EP1441062B1 - Laundry dryer and process to control the heating power - Google Patents

Description

The invention relates to a tumble dryer, in particular an exhaust air dryer, and a method for controlling the heating power of the tumble dryer.

In a conventional clothes dryer type of laundry to be dried is set by means of a program selector switch and the program controls the drying process depending on the area code with a given heating power level and predetermined drying time. Optionally, an optimum degree of moisture at the end of the drying cycle is not achieved or, if appropriate, the laundry is exposed to too high a heat at low humidity, so that the textile quality could be impaired. In other control methods for tumble dryer a residual moisture is determined depending on the selected laundry and controlled during the drying process. Depending on the initial moisture content and the amount of laundry, however, the drying time varies considerably.

DE 31 50 617 A1 discloses a control arrangement for a tumble dryer, which controls the drying process such that at the end of the drying process, a predetermined final moisture content of the laundry is achieved. For this purpose, the control arrangement comprises a measuring device which determines the humidity of the laundry according to the Leitwertprinzip. If the calculated mean of the measured values coincides with a maximum value, the required, remaining drying time is determined from the previously measured time course of the moisture of the laundry. The aim of this control arrangement is to determine the residual drying time required for achieving a desired final moisture content of the laundry from the intermediate measure.

EP 0 915 199 A discloses a method for optimizing energy consumption during drying of a laundry load in a dryer or a washer-dryer machine. The heating power and the throughput of the drying air are lowered in the last drying phase. This lowering may be gradual or stepwise depending on parameters such as e.g. the drying gradient of the laundry.

It is therefore an object of the invention to provide a tumble dryer or a method for controlling the heating power in a tumble dryer, in which a desired drying result with uniform heat load of the laundry to be dried in a given time can be achieved.

This object is achieved with the features of claim 1, 2 and 13, respectively. Advantageous embodiments are the subject of the dependent claims.

In the method according to claim 1, the time is determined, which is required between the achievement of two predetermined moisture levels. If the time required is longer than a predetermined setpoint, the heating power is increased. Otherwise, if the time between the two degrees of humidity is shorter, the heating power is reduced. Preferably, the second time when first determining the time difference is only a fraction of the maximum drying time, for example, 20% thereof. Based on the change in humidity thus the actually achieved drying effect is checked and made when determining a deviation, an adjustment of the heating power. If, for example, a high moisture absorption capacity is provided by the sucked-in ambient air in the case of an exhaust air dryer, then the heating capacity can be considerably reduced if the maximum drying time is sufficient. Only the heating power actually required, which is required to reach a desired degree of humidity at the end of the maximum drying period, is called up. Overheating and drying of the laundry is avoided, as well as insufficient drying until the end of the maximum drying time.

In the method according to claim 2 is also the heating power for heating the dry air, which is applied to the laundry to be dried, adjusted depending on the actual drying progress. Here, the moisture gradient or the current moisture level is determined at certain times and this is compared with a corresponding setpoint. If the amount of the moisture gradient is smaller than the target value, ie the decrease of the moisture is less than desirable, the heating power is increased and vice versa. In the alternative embodiment of claim 2 is falls below the moisture level setpoint at a given time, the heating power is reduced because the drying progress is better than the ideal line of temporal moisture reduction

Very particularly advantageously, the checking of the drying progress is carried out several times during the entire drying process, so that an ideal line of the degree of dryness is approximated as optimally as possible. That the required time between reaching two humidity levels is measured several times and the heating power is adjusted. In one embodiment, the time differences are measured at different degrees of humidity. In a further embodiment, the gradients are determined as a function of time or the actual degree of humidity and an adjustment of the heating power are made at several points in time. Overall, this can be done in discrete time intervals, for example at intervals of 2 to 5 minutes, or continuously, if a corresponding continuous measurement value for the degree of moisture is present.

The current setpoint used for the comparison for the time difference (claim 1), the degree of moisture or the moisture gradient (2) on the one hand depends on the time of comparison with respect to the elapsed drying time and on the other hand, this is advantageous depending on the remaining duration of the drying process determining the initial moisture of the laundry, the amount of laundry, the type of laundry, the drying program selected and the like. This takes into account, for example, that different types of laundry have different ideal patterns of moisture absorption.

Particularly advantageously, the heating power change resulting from the comparison with the desired values is set as a function of, for example, the difference between the desired value and the humidity gradient, degree of humidity or the time difference, so that a return of the moisture profile to the ideal line is approximated as quickly as possible. For example, the heating power is increased the more, the further the actual degree of humidity is above the desired degree of humidity. Conversely, the greater the difference between the desired degree of humidity at the time of comparison and the actual degree of humidity, the greater the reduction in heating power.

If the drying process is started with a low heating power or with heating power 0, then only little or no heating energy is required if the ambient air in an exhaust air dryer provides sufficient moisture absorption capacity during the drying process. If the desired residual moisture is not reached within the specified maximum drying time, i. the moisture of the laundry is higher than desired, so the user is signaled so that he fills, for example, at the next filling a smaller amount of laundry.

In the tumble dryer according to claim 13, the humidity of the laundry to be dried is erfaisbar with a humidity sensor. This is done in a conventional manner, for example with a conductivity sensor or by determining the temperature in the exhaust air. A heater heats the dry air supplied to the laundry, so that the drying process by the heated dry air runs faster. By an input device, the maximum drying time or a desired drying program can be specified. A control device detects this input and the signal from the humidity sensor and controls the heat output of the heater depending on the moisture profile. In this case, the control device controls a higher heating power when the degree of humidity at a certain or several specific times is higher than a preset value for the degree of humidity according to the time. Or the heating power is increased when the time to reach a predetermined humidity level difference is longer than a predetermined target value. In the opposite case, the control device reduces the heating power. As stated above for the method, by controlling the heating power an ideal course of the drying curve while sparing the laundry and adhering to a predetermined drying time is made possible.

Fig. 1

die Zeitabhängigkeit eines idealen Feuchtigkeitsverlaufs und eines tatsächlichen Feuchtigkeitsverlaufs bei Kontrolle zu bestimmten Feuchtegraden und

Fig.. 2

einen idealen und einen tatsächlichen Feuchteverlauf bei Anpassung der Heizleistung in Abhängigkeit der erreichten Feuchtereduzierung.

With reference to figures, embodiments of the invention will be explained. Show it:

Fig. 1

the time dependence of an ideal moisture course and an actual moisture course under control to certain degrees of humidity and

Fig. 2

an ideal and an actual moisture profile with adaptation of the heating power as a function of the achieved humidity reduction.

1 shows, as curve A, the ideal profile of the degree of moisture (rel.H) of the laundry up to a predefined maximum drying time Tmax. The moisture conditions and time relationships are given here only by way of example for explaining the control method. In the ideal curve A at time T1 80% humidity, at time T2 60% humidity, at time T3 40% humidity and at the end of Drying process Tmax 20% moisture of the laundry reached. The ideal curve A is given empirically, the desired residual moisture of 20% being reached at the desired time Tmax. In the ideal curve A, the heat input by a heater of a clothes dryer is initially higher during the drying process and is gradually reduced during the drying process. As a result, the maximum heat load for the laundry is limited, while a uniform drying result is achieved with minimal impairment of the quality of the laundry. The curve B shows an example of an actual moisture profile, which deviates from the ideal line A and should be adapted as possible, so that at the time Tmax the desired residual moisture. 20% is achieved. Deviations between the ideal and the actual curve A, B result from different amounts of laundry, different size or type of textiles, different ambient humidity in a vented dryer and the like

In the control method illustrated in FIG. 1, the heating power of a heater of the tumble dryer is adjusted by determining the time required to reach a predetermined degree of drying, here for example 80%, 60% and 40% laundry moisture. With the actual humidity curve B, 80% laundry moisture is achieved at the time T1a. The time duration T1a since the start of the drying process at the time T0 is greater than the time duration T1 of the ideal line. Thus, the ideal drying result has not been achieved until then, and the heating power is increased when the degree of drying is 80% at time T1a. Since the time deviation here is about 20%, the heating power is increased, for example, by 40% of the maximum possible heating power of the heating device. The curve B is the degree of humidity 60% at the time T2a, which is also after the ideal time T2. Again, the drying result is behind the ideal and since the difference between the periods T2, T2a is low, there is only a slight increase in heating power. This leads to a faster drying of the laundry, so that the degree of moisture 40% is achieved in the curve B at the time T3a before the ideal time T3. Since here the time duration of reaching the drying stage 40% is about 10% lower than that in the ideal curve, the heating power is reduced by 20% of the maximum heating power of the heater. Thus, the drying process slows down in comparison to the ideal curve and in turn, an approximation of the curves A, B so that finally at time Tmax the desired degree of drying of the actual drying curve B is well approximated.

FIG. 2 shows a second embodiment of the adaptation of the heating power, whereby the change of the degree of humidity is taken into account here between predetermined time intervals. The ideal moisture profile is represented by the curve C, while the actual moisture profile is represented by the curve D. In the time interval T0-T4, the moisture decrease ΔH1a of the actual curve D remains behind the moisture decrease ΔH1 of the ideal curve C. Therefore, at the time T4, the heating power is increased and the drying process at the curve D is accelerated. In the time interval T4-T5, the gradient of the dry course of the actual curve D or the difference of the humidity ΔH2a is greater than the gradient of the ideal curve or the difference of the humidity ΔH2, the amounts being taken into account here. In this case, the heating power is reduced at time T5, so that the actual curve D of the ideal curve C is approximated again. This The iteration process can be refined with a correspondingly fine division of the times up to the desired maximum time Tmax and the actual moisture profile can be tracked with small deviations.

Instead of taking into account the gradients in the time intervals, the actual degree of humidity can also be compared with the desired one at the times T4, T5, T6, the heating power being increased if the actual degree of humidity is less than the ideal degree of humidity, and vice versa.

In an embodiment of the above control method is started at time T0 with heating power 0 watts or a low heating power level and, for example, the time T1 (Fig. 1) or T4 (Fig. 2) is selected close to T0, so that if appropriate dryer and warmer Outside air at a vented dryer the required heating energy for the heater can be reduced or set to 0.

In a further embodiment of the control method, an indication to the user of the tumble dryer, if in spite of now the maximum set heating power of the heater, the moisture level is above the desired moisture level. In this case, despite maximum heating power, the desired drying result (ideal curve A or C) could not be achieved, so that the user is made aware of this in the next drying process on the basis of the indication in the form of an acoustic signal, optical signal or a corresponding display pour less amount of laundry into the tumble dryer.

Claims (15)

1. Process for controlling the heating capacity of a laundry dryer, in particular an exhaust air dryer, having the steps:

   a) establishing a maximum drying period (Tmax),

   b) starting the drying process at a first heating capacity to heat the drying air,

   c) determining the time difference (T1a-T0, T2a-T0, ..) between a second and a first point in time, wherein at the first point in time (T0), a first preset degree of moisture is reached and at the second point in time (T1a, T2a, ..), a second preset degree of moisture is reached,

   d) comparing the time difference with a theoretical value (T1-T0, T2-T0, ..) and

   e) increasing the heating capacity if the time difference is greater than the theoretical value, or

   f) reducing the heating capacity if the time difference is less than the theoretical value.
2. Process for controlling the heating capacity of a laundry dryer, in particular an exhaust air dryer, having the steps:

   a) establishing a maximum drying period (Tmax),

   b) starting the drying process at a first heating capacity to heat the drying air,

   c) determining the moisture gradient (ΔHna/ΔT, n = 1, 2 ...) or the degree of moisture at one or more certain points in time,

   d) comparing the moisture gradient (ΔHna/ΔT) or the degree of moisture with a preset theoretical value (ΔHn/ΔT) corresponding to the point in time and

   e) increasing the heating capacity if the moisture gradient or the degree of moisture is greater than the corresponding theoretical value, or

   f) reducing the heating capacity if the moisture gradient or the degree of moisture is less than the corresponding theoretical value.
3. Process according to claim 1 or 2, characterised in that steps c) to f) are executed several times during a drying passage.
4. Process according to claim 1,2 or 3, characterised in that the theoretical value depends on the remaining period of the drying process, the initial moisture of the laundry, the required residual moisture of the laundry after the drying process and/or the point in time of determining the moisture gradient or degree of moisture.
5. Process according to one of the preceding claims, characterised in that the heating capacity change depends on the difference between theoretical value and moisture gradient, degree of moisture or time difference, the remaining period of the drying process, the initial moisture of the laundry, the required residual moisture of the laundry after the drying process and/or the point in time of determining the moisture gradient or degree of moisture.
6. Process according to one of the preceding claims, characterised in that the level of the heating capacity change and/or the theoretical value of the moisture gradient, the degree of moisture or the time difference are established using empirically ascertained comparative values.
7. Process according to one of the preceding claims, characterised in that the first heating capacity is 0 W or only a fraction of the maximum heating capacity of the heating device, preferably less than 20% of the maximum heating capacity of the heating device.
8. Process according to claim 2 or one of the preceding claims dependent on claim 2, characterised in that the degree of moisture is recorded at one or more preset points in time (T4, T5, T6) and then steps d) to f) are executed.
9. Process according to claim 8, characterised in that the preset point or points in time depend on the maximum drying period (Tmax).
10. Process according to one of the preceding claims, characterised in that it is signalled to the user of the laundry dryer that the required degree of residual moisture of the laundry could not be achieved in the established maximum drying period (Tmax).
11. Process according to one of the preceding claims, characterised in that it is signalled to the user of the laundry dryer to add a lower quantity of laundry during the next drying passage when the required degree of residual moisture of the laundry could not be achieved in the established maximum drying period (Tmax).
12. Process according to claim 10 or 11, characterised in that the instruction is indicated by means of an optical or acoustic signal, in particular by means of an alphanumeric display.
13. Laundry dryer, in particular exhaust air laundry dryer, having
    a moisture sensor for determining the moisture of the laundry to be dried,
    a heating device for heating the drying air to be supplied to the laundry, an input device and
    a control device, which records a signal corresponding to the degree of moisture from the moisture sensor and controls a required drying program;
    characterised in that
    the maximum drying period (Tmax) and/or the required drying program can be entered by means of the input device;
    the control device presets the heating capacity of the heating device and controls the drying program according to the required drying program and/or the maximum drying period,
    the control device presets a higher heating capacity when the degree of moisture at a certain point in time is higher than a preset theoretical value for the degree of moisture for this certain point in time or when a time period (T1a, T2a, ..) until reaching a preset degree of moisture difference is longer than a theoretical value of the time period (T1, T2, ..) preset for this degree of moisture difference, and
    the control device presets a lower heating capacity when the degree of moisture at a certain point in time is less than a preset theoretical value for the degree of moisture for this certain point in time or when a time period (T1a, T2a, ..) until reaching a preset degree of moisture difference is shorter than a theoretical value of the time period (T1, T2, ..) preset for this degree of moisture difference.
14. Laundry dryer according to claim 13, characterised in that the control device comprises a calculating unit, with which the one or more theoretical values for the degree of moisture or for the time difference can be calculated as a function of the maximum drying period, of the required drying program, the remaining period of the drying process, the initial moisture of the laundry, the required residual moisture of the laundry after the drying process and/or the point in time of determining the moisture gradient or degree of moisture.
15. Laundry dryer according to claim 13 or 14, characterised in that the control device comprises a memory device, from which the one or more theoretical values for the degree of moisture or for the time difference can be read out as a function of the maximum drying period, of the required drying program, of the remaining period of the drying process, the initial moisture of the laundry, the required residual moisture of the laundry after the drying process and/or the point in time of determining the moisture gradient or degree of moisture.

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