Note: Descriptions are shown in the official language in which they were submitted.
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1
AEROSOL GENERATING DEVICE WITH PUFF DETECTION
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.
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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
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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
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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.
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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
5 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.
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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,
or 80 degrees centigrade above ambient temperature. The heat transfer element
may be
35 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
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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
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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.
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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.
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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.
5 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
10 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
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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
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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
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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.
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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
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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
5 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
10 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-
15 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 Hz.
Such frequencies may correspond to electrical noise. The band-pass filter may
advantageously be configured to remove signal frequencies below 0.2 Hz. This
may remove
slow variations in temperature from the signal that may not correspond to a
puff.
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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.
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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-
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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
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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. However, 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:
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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
5 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.
10 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.
15 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
20 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.
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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.
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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.
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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.
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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.
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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:
5 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-
10 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
15 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.
20 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
25 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;
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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
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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.
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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
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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. Heat
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
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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
5 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
10 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
15 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.
20 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.
25 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
30 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
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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
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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.
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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.
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