Abstract
The present invention relates to an electrical heating assembly of an aerosol-generating device for resistively heating an aerosol-forming substrate. The heating assembly comprises a control circuit configured to provide an AC driving current. The heating assembly further comprises an electrically resistive heating element comprising an electrically conductive ferromagnetic or ferrimagnetic material for heating the aerosol-forming substrate. The heating element is operatively coupled with the control circuit and configured to heat up due to Joule heating when passing an AC driving element provided by the control circuit current through the heating element. The present invention further relates to an aerosol-generating device for use with an aerosol-forming substrate, wherein the aerosol-generating device comprises a heating assembly according to the invention.
Claims
1. An aerosol-generating device for use with an aerosol-forming substrate comprising a heating assembly for restively heating the aerosol-forming substrate, the heating assembly comprising: a control circuit configured to provide an AC driving current; an electrically resistive heating element comprising an electrically conductive ferromagnetic or ferrimagnetic material for heating the aerosol-forming substrate, wherein the heating element is operatively coupled with the control circuit and configured to heat up due to Joule heating when passing an AC driving current provided by the control circuit through the heating element, wherein the heating element is a multi-layer heating element comprising at least one support layer and at least one heating layer, wherein at least the heating layer comprises the electrically conductive ferromagnetic or ferrimagnetic material and is an edge layer of the multi-layer heating element, and wherein a layer thickness of the at least one support layer is larger than a layer thickness of the at least one heating layers.
2. The aerosol-generating device according to claim 1, wherein the multi-layer heating element comprises at least one further heating layer in addition to the at least one heating layer, the at least two heating layers sandwiching the support layer, wherein at least one of the heating layers comprise the electrically conductive ferromagnetic or ferrimagnetic material.
3. The aerosol-generating device according to claim 1, wherein the at least one support layer comprises an electrically conductive material.
4. The aerosol-generating device according to claim 3, wherein a resistivity of the electrically conductive material of the at least one or two heating layers is lower than a resistivity of the electrically conductive material of the at least one support layer.
5. The aerosol-generating device according to claim 1, wherein a relative magnetic permeability of the electrically conductive material of the at least one or two heating layers is larger than a relative magnetic permeability of the electrically conductive material of the at least one support layer.
6. The aerosol-generating device according to claim 1, wherein the electrically conductive material of the at least one or two heating layers is ferromagnetic or ferrimagnetic.
7. The aerosol-generating device according to claim 3, wherein the electrically conductive material of the at least one support layer is paramagnetic.
8. The aerosol-generating device according to claim 2, wherein the two heating layers are edge layers of the multi-layer heating element.
9. The aerosol-generating device according to claim 1, wherein at least one layer of the multi-layer heating element is substantially made of a solid material.
10. The aerosol-generating device according to claim 1, wherein the heating element is of a blade configuration or a rod configuration.
11. The aerosol-generating device according to claim 1, wherein an AC resistance of the heating element is in a range between 10 mΩ and 1500 mΩ for an AC driving current passing through the heating element having a frequency in a range between 500 kHz and 30 MHz.
Description
(1) The invention will be further described, by way of example only, with reference to the accompanying drawings, in which:
(2) FIG. 1 schematically illustrates an exemplary embodiment of an aerosol-generating device comprising an electrical heating assembly according to the present invention for resistively heating an aerosol-forming substrate;
(3) FIGS. 2-3 schematically illustrate a first and a second embodiment of a circuit diagram of the heating assembly according to FIG. 1;
(4) FIGS. 4-7 schematically illustrate a first, a second, a third and a fourth embodiment of a heating blade according to the invention;
(5) FIGS. 8-9 schematically illustrate an exemplary embodiment of a multi-layer heating blade according to the invention; and
(6) FIGS. 10-11 schematically illustrate an exemplary embodiment of a multi-layer heating rode according to the invention.
(7) FIG. 1 schematically illustrates an exemplary embodiment of an aerosol-generating device 1 comprising an electrical heating assembly 100 according to the present invention for resistively heating an aerosol-forming substrate 210.
(8) The aerosol-generating device 1 comprises a device housing 10 which includes a receiving chamber 20 at a proximal end 2 of the device 1 for receiving the aerosol-forming substrate 210 to be heated. In the present embodiment, the aerosol-forming substrate 210 is a solid tobacco-containing aerosol-forming substrate. The substrate 210 is part of a rod-shaped aerosol-generating article 200. The article 200 resembles the shape of a conventional cigarette and is configured to be received with in the receiving chamber 20 of the device 1. In addition to the aerosol-forming substrate 210, the article 200 comprises a support element 220, an aerosol-cooling element 230 and a filter element 240. All these elements are arranged sequentially to the aerosol-forming substrate 210, wherein the substrate is arranged at a distal end of the article 200 and the filter element is arranged at a proximal end of the article 200. The substrate 210, the support element 220, the aerosol-cooling element 230 and the filter element 240 are surrounded by a paper wrapper which forms the outer circumferential surface of the article 200.
(9) The main concept of the heating assembly according to the present invention is based on passing an AC driving current through a resistive heating element 110 which in turn is in thermal proximity or even in close contact with the aerosol-forming substrate 210. Using an AC driving current advantageously allows for using a massive and thus mechanically robust heating element which still provides sufficient Joule heating (due to the skin effect) such as to reach temperatures in a range suitable for heating the aerosol-forming substrate 210.
(10) In the embodiment of the heating assembly 100 as shown in FIG. 1, the heating element 110 is a blade made of a solid electrically conductive ferromagnetic material, for example permalloy, having an AC resistance R in a range between 10 mΩ and 1500 mΩ for an AC driving having a frequency in a range between 500 kHz and 30 MHz. Preferably, the heating blade 210 is made of a solid material. Advantageously, a resistance in this range is sufficiently high for heating the aerosol-forming substrate 210. At the same time, the heating element 110 provides sufficient mechanical stability to get in and out of contact with aerosol-forming substrate 210 without the risk of deformation or breakage. In particular, the blade-shaped configuration of the heating element 110 enables to readily penetrate into the aerosol-forming substrate 210 when inserting the aerosol-generating article 200 into the receiving chamber 20 of the aerosol-generating device 1.
(11) As can be further seen in FIG. 1, the heating blade 110 is fixedly arranged within the device housing 10 of the aerosol-generating device 1, extending centrically into the receiving chamber 20. A tapered proximal tip portion at the proximal end 111 of the heating blade 110 faces towards to a receiving opening at the proximal end 2 of the device 1.
(12) In addition to the heating element 110, the heating assembly 100 comprises a control circuit 120 which is operatively coupled with the heating element 110 and configured to provide an AC driving current in a range between 500 kHz and 30 MHz. Thus, when passing the AC driving current through the heating element 110 the latter heats up due to Joule heating.
(13) The control circuit 120, and thus the heating process, is powered by a DC power supply 140. In the present embodiment, the DC power supply 140 is a rechargeable battery arranged within the device housing 10 at a distal end 3 of the device 1. The battery may be either part of the heating assembly 100 or part of a global power supply of the aerosol-generating device 1 which may be also used for other components of the device 1.
(14) FIG. 2 schematically illustrates a first embodiment of a circuit diagram of the heating assembly 100 as used in the aerosol-generating device 1 shown in FIG. 1. According to this first embodiment, the control circuit 120 basically comprises a DC/AC inverter 121 for inverting the DC current/voltage IDC/+VDC provided by the DC power supply 140 into an AC driving current in a range between 500 kHz and 30 MHz for operating the heating element 110.
(15) In the present embodiment, the DC/AC inverter 121 comprises a Class-E amplifier. The Class-E amplifier comprises a transistor switch T1, for example a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET), a transistor switch driver circuit PG, and a LC load network. The LC load network comprises a series connection of a capacitor C1 and an inductor L1. In addition, the LC load network comprises a shunt capacitor C2 in parallel to the transistor switch T1 and in parallel to a series connection of the capacitor C1 and the inductor L1. Furthermore, the control circuit comprises a choke L2 for supplying the DC supply voltage +VDC to the Class-E amplifier. As mentioned further above, the heating element not only constitutes a resistance, but also a (small) inductance. Therefore, in the circuit diagram according to FIG. 2, the heating element 110 is represented by a series connection of a resistance R110 and an inductor L110. The resistive load R110 of the heating element 110 may also represent the resistive load of the inductor L1. The small number of these components allows for keeping the volume of the DC/AC inverter 121 extremely small, thus allowing to keep the overall volume of the heating assembly 100 very small, too.
(16) The general operating principle of the Class-E amplifier is well known in general. For further details of the Class-E amplifier and its general operating principle reference is made, for example, to the article “Class-E RF Power Amplifiers”, Nathan O. Sokal, published in the bimonthly magazine QEX, edition January/February 2001, pages 9-20, of the American Radio Relay League (ARRL), Newington, 5 CT, U.S.A. The aforementioned article also describes the relevant equations to be considered for dimensioning the various components of the DC/AC inverter 121. In the first embodiment as shown in FIG. 2, the inductor L1 may have an inductance in a range between 50 nH (nanohenry) and 200 nH (nanohenry), the inductor L2 may have an inductance in a range between 0.5 μH (microhenry) and 5 μH (microhenry), and the capacitors C1 and C2 may have a capacitance in a range between 1 nF (nanofarad) and 10 nF (nanofarad).
(17) FIG. 3 schematically illustrates a second embodiment of a circuit diagram of the heating assembly 100. The circuit diagram according to this second embodiment is very similar to the first embodiment shown in FIG. 2. Therefore, identical or similar components are denoted with identical reference signs. In addition to the circuit diagram of FIG. 2, the circuit diagram of the second embodiment comprises a bypass capacitor C3 connected in parallel to the heating element 110, that is, in parallel to the series connection of the resistance R110 and the inductor L110. Advantageously, the capacity of the bypass capacitor C3 is larger, in particular at least two times, preferably at least five times larger, most preferably at least ten times larger than the capacity of the capacitor C1 of the LC network. Accordingly, the bypass capacitor C3 and the inductor L110 of the heating element 110 form a LC resonator through which a major portion of the AC driving current passes through, whereas only a minor portion of the AC driving current passes through the transistor switch via the inductor L1 and the capacitor C1 of the LC network. Due to this, the bypass capacitor C3 advantageously causes a reduction of heat transfer from the heating element 110 towards the control circuit 120, in particular towards the transistor switch T1. The bypass capacitor C3 is arranged close to the heating element 110, but possibly far away from the remaining parts of the control circuit 120. The remaining parts of the control circuit 120 are preferably arranged on a PCB (printed circuit board).
(18) Heat transfer from the heating element 110 towards the control circuit 120 may be further reduced by providing an electrically conductive connector operatively coupling the control circuit 120 with the heating element 110, wherein an AC resistance of the connector 130 is lower than the AC resistance of the heating element 110. This may be achieved, for example, by choosing suitable electrically conductive materials for the connector 130 and the heating element 110. In particular, the respective materials may be chosen such that a relative magnetic permeability of an electrically conductive material of the connector 130 is lower than a relative magnetic permeability of an electrically conductive material of the heating element 110. Due to this, the skin depth is larger and thus the AC resistance is lower in the connector 130 than in the heating element 110. Preferably, the electrically conductive material of the connector 130 is paramagnetic. In the embodiment as shown in FIG. 1, the heating element 120 is operatively coupled by two connector elements 131, 132 which for example are made of tungsten, whereas the heating element 110 is made of permalloy C.
(19) Additionally or alternatively, the heating assembly may comprise a heat absorber which is thermally coupled to at least one of the control circuit 120 or the connector 130 for reducing any adverse heat effects on the control circuit 120. For example, the inductor L1 of the LC circuit shown in FIG. 2 and FIG. 3 may be embedded in a heat absorbing material, for example in a high temperature cement.
(20) FIG. 4 shows an enlarged view of the resistive heating blade 110 as used in the heating assembly 110 according to FIG. 1. In this embodiment, the heating blade comprises a central longitudinal slit 113 extending from a distal end 112 towards a proximal end 111 of the heating blade. However, the heating blade 110 is only partially disrupted by the slit 113 along a length extension of the blade. In contrast, the blade is fully disrupted by the slit 113 along a depth or thickness extension of the blade 110. As a result, the heating blade provides a U-shaped conductor path for the AC driving current (indicated by dashed double arrows) to pass through the blade. At its distal end 112, the conductor path comprises two feeding points 114 for supplying the AC driving current.
(21) At its proximal end 111, the heating blade 110 comprises a tapered tip portion allowing the blade to readily penetrate into the aerosol-forming substrate 210 of the article 200.
(22) The heating blade 110 may have a length in a range between 5 mm (millimeter) and 20 mm (millimeter), in particular, between 10 mm and 15 mm, a width in arrange between 2 mm and 8 mm, in particular, between 4 mm and 6 mm, and a thickness in a range between 0.2 mm and 0.8 mm, in particular between 0.25 mm and 0.75 mm.
(23) FIG. 5 shows a second embodiment of the heating blade 110. In contrast to FIG. 4, the heating blade 110 according to this second embodiment comprises two longitudinal slits 113.1, 113.2 extending parallel to each other along a length portion of the heating blade 110. As a result, the heating blade 110 provides two parallel U-shaped conductor paths for the AC driving current to pass through the blade, wherein the two paths indicated by dashed double arrows) have one common branch. Accordingly, the conductor paths comprises in total three feeding points 114 for supplying the AC driving current. Having two paths in parallel advantageously causes an increase of the dissipated heat and, thus, an increase of the heating efficiency.
(24) FIG. 6 and FIG. 7 show a third and a fourth embodiment of the heating blade 110 which also aim to increase the heat dissipation and, thus, the heating efficiency. In both embodiments, the heating blade 110 comprises a plurality of section-wise slits 113 resulting in a single conductor path having a meander-like or zig-zag-like configuration. Due to this, the total length of the conductor path and thus, the total amount of dissipated heat is significantly increased as compared to the configuration shown in FIG. 4.
(25) According to the third embodiment shown in FIG. 6, the heating blade 110 comprises two longitudinal slits 113.1, 113.2 parallel to each other along a length portion of the heating blade 110. The two longitudinal slits 113.1, 133.2 extend from the proximal end 111 towards the distal end 112 of the blade 110, yet not reaching the latter. In addition, the heating blade 110 comprises a U-shaped slit 113.3 which at least partially encloses the two parallel slits 113.1, 113.2. A base portion of the U-shaped slit 113.3 is arranged in a distal portion of the heating blade 110, whereas the branches of the U-shaped slit 113.3 extend towards the proximal end 111 of the blade 110, yet not reaching the latter. Furthermore, the heating blade 110 comprises a central longitudinal slit 113.4 extending along a length portion of the heating blade 110 from a distal end 112 towards a proximal end 111 of the heating blade 110, yet not reaching the latter. As can be seen from FIG. 6, the central longitudinal slit 113.4 extends parallel to and at least partially between the two longitudinal slits 113.1 and crosses the base portion of the U-shaped slit 113.3. As a result, slits 113.1, 113.2, 113.3, 113.4 provide a meander-shaped or zig-zag-shaped conductor path.
(26) According to the fourth embodiment shown in FIG. 7, the heating blade 110 comprises a central longitudinal slit 113.1 extending along a length portion of the heating blade 110 from a distal end 112 towards a proximal end 111 of the heating blade 110, yet not reaching the latter. Alongside the central longitudinal slit 113.1, the heating blade 110 further comprises a plurality of transverse slits 113.2 extending towards, but not reaching the longitudinal edges of the blade 110, thereby crossing the central slit 113.1 in a transverse configuration. In addition, the heating blade 110 comprises a plurality of side slits 113.3 arranged along both longitudinal edges of the blade 110. The side slits 113.2 are in an offset configuration relative to the transverse slits 113.2. Each side slit 113.2 extends from a respective longitudinal edge of the blade 110 towards the central longitudinal slit 113.1, yet not reaching the latter. As a result, slits 113.1, 113.2, 113.3, 113.4 provide a meander-shaped or zig-zag-shaped conductor path.
(27) FIG. 8 and FIG. 9 schematically illustrate a first embodiment of a multi-layer heating element 110. The multi-layer heating element is of a blade configuration having an outer shape essentially identical to the heating blade 110 as shown in FIG. 4. Therefore, identical or similar components are denoted with identical reference signs. While the heating blade according to FIG. 4 substantially is made of a single electrically conductive solid material or part, the multi-layer heating blade 110 according to FIGS. 8 and 9 comprises two heating layers 110.1, 110.2 as edge layers and one support layer 110.3 sandwiched between the two heating layers 110.1, 110.2. The heating layers 110.1, 110.2 are made of an electrically conductive ferromagnetic solid material, for example, permalloy. As ferromagnetic materials may be rather ductile, the support layer 110.3 is intended to increase the overall mechanical stiffness of the heating blade 110. For this, the support layer 110.3 comprises an electrically conductive solid material, for example tungsten or stainless steel, which is significantly less ductile than material of the heating layers 110.1, 110.2.
(28) When passing an AC driving current through the heating blade 110, the AC driving current is expected to flow at least partially or even mostly within the heating layers 110.1, 110.2, though the AC resistance of the support layer 110.3 could be lower than the AC resistance of the heating layers 110.1, 110.2. As a consequence, heat dissipation mainly occurs within the heating layers 110.1, 110.2. As compared to the support layer taken alone, the overall AC resistance of the multi-layer heating element is significantly increased.
(29) As can be seen in particular from FIG. 9, which is a cross-sectional view through tapered proximal tip portion of the heating blade 110 according to FIG. 8, at least the two heating layers 110.1, 110.2 have the same layer thickness and are made of the same material. Due to this, the overall setup of the heating blade 110 is symmetric and thus compensated for tensile or compressive stress states due to possible differences in the thermal expansion behavior of the various layers.
(30) In the present embodiment, the various layers 110.1, 110.2, 110.3 are connected to each other by cladding.
(31) FIG. 10 and FIG. 11 schematically illustrate a second embodiment of a multi-layer heating element 110. Instead of a blade-configuration, the heating element 110 according to this embodiment is of a rod configuration. In this configuration, the multi-layer heating element 110 comprises an inner core as support layer 110.5 which is surrounded by an outer jacket as heating layer 110.4. The heating layer 110.4 is made of conductive ferromagnetic solid material, for example, permalloy. In contrast, the support layer 110.5 is made of an electrically conductive solid material, for example tungsten or stainless steel, which is significantly less ductile than material of the heating layer 110.4. As described above with regard to the FIGS. 8 and 9, the support layer 110.5 is intended to increase the overall mechanical stiffness of the rod-shaped heating blade 110. Likewise, when passing an AC driving current through the heating blade 110, the AC driving current is expected to flow at least partially or even mostly within the outer heating layers 110.4 where heat dissipation mainly occurs.
(32) As can be seen in particular from FIG. 11, which is a cross-sectional view through the rod-shaped heating element 110 according to FIG. 10, the heating element 110 comprises a central longitudinal slit 113 extending along a length portion of the heating element from its distal end 112 towards its proximal end 112, such as to provide a U-shaped conductor path therethrough.
(33) At its proximal end 111, the rod-shaped heating element 110 comprises a tapered tip portion allowing the heating rod to readily penetrate into an aerosol-forming substrate.
