Patent Publication Number: US-2022218039-A1

Title: Method for regulating the vaporisation of a vaporiser in an inhaler

Description:
The present invention relates to methods for controlling the vaporization of a vaporizer in an inhaler, wherein the vaporizer is heated by means of electrical resistance heating, and wherein an electronic control device controls the current flow through the vaporizer. 
     Typically, a resistive vaporizer is electrically connected to an energy storage device via an electronic switching element, such that when the switching element is closed, the voltage of the energy storage device is applied to the vaporizer and a heating current flows. The switch is usually operated by the electronic control device. 
     The temperature at the vaporizer is typically determined using a temperature-dependent electrical resistance of the vaporizer. The relationship between temperature and the electrical resistance of the vaporizer can be used to adjust the temperature of the vaporizer specifically. The temperature should not exceed a temperature determined by the liquid to be vaporized, as otherwise harmful substances may be produced, in particular by the vaporizer falling dry. 
     The circuit of a vaporizer or heater can be described in simplified terms as a series circuit of electrical resistors. Elements of this series circuit comprise an electrical resistance of the vaporizer (vaporizer resistance), an internal battery resistance, and unwanted parasitic electrical resistances. The parasitic resistances are given, for example, by the following resistances: an electrical resistance belonging to the electrical control device, a current measuring resistor, an electrical resistance of the supply lines, in particular by connecting wires, copper conductive tracks and/or solder joints and, if applicable, an electrical resistance of a possible plug connection. The parasitic resistance is neither constant over time nor reproducible, since plug connections, for example, have an influence on the parasitic resistance depending on the state of aging, contamination and/or deformation which can only be measured with considerable effort. 
     Temperature measurement errors due to parasitic resistance can lead to overheating of the liquid to be vaporized, which can result in bubble boiling or the formation of pollutants. Because of the multiple errors due to measurement and parasitic currents, the vaporizer can be inadequately controlled by known methods. 
     It is the task of the invention to provide a method with which the vaporization can be effectively and reliably controlled and overheating of the liquid to be vaporized can be reliably avoided. 
     According to the invention, the method comprises the following steps: Taking measured values of the current applied to the vaporizer in time sequence starting from an initial point. From the initial point, a current flows through the vaporizer. Due to the current flow and the temperature-dependent electrical resistance of the vaporizer, the vaporizer heats up. Due to the heating of the vaporizer, the temperature-dependent electrical resistance of the vaporizer changes. 
     Advantageously, the measurement can be switched on by a demand request from a user of the inhaler, in particular by a draw on an electronic cigarette. Accordingly, the measurement may be switched off after the request is completed. 
     Subsequently, a transition point between a range of low vaporization and in particular to no vaporization and a range of high vaporization in particular during consumption is determined in a time-dependent current measurement series corresponding to the measured values. The transition point marks the point in time at which vaporization occurs and the vaporizer is not heated significantly further. The invention has recognized that from the transition point onward, vaporization occurs to such a high degree that little or no further heating of the vaporizer occurs. The energy provided by the current flow at the vaporizer is converted to energy for vaporization of the liquid and not, or only to a small extent, to heating of the vaporizer. Therefore, from the transition point, the temperature of the vaporizer changes to a lesser extent than at the time before the transition point. Thus, the transition point in the current measurement series can be understood as a kink in the dependence between current and measurement point or time. From the transition point, a current value I v  corresponding to the transition point is determined at which reliable vaporization takes place. To control the heating power via the current flow, a current interval [I 1 ; I 2 ] is defined as a function of the determined current value I v  and the current flow is controlled within the defined current interval [I 1 ; I 2 ]. Thus, the power of the vaporizer can be precisely controlled. 
     The method according to the invention has the advantage that the vaporizer temperature does not need to be known and the value of the parasitic electrical resistance in particular does not need to be determined in real time and for each individual vaporizer. With the method according to the invention, it is decisive at which respective current or heating power the vaporization occurs through the respective vaporizer. The onset of vaporization is determined on the basis of the measurement series and thus determines the heating current to be applied within the current interval [I 1 ; I 2 ]. 
     Advantageously, the transition point is determined by means of a regression along the current measurement series in order to be able to determine the transition point reliably and effectively. A regression is based on a plurality of measured values, which minimizes measurement errors and/or statistical errors. The regression is advantageous compared to, for example, a finite difference method, in which only in particular two adjacent measured values are considered and thus a measurement inaccuracy has a particularly strong effect on the result. 
     Preferably, the transition point of at least one line of best fit and/or at least one best fit polynomial to the current measurement series is determined in order to provide a numerically effective determination of the transition point. For example, one or more lines of best fit and/or, in particular, quadratic curves of best fit at different measurement points of the measurement series can be determined by the regression. The transition point can be determined from the rises over time belonging to the lines of best fit or the curvatures belonging to the curves of best fit. The curvature can be determined in particular from a coefficient of a quadratic term of the best fit polynomial. 
     Preferably, the transition point is determined by a step change and/or the reaching of a threshold of the rise or slope (1st derivative) of the current measurement series in order to further improve the identification of the transition point. In an advantageous embodiment, the transition point is determined for this purpose by an extreme value of the curvature of the current measurement series. 
     Preferably, two successive measured values are temporally separated from each other by less than 10 ms, preferably less than 5 ms, further preferably less than 2 ms, in order to be able to resolve the transition point well in time and to be able to record an advantageous number of measured values over the duration of a draw. For this purpose, the recorded measured values are preferably recorded over at least 10%, advantageously at least 30%, further advantageously at least 50% of a draw duration. 
     Advantageously, the length of the current interval [I 1 ; I 2 ] is less than 50%, advantageously less than 25%, further advantageously less than 10% of the amount of the current value I v , so that the heating current can be controlled as precisely as possible. 
     In a preferred embodiment, the lower threshold I 1  and/or the upper threshold I 2  are set such that the lower threshold is smaller than the current value I V  and/or the current value I V  is smaller than the upper threshold I 2 , so that the heating current can be reliably controlled around the current value I V  in the current interval [I 1 ; I 2 ]. If the lower threshold I 1  is smaller than the current value I V , dry-out of the vaporizer can be prevented because the vaporizer does not vaporize with a current between the lower threshold I 1  and the current value I V , but heats the vaporizer and/or the liquid. 
     Preferably, the current flow through the vaporizer is pulsed, wherein the duty cycle is increased when the lower threshold I 1  is reached from above and/or reduced when the upper threshold I 2  is reached from below. Thus, a reduction of the input power and an extension of the runtime of a battery supplying the vaporizer with electric current can be achieved. 
     Advantageously, the lower threshold I 1  and/or the upper threshold I 2  is determined as a function of an analysis of the average squared current I{circumflex over ( )}2 over a defined time interval. If the average squared current I{circumflex over ( )}2 falls below a predetermined threshold, which can be determined, for example, from the current measurement series from a time interval after the initial point, this is to be taken as an indication of reduced contact between the vaporizer and the liquid. In this case, the lower threshold I 1  and/or the upper threshold I 2  should be shifted to lower currents. 
     Preferably, the current interval [I 1 ; I 2 ] and/or at least one of the thresholds I 1 ; I 2  is shifted to lower currents over time to prevent the vaporizer from running dry. The current interval [I 1 ; I 2 ] and/or at least one of the thresholds I 1 ; I 2  may also be adjusted to a predetermined time function to effectively control vaporization and allow for adaptation to differential distillation operations. 
     In an advantageous embodiment, data relating to several time-dependent current measurement series are stored in a data memory and compared with each other and/or with fixed parameters. This makes it possible to store the current measurement values and transition points accumulated during the process. An automatic analysis can, for example, analyze at which point in time the vaporization current I V  was reached. If this point in time is reached later than a predefined threshold, this is an indication that the electrical resistance is too high. Furthermore, the average current square during the vaporization process can be evaluated. If this is lower than a predetermined threshold, the depletion of the liquid can be inferred. 
     Preferably, the ambient temperature is measured, and the current interval [I 1 ; I 2 ] and/or at least one of its thresholds I 1 , I 2  is set and/or adjusted as a function of the measured ambient temperature in order to be able to take into account possible influences of the ambient temperature. 
     Advantageously, the control of the current flow is done by switching on and/or maintaining the current flow through the vaporizer at a current less than an upper threshold I 2 , or switching off the current flow through the vaporizer at a current more than a lower threshold I 1 , in order to be able to provide an effective control method within the current interval [I 1 ; I 2 ]. 
    
    
     
       The invention is explained below by means of preferred embodiments with reference to the accompanying figures. Thereby shows 
         FIG. 1  a schematic illustration of an inhaler; 
         FIG. 2  a simplified circuit for current heating of a vaporizer; 
         FIG. 3  a schematic current measurement series with a determined transition point; 
         FIG. 4  an exemplary current measurement series with a transition point; 
         FIG. 5  the determination of a transition point on the basis of the rise of a current measurement series; and 
         FIG. 6  the determination of a transition point on the basis of the curvature of a current measurement series. 
     
    
    
       FIG. 1  schematically shows an inhaler  10  or an electronic cigarette product. The inhaler  10  comprises a housing  11  in which an air channel  30  or vent is provided between at least one air inlet opening  231  and an air outlet opening  24  at a mouth end  32  of the cigarette product  10 . The mouth end  32  of the inhaler  10  thereby denotes the end at which the consumer draws for the purpose of inhalation, thereby applying a negative pressure to the inhaler  10  and generating an air flow  34  in the air channel  30 . 
     Advantageously, the inhaler  10  comprises a base part  16  and a vaporizer tank unit  20  comprising a vaporizer device  1  having a vaporizer  60  controllable by the method of the invention and a liquid reservoir  18 . The vaporizer tank unit may in particular be in the form of a replaceable cartridge. The liquid reservoir  18  may be refillable by the user of the inhaler  10 . Air drawn through the air inlet opening  231  is directed in the air channel  30  to the at least one vaporizer  60 . The vaporizer  60  is connected or connectable 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 an inlet side  61  of the vaporizer  60 . 
     An advantageous volume of the liquid reservoir  18  is 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. 
     The vaporizer  60  vaporizes liquid  50  supplied to the vaporizer  60  from the liquid reservoir  18  by the porous element  19  by means of capillary forces and/or stored in the porous element  19 , and adds the vaporized liquid as an aerosol/vapor to the air stream  34  at an outlet side  64 . 
     The inhaler  10  further comprises an electrical energy storage device  14  and an electronic control device  15 . The energy storage device  14  is generally arranged in the base part  16  and may in particular be a disposable electrochemical battery or a rechargeable electrochemical battery, for example a lithium-ion battery. The vaporizer tank unit  20  is disposed between the energy storage device  14  and the mouth end  32 . The electronic control device  15  comprises at least one digital data processing device, in particular microprocessor and/or microcontroller, in the base part  16  (as shown in  FIG. 1 ) and/or in the vaporizer tank unit  20 . 
     Advantageously, a sensor, for example a pressure sensor or a pressure or flow switch, is arranged in the housing  11 , wherein the control device  15  can determine, based on a sensor signal output by the sensor, that a consumer is drawing on the mouth end  32  of the cigarette product  10  to inhale. In this case, the control device  15  controls the vaporizer  60  to add liquid  50  from the liquid reservoir  18  as an aerosol/vapor into the air stream  34 . 
     The at least one vaporizer  60  is arranged in a part of the vaporizer tank unit  20  facing away from the mouth end  32 . This allows for effective electrical coupling, particularly with the base part  16 , and control of the vaporizer  60 . Advantageously, the air stream  34  passes through an air channel  30  extending axially through the liquid reservoir  18  to the air outlet opening  24 . 
     The liquid  50  stored in the liquid reservoir  18  to be dispensed is, for example, a mixture of 1,2-propylene glycol, glycerol, water, and preferably at least one aroma (flavor) and/or at least one active ingredient, in particular nicotine. However, the indicated components of the liquid  50  are not mandatory. In particular, aroma and/or active ingredients, in particular nicotine, may be omitted. 
       FIG. 2  shows a schematic circuit for current heating of the vaporizer  60 . The vaporizer  60  is an electric vaporizer that can be heated by an electric current due to its electrical resistance. The vaporizer  60  may comprise at least one resistive element, such as a heating wire, for example, a spiral wire or one or a plurality of wire conductors arranged in parallel with each other. The vaporizer  60  may alternatively be designed as a micro-electromechanical system (MEMS), for example with conducting or microchannels, as described in DE 10 2016 120 803 A1, the disclosure content of which is to that extent incorporated in the present application. Bionic or capillary heating structures, such as bionic meshes, are also possible for the vaporizer  60 . Vaporizers  60  with heating structures as described in DE 10 2017 111 119 A1 are also possible, the disclosure content of which is to that extent incorporated in the present application. In general, the invention is not bound to a specific type of vaporizer  60 . 
     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 electrical lines  25 , so that an electric 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 current flow causes heating of the vaporizer  60  and therefore vaporization of liquid in contact with the vaporizer  60 . Vapor/aerosol generated in this manner escapes from the vaporizer  60  and is mixed into the air stream  34 . More precisely, upon detecting an air flow  34  through the air channel  30  caused by drawing of the consumer, the control device  15  controls the heating current source  71 , wherein the liquid in contact with the vaporizer  60  is discharged in the form of vapor/aerosol by spontaneous heating. 
     The vaporization temperature is preferably in the range between 100° C. and 400° C., more preferably between 150° C. and 350° C., even more preferably between 190° C. and 290° C. 
     The vaporizer tank unit  20  is set to dispense an amount of liquid preferably in the range between 1 μl and 20 μl, further preferably between 2 μl and 10 μl, still further preferably between 3 μl and 5 μl, typically 4 μl per puff of the consumer. Preferably, the vaporizer tank unit may be adjustable with respect to the amount of liquid/vapor per puff, i.e., per puff duration from 1 s to 3 s. 
     Advantageously, the drive frequency of the vaporizer  60  generated by the heating current source  71  is generally in the range of 1 Hz to 50 kHz, preferably in the range of 30 Hz to 30 kHz, even more advantageously in the range of 100 Hz to 25 kHz. 
     Advantageously, the vaporizer  60  may be replaceable in the event of contamination, defect or depleted substrate, such that a separable electrical connection may be provided between the vaporizer  60  the base part  16 . This connection can be designed as a spring pin, plug-in or screw connection, for example. 
       FIG. 3  shows a schematic current measurement series  100  indicated by a bold black curve with a determined transition point  101  at a current I v , wherein this illustration shows an example of a current measurement series  100  for a vaporizer  60  with a negative temperature coefficient. In  FIG. 3 , current I is plotted against time t and shown as continuous for illustrative purposes only. 
     At the beginning of a draw at an initial point  110 , determined for example by detecting the draw by means of a pressure sensor or determined by a consumer switching on, the vaporizer  60  is switched on and heated with a heating current. This is followed by a sequential recording in time of measured values  108  (schematically drawn as a curve in  FIG. 3 ) of the current I applied to the vaporizer  60  starting from the initial point  110 . The vaporizer  60  heats up relatively quickly, therefore the measured current I drops. 
     The temporal current measurement series  100  comprises a transition point  101  recognizable as a kink, or at least a strong flattening, which is determined to be the transition point  101  as soon as vaporization starts. This is followed by a two-point control as a function of a current I V  associated with the transition point  101  with the lower threshold and the upper threshold I 2 , wherein the current I is controlled in the current interval [I 1 ; I 2 ]: as soon as the determined current flow I exceeds the upper threshold I 2 , the current source is switched off or the current flow is reduced; as soon as the determined current flow I falls below the lower threshold I 2 , the current source is switched on or the current flow is increased. The difference between the upper threshold I 2  and the current I V  at the transition point  102  and the difference between the current I V  at the transition point  102  and the lower threshold I 1  is advantageously smaller than the current I V  at the transition point  102 , since no or only a small overtemperature should occur at the vaporizer  60  and thus only a small change in current occurs. 
     The advantage of the control method described above is illustrated by the lower current measurement series  200  in  FIG. 3 . The lower current measurement series  200  shows a current curve for a vaporizer  60  which differs in one or more points from the vaporizer  60  of the bold printed current measurement series  100 : the battery voltage is a different one, in particular due to the discharge state or internal resistance; the heating resistance of the vaporizer  60  is a different one, in particular due to manufacturing tolerances; other electrical resistances are present. 
     Thus, for the lower current measurement series  200 , there is a transition point  201  at a different current I w , but again at the onset of vaporization. In this example, a lower threshold I 1  and an upper threshold I 2  can easily be selected within which the current I is controlled so that the vaporizer  60  reliably and effectively vaporizes liquid. 
     The method according to the invention results in a temperature error that is an order of magnitude smaller than in the case of resistive temperature determination according to the prior art. It is advantageous if the absolute value of the current interval |I 2 −I 1 | is less than 50%, advantageously less than 25%, further advantageously less than 10% of the absolute value of the current value I v . The process does not control to a fixed temperature, but to a current corresponding to the vaporization temperature or to a temperature slightly above the vaporization temperature. Since the vaporization temperature depends on the composition of the substrate or, in particular, of the liquid, the temperature is not absolute, but the current I V  leading to vaporization is determined. 
       FIG. 4  shows an exemplary current measurement series  100  of a possible measurement curve with a transition point  101  at a time of about t=201 ms and a realistic noise of the current signal. The current measurement series  100  comprises a plurality of successively recorded measurement values  108  in time, represented by a corresponding number of points, wherein each point represents a measurement value  108  with an associated current I at a time t. 
     Once n values are recorded, the control device  15  calculates a line of best fit  102  from the measured values  108 , for example by linear regression. In this example, two different lines of best fit  102  are shown at times t 1  and t 2 . The time course of the rise  109  of the line of best fit  102  determined in this way is shown in  FIG. 5 . 
     The regression has the advantage that the transition point  101  can be easily localized even if the current measurement series  100  is overlaid with noise. The regression thus smoothes the rise  109  and offers an improvement over finite differences. 
       FIG. 5  shows a determination of a transition point  101  based on the rise  109  of the current measurement series  100  shown in  FIG. 4 . The transition point  101  can be detected by evaluating the first or second time derivative of the current I in real time. 
     The rise  109  is the rise of the line of best fit  102  determined by regression on the current measurement series  100  and is plotted in vs. time t. For example, if the magnitude of the rise  109  falls below a threshold  103 , it can be concluded that vaporization has begun. In this example, the transition point  101  is located where the magnitude of the slope  109  of the line of best fit  102  is less than a threshold  103  of, in this example, 0.002 A/s. The threshold  103  can be determined empirically for the vaporizer  60 . From the time t 0  at which the rise  109  exceeds the threshold  103 , the vaporization current I V  can be determined on the basis of the current measurement series  100 , in this example approx. 2.6 A (compare  FIG. 4 ). 
       FIG. 6  shows a determination of a transition point  101  on the basis of the curvature  106  of the current measurement series  100  shown in  FIG. 4 . An extreme value  107  in the second derivative, in particular a maximum, indicates the transition point  101 . The transition point  101  or the vaporization point of the current measurement series  101  can also be found via the curvature  106  of the current measurement series  100 . For this purpose, instead of a line of best fit  102 , a polynomial, in particular of second order, is locally fitted along the current measurement series  100  to a plurality of successive measured values  108  of the current measurement series  100 . The coefficient of the quadratic term of the polynomial is determined as curvature  106  and plotted against time t. An algorithm for finding an extreme value  107  finds the extreme value  107  at a time t 0  corresponding to the time at which the current measurement series  100  comprises the transition point  101 . 
     LIST OF REFERENCE SIGNS 
     
         
           1  vaporizer device 
           4  carrier 
           10  inhaler 
           11  housing 
           14  energy storage device 
           15  control device 
           16  basis part 
           18  liquid reservoir 
           19  wick structure 
           20  vaporizer tank unit 
           24  air outlet opening 
           30  air channel 
           32  mouth end 
           34  air stream 
           50  liquid 
           60  vaporizer 
           61  inlet side 
           62  liquid channel 
           64  outlet side 
           71  heating current source 
           100 ,  200  current measurement series 
           101 ,  201  transition point 
           102  line of best fit 
           103  threshold 
           104  passage opening 
           105   a ,  105   b  electrical line 
           106  curvature 
           107  extreme value 
           108  measured value 
           109  rise 
           110  initial point 
           131  contact area 
           231  air inlet opening 
         I, I v , I w  current value 
         I 1  lower threshold 
         I 2  upper threshold 
         t 0 , t 1 , t 2  time