DK167066B1 - DRUM TUMBLE WITH FNUG FILTER - Google Patents

Abstract

The clogging of the lint filter of a tumbler dryer with lint and fluff from the laundry being dried causes a reduction of the air transport exceeding that caused by the filling with laundry. This necessitates more frequent regulation of the input temperature (27) to the drum of the tumbler dryer than if the lint filter were clean or totally removed. It is therefore possible to measure the frequency of regulation and compare it to a value obtained by experience gained by drying operations with a clean lint filter. If the frequency of regulation is too high an alarm is triggered, indicating the requirement for cleaning the lint filter. <IMAGE>

Description

5 DK 167066 B1 Tumble dryer

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a dryer with a lint filter, and more particularly to the monitoring of a lint filter in a dryer.

The starting point of the invention is a dryer with an air-flowable, rotatable drum for receiving wet clothes to be dried, an air intake and an airway from the air intake through the drum to a fan adapted to suck air through the airway. The air is heated with an airway heater located in front of the drum which provides a substantially constant effect. The temperature of the air is regulated by a temperature sensor located in the airway between the heating device and the drum to sense the temperature of the air 15 immediately before or upon entering the drum and a control device coupled to the sensor to switch off the heating device when the temperature exceeds a predetermined upper limit and switch on the heater when the temperature falls below a predetermined lower limit.

In order to prevent the fan or the subsequent exhaust air duct from settling with lint from the clothing, a lint filter is provided between the drum and the fan in the airway for filtering lint. In order to indicate in due time that this lint filter must be cleaned, the dryer is provided with a lint filter monitoring device which is designed to give a signal when the addition rate exceeds a predetermined limit value.

Dryers of this kind have been on the market for a number of years. The monitoring device has most often been designed as an electromechanical system that responds to the altered airway pressure when the lint filter stops.

However, these solutions have many practical disadvantages and uncertainties. They can be quite clumsy and bulky in installation. Their sensitivity is very high because the vacuum is small and its variations are small, which often results in error signals or a commutation of the filter cleaning signal, which can be very annoying for the dryer user.

5

The object of the invention is to provide a dryer, where the degree of addition of the fluff filter is monitored purely electronically and where the disadvantages of the known solutions are otherwise avoided.

The object is met by a dryer, wherein the monitoring device is essentially a counting device adapted to trigger the signal delivery if the temperature exceeds the upper limit within a predetermined number of times.

15

The invention rests on a recognition that the frequency of interruptions of the heating device which must occur to keep the temperature below the upper limit is a practically useful measure of the degree of addition of the lint filter.

20

This can be seen from a theoretical consideration of a dryer, where the effect of the heater is adapted to the air flow of the dryer at normal filling and drying at the highest permissible temperature. Without a lint filter, in the dryer, after a relatively short period of oscillation, a dynamic thermal equilibrium would occur, characterized by the fact that the heating device due to the adaptation to the air flow is in continuous operation.

Due to the drying and volume expansion of the wet clothing, a very slowly rising air temperature would be observed immediately at the entrance to the drum, with the drying of the clothing and consequent volume expansion gradually reducing the air flow so that the air became warmer. Towards the end of the drying, it might be necessary to make individual temperature adjustments for a relatively long period of time, by switching off / reconnecting the heating device, so as not to exceed the maximum temperature.

DK 167066 B1 3

If the same situation is now considered, but with a inserted lint filter, its addition with lint from the clothing leads to a reduction in air flow in addition to the normal reduction in drying. This means that more frequent temperature adjustments must be made than if the lint filter was clean or not present at all. Therefore, it is possible to measure how frequently the temperature must be regulated, and compare this with an experience value obtained by drying 10 with a clean lint filter. If the control frequency is too high, a signal must be given that the lint filter must be cleaned.

This theoretical consideration does not lose its validity, although the dryer is not thermally optimally set.

15 First, it must be borne in mind that no absolute criterion can be given as to when the lint filter should be cleaned; the signal should only be a reminder to the user for quite some time. If the heating device is slightly oversized so that the temperature is regulated relatively frequently in advance, the clogging of the lint filter will still cause an increase in the frequency of detection which can be detected.

Similar considerations apply to drying, where the temperature is adjusted down to a lower value for the nature of the clothes, since this is thermally equivalent to an over-dimensioning of the heating device. Thus, an embodiment of the invention, whereby several different drying temperatures can be set in the same dryer, is set forth in claim 2.

If the heating device is under-dimensioned, the fluff filter must otherwise be relatively more clogged before signal is given, but this too is of no major practical importance.

It should also be mentioned that the dryer fan usually blows the exhaust air into an exhaust duct. If it is clogged, it will also reduce the air flow so that the filter cleaning signal is triggered even though the filter is clean. An appropriate troubleshooting instruction could then alert the user or an installer to 5 channel clogging.

The very principle of regulating the dryer temperature in the dryer is in itself not new; for example, conventional bimetallic or bellows regulators with relatively high thermal inertia have been used for it, optionally in a number corresponding to the desired number of drying temperatures, if each regulator can only control at one temperature. However, with the introduction of the filter monitoring according to the invention, a signal processing task (measuring the frequency of the temperature controls and comparison with the experience value) arises, which can justify the use of only one temperature sensor and an actual measuring device for measuring the temperature, as claimed in claim 3; both tasks can be conveniently performed by a microcomputer.

20

The invention is described in more detail below with reference to the drawings which show a preferred embodiment.

FIG. 1 is a schematic vertical section through a dryer.

FIG. 2 shows the temperature course of the input air and the output air during a typical drying process.

30

FIG. 3 shows the temperature of the input air and the output air during a drying process with a partially clogged lint filter.

FIG. 4 is a circuit diagram showing the connection of a temperature sensor to a control unit for a dryer according to the invention DK 167066 B1 5

FIG. 5 is a simplified flowchart of essential parts of a program routine according to the invention for monitoring a lint filter.

5 The dryer according to FIG. 1 is used to dry wet laundry. The clothes (not shown) are placed in a rotatable drum 1, which is closed with a door 2 with sight glass 3. The machine is started via a control panel on the front of the tumbler (not shown).

You can choose between a drying program for rugged fabrics 10 (cotton etc), where drying at higher temperature, and a program for delicate fabrics (synthetic fabrics etc.) where drying at lower temperature. In addition, you can choose an aeration program where the clothes are not dried but only aerated. Moreover, the possibilities for program selection can be varied 15 as needed and market requirements.

After the user has started the dryer via the control panel, the drum 1 is turned into rotation and a fan 4 in the dryer is put into operation. The fan 4 draws air through the clothes in the drum. The air is sucked in through an opening 5 at the bottom of a heater 6 on the rear of the tumbler. In the illustrated embodiment which is gas heated, the air passes through a gas burner 7. The heated air passes through various baffles S, 9 and is then passed through an opening 10 into the drum 1 through its perforated rear wall. Instead of a gas burner, for example, an electric heater or a steam-fed heat exchanger can be used for the heating.

In the front of the dryer, the air exits from the drum through a perforated damper 11 surrounding the door 2, and is conducted via an annular manifold 12 to a suction duct 13 in which the fan 4 is arranged. In front of the fan 4, a lint filter 14 is arranged in the duct 13, in the form of a piece of plastic or metal filter fabric supported by a rib construction. The curved shape shown is selected to increase the filter area. The lint filter must filter out lint from the clothes in the drum, which loosens during the drying process and is fed with the air flow. The fan blows the air out in an exhaust hood at the back of the dryer.

During drying, the temperature of the inlet air is monitored by a temperature sensor 16 in the opening 10, while the temperature of the outlet air is monitored by a temperature sensor 17 in the exhaust duct 15. Both temperature sensors are connected to an electronic control unit in the dryer.

FIG. 2 shows the temperature course of the input air (curve 23) and the outlet air 10 (curve 24) during a typical drying process, together with the ambient temperature of the dryer, curve 25, and the residual moisture (curve 26) in the clothes during drying. The data shown comes from a drying where the dryer is hot, ie. has already undergone a prior drying process and where the lint filter is clean. The heater is designed to work continuously and with constant power. Within approx. 2 minutes from the start of the dryer, the temperature of the inlet air reaches approx. 130 ° C, where it stabilizes with a continued slight rise in the future. The 20 warm air "senses" the clothes in the drum and takes water vapor with them, so that the residual moisture of the clothes falls evenly. As the cooling of the air by evaporation of water from the clothing decreases, the temperature of the outlet air rises. Drying is interrupted when the outlet air temperature exceeds an experimentally determined limit value; experience shows that the clothes have achieved a suitable degree of drying. In the example shown, drying is stopped when the outlet air temperature rises above 60 ° C.

FIG. 3 shows (in a larger solution) the temperature of the inlet air (curve 27) and the outlet air (curve 28) during a drying process under the same conditions, but where the fluff filter is 75% dimmed, ie. only 25% of the lint filter surface is available for air passage. Thus, this is a simulation of operating conditions where the lint filter is partially clogged after prolonged use.

The clogging of the lint filter leads to a reduced air flow in the dryer. The heater, which operates at constant power, heats the reduced air volume to a higher temperature than at full flow. In order not to overheat the clothing, the heat supply is interrupted when the inlet air reaches a temperature of 145 ° C and is started again when the temperature of the inlet air has dropped to 135 ° c. Thus, it is regulated in a narrow band around 130 ° C, which in experience is an optimal drying temperature for cotton clothing and other sturdy fabrics.

10

As can be seen, the clogging of the lint filter leads to the fact that the heat supply must be continuously adjusted to compensate for the reduced air flow.

In the dryer according to the invention, a signal is given to the user that the lint filter must be cleaned when it is found that the frequency of these adjustments of the heat supply exceeds a predetermined limit. Put another way, the controller counts how many times the heater 20 is turned off and on within a given period of time, and if it happens too often, a signal is given to clean the lint filter.

In case the user has chosen drying at a lower temperature (for delicate fabrics), there will also be some regulation activity for pure 25 lint filter to keep the temperature at the lower value. In practice, a normal frequency is set for the controls when the lint filter is clean. When the lint filter is more or less clogged, one must more often regulate one at the normal frequency to keep the temperature at the desired level. In this case, too, the filter monitoring can thus be performed by counting how many times the heater is turned on and off.

Thus, the filter monitoring is based on a measurement of the temperature of the inlet air in the dryer. This measurement forms the basis for the control of the heat supply and for the count of the number of control steps.

As mentioned before, the measurement is carried out with the temperature sensor 16, which is located in the flow opening 10 from the heater 6 to the drum 1. In the preferred embodiment, the temperature sensor is a temperature sensitive resistance whose resistance value decreases with increasing temperature. This NTC resistance is via an analog circuit shown in FIG. 4, connected to an input port on a microcomputer, which performs the control tasks in the dryer. The microcomputer is of the type that has a built-in analog-to-digital converter for digitizing the signal from the analog circuit, but it is not shown further, as such controllers are well known.

As seen in FIG. 4, it is a conventional analog circuit in which the temperature sensor 16 is included in a voltage divider 16, R1, whose center potential is subtracted from a reference potential of another voltage divider R2, R3, at the input of an operational amplifier 20. In order to suppress noise and electromagnetic radiation, the temperature sensor is decoupled with parallel coupled capacitors C, C1, choke coils L in series with the connecting cable and decoupling diodes D for the frame and for the supply voltage. The output of the operational amplifier is fed to the analogue digital converter port 29 of the microcomputer via an active limiter coupling with the operational amplifiers 21 and 22 as well as the limiter diodes D1.

25 The limiter coupling must protect the microcomputer against overvoltages. The digitized output voltage from the circuit of FIG. 4 is a measure of the temperature of the inlet air. The outlet air temperature sensor 17 may be connected to the microcomputer via a similar circuit.

30

In addition to the input ports for the temperature sensors, the microcomputer has various other ports for input signals from the control panel and from other sensors in the dryer, etc., as well as output ports for controlling signal lamps on the control panel, including a lamp to signal the lint filter to be cleaned and for controlling the the heater 6, the fan 4, a drive motor (not shown) for rotating the drum 1, etc. These details are not to be described further here.

DK 167066 B1 9

A program in the microcomputer controls the functions of the dryer. FIG. 5 shows a flowchart of a program routine which performs the essential parts of the filter monitoring 5 according to the invention. The routine is a subroutine in a larger program, which goes through in an endless loop as long as the dryer is in operation, so there is no interrupt control. The routine manipulates different count registers (internal registers in the microcomputer) and maintains different flags as indicator for the dryer state.

General steps

Following the routine call in step 30, steps 31 and 32 are examined to see if the dryer has started and whether the selected program involves heating (a drying process). Otherwise, the routine is abandoned immediately. If the dryer is started in a drying program, in step 33 it is checked whether a filter has already been blocked (filter alarm) at an earlier stage of the routine; then the routine is abandoned as well.

A central function of the routine consists in examining whether the heater is operating (step 34). The current temperature measurement and heater start and stop are performed by other 25 sub-routines in the program; the operating state of the heater is a picture of whether the temperature has exceeded or exceeded the pre-set regulatory limits.

Machine start-up 30 Immediately after starting the dryer, the heater will not be operational yet. The same applies during the dryer's later operation after exceeding the upper control limit. For this later operation, in step 35, a count register for the number of temperature adjustments, called heat counters, is released for countdown.

Next, in step 36, it is investigated whether the heat meter and another count register, the measurement timer, are set to their initial values. This will not be the case at machine startup. Therefore, in step 37, it is marked that the setting has occurred (it is happening now), and in step 38, the measurement time counter is set to a measuring time of 4 minutes.

5

If the user has chosen low temperature drying (step 39), the heat meter in step 41 is set to a value of 9 control phenomena. If the high temperature is selected, the heat meter in step 40 is set to a value of 1 control phenomenon. This means that at the low temperature, filter alarms are given if the temperature needs to be adjusted more than 9 times within 4 minutes. At the high temperature, filter alarms are given if the temperature needs to be adjusted more than once within 4 minutes. These are experience values selected on the basis of a given machine design. For other designs, similar values can be set up on the basis of practical experiments that one of ordinary skill in the art can perform simply and routinely.

20 Regardless of how the counters are set, steps 42 and 43 examine whether the counters are down to zero. This will not be the case at machine startup. The routine is therefore abandoned in step 49.

25 Before first adjustment

At the next run-up after the machine start, the heater will be in operation (assuming it is started at the first complete run-through of the program), so that from step 34 jumps to step 46. Here it is examined whether the heat counter is blocked for countdown. This will not be the case, since it was released at the start of the machine, in step 35. Therefore, the heat counter is counted down (decremented by 1) and then blocked for countdown. The blocking occurs for the sake of the looping nature of the driver and will only be lifted when the heater turns off again (steps 34 and 35). Until this happens, each subsequent run of the routine will run through step 34, step 46, and step 49, without changing the machine state.

DK 167066 B1 11

After regulation

After the heater is switched off for the first time, and at each subsequent interruption of the heater, 5 is jumped from step 36 to step 42 Here it is examined whether the measuring time has expired. If the measurement time has not yet expired, step 43 examines whether the heat meter has been counted down to 0. This is equivalent to examining whether within the measurement time as many regulatory phenomena as the heat meter was set, or in other words to to investigate whether filter alarms should be given. If the heat meter is counted down to 0 within the measurement time, then alarm is given in step 44 and the routine is left in step 49. Each subsequent run of the routine will then lead from step 33 to step 49, without change 15 of the machine state.

If the heat meter is not counted down to 0 within the measurement time, a new measurement must be started. This is done in step 45 by marking that the counters are no longer set, leaving the 20 routine in step 49. The next pass will then jump from step 36 to the setting part in steps 37-41.

As shown in this review of the filter control routine, the measurement time counter, which is a real-time counter, is updated by another program section. The same applies to the indicators that the routine asks for in steps 31-34 to determine the current machine condition.

In the practical design work, the 30 mechanical, electronic and signal processing details will be adapted to the market segment you wish to hit. The illustrated embodiment should therefore be construed as illustrative only, but not as a limitation of the principles of the invention set forth in the preamble of the specification and retained in the claims.

Claims (3)

1. A tumble dryer with an air-permeable, rotatable drum for receiving wet clothes to be dried, with an air inlet and an airway from the air intake through the drum to a fan adapted to suck air through the airway with a pre-drum arranged in the airway heater which provides a substantially constant effect, with a temperature sensor arranged in the airway between the heater and the drum to sense the temperature of the air immediately before or upon entering the drum, with a control device coupled to the sensor to disconnect the heater; when the temperature exceeds a predetermined upper limit and to switch on the heating device when the temperature falls below a predetermined lower limit, with a fluff filter located in the airway for filtering fluff derived from clothing in the drum and with a monitoring device for the filter additive rate with lye, which is adapted to output a signal when the addition rate exceeds a predetermined limit value, characterized in that the monitoring device is essentially a counting device adapted to trigger the signal delivery if the temperature within a predetermined period of time exceeds a predetermined limit value. predetermined number of times exceeds the upper limit. Dryer according to claim 1, wherein the regulating device has at least two settings which differ from each other 30. at least with respect to the upper limit of temperature, characterized in that the counting device has corresponding settings where a lower upper limit of temperature must be is exceeded more frequently than a higher upper limit of temperature to trigger signal delivery. Dryer according to claim 1, wherein the regulating device has at least two settings which differ from each other at least with respect to the upper limit of the temperature, characterized in that the regulating device in all settings is coupled to the same temperature sensor, that the control device is provided with a measuring device coupled to the temperature sensor to measure the temperature, a comparator connected to the measuring device to compare the measured temperature value with one of at least two adjustable upper limit values and a control device coupled to the comparator for controlling the heating device, and the counting device has similar settings where a lower upper limit of temperature must be exceeded more frequently than a higher upper limit of temperature in order for the signal output to be triggered. 15