EP0067896B1 - Method of drying laundry and machine for carrying out the method - Google Patents

Abstract

1. A method of drying laundry, characterized by a determination of the magnitude of the quantity of the laundry to be dried, and in that the magnitude of the heat energy necessary for the drying is automatically adjusted to this magnitude.

Description

The present invention relates to a method for drying laundry and a machine for carrying out this method.

A tumble dryer is known which can be used to dry with a reduced heating power. This is provided in order to be able to dry heat-sensitive items of laundry at a reduced drying temperature. In addition, energy-saving drying is achieved in this way, whereby it must be accepted that the drying process is extended.

Drying with a reduced heating output only makes sense if no more than about half of the maximum permissible quantity has been filled into the dryer. If more is added, the drying time increases significantly, so that the dry goods are subjected to inadmissible mechanical stress, which can ultimately lead to wear and tear on the laundry. The influence of the room temperature is related to this. If the room temperature is high, a larger amount can be dried with reduced heating power. At low room temperature, however, the laundry drying machine should be less heavily loaded.

It should be evident from this that the success of drying with reduced heating output is heavily dependent on the operator. The user of such a machine must therefore have a high level of information with regard to the drying process, or an appropriate experience is required.

Drying with only a lower heating level is inadequate, particularly for machines with a large drum content. However, multiple heating levels or a continuous adjustment of the heating make the operation of the machine even more difficult. Success can hardly be achieved in practice, and undesirable side effects can also occur more frequently.

The object of the present invention is to provide a method and a machine for carrying out this method, which make it possible to carry out the drying process with an optimal effect without the operator having to have any experience in this regard.

In the method of the type mentioned in the introduction, this object is achieved in that the size of the amount of laundry to be dried is determined and the size of the heating power required for drying is automatically adapted to this size.

The stated object is also achieved by a machine, which is characterized in that a measuring device for determining the amount of the material to be dried is present, and in that a control device for controlling the heating power is connected to the output of this measuring device.

• Fig. 1 einen Teil einer ersten Ausführungsform einer Einrichtung zur Steuerung von Heizelementen beispielsweise bei einem Wäschetrockner, und
• Fig. 2 einen Teil einer anderen Ausführungsform der Einrichtung zur Steuerung von Heizelementen, die bei einem Wäschetrockner mit geschlossenem Luftkreis verwendet werden kann.

Exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. Show it:

• Fig. 1 shows a part of a first embodiment of a device for controlling heating elements, for example in a clothes dryer, and
• Fig. 2 shows part of another embodiment of the device for controlling heating elements, which can be used in a clothes dryer with a closed air circuit.

A laundry drying machine, also called a tumbler or drum dryer, contains a perforated drum or a drum which is mounted on the end face. The jacket of the tumbler surrounds the drum, a heating register, a blower and a program control device. The hot air generated by the heating coil is passed through the inner drum with the aid of the fan. It dries the damp laundry while loosening it up. The temperature of the air emerging from the drum can be measured at the outlet from the drum.

The machine is also designed so that the drying process can be slowed down in order to achieve the optimal drying effect. This method of working is optional and can be used gradually, so that the possibility of drying laundry within a short period of time is also retained. Only partially switching off this possibility of slowed drying means that by changing the adaptation characteristics for extremely small filling quantities, the reduction in heating output is retained and damage to the dry goods caused by an excessively high process temperature is avoided.

The program control of the machine can also be used to slow down the drying process. For example, the choice of a program for synthetics can cause the adaptation characteristic to be shifted towards lower heating output.

In its simplest form, the present method can proceed in such a way that, after a certain amount of laundry has been put into the machine and after starting a drying program or choosing a drying time, the machine automatically determines which amount of laundry has been added. Then, taking into account the prevailing room temperature, it chooses the economically and technically correct heating output sizes. The heating output can be adjusted in several stages or continuously.

One of the most important problems in this process is determining the amount of laundry to be dried by the machine itself. This can be achieved, for example, by weighing the laundry. This weighing can be achieved, for example, by means of a horizontally foldable inner part of the tumble door designed as a balance. However, the laundry can also only be weighed in the drum by, for example, one or more drum supports being designed to be resilient or provided with elements which react with a piezo effect to the load on the laundry filling. Such weighing means are generally known and therefore they do not need to be described in more detail here.

Another way to determine the amount of laundry in the drum is to measure the resistance of the laundry in the drum opposed to the flow of air flowing through it.

The technical means by which this method can be carried out are also generally known.

For the processes described so far, it was characteristic that the heating output was adjusted right at the beginning of the drying process. Another possibility is that the heating output is only adapted to the amount of laundry loaded after a certain period of time after the start of the drying process. The main advantage of this method is that at the beginning, i.e. initially dries with full heating power, which shortens the drying process, although at the same time the task mentioned in the introduction is also solved.

With such a method, one can proceed in such a way that after the start of the drying process, the machine and the laundry are brought to the operating temperature by means of the dry air flow. If you now measure the temperature of the air flow at the drum outlet, you will see that the temperature increases largely linearly during the heating phase. If you measure the temperature after a given period of time with different filling quantities, you can see that the temperature has reached different values. For a constant period of time, the size of the temperature is inversely proportional to the amount filled. This means that a small amount of charge causes a high temperature after a given period of time and a large amount of charge causes a low temperature.

Based on this knowledge, a simple method for determining the filling quantity or for assigning a specific heating output to a given filling quantity range is based. A period of predetermined and constant length is selected during which the dry air flow is passed through the laundry and during which the air flow is heated with full heating power. At the end of this period, the temperature of the air flow at the drum outlet is measured. Depending on the temperature of the air at the drum outlet, the size of the heating output can either be left undiminished, or the heating output can be reduced as necessary. The heating output can be reduced continuously or in stages.

The laundry drier, which is designed to carry out such a method, can be equipped with three heating elements 1, 2, 3 (FIG. 1), each 1/3 of the total heating power. Two of these heating elements 1 and 2 can be switched off by means of thermostats 4 and 5, which are arranged in the air flow near the drum outlet. The switching temperatures of thermostats 4 and 5 are selected so that one thermostat opens its contact at a temperature that is lower than the switching temperature of the other thermostat. In parallel to the switching contacts 6, 16 of the thermostats 4 and 5, contacts 7 and 8 are connected, which are controlled by a control device 9 of the machine.

After loading a certain amount of laundry, a program or a drying time is selected and the machine is started up. Since all contacts 6, 7, 8, 16 are initially closed, the air is first heated to full heating power. After a certain time, the contacts 7 and 8 are opened by the control device 9. Thermostats 4 and 5 were exposed to the air emerging from the drum throughout the entire period.

Depending on the switching temperature of thermostats 4 and 5 and the amount of laundry loaded, the following switching states are now possible: If the drum has been filled completely, the temperature of the air flow at the drum outlet will have risen only slightly. As a result, none of the thermostats 4 or 5 responds.

If the drum is only moderately loaded, the temperature of the exiting air flow will be higher. As a result, one of the thermostats 4 and 5 opens its contact during the period of time mentioned which has a lower switching temperature. In Fig. 1, this can be, for example, the thermostat 4, the contact 16 of which was opened during the period mentioned. At the end of the time period mentioned, the time relay 9 opens the contacts 7 and 8. Since the contact 16 of the first thermostat 4 was already open, the current flow through the first heating element 1 is interrupted. The control contact 8 in the second heating element 2 has also been opened by the control device, but the air at the outlet from the drum has not reached the switching temperature of the second thermostat 5, so that its contact 6 remains closed. As a result, the current flows through the second heating element 2 even after the end of the period mentioned. After this period, the air supplied to the drum is heated with a power that is 2/3 of the maximum heating power.

If only a small amount of laundry has been poured into the drum, the temperature in the air stream will have reached a high value after the specified period of time, so that both thermostats 4 and 5 have opened their contacts 6 and 16 during the specified period. After the specified period of time, the air is therefore only heated at 1/3 of the maximum heating output.

The determination of the switching temperatures of the two thermostats 4 and 5 is expediently geared to the drum volume. An optimal adaptation can be determined very easily by tests.

Another option for adaptation is the choice of the number of heating levels. For machines with a small drum volume, a great effect can be achieved with just two heating levels. The distribution of the heating power can also be uneven, e.g. two stages with 1/3 and 2/3 of the maximum heating output.

The control device can work with a relay, but it can also work electronically, in which case, for example, temperature-dependent elements be used to determine the temperature. The specified time period and the signals emitted by these temperature-dependent elements can be processed with the aid of ICs or with the aid of microcomputers.

In the case of multi-stage or stepless adjustment of the heating output to the filling quantity, the adjustment characteristic can be selected according to different criteria. For example, the drying time or the specific energy consumption can be kept almost constant over the entire filling area of the machine.

A major advantage of the method described last is that the level of the ambient temperature of the tumble dryer is also taken into account.

When the ambient temperature is high, the air flow at the drum outlet reaches a higher temperature level than at normal ambient temperature. This means that the drying process that has been started will run at a lower heating output, and yet the drying time will not be extended. This increases the energy saving effect with the machine by using external source heat, such as Waste heat from a washing machine / is used.

If the machine is operated in an extremely cold environment, the air flow at the drum outlet does not reach the normal temperature level at the measurement time. This means that the drying process will run with a higher heating output. If this were not the case and the heating output would decrease normally, the drying process could be too long. These methods thus prevent undesirably long drying times and avoid mechanical overloading of the drying goods, which stress leads to wear on the laundry.

However, the drying process can also be designed so that the laundry filled into the machine is first brought to a certain operating temperature by means of a fully heated air stream. The period of time required to reach the operating temperature is measured. Based on the length of the determined period of time, the size of the heating power used can then be reduced or not.

Such a method can in turn be carried out with the aid of a plurality of heating elements in the heating register of the tumble dryer, which can be switched off depending on the length of the period mentioned.

The methods described so far are particularly advantageous in tumble dryers with an open air circuit because they can also serve as a means of reducing energy consumption. This is less the case for machines with a closed air circuit, because the room air can only have a minor influence on the drying process. Nevertheless, the basic idea of the present method can also be used here.

For physical reasons, the temperature level of the drying process is higher for machines with a closed air circuit than for machines with an open air circuit. With the help of an automatic adjustment of the heating output to the filling quantity, the process temperatures which are dangerously high for a small filling quantity for dry goods can now be avoided without any other disadvantages.

The method described below is particularly advantageous for tumble dryers with a closed air circuit. Most tumble dryers contain a circuit for moisture level control. Such a circuit arrangement (FIG. 2) contains a scanner 10 arranged in the drum space, which is connected to an evaluation circuit 11. With the help of these parts, the electrical conductivity of the dry material is continuously monitored during the drying process. A first output of the evaluation circuit 11 is connected to a humidity degree control device 12. The elements of the circuit arrangement just mentioned are part of a conventional clothes dryer. The time gate 13 shown in Fig. 2 is also part of a conventional clothes dryer. The moisture degree control device 12 and the time gate 13 are components of the program control of the tumble dryer.

In order to achieve the automatic adaptation of the heating power to the filling quantity, the circuit arrangement also contains a counter module 14, the input of which is connected to a second output of the evaluation circuit 11. The circuit arrangement also contains a so-called hit logic 15 which cooperates with the counter module 14 and which is controlled from the time gate 13. The hit logic 15 controls heating elements, which can be switched approximately as shown in FIG. 1.

At the beginning of the drying process, there is only a slight change in the electrical conductivity of the dry material when the drum is full. At the beginning of the drying process with a medium load on the drum, on the other hand, the conductivity of the dry material can be brief, i.e. if there is currently no item of laundry on the scanner 10, practically drop to zero. These reductions are converted into “hit” pulses by the scanning electronics, and these are registered in the counter module 14.

Since the number of said impulses, which has been registered during a certain period of time, is in a direct relationship to the filling quantity, this represents a further means for determining the quantity of dry material in the drum of the tumble dryer then the required adjustment of the heating output is done.

After the drying process has been started with full heating power, after a certain period of time has elapsed, the procedure just explained and with the aid of the “hit” pulses mentioned can be used to compare the number of pulses registered in the counter module 14 with a predetermined value. If the number of said pulses exceeds the specified value, the output of the heating elements is reduced to the next lower level. For the further course of the process, the Sampler 10 used as usual for humidity control.

With this configuration of the machine, too, the heating power can be adjusted in several stages or continuously. Here too there is the possibility of linking the program control with the automatic adjustment. Likewise, this possibility of operating the machine can also be partially or completely switched off here by means of an operating element.

Claims (15)

1. A method of drying laundry, characterized by a determination of the magnitude of the quantity of the laundry to be dried, and in that the magnitude of the heat energy necessary for the drying is automatically adjusted to this magnitude.

2. The method of claim 1, characterized in that the laundry to be dried is weighed.

3. The method of claim 1, characterized in that the magnitude of the quantity of the laundry to be dried is determined by a measuring of the air resistance of the laundry against the air flowing therethrough.

4. The method of claim 1, characterized in that the adjustment of the magnitude of the heat energy is performed with a delay relative to the start of the drying process.

5. The method of claim 4, characterized in that the laundry to be dried is brought to a selected temperature by means of the drying air current, in that the time span necessary to reach said temperature is measured, and in that the adjusting of the heat energy is made based on the length of the measured time span.

6. The method of claim 4, characterized in that the the laundry is dried by aid of air current during a time span of selected length, in that one measures the temperature of the exiting air current, and in that one adjusts now the heating energy according to this temperature.

7. The method of claim 4, characterized by determining how often wet laundry articles contact a humidity feeler, and in that based on the number of these contacts the adjustment of the time of the reduction of the heater and/or of the adjustment of the magnitude of the reduced heat energy is carried out.

8. The method of claim 1 or 4, characterized in that the the adjustment of the heat energy proceeds automatically.

9. The method of claim 1 or 4, characterized in that the programme and time control of the laundry dryer is taken into account in the adjustment of the heat energy.

10. The method of claim 1 or 4, characterized in that the temperature of the environment is taken into account in the adjustment of the heat energy.

11. Apparatus for carrying out the method of claim 1, characterized in that a measuring means for the determination of the quantity of the substance to be dried is present, and in that a control means for controlling the heat energy is connected to the outlet of this measuring means.

12. The apparatus of claim 11, characterized in that the door of the dryer or its drum is provided with a weighing means.

13. The apparatus of claim 11, characterized in that there is provided a time element (9, 13) which places the measuring means for the determination of the quantity of the substance to be dried in operation with a delay relative to the start of the drying process.

14. The apparatus of claim 13 including at least two heater elements, characterized in that at least one of these heater elements (2) is coupled to a source of electric current via the contact (6) of a thermostat (5), that a control contact (8) is connected parallel to the contact (6) of this thermostat (5), and in that this control contact (8) is operable by a programme control system.

15. The apparatus of claim 13, characterized in that there is provided a counter block (14) which is connected to a logic circuit (15) and by which the heating elements can be controlled, in that the input of the counter block (14) is connected to a switching means (10, 11) for the measuring of the electric conductivity of the substance to be dried and the logic circuit (15) is controllable by a time gate (13).

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