DESCRIPTION

The present invention relates to a laundry washing machine according to the preamble of claim 1.

The invention also relates to a corresponding method for controlling a spinning phase in a washing machine.

Washing machines are known wherein the sequence of operational steps is controlled in a manner such that at least one spinning phase is carried out after the wash and rinse phases.

Unlike the wash and rinse phases, which require that water be supplied into the tub, the spinning phase is used for the purpose of wringing out the previously washed and rinsed clothes. No water is therefore taken in; on the contrary, water is extracted from the laundry and discharged. In order to wring out the clothes, during the spin phase the drum of the washing machine is rotated at high speed (over 200 rpm) for a certain period of time. The spinning phase may also comprise low-speed stirring phases (typically between 40 and 80 rpm) preceding the high-speed rotation phases. These stirring phases are useful for stirring the laundry items in the drum, so as to obtain better wringing results. The liquid extracted from the laundry (e.g. a mixture of water and detergents that impregnates the clothes being washed) is then removed by a drain pump. This process reduces as much as possible the moisture content of the laundry prior to the next drying step, which may occur in the open air or in a suitable clothes dryer.

A washing machine may be designed to carry out multiple spinning phases, e.g. at the end of the wash phase and after each rinse phase (which may be one or more; typically two or three rinse phases are executed).

The duration of the various subphases making up the spinning phase (e.g. stirring, highspeed rotation, draining) is usually predetermined experimentally and therefore it generally turns out to be oversized, since it must take into account the most unfavourable conditions in terms of quantity of laundry in the drum, quantity of water absorbed by the laundry, efficiency of the drain duct and pump, presence of foam in the liquid to be discharged. This oversizing causes an excessive duration of the wash cycle, resulting in a reduction in the energetic efficiency of the machine.

Some solutions are known which control the spinning phases in such manner as to optimise its duration and to improve its effectiveness, so that the wash cycle can be completed in a shorter time.

For example, patent EP0711860 describes a washing machine comprising a pressure sensor which, by detecting the pressure in the drain duct, allows to control the operation of the drain pump during a high-speed rotation phase, which ends as soon as the pressure variation reaches a predetermined level. This solution only faces the case wherein the liquid is extracted from the laundry during the spinning phase in shorter or longer times than normally expected. Therefore, this solution has the drawback that it does not optimise the operation of the washing machine in the other phases preceding or following high-speed rotation, resulting in poor energetic efficiency.

The object of the present invention is to provide a washing machine capable of solving the problems suffered by the prior art.

In particular, it is an object of the present invention to provide a washing machine wherein the duration of the phases preceding or following high-speed rotation is optimised as a function of the characteristics of the laundry items in the drum.

In particular, it is an object of the present invention to provide a washing machine wherein the duration of the discharge phase is optimised.

It is a further object of the present invention to provide a washing machine offering more flexibility of use and allowing to reduce the laundry treatment times.

These and other objects of the present invention are achieved through a washing machine and a method for controlling the spin cycle in a washing machine incorporating the features set out in the appended claims, which are intended as an integral part of the present description.

The general idea at the basis of the present invention is to provide a spinning phase with high-speed rotation phases and low-speed rotation phases (also called stirring phases), wherein the duration of the lowest-speed phase depends on the detection of a liquid level, in particular a minimum level, in the drain duct. This solution overcomes the drawbacks of the prior art because it relates the duration of the stirring step to the level of the liquids extracted from the laundry and present in the drain duct. In general, this implies a shorter spinning phase and reduced energy consumption.

In a preferred embodiment, also the high-speed rotation phase has a variable duration, which depends on the detection of a maximum level of a liquid present in the drain duct. This optimises the laundry wringing processes, thereby also optimising the machine's energy consumption.

In one embodiment, the liquid is only discharged during the stirring phases.

Preferably, draining occurs during both the stirring phase and the high-speed rotation phase, thus reducing the laundry wringing times.

Further objects and advantages of the present invention will become more apparent from the following detailed description and from the annexed drawings, which are supplied by way of non-limiting example, wherein:

- Fig. 1 is a schematic representation of an example of a washing machine according to the invention;

- Fig. 2 shows a first example of a spin cycle in a washing machine according to the invention;

- Fig. 3 shows a second example of a spin cycle in a washing machine according to the invention.

Fig. 1 schematically shows an example of embodiment of a washing machine according to the present invention. This washing machine 1 comprises a wash tub 2 in which there is a drum 3 adapted to contain laundry to be washed. The drum 3 rotates around the horizontal axis 4 at variable and typically predetermined revolution speeds, driven by the torque generated by a motor (not shown), typically an electric motor.

When the drum 3 is rotating, the laundry items contained therein are stirred and, through holes in the drum 3 (not shown), the wash liquid can collect in the tub 2; the laundry contained in the drum is thus washed.

The washing machine 1 comprises further elements and devices, such as, for example, a drum access door, a tray for detergents or the like, which are not shown in the drawing nor described herein because they are per se known and considered to be scarcely relevant for the purposes of the present invention. It should therefore be assumed that a washing machine according to the present invention may comprise all such devices, which are considered to be known.

The washing machine 1 also comprises a drain duct 5, in which the wash liquid can collect, communicating with the tub 2. Along the drain duct 5 there is a drain pump 6, which can discharge the wash liquid from the washing machine 1 through a second duct 7, in accordance with the programs of the various operational phases.

Finally, the washing machine comprises a sensor 8 capable of detecting the level of the wash liquid accumulated in the tub 2.

The sensor 8 may, for example, be a pressure transducer, in particular a linear pressure transducer, communicating by means of the portion 9, preferably connected to the lower part of the tub 2 or to the drain duct 5. The pressure transducer reads the pressure of the water column above it; this reading is representative of the quantity and level of the liquid in the tub.

The use of a linear pressure transducer is particularly advantageous in that it allows to introduce, in an economical and flexible manner, different pump control thresholds like those described below.

The sensor 8 is also connected to a control unit (not shown), which comprises a microcontroller and a suitable memory area where the information received from the sensor 8 is stored (whether temporarily or for a longer time). The control unit further comprises a memory area containing the operating programs for treating the laundry.

The control unit is also adapted to control the motor connected to the drum 3.

Thanks to the sensor 8, it is possible to monitor the level of the liquid accumulating in the tub 2 and in the drain duct 5 during the various wash and spinning phases, so as to adapt the operation of the machine, in particular the rotation of the drum 3, to the detected parameters.

The washing machine 1 can execute at least one spinning phase; in particular, the control unit of the washing machine comprises code portions which allow for a pulsed spinning phase, i.e. of the type comprising phases wherein high-speed rotation pulses alternate with laundry stirring phases.

As will be explained more in detail below, said stirring and high-speed rotation phases can take place simultaneously with the wash liquid draining process.

Fig. 2 shows a first example of a pulsed spinning phase according to the present invention. A graph shows the drum revolution speeds (labelled "rpm" on the axis of ordinates, with an arbitrary scale) as a function of time (labelled "t" on the axis of abscissas, with an arbitrary scale).

Since a part of the spinning phase occurs at high drum revolution speeds, prior to this phase it is necessary to verify that the load is well balanced; any concentrated masses might in fact create moments of inertia which would endanger the mechanical stability of the washing machine. To this end, balancing phases are carried out wherein the load is stirred by turning it at a rolling speed, i.e. a speed at which the laundry item (ideally considered as a concentrated mass) cannot make a full drum revolution and is therefore first lifted and then dropped before completing a whole revolution in adherence to the drum.

After the laundry rolling phase, drum balance is checked, e.g. by performing a few revolutions at satellisation speed, i.e. a speed such that one laundry item (having a concentrated mass of 1 kg) can make one full drum revolution while remaining in adherence to the drum walls.

It follows that the satellisation speed depends on the drum diameter; for standard-size drums (having a diameter of approx. 45 cm), it is typically between 80 and 100 rpm. The rolling speed of these drums is preferably between 20 and 45 rpm.

If the washing machine detects no drum unbalance, the actual spinning phase can begin, which comprises stirring phases at a first satellisation speed rl and phases at a higher- speed rotation r2.

In general, the stirring phases at satellisation speed are carried out in order to drain the water extracted from the laundry during the previous phase corresponding to the highspeed rotation pulse. Holding a satellisation speed also allows to avoid losing the load balancing condition previously attained; however, the load balancing is preferably checked because, in particular cases, it might change as a result of the previous wringing of the laundry during the high-speed rotation pulse.

The high-speed rotation pulses occur at a drum revolution speed r2 preferably between 300 and 400 rpm, more preferably between 340 and 360 rpm.

As mentioned above, the stirring phases are carried out at a revolution speed rl slower than r2, preferably between 80 and 100 rpm, more preferably between 90 and 95 rpm; these values are sufficient to keep the laundry satellised.

The revolution speed values rl and r2 are usually set in the design stage, mainly as a function of the drum dimensions.

In at least a portion of some or of all of these phases, the drain pump 6 is turned on to discharge the wash liquid accumulated in the tub 2 and in the duct 5.

Preferably, discharging occurs during at least one, preferably all, of the stirring phases. In one embodiment, the drain pump 6 is controlled in a manner such that the liquid extracted from the laundry accumulates in the tub 2 during the high-speed rotation subphases cl, c2, c3, and is discharged during the stirring subphases ml, m2, m3.

In another preferred embodiment, the drain pump 6 is turned on to discharge the liquid accumulated in the tub during all the various spin cycle subphases.

As aforementioned, the duration of the stirring and high-speed rotation phases may be predetermined experimentally; it is however possible that, in particular conditions, unsatisfactory operation may occur. In particular, it may happen that the liquid is extracted by the drain duct more quickly than expected, resulting in a period of time in which the drain pump operates without load and may be damaged. Thanks to the above- described control of the stirring and/or high-speed rotation phases, a more efficient and flexible operation of the washing machine is attained. Said control is obtained, for example, by using the sensor 8 to establish the most advantageous instant for switching from the stirring phase to the high-speed spinning phase and/or to define the duration of the stirring phase.

Still with reference to Fig. 2, for example, in the high-speed rotation pulse cl the laundry items in the drum are subjected to an acceleration which causes the liquid to be transferred from the laundry to the tub, where it accumulates.

In this embodiment, subphase cl ends when the sensor 8 detects a liquid level in the tub above an upper threshold value, e.g. the drum bottom. In this embodiment, a maximum time is preferably set for the duration of the high-speed rotation subphase, so that, if the water extracted from the laundry is insufficient to reach said upper liquid level, then the phase will end when this maximum time elapses.

Alternatively, the high-speed rotation phases, like c 1 , may have a predefined duration. Phase cl is followed by the stirring phase ml; during this phase, the laundry items are stirred in the drum at the satellisation speed rl, while the drain pump discharges the tub. When the sensor detects a liquid level below a threshold level, the control unit of the washing machine activates the second high-speed rotation pulse c2.

Once the maximum quantity of liquid has been reached again in the duct, a second stirring subphase m2 is carried out.

In this embodiment, in case of substantial absence of foam formation, ml and ml have the same duration, since the pump is always operated at the same speed and must always drain the same quantity of water, defined by the capacity of the drain duct and by the minimum and maximum levels at which the pump is turned on and off.

Of course, for equal foam conditions, if the high-speed rotation phase has a predefined duration, then the quantity of liquid collected in the tub will change depending on the residual moisture of the laundry under treatment; therefore, in this case ml and m2 will have different durations, as shown in Fig. 3.

As in subphase ml, when the sensor detects a liquid level below a threshold level in similar manner, the control unit of the washing machine activates the third high-speed rotation pulse c3.

An alternative embodiment may also be conceived wherein, when the sensor detects a liquid level in the tub below a threshold value, the control unit of the washing machine starts a time count and waits for a predetermined time period, e.g. of twenty seconds, to elapse. Only at the end of this predetermined time, the control unit will activate a highspeed rotation pulse. This teaching is applicable to at least one or to all of the transitions between a low-speed rotation phase, e.g. ml or m2, and a high-speed rotation phase, e.g. c2 or c3.

In this example of embodiment, c3 lasts longer than cl and c2, because it is more difficult to extract liquid from the laundry in the drum, since the laundry has already undergone two high-speed rotation phases cl and c2.

Afterwards, according to the same principle described above, a third stirring phase m3 is carried out, the duration of which is once again established by evaluating the signal sent by the sensor 8, which measures the quantity (and consequently the level) of the liquid in the tub.

In the non-limiting example of Fig. 2, this stirring phase m3 is followed by a final highspeed rotation phase c4, wherein the drum is rotated at a speed which may vary according to a predetermined profile, until the end of the spinning phase.

The spinning phases may be alternated with one or more rinse phases, wherein fresh liquid is supplied into the tub 2.

According to one embodiment, the threshold values of the liquid in the duct at which the pump is turned on and/or off may vary as a function of operating characteristics such as, for example, the liquid threshold value used for the previous high-speed rotation pulse or the number of high-speed rotation pulses already occurred. In this way it is possible to obtain a washing machine offering greater operational flexibility.

Preferably, the pump is held active until a liquid level in the tub is reached which is lower than the bottom of the drum 3, in order to avoid starting a high-speed rotation pulse in the presence of too much water.

In a preferred embodiment, the control unit uses the reading of the sensor 8 to stop a highspeed rotation pulse when the liquid level in the tub 2 exceeds a certain threshold.

With a washing machine according to the present invention it is therefore possible to minimise, or even eliminate, those time periods when the discharge phase goes on ineffectively, in particular in concomitance with multiple high-speed rotation pulses. This translates into lower energy consumption and faster operating cycles.

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

The same invention described herein is applicable, in general, to a washing machine, a washing/drying machine or any centrifugal machine, even intended for applications other than washing laundry, e.g. for industrial use.

Finally, it is conceivable that the revolution speed of the various pulses can be adjusted by the user; in such a case, also the duration of the high-speed rotation pulse may be modified accordingly, even automatically.