warning alarm for the user, for example a visual alarm at the display of the interface unit 50 or an acoustic alarm. Since formation of foam may be caused by an overdose of detergent or a wrong detergent usage, the foam alarm may be useful for the user because it advises him on how to prevent future laundry washing cycle with foam formation, for example the choice of a correct detergent.
Figure 3 illustrates schematic flow chart diagram of a method for operating the laundry washing machine during a washing cycle according to a preferred embodiment of the present invention.
The laundry to be washed is first placed inside the washing drum 4 (step 100). By operating on the interface unit 50 the user selects the desired washing program (step 110).
In a next step (step 120) the washing cycle according to the washing program selected by the user is started. As a next step (step 130) the method provides for a phase wherein a quantity of water Qw and a quantity of detergent Qd are introduced into the washing tub 3 to form a washing liquid for washing the laundry, preferably by means of the water inlet circuit 5 and the products supply unit 6. During the phase, the washing drum 4 is advantageously rotated with a preferred rhythm.
The washing cycle then proceeds with a main washing phase (step 170).
In the preferred embodiment herewith illustrated, the main washing phase comprises cyclical activation (step 172) and deactivation (step 174) of the recirculation pump 21 for transferring a portion of the liquid from the bottom region of the tub 3 to an upper region of the tub 3 so that the liquid is sprayed over the laundry and absorption is facilitated.
During the main washing phase (step 170) the washing drum is then preferably rotated and the washing liquid contained therein is heated and/or maintained to a predetermined temperature according to the washing program selected by the user.
According to the preferred aspect of the present invention, during the main washing phase (step 170) a foam detection procedure (step 200, 200') is performed.
In particular, the foam detection procedure (step 200, 200') is preferably performed after deactivation of the recirculation pump 21 and before the successive activation of the recirculation pump 21.
A first preferred embodiment of the foam detection procedure (step 200) is better described with reference to Figure 4A.
A second preferred embodiment of the foam detection procedure (step 200') is better described with reference to Figure 4B.
The first preferred embodiment of the foam detection procedure (step 200), see Figure 4A, preferably firstly comprises a step wherein the washing drum 4 is stopped (step 210), obviously in case the washing drum 4 was rotating. The stationary condition with the washing drum 4 motionless is maintained for a predetermined period of time, for example 6 sec, in order to guarantee a good measurement (step 230) of the first liquid level L1 in the washing tub 3, preferably detected by the pressure sensor 19. The predetermined period of time corresponds to the duration of the steady phase and preferably to the first monitoring period Δt1 as defined above.
The recirculation pump 21 is then activated (step 240) and after a predetermined period of time, for example 14 sec, a measurement (step 250) of the second liquid level L2 in the washing tub 3 is carried out. The predetermined period of time corresponds to the duration of the recirculation phase and preferably to the second monitoring period Δt2 as defined above.
In a successive step, the level difference LD between the second liquid level L2 and the first liquid level L1 (step 260) is calculated.
According to the invention, if the level difference LD is below a threshold value TV (output "Yes" of step 260), the presence of foam is established (step 270).
If the level difference LD is above, or equal to, the threshold value TV (output "No" of step 260), the method normally proceeds without establishing the presence of foam.
The second preferred embodiment of the foam detection procedure (step 200'), see Figure 4B, preferably firstly comprises a step wherein the washing drum 4 is stopped (step 210), obviously in case the washing drum 4 was rotating.
The recirculation pump 21 is then activated (step 240') and after a predetermined period of time, for example 14 sec, a measurement (step 250') of the second liquid level L2 in the washing tub 3 is carried out. The predetermined period of time corresponds to the duration of the recirculation phase and preferably to the second monitoring period Δt2 as defined above.
The recirculation pump 21 is then deactivated (step 219') and the stationary condition with the washing drum 4 motionless is maintained for a predetermined period of time, for example 6 sec, in order to guarantee a good measurement (step 230') of the first liquid level L1 in the washing tub 3, preferably detected by the pressure sensor 19. The predetermined period of time corresponds to the duration of the steady phase and preferably to the first monitoring period Δt1 as defined above.
In a successive step, the level difference LD between the second liquid level L2 and the first liquid level L1 (step 260') is calculated.
According to the invention, if the level difference LD is below a threshold value TV (output "Yes" of step 260'), the presence of foam is established (step 270'). If the level difference LD is above, or equal to, the threshold value TV (output "No" of step 260'), the method normally proceeds without establishing the presence of foam.
Going back to the washing cycle, as illustrated in Figure 3, after the main washing phase 170 the washing cycle advantageously proceeds with one or more rinsing cycles (steps 180 and 190) during which clean rinse water is added to the laundry and the washing drum is rotated to extract water and dirty particles/detergent from the laundry: the dirty water extracted is drained from the washing tub 3 to the outside.
The washing cycle terminates with a final spinning phase (step 195).
Once the washing cycle has been completed, in case of a laundry washing-drying machine, a drying phase may be also preferably performed.
It has to be noted that if the presence of foam (step 270, 270') has been established during the foam detection procedure (step 200, 200'), then the washing cycle as illustrated in Figure 3 is eventually and properly adapted with execution of one or more foam-reducing actions of the type previously described. Figure 5 shows a variant of the washing cycle previously described with reference to Figure 3.
Corresponding steps of the washing cycle of Figure 3 are identified by the same reference numbers.
This washing cycle differs from the washing cycle previously described with reference to Figure 3 in that the phase of introducing a quantity of water Qw and a quantity of detergent Qd into the washing tub 3 is replaced by a first phase of introducing a first quantity of water Q1w (step 135), a procedure for checking correct functioning of the recirculation pump 21 (step 300) and a phase of introducing a second quantity of water Q2w and a quantity of detergent Qd into the washing tub 3 (step 140).
The correct functioning procedure for the recirculation pump 21, not described herein, allows to obtain information on the correct functioning of the recirculation pump 21 and, in case, taking proper actions.
An action that can be performed when malfunctioning of the recirculation pump 21 is established is the omission of the foam detection procedure for the washing cycle or, in other words, the foam detection procedure is performed if it has been established that the recirculation pump 21 is working correctly.
In a further preferred embodiment of the washing cycle, not illustrated, after the phase of introducing a quantity of water Qw and a quantity of detergent Qd into the washing tub 3 and before the main washing phase (step 170), a step of checking the liquid level L into the washing tub 3 is performed.
If the liquid level L is below or equal to a predetermined minimum level Lmin then the foam detection procedure for the washing cycle is omitted or, in other words, the foam detection procedure is performed if it has been established that the liquid level L in the washing tub 3 is above a predetermined minimum level Lmin.
Figure 6 shows another variant of the washing cycle previously described with reference to Figure 3.
This washing cycle simply shows how the foam detection procedure (step 200, 200') may be advantageously carried out at any proper time during the main washing phase (step 370), independently of the actions which are performed in the same main washing phase.
Analogously, Figure 7 shows a washing cycle wherein the foam detection procedure (step 200, 200') is advantageously carried after introduction of water and detergent in the washing tub 3 (step 130) and before a main washing phase (step 470).
Analogously, Figure 8 shows a washing cycle wherein the foam detection procedure (step 200, 200') is advantageously carried after a main washing phase (step 470).
Advantageously, the method according to the invention allows the detection of foam at different stages of the washing cycle, preferably at an early stage of the washing cycle.
It follows that foam-reduction actions may be performed from the very beginning of the washing cycle. This help to reduce detergent accumulation on the laundry with respect known methods.
Furthermore, detection of foam is advantageously carried out by means of a level sensor which is usually installed in laundry washing machines, without necessity of installing and controlling a dedicated foam sensor.
Therefore the method of the invention allows detecting of foam in a laundry washing machine having reduced complexity and/or size compared to laundry washing machines which detect foam of known type.
It follows that the laundry washing machine performing the method of the invention has higher reliability compared to laundry washing machines which detect foam of known type.
Still advantageously, the method according to the invention assures a more correct functioning of the pumps installed in the laundry washing machine which drain liquid from the washing tub since presence of foam at their inlets is substantially avoided. This, in turn, reduces the noise caused by the pump working with foam.
Advantageously, the method according to the invention reduces or avoids overflow and liquid spillage from the washing tub.
It has thus been shown that the present invention allows all the set objects to be achieved. In particular, it makes it possible to provide a method and a laundry washing machine with a more effective detection system of foam compared to known systems.
It is underlined that the laundry washing machine illustrated in the enclosed figures, and with reference to which some embodiments of the method according to the invention have been described, is of the front-loading type; however it is clear that the method according to the invention can be applied as well to a top-loading laundry washing machine, substantially without any modification. Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the present invention is not limited to those precise embodiments, and that various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.

Claims

A method for determining the presence of foam in a laundry washing machine (1) during a washing cycle, said laundry washing machine (1) comprising a washing tub (3) containing a washing drum (4), a recirculation circuit (20) comprising a recirculation pump (21) for draining liquid from the bottom of said washing tub (3) and to re-admit such liquid into an another part of said washing tub (3), a liquid level sensor (19) for detecting the liquid level in said washing tub (3), said washing cycle comprising at least one phase of introducing a quantity of water (Qw) and a quantity of detergent (Qd) in said washing tub (3) to form a washing liquid, wherein after said at least one phase of introducing a quantity of water (Qw) and a quantity of detergent (Qd) said method comprises the steps of:
- performing a steady phase wherein said recirculation pump (21) is deactivated and a recirculation phase wherein said recirculation pump (21) is activated:

- detecting a first level (L1) of said washing liquid in said washing tub (3) during said steady phase;

- detecting a second level (L2) of said washing liquid in said washing tub (3) during said recirculation phase;

- determining the level difference (LD) between said second level (L2) and said first level (L1);

- comparing the determined level difference (LD) with a threshold value (TV) and if the determined level difference (LD) is below said threshold value (TV) establishing the presence of foam.
The method according to claim 1, wherein said recirculation phase is performed after said steady phase.
The method according to any of the preceding claims, wherein during said steady phase and/or said recirculation phase, said washing drum (4) is kept motionless.
The method according to any of the preceding claims, wherein said first level (L1) is detected in a predetermined first monitoring period (Δt1).
The method according to claim 4, wherein said predetermined first monitoring period (Δt1) corresponds to the time duration of said steady phase.
The method according to any of the preceding claims, wherein said second level (L2) is detected in a predetermined second monitoring period (Δt2).
The method according to claim 6, wherein said predetermined second monitoring period (Δt2) corresponds to the time duration of said recirculation phase.
The method according to any claims from 4 to 7, wherein said first level (L1) is the average first level (AL1) in said predetermined first monitoring period (Δt1).
The method according to any claims from 6 to 8, wherein said second level (L2) is the average second level (AL2) in said predetermined second monitoring period (Δt2).
The method according to any of the preceding claims, wherein said threshold value (TV) is between 2 mm and 12 mm, preferably between 4 mm and 10 mm, more preferably equal to 5 mm.
The method according to any of the preceding claims, wherein if presence of foam has been established then at least one foam reduction action is taken.
The method according to claim 12, wherein said foam reduction action comprises one of the following actions:
- the time reduction of the main washing step with respect to the expected time of the main washing step for the washing cycle;

- the reduction of the activation time of the heating device with respect to the expected activation time of the same for the main washing step of the selected cycle;

- the deactivation of a heating device of said laundry washing machine (1);

- the deactivation of a heating device of said laundry washing machine (1) for a predetermined time;

- the variation of the washing drum rhythm with respect to the expected rotation time for the main washing step of the selected cycle;

- the introduction of one or more additional rinsing steps with respect to the expected rinsing steps for the selected cycle;

- the introduction of a further quantity of water during the main washing step;

- the reduction of the activation time of said recirculation pump (21) with respect to the expected activation time for the selected cycle;

- the complete deactivation of said recirculation pump (21).
The method according to claim 11 or 12, wherein said foam reduction action comprises sending a warning alarm for the user, preferably a visual alarm or an acoustic alarm.
A method for washing laundry during a washing cycle in a laundry washing machine (1) comprising a washing tub (3) containing a washing drum (4), a recirculation circuit (20) comprising a recirculation pump (21) for draining liquid from the bottom of said washing tub (3) and to re-admit such liquid into an another part of said washing tub (3), a liquid level sensor (19) for detecting the liquid level in said washing tub (3), said washing cycle comprising at least one phase of introducing a quantity of water (Qw) and a quantity of detergent (Qd) in said washing tub (3) to form a washing liquid and a main washing phase using said washing liquid, wherein said method comprises a method for determining the presence of foam according to any of the preceding claims if it has been established that said recirculation pump (21) is working correctly and/or if it has been established that the level of said washing liquid in said washing tub (3) before said main washing phase washing is above a predetermined minimum level (Lmin).
A laundry washing machine (1), wherein the laundry washing machine (1) is provided for the method according to any one of the claims 1 to 14.