EP2627814B1 - Method for controlling a braking operation of a drive motor of a washing machine as well as drive device and washing machine - Google Patents

Description

The invention relates to a method for controlling a braking process of a drive motor, by means of which a washing drum of a washing machine is driven. At least temporarily during the braking process, a braking current fed back due to an electrical braking voltage induced by the drive motor is conducted to an ohmic resistance by closing an electrical switch. The invention also relates to a drive device and a washing machine, which are each designed to carry out such a method.

It is state of the art to couple a braking resistor into the circuit of the stator windings in order to brake a drive motor of a washing machine. The drive motor can thus be actively braked; The electrical energy supplied by the drive motor in generator mode is converted into heat at the braking resistor. Such a procedure is, for example, from the publication WO 99/10584 A1 known.

In the subject according to the publication EP 1 512 785 A1 the electrical energy recovered when the laundry drum is braked can either be stored directly in the intermediate circuit capacitor or converted to heat using an ohmic braking resistor. The braking resistor can be connected in parallel to the DC link capacitor as required.

The EP 0 478 807 A1 shows a washing machine in which the duty cycle of the drive motor is adjusted by a control circuit so that the motor temperature does not exceed a certain limit. To reduce the duration of the program, the ratio of the on-time to the off-time can be changed so that the limit temperature is reached as quickly as possible.

The drive circuit of a washing machine after the US 2004/0103694 A1 is thus protected from damage caused by an overvoltage from the generator operation of the Drive motor protected during braking that the braking resistor is provided with a thermal overcurrent shutdown.

It is an object of the invention to provide a solution in a method of the type mentioned at the beginning of how the drive motor can be protected against overload during a braking operation.

This object is achieved according to the invention by a method, a drive device and a washing machine with the features according to the respective independent patent claim. Advantageous and preferred embodiments of the invention are the subject of the dependent claims or the following description. In a method according to the invention, a braking process of a drive motor is controlled, by means of which a washing drum of a washing machine is driven. At least at times during the braking process, a braking current which is fed back on the basis of an electrical braking voltage induced by the drive motor is led to an ohmic resistance, namely by closing an electrical switch. A temperature of the drive motor is determined and a limit value for the temperature is set. The electrical switch is activated during the braking process in such a way that the temperature of the drive motor remains below the specified limit value.

According to the invention, a current flow via the ohmic resistance is thus controlled during the braking process in such a way that the temperature of the drive motor does not exceed a predetermined limit value. The control of the current flow via the resistance or the activation of the electrical switch preferably includes that the average current strength of the braking current and / or a duration of the current flow and / or a point in time at which the electrical switch is closed during the braking process, depending on the determined temperature of the drive motor is / are set. The limit value for the temperature of the drive motor can be determined, for example, in a development process of the drive motor and stored in a control device.

The method according to the invention has the advantage that the drive motor can be braked quickly by leading the braking current to the resistor without the temperature limit being exceeded. In the prior art, the drive motor had to be designed for the most unfavorable operating conditions (worst case) in order to be able to withstand temperature peaks occurring during the braking process. In particular, the drive motor had to be designed for the maximum ambient temperature of the washing machine, for maximum loading of the washing drum and for the longest washing program of the washing machine. The method according to the invention enables the drive motor to be designed for operation at lower temperatures and thus to be produced more cost-effectively. The limit value for the temperature can namely be set in such a way that the drive motor is operated at moderate temperatures and is therefore not overheated. Another advantage of The method according to the invention compared to the prior art consists in the fact that the drive motor does not have to be switched off due to an excessively high temperature during the braking process and a washing process must therefore be interrupted. In the prior art, the drive motor had to be switched off when its temperature exceeded a threshold.

The washing machine preferably has a belt drive, so that the laundry drum is driven by the drive motor via a belt. As a result, the drive motor is subjected to little thermal stress when braking, and it can be braked quickly at the predetermined temperature limit without being thermally overloaded.

The ohmic resistance is preferably formed by a phase strand of a stator of the drive motor, so that the braking current is fed back to the phase strand via the electrical switch. Thus, the electrical energy supplied by the drive motor during the braking process is converted directly into heat at the drive motor, so that it is the use of an additional braking resistor as described in the article in the document EP 1 512 785 A1 is used parallel to the DC link capacitor - superfluous. The drive motor also has a significantly higher heat capacity than a braking resistor and can therefore absorb significantly more heat. It can therefore be braked much faster. If the drive motor is a multi-phase permanent magnet excited motor, for example a permanent magnet excited synchronous motor or a brushless direct current motor, the phase strands can be short-circuited in pairs or all at least temporarily during the braking process of the stator and the braking current can be supplied to the phase strands. It is advantageous if electrical switches already present in an inverter or inverter are used to couple the phase strands to one another.

The ohmic resistance, to which the braking current is conducted during the braking process, can thus be formed by the phase strand of the stator or its ohmic resistance. A resistance value of a stator winding can be, for example, in a value range from 0.5 Ω to 3 Ω; for example, it can be 1 Ω.

The current temperature of the drive motor can be determined before the braking process is initiated, and a time course of a rotational speed of the drive motor for the braking process can be predetermined depending on the temperature before the braking process is initiated. It is thus ensured in a simple manner - in particular without a lot of control or regulating effort during the braking process - that the temperature of the drive motor does not exceed the defined limit value during the braking process before the braking process starts. The predetermination of the course of the rotational speed can be, for example, determining an average deceleration and / or a temporal course of the deceleration of the drive motor. In particular, at the beginning of the braking process - that is, immediately after the braking process has been initiated - relatively high temperature values of the drive motor can occur, so that the deceleration of the drive motor can be predetermined at least for the start of the braking process depending on the determined temperature.

Additionally or alternatively, the course of the speed can also be continuously controlled during the braking process depending on the current temperature of the drive motor. For example, if the temperature of the drive motor rises relatively rapidly - approaching the limit value - its deceleration would be significantly reduced. In contrast, when the temperature of the drive motor rises relatively moderately, the deceleration can be increased according to the situation. The continuous control of the speed curve as a function of the current temperature of the drive motor has the advantage that it is continuously monitored during the braking process whether the temperature of the drive motor is below the specified limit value. The respective instantaneous temperature of the drive motor can thus also be regulated by appropriate activation of the electrical switch and an associated control of the braking current.

In one embodiment it is provided that before the braking process is initiated, the temperature of the drive motor for the braking process is estimated and the electrical switch is controlled as a function of the estimated temperature. In particular, a maximum value of the temperature for the braking process can be estimated before the braking process is initiated. In this embodiment, a is preferred Time course of the speed of the drive motor for the braking process prior to its initiation depending on the estimated temperature, in particular depending on the estimated maximum value, predetermined. In other words, such a temperature of the drive motor can be determined before the braking process is initiated, which temperature could probably arise during the braking process. Such a prediction of the temperature allows the time course of the speed or deceleration of the drive motor to be predetermined reliably before the braking process is initiated, without the predetermined limit value for the temperature being exceeded. Temperature values for different curves of the speed or different deceleration values for the braking process can also be predicted and compared with one another before the braking process is initiated. Such a course of the speed or such a course of the deceleration can then be predetermined for the braking process, which ensures the maximum possible deceleration of the drive motor without its temperature exceeding the specified limit value. Such a procedure has the advantage that the drive motor is braked quickly on the one hand and is not thermally overloaded on the other hand.

Thus, in one embodiment, the electrical switch is actuated during the braking process in such a way that the drive motor is braked with a maximum possible deceleration, taking into account the limit value for the temperature. In this way, the duration of the braking process is reduced to a minimum without the limit value for the temperature of the drive motor being exceeded.

The braking process can be carried out between two successive spin cycles of the drive motor. A period of time between the spin cycles can then be set as a function of the ascertaining temperature of the drive motor, in particular ascertained during the braking process. The time period between the spin cycles is set in particular in such a way that the temperature of the drive motor does not exceed the limit value neither during the later spin cycle nor during a braking process following the later spin cycle. So the time is set so that the temperature of the drive motor can recover enough after the previous spin cycle. Thus, in the later spin cycle, the drive motor can be accelerated, for example, to a predetermined spin speed and then braked again without the Limit for the temperature is exceeded. The time between the spin cycles can also be longer than the actual braking process, i.e. the drive motor can first be braked to a desired speed - in particular completely to zero rpm - and the later spin cycle can only be initiated after the drive motor has been braked.

If the temperature of the drive motor is determined before the braking process is initiated, for example at a spin speed of the drive motor, a point in time at which the braking process is initiated can be determined as a function of this temperature. Thus, for example, the time duration of a spin cycle can be varied depending on the current temperature of the drive motor, namely in such a way that the limit value for the temperature of the drive motor is not exceeded during the spin cycle or during the braking process. In particular, the braking process can be initiated when the temperature of the drive motor in the spin mode exceeds a threshold value less than the limit value. This threshold value can be selected such that a maximum temperature occurring during the braking process is less than the specified limit value.

In principle, the temperature of the drive motor can be measured with a sensor. However, it has proven to be particularly advantageous if the temperature of the drive motor is determined by means of a control device, by means of which the electrical switch and the drive motor are controlled, with the aid of a map stored in the control device and / or with the aid of a mathematical formula stored in the control device is calculated. The washing machine does not need an additional temperature sensor. For example, the temperature of the drive motor can be dependent on its known parameters, such as a winding resistance of the stator winding or the resistance of the phase phase at a fixed temperature and / or a number of pole pairs. The temperature of the drive motor can also be determined taking into account measured values for a phase current of the drive motor and / or measured values for an intermediate circuit voltage of the voltage intermediate circuit and / or values for a phase voltage. In particular in the case of a multi-phase drive motor, such as preferably a permanent magnet-excited synchronous motor or brushless DC motor, the phase current and the intermediate circuit voltage are in any case in usually measured, namely by a control device. The phase voltage that is applied between the phase strands of the drive motor is also generally known in the control device. An electrical power supplied by the drive motor when braking the drive motor and the temperature of the drive motor can thus be determined without much effort. In one embodiment, the drive motor is therefore a multi-phase drive motor, in particular a permanent magnet-excited synchronous motor or brushless DC motor. Such a drive motor can be braked quickly in a technically simple manner, namely by leading the braking current to the ohmic resistance.

The invention also includes a drive device for a laundry drum of a washing machine. The drive device comprises a drive motor for driving the laundry drum and a control device for controlling the drive motor, which is designed, at least temporarily, during a braking operation of the drive motor, to feed back a braking current due to an electrical braking voltage induced by the driving motor to an ohmic resistance by closing an electrical one Switch. A temperature of the drive motor can be determined in the drive device and a limit value for the temperature is set in the control device. The control device is designed to control the electrical switch during the braking process in such a way that the temperature of the drive motor remains below the specified limit value. The resistance to which the braking current is conducted is preferably an ohmic resistance of a phase strand of the drive motor.

The invention also includes a washing machine with such a drive device.

The preferred embodiments presented with reference to the method according to the invention and their advantages apply accordingly to the drive device according to the invention and the washing machine according to the invention and vice versa.

Further advantages of the invention result from the claims, the figures of the drawing and the following description of the figures. All of the features and combinations of features mentioned above in the description, as well as the features mentioned below and / or shown alone in the figures and Characteristic combinations can be used not only in the specified combination, but also in other combinations or on their own.

Fig. 1

in schematischer Darstellung eine Waschmaschine gemäß einer Ausführungsform der Erfindung; und

Fig. 2

beispielhafte zeitliche Verläufe einer Temperatur und einer Drehzahl eines Antriebsmotors der Waschmaschine in einem Schleuderbetrieb, wobei anhand der Verläufe ein Verfahren gemäß einer Ausführungsform näher erläutert wird.

The invention will now be explained in more detail on the basis of individual preferred exemplary embodiments, as well as with reference to the figures of the attached drawing. Show it:

Fig. 1

a schematic representation of a washing machine according to an embodiment of the invention; and

Fig. 2

Exemplary temporal profiles of a temperature and a rotational speed of a drive motor of the washing machine in a spin operation, a method according to one embodiment being explained in more detail using the profiles.

One in Fig. 1 The washing machine 1 shown in a schematic representation comprises a drive device 2 which serves to mechanically drive a washing drum 3 arranged in the washing machine 1. In the laundry drum 3 there are items of laundry 4 which are washed by the washing machine 1. The drive device 2 comprises a drive motor 5 and a circuit arrangement 6 for operating the drive motor 5. In the exemplary embodiment, the drive motor 5 is a brushless DC motor or a permanent magnet-excited synchronous motor and comprises three phase strands 7, 8, 9. The phase strand 7 is connected to a first connection 10 the drive motor 5 electrically connected; the phase strand 8 is connected to a second connection 11 of the drive motor 5, and the phase strand 9 is connected to a third electrical connection 12 of the drive motor 5.

The circuit arrangement 6 comprises a circuit input 13 with a first and a second input connection 14, 15, between which an electrical supply alternating voltage U _V is present. The AC supply voltage U _V is provided by an electrical supply network.

The circuit arrangement 6 also has three output connections 16, 17, 18. The first output connection 16 is connected to the first connection 10 of the drive motor 5 is connected, the second output connection 17 is connected to the second connection 11 of the drive motor 5, and the third output connection 18 is connected to the third connection 12 of the drive motor 5.

With the input connections 14, 15 is an in Fig. 1 only schematically shown power supply 19 coupled that - as from Fig. 1 emerges - can have a bridge rectifier. The power supply unit 19 can also include other components, such as in particular a line filter and the like. The power supply unit 19 provides an intermediate DC voltage U _Z between its output connections 20, 21. A reference potential B is provided at the output terminal 21. An intermediate circuit capacitor 22 is connected between the output connections 20, 21 of the power supply unit 19, that is to say in parallel with the power supply unit 19. The DC link voltage U _Z provided by the power supply unit 19 is therefore present at the DC link capacitor 22.

A voltage divider 23 is connected in parallel with the intermediate circuit capacitor 22 and has two ohmic resistors 24 in the exemplary embodiment. Between the resistors 24 there is a node 25 at which a voltage U _S can be tapped, namely with respect to the reference potential B. The amplitude of the voltage U _S provided by the voltage divider 23 represents a measure of the amplitude of the DC link voltage U _Z.

An inverter 26 is connected in parallel with the power supply unit 19, the intermediate circuit capacitor 22 and the voltage divider 23. The inverter 26 comprises a first circuit branch 27, a second circuit branch 28 and a third circuit branch 29. The first, the second and the third circuit branch 27, 28, 29 are connected on the one hand to the output connection 20 of the power supply 19 and on the other hand to the reference potential B or coupled to the output terminal 21 of the power supply 19. The first circuit branch 27 comprises two electrical switches 30, 31; a node 32 located between the electrical switches 30, 31 is coupled to the first output connection 16 of the circuit arrangement 6. The second circuit branch 28 accordingly has two electrical switches 33, 34; a node 35 located between the electrical switches 33, 34 is coupled to the second output connection 17 of the circuit arrangement 6. Correspondingly, the third circuit branch 29 has two electrical switches 36, 37; one between the Node 38 located at electrical switches 36, 37 is coupled to the third output connection 18 of the circuit arrangement 6 and thus to the third connection 12 of the drive motor 5. The electrical switches 30, 31, 33, 34, 36, 37 are bipolar transistors with insulated gate electrodes (IGBT) in the exemplary embodiment.

The circuit arrangement 6 also comprises a control device 39, which in the exemplary embodiment can have a microprocessor and / or a microcontroller. The control device 39 serves to control the inverter 26, and more precisely the electrical switches 30, 31, 33, 34, 36, 37.

By correspondingly controlling the inverter 26, the control device 39 can control and / or regulate the speed of the drive motor 5 and thus the speed of the laundry drum 3. The control device 39 can also measure the DC link voltage U _Z , namely as a function of the electrical voltage U _S provided by the voltage divider 23. The control device 39 is coupled to the node 25 of the voltage divider 23. The control device 39 thus detects the voltage U _S and can thus draw conclusions about the DC link voltage U _Z.

In order to control the drive motor, an electrical alternating voltage U ₁₂ , U ₂₃ , U _{13 is applied} between the connections 10 and 11 or 11 and 12 or 10 and 12, that is to say to the phase strands 7, 8, 9 of the drive motor 5. The respective amplitudes of these voltages U ₁₂ , U ₂₃ , U ₁₃ are known to the control device 39; namely, it detects the DC link voltage U _Z and controls the inverter 26.

The control device 39 also detects phase currents I ₁ , I ₂ , I ₃ which flow via the phase phases 7, 8, 9 of the drive motor 5. For this purpose, the control device 39 is coupled to a node 41 of the first circuit branch 27, which is located between the electrical switch 31 and an ohmic resistor 40 connected in series with it. The control device 39 is also coupled to a node 42, which is arranged between the electrical switch 34 and an ohmic resistor 43 connected in series therewith in the second circuit branch 28. Furthermore, the control device 39 is coupled to a node 44, which is arranged between the electrical switch 37 and an ohmic resistor 45 connected in series with it in the third circuit branch 29. The control device 39 can therefore be connected to the resistors 40, 43, 45 tap the respective voltages falling and thus detect the respective current strength of the phase currents I ₁ , I ₂ , I ₃ which flow via the phase strands 7, 8, 9 of the drive motor 5.

In the present case, there is interest in a spin operation of the washing machine 1 in which the drive motor 5 is accelerated to high spin speeds. The washing machine 1 comprises a belt drive, that is to say the drive motor 5 is connected to the laundry drum 3 via a belt with a predetermined ratio. For example, the translation can be about 10. This means that the speed of the drive motor 5 is ten times as high as the speed of the laundry drum 3. If the washing drum 3 is accelerated to a speed of 1000 rpm, the speed of the drive motor 5 is approximately 10,000 rpm. A spin operation is known to be divided into several spin cycles in which the drive motor 5 is accelerated to a predetermined spin speed and then braked again to a lower speed, in particular to zero rpm. A method according to an embodiment relating to the control of a braking process in spin operation is described in more detail below.

In order to brake the drive motor 5 quickly, the electrical switches 31, 34, 37 (the lower switches of the inverter 26) can be actuated during a braking operation, and can be closed in pairs or all. Then a braking current I _B flowing due to a braking voltage induced by the drive motor 5 is specifically fed back to the phase strands 7, 8, 9 of the drive motor 5 or it remains in the respective circuit of the phase strands 7, 8, 9 electrical energy supplied during the braking process is then converted into heat at an ohmic resistance of the phase strands 7, 8, 9. The electrical switches 31, 34, 37 can be switched at a frequency of 16 kHz, for example; the duty cycle, which indicates the ratio of the period of time during which the electrical switches 31, 34, 37 are closed to the period, can be set here as desired by the control device 39.

By actuating the electrical switches 31, 34, 37 during the braking process, the phase strands 7, 8, 9 are quasi with one another or against the Reference potential B short-circuited. The fact is thus made use of that, in contrast to universal or asynchronous motors, the magnetic field in a permanent magnet excited synchronous motor is generated by permanent magnets in the rotor and the magnetic field or the excitation field can therefore not be switched off but is permanently effective. If the windings of the stator, i.e. the phase strands 7, 8, 9, are short-circuited, an electrical braking voltage is still induced in this winding by the rotary movement and the magnetic field of the rotor, and a braking current I _B (short-circuit current) flows. Since the drive motor 5 when the phase strands 7, 8, 9 of the stator are short-circuited, electrical energy is no longer supplied to or removed from the stator - the electrical switches 30, 33, 36 remain open - the entire kinetic energy of the rotating drive motor 5 and the laundry drum 3 and the laundry items 4 are converted into ohmic loss energy, that is to say heat in the phase strands 7, 8, 9. Such a procedure has the advantage that the laundry drum 3 can be braked with a significantly greater deceleration than in the case of a natural runout, that is to say when it is idling.

Since the energy at the ohmic resistance of the phase strands 7, 8, 9 is converted into heat, the temperature of the drive motor 5, and more precisely its stator, can increase significantly during the braking process. In the exemplary embodiment, the instantaneous temperature of the drive motor 5 is therefore calculated by the control device 39. Specifically, the control device 39 can control the temperature of the drive motor 5 depending on the measured values for the branch currents I ₁ , I ₂ , I ₃ or for the braking current I _B , as well as depending on the measured values for the DC link voltage U _Z and on the values of String voltages U ₁₂ , U ₂₃ , U ₁₃ calculated. The control device 39 can also take into account the loading of the laundry drum 3, that is to say the weight of the laundry items 4, and also the ohmic resistance of the phase strands 7, 8, 9. The temperature can be calculated, for example, in such a way that first the electrical power - be it a power absorbed by the drive motor 5 or supplied by the drive motor 5 - and the temperature is calculated from this electrical power.

In addition, a maximum limit value for the temperature is stored in the control device 39, and the control device 39 controls the switches 31, 34, 37 in this way during the braking process that the temperature of the drive motor 5 does not exceed the specified limit. The limit value for the temperature can already be stored in the control device 39 during the development process of the drive device 2, namely, for example, in a memory of the control device 39.

Now referring to Fig. 2 A possible course of a spin operation of the washing machine 1 is described in more detail. Fig. 2 shows in its upper part a time course of a temperature T of the drive motor 5 during the spin operation. In its lower part shows Fig. 2 a time course of a speed n of the drive motor 5 during the spin operation. Time t is plotted on the X axes. The specified limit for the temperature T is designated T _G.

The spin operation begins at a time t ₀ . The drive motor 5 is accelerated to a first speed value n ₁ , it reaches the speed n ₁ at a time t ₁ . Between time t ₁ and a further time t ₂ , drive motor 5 is operated at constant speed n ₁ . Between the time t ₂ and a further time t ₃ , the drive motor 5 is accelerated to a second speed value n ₂ and operated at this speed value n ₂ until a time t ₄ .

During a time interval between t ₀ and t ₄ , the temperature T of the drive motor 5 rises, namely initially with a relatively large and then gradually decreasing gradient. At time t ₀ , the temperature T of the drive motor 5 is T ₀ , which corresponds, for example, to an ambient temperature of the washing machine 1 or a reference value. At time t ₄ , temperature T reaches a value of T ₁ . During the time interval from t ₀ to t ₄ , the temperature T rises by ΔT ₁ .

During the spin cycle of the drive motor 5 from t ₀ to t ₄ , the control device 39 calculates the instantaneous temperature T of the drive motor 5. Before the time t ₄ , the control device 39 also calculates the temperature T of the drive motor 5 for a subsequent braking operation after the time t ₄ , This means that the control device 39 makes a prediction about the temperature T before the braking process is initiated, which could occur during the braking process. As a rule, a maximum of the temperature T occurs immediately after initiation of the Braking on what from the course of the temperature T according Fig. 2 evident. Before the time t ₄ , the control _device 39 calculates a maximum value T _{max1 of} the temperature T. _Specifically , the control _{device 39} first calculates the maximum value T _max1 for a maximum deceleration of the drive motor 5, that is to say for a duty cycle of 100% when the electrical switches are actuated 31, 34, 37. If this maximum value T _{max1 exceeds} the limit value T _G , the control _device 39 calculates a maximum value T _max1 for a lower duty cycle and thus for a lower deceleration of the drive motor 5. If this new estimated maximum value T _{max1 is} now smaller than that Limit value T _G , the course of the deceleration or the speed n assigned to it is selected for the upcoming braking process. The control device 39 therefore checks before the time t ₄ for which curve of the rotational speed n the respectively calculated maximum value T _{max1 is} even smaller than the defined limit value T _G. The limit value T _G can, for example, be 110 K greater than the reference value T ₀ .

If the control _device 39 determines that the predicted maximum value T _{max1 is} smaller than the limit value T _G , it determines the deceleration of the drive motor 5 for the subsequent braking operation even before the time t ₄ . Specifically, the control device 39 predetermines a time course of the deceleration or the speed n of the drive motor 5 before the time t ₄ . The control device 39 defines a maximum possible delay at which the limit value T _{G is} not exceeded.

The course of the speed n or the deceleration can also be predetermined as a function of the instantaneous temperature T, which was determined before the braking process was initiated. This can be such that an average deceleration of the drive motor 5 is set to approximately 90 rpm / s when the instantaneous temperature T is less than T ₀ + 100 K, that is to say does not exceed the reference value T ₀ by 100 K. The average deceleration can be set to approximately 70 rpm / s if the temperature T exceeds T ₀ + 100 K before the braking process is initiated. The average deceleration can be further reduced to about 65 rpm if the temperature T exceeds the value T ₀ + 105 K before the braking process is initiated. If the temperature T exceeds the value T ₀ + 110 K, the drive motor 5 can be switched off.

The braking process is initiated at time t ₄ . The temperature T reaches the maximum value T _max1 at a time t ₅ , in order then to decrease again. Between the time t ₄ and a time t ₆ , the drive motor 5 is braked, namely completely to speed n = 0 rpm. The drive motor 5 is therefore at a standstill t ₆ . The actual braking process of the drive motor 5 has ended. Another spin cycle or acceleration process of the drive motor 5 is not yet initiated at time t ₆ . The control device 39 waits until the temperature T of the drive motor 5 recovers and drops, for example, to a predetermined value T ₁₀ . The control device 39 can thus set a time period .DELTA.t ₁ between two successive spin cycles of the drive motor 5, namely depending on the temperature T of the drive motor 5 calculated during this time. After the time period .DELTA.t ₁ after the time t ₄ , the control device 39 conducts another Spin cycle of the drive motor 5, namely at a time t ₇ . As in the first spin cycle, the drive motor 5 is first accelerated to the first speed value n ₁ and then to the second speed value n ₂ in the second spin cycle, in order then to be braked again at a time t ₈ . During a time interval from t ₇ to t ₈ , the temperature T of the drive motor 5 rises, namely from the value T ₁₀ to a value T ₂ = T ₀ + ΔT ₂ . The control device 39 determines the temperature T and, before the time t _8, calculates a maximum value T _max2 for the subsequent braking process of the drive motor 5. The control device 39 determines a course of the deceleration or the speed n of the drive motor 5 for the following braking process, namely such that the maximum value T _{max2 is} less than the limit value T _G. For example, the control unit 39 can set a maximum deceleration for the drive motor 5 taking into account the limit value T _G. At time t ₈ , the braking process is initiated, and the temperature T of the drive motor 5 reaches the maximum value T _max2 and then drops. The drive motor 5 is braked, namely completely to the speed n of 0 rpm. At a time t ₉ , the drive motor 5 is stopped. The braking process is thus ended at time t ₉ . The temperature T of the drive motor 5 can, however, continue to recover, namely until a further point in time t ₁₀ , at which a further spin cycle of the drive motor 5 is initiated. A period of time .DELTA.t ₂ between the spin cycles of the drive motor 5 is determined by the control device 39 depending on the period of time .DELTA.t ₂ Temperature T of the drive motor 5 set. The third spin cycle of the drive motor 5 can then be initiated as soon as the temperature T of the drive motor 5 drops to a value T ₂₀ .

At time t ₁₀ , the third spin cycle of the drive motor 5 begins, in which it is first accelerated to the first speed value n ₁ and then to the second speed value n ₂ . A braking operation is to be initiated at a time t ₁₁ . During a time interval from t ₁₀ to t ₁₁ , the temperature T of the drive motor 5 rises, namely from T ₂₀ to T ₃ = T ₀ + ΔT ₃ . Before the time t _11, the control _device 39 determines the current temperature of the drive motor 5 and also calculates a maximum value T _max3 to which the temperature T of the drive motor 5 could rise in a subsequent braking operation. The control device 39 determines that a rapid braking of the drive motor 5 would lead to the limit value T _{G being} exceeded. For this reason, the control device 39 determines a comparatively flat course of the speed n or a relatively moderate deceleration of the drive motor 5 for the subsequent braking operation. Specifically, the control device 39 _{predetermines} such a course of the speed n for the braking process at which the maximum value T _{max3 is} less than the limit value T _G. At time t ₁₁ , the braking process begins, in which the drive motor 5 is braked completely until a time t ₁₂ . Here too, the control device 39 can set a time period Δt ₃ between the third spin cycle and a further spin cycle of the drive motor 5.

The control device 39 can therefore predict the temperature T of the drive motor 5 for the respective braking process, even before the braking process is actually initiated. In this prediction, the control device 39 takes into account the loading of the laundry drum 3 or the weight of the laundry items 4, as well as the instantaneous speed n of the drive motor 5. The control device 39 can use this to determine the mechanical energy or the torque of the drive motor 5 from the mechanical one Energy determines the electrical energy and from the electrical energy, taking into account the ohmic resistance of the phase strands 7, 8, 9, the temperature T of the drive motor 5.

As already stated, the control device 39 controls the electrical switches 31, 34, 37 during the braking process of the drive motor 5. At the beginning of everyone However, during the braking process, the control device 39 can first charge the intermediate circuit capacitor 22 with the energy supplied by the drive motor 5. In this case, the electrical switches 30, 33, 36 are first activated, while the switches 31, 34, 37 remain open. If the intermediate circuit capacitor 22 is charged, the switches 30, 33, 36 are opened and the switches 31, 34, 37 - as described above - are activated.

The duty cycle of the actuation of the switches 31, 34, 37 and thus the course of the speed n of the drive motor 5 can also be regulated continuously during the respective braking process, namely depending on the current temperature T of the drive motor 5 Temperature T can be reached, depending on the situation, it can be ensured that the temperature T does not exceed the limit value T _G. In the event that the temperature T is to exceed the limit value T _G , the drive motor 5 is switched off; it is then waited for the temperature T to fall below the limit value T _G again. Then the drive motor 5 is put into operation again.

Instead of converting the energy supplied by the drive motor 5 during the braking process into heat at the ohmic resistance of the phase strands 7, 8, 9, a separate braking resistor can be used in the circuit arrangement 6. Such a braking resistor can then be connected in parallel to the intermediate circuit capacitor 22 as required, namely via an electrical switch. Then the energy supplied by the drive motor 5 can first be stored in the intermediate circuit capacitor 22 and then converted into heat at the braking resistor. The electrical switch, via which the braking current I _{B is fed} to the separate braking resistor, is then controlled in accordance with the method described above, namely so that the temperature T of the drive motor 5 does not exceed the limit value T _G.

LIST OF REFERENCE NUMBERS

1

Washing machine

2

driving device

3

washing drum

4

laundry

5

drive motor

6

circuitry

7

phase conductor

8th

phase conductor

9

phase conductor

10

first connection of the drive motor

11

second connection of the drive motor

12

third connection of the drive motor

13

circuit input

14

first input port

15

second input connector

16

first output connector

17

second output connector

18

third output connector

19

power adapter

20

output port

21

output port

22

Link capacitor

23

voltage divider

24

Ohmic resistors

25

junction

26

inverter

27

circuit branch

28

circuit branch

29

circuit branch

30

electrical switch

31

electrical switch

32

junction

33

electrical switch

34

electrical switch

35

junction

36

electrical switch

37

electrical switch

38

junction

39

control device

40

Ohmic resistance

41

junction

42

junction

43

Ohmic resistance

44

junction

45

Ohmic resistance

U _V

AC supply voltage

U _S

tension

U _Z

Intermediate circuit voltage

U ₁₂

AC

U ₂₃

AC

U ₁₃

AC

I ₁ , I ₂ , I ₃

phase currents

I _B

braking power

t

time

n

rotational speed

T

temperature

T _G

limit

T ₁ , T ₁₀ , T ₂ , T ₂₀ , T ₃ , T _max1 , T _max2 , T _max3

temperature values

n ₁ , n ₂

Speed values

t ₀ to t ₁₂

timings

Δt ₁ , Δt ₂ , Δt ₃

time

ΔT ₁ , ΔT ₂ , ΔT ₃

temperature differences

Claims (12)

1. Method for controlling a braking cycle of a drive motor (5), which drives a washing drum (3) in a washing machine (1), by which during the braking cycle an electrical braking current (I_B) which is fed back due to an electrical braking voltage (U₁₂, U₂₃, U₁₃) induced by the drive motor (5) is at least intermittently guided to an ohmic resistance (7, 8, 9) by closing an electrical switch (31, 34, 37), characterised in that a temperature (T) of the drive motor (5) is determined, a limiting value (T_G) is defined for the temperature (T) and the electrical switch (31, 34, 37) is actuated during the braking cycle in such a way that the temperature (T) of the drive motor (5) remains below the defined limiting value (T_G).
2. Method according to claim 1, characterised in that the ohmic resistance (7, 8, 9) is formed by a phase winding (7, 8, 9) of a stator of the drive motor (5).
3. Method according to one of the preceding claims, characterised in that before the braking cycle is initiated the temperature (T) of the drive motor (5) is determined and, before the braking cycle is initiated, a temporal course of a rotation speed (n) of the drive motor (5) is predetermined for the braking cycle as a function of the temperature (T).
4. Method according to one of the preceding claims, characterised in that before the braking cycle is initiated an estimate is made for the braking cycle of the temperature (T) of the drive motor (5), in particular a maximum value (T_max1, T_max2, T_max3) of the temperature (T), and the electrical switch (31, 34, 37) is actuated as a function of the estimated temperature (T), in particular before the braking cycle is initiated a temporal course of a rotation speed (n) of the drive motor (5) is predetermined for the braking cycle as a function of the estimated temperature (T).
5. Method according to one of the preceding claims, characterised in that the electrical switch (31, 34, 37) is actuated during the braking cycle in such a way that the drive motor (5) is braked with a maximum possible deceleration taking into account the limiting value (T_G) for the temperature (T).
6. Method according to one of the preceding claims, characterised in that the braking cycle is carried out between two successive spin cycles of the drive motor (5) and a time interval (Δt₁, Δt₂, Δt₃) between the spin cycles is set as a function of the temperature (T) of the drive motor (5) which has been determined.
7. Method according to one of the preceding claims, characterised in that before the braking cycle is initiated, the temperature (T) of the drive motor (5) is determined and a time point (t₄, t₈, t₁₁) which depends on this temperature (T) is set for the initiation of the braking cycle.
8. Method according to one of the preceding claims, characterised in that the temperature (T) of the drive motor (5) is determined by means of a control device (39), by which the electrical switch (31, 34, 37) is actuated, using a characteristic stored in the control device (39) and/or a mathematical formula stored in the control device (39).
9. Method according to claim 8, characterised in that the temperature (T) of the drive motor (5) is calculated as a function of measured values for a phase current (I₁, I₂, I₃) in the drive motor (5) and/or of measured values for an intermediate circuit DC voltage (U_Z), with which the drive motor (5) is supplied, and/or of measured values for the braking current (I_B).
10. Method according to one of the preceding claims, characterised in that the drive motor (5) is a polyphase drive motor, in particular a permanent magnet excited synchronous motor.
11. Drive device (2) for a washing drum (3) in a washing machine (1), with

    - a drive motor (5) for driving the washing drum (3) and

    - a control device (39), for actuating the drive motor (5), which is arranged, during a braking cycle of the drive motor (5), to guide an electrical braking current (I_B), which is fed back due to an electrical braking voltage (U₁₂, U₂₃, U₁₃) induced by the drive motor (5), at least intermittently to an ohmic resistance (7, 8, 9), by closing an electrical switch (31, 34, 37) in the drive device (2),

    characterised in that
    a temperature (T) of the drive motor (5) can be determined in the drive device (2), a limiting value (T_G) for the temperature (T) is stored in the control device (39) and the control device (39) is arranged to actuate the electrical switch (31, 34, 37) in such a way during the braking cycle that the temperature (T) of the drive motor (5) remains below the defined limiting value (T_G).
12. Washing machine with a washing drum (3) and a drive device (2) according to claim 11.

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