The present disclosure relates to an aerosol-generating device for generating an aerosol from an aerosol-forming substrate. The present disclosure also relates to an aerosol generating system comprising the aerosol-generating device and a method of detecting a user puffing on the aerosol-generating device.

Aerosol-generating devices configured to generate an aerosol from an aerosol forming substrate, such as a tobacco-containing substrate, are known in the art. Such devices typically generate aerosol from the substrate through the application of heat to the substrate, rather than combustion of the substrate. In use, the aerosol-generating device may receive the aerosol-forming substrate, for example in a chamber of the device. The device may provide power to a heater assembly to heat the heater assembly, the heat being transferred to the aerosol-forming substrate to release volatile compounds which condense to form an aerosol. Some aerosol-generating devices comprise a puff detection system capable of automatically detecting when a user puffs on the device. Puff detection may be used in different ways. For example, a controller of the aerosol-generating device may count the number detected puffs on a particular received aerosol-generating article. If the number of puffs reaches or exceeds a predetermined number of puffs, the controller may inform the user of the device or may event prevent use of the device until the aerosol-generating article has been replaced. In another example, puff detection may be used to control the immediate supply of power to a heating element or other aerosol-generating element so that increased power is provided when a puff is detected.

An example known aerosol-generating device having a puff detection system comprises a heater assembly comprising a heater blade. The heater blade is configured, in use, to penetrate the aerosol-forming substrate of a received aerosol-generating article. In use, power is supplied to the heating blade to heat the received aerosol-generating article to release volatile compounds. During a user puff, air is drawn through the aerosol-forming substrate. This air has a cooling effect on the heater blade and so results in a drop in resistance of at least one heater track formed of a material having a temperature dependent resistance. By monitoring the resistance of said at least one heater track, puffs can be detected corresponding to the drop in resistance.

This arrangement is not practical for aerosol-generating devices that employ an external heater assembly that heat the aerosol-forming substrate from outside the substrate rather than from within. For example, a resistive heater assembly may surround a chamber wall of the aerosol-generating device, the chamber wall defining a chamber for receiving the aerosol-generating article. In use, the heater assembly heats the chamber wall and that heat is then transferred to aerosol-forming substrate of the received aerosol-generating article. The puff detection system described above is not suitable for use in aerosol-generating devices comprising such an external heater system because air, drawn through the aerosol forming substrate when a user puffs, does not pass over the external heating element. The cooling effect of such a user puff on the heating element is so small that it is difficult to measure.

It would be desirable to provide an aerosol-generating device with a puff detection system that is more responsive to user puffs than known systems. A more responsive puff detection system would allow for a more accurate puff count, for example to reduce the possibility that a maximum number of puffs of a particular aerosol-generating article is exceeded. A more responsive puff detection system may also be used to control the immediate delivery of power to the heating element. It would also be desirable to provide an aerosol-generating device having a puff detection system that has improved responsiveness regardless of whether the aerosol-generating device comprises an internal heater assembly or an external heater assembly.

In a first aspect there is provided an aerosol-generating device for generating an aerosol from an aerosol-forming substrate. The aerosol-generating device may comprise a device housing. The device housing may define a chamber for receiving the aerosol-forming substrate. The aerosol-generating device may comprise an airflow channel. The airflow channel may extend from an air inlet in the device housing. The airflow channel may extend through the chamber. Alternatively, the airflow channel may be in fluid communication with the chamber. The aerosol-generating device may comprise a puff sensor assembly. The puff sensor assembly may comprise a heat transfer element. The puff sensor assembly may comprise a temperature sensor. The temperature sensor may be in contact with the heat transfer element. A first portion of the airflow channel may be at least partially defined by an airflow channel wall. A second portion of the airflow channel may be at least partially defined by the heat transfer element. The second portion of the airflow channel may be adjacent to the first portion. The second portion may be outside of the chamber. At least one of the thermal conductivity or thermal diffusivity of the heat transfer element may be greater than the respective thermal conductivity or thermal diffusivity of the airflow channel wall. For example, the thermal conductivity of the heat transfer element may be greater than the thermal conductivity of the airflow channel wall. Alternatively or additionally, the thermal diffusivity of the heat transfer element may be greater than the thermal diffusivity of the airflow channel wall. At least one of the thermal conductivity or thermal diffusivity of the heat transfer element may be 2 times, 5 times, 10 times, 25 times or 100 times the respective thermal conductivity or thermal diffusivity of the airflow channel wall. Both of the thermal conductivity and thermal diffusivity of the heat transfer element may be 2 times, 5 times, 10 times, 25 times or 100 times the respective thermal conductivity and thermal diffusivity of the airflow channel wall.

The aerosol-generating device may comprise a heater assembly for heating the aerosol-forming substrate received in the chamber. Alternatively, the chamber may be configured for receiving a cartridge containing an aerosol-forming substrate wherein the cartridge comprises a heater assembly.

The second portion of the airflow channel may be upstream of the chamber. The second portion of the airflow channel may be downstream of the chamber. This can ensure that the second portion of the airflow channel is not covered by aerosol-forming substrate received in the device and is in direct contact with the airflow. Positioning the second portion upstream of the chamber may have an advantage of cooler ambient air contacting the second portion. Positioning the second portion upstream of the chamber may have an advantage of minimising the possibility of aerosol condensates being deposited on the second portion of the airflow channel. The airflow channel may comprise a plurality of parallel branches, and the second portion may be positioned in a first branch parallel to a second branch containing the chamber. The second portion of the airflow channel may be adjacent to the chamber. The chamber may be external to the airflow channel. In that case, the chamber be adjacent to and in fluid communication with the second portion of the airflow channel.

In use, an aerosol-forming substrate may be received in the chamber. Electric power from a power source of the aerosol-generating device may be supplied to heater assembly. If the heater assembly is part of a received cartridge, the aerosol-generating device may comprise electrical connections for connecting to corresponding electrical connections on the cartridge when the cartridge is received in the chamber. Power may be supplied via the electrical connections of the device and cartridge. In either case, the heater assembly heats the aerosol-forming substrate such that volatile compounds are vaporised. As the airflow channel extends through, or is in fluid communication with, the chamber, the vapour passes into the airflow channel. In use, air may be drawn through the airflow channel by a user puffing on the aerosol-generating device or on an aerosol-generating article received in the device and containing the aerosol-forming substrate. The air may enter the airflow channel at the air inlet.

Because the second portion of the airflow channel may be at least partially defined by the heat transfer element, air drawn through the airflow channel will pass over the heat transfer element. Preferably, the air drawn through the channel from outside of the device has a lower temperature than the heat transfer element and so the passing air has a cooling effect on the heat transfer element. This cooling effect may be a result of heat transferring from the heat transfer element to the cooler air passing the heat transfer element. This transfer of heat may advantageously result in a reduction in the temperature of the heat transfer element.

The temperature sensor may be in contact with the heat transfer element and so changes in the temperature of the heat transfer element may be detected by the temperature sensor. In particular, reductions in the detected temperature of the heat transfer element may be detected by the temperature sensor. Signals from the temperature sensor may be received at a controller of the aerosol-generating device configured to detect a user puff based on said reductions in temperature of the heat transfer element.

The responsiveness of the puff sensor assembly to user puffs may depend on how quickly the cooling caused by air passing through the second portion is detected by the temperature sensor. This, in turn, may depend on how quickly heat is transferred through the heat transfer element. For example, a first surface of the heat transfer element may at least partially define the second potion of the airflow channel. The temperature sensor may be in contact with a second surface of the heat transfer element. Cooling air in the airflow channel will cause immediate cooling of the first surface of the heat transfer element as it flows over that first surface but there may be a delay before there is a significant temperature change at the second surface of the heat transfer element that can be detected by the temperature sensor. The quicker the flow of heat from the second surface to the first surface, the more responsive the puff sensor assembly may be to a puff.

Heat moves more quickly through materials with a higher thermal conductivity. So, if the heat transfer element has a thermal conductivity greater than the airflow channel wall, heat will move more quickly through the heat transfer element than through the airflow channel wall. Thus, the temperature sensor contacting the heat transfer element rather than the airflow channel wall, for example, may advantageously result in a puff detection assembly that has an improved responsiveness to puffs. This may be because changes in the detected temperature of the heat transfer element during a user puff may be fast and pronounced. Based on such a change, a controller of the aerosol-generating device may advantageously be able to reliably determine a user puff even if an inexpensive temperature sensor is used.

The heat transfer element may have a thermal conductivity of at least 100 Watts per metre-Kelvin. The heat transfer element may have a thermal conductivity not greater than 300 Watts per metre-Kelvin.

A heat transfer element having a thermal diffusivity greater than the thermal diffusivity of the airflow channel wall may also result in a puff detection assembly that has an improved responsiveness to puffs which may be because changes in the detected temperature of such a heat transfer element during a user puff may be fast and pronounced. The thermal diffusivity of a material is defined as the thermal conductivity of that material divided by the product of its density and specific heat capacity at constant pressure. The product of density and specific heat capacity at constant pressure is also known as the volumetric heat capacity. The thermal diffusivity of a material is relevant when a system is not in steady state. It describes the rate of temperature spread through the material to reach a thermal equilibrium. This property may not be described by thermal conductivity alone. For example, a first and second material may both have the same thermal conductivity but the first material may have a larger volumetric heat capacity than the second material such that the first material has a smaller thermal diffusivity than the second material. The higher the volumetric heat capacity, the greater the change in energy required for a unit of volume of the material to change temperature by one degree Kelvin. So, the first material and second material may have the same thermal conductivity (i.e. the same ability to conduct heat), but the temperature of the second material, with the higher thermal diffusivity, will change more quickly than the first material if both are subject to the same starting non-steady state conditions. This is because less energy is required to achieve each degree Kelvin of temperature change per unit volume of the first material compared to the second material.

By providing a heat transfer element having a thermal diffusivity greater than the thermal diffusivity of the airflow channel wall, the detected change in temperature of the heat transfer element may advantageously be faster and more pronounced than a change in temperature of the airflow channel wall immediately after the start of a puff. As described above, a fast and pronounced change in the detected temperature of the heat transfer element during a user puff advantageously allows for the user puff to be reliably determined by a controller of the aerosol-generating device.

The heat transfer element may have a thermal diffusivity of at least 50 millimetres squared per second. Preferably, the heat transfer element may have a thermal diffusivity of greater than 60, 70, 80 or, most preferably, 90 millimetres squared per second.

As thermal diffusivity is related to thermal conductivity, a material having a high thermal diffusivity may also have a high thermal conductivity. So, the heat transfer element may have both a greater thermal diffusivity and a greater thermal conductivity than the airflow channel wall.

A puff sensor assembly comprising a heat transfer element at least partially defining a second portion of the airflow channel is advantageously compatible with aerosol-generating devices comprising an external heater assembly or an internal heater assembly. In either case, air drawn through the airflow channel may have a cooling effect on the heat transfer element allowing for quick and reliable detection of a user puff by the controller. Preferably, when the aerosol-generating device is in use, the heat transfer element may be heated above ambient temperature. During puffs, between puffs or both during puffs and between puffs, the heat transfer element may be heated to a temperature of at least 5 degrees centigrade above ambient temperature. The heat transfer element may be heated to a temperature of at least 10, 20, 40 or 80 degrees centigrade above ambient temperature. The heat transfer element may be heated to a temperature of between 5 degrees centigrade and 80 degrees centigrade above ambient temperature. The heating may occur before a first puff by the user. Heating of the heat transfer element above ambient temperature advantageously increases the difference between the temperature of the heat transfer element and the temperature of air drawn through airflow channel. This may increase the rate of cooling of the heat transfer element in response to a user puff and so advantageously results in an even more pronounced or sudden drop in temperature of the heat transfer element further improving the speed and reliability of puff detection using the puff detection assembly.

As described above, a heat transfer element having a thermal conductivity greater than that of the airflow channel wall results in heat moving more quickly through the heat transfer element than through the airflow channel wall. This may also be advantageous when heating the heat transfer element above ambient temperature. Such a heat transfer element will heat up above ambient temperature relatively quickly compared to the airflow channel wall which means that the puff detection assembly will be ready for puff detection quickly after the heating process of the heat transfer element has been initiated. It may be particularly preferable to provide a heat transfer element having a thermal diffusivity that is higher than the thermal diffusivity of the airflow channel wall for similar reasons.

The aerosol-generating device may comprise a heating element and, in use and between puffs, the heat transfer element may be heated by the heating element to a temperature of at least 5 degrees centigrade above ambient temperature.

In embodiments where the aerosol-generating device comprises a heater assembly for heating the aerosol-forming substrate received in the chamber, the heater assembly may comprise a heating element. The heating of the heat transfer element may be the result of a transfer of heat from the heating element of the heater assembly to the heat transfer element. In use and between puffs, the heat transfer element may be heated by the heating element to a temperature of at least 5 degrees centigrade above ambient temperature. The heat transfer element may be heated by the heating element to a temperature of at least 10, 20, 40 or 80 degrees centigrade above ambient temperature. The heat transfer element may be heated by the heating element to a temperature of between 5 degrees centigrade and 80 degrees centigrade above ambient temperature. The heat may transfer directly from the heater assembly to the heat transfer element. For example, the heat transfer element may be in contact with the heater assembly and heat may be transferred by conduction with the point of contact between the heater transfer element and the heating element being outside of the chamber. If the heater assembly is part of a cartridge, there may be contact between the heater assembly and the heat transfer element when the cartridge is received in the chamber.

Alternatively, the heater assembly and the heat transfer element may be spaced apart and heat may be transferred by radiation and alternatively or additionally by conduction through other components of the aerosol-generating device between the heater assembly and heater transfer element. The shorter the distance between the heater assembly and the heat transfer element the greater amount of heat transfer from the heater assembly to the heat transfer element. Preferably, the distance between the heater assembly and the heat transfer element is less than 50 millimetres. Even more preferably the distance between the heater assembly and the heat transfer element is less than 10 millimetres or less than 5 millimetres. The distance between the heater assembly and the heat transfer element may be 0 millimetres. The distance between the heater assembly and the heat transfer element may be measured as a minimum distance between a heating element of the heater assembly and the heat transfer element. If the heater assembly is part of a cartridge, the distance between the heater assembly and the heat transfer element may be measured when the cartridge is received in the chamber.

Alternatively or additionally, the puff sensor assembly may comprise a dedicated heating element for heating the heat transfer element. For example, the temperature sensor may be a heatable thermistor. Such a temperature sensor may heat up when supplied with power. The heat from the heatable thermistor may transfer to the heat transfer element in use. A thermistor in contact with the heat transfer element may advantageously cause targeted heating of the heat transfer element. Because the airflow channel wall has a lower thermal conductivity than the heat transfer element, conduction of heat away from the heat transfer element through the airflow channel wall may be relatively low.

Passive heating of the heat transfer element by the heater assembly advantageously has lower power consumption and complexity than active heating by a dedicated heating element, for example when a heatable thermistor is used. However, an active heating arrangement may have the advantage that the puff sensor assembly can be placed anywhere along the length of the airflow channel. An active heating arrangement may also have the advantage that the heat transfer element can be heated before the heater assembly for heating the aerosol-forming substrate is activated. In this way, the heater assembly for heating the aerosol-forming substrate can activated in response to a detected user puff. An active heating arrangement may also be controlled so that the heat transfer element is heated only when the heater assembly for heating the aerosol-forming substrate is not activated. For example, the heat transfer element may be intermittently or periodically heated for to maintain its temperature above a threshold during periods between detected puffs.

It is preferable that, in use, as much heat generated by the heater assembly as possible is absorbed by the aerosol-forming substrate received in the chamber. While it may be advantageous for some of the heat to escape the chamber and be transferred to the heat transfer element, as described above, heat that escapes beyond the heat transfer element to other components of the aerosol-generating device may be considered lost. The airflow channel wall having a thermal conductivity lower than that of the heat transfer element may advantageously reduce heat loss. A suitable material for the airflow channel wall may be a material comprising plastics such as thermoplastics, for example polypropylene, polyetheretherketone (PEEK) and polyethylene. Such materials advantageously have a relatively low thermal conductivity.

The heat transfer element may extend along less than 10 percent of the length of the airflow channel. Preferably, the heat transfer element may extend along less than 5 percent of the length of the airflow channel. The heat transfer element may extend between 2 millimetres and 10 millimetres along the length of the airflow channel. This may advantageously reduce heat loss because only a small proportion of the airflow channel may be defined by the heat transfer element which has a greater thermal conductivity than the airflow channel wall. The airflow channel may then be predominantly defined by the airflow channel wall having a lower thermal conductivity, at least outside the chamber.

The heat transfer element may be embedded in the airflow channel wall. Preferably, the heat transfer element may be press-fit into the airflow channel wall. Such a heat transfer element may effectively be isolated from the chamber by the airflow channel wall such that heat losses by conduction through the heat transfer element are reduced. This may be particularly preferable when the puff sensor assembly comprises a dedicated heater for heating the heat transfer element in use.

The heat transfer element may be press-fit into a portion of the airflow channel wall that defines a channel with a diameter equal to or, preferably, slightly smaller than the heat transfer element before the heat transfer element is pressed into the airflow channel wall. Pressing the heat transfer element into the airflow channel wall may then deform the airflow channel wall slightly such that it may retain the heat transfer element in place after it has been pressed into the airflow channel. The airflow channel wall may comprise a step formed at an abrupt change in diameter of the airflow channel. The heat transfer element may abut the step. Upstream of the heat transfer element, the airflow channel wall may define a tapered airflow channel. The diameter of the airflow channel may decrease in a downstream direction. At its smallest diameter, the airflow channel may have a diameter smaller than the heat transfer element. The tapering of the airflow channel may end with a step increase in the diameter of the channel defined by the airflow channel wall. This step increase may provide a surface against which the heat transfer element can abut when inserted into the airflow channel wall.

The airflow channel wall may comprise an opening. The opening may be adjacent the heat transfer element. The temperature sensor may contact the heat transfer element through the opening.

The thickness of the heat transfer element may be between 0.1 millimetres and 2 millimetres. Preferably, the thickness of the heat transfer element may be between 0.1 millimetres and 0.5 millimetres. Such thicknesses may result in a heat transfer element that has suitable strength to withstand the processes involved in manufacturing the aerosol generating device, particularly when the heat transfer element is press-fit into the airflow channel, while also resulting in a heat transfer element that has a low mass per unit length. The lower the mass per unit length of the heat transfer element, the more rapidly the heat transfer element will cool when air is drawn through the airflow channel during a user puff.

Furthermore, the time taken for a second surface of the heat transfer element, contacted by the temperature sensor, to cool following a user drawing air through the airflow channel may depend on the shortest distance between the temperature sensor and a first surface of the heat transfer element that at least partially defines the second portion of the airflow channel. The shorter this distance, the quicker a drop in temperature may be detected indicative of a user puff. The shortest distance between the temperature sensor and the first surface of the heat transfer element may depend on the thickness of the heat transfer element. For example, if the first surface of the heat transfer element is opposite to the second surface, the shortest distance between the temperature sensor and the second surface of the heat transfer element may be equal to the thickness of the heat transfer element. A thickness of less than 2 millimetres or, preferably, less than 0.5 millimetres may advantageously be suitably low such that cooling is detected by the temperature quickly during a user puff, providing a responsive puff sensor assembly.

As above, a first surface of the heat transfer element may at least partially define the second portion of the airflow channel. The larger the surface area of the first surface, the greater the cooling effect of air passing through the airflow channel during a puff. The surface area of the first surface heat transfer element may preferably be at least 1 , 2, 5, 10 or 20 millimetres squared. The heat transfer element may comprise or consist of a metal. The heat transfer element may comprise or consist of aluminium. Aluminium is particularly preferred as a material with a relatively low density compared to other metals and a thermal conductivity of 247 Watts per metre-Kelvin.

The heat transfer element may be in the form of a sheet having a length, width and thickness. This may advantageously result in a heat transfer element having a large surface area to mass ratio compared to other shapes of heat transfer element promoting rapid cooling of the heat transfer element when air passes over a surface of the heat transfer element. Preferably, the thickness of the heat transfer element may be substantially smaller than the length and the width. For example, the thickness of the heat transfer element may be at least five times smaller than the length and the width. Preferably, the thickness of the heat transfer element may be at least ten times smaller than the length and the width.

The heat transfer element may be tubular. This is another shape of heat transfer element that may have a high surface area to mass ratio. An inner surface of the tubular heat transfer element may at least partially define the second portion of the airflow channel. In other words, the airflow channel may be defined through the heat transfer element. The tubular heat transfer element may surround the airflow channel. When the heat transfer element is tubular, the thickness of the heat transfer element may be the shortest distance between the inner surface of the tubular heat transfer element and an outer surface of the tubular heat transfer element.

A number of preferable features of heat transfer element have been described above. Each improves the responsiveness of the heat transfer element to changes temperature during a user puff, each resulting in a pronounced or sudden drop in temperature of the heat transfer element and so improving the speed and reliability of puff detection by the puff detection assembly. Of course, a heat transfer element combining two or more of these preferable features may result in an even more responsive puff detection assembly.

As described above, the temperature sensor may be in contact with a second surface of the heat transfer element that is different to the first surface of the heat transfer element at least partially defining the second portion of the airflow channel, such that the heat transfer element is between the airflow channel and the temperature sensor. For example, when the heat transfer element is in the form of a sheet, the first surface may be opposite to the second surface. When the heat transfer element is a tubular heat transfer element, an inner surface of the tubular heat transfer element may at least partially define the air flow path and the temperature sensor may be in contact with an outer surface of the tubular heat transfer element. The advantage of such arrangements is that the heat transfer element may protect the temperature sensor from dust, dirt or residues from a received aerosol-forming substrate through the airflow channel.

The aerosol-generating device may comprise a mouthpiece.

Alternatively, the aerosol-generating device may be configured to receive an aerosol generating article, the aerosol-generating article comprising the aerosol-forming substrate at or in the vicinity of a distal end. The aerosol-generating article may comprise a mouthpiece at a proximal end. For example, during operation the aerosol-generating article may be partially received in the chamber of the aerosol-generating device such that the mouthpiece at the proximal end protrudes out of the chamber.

When the aerosol-generating device comprises a heater assembly for heating the aerosol-forming substrate received in the chamber, the heat transfer element may partially define the airflow channel upstream or downstream of the heater assembly. However, it is preferred that the transfer element partially defines the airflow channel upstream of the heater assembly. This is because air in the airflow channel downstream of the heater assembly may be hotter than air in the airflow channel upstream of the heater assembly. This may be a result of heating of the air downstream of the heater assembly having been heated after passing through or by the chamber. So, the cooler air upstream of the heater assembly will advantageously have a greater cooling effect which may result in a more sudden and pronounced drop in temperature of the heat transfer element.

As used herein, the terms ‘upstream’ and ‘downstream’ are used to describe the relative positions of components, or portions of components, of the aerosol-generating device in relation to the direction a fluid passes through the aerosol-generating device during use. The term ‘downstream’ refers to a position relatively closer to the mouth end of the device. The term ‘upstream’ refers to a position relatively further from the mouth end, closer to an opposed end.

The chamber may be a heating chamber. The chamber may have a cylindrical shape. The chamber may have a hollow cylindrical shape. The chamber may be tubular. The chamber may have a circular cross-section. If desirable, the chamber may have a shape deviating from a cylindrical shape or a cross-section deviating from a circular cross-section. The chamber may have a shape corresponding to the shape of the aerosol-generating article to be received in the chamber. The chamber may have an elliptical or rectangular cross- section. The chamber may have a base at an upstream end of the chamber. The base may be circular. One or more air inlets may be arranged at or adjacent the base. The airflow channel may run through the chamber. Downstream of the chamber, a mouthpiece may be arranged between an aerosol-generating article and a user. Alternatively, a user may directly draw on the aerosol-generating article. The airflow channel may extend through the mouthpiece.

The device housing defining the chamber may connect the base of the chamber at the upstream end of the chamber and the downstream end of the chamber. The downstream end of the chamber may be open. The open downstream end may be configured for insertion of the aerosol-generating article.

When the aerosol-generating device comprises a heater assembly comprising a heating element, the heating element may surround the chamber. The heating element may surround the chamber along a portion of the length of the chamber. The heating element may surround a region of the chamber that receives the aerosol-forming substrate. The device housing defining the portion of the chamber that is surrounded by the heating element may be made of a metal, such as stainless steel, or a ceramic. Alternatively, the heating element may be incorporated into the device housing such that the heating element defines part of chamber. The heating element may surround the aerosol-forming substrate received in the chamber.

The chamber may be tubular and the aerosol-generating device may comprise a heater assembly for heating the aerosol-forming substrate received in the chamber. The heater assembly may comprise a heating element that surrounds the exterior of the chamber.

Alternatively, the cartridge may comprise the heating element.

In use, power may be supplied to the heating element, causing the heating element to heat up. The heat may then be transferred to a received aerosol-forming substrate, for example by conduction through the device housing forming the chamber.

In one example, the aerosol-generating device may comprise the heater assembly and the heating element may be a resistive heating element. The heating element may comprise an electrically resistive material. Suitable electrically resistive materials include but are not limited to: semiconductors such as doped ceramics, electrically “conductive” ceramics (such as, for example, molybdenum disilicide), carbon, graphite, metals, metal alloys and composition materials made of ceramic material and a metallic material. Such composite materials may comprise doped and undoped ceramics.

The aerosol-generating device may comprise a power supply which may be configured to supply current to the resistive heating element.

The heating element may comprise a substrate layer of flexible material. The substrate layer may comprise a thermally stable polymer, preferably polyimide.

The heating element may be arranged on the substrate layer. The heating element may be a resistive heating element. The heating element may contain wire connections configured for being connected with a controller of the aerosol-generating device. The heating element may comprise heating tracks arranged on the substrate layer. The heating tracks may comprise a thermally conductive material, preferably a metal such as stainless steel. The heating tracks may be electrically connected to said wire connections.

The heating element may take other forms. For example, a metallic grid or grids, a flexible printed circuit board, a molded interconnect device (MID), ceramic heater, flexible carbon fibre heater or may be formed using a coating technique such as plasma vapour deposition, on a suitably shaped substrate.

In another example, the heater assembly may comprise one or more inductor coils and the heating element may comprise one or more susceptor elements.

The one or more susceptor elements may be configured to be heatable by an alternating magnetic field generated by the inductor coil or coils. In use, electrical power supplied to an inductor coil (for example, by the above-mentioned power source of the device) results in the inductor coil inducing eddy currents in a susceptor element. These eddy currents, in turn, result in the susceptor element generating heat. The electrical power is supplied to the inductor coil as an alternating magnetic field. The alternating current may have any suitable frequency. The alternating current may preferably be a high frequency alternating current. The alternating current may have a frequency between 100 kilohertz (kHz) and 30 megahertz (MHz). When an aerosol-forming substrate is received in the chamber, the heat generated by the susceptor element may heat the aerosol-forming substrate to a temperature sufficient to cause aerosol to evolve from the substrate. The susceptor element is formed of a material having an ability to absorb electromagnetic energy and convert it into heat. By way of example and without limitation, the susceptor element may be formed of a ferromagnetic material, such as a steel.

The aerosol-generating device may comprise the susceptor element. Preferably, the susceptor element may surround the chamber or form at least part of a chamber, as described above, and the inductor coil may be a helical coil that surrounds the susceptor element. Preferably, the inductor coil may surround the susceptor element radially outward of the susceptor element. Locating the inductor coil radially outward of the susceptor portion avoids the inductor coil being damaged by contact with an aerosol-forming substrate during insertion of the article into the chamber.

Alternatively, the susceptor element may be part of a cartridge to be received in the chamber. The cartridge may comprise the susceptor element. The cartridge may also comprise the inductor coil. Alternatively, the aerosol-generating device may comprise the inductor coil. The inductor coil of the aerosol-generating device may be configured such that it surrounds or is adjacent to the susceptor element of the cartridge when the cartridge is received in the chamber. As used herein, a “susceptor” or “susceptor element” means a conductive element that heats up when subjected to a changing magnetic field. This may be the result of eddy currents induced in the susceptor element or hysteresis losses (or both eddy currents induced in the susceptor element and hysteresis losses). Possible materials for the susceptor include graphite, molybdenum, silicon carbide, stainless steels, niobium, aluminium and virtually any other conductive elements. Advantageously the susceptor element is a ferrite element. The material and the geometry for the susceptor element can be chosen to provide a desired electrical resistance and heat generation. The susceptor element may comprise, for example, a mesh, flat spiral coil, fibres or a fabric. Advantageously, the susceptor is in contact with the first aerosol-forming substrate. The susceptor element may advantageously be fluid permeable.

The aerosol-generating device may comprise a controller. The controller may be a microprocessor, which may be a programmable microprocessor, a microcontroller, or an application specific integrated chip (ASIC) or other electronic control circuitry. The controller may be configured to receive signals from the temperature sensor to periodically determine a temperature measured by the temperature sensor. The controller may be configured to detect a user puff based on a drop in the measured temperature. The controller may comprise a memory. The controller may store a count of the number of detected puffs. The count may relate to a particular received aerosol-generating article. The controller may be configured such that, if the number of puffs reaches or exceeds a predetermined number of puffs, the controller may provide a warning signal to the user. The warning signal may, for example, be a haptic, audio or optical signal. The controller may be configured such that, if the number of puffs reaches or exceeds a predetermined number of puffs, it prevents use of the device until the aerosol-generating article has been replaced. Preventing use of the device may be carried out only after a warning signal has been provided. The predetermined number of puffs may relate to an average maximum number of puffs before the aerosol generated from a particular type of aerosol-forming substrate is unsatisfactory as a result of degradation of the substrate. The predetermined number of puffs may depend on the type of substrate that the aerosol-generating device is configured to be used with. For example, if the aerosol-forming substrate is solid substrate comprising tobacco, the predetermined number of puffs may be 14 puffs before the substrate is degraded. The predetermined number of puffs may be determined or selected by a user. The predetermined number of puffs may be determined or selected by a user within a predetermined range.

The controller of the aerosol-generating device may be configured to receive signals from the temperature sensor. The controller may be configured to repeatedly determine a measured temperature of the temperature sensor. The controller may be configured to detect a user puff based on a drop in the measured temperature.

The controller may be configured to increase a supply of power to the heater assembly in response to a detected puff. For example, the heater assembly for heating the aerosol-forming substrate may be supplied with a first power between user puffs, but may be supplied with a second power, higher than the first power, during a detected user puff or for a predetermined time period following a detected user puff.

As described previously, the aerosol-generating device may comprise a power supply. The power supply may be a DC power supply having a DC supply voltage in the range of about 2.5 Volts to about 4.5 Volts and a DC supply current in the range of about 1 Amp to about 10 Amps (corresponding to a DC power supply in the range of about 2.5 Watts to about 45 Watts). The power supply may be a battery, such as a rechargeable lithium ion battery. Alternatively, the power supply may be another form of charge storage device such as a capacitor. The power supply may be rechargeable. The power supply may have a capacity that allows for the storage of enough energy for one or more uses of the aerosol generating device. 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.

As described above, the power supply may be configured to supply an alternating current. In such case, the aerosol-generating device may advantageously comprise a direct current to alternating current (DC/ AC) inverter for converting a DC current supplied by the DC power supply to an alternating current. The DC/AC converter may comprise a Class-D or Class-E power amplifier. The power supply may be configured to provide the alternating current.

The power supply may be connectable to the heater assembly. Advantageously, the power supply may be controllable by the controller. In particular, the controller may be configured such that, if the count stored in the memory of the controller exceeds the predetermined number of puffs, the power supply is prevented from supplying power to the heater assembly.

The controller may comprise a band-pass filter. The band-pass filter may be configured to filter the signals received from the temperature sensor. The band-pass filter may advantageously be configured to remove from the signal frequencies above 100 Flz. Such frequencies may correspond to electrical noise. The band-pass filter may advantageously be configured to remove signal frequencies below 0.2 Flz. This may remove slow variations in temperature from the signal that may not correspond to a puff. The heat transfer element may comprise a thermal paste that is in contact with the temperature sensor. The thermal paste may advantageously ensure contact between the heat transfer element and the temperature sensor. The thermal paste is advantageously electrically insulating. Thermal paste typically consists of a polymerizable liquid matrix and large volume fractions of electrically insulating, but thermally conductive filler.

The aerosol-generating device may be an electrically operated smoking device. The device may be a handheld aerosol-generating device. The aerosol-generating device may have a size comparable to a conventional cigar or cigarette. The aerosol-generating device may have a total length between 30 mm and 150 mm. The aerosol-generating device may have an external diameter between 5 mm and 30 mm.

In a second aspect there is provided an aerosol-generating system. The aerosol generating system may comprise an aerosol-generating device according to the first aspect. The aerosol-generating system may comprise a heater assembly for heating an aerosol forming substrate received in the chamber.

The aerosol-generating system may comprise an aerosol-generating article. The aerosol-generating article may comprise an aerosol-forming substrate. The aerosol generating article may be received in the chamber.

The aerosol-generating article may comprise a rod comprising the aerosol-forming substrate. The rod may be circumscribed by a wrapper. The aerosol-forming substrate may comprise tobacco.

As used herein, the term ‘aerosol-forming substrate’ relates to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds may be released by heating the aerosol-forming substrate. An aerosol-forming substrate may conveniently be part of an aerosol-generating article or smoking article.

The aerosol-forming substrate may be a solid aerosol-forming substrate. Alternatively, the aerosol-forming substrate may comprise both solid and liquid components. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds which are released from the substrate upon heating. Alternatively, the aerosol-forming substrate may comprise a non-tobacco material. The aerosol-forming substrate may further comprise an aerosol former that facilitates the formation of a dense and stable aerosol. Examples of suitable aerosol formers are glycerine and propylene glycol.

In a particularly preferred embodiment, the aerosol-forming substrate comprises a gathered crimpled sheet of homogenised tobacco material. As used herein, the term ‘crimped sheet’ denotes a sheet having a plurality of substantially parallel ridges or corrugations. The aerosol-generating system may comprise a cartridge containing an aerosol forming substrate. The cartridge may be receivable in the chamber of the aerosol-generating device. The aerosol-forming substrate may be solid or liquid or comprise both solid and liquid components. Preferably, the aerosol-forming substrate is a liquid.

The aerosol-forming substrate may comprise plant-based material. The aerosol forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. Preferably, the aerosol-forming substrate may alternatively comprise a non-tobacco-containing material.

The cartridge may comprise a heating element, for example a resistive heating element or a susceptor element. The heating element may be fluid permeable. In use, vapourised aerosol-forming substrate may pass through the fluid permeable element and subsequently cool to form an aerosol delivered to a user. Preferably, the cartridge comprises a cartridge housing configured to engage the chamber of the aerosol-generating device in use. The cartridge housing may have an external surface surrounding the aerosol-forming substrate contained by the cartridge. At least a portion of the external surface may be formed by the fluid permeable heating element. The portion of the external surface formed by the fluid permeable heating element may be in fluid communication with air flowing through airflow channel of the aerosol-generating device in use and when the cartridge is received in the chamber of the aerosol-generating device. Therefore, in use, the vapourised aerosol forming substrate may pass from the cartridge to the airflow channel through the heating element and subsequently cool in the airflow channel to form an aerosol delivered to a user.

As used herein a “fluid permeable” element means an element that allowing liquid or gas to permeate through it. The heating element may have a plurality of openings formed in it to allow fluid to permeate through it. In particular, the heating element allows the aerosol forming substrate, in either gaseous phase or both gaseous and liquid phase, to permeate through it.

In a third aspect there is provided a method of detecting a user puffing on an aerosol generating system. In particular, a method of detecting a user puffing on the aerosol generating system of the second aspect is provided. For example, a user may puff on the aerosol-generating device. A user may puff on a mouthpiece of the aerosol-generating device. Alternatively, a user may puff on a mouthpiece of an aerosol-generating article containing aerosol-forming substrate, received in the aerosol-generating device. The article may be received in a chamber of the aerosol-generating device.

The method may comprise receiving an aerosol-forming substrate in the chamber of the aerosol-generating device. The method may comprise heating the received aerosol- forming substrate. The method may comprise heating the heat transfer element. The method may comprise receiving signals from the temperature sensor at a controller of the aerosol generating device to repeatedly determine a measured temperature of the temperature sensor. The method may comprise detecting a user puff based on a drop in the measured temperature.

The step of heating the heat transfer element may comprise supplying power to a heater assembly comprising a heating element used to heat the received aerosol-forming substrate. The aerosol-generating device may preferably comprise the heater assembly. The aerosol-generating device may preferably comprise the heating element.

Alternatively, the puff sensor assembly may comprise a heating element for heating the heat transfer element. The step of heating the heat transfer element may comprise using the heating element of the puff sensor assembly to heat the heat transfer element.

In use and between puffs, the heat transfer element may be heated to a temperature of at least 5, 10, 20, 40 or 80 degrees centigrade above ambient temperature. The heat transfer element may be heated to a temperature of between 5 degrees centigrade and 80 degrees centigrade above ambient temperature.

The method may further comprise the step of filtering out fluctuations in the temperature measurements not indicative of a user puff using a band-pass filter.

In a fourth aspect there is provided an aerosol-generating device for generating an aerosol from an aerosol-forming substrate, the aerosol-generating device comprising: a device housing defining a chamber for receiving the aerosol-forming substrate; a heater assembly comprising a heating element for heating the aerosol-forming substrate received in the chamber to generate an aerosol; an airflow channel extending from an air inlet in the device housing and through or in fluid communication with the chamber; and a puff sensor assembly outside of the chamber and comprising a temperature sensor, a portion of the puff sensor assembly partially defining the airflow channel; wherein the heating element is configured such that in use, and between puffs, the puff sensor assembly is heated to a temperature of at least 5degrees centigrade above ambient temperature.

The heating element may be configured such that in use, and between puffs, the puff sensor assembly is heated to a temperature of at least 10, 20, 40 or 80 degrees centigrade above ambient temperature. The heating element may be configured such that in use, and between puffs, the puff sensor assembly is heated to a temperature of between 5 degrees centigrade and 80 degrees centigrade above ambient temperature The aerosol-generating device may operate similarly to the aerosol-generating device of the first aspect, in that the puff sensor assembly may be used to detect puffs based on a reduction in the temperature detected by the puff sensor assembly. In particular, the puff sensor assembly may comprise a temperature sensor and a heat transfer element. The temperature sensor may be in contact with the heat transfer element. A first portion of the airflow channel may be at least partially defined by an airflow channel wall. A second portion of the airflow channel may be at least partially defined by the heat transfer element. In use, reductions in the detected temperature of the heat transfer element may be detected by the temperature sensor following a user drawing air through the airflow channel during use, as described in relation to the first aspect.

The heating of the puff sensor assembly by at least 5 degrees centigrade above ambient temperature advantageously increases the difference between the temperature of the puff sensor assembly and air passing through airflow channel in use. This increases the rate of cooling of the puff sensor assembly in response to a user puff and so advantageously results in a pronounced or sudden drop in temperature of the puff sensor assembly, improving the speed and reliability of puff detection by the aerosol-generating device. A greater temperature difference may provide a greater rate of cooling.

Because the heating of the puff sensor assembly is by a heater assembly comprising a heating element for heating the aerosol-forming substrate received in the chamber, rather than a dedicated heater that is part of the puff sensor assembly, the power consumption of the puff sensor assembly itself is minimal. Furthermore, the puff sensor assembly can be manufactured more simply and cheaply than a puff sensor assembly comprising a heating element in addition to the heating element of the heater assembly.

Features described in relation to one aspect may be applied to other aspects of the disclosure. In particular advantageous or optional features described in relation to the first aspect of the disclosure may be applied to the second, third and fourth aspects of the invention. For example, the advantageous or options features of the puff sensor assembly and, in particular, the heat transfer element of the puff sensor assembly described in relation to the aerosol-generating device of the first aspect can be applied to the aerosol-generating device of the fourth aspect.

The invention is defined in the claims. Flowever, below there is provided a non- exhaustive list of non-limiting examples. Any one or more of the features of these examples may be combined with any one or more features of another example, embodiment, or aspect described herein.

EX1 . An aerosol-generating device for generating an aerosol from an aerosol forming substrate, the aerosol-generating device comprising: a device housing defining a chamber for receiving the aerosol-forming substrate; an airflow channel extending from an air inlet in the device housing and through, or in fluid communication with, the chamber; and a puff sensor assembly comprising a heat transfer element and a temperature sensor in contact with the heat transfer element; wherein a first portion of the airflow channel is at least partially defined by an airflow channel wall and a second portion of the airflow channel is at least partially defined by the heat transfer element, the second portion of the airflow channel being adjacent to the first portion and outside of the chamber.

EX2. An aerosol-generating device according to example EX1 , wherein the heat transfer element has a thermal conductivity that is greater than the airflow channel wall.

EX3. An aerosol-generating device according to example EX1 or EX2, wherein the heat transfer element has a thermal diffusivity that is greater than the airflow channel wall.

EX4. An aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device comprises a heater assembly for heating the aerosol-forming substrate received in the chamber.

EX5. An aerosol-generating device according to any of examples EX1 to EX3, wherein chamber is configured for receiving a cartridge containing an aerosol-forming substrate wherein the cartridge comprises a heater assembly.

EX6. An aerosol-generating device according to any one of the preceding examples wherein, in use, air is drawn through the airflow channel by a user puffing on the aerosol generating device or on an aerosol-generating article received in the device and containing the aerosol-forming substrate.

EX7. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element has a thermal conductivity of at least 100 Watts per metre-Kelvin.

EX8. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element has a thermal conductivity not more than 300

Watts per metre-Kelvin.

EX9. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element has a thermal diffusivity of at least 50 millimetres squared per second, preferably greater than 60, 70, 80 or 90 millimetres squared per second. EX10. An aerosol-generating device according to any one of the preceding examples, wherein, when the aerosol-generating device is in use, the heat transfer element is heated above ambient temperature.

EX11 . An aerosol-generating device according to any one of the preceding examples, wherein in use and between puffs, the heat transfer element is heated to a temperature of at least 5, 10, 20, 40 or 80 degrees centigrade above ambient temperature.

EX12. An aerosol-generating device according to example EX10 or EX11 , wherein the heating occurs before a first puff by the user.

EX13. An aerosol-generating device according to any one of the preceding examples, comprising a heater assembly comprising a heating element wherein, in use and between puffs, the heat transfer element is heated by the heating element to a temperature of at least 5, 10, 20, 40 or 80 degrees centigrade above ambient temperature.

EX14. An aerosol-generating device according to example EX13, wherein the distance between the heat transfer element and heating element is less than 50 millimetres.

EX15. An aerosol-generating device according to example EX13 or EX14, wherein the distance between the heater assembly and the heat transfer element is less than 10 millimetres or less than 5 millimetres.

EX16. An aerosol-generating device according to any of examples EX13 to EX15, wherein the heat transfer element is in contact with the heater assembly.

EX17. An aerosol-generating device according to any of examples EX13 to EX16, wherein the puff sensor assembly comprises a heating element for heating the heat transfer element.

EX18. An aerosol-generating device according to example EX17, wherein the temperature sensor is a heatable thermistor.

EX19. An aerosol-generating device according to any one of the preceding examples, wherein the airflow channel wall is formed of material comprising plastics such as thermoplastics.

EX20. An aerosol-generating device according to example EX19, wherein the airflow wall is formed of polypropylene, polyetheretherketone (PEEK) or polyethylene.

EX21. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element extends along less than 10 percent of the length of the airflow channel.

EX22. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element extends along less than 5 percent of the length of the airflow channel. EX23. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element extends between 2 millimetres and 10 millimetres along the length of the airflow channel.

EX24. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element is embedded in the airflow channel wall.

EX25. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element is press-fit into the airflow channel wall.

EX26. An aerosol-generating device according to example EX25, wherein the heat transfer element is press-fit into a portion of the airflow channel wall that defines a channel with a diameter equal to or, preferably, slightly smaller than the heat transfer element.

EX27. An aerosol-generating device according to any one of the preceding examples, wherein the airflow channel defined by the airflow channel wall is tapered upstream of the heat transfer element.

EX28. An aerosol-generating device according to any one of the preceding examples, wherein the airflow channel wall comprises an opening.

EX29. An aerosol-generating device according to any example EX28, wherein the opening is adjacent the heat transfer element.

EX30. An aerosol-generating device according to example EX28 or EX29, wherein the temperature sensor is received through the opening such that it is in contact with the heat transfer element.

EX31. An aerosol-generating device according to any one of the preceding examples, wherein the thickness of the heat transfer element is between 0.1 millimetres and 2 millimetres.

EX32. An aerosol-generating device according to any one of the preceding examples, wherein the thickness of the heat transfer element is between 0.1 millimetres and 0.5 millimetres.

EX33. An aerosol-generating device according to any one of the preceding examples, wherein a first surface of the heat transfer element at least partially defines the second portion of the airflow channel.

EX34. An aerosol-generating device according to example EX33, wherein the temperature sensor is in contact with a second surface of the heat transfer element that is different to the first surface of the heat transfer element such that the heat transfer element is between the airflow channel and the temperature sensor.

EX35. An aerosol-generating device according to example EX33 or EX34, wherein the first surface is opposite to the second surface. EX36. An aerosol-generating device according to any of examples EX33 to EX35, wherein the surface area of the first surface heat transfer element is at least 1 , 2, 5, 10 or 20 millimetres squared.

EX37. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element is comprises or consists of a metal.

EX38. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element comprises or consists of aluminium.

EX39. An aerosol-generating device according to any one of the preceding examples, wherein the heat transfer element is in the form of a sheet having a length, width and thickness.

EX40. An aerosol-generating device according to any one of examples EX1 to EX38, wherein the heat transfer element is tubular.

EX41. An aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device comprises a mouthpiece.

EX42. An aerosol-generating device according to any one of examples EX1 to EX40, wherein the aerosol-generating device is configured to receive an aerosol-generating article, the aerosol-generating article comprising an aerosol-forming substrate at or in the vicinity of a distal end, the aerosol-generating article comprising a mouthpiece at a proximal end.

EX43. An aerosol-generating device according to any one of the preceding examples, wherein the transfer element partially defines the airflow channel upstream of the heater assembly.

EX44. An aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device comprises a heater assembly comprising a heating element, the heating element surrounding the chamber.

EX45. An aerosol-generating device according to example EX44, wherein the device housing defining the portion of the chamber that is surrounded by the heating element is made of a metal, such as stainless steel, or a ceramic.

EX46. An aerosol-generating device according to any of examples EX1 to EX43, wherein the heating element is incorporated into the device housing such that the heating element defines part of chamber.

EX47. An aerosol-generating device according to any one of the preceding examples, further comprising a controller.

EX48. An aerosol-generating device according to example EX47, wherein the controller comprises a band-pass filter configured to filter the signals received from the temperature sensor. EX49. An aerosol-generating device according to example EX48, wherein the band pass filter is configured to remove from the signal frequencies above 100 Hz.

EX50. An aerosol-generating device according to examples EX48 or EX49, wherein the band-pass filter is configured to remove signal frequencies below 0.2 Hz.

EX51. An aerosol-generating device according to any one of the preceding examples, the heat transfer element comprises a thermal paste that is in contact with the temperature sensor.

EX52. An aerosol-generating device according to any one of the preceding examples that is an electrically operated smoking device.

EX53. An aerosol-generating device according to any one of the preceding examples, wherein the aerosol-generating device is a handheld aerosol-generating device.

EX54. An aerosol-generating system comprising an aerosol-generating device according to any one of the preceding examples and an aerosol-generating article comprising an aerosol-forming substrate, the aerosol-generating article being receivable in the chamber.

EX55. An aerosol-generating system according to example EX57, the system comprising an aerosol-generating article.

EX56. An aerosol-generating system according to example EX58, wherein the aerosol-generating article comprises the aerosol-forming substrate.

EX57. An aerosol-generating system according to example EX55 or EX56 wherein the aerosol-generating article comprises a rod comprising the aerosol-forming substrate.

EX58. An aerosol-generating system according to example EX57, wherein the rod is circumscribed by a wrapper.

EX59. An aerosol-generating system according to example EX54, wherein the aerosol-generating system comprises a cartridge containing an aerosol-forming substrate.

EX60. An aerosol-generating system according to example EX59, wherein the cartridge is receivable in the chamber of the aerosol-generating device.

EX61. An aerosol-generating system according to example EX62 or EX63, wherein the aerosol-forming substrate is a solid or liquid or comprise both solid and liquid components.

EX62. An aerosol-generating system according to example EX59 or EX60, wherein the aerosol-forming substrate is a liquid.

EX63. An aerosol-generating system according to any one of examples EX59 to EX62, wherein the cartridge comprises a heating element, for example a resistive heating element or a susceptor element. EX64. An aerosol-generating system according to example E63, wherein the heating element is fluid permeable.

EX65. A method of detecting a user puffing on the aerosol-generating system of any of examples EX54 to EX64, the method comprising: receiving an aerosol-forming substrate in a chamber of the aerosol-generating device; heating the received aerosol-forming substrate; heating the heat transfer element; receiving signals from the temperature sensor at a controller of the aerosol generating device to repeatedly determine a measured temperature of the temperature sensor; and detecting a user puff based on a drop in the measured temperature.

EX66. A method according to example EX65, wherein the step of heating the heat transfer element comprises supplying power to a heater assembly comprising a heating element used to heat the received aerosol-forming substrate.

EX67. A method according to example EX65, wherein the puff sensor assembly may comprise a heating element for heating the heat transfer element and the step of heating the heat transfer element comprises using the heating element of the puff sensor assembly to heat the transfer element.

EX68. A method according to any one of examples EX65 to EX67, wherein in use and between puffs, the heat transfer element is heated to a temperature of at least 5, 10, 20, 40 or 80 degrees centigrade above ambient temperature.

EX69. A method according to any one of examples EX65 to EX68 further comprising the step of filtering out fluctuations in the temperature measurements not indicative of a user puff using a band-pass filter.

EX70. An aerosol-generating device for generating an aerosol from an aerosol forming substrate, the aerosol-generating device comprising: a device housing defining a chamber for receiving the aerosol-forming substrate; a heater assembly comprising a heating element for heating the aerosol-forming substrate received in the chamber to generate an aerosol; an airflow channel extending from an air inlet in the device housing and through or in fluid communication with the chamber; and a puff sensor assembly outside of the chamber and comprising a temperature sensor, a portion of the puff sensor assembly partially defining the airflow channel; wherein the heating element is configured such that in use, and between puffs, the puff sensor assembly is heated to a temperature of at least 5, 10, 20, 40 or 80 degrees centigrade above ambient temperature.

Features described in relation to one example or embodiment may also be applicable to other examples and embodiments.

Examples will now be further described with reference to the figures in which:

Figure 1 shows a schematic of a cross-sectional view of a first aerosol-generating device comprising a puff sensor assembly and an aerosol-generating article received in a chamber of the device;

Figure 2 shows a cross-sectional view of the puff sensor assembly and an airflow channel of the aerosol-generating device of Figure 1 ;

Figure 3 shows a horizontal cut through of the puff sensor assembly and airflow channel of Figure 2;

Figure 4 shows a cross-section of an airflow channel wall of the aerosol-generating device of Figure 1 with a heat transfer element prior to being press fit into the airflow channel wall;

Figure 5 shows a similar cross-section of the airflow channel wall after the heat transfer element has been press fit and with a temperature sensor in place;

Figure 6 illustrates a method of detecting a user puffing on the aerosol-generating device of Figure 1 ;

Figure 7 shows a schematic of a cross-sectional view of a second aerosol-generating device comprising an inductive heater assembly;

Figure 8 shows a schematic of a cross-sectional view of a third aerosol-generating device comprising a heater assembly comprising a heating element that extends upstream of the chamber to contact the puff sensor assembly; and

Figure 9 shows a schematic of a cross-sectional view of a fourth aerosol-generating device comprising a chamber configured for receiving a cartridge comprising an aerosol forming substrate and a cartridge received in the chamber.

Figure 1 is a schematic of a cross sectional view of a first aerosol-generating device 100. The aerosol-generating device 100 comprises a chamber 10 defined by a device housing 11. The chamber 10 is tubular, made of a stainless steel and has at an upstream end a base 12. The chamber 10 is configured for receiving an aerosol-generating article 200.

An aerosol-generating article 200 received in the chamber 10. The aerosol generating article 200 contains an aerosol-forming substrate 202. The aerosol-forming substrate is a solid tobacco-containing substrate. In particular, the aerosol-forming substrate is a gathered sheet of homogenised tobacco. As shown in Figure 1 , the aerosol-generating article and chamber are configured such that a mouth end of the aerosol-generating article 200 protrudes out of the chamber 10 and out of the aerosol-generating device when the aerosol-generating article is received in the chamber. This mouth end forms a mouthpiece 204 on which a user of the aerosol-generating device may puff in use.

An aerosol-generating device 100 together with an aerosol-generating article 200 may be referred to as an aerosol-generating system.

The aerosol-generating device 100 comprises a heater assembly comprising a heating element 110. The heating element 110 surrounds the chamber 10 along a portion of the chamber in which the aerosol-forming substrate 202 of the aerosol-generating article 200 is received. In an alternative embodiment, the heating element 110 forms the portion of the chamber wall that defines the part of the chamber that receives the aerosol-forming substrate. The heating element 110 is a resistive heating element.

An airflow channel 120 extends from an air inlet 122 of the aerosol-generating device 100. Upstream of the chamber, the airflow channel 120 is primarily defined by an airflow channel wall 124. Downstream of the airflow channel wall 124, the airflow channel 120 passes through an air inlet defined in the base 12 of the chamber. The airflow channel 120 then extends through the chamber 10.

The aerosol-generating device 100 further comprises a puff sensor assembly. The puff sensor assembly comprises a heat transfer element 132. The heat transfer element 132 is annular. An inner, or first, surface of the heat transfer element 132 defines a portion of the airflow channel 120 upstream of the chamber and heater assembly. This portion of the airflow channel 120 defined by the heat transfer element 132 is adjacent to portions of the airflow channel defined by the airflow channel wall 124, as shown in Figure 1. The heat transfer element 132 has a thickness of 0.8 millimetres and a length of 5 millimetres and an inner circumference of 30mm. The heat transfer element 132 is made of aluminium.. The heat transfer element is press fit into the airflow channel wall 124.

The puff sensor assembly and the airflow channel wall 124 are shown more clearly in Figures 2 and 3. Figure 2 is a cross-sectional view of the puff sensor assembly and airflow channel wall 124 from above. Figure 3 is a horizontal cut through of the puff sensor assembly and airflow channel wall 124. Figure 3 shows only a part of the airflow channel. It does not show the full extent of the airflow channel wall 124 upstream of the heat transfer element or the chamber 10 downstream of the heat transfer element.

The airflow channel wall 124 is made of polyetheretherketone (PEEK). The thermal conductivity and thermal conductivity of PEEK are considerably lower than aluminium. So, the heat transfer element 132 has a thermal conductivity and thermal diffusivity that is greater than the corresponding parameters for the airflow channel wall 124. The puff sensor assembly further comprise a temperature sensor 134 in contact with the heat transfer element 132. In particular, the temperature sensor 134 is in contact with the outer, or second, surface of the tubular heat transfer element 132. This second surface is opposite the first surface such that the heat transfer element is between the airflow channel and the temperature sensor. Therefore, the heat transfer element 132 protects the temperature sensor 134 from any dust and dirt passing through or in the airflow channel.

The temperature sensor 134 comprises a housing 136, electrical connections 138 and a sensing element 138. The temperature sensor is a negative temperature coefficient (NTC) thermistor. This is shown more clearly in Figure 3. The temperature sensor 134 is connected to a controller 140 of the aerosol-generating device.

Figures 4 and 5 show how the heat transfer element 132 is press fit into the airflow channel wall 124. Figure 4 shows a cross-section of the airflow channel wall 124 with the heat transfer element 132 about to be press fit. Figure 5 shows a similar cross-section of the airflow channel wall 124 after the heat transfer element 132 has been press fit and with the temperature sensor 134 in place.

Figures 4 and 5 show how an upstream portion 127 of the airflow channel wall 124 defines a tapered airflow channel 122 with a diameter that decreases in a downstream direction. The tapering of the airflow channel 122 ends with a step increase 129 in diameter of the channel defined by the inner surface of the airflow channel wall 124. The inner surface of a downstream portion 131 of the airflow channel wall 124, downstream of the step increase in diameter, defines a channel having an inner surface with a diameter that remains constant.

The diameter of the airflow channel defined by the downstream portion 131 of the airflow channel wall 124 is slightly smaller than the diameter of the tubular heat transfer element 132. Thus, when the heat transfer element 132 is inserted into the downstream portion 131 , in the direction shown by the arrow in Figure 4, the airflow channel wall 124 must deform slightly to accommodate the heat transfer element. An airflow channel 132 formed of PEEK is suitably flexible and resilient to allow for this deformation and to push against the inserted heat transfer element 132, holding it in place. In the manufacturing of the device, the heat transfer element 132 is pushed into the downstream portion of the airflow channel wall 124 such that it abuts the step formed by the step change in diameter of the inner surface of the airflow channel wall 124.

The airflow channel wall 124 further comprises an opening 125 in the downstream portion. This opening 125 is for receiving the temperature sensor 134 such that the sensing element 138 of the temperature sensor 134 is in contact with the heat transfer element 132.

The aerosol-generating device 100 further comprises a power supply 142 in form of a rechargeable battery for powering the heating element 20 controllable by the controller 140. The power supply is connected to the controller and the heating element 110 via electrical wires and connections that are not shown in the Figures. The aerosol-generating device may comprise further elements, not shown in the Figures, such as a button for activating the aerosol-generating device.

A method of detecting a user puffing on the aerosol-generating device 100 is described in relation to Figure 6. Figure 6 is a flow chart showing the steps of the method. At step 502 a user of the aerosol-generating device 100 inserts an aerosol-forming substrate 202 into the chamber of the aerosol-generating device 100. As described above, the aerosol forming substrate 202 is contained an aerosol-generating article 200, so step 502 comprises inserting the article 200 into the chamber 10 of the device such that the aerosol-forming substrate 202 is received in a portion of the chamber 10 surrounded by the heating element 110, as shown in Figure 1 .

At step 504, the received aerosol-forming substrate 102 is heated. This is following a user of the aerosol-generating device turning the device on, for example using a button or switch on the aerosol-generating device. This causes the controller 140 to supply electrical power from the power supply 142 to the heating element 110 such that an electrical current passes through the heating element 110 causing the heating element 110 to heat up. Fleat is transferred to the aerosol-forming substrate such that volatile compounds are vaporised from the aerosol-forming substrate.

At step 506, the heat transfer element is heated. In the aerosol-generating device 100 this is achieved by the radiation of heat from the heating element 110 and by the conduction of heat through the portion of airflow channel wall 124 that separates the heat transfer element 132 from the heating element 110 (after the device has been turned on). The heating of the heat transfer element by the heating element 110 is particularly effective because the distance between the heat transfer element and the heating element 110 is 5 millimetres.

In some embodiments, the heat transfer element 132 is additionally or alternatively provided by the temperature sensor 134 itself. For example, the temperature sensor may be a self-heating thermistor connected to the power supply 142 which may be configured to pass a current through the thermistor causing it to heat up. That heat is then be conducted to the heat transfer element 132.

At step 508, signals are received from the temperature sensor 134 at the controller 140. The controller 140 can then determine a measured temperature of the temperature sensor based on this signal. In particular, when the temperature sensor 134 is a thermistor, the signal can be related to the resistance of the thermistor. The resistance of a thermistor is highly dependent on temperature with an increase in temperature of the thermistor resulting in either an increase or decrease of resistance depending on whether the thermistor has a positive or negative temperature co-efficient. So, in such embodiments, the controller 140 can receive a signal related to the resistance of the thermistor which is used to infer the temperature of the thermistor.

At step 510, a user puff is detected based on a drop in the measured temperature by the controller 140, the temperature being repeatedly determined as per step 508.

Before the device is switched on the temperature measured by the temperature sensor 134 will be low. It will be equal to or close to room temperature if the device has not been used recently. Following the switching on of the device, the measured temperature will rapidly increase as the heat transfer element 132 is heated by the heating element 110. Once the device reaches operating temperature, the temperature measured by the temperature sensor 134 will become steady as the heat transfer element 132 reaches a steady state.

In use of the aerosol-generating device 100, a user will puff on the mouthpiece 204 of the received aerosol-generating article 200 resulting in air being drawn through the airflow channel 120 towards the user’s mouth. During a puff, air will be drawn from outside of the aerosol-generating device into the airflow channel 120 through air inlet 122. The air will be drawn through the portions of the airflow channel defined by the airflow channel wall 124 and the heat transfer element 132, through the air inlet defined in the base 12 of the chamber 10 and into the chamber. Because the aerosol-generating article 200 is received in the chamber, the air drawn into the chamber with enter the aerosol-generating article 200 at its distal end. Thus, the air passes through the aerosol-forming substrate 202. In doing so, volatile compounds generated by the heating of the substrate 202 will become entrained in the air. As the air continues towards the mouth end of the aerosol-generating article 200, the volatile compounds cool to form an aerosol. The direction of airflow through the aerosol-generating device, and the aerosol-generating article, is represented in Figure 1 by the dashed arrow.

During a puff, air drawn through the airflow channel 120 will cool the warm inner surface of the airflow channel 120. The aluminium of the heat transfer element 132 has a much higher thermal conductivity and thermal diffusivity than the PEEK of the airflow channel wall 124. So, the heat transfer element 132 cools down more rapidly than the airflow channel wall 124 in response to a user puff. The cooling also spreads quickly through the heat transfer element 132 and so a drop in measured temperature is rapidly detected by the temperature sensor 134 and controller. The dimensions of the heat transfer element 132 has a thickness of 0.5 millimetres and has a length such that it extends 4 millimetres along the length of the airflow channel. A tubular heat transfer element having such dimensions advantageously has a relatively low mass and a relatively high surface area to mass ratio or surface area to volume ratio. So, during a puff, there is a pronounced and rapid drop in the temperature of the heat transfer element 132 as measured by the temperature sensor 134. The controller 140 uses such drops in temperature to reliably and accurately detect a user puff.

The controller 140 comprises a memory, not shown, that stores a count of the number of detected puffs. Each time a puff is detected, the count is increased by one. The memory also stores a predetermined value representing the maximum number of times a user can puff on the aerosol-forming substrate 202 before it is degraded. The controller 140 is configured such that, if the number of puffs of the count reaches or exceeds the predetermined value, the controller prevents use of the device until the aerosol-generating article has been replaced.

The controller 140 comprises a bandpass filter, not shown, to filter the signals received from the temperature sensor. The band-pass filter removes from signal frequencies above 100 Hz and signal frequencies below 0.2 Hz.

Figure 7 is a schematic of a cross sectional view of a second aerosol-generating device 400. The second aerosol-generating device 400 operates in a similar manner to the first aerosol-generating device 100. Identical numbering has been used for features of the second aerosol-generating device 400 that correspond to features of the first aerosol generating device 100. For example, the puff sensor assembly in both devices is identical.

The difference between the second aerosol-generating device 400 and the first aerosol-generating device 100 is that the second aerosol-generating device 400 comprises an inductive heater assembly comprising a susceptor element 402 and an inductor coil 404. The susceptor element 402 surrounds the chamber 10 along a portion of the chamber in which the aerosol-forming substrate 202 of the aerosol-generating article 200 is received. In an alternative embodiment, the susceptor element 402 forms the portion of a chamber wall that defines the part of the chamber that receives the aerosol-forming substrate.

The inductor coil 404 surrounds the susceptor element. The inductor coil 404 in this embodiment is a helical inductor coil.

In the second aerosol-generating device 400, the power supply 142 is configured to supply an alternating current to the inductor coil 404 when the device is in use. The alternating current is a high frequency alternating current. This results in heating of the susceptor element 402 and that heat is transferred to a received aerosol-forming substrate 202 to cause volatile compounds to be generated in the same way as the resistive heating element 110 as described above in relation to step 504 of Figure 6.

Figure 8 is a schematic of a cross sectional view of a third aerosol-generating device 500. Again, the third aerosol-generating device 500 operates in a similar manner to the first aerosol-generating device 100. Identical numbering has been used for features of the third aerosol-generating device 500 that correspond to features of the first aerosol-generating device 100.

Like the first aerosol-generating device 100, the third aerosol-generating device 500 comprises a resistive heater assembly. However, in the third aerosol-generating device 500, the resistive heating element 502 does not just surround the chamber. The resistive heating element 502 also extends beyond the chamber, upstream of the base 12. The heat transfer element 504 is identical to the heat transfer element 132 in terms of physical characteristics such as material properties and size. However, in the third aerosol-generating device 500, the heat transfer element 504 is positioned immediately upstream of the base 12 of the chamber 10. As such, the resistive heating element 502 is in contact with the heat transfer element 504. In use of the aerosol-generating device 500, the heat transfer element 504 is heated by the resistive heating element 502.

In some embodiments, the resistive heating assembly may be replaced with an inductive heating assembly in which the susceptor element extends upstream of the chamber to contact the heat transfer element.

Figure 9 is a schematic of a cross sectional view of a fourth aerosol-generating device 600. The fourth aerosol-generating device 600 comprises a chamber 610 configured to receive a cartridge containing aerosol-forming substrate, rather than an aerosol-generating article. The aerosol-generating device 600 receives a cartridge 700. The cartridge 700 comprises a cartridge housing 704 having an external surface surrounding and containing a liquid aerosol-forming substrate 702. The liquid substrate, in some embodiments, is held in a capillary material, not shown. As shown in Figure 9, the cartridge 700 is completely contained by the aerosol-generating device 600 when received in the chamber. In order to insert and remove the cartridge 700 from the chamber 610, the aerosol-generating device 600 comprises a means for accessing the chamber, not shown. For example, a top portion of the aerosol-generating device 600 may be hinged allowing it to be opened to access the chamber and closed to close the chamber, holding the cartridge 700 within the chamber 610.

The fourth aerosol-generating device 600 comprises an airflow channel 620 that extends from an air inlet 622 of the aerosol-generating device 600. The airflow channel 620 is primarily defined by an airflow channel wall 624. An opening 625 is provided in the airflow channel wall 624 corresponding to the chamber 610. After passing the opening 625, the airflow channel 620 extends through a mouthpiece 623 which, unlike in previously described aerosol-generating devices, is part of aerosol-generating device 600. In use, a user draws on the mouthpiece 623 when taking a puff.

The aerosol-generating device 600 further comprises a puff sensor assembly. The puff sensor assembly comprises a heat transfer element 632 and a temperature sensor 634. The puff sensor assembly is identical to that shown in Figure 1. For example, the heat transfer element 632 is annular and defines a portion of the airflow channel 620.

Unlike the first, second and third aerosol-generating devices 100, 400, 500, the fourth aerosol-generating device 600 does not comprise a heater assembly. Instead, the cartridge 700 comprises a heater assembly comprising a resistive heating element 706. The heating element 706 is fluid permeable and forms a portion of the external surface of cartridge housing 704. As shown in Figure 9, when the cartridge 700 is received in the chamber 610, the fluid permeable heating element defines a portion of the airflow channel 620. As such, the heating element 606 is in fluid communication with air flowing through airflow channel of the aerosol-generating device.

The aerosol-generating device 600 further comprises a power supply 642 in form of a rechargeable battery for powering the heating element 606 controllable by a controller 640. The power supply is connected to the controller via electrical wires and connections that are not shown in the Figures. Furthermore, the aerosol-generating device and cartridge comprise corresponding electrical connectors, not shown, for the electrical connection of the cartridge 700 with the device when the cartridge is received in the chamber. Suitable wires, not shown, connect the power supply 642 to the electrical connectors of the device. Suitable wires, not shown, connect the electrical connectors of the cartridge with the heating element 606. Thus, when the cartridge is received in the chamber, power can be supplied to the heating element 606 from the power supply 642.

In use, power is supplied to the heating element 606. The power heats the liquid aerosol-forming substrate 702, such that the aerosol-forming substrate is at least partially vapourised. Vapourised aerosol-forming substrate passes from the cartridge 700 to the airflow channel 620 through the heating element 606 and subsequently cools in the airflow channel to form an aerosol to be delivered to a user.

Other than the differences described above, the fourth aerosol-generating device 600 operates in the same manner to that described above, in relation to the first aerosol generating device 100.