EP3467181A1

EP3467181A1 - Method for washing laundry in a laundry washing machine

Info

Publication number: EP3467181A1
Application number: EP17194511.6A
Authority: EP
Inventors: Martino Bondi
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2017-10-03
Filing date: 2017-10-03
Publication date: 2019-04-10
Anticipated expiration: 2037-10-03
Also published as: EP3467181B1

Abstract

The invention relates to a method for washing laundry in a laundry washing machine (1) of the type comprising a washing tub (3) enclosing a rotatable washing drum (4) adapted to receive laundry to be washed, and an electric motor (40) connected to said washing drum (4) for rotating said washing drum (4);
the method comprising at least a spinning phase to extract liquid from said laundry during which said washing drum (4) is rotated by means of said electric motor (40), wherein said spinning phase comprises the steps of:
a) activating said electric motor (40) to bring the rotating speed (Ws) of said washing drum (4) up to a target rotating speed (Wst);
b) rotating said washing drum (4) at said target rotating speed (Wst);
c) monitoring at least one parameter relating to the electric power (P) absorbed by said electric motor (40);
d) terminating said spinning phase when said at least one parameter decreases at a decreasing rate (Dpr) which is below, or equal to, a minimum threshold value (∆Pr).

Description

The present invention concerns the field of laundry washing techniques. Specifically, the invention relates to a method for controlling a spinning phase in a laundry washing machine capable of performing a more efficient washing program.

BACKGROUND ART

Nowadays the use of laundry washing machines, both "simple" laundry washing machines (i.e. laundry washing machines which can only wash and rinse laundry) and laundry washing-drying machines (i.e. laundry washing machines which can also dry laundry), is widespread.
In the present description the term "laundry washing machine" will refer to both a simple laundry washing machine and a laundry washing-drying machine. Laundry washing machines generally comprise an external casing, or cabinet, provided with a washing tub which contains a rotatable perforated drum where the laundry is placed. A loading/unloading door ensures access to the drum. Laundry washing machines typically comprise a water inlet circuit and a products supply unit for the introduction of water and treating products (i.e. detergent, softener, etc.) into the washing tub.
Known laundry washing machines are also provided with a draining device for draining washing liquid from the washing tub.
According to the known technique, a complete washing program typically includes different phases during which the laundry to be washed is subjected to adequate treatments.
A washing program usually comprises a laundry wetting phase wherein a proper amount of water and detergent is introduced in the washing tub so that at the end of the phase the laundry is preferably completely soaked.
The washing program then typically proceeds with a main washing phase during which the drum is rotated and the water contained therein is heated to a predetermined temperature based on the washing program selected by the user.
A successive step of the washing program typically comprises a rinsing phase which usually comprises one or more rinsing cycles. In a rinsing cycle clean, rinse water is first added to the laundry, the drum is then rotated in a spinning phase to extract dirty water from the laundry and finally the dirty water extracted is drained from the washing tub to the outside.
After the rinsing phase, a final spinning phase allows the extraction of the residual water contained in the wet laundry. The drum is rotated at high speed to extract residual water from the laundry. The water extracted during the final spinning phase is again drained from the washing tub to the outside.
According to known techniques, a spinning phase, in particular the final spinning phase, is controlled on the base of parameters calculated by the machine and/or selected by the user. Control of a spinning phase typically relates to the rotating speed of the drum and/or duration of the spinning phase.
In particular, the spinning phase duration is preferably set according to one or more parameters like: the washing program selected by the user, the specific parameters selected by the user like the type of fabric (cotton, wool, synthetic, etc.), the weight of the load, the number of rinse cycles etc, or parameters calculated/estimated by the machine, for example the calculation/estimation of the load weight.
A drawback of known techniques derives from the fact that the real load weight does not usually correspond to the value inputted by the user and/or calculated/estimated by the machine. The load weight, for example, is typically a choice among three possible load weights (low, medium, high) and hence the user eventually indicates an approximative weight of the load. The inputted load weight therefore sometimes diverges greatly from its real weight. Furthermore, a total incorrect data may also be inputted into the machines by mistake by the user.
Also, calculation and/or estimation of the load weight by the machine may not correctly correspond to the real weight of the laundry.
Incorrectness of the load weight may lead to a wrong spinning duration, which can be therefore longer or shorter than the expected optimal duration.
Furthermore, even if the load weight value is substantially correct, either inputted by the user or calculated/estimated by the machine, the optimal spinning duration may not be univocally evaluated since it strongly depends on the type of laundry and its water absorption rate.
Longer duration of the spinning phase, in particular the final spinning phase, may cause textile stress, higher energy consumption, prolonged noise, mechanical structure stress of the machine and reduction of the components life.
Shorter duration of the spinning phase, in particular the final spinning phase, may lead to an undesired residual water in the laundry.
The object of the present invention is therefore to overcome the drawbacks posed by the known technique.
It is an object of the invention to provide a method for controlling a spinning phase in a washing program, preferably the final spinning phase, that makes it possible to control the optimal duration of the same.
It is another object of the invention to provide a method for controlling a spinning phase in a washing program, preferably the final spinning phase, that makes it possible to reduce textile stress of the laundry.
It is a further object of the invention to provide a method for controlling a spinning phase in a washing program, preferably the final spinning phase, that makes it possible to reduce energy consumption.
It is a further object of the invention to provide a method for controlling a spinning phase in a washing program, preferably the final spinning phase, that makes it possible to reduce noise.
It is another object of the invention to provide a method for controlling a spinning phase in a washing program, preferably the final spinning phase, that makes it possible to reduce mechanical structure stress of the machine and hence increasing its reliability.

DISCLOSURE OF INVENTION

Applicant has found that by terminating a spinning phase in a washing program, for example by stopping the rotation of the washing drum, based on a parameter relating to the electric power absorbed by the electric motor rotating the washing drum, it is possible to reach the mentioned objects.
In a first aspect thereof the present invention relates, therefore, to a method for washing laundry in a laundry washing machine of the type comprising:

a washing tub enclosing a rotatable washing drum adapted to receive laundry to be washed;
an electric motor connected to said washing drum for rotating said washing drum;

a) activating said electric motor to bring the rotating speed of said washing drum up to a target rotating speed;
b) rotating said washing drum at said target rotating speed;
c) monitoring at least one parameter relating to the electric power absorbed by said electric motor;
d) terminating said spinning phase when said at least one parameter decreases at a decreasing rate which is below, or equal to, a minimum threshold value.

In a preferred embodiment of the invention, the step d) of terminating the spinning phase comprises the action of stopping the rotation of the washing drum.
In a further preferred embodiment of the invention, the step d) of terminating the spinning phase comprises the action of reducing the rotation speed of the washing drum from the target rotating speed.
Preferably, the rotation speed of said washing drum is reduced at a value at which the laundry detaches from the inner side walls of the washing drum.
In a preferred embodiment of the invention, the step d) of terminating the spinning phase comprises the action of deactivating the electric motor. Preferably, said at least one parameter is calculated or detected or an estimated value.
According to a preferred embodiment of the invention, the at least one parameter coincides with the electric power absorbed by the electric motor.
Preferably, the electric power is a calculated or a detected or an estimated value. Preferably, the electric power absorbed by the electric motor is the active electric power absorbed by the electric motor.
In a preferred embodiment of the invention, the minimum threshold value is comprised between 1 and 40 Watt/min, more preferably equal to 5 Watt/min. According to a preferred embodiment of the invention, the decreasing rate is evaluated at predetermined time intervals.
In a preferred embodiment of the invention, the minimum threshold value is a prefixed value.
According to a preferred embodiment of the invention, the target rotating speed is a predetermined fixed speed or a value selected by the user through an interface or a value set according to the load weight.
Preferably, the target rotating speed is the speed at which the laundry is stuck, or at least partially stuck, against the inner side wall of the washing drum by means of the centrifugal force.
Preferably, the spinning phase is the final spinning phase of a washing program. In a preferred embodiment of the invention, the step c) starts when the washing drum reaches the target rotating speed.
In a further preferred embodiment of the invention, the said step c) starts at a predetermined period of time after activation of the electric motor in said step b) or at a predetermined period of time after said drum rotating speed reaches said target rotating speed.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention will be highlighted in greater detail in the following detailed description of preferred embodiments of the invention, provided with reference to the enclosed drawings. In said drawings:

Figure 1 shows a perspective view of a laundry washing machine implementing a preferred embodiment of the method according to the invention;
Figure 2 shows a schematic front view of the laundry washing machine of Figure 1;
Figure 3 is a simplified flow chart of the basic operations of a method for washing laundry in the laundry washing machine of Figure 1 according to a first preferred embodiment of the invention;
Figure 4 shows in detail an operation of the flow chart of Figure 3;
Figure 5 shows the rotating speed of the washing drum and the power absorbed by the electrical motor rotating the same as a function of time in a spinning phase according to a first preferred embodiment of the method of the invention;
Figure 6 shows a second embodiment of Figure 4.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

The present invention has proved to be particularly advantageous when applied to laundry washing machines, as described below. It should in any case be underlined that the present invention is not limited to laundry washing machines. On the contrary, the present invention can be conveniently applied to laundry washing-drying machines (i.e. laundry washing machines which can also dry laundry).
With reference to Figures 1 and 2 a laundry washing machine 1 is illustrated, in which a method according to a first preferred embodiment of the invention is advantageously implemented.
The laundry washing machine 1 preferably comprises an external casing or housing 2, a washing tub 3, a container 4, preferably a perforated washing drum 4, where the laundry to be treated can be loaded.
The washing tub 3 and the washing drum 4 both preferably have a substantially cylindrical shape.
The housing 2 is provided with a loading/unloading door 8 which allows access to the washing drum 4.
The washing tub 3 is preferably suspended in a floating manner inside the housing 2, advantageously by means of a number of coil springs and shock-absorbers, not illustrated.
A water supply circuit 5 is arranged in the upper part of the laundry washing machine 1 and is suited to supply water into the tub 3 from an external water supply line E. The water supply circuit of a laundry washing machine is well known in the art, and therefore it will not be described in detail. The water supply circuit 5 preferably comprises a controlled supply valve 5a which is properly controlled, opened and closed, during the washing program.
The laundry washing machine 1 advantageously comprises a removable drawer 6 provided with various compartments suited to be filled with treating agents (i.e. detergent, softener, rinse conditioner, etc.).
In a preferred embodiment, the water is supplied into the washing tub 3 from the water supply circuit 5 by making it flow through the drawer 6 and then through a supply pipe 9.
The water which reaches the washing tub 3 can, in this case, 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, preferably bypassing the compartments of the drawer 6.
In an alternative embodiment of the invention, a further separate water supply pipe can be provided, which supplies exclusively clean water into the washing tub 3.
The bottom region 3a of the tub 3 preferably comprises a seat 15, or sump, suitable for receiving a heating device 10. The heating device 10, when activated, heats the liquid inside the sump 15.
Laundry washing machine 1 preferably comprises a water outlet circuit 25 suitable for withdrawing liquid from the bottom region 3a of the tub 3.
The water outlet circuit 25 preferably comprises a draining conduit 27, a draining pump 26 and an outlet pipe 28 ending outside the housing 2.
The water outlet circuit 25 preferably further comprises a filtering device 12 arranged between the draining conduit 27 and the draining pump 26. The filtering device 12 is adapted to retain all the undesirable bodies (for example buttons that have come off the laundry, coins erroneously introduced into the laundry washing machine, etc.).
The draining conduit 27 connects the bottom region 3a of the tub 3 to the filtering device 12.
In a further embodiment, not illustrated, the filtering device 12 may be provided directly in the tub 3, preferably obtained in a single piece construction with the latter.
Activation of the drain pump 26 drains the liquid, i.e. dirty water or water mixed with washing and/or rinsing products, from the tub 3 to the outside.
The laundry washing machine 1 then preferably comprises one or more recirculation circuits, not illustrated, adapted to drain liquid from the bottom region 3a of the tub 3 and to re-admit such a liquid into another region of the tub 3.
Preferably, laundry washing machine 1 comprises a device 19 suited to sense (or detect) the liquid level inside the tub 3.
The sensor device 19 preferably comprises a pressure sensor which senses the pressure in the tub 3. From the values sensed by the sensor device 19 it is possible to determine the liquid level of the liquid inside the tub 3. In another embodiment, not illustrated, laundry washing machine may preferably comprise (in addition to or as a replacement of the pressure sensor) a level sensor (for example mechanical, electro-mechanical, optical, etc.) adapted to sense (or detect) the liquid level inside the tub 3.
The washing drum 4 is preferably rotated by an electric motor 40. The electric motor 40 preferably transmits the rotating motion to the shaft 4a of the washing drum 4, advantageously by means of a belt/pulley system, as schematically illustrated in Figure 2. In a different embodiment of the invention, the electric motor 40 can be directly associated with the shaft 4a of the washing drum 4.
The electric motor 40 may be any suitable type of electric motor. Preferably the electric motor 40 is a brushless electric motor. The electric motor 40 preferably rotates the washing drum 4 at various speeds in either rotational directions. Laundry washing machine 1 advantageously comprises a control unit 22 connected to the various parts of the laundry washing machine 1 in order to ensure its operation. The control unit 22 is preferably connected to the water inlet circuit 5, the water outlet circuit 25, the recirculation circuits, the heating device 10 and the electric motor 40 moving the drum 4 and receives information from the various sensors provided on the laundry washing machine 1, like the pressure sensor 19, a temperature sensor, a washing drum speed sensor, etc.
In particular, the control unit 22 provides motor control signals to rotate the washing drum 4 to a rotating speed Ws according to desired speed profiles during the washing program, as better described below. Also, the control unit 22 preferably acquires and elaborates electric motor parameters, like the motor speed Ms, the current IMOT flowing therethrough, the electric motor voltage VMOT, direction, torque etc.. Such parameters may be preferably acquired by means of proper sensors, as known in the art.
While in the embodiment illustrated and described herein a unique control unit 22 is provided, it is clear that in different embodiments two or more control units may be provided, preferably interconnected therebetween. A dedicated control unit 22' may be for example provided for controlling the electric motor 40, as indicated with a dashed box in Figure 2.
The control unit 22 is advantageously connected also to an interface unit 22a which is accessible to the user and by means of which the user selects and sets the washing parameters from time to time, in particular the desired washing program. Advantageously, 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, the type of fabric of the load, etc. The interface unit 22a preferably displays machine working conditions, such as the remaining cycle time, alarm signals, etc. For this purpose the interface unit 22a preferably comprises a display.
A first embodiment of the method according to the invention is described here below with reference to Figures 3 to 5.
The laundry to be washed is first placed inside the washing drum 4 (step 100 of Figure 3). By operating on the interface unit 22a the user selects the desired washing program (step 110) depending, for example, on the type and on the dirty-level of the products to wash. Furthermore, as said before, in a preferred embodiment it is possible for the user to insert some parameters directly by the interface unit 22a, for example the value of the washing temperature, the choice the load weight (low, middle, high) the rotating speed Ws of the washing drum 4 in the spinning phase, etc.
Once the user has selected the desired washing program, the control unit sets the laundry washing machine 1 so that it starts the washing program.
In a further embodiment, the selection of the desired washing program (step 110) may be performed before placing the laundry into the washing drum 4 (step 100). Successively, the washing program performs different phases for washing the laundry.
Preferably, the washing program comprises a laundry wetting phase (step 120) wherein a proper amount of water and detergent is introduced in the washing tub 3 so that at the end of the phase the laundry is preferably completely soaked. During the wetting phase, the washing drum 4 is preferably rotated at low speed (for example a speed value lower than 100 rpm).
The washing program then preferably proceeds with a main washing phase (step 130) during which the washing drum 4 is rotated and the water contained therein is heated to a predetermined temperature based on the washing program selected by the user. The main washing phase (step 130) preferably terminates with a draining step wherein dirty water is extracted from the washing tub 3 to the outside, preferably through the water outlet circuit 25.
A successive step of the cycle preferably comprises a rinsing phase, globally indicated with 140, which usually comprises one or more rinsing cycles (steps 145). In a rinsing cycle 145 clean, rinse water is first added to the laundry (step 146), the washing drum 4 is then rotated to extract dirty water from the laundry (step 147), also indicated as short spinning phase, and the dirty water extracted from the laundry is drained from the washing tub 3 to the outside.
During the short spinning phase, the washing drum speed Ws is preferably comprised between 150 and 2000 rpm.
After the rinsing phase (step 140) the washing program preferably comprises a final spinning phase (step 150). In the final spinning phase (step 150) the washing drum 4 is rotated at high speed Ws (for example about 150-2000 rpm) to extract residual water from the laundry, as better illustrated in the following with respect to Figure 5. The water extracted during the final spinning phase (step 150) is again drained from the washing tub 3 to the outside.
Once the final spinning phase (step 150) terminates, the washing program is completed. At this point, the user may take the laundry out. In case the washing program is performed in a laundry washing-drying machine, after the final spinning phase, the laundry may be advantageously subjected to a drying phase inside the washing drum 4 (step 200 in Figure 3).
Hereinafter, we will focus on the final spinning phase (step 150) according to an advantageous aspect of the invention.
A preferred embodiment of the final spinning phase (step 150) of the invention is shown in detail in Figure 4 (indicated with block 150). Figure 5 depicts the washing drum rotating speed Ws and the electrical power P absorbed by the electric motor 40 as a function of time in said final spinning phase (step 150).
In a first step (step 152), the electric motor 40 is activated (Electric motor ON - at time t=t1) to bring the rotating speed Ws of the washing drum 4 to a target rotating speed Wst.
The target rotating speed Wst is the speed required to extract the residual water from the laundry. At such target rotating speed Wst, the laundry is typically stuck, or at least partially stuck, against the inner side wall of the washing drum 4 by means of the centrifugal force.
The laundry is therefore displaced so as to form an inner cavity substantially at the central area of the washing drum 4.
In a preferred embodiment of the invention, the target rotating speed Wst is a predetermined fixed speed, preferably a speed comprised between 800 and 1500 rpm.
In a further preferred embodiment of the invention, the target rotating speed Wst may be set by the user through the interface 22a, as explained above with reference to step 110 of the method.
In different embodiments, nevertheless, the target rotating speed Wst may be differently set. For example, the target rotating speed Wst may be set according to the load weight, being the load weight either preferably selected by the user or estimated by the machine.
It has to be noted that the drum rotating speed Ws may be directly detected through a dedicated sensor associated to the washing drum 4. In a further preferred embodiment, the drum rotating speed Ws is preferably obtained indirectly by knowing the motor speed Ms.
During this first step (step 152), the electric motor 40 is preferably driven at its maximum power Pmax, for example at a value preferably comprised between 200 and 2000 Watt, more preferably at 1500 Watt.
After the electric motor 40 is activated, at time t=t1, the drum rotating speed Ws is monitored (step 154). Once the drum rotating speed Ws reaches the target rotating speed Wst (output "Yes" of block 156), at time t=t2, the electric motor 40 is opportunely driven to maintain the drum rotating speed Ws at the target rotating speed Wst (step 158).
Preferably, the control unit 22 provides motor control signals to maintains the washing drum 4 at the target rotating speed Wst.
In the preferred embodiment described herewith, the electric motor 40 is preferably driven at its maximum power Pmax during all the time interval t1÷t2. The drum rotating speed Ws preferably linearly increases during the time interval t1÷t2.
In different embodiments, nevertheless, the electric motor 40 may be differently driven to bring the rotation speed Ws of the washing drum 4 to the target rotating speed Wst. For example, the electric motor 40 may be driven intermittently until the drum rotating speed Ws reaches the target rotating speed Wst.
The drum rotating speed Ws may therefore not increase linearly, but with a different trend over the time.
At the time t=t2, as the washing drum 4 reaches the target rotating speed Wst, the motor electrical power P absorbed by the electric motor 40 falls rapidly from its maximum value Pmax to a lower power Pi, for example at a value comprised between 50 and 1000 Watt, more preferably at 700 Watt.
From time t2 on, the electric power P absorbed by the electric motor 40 decreases, due in particular to the progressive extraction of water from the laundry.
According to an aspect of the invention, the electric power decreasing rate Dpr is monitored (step 162).
Preferably, the power P absorbed by the electric motor 40 is calculated from values of the current IMOT flowing through the electric motor 40 and the electric motor voltage VMOT applied to the same.
In a preferred embodiment, said values are acquired by respective sensors.
In other preferred embodiments, the power P absorbed by the electric motor 40 is obtained by a dedicated motor power sensor.
In further preferred embodiments, the value of the current IMOT and/or the value of the motor voltage VMOT and/or the value of the electric power P of electric motor 40 may be obtained by means of an estimation process.
The electric power P absorbed by the electric motor 40, calculated and/or detected and/or estimated, preferably is the active power absorbed by the electric motor 40 (Watt). In different embodiments, nevertheless, the electric power P may be of different type, for example the average active electric power in a predetermined time interval or the reactive electric power.
According to an advantageous aspect of the invention, if the electric power decreasing rate Dpr is above a minimum threshold value ΔPr, (output "No" of block 164), the electric motor 40 is driven to maintain the drum rotating speed Ws at the target rotating speed Wst (step 166).
If the electric power decreasing rate Dpr is below, or equal to, the minimum threshold value ΔP, (output "Yes" of block 164 - at time t=t3), the electric motor 40 is deactivated (Electric motor OFF, step 168).
Saying that electric power decreasing rate Dpr is below, or equal to, the minimum threshold value ΔPr, means that the electric power P absorbed by the electric motor 40 has a substantially flat trend or, in other words, the motor electric power absorption is substantially constant.
Tests carried out by the applicant have proved that such a situation takes place when all, or substantially all, the water in the laundry has been extracted.
According to the invention, therefore, the applicant has established that the end of the final spinning phase (Electric motor OFF, step 168) takes place when the electric power decreasing rate Dpr is below, or equal to, a minimum threshold value ΔPr.
After the electric motor 40 is deactivated (step 168 - at time t=t3), the drum rotating speed Ws rapidly falls to zero (at time t=tf).
At this point, the washing program can be considered terminated and the user may take the laundry out.
The minimum threshold value ΔPr is preferably a prefixed value, for example ΔP=5Watt/min.
Preferably, the minimum threshold value ΔPr is comprised between 1 and 40 Watt/min.
In further preferred embodiments, the minimum threshold value ΔPr may be opportunely set according to different parameters, like for example the size/diameter of the washing drum, the type of laundry to be washed, the load in terms of weight of the laundry to be washed (either estimated or selected by the user through the interface unit), etc.
Advantageously, duration of the final spinning (time interval t1÷tf in Figure 5) does not depend on parameters calculated/estimated by the machine and/or parameters selected by the user.
This solves problems related to incorrectness of data calculated/estimated by the machine and/or mistakes in selection made by the user.
Advantageously, lower textile stress, lower energy consumption, reduced noise, lower mechanical structure stress and increasing of the components life compared to known techniques are obtained.
Also, optimal extraction of water from laundry is obtain.
Figure 6 illustrates a preferred embodiment for monitoring the power decreasing rate in a final spinning phase (step 150') according to the invention.
Phases and/or steps with the same reference numbers of the embodiment previously described correspond to respective phases and/or steps previously described and, therefore, are not described in detail hereinafter.
As far as it concerns the washing drum rotating speed Ws and the electrical power P absorbed by the electric motor 40 as a function of time in this final spinning phase (step 150') we can refer again to Figure 5.
In a first step (step 152), the electric motor 40 is activated to bring the rotating speed Ws of the washing drum 4 to a target rotating speed Wst.
After the electric motor 40 is activated, at time t=t1, the drum rotating speed Ws is monitored (step 154). Once the drum rotating speed Ws reaches the target rotating speed Wst (output "Yes" of block 156), at time t=t2, the electric motor 40 is opportunely driven to maintain the drum rotating speed Ws at the target rotating speed Wst (step 158).
From time t2 on, the electric power P absorbed by the electric motor 40 decreases, due in particular to the progressive extraction of water from the laundry.
According to an aspect of the invention, the electric power decreasing rate Dpr is monitored.
Preferably, two temporary variables P1 and P2 are used to calculate the power decreasing rate Dpr.
The first temporary variable P1 is initialized, at time t=t2, with the electric power P absorbed by the electric motor 40 (step 159). Preferably, the first temporary variable P1 is set to value Pi.
A predetermined time interval Δtw is waited (step 161) and then the second temporary variable P2 is set with the electric power P absorbed by the electric motor 40 (step 163).
The predetermined time interval Δtw is preferably a fixed value, for example a value preferably comprised between 1 and 30 sec.
If the difference between the two values P2 and P1 is above a minimum threshold value ΔP, (output "No" of block 165), the electric motor 40 is driven to maintain the drum rotating speed Ws at the target rotating speed Wst (step 166). The first temporary variable P1 is then set with the second temporary variable P2 and back to the step 161.
If the difference between the two values P2 and P1 is below, or equal to, the minimum threshold value ΔP, (output "Yes" of block 165 - at time t=t3), the electric motor 40 is deactivated (Electric motor OFF, step 168).
After the electric motor 40 is deactivated (step 168 - at time t=t3), the drum rotating speed Ws rapidly falls to zero (at time t=tf).
At this point, the washing program can be considered terminated and the user may take the laundry out.
The minimum threshold value ΔP is preferably a prefixed value, for example a value comprised between 1 and 40 Watt, more preferably a ΔP=5Watt.
In further preferred embodiments, the minimum threshold value ΔP may be opportunely set according to different parameters, like for example the size/diameter of the washing drum, the type of laundry to be washed, the load in terms of weight of the laundry to be washed (either estimated or selected by the user through the interface unit), etc.
According to the preferred embodiment of Figure 6, the decreasing rate of the electric power is evaluated as the decreasing of the electric power over successive predetermined time intervals Δtw, i.e. (P2-P1)/Δtw.
The predetermined time interval Δtw is preferably a fixed value and hence the decreasing of the electric power is evaluated over successive predetermined equal time intervals Δtw.
In different preferred embodiments, evaluation of the decreasing rate may be carried out over successive predetermined time intervals having different durations between them.
In the preferred embodiments of the method above described, monitoring of power decreasing rate preferably initiates as soon as the drum rotating speed Ws reaches the target rotating speed Wst and the electric motor 40 is opportunely driven to maintain the drum rotating speed Ws at the target rotating speed Wst, namely at time t=t2.
In further preferred embodiments, monitoring of power decreasing rate preferably may initiate according to different strategies. For example, as depicted in Figure 5, monitoring of the power decreasing rate preferably may initiate (time t=t2') after a predetermined period of time Δt1 from activation of the motor (time t=t1), said predetermined period of time Δt1 being chosen so as to be sure that the washing drum is already driven at its target speed Wst. Alternatively, as depicted again in Figure 5, monitoring of power decreasing rate preferably may initiate (time t=t2') after a predetermined period of time (Δt2) from the time (time t=t2) when the drum rotating speed Ws reaches the target rotating speed Wst.
In the preferred embodiments of the method above described, ending of the spinning phase depends on the trend of the electric power over the time, preferably when the electric power decreasing rate is below, or equal to, a minimum threshold value.
In further preferred embodiments, nevertheless, ending of the spinning phase may depend on the trend of one or more parameters relating to the electric power absorbed by the electric motor.
For example, ending of the spinning phase may depend on the current decreasing rate of the current IMOT flowing through the electric motor. In such situation, it is assumed that the motor voltage VMOT has a known predetermined voltage wave shape or an estimated voltage wave shape.
It has thus been shown that the present invention allows all the set objects to be achieved. In particular, it makes it possible to control the optimal duration of the spinning phase.
It is underlined that the method of the invention has been described with reference to the final spinning phase.
However, the method according to the invention can be advantageously applied to any spinning phase of the washing program.
For example, the control of the spinning phase duration may be applied to short spinning phases during the rinse cycle(s).
In this case, the spinning phase may preferably terminate by stopping the rotation of the washing drum or, alternatively, it may preferably terminate by reducing the rotation speed of the washing drum. In particular, the rotation speed of the washing drum may be reduced at a value at which the laundry detaches from the inner side walls of the washing drum.
While the present invention has been described with reference to the particular embodiments shown in the figures, it should be noted that the present invention is not limited to the specific embodiments illustrated and described herein; on the contrary, further variants of the embodiments described herein fall within the scope of the present invention, which is defined in the claims.

Claims

A method for washing laundry in a laundry washing machine (1) of the type comprising:
- a washing tub (3) enclosing a rotatable washing drum (4) adapted to receive laundry to be washed;

- an electric motor (40) connected to said washing drum (4) for rotating said washing drum (4);
the method comprising at least a spinning phase to extract liquid from said laundry during which said washing drum (4) is rotated by means of said electric motor (40), characterized in that said spinning phase comprises the steps of:
a) activating said electric motor (40) to bring the rotating speed (Ws) of said washing drum (4) up to a target rotating speed (Wst);

b) rotating said washing drum (4) at said target rotating speed (Wst);

c) monitoring at least one parameter relating to the electric power (P) absorbed by said electric motor (40);

d) terminating said spinning phase when said at least one parameter decreases at a decreasing rate (Dpr) which is below, or equal to, a minimum threshold value (ΔPr).
The method according to claim 1, wherein said step d) of terminating said spinning phase comprises the action of stopping the rotation of said washing drum (4).
The method according to claim 1, wherein said step d) of terminating said spinning phase comprises the action of reducing the rotation speed (Ws) of said washing drum (4) from said target rotating speed (Wst).
The method according to any preceding claim, wherein said step d) of terminating said spinning phase comprises the action of deactivating said electric motor (40).
The method according to any preceding claim, wherein said at least one parameter is calculated or detected or an estimated value.
The method according to any preceding claim, wherein said at least one parameter coincides with the electric power (P) absorbed by said electric motor (40).
The method according to claim 6, wherein said electric power (P) is a calculated or a detected or an estimated value.
The method according to claim 6 or 7, wherein said electric power (P) absorbed by said electric motor (40) is the active electric power (P) absorbed by said electric motor (40).
The method according to any claim from 6 to 8, wherein said minimum threshold value (ΔPr) is comprised between 1 and 40 Watt/min, preferably equal to 5 Watt/min.
The method according to any preceding claim, wherein said decreasing rate (Dpr) is evaluated at predetermined time intervals (Δtw).
The method according to any preceding claim, wherein said minimum threshold value (ΔPr) is a prefixed value.
The method according to any preceding claim, wherein said target rotating speed (Wst) is a predetermined fixed speed or a value selected by the user through an interface (22a) or a value set according to the load weight.
The method according to any preceding claim, wherein said spinning phase is the final spinning phase of a washing program.
The method according to any preceding claim, wherein said step c) starts when said washing drum (4) reaches said target rotating speed (Wst).
The method according to any claim from 1 to 13, wherein said step c) starts at a predetermined period of time after activation of said electric motor (40) in said step b) or at a predetermined period of time after said drum rotating speed (Ws) reaches said target rotating speed (Wst).