EP0370875B1 - Laundry drier with an automatic control system - Google Patents

Abstract

Laundry dryer equipped with an automatic operating control system, characterised in that the automatic operating control system comprises at least one means triggering the end of a drying cycle when the rate of variation of the outlet air temperature per unit time ( DELTA T/t), calculated from a measured outlet-air temperature (T) at least higher than a corresponding experimentally predetermined minimum outlet-air temperature (Tm), is higher, for a predetermined validation time (tv), than a corresponding experimentally predetermined minimum rate (a./t) of variation of the outlet air-temperature at the end of the drying cycle per unit time. <IMAGE>

Description

The present invention relates to a dryer provided with an automatic operating control system.

Known dryers are either mechanical type programmer devices where their user must determine a drying time for a given volume of laundry introduced into their drum, or automatic devices which determine the drying times themselves.

Known tumble dryers with a mechanical type programmer thus require from their user a delicate determination of the drying time which conditions a good drying result.

Choosing too long a drying time results in a too dry laundry, difficult to iron. Choosing too short a time results in a cloth that is too damp to be stored.

In summary, this difficulty of use frequently results in these known devices insufficiently dried laundry or laundry damaged by excessive drying.

Known automatic dryers often include in their drying cycle a first phase or a measurement is automatically made of the time elapsing from the moment they start up until the temperature of their outlet air reaches a predetermined value or a predetermined rate of change per unit of time, this measured time which is a drying time being more or less long depending on the quantity of laundry to be dried, and a second phase where an additional drying time is calculated according to the drying time measured in the first phase and executed automatically.

These known automatic dryers release their user from a delicate task of determining the drying time, but these devices are not immune to a poor drying result. Indeed, a duration additional drying systematically determined as a function of the drying time measured in a first phase mentioned above proves unsatisfactory for achieving a good drying result since variable physical factors such as unforeseen variations in the electric voltage which supplies the resistors heating of these dryers or variations in the ambient temperature can profoundly modify the length of this additional drying time. In addition, systematic execution of this calculated additional drying time can lead to either insufficient drying or excessive drying of the laundry.

On the other hand, GB-A-1,516,501 has also proposed a dryer in which the cycle is stopped in the terminal phase by detecting the temperature variation during the cycle and by comparing to a threshold. However, this threshold is set or changed manually.

The object of the present invention, with the aim of avoiding these drawbacks, is to make an economic dryer provided with an automatic operating control system effectively giving excellent drying results for selected degrees of humidity of the laundry.

• mesure de la température Ti d'air de sortie initiale,
• mesure de la température T(to) d'air à la fin de la phase initiale,
• estimation de la charge de linge à l'intérieur du tambour en utilisant la température initiale Ti et la variation de température pendant la phase initiale ;
• en fonction, notamment, de la charge de linge déterminée et du degré d'humidité voulu, choix d'un des paramètres stockés permettant d'obtenir à partir de la température T(to) une température minimale Tm,
• en fonction, notamment, de la puissance de chauffe, choix d'un taux minimal (a^°/t) de variation de température parmi les taux de variation stockés,
• arrêt du cycle de séchage, lorsque le taux de variation de température d'air de sortie par unité de temps (Δ T/t) calculé à partir d'une température (T) mesurée d'air de sortie supérieure à la température minimale Tm est, pendant un temps prédéterminé (tv) de validation, supérieur au taux minimal (a°/t), ou après avoir atteint la température minimale Tm, à la fin d'un temps prédéterminé tv1.

The subject of the present invention is a method for automatically controlling the operation of a dryer of the type comprising a rotary laundry drum, a drying system by circulation of hot air through the drum and a control system comprising at least a heating power control device, a drum outlet air temperature sensor, storage means making it possible to store experimentally determined parameters for the calculation of a minimum outlet air temperature and of the variation rates experimentally determined temperature and calculation means, the drying cycle comprising an initial phase in which the outlet air temperature increases rapidly, a main phase in which the outlet air temperature stabilizes and follows a slight slope and a terminal phase in which the outlet air temperature rises again rapidly, the method comprising the following steps:

• measurement of the initial outlet air temperature Ti,
• measurement of the air temperature T (to) at the end of the initial phase,
• estimation of the load of laundry inside the drum using the initial temperature Ti and the temperature variation during the initial phase;
• depending, in particular, on the determined load of laundry and the desired degree of humidity, choice of one of the stored parameters making it possible to obtain from the temperature T (to) a minimum temperature Tm,
• depending, in particular, on the heating power, choice of a minimum rate (a ^° / t) of temperature variation from the stored variation rates,
• stop the drying cycle, when the rate of change of outlet air temperature per unit of time (Δ T / t) calculated from a measured temperature (T) of outlet air above the minimum temperature Tm is, during a predetermined validation time (tv), greater than the minimum rate (a ° / t), or after having reached the minimum temperature Tm, at the end of a predetermined time tv1.

• la figure 1 représente une vue schématique partielle d'un sèche-linge réalisé selon l'invention, et
• la figure 2 représente une courbe de températures d'air de sortie mesurées durant l'opération de séchage dans le sèche-linge de la figure 1.

To better understand the invention, an embodiment is illustrated below, illustrated by the attached drawings, in which:

• FIG. 1 represents a partial schematic view of a dryer produced according to the invention, and
• FIG. 2 represents a curve of outlet air temperatures measured during the drying operation in the dryer of FIG. 1.

The invention is applicable to tumble dryers having either a drying air circuit open to the outside, or a closed drying air circuit provided with a humidity condenser.

A dryer 1 produced according to the invention, schematically illustrated in FIG. 1, mainly comprises a rotary laundry drum 2, a ventilation and heating duct 3 in which a forced current of air 4 represented by arrows in lines discontinuous is created, heated and introduced into this drum 2, an air outlet duct 5 collecting the hot and humid air 9 leaving the drum 2, and a filter 6 disposed at the inlet of this air outlet duct 5 to retain linen stuffing. The inlet air stream 4 is created and conveyed by a fan 7 and heated by electric heating resistors 8 in the ventilation and heating duct 3.

In a drying cycle, the outlet air temperature T 9 measured in the air duct 5 changes as a function of time t and substantially along a curve C having a general shape illustrated in FIG. 2. This curve C comprises three sections corresponding to three phases I, II, III of drying the laundry. In an Initial phase I, the damp linen present in the drum 2 and the various parts of the dryer which are in contact with the hot drying air are heated, the temperatures T of outlet air 9 measured in the sheath 5 thus rise from an initial temperature Ti, along a relatively steep slope.

In a next phase or main phase II where the heat supplied by the electrical resistors 2 is, for the most part, absorbed by the linen present in the drum 2, the temperatures T of outlet air 9 measured in the sheath 5 stabilize and have a rising slope with a slight slope. In a terminal phase III where the laundry reaches a dry and very dry state, the temperatures T of the outlet air 9 measured in the sheath 5 again increase rapidly.

The dryer 1 is provided with a system 10 for automatic operation control.

According to an important characteristic, in the dryer 1, the automatic operating control system 10 comprises at least one means triggering the end of a drying cycle when the rate of change of outlet air temperatures 9 per unit of time Δ T / t calculated from a measured temperature T or entry of outlet air at least greater than a minimum temperature Tm of outlet air 9 predetermined experimentally corresponding, is for a predetermined time tv validation greater than one minimum rate corresponding to experimentally predetermined ° / t of variation in outlet air temperatures 9 at the end of the drying cycle (phase III) per unit of time.

The degrees of humidity of laundry at the end of drying are for example of the order of 13% to more or less 3% of humidity for a laundry ready to iron, 3% to more or less 3% of humidity for a dry laundry, and 0% to 2% for very dry laundry.

In the dryer 1, the automatic operation control system 10 comprises means for recording the minimum temperatures Tm of outlet air 9 experimentally predetermined as a function of the specific characteristics of the dryer 1, such as those of a drying air circuit open to the outside or closed and provided with a humidity condenser, thresholds S of outlet air temperature 9 in the interval between main phase II and terminal phase III of the cycle drying, experimentally predetermined and corresponding to the prefixed quantities by weight of linen to be dried, with a view to obtaining, at the end of drying, the humidity levels of selected linen.

The curve C of the outlet air temperatures 9 illustrated in FIG. 2 shows that an end of drying is practically located in terminal phase III of the drying cycle. To avoid an error in ordering a premature end of drying of the laundry, an outlet air temperature T 9 which triggers an end of drying must be one of the measured outlet air temperatures T 9 entered in this terminal phase III . For this reason, a triple condition is imposed, namely a temperature T of outlet air 9 at least greater than a minimum temperature Tm predetermined experimentally, and a rate of change of temperature of outlet air 9 per unit of time Δ T / t must be at least greater than a minimum rate a ° / t of variation of outlet air temperature 9 per unit of time, predetermined experimentally, and be confirmed during a predetermined time tv validation.

However, for a small quantity of laundry and a degree of humidity of ready-to-iron laundry (13% ± 3%), an end of drying is practically located in the interval between main phase II and terminal phase III of the cycle. drying. For this reason, a double condition is imposed, namely an outlet air temperature T triggering an end of drying must be at least greater than a minimum temperature Tm predetermined experimentally, during a predetermined validation time.

The minimum temperature Tm is one of the outlet air temperatures 9 in the terminal phase III of the drying cycle. This minimum temperature Tm is greater than a value T (to) of the outlet air temperature 9 measured or entered at a time to after the start of the dryer 1 which is in the interval between the initial phase I and the main phase II of curve C. This minimum temperature Tm is equal to a value T (to) of outlet air temperature 9, increased by a temperature rise Δ T determined experimentally as a function of the specific characteristics of the dryer 1 and of a threshold S of outlet air temperature 9, corresponding to a quantity by weight of prefixed linen to to dry, and to a selected humidity level of laundry at the end of drying. The fact that Tm is directly dependent on T (to) allows the automatic operating control system to be very insensitive to the effects induced on the absolute temperature of the outlet air, by the possible variations in ambient temperature, of the heating power or the quantity of laundry.

The system 10 for automatically controlling the operation of the dryer 1 comprises means for recording the thresholds S of the outlet air temperature 9 determined experimentally as a function of the selected degrees of humidity of the laundry at the end of drying, the quantities in prefixed weights of laundry to be dried, heating powers supplied by electric resistors 8.

In an alternative embodiment, the thresholds S of outlet air temperatures 9 are additionally determined experimentally as a function of variations in the electric voltage supplying these electrical resistors 8, which improves the operating control accuracy of the dryer 1 .

The automatic operating control system 10 comprises means for recording the minimum rate of temperature variation a ° / t of outlet air per unit of time. The minimum rates a ° / t of variations in outlet air temperatures 9 per unit of time are temperature rates determined experimentally as a function of the specific characteristics of the dryer 1 and of the heating powers used supplied by the electrical resistors 8 The predetermined validation time tv avoids a premature triggering of the end of drying of the laundry. In fact, incidental incidents such as a linen blocked in front of the filter 6, a sudden variation in the uncontrolled electrical voltage supplying the heating resistors 8, can induce a rate of variation in outlet air temperatures 9 per unit of time Δ T / t greater than a predetermined minimum rate a ° / t, and an outlet air temperature T greater than a predetermined minimum temperature Tm, which triggers the end of drying of the laundry.

According to another characteristic in the dryer 1, the automatic operating control system 10 comprises a means for triggering the end of the drying cycle which is activated, for a small quantity by weight of laundry to be dried or quantity less than an experimentally preset quantity of laundry, and for a chosen degree of moisture in the laundry at the end of drying, of the order of 13% to plus or minus 3% or degree of humidity of laundry ready to iron, when the temperature T of outlet air 9 measured or captured is, during a predetermined validation time tv, greater than a minimum temperature Tm corresponding to experimentally predetermined outlet air.

d'air de sortie 9 par unité de temps et enfin une identification de la quantité en poids de linge dans le sèche-linge par comparaison de cette variation de température

d'air de sortie par unité de temps, avec des valeurs limites inférieures et supérieures de variations de températures d'air de sortie 9 par unité de temps, prédéterminées expérimentalement correspondantes aux quantités en poids préfixées de linge.According to another characteristic, in the dryer 1, the automatic operating control system 10 comprises means for automatically determining the quantity by weight of laundry in the dryer, performing temperature measurements at the start of the dryer. initials Ti of outlet air, and at a time to in the interval between the initial phase I and the main phase II of the drying cycle after this start-up, measurements of the temperature T (to) of outlet air, then a calculation of the temperature variation

outlet air 9 per unit of time and finally an identification of the quantity by weight of laundry in the dryer by comparison of this variation in temperature

of outlet air per unit of time, with lower and upper limit values for variations in outlet air temperatures 9 per unit of time, experimentally predetermined corresponding to the quantities by weight prefixed with linen.

à la fois prédéterminées expérimentalement et classées selon différentes conditions de puissance de chauffe et différentes quantités en poids préfixées de linge, des tables des seuils S de température d'air de sortie à la fois prédéterminées expérimentalement et classés selon différents degrés d'humidité de fin de séchage choisis et différentes quantités en poids préfixées de linge, des tables de températures minimales Tm d'air de sortie classées selon différents seuils S et des tables des taux minimum de variation de température d'air de sortie par unité de temps a°/t classés selon différentes puissances de chauffe, et d'autre part opère successivement des mesures de températures initiales Ti d'air de sortie, de tension électrique alimentant les résistances électriques 8 fournissant des puissances de chauffe (cette mesure de tension pouvant être optionnelle), de température T(to) d'air de sortie 9 au temps to après le démarrage du sèche-linge 1 et dans l'intervalle entre la phase initiale I et la phase principale II du cycle de séchage, un calcul de la variation de températures d'air de sortie

par unité de temps, une identification de la quantité de linge dans le sèche-linge par comparaison de la variation de températures d'air de sortie

par unité de temps calculée, avec des limites inférieures et supérieures de variation de température d'air de sortie inscrites dans les tables enregistrées et correspondant à des quantités en poids préfixées de linge, une lecture du degré d'humidité de fin de séchage choisi, une identification du seuil S de températures d'air de sortie dans les tables enregistrées des seuils S correspondant à la quantité en poids de linge identifiée et au degré d'humidité de fin de séchage lu, une identification de la température minimale Tm dans les tables enregistrées de Tm correspondant au seuil S identifié, une comparaison de la température T d'air de sortie 9 mesurée avec la température minimale Tm identifiée, un calcul du taux de variation de température d'air de sortie par unité de temps Δ T/t dès que la température T d'air de sortie mesurée est supérieure à la température minimale Tm identifiée et un déclenchement de fin de séchage lorsque le taux de variation de température Δ T/t d'air de sortie par unité de temps calculé est supérieur pendant un temps prédéterminé de validation à un taux minimal a°/t inscrit dans des tables enregistrées et correspondant à la puissance de chauffe utilisée.In the exemplary embodiment illustrated, the dryer is provided with an automatic operating control system 10, constituted by an electronic circuit comprising a known device for measuring electrical voltage, a known device for controlling selected heating powers supplied. by electrical resistors 8, a known sensor of outlet air temperatures 9, and a microcontroller or microprocessor which, on the one hand records in its memories tables of lower and upper limit values of variation of outlet air temperature per time unit

both experimentally predetermined and classified according to different heating power conditions and various quantities by weight of prefixed linen, tables of thresholds S of the outlet air temperature both experimentally predetermined and classified according to different degrees of humidity at the end chosen drying rates and different quantities by weight of laundry, minimum temperature tables Tm of outlet air classified according to different thresholds S and tables of minimum rates of change of outlet air temperature per unit of time a ° / t classified according to different heating powers, and on the other hand operates successively initial temperature measurements Ti of outlet air, of electric voltage supplying the electrical resistors 8 supplying heating powers (this voltage measurement can be optional), temperature T (to) of outlet air 9 at time to after starting the dryer e 1 and in the interval between the initial phase I and the main phase II of the drying cycle, a calculation of the variation in outlet air temperatures

per unit of time, an identification of the quantity of laundry in the dryer by comparing the variation in outlet air temperatures

per unit of time calculated, with lower and upper limits of variation of outlet air temperature entered in the recorded tables and corresponding to prefixed quantities by weight of laundry, a reading of the degree of humidity at the end of drying chosen, an identification of the threshold S of outlet air temperatures in the tables recorded of the thresholds S corresponding to the quantity by weight of laundry identified and to the degree of humidity at the end of drying read, an identification of the minimum temperature Tm in the tables of Tm corresponding to the threshold S identified, a comparison of the outlet air temperature T 9 measured with the identified minimum temperature Tm, a calculation of the rate of change of outlet air temperature per unit of time Δ T / t as soon as the measured outlet air temperature T is higher than the minimum temperature Tm identified and an end of drying trigger when the rate of vari ation of temperature Δ T / t of outlet air per unit of time calculated is greater during a predetermined validation time at a minimum rate a ° / t entered in recorded tables and corresponding to the heating power used.

The prefixed quantities by weight of linen are for example one kilogram, two kilograms and a quantity greater than three kilograms.

When the quantity by weight of laundry identified by the microcontroller is less than a small predetermined quantity of laundry, for example one kilogram of laundry, an end of drying trigger is directly executed as soon as the temperature T of the outlet air 9 is higher at the minimum temperature Tm relative to the threshold S identified by the microcontroller and corresponding to this small predetermined quantity of laundry.

The preset tables of predetermined values experimentally recorded in the memories of the microcontroller are tables and sub-tables.

par unité de temps, à la fois prédéterminées expérimentalement et classées d'abord suivant des tranches prédéterminées de valeurs de température initiale Ti, puis suivant des tranches prédéterminées de valeurs de tension électrique V d'alimentation des résistances électriques chauffantes 8 (ce classement pouvant être optionnelle), enfin suivant des quantités en poids préfixées de linge, les tranches de température initiale Ti étant par exemple des tranches de températures allant de 0 à 40 degrés centigrades et variant par 5° centigrades, et des tranches de tension V étant par exemple des tranches de tension électrique allant de 187 à 242 Volts et variant par 11 Volts, c'est-à-dire de l'ordre de 5% de cette tension V, - des tables des seuils S de température d'air de sortie à la fois prédéterminés expérimentalement et classés d'abord suivant les degrés d'humidité de linge en fin de séchage puis suivant les quantités en poids préfixées de linge, - des tables des températures minimales Tm d'air de sortie 9, classées suivant les seuils S de température d'air de sortie, - et des tables des taux minimum a°/t de variation de température d'air de sortie par unité de temps, classés suivant des puissances de chauffe utilisées.In the example illustrated, these tables include tables of the lower and upper limit values of variation of outlet air temperatures.

per unit of time, both experimentally predetermined and classified first according to predetermined sections of initial temperature values Ti, then according to predetermined sections of electrical voltage V supply values for the electric heating resistors 8 (this classification can be optional), finally according to the prefixed quantities by weight of linen, the initial temperature bands Ti being for example temperature bands ranging from 0 to 40 degrees centigrade and varying by 5 ° centigrade, and voltage bands V being for example electrical voltage ranges from 187 to 242 Volts and varying by 11 Volts, that is to say of the order of 5% of this voltage V, - tables of thresholds S of outlet air temperature at the times predetermined experimentally and classified first according to the degrees of humidity of the laundry at the end of drying and then according to the quantities by weight of the prefixed laundry , - tables of minimum temperatures Tm of outlet air 9, classified according to the thresholds S of outlet air temperature, - and tables of minimum rates a ° / t of variation of outlet air temperature per unit of time, classified according to the heating powers used.

The dryer 1 thus produced gives excellent desired drying results. Triggering of end-drying under a triple condition imposed by an outlet air temperature T greater than a minimum temperature Tm experimentally predetermined and by a rate of change in outlet air temperature Δ T / t greater, for a while experimentally, avoids both insufficient drying and excessive drying.

Special thresholds S of the outlet air temperature, determined experimentally and assigned respectively to the different pre-determined quantities by weight of laundry to be dried, in drying control, significantly improve the control accuracy of the dryer 1 and the regularity of the results. drying results.

The dryer 1 has the advantage of eliminating from its construction, a device for measuring the resistivity of the linen or resistivity probe which, usually used in dryers known for controlling the degree of humidity of the linen to be dried, is sensitive to the nature of the laundry (surface resistivity detected) and requires in addition to an electronic processing circuit, electrical insulation means and rotating contacts, the aging of which makes random control and drying results uncertain .

The dryer 1 also has the advantage of avoiding a time control of operation which, usually used in known dryers, is sensitive to variations in the parameters of use such as electric voltage supply to the heating resistors and temperature. ambient.

Claims (8)

1. Method of automatically controlling the operation of a laundry drier (1) of the type including a rotary laundry drum (2), a system for drying by circulation of hot air through the drum (2) and a control system (10) comprising at least one heating-power control device, a sensor detecting the outlet-air temperature of the drum (2), storage means making it possible to store parameters determined experimentally for calculating a minimum outlet-air temperature and temperature-variation rates determined experimentally, and computing means, the drying cycle comprising an initial phase in which the outlet-air temperature rapidly increases, a main phase in which the outlet-air temperature stabilizes and follows a gentle slope and a final phase in which the outlet-air temperature rapidly increases once again, the method including the following steps:

   - measurement of the initial outlet-air temperature T_i,

   - measurement of the air temperature T(t₀) at the end of the initial phase,

   - estimation of the laundry load inside the drum (2) by using the initial temperature T_i and the temperature variation during the initial phase;

   - choice, depending in particular on the determined laundry load and on the desired degree of moisture, of one of the stored parameters enabling a minimum temperature T_m to be obtained from the temperature T(t₀),

   - choice, depending in particular on the heating power, of a minimum temperature-variation, rate (a°/t) from the stored variation rates,

   - stopping the drying cycle when the outlet-air temperature-variation rate per unit of time (Δ T/t), calculated from a measured outlet-air temperature (T) greater than the minimum temperature T_m, is, during a predetermined validation time (t_v), greater than the minimum rate (a°/t), or after the minimum temperature T_m has been reached at the end of a predetermined time (t_v1).
2. Method according to Claim 1, characterized in that the load of the drum (2) is determined by calculating the outlet-air temperature variation:

   

   per unit of time, and by comparing this temperature variation with lower and upper outlet-air temperature-variation values per units of time which are predetermined experimentally and correspond to fixed laundry loads.
3. Method according to Claims 1 and 2, characterized in that the parameters determined experimentally for calculating a minimum air temperature T_m depend on the specific characteriztics of the laundry drier (1) and on the outlet-air temperature thresholds (S) in the interval between the main phase and the final phase of the drying cycle, these being predetermined experimentally as a function of the prefixed quantities, by weight, of laundry to be dried, with a view to obtaining, at the end of drying, chosen degrees of moisture of the laundry.
4. Method according to Claims 1 to 3, characterized in that the minimum temperature T_m is equal to the temperature T(t₀) increased by a temperature rise given by the parameter chosen from the experimentally determined parameters.
5. Method according to Claims 3 and 4, characterized in that the outlet-air temperature thresholds (S) are determined experimentally as a function of the chosen degrees of moisture of, the laundry at the end of drying, of the prefixed quantities, by weight, of laundry to be dried and of the heating powers used.
6. Method according to Claims 3 and 4, characterized in that the outlet-air temperature thresholds (S) are determined experimentally as a function of the chosen degrees of moisture of the laundry at the end of drying, of the prefixed quantities, by weight, of laundry to be dried, of the heating powers used and of the variations in the electrical voltage supplying the electrical resistance elements which provide these heating powers.
7. Method according to any one of Claims 1 to 6, characterized in that the minimum outlet-air temperature-variation rates (a°/t) per unit of time are determined experimentally as a function of the specific characteriztics of the laundry drier (1) and of the heating powers used.
8. Method according to any one of the preceding claims, characterized in that, for a laundry load less than an experimentally pre-established quantity and for a chosen degree of moisture corresponding to "ready to iron" laundry, the end of the drying is triggered when the measured outlet-air temperature (T) is, during a predetermined validation time (t_v), greater than a corresponding minimum outlet-air temperature (T_m).

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