The present invention relates to a method for detecting the level of a wash liquid in a washing machine, in particular a household laundry washing machine or dishwasher, according to the preamble of claim 1.
In the washing machines known in the art, the level of a wash liquid is usually detected by measuring the pressure of said washing liquid through a pressure switch.
A type of pressure switch known in the art is the so-called "state" pressure switch, which essentially operates like an on-off switch, since it allows the wash liquid to be supplied into the machine tub when the wash liquid pressure is lower than a limit value, and stops the wash liquid supply as soon as the wash liquid pressure reaches said limit value.
However, it has been observed that using a state pressure switch involves a number of drawbacks, the most important of which is that that such a pressure switch does not allow to detect different levels of the wash liquid contained in the tub of the washing machine. This drawback has become increasingly important in recent years, mainly because the control boards of washing machines can implement a plurality of functions associated with different levels of the wash liquid in the wash tub.
A known solution conceived in order to overcome this drawback and detect the level of a wash liquid in a washing machine utilizes a so-called "analogue" pressure switch. An example of such an analogue pressure switch is described in French patent No.
A further method for determining the water quantity in the washing container of a washing machine is known from
An analogue pressure switch essentially consists of a casing containing a coil within which a ferromagnetic core is moved by a rubber diaphragm that expands through the effect of the pressure exerted by the wash liquid.
The coil is a part of an oscillating electric circuit that outputs a signal having a frequency that varies as a function of the different positions taken by the core within the coil itself, i.e. according to the deformation of the diaphragm caused by the pressure of the wash liquid.
The resonance frequency of the oscillating electric circuit changes in a substantially linear manner as a function of the displacement of the ferromagnetic core relative to the coil.
As a consequence, a control circuit of the washing machine is calibrated during the washing machine production or testing stages and is programmed in a manner such that it associates a certain value of the frequency of the oscillating electric circuit with a certain value of the pressure of the wash liquid in the washing machine.
It follows that the washing machine control circuit can detect the corresponding level of the wash liquid. This allows the control circuit to send appropriate commands to the various components of the washing machine, in particular pertaining to the washing machine wash liquid supply, according to the wash liquid level detected in the washing machine.
Although the analogue pressure switch allows for the detection of a plurality of different wash liquid levels in the tub of the washing machine, its use causes some problems which are related, in particular, to the fact that the analogue pressure switch is less accurate than the state pressure switch in detecting the wash liquid level.
A further drawback of the above-described analogue pressure switch is that the margin of error in measuring the fluid pressure increases over time and with the wear of the parts making up said analogue pressure switch.
In this frame, it is the main object of the present invention to overcome the above-mentioned drawbacks.
In particular, it is an object of the present invention to provide a method for detecting the level of a wash liquid in a washing machine, in particular a household laundry washing machine or dishwasher, which allows to detect a plurality of different wash liquid levels in the washing machine.
It is another object of the present invention to provide a method for detecting the level of a wash liquid in a washing machine, in particular a household laundry washing machine or dishwasher, which allows to carry out precise and accurate measurements of the different wash liquid levels in the washing machine.
It is a further object of the present invention to provide a method for detecting the level of a wash liquid in a washing machine, in particular a household laundry washing machine or dishwasher, which is not affected by the passing of time or by the wear of the parts that make up the pressure switch used for the measurement.
Said objects are achieved by the present invention through a method for detecting the level of a wash liquid in a washing machine, in particular a household laundry washing machine or dishwasher, and through a related washing machine incorporating the features set out in the appended claims, which are intended as an integral part of the present description.
Further objects, features and advantages of the present invention will become apparent from the following detailed description and from the annexed drawing, which is supplied by way of non-limiting explanatory example.
Said washing machine 10 comprises a tub 11 which houses a drum 12 adapted to contain a certain quantity of laundry (not shown in the drawing).
Preferably, said drum 12 is rotatable about a substantially horizontal axis, being in particular driven by a motor 13 and transmission means 14.
However, for the purposes of the present invention, drum 12 may also be produced in a way to alternatively rotate about a substantially vertical axis.
Said washing machine 10 also comprises an analogue pressure switch 15 associated with tub 11 in a manner such that it detects the pressure of the wash liquid in said tub 11 and, consequently, a level L of the wash liquid in said tub 11.
Said washing machine 10 further comprises:
In particular, said means for managing and controlling washing machine 10 comprise an electronic board 20 adapted to store and execute a plurality of wash programs, which typically comprise wash cycles that may vary depending on load, cloth type, dirtiness degree or required rinsing performance for the laundry to be washed.
According to the present invention, the method for detecting a level L of a wash liquid in washing machine 10 is characterized in that said analogue pressure switch 15 is subjected to a calibration process, said calibration process being implemented during an operational step of washing machine 10.
For the purposes of the present invention, an operational step is essentially a step of use of the washing machine by a user.
In particular, said calibration process comprises the following self-calibration steps:
Preferably, said initial frequency F0 of the analogue pressure switch 15 is detected when tub 11 of washing machine 10 contains substantially no wash liquid.
In fact, since the frequency difference ΔF with respect to the initial frequency F0 is a function of level L of the wash liquid in tub 11 of the washing machine, said level L can be calculated by detecting the variation of frequency ΔF with respect to an initial frequency F0 of analogue pressure switch 15, said initial frequency F0 being detected when tub 11 of washing machine 10 contains substantially no wash liquid.
More in detail, analogue pressure switch 15 follows a linear law which can be expressed as a y = αx + β function, wherein:
As a consequence, according to the method of the present invention, the level L is calculated as a ratio between the variation of frequency ΔF and angular coefficient α.
Said self-calibration steps are preferably repeated on a periodical basis during the operational step of washing machine 10 according to the present invention.
In particular, said self-calibration steps may be repeated at every beginning and/or end of the wash cycles of each wash program. In fact, at the beginning and at the end of a wash cycle tub 11 contains substantially no wash liquid, since any wash liquid residue remaining in the laundry is substantially insignificant for determining level L of a wash liquid according to the present invention, and anyway it cannot affect the application of the method according to the present invention.
Said self-calibration steps may also be repeated every time a wash program of washing machine 10 according to the present invention is started; alternatively, said self-calibration steps may be carried out after a predefined number of wash programs.
The advantages of a method for detecting the level of a wash liquid in a washing machine, in particular a household laundry washing machine or dishwasher, as well as of a related washing machine according to the present invention are apparent from the above description.
In particular, such advantages consist in the fact that the method according to the present invention allows to detect a plurality of different levels of the wash liquid in the washing machine while at the same time providing precise and accurate measurements of the different levels of the wash liquid in the washing machine.
Another advantage of the present invention is that the method for detecting the level of a wash liquid in a washing machine, in particular a household laundry washing machine or dishwasher, is not affected by the passing of time or by the wear of the parts that make up the pressure switch used for the measurement.
The method and washing machine described herein by way of example may be subject to many possible variations without departing from the novelty spirit of the inventive idea; it is also clear that in the practical implementation of the invention the illustrated details may have different shapes or be replaced with other technically equivalent elements.
In particular, among the many possible variants, the method may comprise a steam treatment for the laundry contained in drum 12, said steam treatment being in particular carried out in a manner such that a first wash liquid level L1 is kept below drum 12, so that the laundry will not absorb the wash liquid but will only be moistened by steam.
A further variant provides for activating a recirculation circuit (not shown in the drawing) for recirculating the wash liquid in washing machine 10, said activation taking place, in particular, when analogue pressure switch 15 detects a predetermined level L of the wash liquid in said tub 11. The recirculation circuit, which in a laundry washing machine terminates at an aperture obtained in the upper portion of tub 11 and serves to improve the soaking of the textile items during the wash treatment, may operate intermittently: in such a case, the recirculation circuit may also be deactivated when analogue pressure switch 15 detects a predetermined lower level L2 of the wash liquid in said tub 11 (wherein L2<L, L2 being preferably a level at which wash liquid heating means are completely immersed in the wash liquid). When a variable-speed motor is applied to the recirculation circuit, it is particularly advantageous to change the flow rate of the wash liquid flowing in the recirculation circuit as a function of the level detected by analogue pressure switch 15.
Reference has been made in the present description and in the annexed drawing to a household laundry washing machine; it is however clear that washing machine 10 may be a dishwasher and that the present invention is also applicable to said dishwasher. In such a case, the recirculation circuit will be the hydraulic circuit adapted to supply wash liquid to an upper sprayer and/or a lower sprayer.
It can therefore be easily understood that the present invention is not limited to the above-described method and washing machine, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.