WO2025162912A1

WO2025162912A1 - Aerosol generating systems and methods of controlling aerosol generating systems

Info

Publication number: WO2025162912A1
Application number: PCT/EP2025/052080
Authority: WO
Inventors: Bernhard Groiss; Tilen CEGLAR; Jaakko MCEVOY
Original assignee: JT International SA
Current assignee: JT International SA
Priority date: 2024-01-30
Filing date: 2025-01-28
Publication date: 2025-08-07
Anticipated expiration: 2026-07-30

Abstract

A method of controlling an aerosol generating system (10), the method comprising: heating (50) a liquid aerosol generating substrate during a first user inhalation to generate an inhalable aerosol, measuring (52) a pressure in a flow path (34) of the aerosol generating system (10) during the first user inhalation to obtain a signal (53) representative of pressure, cumulatively integrating (54) said signal (53) representative of pressure during the first user inhalation, and terminating (56) the heating of the liquid aerosol generating substrate during a user inhalation based on the cumulative integral of the measured pressure.

Description

AEROSOL GENERATING SYSTEMS AND METHODS OF CONTROLLING AEROSOL GENERATING SYSTEMS

Technical Field

The present invention relates generally to aerosol generating systems. The invention relates particularly, but not exclusively, to cartridges for aerosol generating systems that comprise a base part and a separable cartridge.

Technical Background

Aerosol generating systems, also commonly termed electronic cigarettes, are an alternative to conventional cigarettes. Instead of generating a combustion smoke, they vaporise a liquid aerosol generating substrate which can be inhaled by a user. The liquid typically comprises an aerosol generating substance, such as glycerine or propylene glycol, that creates the vapour when heated. Other common substances in the liquid are nicotine and various flavourings.

An aerosol generating system is a hand-held inhaler system, typically comprising a mouthpiece section, a reservoir configured to hold liquid aerosol generating substrate in a reservoir chamber, and a power supply unit. Vaporisation is achieved in a vaporisation region, such as a vaporisation chamber, by a vaporiser or heater unit which typically comprises a heating element in the form of a heating coil and a fluid transfer medium such as a wick. Vaporisation occurs when the heater heats the liquid in the wick until the liquid is transformed into vapour. The vapour is conveyed from the vaporisation region to an outlet in the mouthpiece section by means of a vapour outlet pathway.

In general terms, a vapour is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapour can be condensed to a liquid by increasing its pressure without reducing the temperature, whereas an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. It should, however, be noted that the terms “aerosol” and “vapour” may be used interchangeably in this specification, particularly with regard to the form of the inhalable medium that is generated for inhalation by a user.

Conventional cigarette smoke comprises nicotine as well as a multitude of other chemical compounds generated as the products of partial combustion and/or pyrolysis of the plant material. Electronic cigarettes on the other hand deliver primarily an aerosolised version of an initial starting e-liquid composition comprising nicotine and various food safe substances such as propylene glycol and glycerine, etc., but are also efficient in delivering a desired nicotine dose to the user. Electronic cigarettes need to deliver a satisfying amount of vapour for an optimum user experience whilst at the same time maximising energy efficiency.

In some situations, liquid aerosol generating substrate can leak from an aerosol generating system. Such leakage is undesirable, and can be unpleasant for the user. Current systems typically leak through two mechanisms. Firstly, liquid aerosol generating substrate can leak from the reservoir via the wick into the inlet and outlets of the system, for example due to pressure difference and capillary force. Such leakage occurs mostly in storage and during transport. Secondly, during aerosol production vapour that is generated in the system can condense on the inner walls of the system, particularly in the vapour outlet pathway. After several cycles of use the condensed vapour can accumulate to a degree where drops of liquid leak out of the outlet. This second type of leakage is typically more short term, and occurs while the user uses the system. Currently, aerosol generating systems are not typically designed to mitigate leakage of this second type.

Summary

According to a first aspect of the invention we provide a method of controlling an aerosol generating system, the method comprising: heating a liquid aerosol generating substrate during a first user inhalation to generate an inhalable aerosol, measuring a pressure in a flow path of the aerosol generating system during the first user inhalation to obtain a signal representative of pressure, cumulatively integrating said signal representative of pressure during the first user inhalation, and terminating the heating of the liquid aerosol generating substrate during a user inhalation based on the cumulative integral of the measured pressure.

The method is preferably carried out during a usage session. The term “usage session” as used herein refers to a continuous time period during which an aerosol generating system is operated by a user to generate an inhalable aerosol. During a usage session a user may inhale aerosol generated by the aerosol generating system in a plurality of user inhalations (commonly referred to as “puffs”). A typical usage session may last 2-4 minutes, and may contain approximately 10-20 puffs (although these numbers may vary between individual users and different types of system). Each user inhalation typically has a distinct start time and end time. Liquid-based systems of the type described herein commonly include a mechanism for detecting user inhalations within a usage session. The vaporiser or heater unit of such a system is typically operated when an inhalation is detected, and is not operated when an inhalation is not detected, in order to prevent waste of the aerosol generating substrate.

During use of a liquid-based aerosol generating system, vapour produced in the vaporisation region is guided along a vapour outlet pathway via a vapour outlet channel toward a user’s mouth. When the vapour contacts the inner surface of the vapour outlet channel it may condense when a saturation pressure point is reached. Typically, the majority of the vapourised liquid is inhaled by the user before significant condensation occurs. However, towards the end of a user inhalation some aerosol is typically left in the vapour outlet pathway. This is because in traditional liquid-based aerosol generating systems heating typically occurs for the entire duration of a user inhalation (i.e. from detection of a start of a puff to detection of an end of the same puff). Thus, towards the very end of an inhalation, some aerosol is produced which is not inhaled by the user. This excess aerosol is left in the vapour outlet pathway, where it condenses. Over time, sufficient condensate may build up in the vapour outlet pathway that droplets may form, which can leak from the vapour outlet pathway.

In the method described herein, heating is terminated during a user inhalation based on a cumulative integral obtained from a signal representative of a measured pressure during a first user inhalation. Because heating is terminated during a user inhalation, rather than at the end of a user inhalation, condensation in the vapour outlet pathway due to uninhaled aerosol may be minimised.

The cumulative integral of the pressure signal is mathematically related to the volume of aerosol which has been inhaled by a user over a given time. The cumulative integral can thus be used as a predictor of the likely total duration of a user inhalation. The cumulative integral increases overtime at a steady rate, meaning that it can be easier to distinguish between user inhalations having differing total durations by monitoring the cumulative integral than by monitoring other parameters of a user inhalation.

For clarity, it should be noted that heating may be terminated during any user inhalation of a usage session. Thus, the user inhalation during which heating is terminated may occur prior to the end of the usage session (i.e. prior to the final inhalation of the usage session). In this way, heating is terminated before the end of a puff that occurs during (i.e. prior to the end of) the usage session. This may help to prevent the build up of condensation within the vapour outlet pathway of the system during the usage session. Of course, heating may be terminated during (i.e. prior to the end time of) a final user inhalation of the usage session as well as during (i.e. prior to an end time of) the user inhalation occurring prior to that final user inhalation.

The method may comprise terminating the heating of the liquid aerosol generating substrate based on the cumulative integral of the measured pressure during (i.e. prior to an end time of) a plurality of user inhalations of a usage session. For example, heating may be terminated during (i.e. prior to an end time of) each user inhalation in the usage session, or during (i.e. prior to an end time of) selected user inhalations of the usage session. The plurality of user inhalations may be selected according to a predefined sequence or schedule, for example, every second inhalation, every third inhalation, every fourth inhalation, or every fifth inhalation, etc.

Terminating the heating of the liquid aerosol generating substrate based on the cumulative integral of the measured pressure may comprise: selecting a first threshold value using the cumulative integral, and terminating heating of the liquid aerosol generating substrate when the first threshold value is reached. Utilising a threshold value may simplify the control of the heating. Because the threshold value is selected using the cumulative integral (as opposed to being predetermined) the threshold value is bespoke to the user’s inhalation style, resulting in an improved user experience.

Heating of the liquid aerosol generating substrate may be terminated when the first threshold value is reached during the first user inhalation. That is, the first threshold value may be determined in the first user inhalation and also applied to the first user inhalation. In this way, heating may be terminated prior to an end time of the first inhalation, meaning that condensation is minimised in the first inhalation.

The first threshold value may be determined in the first inhalation, and applied to one or more subsequent inhalations. For example, the method may further comprise: heating the liquid aerosol generating substrate during a second user inhalation subsequent to the first, and terminating the heating of the liquid aerosol generating substrate during the second user inhalation when the first threshold value is reached. In this way heating may be terminated prior to an end time of the second inhalation, meaning that condensation is minimised in the second inhalation. Heating may be terminated prior to an end time of the second inhalation in addition to being terminated prior to an end time of the first inhalation. Alternatively, heating may not be terminated prior to the end of the first inhalation, which may be used solely for selecting the first threshold value. The first threshold value may be applied to one or more further inhalations subsequent to the second inhalation, such that heating may be terminated prior to an end time of a plurality of inhalations in a usage session, and preferably prior to an end time of each inhalation in a usage session. In some examples, the cumulative integral may be based on the entire duration of the first inhalation, which may allow for a more accurate threshold value to be determined for use in the second (and subsequent) inhalations.

The first threshold value may be a threshold time. Selecting the threshold time may comprise: cumulatively integrating the signal representative of pressure for a first duration to obtain a first cumulative value; comparing the first cumulative value with one or more stored cumulative values; and selecting the threshold time based on a result of the comparison. In this way, heating may be terminated in subsequent inhalations based on the threshold time without the need to cumulatively integrate the signal representative of pressure in those subsequent inhalations. The first duration may be an average inhalation duration, and may be approximately 3 seconds.

The first threshold value may be a threshold integral. Selecting the threshold integral may comprise: cumulatively integrating the signal representative of pressure for a full duration of the first user inhalation to obtain a first puff integral; and selecting the threshold integral using the first puff integral. In this way, the first threshold value may be dynamically selected for a user without the need to compile a database of stored cumulative values.

The threshold integral may comprise a selected percentage of the first puff integral. The selected percentage is preferably in the range 80%-98%, e.g. 90%-95%. In this way, heating may be terminated towards the end of a user inhalation, ensuring that a satisfying amount of vapour is delivered to the user whilst avoiding generating vapour that is unlikely to be inhaled.

The method may further comprise: measuring a pressure in a flow path of the aerosol generating system during the second user inhalation to obtain a signal representative of pressure, cumulatively integrating said signal representative of pressure during the second user inhalation, and terminating the heating of the liquid aerosol generating substrate during the second user inhalation when the threshold integral is reached.

Selecting the threshold integral may comprise: cumulatively integrating the signal representative of pressure for a full duration of a plurality of user inhalations to obtain a puff integral for each of the plurality of user inhalations; and selecting the threshold integral using the plurality of puff integrals. The plurality of inhalations may all occur during the same usage session. In this way, an average threshold integral may be obtained, which may provide for a more consistent user experience. The threshold integral may comprise a selected percentage of an average of the plurality of puff integrals, wherein the selected percentage is preferably in the range 80%-95%, e.g. 90%- 95%.

The method may further comprise: during a third user inhalation subsequent to the first user inhalation, selecting a second threshold value using the cumulative integral, and replacing the first threshold value with the second threshold value such that for one or more subsequent user inhalations heating of the liquid aerosol generating substrate is terminated when the second threshold value is reached rather than when the first threshold value is reached. In this way, the threshold value may be dynamically adjusted during a usage session, which may be advantageous in the event that the user does not have a consistent inhalation duration or volume.

The signal representative of pressure may be cumulatively integrated from a start time of a user inhalation. This may improve accuracy.

The method may further comprise detecting a user inhalation, and initiating heating in response to the detection.

According to a second aspect of the invention, we provide an aerosol generating system comprising: a controller; a reservoir having a reservoir chamber for containing a liquid aerosol generating substrate and in fluid communication with a vaporisation region; a heater in thermal communication with the vaporisation region; and a pressure sensor in fluid communication with an air flow pathway through the aerosol generating system; wherein the controller is operable to cause the aerosol generating system to: cause the heater to heat a liquid aerosol generating substrate during a first user inhalation to generate an inhalable aerosol, utilise the pressure sensor to measure a pressure in the air flow pathway during the first user inhalation to obtain a signal representative of pressure, cumulatively integrate said signal representative of pressure during the first user inhalation, and cause the heater to terminate the heating of the liquid aerosol generating substrate during a user inhalation based on the cumulative integral of the measured pressure.

The controller may be operable to cause the aerosol generating system to carry out the steps of the method of the first aspect of the invention.

In the context of this disclosure, an aerosol generating system may comprise an electronic cigarette, which may include a cartridge removably connected to a base part. The features described above may be included in the cartridge of the aerosol generating system, or in the base part of the system, or shared between the cartridge and the base part.

Thus, according to a third aspect of the invention, we provide a base part for an aerosol generating system, the base part being operable to connect, in use, to a cartridge comprising a reservoir having a reservoir chamber for containing a liquid aerosol generating substrate and in fluid communication with a vaporisation region, wherein the base part comprises: a controller operable to cause the aerosol generating system to carry out the steps of the method of the first aspect of the invention when the base part is connected to a cartridge.

A heater in thermal communication with the vaporisation region may be included in either the base part or the cartridge. A pressure sensor in fluid communication with an air flow pathway through the aerosol generating system may be included in either the base part or the cartridge.

As used herein, the term “electronic cigarette” may include an electronic cigarette configured to deliver an aerosol to a user, including an aerosol for inhalation/vaping. An aerosol for inhalation/vaping may refer to an aerosol with particle sizes of 0.01 to 20 pm. The particle size may be between approximately 0.015 pm and 20 pm. The electronic cigarette may be portable. It is to be appreciated that the cartridge and/or the base part of the system may include any one or more components conventionally included in these parts of an aerosol generating system, as discussed in the description below.

The features set out above may be combined together in any combination that is not explicitly excluded, and also with features selected from the detailed description below.

Brief Description of the Drawings

There now follows a detailed description of the invention, by way of example only, with reference to the accompanying drawing, in which:

Figure 1 schematically shows an aerosol generating system including a base part and disposable cartridge;

Figure 2 illustrates a method of operating an aerosol generating system;

Figure 3 graphically illustrates the application of a threshold value;

Figure 4 graphically illustrates a signal representative of pressure measured overtime for an example user inhalation; and

Figure 5 graphically illustrates a cumulative integral of the signal illustrated in Figure 4.

Detailed Description

Figure 1 schematically shows one example of an aerosol generating system 10, such as an electronic cigarette. The aerosol generating system 10 includes a base part 12 and a cartridge 14 (also referred to in the art as a “capsule” or “pod”). The cartridge 14 is removably connectable to the base part 12, and may be disposable. The base part 12 is thus the main body of the electronic cigarette and is generally re-usable.

The base part 12 comprises a housing 16 accommodating therein a power supply unit in the form of a rechargeable battery 18. The aerosol generating system 10 further includes a controller 20, and may further include a user interface (not shown) for permitting a user to control the operation of the aerosol generating system 10 via the controller 20.

In the example shown in Figure 1 , the cartridge 14 includes a liquid storage reservoir 22 defining a reservoir chamber 24 configured for containing therein a liquid to be vaporised. The liquid may comprise an aerosol generating substrate such as propylene glycol and/or glycerine and may contain other substances such as nicotine and acids. The liquid may also comprise flavourings such as e.g. tobacco, menthol or fruit flavour. The cartridge 14 further includes a vaporising unit 26. In the example shown in Figure 1 , the vaporising unit 26 comprises a heating element 28, such as a resistive heating wire, and a fluid transfer element 30, such as a ceramic or fibrous wick. The fluid transfer element 30 is located in fluid communication with the reservoir chamber 24, and is configured to draw vaporisable liquid from the reservoir chamber 24 towards the heating element 28 in a vaporisation zone 32. The vaporisation zone 32 is in fluid communication with an air flow pathway 34 through the aerosol generating system.

A vapour transfer channel 36 extends from one or more air inlets 38 through and/or past the vaporisation zone 32, to one or more aerosol outlets 40 provided in a mouthpiece region 42 of the cartridge. The vapour transfer channel 36 includes a vapour outlet channel 36a, being the portion ofthe vapour transfer channel 36 which is downstream of the vaporisation zone 32, and a vapour inlet channel 36b, being the portion of the vapour transfer channel 36 which is upstream of the vaporisation zone 32. The vapour outlet channel 36a has an inner surface 44 defining a vapour outlet pathway. Similarly, the vapour inlet channel 36b has an inner surface defining an air inlet pathway. Together the air inlet pathway and the vapour outlet pathway define the air flow path 34 through the cartridge. A sensor 46 is located in fluid communication with the air flow path, and is operable in use to output signal representative of the pressure within the air flow path. The sensor 46 may be any sensor which can detect airflow, and should be able to deliver an analogue electrical signal or digital information that is representative ofthe amplitude ofthe air flow. In the example shown in Figure 1 , the sensor 46 is a microphone, but another type of pressure sensor may be used if preferred.

When the base part 12 is attached to the cartridge 14, power may be supplied to the vaporisation unit 26 from the battery 18 via heater contacts 48 to heat up liquid in the vaporisation zone 32, thereby generating a vapour. A user of the system may draw on the mouthpiece to encourage air to flow along the air flow pathway 34 defined by the vapour transfer channel 36; that is, to encourage air to flow from the inlet 38, through the vaporisation zone 32, and towards the outlet 40. The pressure within the vapour transfer channel 36 changes during the user inhalation due to the airflow, and may be measured by the pressure sensor 46. Vapour entrained in the airflow cools and condenses in the vapour outlet channel 36a to form an aerosol for inhalation by the user through the outlet 40.

Some condensation of the vapour is an inherent part of aerosol generation. Such condensation is not problematic when the resulting liquid droplets remain entrained in the airflow for inhalation by the user. However, condensation can be more problematic when it occurs on the inner surface 44 of the vapour outlet channel 36a. This is because condensed droplets can accumulate on the inner surface 44. Over time such condensed droplets may combine into droplets which are large enough to flow along the vapour outlet channel 36a. If the condensed liquid reaches the outlet 40 it may escape the cartridge. This can cause an unpleasant taste for the user and/or may result in liquid escaping onto other of the user’s belongings.

Figure 2 illustrates a method of operating an aerosol generating system which aims to mitigate the above-described problem of condensation within the vapour outlet channel. In a first block 50, a liquid aerosol generating substrate is heated during a first user inhalation to generate an inhalable aerosol. In particular, the controller 20 is operable to cause the heater 28 to generate an amount of heat sufficient to vaporise liquid aerosol generating substrate held in the fluid transfer medium 30. In the example shown, prior to initiating heating, the first user inhalation is detected by the controller, which is operable to monitor the output of the pressure sensor 46 for airflow changes indicative of a user inhalation (e.g. a sharp increase in airflow). Heating is then initiated by the controller in response to the detection. It will be appreciated, however, that heating may be initiated in response to another input if required, such as a user activating a button on a user interface of the aerosol generating system.

In a second block 52, the pressure in the flow path 34 of the aerosol generating system is measured during the first user inhalation to obtain a signal representative of pressure. As noted above, the signal representative of pressure may be any analogue or digital signal representative of the pressure within the flow path resulting from the airflow due to the user inhalation.

An example of a signal 53 representative of a pressure measured during a user inhalation is shown in Figure 4, which graphically illustrates a change in flow rate over time, as measured by sensor 46 during a user inhalation. In Figure 4, it can be seen that a user inhalation typically comprises a well defined start time ti, preceding which the flow rate is negligible or zero and after which the flow rate rises rapidly to a maximum value at t₂. From this maximum the flow rate typically fluctuates, and often falls gradually, until the user ceases inhaling at an end time t₃, at which the flow rate returns to negligible or zero. The length of time between the start time ti and the end time t₃ represents a total duration of the inhalation.

In a third block 54, the signal representative of pressure is cumulatively integrated during the first user inhalation. An example of a cumulatively integrated signal representative of a pressure is shown in Figure 5, which graphically illustrates a cumulative integral of the flow rate shown in Figure 4. As can be seen in Figure 5, the cumulative integral rises in a substantially linear manner over the total duration of the inhalation, between the start time ti and the end time t₃, after which the cumulative integral remains constant (since there is no more flow).

In the example shown, the signal output by the pressure sensor 46 (i.e. the signal representative of pressure) is supplied to the controller 20, which integrates that signal cumulatively, as discussed above. Alternatively, the integration could be performed by the pressure sensor itself, and the cumulative integral provided to the controller.

Finally, at block 56, the heating of the liquid aerosol generating substrate is terminated during a user inhalation based on the cumulative integral of the measured pressure. In particular, the controller 20 is operable to cause the heater 28 to cease generating heat based on the cumulative integral of the measured pressure, such that vapour generation also ceases based on the cumulative integral of the measured pressure. As vapour generation ceases during a user inhalation, rather than at the end of a user inhalation, condensation in the vapour outlet pathway 36a due to uninhaled aerosol may be minimised.

An example implementation of block 56 is illustrated in Figure 3, which shows an exemplary signal 53 representative of pressure measured over time during a user inhalation, together with an exemplary heating profile 55. As discussed above with respect to Figure 4, the signal 53 representative of pressure comprises a start time ti and an end time t₃. Similarly, the heating profile 55 comprises a start time t_H. The heating start time t_H is similar to ti, but does not coincide with ti in this example, because heating is initiated following detection of the start of the user inhalation - t_H is thus a few microseconds after ti. Heat is applied according to the heating profile 55 so as to maintain the heater 28 at a substantially constant temperature until a termination time tr. The termination time h is prior to the end time t₃ of the user inhalation, and may be for example 0.1 -0.5s prior to the end time, such as 0.3s prior to the end time t₃.

It will be appreciated that in practice the end time of a user inhalation is dependent on a number of unknown and user-specific factors, such that in order to terminate heating prior to the end time t₃, that end time must be estimated by the controller of the aerosol generating system. For any given inhalation, once the inhalation has been completed it is straightforward to determine when would have been a preferred time to cease heating prior to the end of the inhalation in order to avoid uninhaled vapour being left in the outlet pathway. Based on this observation, it can be understood that it is theoretically possible to compare the profile of an initial portion of a current user inhalation (i.e. the signal representative of pressure) to a plurality of stored inhalation profiles, in order to find a stored profile which most closely matches that of the current inhalation. In this way, the current inhalation profile may be matched to a closest one of the plurality of stored inhalation profiles whilst the current inhalation is ongoing, and an estimate of the end time of the current inhalation may be made. In practice however, this method is hard to carry out accurately, because inhalation profiles typically rise very steeply from zero in the first few milliseconds of the inhalation. This makes it hard to discriminate between different inhalation profiles until after an inhalation is complete.

Rather than looking at the inhalation profile itself, the method described herein instead uses the cumulative integral of the signal 53 representative of pressure to make an estimation of the end time of the user inhalation. In particular, a first threshold value 57 is selected using the cumulative integral, and heating is terminated when that first threshold value is reached.

In the example shown in Figure 3, the first threshold value 57 is a threshold time. Thus, heating is terminated when the threshold time (i.e. termination time t_T) is reached, prior to the end of the user inhalation.

In order to select the threshold time, the signal 53 representative of pressure is cumulatively integrated for a first duration to obtain a first cumulative value. The first cumulative value is then compared with one or more stored cumulative values, and the threshold time is selected based on a result of the comparison. In one example, each of the stored cumulative values represents a cumulative integral of a different historical inhalation signal for the first duration. Since each historical inhalation has a known end time, a threshold time may be selected to be a predefined duration prior to that known end time (e.g. 0.3s prior to the known end time). Thus, for each historical inhalation profile, a threshold time is stored (e.g. in a memory accessible to the controller 20) together with a cumulative value derived from the historical inhalation profile. The threshold time t_T for a current inhalation may thus be selected from the plurality of stored threshold times by choosing the stored threshold time which corresponds to the stored cumulative value that is closest to the first cumulative value obtained from the measured signal 53. This method is more straightforward to apply in practice that the method discussed above, of comparing inhalation profiles themselves, because the gradient of the cumulative integral is less steep and more linear, making is easier to discriminate between puffs of different volume.

The threshold time t_T can be applied to the user inhalation from which the first cumulative value is derived (i.e. to the current user inhalation). Alternatively, or additionally, the threshold time t_T can be applied to subsequent user inhalations following the user inhalation from which the first cumulative value was derived. Thus the signal representative of pressure need not be integrated for each inhalation, and may only be integrated when it is desired to determine the threshold time, or a new threshold time.

In an alternative example shown in Figures 4 and 5, the first threshold value 57 is a threshold integral l_T. In this example, rather than comparing the cumulative integral to one or more stored historical cumulative integrals, instead a first user inhalation (or a first set of user inhalations) is used to determine the first threshold value directly. In particular, selecting the threshold integral may comprise cumulatively integrating the signal representative of pressure for a full duration of the first user inhalation to obtain a first puff integral, and selecting the threshold integral using the first puff integral. As every user has a different average puff volume, a bespoke threshold of this type could be calculated from the first puff of a user’s session and applied to following puffs in that session.

In the example illustrated in Figures 4 and 5, the threshold integral l_T is selected to be a predefined percentage of the first puff integral. The selected percentage is preferably in the range of 80%-98% of the first puff integral. In the example shown the first puff integral reaches a maximum value of approximately 53.5, and the threshold integral l_T has a value of approximately 50 (approximately 95% of the maximum value).

In order to apply the threshold integral l_T in a subsequent (e.g. second) inhalation it is necessary to measure the pressure in the flow path of the aerosol generating system during the second user inhalation to obtain a signal representative of pressure, and to cumulatively integrate the signal representative of pressure during the second user inhalation. Heating of the liquid aerosol generating substrate during the second user inhalation can then be terminated when the threshold integral is reached.

The threshold integral l_T may be derived from a single user inhalation (e.g. the first user inhalation), as discussed above. Alternatively, the threshold integral l_T may be derived from a plurality of user inhalations (e.g. a set of consecutive inhalations) in order to obtain an average threshold integral l_T for the user.

In some examples, a new threshold value may be determined part way through a usage session in order to replace the first threshold value. For example, a second threshold value may be selected during a third user inhalation subsequent to the first user inhalation using the cumulative integral of a signal representative of pressure measured during the third user inhalation. When the threshold value is an average threshold integral l_T, the average threshold integral may be adjusted dynamically during a usage session. For example, the average threshold integral l_T may be a rolling average based on a last N inhalations, where N = 2, 3, 4 etc.

As described above, the methods set out herein make use of a pressure sensor in order to determine when to cut power to a heater of an aerosol generating system, where the output of the sensor is integrated during a user inhalation. The type of sensor 46 that is used is not critical, although in practice a microphone or integrated pressor sensor may provide a simple implementation. The sensor output could be integrated cumulatively over a set period of time (e.g. 1-3 seconds), and the value resulting from that integration compared to a lookup table (e.g. of historical integration data) in order to determine when to cut power to the heater. As an alternative, the integration could be for a variable length of time for each user. In this case the integration may be cumulative over the duration of a puff, and a personalised threshold can be determined for each user in a first puff (or set of puffs), which is then used as a cut off for heating in a future puff.

Heating is terminated during (as opposed to at the end of, or after the end of) a user inhalation that occurs during (i.e. prior to the final puff of) a usage session). Heating may be terminated during each inhalation of a usage session, or during a subset of the inhalations according to predefined criteria (e.g. in accordance with a predefined sequence or schedule). In this way, the build up of condensation during a usage session caused by unconsumed vapour remaining in the vapour outlet pathway may be reduced.

Although the methods above have been described in relation to an aerosol generating system comprising a liquid reservoir and a resistive heater it will be appreciated that this is not essential, and the insulation channel could be used in other types of aerosol generating system which utilise a liquid aerosol forming substrate such as systems including an inductive heating system. Furthermore, the use of the method is not limited to a system of the type shown, and some or all components which are depicted herein as being included in the cartridge may alternatively be included in a base part of a system instead.

Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments. Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

1. A method of controlling an aerosol generating system (10) during a usage session, the method comprising: heating (50) a liquid aerosol generating substrate during a first user inhalation to generate an inhalable aerosol, measuring (52) a pressure in a flow path (34) of the aerosol generating system (10) during the first user inhalation to obtain a signal (53) representative of pressure, cumulatively integrating (54) said signal (53) representative of pressure during the first user inhalation, and terminating (56) the heating of the liquid aerosol generating substrate based on the cumulative integral of the measured pressure during a user inhalation of the usage session prior to the end of the usage session .

2. The method of claim 1 , wherein terminating the heating of the liquid aerosol generating substrate based on the cumulative integral of the measured pressure comprises: selecting a first threshold value (57) using the cumulative integral, and terminating heating of the liquid aerosol generating substrate during the user inhalation when the first threshold value (57) is reached.

3. The method of claim 2, wherein heating of the liquid aerosol generating substrate is terminated when the first threshold value (57) is reached during the first user inhalation.

4. The method of claim 2 or claim 3, wherein the method further comprises: heating the liquid aerosol generating substrate during a second user inhalation subsequent to the first, and terminating the heating of the liquid aerosol generating substrate during the second user inhalation when the first threshold value (57) is reached.

5. The method of any preceding claim, wherein the method comprises: terminating (56) the heating of the liquid aerosol generating substrate based on the cumulative integral of the measured pressure during a plurality of user inhalations of the usage session,

6. The method of any one of claims 2 to 5, wherein the first threshold value (57) is a threshold time (t_T), and wherein selecting the threshold time (t_T) comprises: cumulatively integrating the signal (53) representative of pressure for a first duration to obtain a first cumulative value; comparing the first cumulative value with one or more stored cumulative values; and selecting the threshold time (t_T) based on a result of the comparison.

7. The method of claim 4 or claim 5 as it depends from claim 4, wherein the first threshold value (57) is a threshold integral (IT), and wherein selecting the threshold integral (IT) comprises: cumulatively integrating the signal (53) representative of pressure for a full duration of the first user inhalation to obtain a first puff integral; and selecting the threshold integral (l_T) using the first puff integral.

8. The method of claim 7, wherein the threshold integral comprises a selected percentage of the first puff integral, wherein the selected percentage is preferably in the range 80%-98%.

9. The method of claim 7 or claim 8, wherein the method further comprises: measuring a pressure in a flow path (34) of the aerosol generating system (10) during the second user inhalation to obtain a signal representative of pressure, cumulatively integrating said signal representative of pressure during the second user inhalation, and terminating the heating of the liquid aerosol generating substrate during the second user inhalation when the threshold integral (l_T) is reached.

10. The method of any one of claims 7 to 9, wherein selecting the threshold integral (l_T) comprises: cumulatively integrating the signal (53) representative of pressure for a full duration of a plurality of user inhalations to obtain a puff integral for each of the plurality of user inhalations; and selecting the threshold integral (l_T) using the plurality of puff integrals.

11. The method of claim 10, wherein threshold integral (l_T) comprises an average of a selected percentage of each of the plurality of puff integrals, wherein the selected percentage is preferably in the range 80%-98%.

12. The method of any one of claims 2 to 11 , wherein the method further comprises: during a third user inhalation subsequent to the first user inhalation, selecting a second threshold value using the cumulative integral, and replacing the first threshold value with the second threshold value such that for one or more subsequent user inhalations heating of the liquid aerosol generating substrate is terminated when the second threshold value is reached rather than when the first threshold value is reached.

13. The method of any preceding claim, wherein the signal (53) representative of pressure is cumulatively integrated from a start time of a user inhalation.

14. The method of any preceding claim, further comprising detecting a user inhalation and initiating heating in response to the detection.

15. An aerosol generating system (10) comprising: a controller (20); a reservoir (22) having a reservoir chamber (24) for containing a liquid aerosol generating substrate and in fluid communication with a vaporisation region (32); a heater (28) in thermal communication with the vaporisation region (32); and a pressure sensor (46) in fluid communication with an air flow pathway (34) through the aerosol generating system; wherein the controller (20) is operable to cause the aerosol generating system (10) to carry out the steps of the method of any one of claims 1 to 14.