Patent Description:
The popularity and use of reduced-risk or modified-risk devices (also known as aerosol generating devices or vapour generating devices) has grown rapidly in recent years as an alternative to the use of traditional tobacco products. Various devices and systems are available that heat or warm aerosol generating substances to generate an aerosol for inhalation by a user.

A commonly available reduced-risk or modified-risk device is the heated substrate aerosol generating device, or so-called heat-not-burn device. Devices of this type generate an aerosol or vapour by heating an aerosol generating substrate to a temperature typically in the range <NUM> to <NUM>. Heating the aerosol generating substrate to a temperature within this range, without burning or combusting the aerosol generating substrate, generates a vapour which typically cools and condenses to form an aerosol for inhalation by a user of the device. In general terms, a vapour is a substance in the gas phase at a temperature lower than its critical temperature, which means that the vapour can be condensed to a liquid by increasing its pressure without reducing the temperature, whereas an aerosol is a suspension of fine solid particles or liquid droplets, in air or another gas. It should, however, be noted that the terms 'aerosol' and 'vapour' may be used interchangeably in this specification, particularly with regard to the form of the inhalable medium that is generated for inhalation by a user.

Currently available aerosol generating devices can use a number of different approaches to provide heat to the aerosol generating substrate. One such approach is to provide an aerosol generating device which employs an induction heating system. In such a device, an induction coil is provided in the device and an inductively heatable susceptor is provided to heat the aerosol generating substrate. When a user activates the device, electrical energy is supplied to the induction coil, which generates an alternating electromagnetic field. The susceptor couples with the electromagnetic field to induce local eddy currents and/or larger scale circulating currents to flow in the susceptor. The flow of currents in the susceptor generates resistive heating. Depending on the material of the susceptor, it may also undergo heating by magnetic hysteresis. Heat is transferred from the susceptor to the aerosol generating substrate, for example by thermal conduction, and an aerosol is generated as the aerosol generating substrate is heated.

It is generally desirable to heat an aerosol generating substrate rapidly, in order to attain and maintain a sufficiently high temperature in the aerosol generating substrate to generate a vapour. The present disclosure seeks to provide an aerosol generating device that rapidly heats an aerosol generating substrate to a desired temperature, while at the same time maximising the energy efficiency of the device.

<CIT> describes an aerosol provision device that comprises a tubular heater component configured to receive an article comprising aerosol generating material, wherein the heater component is heatable by penetration with a varying magnetic field. The device further comprises an inductor coil extending around the heater component, wherein the inductor coil is configured to generate the varying magnetic field. The heater component has an internal diameter of between about <NUM> and about <NUM>.

<CIT> describes an aerosol-generating device comprising: an inductive heating arrangement configured to heat an aerosol-forming substrate, the inductive heating arrangement comprising: a susceptor arrangement that is heatable by penetration with a varying magnetic field to heat the aerosol-forming substrate, at least a first inductor coil, and at least a second inductor coil, and a controller, wherein the controller is configured to drive the first inductor coil with a first alternating pulse width modulated signal for generating a first altemating magnetic field for heating a first portion of the susceptor arrangement, wherein the controller is configured to drive the second inductor coil with a second altemating pulse width modulated signal for generating a second altemating magnetic field for heating a second portion of the susceptor arrangement, and wherein the controller is configured to supply the first altemating pulse width modulated signal and the second altemating pulse width modulated signal with complementary duty cycles.

<CIT> describes an aerosol-generating device including a chamber; an inductor coil disposed around at least a portion of the chamber; an elastic susceptor element disposed within the chamber and having a tubular shape configured to receive at least a portion of an aerosol-generating article within the elastic susceptor element; and a power supply and a controller connected to the inductor coil and configured to provide an altemating electric current to the inductor coil such that the inductor coil generates an alternating magnetic field to inductively heat the elastic susceptor element and thereby heat at least a portion of the aerosol-generating article received within the elastic susceptor element.

According to a first aspect of the present disclosure, there is provided an aerosol generating device comprising: a heating chamber for receiving an aerosol generating article, the heating chamber comprising a chamber wall that defines an interior volume of the heating chamber; and at least one inductively heatable susceptor mounted in the interior volume of the heating chamber such that there is an outer air gap between the susceptor and the chamber wall and, when an aerosol generating article is received in the heating chamber, there is an inner air gap between the susceptor and the aerosol generating article. The heating chamber is open to the atmosphere at a proximal end and closed at a distal end, the inner air gap providing a first air path from the proximal end to the distal end and the outer air gap providing a second air path from the proximal end to the distal end.

The inner air gap reduces thermal conduction between the susceptor and the aerosol generating article, while the outer air gap reduces thermal conduction between the susceptor and the chamber wall. Providing air gaps adj acent to both the inner and outer surfaces of the susceptor results in efficient transfer of heat from the susceptor to the surrounding air.

The device may be configured so that, when an aerosol generating article is received in the heating chamber, no part of the susceptor is in contact with the aerosol generating article. This reduces the risk of burning the wrapper or substrate of the aerosol generating article by direct conduction of heat from the susceptor. Instead, by preheating the air that flows through the aerosol generating article, heat is distributed more uniformly through the aerosol generating substrate.

The device may comprise a plurality of susceptors disposed circumferentially around an axis of the heating chamber. A plurality of susceptors may facilitate the manufacture or assembly of the device and, if the susceptors are electrically isolated from each other, this may prevent the circulation of induced currents continuously around the device.

Each susceptor may be in the form of a plate curved in an arc about the axis. Such plates are easy to manufacture and may be combined to form a segmented cylindrical surface, which is uniformly spaced from both the chamber wall and the aerosol generating article.

The device may comprise a frame received in the heating chamber, the frame not being inductively heatable, and the at least one susceptor being mounted in the frame. This provides a convenient way of manufacturing the device. The frame can also be configured to be removable from the heating chamber, for example to permit cleaning or replacement of the susceptors.

The frame may comprise guides for centering the aerosol generating article in the heating chamber. This ensures the desired spacing to form the inner air gap between the susceptors and the aerosol generating article. The frame may thereby also help to retain the aerosol generating article in the device.

The frame may comprise a seat for a distal end of the aerosol generating article. This can maintain an air gap between the distal end of the aerosol generating article and a base of the heating chamber to ensure that air can flow from the heating chamber into the distal end of the aerosol generating article.

Such a device may be used in a method comprising: inserting at least part of an aerosol generating article into the heating chamber; and drawing air through the aerosol generating article away from the distal end of the heating chamber, thereby causing incoming air to flow along the first air path and the second air path towards the distal end of the heating chamber. At the same time, the at least one susceptor may be inductively heated to increase the temperature of the incoming air as it flows past the susceptor along the first air path and along the second air path.

Air in the first air path flows over an inner surface of the susceptor and air in the second air path flows over an outer surface of the susceptor. Providing airflow over both the inner and outer surfaces of the susceptor results in efficient transfer of heat from the susceptor to raise the temperature of the air drawn through the aerosol generating article.

According to another aspect of the present disclosure, an aerosol generating device may comprise a heating chamber for receiving an aerosol generating article, the heating chamber comprising a chamber wall that defines an interior volume of the heating chamber; and a method of assembling the aerosol generating device may comprise: mounting one or more inductively heatable susceptors in a frame; and inserting the frame and the one or more susceptors into the heating chamber such that there is an outer air gap between each of the one or more susceptors and the chamber wall and, when an aerosol generating article is received in the heating chamber, there is an inner air gap between the susceptor and the aerosol generating article.

The susceptors preferably comprise a material that is electrically conductive and magnetically permeable, preferably a metallic material. If the susceptors are formed of such a material, they will be capable of undergoing inductive heating. The metallic material is typically selected from the group consisting of stainless steel and carbon steel. The inductively heatable susceptor could, however, comprise any suitable material including one or more, but not limited, of aluminium, iron, nickel, stainless steel, carbon steel, and alloys thereof, e.g. nickel chromium or nickel copper.

The aerosol generating device may include a power source and controller, e.g., comprising control circuitry, which may be configured to operate at a high frequency. The power source and circuitry may be configured to operate at a frequency of between approximately <NUM> and <NUM>, possibly between approximately <NUM> and <NUM>, and possibly at approximately <NUM>. The power source and circuitry could be configured to operate at a higher frequency, for example in the MHz range, depending on the type of inductively heatable susceptor that is used.

The aerosol generating substrate may comprise any type of solid or semi-solid material. Example types of aerosol generating solids include powder, granules, pellets, shreds, strands, particles, gel, strips, loose leaves, cut filler, porous material, foam material or sheets. The aerosol generating substrate may comprise plant derived material and in particular, may comprise tobacco. It may advantageously comprise reconstituted tobacco, for example including tobacco and any one or more of cellulose fibres, tobacco stalk fibres and inorganic fillers such as CaCO<NUM>.

Consequently, the aerosol generating device may be referred to as a "heated tobacco device", a "heat-not-burn tobacco device", a "device for vaporising tobacco products", and the like, with this being interpreted as a device suitable for achieving these effects. The features disclosed herein are equally applicable to devices which are designed to vaporise any aerosol generating substrate.

The aerosol generating substrate may form part of an aerosol generating article and may be circumscribed by a paper wrapper. When the aerosol generating substrate is received in the heating chamber of the aerosol generating device, other parts of the aerosol generating article may remain outside the heating chamber to provide, for example, a mouthpiece for the user.

The aerosol generating article may be formed substantially in the shape of a stick, and may broadly resemble a cigarette, having a tubular region with an aerosol generating substrate arranged in a suitable manner. The aerosol generating article may include a filter segment, for example comprising cellulose acetate fibres, at a proximal end of the aerosol generating article. The filter segment may constitute a mouthpiece filter and may be in coaxial alignment with the aerosol generating substrate. One or more vapour collection regions, cooling regions, and other structures may also be included in some designs. For example, the aerosol generating article may include at least one tubular segment upstream of the filter segment. The tubular segment may act as a vapour cooling region. The vapour cooling region may advantageously allow the heated vapour generated by heating the aerosol generating substrate to cool and condense to form an aerosol with suitable characteristics for inhalation by a user, for example through the filter segment.

The aerosol generating substrate may comprise an aerosol former. Examples of aerosol formers include polyhydric alcohols and mixtures thereof such as glycerine or propylene glycol. Typically, the aerosol generating substrate may comprise an aerosol former content of between approximately <NUM>% and approximately <NUM>% on a dry weight basis. In some embodiments, the aerosol generating substrate may comprise an aerosol former content of between approximately <NUM>% and approximately <NUM>% on a dry weight basis, and possibly approximately <NUM>% on a dry weight basis.

Upon heating, the aerosol generating substrate may release volatile compounds. The volatile compounds may include nicotine or flavour compounds such as tobacco flavouring.

Referring initially to <FIG> and <FIG>, there is shown diagrammatically an example of an aerosol generating system <NUM>. The aerosol generating system <NUM> comprises an aerosol generating device <NUM> and an aerosol generating article <NUM> for use with the device <NUM>. The aerosol generating device <NUM> comprises a main body <NUM> housing various components of the aerosol generating device <NUM>. The main body <NUM> can have any shape that is sized to fit the components described in the various embodiments set out herein and to be comfortably held by a user unaided, in a single hand.

A first end <NUM> of the aerosol generating device <NUM>, shown towards the bottom of <FIG> and <FIG>, is described for convenience as a distal, bottom, base or lower end of the aerosol generating device <NUM>. A second end <NUM> of the aerosol generating device <NUM>, shown towards the top of <FIG> and <FIG>, is described as a proximal, top or upper end of the aerosol generating device <NUM>. During use, the user typically orients the aerosol generating device <NUM> with the first end <NUM> downward and/or in a distal position with respect to the user's mouth and the second end <NUM> upward and/or in a proximal position with respect to the user's mouth.

The aerosol generating device <NUM> comprises a heating chamber <NUM> positioned in the main body <NUM>. The heating chamber <NUM> defines an interior volume in the form of a cavity <NUM> having a substantially circular cross-section for receiving at least part of a substantially cylindrical aerosol generating article <NUM>. The heating chamber <NUM> has a longitudinal axis defining a longitudinal direction. A proximal end <NUM> of the heating chamber <NUM> is open towards the second end <NUM> of the aerosol generating device <NUM>. The heating chamber <NUM> is typically held spaced apart from the inner surface of the main body <NUM> to minimise heat transfer to the main body <NUM>.

The aerosol generating device <NUM> further comprises a power source <NUM>, for example one or more batteries which may be rechargeable, and a controller <NUM>.

The aerosol generating device <NUM> can optionally include a sliding cover <NUM> movable transversely between a closed position (see <FIG>) in which it covers the open end <NUM> of the heating chamber <NUM> to prevent access to the heating chamber <NUM> and an open position (see <FIG>) in which it exposes the open first end <NUM> of the heating chamber <NUM> to provide access to the heating chamber <NUM>. The sliding cover <NUM> can be biased to the closed position in some embodiments.

The heating chamber <NUM>, and specifically the cavity <NUM>, is arranged to receive a correspondingly shaped generally cylindrical or rod-shaped aerosol generating article <NUM>. The aerosol generating article <NUM> typically comprises a pre-packaged aerosol generating substrate <NUM>. The aerosol generating article <NUM> is a disposable and replaceable article (also known as a "consumable") which may, for example, contain tobacco as the aerosol generating substrate <NUM>. The aerosol generating article <NUM> has a proximal end <NUM> (or mouth end) and a distal end <NUM>. The aerosol generating article <NUM> further comprises a mouthpiece segment <NUM> positioned downstream of the aerosol generating substrate <NUM>. The aerosol generating substrate <NUM> and the mouthpiece segment <NUM> are arranged in coaxial alignment inside a wrapper <NUM> (e.g., a paper wrapper) to hold the components in position to form the rod-shaped aerosol generating article <NUM>.

The mouthpiece segment <NUM> can comprise one or more of the following components (not shown in detail) arranged sequentially and in co-axial alignment in a downstream direction, in other words from the distal end <NUM> towards the proximal (mouth) end <NUM> of the aerosol generating article <NUM>: a cooling segment, a centre hole segment and a filter segment. The cooling segment typically comprises a hollow paper tube having a thickness which is greater than the thickness of the wrapper <NUM>. The centre hole segment may comprise a cured mixture containing cellulose acetate fibres and a plasticizer, and functions to increase the strength of the mouthpiece segment <NUM>. The filter segment typically comprises cellulose acetate fibres and acts as a mouthpiece filter. As heated vapour flows from the aerosol generating substrate <NUM> towards the proximal (mouth) end <NUM> of the aerosol generating article <NUM>, the vapour cools and condenses as it passes through the cooling segment and the centre hole segment to form an aerosol with suitable characteristics for inhalation by a user through the filter segment.

The heating chamber <NUM> has a side wall (or chamber wall) <NUM> extending between a base <NUM>, located at a distal end <NUM> of the heating chamber <NUM>, and the open end <NUM>. The chamber wall <NUM> and the base <NUM> are connected to each another and can be integrally formed as a single piece. In the illustrated embodiment, the chamber wall <NUM> is tubular and, more specifically, cylindrical. In other embodiments, the chamber wall <NUM> can have other suitable shapes, such as a tube with an elliptical or polygonal cross section. In yet further embodiments, the chamber wall <NUM> can be tapered. The chamber wall <NUM> and the base <NUM> are formed of a heat-resistant plastics material, such as polyether ether ketone (PEEK).

In the illustrated embodiment, the base <NUM> of the heating chamber <NUM> is closed, e.g. sealed or air-tight. That is, the heating chamber <NUM> is cup-shaped. This can ensure that air drawn from the open end <NUM> is prevented by the base <NUM> from flowing out of the second end <NUM> and is instead guided through the aerosol generating substrate <NUM>. It can also ensure that a user inserts the aerosol generating article <NUM> into the heating chamber <NUM> an intended distance and no further.

The aerosol generating device <NUM> comprises at least one inductively heatable susceptor <NUM>. It may comprise a plurality of the inductively heatable susceptors <NUM> circumferentially spaced around the heating chamber <NUM>. The inductively heatable susceptors <NUM> may be elongate in the longitudinal direction of the heating chamber <NUM>.

The aerosol generating device <NUM> comprises an electromagnetic field generator <NUM> for generating an electromagnetic field. The electromagnetic field generator <NUM> comprises a substantially helical induction coil <NUM>. The induction coil <NUM> has a circular cross-section and extends helically around the substantially cylindrical heating chamber <NUM>. The induction coil <NUM> can be energised by the power source <NUM> and controller <NUM>. The controller <NUM> includes, amongst other electronic components, an inverter which is arranged to convert a direct current from the power source <NUM> into an alternating highfrequency current for the induction coil <NUM>.

The chamber wall <NUM> of the heating chamber <NUM> includes a coil support structure <NUM> formed in the outer surface <NUM>. In the illustrated example, the coil support structure <NUM> comprises a coil support groove <NUM>, which extends helically around the outer surface <NUM>. The induction coil <NUM> is positioned in the coil support groove <NUM> and is, thus, securely and optimally positioned with respect to the inductively heatable susceptors <NUM>.

In order to use the aerosol generating device <NUM>, a user displaces the sliding cover <NUM> (if present) from the closed position shown in <FIG> to the open position shown in <FIG>. The user then inserts an aerosol generating article <NUM> through the open end <NUM> of the heating chamber <NUM>, so that the aerosol generating substrate <NUM> is received in the cavity <NUM> and at least part of the mouthpiece segment <NUM> projects from the open end <NUM> to permit engagement by a user's lips.

Upon activation of the aerosol generating device <NUM> by a user, the induction coil <NUM> is energised by the power source <NUM> and controller <NUM> which supply an altemating electrical current to the induction coil <NUM>, and an alternating and time-varying electromagnetic field is thereby produced by the induction coil <NUM>. This couples with the inductively heatable susceptors <NUM> and generates eddy currents and/or magnetic hysteresis losses in the susceptors <NUM> causing them to heat up. Heat is then transferred from the inductively heatable susceptors <NUM> to the aerosol generating substrate <NUM>, for example by conduction, radiation or convection. This results in heating of the aerosol generating substrate <NUM> without combustion or burning, and a vapour is thereby generated. The generated vapour cools and condenses to form an aerosol which can be inhaled by a user of the aerosol generating device <NUM> through the mouthpiece segment <NUM>, and more particularly through the filter segment.

The vaporisation of the aerosol generating substrate <NUM> is facilitated by the addition of air from the surrounding environment, for example through the open end <NUM> of the heating chamber <NUM>, the air being heated as it flows between the aerosol generating article <NUM> and the inner surface <NUM> of the chamber wall <NUM>. More particularly, when a user sucks on the filter segment, air is drawn into the heating chamber <NUM> through the open end <NUM> as illustrated by the arrows A in <FIG>. The air entering the heating chamber <NUM> flows from the open end <NUM> towards the closed end <NUM>, between the aerosol generating article <NUM> and the chamber wall <NUM>. When the air reaches the closed end <NUM> of the heating chamber <NUM>, it turns through approximately <NUM>° and enters the distal end <NUM> of the aerosol generating article <NUM>. The air is then drawn through the aerosol generating article <NUM>, as illustrated by the arrow B in <FIG>, from the distal end <NUM> towards the proximal (mouth) end <NUM> along with vapour generated from the substrate <NUM>.

A user can continue to inhale aerosol all the time that the aerosol generating substrate <NUM> is able to continue to produce a vapour, e.g. all the time that the aerosol generating substrate <NUM> has vaporisable components left to vaporise into a suitable vapour. The controller <NUM> can adjust the magnitude of the altemating electrical current passed through the induction coil <NUM> to ensure that the temperature of the inductively heatable susceptors <NUM>, and in turn the temperature of the aerosol generating substrate <NUM>, does not exceed a threshold level. Specifically, at a particular temperature, which depends on the constitution of the aerosol generating substrate <NUM>, the aerosol generating substrate <NUM> will begin to burn. This is not a desirable effect and temperatures above and at this temperature are avoided. The material from which the chamber wall <NUM> and the base <NUM> are formed is chosen to be able to resist being heated repeatedly to temperatures up to the threshold during the expected lifetime of the aerosol generating device.

To assist with temperature regulation, in some examples the aerosol generating device <NUM> is provided with a temperature sensor (not illustrated). The controller <NUM> is arranged to receive an indication of the temperature of the aerosol generating substrate <NUM> from the temperature sensor and to use the temperature indication to control the magnitude of the altemating electrical current supplied to the induction coil <NUM>. Means such as pressure or flow sensors (not illustrated) may be provided to detect airflow through the heating chamber <NUM> and to energise the induction coil <NUM> only when the user is actively inhaling through the device <NUM>.

A single inhalation by a user is generally referred to a "puff". In some scenarios, it is desirable to emulate a cigarette smoking experience, which means that the aerosol generating device <NUM> is typically capable of holding sufficient aerosol generating substrate <NUM> to provide ten to fifteen puffs.

In line with emulating the experience of cigarette smoking, the power source <NUM> is usually sufficient to repeat this cycle (bringing the aerosol generating substrate <NUM> up to the desired temperature and maintaining that temperature and vapour generation for ten to fifteen puffs) ten times, or even twenty times, thereby emulating a user's experience of smoking a packet of cigarettes, before there is a need to replace or recharge the power source <NUM>.

In general, the efficiency of the aerosol generating device <NUM> is improved when as much as possible of the heat that is generated by the inductively heatable susceptors <NUM> results in heating of the aerosol generating substrate <NUM>. To this end, the aerosol generating device <NUM> is usually configured to provide heat in a controlled manner to the aerosol generating substrate <NUM> while reducing heat loss to other parts of the aerosol generating device <NUM>. In particular, heat flow to parts of the aerosol generating device <NUM> that the user handles is kept to a minimum, thereby keeping these parts cool and comfortable to hold.

<FIG> illustrates a pattern of airflow through a heating chamber <NUM> of an aerosol generating device <NUM>. The heating chamber <NUM> is cup-shaped, having a closed distal end <NUM> and an open proximal end <NUM>. The generally cylindrical chamber wall <NUM> is surrounded by an induction coil <NUM>. A aerosol generating article <NUM> is received in the heating chamber <NUM> such that the aerosol generating substrate <NUM> is fully within the chamber <NUM> but the proximal end <NUM> of the aerosol generating article <NUM> remains outside the heating chamber <NUM>. The distal end <NUM> of the aerosol generating article <NUM> is not advanced fully to the base <NUM> of the chamber <NUM>, in order that there should remain a gap <NUM>, through which air can enter the distal end <NUM> of the aerosol generating article <NUM> from the heating chamber <NUM>.

One or more susceptors <NUM> are disposed circumferentially around the interior volume <NUM> of the heating chamber <NUM>. The susceptors <NUM> are axially aligned with the induction coil <NUM>. Each susceptor <NUM> is radially positioned such that there is an inner air gap <NUM> between the susceptor <NUM> and the wrapper <NUM> of the aerosol generating article <NUM> and an outer air gap <NUM> between the susceptor <NUM> and the chamber wall <NUM>. When a user inhales through the aerosol generating article <NUM>, air is drawn out of the distal end of the heating chamber <NUM>, reducing the pressure there. This causes atmospheric air to flow in from the proximal end <NUM> of the heating chamber to equalise the pressure. The inner air gap <NUM> between the susceptors <NUM> and the aerosol generating article <NUM> provides a first path <NUM> for air to flow from the proximal end <NUM> to the distal end <NUM> of the heating chamber <NUM>. The outer air gap <NUM> between the susceptors <NUM> and the chamber wall <NUM> provides a second path <NUM> for air to flow from the proximal end <NUM> to the distal end <NUM> of the heating chamber <NUM>. Air flowing along the first air path <NUM> passes over an inner surface of the susceptor <NUM> and air flowing along the second air path <NUM> passes over an outer surface of the susceptor <NUM>. Air flowing along both paths <NUM>,<NUM> therefore remains close to the susceptor <NUM> over a significant distance, during which heat is transferred from the susceptor <NUM> to the air. Providing airflow over both the inner and outer surfaces of the susceptor <NUM> results in efficient heat transfer. The air is accordingly pre-heated to a high temperature before entering the distal end <NUM> of the aerosol generating article <NUM>. The hot air is then distributed through all parts of the aerosol generating substrate <NUM>, whereas heat that may be transferred from the susceptors <NUM> by conduction or radiation will have a greater effect at the radially outer parts of the substrate <NUM> and may risk buming the substrate <NUM> or the wrapper <NUM> of the aerosol generating article <NUM>.

<FIG> shows a first example of a possible susceptor configuration in the device of <FIG>, seen in transverse cross section. The device comprises a single susceptor <NUM>, in the form of a plate or sheet that is curved in an arc about the axis of the heating chamber <NUM> to form a C-shape or an almost complete cylinder. Opposite edges <NUM> of the plate are spaced slightly apart from one another to leave a small circumferential gap <NUM>. As already seen in <FIG>, the susceptor <NUM> is radially positioned such that there is an inner air gap <NUM> between the susceptor <NUM> and the wrapper <NUM> of the aerosol generating article <NUM> and an outer air gap <NUM> between the susceptor <NUM> and the chamber wall <NUM>. No part of the susceptor <NUM> is in contact with the aerosol generating article <NUM> so there is a reduced risk that the wrapper <NUM> or the substrate <NUM> of the aerosol generating article <NUM> may be burned through the excessive conduction of heat.

The circumferential gap <NUM> in the susceptor <NUM> may be beneficial if it is not desired that currents induced in the susceptor <NUM> should be able to circulate continuously around its circumference. The gap <NUM> may also facilitate assembly of the device, as described below. It will readily be understood that additional gaps <NUM> could be provided, thereby dividing the plate into two, three, four or more discrete, arcuate susceptors <NUM> that together form a segmented cylinder. It will also be readily understood that a single susceptor <NUM> could be formed without any gap <NUM>, as a continuous cylinder.

This generally cylindrical form of the susceptor <NUM> or the plurality of susceptors <NUM> may have advantages. First, the susceptors <NUM> are at a uniform distance from the induction coil <NUM> so would be expected to heat up uniformly. Secondly, the susceptors <NUM> are also at a uniform distance from the aerosol generating article <NUM> so would be expected to radiate heat to the aerosol generating substrate <NUM> uniformly around its circumference. Thirdly, the inner and outer air gaps <NUM>,<NUM> have a uniform cross section around their circumference so the flow of air along the first and second air paths <NUM>,<NUM> may be smoother or more uniform. However, such a susceptor <NUM> has the disadvantage that, as it does not contact the aerosol generating article <NUM>, alternative means (not shown in <FIG>) must be provided to support the aerosol generating article <NUM> in the device.

<FIG> shows an alternative example of a possible susceptor configuration in the device of <FIG>, seen in transverse cross section. In this example there are four susceptors <NUM> distributed around the circumference of the heating chamber <NUM>. Each susceptor <NUM> comprises a flat plate that is generally tangential to the surface of the aerosol generating article <NUM>. A rib <NUM> projects radially inwards from the centre of each susceptor plate <NUM> and contacts the wrapper <NUM> of the aerosol generating article <NUM> along a narrow line. The ribs <NUM> of the four susceptors <NUM> thus support the aerosol generating article <NUM> between them. The ribs <NUM> may be formed as beads on the susceptor plates <NUM>, as shown, or they may be formed by deforming the susceptor plates. The ribs <NUM> serve to minimise the area of contact between the susceptors <NUM> and the aerosol generating article <NUM> but they could alternatively be omitted so that the aerosol generating article <NUM> is instead supported by direct tangential contact with the inner surfaces of flat susceptor plates <NUM>. It will readily be understood that in alternative examples the number of susceptors <NUM> could be more or less than four.

The configuration of susceptors <NUM> seen in <FIG> provides inner air gaps <NUM> between the susceptors <NUM> and the wrapper <NUM> of the aerosol generating article <NUM> and an outer air gaps <NUM> between the susceptors <NUM> and the chamber wall <NUM>. Thereby air flowing along the first and second air paths <NUM>,<NUM> through the heating chamber <NUM> passes over the inner and outer surfaces of the susceptors <NUM> to be heated before it enters the distal end <NUM> of the aerosol generating article <NUM>.

<FIG> illustrate a susceptor assembly according to a first embodiment of the present invention. This embodiment comprises two susceptors <NUM>, each having an almost semi-circular cross section, so that together they form a cylinder with two opposing gaps. The susceptors <NUM> are mounted in a frame <NUM>, which holds them in the desired relationship to one another and to the other components of the vapour generating system. The frame <NUM> is formed from a material such as PEEK, in which no significant currents are induced by the operation of the induction coil <NUM>.

The frame <NUM> comprises a generally cup-shaped cage, having a number of longitudinal struts <NUM>,<NUM> that are joined by a base <NUM> at the distal end and by a collar <NUM> at the proximal end. The struts <NUM>,<NUM> have outer surfaces <NUM> at a radius such that the frame <NUM> fits closely inside the heating chamber <NUM> (not seen in <FIG>). The collar <NUM> may have a larger radius to abut the rim of the open end <NUM> of the heating chamber <NUM>. The collar <NUM> may be used to withdraw the frame <NUM> and susceptors <NUM> from the heating chamber <NUM>, for example for cleaning or replacement. The struts <NUM>,<NUM> have inner surfaces <NUM> at a radius such that they support the aerosol generating article <NUM> within the heating chamber <NUM>. Proximal ends of the inner surfaces <NUM> may be provided with ramps <NUM> to guide the aerosol generating article <NUM> into position and to compress it slightly as it is pushed in the distal direction, whereby the aerosol generating article <NUM> is held securely in the device <NUM> by the inner surfaces <NUM>. The distal end of the aerosol generating article <NUM> is stopped by the base <NUM> of the frame <NUM> before it reaches the base <NUM> of the heating chamber <NUM>. The base <NUM> thereby forms a seat for the aerosol generating article <NUM>, while defining air gaps <NUM> through which air can flow from the heating chamber <NUM> into the aerosol generating article <NUM>.

Two opposing struts <NUM> are used to mount the susceptors <NUM>. Each of them comprises a pair of back-to-back, circumferentially facing, blind slots <NUM>. Each slot <NUM> receives a longitudinal edge <NUM> of one of the susceptors <NUM>. Intermediate struts <NUM> support the susceptors <NUM> to hold them in the slots <NUM>. The slots are formed in the frame <NUM> at a radius such that, when the frame <NUM> is inserted into the heating chamber <NUM> of the device <NUM>, there is an outer air gap <NUM> between the susceptor <NUM> and the chamber wall <NUM>; and such that, when a aerosol generating article <NUM> is inserted into the frame <NUM>, there is an inner air gap <NUM> between the susceptor <NUM> and the aerosol generating article <NUM>.

<FIG> illustrate a susceptor assembly <NUM> according to a second embodiment of the present invention. This embodiment also comprises two susceptors <NUM>, each having the general form of an arcuate plate that forms a segment of a cylinder centred on the axis of the device <NUM>, but in this case the gaps between the susceptors <NUM> are larger than in <FIG>. The longitudinal edges of the susceptors are turned outwards to form flanges <NUM>.

The frame <NUM> of this embodiment comprises a pair of longitudinal struts <NUM>, the distal ends of which are connected to one another by a ring <NUM>. Notches <NUM> are formed in a proximal edge of the ring <NUM>, adjacent to the struts <NUM>. The proximal end of each strut <NUM> is turned outwards to form a flange <NUM>. A longitudinal slot <NUM> is formed in each strut <NUM> and extends to the proximal end of the strut <NUM>. Part of the way along each slot <NUM> is a retaining feature <NUM>, where the slot <NUM> is slightly narrowed. A separate collar <NUM> includes two outwardly facing recesses <NUM>. In each recess <NUM> is a projection <NUM> that extends radially outwards and has a T-shaped profile.

The components are assembled as shown in <FIG> to form the susceptor assembly <NUM>. Each susceptor <NUM> slides between a pair of the struts <NUM> until the distal ends of the susceptor flanges <NUM> locate in the notches <NUM> of the ring <NUM>. The collar <NUM> then slides in the distal direction so that the projections <NUM> of the collar <NUM> engage and travel along the longitudinal slots <NUM> of the struts <NUM>. At the ends of the slots <NUM>, the projections <NUM> snap fit behind the retaining features <NUM> to retain the collar <NUM> in the frame <NUM>. Further notches <NUM> are created where the struts <NUM> adjoin the recesses <NUM> of the collar <NUM> and the proximal ends of the susceptor flanges <NUM> locate in those notches <NUM> to secure the susceptors <NUM> in position.

The flanges <NUM> at the proximal ends of the struts <NUM> may be used to insert the susceptor assembly <NUM> into the heating chamber <NUM> of a vapour generating device <NUM>, or subsequently to remove the susceptor assembly, e.g. for cleaning or replacement. When the susceptor assembly <NUM> is positioned in the heating chamber <NUM>, the out-tumed susceptor flanges <NUM> maintain an outer air gap <NUM> between the cylindrical outer surface of each susceptor <NUM> and the chamber wall <NUM>. The radius of the inner surfaces of the susceptors <NUM> is greater than the radius of the aerosol generating article <NUM> for use with the device <NUM>, whereby an inner air gap <NUM> is maintained between each susceptor <NUM> and the aerosol generating article <NUM>. The illustrated susceptor assembly <NUM> does not provide any means for locating the aerosol generating article <NUM>, although the collar <NUM> and the ring <NUM> could easily be adapted to guide it into position. The ring <NUM> also does not provide any end stop for the aerosol generating article <NUM> to ensure that there is a gap <NUM> for air to flow into its distal end <NUM>. However, the base <NUM> of the heating chamber <NUM> itself may be formed to provide such a feature, as seen in <FIG>, for example.

As long as it falls within the scope of the appended claims, any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

Claim 1:
An aerosol generating device (<NUM>) comprising:
a heating chamber (<NUM>) for receiving an aerosol generating article (<NUM>), the heating chamber (<NUM>) comprising a chamber wall (<NUM>) that defines an interior volume (<NUM>) of the heating chamber (<NUM>); and
at least one inductively heatable susceptor (<NUM>) mounted in the interior volume (<NUM>) of the heating chamber (<NUM>) such that there is an outer air gap between the susceptor (<NUM>) and the chamber wall (<NUM>) and, when an aerosol generating article (<NUM>) is received in the heating chamber (<NUM>), there is an inner air gap between the susceptor (<NUM>) and the aerosol generating article (<NUM>);
characterised in that the heating chamber (<NUM>) is open to the atmosphere at a proximal end (<NUM>) and is closed at a distal end (<NUM>), the inner air gap providing a first air path from the proximal end (<NUM>) to the distal end (<NUM>) and the outer air gap providing a second air path from the proximal end (<NUM>) to the distal end (<NUM>).