Heating assembly for an aerosol generating system

Abstract

A heating assembly for heating an aerosol-forming substrate is provided, including: a heater including an electrically resistive heating element and a heater substrate; and a heater mount coupled to the heater; wherein the heating element includes a first portion and a second portion configured such that, when an electrical current is passed through the heating element, the first portion is heated to a higher temperature than the second portion as a result of the electrical current; and wherein the heater mount surrounds the second portion of the heating element.

Claims

1. A heating assembly for heating an aerosol-forming substrate, comprising: a heater comprising an electrically resistive heating element and a heater substrate, wherein the heater substrate is electrically insulating and defines a shape of the heater; and a heater mount coupled to the heater, wherein the heating element comprises a first portion and a second portion configured such that, when an electrical current is passed through the heating element, the first portion is heated to a higher temperature than the second portion, wherein the first portion of the heating element is disposed on a heating area of the heater substrate and the second portion of the heating element is disposed on a holding area of the heater substrate, and wherein the heater mount is fixed to the holding area of the heater substrate.

2. The heating assembly according to claim 1, wherein the heater mount comprises a polymeric material.

3. The heating assembly according to claim 1, wherein the first portion of the heating element is formed from a first material and the second portion of the heating element is formed from a second material, and wherein the first material has a greater electrical resistivity coefficient than that of the second material.

4. The heating assembly according to claim 1, wherein the second portion of the heating element comprises two sections, each of the two sections being separately connected to the first portion of the heating element and defining an electrical flow path from one section of the second portion to the first portion and then to another section of the second portion.

5. The heating assembly according to claim 1, wherein the heating element comprises a third portion configured for electrical connection to a power supply, and wherein the third portion is disposed on an opposite side of the heater mount to the first portion of the heating element.

6. The heating assembly according to claim 5, wherein the third portion is formed from a different material than the first and second portions.

7. The heating assembly according to claim 1, wherein the first portion of the heating element is spaced from the heater mount.

8. The heating assembly according to claim 1, wherein under normal operating conditions, when the first portion of the heating element is at a temperature of between about 300 C. and about 550 C., at points of contact with the heater mount the second portion is at a temperature of less than 200 C.

9. The heating assembly according to claim 1, wherein the first portion has a greater temperature coefficient of resistance than that of the second portion.

10. The heating assembly according to claim 1, wherein if a maximum temperature of the first portion is T.sub.1, an ambient temperature is T.sub.0, and a temperature of the second portion of the heater element in contact with the heater mount is T.sub.2, then:
(T.sub.1T.sub.0)/(T.sub.2T.sub.0)>2.

11. The heating assembly according to claim 1, wherein the heater substrate comprises a planar surface on which the heating element is disposed and a tapered end configured to removably insert into the aerosol-forming substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic diagram of an aerosol generating device;

(3) FIG. 2 is a schematic cross-section of a front end of an aerosol-generating device of the type shown in FIG. 1, with the heater inserted into a smoking article;

(4) FIG. 3 is a schematic illustration of a heater in accordance with the present invention;

(5) FIG. 4 shows the heater of FIG. 3 with a heater mount assembled to it;

(6) FIG. 5 is a cross-section of the heater of FIG. 3;

(7) FIG. 6 is an illustration of the temperature profile along a heater of the type shown in FIG. 3.

DETAILED DESCRIPTION

(8) In FIG. 1, the components of an embodiment of an electrically heated aerosol-generating system 100 are shown in a simplified manner. Particularly, the elements of the electrically heated aerosol-generating system 100 are not drawn to scale in FIG. 1. Elements that are not relevant for the understanding of this embodiment have been omitted to simplify FIG. 1.

(9) The electrically heated aerosol generating system 100 comprises an aerosol-generating device having a housing 10 and an aerosol-forming article 12, for example a tobacco stick. The aerosol-forming article 12 includes an aerosol-forming substrate that is pushed inside the housing 10 to come into thermal proximity with heater 14. The aerosol-forming substrate will release a range of volatile compounds at different temperatures. By controlling the maximum operation temperature of the electrically heated aerosol generating system 100 to be below the selective release of undesirable compounds may be controlled by preventing the release of select volatile compounds.

(10) Within the housing 10 there is an electrical energy supply 16, for example a rechargeable lithium ion battery. A controller 18 is connected to the heater 14, the electrical energy supply 16, and a user interface 20, for example a button or display. The controller 18 controls the power supplied to the heater 14 in order to regulate its temperature. Typically the aerosol-forming substrate is heated to a temperature of between 250 and 450 degrees centigrade.

(11) FIG. 2 is a schematic cross-section of a front end of an aerosol-generating device of the type shown in FIG. 1, with the heater 14 inserted into the aerosol-forming article 12, which in this embodiment is a smoking article. The aerosol-generating device is illustrated in engagement with the aerosol-generating article 12 for consumption of the aerosol-generating article 12 by a user.

(12) The housing 10 of aerosol-generating device defines a cavity, open at the proximal end (or mouth end), for receiving an aerosol-generating article 12 for consumption. The distal end of the cavity is spanned by a heating assembly 24 comprising a heater 14 and a heater mount 26. The heater 14 is retained by the heater mount 26 such that an active heating area of the heater is located within the cavity. The active heating area of the heater 14 is positioned within a distal end of the aerosol-generating article 12 when the aerosol-generating article 12 is fully received within the cavity.

(13) The heater 14 is shaped in the form of a blade terminating in a point. That is, the heater has a length dimension that is greater than its width dimension, which is greater than its thickness dimension. First and second faces of the heater are defined by the width and length of the heater.

(14) An exemplary aerosol-forming article, as illustrated in FIG. 2, can be described as follows. The aerosol-generating article 12 comprises four elements: an aerosol-forming substrate 30, a support element, such as a hollow tube 40, a transfer section 50, and a mouthpiece filter 60. These four elements are arranged sequentially and in coaxial alignment and are assembled by a cigarette paper 70 to form a rod. When assembled, the aerosol-forming article is 45 millimetres long and has a diameter of 7 millimetres.

(15) The aerosol-forming substrate comprises a bundle of crimped cast-leaf tobacco wrapped in a filter paper (not shown) to form a plug. The cast-leaf tobacco includes one or more aerosol formers, such as glycerine.

(16) The hollow tube 40 is located immediately adjacent the aerosol-forming substrate 30 and is formed from a tube of cellulose acetate. The tube 40 defines an aperture having a diameter of 3 millimetres. One function of the hollow tube 40 is to locate the aerosol-forming substrate 30 towards the distal end 23 of the rod 21 so that it can be contacted with the heater. The hollow tube 40 acts to prevent the aerosol-generating substrate 30 from being forced along the rod towards the mouthpiece when a heater is inserted into the aerosol-forming substrate 30.

(17) The transfer section 50 comprises a thin-walled tube of 18 millimetres in length. The transfer section 50 allows volatile substances released from the aerosol-forming substrate 30 to pass along the article towards the mouthpiece filter 60. The volatile substances may cool within the transfer section to form an aerosol.

(18) The mouthpiece filter 60 is a conventional mouthpiece filter formed from cellulose acetate, and having a length of approximately 7.5 millimetres.

(19) The four elements identified above are assembled by being tightly wrapped within a cigarette paper 70. The paper in this specific embodiment is a standard cigarette paper having standard properties or classification. The paper in this specific embodiment is a conventional cigarette paper. The interface between the paper and each of the elements locates the elements and defines the aerosol-forming article 12.

(20) As the aerosol-generating article 12 is pushed into the cavity, the tapered point of the heater engages with the aerosol-forming substrate 30. By applying a force to the aerosol-forming article, the heater penetrates into the aerosol-forming substrate 30. When the aerosol-forming article 12 is properly engaged with the aerosol-generating device, the heater 14 is inserted into the aerosol-forming substrate 30. When the heater is actuated, the aerosol-forming substrate 30 is warmed and volatile substances are generated or evolved. As a user draws on the mouthpiece filter 60, air is drawn into the aerosol-forming article and the volatile substances condense to form an inhalable aerosol. This aerosol passes through the mouthpiece filter 60 of the aerosol-forming article and into the user's mouth.

(21) FIG. 3 illustrates a heater element 14 of the type shown in FIG. 2 in greater detail. The heater 14 comprises an electrically insulating heater substrate 80, which defines the shape of the heating element 14. The heater substrate 80 is formed from an electrically insulating material, which may be, for example, alumina (Al.sub.2O.sub.3) or stabilized zirconia (ZrO.sub.2). It will be apparent to one of ordinary skill in the art that the electrically insulating material may be any suitable electrically insulating material and that many ceramic materials are suitable for use as the electrically insulating substrate. The heater substrate 80 is substantially blade-shaped. That is, the heater substrate has a length that in use extends along the longitudinal axis of an aerosol-forming article engaged with the heater, a width and a thickness. The width is greater than the thickness. The heater substrate 80 terminates in a point or spike 90 for penetrating an aerosol-forming substrate 30.

(22) A heating element 82 formed from electrically conductive material is deposited on a planar surface of the heater substrate 80 using evaporation or any other suitable technique. The heating element is formed in three distinct portions. A first portion 84 is formed from platinum. The first portion is positioned in the active heating area 91. This is the area of the heater which reaches the maximum temperature and provides heat to an aerosol-forming substrate in use. The first portion is U-shaped or in the shape of a hairpin. A second portion 86 is formed from gold. The second portion comprises two parallel tracks, each connected to an end of the first portion 84. The second portion spans the holding area 93 of the heater, which is the area of the heater that is in contact with the heater mount 26, as shown in FIG. 4. A third portion 88 is formed from silver. The third portion is positioned in the connecting area 95 and provides bonding pads to which external wires can be fixed using solder paste or other bonding techniques. The third portion comprises two parallel pads, each connected to an end of one of the parallel tracks of the second portion 86, opposite to the first portion 84. The third portion 88 is positioned on an opposite side of the holding area 93 to the first portion.

(23) The shape, thickness and width of the first, second and third portions may be chosen to provide the desired resistance and temperature distribution in use. However, the first portion has a significantly greater electrical resistance per unit length than the second and third portions and, as a result, when an electrical current passes through the heating element 82, it is the first portion that generates the most heat and so reaches the highest temperature. The second and third portions are configured to have a very low electrical resistance and so provide very little Joule heating. The total electrical resistance of the heating element is about 0.80 Ohms at 0 C., rising to about 2 Ohms when the active heating area 91 reaches 400 C. The battery voltage of the lithium ion battery is around 3.7 Volts so that the typical peak current supplied by the power supply (at 0 C.) is around 4.6 A.

(24) Platinum has a positive temperature coefficient of resistance and so the electrical resistance of the first portion 84 increases with increasing temperature. Gold and silver have lower temperature coefficients of resistance, and the second and third portions will not experience as great a temperature rise as the first portion. This means that changes in resistance of the second and third portions will be small compared to changes in the resistance of the first portion. As a result, the resistance of the heating element 82 can be used to provide a measure of the temperature of the first portion 84 of the heating element, which is the temperature of the portion of the heater in contact with the aerosol-forming substrate. An arrangement for using a resistive element as both a heater and a temperature sensor is described in EP2110033 B1.

(25) FIG. 4 shows the heater 14 assembled to a heater mount 26 to form a heating assembly. The heater mount 26 is formed from polyether ether ketone (PEEK) and is injection moulded around the heater to surround the holding area 93. The heater substrate 80 may be formed with notches or protrusion in the holding area to ensure a strong fixing between the heater mount and the heater. In this embodiment the heater mount 26 has a circular cross-section to engage a circular housing 10 of the aerosol-generating device.

(26) However, the heater mount may be moulded to have any desired shape and any desired engagement features for engaging with other components of the aerosol-generating device.

(27) FIG. 5 is schematic-cross section of the heater of FIG. 3. FIG. 5 illustrates that there is overlap between the first, second and third portions of the heating element. The construction of the heater can be described as follows. The heater substrate 80 is covered with layers of glass 92, 96, on both the first and second surfaces. This protects the substrate and improves the distribution of heat across the surface of the heater in the active heating area. The gold tracks forming the second portion 86 of the heating element are then deposited onto the glass layer 92. The platinum track, forming the first portion 84 of the heating element, is then deposited on the glass layer 92, in an overlapping relation with the gold tracks to ensure a low electrical resistance contact between the first and second portions. The silver connection pads forming the third portion 88 of the heating element are also deposited on the glass layer 92, in an overlapping relation with the gold tracks to ensure a low electrical resistance contact between the third and second portions. Finally an overlying glass layer 94 is formed, covering the heating element 82 and protecting the heating element from corrosion. The heater mount can then be moulded around the heater.

(28) The heater is configured so that the active heating area, corresponding to the first portion of the heating element, is spaced from the heater mount. The area of the heater that extends into the cavity of the aerosol-generating device is referred to as the insertion area 97. The part of the second portion 86 of the heating element that extends into the insertion area 97 provides an energy transfer area.

(29) FIG. 6 is plot 100 showing the temperature of the heater as a function of distance along the length of the heater during operation of the heater illustrated in FIG. 3. The heater is shown below the plot such that the plot of temperature is aligned with the heater. Ideally the heater is hot in the insertion area 97 and cool in the holding area 93 and connection area 95. An ideal temperature profile is shown by dotted line 106. In reality the temperature profile can never be so sharply stepped. It can be seen from the actual temperature plot 100 that the heater is hottest in the active heating area, where the first portion of the heating element is positioned. The peak temperature is around 420 C. during aerosol generation. In the energy transfer area between the active heating area and the holding area, the temperature drops rapidly. In this embodiment, at the heater mount, it is desirable that the temperature of the heater is lower than 200 C., as shown by line 102. The maximum temperature allowable at the heater mount will depend on the material used to form the heater mount. The position of the closest part of heater mount to the active heating area is shown as line 104. The heater is configured to ensure that the temperature at the heater mount 26 is less that 200 C. when the active area of the heater reaches its maximum temperature in use. In the example shown in FIG. 6 the distance between the platinum portion of the heating element and the heater mount is 3 mm. This is sufficient a distance to ensure the required temperature drop. Gold is chosen as the material for the second portion of the heating element because, in addition to a high electrical conductivity, gold has a relatively low thermal conductivity, ensuring a rapid temperature drop between the active heating area and the holding area. An additional temperature drop to approximately 50 C. is further desirable in at least a portion of connecting area 95 in including third portion 88 of the heating element. In particular, it is desirable to minimize the temperature of element 14 closest to controller 18, the electrical energy supply 16, and a user interface 20. For example, such temperature minimization will reduce or eliminate the need to correct for thermal induced variation in the electronic chips and/or systems comprising controller 18, supply 16, and interface 20.

(30) The exemplary embodiments described above illustrate but are not limiting. In view of the above discussed exemplary embodiments, other embodiments consistent with the above exemplary embodiments will now be apparent to one of ordinary skill in the art.