Method for regulating evaporation from a vaporizer in an inhaler

Abstract

A method for regulating evaporation of a vaporizer (60) in an inhaler (10), wherein the vaporizer (60) is heated by means of resistance heating and wherein an electronic control device (15) regulates a current flowing through the vaporizer (60), the method comprising the following steps: determining a starting point (110) corresponding to the start of a puff by a consumer; recording measured values ​​(108) of the current applied to the vaporizer (60) in temporal succession from the starting point (110); determining a transition point (101) between a region of low evaporation and a region of high evaporation in a time-dependent series of current measurements (100) corresponding to the measured values ​​(108); determining a current value (I 101) corresponding to the transition point (101); v ); According to the determined current value (I v ) specifies a current interval [I1; I2]; and adjusts the passing current within the specified current interval [I1; I2].

Description

Technical Field

[0001] The invention relates to a method for regulating evaporation of an evaporator in an inhaler, wherein the evaporator is heated by means of electrical resistance heating and wherein an electronic control device regulates the current flowing through the evaporator. Background Art

[0002] Typically, the resistance evaporator is electrically connected to the energy store via an electronic switching element, so that when the switching element is closed, the voltage of the energy store is applied to the evaporator and a heating current flows. The switch is usually operated by an electronic control unit.

[0003] The temperature at the evaporator is typically determined using a temperature-dependent resistance of the evaporator. The temperature of the evaporator can be set in a targeted manner by means of the relationship between the temperature of the evaporator and the resistance. The temperature should not exceed the temperature determined by the liquid to be evaporated, since otherwise pollutants could form, in particular due to drying out of the evaporator.

[0004] The circuit of the evaporator or heater can be described in a simplified manner as a series circuit of resistors. The elements of this series circuit include the resistance of the evaporator (evaporator resistance), the internal resistance of the battery and undesired parasitic resistances. The parasitic resistance is given, for example, by the following resistances: the resistance belonging to the electrical control device, the current measuring resistance, the resistance of the lead wires (especially via the connecting wires, copper rails and / or soldering points) and the resistance of the plug-in connection if necessary. The parasitic resistance is neither constant over time nor reproducible, because, for example, the plug-in connection has an influence on the parasitic resistance depending on the aging state, contamination and / or deformation, which influence can only be measured with considerable effort.

[0005] Temperature measurement errors due to parasitic resistances can lead to overheating of the liquid to be evaporated, which can lead to bubbling boiling or the formation of harmful substances. Due to various errors caused by measurement and parasitic currents, evaporators can only be regulated inadequately using known methods. Summary of the invention

[0006] The object of the present invention is to provide a method with which evaporation can be regulated efficiently and reliably and overheating of the liquid to be evaporated can be safely avoided.

[0007] According to the invention, the method comprises the following steps: From a starting point, measured values ​​of the current applied to the evaporator are recorded sequentially in time. From the starting point, the current flows through the evaporator. Due to the current flow and the temperature-dependent resistance of the evaporator, the evaporator warms up. Due to the warming of the evaporator, the temperature-dependent resistance of the evaporator changes.

[0008] The measurement can advantageously be switched on by a request from a user of the inhaler, in particular by drawing on an electronic cigarette. Accordingly, the measurement can be switched off after the request has ended.

[0009] Subsequently, in particular during consumption, in a time-dependent current measurement series corresponding to the measured values, a transition point between a range of low evaporation and in particular up to no evaporation and a range of high evaporation is determined. The transition point marks a point in time at which evaporation occurs and the evaporator is not significantly further heated. The invention has recognized that from the transition point onwards, evaporation occurs to such a high degree that no or almost no further warming of the evaporator occurs. The energy provided by the current at the evaporator is converted into energy for evaporating the liquid and is not or only partially converted into warming of the evaporator. Therefore, from the transition point onwards, the temperature of the evaporator changes to a smaller extent than at the time before the transition point. Therefore, the transition point in the current measurement series can be understood as a turning point in the correlation between the current and the measurement point or time. The current value I corresponding to the transition point is determined from the transition point. v In order to adjust the heating power via the current, it is then determined according to the current value I v A current interval [I1; I2] is specified and the through current is adjusted within the specified current interval [I1; I2]. Thus, the power of the evaporator can be accurately adjusted.

[0010] The method according to the invention has the advantage that the evaporator temperature does not have to be known and in particular the value of the parasitic resistance does not have to be determined in real time and for each individual evaporator. With the method according to the invention it is decisive at which respective current or heating power evaporation occurs by the respective evaporator. The occurrence of evaporation is determined from the measurement series and thus the heating current to be applied in the current interval [I1; I2].

[0011] Advantageously, the transition point is determined along the current measurement series by means of a regression in order to be able to determine the transition point reliably and efficiently. The regression is based on a plurality of measured values, whereby measurement errors and / or statistical errors can be minimized. The regression is advantageous compared to, for example, the finite difference method, in which only two adjacent measured values ​​are taken into account, and therefore measurement inaccuracies have a particularly strong influence on the result.

[0012] The transition point of at least one best-fit straight line and / or at least one best-fit polynomial for the current measurement series is preferably determined in order to provide a digitally efficient determination of the transition point. For example, one or more best-fit straight lines and / or in particular quadratic best-fit curves can be determined by regression at different measurement points of the measurement series. The transition point can be determined from the time course of the slope of the best-fit straight line or the curvature of the best-fit curve. In this case, the curvature can be determined in particular from the coefficients of the quadratic term of the best-fit polynomial.

[0013] The transition point is preferably determined by a jump and / or reaching a threshold value of the slope or gradient (first derivative) of the current measurement series in order to further improve the identification of the transition point. To this end, in an advantageous embodiment, the transition point is determined by an extreme value of the curvature of the current measurement series.

[0014] Two temporally consecutive measured values ​​are temporally spaced less than 10 ms, preferably less than 5 ms, further preferably less than 2 ms from one another, in order to be able to resolve the transition points well in time and to be able to record an advantageous number of measured values ​​over the duration of the puff. For this purpose, the recorded measured values ​​are preferably recorded over at least 10%, advantageously at least 30%, further advantageously at least 50% of the puff length.

[0015] The length of the current interval [I1;I2] is less than the current value I V 50%, advantageously less than 25%, further advantageously less than 10% of the value of , so that the heating current can be adjusted as accurately as possible.

[0016] In a preferred embodiment, the lower threshold value I1 and / or the upper threshold value I2 are defined such that the lower threshold value is smaller than the current value I V and / or current value I V is smaller than the upper threshold value I2, so that the heating current can reliably be around the current value I in the current interval [I1; I2]. V If the lower threshold I1 is less than the current value I v , the evaporator can be prevented from drying up, because the evaporator is under the lower threshold I1 and the current value I v The current between the two does not evaporate, but rather heats the evaporator and / or the liquid.

[0017] The current through the evaporator is pulsed, wherein the duty cycle is increased from above when the lower threshold value I1 is reached and / or is reduced from below when the upper threshold value I2 is reached. This allows a reduction in input power and an increase in the operating time of the battery supplying current to the evaporator.

[0018] Advantageously, the lower threshold value I1 and / or the upper threshold value I2 are defined as a function of an analysis of the average secondary current I^2 over a defined time interval. If the average secondary current I^2 falls below a predetermined threshold value, which can be determined, for example, from a series of current measurements in a time interval after the starting point, this is evaluated as a sign of reduced contact between the evaporator and the liquid. In this case, the lower threshold value I1 and / or the upper threshold value I2 should be shifted toward a lower current.

[0019] Preferably, the current interval [I1; I2] and / or at least one of the threshold values ​​I1; I2 is shifted over time towards a lower current in order to prevent the evaporator from drying out. The current interval [I1; I2] and / or at least one of the threshold values ​​I1; I2 can also be adapted to a predetermined time function in order to be able to effectively control the evaporation and to enable adaptation to the differential distillation process.

[0020] In an advantageous embodiment, data about a plurality of time-dependent current measurement series are stored in a data memory and compared with one another and / or with fixed parameters. It is thus possible to store the current measurement values ​​and transition points accumulated during the method. For example, the automatic analysis can check at which point in time the evaporation current I v If this point in time is reached later than a predefined threshold value, this is a sign of too high a resistance. Furthermore, the average current square can be evaluated during the evaporation process. If this is below a predefined threshold value, consumption of the liquid can be inferred.

[0021] Preferably, the ambient temperature is measured and the current interval [I1; I2] and / or at least one of its threshold values ​​I1, I2 is defined and / or adapted as a function of the measured ambient parameter in order to be able to take into account possible influences of the ambient temperature.

[0022] The through current is regulated by switching on and / or maintaining the through current flowing through the evaporator when the current is less than an upper threshold value I2, or by shutting off the through current flowing through the evaporator when the current is greater than a lower threshold value I1, so as to provide an advantageous regulation method within the current interval [I1; I2]. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is described below according to preferred embodiments with reference to the accompanying drawings.

[0024] Figure 1 A schematic diagram showing an inhaler;

[0025] Figure 2 A simplified circuit for current heating of the evaporator is shown;

[0026] Figure 3showing an exemplary series of current measurements with determined transition points;

[0027] Figure 4 An exemplary series of current measurements with transition points is shown;

[0028] Figure 5 showing the determination of the transition point from an increase in the series of current measurements; and

[0029] Figure 6 It is shown that the transition point is determined from the curvature of the current measurement series. DETAILED DESCRIPTION

[0030] Figure 1 An inhaler 10 or an electronic cigarette product is schematically shown. The inhaler 10 comprises a housing 11, wherein an air channel 30 or chimney is provided between at least one air inlet 231 and an air outlet 24 at a mouth end 32 of the smoking product 10. Here, the mouth end 32 of the inhaler 10 represents the end which the consumer draws for the purpose of inhalation, and thereby exerts a negative pressure on the inhaler 10 and generates an air flow 34 in the air channel 30.

[0031] The inhaler 10 advantageously consists of a base part 16 and an evaporator tank unit 20, which comprises an evaporator device 1 with an evaporator 60 and a liquid reservoir 18, which can be adjusted by the method according to the invention. The evaporator tank unit can be designed in particular in the form of a replaceable cartridge. The liquid reservoir 18 can be refillable by a user of the inhaler 10. The air sucked in through the air inlet 231 is guided in the air channel 30 to at least one evaporator 60. The evaporator 60 is connected or can be connected to the liquid reservoir 18, in which at least one liquid 50 is stored. For this purpose, a porous and / or capillary liquid conducting element 19 is advantageously arranged at the inlet side 61 of the evaporator 60.

[0032] An advantageous volume of the liquid reservoir 18 lies in the range between 0.1 ml and 5 ml, preferably between 0.5 ml and 3 ml, further preferably between 0.7 ml and 2 ml or 1.5 ml.

[0033] The evaporator 60 evaporates the liquid 50 , which is transported from the liquid reservoir 18 to the evaporator 60 and / or stored in the porous element 19 by means of capillary forces, and adds the evaporated liquid to the gas flow 34 at the outlet 64 as an aerosol / vapor.

[0034] The inhaler 10 further comprises an electrical energy storage device 14 and an electronic control device 15. The energy storage device 14 is usually arranged in a base part 16 and can be, in particular, an electrochemical disposable battery or a rechargeable electrochemical battery, such as a lithium-ion battery. The vaporizer tank unit 20 is arranged between the energy storage device 14 and the mouth end 32. In the base part 16 (such as Figure 1 ) and / or in the evaporation tank unit 20, the electronic control device 15 includes at least one digital data processing device, in particular a microprocessor and / or a microcontroller.

[0035] A sensor, such as a pressure sensor or a pressure or flow switch, is advantageously arranged in the housing 11, wherein the control device 15 can determine based on the sensor signal output by the sensor that the consumer draws a puff at the mouth end 32 of the smoking product 10 in order to inhale. In this case, the control device 15 actuates the vaporizer 60 in order to add the liquid 50 from the liquid reservoir 18 as an aerosol / vapor to the air flow 34.

[0036] At least one evaporator 60 is arranged in the part of the evaporator tank unit 20 facing away from the mouth end 32. In particular, an effective electrical coupling to the base part 16 and actuation of the evaporator 60 are thereby possible. The air flow 34 advantageously leads to the air outlet 24 via an air channel 34 extending through the liquid reservoir 18.

[0037] The liquid 50 to be metered stored in the liquid reservoir 18 is, for example, a mixture of 1,2-propylene glycol, glycerol, water and preferably at least one flavoring substance (flavor) and / or at least one active ingredient, in particular nicotine. However, the given composition of the liquid 50 is not mandatory. In particular, the flavor and / or active ingredient, in particular nicotine, can be omitted.

[0038] exist Figure 2 , a schematic circuit for heating the evaporator 60 by electric current is shown in . The evaporator 60 is a resistance heater, which can be heated by electric current due to its resistance. The evaporator 60 can have at least one resistance element, such as a heating wire, such as a spiral wire or one or more wires arranged parallel to each other. The evaporator 60 can alternatively be implemented as a micro-electromechanical system (MEMS) as described in DE 10 2016 120 803 A1, for example with a line or a microchannel, the disclosure of which is incorporated into the present application in this regard. Bionic or capillary heating structures, such as bionic networks, are also possible for the evaporator 60. An evaporator 60 with a heating structure as described in DE 10 2017 111 119 A1 is also possible, the disclosure of which is incorporated into the present application in this regard. In general, the present invention is not restricted to a specific type of evaporator 60.

[0039] The vaporizer tank unit 20 is preferably connected and / or connectable to a heating current source 71 controllable by the control device 15, which is connected to the vaporizer 60 via the line 25, so that the heating current Ih generated by the heating current source 71 flows through the vaporizer 60. Due to the ohmic resistance of the electrically conductive vaporizer 60, the passage of the current leads to heating of the vaporizer 60 and thus to evaporation of the liquid attached to the vaporizer 60. The vapor / aerosol generated in this way escapes from the vaporizer 60 and is mixed with the air flow 34. More precisely, when determining the air flow 34 caused by the consumer's puff through the air channel 30, the control device 15 controls the heating current source 71, wherein the liquid attached to the vaporizer 60 is discharged in the form of vapor / aerosol by spontaneous heating.

[0040] The evaporation temperature is preferably in the range between 100°C and 400°C, further preferably between 150°C and 350°C, even further preferably between 190°C and 290°C.

[0041] The vaporizer tank unit 20 is adjusted so that the amount of liquid is preferably dosed in the range of between 1 μl and 20 μl, further preferably between 2 μl and 10 μl, further preferably between 3 μl and 5 μl, typically 4 μl per puff of the consumer. Preferably, the vaporizer tank unit can be adjustable in terms of the amount of liquid / vapor per puff, i.e. per puff duration of 1 s to 3 s.

[0042] The actuation frequency of the evaporator 60 generated by the heating current source 71 is generally advantageously in the range of 1 Hz to 50 kHz, preferably in the range of 30 Hz to 30 kHz, further advantageously in the range of 100 Hz to 25 kHz.

[0043] Advantageously, the evaporator 60 can be replaceable in the event of contamination, defects or depleted substrate, so that a detachable electrical connection can be provided between the evaporator 60 and the base part 16. This connection can be configured, for example, as a spring pin, plug-in or screw connection.

[0044] Figure 3 The thick black curve shows the current I V Schematic current measurement series 100 for a determined transition point 101 at , wherein the illustration shows an example of a current measurement series 100 for an evaporator 60 with a negative temperature coefficient. Figure 3 In FIG. 1 , the current I is plotted against the time t and is shown as continuous only for illustrative purposes.

[0045] At the start of the puff at a starting point 110, which is determined, for example, by detecting the puff with the aid of a pressure sensor or by switching it on by the consumer, the vaporizer 60 is switched on and heated with a heating current. The measured values ​​108 of the current I applied to the vaporizer 60 are then recorded sequentially in time from the starting point 110 (at Figure 3 ). The evaporator 60 heats up relatively quickly, so the measured current I decreases.

[0046] The time current measurement series 100 has a transition point 101 which can be identified as a turning point, or at least has a strong flattening which is determined as the transition point 101 as soon as evaporation begins. This is followed by a current I associated with the transition point 101 with a lower threshold value I1 and an upper threshold value I2. v Two-point regulation is performed, in which the current I is regulated in the current interval [I1; I2]: once the determined through current I exceeds the upper threshold value I2, the current source is turned off or the through current is reduced; once the determined through current I does not exceed the lower threshold value I2, the current source is turned on or the through current is increased. The upper threshold value I2 and the current I at the transition point 102 v The difference between the current I v The difference from the lower threshold I1 is advantageously smaller than the current I at the transition point 102 v , since no overtemperature or only a low overtemperature and therefore also only small current changes should occur at the evaporator 60 .

[0047] The advantages of the previously described method for adjusting Figure 3 The following current measurement series 200 in the embodiment of the present invention illustrates this. The following current measurement series 200 shows the current course of the evaporator 60 which differs from the evaporator 60 of the current measurement series 100 printed in bold at one or more points: the battery voltage is another battery voltage, in particular due to the discharge state or internal resistance; the heating resistor of the evaporator 60 is another heating resistor, in particular due to manufacturing tolerances; other resistors are present.

[0048] Therefore, for the following current measurement series 200, it is found that at another current I w The transition point 201 at , which however again occurs at the start of evaporation. In this example, the lower threshold I1 and the upper threshold I2 can be easily selected within which the current I is adjusted so that the evaporator 60 evaporates the liquid reliably and effectively.

[0049] The method according to the invention results in a temperature error which is one order of magnitude smaller than in the case of resistive temperature determination according to the prior art. V50%, advantageously less than 25%, further advantageously less than 10% of the value of . The method is not regulated to a fixed temperature, but to a current corresponding to the evaporation temperature or to a temperature slightly above the evaporation temperature. Since the evaporation temperature depends on the composition of the substrate or in particular the liquid, the temperature is not absolute, but the current I that causes the evaporation v is determined.

[0050] Figure 4 An exemplary current measurement series 100 of a possible measurement curve is shown with a transition point 101 at a time of approximately t=201 ms and the actual noise of the current signal. The current measurement series 100 comprises a plurality of measured values ​​108 recorded successively in time, which are represented by a corresponding number of points, wherein each point represents a measured value 108 with an associated current I at time t.

[0051] Once n values ​​have been recorded, the control device 15 calculates the best fit straight line 102 from the measured values ​​108, for example by linear regression. In this example, two different best fit straight lines 102 are shown at the times t1 and t2. The time course of the slope 109 of the best fit straight line 102 thus determined is shown in FIG. Figure 5 Shown in.

[0052] Regression has the advantage that even if the current measurement series 100 is superimposed with noise, the transition point 101 can be well located. Thus, regression flattens the slope 109 and provides an improvement over finite differences.

[0053] Figure 5 Show according to Figure 4 The slope 109 of the current measurement series 100 shown in FIG. 1 determines the transition point 101. The transition point 101 can be detected in real time by evaluating the first or second time derivative of the current I.

[0054] The slope 109 is the slope of the best fit straight line 102 determined by regression of the current measurement series 100 and is plotted against the time t. If, for example, the value of the slope 109 drops below a threshold value 103, then the start of evaporation can be inferred. In this example, the transition point 101 is located at the point where the value of the slope 109 of the best fit straight line 102 is less than the threshold value 103, which is 0.002 A / s in this example. For the evaporator 60, the threshold value 103 can be determined empirically. From the time t0 at which the slope 109 exceeds the threshold value 103, the evaporation current I can be determined from the current measurement series 100. v , here for example about 2.6 A (see Figure 4 ).

[0055] Figure 6 Show according to Figure 4The curvature 106 of the current measurement series 100 shown in FIG. determines the transition point 101. The extreme value 107, in particular the maximum value, in the second-order derivative represents the transition point 101. The transition point 101 or the evaporation point of the current measurement series 101 can also be found by the curvature 106 of the current measurement series 100. For this purpose, instead of the best fit straight line 102, a polynomial, in particular a second-order polynomial, is locally fitted to a plurality of consecutive measured values ​​108 of the current measurement series 100 along the current measurement series 100. The coefficients of the quadratic terms of the polynomial are determined as the curvature 106 and plotted against the time t. The algorithm for finding the extreme value 107 finds the extreme value 107 at the time point t0, which corresponds to the time point at which the current measurement series 100 has the transition point 101.

[0056] List of reference numerals:

[0057] 1 Evaporator equipment

[0058] 4 Carrier

[0059] 10. Inhaler

[0060] 11 Housing

[0061] 14 Accumulator

[0062] 15 Control Device

[0063] 16 Basics

[0064] 18 Liquid Storage

[0065] 19 core structure

[0066] 20 Evaporation tank unit

[0067] 24 Air outlet

[0068] 30 Air channels

[0069] 32 Mouth end

[0070] 34 Airflow

[0071] 50 Liquid

[0072] 60 Evaporator

[0073] 61 Entrance side

[0074] 62 Liquid Channel

[0075] 64Export side

[0076] 71 Heating current source

[0077] 100, 200 Current Measurement Series

[0078] 101, 201 Turning Point

[0079] 102 Best Fit Straight Line

[0080] 103 Threshold

[0081] 104 Through Holes

[0082] 105a, 105b Electric lines

[0083] 106 Curvature

[0084] 107 Extreme Value

[0085] 108 measurements

[0086] 109 Slope

[0087] 110 Starting Point

[0088] 131 Contact Area

[0089] 231 Air Inlet

[0090] I.l v ,I w Current value

[0091] I1 Lower Threshold

[0092] I2 upper threshold

[0093] Time points t0, t1, and t2.

Claims

1. A method for regulating the evaporation of an evaporator (60) in an inhaler (10), wherein the evaporator (60) is heated by means of resistive heating and wherein an electronic control device (15) regulates the current flowing through the evaporator (60), characterized in that Follow these steps: Recording measured values ​​(108) of the current applied to the evaporator (60) sequentially over time starting from a starting point (110); determining a transition point (101) between a range of low evaporation and a range of high evaporation in a time-dependent series of current measurements (100) corresponding to the measured values ​​(108); Determine the current value I corresponding to the transition point (101) v ; According to the determined current value I v A current interval [I1; I2] is specified; and The through current is adjusted within the specified current range [I1; I2].

2. The method according to claim 1, characterized in that The determination is performed in real time.

3. The method according to claim 1, characterized in that: The transition point (101) is determined based on a regression of the series of current measurements (100).

4. The method according to claim 3, characterized in that The transition point (101) is determined based on at least one best-fit straight line and / or at least one best-fit polynomial to the series of current measurements (100).

5. The method according to any one of the preceding claims 1 to 4, characterized in that The transition point (101) is determined by a jump and / or reaching a threshold value (103) of a slope (109) of the series of current measurements (100).

6. The method according to any one of the preceding claims 1 to 4, characterized in that The transition point (101) is determined by an extreme value (107) of the curvature (106) of the current measurement series (100).

7. The method according to any one of the preceding claims 1 to 4, characterized in that Two temporally consecutive measured values ​​(108) are temporally spaced apart from one another by less than 10 ms.

8. The method according to any one of the preceding claims 1 to 4, characterized in that Two temporally consecutive measured values ​​(108) are spaced apart in time from one another by less than 5 ms.

9. The method according to any one of the preceding claims 1 to 4, characterized in that Two temporally consecutive measured values ​​(108) are spaced apart in time from one another by less than 2 ms.

10. The method according to any one of the preceding claims 1 to 4, characterized in that The recorded measured values ​​(108) are recorded over at least 10% of the puff length.

11. The method according to any one of the preceding claims 1 to 4, characterized in that The recorded measured values ​​(108) are recorded over at least 30% of the puff length.

12. The method according to any one of the preceding claims 1 to 4, characterized in that The recorded measured values ​​(108) are recorded over at least 50% of the puff length.

13. The method according to any one of the preceding claims 1 to 4, characterized in that The value of the current interval |I2-I1| is less than the current value I V 50% of the value.

14. The method according to any one of the preceding claims 1 to 4, characterized in that The value of the current interval |I2-I1| is less than the current value I V 25% of the value.

15. The method according to any one of the preceding claims 1 to 4, characterized in that The value of the current interval |I2-I1| is less than the current value I V 10% of the value.

16. The method according to any one of the preceding claims 1 to 4, characterized in that The lower threshold value I1 and / or the upper threshold value I2 are defined such that the lower threshold value is smaller than the current value I V and / or current value I V Less than the upper threshold value I2.

17. The method according to claim 16, characterized in that The current flowing through the evaporator (60) is pulsed, wherein the duty cycle is increased from above when the lower threshold value I1 is reached and / or is reduced from below when the upper threshold value I2 is reached.

18. The method according to claim 16, characterized in that The lower threshold value I1 and / or the upper threshold value I2 is defined as a function of an evaluation of the average secondary current Î2 over a defined time interval.

19. The method according to any one of the preceding claims 1 to 4, characterized in that The current interval [I1; I2] and / or its threshold values ​​I1 and / or I2 are shifted towards lower currents over time.

20. The method according to any one of the preceding claims 1 to 4, characterized in that Data relating to a plurality of time-dependent current measurement series (100) are stored in a data memory and compared with one another and / or with fixed parameters.

21. The method according to any one of the preceding claims 1 to 4, characterized in that The ambient temperature is measured and the current interval [I1; I2] and / or at least one of its threshold values ​​I1, I2 is defined and / or adapted as a function of the measured ambient parameter.

22. The method according to any one of the preceding claims 1 to 4, characterized in that The through current is regulated by switching on and / or maintaining the through current flowing through the evaporator (60) when the current is less than an upper threshold value I2 or by shutting off the current flowing through the evaporator (60) when the current is greater than a lower threshold value I1.

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