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Title:
AEROSOL-GENERATING SYSTEM WITH LIQUID LEVEL DETERMINATION AND METHOD OF DETERMINING LIQUID LEVEL IN AN AEROSOL-GENERATING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2017/144191
Kind Code:
A1
Abstract:
There is provided an electrically operated aerosol-generating system (100) comprising a liquid storage portion (113) storing a liquid (115) from which aerosol may be generated, an electric heater (119), a capillary wick (117) positioned between the liquid (115) in the liquid storage portion (113) and the electric heater (119) and configured to convey liquid (115) from the liquid storage portion (113) to the electric heater (119) and electric circuitry (109) connected to the electric heater (119), the electric circuitry (109) configured to: activate the electric heater (119) for a vaporising period in response to a user input to vaporise liquid (115) in the capillary wick (117), a first predetermined time after the vaporising period activate the heater (119) for a second period, record a temperature measurement of the heater (119) during the second period, and determine a liquid level in the liquid storage portion (113) based on the temperature measurement.

Inventors:
REEVELL TONY (GB)
Application Number:
EP2017/050374
Publication Date:
August 31, 2017
Filing Date:
January 10, 2017
Export Citation:
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Assignee:
PHILIP MORRIS PRODUCTS SA (CH)
International Classes:
A24F47/00
Domestic Patent References:
WO2012085203A12012-06-28
Foreign References:
EP2468117A12012-06-27
US20150359263A12015-12-17
US20140096781A12014-04-10
US20140345633A12014-11-27
US20140338680A12014-11-20
Attorney, Agent or Firm:
REDDIE & GROSE LLP (The White Chapel Building, 10 Whitechapel High Street, London E1 8QS, WC1X 8PL, GB)
Download PDF:
Claims:
Claims

1 . An electrically operated aerosol-generating system comprising: a liquid storage portion storing a liquid from which aerosol may be generated; an electric heater; a capillary wick positioned between the liquid in the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater; and electric circuitry connected to the electric heater, the electric circuitry configured to: activate the electric heater for a vaporising period in response to a user input to vaporise liquid in the capillary wick, a first predetermined time after the vaporising period activate the heater for a second period, record a temperature measurement of the heater during or immediately following the second period, and determine a liquid level in the liquid storage portion based on the temperature measurement.

2. An electrically operated aerosol-generating system according to claim 1 , wherein the first predetermined time is shorter than a time needed for an amount of liquid in the wick to reach equilibrium following the vaporising period.

3. An electrically operated aerosol-generating system according to claim 1 or claim 2, wherein the electric circuitry is configured to activate the heater such that the temperature of the heater is lower than a vaporisation temperature of the liquid during the second period.

4. An electrically operated aerosol-generating system according to any one of the

preceding claims, wherein the electric circuitry is configured to activate the heater for a third period a second predetermined time after the second period and to record a temperature measurement of the heater during the third period, and to determine a liquid level in the liquid storage portion based on a combination of the temperature measurement of the heater during the third period and the temperature measurement of the heater during the second period.

5. An electrically operated aerosol-generating system according to claim 4, wherein the electric circuitry is configured to activate the heater such that the temperature of the heater is lower than a vaporisation temperature of the liquid during the third period.

6. An electrically operated aerosol-generating system according to claim 4 or 5,

wherein the sum of the first predetermined time, the first period and the second predetermined time is shorter than a time needed for an amount of liquid in the wick to reach equilibrium following the vaporising period.

7. An electrically operated aerosol-generating system according to any preceding

claim, wherein the capillary wick has a fibrous or spongy structure.

8. An electrically operated aerosol-generating system according to any preceding

claim, wherein the liquid in the liquid storage portion is retained in a liquid carrier material.

9. An electrically operated aerosol-generating system according to any preceding

claim wherein the second period is between 0.05 and 0.5 seconds.

10. An electrically operated aerosol-generating system according to any preceding

claim, wherein the first predetermined time period is between 0.2 and 2 seconds. 1 1 . An electrically operated aerosol-generating system according to any preceding

claim wherein the electric circuitry comprises a memory, wherein the memory stores a look-up table relating temperature measurements to liquid levels.

12. An electrically operated aerosol-generating system according to any preceding

claim, wherein the electric circuitry is configured to determine whether to

subsequently activate the heater for a second period a first predetermined time after the vaporising period based a previously determined liquid level or based on stored heater activation data.

13. An electrically operated aerosol-generating system according to any preceding

claim wherein the electrically operated aerosol-generating system is an electrically operated smoking system.

14. A method for determining a liquid level of liquid in an electrically operated aerosol- generating system, the electrically operated aerosol-generating system comprising a liquid storage portion storing a liquid from which aerosol may be generated, an electric heater, a capillary wick positioned between the liquid in the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater, and electric circuitry connected to the electric heater, the electric circuitry configured to control activation of the electric heater, comprising:

activating the electric heater for a vaporising period in response to a user input to vaporise liquid in the capillary wick,

a first predetermined time after the vaporising period, activating the heater for a second period,

recording a temperature measurement of the heater during or immediately following the second period; and

determining a liquid level in the liquid storage portion based on the temperature measurement.

15. A computer readable storage medium having stored thereon a computer program which, when run on programmable electric circuitry in an electrically operated aerosol-generating system, the electrically operated aerosol-generating system comprising, a liquid storage portion storing a liquid from which aerosol may be generated, an electric heater, a capillary wick positioned between the liquid in the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater, and programmable electric circuitry connected to the electric heater and configured to control activation of the electric heater, causes the programmable electric circuitry to perform the method of claim.

Description:
AEROSOL-GENERATING SYSTEM WITH LIQUID LEVEL DETERMINATION AND METHOD OF DETERMINING LIQUID LEVEL IN AN AEROSOL-GENERATING SYSTEM

The present invention relates to an electrically operated aerosol-generating system. In particular, the present invention relates to an electrically operated aerosol-generating system in which an aerosol-forming substrate is liquid and is contained in a liquid storage portion.

WO 2012/085203 A1 discloses an electrically heated smoking system having a liquid storage portion. The liquid storage portion includes a liquid aerosol-forming substrate and is connected to a vaporizer comprising an electric heater which is powered by a battery supply. The electric heater is activated by suction on a mouthpiece by a user. The heated aerosol- forming substrate contained in the vaporiser is vaporised by the activated heater. Air drawn along or through the vaporiser by user suction entrains and cool the vapour to generate an aerosol. The generated aerosol is drawn into the mouthpiece and subsequently into the mouth of a user. An amount of depletion of liquid aerosol-forming substrate is determined based on a relationship between a power applied to the heating element and a resulting temperature change of the heating element once the heating element is activated. The determined amount of depletion is indicated to the user.

This approach relies on the fact that when there is less liquid in the vicinity of the heating element, for a given applied power, the heating element will be heated at a higher rate. So if the liquid aerosol-forming substrate is depleted to a level such that there is a significant reduction in liquid in the vicinity of the heating element when the user activates the heater, then there will be a significantly higher temperature change of the heating element than under normal conditions, when the liquid storage portion is full of liquid. This means that liquid depletion can only be determined when the level of liquid in the liquid storage portion has been significantly depleted. It also means that liquid level can only be determined as a user is sucking on the mouthpiece.

It would be desirable to provide an aerosol-generating system that determines the level of liquid in a liquid storage portion more accurately, particularly at times when the liquid storage portion is not nearly empty.

In a first aspect of the invention, there is provided an electrically operated aerosol- generating system comprising:

a liquid storage portion storing a liquid from which aerosol may be generated;

an electric heater; a capillary wick positioned between the liquid in the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater; and

electric circuitry connected to the electric heater, the electric circuitry configured to: activate the electric heater for a vaporising period in response to a user input to vaporise liquid in the capillary wick,

a first predetermined time after the vaporising period activate the heater for a second period,

record a temperature measurement of the heater during or immediately following the second period, and

determine a liquid level in the liquid storage portion based on the temperature measurement.

During the vaporising period liquid in the wick is vaporised by the heat generated by the electric heater. This means that liquid from the liquid storage portion will be drawn into the capillary wick by capillary action to replace the liquid that has been vaporised. The rate at which liquid is drawn into the wick is dependent on the level of liquid in the liquid storage portion. If there is large amount of liquid in the liquid storage portion, the liquid will be drawn into the wick at faster rate than if there is only a small amount of liquid remaining in the liquid storage portion.

"Liquid level" as used herein refers to an amount of liquid in the liquid storage portion.

It may be a percentage or proportion of a maximum amount of liquid or it may be an absolute amount of liquid. The amount may be a mass or a volume of liquid, or a density of liquid within a carrier material.

As described, for a given power applied to the electric heater, the rate of increase of heater temperature is dependent on the environment surrounding the heater and in particular on the amount of liquid in the vicinity of the heater. When there is less liquid in the vicinity of the heating element, for a given applied power the heating element will be heated to a higher temperature. So the temperature measurement taken during the second period, or immediately after the second period, provides information about the amount of liquid in the wick and therefore the rate that liquid has been drawn into the wick following the vaporising period. The temperature measurement is preferably made during the second period but may be made immediately after the second period. "Immediately after" in this context means between 0 and 2 seconds after the second period. If the temperature measurement is made after the second period, preferably it is made between 0 and 0.5 seconds after the second period. The electrically operated aerosol-generating system may be an electrically operated smoking system. The electrically operated aerosol-generating system may be configured to deliver aerosol to a user through a mouthpiece portion. A user may puff on the mouthpiece portion to draw air into the system and draw generated aerosol out of the system into the user's mouth. Airflow as a result of a user puff may be detected and used as a trigger to start the vaporising period. The vaporising period may also be ended at a time dependent on detected airflow through the system.

The first predetermined time is advantageously shorter than a time needed for an amount of liquid in the wick to reach equilibrium following the vaporising period. This means that the temperature measurement is made as liquid is still wicking on to the capillary wick and the temperature measurement is directly related to the wicking rate of the liquid. Equilibrium in this context means a condition in which liquid is no longer being drawn into the wick because the wick is saturated or has reached hydrostatic equilibrium with the liquid within the liquid storage portion.

However, the time taken to reach equilibrium may be dependent on the liquid level within the liquid storage portion. It is possible for the first predetermined time to be greater than the time needed for an amount of liquid in the wick to reach equilibrium following the vaporising period during some conditions, such as when the liquid storage portion is relatively full of liquid and to only be shorter than a time needed for an amount of liquid in the wick to reach equilibrium following the vaporising period when the liquid storage portion is becoming empty.

Advantageously, the electric circuitry is configured to activate the heater such that the temperature of the heater is lower than a vaporisation temperature of the liquid during the second period. This means that the liquid level determination can be made without vaporising a significant amount of liquid. This both reduces liquid consumption and reduces the possibility of generated aerosol condensing within the system because it has not been drawn out by a user puff.

Advantageously, the step of activating the heater for a second period is carried out only in absence of a further user input during the first predetermined time. Advantageously, the step of activating the heater for a second period comprises applying a predetermined power to the heater.

By measuring heater temperature during a period when a user is not puffing on the device, a more reliable measurement can be obtained. The temperature of the heater may be dependent not only on the amount of liquid in the vicinity of the heater but also on other factors, one of which may be airflow rate past the heater. Airflow past the heater as a result of a user puff may have a cooling effect on the heater. As airflow as a result of a user puff is not consistent from puff to puff and from user to user, this inevitably makes a determination of liquid level based on temperature during a user puff less reliable. By measuring temperature at a time when the user is not puffing the measurement is independent of user puff strength.

Most previous methods of determining liquid levels in systems of this type have relied on measuring liquid consumption by monitoring heater activation. That requires knowledge of an initial liquid level and relies on storing heater activation data over time. The present invention does not require storage of any heater activation data or knowledge of an initial liquid level. This is particularly advantageous for systems in which the liquid storage portion is refillable by the user to different levels.

The electric circuitry may be configured to activate the heater for a third period at a second predetermined time after the second period, to record a temperature measurement of the heater during the third period, and to determine a liquid level in the liquid storage portion based on a combination of the temperature measurement of the heater during the third period and the temperature measurement of the heater during the second period. In particular, the liquid level in the liquid storage portion may be based on a difference between the temperature measurement of the heater during the third period and the temperature measurement of the heater during the second period.

The temperature measurement of the heater during the third period and the temperature measurement of the heater during the second period are indicative of the amount of liquid in the vicinity of the heater at those times. A difference between those measurements therefore provides a measure of the wicking rate. This arrangement has the advantage that it is independent of the level of liquid around the heater at the end of the vaporising period. Although the amount of liquid remaining in the vicinity of the heater at the end of the vaporisation period is generally quite consistent (and low), if the vaporising period has been very short (because of a short or aborted user puff for example), there may be unusually high levels of liquid remaining in the wick in the vicinity of the heater.

As an alternative, or in addition, the length of the vaporising period or the total power applied during the vaporising period (or some other parameter of the vaporising period) may be factored into the determination of liquid level. It can be assumed that the longer the vaporising period or the more power applied during the vaporising period, the less liquid is in the vicinity of the heater at the end of the vaporisation period. This can be factored into a calculation of wicking rate based on a single temperature measurement.

Advantageously, the electric circuitry is configured to activate the heater such that the temperature of the heater is lower than a vaporisation temperature of the liquid during the third period. Preferably, the sum of the first predetermined time, the first period and the second predetermined time is shorter than a time needed for an amount of liquid in the wick to reach equilibrium following the vaporising period. This means that the temperature measurement is made as liquid is still wicking on to the capillary wick when the heater temperature is measured during the third period.

The system may comprise one or more capillary wicks. The one or more capillary wicks are arranged to transfer liquid aerosol-forming substrate from the liquid storage portion to the heater. The one or more capillary wicks may comprise a capillary material. A capillary material is a material that actively conveys liquid from one end of the material to another.

The structure of the capillary material may comprise a plurality of small bores or tubes, through which the liquid can be transported by capillary action. The capillary material may have a fibrous structure. The capillary material may have a spongy structure. The capillary material may comprise a bundle of capillaries. The capillary material may comprise a plurality of fibres. The capillary material may comprise a plurality of threads. The capillary material may comprise fine bore tubes. The fibres, threads or fine-bore tubes may be generally aligned to convey liquid to the aerosol-generating means. The capillary material may comprise a combination of fibres, threads and fine-bore tubes. The capillary material may comprise sponge-like material. The capillary material may comprise foam-like material.

The capillary material may comprise any suitable material or combination of materials. Examples of suitable materials are a sponge or foam material, ceramic- or graphite-based materials in the form of fibres or sintered powders, foamed metal or plastics materials, a fibrous material, for example made of spun or extruded fibres, such as cellulose acetate, polyester, or bonded polyolefin, polyethylene, terylene or polypropylene fibres, nylon fibres or ceramic. The capillary material may have any suitable capillarity and porosity so as to be used with different liquid physical properties. The liquid aerosol-forming substrate has physical properties, including but not limited to viscosity, surface tension, density, thermal conductivity, boiling point and atom pressure, which allow the liquid to be transported through the capillary material by capillary action.

The one or more capillary wicks may have a first end and a second end. The first end may extend into the liquid storage portion to draw liquid held in the liquid storage portion to the heater. The second end may extend into an air passage of the aerosol-generating system. The second end may comprise one or more heating elements. The first end and the second end may extend into the liquid storage portion. The heater may comprise one or more heating elements which may be arranged at a central portion of the wick between the first and second ends. In use, when the one or more heating elements are activated during the vaporisation period, the liquid in the one or more capillary wicks is vaporised at and around the one or more heating elements. The heating elements may comprise a heating wire or filament. The heating wire or filament may support or encircle a portion of the one or more capillary wicks.

The liquid may have physical properties, including viscosity, which allow the liquid to be transported through the one or more capillary wicks by capillary action.

The liquid may comprise nicotine. The nicotine containing liquid may be a nicotine salt matrix. The liquid may comprise plant-based material. The liquid may comprise tobacco. The liquid may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the liquid upon heating. The liquid may comprise homogenised tobacco material. The liquid may comprise a non-tobacco-containing material. The liquid may comprise homogenised plant-based material.

The liquid may comprise at least one aerosol-former. An aerosol-former is any suitable known compound or mixture of compounds that, in use, facilitates formation of a dense and stable aerosol and that is substantially resistant to thermal degradation at the temperature of operation of the system. Suitable aerosol-formers are well known in the art and include, but are not limited to: polyhydric alcohols, such as triethylene glycol, 1 ,3- butanediol and glycerine; esters of polyhydric alcohols, such as glycerol mono-, di- or triacetate; and aliphatic esters of mono-, di- or polycarboxylic acids, such as dimethyl dodecanedioate and dimethyl tetradecanedioate. Aerosol formers may be polyhydric alcohols or mixtures thereof, such as triethylene glycol, 1 ,3-butanediol and glycerine. The liquid aerosol-forming substrate may comprise other additives and ingredients, such as flavourants.

The liquid may comprise water, solvents, ethanol, plant extracts and natural or artificial flavours. The liquid may comprise nicotine and at least one aerosol former. The aerosol former may be glycerine. The aerosol-former may be propylene glycol. The aerosol former may comprise both glycerine and propylene glycol. The liquid may have a nicotine concentration of between about 0.5% and about 10%.

A carrier material may be arranged in the liquid storage portion for holding the liquid. The carrier material may be made from any suitable absorbent body of material, for example, a foamed metal or plastics material, polypropylene, terylene, nylon fibres or ceramic. The liquid may be retained in the carrier material prior to use of the aerosol-generating system. The liquid may be released into the carrier material during use. The liquid may be released into the carrier material immediately prior to use. For example, the liquid may be provided in a capsule. The shell of the capsule may melt upon heating by the heating means and releases the liquid aerosol-forming substrate into the carrier material. The capsule may contain a solid in combination with the liquid. The second period may between 0.05 and 0.5 seconds. It is only necessary to very briefly activate the heater and measure the temperature before it approaches the vaporisation temperature of the liquid.

The first predetermined time period may be between 0.2 and 2 seconds. It is desirable to provide a short time period of cooling of the heater before reactivating it to ensure that the heater returns to a predicable temperature and so that it remains below the vaporisation temperature of the liquid during the subsequent activation of the heater. However, as explained, it is also desirable to measure the temperature while liquid is being drawn onto the wick, i.e. before equilibrium is reached. The time period chosen for the first predetermined time period will depend on the properties of the capillary wick being used and on the properties of the liquid and the heater.

The electric circuitry may comprise a memory, wherein the memory stores a look-up table relating temperature measurements to liquid levels. The electric circuitry may be configured to compare measured temperatures with stored temperature measurements to determine a liquid level. The relationship between the measured temperature or temperature difference and the liquid level in the liquid storage portion may be determined empirically for a particular design of aerosol-generating system and stored in the memory as part of a manufacturing process.

The electric circuitry may comprise any suitable components. The electric circuitry may comprise a microprocessor. The microprocessor may be a programmable microprocessor.

The electric circuitry may be arranged control the supply of power to the heater. The electric circuitry may be configured to supply a predetermined power to the heater. The heater may be activated on supply of the predetermined power by the electric circuitry. The electric circuitry may be configured to monitor the power supplied to the aerosol-generating means.

The heater may comprise one or more heating elements. The one or more heating elements may be arranged appropriately so as to most effectively heat the liquid in the capillary wick. The one or more heating elements may be arranged to heat the liquid primarily by means of conduction. The one or more heating elements may be arranged substantially in direct contact with the liquid and wick. The one or more heating elements may be arranged to transfer heat to the liquid via one or more heat conductive elements.

The one or more electric heating elements may comprise an electrically resistive material. Suitable electrically resistive materials may include: semiconductors such as doped ceramics, electrically "conductive" ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys and composite materials made of a ceramic material and a metallic material.

The one or more electric heating elements may take any suitable form. For example, the one or more electric heating elements may take the form of one or more heating blades. The one or more electric heating elements may take the form of a casing or substrate having different electro-conductive portions, or one or more electrically resistive metallic tube. The heater may comprise one or more heater filaments in the form of a coil extending around the wick.

The heater may be a substantially flat. As used herein, "substantially flat" refers to a heater that is in the form of a substantially two dimensional topological manifold. Thus, the substantially flat heater extends in two dimensions along a surface substantially more than in a third dimension. In particular, the dimensions of the substantially heater in the two dimensions within the surface is at least 5 times larger than in the third dimension, normal to the surface. An example of a substantially flat heater is a structure between two substantially parallel surfaces, wherein the distance between these two surfaces is substantially smaller than the extension within the surfaces. In some embodiments, the substantially flat heater is planar. In other embodiments, the substantially flat heater is curved along one or more dimensions, for example forming a dome shape or bridge shape.

The heater may comprise a plurality of heater filaments. The term "filament" is used throughout the specification to refer to an electrical path arranged between two electrical contacts. A filament may arbitrarily branch off and diverge into several paths or filaments, respectively, or may converge from several electrical paths into one path. A filament may have a round, square, flat or any other form of cross-section. A filament may be arranged in a straight or curved manner.

The plurality of filaments may be an array of filaments, for example arranged parallel to each other. The filaments may form a mesh. The mesh may be woven or non-woven. The plurality of filaments may be positioned adjacent to or in contact with the capillary wick holding the aerosol-forming substrate. The filaments may define interstices between the filaments and the interstices may have a width of between 10 μηη and 100 μηη. The filaments may give rise to capillary action in the interstices, so that in use, liquid to be vaporised is drawn into the interstices, increasing the contact area between the heater assembly and the liquid.

In one example, the heater comprises a mesh of filaments formed from 304L stainless steel. The filaments have a diameter of around 16 μηη. The mesh is connected to electrical contacts that are separated from each other by a gap and are formed from a copper foil having a thickness of around 30 μηη. The electrical contacts are provided on a polyimide substrate having a thickness of about 120 μηι. The filaments forming the mesh define interstices between the filaments. The interstices in this example have a width of around 37 μηη, although larger or smaller interstices may be used. Using a mesh of these approximate dimensions allows a meniscus of aerosol-forming substrate to be formed in the interstices, and for the mesh of the heater assembly to draw aerosol-forming substrate by capillary action. The heater is placed in contact with a capillary wick holding a liquid aerosol-forming substrate. The capillary material is held within a rigid housing and the heater extends across an opening in the housing.

The heating means may comprise inductive heating means.

The electric circuitry may be arranged to measure the electrical resistance of the one or more electric heating elements. The electric circuitry may be arranged to measure the electrical resistance of the one or more electric heating elements by measuring the current through the one or more electric heating elements and the voltage across the one or more electric heating elements. The electric circuitry may be configured to determine the electrical resistance of the at least one heating element from the measured current and voltage. The electric circuitry may comprise a resistor, having a known resistance, in series with the at least one heating element and the electric circuitry may be arranged to measure the current through the at least one heating element by measuring the voltage across the known- resistance resistor and determining the current through the at least one heating element from the measured voltage and the known resistance.

The electric circuitry may be configured to ascertain the temperature of the one or more electric heating elements from the measurements of electrical resistance. If the one or more heating elements have suitable characteristics, such as a suitable temperature coefficient of resistance, the temperature of the one or more heating elements may be ascertained from measurements of the electrical resistance of the one or more heating elements.

The electrically operated aerosol-generating system may comprise two temperatures sensors, a first temperature sensor and a second temperature sensor. The first temperature sensor may be the temperature sensor arranged in the liquid storage portion for sensing the temperature of liquid aerosol-forming substrate held in the liquid storage portion. The second temperature sensor may being arranged to sense the temperature of the heater.

The electric circuitry may be configured to determine whether to subsequently activate the heater for a second period a first predetermined time after the vaporising period based on a previously determined liquid level or based on stored heater activation data. It may not be necessary or desirable to subsequently activate the heater after every vaporising period. For example, it may be desirable to determine liquid level infrequently when the most recent determination was that the liquid level is high, say over 50% of maximum capacity. It may be desirable to determine liquid level more frequently as the determined liquid level gets lower. It may be appropriate to determine liquid level only after the first vaporisation period of each session of use of the system. In the case of a smoking system this means determining liquid level only after the first puff of each smoking session.

Additional parameters may be factored into the determination of liquid level, including one or more of device orientation, liquid temperature, ambient temperature, type of liquid and type of heater and wick assembly. For example, the system may include one or more accelerometer to determine the orientation of the system. The orientation of the system may affect wicking rate and so may be factored into the determination of liquid level. The electric circuitry may be used with different liquid storage portions and different heaters. The wicking rate may depend on the properties of the wick and of the liquid. The temperature of the heater for a given applied power may depend on the characteristics of the heater. The identity of the type of liquid and the type of heater in the system may be used in the determination of the liquid level.

The electrically operated aerosol-generating system may further comprise a user interface, wherein the electric circuitry is configured to indicate the determined liquid level in the liquid storage portion through the user interface. The user interface may be a display screen, one or more visual indicators, such as LEDs, an audio indicator such as speaker, a haptic indicator, or some combination of different indicators.

The liquid level may be indicated to the user as an absolute amount of liquid, a percentage of a maximum liquid level, or as a determination that the liquid level is more or less than a threshold liquid level. The liquid level be an average liquid level obtained from a plurality of liquid level determinations. The liquid level determined based on wicking rate may be combined with other determinations of liquid level and with liquid consumption estimates or measurements, for example consumption estimates based on heater activation time to provide a refined liquid level estimate.

The aerosol-generating system may comprise one or more electric power supplies. The power supply may be a battery. The battery may be a Lithium based battery, for example a Lithium-Cobalt, a Lithium-Iron-Phosphate, a Lithium Titanate or a Lithium-Polymer battery. The battery may be a Nickel-metal hydride battery or a Nickel cadmium battery. The power supply may be another form of charge storage device such as a capacitor. The power supply may require recharging and be configured for many cycles of charge and discharge. The power supply may have a capacity that allows for the storage of enough energy for one or more smoking experiences; for example, the power supply may have sufficient capacity to allow for the continuous generation of aerosol for a period of around six minutes, corresponding to the typical time taken to smoke a conventional cigarette, or for a period that is a multiple of six minutes. In another example, the power supply may have sufficient capacity to allow for a predetermined number of puffs or discrete activations of the heating means and actuator.

The aerosol-generating system may comprise a user input, such as a switch or button. This enables the user to turn the system on. The switch or button may activate the aerosol-generating means. The switch or button may initiate aerosol generation. The switch or button may prepare the control electronics to await input from a puff detector.

The aerosol-generating system may comprise a housing. The housing may be elongate. The housing may comprise any suitable material or combination of materials. Examples of suitable materials include metals, alloys, plastics or composite materials containing one or more of those materials, or thermoplastics that are suitable for food or pharmaceutical applications, for example polypropylene, polyetheretherketone (PEEK) and polyethylene. The material may be light and non-brittle.

The housing may comprise a cavity for receiving the power supply. The housing may comprise a mouthpiece. The mouthpiece may comprise at least one air inlet and at least one air outlet. The mouthpiece may comprise more than one air inlet. One or more of the air inlets may reduce the temperature of the aerosol before it is delivered to a user and may reduce the concentration of the aerosol before it is delivered to a user.

The aerosol-generating system may be portable. The aerosol-generating system may have a size comparable to a conventional cigar or cigarette. The aerosol-generating system may have a total length between about 30 mm and about 150 mm. The aerosol- generating system may have an external diameter between about 5 mm and about 30 mm.

The aerosol-generating system may comprise a main unit and a cartridge. The main unit may comprise the electric circuitry. The cartridge may comprise the liquid storage portion for holding the liquid. The main unit may be configured to removably receive the cartridge.

The main unit may comprise one or more power supplies. The main unit may comprise the heater. The cartridge may comprise the heater. Where the cartridge comprises the heater, the cartridge may be referred to as a 'cartomiser'.

The aerosol-generating system may comprise an aerosol-generating component comprising the heater. The aerosol-generating component may be separate to the main unit and the cartridge. The aerosol-generating component may be removably receivable by at least one of the main unit and the cartridge.

The cartridge may be removably coupled to the main unit. The cartridge may be removed from the main unit when the liquid has been consumed. The cartridge is preferably disposable. However, the cartridge may be reusable and the cartridge may be refillable with liquid. The cartridge may be replaceable in the main unit. The main unit may be reusable.

As used herein, the term 'removably received' is used to mean that the cartridge and the main unit can be coupled and uncoupled from one another without significantly damaging either the main unit or the cartridge.

In a second aspect of the invention, there is provided a method for determining a liquid level of liquid in an electrically operated aerosol-generating system, the electrically operated aerosol-generating system comprising a liquid storage portion storing a liquid from which aerosol may be generated, an electric heater, a capillary wick positioned between the liquid in the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater, and electric circuitry connected to the electric heater, the electric circuitry configured to control activation of the electric heater, comprising: activating the electric heater for a vaporising period in response to a user input to vaporise liquid in the capillary wick,

a first predetermined time after the vaporising period, activating the heater for a second period,

recording a temperature measurement of the heater during or immediately following the second period; and

determining a liquid level in the liquid storage portion based on the temperature measurement.

The method may further comprise activating the heater for a third period at a second predetermined time after the second period, recording a temperature measurement of the heater during the third period, and determining a liquid level in the liquid storage portion based on a combination of the temperature measurement of the heater during the third period and the temperature measurement of the heater during the second period. In particular, the liquid level in the liquid storage portion may be based on a difference between the temperature measurement of the heater during the third period and the temperature measurement of the heater during the second period.

In a third aspect of the invention, there is provided a computer readable storage medium having stored thereon a computer program which, when run on programmable electric circuitry in an electrically operated aerosol-generating system, the electrically operated aerosol-generating system comprising, a liquid storage portion storing a liquid from which aerosol may be generated, an electric heater, a capillary wick positioned between the liquid in the liquid storage portion and the electric heater and configured to convey liquid from the liquid storage portion to the electric heater, and programmable electric circuitry connected to the electric heater and configured to control activation of the electric heater, causes the programmable electric circuitry to perform the method of the second aspect of the invention.

It should be clear that the invention can be implemented as a software update on existing hardware. In particular, it is possible to provide a software update to existing aerosol-generating systems that comprise a programmable microprocessor for controlling the operation of the system and a data interface that allows for the uploading of software to the microprocessor.

Features of the invention described in relation to one aspect of the invention may be applied to other aspects of the invention. On particular features of the way that the electric circuitry of the first aspect is configured to operate may be applied to the method of the second aspect of the invention.

The invention will be further described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 shows one example of an electrically operated aerosol-generating system having a liquid storage portion;

Figure 2 is a plot showing five medians of temperature profiles of the heating element during multiple puffs of an electrically operated aerosol-generating system;

Figure 3 is an illustration of the wicking of liquid at low liquid level;

Figure 4 is an illustration of the wicking of liquid from liquid held in a carrier material; Figure 5 is an illustration of activation of a heater in accordance with a first aspect of the invention; and

Figure 6 is an illustration of activation of a heater in accordance with a second aspect of the invention.

Figure 1 shows one example of an electrically operated aerosol generating system according to the present invention. Many other examples are possible, however. Figure 1 is schematic. In particular, the components shown are not to scale either individually or relative to one another. The aerosol generating system needs to include or receive an aerosol- forming substrate. The aerosol generating system requires a heater, for generating aerosol from the liquid and a wick or capillary material for conveying the liquid to the heater. But other aspects of the system could be changed. For example, the overall shape and size of the housing could be altered.

In Figure 1 , the device is a smoking device having a liquid storage portion. The smoking device 100 of Figure 1 comprises a housing 101 having a mouthpiece end 103 and a body end 105. In the body end, there is provided an electric power supply in the form of battery 107 and electric circuitry in the form of hardware 109 and a puff detection device 1 1 1 . In the mouthpiece end, there is provided a liquid storage portion in the form of cartridge 1 13 containing liquid 1 15, a capillary wick 1 17 and a heater 1 19 comprising at least one heating element. Note that the heater is only shown schematically in Figure 1 . One end of the capillary wick 1 17 extends into the cartridge 1 13 and the other end of the capillary wick 1 17 is surrounded by the heater 1 19. The heater is connected to the electric circuitry via connections 121. The housing 101 also includes an air inlet 123, an air outlet 125 at the mouthpiece end and an aerosol-forming chamber 127.

In use, operation is as follows. Liquid 1 15 is conveyed by capillary action from the liquid storage portion 1 13 from the end of the wick 1 17 which extends into the liquid storage portion to the other end of the wick which is surrounded by heater 1 19. When a user draws on the aerosol generating system at the air outlet 125, ambient air is drawn through air inlet 123. In the arrangement shown in Figure 1 , the puff detection system 1 1 1 senses the puff and activates the heater 1 19. The battery 107 supplies electrical energy to the heater 1 19 to heat the end of the wick 1 17 surrounded by the heater. The liquid in that end of the wick 1 17 is vaporized by the heater 1 19 to create a supersaturated vapour.

The supersaturated vapour created is mixed with and carried in the air flow from the air inlet 123. In the aerosol-forming chamber 127, the vapour condenses to form an inhalable aerosol, which is carried towards the outlet 125 and into the mouth of the user.

The liquid being that has been vaporized is replaced by further liquid moving along the wick 1 17 by capillary action.

The capillary wick can be made from a variety of porous or capillary materials and preferably has a known, pre-defined capillarity. Examples include ceramic- or graphite-based materials in the form of fibres or sintered powders. Wicks of different porosities can be used to accommodate different liquid physical properties such as density, viscosity, surface tension and vapour pressure. The wick must be suitable so that a required amount of liquid can be delivered to the heating element.

The heater in this example comprises a heating wire or filament extending around the capillary wick. The temperature of heating element measured by measuring resistance of heater. The heating wire has a temperature coefficient of resistance that allows for an accurate determination of the heater temperature to be made from a measurement of electrical resistance. The electric circuitry may comprise a resistor, having a known resistance, connected in series with the heating wire and the electric circuitry may be arranged to measure the current through the at least one heating element by measuring the voltage across the known-resistance resistor and determining the current through the at least one heating element from the measured voltage and the known resistance.

The rate of increase of temperature of the heating element when a given amount of power is applied to the heater is dependent on the environment surrounding the heater, and in particular is dependent on the amount of liquid in the vicinity of the heater. The more liquid there is around the heating element the more heat will be lost to the liquid, which slow the rate of temperature increase of the heating element. So the temperature of the heating element as the heating element is heating up is dependent on the amount on liquid in the wick, which is in turn dependent on the wicking rate of the liquid at times before equilibrium has been reached.

Figure 2 is a plot showing five medians of temperature profiles being measured during multiple puffs of an aerosol-generating system when the electric heater is activated because of a user request for generating aerosol. The temperature T of the heating element is shown on the y-axis and the puff time t is shown on the x-axis. Curve 201 is the median of a first set of puffs, each puff having a 2-second puff duration. Similarly, curve 203 is the median of a second set of puffs, curve 205 is the median of a third set of puffs, curve 207 is the median of a fourth set of puffs and curve 208 is the median of a fifth set of puffs. In each curve, the vertical bars (for example shown at 209) indicate the standard deviation around the median for those temperatures. Thus, the evolution of the measured temperature over the life of the liquid storage portion is shown. This behaviour was observed and confirmed for all liquid formulations vaporized and for all power levels used.

As can be seen from Figure 2, the temperature response of the heating element is reasonably stable over curves 201 , 203 and 205. That is to say, the standard deviation around the median for the first three sets of puffs is reasonably small. Over curve 207, two effects are noticed. Firstly, the standard deviation around the median for the third set of puffs is greater. Secondly, the temperature of the heating element during each puff has significantly increased. These two effects are the result of the liquid storage portion becoming empty so that less liquid is delivered through the wick to the heater.

Over curve 208, the standard deviation around the median for the fifth set of puffs is smaller once again. That is to say, the temperature range over the puffs is reasonably stable. However, the temperature of the heating element during each puff has increased further. This is because the liquid storage portion is substantially empty.

The temperature increase in curve 207, as compared with curve 205, is particularly evident after around 0.4 seconds of the puff (shown by dotted line 21 1 ). Detecting differences in the amount of liquid in the vicinity of the heating element can therefore be accurately based on the temperature level of the heating element after 0.4 seconds of the puff duration.

Figure 2 demonstrates that there is a clear temperature increase of the heating element as the liquid storage portion becomes empty. This is particularly evident after the first 0.4 seconds of a puff. This temperature increase can be utilized to determine when the liquid storage portion is empty or nearly empty. It can also be seen in Figure 2 that the slope of the temperature profile between 0 seconds and 0.2 seconds increases as the liquid storage portion becomes empty. Thus, a measure of the rate of temperature increase during an initial time of a puff over the life of the liquid storage portion can provide an alternative or additional means to detect an amount of the remaining liquid in the liquid storage portion.

However, this technique can also be used to determine liquid level even when the liquid storage portion is relatively full if measurement is made while liquid is being drawn onto the wick following a vaporising period. The rate of wicking of the liquid onto the wick is dependent on the liquid level in the liquid storage portion. The rate of wicking can be determined by determining the amount of liquid on the wick at a first time, determining the amount of liquid on the wick a predetermined time later (while the liquid is still wicking onto the coil), and then dividing the difference in the amounts of liquid by the predetermined time. The amount of liquid in the wick is related to the temperature of the heating element early in a heater activation, as described above. So by measuring the temperature of the heating element at different times as liquid is still being drawn onto the wick, a measure of wicking rate can be obtained.

Figure 3 illustrates one example of how liquid level in a liquid storage portion can affect the rate at which liquid is wicked to the heating element. The wick 300 in Figure 3 is a bundle of fibres that, in effect, give rise to a plurality of capillary tubes through which liquid is drawn. A heating element 310, in the form of a coiled filament, is wound around one end of the wick 300. The opposite end of the wick extends into a liquid storage tank 320, which is half filled with liquid. Figure 3 illustrates the progress of liquid as it is drawn up the wick 300 to the heating element 310, with the initial state shown on the left and the final state (equilibrium) shown on the right. When the system is tilted, as shown in Figure 3, the area of wick, and specifically the area of the end of the wick, in contact with the liquid is reduced. This reduces the wicking rate. The liquid transfers sideways across the wick into that part of the wick not in contact with the wick. This is a slower process than wicking up the capillary tubes.

The lower the liquid level, the smaller the area of the end of the wick in contact with the wick and so the lower the wicking rate. Of course the system will not always be tilted at a one particular angle from the vertical, but nor will it remain perfectly vertical. It is also the case that some liquid will be drawn into the wick through sidewalls of the wick. On average the lower the liquid level in the liquid tank the lower the wicking rate of liquid onto the wick.

Figure 4 shows second example of how liquid level affects wicking rate. Figure 4 illustrates a wick 400, a heating element 410 and a liquid tank 420 as in Figure 3. But in the example shown in Figure 4 the liquid tank 420 comprises a liquid carrier material 430. As the liquid in the liquid tank is consumed and the liquid level drops, the liquid is distributed across the liquid carrier material and so the liquid density drops. This means that as the liquid level drops the amount of liquid in contact in contact with the end of the wick is reduced. This reduces the wicking rate. Figure 4a shows a relatively full liquid tank and Figure 4b shows an emptier liquid tank, with a corresponding lower wicking rate up the wick.

Liquid level based on wicking rate can be determined in a number of ways. Figure 5 illustrates a first embodiment of a control process for determining liquid level by determining wicking rate based on a single heater activation. The process of Figure 5 relies on an assumption that following a heater activation to vaporise liquid in the wick, the level of liquid in the vicinity of the wick is consistent. So a measure of liquid level immediately after a user activation of the heater is not measured but has been determined during a calibration process during manufacture or device development.

Figure 5 illustrates the activation of the heater over time. In Figure 5 power is applied to the heater in response to a user puff, as illustrated by vaporising period 500. The application of power to the heater in response to the user puff is ended at time to. At time to the liquid in the wick is depleted as a result of vaporisation. At time ti , which is a predetermined, constant period after to, power is applied to the heater again for a second period 510. The second period 510 is shorter than the vaporising period 500 and is sufficiently short that the heater does not reach the vaporisation temperature of the liquid during the second period. At time t.2, which is at or close to the end of the second period 510, the temperature of the heater is measured. The time t.2 is chosen to be a time at which liquid is still being drawn onto the wick, before equilibrium is reached, even when the liquid storage portion is full. Because the liquid level in the wick at time to, and the temperature and cooling rate of the heater is assumed to be consistent from puff to puff, the temperature of the heater at time t.2 is directly related to the wicking rate of liquid onto the wick and so is related to the liquid level in the liquid storage portion, as described.

Empirical data for particular designs of aerosol-forming substrate and for the particular system design can be stored in memory in the electric circuitry. This empirical data can relate the temperature of the heating element at a t.2 with the amount of liquid remaining in the liquid storage portion. The empirical data can then be used to determine how much liquid is remaining and may be used to provide a user with an indication of liquid level or that liquid level is estimated to be below a threshold level.

Figure 6 is a second embodiment of a control process for determining liquid level based on two heater activations. In Figure 6 power is applied to the heater in response to a user puff, as illustrated by vaporising period 600. The application of power to the heater in response to the user puff is ended at time to. At time to the liquid in the wick is depleted as a result of vaporisation. At time ti, which is a set period after to, power is applied to the heater again for a second period 610. The second period 610 is shorter than the vaporising period 600 and is sufficiently short that the heater does not reach the vaporisation temperature of the liquid. At time t.2, which is at or close to the end of the second period 610, the temperature of the heater is measured. At time t.3, which is a set period after to, power is applied to the heater again for a third period 620. The third period 620 is also shorter than the vaporising period 600 and is sufficiently short that the heater does not reach the vaporisation temperature of the liquid. At time t 4 , which is at or close to the end of the third period 620, the temperature of the heater is measured again. The time t 4 is chosen to be a time at which liquid is still being drawn onto the wick, before equilibrium is reached, even when the liquid storage portion is full.

The liquid level at the heater at time t.2 is determined from the temperature measurement at time t.2. The liquid level at the heater at time t 4 is determined from the temperature measurement at time t 4 . The wicking rate is determined from the difference between the liquid level at the heater at time t.2 and the liquid level at the heater at time t 4 , divided by the time difference between t.2 and t 4 . The determined wicking rate can be related to the liquid level in the liquid storage portion using empirical data stored in a memory in the electric circuitry, as described. The user can then be provided with an indication of liquid level.

The determination of liquid level as described with reference to Figure 5 or Figure 6 may be repeated after successive user activations of the heater and an average liquid level may be determined and indicated to a user. It is also possible to combine the described methods of liquid level estimation with other techniques such as techniques that determine liquid consumption based on a number or measurement of user activations of the heater to provide a refined estimate of liquid level.

The estimation of liquid level may also be modified to account for other effects, such as ambient temperature or liquid temperature, that might affect wicking rate, or the length of vaporising period, that might affect the amount of liquid in the wick immediately following the vaporising period.

The invention is applicable to different physical arrangements of wick, heater and liquid storage portion. Empirical data can be stored for each possible arrangement, and for different liquids and users. For example, the wick may extend at both ends into the liquid storage portion with the heater at position intermediate the two ends. The heater, wick and liquid storage portion may also be provided in a cartridge or "cartomiser" separable from the electric circuitry. The electric circuitry may store empirical data relating to a plurality of different cartridge or cartomiser designs that may store different liquids. The invention has a number of advantages. Measuring the wicking rate provides a means to estimate the liquid level without having to continually monitor and store information about the system usage. The methods of the present invention are therefore cheaper and simpler to implement than prior methods that rely on continually monitoring heater usage.

The invention may apply equally to cartomisers and tank based systems where the liquid storage portion can be refilled. The invention may be used in systems where the starting liquid level is not known.

The invention uses automated activation of the heater that does not rely on measurement during a user activation. Automated activation can be controlled more precisely than user activation. The automated activation does not need to be implemented every time a user uses the device. Power consumption can be greatly reduced by infrequent use of the self-activation.

The invention may be implemented through modification to control programs in existing systems. It may be possible simply to provide software and data to existing systems in order to implement the invention.