DESCRIPTION

The present invention refers to a method for controlling a washing machine, for example a laundry washing machine or a dishwasher, and a washing machine configured for implementing the method.

Nowadays washing machines, for example laundry washing machines and dishwashers, comprise a washing tub wherein items to be washed can be loaded via an access opening closable by a door or porthole.

In particular, in known laundry washing machines the items to be washed (i.e. the laundry) are loaded within a rotating drum contained within the washing tub, and in known dishwasher items to be washed (i.e. crockery or tableware) are typically loaded within racks removably mounted within the washing tub. Known washing machines typically comprise a plurality of electric loads (user interface (s), pump(s), valve (s), electric motor (s), etc.), and an electronic control unit configured for controlling such electric loads, in particular during the washing cycles.

In known washing machines, water is admitted in the tub by a water supply circuit connected to water delivery mains present outside the machine; before or after entering the tub, water can be mixed with a washing and/or rinsing additive and/or it can be heated to a desired temperature.

Typically, the water supply circuit comprises one or more electro-valves controlled by the control unit for selectively regulating the admission of water from the water delivery means.

After a washing cycle, the washing liquid, i.e. water, or water mixed with washing/rinsing additive (s), is discharged from the tub by a discharge circuit, typically comprising a drain pump, controlled by the control unit.

Nowadays, in order to reduce electric power consumption, most of known washing machines are configured in such a way that, after a washing cycle, and/or when they are not operated for a certain time, they are automatically taken in a "stand-by" condition, i.e. a condition in which all, or most of, their electric loads are not supplied with electric power.

In fact, it is known that many electric loads, when electrically powered (i.e. when electrically connected to an electric power supply), absorb electric power even when they are not operating, and therefore the only way to completely nullify their electric energy absorption is temporarily cutting off their power supply (i.e. disconnecting them from the electric power supply).

In known washing machines, sometimes the electro-valve(s) of the water supply circuit can start to leak, and therefore water coming from the water delivery mains present outside the machine can enter the washing tub and accumulate in the bottom of the latter. If the washing machine is used frequently, it is possible that the user does not notice the leak, since nowadays many washing cycles start with the drain of possible residual liquid from the bottom of the washing tub.

In addition, in most of known washing machines, during the washing cycle the liquid level within the tub is monitored by a level detection device, and the control unit is typically configured for generating an alert message (e.g. a specific sound), and/or to interrupt the washing cycle in case the water level within the tub is higher than expected, as it can happen in case of leakage of the electro-valve(s).

Anyway, this control of the liquid level is active at most during the washing cycles, and not, for example, when the washing machine is in above mentioned stand-by condition.

In known washing machine there is therefore the problem that, while the washing machine is in the stand-by condition, it is very difficult that the user can notice the leak, and therefore the water level within the tub can raise until overflowing outside the washing machine, for example via the opening for loading the items to be washed in the washing tub (if the door or porthole of the machine is opened), and/or via other openings connecting the internal of the washing tub to the external environment (e.g. the air-gap provided in the washing machines for preventing that a liquid can flow back from the washing tub to the water delivery mains to which the washing machine is fluidly connected).

The aim of the present invention is therefore to provide a solution for avoiding that liquid could overflow from the tub of a washing machine, for example a laundry washing machine, a washer drier, a dishwasher, while the washing machine is in a stand-by condition in which at least some of its electrical loads are not supplied with electric power.

Applicant has found that by activating a liquid level detector of a washing machine while the latter is in a stand-by condition, it is possible detecting an anomalous increase of the liquid level within the washing tub also during such a stand-by condition and, consequently, activating a drain pump and/or generating an alert, so as to reduce the risk that the liquid could overflow from the washing machine.

In particular, above aim is solved by a method for operating a washing machine comprising a washing tub, one or more electro valves through which a liquid is admitted into the washing tub, a liquid level detector configured for detecting a quantity indicative of the liquid level within the washing tub, a drain pump configured for draining liquid from the washing tub, a plurality of further electric loads, a control unit configured for controlling the one or more electro valves, the liquid level detector, the drain pump, and the plurality of further electric loads, wherein the method comprises taking the washing machine in a stand-by condition in which the one or more electro valves and one or more of the plurality of further electric loads are disconnected from electric power supply, wherein the method comprises the following steps:

- while the washing machine is in the stand-by condition, supplying electric power to the liquid level detector for at least a first switch-on time interval;

- during the first switch-on time interval, detecting by the liquid level detector a first value of a quantity indicative of the liquid level within the washing tub;

- activating the drain pump for draining liquid from the washing tub and/or generating an alert, if the first value meets a first prefixed condition.

In a preferred embodiment, the first prefixed condition for the first value comprises reaching or exceeding a prefixed first threshold value.

In a preferred embodiment, the first switch-on time interval is comprised between 5 and 15 seconds.

More preferably the first switch-on time interval is 10 seconds.

In an advantageous embodiment, the method comprises, while the washing machine is in the stand-by condition, and after the phase of supplying electric power to the liquid level detector for at least a first switch-on time interval, the following phase:

- disconnecting the liquid level detector from electric power supply for a first switch-off time interval.

Preferably, the first switch-off time interval is comprised between 50 and 70 seconds.

More preferably, the first switch-off time interval is 60 seconds.

In an advantageous embodiment, the method comprises: - detecting or estimating a starting value of a quantity indicative of the liquid level within the washing tub at the beginning of the stand-by condition,

- comparing the first value to the starting value,

- activating the drain pump if the difference between the first value and the starting value reaches or exceeds a prefixed second threshold value.

In a further advantageous embodiment, the method comprises, while the washing machine is in the stand-by condition, and after the phase of supplying electric power to the liquid level detector for at least a first switch-on time interval, the following phases:

- while the washing machine is in the stand-by condition, supplying electric power to the liquid level detector for a second switch-on time interval,

- during the second switch-on time interval, detecting by the liquid level detector a second value of a quantity indicative of the liquid level within the washing tub,

- comparing the second value to the first value,

- activating the drain pump and/or generating an alert if the difference between the second value and said first value reaches or exceeds a prefixed third threshold value. Preferably, the phase of disconnecting the liquid level detector from electric power supply for a first switch-off time interval is performed between the phase of supplying electric power to the liquid level detector for a first switch-on time interval and the phase of supplying electric power to the liquid level detector for a second switch-on time interval.

Preferably, the method comprises, while the washing machine is in the stand-by condition, and after the phase of supplying electric power to the liquid level detector for a second switch-on time interval, the following phase: - disconnecting the liquid level detector from electric power supply for a second switch-off time interval.

In a preferred embodiment, the second switch-off time interval is comprised between 50 and 70 seconds.

More preferably, the second switch-off time interval is 60 seconds.

In a preferred embodiment, the phase of supplying electric power to the liquid level detector for at least a first switch-on time interval while the washing machine is in the stand-by condition, is performed after a prefixed first delay time since the washing machine has been taken in the stand-by condition, during which the liquid level detector is disconnected from electric power supply.

Preferably, the first delay time is comprised between 50 and 70 seconds.

More preferably, the first delay time is 60 seconds.

In a further advantageous embodiment, the phase of supplying electric power to the liquid level detector for at least a first switch-on time interval, is started simultaneously with taking the washing machine in the stand-by condition.

In a preferred embodiment, the phase of supplying electric power to the liquid level detector for at least a second switch-on time interval while the washing machine is in the stand-by condition, is performed after a prefixed second delay time has lapsed since when the washing machine has been taken in the stand-by condition.

In an advantageous embodiment, the plurality of further electric loads comprises a user interface, wherein when the washing machine is in the stand-by condition, the user interface is disconnected from electric power supply.

In an advantageous embodiment, while the washing machine is in the stand-by condition, once the drain pump has been activated for draining liquid from the washing tub, the drain pump is kept active until the value of a quantity indicative of the liquid level within the washing tub detected by the liquid level detector meets a second prefixed condition and/or for a prefixed activation time.

In a further advantageous embodiment, while the washing machine is in the stand-by condition, the drain pump is electrically powered for all the duration of the stand-by condition.

In a further advantageous embodiment, while the washing machine is in the stand-by condition, the drain pump is electrically powered only if the first value meets the first prefixed condition.

In a preferred embodiment, while the washing machine is in the stand-by condition, the following three phases are repeated a plurality of times in this order;

- supplying electric power to the liquid level detector for at least a first switch-on time interval;

- during the first switch-on time interval, detecting by the liquid level detector a first value of a quantity indicative of the liquid level within the washing tub;

- disconnecting the liquid level detector from electric power supply for a first switch-off time interval.

Preferably, while the washing machine is in the stand-by condition, the three phases are repeated a plurality of times at prefixed time intervals.

Preferably, while the washing machine is in the stand-by condition, during the repetition of the three phases, the drain pump is activated if the first level meets the first prefixed condition.

In an advantageous embodiment, while the washing machine is in the stand-by condition, if the first value detected by the liquid level detector meets the first prefixed condition, the liquid level detector is kept electrically powered for all the rest of the stand-by condition. In a further advantageous embodiment, the method comprises supplying electric power to the liquid level detector for the whole duration of the stand-by condition.

In a further advantageous embodiment, the washing machine comprises a door or porthole configured for selectively closing the washing tub, and a closure detection device, operatively connected to the control unit, configured for detecting if the door or porthole is opened or closed, wherein the method comprises, while the washing machine is in the stand-by condition, and before the step of activating the drain pump for draining liquid from the washing tub and/or generating an alert, if the first value meets a first prefixed condition, the following step:

- detecting by the closure detection device if the door or porthole is closed or opened, and making use of a first prefixed condition if the door or porthole is closed, and of a different first prefixed condition if the door or porthole is opened.

It is highlighted that the first prefixed condition to be used depending on the closure state of the door, can be advantageously selected, for example by the electronic control unit, between a plurality of first prefixed conditions stored in a memory device of the washing machine, preferably comprised and/or functionally associated to the control unit. In a further advantageous embodiment, the first prefixed condition to be used depending on the closure state of the door, can be advantageously set and/or calculated and/or processed, for example by the electronic control unit, depending on data indicative of the closure state of the door, and, optionally, also to other data related to the washing machine.

Advantageously, if the door or porthole is closed, the value of the prefixed first threshold is higher than the value of the first threshold if the door or porthole is opened. In a further advantageous embodiment, if the door or porthole is closed, the value of the prefixed second threshold is higher than the value of the second threshold if the door or porthole is opened.

In a still further advantageous embodiment, if the door or porthole is closed, the prefixed value of the third threshold is higher than the value of the third threshold if the door or porthole is opened.

Above aim is solved also by a washing machine comprising:

- a washing tub,

- one or more electro valves through which a liquid is admitted into the washing tub,

- a liquid level detector configured for detecting the liquid level within the washing tub,

- a drain pump configured for draining a liquid from the washing tub,

- a plurality of further electric loads,

- a control unit configured for controlling the liquid level detector, the drain pump, and the plurality of further electric loads, wherein the control unit is configured for controlling the one or more electro valves, the liquid level detector, the drain pump, and the plurality of further electric loads, in such a way to perform a method according to the invention.

Other advantages and features of a washing machine according to the present invention will be clear from the following detailed description, provided only as a not limitative example, in which:

Fig 1 is a perspective view of a washing machine, in particular a laundry washing machine, according to the invention;

Fig. 2 is a schematic frontal cross section of a washing machine, in particular a laundry washing machine, according to the invention, with some parts not illustrated; Fig. 3 is a flow chart illustrating some operations of a first embodiment of a method according to the invention;

Fig. 4 is a flow chart illustrating some operations of a second embodiment of a method according to the invention;

Fig. 5 is a flow chart illustrating some operations of a part of a further embodiment of a method according to the invention.

In the figures, same parts are indicated with the same reference numbers.

Advantageously, the washing machine 10 illustrated in the attached figures is a laundry washing machine, and in particular a laundry washing machine of the front-loading type; it is however clear that the invention can be applied, without any substantial modification, also to top-loading washing machines, both of the "horizontal axis" and of the "vertical axis" type.

In addition, the invention can be applied, without any substantial modification, also to washer-driers (i.e. laundry washing machines that, in addition to be able to wash the laundry, are also provided with a drying system for drying the laundry).

It is also clear that the invention can be applied, without any substantial modification, also to dishwashers, not illustrated.

The washing machine 10 advantageously comprises a cabinet 20, or housing, preferably substantially parallelepiped, advantageously provided with feet 22 configured to be positioned on a horizontal surface 23, for example the floor of a building.

The cabinet 20 houses a washing tub 30 wherein items to be washed (i.e. laundry in the case of a laundry washing machine or washer-drier, or crockery or tableware in the case of a dishwasher) can be loaded via an access opening, not illustrated, closable by a door or porthole 4, preferably hinged to cabinet 20.

In the advantageous embodiment in which the washing machine 10 is a laundry washing machine or washer-drier, like in the example illustrated in figures 1 and 2, the washing tub 30 can be preferably suspended to the cabinet 20 through springs and dampers, not illustrated.

In the advantageous embodiment in which the washing machine 10 is a laundry washing machine or washer-drier, like in the example illustrated in figures 1 and 2, the washing tub 30 advantageously contains a drum 40 rotatable with respect to a rotation axis, not illustrated, in which the laundry can be loaded.

In the so called "horizontal-axis" laundry washing machines, the rotation axis of the drum 40 is advantageously horizontal, or slightly inclined, while in the so called "vertical-axis" laundry washing machines the axis is vertical.

In the advantageous embodiment in which the washing machine 10 is a laundry washing machine or washer-drier, like in the example illustrated in figures 1 and 2, it comprises at least one (preferably two or more) lifter 41 (called also elevator, or rib, or diverter), adapted to improve the stirring of the laundry during the rotation of the drum 40.

In a further advantageous embodiment, not illustrated, in which the washing machine is a dishwasher, the washing tub 30 advantageously contains one or more racks, not illustrated, wherein the items to be washed can be loaded.

The washing machine 10 advantageously comprises a water inlet circuit 60, adapted to feed water, or water mixed with washing/rinsing additives, into the tub 30; the water inlet circuit 60 advantageously comprises a first pipe 61, a first end of which is preferably connected or connectable to water delivery mains, not illustrated, external to the washing machine 10, for example the water delivery mains of a building (not illustrated). A second end of the first pipe 61 is fluidly connected to one or more electro-valves 70, configured for allowing/preventing the passage of water from the first pipe 61 to a second pipe 62 fluidly connected to the internal of the washing tub 30.

In the advantageous embodiment in which the washing machine 10 is a laundry washing machine or washer-drier, like in the example illustrated in figures 1 and 2, preferably, between the one or more electro-valves 70 and the second pipe 62, there is an additive drawer 80, arranged in such a way that water coming from the first pipe 61 and passing through the one or more electro-valves 70 can mix with an additive (e.g. a detergent and/or a softener) contained in the additive drawer 80, before being admitted into the washing tub 30 via the second duct 62.

In a further advantageous embodiment, not illustrated, in which the washing machine 10 is a dishwasher, such an additive drawer 80 is preferably not provided, and water coming from the water delivery mains external to the washing machine 10 is admitted into the washing tub 30, without being mixed with an additive, passing through the first pipe 61, the one or more electro valves 80 and the second pipe 62; in this case, preferably, the washing machine 10 comprises an additive dispenser positioned, preferably, on the inner side of the door or porthole facing the internal of the washing tub 30, and configured for delivering an additive within the washing tub 30 during a washing cycle, so that such an additive mixes with the water present in the washing tub 30.

Advantageously, the washing tub 30 is fluidly connected to a drain circuit 90 configured for draining liquid from the bottom of the washing tub 30.

Advantageously, the drain circuit 90 comprises one or more draining ducts 91 and a drain pump 92, configured for withdrawing liquid from the bottom of the washing tub 30 and draining such a liquid outside the washing machine 10. Preferably, the drain circuit 90 comprises a filter 93 fluidly connected upstream the drain pump 92 for preventing foreign bodies to reach and obstruct/damage the latter.

In an advantageous embodiment, like for example the embodiment illustrated in figures 1 and 2, the washing machine 10 can comprise a check valve 94 that is arranged, preferably, at the outlet of the washing tub 30 or at the inlet of the drain circuit 90, for keeping the washing liquid within the washing tub 30 during part of the washing cycles.

For example, in an advantageous embodiment, like the one illustrated in figures 1 and 2, the check valve 94 comprises a float 95 (e.g. a hollow plastic ball) which is freely moveable or floatable within the drain circuit 90 in such a way to engage with a valve seat 96 and fluidly separating the washing tub 2 from the drain circuit 90 when the liquid level in the drain circuit 90 raises over a certain value.

The washing machine 10 can advantageously comprise a recirculation circuit, not illustrated, configured for withdrawing liquid from the washing tub 30 and re-admitting such a liquid into a different region of the washing tub 30, so as to reach more effectively all the items to be washed loaded into the latter.

The washing machine 10 comprises also a liquid level detector 100 configured for detecting a quantity indicative of the level of liquid within the washing tub 30.

It is underlined that in the present application the expression "a quantity indicative of the level of liquid within the washinq tub" means a quantity that has a specific and biunivocal relation with the level of the liquid within the washing tub 30; for example, the quantity indicative of the level of liquid within the washinq tub could be the liquid level itself (for example if the liquid level detector is an optical sensor configured for sensing directly the level of the liquid), or a quantity, for example the pressure of the liquid within the washing tub 30, which value has a biunivocal relation with (for example it is directly proportional to) the level of the liquid within the washing tub 30.

It is underlined that the level of the liquid in the washing tub 30 is advantageously defined with respect to a reference level L _ref about which the level detector 100 is set, and that can be a pre-set reference level, or, in a further advantageous embodiment, a level that can be set by the user, for example by operating on a user interface 50, if provided, that will be better described in the following.

For example, in an advantageous embodiment, like the one illustrated in figures 1 and 2, the reference level L _ref against which the level of the liquid within the washing tub 30 is measured can be the level of the valve seat 96 of the check valve 94.

In a further advantageous embodiment, not illustrated, the reference level L _ref can be, for example, the level of the lowest point of the washing tub 30, or the level of the bottom of the casing 20, or the level of a surface 23 on which the washing machine 10 is configured to be positioned; anyway, other reference levels L _ref can be used.

In a preferred embodiment, the liquid level detector 100 comprises an air chamber 101 having a liquid inlet provided at the washing tub 30 and in fluid communication with the internal of the latter; the air chamber 101 is preferably fluidly connected, more preferably by a third pipe 102, to a sensing element 103 of the liquid level detector 100.

Advantageously, the sensing element 103 can be a pressure sensor; advantageously, the sensing element 103 can comprise an electronic unit, not illustrated, configured for calculating/determining the liquid level within the washing tub 30 from the detected pressure; alternatively, or in addition, the electronic unit of the sensing element 103 can be connected to a control unit 200 of the washing machine 30, that will be better described in the following.

In an advantageous embodiment, during a washing cycle, when a washing/rinsing liquid contained in the washing tub 30 reaches a certain level at which it enters the air chamber 101, such a washing/rinsing liquid compresses the air contained in the air chamber 101, which pressure is transmitted by the third pipe 102 to the sensing element 103, for example a pressor sensor, configured for detecting the pressure in the air chamber 101. The pressure detected by the sensing element 103 is then used, directly by the sensing element 103 (e.g. if provided with an integrated electronic unit), or by an external electronic unit, e.g. the control unit 200 of the washing machine 10, that will be better described in the following, to which the sensing element 103 is connected, for calculating the level of the liquid within the washing tub 30.

Advantageously, as mentioned above, the washing machine 10 can comprise a user interface 50, comprising advantageously one or more electric or electronic input/output devices, like, for example, a display 51 (e.g. a so called "touch-screen" display), one or more knobs 52, one or more switch 53, one or more speaker, not illustrated, etc.

As mentioned above, the washing machine 10 advantageously comprises a control unit 200, for example an electronic board provided with a microcontroller, schematically illustrated in figure 2 as a rectangle, configured for controlling the one or more electro-valves 70, the liquid level detector 100, the drain pump 92, and a plurality of further electric loads of the washing machine 10.

Such a plurality of further electric loads can comprise, for example, the user interface 50, and/or an electric heater for heating the washing liquid, not illustrated, and/or an electric motor, not illustrated, and/or a speaker, not illustrated, and/or one or more further sensors, for example a turbidity sensor, a temperature sensor, etc., not illustrated. In a preferred embodiment, the control unit 200 can be advantageously configured/programmed in such a way to control the one or more electro-valves 70 depending on the washing cycle and/or on the value of a quantity indicative of the liquid level within the washing tub 30 detected by the liquid level detector 100.

The method according to the invention comprises taking the washing machine 10 in a stand-by condition in which the one or more electro-valves 70 and one or more of the plurality of further electric loads are disconnected from the electric power supply.

It is highlighted that, in the present application, in case the electric power is supplied by an alternated current, the moments in which the alternated electric power is periodically inverted (i.e. when its value is zero) are not considered as an interruption of the power supply; in the case of an alternated current, the power supply is considered disconnected if it is not supplied for at least a full period of the periodic electric power.

For example, in the stand-by condition, the electric loads that can be disconnected from the electric power supply can be the user interface 50 (if provided), and/or an electric heater (if provided), and/or a temperature sensor (if provided), and/or an electric motor (if provided), etc.

By disconnecting the electric power supply, it is guaranteed that such electric loads do not absorb electric power when they are not operating, and therefore the overall energy consumption of the washing machine 10 is reduced. Advantageously, the control unit 200 can be configured for taking the washing machine 10 in the stand-by condition automatically at the end of a washing cycle, and/or after receiving a specific command by the user, for example by the user interface 50 (if provided).

The method according to the invention comprises, while the washing machine 10 is in above mentioned stand-by condition, supplying electric power to the liquid level detector 100 for at least a first switch-on time interval tom.

The first switch-on time interval tom is preferably comprised between 5 and 15 seconds, more preferably 10 seconds.

According to the inventive method, during such a first switch- on time interval tom, a first value LI of a quantity indicative of the liquid level within the washing tub 30 is detected by the liquid level detector 100.

Then, according to the invention, if the first value LI meets a first prefixed condition, the drain pump 92 is activated for draining liquid from the washing tub 30 and/or an alert (e.g. a sound) is generated.

In a first advantageous embodiment, the drain pump 92 is electrically powered (and therefore it can be activated in order to drain the liquid from the washing tub 30) for all the duration of the stand-by condition.

In a different advantageous embodiment, in the stand-by condition the drain pump 92 is electrically powered (and therefore it can be activated in order to drain the liquid from the washing tub 30) only if the first value LI meets a first prefixed condition.

In a further advantageous embodiment, while the washing machine 10 is in the stand-by condition, once the drain pump 92 has been activated for draining liquid from the washing tub 30, it is kept active until a quantity indicative of the level of liquid within the washing tub 30 detected by the liquid level detector 100 meets a second prefixed condition (for example if the value of a quantity indicative of the level of liquid within the washing tub 30 detected by the liquid level detector 100 is below a prefixed value L _O FF) and/or for a prefixed activation time tact (for example in the range between 1-2 minutes).

In a first advantageous embodiment, the first prefixed condition for the first value LI is or comprises reaching or exceeding a prefixed first threshold value Lthri; in this first advantageous embodiment, therefore, if the liquid level within the washing tub 30 during the stand-by condition, i.e. when the one or more electro-valves 70 are not operating, is increasing over a prefixed threshold value (which increase corresponds to an increased value of the detected value LI), this could mean that the one or more electro-valves 70 are leaking, and therefore the drain pump 92 is activated for draining the liquid from the washing tub 30, so as to avoid further raise of the liquid level, and/or an alert is generated, for example a sound is emitted by a speaker, not illustrated, provided in the washing machine 10, for informing the user about the leakage.

It is highlighted that the prefixed first threshold value L _thri can be selected, for example during the design of the washing machine 10, depending on the specific dimensions and/or shape or the washing tub 30 and/or drain circuit 90, in such a way that, while the first value LI is below such first threshold value Lthri, liquid can't overflow from the washing tub 30. Preferably, if the quantity indicative of the level of liquid within the washinq tub is the liquid level itself, the first threshold value L _thri could be comprised between 70-140 mm.

In this first advantageous embodiment (in which the first prefixed condition for the first value LI is or comprises reaching or exceeding a prefixed first threshold value Lthri), if the drain pump 92, once activated, it is kept active until a quantity indicative of the level of liquid within the washing tub 30 detected by the liquid level detector 100 is below a prefixed value L _OFF , this prefixed value L _OFF can be the same as the prefixed first threshold value L _thri or, preferably, it can be a different value, more preferably a value lower than the prefixed first threshold value L _thri so as to introduce an hysteresis in the activation/deactivation of the drain pump 92.

Other possible advantageous first prefixed conditions according to the invention for the first value LI will be described in the following.

In an advantageous embodiment, while the washing machine 10 is in the stand-by condition, and after the phase of supplying electric power to the liquid level detector 100 for at least a first switch-on time interval tom, the method comprises disconnecting the liquid level detector from electric power supply for a first switch-off time interval t _O FFi; in this way, the overall energy consumption during the stand-by condition is reduced.

In a preferred embodiment, the first switch-off time interval to _FFi is comprised between 50 and 70 seconds, more preferably 60 seconds.

In a further advantageous embodiment, while the washing machine 10 is in the stand-by condition, if the first value LI detected by the liquid level detector 100 meets a first prefixed condition, the liquid level detector 100 is kept electrically powered for all the rest of the stand-by condition.

In an advantageous embodiment, the method comprises detecting or estimating a starting value L0 of a quantity indicative of the liquid level within the washing tub 30 at the beginning of the stand-by condition; this starting value L0 can be, for example, the last value of the quantity indicative of liquid level detected before taking the washing machine 10 in the stand-by condition. In another advantageous embodiment, the starting value L0 could be for example estimated as the value of the quantity indicative of the level of the liquid that could remain within the washing tub 30 after the last drain phase of a washing cycle, for example due to the specific layout of the drain circuit 90. In this advantageous embodiment, the first value LI is compared to the starting value L0, and the drain pump 92 is activated if the difference between the first value LI and the starting value L0 reaches or exceeds a prefixed second threshold value L _thr 2; in this case, therefore, the first prefixed condition that has to be met by the first value LI is related to its difference from the starting value L0; it is clear that this difference grows together with the amount of the leak in the one or more electro-valves 70.

It is highlighted that the prefixed second threshold value L _thr 2 can be selected, for example during the design of the washing machine 10, depending on the specific dimensions and/or shape or the washing tub 30 and/or drain circuit 90, in such a way that, while the difference between the first value LI and the starting value L0 is below such second threshold value L _thr 2, liquid can't overflow from the washing tub 30.

For example, if the quantity indicative of the level of liquid within the washinq tub is the liquid level itself, the second threshold value L _thr 2 could be advantageously comprised between 70-140 mm.

In a further advantageous embodiment of the invention, the method comprises, while the washing machine 10 is in the stand-by condition, and after the phase of supplying electric power to the liquid level detector 100 for at least a first switch-on time interval tom, the phase of supplying electric power to the liquid level detector 100 for a second switch-on time interval to _N2 , during which a second value L2 of a quantity indicative of the liquid level within the washing tub 30 is detected by the liquid level detector 100. In this advantageous embodiment, the second value L2 is compared with the first value LI, and, if the difference between the second value L2 and the first value LI reaches or exceeds a prefixed third threshold value L _thr 3 the drain pump 92 is activated for draining the liquid from the washing tub 30, and/or an alert is generated, for example by a speaker, not illustrated. In this case, therefore, the first prefixed condition that has to be met by the first value LI is related to the difference of the second value L2 from the first value LI; it is clear that this difference grows together with the amount of the leak in the one or more electro-valves 70.

It is highlighted that the prefixed third threshold value L _thr 3 can be selected, for example during the design of the washing machine 10, depending on the specific dimensions and/or shape or the washing tub 30 and/or drain circuit 90, in such a way that, while the difference between the second value L2 and the first value LI is below such third threshold value L _thr 3, liquid can't overflow from the washing tub 30.

For example, if the quantity indicative of the level of liquid within the washinq tub is the liquid level itself, the third threshold value L _thr 3 could be advantageously comprised between 50-100 mm.

In this advantageous embodiment, the phase of disconnecting the liquid level detector from electric power supply for a first switch-off time interval t _O FFI is preferably performed between the phase of supplying electric power to the liquid level detector 100 for a first switch-on time interval tom and the phase of supplying electric power to the liquid level detector 100 for a second switch-on time interval to _N 2. Alternatively, in a further advantageous embodiment, the phase of supplying electric power to the liquid level detector 100 for a first switch-on time interval tom and the phase of supplying electric power to the liquid level detector 100 for a second switch-on time interval to _N 2 are performed without disconnecting the liquid level detector 100 from electric power supply between these phases (i.e. the liquid level detector 100 is continuously supplied with electric power at least from the beginning of the first switch-on time interval to _Ni to the end of the second switch-on time interval to _N 2). Preferably, while the washing machine 10 is in the stand-by condition, and after the phase of supplying electric power to the liquid level detector 100 for a second switch-on time interval toN2, the method comprises the phase of disconnecting the liquid level detector 100 from electric power supply for a second switch-off time interval t _O FF2, so as to reduce electric consumption. Preferably, the second switch-off time interval t _OFF 2 is comprised between 50 and 70 seconds, more preferably 60 seconds.

In a preferred embodiment, the phase of supplying electric power to the liquid level detector 100 for at least a first switch-on time interval tom while the washing machine 10 is in the stand-by condition is performed after a prefixed first delay time t _di since when the washing machine 10 has been taken in the stand-by condition, during which the liquid level detector 100 is disconnected from electric power supply; in other words, in this advantageous embodiment when the washing machine 10 is taken in the stand-by condition, the liquid level detector 100 is disconnected from the electric power supply, and it is then connected to the electric power supply, so as to be supplied with electric power, only after the first delay time tdi·

Preferably, the first delay time t _i is comprised between 30 and 90 seconds, more preferably between 50 and 70 seconds, even more preferably 60 seconds.

In an advantageous embodiment, the phase of supplying electric power to the liquid level detector 100 for at least a second switch-on time interval toN2, is performed after a prefixed second delay time t _d 2 has lapsed since when the washing machine 10 has been taken in the stand-by condition. Preferably, the second switch-on time interval to _N 2 is comprised between 30 second and 90 seconds more preferably between 55 seconds and 85 second, even more preferably 70 seconds.

In a different advantageous embodiment, the phase of supplying electric power to the liquid level detector for at least a first switch-on time interval tom is started simultaneously with taking the washing machine 10 in the stand-by condition. In a different advantageous embodiment, electric power is supplied to the liquid level detector 100 for the whole duration of the stand-by condition.

Preferably, during the stand-by condition, the user interface 50 is disconnected from electric power supply.

Preferably, while the washing machine 10 is in the stand-by condition, the following three phases are repeated a plurality of times in this order:

- supplying electric power to the liquid level detector 100 for at least a first switch-on time interval tom;

- during the first switch-on time interval tom, detecting by the liquid level detector 100 a first value Li of a quantity indicative of the liquid level within the washing tub 30;

- disconnecting the liquid level detector 100 from electric power supply for a first switch-off time interval t _O FFi· Preferably these three phases are repeated a plurality of times at prefixed time intervals.

Preferably, in this advantageous embodiment the drain pump 92 is activated if, during the repetition of the three phases, the first value Li meets the first prefixed condition, for example it reaches or exceeds the prefixed first threshold value Lt _hri .

In a further advantageous embodiment, the washing machine 10 comprises a closure detection device, schematically illustrated in figure 2 as a rectangle 44, like for example a sensor (e.g. a magnetic sensor), operatively connected to the control unit 200 and configured for detecting if the door or porthole 4 is opened or closed. In this advantageous embodiment, the method according to the invention can advantageously comprise, while the washing machine 10 is in the stand-by condition, and before the step of activating the drain pump 92 for draining liquid from the washing tub 30 and/or generating an alert, if the first value LI meets a first prefixed condition, the further step of detecting by the closure detection device 44 if the door or porthole 4 is closed or opened, and making use of a first prefixed condition if the door or porthole 4 is closed, and of a different first prefixed condition if the door or porthole 4 is opened.

For example, if the first prefixed conditions comprises reaching or exceeding a prefixed first threshold value Lthri, such a prefixed first threshold value L _thri can advantageously have a value, for example 200 mm (in case the quantity indicative of the level of liquid within the washinq tub is the liquid level itself), if the door or pothole 4 is closed, and a different value, for example 140 mm if the door or porthole 4 is opened; in fact, if the door or pothole 4 is closed the liquid can't overflow via the opening closed by the door or pothole 4, and therefore an higher value of the prefixed first threshold value L _thri can be used.

In a further advantageous embodiment, in which the first prefixed condition is related to the difference between the first value LI and the starting value L0, and in particular requires that the difference between the first value LI and the starting value L0 reaches or exceeds a prefixed second threshold value L _thr 2, such a prefixed second threshold value L _thr 2 can advantageously have a value, for example 200 mm (in case the quantity indicative of the level of liquid within the washinq tub is the liquid level itself), if the door or pothole 4 is closed, and a different value, for example 140 mm if the door or porthole 4 is opened; in fact, if the door or pothole 4 is closed the liquid can't overflow via the opening closed by the door or pothole 4, and therefore the prefixed second threshold value L _thr 2 can have an higher value.

In a further advantageous embodiment, in which the first prefixed condition is related to the difference between the second value L2 and the first value Li, and in particular requires that the difference between the second value L2 and the first value Li reaches or exceeds a prefixed third threshold value L _thr 3, such a prefixed third threshold value L _thr 3 can advantageously have a value, for example 160 mm (in case the quantity indicative of the level of liquid within the washinq tub is the liquid level itself), if the door or pothole 4 is closed, and a different value, for example 100 mm if the door or porthole 4 is opened; in fact, if the door or pothole 4 is closed the liquid can't overflow via the opening closed by the door or pothole 4, and therefore the prefixed third threshold value L _thr 3 can have an higher level.

An advantageous example of a first flow chart 1000 illustrating an advantageous embodiment of the logical steps performed by the control unit 200 for implementing a possible embodiment of the method according to the invention is illustrated in figure 3.

The first flow chart 1000 starts with a first step 1001 in which it is checked (advantageously by the control unit 200) if the washing machine 10 is in the stand by condition; if NOT (indicated by letter "N" in the drawings), first step 1001 is repeated, if YES (indicated by letter "Y" in the drawings), a second step 1002 is performed, in which the liquid level detector 100 is supplied with electric power, and the water level (or better a first value Li of a quantity indicative of the liquid level) in the washing tub 30 is detected by the liquid level detector 100, and then the liquid level detector 100 (called pressure switch in figure 3) is switched off (third step 1003). Then, a fourth step 1004 is performed, in which it is checked if the first switch-off time interval t _O FFIfor the liquid level detector 100 (called "off time" in figure 3) has been reached; if NOT, fourth step 1004 is repeated, if YES, the liquid level detector 100 is electrically powered (fifth step 1005) again for a second switch-on time interval to _N 2 (sixth step 1006, "on time"), and then water level (or better a second value L2 of a quantity indicative of the liquid level) within the washing tub 30 is checked again (seventh step 1007).

If (eight step 1008, option NOT) the level is not increasing over a certain threshold (or, in other words, if the difference between L2 and LI is below a third threshold), the flow chart comes back to the third step 1003, while if (eight step 1008, option YES) the level is increasing over a certain threshold (or, in other words, if the difference between L2 and LI reaches or exceeds a third threshold value L _th r _f) , an alert (called alarm in figure 3) is generated and the drain pump 92 is operated for draining the water from the washing tub 30 (ninth step 1009), after which (tenth step 1010) the alert is transmitted to the user interface 50, or to an APP of an external device, not illustrated, to which the washing machine 10 is connected, and the drain continues until completely emptying the washing tub 30.

A further advantageous example of the logical steps performed by the control unit 200 for implementing a possible embodiment of a method according to the invention is illustrated in the second a second flow chart 2000 of figure 4.

The second flow chart 2000 starts with a first step 2001 in which it is checked if the washing machine 10 is in the stand by condition; if NOT, first step 2001 is repeated, if YES, a second step 2002 is performed, in which the liquid level detector 100 is supplied with electric power, and the water level (or better a first value LI of a quantity indicative of the liquid level) in the washing tub 30 is detected. Then, a third step 2003 is performed, in which it is checked if a certain time has lapsed; if NOT, third step 2003 is repeated, if YES, the water level (or better a second value L2 of a quantity indicative of the liquid level) within the washing tub 30 is checked again (fourth step 2004).

If (fifth step 2005, option NOT) the level is not increasing over a certain threshold (or, in other words, if the difference between L2 and LI is below a third threshold), the second flow chart 2000 comes back to the third step 2003, while if (fifth step 2005, option YES) the level is increasing over a certain threshold (or, in other words, if the difference between L2 and LI reaches or exceeds a third threshold L _th r _f) , an alert (called alarm in figure 4) is generated and the drain pump 92 is operated for draining the water from the washing tub 30 (sixth step 2006), after which (seventh step 2007) the alert is transmitted to the user interface 50, or to an APP of an external device, not illustrated, to which the washing machine 10 is connected, and the drain continues until completely emptying the washing tub 30.

Figure 5 shows an advantageous example an alternative logical step 3000 that can be performed, in the first flow chart 1000 or in the second flow chart 2000, as an alternative, respectively, to step 1001 and to step 2001, in an advantageous embodiment in which the washing machine 10 comprises a closure detection device 44, operatively connected to the control unit 200 and configured for detecting if the door or porthole 4 is opened or closed.

This alternative logical step 3000 advantageously comprises, a first step 3001 in which it is checked if the washing machine 10 is in the stand by condition; if NOT, first step 3001 is repeated, if YES, a second step 3011 is performed, in which it is checked by the closure detection device 44 if the door or porthole 4 is closed. If NOT, (i.e. the door or porthole 4 is opened), a low threshold level (e.g. Lthri, Lthr2 or Lth3) is selected and used (step 3012), while if YES (i.e. the door or porthole 4 is closed) a high threshold level (e.g. the Lthri, Lthr2 or Lttm) is selected and used (step 3013), since in this case the liquid can't overflow via the opening closed by the door or porthole 4, and therefore the level causing the overflow is higher. Then, the flow chart can continue respectively with step 1002 or 2002, depending if it is the first flow chart 1000 or the second flow chart 2000.

It is seen therefore how the invention achieves the proposed aim and objects, there being provided a method for operating a washing machine, for example a laundry washing machine or a dishwasher, that, by activating the liquid level detector when the washing machine is in the stand-by condition, and by activating the drain pump and/or generating an alert if the liquid level grows abnormally, allows preventing the risk of liquid overflow even in the stand-by condition.

In addition, the particular embodiment in which the liquid level detector is electrically powered only after a prefixed first delay time t _i since when the washing machine has been taken in the stand-by condition allows keeping reduced the energy consumption while the washing machine is in the stand by condition.