Patent Publication Number: US-11028522-B2

Title: Method for controlling the intake of washing liquid in a laundry washing machine, and laundry washing machine actuating that method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 13/988,039 filed Jan. 17, 2014, the contents of which is hereby incorporated by reference in its entirety, which is a national phase filing of International Application No. PCT/EP2011/070753, filed Nov. 23, 2011, which claims priority to European Application No. 10193012.1, filed Nov. 29, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of laundry washing and drying, particularly to laundry washing machines, meaning with this term laundry washers and laundry washers/dryers. Specifically, the invention relates to a method for controlling the intake of washing liquid, e.g. water, or a mixture of water and a washing agent, such as a detergent, in a laundry washing machine, and to a laundry washing machine implementing such a method. 
     OVERVIEW OF THE RELATED ART 
     Controlling the amount of washing water supplied to a laundry washing machine is an important issue, especially nowadays that electric energy consumption and, in general, environmental responsibility are very felt. 
     EP 1423563 discloses a method for washing in a washing machine, which can measure an accurate washing load before actual washing is carried out. The method includes (a) introducing laundry into a drum of the washing machine, (b) measuring an initial washing load caused by the introduced laundry, (c) repeating water supply to the drum for a fixed time period for maintaining a minimum water level determined by the initial washing load, taking water absorbed to the laundry into account, (d) after the preset water supply time period, determining a final washing load in the drum based on a number of water resupply times for an elapsed time from the initial water supply, and (e) washing the laundry by a washing method preset according to the determined final washing load. 
     WO 2008000610 discloses a method for handling laundry in a washing machine with a water level sensor, for determining the hydrostatic pressure of the fluid in the lye container. Water is introduced in the lye container to a pre-determined hydrostatic pressure p 1  with a preset pressure difference between hydrostatic pressure p 1  and a hydrostatic pressure p 2 . Firstly, (a) water is introduced to the lye container at a hydrostatic pressure below p 1  until the hydrostatic pressure p 1  is reached and (b) the introduction of water is then stopped until the hydrostatic pressure has dropped to p 2 . Furthermore, (c) the period tn for the n-th sequence of steps a) and b) is measured and (d) water introduction in step (a) stopped when (d 1 ) the sum of the periods t 1  to tn is greater than a given value tmax or (d 2 ) the period tn is greater than a given period tmin. 
     WO 2006018382 aims at optimizing the completeness, uniformity and reproducibility of a wetting process in a program-controlled washing machine, which can be adjusted according to the amount of laundry in a washing drum, which is rotationally mounted in a lye container about a non-vertical axis by means of a water supply system and by means a control device, said process being temporally controlled by the supply of water into the lye container. The wetting process is divided up into a series of phases (Ph 1 -Ph 3 ) corresponding to the various amounts (small, medium, large) of laundry that is to be treated. As a result, it is possible to adapt the wetting process according to the number and formation of individual phases in relation to the amount of laundry that is to be treated. 
     In DE 19946245 the value is registered by the program control and is in addition to the initial weighing carried out by a weight sensor before water is introduced into the drum. The process involves calculating an actual laundry weight value from the initial measuring value and the additional value by means of an adjusting circuit integrated into the program control. The program control continues the washing program with washing parameters which relate to the actual weight value. 
     SUMMARY OF THE INVENTION 
     The Applicant has found that none of the abovementioned methods is satisfactory from the point of view of the water and electric power consumptions. 
     According to an aspect of the present invention there is provided a method for managing the load of washing liquid in a laundry washing machine comprising a washing tub, in which washing liquid may be loaded, and a rotatable drum, rotatably accommodated in the washing tub, for containing the laundry to be washed. The method includes performing a sequence of partial loads of washing liquid into said washing tub. Each partial load provides for loading a corresponding liquid amount in the washing tub. For at least one of said partial loads in the sequence, the method provides for loading into the washing tub a predetermined amount of washing liquid which depends on at least one indicative parameter related to one or more of the previous partial loads in the sequence. 
     In principle, an embodiment of the present invention provides for carrying out a sequence of partial water loads; the amount of water in each partial load of the sequence is selected among a collection of already predetermined partial amounts based on indicative parameters of the previous partial loads in the sequence. As will become more clear in the following of the present description, with the expression “load of a predetermined amount of water” (or of washing liquid) it is intended both a partial load of an amount of water (washing liquid) whose value has been previously fixed (e.g., a partial load of X liters, wherein X is a prefixed value) and a partial load of an amount of water (washing liquid) dosed so that the overall amount of water (washing liquid) loaded before that partial load plus the amount of water (washing liquid) loaded by that partial load reaches a previously fixed value (e.g., a partial load of an amount of water such that the overall amount of loaded water reaches Y liters, wherein Y is a further prefixed value). 
     It is underlined that, even if the above mentioned partial load of an amount of water dosed so that the overall amount of water loaded before that partial load plus the amount of water loaded by that partial load reaches a previously fixed value is not a fixed value, since it depends on how much water has been loaded before this partial load (i.e., on how many partial loads have been performed before this partial load), the latter is anyway a load of a “predetermined” amount of water, since the amount of water loaded in this partial load is exactly the difference from the above mentioned predetermined fixed value and one or more predetermined values corresponding to the partial loads performed before. 
     It is also underlined that the amount of water loaded in all the above mentioned partial water loads is advantageously directly measured by a suitable metering device, for example a flowmeter associated to the water load system of the laundry machine in such a way to directly measure the exact amount of water admitted into the washing tub; this ensures that the amount of water admitted into the washing tub at each partial load is exactly the predetermined amount selected among the collection of already predetermined partial amounts based on indicative parameters of the previous partial loads in the sequence. In this way the amount of water admitted at any partial load isn&#39;t affected by for example by the pressure of water provided by the water socket to which the laundry machine is connected, as it would be if, for example, the admitted amount of water would be calculated as a function of the time in which the electrovalve provided at the inlet of the water load system of the laundry machine is open (in which case the actual amount of water admitted into the tub would depend on the pressure of water). 
     According to an embodiment of the present invention, said loading into the washing tub a predetermined amount of washing liquid, for at least one of said partial loads in the sequence, is conditioned to the fact that a predetermined level of free washing liquid in the laundry washing machine is not attained yet. 
     Preferably, said at least one indicative parameter related to one or more of the previous partial loads in the sequence comprises at least one among the level of free washing liquid and/or the value of the pressure in said washing tub reached before said at least one of said partial loads in the sequence, the time taken by the level of free water/pressure in the washing tub for falling below a minimum level from the end of the previous partial load, the total amount of water loaded by the previously performed partial loads, and the number of partial loads already performed. 
     Advantageously, said loading into the washing machine a predetermined amount of washing liquid for at least one of said partial loads in the sequence comprises loading a previously fixed amount of washing liquid selected among a collection of already predetermined partial amounts. 
     According to an embodiment of the present invention said loading into the washing machine a predetermined amount of washing liquid for at least one of said partial loads in the sequence comprises loading an amount of washing liquid dosed in such a way that the overall liquid amount of washing liquid in the laundry washing machine before said at least one of said partial loads plus said dosed amount reaches a previously fixed quantity. 
     According to a further embodiment of the present invention, said previously fixed quantity is calibrated for the washing of at least one among substantially half a standard load of laundry the laundry washing machine is configured to house, and substantially the standard load of laundry the laundry washing machine is configured to house. 
     Preferably, before said loading into the washing machine a predetermined amount of washing liquid for at least one of said partial loads in the sequence, the method provides for selecting whether the next partial load is to be cold washing liquid or hot washing liquid. 
     Another aspect of the present invention relates to a laundry washing machine comprising a washing tub, in which washing liquid may be loaded, and a rotatable drum, rotatably accommodated in the washing tub, for containing the laundry to be washed. The laundry washing machine further includes a metering device for measuring the amount of water loaded into the washing tub, a dosing device, for activating/deactivating the loading of water into the washing tub, and a control unit, operatively connected to said metering device and to said dosing device for managing the load of washing liquid in said washing tub in such a way to perform a sequence of partial loads of washing liquid into said washing tub. Each partial load provides for loading a corresponding liquid amount in the washing tub. Said control unit is configured for loading into the washing tub a predetermined amount of washing liquid, for at least one of said partial loads in the sequence, which depends on at least one indicative parameter related to one or more of the previous partial loads in the sequence. 
     Advantageously, said control unit is configured to condition said loading into the washing tub a predetermined amount of washing liquid, for at least one of said partial loads in the sequence, to the fact that a predetermined level of free washing liquid in the laundry washing machine is not attained yet. 
     According to an embodiment of the present invention, said at least one indicative parameter related to one or more of the previous partial loads in the sequence comprises at least one among the level of free washing liquid and/or the value of the pressure in said washing tub reached before said at least one of said partial loads in the sequence, the time taken by the level of free water/pressure in the washing tub for falling below a minimum level from the end of the previous partial load, the total amount of water loaded by the previously performed partial loads, and the number of partial loads already performed. 
     Advantageously, said control unit is configured in such a way that loading into the washing machine a predetermined amount of washing liquid for at least one of said partial loads in the sequence comprises loading a previously fixed amount of washing liquid selected among a collection of already predetermined partial amounts. 
     Preferably, said control unit is configured in such a way that loading into the washing machine a predetermined amount of washing liquid for at least one of said partial loads in the sequence comprises loading an amount of washing liquid dosed in such a way that the overall liquid amount of washing liquid in the laundry washing machine before said at least one of said partial loads plus said dosed amount reaches a previously fixed quantity. 
     According to an embodiment of the present invention, said control unit is configured in such a way that said previously fixed quantity is calibrated for the washing of at least one among substantially half a standard load of laundry the laundry washing machine is configured to house, and substantially the standard load of laundry the laundry washing machine is configured to house. 
     According to a further embodiment of the present invention, said dosing device is adapted for allowing selectively providing, at its outlet, cold water or hot water, and wherein said control unit is configured in such a way that before said loading into the washing machine a predetermined amount of washing liquid for at least one of said partial loads in the sequence, said control unit selects whether the next partial load is to be cold washing liquid or hot washing liquid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will appear more clearly from the reading of the following detailed description of some invention embodiments, provided merely by way of non-limitative examples. The description that follows will be better understood making reference to the attached drawings, wherein: 
         FIG. 1  schematically shows a laundry machine according to an embodiment of the present invention; 
         FIGS. 2A-2C  show in terms of blocks some steps of a method according to an embodiment of the present invention; 
         FIGS. 3A and 3B  are diagrams showing an example of the evolution in time of the amount of loaded water and of the corresponding level of water in a washing tub of the laundry machine, respectively for a half laundry load and a full laundry load, for the method of  FIGS. 2A-2C ; 
         FIGS. 4A-4B  show in terms of blocks some steps of a method according to a further embodiment of the present invention; 
         FIGS. 5A-5B  show in terms of blocks some steps of a method according to a still further embodiment of the present invention, and 
         FIG. 6  is a diagram showing an example of the evolution in time of the amount of loaded water and of the corresponding level of water in a washing tub of the laundry machine for the method of  FIGS. 5A-5B . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Referring to the drawings, in  FIG. 1  there is schematically shown a laundry machine  100 , for example a laundry washer. The laundry machine  100  comprises a cabinet  105  enclosing a washing tub  110  and, rotatably accommodated therein, a laundry drum  115 , for containing the laundry to be washed. The laundry machine  100  has a water load system and a waste washing liquid discharge system. The water load system preferably comprises a dosing device, e.g. an electrovalve,  120 , whose inlet is connectable (for example via a hose) to a water socket (not shown). In some embodiments of the invention, the laundry machine may be equipped with a dosing device adapted for allowing selectively providing, at its outlet, cold water or hot water; for example this different dosing device may comprise two electrovalves, one advantageously connectable to a cold water socket and the other advantageously connectable to a hot water socket, or an electrovalve with only one outlet and two inlets one advantageously connectable to a cold water socket and the other advantageously connectable to a hot water socket. A metering device, for example a flowmeter  125  is advantageously connected to the dosing device (e.g., electrovalve) outlet. The electrovalve  120  is preferably controlled by a control unit  130 , which receives the readings from the flowmeter  125 . The loaded water is preferably made to pass through a container of detergents  135  and then supplied to the washing tub  110 ; advantageously, a by-pass circuit may be provided, internally or externally to the container of detergents  135 , adapted for allowing the loaded water to be adducted to the washing tub directly, i.e. without being mixed with one or more detergents contained in the container  135 . The washing liquid discharge system advantageously comprises a discharge duct  145 , for example at the bottom of the washing tub  110 , preferably closable by a valve  150 ; downstream the valve  150 , an anti-fluff/anti-clog filter  155  is preferably provided, upstream a discharge pump  160  whose outlet is connected to a discharge hose  165 , preferably connectable to a drain socket (not shown). A pressure sensor  170  (which may be a pressure switch) is advantageously provided, adapted to sense the pressure of the washing liquid present in the washing tub  110  and to provide the measure to the control unit  130 . 
       FIGS. 2A-2C  illustrate in terms of blocks some steps of a method according to an embodiment of the present invention. 
     The method starts at  201 . At the beginning, a pre-load of a preliminary fixed amount (e.g., 2 litres) of water is preferably made (block  203 ), for example by opening the electrovalve  120  (or, in case there are two electrovalves for the intake of cold and hot water, by opening preferably the electrovalve corresponding to the cold water). After the water pre-load, depending on the washing program selection made by the user, the control unit  130  advantageously selects (block  205 ) whether the next water load is to be cold water or hot water; step  205  is not present in case the laundry machine has only one electrovalve for the intake of cold water. Then (i.e. after block  205 , if the latter is present, or directly after block  203 , if block  205  is not present), a load of a further preliminary fixed amount (e.g., 6 l) of water is performed (block  207 ); this water load is advantageously controlled by means of the flowmeter  125 , and the amount of water to be loaded is preferably the amount of water that would be sufficient for washing a minimum laundry load (e.g., a laundry load ranging from 0 to 1 kg). 
     Once a load of water has been performed, the level of free water varies because of the presence of the laundry in the laundry drum  115 , which laundry absorbs water until becoming completely drenched. The amount of water absorbed by the laundry and the speed of the absorption strongly depend on the amount (clearly a greater amount of laundry absorbs more water that a smaller amount of the same type of laundry) and on the type of the laundry (for example if the laundry is made of cotton it absorbs more water that if it would be made of synthetic fibres) located in the laundry drum  115 . Another cause of variation in the level of free water is given by the rotation of the laundry drum  115 : with the rotation of the laundry drum  115 , the laundry is squeezed and a portion of the water previously absorbed by the laundry is released in the washing tub  110 , going to increase the level of free water. 
     For this purpose, the control unit  130  sets a timer time to a start value (e.g., equal to 4-5 minutes), and then enters a wait loop (blocks  209  and  211 ): during this wait loop, the timer time is progressively decreased, and the pressure in the washing tub  110 , advantageously measured by the pressure switch  170 , is monitored; the measured pressure provides an indication of the level of free water present in the washing tub  110 . The measured pressure is advantageously converted into a measure of the level of free water in the washing tub  110 , which is compared to a predetermined minimum level emptyl (for example, a level of 30 mm). In a further embodiment the measured pressure is compared to a predetermined minimum pressure level enptyp (i.e., the pressures are not converted in levels of free water). According to a still further embodiments of the present invention, instead of monitoring the pressure in the washing tub  110 , the level of free water is directly measured, for example by a an optical device or a level sensor, and it is compared to the predetermined minimum level emptyl. 
     As long as the measured level of free water is higher than the minimum level emptyl (or as long as the measured pressure is higher than the minimum pressure level emptyp) and the value of the timer time is higher than zero, the loop is reiterated (exit branch “Y” of block  209 ), with the timer time that is decreased, preferably by a unit, every reiteration. As soon as one of the two abovementioned conditions become false (exit branch “N” of block  209 ), the control unit  130  exits the wait loop, and the timer timer is stopped. 
     If the exit from the wait loop has been determined by the expiration of the timer time (exit branch “Y” of block  212 ), the control unit  130  assesses that the amount of water that has been loaded until now in the washing tub  110  is sufficient to guarantee a correct washing of the laundry; in this case, the load of water is considered to be completed, and the method is terminated (block  213 ). 
     Conversely (exit branch “N” of block  212 ), if the measured level of free water falls below the minimum level emptyl before the expiration of the timer time (or if the measured pressure falls below the minimum pressure level emptyp), the control unit  130  assesses that the amount of water that has been loaded until now in the washing tub  110  is not sufficient to guarantee a correct washing of the laundry, and further loads of water should be performed. 
     The control unit  130  advantageously operates as a state machine, having a plurality of states ST. Specifically, according to an embodiment of the present invention, the control unit  130  is configured to operate in the following states:
         ST=HALF (the start state), corresponding to a condition in which the laundry load located in the laundry drum  115  is considered to be equal to about half the standard laundry load the laundry drum  115  is configured to accommodate;   ST=ADJ_HALF, corresponding to a first adjustment condition;   ST=FULL, corresponding to a condition in which the laundry load located in the laundry drum  115  is considered to be substantially equal to the standard laundry load;   ST=ADJ_FULL, corresponding to a second adjustment condition;   ST=MAX, corresponding to a condition in which the laundry load located in the laundry drum  115  is considered to be substantially equal to the maximum laundry load the laundry drum  115  is configured to accommodate, and   ST=END, corresponding to a condition in which the control unit  130  forces the ending of the control procedure.       

     Coming back to the flow chart of  FIG. 2A , once the control unit  130  has assessed that further loads of water have to be performed, the state ST thereof is checked (block  214 ); preferably, the control unit  130  checks whether its state ST is equal to HALF (exit branch “Y” of block  214 ) or not (exit branch “N” of block  214 ). In the latter case, the control unit  130  performs a further check, controlling if its state ST is equal to ADJ_HALF (block  215  shown in  FIG. 2B ). 
     If the state ST has been assessed to be HALF, the control unit  130  carries out water load operations specifically calibrated to a laundry load corresponding to about half the standard laundry load (however, as can be read in the following, there could be an exception in which, even with the state ST equal to HALF, the load is performed with a smaller amount of water). 
     Firstly, a check is made on the time taken by the level of free water in the washing tub  110  for falling below the minimum level emptyl from the end of the previous partial load (or on the time taken by the measured pressure in the washing tub  110  for falling below the minimum pressure level emptyp from the end of the previous partial load). This check is carried out by comparing the time dtime elapsed during the last wait loop—corresponding to the difference between the value assumed by the timer time at the beginning of the last wait loop and the value assumed when the level of free water falls below emptyl (or the measured pressure falls below emptyp)—with a predetermined threshold xx, set based on the specific model of the laundry machine  100  (block  216 ). At the same time, the control unit  130  checks the value of a refill counter ref_cnt (initially set to zero) indicative of the number of so-called “adjustment loads” performed until now. As will be described in the following, performing an adjustment load provides for loading in the washing tub  110  an additional, predetermined, small amount of water (e.g., 0.5 l). 
     If the time dtime is lower than the threshold xx—meaning that the water in the washing tub  110  has been rapidly absorbed by the laundry located in the laundry drum  115 —or if the refill counter ref_cnt is equal to m (e.g., m=1)—meaning that m adjustment loads have been already performed —, the control unit  130  manages the carrying out of a load of a substantial amount of water (exit branch “Y” of block  216 ). Conversely, if the time dtime is higher than the threshold xx—meaning that the water in the washing tub  110  has been slowly and/or slightly absorbed by the laundry—or if the refill counter ref_cnt is lower than m—e.g., it is equal to zero, meaning that no adjustment loads have been performed —, the control unit  130  manages the carrying out of an adjustment load (exit branch “N” of block  216 ). 
     In the former case (exit branch “Y” of block  216 ), depending on the washing program selection made by the user, the control unit  130  selects (block  217 ) whether the water load to be performed is to be cold water or hot water (again, step  217  is not present in case the laundry machine has only one electrovalve for the intake of cold water). Then, the electrovalve  120  is opened and a load of water is performed (block  218 ); this load of water, preferably controlled by means of the flowmeter  125 , is dosed in such a way that the overall amount of water loaded in the washing tub  110  (i.e., comprising the water amounts of the previous loads as well) corresponds to a predetermined amount of water—referred to as “half load amount”—calibrated for the washing of about half the standard laundry load the laundry drum  115  is configured to accommodate. For example, making reference to a laundry drum  115  configured to accommodate a standard laundry load of 9 Kg, the half load amount may be equal to about 13 liters. Once the water load is performed, the state ST of the control unit  130  is switched to ADJ_HALF (block  219 ), the refill counter ref_cnt is reset to zero (block  220 ), and the timer time is increased by an incremental amount (e.g., 2 minutes) for allowing the carrying out of refills of further water loads (block  221 ). At this point, the control unit  130  re-enters the wait loop (returning to block  209 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     In the second case (exit branch “N” of block  216 ), after having selected—if possible—(block  222 ) whether the water load to be performed is to be cold water or hot water, the electrovalve  120  is opened and an adjustment load of a small amount of water (e.g., 0.5 liters) is performed (block  223 ). Then, the refill counter ref_cnt is increased by one (block  224 ) to signal that an adjustment load has been carried out, and the timer time is increased by an incremental amount (e.g., 1 minute) for allowing the carrying out of refills of further water loads (block  225 ). At this point, the control unit  130  re-enters the wait loop (returning to block  209 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     It has to be underlined that, according to an embodiment of the present invention, the previously described adjustment load carried out in the block  223  can be performed only once, and in case the water in the washing tub  110  has been slowly and/or slightly absorbed by the laundry, for example because the laundry is almost drenched in water. Thus, the small water amount of the adjustment load might be sufficient to correctly wash the laundry, avoiding to waste excessive amounts of water (such as the water load provided in the block  218 ). 
     Returning back to block  214 , if the control unit  130  has assessed that its state ST is different than HALF (exit branch “N” of block  214 ), a further check is performed, for controlling if the state ST is equal to ADJ_HALF (block  215 ). 
     In the affirmative case (exit branch “Y” of block  215 ), the control unit  130  carries out operations directed to perform an adjustment load, i.e., a load of a small amount of water. 
     After having selected—if possible—(block  226 ) whether the water load to be performed is to be cold water or hot water, the electrovalve  120  is opened and an adjustment load of a small amount of water (e.g., 0.5 liters) is performed (block  227 ). Then, the refill counter ref_cnt is increased by one (block  228 ) to signal that an adjustment load has been carried out. 
     At this point, a check is made on the time taken by the level of free water in the washing tub  110  for falling below the minimum level emptyl from the end of the previous partial load (or on the time taken by the measured pressure in the washing tub  110  for falling below the minimum pressure level emptyp from the end of the previous partial load). Again, this check is carried out by comparing the time dtime elapsed during the last wait loop—corresponding to the difference between the value assumed by the timer time at the beginning of the last wait loop and the value assumed when the level of free water falls below emptyl—with a predetermined threshold, for example the threshold xx (block  229 ). At the same time, the control unit  130  checks the value of the refill counter ref_cnt for assessing the number of adjustment loads performed until now. 
     If the time dtime is lower than the threshold xx—meaning that the water in the washing tub  110  has been rapidly absorbed by the laundry located in the laundry drum  115 —or if the refill counter ref_cnt is at least equal to n (e.g., n=2)—meaning that at least n adjustment loads have been already performed—(exit branch “Y” of block  229 ), the control unit  130  sets its state ST to FULL (block  230 ), and then resets the refill counter ref_cnt to zero (block  231 ). It has to be appreciated that in this case, the control unit  130  has assessed that it is required to perform a further load of a substantial amount of water since the amount of laundry located in the laundry drum  115  is too much for the amount of water loaded in the washing tub  110  until now—the absorption rate being very high—or since even if at least two adjustment loads have been already performed, the level of free water fell below the minimum level emptyl (or the measured pressure in the washing tub  110  fell below the minimum pressure level emptyp) before the expiration of the timer time (in the previous wait loop). Then, the timer time is increased by an incremental amount (e.g., 1 minute) for allowing the carrying out of refills of further water loads (block  232 ). At this point, the control unit  130  re-enters the wait loop (returning to block  209 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     If instead the time dtime is higher than the threshold xx—meaning that the water in the washing tub  110  has not been rapidly absorbed by the laundry located in the laundry drum  115 —or if the refill counter ref_cnt is lower than n—meaning that at most n−1 adjustment loads (e.g., one) have been already performed—(exit branch “N” of block  229 ), the control unit  130  assesses that it would be possible not to perform a further load of a substantial amount of water since the water already loaded until now would be sufficient, or since a simple adjustment load would be sufficient. In this case, the state ST is kept to ADJ_HALF, and, after having increased the timer time by an incremental amount (e.g., 1 minute) (block  232 ), the control unit  130  directly re-enters the wait loop (returning to block  209 ). 
     Returning back to block  215 , if the control unit  130  has assessed that its state ST is different than ADJ_HALF (exit branch “N” of block  215 ), a further check is performed, for controlling if the state ST is equal to FULL (block  233 ). 
     In the affirmative case (exit branch “Y” of block  234 ), the control unit  130  carries out water load operations specifically calibrated to a laundry load corresponding to about the standard laundry load the laundry drum  115  is configured to accommodate. 
     After having selected—if possible—(block  234 ) whether the water load to be performed is to be cold water or hot water, the electrovalve  120  is opened and a load of water is performed (block  235 ); this load of water, controlled preferably by means of the flowmeter  125 , is dosed in such a way that the overall amount of water loaded in the washing tub  110  (i.e., comprising the water amounts of the previous loads as well) corresponds to a predetermined amount of water—referred to as “full load amount”-calibrated for the washing of about the standard laundry load the laundry drum  115  is configured to accommodate. For example, making reference to a laundry drum  115  configured to accommodate a standard laundry load of 9 Kg, the full load amount may be equal to about 19.5 liters. Then, the timer time is increased by an incremental amount (e.g., 2 minute) for allowing the carrying out of refills of further water loads (block  236 ), and the state ST of the control unit  130  is switched to ADJ_FULL (block  237 ). At this point, the control unit  130  re-enters the wait loop (returning to block  209 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     Returning back to block  233 , if the control unit  130  has assessed that its state ST is different than FULL (exit branch “N” of block  233 ), a further check is performed, for controlling if the state ST is equal to ADJ_FULL (block  238 ). 
     In the affirmative case (exit branch “Y” of block  238 ), the control unit  130  carries out operations directed to perform an adjustment load, i.e., a load of a small amount of water. 
     After having selected—if possible—(block  239 ) whether the water load to be performed is to be cold water or hot water, the electrovalve  120  is opened and an adjustment load of a small amount of water (e.g., 0.5 liters) is performed (block  240 ). Then, the refill counter ref_cnt is increased by one (block  241 ) to signal that an adjustment load has been carried out, and the timer time is increased by an incremental amount (e.g., 2 minutes) for allowing the carrying out of refills of further water loads (block  242 ). 
     At this point, the control unit  130  checks the value of the refill counter ref_cnt (block  243 ). 
     If the value of the refill counter ref_cnt is higher than n (exit branch “Y” of block  243 ), meaning that at least n+1 (e.g., 3) adjustment loads have been already performed, the control unit  130  sets its state ST to MAX (block  244 ), and then resets the refill counter ref_cnt to zero (block  245 ). It has to be appreciated that in this case, the control unit  130  has assessed that it is required to perform a further load of a substantial amount of water since even if at least three adjustment loads have been already performed, the level of free water fell below the minimum level emptyl (or the measured pressure in the washing tub  110  fell below the minimum pressure level emptyp) before the expiration of the timer time (in the previous wait loop). Then, the control unit  130  re-enters the wait loop (returning to block  209 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     If instead the refill counter ref_cnt is not higher than n (exit branch “N” of block  243 ), the control unit  130  assesses that it would be possible not to perform a further load of a substantial amount of water since the water already loaded until now would be sufficient, or since a simple adjustment load would be sufficient. In this case, the state ST is kept to ADJ_FULL, and the control unit  130  directly re-enters the wait loop (returning to block  209 ). 
     Returning back to block  238 , if the control unit  130  has assessed that its state ST is different than ADJ_FULL (exit branch “N” of block  238 ), a further check is performed, for controlling if the state ST is equal to MAX (block  246 ). 
     In the affirmative case (exit branch “Y” of block  246 ), the control unit  130  carries out water load operations specifically calibrated to a laundry load corresponding to the maximum laundry load the laundry drum  115  is configured to accommodate. 
     After having selected—if possible—(block  247 ) whether the water load to be performed is to be cold water or hot water, the electrovalve  120  is opened and a load of water is performed (block  248 ); this load of water, preferably controlled by means of the flowmeter  125 , is dosed in such a way that the amount of water loaded in the washing tub  110  (i.e., comprising the water amounts of the previous loads as well) corresponds to a predetermined amount of water—referred to as “maximum load amount”—calibrated for the washing of about the maximum laundry load the laundry drum  115  is configured to accommodate. For example, making reference to a laundry drum  115  configured to accommodate a standard laundry load of 9 Kg, the maximum load amount may be equal to about 25 liters. Then, the timer time is reset to zero (block  249 ) and the state ST of the control unit  130  is switched to END (block  250 ). At this point, the control unit  130  re-enters the wait loop (returning to block  209 ). In this case, since the timer time has been reset, and the state ST of the control unit is END, the method is immediately terminated (block  213 ). 
     Reassuming, according to an embodiment of the present invention, the method of  FIGS. 2A-2C  provides for performing a sequence of partial water loads. The amount of water in each partial water load of the sequence is selected among a collection of predetermined amounts. Specifically, said collection of predetermined amounts include:
         the preliminary fixed amount (e.g., 2 liters) of the load performed at block  203 ;   the preliminary fixed amount (e.g., 6 liters) of the load performed at block  207 ;   the predetermined small amounts (e.g., 0.5 liters) of the adjustment loads performed at blocks  223 ,  227 ,  240 ;   the amount of the load performed at block  218 , which is dosed in such a way that the overall amount of water (i.e., the sum of the water loaded until that moment with the amount of the load performed at block  218 ) reaches the predetermined half load amount (e.g., 13 liters);   the amount of the load performed at block  235 , which is dosed in such a way that the overall amount of water (i.e., the sum of the water loaded until that moment with the amount of the load performed at block  235 ) reaches the predetermined full load amount (e.g., 19.5 liters), and   the amount of the load performed at block  248 , which is dosed in such a way that the overall amount of water (i.e., the sum of the water loaded until that moment with the amount of the load performed at block  248 ) reaches the predetermined maximum load amount (e.g., 25 liters).       

     After the carrying out of a preliminary set of steps, including the loads performed at blocks  203  and  207 , the amount of water in each subsequent partial load is selected from the previously listed predetermined amount based on indicative parameters of previously performed partial loads. 
     Specifically, these indicative parameters may advantageously include the time taken by the level of free water in the washing tub (or by the pressure in the washing tub) for falling below the minimum level emptyl (or emptyp) from the end of the previous partial load, the total amount of water loaded by the previously performed partial loads, and the number of adjustment loads just performed. 
       FIG. 3A  is an exemplary diagram showing the evolution in time of the amount of loaded water (expressed in liters) and of the level of free water (expressed in millimeters) in the washing tub  110  of the laundry machine  100  during the execution of the method of  FIGS. 2A-2C  according to the invention for a half laundry load (e.g., a laundry load of about 4 Kg). 
     The amount of water loaded through the opening of the electrovalve  120  is identified with the reference  305 , while the level of free water in the washing tub  110  (but also the pressure in the washing tub has the same behaviour) is identified with the reference  310 . In this example, the predetermined minimum level emptyl is equal to 30 millimeters. 
     The evolution in time of the amount of loaded water  305  is a non-decreasing function, comprising a respective increasing portion at each water load operation. The evolution in time of the level of free water  310  is strongly nonlinear. Indeed, the laundry absorbs water in an unpredictable way, based on the amount and type thereof; moreover, with the rotation of the laundry drum  115 , the laundry is squeezed, and a portion of the water previously absorbed by the laundry is released in the washing tub  110 , going to increase the level of free water. However, when the electrovalve  120  is opened for performing a load of water, the level of free water substantially increases, while, when the electrovalve  120  is closed and no water is added in the washing tub  110 , the level of free water substantially decreases because of the absorption. 
     Making reference in particular to the example at issue, after the carrying out of the first two predetermined loads of water—i.e., the ones corresponding to the blocks  203  and  207 —the level of free water reaches a first peak (see reference  312 ). The control unit  130  is in the state ST=HALF. Then, the timer time is set, and the wait loop is initiated; the level of free water decreases because of the absorption by the laundry load; said absorption is relatively quick, because the laundry is still not much drenched. For this reason, the level of free water falls below the minimum level emptyl before the timer time expiration (see reference  314 ). Since the duration in time of the decreasing (i.e., the time dtime) was relatively short, the electrovalve  120  is opened until the amount of loaded water reaches the half load amount (in the example at issue, 13 liters); as a consequence, the level of free water increases until reaching a second peak (see reference  316 ). Then, the control unit  130  state ST switches to ADJ_HALF. At this point, a further wait loop is initiated, and the level of free water decreases again. This time, the absorption is slower (compared to the previous one) because the laundry has started to become more drenched, but not so slow to leave the timer time to expire before the level of free water falls below the minimum level emptyl (see reference  318 ). Then, the electrovalve  120  is opened for performing a first adjustment load; as a consequence, the level of free water increases again until reaching a third peak (see reference  320 ). Since in this case the duration in time of the decreasing (dtime) was not so short, the control unit  130  maintains its state ST to ADJ_HALF; in this way, if a further load was necessary, this load must be an adjustment load again. This is the case of the example at issue, wherein the level of free water falls again below the minimum level emtyl before the expiration of the timer time (see reference  322 ). After the second adjustment load, the level of free water increases again until reaching a fourth peak (see reference  324 ); this time, when the next wait loop is initiated, and the level of free water starts to decrease again, the amount of water that has been loaded until now slows the decreasing to such an extent that the timer time expires before the reaching of the minimum level emtyl (see reference  326 ). At this point, the method is terminated, since the control unit  130  has assessed that the water loaded in the washing tub  110  is sufficient to allow a correct washing of the laundry. The subsequent variations of the level of free water depicted in  FIG. 3A  are caused by the operations performed during the carrying out of the selected washing program, and will not be described. 
       FIG. 3B  is a further exemplary diagram showing the evolution in time of the amount of loaded water (in liters) and of the level of free water (expressed in millimeters) in the washing tub  110  of the laundry machine  100  during the execution of the method of  FIGS. 2A-2C  according to the invention for a full laundry load (e.g., 8 Kg). 
     The amount of water loaded through the opening of the electrovalve  120  is identified with the reference  330 , while the level of free water in the washing tub  110  is identified with the reference  335 . Again, the predetermined minimum level emptyl is equal to 30 millimeters. 
     After the carrying out of the first two predetermined loads of water—i.e., the ones corresponding to the blocks  203  and  207 —the level of free water reaches a first peak (see reference  337 ). The control unit  130  is in the state ST=HALF. Then, the timer time is set, and the wait loop is initiated; the level of free water decreases because of the absorption by the laundry load; said absorption is relatively quick, because the laundry is still not much drenched. For this reason, the level of free water falls below the minimum level emptyl before the timer time expiration (see reference  339 ). Since the duration in time of the decreasing (dtime) was relatively short, the electrovalve  120  is opened until the amount of loaded water reaches the half load amount (in the example at issue, 13 liters); as a consequence, the level of free water increases until reaching a second peak (see reference  341 ). Then, the control unit  130  state ST switches to ADJ_HALF. At this point, a further wait loop is initiated, and the level of free water decreases again. This time, the absorption is slower (compared to the previous one) because the laundry has started to become more drenched, but not so slow to leave the timer time to expire before the level of free water falls below the minimum level emptyl (see reference  343 ). Then, the electrovalve  120  is opened for performing a first adjustment load; as a consequence, the level of free water increases again until reaching a third peak (see reference  345 ). Since in this case the duration in time of the decreasing (dtime) was not so short, the control unit  130  maintains its state ST to ADJ_HALF; in this way, if a further load was necessary, this load must be an adjustment load again. This is the case of the example at issue, wherein the level of free water falls again below the minimum level emtyl before the expiration of the timer time (see reference  347 ). After the second adjustment load, the level of free water increases again until reaching a fourth peak (see reference  349 ). Once more, the level of free water falls again below the minimum level emtyl before the expiration of the timer time (see reference  351 ). Since even after two adjustment loads the absorption is not sufficiently slow (meaning that the amount of laundry located in the laundry drum  115  is too much for the amount of water loaded in the washing tub  110  until now), the control unit  130  state ST is switched to FULL, so as the subsequent load involves a substantial amount of water. Thus, the electrovalve  120  is opened until the amount of loaded water reaches the full load amount (in the example at issue, 19.5 liters), and the level of free water increases again until reaching a fifth peak (see reference  353 ). This time, when the next wait loop is initiated, and the level of free water starts to decrease again, the amount of water that has been loaded until now slows the decreasing to such an extent that the timer time expires before the reaching of the minimum level emtyl. At this point, the method is terminated, since the control unit  130  has assessed that the water loaded in the washing tub  110  is sufficient to allow a correct washing of the laundry. 
     The proposed method allows to optimise the water load operations, strongly reducing the waste of water and electric power. With the proposed method, the water load results to be calibrated for the actual amount of laundry to be washed; therefore, avoiding to perform a load of an excessive amount of water, the electric power required for the water heating during the washing operations is strongly reduced. It has to be appreciated that said calibration is advantageously performed by the control unit  130  in an automatic manner, without the need that an user has to explicitly specify to the laundry machine  100  which is the actual amount of laundry to be washed. 
       FIGS. 4A-4B  illustrate several steps of a simplified version of the previously described method according to a further embodiment of the present invention. 
     Without entering into excessive details, compared to the method of  FIGS. 2A-2C , the method of  FIGS. 4A-4B :
         provides for five states ST only instead of six, lacking the state ST=ADJ_FULL corresponding to the second adjustment condition;   does not provide for comparing the time dtime elapsed during the last wait loop with a threshold xx, and   does not take into account the number of adjustment loads actually performed.       

     Although substantially equivalent to the method of  FIGS. 2A-2C  in its main features, the method of  FIGS. 4A-4B  is faster, since it provides for the carrying out of a lower number of water loads, but it is also less accurate, since the resulting overall water load cannot be accurately calibrated for the actual amount of laundry to be washed. 
       FIGS. 5A-5B  illustrate in terms of blocks some steps of another method for loading water in a laundry machine according to a still further embodiment of the present invention. 
     The first steps of the method of  FIGS. 5A-5B  substantially coincide with the ones of the method of  FIGS. 2A-2C . Specifically, the method starts at  501 . At the beginning, a pre-load of a preliminary fixed amount (e.g., 2 litres) of water is preferably made (block  503 ), for example by opening the electrovalve  120  (or, in case there are two electrovalves for the intake of cold and hot water, by opening preferably the electrovalve corresponding to the cold water). After the water pre-load, depending on the washing program selection made by the user, the control unit  130  advantageously selects (block  505 ) whether the next water load is to be cold water or hot water; step  505  is not present in case the laundry machine has only one electrovalve for the intake of cold water. Then (i.e., after block  505 , if the latter is present, or directly after block  503 , if block  505  is not present), a load of a further preliminary fixed amount (e.g., 6 l) of water is performed (block  507 ); this water load is advantageously controlled by means of the flowmeter  125 , and the amount of water to be loaded is preferably the amount of water that would be sufficient for washing a minimum laundry load (e.g., a laundry load ranging from 0 to 1 kg). 
     Even in this case, the control unit  130  sets a timer time to a start value (e.g., equal to 4-5 minutes), and then enters a wait loop (blocks  509  and  511 ): during this wait loop, the timer time is progressively decreased, and the level of free water (or the pressure) present in the washing tub  110  is monitored (for example, through the pressure sensor  170 ). The measured level of free water (or the measured pressure in the tub  110 ) is then compared to a predetermined minimum level emptyl, for example, a level of 30 mm (or the pressure is compared to a predetermined minimum level emptyp). 
     As long as the measured level of free water is higher than the minimum level emptyl (or pressure in the tub is higher than the minimum level emptyp) and the value of the timer time is higher than zero, the loop is reiterated (exit branch “Y” of block  509 ), with the timer time that is decreased, preferably by a unit, every reiteration. As soon as one of the two abovementioned conditions become false (exit branch “N” of block  509 ), the control unit  130  exits the wait loop, and the timer timer is stopped. 
     If the exit from the wait loop has been determined by the expiration of the timer time (exit branch “Y” of block  512 ), the control unit  130  assesses that the amount of water that has been loaded until now in the washing tub  110  is sufficient to guarantee a correct washing of the laundry; in this case, the load of water is considered to be completed, and the method is terminated (block  513 ). 
     Conversely (exit branch “N” of block  512 ), if the measured level of free water falls below the minimum level emptyl (or if pressure in the tub falls below the minimum level emptyp) before the expiration of the timer time, the control unit  130  assesses that the amount of water that has been loaded until now in the washing tub  110  it is not sufficient to guarantee a correct washing of the laundry, and further loads of water should be performed. 
     Once the control unit  130  has assessed that further loads of water have to be performed, a check is made on the time taken by the level of free water in the washing tub  110  for falling below the minimum level emptyl from the end of the previous partial load (on the time taken by the pressure in the tub for falling below the minimum level emptyp from the end of the previous partial load). In the same way as the method of  FIGS. 2A-2C , this check is carried out by comparing the time dtime elapsed during the last wait loop—corresponding to the difference between the value assumed by the timer time at the beginning of the last wait loop and the value assumed when the level of free water falls below emptyl (or the measured pressure falls below emptyp)—with the predetermined threshold xx (block  516 ). 
     If the time dtime is lower than the threshold xx (exit branch “Y” of block  516 )—meaning that the water in the washing tub  110  has been rapidly absorbed by the laundry located in the laundry drum  115  —, the control unit  130  manages the carrying out of a load of a predetermined substantial amount of water (e.g., 2 liters), herein referred to as “primary main load”. Specifically, depending on the washing program selection made by the user, the control unit  130  selects (block  517 ) whether the water load to be performed is to be cold water or hot water (again, step  517  is not present in case the laundry machine has only one electrovalve for the intake of cold water). Then, the electrovalve  120  is opened and the primary main load is performed (block  518 ), preferably under the control of the flowmeter  125 . In order to signal that a load of a substantial amount of water has been performed, the control unit  130  switches to a corresponding state ST=MAIN_EXE (block  519 ). Then, the timer time is increased by an incremental amount (e.g., 2 minutes) for allowing the carrying out of refills of further water loads (block  521 ). At this point, the control unit  130  re-enters the wait loop (returning to block  509 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     Conversely, if the time dtime is higher than the threshold xx (exit branch “N” of block  516 )—meaning that the water in the washing tub  110  has been slowly and/or slightly absorbed by the laundry —, the control unit  130  performs a check on its state ST (block  524 ). If the state ST is equal to MAIN_EXE, the control unit  130  assesses that a load of a substantial amount of water has been just performed, and thus controls the carrying out of an adjustment load of a small amount of water (exit branch “Y” of block  524 ). If instead the state ST is different than MAIN_EXE, the control unit  130  controls the carrying out of a further load of a substantial amount of water (exit branch “N” of block  524 ). 
     In the former case (exit branch “Y” of block  524 ), depending on the washing program selection made by the user, the control unit  130  selects (block  526 ) whether the water load to be performed is to be cold water or hot water (again, step  526  is not present in case the laundry machine has only one electrovalve for the intake of cold water). Then, the electrovalve  120  is opened and an adjustment load of a small amount of water (e.g., 0.5 liters) is performed (block  528 ), preferably under the control of the flowmeter  125 . In order to signal that an adjustment load has been performed, the control unit  130  switches to a corresponding state ST=ADJ_EXE (block  530 ). At this point, the control unit  130  re-enters the wait loop (returning to block  509 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     In the latter case (exit branch “N” of block  524 ), depending on the washing program selection made by the user, the control unit  130  selects (block  532 ) whether the water load to be performed is to be cold water or hot water (again, step  532  is not present in case the laundry machine has only one electrovalve for the intake of cold water). Then, the control unit  130  manages the opening of the electrovalve  120  for carrying out a load of a predetermined substantial amount of water (e.g., 1 liter)—herein referred to as “secondary main load”—, preferably under the control of the flowmeter  125 . In order to signal that a load of a substantial amount of water has been performed, the control unit  130  switches to the state ST=MAIN_EXE (block  536 ). Then, the timer time is increased by an incremental amount (e.g., 2 minutes) for allowing the carrying out of refills of further water loads (block  538 ). At this point, the control unit  130  re-enters the wait loop (returning to block  509 ), with a refreshed timer time having a value equal to the one assumed at the end of the previous wait loop plus the incremental amount. 
     In the same way as the method of  FIGS. 2A-2C , the method of  FIGS. 5A-5B  provides for performing a sequence of partial water loads, too. Even in this case, the amount of water in each partial water load of the sequence is selected among a collection of predetermined amounts, including:
         the preliminary fixed amount (e.g., 2 liters) of the load performed at block  503 ;   the preliminary fixed amount (e.g., 6 liters) of the load performed at block  507 ;   the predetermined substantial amount of water (e.g., 2 liters) of the primary main load performed at block  518 ;   the predetermined small amounts (e.g., 0.5 liters) of the adjustment load performed at block  528 , and   the predetermined substantial amount of water (e.g., 1 liter) of the secondary main load performed at block  534 .       

     After the carrying out of a preliminary set of steps, including the loads performed at blocks  503  and  507 , the amount of water in each subsequent partial load is selected from the previously listed predetermined amount based on the time dtime taken by the level of free water in the washing tub for falling below the minimum level emptyl from the end of the previous partial load (or on the time taken by the pressure in the tub for falling below the minimum level emptyp from the end of the previous partial load), and the amount of water employed in the previously performed loads. Specifically, as long as the time dtime is lower than the threshold xx, it means that the water has been rapidly absorbed by the laundry; therefore, the water load is carried out by means of the primary main loads. Once the time dtime has been assessed to be higher than the threshold, the water load is carried out by alternating between adjustment loads and secondary main loads. 
       FIG. 6  is an exemplary diagram showing the evolution in time of the amount of loaded water (expressed in liters) and of the level of free water (expressed in millimeters) in the washing tub  110  of the laundry machine  100  during the execution of the method of  FIGS. 5A-5B  for a full laundry load (e.g., a laundry load of about 8 Kg). 
     The amount of water loaded through the opening of the electrovalve  120  is identified with the reference  605 , while the level of free water in the washing tub  110  is identified with the reference  610 . In this case, the predetermined minimum level emptyl is equal to 80 millimeters. 
     Without entering into excessive details, in this example the water load procedure lasts a longer time compared to the examples illustrated  FIGS. 3A and 3B . Indeed, unlike the method of  FIGS. 2A-2C , the method of  FIG. 5A-5B  only provides for performing loads of fixed amounts of water (e.g., 0.5, 1.2 liters); therefore, in order to reach an overall amount of water that fits the actual load of laundry located in the laundry drum, it is necessary to carry out a higher number of loads. 
     The previous description presents and discusses in detail several embodiments of the present invention; nevertheless, several changes to the described embodiments, as well as different invention embodiments are possible, without departing from the scope defined by the appended claims. 
     For example, even if the methods herein described begin with the carrying out of pre-loads of preliminary fixed amounts of water, the concepts of the present invention apply in case said pre-loads are not performed.