EP2935676A1

EP2935676A1 - Method for controlling the draining of wash liquid in a laundry washing machine, and related laundry washing machine

Info

Publication number: EP2935676A1
Application number: EP13831871.2A
Authority: EP
Inventors: Nicola Colucci; Alessio Zimar
Original assignee: Indesit Co SpA
Current assignee: Whirlpool EMEA SpA
Priority date: 2012-12-21
Filing date: 2013-12-20
Publication date: 2015-10-28
Anticipated expiration: 2033-12-20
Also published as: RU2015126088A; WO2014097251A1; EP2935676B1

Abstract

The present invention relates to a washing machine (1) as well as to a method for controlling the draining of wash liquid in a laundry washing machine (1), whereby said laundry washing machine (1) comprises a tub (2, 2b), draining means (7, 8) for draining wash liquid from said tub (2, 2b), a drum (3) adapted to contain laundry to be washed, and motor means for rotating said drum (3) and, whereby said method comprises the steps of starting (101) a first drain stage, wherein said draining means (7, 8) are activated (103), measuring (105) a flow of wash liquid drained by said draining means (7, 8), verifying (106) that said flow is lower than a predetermined alarm flow rate value (K) or higher than a predetermined alarm flow value (K) and lower than a predetermined nominal flow value (Z) and, starting (207) a second drain stage, wherein said draining means (7, 8) are activated cyclically to carry out up to a predetermined number of drain operations (C), while said flow remains lower than said predetermined alarm flow value (K) or higher than said alarm flow value (K) and lower than said nominal flow value (Z), and there is said wash liquid to be drained.

Description

METHOD FOR CONTROLLING THE DRAINING OF WASH LIQUID IN A LAUNDRY WASHING MACHINE, AND RELATED LAUNDRY WASHING MACHINE

DESCRIPTION

[FIELD OF THE INVENTION]

The present invention relates to the field of laundry washing machines. In particular, the present invention relates to a method for controlling the wash liquid drain stage in a laundry washing machine, preferably comprising a linear pressure switch.

[PRIOR ART]

In known laundry washing machines, water and detergent, i.e. wash liquid, must be supplied into the wash tub during the various laundry wash stages. Typically, this water is taken from the domestic water mains, and the intake water flow is controlled by an electrovalve. The water intake stage is called "supply stage".

At certain times it is also necessary to drain the wash liquid into a domestic drain system, typically by means of a drain pump included in the washing machine. This wash liquid outflow stage is called "drain stage".

Washing machines are known which measure the water flow entering the tub by detecting, through a linear pressure switch, the changes in the level of the wash liquid in the tub. One example of such a washing machine is described in patent application EP2413106A1 by the present Applicant.

Other washing machines are also known which control the execution of the spin and rotation stages according to the reading of the level of the wash liquid in the tub, still obtained by means of a linear pressure switch. One example of such a washing machine is described in patent application WO201 1077361 Al by the present Applicant.

However, the drain stages are not controlled in an optimal manner by the laundry washing machines known in the art. These drain stages, during which the drain pump is operated in order to remove the wash liquid from the tub, are in fact very delicate, since they might lead to problems which may range from the obstruction of domestic drain pipes external to the washing machine to a faulty operation of the washing machine's drain pump. As a matter of fact, the drain pump can be adversely affected by the presence of excessive foam or foreign or residual bodies, such as buttons, pins or lint, which might partially or totally obstruct the draining means.

Should a malfunction arise during the drain stage, wash liquid might spill outside the washing machine, thus creating much discomfort for the user.

[OBJECTS AND SUMMARY OF THE INVENTION]

It is one object of the present invention to provide a method for controlling the draining of wash liquid in a laundry washing machine, which overcomes some of the problems suffered by the prior art.

In particular, it is one object of the present invention to provide a method for controlling the draining of wash liquid in a laundry washing machine, which can more effectively deal with any problems or criticalities that might arise in the draining means.

It is another object of the present invention to provide a method for controlling the draining of wash liquid in a laundry washing machine, which ensures better control of the draining means.

Finally, it is a further object of the present invention to provide a method for controlling the draining of wash liquid in a laundry washing machine, which ensures a more efficient operation of the washing machine, with reduced energy consumption and component wear.

These and other objects of the present invention are achieved through a method for controlling the draining of wash liquid in a laundry washing machine, and a laundry washing machine thereof, incorporating the features set out in the appended claims, which are intended to be an integral part of the present description.

A general idea at the basis of the present invention is to provide a method for controlling the draining of wash liquid in a laundry washing machine, which comprises a tub, draining means for draining wash liquid from the tub, a drum adapted to contain laundry to be washed, and motor means for rotating the drum. According to the method, the following is carried out: starting a first drain stage, wherein the draining means are activated; measuring a flow of wash liquid drained by the draining means; verifying that said flow is higher than a predetermined alarm flow value and lower than a predetermined nominal flow value; starting a second drain stage, wherein the draining means are activated cyclically to carry out up to a predetermined number of drain operations, while said flow remains higher than said alarm flow value and lower than said nominal flow value, and there is said wash liquid to be drained. This solution allows to overcome the drawbacks of the prior art; in fact, it allows to effectively deal with situations in which the liquid is not drained correctly, thereby preventing further problems from arising in the drain system. For example, this solution prevents the onset of complications in the washing machine by providing for a non- continuous drain operation, during which the draining means have less probability of suffering damage. Furthermore, for example, this solution allows to cope with drain problems involving components external to the washing machine, such as, for example, clogged domestic drain pipes: this, in fact, gives domestic drain systems more opportunities to perform the drain operation, without any forcing that might cause liquid spillage.

Moreover, the method preferably provides, after the predetermined number of drain operations have been carried out, for activating the motor means in order to carry out at least one spin stage. Preferably, the spin stage comprises a rotation of the drum at a revolution speed comprised between 200 and 280 revolutions per minute, and the rotation means are activated in such a way as to reach the revolution speed, starting from a standstill, in at least 10 seconds, preferably according to an increasing speed ramp. These measures allow to deal with non-optimal drain situations by sending controlled pressure waves, caused by the spin, that could clear the drain, advantageously removing the obstruction and restoring the optimal drain conditions.

A further general idea at the basis of the present invention is to provide a method for controlling the draining of wash liquid in a laundry washing machine comprising a tub and draining means for draining wash liquid from the tub; according to the method, the following is carried out: starting a first drain stage by activating the draining means; measuring a flow of wash liquid drained by the draining means; verifying that the flow is lower than a predetermined alarm flow value; starting a second drain stage, wherein the draining means are activated cyclically to carry out a predetermined number of drain operations, while the flow remains lower than the alarm flow value and there is wash liquid to be drained.

Also this solution allows to overcome the drawbacks of the prior art; in fact, it allows to effectively deal with situations in which the liquid is not drained correctly, thereby preventing further problems from arising in the drain system. For example, this solution prevents the onset of complications in the washing machine by providing for a non- W 201

4

continuous drain operation, during which the draining means have less probability of suffering damage. Furthermore, for example, this solution allows to cope with drain problems involving components external to the washing machine, such as, for example, clogged domestic drain pipes: this, in fact, gives domestic drain systems more opportunities to perform the drain operation, without any forcing that might cause liquid spillage.

In general, these solutions enhance the control of the washing machine, allowing it to operate more efficiently, since the draining means are less stressed and only use energy when it can effectively be exploited for draining wash liquid.

Advantageously, the method can be implemented in a commercial laundry washing machine, which will need no additional sensors, since the method will use elements typically already present in the machine, although controlled by an improved control logic. Thus, the production costs of the washing machine and of the devices associated therewith will not increase.

Further objects and advantages of the present invention will become more apparent from the following detailed description and from the dependent claims, which are an integral part of the present description and which define particular advantageous aspects of the present invention.

[BRIEF DESCRIPTION OF THE DRAWINGS]

Some preferred and advantageous embodiments of the present invention will now be described by way of non-limiting example with reference to the annexed drawings, wherein:

Figure 1 shows an example of embodiment of a laundry washing machine according to the present invention.

- Figure 2 shows a flow chart that exemplifies a method for controlling the draining of wash liquid in a laundry washing machine according to the present invention.

Figure 3 shows a flow chart that exemplifies a further method for controlling the draining of wash liquid in a laundry washing machine according to the present invention.

The above-mentioned drawings show different aspects and embodiments of the .present invention and, where appropriate, similar structures, components, materials and/or W

elements in the various drawings are designated by the same reference numerals.

[DETAILED DESCRIPTION OF THE INVENTION]

Figure 1 diagrammatically shows one example of embodiment of a washing machine 1 according to the present invention. The term "washing machine" refers herein to any machine capable of performing at least one wash treatment on textile items, e.g. washing and/or washing/drying machines.

The washing machine 1 comprises a wash tub 2 in which there is a drum 3 adapted to contain laundry to be washed. The drum 3 is rotated about the axis 4 by the torque transmitted by an electric motor (not shown).

During the wash step, when the drum 3 is rotating, the laundry items contained therein are stirred and, through holes in the drum 3 (not shown), they come into contact with the wash liquid collected in the tub 2; the laundry contained in the drum is thus imbibed and washed.

The wash liquid typically comprises water and a mixture of detergents; the water intake is controlled by an electro valve 5 that lets in water coming from the domestic water mains; this water is typically mixed with a detergent inside a hopper 6 before entering into the tub 2. Since said water represents the prevailing fraction of the wash liquid, in the present description the generic term "water" will be used to indicate both the liquid taken in from the outside through the domestic water mains and the wash liquid contained in the tub, mainly consisting of water.

Once the laundry wash stage has been completed, a drain stage is carried out wherein the water is carried by the drain duct 7 to the drain pump 8 and is then expelled from the washing machine 1.

During the water supply and drain stages, the wash liquid stays in the lower portion 2b of the tub 2, typically under the level 2c of the surface of the drum 3, where the laundry items to be washed are located. The level 2c is predetermined, and is preferably tangential to the outer surface of the drum 3.

The level of the wash liquid accumulated in the portion 2b is detected by a sensor, e.g. a linear pressure switch 9 communicating with the lower portion 2b of the tub 2 via the duct 10. The pressure switch 9 can detect the pressure generated by the water column accumulated in the portion 2b, and can therefore determine the height thereof with good accuracy. The washing machine 1 also comprises additional elements and devices, such as, for example, a drum access door, a detergent compartment or the like, which are neither shown in the drawing nor described herein because they are per se known. It should therefore be assumed that a washing machine according to the present invention may comprise all such devices not shown in the drawings as well as other devices, which are considered to be prior art.

The sensor 9 is also connected to a control unit 1 1 , which comprises a microcontroller capable of receiving information from the linear pressure switch 9. In order to reduce the number of apparatuses included in the washing machine, this control unit 1 1 may additionally comprise, for example, a memory area containing, among other things, the laundry treatment operating programs, and may be adapted to control the general operation of the washing machine as well as the proper succession of the various laundry treatment stages. The microcontroller of the control unit 1 1 is of a type also implementing a timer functionality, and can therefore take measurements by means of the linear pressure switch, at time intervals, with good accuracy.

The washing machine 1 is therefore adapted to implement the method of the present invention for controlling the draining of the wash liquid, as described below.

In particular, the linear pressure switch 9 that measures the level of the water contained in the portion 2b of the tub is further exploited to measure the drained wash liquid flow. During the water supply and drain stages, in fact, the level of the liquid in the portion 2b rises or falls at a speed that depends on the flow of water being respectively supplied or drained. As water is supplied into or drained from the tub portion 2b, the level of the water (which varies over time) is measured by the pressure switch 9.

The water flow is typically expressed as a volume per time unit, e.g. litres per minute [1/min].

According to one embodiment of the present invention, the linear pressure switch 9 measures, at a first time instant, a first level of the water contained in the portion 2b. The linear pressure switch 9 then signals to the control unit 11 the reaching of this first water level, and the control unit 11 records the first time instant at which this has occurred. Subsequently, the level of the water in the portion 2b will rise or fall, and the linear pressure switch 9 will measure, at a second time instant, a second water level. Again, the linear pressure switch 9 will signal to the control unit 1 1 the reaching of this second water level, and the control unit 1 1 will record the second time instant at which this has occurred.

The control unit 1 1 can therefore measure the time elapsed between the first-level and second-level measurements. The volume of water supplied or drained between these two time instants can thus be calculated from the difference between the initial and final water volumes present in the tub portion 2b; such volumes are known from the design specifications of the shape of the tub 2.

The water flow is calculated by dividing the volume of water supplied or drained between the first level and the second level by the time elapsed between the two readings.

In other words, the shape of the tub 2 being known, one can find the correspondence between the readings of the linear pressure switch 9 at successive instants and the volume of water supplied into or drained from the tub within the same time interval, thereby computing the water flow, in particular the drained wash liquid flow.

It is also conceivable that the drained water flow can be calculated by means of other systems known in the art, such as, for example, known flow sensors.

In fact, the method provides for measuring the flow of wash liquid being currently drained in order to control the drain stage, as will be described in detail hereafter.

Figure 2 is a flow chart that exemplifies one embodiment of a method for controlling the draining of wash liquid in a laundry washing machine. Said method is preferably implemented, in the washing machine 1, through suitable control means, such as the control unit 1 1 , which is operationally connected to further devices of the washing machine 1 , in order to implement the method described below.

As soon as the washing machine 1 completes a wash and/or spin stage, the start 101 of a wash liquid drain stage is signalled.

The level of the liquid accumulated in the tub 2, the revolution speed of the drum 3 and the status of the electrovalve 5 are then checked.

If the level exceeds the "empty" condition (preferably when there is only residual steam in the duct 2b), the drum 3 is not moving, and the electrovalve is not open, the draining means will be activated 103.

Otherwise, if the wash liquid level is "empty", or the drum 3 is moving, or the electrovalve is open, the drain stage will be stopped 104 and may then be resumed at a later time.

As already described, by activating 103 the draining means, or, preferably, by activating the pump 8 that removes the water from the duct 7, the wash liquid is drained.

Preferably, the draining means are activated 103 for a predetermined time, preferably 10 seconds. At the same time, the liquid level in the portion 2b of the tub 2 is monitored to verify that it is above the "empty" level.

At the end of the predetermined duration, a measurement 105 is taken of the wash liquid flow currently being drained by the draining means. Said measurement is preferably conducted by means of a plurality of readings taken by the pressure switch 9 and is calculated in a differential manner, as previously described. Preferably, the frequency of the readings taken by the linear pressure switch 9 may be as high as one reading per second.

If the liquid level is "empty", then the drain stage 104 will be stopped.

Otherwise, a verification 106 of the flow measured at step 105 will be carried out.

If the measured flow, i.e. the flow of wash liquid currently being drained by the draining means, exceeds a predetermined value "Z", called "nominal flow", it will be considered that the liquid drain is going on according to the design specifications with no problem. Therefore, the process will go back to the check 102, so that the drain operation can be continued in the event that in the tub there is still some liquid to be drained. The nominal flow Z is preferably at least 3.0 1/min, more preferably between 4.0 1/min and 6.0 1/min; however, the operation of the drain punip may be such as to allow reaching values of 14 1/min to 17 1/min. At any rate, the nominal flow value Z is preferably lower than the maximum flow obtainable by the drain pump, and only represents an indication of a flow corresponding to a "regular" operation of the washing machine's drain system. Another flow value taken as a reference is the predetermined value "K", called "alarm flow". Said alarm flow value K is preferably equal to or smaller than 2.5 1/min, more preferably equal to or smaller than 1.5 1/min. Under said alarm flow value K, the draining means are considered to be in alarm conditions, because the wash liquid is not being completely drained or is taking place at an alarmingly reduced speed. (Of course, it is conceivable to provide that the washing machine will behave in a particular manner in the event that the measured flow is lower than the alarm flow K).

According to the present invention, it is conceivable that the washing machine will adopt an appropriate behaviour when the measured flow is comprised between the alarm flow K and the nominal flow Z; these conditions correspond to a partially clogged drain, i.e. the draining operation is clearly difficult, but not alarming. Such difficulty may be due, for example, to a partial obstruction of the drain duct 7, also due to excessive foam or foreign bodies or sedimented residues, or even to partial clogging of the domestic drain system.

If the flow is higher than the alarm flow K but lower than the nominal flow Z, it must be assumed that the drain is affected by particular problems.

In such a case, a different drain stage 207 will be activated to cope with the drain difficulty.

In particular, the drain pump 8 is activated for a predetermined number "C" of drain operations, preferably according to a suitable "duty cycle". Preferably, the predetermined number C of drain operations is 5.

In particular, the drain pump 8 is preferably turned on for a minute and is then kept off for a wait time preferably lasting one minute. Other activation and/or wait times are also possible, preferably longer than 30 seconds but shorter than 90 seconds.

In this way, a sufficiently short cyclic activation of the drain pump 8 can allow the pressure waves thus generated to contribute to clearing the drain portion 7.

In the event that, following one or more drain operations thus carried out, the liquid level becomes "empty", the drain stage will end 104.

Preferably, a measurement 208 is taken of the flow currently drained after each drain operation, or at least after one of them. Said measurement can preferably be taken as previously described.

If the level is higher than "empty" and the draining must continue, the method provides for verifying 106 again the flow measured at step 208. In fact, it may happen that the problematic drain condition has cleared up spontaneously as described above, and the drained flow has returned above the nominal value Z again; in such a case, the problem is solved and the first drain stage, previously interrupted, can be continued by going back to step 102.

If, on the contrary, it is verified that the drained liquid flow is still lower than the nominal value Z, but higher than the alarm value K, the above-described steps 207 and 208 are carried out again. If at step 208 it is verified that the predetermined number C of drain operations have already been carried out, it must be assumed that the problem is a persistent one.

Therefore, the C drain operations are executed and, if in the tub 2 there is still any wash liquid to be drained, a spin stage 209 is carried out.

Preferably, the spin stage 209 is not a common spin stage, since it is less intense.

Preferably, the spin stage 209 comprises a rotation of the drum at a revolution speed comprised between 200 and 280 revolutions per minute, as opposed to a typical value of 350 revolutions per minute of an ordinary spin stage. In other words, it is preferable that the spin stage 209 takes place at a drum revolution speed between 60% and 80% of the typical revolution speed (100%) used in the normal spin stage, depending on the specific characteristics of the washing machine.

Furthermore, the drum rotation means are preferably activated in a more gradual manner in order to reach the revolution speed, from a standstill, in at least 10 seconds, preferably according to an increasing speed ramp, preferably a linear one.

Such measures and, in general, the spin stage 209 allow to cope with non-optimal drain conditions and to send controlled pressure waves, generated by the spin 209, in order to try to clear the obstruction in the drain, e.g. by removing any foreign bodies or obstructions, such as accumulated lint. In this manner, after the spin stage 209 the drain system may turn out to be unobstructed, and optimal drain conditions may be restored. Following the spin stage 209, the method provides for resuming the drain stage from the above-described step 102.

The spin stage 209 is only carried out after an adequate number of drain attempts, preferably 5. Moreover, such attempts after which the spin stage 209 is carried out do not excessively stress the draining means, thereby advantageously preventing the washing machine from suffering any further damage.

Figure 3 shows a flow chart that exemplifies a further embodiment of a method for controlling the draining of wash liquid in a laundry washing machine. Said method is preferably implemented, in the washing machine 1, through suitable control means, such as the control unit 1 1 , which is operationally connected to further devices of the washing machine 1 , in order to implement the method described below.

As soon as the washing machine 1 completes a wash and/or spin stage, the start 101 of a wash liquid drain stage is signalled. The level of the liquid accumulated in the tub 2, the revolution speed of the drum 3 and the status of the electrovalve 5 are then checked.

If the liquid level is "empty", then the drain stage 104 will be stopped.

If the measured flow, i.e. the flow of wash liquid currently being drained by the draining means, exceeds a predetermined value "Z", called "nominal flow", it will be considered that the liquid drain is going on according to the design specifications with no problem. Therefore, the process will go back to the check 102, so that the drain operation can be continued in the event that in the tub there is still some liquid to be drained. The nominal flow Z is preferably at least 3.0 1/min; however, the operation of the drain pump may be such as to allow reaching values of 14 1/min to 17 1/min. At any rate, the nominal flow value Z is preferably lower than the maximum flow obtainable by the drain pump, and only represents an indication of a flow corresponding to a "regular" operation of the washing machine's drain system.

A different case arises when the measured flow is lower than a predetermined value "K", called "alarm flow". Said alarm flow value K is preferably equal to or smaller than 2.5 1/min, more preferably equal to or smaller than 1.5 1/min.

(Of course, the washing machine may also take on a different behaviour when the measured flow is comprised between the alarm flow K and the nominal flow Z.)

If the flow is lower than the alarm flow K, it must be assumed that the drain system is being affected by problems. Such problems may relate to factors which are external or internal to the washing machine, e.g. problems in the domestic drain system or a clogged portion 7 of the draining means, respectively.

In such a case, a different drain stage 107 will be activated to cope with the drain difficulty.

In particular, the drain pump 8 is activated cyclically for a predetermined number "D" of drain operations, preferably according to a suitable "duty cycle". Preferably, the predetermined number D of drain operations is 10.

In particular, the drain pump 8 is preferably turned on for two minutes and is then kept off for a wait time preferably lasting two minutes. Other activation and/or wait times are also possible, preferably longer than 30 seconds or, more preferably longer than 60 seconds.

Preferably, a measurement 108 is taken of the flow currently drained after each drain operation, or at least after one of them. Said measurement can preferably be taken as previously described.

If the level is higher than "empty" and the draining must continue, the method provides for verifying 106 the flow measured at step 108. In fact, it may happen that the problematic drain condition has cleared up spontaneously as described above, and the drained flow has returned above the nominal value Z again; in such a case, the problem is solved and the first drain stage, previously interrupted, can be continued by going back to step 102.

If, on the contrary, it is verified that the drained liquid flow is still lower than the alarm value K, the above-described steps 107 and 108 are carried out again.

If at step 108 it is verified that the predetermined number D of drain operations have already been carried out, it must be assumed that the problem cannot be solved spontaneously.

It is therefore provided, once the D drain operations have been completed - if in the tub 2 there is still any wash liquid that cannot be drained at the moment - that a malfunction is signalled 109 and the draining of the wash liquid is stopped. In such conditions, a visual and/or acoustic signal is sent to the user, so that the latter can notice the alarm situation and take appropriate actions to find a remedy.

Said malfunction signal 109 is only provided after an adequate number of draining attempts, preferably 10, have been carried out without solving the problem.

Moreover, such attempts after which said malfunction signal 109 is issued do not excessively stress the draining means, thereby advantageously preventing the washing machine from suffering any further damage.

It is apparent that many changes may be made to the present invention by those skilled in the art without departing from the protection scope thereof as stated in the appended claims.

By adopting suitable technical measures, the present invention is also applicable to different types of washing machines, such as dishwashers.

Claims

1. A method for controlling the draining of wash liquid in a laundry washing machine (1), said laundry washing machine (1) comprising a tub (2, 2b), draining means (7, 8) for draining wash liquid from said tub (2, 2b), a drum (3) adapted to contain laundry to be washed, and motor means for rotating said drum, said method comprising the steps of:

starting (101) a first drain stage, wherein said draining means (7, 8) are activated (103); measuring (105) a flow of wash liquid drained by said draining means (7, 8);

verifying (106) that said flow is higher than a predetermined alarm flow value (K) and lower than a predetermined nominal flow value (Z);

starting (207) a second drain stage, wherein said draining means (7, 8) are activated cyclically to carry out up to a predetermined number of drain operations (C), while said flow remains higher than said alarm flow value (K) and lower than said nominal flow value (Z) and there is said wash liquid to be drained.

2. A method according to claim 1 , further comprising the step of: activating said motor means, after said predetermined number of drain operations (C) have been carried out, in order to execute at least one spin stage (209).

3. A method according to claim 2, wherein said spin stage (209) comprises a rotation of said drum (3) at a revolution speed preferably comprised between 200 and 280 revolutions per minute, wherein during said spin stage (209) said motor means are activated in such a way as to reach said revolution speed, starting from standstill, preferably in at least 10 seconds.

4. A method according to any one of claims 1 to 3, further comprising the step of: measuring (208) at least one second flow of wash liquid drained by said draining means (7, 8) after at least one of said drain operations.

5. A method according to claim 4, further comprising the step of: starting a drain stage different from said second drain stage in the event that, following one of said drain operations, said measured second flow is lower than said alarm flow value (K) or higher than said nominal flow (Z).

6. A method according to any one of claims 1 to 5, wherein each one of said drain operations comprises a stage of activation of said draining means (7, 8), wherein said activation stage preferably lasts longer than 30 seconds and less than 90 seconds, and 15

comprises a wait stage during which said draining means (7, 8) are not active, said wait stage preferably lasting longer than 30 seconds and less than 90 seconds.

7. A method according to any one of claims 1 to 6, wherein said liquid flow is measured (105, 208) through a plurality of pressure readings taken by a linear pressure switch (9) within at least one time interval.

8. A method according to claim 7, wherein said liquid flow is measured by differentially calculating a ratio between a water volume estimated on the basis of said pressure readings and said at least one time interval.

9. A method according to any one of claims 1 to 8, wherein said alarm flow value (K) is smaller than 2.5 1/min, more preferably smaller than 1.5 1/min, and wherein said nominal flow value (Z) is greater than 3.0 1/min, more preferably between 4.0 1/min and 6.0 1/min.

10. A laundry washing machine (1) comprising a tub (2, 2b) adapted to contain a wash liquid, draining means (7, 8) for draining said wash liquid from said tub (2, 2b), a drum (3) adapted to contain laundry to be washed, motor means for rotating said drum, sensing means (9, 10) adapted to measure a flow of said drained wash liquid, and a control unit (11) operationally connected to said draining means (7, 8) and to said sensing means (9, 10), characterized in that it is adapted to implement the method for controlling the draining according to any one of claims 1 to 9.

1 1. A method for controlling the draining of wash liquid in a laundry washing machine (1), said laundry washing machine (1) comprising a tub (2, 2b) and draining means (7, 8) for draining wash liquid from said tub (2, 2b), said method comprising the steps of: starting (101) a first drain stage, wherein said draining means (7, 8) are activated (103); measuring (105) a flow of wash liquid drained by said draining means (7, 8);

verifying (106) that said flow is lower than a predetermined alarm flow value (K);

starting (107) a second drain stage, wherein said draining means (7, 8) are activated cyclically to carry out up to a predetermined number of drain operations (D), while said flow remains lower than said alarm flow value (K) and there is said wash liquid to be drained.

12. A method according to claim 11, further comprising the step of: measuring (108) at least one second flow of wash liquid drained by said draining means (7, 8) after at least one of said drain operations.

13. A method according to claim 12, further comprising the step of: starting a drain stage different from said second drain stage in the event that, following one of said drain operations, said measured second flow is higher than said alarm flow value (K).

14. A method according to any one of claims 11 to 13, wherein each one of said drain operations comprises a stage of activation of said draining means (7, 8), wherein said activation stage preferably lasts longer than 30 seconds, more preferably longer than 60 seconds, and comprises a wait stage during which said draining means (7, 8) are not active, said wait stage preferably lasting longer than 30 seconds, more preferably longer than 60 seconds.

15. A method according to any one of claims 1 1 to 14, wherein said liquid flow is measured- (105, 108) through a plurality of pressure readings taken by a linear pressure switch (9) within at least one time interval.

16. A method according to claim 15, wherein said liquid flow is measured by differentially calculating a ratio between a water volume estimated on the basis of said pressure readings and said at least one time interval.

17. A method according to any one of claims 1 1 to 16, wherein said draining means (7, 8) comprise at least one hydraulic pump (8).

18. A method according to any one of claims 1 1 to 17, further comprising the step of: signalling a malfunction (109) after said predetermined number of drain operations have been carried out, in the event that there is still any residual wash liquid to be drained.

19. A method according to any one of claims 1 1 to 18, wherein said alarm flow value (K) is smaller than 2.5 1/min, more preferably smaller than 1.5 1/min.

20. A laundry washing machine (1) comprising a tub (2, 2b) adapted to contain a wash liquid, draining means (7, 8) for draining said wash liquid from said tub (2, 2b), sensing means (9, 10) adapted to measure a flow of said drained wash liquid, and a control unit (11) operationally connected to said draining means (7, 8) and to said sensing means (9, 10), characterized in that it is adapted to implement the method for controlling the draining according to any one of claims 1 1 to 19.