METHOD FOR THE DETECTION OF FOAM IN A LAUNDRY WASHING MACHINE

Abstract

 The present invention relates to a method for operating a laundry washing machine (1; 200) having washing tub (3) containing a washing drum (4) and a heating device (20) for heating liquid in the washing tub (3). The method comprises the steps of: introducing a quantity of water and a quantity of detergent in the washing tub (3) to form a washing liquid; heating the washing liquid; determining the temperature increasing speed (TS); comparing the determined temperature increasing speed (TS) with a threshold value (TV) and if the determined temperature increasing speed (TS) is above the threshold value (TV) establishing the presence of foam.

Description

[0001] The present invention concerns the field of laundry washing techniques.

[0002] In particular, the present invention refers to a method for detecting foam in a laundry washing machine during a washing cycle.

[0003] Further, the present invention relates to a corresponding laundry washing machine.

BACKGROUND ART

[0004] 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.

[0005] In the present description the term "laundry washing machine" will refer to both simple laundry washing machines and laundry washing-drying machines.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] Usually the draining system drains the washing liquid out of the laundry washing machine and/or it re-circulates the same inside the tub so that the washing liquid is conveyed again on the laundry.

[0010] 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.

[0011] A washing cycle usually comprises an initial wetting phase wherein a proper amount of water and detergent is introduced in the washing tub which creates the washing liquid for wetting the laundry.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] Furthermore, excessive foam may cause overflow involving liquid spillage.

[0017] 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.

[0018] Nevertheless, already during the wetting phase 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The object of the present invention is therefore to overcome the drawbacks posed by the known technique.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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

[0028] The applicant has found that by determining the temperature increasing speed of a liquid in the washing tub of a laundry washing machine it is possible to establish the presence of foam in the washing tub.

[0029] The present invention relates, therefore, to a method for operating a laundry washing machine during a washing cycle, the laundry washing machine comprising a washing tub containing a washing drum and a heating device for heating liquid in said washing tub, wherein said method comprises the steps of:

• introducing a quantity of water and a quantity of detergent in the washing tub to form a washing liquid;
• heating said washing liquid;
• detecting the washing liquid temperature in the washing tub and/or in the draining region thereof;
• determining the temperature increasing speed;
• comparing the determined temperature increasing speed with a threshold value and if the determined temperature increasing speed is above said threshold value establishing the presence of foam.

[0030] Preferably, the washing liquid temperature is detected in a predetermined monitoring period.

[0031] Preferably, the predetermined monitoring period is between 20s and 30 min, more preferably 1 min.

[0032] According to a preferred embodiment of the invention, the predetermined monitoring period is placed within the heating step.

[0033] In a preferred embodiment of the invention, the predetermined monitoring period is placed at the beginning of the heating step.

[0034] Preferably, the temperature increasing speed is determined in the predetermined monitoring period.

[0035] More preferably, the temperature increasing speed is the average temperature increasing speed in the predetermined monitoring period.

[0036] In a preferred embodiment of the invention, the threshold value is between 0,1°C/min and 10°C/min, preferably between 4°C/min and 8°C/min, more preferably equal to 7°C/min.

[0037] According to a preferred embodiment of the invention, the threshold value is correlated to the type of the heating device.

[0038] Preferably, the threshold value is correlated to the power dissipation of the heating device.

[0039] In a preferred embodiment of the invention, the heating step is performed after a wetting step of the washing cycle.

[0040] The wetting step preferably comprises an introduction of a quantity of water and a quantity of detergent in the washing tub.

[0041] According to a preferred embodiment of the invention, the threshold value is a function of said quantity of water.

[0042] Preferably, the threshold value is directly proportional to said quantity of water. According to a further preferred embodiment of the invention, the threshold value is a function of said quantity of water and of the power dissipation of the heating device.

[0043] In a preferred embodiment of the invention, the washing drum rotates during the heating step.

[0044] Preferably, the washing drum rotates during the wetting step.

[0045] According to a preferred embodiment of the invention, if presence of foam has been established then at least one foam reduction action is taken.

[0046] In a preferred embodiment of the invention, 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 the heating device;
• the deactivation of the heating device for a predetermined time;
• 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 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.

[0047] In a further 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. Preferably, clean water is introduced in the washing tub to re-instate a sufficient quantity of washing liquid after the drainage step.

[0048] According to a preferred embodiment of the invention, the foam reduction action comprises sending a warning alarm for the user, preferably a visual alarm or an acoustic alarm.

[0049] In a preferred embodiment of the invention, the laundry washing machine comprises a recirculation circuit comprising a recirculation pump for draining liquid from the bottom of the washing tub and to re-admit such liquid into an another part of the washing tub wherein the foam-reducing action comprises the step or reducing the activation time of the recirculation pump with respect to the expected activation time for the selected cycle.

[0050] In a further aspect thereof the present invention relates to a laundry washing machine, wherein the laundry washing machine is provided for the method described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] 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:

• FIG 1 illustrates a perspective view of a laundry washing machine according to a preferred embodiment of the present invention;
• FIG 2 illustrates a schematic sectional front view of the laundry washing machine according to the preferred embodiment of the present invention;
• FIG 3 illustrates a schematic set of diagrams as functions of the time during a time slot of a washing cycle in a first situation according to the preferred embodiment of the present invention;
• FIG 3A shows and enlarged view of a detail of FIG 3;
• FIG 4 illustrates a schematic set of diagrams as functions of the time during the time slot of the washing cycle in a second situation according to the preferred embodiment of the present invention;
• FIG 4A shows and enlarged view of a detail of FIG 4;
• FIG 5 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 6 shows a further preferred embodiment of Figure 2.

DETAILED DESCRIPTION OF THE INVENTION

[0052] 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).

[0053] In the present description, therefore, the term "laundry washing machine" will refer to both simple laundry washing machines and laundry washing-drying machines.

[0054] With reference to Figures 1 and 2 a laundry washing machine 1 according to a preferred embodiment of the invention is described.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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 water coming from an external supply line E, hereinafter indicated as mains water supply E.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] Laundry washing machine 1 advantageously comprises a draining system 15.

[0066] The draining system15 advantageously comprises a drain pump 16, a first pipe 17 connecting the washing tub 3 to the drain pump 16 and an outlet pipe 18 ending outside the cabinet 2. The draining system15 is suited to drain the liquid, for example dirty water or water mixed with washing and/or rinsing products, from the washing tub 3 to the outside.

[0067] The draining system15 preferably comprises a filtering device, not shown in the figures, placed between the bottom of the washing tub 3 and the drain pump 16 and 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.) that have passed through the holes located on the surface of the washing drum 4, or fallen onto the bottom of the washing tub 3 while passing between the washing drum 4 and the washing tub 3, which could damage or obstruct the drain pump 16.

[0068] This filtering device can preferably be removed, and then for example cleaned, through a gate 14 placed advantageously on the front or back wall of the cabinet 2 of the laundry washing machine 1; in a further embodiment, not illustrated, the filtering device can be accessed for example by the internal of the washing drum 4, for example by a suitable opening obtained therein and selectively closed by a suitable cover, or by a removable lifter of the washing drum 4.

[0069] Advantageously laundry washing machine 1 comprises a device 19 suited to sense (or detect) the water level inside the washing tub 3.

[0070] 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 free water 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 water level inside the washing tub 3.

[0071] Advantageously, the laundry washing machine 1 comprises a heating device 20 adapted to come into contact with the liquid in the washing tub 3 and to heat it. The heating device 20, 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.

[0072] Preferably the laundry washing machine 1 comprises a temperature sensor 21 for sensing the temperature of the liquid in the washing tub 3.

[0073] In the preferred embodiment here illustrated the temperature sensor 21 is preferably integrated with the heating device 20, i.e. they are supported by a common housing.

[0074] In different embodiments, the temperature sensor may be placed in other suitable locations adapted to detect the temperature of the liquid in the washing tub 3. 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 draining system15, the electric motor 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 pressure sensor 19 (or the level sensor) on the bottom of the washing tub 3, the temperature sensor 21, etc.

[0075] In particular, the temperature detected by the temperature sensor 21 is preferably continuously received by the control unit 22 and advantageously used according to the present invention, as better described below.

[0076] Alternatively, the temperature detected by the temperature sensor 21 is acquired by the control unit 22, when necessary, at a pre-determined time.

[0077] 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.

[0078] 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.

[0079] The temperature sensor 21 is provided for detecting the temperature of the liquid in the washing tub 3 or in a draining region thereof.

[0080] According to an advantageous aspect of the present invention, the temperature sensor 21 is utilized to determine the presence and/or amount of foam in the washing tub 3 and/or the draining region thereof during a heating phase of the washing cycle.

[0081] During the heating of the liquid in the washing tub 3, preferably by activation of the heating device 20, the temperature WT of the washing liquid in the washing tub 3 or in a draining region thereof is detected by the temperature sensor 21. From the detected values it is then determined, preferably by the control unit 22, the increasing speed TS of the washing liquid temperature WT. 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 temperature increasing speed TS is above a threshold value TV.

[0082] If the temperature increasing speed TS is below, or equal to, the threshold value TV then presence of only water or a low amount of foam is detected.

[0083] Preferably, 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 temperature increasing speed TS is above a threshold value TV during a predetermined monitoring period Δt.

[0084] If the temperature increasing speed TS is below, or equal to, the threshold value TV within the monitoring period Δt then presence of only water or a low amount of foam is detected.

[0085] In particular, it is determined if the average temperature increasing speed ATS is above the threshold value TV within the monitoring period Δt, i.e. if:

or

wherein ti is the initial time of the monitoring period Δt and tf is the ending time of the monitoring period Δt for the washing temperature WT.

[0086] 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, as will be better described later.

[0087] FIG 3 illustrates a schematic set of diagrams as functions of the time during a time slot of the washing cycle in a first situation according to the preferred embodiment of the present invention.

[0088] The first situation corresponds to a normal functioning condition of the washing cycle, i.e. without formation of foam in the washing tub 3.

[0089] The time slot between t = 0 s and t = 4500 s of the washing cycle is shown in FIG 3. This time slot corresponds to initial phases of the washing cycle, in particular a wetting phase (t0÷t1) and a main washing phase (t1÷t4).

[0090] During the wetting phase, between t0=0 s and t1≅1500 s, a quantity of water Qw and a quantity of detergent Qd are introduced into the washing tub 3, preferably by means of the water inlet circuit 5 and the products supply unit 6. During the wetting phase, water and detergent are introduced into the washing tub 3 to form a washing liquid for washing the laundry.

[0091] During the wetting phase the washing drum 4 is advantageously rotated with a preferred rhythm, for example in clockwise and/or anticlockwise direction, at a low speed (e.g. at [10-300] rpm), and advantageously with stop interval time between successive rotations.

[0092] Correspondingly, a liquid level 44 in the washing tub 3, preferably detected by the pressure sensor 19, rises from 0 mm to about 100 mm.

[0093] In FIG 3, the liquid level 44 oscillates around 100 mm due to oscillations of the liquid level 44 inside the washing tub 3 caused by washing drum rotations.

[0094] The liquid level 44 of about 100 mm in the washing tub 3 is preferably sufficient to entirely cover the heating device 20 so that it is advantageously totally immersed in the liquid.

[0095] The washing liquid temperature WT, also indicate with the reference number 45 in FIG 3, in the wetting phase remains substantially constant, T1≅20°C, corresponding to the temperature of the water coming from the mains water supply E.

[0096] Being the first situation illustrated in FIG 3 a normal functioning condition of the washing cycle, in the wetting phase the formation of foam is substantially prevented.

[0097] At time t1≅1500s the main washing phase is started. The main washing phase comprises a heating phase (t1÷t2) and a maintaining phase (t2÷t4). During the heating phase the heating device 20 is activated, as perceivable in FIG 3 from the driving signal 47 of the heating device 20, and the washing drum 4 is rotated with a preferred rhythm. During the maintaining phase (t2÷t4) the heating device 20 is deactivated and the washing drum 4 is rotated with a preferred rhythm. During the heating phase (t1÷t2) the washing liquid temperature WT rises substantially linearly. The heating phase terminates at time t2≅2250s, when the washing liquid temperature WT reaches a pre-fixed temperature T2. In the preferred embodiment here illustrated the pre-fixed temperature T2 is set to 40°C corresponding, for example, to a 40°C cotton cycle selected by the user.

[0098] During the heating phase (t1÷t2) the washing liquid temperature WT is also monitored.

[0099] In particular, within the heating phase (t1÷t2) the temperature increasing speed TS is calculated.

[0100] The temperature increasing speed TS is compared with a threshold value TV and if the temperature increasing speed TS is above the threshold value TV it is determined the presence and/or a high amount of foam in the washing tub 3. Otherwise, presence of only water or a low amount of foam is determined.

[0101] In particular, the temperature increasing speed TS is calculated in a predetermined monitoring period Δt.

[0102] In the normal situation of FIG 3, the presence of only water or a low amount of foam has been detected during the predetermined monitoring period Δt=t1÷t3. The calculated temperature increasing speed TS in the monitoring period Δt was eventually below, or equal to, the threshold value TV.

[0103] Preferably, monitoring of the washing liquid temperature WT and calculation of the temperature increasing speed TS is carried out continuously in successive monitoring periods Δt within the heating phase.

[0104] More preferably, monitoring of the washing liquid temperature WT and calculation of the temperature increasing speed TS is carried out immediately at the beginning of the heating phase, i.e. at time t1.

[0105] In different embodiments, a monitoring period or a plurality of monitoring periods may be differently distributed over the heating phase (t1÷t2), for example a monitoring period of 2min every 2min.

[0106] Preferably, the temperature increasing speed TS is calculated as the average temperature increasing speed ATS in the monitoring period Δt, i.e. ATS=(T3-T1)/(t3-t1)=(T3-T1)/Δt referring to FIG 3A where T3 is the temperature detected at time t3 whereas T1 is the temperature detected at time t1.

[0107] In different embodiments, the temperature increasing speed TS may be differently calculated, for example the temperature increasing speed TS is continuously calculated (instantaneous speed).

[0108] The monitoring period Δt is preferably set at a predetermine value, for example 1 min.

[0109] Preferably, the predetermined monitoring period is between 20s and 30min.

[0110] In a further embodiment, the monitoring period Δt may be automatically reduced if, for example, the driving signal 47 of the heating device 20 is deactivated before the expiring of the monitoring period Δt. This may happen, for example, if the washing liquid temperature WT reaches a pre-fixed target value, such as 40°C in a 40°C cotton cycle, or a maximum safety value.

[0111] The threshold value TV for the temperature increasing speed TS is preferably set at a predetermine value, for example a fixed value of 7°C/min.

[0112] Preferably, the threshold value is between 0,1°C/min and 10°C/min, more preferably between 4°C/min and 8°C/min.

[0113] In different embodiments, nevertheless, the threshold value TV may be differently set.

[0114] Actually, the temperature increasing speed TS is affected by the quantity of water Qw introduced into the washing tub 3 during the wetting phase and/or by the type of heating device used in the laundry washing machine. Therefore, the threshold value TV may be preferably correlated to the quantity of water Qw introduced into the washing tub 3 and/or the type of heating device.

[0115] Preferably, the threshold value TV may be evaluated as a function of the quantity of water Qw introduced into the washing tub 3 during the wetting phase: TV=f(Qw)

[0116] Preferably, the threshold value TV is directly proportional to the quantity of water Qw.

[0117] In a further preferred embodiment, the threshold value TV may be set according to the specific quantity of water Qw introduced into the washing tub 3 during the wetting phase. The following table exemplary shows a correlation between the threshold value TV and the quantity of water Qw, wherein the power dissipation of the resistor 20 is a known value and equal to 1000 Watt:

Table 1

Quantity of water Qw (litre)	Threshold value TV (°C/s)
10	3
14	2
20	2

[0118] The threshold value TV may also preferably be correlated to the type of heating device used in the laundry washing machine.

[0119] More preferably, the threshold value TV may be correlated to the power dissipation of the resistor 20. The following table exemplary shows a correlation between the threshold value TV and power dissipation of the resistor 20, wherein the quantity of water Qw introduced into the washing tub 3 during the wetting phase is a known value and equal to 10 litres:

Table 2

Power of the resistor (Watt)	Threshold value TV (°C/s)
1000	3
1750	4
1950	6

[0120] In further preferred embodiments, the threshold value TV is preferably correlated to both the quantity of water Qw introduced into the washing tub 3 and the type of heating device.

[0121] The following table exemplary shows a correlation between the threshold value TV, the quantity of water Qw introduced into the washing tub 3 during the wetting phase and the power dissipation of the resistor 20:

Table 3

Threshold value TV (°C/s)		Power of the resistor (Watt)
		1000	1750	1950
Quantity of water Qw (litre)	10	3	4	6
	14	2	4	5
	20	2	3	4

[0122] As said above, the situation shown in FIG 3 corresponds to a normal functioning condition of the washing cycle, i.e. substantially without formation of foam in the washing tub 3. The washing cycle after the main washing phase (t1÷t4) normally proceeds with the remaining phases of the cycle, i.e. rinsing phases, balancing phases, spinning phases etc. (not illustrated in FIG 3). Therefore, no foam-reducing action is taken for the washing cycle.

[0123] FIG 4 illustrates a second situation according to the preferred embodiment of the present invention.

[0124] The second situation corresponds to an undesired functioning condition of the washing cycle, i.e. with formation of foam in the washing tub 3 during the wetting phase.

[0125] The time slot between t = 0 s and t = 4500 s of the washing cycle is shown in FIG 4. This time slot corresponds to initial phases of the washing cycle, in particular a wetting phase (t0÷t1) and a main washing phase (t1÷t4).

[0126] During the wetting phase, between t=0 s and t1≅1800 s, a quantity of water Qw and a quantity of detergent Qd are introduced into the washing tub 3, preferably by means of the water inlet circuit 5 and the products supply unit 6. During the wetting phase, water and detergent are introduced into the washing tub 3 to form the washing liquid for washing the laundry.

[0127] During the wetting phase the washing drum 4 is advantageously rotated with a preferred rhythm, for example in clockwise and/or anticlockwise direction, at a low speed (e.g. at [10-300] rpm), and advantageously with stop interval time between successive rotations.

[0128] Correspondingly, a liquid level 44 in the washing tub 3, preferably detected by the pressure sensor 19, rises from 0 mm to about 100 mm.

[0129] In FIG 4, the liquid level 44 oscillates around 100 mm due to oscillations of the liquid level 44 inside the washing tub 3 caused by washing drum rotations.

[0130] The liquid level 44 of about 100 mm in the washing tub 3 is preferably sufficient to entirely cover the heating device 20 so that it is always advantageously immersed in the liquid.

[0131] The washing liquid temperature WT in the wetting phase remains substantially constant, T1≅20°C, corresponding to the temperature of the water coming from the mains water supply E.

[0132] The second situation illustrated in FIG 4 illustrates an undesired functioning condition of the washing cycle since during the wetting phase an amount of foam is generated.

[0133] In particular, foam is formed in the washing tub 3 during the wetting phase due to rotations of the washing drum 4 which moves/agitates the washing liquid inserted in the washing tub 3.

[0134] At time t1≅1800s the main washing phase is started. The main washing phase comprises an initial heating phase. During the heating phase the heating device 20 is opportunely activated/deactivated according to a particular control methodology, as perceivable in FIG 4 from the driving signal 47 of the heating device 20. The washing drum 4 is also rotated with a preferred rhythm.

[0135] Due to the presence of foam in the washing tub 3, the washing liquid temperature WT rapidly rises starting from the initial time t1 of the heating phase. According to an advantageous aspect of the invention, the rapid rising of the washing liquid temperature WT in the heating phase is indicative of the presence of foam in the washing tub 3.

[0136] As described above, advantageously, during the heating phase the washing liquid temperature WT is monitored.

[0137] In particular, within the heating phase the temperature increasing speed TS is calculated.

[0138] In the present situation, as shown in FIG 4, the presence and/or a high amount of foam in the washing tub 3 is detected since the calculated temperature increasing speed TS is actually above the threshold value TV.

[0139] Preferably, calculation of the temperature increasing speed TS is carried out immediately at the beginning of the heating phase, i.e. at time t1, and therefore the presence and/or a high amount of foam in the washing tub 3 is substantially immediately detected.

[0140] In particular, the temperature increasing speed TS is calculated in a predetermined monitoring period Δt.

[0141] As illustrated in FIG 4A, the presence of foam has been detected during the predetermined monitoring period Δt=t1÷t3. More particularly, the temperature increasing speed TS has been calculated as the average temperature increasing speed ATS in the monitoring period Δt, i.e. ATS=(T3-T1)/(t3-t1)=(T3-T1)/Δt. Detection of the presence of foam in the washing tub 3 according to the method above described is advantageously used to take one or more foam-reducing actions.

[0142] Hereinafter, possibly foam-reducing actions that can be preferably performed are described.

[0143] 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.

[0144] 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. The main washing phase precedes successive steps of the washing cycle such as rinsing phases, balances phases, spinning phases etc..

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] Additional rinsing phases enhances dissolution of the foam and its drainage to the outside.

[0151] 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.

[0152] The introduction of additional water decreases the concentration of detergent in the washing tub 3 thus advantageously reducing the possibility of foam generation.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] FIG 5 illustrates a schematic flow chart diagram of a simplified method for operating the laundry washing machine and for detecting the foam 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).

[0157] 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 wetting 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 wetting phase, the washing drum 4 is advantageously rotated with a preferred rhythm.

[0158] At a predetermined time t1 a heating phase is started (step 140), preferably by activating the heating device 20.

[0159] From time t1 on and for a period Δt=1min the washing liquid temperature WT in the washing tub 3 is monitored, preferably by means of the temperature sensor 21.

[0160] At the end of the monitoring period Δt, the temperature increasing speed TS, or preferably the average temperature increasing speed ATS, is calculated (step 150). If the temperature increasing speed TS has a value below, or equal, to a threshold value TV (output "No" of step 160), the method normally proceeds with the main washing phase (step 170) with steps according to the washing cycle selected.

[0161] For example the heating device 20 is kept activated for more 10 min (step 172) and the washing drum 4 is rotated with a preferred rhythm (step 174).

[0162] The main washing phase (step 170) lasts for a predetermined period, for example 60min.

[0163] The washing cycle then 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.

[0164] The washing cycle terminates with a final spinning phase (step 200).

[0165] Once the washing cycle has been completed, in case of a laundry washing-drying machine, a drying phase may be also preferably performed.

[0166] Going back to step 160, if the temperature increasing speed TS, or the average temperature increasing speed ATS, has a value above the threshold value TV (output "Yes" of step 160), the main washing phase is modified, through a preferred foam-reducing action.

[0167] For example the heating device 20 is de-activated and the washing drum 4 is not rotated anymore (step 176) for a predetermined time, for example 10 min.

[0168] Then advantageously the method proceeds with two successive rinsing cycles (steps 177 and 178) during which clean rinse water is added to the laundry and liquid is drained from the washing tub 3 to the outside.

[0169] The washing cycle then advantageously proceeds with said one or more rinsing cycles (steps 180 and 190) and the final spinning phase (step 200).

[0170] Figure 6 shows a construction variant of the laundry washing machine 200 where the method according to the invention is advantageously performed. Corresponding characteristics and/or components of the laundry washing machine 1 of Figure 2 are identified by the same reference numbers.

[0171] The laundry washing machine 200 comprises a water outlet circuit 215 provided with a recirculation circuit 216 adapted to drain the liquid from the bottom of the washing tub 3, and to re-admit such liquid into an another part of the washing tub 3, preferably into an upper region of the washing tub 3. The recirculation circuit 216 comprises a recirculation pump 217 and a recirculation pipe 61. The recirculation pipe 61 ends with a terminal nozzle 61a in the upper region of the washing tub 3.

[0172] The drain pump 16 and the recirculation pump 217 are preferably arranged downstream of a common filter 218.

[0173] The drain pump 16 and the recirculation pump 217 are properly controlled by the control unit 22 in order to allow drainage towards the outside through the outlet duct 18 and/or towards the washing tub 3 through the recirculation pipe 61. Functioning of this laundry washing machine 200 and detection of foam are advantageously carried out as above described for the first embodiment.

[0174] Also foam-reducing actions previously described may be advantageously performed in this laundry washing machine 200.

[0175] A further foam-reducing action that can be performed after detection of foam in the washing tub 3 in this laundry washing machine 200 preferably comprises the variation/reduction of the activation time of the recirculation pump 217 with respect to the expected activation time for the selected cycle. This enhances a more rapid dissolution of the foam.

[0176] Advantageously, the method according to the invention allows the detection of foam at an early stage of the washing cycle, preferably just after the wetting phase.

[0177] 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.

[0178] Furthermore, detection of foam is advantageously carried out by means of a temperature 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.

[0179] 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.

[0180] 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.

[0181] Advantageously, the method according to the invention reduces or avoids overflow and liquid spillage from the washing tub.

[0182] 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.

[0183] It is underlined that the laundry washing machines illustrated in the enclosed figures, and with reference to which some embodiments of the method according to the invention have been described, are 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.

[0184] Although in the illustrative embodiments of the present invention the method has been applied referring to the heating phase which follows the wetting phase substantially at the beginning of the washing cycle, it is to be understood that the present invention is not limited to those precise embodiments and that the method can be applied to any heating phase within a washing cycle.

[0185] 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

1. A method for operating a laundry washing machine (1; 200) during a washing cycle, said laundry washing machine comprising a washing tub (3) containing a washing drum (4) and a heating device (20) for heating liquid in said washing tub (3), wherein said method comprises the steps of:

- introducing a quantity of water and a quantity of detergent in the washing tub (3) to form a washing liquid;

- heating said washing liquid;

- detecting the washing liquid temperature (WT) in the washing tub (3) and/or in the draining region thereof;

- determining the temperature increasing speed (TS);

- comparing the determined temperature increasing speed (TS) with a threshold value (TV) and if the determined temperature increasing speed (TS) is above said threshold value (TV) establishing the presence of foam.

2. The method according to claim 1, wherein said washing liquid temperature (WT) is detected in a predetermined monitoring period (Δt).

3. The method according to claim 2, wherein said predetermined monitoring period (Δt) is between 20s and 30 min, preferably 1 min.

4. The method according to claim 2 or 3, wherein said predetermined monitoring period (Δt) is placed within said heating step.

5. The method according to any claims from 2 to 4, wherein said temperature increasing speed (TS) is determined in said predetermined monitoring period (Δt).

6. The method according to any of the preceding claims, wherein said threshold value (TV) is between 0,1°C/min and 10°C/min, preferably between 4°C/min and 8°C/min, more preferably equal to 7°C/min.

7. The method according to any of the preceding claims, wherein said heating step is performed after a wetting step of the washing cycle.

8. The method according to claim 7, wherein said wetting step comprises an introduction of a quantity of water (Qw) and a quantity of detergent (Qd) in said washing tub (3).

9. The method according to claim 8, wherein said threshold value (TV) is a function (f(Qw)) of said quantity of water (Qw).

10. The method according to any of the preceding claims, wherein said washing drum (4) rotates during said heating step.

11. The method according to any claims from 7 to 10, wherein said washing drum (4) rotates during said wetting step.

12. 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.

13. 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 (20) with respect to the expected activation time of the same for the main washing step of the selected cycle;

- the deactivation of the heating device (20);

- the deactivation of the heating device (20) for a predetermined time;

- 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 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.

14. The method according to claim 12 or 13, wherein said laundry washing (200) machine comprises a recirculation circuit (216) comprising a recirculation pump (217) for draining liquid from the bottom of the washing tub (3) and to re-admit such liquid into an another part of the washing tub (3) wherein said foam-reducing action comprises the step or reducing the activation time of said recirculation pump (217) with respect to the expected activation time for the selected cycle.

15. A laundry washing machine (1; 200), wherein the laundry washing machine (1; 200) is provided for the method according to any one of the claims 1 to 14.

Drawing