WO2013167488A2

WO2013167488A2 - Method for operating a dryer at variable speed of a drive motor and dryer suitable therefor

Info

Publication number: WO2013167488A2
Application number: PCT/EP2013/059256
Authority: WO
Inventors: Klaus Grunert; Uwe-Jens Krausch; Günter Steffens; Andreas Stolze
Original assignee: BSH Bosch und Siemens Hausgeräte GmbH
Priority date: 2012-05-09
Filing date: 2013-05-03
Publication date: 2013-11-14
Also published as: WO2013167488A3; DE102012207742A1

Abstract

The invention relates to a method for operating a dryer (1) comprising a program control unit (8), a drum (3) for pieces of laundry to be dried, a process air duct (2) in which a process air blower (6) for conveying the process air and a heating unit (4) for heating the process air are located, and a variable-speed motor (13) which drives the drum (3) and the process air blower (6). The method comprises a heat-up phase, a semi-stationary drying phase and a cool-down phase, the variable-speed drive motor (13) being operated at an average speed α₁ and the process air blower (6) being operated at an average speed ω₁ during the semi-stationary drying phase, and the drive motor (13) being operated at a speed α₂ which is smaller than α₁ and the process air blower (6) being operated at a speed ω₂ which is smaller than ω₁ at least intermittently during the cool-down phase. The invention further relates to a dryer suitable for performing said method.

Description

Method for operating a variable speed dryer of a drive motor and a suitable dryer for this purpose

The invention relates to a method for operating a variable speed dryer of a drive motor and a suitable for carrying out this process Trockner. The invention particularly relates to a method for operating a dryer with a program control, a drum for laundry to be dried, a process air duct in which a process air blower for the transport of the process air and a heater for heating the process air, and with a variable speed drive motor, the the drum and the process air blower, the method comprising a heating phase, a quasi-stationary drying phase and a cooling phase, and a particularly suitable for carrying out this method dryer.

In a dryer, air (so-called process air) is passed through a process air blower via a heater in a drum containing the laundry items to be dried as a drying chamber. The hot process air absorbs moisture from the items to be dried. In an exhaust air dryer, the moist, warm process air is directed to the outside, for example, in a room or by means of a hose from the installation room addition. In a condensation dryer, on the other hand, the moist, warm process air is passed, after passing through the drum, into a heat exchanger, which is usually preceded by a lint filter. In this heat exchanger (for example, air-to-air heat exchanger or heat sink of a heat pump), the moist, warm process air is cooled, so that the water contained in it condenses. The condensed water (condensate) is then usually collected in a suitable container and the cooled and dried air again fed to the heater and then the drum.

The drying process in a tumble dryer is generally divided into three phases. In this case, a heating phase first takes place during which the temperature of the process air rises until a certain temperature value is reached. This is followed by a quasi-stationary drying phase in which the temperature of the process air is essentially constant. During this phase the main drying of the laundry bridge. The drying process is then completed with a cooling phase in which the heating is generally switched off. The process air blower generally remains switched on during the cooling phase in order to exploit the residual thermal energy still present in the drum and process air circuit. Such a drying process is known to be very energy consuming. Thus, it is of great interest to reduce the energy consumption of drying processes in order to save costs and to protect the environment. Against this background, it is known to use only one motor for driving the drum and the process air blower ("single engine concept").

DE 199 04 993 A1 discloses a condensation clothes dryer with a single motor for driving drum and process air and cooling air blower. The drive with a single motor is usually problematic in that during the heating phase, a strong heat release would take place when the cooling air blower generates a strong cooling air flow, on the other hand, however, a strong process air flow is desired. This problem is overcome by DE 199 04 993 A1, in that the blower wheel of the process air blower has a straight-shifter design, so that it has no preferential direction of rotation, whereas the blower wheel of the cooling-air blower has curved vanes and thus a preferential direction of rotation. In the heating phase, the motor is operated in a direction of rotation which is opposite to the preferred direction of rotation of the cooling air blower. However, this has the disadvantage that the process air blower has a lower efficiency in comparison to operated in the preferred direction curved scoop process air blowers. DE 10 2008 019 921 A1 describes a tumble dryer with an electric machine which drives at least the drum, in which the rotational speed of the electric machine is varied by a control effected by a control and / or regulating unit. The electric machine can also additionally drive at least the process air blower. Furthermore, various speed work areas or drying programs are described, so that the electric machine is operated in each case with a speed in certain ranges of values. US Pat. No. 6,745,495 discloses a clothes dryer having a first motor that drives the drum and a variable speed motor that drives the process air blower. The dryer may also include a temperature and / or pressure sensor so that the speed of the variable speed motor that drives the process air blower is controlled by a controller depending on the measured temperature and / or pressure values. However, this has the disadvantage that different motors for driving the drum and the process air blower are necessary, which in turn increases energy consumption.

EP 1 775 368 B1 discloses a clothes dryer with an asynchronous three-phase motor which drives the drum and an electronic commutation motor, in particular of the permanent magnet type, which drives the process air blower. In a corresponding drying process, the process air volume flow is adjusted by the speed of the process air blower, so that the process air volume flow is lowest, for example during the last drying phase. Although this could reduce the energy consumption, however, there is also the disadvantage that different motors are required to drive the drum and the process air blower, which in turn adversely affects energy consumption. EP 1 688 532 B1 describes a method for controlling the operation of a tumble dryer, in which first the process air flow in the process air cycle is determined, this is then compared with a desired process air flow and then the speed of the motor that drives the process air blower is adjusted in such a way that the desired process air flow is achieved. At least one of the parameters engine speed, air temperature and engine speed is used to determine the process air flow. The motor that drives the process air blower is preferably a brushless permanent magnet motor. Again, the use of various motors for driving the drum and the process air blower is described, which in turn increases energy consumption.

Thus, in the known laundry drying method, either a single motor is used, which reduces energy consumption, but no speed adjustment of the process air blower takes place at the respective drying phase, which in turn adversely affects the energy consumption, or there is a speed adjustment of the process air blower to the respective drying phase, but then a separate motor used for the process air blower. This was justified by the fact that it would not be desirable to vary the drum speed in the same way as the speed of the process air blower, since, for example, at reduced speed, a wash could take place in the drum, which does not lead to optimal drying results of the laundry.

DE 10 2009 026 649 A1 describes a method for controlling a drying process in a domestic appliance for drying a moist material, in which a process air flow in a process air duct is conveyed by means of a process air blower and the drying process is started with a heating phase, before it enters a drying process Main drying phase passes. During the heating phase, the process air blower is at least temporarily operated at a higher speed than in the main drying phase, so that the heating phase of a drying process can be completed as quickly as possible. To drive the process air blower and / or the cooling air blower, a brushless DC motor is particularly preferably used. There is no information that a variable speed drive motor is provided, which drives the drum and the process air blower. Post-published EP 2 549 009 A1 describes a method for controlling the operation of a tumble dryer, comprising a drying chamber and a process air system comprising a fan with a variable speed. The speed of the water removal is evaluated and the speed of the blower adjusted accordingly. About in the quasi-stationary drying phase and in the cooling phase to be set speeds of the process air blower are not specified.

Against this background, it was an object of the present invention to provide a method for operating a variable speed motor of a drive motor, which overcomes the disadvantages of the known laundry drying method. The object of the invention was also to provide a suitable dryer for this purpose. The solution of this object is achieved according to this invention by a method and by a dryer with the features of the corresponding independent claims. Preferred embodiments of the method according to the invention are listed in corresponding dependent claims. Preferred embodiments of the method according to the invention correspond to preferred embodiments of the dryer according to the invention and vice versa, although this is not explicitly stated herein.

The invention thus relates to a method for operating a dryer with a program control, a drum for items to be dried, a process air duct in which a process air blower for the transport of the process air and a heater for heating the process air, and with a variable speed drive motor, which drives the drum and the process air blower, the method comprising a heating phase, a quasi-stationary drying phase and a cooling phase, and wherein in the quasi-stationary drying phase the variable speed drive motor is operated at an average speed CH and the process air blower is operated at a medium speed ooi, and during the Cooling phase, at least temporarily, the engine with a speed a ₂ less than CH and the process air fan with a speed ω _{2 is} less than ooi operated. Dryer here means in particular a dryer for items of laundry, wherein the type of clothes dryer is not restricted according to the invention and may also include washer-dryer, so household appliances for washing and drying laundry. In particular, exhaust air dryers and condensation dryers are meant, wherein condensation dryers are preferred according to the invention.

Variable speed drive motor herein means that the speed of the drive motor during the process according to the invention, ie the drying process, can be varied. The transition between a heating phase and a quasi-stationary drying phase is generally characterized by the attainment of a predetermined temperature of the process air temperature. This can be, for example, the temperature at which a temporal change in the temperature of the process air reaches a minimum. It Then, in the quasi-stationary drying phase, the wet laundry items would be dried at an approximately constant temperature. Only then, if heating and process air blower would be operated unchanged, a further increase in the process air temperature would take place. According to the invention, the method would preferably be operated such that a maximum permissible temperature T _{max of} the process air is not exceeded.

The cooling phase is generally the last phase of the drying process, in which the heating is switched off, at least temporarily. The cooling phase generally begins with a significant reduction in heating power of the heater or shutdown of the heater at the end of the quasi-stationary drying phase. Preferably, the heater is turned off in the cooling phase.

A reduction of the speed of the variable-speed drive motor causes in the method according to the invention a reduction of the speed of the process air blower.

In the method according to the invention, the speed ai of the variable-speed drive motor is preferably in a speed range from 500 rpm to 4000 rpm and particularly preferably in a speed range from 2800 rpm to 3500 rpm. In addition, the rotational speed a _{2 of} the variable-speed drive motor is preferably in a rotational speed range from 1800 rpm to 2500 rpm and particularly preferably in a rotational speed range from 1900 rpm to 2300 rpm.

Moreover, it is preferred according to the invention that ai is equal to ooi and a _{2 is} equal to oo ₂ , ie that the process air blower and the variable-speed drive motor are operated at the same speed.

In addition, it is advantageous in embodiments of the invention that in the quasi-stationary drying phase at least temporarily the variable-speed drive motor with a mean speed a _{3 is} less than CH and the process air blower with a speed ω _{3 is operated} smaller than ooi. This mode of operation is preferred when in the quasi-stationary drying phase the heater is operated at a reduced power. This is especially advantageous when the to be dried Laundry items are dried at least superficially. Then it can be very advantageous to reduce the heating, since an increase in the temperature of the process air here would not accelerate a drying process would result.

In a preferred embodiment, in addition, in the quasi-stationary drying phase, the process air blower is operated at a reduced rotational speed in at least one time interval by the variable-speed drive motor being operated at a reduced rotational speed a ₃ . In this case, the at least one time segment in the quasi-stationary drying phase in which the process air blower is operated at a reduced rotational speed preferably corresponds to a period in the quasi-stationary drying phase in which the heating power is reduced. In particular, in the quasi-stationary drying phase, the heating power is reduced when there is no more surface moisture on the laundry. This can be determined, for example, by a sudden increase in the temperature of the process air emerging from the drum. At full heat output then the process air temperatures would rise too high, so there is a risk of damage to the laundry or fire. Such periods of time with reduced heating power thus occur, especially towards the end of the quasi-stationary drying phase. If the process air blower continues to run at high speed during these periods, the process air temperature drops sharply. As a result, when the heater is switched on again, a higher energy input is required to further dry the items of laundry. In addition, this can delay the drying process. Thus, a reduced speed of the process air blower in time periods with reduced heating power continues to allow a high drying speed and an energy-efficient drying process.

In this case, the speed of the engine is preferably adapted to the maximum permissible process air temperature T _max . This can be done by measuring the current process air temperature with a temperature sensor and reducing the heating power and the engine speed if a threshold value stored or determined in the program control is exceeded. On the other hand, depending on the drying program used by the user, fixed periods of time at which the engine speed is reduced can already be stored in the program control. However, since the heating is still operated, albeit to a lesser extent, it is advantageous that a _{3 is} greater than a ₂ and ω _{3 is} greater than oo ₂ .

According to the invention, the drive motor is at least temporarily operated during the cooling phase at a speed a ₂ less than CH and the process air blower with a speed oo ₂ smaller than ω-ι. It is preferred that the rotational speeds a ₂ and ω _{2 are} average rotational speeds in the cooling phase.

An at least temporary operation of the variable-speed drive motor with a speed a ₂ smaller than αι and the process air blower with a speed ω ₂ smaller than ooi means that the speeds a ₂ and ω _{2 can} also be increased again. According to the invention therefore can be provided for the quasi-stationary drying phase, a time-dependent speed profile for the drive motor and the process air blower and preferably stored in the program control of the dryer. In a preferred embodiment of the method according to the invention, "temporary operation" means that in the program control for a drying program at least a period of time is predetermined in which the process air blower is operated at a reduced speed by operating the drive motor at a reduced speed as described means that in each case for a user to be selected by the drying program in the program control, a value for a time t _S tart is deposited, to which the above period begins, and a value At indicating the duration of the at least one period Instead of the value At, a time t _En de, to which the above-mentioned time period ends, can be stored in the program control, in which case:

tEnde ⁼ tstart ⁺ At.

In this case, the value tstart is preferably specified as a function of the time of program start t ₀ . Alternatively, the value t _S tart may also be stored as a function of another time of the drying program, for example as a function of the time at which the quasi-stationary drying phase t _{quasistatTrock begins} . For example, the values for tstart = t ₀ + 60 min and At = 10 min (or t _En de = t ₀ + 70 min) can be stored in the program control for a specific drying program. Although preferably these values are stored in the program control for the respective drying program, this does not exclude that identical values are used for determining the above-mentioned time period for all available drying programs and thus these values are not stored in the program control in connection with a special drying program are. This embodiment has the advantage that the determination of the above-mentioned period of time can be carried out in a simple manner independently of other parameters which, for example, would have to be measured first using special sensors.

For the course of a drying process in a dryer and thus the sequence of the method according to the invention, it is advantageous if the temperature of the process air and / or a loading of the drum with laundry items are taken into account. The temperature of the process air should preferably not exceed a predetermined upper limit T _max . This upper limit generally differs for laundry items of different types, with the upper limit of the temperature T _{max being} generally lower for delicate laundry items.

In a preferred embodiment of the method according to the invention, therefore, the rotational speeds a ₂ and ω _{2 are set} as a function of a temperature of the process air measured with a temperature sensor and / or a loading of the drum.

In a further embodiment, the at least one time interval in which the process air blower is operated at a reduced rotational speed by the drive motor being operated at a reduced rotational speed is determined as a function of the temperature of the process air. For this purpose, the dryer has at least one temperature sensor arranged in the process air circuit. This temperature sensor is preferably arranged at the drum inlet, that is to say at the point at which the process air from the process air duct passes into the drum, or at the drum outlet, ie at the point at which the process air from the drum passes into the process air duct. For example, the temperature sensor may be an NTC temperature sensor, but according to the invention there are no limits to the type of temperature sensor. For example, if the measured temperature reaches a certain threshold during the cooling phase and optionally during the quasi-stationary exceeds the drying phase, the drive motor and thus also the process air blower are operated at a reduced speed. This can happen, in particular, until the measured temperature falls below the aforementioned threshold value or another specific temperature value. In addition, the time interval of the reduced engine speed can be determined not only as a function of individual temperature values but also as a function of a temperature profile. This embodiment has the advantage that the rotational speed of the drive motor ("engine speed") and thus also a drum and blower speed can each be adapted to the current temperature conditions, for example, the engine speed can be adapted to a predefined value for the maximum allowable process air temperature and excessive temperature reduction can be avoided.

According to the invention, it is thus preferred that at least one time period in which the process air blower is operated at a reduced rotational speed ω _{2 by} operating the engine at a reduced rotational speed a ₂ is determined as a function of the load of the dryer with laundry items to be dried. The loading of the dryer can be determined by means of various parameters, for example via the weight of the drum, moisture contentV course and load of the drive motor, for example as a function of engine speed and / or engine torque. Thus, different speed profiles of the drive motor for different loads can be stored in the program control, which are then used accordingly to achieve an optimal result. In particular, a speed reduction and / or a duration of the abovementioned period of reduced engine speed can also be determined jointly as a function of temperature and load. This allows a particularly good adaptation to the current state of drying and thus a particularly energy-saving process.

Regardless of how softly the process air blower is operated at a reduced speed by operating the drive motor at a reduced speed, the value of the reduced speed or the variation of the value of the reduced speed over the cooling phase or a time period thereof can also be used be determined advantageously depending on the temperature and / or the loading. This made possible light that, for example, in a strong increase in temperature, the speed is less reduced, for example, as a stronger cooling is desired. Advantageously, for example, even with detected low load, the speed can be reduced less.

Furthermore, it is preferred that the drive motor is operated only in one direction of rotation during an entire drying program. In this way, conditional wear and extensions of the drying program are avoided by a change of direction.

The type of variable speed drive motor used in the method according to the invention is not restricted. However, it has proved to be particularly advantageous if the variable-speed drive motor is a brushless synchronous motor. Brushless synchronous motors (BLDC or PMS motors) have a relatively high efficiency and are therefore very energy efficient. In addition, the speed of the process air blower can be set as desired without much effort by such a motor. The inertia of the rotor of BLDC motors is comparatively low, so that a good dynamic characteristic is achieved. In addition, brushless drive motors are relatively low maintenance, since there are no brushes as wearing parts. This extends the life of the drive motor and thus of the dryer. In addition, such motors can be installed in hard to reach places. In addition, the ratio of output power to size is particularly high for BLDC motors, which allows a comparatively small footprint.

According to the invention, it is preferred that in the process according to the invention a dryer is used which has a heat exchanger. It is then preferred that a cooling medium is passed through the heat exchanger during a drying process. According to the type of heat exchanger is not limited, so that the cooling medium may be, for example, the refrigerant of a heat pump or cooling air of an air-to-air heat exchanger. In the method according to the invention, however, an air-air heat exchanger is preferably used, so that the cooling medium is preferably cooling air. Preferably, a cooling air duct is then present in the heat exchanger, through the air, in particular from a mounting room of the dryer, as a cooling medium by means of a cooling air blower. is passed through. In this case, the cooling air blower preferably has a preferred direction of rotation. In a preferred embodiment of the invention, the cooling air is then passed through the cooling air duct, that the cooling air blower is operated by the speed of the cooling air blower is less in the cooling phase than in the quasi-stationary dry phase.

According to the invention, it is particularly preferred that the variable-speed drive motor additionally drives a cooling-air blower in a cooling-air duct of an air-to-air heat exchanger. The speed of the drive motor largely corresponds to the speed of the cooling air blower. If the process air blower, cooling air blower and drum are driven by the same drive motor, the volume flow of the cooling air is reduced whenever the flow rate of the process air is reduced. Since too much and / or too rapid cooling of the process air is to be avoided just by reducing the process air flow and thus the residual heat should be better utilized, this effect is further supported by a simultaneous reduction of the cooling air volume flow.

According to the invention, it is preferable that a reduced speed of the motor is in a speed range of 1800 to 2500 rpm. Thus, the speed of the process air blower and possibly the cooling air blower is preferably in the speed range from 1800 to 2500 U / min.

During the cooling phase, the process air gradually cools down. It is therefore preferred that the rotational speeds a ₂ and ω ₂ decrease continuously during the cooling phase. By the invention, an energy saving can be achieved because only one drive motor for driving the drum and the process air blower is used by the reduced speed of the process air blower in the cooling phase in the drum and in the process air circuit residual heat can be better utilized. The reduced speed of the variable-speed drive motor or the process air blower requires a lower process air volume flow. Thus, the laundry items are cooled more slowly, which also in the cooling phase still a significant moisture removal The laundry may take place and the heating may also be switched off earlier in the drying process. Thus, despite a slower cooling of the laundry, it is possible that the duration of the drying process is not extended altogether. In addition, a lower drum speed is caused by the lower engine speed in the cooling phase. This simultaneous reduction in the speed of the process air blower and drum was often considered to be disadvantageous because the drum speed influences the laundry load and thus the drying result. However, it has surprisingly been found that the tumble in the drum is almost unchanged during the cooling phase by reducing the drum speed. The fact that in the cooling phase, the laundry items are already almost dry and thus have a corresponding volume, the drum is largely filled during the cooling phase, resulting in a movement of the laundry items with the drum without laundry. Thus, a uniform loading of the laundry with the process air is guaranteed even at reduced drum speed.

In general, the speed of the drum is much lower than the speed of the motor, which can be achieved by a strong reduction. This can be done, for example, in the ratio 1: 55, so that the drum at a speed of the engine of speed of 2750 U / min has a speed of 50 rev / min. When using a heavily understated operated drum, the effects of the reduced speed of the drive motor on the laundry case in the drum are comparatively low.

In any case, the drive power for the drum is reduced according to the invention in the cooling phase, which additionally saves energy.

In addition, in the heating phase in at least one time section, the process air blower is particularly preferably operated at a reduced rotational speed, ie a reduced rotational speed compared to an average rotational speed CH in the quasi-stationary drying phase, by the variable-speed drive motor having a reduced rotational speed, ie one compared to an average rotational speed in the quasi-stationary drying phase, reduced speed is operated. The heating phase is the first phase of the drying process, during which the temperature of the process air rises until a certain temperature is reached. By reducing the speed of the process air blower, it is achieved that the process air can heat up more quickly, since the volume flow of the process air is lower. As a result, a predetermined temperature value predetermined for the quasi-stationary drying phase is reached more quickly, so that the heating phase is thereby shortened. This in turn affects both the energy balance as well as the drying time advantageous.

The engine speed can be reduced in various ways in the context of the invention. In the simplest case, the rotational speed α is lowered to a constant value which is below the average rotational speed CH during the quasi-stationary drying phase. However, it is also advantageous that the rotational speed α of the drive motor is increasingly reduced during the cooling phase. This means that the rotational speed is reduced more and more over time according to a so-called "ramp." This reduction of the rotational speed can take place stepwise or continuously, since the residual heat still present in the process air duct usually decreases more and more after the heating has been switched off, Alternatively, changing intervals of lower and higher reduced rotational speeds could also be envisaged.Also, a dryer with a program control, a drum for laundry items to be dried, is conceivable. a process air duct in which there are a process air blower for the transport of the process air and a heater for heating the process air, and with a variable speed drive motor which drives the drum and the process air blower, wherein the Progr ammsteuerung is set up to carry out a method comprising a heating phase, a quasi-stationary drying phase and a cooling phase, and wherein in the quasi-stationary drying phase of the variable speed drive motor with an average speed CH and the process air blower is operated at a medium speed ooi, and during the Cooling phase at least temporarily the variable speed drive motor with a speed a _{2 is} less than CH and the process air fan with a speed ω _{2 is} less than ooi operated. The type of variable-speed drive motor according to the invention is not limited, as long as a variation of its speed can be achieved. As mentioned, however, it has proved to be particularly advantageous if a BLDC motor is used as the drive motor. A BLDC motor is a brushless synchronous motor (brushless DC motor) equipped with a permanent magnet rotor. Another name for this motor is "PMS motor", where "PMS" stands for "permanent magnet synchronous." The fixed stator of such a motor comprises coils that are controlled by an electronic circuit offset in time to create a rotating field In the case of BLDC motors, it is possible to make the electronic commutation dependent on the rotor position, the rotor speed and the torque, using sensor-controlled or sensorless detection to detect the rotor position and speed.

In any case, the use of a BLDC motor as a motor makes it possible to change the speed in a simple manner and in particular also a high speed. Thus, by using a BLDC motor, a better implementation of the method according to the invention is possible. In particular, a speed a _{2 of} the motor in the cooling phase can be set in a simple manner, which is smaller than a speed CH in the quasi-stationary drying phase. The rotational speed in the cooling phase is preferably about 20 to 50% lower than in the quasi-stationary drying phase. In addition, it has been found that when using a BLDC motor under otherwise identical conditions, especially at the same speed, a higher energy efficiency compared to other electric motors is given. In a preferred embodiment, the dryer also has a display device for different states of the dryer. For this purpose, an optical display device is preferably used. By way of example, the display device can provide information about the operation of the dryer by outputting a text or by illuminating different-colored light-emitting diodes, for example via the sequence of a method according to the invention with an optimized cooling phase of the dryer. The dryer according to the invention preferably has a heat exchanger, which is particularly preferably an air-to-air heat exchanger. In a preferred embodiment of the invention, therefore, the dryer has an air-to-air heat exchanger with a cooling air duct, in which a cooling air blower is driven, which is driven by the variable speed drive motor.

In order to be able to take into account the temperature of the process air during operation of the dryer, the dryer in the process air duct preferably has at least one temperature sensor. It is particularly preferred that the at least one temperature sensor is arranged on the drum inlet or drum outlet.

Furthermore, it is preferred that the drive motor additionally drives the cooling air blower.

The dryer according to the invention can be designed as a pure dryer, but also as a washer-dryer. A washer-dryer is here understood to mean a combination appliance which has a washing function for washing laundry and a drying function for drying wet laundry.

The heater is in particular an electric heater or a gas heater, wherein an electric heater is preferably used.

The invention has numerous advantages. Thus, the simultaneous realization of a single-motor concept at a reduced speed of the drive motor in the cooling phase, a much higher energy savings can be achieved than in known dryers, especially when adapting the speeds of the process air blower to the drying phase using a separate motor to operate the drum. Despite the energy savings by the method according to the invention, an extension of the drying time can be avoided because the cooling phase can start earlier due to the further drying still taking place during the cooling phase. In addition, a reduction in engine speed also means a quieter drying process, which is particularly desirable by the users. Last but not least, the reduced drum speed at the end of the drying process also results in a gentler treatment of the laundry. Further details of the invention will become apparent from the following description of a non-limiting embodiment of a dryer according to the invention, in which a method according to the invention can be carried out for its operation. Reference is made to the single figure of the accompanying drawings.

The figure shows a vertical section through a dryer, which is designed as a condensation dryer, wherein the arrows indicate the flow direction of the process air. Other embodiments are conceivable. The dryer 1 shown has a rotatable about a horizontal axis of the drum 3 for receiving to be dried, not shown here, laundry items, within which are mounted drivers 5 for moving laundry items during a drum rotation. The process air is guided in the process air duct 2 by means of a process air blower 6 through an air-air heat exchanger 14 and an electric heater 4 through the drum 3. In this case, heated by the electric heater 4 heated air through the drum inlet 19 from the rear, i. from the door 12 opposite side of the drum 3, passed through the perforated bottom in the drum 3.

After exiting the drum 3, the process air laden with moisture flows through the filling opening of the drum 3 through a lint 1 1 inside a door 12 closing the filling opening. The process air flow in the door 12 is then deflected downwards through the drum outlet 18 into the process air duct 2 and directed to the air-to-air heat exchanger 14, can be transported by the cooling air in a cooling air passage 15 by means of a cooling air blower 16. In the air-air heat exchanger 14 condenses due to cooling a more or less large part of the process air from the laundry absorbed moisture and is collected in a condensate pan 17.

The control of the dryer 1 via a program control 8, which can be controlled by the user via an operating unit 7. Two temperature sensors 9, 10, a temperature sensor 9 at the drum outlet 18 and a temperature sensor 10 at the drum inlet 19 are connected to the program control 8. In the embodiment shown in the figure, the process air blower 6, the cooling air blower 16 and the drum 3 are driven by the drive motor 13. The drive motor 13 in this embodiment is a brushless synchronous motor (BLDC or PMS motor). The drum is heavily stocked, for example in the ratio 1: 55, whereas process air and cooling air blower are not stocky, but are driven by the drive motor with a speed ratio of 1: 1.

When carrying out a method according to the invention, a loading of the drum 3 with items of laundry is first determined, for example, by a conventional method, for example a determination of the weight increase of the drum 3. Subsequently, threshold values of the process air _temperature , eg T _max2 and T _max1 , are defined with regard to a relationship between loading and maximum permissible process air _temperature stored in the program control 8.

By means of the two temperature sensors 9 and 10, the temperature T of the process air is measured when carrying out the method. In the event that the process air _temperature during the quasi-stationary drying _phase exceeds a predetermined threshold T _max1 , the heating power of the heater 4 is reduced and the speed of the drive motor 13 is lowered below its average speed αι during the quasi-stationary drying phase. For example, with a user-selected drying program, the average speed of the drive motor 13 may be 2750 rpm, which is then _lowered to 2200 rpm when the first threshold T _{max1 is exceeded} . When the process air _temperature drops again below a second threshold value T _m ax2 with T _max2 less than or equal to T _max1 due to the deactivation of the heater 4, the heating power is increased again and the engine speed α is increased again.

During the cooling phase, ie in the present case when the heater 4 is switched off at the end of the drying process, the rotational speed of the drive motor 13 is lowered, for example, continuously until the end of the drying process. To control these processes, the program control 8 is used. LIST OF REFERENCE NUMBERS

dryer

Process air duct

drum

(Electric heating

takeaway

Process air fan

operating unit

program control

Temperature sensor at the drum exit

Temperature sensor at the drum entrance

lint

door

Variable speed drive motor; in particular BLDC motor heat exchanger; in particular air-air heat exchanger cooling air duct

Cooling fan

Drain pan

drum exit

drum input

Claims

Method for operating a dryer (1) with a program control (8), a drum (3) for items to be dried, a process air duct (2) in which a process air blower (6) for conveying the process air and a heater (4) for heating the process air, and with a variable-speed drive motor (13) which drives the drum (3) and the process air blower (6), the method comprising a heating phase, a quasi-stationary drying phase and a cooling phase,

characterized in that in the quasi-stationary drying phase of the variable-speed drive motor (13) with a mean speed CH and the process air blower (6) is operated at a mean speed ω-ι, and during the cooling phase, at least temporarily, the variable-speed drive motor (13) at a speed a ₂ less than CH and the process air blower (6) is operated at a speed ω ₂ smaller than ooi.

A method according to claim 1, characterized in that the rotational speed ai of the variable-speed drive motor (13) in a speed range from 500 rev / min to 4000 rev / min.

Method according to one of claims 1 and 2, characterized in that the rotational speed a _{2 of} the variable-speed drive motor (13) in a rotational speed range from 1800 rev / min to 2500 rev / min.

Method according to one of claims 1 to 3, characterized in that CH is the same and a ₂ is ω ₂ .

A method according to claim 1, characterized in that in the quasi-stationary drying phase at least temporarily the variable-speed drive motor (13) with a mean speed a ₃ less than CH and the process air blower (6) is operated at a speed ω ₃ smaller than ooi. A method according to claim 5, characterized in that a _{3 is} greater than a ₂ and ω ₃ greater than ω ₂ .

Method according to one of claims 1 to 6, characterized in that the rotational speeds a ₂ and ω _{2 are} average rotational speeds in the cooling phase.

Method according to one of claims 1 to 7, characterized in that the variable-speed drive motor (13) is a brushless synchronous motor.

Method according to one of claims 1 to 8, characterized in that the variable-speed drive motor (13) additionally drives a cooling air blower (16) in a cooling air duct (15) of an air-to-air heat exchanger (14).

Method according to one of Claims 1 to 9, characterized in that the rotational speeds a ₂ and ω _{2 are set} as a function of a temperature of the process air measured with a temperature sensor (9, 10) and / or a loading of the drum (3).

Method according to one of claims 1 to 10, characterized in that the rotational speeds a ₂ and ω ₂ decrease during the cooling phase.

Dryer (1) with a program control (8), a drum (3) for items to be dried, a process air duct (2) in which a process air blower (6) for conveying the process air and a heater (4) for heating the process air and with a variable speed drive motor (13) driving the drum (3) and the process air blower (6),

characterized in that the program control (8) is adapted to carry out a method comprising a heating phase, a quasi-stationary drying phase and a cooling phase, wherein in the quasi-stationary drying phase of the variable speed drive motor (13) with a middle Speed αι and the process air blower (6) is operated at a medium speed ooi, and during the cooling phase at least temporarily the variable speed drive motor (13) with a speed a ₂ <CH and the process air blower (6) with a speed ω ₂ <ωι operated ,

13. dryer (1) according to claim 12, characterized in that the variable-speed drive motor (13) is a brushless synchronous motor.

14. dryer (1) according to claim 12 or 13, characterized in that it comprises an air-to-air heat exchanger (14) having a cooling air passage (15) in which a cooling air blower (16) is arranged, of the variable speed drive motor ( 13) is driven.

15. Dryer (1) according to one of claims 12 to 14, characterized in that in the process air channel (2) at least one temperature sensor (9, 10) is arranged.