Tumble dryer and method for drying laundry using a tumble dryer

Abstract

A tumble dryer has a drum for laundry, a drive motor for the drum, an air supply to the drum and an air discharge from the drum, a fan, including a fan drive, for generating an air stream to the drum through the air supply and away from the drum through the air discharge, and also heating means for heating the air stream. The temperature of and the moisture in the air which is discharged from the drum are detected. The profile of said temperature and moisture is compared with prespecification curves, which are stored in a memory, for the profile of said temperature and moisture by means of calculation means depending on the drying phase of the laundry. The operating point of the prespecification curve at which the drying program is located is determined in this way. The control arrangement influences the further drying program, on the basis of the operating point, by way of adjusting the temperature and/or the intensity of the air stream.

Claims

1. Tumble dryer comprising: a drum for holding laundry which is to be dried, a drive motor for said drum, an air supply to said drum, an air discharge from said drum, a fan for generating an air stream to said drum through said air supply and away from said drum through said air discharge, a fan drive for said fan, heating means for heating said air stream, temperature detection means for detecting a temperature of air which is supplied to said drum or air which is discharged from said drum, moisture detection means for detecting a moisture in said air which is supplied to said drum or said air which is discharged from said drum, a control arrangement comprising: a memory, wherein at least one prespecification curve for a profile of temperature or moisture with respect to time for a specific drying program for laundry is stored in said memory, calculation means, wherein said calculation means are designed to compare currently detected values for said temperature or said moisture with a prespecification curve depending on a drying phase of said laundry during a drying program and to determine an operating point of said prespecification curve at which said drying program is located, wherein said control arrangement is designed for influencing a further drying program, on a basis of said operating point, by way of adjusting said temperature of said air stream by influencing said heating means and/or by way of adjusting an intensity of said air stream by influencing said fan.

2. Tumble dryer according to claim 1, wherein said air supply is provided at most 10% below a highest point of said drum.

3. Tumble dryer according to claim 2, wherein said air supply is provided above said highest point of said drum.

4. Tumble dryer according to claim 1, wherein said fan is at most 50 cm away from said drum.

5. Tumble dryer according to claim 1, wherein said fan drive is a dedicated drive only for said fan, wherein said fan drive is designed as one structural unit together with said fan.

6. Tumble dryer according to claim 1, wherein said fan has an inductively heatable fan rotor as heating means, wherein said fan rotor has a plurality of fan blades, wherein at least one of said fan blades is at least partially composed of, or contains, a material which can be heated by means of a magnetic field generating means.

7. Tumble dryer according to claim 6, wherein said at least one magnetic field generating means is arranged adjacent to said fan rotor or at least partially surrounds said fan rotor and is arranged on a fan housing of said fan.

8. Tumble dryer according to claim 7, wherein said at least one magnetic field generating means has or is at least one induction coil, wherein said temperature detection means comprise said fan rotor and said magnetic field generating means as an induction coil.

9. Tumble dryer according to claim 8, wherein said temperature of said air which is discharged from or supplied to said drum can be determined from an activation of said induction coil.

10. Tumble dryer according to claim 7, wherein said at least one magnetic field generating means has at least one permanent magnet.

11. Tumble dryer according to claim 6, wherein said at least one magnetic field generating means is arranged outside a fan housing or outside said air supply.

12. Tumble dryer according to claim 6, wherein said at least one magnetic field generating means runs outside said fan rotor with a radial extent.

13. Tumble dryer according to claim 12, wherein said at least one magnetic field generating means is arranged radially outside said fan rotor and in an encircling manner as an induction coil with a coil center axis which runs parallel to a rotation axis of said fan rotor or coincides with said rotation axis of said fan rotor.

14. Tumble dryer according to claim 1, wherein said moisture detection means comprise said fan and, respectively, a fan drive, wherein a level of said moisture can be determined from an activation of said fan drive of said fan in such a way that a high torque is to be provided by said drive when there is a high level of said moisture in said air which is moved by said and a low torque is to be provided by said fan drive when there is a low level of said moisture in said air which is conveyed by said fan.

15. Tumble dryer according to claim 14, wherein said level of said moisture can be determined by monitoring a phase shift between current and voltage in said fan drive.

16. Tumble dryer according to claim 1, wherein said drum is internally free of sensors.

17. Tumble dryer according to claim 16, wherein said drum does not have any sensors on an outer side either.

18. Method for drying laundry, which is to be dried, using a tumble dryer, wherein said tumble dryer has: a drum for holding laundry which is to be dried, a drive motor for said drum, an air supply to said drum, an air discharge from said drum, a fan for generating an air stream to said drum through said air supply and away from said drum through said air discharge, a fan drive for said fan, heating means for heating said air stream, temperature detection means for detecting a temperature of said air which is supplied to said drum or said air which is discharged from said drum, moisture detection means for detecting a moisture in said air which is supplied to said drum or said air which is discharged from said drum, a control arrangement comprising: a memory in which at least one prespecification curve for a profile of said temperature or said moisture with respect to time for a specific drying program for laundry is stored, calculation means in order to compare currently detected values for said temperature or said moisture with a prespecification curve during a drying program and in order to determine an operating point of said prespecification curve at which said drying program is located, the method comprising the steps of: detecting current values for said temperature and/or said moisture during a drying program, comparing said current values for said temperature and/or said moisture with a prespecification curve, determining said operating point of the prespecification curve at which said drying program is located on a basis of said comparison, influencing a further drying program on a basis of said operating point, in terms of adjusting said temperature of said air stream by influencing said heating means or in terms of adjusting an intensity of said air stream by influencing said fan.

19. Method according to claim 18, wherein said further drying program is influenced in terms of said temperature or said intensity of said air stream, wherein then: said temperature of said air stream to said drum is at least 5° C. below an average for said temperature of said air stream used up until this point, said intensity of said air stream to said drum is at least 20% above said average for said intensity of said air stream used up until this point.

20. Method according to claim 18, wherein said further drying program, primarily during a period of a last quarter of said drying program, is influenced in terms of said temperature or an intensity of said air stream.

21. Method according to claim 19, wherein a fan direction and, respectively, a direction of said air stream is reversed several times at intervals in order to then draw off said air from said drum into said air supply in order to acquire information about said exhaust air in this way.

22. Method according to claim 21, wherein information relates to said temperature of or said moisture in said exhaust air.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are schematically illustrated in the drawings and will be explained in more detail below. In the drawings:

(2) FIG. 1 shows a schematic illustration of a tumble dryer according to the invention comprising an inductively heated fan together with a separate fan drive,

(3) FIG. 2 shows an enlarged illustration of an alternative refinement of an air supply with a branch to a separate outlet out of a housing,

(4) FIG. 3 shows an illustration of profiles of drying parameters with respect to time,

(5) FIG. 4 shows an illustration of profiles of the moisture in the air and in the laundry with respect to time with four phases, and

(6) FIG. 5 shows an illustration of profiles of the temperature of the air which is introduced into a drum of the tumble dryer and of the laundry with respect to time with four phases.

DETAILED DESCRIPTION

(7) FIG. 1 illustrates how a tumble dryer 11 according to the invention can be constructed in principle. The tumble dryer 11 has a housing 12 with a drum 14 which is arranged in a drum holder 18. The drum 14 can be driven by a drum drive 15 by means of a drive belt 16, as is known in principle. In this case, the drum 14 usually revolves at a single possible revolution speed which then also remains constant. However, this can also be varied. In this case, the drum 14 does not have any sensors or the like at all, in particular none for temperature or moisture.

(8) A duct-like air supply 20 extends to the top right of the drum holder 18, as is known per se from the prior art. This high position is important and advantageous, as has been explained above. A fan 21 together with a fan rotor 22 and a fan drive 24, advantageously as one structural unit, are arranged in the air supply 20. The fan rotor 22 is, as has been explained in the introductory part, composed of inductively heatable material, primarily the individual rotor blades are composed of said material. Therefore, said fan rotor can be inductively heated by two induction coils 26a and 26b which are arranged outside the air supply 20 opposite the fan rotor 22 and such that they surround said fan rotor. This is also known from the prior art. The heating can be varied depending on the strength of the magnetic field which is generated by the induction coils 26a and 26b and also depending on the rotation speed of the fan rotor 22. A fan 21 of this kind, which can be inductively heated, is well known.

(9) The drum drive 15, the fan drive 24 and the induction coils 26a and 26b are connected to a control arrangement 28 of the tumble dryer 11. Said control arrangement carries out the method explained in the introductory part and also the rest of the operation of the tumble dryer. The control arrangement 28 advantageously has an appropriately designed processor.

(10) In addition, an air discharge 40 is also arranged at the top left of the drum holder 18, which air discharge leads to a condenser 42 by way of water being separated off in a known manner from the moist air which is drawn off from the drum 14. It can be seen that the drum 14, the air discharge 40 and the air supply 20 form a kind of circuit, wherein the air in said circuit is moved or circulated in the counterclockwise direction to all intents and purposes. This air flow direction corresponds to that during the normal conventional drying operation. Instead of the condenser 42 in the air discharge 40, the tumble dryer 11 can also utilize a heat pump or remove moisture in some other way from the air which is drawn off from the drum 14 at the air discharge 40.

(11) The control arrangement 28 is designed to ascertain the temperature of the fan rotor 22 and, respectively, of the inductively heatable parts which are present on said fan rotor on the basis of the activation of the induction coils 26a and 26b. Therefore, the temperature of air flowing past said fan rotor can be indirectly detected, this also being advantageous or even necessary during normal heating operation. Furthermore, the control arrangement 28 activates the fan drive 24 of the fan 21, so that said control arrangement knows or can ascertain the power to be applied by said fan. As has been explained in the introductory part, conclusions can be drawn about the moisture in the transported air as a result. Finally, the control arrangement 28 can advantageously contain a converter or inverter for the fan drive 24 or can be designed as one structural unit with said converter or inverter. Similarly, said control arrangement can have an induction generator or form one structural unit with said induction generator for the purpose of activating the induction coils 26a and 26b. Therefore, in one refinement of the invention, a central control unit could be provided, which central control unit performs the abovementioned control functions and power supply.

(12) The control arrangement can also be a combination of an inverter and a controller or microcontroller and measuring means, for example a current measuring coil or a current shunt. A zero crossing identification can also be provided. FIG. 2 illustrates an enlargement of an alternative tumble dryer 111 as a variant which has an additional outlet 130 in its housing 112. This outlet 130 issues at a branch 132 which extends from the air supply 120 or is connected to said air supply at the top. Said outlet is closed off by a branch valve 134 which can be opened in the downward direction and closed in the upward direction, that is to say can be moved, by a valve actuator 136. The valve actuator 136 can be a rod-type drive, or alternatively an electromagnet or the like.

(13) A relatively small second fan rotor 123 is fastened to a fan 121 on the same shaft on which a relatively large first fan rotor 122 is also seated. The second fan rotor 123 is designed for conveying air in the opposite rotation direction to the first fan rotor 122. That is to say, if the fan drive 124 rotates in its normal direction, the first fan rotor 122 conveys air through the air supply 120 in accordance with the large arrow into the drum holder 118 and therefore also into the drum 114 in line with normal operation. Said fan rotor can be heated in the above-described manner by induction coils 126a and 126b in order to thereby heat the conveyed air for the operation of the dryer. The second fan rotor 123 can likewise be partially or entirely composed of inductively heatable material. If, specifically, the fan drive 124 rotates in the opposite rotation direction for which the second fan rotor 123 is designed, the air stream is generated in line with the relatively thin arrow and air is drawn off from the drum 114 into the air supply 120. When the branch valve 134, illustrated in dashed lines, is open in the downward direction, said air flows upward through the outlet 130, here out of the housing 112 by way of example. As an alternative, said air could also be guided back into the duct of the air discharge 40 via a return, as a result of which the escape of lint can be reduced or avoided. This air from the drum 114 naturally does not have to be heated; in this case, the heating function provided by means of the induction coils 126a and 126b serves to detect the temperature of this drawn-off air in this way. As explained in the introductory part, this is done on the basis of the operating values of the induction coils 126a and 126b. The first fan rotor 122 may have no effect in this second opposite conveying direction; it may possibly contribute to conveying air in this direction, but this is not necessary. Finally, the second fan rotor 123 is provided for this purpose.

(14) If, in line with FIG. 1, only one single fan rotor 22 is provided on the fan 21, said fan rotor should be designed for operation in both directions. A considerably improved degree of efficiency can be provided for blowing air into the drum 14 through the air supply 20, but this should also be possible, at least in principle, in the other direction. The fan 21 or 121 can be operated as desired and autonomously by the fan drive 24 or 124 which is independent of the drum drive 15 in each case.

(15) The process of drawing off air from the drum 114 for detecting the temperature of this air does not have to last for long; for example, it can be provided only for 2 seconds to 10 seconds.

(16) At the same time as the temperature of the drawn-off or discharged air from the drum 114 is detected, the instantaneous power of the fan drive 124 can also be detected in general by monitoring the fan drive 124 and its operating values. As has already been explained above, the moisture in the drawn-off air and therefore within the drum 114 can be determined from said instantaneous power. The more power the fan drive 124 has to apply for the drawing-off process at a specific rotation speed, the more moisture this air contains. The laundry in the drum 114 then also contains more moisture.

(17) Determining the moisture in the air which is discharged from the drum, possibly also in the air which is supplied to the drum 114, advantageously takes place by means of determining a phase shift in the fan drive 124 since the torque required changes with the dependency of the viscosity of the air on its moisture content. Air with a high moisture content is simply more difficult to convey than dry air. A corresponding reference in the control arrangement or a preceding “calibration” in dry air allows this determination. A measurement of this kind can be readily carried out in the dual fan 121 illustrated in FIG. 2. In this case, the difference between drawing off the air from the drum 114 and blowing air into the drum is measured. Useful information about this process can be obtained from the difference.

(18) Heating the air by means of the inductively heated fan rotor 22 and, respectively, 122 or 123 allows evaluation of the energy, which is absorbed by the induction coils 126a and 126b, in parallel. The profile of the absorbed energy can be identified by way of corresponding control variables on an induction generator, not illustrated, this providing information about the temperature of the fan rotors since comparison with existing characteristic curves is possible. Dynamic electromagnetic excitation of the induction coils 126a and 126b can provide further information about the temperature of the air. If regulation to the energy input or the power output to the induction coils 126a and 126b is performed with the objective of not heating the air, but rather of keeping the fan rotor at the temperature of the conveyed air, the change in comparison to known characteristic curves can then also provide an indication of the moisture in the air or the change in said moisture.

(19) The combination of the two items of information relating to detecting the moisture and the temperature allows a process to be conducted independently of a direct temperature measurement since known characteristic values can be recorded and compared with those currently existing in the process. Therefore, process-oriented regulation to the parameters moisture and ideal air temperature is possible. Known parameters such as external temperature and pressure, which can be measured by sensors here, can additionally assist in the regulation operation. In particular, the influences of the laundry, which are very random on account of the different composition of said laundry, can be more quickly identified since further parameters such as drum movement and therefore laundry movement can be included in the evaluation of the measurement results.

(20) FIG. 3 illustrates various profiles of parameters with respect to time t. The profile 1 is the relative moisture in the laundry. The parameter 2 in the graph illustrated below is the mass flow of the moisture which has been removed, indicated in kg/(m.sup.2s). The parameter of the profile 3 is the surface temperature T.sub.WO of the laundry. The profile 4 of the corresponding parameter shows the core temperature T.sub.WK of the laundry, and the profile 5 is the temperature T.sub.L of the supplied air. All temperatures are indicated in ° C.

(21) In section I, heating of the laundry and evaporation of the moisture takes place at the surface of the material. The drying intensity is not high since, firstly, the transferred heat is required not only for evaporating the moisture but rather, primarily, also for heating all the laundry. Secondly, the thermal moisture conductivity which increases owing to the temperature difference between the surface and the core slows down the removal of the moisture.

(22) A definition of the thermal moisture conductivity is such that the moisture content of the laundry continuously changes during drying. This creates a concentration gradient between the surface of the textile, from which moisture is continually removed, and the inner layers of the items of laundry, said concentration gradient consequently causing the transportation of moisture from locations of relatively high moisture concentration to locations of low moisture concentration in line with moisture diffusion, also called moisture conductivity. The moisture is therefore transported to the surface of the laundry or to the location of the evaporation boundary, converted into vapor there, said vapor being mixed with the heated air, and discharged to the surrounding area. In the process, the evaporation boundary moves over the course of the drying process or drying program from the surface of the laundry into the interior of the laundry.

(23) Since heat is supplied for the evaporation process, the material which is to be dried is also heated in addition to the moisture being removed. The supply of heat over the surface creates a temperature difference between the surface and the inner layers or the core.

(24) On account of effects which are linked to the bonding of liquids into capillaries, moisture has the tendency to migrate from locations of relatively high temperature to locations of relatively low temperature. This phenomenon is called thermal moisture. If the surface temperature is greater than the core temperature, the vectors of the moisture conductivity and the thermal moisture conductivity have different mathematical signs, that is to say the drying process slows down. The influence of the thermal moisture conductivity falls as the product to be dried increasingly heats through as a reduction in the temperature gradient. The temperature difference over the cross section of the laundry also reduces as the laundry increasingly heats up, this leading to an increase in the drying speed.

(25) In section II, the drying speed is constant. The temperature of the surface and of inner layers or the core differ only slightly and are subject only to small changes. A stationary state is established, the influence of the thermal moisture conductivity lapses and the drying process is determined solely by the moisture conductivity.

(26) In section III, the drying speed drops again. The evaporation boundary moves as heating increases from the surface to the inner layers or the core of the laundry. The heat which is supplied by means of the air is no longer used only or predominantly for evaporating the moisture, but rather increasingly for heating the laundry. In section III, the partial pressure difference between the inner and outer layers of the laundry is critical for the transportation of moisture to the surface of the laundry. At the end of section III, removal of the moisture from the laundry is terminated, and the temperature of the laundry approaches the temperature of the air. Overall, the drying speed depends on the conditions of the heat transfer at the surface of the laundry and the distance of the water vapor from the evaporation boundary.

(27) In FIG. 4, triangles mark the time profile of the moisture f.sub.L in the air as has been measured during a drying process. During phase 1 for the first 9 minutes, this moisture in the air rises sharply to almost 100%. It remains at this high value during phase 2 for approximately a further 12 minutes. During phase 1, the time profile of the moisture f.sub.W of the laundry, which is marked by rectangles, drops only slightly. This moisture f.sub.W in the laundry has been determined experimentally for the same time and cannot be directly detected with the tumble dryer according to FIG. 1 or FIG. 2. During phase 2, the moisture f.sub.W in the laundry drops sharply, this not being surprising since the air which is discharged during this phase is saturated to the maximum or almost to the maximum, see the moisture f.sub.L.

(28) In following phase 3 which lasts for approximately 20 minutes, the moisture f.sub.W is still dropping, but this drop flattens out. Accordingly, the moisture f.sub.L also drops sharply. During the last phase 4 which lasts for approximately 5 minutes, hardly any more moisture can be discharged into the air, but the laundry is dry or completely dry since the moisture f.sub.W in said laundry has reached zero or is even slightly below zero.

(29) In FIG. 5, in a manner split into the four phases in line with FIG. 4, a profile for the temperature T.sub.L of the discharged air is illustrated using triangles during the same drying process. Similarly, a profile for the temperature T.sub.W of the laundry is illustrated using rectangles. Said profile corresponds approximately to the core temperature T.sub.WK of the profile 4 in FIG. 3. The temperature T.sub.W of the laundry, like the moisture f.sub.W in the laundry previously, has been determined experimentally.

(30) It can be seen that, in phase 1, the temperature T.sub.L is quickly increased to approximately 40° C. In phase 2, the temperature T.sub.L is once again increased to somewhat above 50° C. However, in phase 1, the temperature of the laundry T.sub.W, which is illustrated using rectangles, increases in a somewhat delayed manner. A temperature increase is then sharply reduced during phase 2.

(31) It is only at the beginning of phase 3, when the temperature T.sub.L has also been increased to a certain extent, that the temperature T.sub.W once again increases slightly, with two short drops, even though the temperature T.sub.L has corresponding dips.

(32) In the relatively short phase 4, the temperature T.sub.W even increases yet further, while the temperature T.sub.L is lower and, if anything, remains the same or even drops to a certain extent.

(33) Both the theoretical examination and also the considerations on the basis of experiments suggest that the drying process can be optimized when the measurement of the parameters for the temperature and moisture is optimized.

(34) Specifically, it is recommended to accelerate the process of increasing the temperature of the laundry in phase 1, so that the evaporation begins as quickly as possible. In phase 2, the temperature T.sub.W is equal to the temperature T.sub.L, so that the supplied energy is utilized for the evaporation. In phase 3, an increase in the temperature T.sub.L is hardly expedient or not expedient at all since this only leads to an increase in the temperature T.sub.W and not to an acceleration of the evaporation on account of the thermodynamic effects. Phase 4 is necessary on account of the non-uniform moisture distribution which is more difficult to remove since it involves “bound moisture”. The combination of heating power, air flow rate or convection and drum movement is critical here. The focus below is on heating power.

(35) In respect of the four phases, the functioning is separated into: heating up the laundry, constantly heating the laundry, constant drying phase without heat or with a small amount of heat, blowing air through the laundry without heat or with a small amount of heat.

(36) If the existing heating systems are used, an improvement can then be achieved by means of the regulation and control.

(37) In parallel, a combination of an air heating system with an integrated heating arrangement in the fan allows optimization of the measurement function with fewer components and increased data detection. The objective here is to utilize indirect information from the process for the process. Ultimately, parameters which have a direct relationship to convection and evaporation of water in the dryer should be directly detected and used for regulating the process. Owing to said possibility of controlling the drum movement or the drive motor for the drum as desired, a mentioned method for detecting parameters can be assisted in an optimum manner for regulation of the process.

(38) Therefore, it is possible to not necessarily replace existing sensors but to add to them. Above all, attempts can be made to dispense with sensors in the drum itself since these are difficult to fit and to evaluate.

(39) With the knowledge of these profiles with respect to time in line with FIGS. 3 to 5, it is possible, by way of detecting the temperature of and the moisture in the air in the drum, which can be performed in the drum without sensors according to the invention, to draw conclusions about the point of a profile of this kind at which the drying process is located. Said drying process can then be optimized, in particular in respect of the temperature T.sub.L no longer having to be so high toward the end. Therefore, energy can be saved and the laundry which is to be dried can also be treated gently. As a result, it is possible to improve drying of laundry using a tumble dryer, in particular the above-described tumble dryer according to the invention.