EP0483731A2 - Drier and method to monitor the temperature of a drier - Google Patents

Abstract

A drier (10) is provided with an internal space (12) for holding washing (13) to be dried and with a fan (16) for producing an airflow (18) which is passed through the internal space (12). The drier (10) furthermore has at least one heater (17), connected to an electrical power source (28), for heating the airflow (18) to a preselected temperature. Furthermore, a thermostat device (26), which is connected to the heater (17), is provided for detecting the temperature of the airflow (18), the thermostat device (26) being set up to disconnect the heater (17) from the power source (28) if an upper temperature value is exceeded and to connect the heater (17) to the power source (28) again when the temperature falls below a lower value. The drier (10) additionally has a monitoring circuit (32), which is connected to the thermostat device (26), in order to produce a signal, which is dependent on the disconnections, for an indicator unit (35). In this case, the monitoring circuit (32) has a counter circuit for counting the disconnections that occurred during a drying process and is connnected to the indicator unit (35). (Fig. 1). A procedure to be carried out on the drier is also described. <IMAGE>

Description

The invention relates to a tumble dryer with an interior for receiving laundry to be dried, with a blower for generating an air flow directed through the interior, with at least one heater connected to an electrical energy source for heating the air flow to a preselected temperature, with a thermostat device connected to the heater and provided for detecting the temperature of the air flow, which for switching off the heater from the energy source when an upper temperature value is exceeded and for reactivating the Heating to the energy source when the temperature falls below a minimum value, and with a monitoring circuit connected to the thermostat device in order to generate a signal dependent on the shutdowns for a display unit.

A clothes dryer of the type mentioned above is known from EP-A-0 312 072.

• Messen der Temperatur des Luftstromes,
• Abschalten der Heizung, wenn die gemessene Temperatur größer wird als ein oberer Sollwert,
• Wiedereinschalten der Heizung, wenn nach dem Abschalten die gemessene Temperatur kleiner wird als ein unterer Sollwert, und
• Ermitteln eines Wertes, der mit dem Abschalten in Zusammenhang steht.

The invention further relates to a method for temperature monitoring in a clothes dryer, which has an interior for receiving laundry to be dried, through which an air stream heated by a heater to a preselected temperature is passed, with the steps:

• Measuring the temperature of the air flow,
• Switching off the heating if the measured temperature is higher than an upper setpoint,
• The heating is switched on again if the measured temperature becomes lower than a lower setpoint after switching off, and
• Find a value related to shutdown.

A method of the type mentioned above is carried out on the clothes dryer known from EP-A-0 312 072.

It is generally known to monitor the heating provided for the air flow with a thermostat in tumble dryers and to switch off the heating by the thermostat if the air flow exceeds a certain upper temperature value. This is to prevent the laundry to be dried from being damaged by excessively hot air.

When the air flow that continues to be conveyed by the fan has cooled to a lower temperature value, the thermostat switches the heating on again. In this way, the air flow that is passed through the interior of the tumble dryer is regulated between two temperature values. For this purpose, the thermostat generally has an opening contact which is connected in series with the heater and the electrical energy source supplying the heater.

As is known, the air stream emerging from the interior of the tumble dryer is frequently passed through a fluff filter in order to retain the fluff which arises when the laundry is drying. In so-called exhaust air dryers, the air flow is led directly outside, while in so-called air recirculation dryers it is returned to the blower via a condenser for separating the moisture absorbed. Since it is inevitable that the fluff filter and possibly the condenser become clogged with fluff over time, the strength of the air flow decreases, and the air flow sometimes even comes to a complete standstill. A failure of the air circulation in tumble dryers can also be caused by the fan failing.

If the air flow decreases or fails, not only does the drying effect of the tumble dryer decrease, but the thermostat will switch off the heating at shorter and shorter intervals due to the poorer heat dissipation from the heating. This is undesirable not only because of the lack of drying effect, but also because the frequent switching cycles overload the heating and the thermostats.

In the tumble dryer known from EP-A-0 312 072, a monitoring circuit is therefore provided which measures the cooling down time between switching off and switching on the heating again. If this cooling time of a decreasing or failing air flow exceeds a certain period of time, the tumble dryer is switched off. At the same time, this malfunction is visually displayed on a display unit. In this way, it should be avoided that ever longer cooling times, which inevitably go hand in hand with ever shorter heating times, lead to destruction of the heating and / or the thermostat. In addition, the user is advised by the display unit to clean the fluff filter and / or the condenser of fluff if necessary.

The predetermined period of time, which the cooling time in the known tumble dryer must not exceed, is determined with the aid of the output voltage of an RC element, which increases exponentially over time. Immediately when the heating is switched off, the capacitor of this RC element begins to charge, so that the output voltage is a measure of the time which has passed since the heating was switched off. The output voltage of the RC element is preselected using a comparator DC voltage value compared, which DC voltage value corresponds to a certain period of time that the RC element needs to deliver exactly this value as the output voltage.

In other words, the known time constant of the RC element is used as a time reference to measure the switch-off time of the heating.

In addition, it is also known from EP-A-0 312 072 to start a stopwatch in each case after the heating has been switched off and switches off the known tumble dryer when a certain period of time is exceeded.

In the known tumble dryer, it is disadvantageous that the monitoring circuit delivers the error signal on the basis of a time measurement. This is because time measurements can only be carried out with a high level of design effort with reliable accuracy and reproducibility, while the simple use of an RC element leads to very inaccurate measurement results, since among other things the time constant of an RC element depends on the ambient temperature. Since the permissible cooling time will also depend on the selected temperature of the air flow, different RC elements must be provided for the different drying programs of the tumble dryer, which leads to a structurally high effort.

But regardless of the disadvantages associated with time measurement, the cooling time is not a suitable and reliable measured variable for detecting the condensation on the condenser and the fluff filter or the failure of the fan. So, in spite of any influence on the air flow, that, for example, at a relatively low drying temperature, for example for wool or when the RC elements age, the monitoring circuit does not determine that the maximum permissible cooling time has been exceeded. In addition, the permissible cooling times for the various dryer programs and air flow temperatures differ so significantly that they can only be determined empirically and therefore unreliably.

The object of the present invention is therefore to further develop a clothes dryer and a method of the type mentioned at the outset in such a way that these disadvantages are avoided. In particular, it should be possible to reliably detect a malfunction in the air flow. The method should be simple to carry out and the tumble dryer should have a structurally simple and reliable structure.

With regard to the tumble dryer mentioned at the outset, this object is achieved in that the monitoring circuit has a counter circuit for counting the shutdowns of the heating which take place during a drying process, and in that the counter circuit is connected to the display unit.

With regard to the method mentioned at the outset, this object is achieved in that the number of shutdowns which take place during a drying process is counted and displayed.

The object underlying the invention is completely achieved in this way. The counting of the shutdowns that take place during a drying process is namely a simple and easy to carry out method with which a Slackening of the air flow is detected safely. The "worse" because the decreasing air flow removes the heat from the heater, the more often the heater will reach the upper temperature value and will be switched off by the thermostat device.

Furthermore, it is advantageous that the counting of events can be effected with simple circuitry means, which significantly reduces the design effort compared to the known time measurement method. Malfunctions can practically not occur here, so that safe monitoring of the tumble dryer is ensured.

In one embodiment of the new tumble dryer, it is preferred if the monitoring circuit has a decoding circuit which is connected to at least one of the output lines of the counter circuit corresponding to a certain number of shutdowns and via a signal line to the display unit, and if the decoding circuit generates an error signal, when a certain number of shutdowns has occurred.

This measure has the advantage over the known time measurement method that a one-off exceeding of the cooling time, as can occur for many reasons, does not yet lead to the output of an error signal. Furthermore, it is advantageous that for different drying programs and temperatures, the number of shutdowns can easily be determined, which indicates a malfunction in the air flow.

It is further preferred if the specific number of shutdowns is greater than three.

This measure is particularly advantageous because, as the applicant has found out, as a rule no more than three shutdowns occur during a drying process, even with different drying programs and temperatures, provided that the air flow is not caused by flocculation or the like. being affected. Only after three shutdowns during a drying process is the user indicated on the display unit that he must clean the condenser and the fluff filter.

In one embodiment of the tumble dryer according to the invention, it is preferred if the monitoring circuit is connected via a control line to a switching unit provided between the heater and the energy source for switching off the heating, the switching unit being opened or closed depending on the error signal.

This measure is particularly advantageous because it ensures that a malfunction in the air circuit not only leads to a warning to the user, but because the heating is then finally switched off in a manner known per se.

It is further preferred if the decoding circuit has a diode coupling network which is connected to at least two output lines of the counter circuit and to the signal line and the control line.

As a result of this measure, the error signal is generated in a structurally simple manner from the output lines of the counter circuit, namely via a diode coupling network. It is a so-called wired logic that can be implemented with little design effort.

It is further preferred if the decoding circuit has a memory unit, the input of which is connected to one of the output lines of the counter circuit and the output of which is connected to the signal line and the control line.

This measure has the advantage that once an error signal has been generated, it is stored in the monitoring circuit so that it cannot be lost even if the counter circuit continues to count or overflow due to further switch-off processes. The user who may be absent during the drying operation of the tumble dryer can also recognize afterwards that the fluff filter and possibly the condenser must be cleaned.

Furthermore, it is preferred if the decoding circuit has a selection circuit, via which the decoding circuit can optionally be connected to one of the output lines of the counter circuit.

This measure is particularly advantageous because, in a structurally simple manner, different counter outputs, which correspond to different numbers of shutdowns, can be selected in order to indicate a malfunction or to finally switch off the heating.

In this exemplary embodiment, it is particularly preferred if the selection circuit is connected to a program control unit for selecting different drying programs, certain output lines of the counter circuit being connected to the decoding circuit as a function of the respective drying program.

This measure advantageously has the effect that the number of shutdowns which leads to the generation of the error signal is determined as a function of the respective drying program. This ensures that, for example, a higher number of shutdowns is tolerated at high drying temperatures and / or long drying times than at short times and / or low temperatures. This also contributes to the safe functioning monitoring of the new tumble dryer.

It is further preferred if the monitoring circuit has a clock generator in order to alternately switch the display unit on and off.

This measure has the advantage that the user is given a periodic warning signal which he does not overlook as easily as a static signal. This ensures in a structurally simple manner that the user notices the error signal and consequently cleans the fluff filter and / or capacitor or checks the blower.

In this exemplary embodiment, it is further preferred if the monitoring circuit has a pulse shaper circuit connected between the thermostat device and an input of the counter circuit.

This measure ensures that only shutdowns that have actually occurred are registered by the monitoring circuit, while voltage fluctuations and the like are not counted. This known and structurally simple measure thus leads to a safe function of the monitoring circuit in the tumble dryer according to the invention.

It is further preferred if the thermostat device has a temperature-dependent opening contact connected between the heater and the energy source and if the heater and the opening contact are connected via their common connection point to an input of the pulse shaping circuit.

This measure is particularly advantageous in terms of design, because the connection point between the opening contact and the heating is provided with a different voltage level depending on whether the opening contact is open when an upper temperature value is exceeded or is closed when a lower temperature value is undershot. A change in this voltage level by opening the opening contact to switch off the heating is converted by the pulse shaper circuit into a counting pulse to be detected by the counter circuit.

It is further preferred if the monitoring circuit has a reset device at least for the counter circuit in order to set the counter circuit to zero at the beginning of a new drying process.

This measure, which is known per se, has the advantage that each drying process begins with an erased counter circuit, so that in a previous drying process Shutdowns carried out do not lead to an excessive number of shutdowns being simulated during the new drying process.

It is also preferred if the tumble dryer has a timer which switches the tumble dryer off after a cooling time after the switching unit has been opened.

This measure is particularly advantageous because the fan and the motor rotating the drum are not switched off simultaneously with the heating. The laundry in the drum continues to move in this way and is cooled even by the now slowly cooling air flow. Only after a cooling time preselected by the program control unit has elapsed, does the timer switch off the other consumers of the tumble dryer, thereby preventing the laundry from sticking to the still hot drum and being damaged.

With regard to the method according to the invention, it is preferred if, as a further step, it has the generation of an error signal if the heating has been switched off a number of times during a drying process.

This measure is particularly advantageous because the number of shutdowns that occurred during a drying process forms the basis for the generation of the error signal. The error signal is advantageously obtained from an easy-to-determine variable and it prevents a one-off exceeding of the cooling time of the heater as it is can occur for many reasons, already leads to the output of an error signal.

Furthermore, it is preferred if the method provides, as a further step, preventing the restarting when the error signal has been generated.

This step advantageously prevents the heater from being switched on again despite a malfunction in the air circuit, which could otherwise lead to destruction of the heater and / or the thermostat.

It is further preferred if the method according to the invention is carried out on a clothes dryer according to the invention.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the combinations specified in each case, but also in other combinations or on their own without departing from the scope of the present invention.

Fig. 1

einen erfindungsgemäßen Wäschetrockner in einer Seitenansicht, im Schnitt und stark vereinfacht;

Fig. 2

in einer schematischen Darstellung eine Überwachungsschaltung des Wäschetrockners aus Fig. 1;

Fig. 3

eine detailliertere Darstellung der Überwachungsschaltung aus Fig. 2; und

Fig. 4

eine Darstellung wie Fig. 3, jedoch in einer anderen schaltungstechnischen Realisierung;

Fig. 5

in einer schematischen Darstellung ein weiteres Ausführungsbeispiel für die Zählerschaltung und die Dekodierschaltung aus der Überwachungsschaltung nach Fig. 2;

Fig. 6

eine Darstellung wie Fig. 5, jedoch in einer anderen schaltungstechnischen Ausführung;

Fig. 7

in einer Darstellung wie Fig. 3 ein weiteres Ausführungsbeispiel der Überwachungsschaltung;

Fig. 8

in einer schematischen Darstellung ein Ausführungsbeispiel für eine potentialfreie Überwachung der Thermostateinrichtung;

Fig. 9

in einer Darstellung wie Fig. 8 ein weiteres Ausführungsbeispiel für die potentialfreie Überwachung der Thermostateinrichtung; und

Fig. 10

in einer Darstellung wie Fig. 8 noch ein weiteres Ausführungsbeispiel für die potentialfreie Überwachung der Thermostateinrichtung.

An embodiment of the invention is shown in the drawing and is explained in more detail in the following description. Show it:

Fig. 1

a clothes dryer according to the invention in a side view, in section and greatly simplified;

Fig. 2

in a schematic representation, a monitoring circuit of the clothes dryer from Fig. 1;

Fig. 3

a more detailed representation of the monitoring circuit of Fig. 2; and

Fig. 4

a representation like Figure 3, but in a different circuit implementation.

Fig. 5

a schematic representation of another embodiment for the counter circuit and the decoding circuit from the monitoring circuit of FIG. 2;

Fig. 6

a representation like Figure 5, but in a different circuit design;

Fig. 7

3 shows a further exemplary embodiment of the monitoring circuit;

Fig. 8

a schematic representation of an embodiment for a potential-free monitoring of the thermostat device;

Fig. 9

in a representation like FIG. 8, a further exemplary embodiment for the potential-free monitoring of the thermostat device; and

Fig. 10

8 shows yet another exemplary embodiment for the potential-free monitoring of the thermostat device.

In Fig. 1, 10 designates a clothes dryer, which has a cuboid housing 11. The clothes dryer 10 has an interior 12 in which laundry 13 to be dried is located. The interior 12 has a drum 14 of essentially horizontal cylindrical shape. The drum 14 can be rotated about a horizontal axis by means of drive means (not shown in FIG. 1).

An air circuit is provided to dry the laundry 13. The air circuit comprises a blower 16 with a downstream heater 17, the blower 16 discharging a warm air flow 18 generated therein into a downstream duct 19. The channel 19 opens into an end wall 20 of the drum 14 and thus guides the warm air flow 18 into the interior 12. The warm air stream, which is loaded with both steam and lint, flows at 18 ′ through an end wall 21 of the drum 14 opposite the end wall 20 into a channel 22. A fluff filter 23 is arranged in the channel 22, through which the fluff is filtered out of the air flow 18 ′.

In the case of so-called exhaust air dryers, the duct 22 leads outside, while in the case of so-called circulating air dryers the duct 22 is returned to the blower 16 via a condenser indicated at 24. The air flow 18 ′ is dried in the condenser 24 in a manner known per se.

As can be seen in FIG. 1, the heater 17 is connected to a thermostat device, indicated at 26, which has an opening contact 27. The opening contact 27 is with the heater 17 and an electrical energy source 28 as well a switching unit 29 connected in series. The opening contact 27 serves to monitor the temperature of the air flow 18 and is set up to interrupt the connection between the heater 17 and the energy source 28 when the air flow 18 assumes a temperature above the response threshold of the thermostat device 26. When the heater 17 cools down after being switched off, the temperature of the air flow 18 drops and the thermostat device 26 closes the opening contact 27 again as soon as the temperature of the air flow 18 comes to be below a lower temperature value. In this way, the temperature of the air flow 18 is regulated between an upper temperature value and a lower temperature value.

The heater 17 and the opening contact 27 are connected at their common connection point 31 to a monitoring circuit 32 which, in a manner to be described in more detail, counts the number of shutdowns of the heater 17. Depending on the number of shutdowns, the monitoring circuit 32 outputs a control signal which reaches the switching unit 29 via a control line 33. The switching unit 29 is opened via the control line 33 when the number of shutdowns of the heater 17 exceeds a preselected reference value. By opening the switching unit 29, the heater 17 is switched off by the electrical energy source 28 regardless of the state of the thermostat device 26, so that the air flow 18 is not further heated.

The monitoring circuit 32 is also connected via a signal line 34 to a display unit 35, via which it is displayed whether the number of times the heater 17 has been switched off has exceeded the preselected reference value.

In the vicinity of the display unit 35, a program control unit 36 is indicated in FIG. 1, which is operated via a rotary knob 37. The program control unit 36 serves to set a specific drying program and / or a specific drying temperature and duration. The program control unit 36 is also connected to the monitoring circuit 32 via a connecting line 38. The connecting line 38 can be designed as a multi-core data bus, as is indicated by the two slashes in the connecting line 38.

As a rule, the opening contact 27 will only open a few times during a drying process. However, if the air circuit malfunctions, be it that the condenser 24 and / or the fluff filter 23 are blocked by fluff, or that the fan 16 has failed, the air flows past the heater 17 considerably more slowly. In this way, the air flow 18 reaches the upper cut-off temperature considerably more often during a drying process, and the thermostat device 26 switches off the heater 17 more frequently than normal during a single drying process. In the monitoring circuit 32, the number of shutdowns of the heater 17 is compared with a reference value specified by the program control unit 36 via the connecting lines 38. If the number of times the heater 17 is switched off exceeds this reference value, the monitoring circuit 32 opens the switching unit 29 via the control line 33 and thus switches the heater 17 off. At the same time, the display unit 35 is controlled via the signal line 34, the one Glow lamp, a light emitting diode, an acoustic signal generator or a sight glass can be. The user recognizes or hears via the display unit 35 that he has to clean the fluff filter and / or the condenser 24 or that the fan 16 has failed.

FIG. 2 shows the monitoring circuit 32 from FIG. 1 in the form of a schematic block diagram. It can be seen that the electrical energy source 28 is connected via an on / off switch 40 to the switching unit 29, which is a relay 41 in the example shown. From the relay 41 leads on the one hand a line to the heater 17 and on the other hand a control line indicated by dashed lines to a timer 42 via which the on / off switch 40 is connected to further consumers 10 'of the clothes dryer 10.

The connection point 31 between the heater 17 and the opening contact 27 is connected to a pulse shaping circuit 44 via an input line 43. The pulse shaper circuit 44 is connected via a line 45 to an input of a counter circuit 46. The counter circuit 46 is in turn connected with its output lines indicated at 47 to a decoding circuit 48, from which the control line 33 goes to the relay 41. An inner section 34 ′ of the signal line 34 leads from the decoding circuit 48 to a clock generator 49, which is connected via a line 50 to a display driver 51 for the display unit 35, which in this case is designed as a light-emitting diode 52.

Furthermore, it can be seen that the monitoring circuit 32 has a reset device 54 which is connected both to the pulse shaping circuit 44 and to the counter circuit 46 and the decoding circuit 48. The reset circuit 54 is connected to the program control unit 36 via one of the connecting lines 38, which is shown at 38 ″ in FIG. 2. The program control unit 36 is likewise connected to the decoding circuit 48 via the connecting lines 38 ′ and there, in a manner to be described in more detail below, effects the selection of a reference value for the number of times the heater 17 was switched off.

The monitoring circuit 32 described so far operates as follows:
The heater 17 of the tumble dryer 10 is switched on in a manner known per se via the on / off switch 40. During the drying process now taking place, the air stream 18 reaches a temperature which is so high that the opening contact 27 interrupts the power supply to the heater 17. The connection point 31, which has hitherto been at ground potential, is pulled to a higher voltage level by opening the opening contact 27. This change in the voltage of the connection point 31 is conducted via the input line 43 to the pulse shaping circuit 44, which in turn conducts a counting pulse to the counter circuit 46 via the line 45. The counter circuit 46 represents on the output lines 47 the counted number of shutdowns of the heater 17.

In the decoding circuit 48, the output lines 47 and the reference value, which is connected via the connecting lines 36 ' is set, an error signal is generated as soon as the number of shutdowns of the heater 17 has exceeded the reference value. The error signal causes the relay 41 to be opened via the control line 33, so that the heater 17 is switched off. On the other hand, the clock generator 49 is controlled via the inner control line 34 ', which causes via its output line 50 that the display driver 51 periodically switches the light-emitting diode 52 on and off again.

This blinking of the light emitting diode 52 signals to the user that the heating 17 has been switched off too many times, so that he will clean the fluff filter 23 and the capacitor 24.

In order to protect the laundry 13 located in the drum 14, further consumers 10 ′ of the clothes dryer 10, such as the fan 16 or a motor driving the drum 14 is only switched off via the timer 42 after a cooling time which may have been set as a function of the program. The laundry can therefore not stick to the drum 14 even after opening the relay 41, but is moved and ventilated until the drum 14 and the air flow 18 have cooled.

If the drying program has ended without prematurely switching off the heater 17, a new drying program can be started. When this new drying program is started, the program control unit 36 causes the reset device 54 to reset the pulse shaping circuit 44, the counter circuit 46 and the decoding circuit 48 to their initial state via the connecting line 38 ″. The shutdowns now taking place are counted from zero again.

The monitoring circuit 32 is shown in more detail in FIG. 3 than in FIG. 2.

It can be seen that the pulse shaping circuit 44 has a Schmitt trigger 56, the inverting output of which is connected to a clock input 57 of a counter module 58. The counter module 58 is connected on its output lines 47 to a selection circuit 60, which optionally connects one of the output lines 47 to a clock input 61 of a memory unit 62, which in this case is a D flip-flop 63. As already mentioned, the selection circuit 60 is controlled by the program control unit 36 via the connecting line 38 ′.

The individual output lines 47 of the counter module 58 correspond - as already mentioned - to different numerical values for the number of times the heater 17 is switched off, so that the reference value is determined in that the program switching device 36 selects a selected output line 47 which e.g. corresponds to four shutdowns, connects to the storage unit 62.

The D flip-flop 63 is connected to the clock generator 49 via a diode 64. The clock generator 49 has a Schmitt trigger 68 which is fed back through a resistor 66 and a capacitor 67 and thus oscillates, the output of which drives a transistor 70 via a further Schmitt trigger 69, which serves as a display driver for the light-emitting diode 52.

If the output Q of the D flip-flop 63 is logic L, the input of the Schmitt trigger 69 is also logic L, so that the transistor 70 is turned on and the light emitting diode 52 Emits light and indicates that the tumble dryer 10 is functioning properly. In this way, the light-emitting diode 52 can additionally take on the function of an operating display, which leads to a significant reduction in costs, since the indicator lamp previously provided for this purpose can be omitted. If the output Q of the D flip-flop 63 goes to logic H, the input of the Schmitt trigger 69 is released via the diode 64, so that the clock pulses of the clock generator 49 now reach the transistor 70 via the Schmitt trigger 69. The diode 52 starts to flash.

Furthermore, it can be seen in FIG. 3 that the reset device 54 has, in a known manner, an RC element 71 which is connected to a voltage VCC, which is supplied by the program control unit 36 via the connecting line 38 ″. If the program control unit 36 switches on the voltage VCC at the beginning of a new drying process, the capacitor of the RC element 71 takes on this voltage value only with a delay, so that the Schmitt trigger 56, the counter module 57 and the D flip-flop 63 receive the voltage VCC have already applied, while their reset inputs RST are still held at ground or logic L via the capacitor of the RC element 71. Only after a time determined by the time constant of the RC element 71, the reset inputs RST go to logic H and release the corresponding modules.

FIG. 4 shows another embodiment of the monitoring circuit in a representation similar to FIG. 3.

In contrast to FIG. 3, the signal line 34 'in FIG. 4 is connected to one of the two inputs of the Schmitt trigger 68. If the output Q of the D flip-flop 63 'is logic L, the input of the Schmitt trigger 68 is thus also logic L, so that the transistor 70 blocks and the LED 52 does not light.

If the output Q of the D flip-flop 63 'goes to logic H, the input of the Schmitt trigger 68 also becomes logic H, so that the clock generator 49 now begins to generate clock pulses. These clock pulses from the clock generator 49 now reach the transistor 70 via the Schmitt trigger 69, so that the light-emitting diode 52 starts to flash.

The reset circuit 54 'shown in FIG. 4 differs from the reset circuit 54 from FIG. 3 in that it has a further inverting Schmitt trigger 72, the RC element 71' of which consists of a capacitor and two resistors. With this circuit, the counter module 58 'and the D flip-flop 63' logically require H at their RST inputs for a reset. When switching on the supply voltage e.g. Via the program control unit 36 or through an opening contact when the dryer door is opened, the capacitor assumes its final voltage value only with a delay, so that the voltage VCC is still present for a certain time at the reset inputs of the counter module 58 'and the D flip-flop 63'; the blocks are reset. Only after a time determined by the time constant of the RC element, the reset inputs RST in this case go to logic L and thus release the corresponding blocks.

Finally, in FIG. 5, the counter circuit 46 is equipped with a binary counter 73 in a further exemplary embodiment. The binary counter 73 is led with its output lines 74 via two diodes 75, which represent a diode coupling network 76, to a common interconnection point 77, which is connected to ground via a resistor 78. The diode coupling network 76 thus represents a wired OR logic. The signal line 34 'assumes a voltage level which corresponds to a logic H as soon as one of the diodes 75/1 or 75/2 via its assigned output line 74 of the binary counter 73 itself to logic H is laid.

When the inner control line 34 'goes logic high, the Schmitt trigger 48 of the clock generator 49 is released and supplies periodic clock pulses to the transistor 70, so that the LED 52 starts to flash.

The output lines 74, which are connected to the diodes 75, represent two consecutive positions of the binary counter 73, the diode 75/1, for example, corresponding to four switch-offs and the diode 75/2 consequently eight switch-offs. The wired OR logic ensures that the relay 41 is switched off in any case and the light emitting diode 52 remains switched on when the preselected number of switch-offs of the heater 17 has been reached. If, for example, several disconnections follow one another directly, the binary counter 73 has switched the output line 74/1 assigned to the diode 75/1 to logic L again after four further disconnections, while the output line 74/2 assigned to the diode 75/2 has now switched to logic H is. If further shutdowns occur, the second diode 75/2 ensures that the connection point 77 remains at logic H, even if the connection line 74/1 goes back to logic L again.

In FIG. 6, the binary counter 73 from FIG. 5 is replaced by a shift register 79, which, with its output lines 80, also the selection circuit 60 already known from FIG. 4 and connected via this to the clock generator 49 and the relay 41. The D input of the shift register 79 is permanently set to logic H, so that with each pulse on line 45 a further output 80 of the shift register 79 always changes from logic L to logic H.

Therefore, no further memory element or diode coupling network is required to maintain the error signal.

7, the program control unit 36 is divided into an input unit 36 ″ and a program switching unit 36 ′. The program switching mechanism 36 'contains a microprocessor 81 which serves to control the various dryer programs.

In such devices, a clogging indicator can be integrated particularly easily into the existing system. Here the task of the counter module, the reset circuit and the clock generator from the monitoring circuit 32 can be taken over by the existing microprocessor 81. All that remains is to implement the pulse shaper circuit 44, the display driver 71 with the signal lamp 52 and the relay driver (not shown) for the relay 41 as additional hardware expenditure for realizing the flow indicator.

1 to 7, the pulse shaper circuit 44 is galvanically coupled to the thermostat device 26. However, it is also possible to monitor the thermostat potential-free. Three such possibilities are shown in FIGS. 8 to 10.

In FIG. 8, an optocoupler 82 is connected in parallel to the opening contact 27 and has a glow lamp as a transmitter and a photo resistor as a receiver.

In Fig. 9, a relay 83 is connected in parallel to the opening contact 27, via the contacts of which the blending circuit is controlled.

10, finally, a transformer 84 is provided in parallel with the opening contact 27, the secondary winding of which provides the thermostat signal in low voltage.

Claims (17)

Laundry dryer with an interior (12) for receiving laundry (13) to be dried, with a blower (16) for generating an air flow (18) directed through the interior (12), with at least one heater connected to an electrical energy source (28) (17) for heating the air flow (18) to a preselected temperature, with a thermostat device (26) connected to the heater and provided for detecting the temperature of the air flow (18), which is used to switch off the heater (17) from the energy source (28 ) when a temperature upper limit is exceeded and to switch the heating (17) on to the energy source (28) when the temperature falls below a minimum value, and with a monitoring circuit (32) connected to the thermostat device (26) in order to switch on a display unit (35) generate the signal dependent on shutdowns, characterized in that
the monitoring circuit (32) has a counter circuit (46) for counting the shutdowns of the heating (17) which take place during a drying process, and that the counter circuit (46) is connected to the display unit (35). Clothes dryer according to Claim 1, characterized in that the monitoring circuit (32) has a decoding circuit (48) which also has at least one of the output lines (47) of the counter circuit (46) corresponding to a particular number of shutdowns and via a signal line (34) the display unit (35) connected, and that the decoding circuit (48) generates an error signal when a certain number of shutdowns has occurred. Clothes dryer according to claim 2, characterized in that the certain number of shutdowns is greater than three. Clothes dryer according to one of claims 2 or 3, characterized in that the monitoring circuit (32) via a control line (33) with a switching unit (29) provided between the heater (17) and the energy source (28) for switching off the heater (17) is connected, the switching unit (29) being opened or closed as a function of the error signal. Clothes dryer according to claim 4, characterized in that the decoding circuit (48) has a diode coupling network (76) which has at least two output lines (47/1, 47/2), the counter circuit (46) and with the signal line (34) and the Control line (33) is connected. Clothes dryer according to Claim 4, characterized in that the decoding circuit (48) has a memory unit (62), the input (61) of which is connected to one of the output lines (47) of the error circuit (46) and the output of which is connected to the signal line (34) and the control line (33) is connected. Clothes dryer according to one of claims 2 to 6, characterized in that the decoding circuit (48) has a selection circuit (60), via which the decoding circuit (48) can optionally be connected to one of the output lines (47) of the counter circuit (46). Clothes dryer according to claim 7, characterized in that the selection circuit (60) is connected to a program control unit (36) for selecting different drying programs, with certain output lines (47) of the counter circuit (46) with the decoding circuit (48) depending on the respective drying program ) are connected. Clothes dryer according to one of the preceding claims, characterized in that the monitoring circuit (32) has a clock generator (49) in order to alternately switch the display unit (35) on and off. Clothes dryer according to one of the preceding claims, characterized in that the monitoring circuit (32) has a pulse shaper circuit (44) connected between the thermostat device (26) and an input (57) of the counter circuit (46). Clothes dryer according to claim 10, characterized in that the thermostat device (26) has a temperature-dependent opening contact (27) connected between the heater (17) and the energy source (28) and that the heater (17) and the opening contact (27) have their common connection Connection point (31) are connected to an input of the pulse shaping circuit (44). Clothes dryer according to one of the preceding claims, characterized in that the monitoring circuit (32) has a reset device (54) at least for the counter circuit (46) in order to set the counter circuit (46) to zero at the start of a new drying process. Clothes dryer according to claim 4, characterized in that it has a timer (42) which switches off the clothes dryer (10) after a cooling time after opening the switching unit (29). Method for temperature monitoring in a tumble dryer (10), which has an interior (12) for receiving laundry (13) to be dried, through which an air stream (18) heated by a heater (17) to a preselected temperature is passed, with the Steps: - measuring the temperature of the air flow (18), - switching off the heating (17) when the measured temperature becomes higher than an upper setpoint, - switching on the heating (17) again if, after switching off, the measured temperature becomes lower than a lower setpoint, and Determining a value which is associated with the shutdown,
characterized in that
the number of shutdowns occurring during a drying process is counted and displayed. A method according to claim 14, characterized by the further step: - Generating an error signal when the heating has been switched off a number of times during a drying process. A method according to claim 15, characterized by the further step: - Prevention of restarting when the error signal has been generated. Method according to one of claims 14 to 16, characterized in that it is carried out on a clothes dryer according to one of claims 1 to 13.

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