Heated aerosol-generating device and method for generating aerosol with consistent properties

Abstract

There is provided a method of compensating for changes to a solid aerosol-forming substrate during heating of the substrate by a heating element over a period containing a first plurality of user puffs and a second plurality of user puffs, the changes including warming of the substrate and depletion of the substrate, the method including: compensating for the warming of the substrate by reducing heating of the heating element during the first plurality of user puffs; and after compensating for the warming of the substrate, compensating for the depletion of the substrate by increasing heating of the heating element during the second plurality of user puffs. There is also provided a system for compensating for changes to a solid aerosol-forming substrate during heating of the substrate by a heating element over a period containing a first plurality of user puffs and a second plurality of user puffs.

Claims

1. A method of compensating for changes to a solid aerosol-forming substrate during heating of the substrate by a heating element over a period containing a first plurality of user puffs and a second plurality of user puffs, the changes comprising warming of the substrate and depletion of the substrate, the method comprising: compensating for the warming of the substrate by reducing heating of the heating element during the first plurality of user puffs; and after compensating for the warming of the substrate, compensating for the depletion of the substrate by increasing heating of the heating element during the second plurality of user puffs.

2. The method of claim 1, wherein a constant amount of an aerosol constituent is delivered during the first plurality of user puffs and the second plurality of user puffs.

3. The method of claim 2, wherein the aerosol constituent comprises nicotine.

4. The method of claim 1, wherein a property of an aerosol delivered during the first plurality of user puffs and the second plurality of user puffs is consistent.

5. The method of claim 4, wherein the property comprises flavour, taste, or feel of the aerosol.

6. The method of claim 1, wherein an aerosol delivered during the first plurality of user puffs is substantially comparable to an aerosol delivered during the second plurality of user puffs.

7. The method of claim 1, wherein the depletion of the substrate changes an amount or distribution of aerosol-forming substituents in the aerosol-forming substrate.

8. The method of claim 1, wherein reducing heating of the heating element comprises reducing electrical power supplied to the heating element to reduce a temperature of the heating element to a first temperature.

9. The method of claim 8, wherein increasing heating of the heating element comprises increasing electrical power supplied to the heating element to increase a temperature of the heating element to a second temperature higher than the first temperature.

10. The method of claim 8, wherein reducing heating of the heating element comprises altering a duty cycle of electric current provided to the heating element.

11. The method of claim 10, wherein increasing heating of the heating element comprises further altering the duty cycle of the electric current provided to the heating element.

12. The method of claim 8, wherein the electrical power supplied to the heating element is controlled based on an electrical resistance of the heating element.

13. A system for compensating for changes to a solid aerosol-forming substrate during heating of the substrate by a heating element over a period containing a first plurality of user puffs and a second plurality of user puffs, the changes comprising warming of the substrate and depletion of the substrate, the system comprising the heating element and a controller configured to perform operations comprising: compensating for the warming of the substrate by reducing heating of the heating element during the first plurality of user puffs; and after compensating for the warming of the substrate, compensating for the depletion of the substrate by increasing heating of the heating element during the second plurality of user puffs.

14. The system of claim 13, wherein a constant amount of an aerosol constituent is delivered during the first plurality of user puffs and the second plurality of user puffs.

15. The system of claim 14, wherein the aerosol constituent comprises nicotine.

16. The system of claim 13, wherein a property of an aerosol delivered during the first plurality of user puffs and the second plurality of user puffs is consistent.

17. The system of claim 16, wherein the property comprises flavour, taste, or feel of the aerosol.

18. The system of claim 13, wherein an aerosol delivered during the first plurality of user puffs is substantially comparable to an aerosol delivered during the second plurality of user puffs.

19. The system of claim 13, wherein the depletion of the substrate changes an amount or distribution of aerosol-forming substituents in the aerosol-forming substrate.

20. The system of claim 13, wherein reducing heating of the heating element comprises controlling electrical power supplied to the heating element to reduce a temperature of a heating element to a first temperature.

21. The system of claim 20, wherein increasing heating of the heating element comprises controlling electrical power supplied to the heating element to increase the temperature of the heating element to a second temperature higher than the first temperature.

22. The system of claim 20, wherein reducing heating of the heating element comprises altering a duty cycle of electric current provided to the heating element.

23. The system of claim 22, wherein increasing heating of the heating element comprises further altering the duty cycle of the electric current provided to the heating element.

24. The system of claim 20, wherein the electrical power supplied to the heating element is controlled based on an electrical resistance of the heating element.

Description

(1) Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic illustration of an electrically heated smoking device in accordance with the invention;

(3) FIG. 2 is a schematic cross-section of the front end of a first embodiment of a device of the type shown in FIG. 1;

(4) FIG. 3 is a schematic illustration of a flat temperature profile for a heating element;

(5) FIG. 4 is a schematic illustration of reducing aerosol delivery with a flat a temperature profile;

(6) FIG. 5 is a schematic illustration of a temperature profile for a heating element in accordance with an embodiment of the invention;

(7) FIG. 6 is a schematic illustration of a constant aerosol delivery in accordance with an embodiment of the invention;

(8) FIG. 7 illustrates control circuitry used to provide temperature regulation of a heating element in accordance with one embodiment of the invention; and

(9) FIG. 8 illustrates some alternative target temperature profiles in accordance with the present invention.

(10) In FIG. 1, the components of an embodiment of an electrically heated aerosol-generating device 100 are shown in a simplified manner. Particularly, the elements of the electrically heated aerosol-generating device 100 are not drawn to scale in FIG. 1. Elements that are not relevant for the understanding of this embodiment have been omitted to simplify FIG. 1.

(11) The electrically heated aerosol-generating device 100 comprises a housing 10 and an aerosol-forming substrate 12, for example a cigarette. The aerosol-forming substrate 12 is pushed inside the housing 10 to come into thermal proximity with the heating element 14. The aerosol-forming substrate 12 will release a range of volatile compounds at different temperatures. By controlling the operation temperature of the electrically heated aerosol-generating device 100 to be below the release temperature of some of the volatile compounds, the release or formation of these smoke constituents can be avoided.

(12) Within the housing 10 there is an electrical energy supply 16, for example a rechargeable lithium ion battery. A controller 18 is connected to the heating element 14, the electrical energy supply 16, and a user interface 20, for example a button or display. The controller 18 controls the power supplied to the heating element 14 in order to regulate its temperature. Typically the aerosol-forming substrate is heated to a temperature of between 250 and 450 degrees centigrade.

(13) In the described embodiment the heating element 14 is an electrically resistive track or tracks deposited on a ceramic substrate. The ceramic substrate is in the form of a blade and is inserted into the aerosol-forming substrate 12 in use. FIG. 2 is a schematic representation of the front end of the device and illustrates the air flow through the device. It is noted that FIG. 2 does not accurately depict the relative scale of elements of the device. A smoking article 102, including an aerosol forming substrate 12 is received within the cavity 22 of the device 100. Air is drawn into the device by the action of a user sucking on a mouthpiece 24 of the smoking article 102. The air is drawn in through inlets 26 forming in a proximal face of the housing 10. The air drawn into the device passes through an air channel 28 around the outside of the cavity 22. The drawn air enters the aerosol-forming substrate 12 at the distal end of the smoking article 102 adjacent a proximal end of a blade shaped heating element 14 provided in the cavity 22. The drawn air proceeds through the aerosol-forming substrate 12, entraining the aerosol, and then to the mouth end of the smoking article 102. The aerosol-forming substrate 12 is a cylindrical plug of tobacco based material.

(14) Current aerosol-generating devices are configured to provide a constant temperature during operation, as illustrated in FIG. 3. Following activation of the device power is delivered to the heating element until a target temperature 50 is reached. Once the target temperature 50 has been reached, the heating element is maintained at that temperature until the device is deactivated. FIG. 4 is a schematic illustration of the delivery of a key aerosol constituent using a flat temperature profile as shown in FIG. 3. The line 52 represents the amount of the key aerosol constituent, such as glycerol or nicotine, being delivered during the activation of the device. It can be seen that the delivery of the constituent peaks and then falls with time as the substrate become depleted and thermodiffusion effects weaken.

(15) FIG. 5 is schematic illustration of a temperature profile for a heating element in accordance with an embodiment of the present invention. Line 60 represents the temperature of the heating element over time.

(16) In a first phase 70, the temperature of the heating element is raised from an ambient temperature to a first temperature 62. The temperature 62 is within an allowable temperature range between a minimum temperature 66 and a maximum temperature 68. The allowable temperature change is set so that desired volatile compounds are vaporised from the substrate but undesirable compounds, which are vaporised at higher temperatures, are not vaporised. The allowable temperature range is also below the temperature at which combustion of the substrate could occur under normal operation conditions, i.e. normal temperature, pressure, humidity, user puff behaviour and air composition.

(17) In a second phase 72, the temperature of the heating element is reduced to a second temperature 64. The second temperature 64 is within the allowable temperature range but is lower than the first temperature.

(18) In a third phase 74, the temperature of the heating element is progressively increased until a deactivation time 76. The temperature of the heating element remains within the allowable temperature range throughout the third phase.

(19) FIG. 6 is a schematic illustration of the delivery profile of a key aerosol constituent with the heating element temperature profile as illustrated in FIG. 5. After an initial increase in delivery following activation of the heating element, the delivery stays constant until the heating element is deactivated. The increasing temperature in the third phase compensates for the depletion of the substrate's aerosol former.

(20) FIG. 7 illustrates control circuitry used to provide the described temperature profile in accordance with one embodiment of the invention.

(21) The heater 14 is connected to the battery through connection 42. The battery (not shown in FIG. 7) provides a voltage V2. In series with the heating element 14, an additional resistor 44, with known resistance r, is inserted and connected to voltage V1, intermediate between ground and voltage V2. The frequency modulation of the current is controlled by the microcontroller 18 and delivered via its analog output 47 to the transistor 46 which acts as a simple switch.

(22) The regulation is based on a PID regulator that is part of the software integrated in the microcontroller 18. The temperature (or an indication of the temperature) of the heating element is determined by measuring the electrical resistance of the heating element. The determined temperature is used to adjust the duty cycle, in this case the frequency modulation, of the pulses of current supplied to the heating element in order to maintain the heating element at a target temperature or adjust the temperature of the heating element towards a target temperature. The temperature is determined at a frequency chosen to match the control of the duty cycle, and may be determined as often as once every 100 ms.

(23) The analog input 48 on the microcontroller 18 is used to collect the voltage across the resistance 44 and provides the image of the electrical current flowing in the heating element. The battery voltage V+ and the voltage across resistor 44 are used to calculate the heating element resistance variation and or its temperature.

(24) The heater resistance to be measured at a particular temperature is R.sub.heater. In order for microprocessor 18 to measure the resistance R.sub.heater of the heater 14, the current through the heater 14 and the voltage across the heater 14 can both be determined. Then, the following well-known formula can be used to determine the resistance:
V=IR (1)

(25) In FIG. 6, the voltage across the heater is V2−V1 and the current through the heater is I. Thus:

(26) $\begin{matrix} R_{heater} = \frac{V 2 - V 1}{I} & (2) \end{matrix}$

(27) The additional resistor 44, whose resistance r is known, is used to determine the current I, again using (1) above. The current through the resistor 44 is I and the voltage across the resistor 24 is V1. Thus:

(28) $\begin{matrix} I = \frac{V 1}{r} & (3) \end{matrix}$

(29) So, combining (2) and (3) gives:

(30) $\begin{matrix} R_{heater} = \frac{(V 2 - V 1)}{V 1} r & (4) \end{matrix}$

(31) Thus, the microprocessor 18 can measure V2 and V1, as the aerosol-generating system is being used and, knowing the value of r, can determine the heater's resistance at a particular temperature, R.sub.heater.

(32) The heater resistance is correlated to temperature. A linear approximation can be used to relate the temperature T to the measured resistance R.sub.heater at temperature T according to the following formula:

(33) $\begin{matrix} T = \frac{R_{heater}}{{AR}_{0}} + T_{0} - \frac{1}{A} & (5) \end{matrix}$
where A is the thermal resistivity coefficient of the heating element material and R.sub.0 is the resistance of the heating element at room temperature T.sub.0.

(34) Other, more complex, methods for approximating the relationship between resistance and temperature can be used if a simple linear approximation is not accurate enough over the range of operating temperatures. For example, in another embodiment, a relation can be derived based on a combination of two or more linear approximations, each covering a different temperature range. This scheme relies on three or more temperature calibration points at which the resistance of the heater is measured. For temperatures intermediate the calibration points, the resistance values are interpolated from the values at the calibration points. The calibration point temperatures are chosen to cover the expected temperature range of the heater during operation.

(35) An advantage of these embodiments is that no temperature sensor, which can be bulky and expensive, is required. Also the resistance value can be used directly by the PID regulator instead of temperature. The resistance value is directly correlated to the temperature of the heating element, asset out in equation (5). Accordingly, if the measured resistance value is within a desired range, so too will the temperature of the heating element. Accordingly the actual temperature of the heating element need not be calculated. However, it is possible to use a separate temperature sensor and connect that to the microcontroller to provide the necessary temperature information.

(36) FIG. 8 illustrates an example target temperature profile, in which the three phases of operation can be clearly seen. In a first phase 70, the target temperature is set at T.sub.0. Power is provided to the heating element to increase the temperature of the heating element to T.sub.0 as quickly as possible. As described a PID regulator is used to maintain the temperature of the heating element as close to the target temperature as possible throughout operation of the device. At time t.sub.1 the target temperature is changed to T.sub.1, which means that the first phase 70 is ended and the second phase begins. The target temperature is maintained at T.sub.1 until time t.sub.2. At time t.sub.2 the second phase is ended and the third phase 74 is begun. During the third phase 74, the target temperature is linearly increased with increasing time until time t.sub.3, at which time the target temperature is T.sub.2 and power is no longer supplied to the heating element.

(37) A target temperature profile of the shape shown in FIG. 8 gives rise to an actual temperature profile of the shape shown in FIG. 5. The values of T.sub.0, T.sub.1, T.sub.2 can be adjusted to suit particular substrates and particular device, heating element and substrate geometries. Similarly the values of t.sub.1, t.sub.2, and t.sub.3 can selected to suit the circumstances.

(38) In one example, the first phase is 45 seconds long and T.sub.0 is set at 360° C., the second phase is 145 seconds long and T.sub.1 is 320° C., and the third phase is 170 seconds long and T.sub.3 is 380° C. The smoking experience lasts for a total of 360 seconds.

(39) In another example, the first phase is 60 seconds long and T.sub.0 is set at 340° C., the second phase is 180 seconds long and T.sub.1 is 320° C., and the third phase is 120 seconds long and T.sub.3 is 360° C. Again, the heating cycle or smoking experience lasts for a total of 360 seconds.

(40) In yet another example, the first phase is 30 seconds long and T.sub.0 is set at 380° C., the second phase is 110 seconds long and T.sub.1 is 300° C., and the third phase is 220 seconds long and T.sub.3 is 340° C.

(41) The duration and temperature targets for each phase of operation are stored in memory within the controller 18. This information may be part of the software executed by the microcontroller. However, it may be stored in a look-up table so that different profiles can be selected by the microcontroller. The consumer may select different profiles via user interface based on user preference or based on the particular substrate being heated. The device may include means for identifying the substrate, such as an optical reader, and a heating profile automatically selected based on the identified substrate.

(42) In another embodiment only the target temperatures T.sub.0, T.sub.1, and T.sub.2 are stored in memory and the transition between the phases is triggered by puff counts. For example, the microcontroller may receive puff count data from a flow sensor and may be configured to end the first phase after two puffs and end the second phase after a further five puffs.

(43) Each of the embodiments described above results in a more even delivery of aerosol over the course of the heating of the substrate when compared to a flat heating profile as illustrated in FIG. 3. The optimal heating profile depends on several factors and can be determined experimentally for a given device and substrate geometry and substrate composition. For example, the device may include more than one heating element and the arrangement of the heating elements will influence the depletion of the substrate and thermodiffusion effects. Each heating element may be controlled to have a different heating profile. The shape and size of the substrate in relation to the heating element may also be a significant factor.

(44) It should be clear that, the exemplary embodiments described above illustrate but are not limiting. In view of the above discussed exemplary embodiments, other embodiments consistent with the above exemplary embodiments will now be apparent to one of ordinary skill in the art.

Heated aerosol-generating device and method for generating aerosol with consistent properties

Assignee

Inventors

Cpc classification

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A24F40/57

HUMAN NECESSITIES

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H05B1/0244

ELECTRICITY

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H05B3/0014

ELECTRICITY

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H05B1/0225

ELECTRICITY

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H05B2203/021

ELECTRICITY

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A24F40/20

HUMAN NECESSITIES

International classification

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A24F40/57

HUMAN NECESSITIES

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H05B3/00

ELECTRICITY

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A24F40/20

HUMAN NECESSITIES

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H05B1/02

ELECTRICITY

Abstract

Claims

Description