EP2034078A1

EP2034078A1 - Method for quickly assessing the amount of water to be loaded in a washing machine provided with a water recirculation system and washing machine capable of carrying out such method

Info

Publication number: EP2034078A1
Application number: EP07115685A
Authority: EP
Inventors: Raffaele Paganini; Rocco Petrigliano
Original assignee: Whirlpool Corp
Current assignee: Whirlpool Corp
Priority date: 2007-09-05
Filing date: 2007-09-05
Publication date: 2009-03-11
Anticipated expiration: 2027-09-05
Also published as: EP2034078B1; DE602007012541D1

Abstract

A method for controlling the program of a washing machine having a water recirculation system comprises recording the amount of water supplied to the tub of the washing machine, assessing the amount of free water present in the tub, assessing the amount of water absorbed by the load by subtracting the amount of free water from the amount of water supplied to the tub, estimating a specific absorption of the load based on the water absorbed and on free water, calculating a load equivalent based on the specific absorption and on the amount of water absorbed by the load, such load equivalent being related to the load in the machine and being used for controlling the program thereof, a correction recursive function being used in calculating the load equivalent at least when the water recirculation pump is on. The method allows a quick evaluation of the water to be loaded in a washing machine and controls directly the electrovalve for loading water to the machine.

Description

The present invention relates to a method of controlling the program of a washing machine comprising the recording of the quantity of water supplied to the tub of the washing machine, assessing the amount of free water present in the tub, assessing the amount of water absorbed by the load by subtracting the amount of free water from the amount of water supplied to the tub, estimating a specific absorption of the load based on the water absorbed and on free water, calculating a load equivalent based on the specific absorption and on the amount of water absorbed by the load, such load equivalent being related to the load in the machine and being used for controlling the program thereof.
Such a method is disclosed by EP-A-1350881 in which a certain amount of clothes, loaded into the washing machine, is determined by measuring the water absorption of the load while measuring the water level in the tub. If such known method is valid for a washing machine in which the filled water remains inside the tub, it will not work in an effective way if a re-circulation system is used where the water is re-circulated on the load by means of a pump, preferably when the drum is rotated.
Washing machines in which re-circulation may be carried out are well known in the art, and offer many advantages as far as energy saving and water saving are concerned. But, as said above, the advantages of the above known method for a quick assessment of the load based on the calculation of a load equivalent are not available in a washing machine using a re-circulation system since in this latter, during water filling, the pump is also activated, preferably at certain time intervals, to re-circulate the water in order to speed up the wetting time. During re-circulation, the measure of the water level in the tub (i.e. of the water pressure by a continuous pressure sensor) and therefore the load estimation computation based on filled water and water level is so heavily affected that it cannot be applied. Therefore the advantage of reducing the wetting time of the laundry by using re-circulation is jeopardized by the fact that the above method of reducing the load evaluation time and therefore the water filling time cannot be used.
It is therefore an object of the present invention to provide a method which allows to exploit the advantages of the method mentioned at the beginning of the description in a washing machine using a re-circulation system, therefore reducing further the wetting time at the beginning of the washing cycle.
The above object is reached thanks to the features listed in the appended claims. According to the invention, when the re-circulation pump is on, a specific correction function is applied to the value of the specific absorption or of the load assessed with the already known methodology based on an evaluation of water absorbed by the load and of free water. This allows applying the control algorithm according to the known technology also when the re-circulation pump is active, i.e. when the low value of free water (due to re-circulation) would give a wrong estimation of the actual load, with a too high estimated amount of water to be fed to the tub.
The method according to the present invention makes use of a continuous water pressure sensor that enables a better control of overflow and leakage, thanks to the continuous level monitoring and "trend" analysis in addition to the level measurement. Moreover such kind of sensor allows a better foam detection, improves spinning performances by avoiding water ring formation and detects foam before and during the distribution.
The present invention will be described further, by way of not-limiting example, with reference to the attached drawings, in which:

Figure 1 is a simplified view of a washing machine according to the invention,
Figure 2 is a diagram showing the free water vs. the water pressure in the tub, such diagram being used in the method according to the invention,
Figure 3 shows an experimental diagram (for an actual load of 5 kg) of water level and total water vs. time, such diagram showing also the value of the assessed load,
Figure 4 is a diagram showing how the correction function according to the invention is applied to the assessed specific absorption or load for taking care of the re-circulation (i.e. when the re-circulation pump is on).

In a washing machine according to the invention, a flow meter 10 in the water supply line (donwstream an electrovalve EV) and a continuous water level sensor 11 are used, so that two information can be directly measured and one can be deduced, i.e.:

total supplied water [liters]
water amount in the tub "free water"[from pressure to liters experimental curve shown in figure 2
water amount in the load ("absorbed water" AW) as the difference between total supplied water and free water.

Both flow meter 10 and level sensor 11 are connected to a central processor unit 13 of the program control system. The "absorbed water" depends on the load quantity and the specific absorption SA.
The specific absorption is a function of the total amount of water supplied to the tub and the free water.
Load Equivalent(LE) = absorbed water / Specific Absorption
Absorbed water= Tot Litres - FreeWater
Free Water = f (Water Level)
Specific Absorption = f (Tot Litres, Water Level)
The load quantity can be computed starting from values measured by the flow meter (water supplied to the tub) and from the continuous water level sensor. From such value and from the experimental curve/equation that links the water level with the free water, it is possible to determine this latter. From the values of total amount of supplied water and from free water it is determined the absorbed water. From a diagram/equation in which the specific absorption is plotted vs. absorbed water, a first value of specific absorption SA* is determined, based on the absorbed water.
Then, from another diagram/correlation in which an additional compensation SA** is plotted vs. free water (more FW means more SA), a second value of specific absorption SA (SA= SA*+SA**) is determined, i.e. the specific absorption of the standard cotton for a specific washing machine. Then this value is a 3D surface function of total amount of water supplied to the tub, and water level in the tub (see Fig 3 in EP-A-1350881 filed by the Applicant) . At the end the cotton load equivalent is determined as a ratio between water absorbed and specific absorption SA.
The above known algorithm is applied continuously in the main loop software control of the washing machine. The main benefit of such continuous implementation is that when the load information is obtained, one can also set the desired water quantity to be used. In order to know the correct water quantity to be used for an estimated load equivalent, a chart is used which links the liters to be used for load equivalents. Once the load quantity is estimated, the water quantity to be filled can be controlled according to the above "Liter to use" chart or look-up table.
The above known methodology is correct for the initial water-filling step when the drum is idle or it is rotated at tumbling speed. If the washing machine is provided with a re-circulation system comprising a re-circulation pump P and a re-circulation circuit R with a nozzle N, the known methodology cannot be applied.
The re-circulation pump can be controlled according to different methods. One is based on a water level (hysteresis on water level), another is based on time control based on a duty cycle. Particularly during the water filling stage, the re-circulation pump is controlled according to the first method mentioned above. This means that the re circulation pump is switched on and off several times during the water filling phase. For instance, for a predetermined tub, the pump P is off when the water level is lower 5 mm and it is on when the water level is above 15 mm. It is worth noting that during the water heating phase, when the heater H (figure 1) is switched on, the hysteresis threshold levels are changed (for instance pump off if level < 30 mm and pump on if level > 45 mm) in order to guarantee a proper working condition for the heater H (i.e. submerged at a predetermined water depth). During the main wash as well during the rinsing phase, after the water heating phase, the control of the re-circulation pump can be carried out with a predetermined duty cycle (for instance 1-4 min on; 3 min off).
During the initial phase of the washing cycle, particularly with reference to the range of 0 to 200 sec in the experimental diagram of figure 3, the re-circulation pump P is switched on and off 3 times. During such short phase the specific absorption, as well as the derived estimated load, does vary a lot if calculated with the re-circulation pump in an idle or active configuration.
According to the invention, when the pump P is off, the specific absorption in steady state condition is a function F1 of the total absorbed liters and of the predictive water level (pWL). The predictive water level, as explained in the already mentioned EP-A-1350881 , is a combination of water level and its derivative (pWL=WL+k*∂WL/∂t)
SA = F1 (Total liters, Predictive water level) When the pump is on, the specific absorption in steady condition is a function F2 of the same parameters as before:
SA = F2 (Total liters, Predictive water level)
When the pump P switches from Off to On or On to Off, the transition from F1 to F2 and vice versa can be described as a dynamics of first order with a determinate time characteristic (Tau1 when pump is switched off and Tau2 when is switched on) according to the experimental data. One example of the dynamic is given in figure 4 that is valid for a washing machine using an average of 19 liters of water. In this particular case the function F1 and F2 are the same but F2 is 4/3 times of F1 (F2=4/3*F1, where 4/3 is called also hold-up factor); then is useful to describe the temporal dynamic as follow:
Load Equivalent =k_holdUp * absorbed water / Specific Absorption
Where Specific Absorption is F1 and
k_holdUp describe the dynamic previously mentioned.
(Pump Off) k_holdUp(t) = k_holdUp(t-1) +(1- k_holdUp(t-1))/Tau1
(Pump On) k_holdUp(t) = k_holdUp(t) +(0.75- k_holdUp(t-1 ))/Tau2.
The recursive factor k_holdUp (depending on its previous value) is evaluated every one second. In this way the Load Equivalent is continuously carry out without to wait the steady state conditions and so the fill phase is accelerated.
With reference to figure 3, it is clear how the complete filling of the tub is reached in a very short time (175 sec), about 25% lower than the filling time according to the known algorithm (which was already the "best in class"). On figure 3 with the reference L is indicated the above-mentioned level of free water (measure in mm of water), with A liters of water loaded in the tub, with B the estimated load and with C the temperature of the water in the tub.
The method according to the present invention allows managing the tub water filling of a washer with a re-circulation system using a technology according to EP-A-1350881 , in which the calculated values of specific absorbtions and loads would be negatively affected by the quick water absorption due to the recirculation pump. The invention manages also the transients between switching-on and switching-off of the re-circulation pump, which would give false value of specific absorption and load.

Claims

A method for controlling the program of a washing machine, comprising recording of the amount of water supplied to the tub of the washing machine, assessing the amount of free water present in the tub (T), assessing the amount of water absorbed by the load by subtracting the amount of free water from the amount of water supplied to the tub (T), estimating a specific absorption of the load based on the water absorbed and on free water, calculating a load equivalent based on the specific absorption and on the amount of water absorbed by the load, such load equivalent being related to the load in the machine and being used for controlling the program thereof, characterised in that it comprises washing recirculation steps during which the water is pumped on the load while the drum is rotated, a correction function being used in calculating the load equivalent at least when the water pump is on.
A method accroding to claim 1, wherein such correction function is a recursive function evaluated every predetermined interval time.
A method accroding to claim 2, wherein such recursive function is a factor to be applied to the specific absorption or to the load equivalent and it is as follows:
Y=Y_b+ (k1-Y_b)/k2 when the recirculation pump is on, and
Y= Y_b + (k3-Y_b)/k4 when the recirculation pump is off, where k1, k2, k3 and k4 are experimental constants, and Y_b is the value of the recursive function calculated at a predetermined interval time before the recursive function is calculated again.
A method according to claim 3, characterised in that the recursive function is calculated at least every 1 second.
A method according to claim 3 or 4, particularly in which the recursive function is applied to the specific absorption, wherein the experimental constants are as follows: k1 = 0,75, K2 = 25, k3 = 1 and k4 = 50.
Washing machine, having means (10) for determining the amount of water supplied to the machine, such means being connected to a central process unit (13) of the machine, comprising a continuous water level sensor (11) connected to such central process unit (13), this latter being adapted to assess the amount of free water present in the tub, to assess the amount of water absorbed by the load by subtracting the amount of free water from the amount of water supplied to the tub, to estimate a specific absorption of the load based on the water absorbed and on free water, and to calculate a load equivalent based on the specific absorption and on the amount of water absorbed by the load, such load equivalent being related to the load in the machine, characterised in that it further comprises a recirculation system (P, R) for recirculating water on the load and in that its cental process unit (13) is adapted to apply a correction function to the calculated specific absorption or to load equivalent at least when the recirculation pump is on.
Washing machine according to claim 6 in which the water supplied to the tub is determined on the basis of electrovalve flow rate.
Washing machine according to claim 6, wherein such correction function is a recursive function evaluated every predetermined time interval.
Washing machine according to claim 8, wherein such recursive function is a factor to be applied to the load equivalent and it is as follows:
Y(t)=Y(t-1) + (k1-Y(t-1))/k2 when the recirculation pump is on, and
Y(t)= Y(t-1) + (k3-Y(t-1))/k4 when the recirculation pump is off, where k1, k2, k3 and k4 are experimental constants, and Y_b is the value of the recursive function calculated at a predetermined time before the recursive function is calculated again.