Heating unit for an aerosol generating system

Abstract

A heating unit for heating an aerosol-forming substrate, the heating unit comprising: a heater (14) comprising an electrically resistive heating element (82); and a heater support (26) attached to the heater (14); wherein the heating element comprises a first portion (84) and a second portion (86) configured such that, when an electric 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 electric current; and wherein the heater support (26) surrounds the second portion (86) of the heating element and is formed from a moldable polymeric material.

Description

Heating unit for an aerosol generating system The description relates to a heating unit suitable for use in an aerosol generating system. In particular, the invention relates to a heating unit suitable for insertion within an aerosol-forming substrate of a smoking article for internally heating the aerosol-forming substrate. There is increased demand for portable aerosol-generating devices capable of delivering aerosol for inhalation by the user. One particular area of ​​demand is for heated smoking devices, in which an aerosol-forming substrate is heated to release volatile flavoring components without combustion of the substrate. The released volatile compounds are then carried in an aerosol to the user. Any aerosol-generating device that operates by heating an aerosol-forming substrate 15 must include a heating unit. A number of different types of heating units have been proposed for different types of aerosol-forming substrates. One type of heating unit that has been proposed for heated smoking devices works by inserting a heater into a solid aerosol-forming substrate, such as a tobacco plug. This arrangement allows the substrate to be heated directly and effectively. However, there are a number of technical challenges with this type of heating unit, including meeting requirements for size, robustness, low manufacturing cost, sufficient operating temperatures, and effective localization of the generated heat. It would be convenient to provide a robust and inexpensive heating unit for a 25 aerosol generating device that provides a localized heat source for heating an aerosol forming substrate. In a first aspect of the invention, a heating unit is provided for heating an aerosol-forming substrate; the heating unit comprises: a heater comprising an electrically resistive heating element and a heating substrate; and a heater support attached to the heater; wherein the heating element comprises a first portion and a second portion configured such that, when an electric 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 positioned on a heating area of ​​the heating substrate and the second portion of the heating element is positioned on a containment area of ​​the heating substrate; and wherein the heater support is fixed to the containment area of ​​the heating substrate. As used in this description, the term “aerosol-forming substrate” refers to a substrate capable of releasing volatile compounds that can form an aerosol. Such volatile compounds can be released by heating the aerosol-forming substrate. An aerosol-forming substrate may conveniently be part of an aerosol-generating article or smoking article. As used in this description, the terms “aerosol-generating article” and “smoking article” refer to an article comprising an aerosol-forming substrate capable of releasing volatile compounds that can form an aerosol. For example, an aerosol-generating article may be a smoking article that generates an aerosol that can be inhaled directly into the user’s lungs through the user’s mouth. An aerosol-generating article may be disposable. A smoking article comprising an aerosol-forming substrate comprising tobacco is called a tobacco stick. The first portion heats up to a higher temperature than the second portion as a result of the electric current passing through the heating element. In one mode, the first portion of the heating element is set to reach a temperature between approximately 300°C and approximately 550°C during use. Preferably, the heating element is set to reach a temperature between approximately 320°C and approximately 350°C. The heater support provides structural support to the heater and allows it to be securely attached within an aerosol generating device. The heater support may comprise a polymeric material and is advantageously formed from a moldable polymeric material, such as polyether ether ketone (PEEK). The use of a moldable polymer allows the heater support to be molded around the heater, thus holding it securely. This also allows the heater support to be produced economically with a desired shape and external dimensions. The heater support may have mechanical elements, such as handles or notches, that allow the heater support to be attached to the heater. Of course, other materials can be used for the heater support, such as a ceramic material. Advantageously, the heater support can be formed from a moldable ceramic material. Using a polymer to contain the heater means that the heater temperature in the vicinity of the heater support must be controlled to remain below the temperature at which the polymer melts or degrades. At the same time, the temperature of the heater portion within the aerosol-forming substrate must be sufficient to produce an aerosol with the desired properties. It is therefore advisable to ensure that the second portion of the heating element, at least at the points of contact with the heater support, remains below a maximum permissible temperature during use. In an electrically resistive heater, the heat produced depends on the resistance of the heating element. For a given current, the higher the resistance of the heating element, the more heat is produced. It is advantageous for most of the heat to be produced by the first portion of the heating element. Consequently, it is advantageous for the first portion of the heating element to have a higher electrical resistance per unit length than the second portion. Advantageously, the heating element comprises portions formed from different materials. The first portion of the heating element can be formed from one material, and the second portion from a second material, where the first material has a higher electrical resistivity coefficient than the second. For example, the first material could be Ni-Cr (nickel-chromium), platinum, tungsten, or wire alloys, and the second material could be gold, silver, or copper. The dimensions of the first and second portions of the heating element can be different to provide a lower electrical resistance per unit length in the second portion. The materials for the first and second portions of the heating element can be selected for their thermal as well as their electrical properties. Advantageously, the second portion of the heating element has low thermal conductivity to reduce heat conduction from the heating area to the heater support. Consequently, the material choice for the second portion of the heating element can be a balance between high and low thermal conductivity, at least in the region between the first portion of the heating element and the heater support. In practice, gold has been found to be a good choice for the material of the second portion of the heating element. Alternatively, silver can comprise the material for the second portion. Advantageously, the second portion of the heating element comprises two sections, each of which is separately connected to the first portion of the heating element to define a path for the electrical current flow from one section of the second portion to the first portion and then to the other section of the second portion. The heater support can surround both sections of the second portion. Of course, it is possible for the second portion to comprise more than two sections, each electrically connected to the first portion. The heating element may comprise a third portion configured for electrical connection to the power supply, wherein the third portion is positioned on an opposite side of the heater support to the first portion of the heating element. The third portion may be formed from a different material than the first and second portions and may be chosen to provide low electrical resistance and good connection properties, e.g., ease of soldering. In practice, silver has been found to be a good choice for the third portion. Alternatively, gold may be used as the material for the third portion. The third portion may comprise a plurality of sections, each connected to a section of the second portion of the heating element. There may be overlap between the different portions of the heating element to ensure good electrical connection. For example, the first and third portions may overlap or partially underlie the second portion. Furthermore, the heating element may comprise more than three distinct portions. The heating substrate is advantageously formed from an electrically insulating material and can be a ceramic material such as zirconium or aluminum. The heating substrate can provide mechanically stable support for the heating element over a wide temperature range and can provide a rigid structure suitable for insertion into an aerosol-forming substrate. The heating substrate can comprise a flat surface on which the heating element is positioned and a tapered end configured to allow its insertion into an aerosol-forming substrate. The heating substrate advantageously has a thermal conductivity of less than or equal to 2 Watts per meter Kelvin. 60 In one embodiment, the first portion of the heating element is formed from a material with a defined temperature-resistivity relationship. This allows the heater to be used both to heat the aerosol-forming substrate and to monitor the temperature during use. Advantageously, the first portion has a higher temperature-resistivity coefficient than the second portion. This ensures that the resistance value of the heating element predominantly reflects the temperature of the first portion. Platinum has been found to be a good choice for the first portion of the heating element. Advantageously, the first portion of the heating element is separated from the heater support. The portion of the heater between the first portion of the heating element and the heater support advantageously has a thermal gradient between a higher temperature at the first portion of the heating element and a lower temperature at the heater support. The distance between the first portion of the heating element and the heater support is chosen to ensure a sufficient temperature drop. However, it is also advantageous that the distance not be greater than necessary, both to reduce the size of the heating unit and to ensure that the heating unit is as robust as possible. The greater the length of the heater beyond the heater support, the more prone it is to break or bend if dropped or during repeated insertion and removal from solid spray-forming substrates. 10 Advantageously, under normal operating conditions, when the first portion of the heating element is at a temperature of between approximately 300 and approximately 550 degrees Celsius at the points of contact with the heater support, the second portion is at a temperature of less than 200 degrees Celsius. “Normal operating conditions” in this context means at standard ambient pressure and temperature, which is a temperature of 298, 15 K (25 °C, 77 °F) and a absolute pressure out of 100 15 kPa (14,504 psi , 0.986 atm). Normal operating conditions include the operation of the heating unit when positioned inside or outside an aerosol generating device housing. Advantageously, the heating unit is configured so that if the maximum temperature of the first portion is T1, the ambient temperature is T0, and the temperature of the second portion of the heating element in contact with the heater support is T2, then: (T1-T0) / (T2-T0) >2 The heating unit may comprise one or more layers of material covering the heating element. Advantageously, a protective layer, such as glass, may be provided over the heating element to prevent oxidation or other corrosion. This protective layer may completely cover the heating substrate. The protective layer, or other layers, may also provide improved heat distribution over the heater and make it easier to clean. An underlying layer of material, such as glass, may also be provided between the heating element and the heating substrate to further improve heat distribution. This underlying layer may also be used to enhance the forming process of the heating element. The dimensions of the heater can be chosen to suit the application of the heating unit, and it should be clear that the width, length, and thickness of the heater can be selected independently of each other. In one embodiment, the heater is essentially sheet-shaped and has a tapered end for insertion into an aerosol-forming substrate. The heater can have a length of between approximately 10 mm and approximately 30 mm, and advantageously between approximately 15 mm and approximately 25 mm. The surface of the heater on which the heating element is positioned can have a width of between approximately 2 mm and approximately 10 mm, and advantageously between approximately 3 mm and approximately 6 mm. The heater can have a thickness of between approximately 0.2 mm and approximately 0.5 mm, and preferably between 0.3 mm and 0.4 mm.The active heating area of ​​the heater, which corresponds to the portion of the heater where the first portion of the heating element is positioned, can have a length of between 5 mm and 20 mm and advantageously is between 8 mm and 15 mm. The heater support can contact the heater over a length of between 2 mm and 5 mm and advantageously over a length of approximately 3 mm. The distance between the heater support and the first portion of the heating element can be at least 2 mm and advantageously at least 2.5 mm. In a preferred embodiment, the distance between the heater support and the first portion of the heating element is 3 mm. In a second aspect of the invention, an aerosol generating device is provided comprising: a housing, a heating unit according to the first aspect of the invention, wherein the heater support is coupled to the housing, an electrical power supply connected to the heating element, and a control element configured to control the power supplied from the power supply to the heating element; where the housing defines a cavity surrounded by the first portion of the heating element, the cavity is configured to receive an aerosol-forming article containing an aerosol-forming substrate. As used in this description, an “aerosol-generating device” refers to a device that interacts with an aerosol-forming substrate to generate an aerosol. The aerosol-forming substrate may be part of an aerosol-generating article, for example, part of a smoking article. An aerosol-generating device may be a smoking device that interacts with an aerosol-forming substrate of an aerosol-generating article to generate an aerosol that is directly inhalable into a user’s lungs through the user’s mouth. An aerosol-generating device may also be a container. The heater support can form a surface that closes one end of the cavity. 65 The device is preferably a portable device that the user can comfortably hold between the fingers of one hand. The device may have an essentially cylindrical shape and a length of between 70 and 120 mm. The maximum diameter of the device is preferably between 10 and 20 mm. In one embodiment, the device has a polygonal cross-section and a protruding button formed on one face. In this embodiment, the diameter of the device is between 12.7 and 13.65 mm measured from one flat face to an opposite flat face; between 13.4 and 14.2 mm measured from one edge to an opposite edge (i.e., from the intersection of two faces on one side of the device to a corresponding intersection on the other side); and between 14.2 and 15 mm measured from the top of the button to an opposite flat face of the button. The device may be an electrically heated smoking device. 10 The device may include heaters other than the heating unit described in the first aspect. For example, the device may include an external heater located around the perimeter of the cavity. An external heater may have any suitable shape. For example, an external heater may take the form of one or more flexible heating paper wraps on a dielectric substrate, such as a polyamide. The flexible heating paper wraps may be shaped to fit the perimeter of the cavity.Alternatively, an external heater may take the form of a metal grid or grids, a flexible printed circuit board, a molded interconnect device (MID), a ceramic heater, a flexible carbon fiber heater, or it may be formed by using a coating technique, such as plasma vapor deposition, onto a suitably shaped substrate. An external heater may also be formed by using a metal with a defined temperature-resistivity relationship. In such illustrative devices, the metal may be formed as a track between two layers of suitable insulating materials. An external heater formed in this way may be used to heat and monitor the external heater's temperature during operation. 25 The power supply can be any suitable power source, for example, a DC voltage source such as a battery. In one embodiment, the power supply is a lithium-ion battery. Alternatively, the power supply can be a nickel-metal hydride battery, a nickel-cadmium battery, or a lithium-based battery, for example, a lithium-cobalt battery, a lithium-iron-phosphate battery, a lithium titanate battery, or a lithium-polymer battery. 30 The control element can be a simple switch. Alternatively, the control element can be electrical circuits and may comprise one or more microprocessors or microcontrollers. In a third aspect of the invention, an aerosol generating system is provided comprising an aerosol generating device 35 according to the second aspect of the invention and one or more aerosol forming articles configured to be received in the cavity of the aerosol generating device. The aerosol-forming article may be a smoking article. During operation, a smoking article containing the aerosol-forming substrate may be partially contained within the aerosol-generating device. The smoking article may have an essentially cylindrical shape. The smoking article may be essentially elongated. The smoking article may have a length and a circumference essentially perpendicular to the length. The aerosol-forming substrate may have an essentially cylindrical shape. The aerosol-forming substrate may be essentially elongated. The aerosol-forming substrate may also have a length and a circumference essentially perpendicular to the length. The smoking article may have a total length between approximately 30 mm and approximately 100 mm. The smoking article may have an external diameter between approximately 5 mm and approximately 12 mm. The smoking article may include a filter plug. The filter plug may be located at a downstream end of the smoking article. The filter plug may be a cellulose acetate filter plug. The filter plug is approximately 7 mm long in one embodiment, but may have a length between approximately 5 mm and approximately 10 mm. In one embodiment, the smoking article has a total length of approximately 45 mm. The smoking article may have an external diameter of approximately 7.2 mm. Furthermore, the aerosol-forming substrate may have a length of approximately 10 mm. Alternatively, the aerosol-forming substrate may have a length of approximately 12 mm. Additionally, the diameter of the aerosol-forming substrate may be between approximately 5 mm and approximately 12 mm. The smoking article may include an outer paper wrapper. Furthermore, the smoking article may include a gap between the aerosol-forming substrate and the filter plug. The gap may be approximately 18 mm, but may be in the range of approximately 5 mm to approximately 25 mm. 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 65 may comprise a tobacco-containing material, which contains volatile tobacco-flavored compounds that 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 glycerin and propylene glycol. 5 If the aerosol-forming substrate is a solid aerosol-forming substrate, it may comprise, for example, one or more of the following: powder, granules, pills, fragments, spaghetti, strips, or sheets containing one or more of the following: herb leaf, tobacco leaf, tobacco rib fragments, reconstituted tobacco, homogenized tobacco, extruded tobacco, molded tobacco leaf, and expanded tobacco. The solid aerosol-forming substrate may be in loose form or may be provided in a suitable container or cartridge. Optionally, the solid aerosol-forming substrate may contain additional tobacco or non-tobacco flavored volatile compounds that are released upon heating of the substrate. The solid aerosol-forming substrate may also contain capsules that, for example, include additional tobacco or non-tobacco flavoring volatile compounds, and such capsules may melt during heating of the solid aerosol-forming substrate. 15 As used herein, homogenized tobacco refers to a material formed by agglomerating tobacco particles. Homogenized tobacco may be in the form of a sheet. Homogenized tobacco material may have an aerosol-forming content greater than 5% by dry weight. Alternatively, homogenized tobacco material may have an aerosol-forming content of between 5% and 30% by dry weight. Sheets of homogenized tobacco material 20 may be formed by agglomerating tobacco particles obtained by milling or otherwise combining sheets of tobacco leaf or tobacco leaf stems, or both.Alternatively or additionally, homogenized tobacco material sheets may comprise one or more of the following: tobacco powder, tobacco fines, and other particulate tobacco byproducts that are formed, for example, during the treatment, handling, and transport of tobacco. Homogenized tobacco material sheets may comprise one or more intrinsic binders, i.e., endogenous tobacco binders, one or more extrinsic binders, i.e., exogenous tobacco binders, or a combination thereof to aid in agglomerating the tobacco particles; alternatively or additionally, homogenized tobacco material sheets may comprise other additives, including, but not limited to, tobacco and other fibers, aerosol formers, humectants, plasticizers, flavorings, fillers, aqueous and non-aqueous solvents, and combinations thereof. Optionally, the solid aerosol-forming substrate may be supplied or incorporated into a thermally stable carrier. The carrier may be in the form of a powder, granules, pills, fragments, spaghetti, strips, or sheets. Alternatively, the carrier may be a tubular carrier having a thin layer of the solid substrate deposited on its inner surface, its outer surface, or both. Such a tubular carrier may be formed, for example, from paper or a paper-like material, a nonwoven carbon fiber blanket, a low-mass open-mesh metal sieve, a perforated metal sheet, or any other thermally stable polymer matrix. In a particularly preferred embodiment, the aerosol-forming substrate comprises a crinkled, crimped sheet material 40 of homogenized tobacco material. As used herein, the term “crimped sheet” refers to a sheet having a plurality of essentially parallel ridges or corrugations. Preferably, when the aerosol-generating article has been assembled, the essentially parallel ridges or corrugations extend along, or are parallel to, the longitudinal axis of the aerosol-generating article. This advantageously facilitates the crinkled sheet of homogenized tobacco material 45 to form the aerosol-forming substrate.However, it will be noted that the crinkled sheets of homogenized tobacco material incorporated into the aerosol-generating article may alternatively or additionally have a plurality of essentially parallel ridges or corrugations arranged at an acute or obtuse angle to the longitudinal axis of the aerosol-generating article when the article has been assembled. In certain embodiments, the aerosol-forming substrate may comprise a crinkled sheet of homogenized tobacco material 50 having an essentially uniform texture over a substantial portion of its entire surface. For example, the aerosol-forming substrate may comprise a crinkled sheet of homogenized tobacco material comprising a plurality of essentially parallel ridges or corrugations that are essentially uniformly spaced across the width of the sheet. 55 The aerosol-forming solid substrate can be deposited on the carrier surface in the form of, for example, a sheet, foam, gel, or suspension. The aerosol-forming solid substrate can be deposited across the entire carrier surface, or alternatively, it can be deposited in a pattern to provide a non-uniform flavor delivery during use. 60 The aerosol generating system is a combination of an aerosol generating device and one or more aerosol generating items for use with the device. However, the aerosol generating system may include additional components, such as, for example, a charging unit for recharging an electrical power supply integrated into a power supply device or an electrically powered aerosol generating device. 65 In a fourth aspect of the invention, a method of manufacturing a heating unit is provided, comprising: provide a heating substrate; depositing one or more electrically resistive heating elements onto the substrate, each heating element comprising a first portion and a second portion configured such that, 5 when an electric 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 electric current, wherein the first portion of the heating element is deposited onto a heating area of ​​the heating substrate and the second portion of the heating element is deposited onto a containment area of ​​the heating substrate; and 10 mold a heater support to the containment area of ​​the heating substrate. Advantageously, the heater support is formed by injection molding. The heater support can be formed from an injection-molded polymer, such as PEEK. 15 Advantageously, the heating substrate is essentially sheet-shaped. The components of the heating unit can be as described with reference to the first aspect of the invention. The molding stage may involve molding the heater support to surround the substrate containment area. The heater support may directly cover the second portion of the heating element. In a further aspect of the invention, a heater is provided for heating an aerosol-forming substrate, the heater comprising: a heater comprising an electrically resistive heating element and a heating substrate 25; wherein the heating element comprises a first portion formed from a first material and a second portion formed from a second material different from the first material, configured such that, when an electric 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 electric current. In a further aspect of the invention, a heating unit is provided for heating an aerosol-forming substrate, the heating unit comprising: a heater comprising an electrically resistive heating element; and 35 a heater support attached to the heater; wherein the heating element comprises a first portion and a second portion configured such that, when an electric 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 electric current; and wherein the heater support surrounds the second portion of the heating element and is formed from a moldable polymeric material. Although the description refers to various aspects, it is important to note that the features described in relation to one aspect of the description may apply to other aspects. In particular, the aspects of the heater, unit, device, system, or method described in one aspect of the invention may apply to any other aspect of the invention. Furthermore, although the description refers to smoking devices, it is important to note that medical inhaler-type devices may utilize the features, apparatus, and functionalities described herein. The following will describe in detail some embodiments of the invention, by way of example, with reference 50 to the accompanying drawings, in which: Figure 1 is a schematic diagram of an aerosol generating device; Figure 2 is a schematic cross-section of the front end of an aerosol generating device of the type 55 shown in Figure 1, with the heater inserted into the smoking article; Figure 3 is a schematic illustration of a heater according to the present invention; Figure 4 shows the heater of Figure 3 with a heater bracket assembled to it; 60 Figure 5 is a cross-section of the heater in Figure 3; Figure 6 is an illustration of the temperature profile along a heater of the type shown in Figure 3. 65 Figure 1 shows a simplified representation of the components of one modality of an electrically heated aerosol generating system 100. Specifically, the elements of the electrically heated aerosol generating system 100 are not drawn to scale in Figure 1. Elements that are not relevant to understanding the modality have been omitted to simplify Figure 1. 5 The electrically heated aerosol generating system 100 comprises an aerosol generating device with 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 into the housing 10 to come into thermal proximity with the heater 14. The aerosol forming substrate will release a range of volatile compounds at different temperatures. By controlling the maximum operating temperature of the electrically heated aerosol generating system 100 to be below the selective release of undesirable components, the release of certain volatile compounds can be controlled. Inside the housing (10) is an electrical power supply (16), for example, a rechargeable lithium-ion battery. A controller 18 is connected to the heater 14, the electrical power supply 16, and a user interface 15 20, for example, a button or monitor. 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 between 250 and 450 degrees Celsius. Figure 2 is a schematic cross-section of the front end of an aerosol-generating device 20 of the type shown in Figure 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 coupling with the aerosol-generating article 12 for consumption of the aerosol-generating article 12 by a user. The housing 10 of the aerosol-generating device defines a cavity, open at the proximal end (or mouth-side end 25), to receive an aerosol-generating article 12 for consumption. The distal end of the cavity encompasses a heating unit 24 comprising a heater 14 and a heater holder 26. The heater 14 is retained by the heater holder 26 such that an active heating area of ​​the heater is located within the cavity. The active heating area of ​​the heater 14 is located within the distal end of the aerosol-generating article 12 when the aerosol-generating article 12 is fully received 30 within the cavity. Heater 14 is shaped like a sheet that ends 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. The first and second faces of the heater are defined by the heater's width and length. 35 An illustrative aerosol-forming article, as shown in Figure 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 filter nozzle 60. These four elements are arranged sequentially and in coaxial alignment and are assembled using cigarette paper 40 70 to form a rod. When assembled, the aerosol-forming article has a length of 45 millimeters and a diameter of 7 millimeters. The aerosol-forming substrate comprises an array of curled tobacco leaves wrapped in filter paper (not shown) to form a plug. The molded tobacco leaves include one or more aerosol formers, such as glycerin. The hollow tube 40 is located immediately adjacent to the aerosol-forming substrate 30 and is formed from a cellulose acetate tube. The tube 40 defines an opening with a diameter of 3 millimeters. One function of the hollow tube 40 is to position the aerosol-forming substrate 30 toward the distal end 23 of the rod 21 so that it can be in contact with the heater. The hollow tube 40 prevents the aerosol-forming substrate 30 from being forced along the rod toward the nozzle when the heater is inserted into the aerosol-forming substrate 30. The transfer section 50 comprises a thin-walled tube 18 millimeters in length. The transfer section 50 allows volatile substances released by the aerosol-forming substrate 30 to pass along the length of the article to the filter nozzle 60. The volatile substances can be cooled within the transfer section to form an aerosol. The 60 filter nozzle is a conventional filter nozzle made of cellulose acetate, which is approximately 7.5 millimeters long. 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 with 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 positions the elements and defines the aerosol-forming article 12. 65 As the aerosol-generating article 12 is pushed into the cavity, the conical point of the heater engages the aerosol-forming substrate 30. Applying force to the aerosol-forming article causes the heater to penetrate the aerosol-forming substrate 30. When the aerosol-forming article 12 is properly fitted into the aerosol-generating device, the heater 14 is inserted into the aerosol-forming substrate 30. When the heater is activated, the aerosol-forming substrate 30 is heated, and the volatile substances 5 are generated or produced. As the user inhales through the filter nozzle 60, air enters the aerosol-forming article, and the volatile substances condense to form an inhalable aerosol. This aerosol passes through the filter nozzle 60 of the aerosol-forming article and enters the user's mouth. Figure 3 illustrates a heating element 14 of the type shown in Figure 2 in more detail. The heater 14 comprises an electrically insulating heating substrate 80, which defines the shape of the heating element 14. The heating substrate 80 is formed from an electrically insulating material, which can be, for example, aluminum (Al₂O₃) or stabilized zirconium (ZrO₂). It will be evident to a person skilled in the art that the electrically insulating material can be any suitable electrically insulating material and that many ceramic materials are suitable for use as the electrically insulating substrate. The heating substrate 80 is essentially sheet-shaped. That is, the heating substrate has a length that, during use, extends along the longitudinal axis of an aerosol-forming article coupled with the heater, a width, and a thickness. The width is greater than the thickness.The heating substrate 80 terminates in a point or tip 90 to penetrate an aerosol-forming substrate 30. 20 A heating element 82 formed from the electrically conductive material is deposited onto a flat surface of the heating 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 that reaches the maximum temperature and provides heat to an aerosol-forming substrate during use. The first portion is U-shaped or shaped like a hairpin. A second portion 86 is formed from gold. The second portion comprises two parallel tracks, each connected to one end of the first portion 84. The second portion spans the heater's containment area 93, which is the area of ​​the heater in contact with the heater holder 26, as shown in Figure 4. A third portion 88 is formed from silver.The third portion is positioned in the connection area 95 and provides bonding pads to which the external wires 30 are attached using solder paste or other bonding techniques. The third portion comprises two parallel pads, each connected to one end of one of the parallel tracks of the second portion 86, opposite the first portion 84. The third portion 88 is positioned on one side of the containment area 93 opposite the first portion. 35 The shape, thickness, and width of the first, second, and third portions can be chosen to provide the desired resistance and temperature distribution during use. However, the first portion has a significantly higher electrical resistance per unit length than the second and third portions, and as a result, when an electric current passes through the heating element 82, the first portion generates most of the heat and therefore reaches the highest temperature. The second and third portions 40 are configured to have very low electrical resistance and therefore provide very little Joule heating. The total electrical resistance of the heating element is approximately 0.80 ohms at 0°C, rising to approximately 2 ohms when the active heating area 91 reaches 400°C.The battery voltage of the lithium-ion battery is approximately 3.7 Volts, so the typical maximum current supplied by the power supply (at 0ºC) is approximately 4.6A. 45. Platinum has a positive temperature coefficient of resistance, and therefore 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 high a temperature rise as the first portion. This means that the change in resistance of the second and third portions will be small compared to the changes in 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 a heater or temperature sensor is described in EP2110033 B1.55 Figure 4 shows the heater 14 assembled to a heater support 26 to form a heating unit. The heater support 26 is formed from polyether ether ketone (PEEK) and injection-molded around the heater to enclose the containment area 93. The heater substrate 80 can be formed with notches or protrusions in the containment area to ensure a strong bond between the heater support 60 and the heater. In this embodiment, the heater support 26 has a circular cross-section to accommodate a circular housing 10 of the aerosol generating device. However, the heater support can be molded into any desired shape and with any desired mating elements to accommodate other components of the aerosol generating device. 65 Figure 5 is a schematic cross-section of the heater in Figure 3. Figure 5 illustrates the overlap between the first, second, and third portions of the heating element. The heater construction can be described as follows. The heating substrate 80 is coated with glass layers 92, 96 on both the first and second surfaces. This protects the substrate and improves heat distribution across the heater surface 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 onto the glass layer 92, overlapping the gold tracks to ensure low electrical resistance contact between the first and second portions.The silver connecting pads that form the third portion 88 of the heating element are also deposited onto the glass layer 92, overlapping the gold tracks 10 to ensure low electrical resistance contact between the third and second portions. Finally, an overlapping glass layer 94 is formed, covering the heating element 82 and protecting it from corrosion. The heater support can then be molded around the heater. The heater is configured so that the active heating area, corresponding to the first portion of the heating element 15, is separated from the heater support. The area of ​​the heater that extends into the cavity of the aerosol generating device is referred to as the insertion area 97. The portion of the second portion 86 of the heating element that extends into the insertion area 97 provides an energy transfer area. 20 Figure 6 is a graph 100 showing the heater temperature as a function of distance along the heater's length during the heater's operation, as illustrated in Figure 3. The heater is shown below the graph so that the temperature graph aligns with it. Ideally, the heater heats up in the insertion area 97 and cools down in the containment area 93 and the connection area 95. An ideal temperature profile is shown by the dotted line 106. In reality, the temperature profile 25 can never be stepped very rapidly. It should be noted from the actual temperature graph 100 that the heater is hottest in the active heating area, which is located where the first portion of the heating element is positioned. The maximum temperature is approximately 420°C during aerosol generation.In the energy transfer zone between the active heating area and the containment area, the temperature drops rapidly. In this configuration, the heater support temperature should ideally be 30°C lower than 200°C, as shown by line 102. The maximum permissible temperature in the heater support depends on the material used to form the support. The position of the part of the heater support closest to the active heating area is shown by line 104. The heater is configured to ensure that the temperature in the heater support (26) is less than 200°C when the active heating area reaches its maximum operating temperature. In the example shown in Figure 6, the distance (35) between the platinum portion of the heating element and the heater support is 3 mm. This distance is sufficient to ensure the required temperature drop.Gold is chosen as the material for the second portion of the heating element because, in addition to high thermal conductivity, gold has relatively low thermal conductivity, ensuring a rapid temperature drop between the active heating area and the containment area. A further temperature drop to approximately 50°C is desirable in at least a portion of the connection area, including the third portion of the heating element. In particular, it is desirable to minimize the temperature of the element closest to the controller, the power supply, and a user interface. For example, such temperature minimization will reduce or eliminate the need to correct for thermally induced variations in the electronic chips and / or systems comprising the controller, the power supply, and the interface. The illustrative methods described above are illustrative but not exhaustive. Based on the illustrative methods analyzed above, other methods consistent with the previous illustrative methods will now be evident to an expert in the technique.

Claims

1. A heating unit for heating an aerosol-forming substrate, the heating unit comprising: a heater (14) comprising an electrically resistive heating element (82); and a heater support (26) coupled to the heater (14); wherein the heating element comprises a first portion (84) and a second portion (86) configured such that, when an electric 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 electric current; and wherein the heater support (26) surrounds the second portion (86) of the heating element and is formed from a moldable polymeric material.

2. A heating unit according to claim 1, further comprising a protective layer (94) covering the heating element. 3.A heating unit according to claim 2, wherein the protective layer (94) is formed of glass.

4. A heating unit according to any preceding claim, wherein the first portion (84) of the heating element is formed from a first material and the second portion (86) of the heating element is formed from a second material, wherein the first material has a higher electrical resistivity coefficient than the second material.

5. A heating unit according to any preceding claim, wherein the second portion (86) of the heating element comprises two sections, each of the two sections being separately connected to the first portion (84) of the heating element to define an electric flow path from one section of the second portion to another section of the second portion. 6.A heating unit according to any preceding claim, wherein the heating element comprises a third portion (88) configured for electrical connection to a power supply (16), wherein the third portion is positioned on a side opposite the heater support (26) to the first portion of the heating element.

7. A heating unit according to claim 6, wherein the third portion (88) is formed from a different material than the first and second portions.

8. A heating unit according to any preceding claim, wherein the first portion (84) of the heating element is separated from the heater support (26). 9.A heating unit according to any preceding claim, wherein under normal operating conditions, when the first portion (84) of the heating element is at a temperature between 300 and 550 degrees Celsius, at the points of contact with the heater support (26) the second portion is at a temperature of less than 200 degrees Celsius.

10. A heating unit according to any preceding claim, wherein the first portion (84) has a temperature resistance coefficient greater than the second portion (86).

11. A heating unit according to any preceding claim, wherein if the maximum temperature of the first portion is T1, the ambient temperature is T0, and the temperature of the second portion of the heating element in contact with the heater support is T2, then: (T1-T0) / (T2-T0) >2. 12.An aerosol generating device comprising: a housing (10); a heating unit according to any preceding claim, wherein the heater support (26) is coupled to the housing; an electrical power supply (26) connected to the heating element; and a control element (18) configured to control the power supply from the power supply to the heating element.

13. An aerosol generating device according to claim 12, wherein the housing (10) defines a cavity surrounded by the first portion (84) of the heating element, the cavity being configured to receive an aerosol-forming article (12) containing an aerosol-forming substrate.

14. An aerosol generating device according to claim 12 or 13, wherein the device is a portable smoking device. 65 Figure 2 Figure 1 Figure 4 Figure 3 Figure 6 Distance Temperature (°C) Figure 5.

Images