INDUCTIVE HEATER ASSEMBLY WITH TEMPERATURE SENSOR

Abstract

An inductive heater assembly for an aerosol-generating device is provided, the assembly including: at least one inductor coil configured to generate a varying magnetic field when a varying electric current flows through the coil; at least one susceptor arranged to be penetrated by the magnetic field generated by the coil to heat the susceptor; at least one temperature sensor arranged to determine a temperature of the susceptor, the temperature sensor includes first and second resistive sensing elements, the first element being connected to the second element, and the first element being positioned relative to the second element such that a current induced in the first element by the magnetic field opposes a current induced in the second element by the magnetic field. An aerosol-generating device including the inductive heater assembly, control circuitry, and a power source, is also provided.

Claims

1.-15. (canceled)

16. An inductive heater assembly for an aerosol-generating device, the inductive heater assembly comprising: at least one inductor coil configured to generate a varying magnetic field when a varying electric current flows through the at least one inductor coil; at least one susceptor arranged to be penetrated by the varying magnetic field generated by the at least one inductor coil to heat the susceptor; at least one temperature sensor arranged to determine a temperature of the at least one susceptor, wherein the at least one temperature sensor comprises a first resistive sensing element and a second resistive sensing element, wherein the first resistive sensing element is connected to the second resistive sensing element, and wherein the first resistive sensing element is positioned relative to the second resistive sensing element such that a current induced in the first resistive sensing element by the varying magnetic field opposes a current induced in the second resistive sensing element by the varying magnetic field.

17. The inductive heater assembly according to claim 16, wherein the first and the second resistive sensing elements each comprise resistive wires having first and second ends and are arranged adjacent each other along their respective lengths.

18. The inductive heater assembly according to claim 17, wherein the first and the second resistive sensing elements are wound together to form a bifilar coil.

19. The inductive heater assembly according to claim 18, wherein each turn of the bifilar coil is spaced apart from its adjacent turns.

20. The inductive heater assembly according to claim 17, wherein the first and the second resistive sensing elements are electrically connected in series at their respective second ends.

21. The inductive heater assembly according to claim 16, wherein the temperature sensor is arranged around at least a portion of an external surface of the susceptor.

22. The inductive heater assembly according to claim 21, wherein a length of the temperature sensor is less than fifty percent of a length of the susceptor.

23. The inductive heater assembly according to claim 21, wherein the temperature sensor extends along substantially an entire length of the susceptor.

24. The inductive heater assembly according to claim 16, wherein the temperature sensor is in contact with the susceptor.

25. The inductive heater assembly according to claim 16, further comprising a plurality of inductor coils, wherein a separate temperature sensor is provided for each of the inductor coils.

26. An aerosol-generating device, comprising: an inductive heater assembly according to claim 16; control circuitry; and a power source, wherein the control circuitry is configured to control a supply of electrical current from the power source to the inductive heater assembly to controllably heat the susceptor, and wherein the control circuitry is connected to the at least one temperature sensor of the inductive heater assembly and is configured to determine a temperature of the susceptor by determining a resistance of the at least one temperature sensor.

27. The aerosol-generating device according to claim 26, wherein the at least one temperature sensor is connected in series with a reference resistor to form a potential divider, and wherein an output signal from the at least one temperature sensor is taken from a point of connection between the at least one temperature sensor and the reference resistor.

28. The aerosol-generating device according to claim 26, wherein the control circuitry further comprises a capacitor to filter an output signal from the at least one temperature sensor to reduce noise in the output signal.

29. The aerosol-generating device according to claim 28, wherein the capacitor is connected in parallel across the reference resistor.

30. The aerosol-generating device according to claim 28, wherein the capacitor is configured to reduce noise in the frequency range of the varying magnetic field.

Description

[0085] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0086] FIG. 1 is a schematic part cross-sectional view of a heater assembly in accordance with an example of the present invention.

[0087] FIG. 2 is an enlarged and simplified view of a temperature sensor of a heater assembly in accordance with an example of the present invention.

[0088] FIG. 3 is a schematic part cross-sectional view of a heater assembly comprising a temperature sensor in accordance with another example of the present invention.

[0089] FIG. 4 is a schematic part cross-sectional view of a heater assembly in accordance with another example of the present invention.

[0090] FIG. 5 is a schematic part cross-sectional view of a heater assembly in accordance with another example of the present invention.

[0091] FIG. 6 is a schematic part cross-sectional view of an aerosol-generating device in accordance with another example of the present invention and an aerosol-generating article for use in the device.

[0092] FIG. 8 shows the upper part of the aerosol-generating device of FIG. 7 when the aerosol-generating article is received in the device.

[0093] FIGS. 8A to 8C show various filter circuits for an aerosol-generating device in accordance with another example of the present invention for filtering.

[0094] FIG. 9 shows the filter circuit of FIG. 8B connected to a microcontroller.

[0095] FIG. 1 shows an inductive heater assembly 10 comprising a susceptor 11 and an inductor coil 12. The inductor coil 12 is configured to generate a varying magnetic field when a varying electric current flows through the inductor coil 12. The susceptor 11 is arranged relative to the inductor coil 12 in such a way that the susceptor 11 is heatable by penetration of the varying magnetic field that may be generated by the inductor coil 12. The susceptor 11 is configured to heat an aerosol-forming substrate. Put another way, when the susceptor 11 is heated by penetration of the varying magnetic field, the aerosol-forming substrate may be heated by the susceptor. The aerosol-forming substrate heatable by the susceptor may be received in a cavity 14 of the inductive heater assembly 10. In the example of FIG. 1, the susceptor 11 is a tubular susceptor 11 which defines a cavity 14 for receiving an aerosol-forming substrate.

[0096] A temperature sensor 13 is provided in thermal contact or proximity with the susceptor 11 at a location along the length of the susceptor. As a result, the temperature sensor 13 may be used to measure the temperature of the susceptor 11. The temperature sensor 13 is a resistive temperature sensor that changes resistance as function of it temperature. The resistance of the temperature sensor 13 increases with increasing temperature in accordance with a known or determinable relationship. By measuring the resistance of the temperature sensor 13, the temperature of the temperature sensor 13 can be determined based on the relationship between temperature and resistance, which provides an indication of the temperature of the susceptor 11.

[0097] The temperature sensor 13 is in the form of a bifilar coil of copper wire which is wound around the susceptor 11. The copper wire is approximately 60 μm in diameter and each turn of the bifilar coil touches its adjacent turn(s). The copper wire is insulated or enameled to prevent electrically shorting between turns. The temperature sensor 13 is approximately 4.5 mm in length and surrounds around ten percent of the length of the susceptor 11. The internal diameter of the temperature sensor 13 is approximately 7.2 mm. The free end 13a of the bifilar coil of the temperature sensor 13 extends out of the heater assembly 10 such that it can be connected to control circuitry (not shown).

[0098] FIG. 2 shows an enlarged and simplified view of the temperature sensor 13 of the heater assembly 10 of FIG. 1. For clarity, only a couple of turns of the bifilar coil are shown. The temperature sensor comprises a first 41 and second 42 resistive sensing elements which are arranged adjacent each other along their respective lengths and are wound together into a bifilar coil around the susceptor 11. The first 41 and second 42 resistive sensing elements have first ends 41a, 42a respectively and second ends 41b, 42b respectively. The first 41 and second 42 resistive sensing elements are electrically connected in series at their respective second ends 41b, 42b. The first ends 41a, 41b may be used to connect the temperature sensor 13 to control circuitry (not shown).

[0099] A current I1 induced in the first resistive sensing element 41 by the varying magnetic field generated by the inductor coil 12 opposes a current I2 induced in the second resistive sensing element 42 by the varying magnetic field. As can be seen from FIG. 2, the current I2 induced in the second resistive sensing element 42 flows in an opposing direction to the current I1 induced in the first resistive sensing element 41. Consequently, the magnetic field produced by the second resistive sensing element 42 is substantially equal to and opposes that created by the first resistive sensing element 41 such that the magnetic fields of the first 41 and second 42 resistive sensing elements cancel each other to a significant extent. Accordingly, the self-inductance of the temperature sensor 13 is substantially reduced and the effects of noise from operating the temperature sensor in a varying magnetic field are also reduced. The temperature sensor 13 is therefore able to accurately determine temperature even when operating in the varying magnetic field.

[0100] FIG. 3 shows a heater assembly 100 according to a different example of the present invention. The heater assembly 100 is substantially the same as the heater assembly 10 of FIG. 1 and comprises a susceptor 111, an inductor coil 112 and a temperature sensor 113 in the form of a bifilar coil. The only difference in this arrangement is that the turns of the bifilar coil are spaced apart and the temperature sensor extends along substantially the entire length of the susceptor 111. In this example, the spacing between the turns of the bifilar coil assist in reducing shielding of the susceptor 111 from the varying magnetic so that the susceptor 111 is penetrated by the varying magnetic field. In other words, the spacing between the turns of the bifilar coil allow the varying magnetic field to pass through the temperature sensor 113 to the susceptor 111.

[0101] FIG. 4 shows an inductive heater assembly 10 comprising a first susceptor 11 and a second susceptor 15. The inductive heater assembly 10 also comprises a first inductor coil 12 and a second inductor coil 16. The first inductor coil 12 is configured to generate a first varying magnetic field when a first varying electric current flows through the first inductor coil 12. The second inductor coil 16 is configured to generate a second varying magnetic field when a second varying electric current flows through the second inductor coil 16. The first susceptor 11 is arranged relative to the first inductor coil 12 in such a way that the first susceptor 11 is heatable by penetration of the first varying magnetic field. The second susceptor 15 is arranged relative to the second inductor coil 16 in such a way that the second susceptor 15 is heatable by penetration of the second varying magnetic field. Therefore, when the first susceptor 11 is heated by penetration of the first varying magnetic field, an aerosol-forming substrate (not shown) located within the first susceptor 11 may be heated by the first susceptor 11. Likewise, when the second susceptor 15 is heated by penetration of the second varying magnetic field, an aerosol-forming substrate (not shown) located within the second susceptor 15 may be heated by the second susceptor 15.

[0102] The inductive heater assembly 10 of FIG. 4 comprises a first temperature sensor 13 and a second temperature sensor 17. The first 13 and second 17 temperature sensors of FIG. 4 are the same as the temperature sensor 13 of FIGS. 1 and 2. The first temperature sensor 13 is provided in thermal contact with the first susceptor 11. As a result, the first temperature sensor 13 may be used to measure the temperature of the first susceptor 11. The second temperature sensor 17 is provided in thermal contact with the second susceptor 15. As a result, the second temperature sensor 17 may be used to measure the temperature of the second susceptor 15.

[0103] In the example of FIG. 4, the first susceptor 11 is a tubular susceptor, which defines a first portion 14 of a cavity for receiving an aerosol-forming substrate. Likewise, the second susceptor 15 is also a tubular susceptor, which defines a second portion 18 of a cavity for receiving an aerosol-forming substrate.

[0104] The arrangement of FIG. 4 enables selective heating of the first susceptor 11 and the second susceptor 15. Such selective heating enables the inductive heater assembly 10 to heat different portions of an aerosol-forming substrate at different times when an aerosol-forming substrate is received in the first 14 and second 18 portions of the cavity. Furthermore, the arrangement of FIG. 4 may enable one of the susceptors 11, 15 to be heated to a different temperature than the other susceptor 15, 11. Such temperatures may be advantageously measured by using the temperature sensors 13 and 17.

[0105] FIG. 5 shows an inductive heater assembly 10 comprising a single susceptor 11 having a first region 111 and a second region 112. The inductive heater assembly 10 also comprises a first inductor coil 12 and a second inductor coil 16. The first inductor coil 12 is configured to generate a first varying magnetic field when a first varying electric current flows through the first inductor coil 12. The second inductor coil 16 is configured to generate a second varying magnetic field when a second varying electric current flows through the second inductor coil 16. The first region 111 is arranged relative to the first inductor coil 12 in such a way that the first region 111 is heatable by penetration of the first varying magnetic field. The second region 112 is arranged relative to the second inductor coil 16 in such a way that the second region 112 is heatable by penetration of the second varying magnetic field. Therefore, when the first region 111 is heated by penetration of the first varying magnetic field, an aerosol-forming substrate (not shown) located within the first region 111 may be heated by the first region 111. Likewise, when the second region 112 is heated by penetration of the second varying magnetic field, an aerosol-forming substrate (not shown) located within the second region 112 may be heated by the second region 112.

[0106] The inductive heater assembly of FIG. 5 comprises a first temperature sensor 13 and a second temperature sensor 17. The first 13 and second 17 temperature sensors of FIG. 5 are the same as the temperature sensor 13 of FIGS. 1 and 2. The first temperature sensor 13 is provided in thermal contact with the first region 111. As a result, the first temperature sensor 13 may be used to measure the temperature of the first region 111. The second temperature sensor 17 is provided in thermal contact with the second region 112. As a result, the second temperature sensor 17 may be used to measure the temperature of the second region 112.

[0107] In the arrangement of FIG. 5, the susceptor 11 is a tubular susceptor, the tubular susceptor defining a cavity 14 for receiving an aerosol-forming substrate. The inductive heater assembly 10 of FIG. 5 enables selective heating of the first region 111 and the second region 112. Such selective heating enables the inductive heater assembly 10 to heat different portions of an aerosol-forming substrate at different times, when an aerosol-forming substrate is received in the cavity 14. Furthermore, the inductive heater assembly 10 of FIG. 5 may enable one of the regions 111, 112 to be heated to a different temperature than the other region 112, 111. Such temperatures may be advantageously measured by using the temperature sensors 13 and 17.

[0108] FIG. 6 shows schematic cross-sections of an aerosol-generating device 200 and an aerosol-generating article 300 for use with the aerosol-generating device 200. Together, the aerosol-generating article 300 and aerosol-generating device 200 comprise an aerosol-generating system.

[0109] The aerosol-generating device 200 comprises a substantially cylindrical device housing 202, with a shape and size similar to a conventional cigar. The aerosol-generating device 200 further comprises a power supply 206, in the form of a rechargeable battery, control circuitry 208 including a microcontroller, an electrical connector 209, and the above described inductive heater assembly 10. In the example of FIG. 6, the inductive heater assembly 10 is similar to that of FIG. 4. However, other inductive heater assemblies may be used. In particular, inductive heater assemblies comprising one inductor coil and one susceptor may be used. Alternatively, inductive heater assemblies comprising more than two inductor coils and more than two susceptors may be used. In a preferred alternative, inductive heater assemblies comprising one susceptor, two inductor coils and two temperature sensors may be used; in particular, the inductive heater assembly of FIG. 5 can be used.

[0110] The power supply 206, control circuitry 208 and inductive heater assembly 10 are all housed within the device housing 202. The inductive heater assembly 10 of the aerosol-generating device 200 is arranged at the proximal end of the device 200. The electrical connector 209 is arranged at a distal end of the device housing 202.

[0111] As used herein, the term “proximal” refers to a user end, or mouth end of the aerosol-generating device or aerosol-generating article. The proximal end of a component of an aerosol-generating device or an aerosol-generating article is the end of the component closest to the user end, or mouth end of the aerosol-generating device or the aerosol-generating article. As used herein, the term “distal” refers to the end opposite the proximal end.

[0112] The control circuitry 208 is configured to control the supply of power from the power supply 206 to the inductive heater assembly 10. The control circuitry 208 further comprises a DC/AC inverter, including a Class-D power amplifier. The control circuitry 208 is also configured to control recharging of the power supply 206 from the electrical connector 209. The control circuitry 208 further comprises a puff sensor (not shown) configured to sense when a user is drawing on the aerosol-generating device.

[0113] The inductive heater assembly 10 comprises a first inductor coil 12 and a second inductor coil 16. The inductive heater assembly 10 also comprises a first susceptor 11 and a second susceptor 15. As described with reference to FIG. 4, the first susceptor 11 is a tubular susceptor, which defines a first portion 14 of the cavity for receiving an aerosol-forming substrate. Likewise, the second susceptor 15 is a tubular susceptor, which defines a second portion 18 of the cavity for receiving the aerosol-forming substrate. The first 12 and second 16 inductor coils are also tubular in the example of FIG. 6, and they are disposed concentrically around, respectively, the first susceptor 11 and the second susceptor 15.

[0114] The first inductor coil 12 is connected to the control circuitry 208 and the power supply 206, and the control circuitry 208 is configured to supply a first varying electric current to the first inductor coil 12. When the first varying electric current is supplied to the first inductor coil 12, the first inductor coil 12 generates a first varying magnetic field, which heats the first susceptor 11 by induction.

[0115] The second inductor coil 16 is connected to the control circuitry 208 and the power supply 208, and the control circuitry 208 is configured to supply a second varying electric current to the second inductor coil 16. When the second varying electric current is supplied to the second inductor coil 16, the second inductor coil 16 generates a second varying magnetic field, which heats the second susceptor 15 by induction.

[0116] The inductive heater assembly 10 comprises a first temperature sensor 13 in thermal contact with the first susceptor 11. The inductive heater assembly 10 comprises a second temperature sensor 17 in thermal contact with the second susceptor 15. The first 13 and second 17 temperature sensors may be used to respectively measure the temperatures of the first susceptor 11 and the second susceptor 15 as described with reference to FIG. 4.

[0117] The device housing 202 also defines an air inlet 280 in close proximity to the distal end of the first portion 14 of the cavity for receiving the aerosol-forming substrate. The air inlet 280 is configured to enable ambient air to be drawn into the device housing 202.

[0118] The aerosol-generating article 300 shown in FIG. 6 is generally in the form of a cylindrical rod having a diameter similar to the inner diameter of the cavity 14, 18 for receiving the aerosol-forming substrate. The aerosol-generating article 300 comprises a cylindrical cellulose acetate filter plug 304 and a cylindrical aerosol-generating segment 310 wrapped together by an outer wrapper 320 of cigarette paper.

[0119] The filter plug 304 is arranged at a proximal end of the aerosol-generating article 200, and forms the mouthpiece of the aerosol-generating system, on which a user draws to receive aerosol generated by the system.

[0120] The aerosol-generating segment 310 is arranged at a distal end of the aerosol-generating article 300, and has a length substantially equal to the combined length of the first 14 and second 18 portions of the cavity. The aerosol-generating segment 310 comprises a plurality of aerosol-forming substrates, including: a first aerosol-forming substrate 312 at a distal end of the aerosol-generating article 300 and a second aerosol-forming substrate 314 at a proximal end of the aerosol-generating segment 310, adjacent the first aerosol-forming substrate 312. It will be appreciated that in some embodiments two or more of the aerosol-forming substrates may be formed from the same materials. However, in this embodiment, each of the aerosol-forming substrates 312, 314 is different. The first aerosol-forming substrate 312 comprises a gathered and crimped sheet of homogenised tobacco material, without additional flavourings. The second aerosol-forming substrate 314 comprises a gathered and crimped sheet of homogenised tobacco material including a flavouring in the form of menthol. In other examples, an aerosol-forming substrate may comprise a flavouring in the form of menthol, and not comprise tobacco material or any other source of nicotine. Each of the aerosol-forming substrates 312, 314 may also comprise further components, such as one or more aerosol formers and water, such that heating the aerosol-forming substrate generates an aerosol with desirable organoleptic properties.

[0121] The proximal end of the first aerosol-forming substrate 312 is exposed, as it is not covered by an outer wrapper 320. The outer wrapper 320 comprises a line of perforations 322 circumscribing the aerosol-generating article 300 at the interface between the first aerosol-forming substrate 312 and the second aerosol-forming substrate 314. The perforations 322, enable air to be drawn into the aerosol-generating segment 310.

[0122] In the example of FIG. 6, the first aerosol-forming substrate 312 and the second aerosol-forming substrate 314 are arranged end-to-end. However, it is envisaged that in other embodiments, a separation may be provided between the first aerosol-forming substrate 312 and the second aerosol-forming substrate 314.

[0123] FIG. 7 shows an enlarged view of the proximal end of the aerosol-generating device 200 of FIG. 6 in which the aerosol-generating article 300 has been received. The aerol-generating article 300 is received such that the first aerosol-forming substrate 312 is located with the first portion 14 of the cavity and the second aerosol-forming substrate 314 is located within the second portion 18 of the cavity.

[0124] In use, a user draws on the filter plug 304 which in turn draws air through air inlet 280 which is detected by the puff detector (not shown). In response, the control circuitry (not shown in FIG. 7) activates one or more of inductor coils 12 and 16 to heat one or more of susceptors 11 and 15 which causes an aerosol to be generated from one or more of the first 312 and second 314 aerosol-forming substrates. Air flows from the air inlet 280 through the aerosol-generating device 200 and aerosol-generating article 300 along defined airflow pathways (denoted by straight arrows in FIG. 7). The generated aerosol is entrained in the airflow, which passes out of the aerosol-generating article 300 through filter 304 and into the mouth of a user.

[0125] FIGS. 8A to 8C show various filter circuits 400a to 400c for filtering the signal produced by the temperature sensor 13 of the above-described inductive heater assemblies 10 when operating in a varying magnetic field. The filter circuits 400a to 400c assist in reducing residual noise which is not removed by the bifilar arrangement of the temperature sensor 13.

[0126] In each of the filter circuits 400a to 400c, the temperature sensor 13 having a resistance Rs is placed in series with a reference resistor 51 having a known resistance Rr. In the examples of FIGS. 8A to 8C, the reference resistor 51 has a value of 100 ohms. The temperature sensor 13 and reference resistor 51 form a potential divider between a supply voltage Vcc and ground. An output signal or voltage Vo is taken from the point of connection between temperature sensor 13 and reference resistor 51.

[0127] Each of the filter circuits 400a to 400c also comprises a capacitor 53 having a capacitance C to assist with filtering out residual noise from the varying magnetic field. The capacitor 53 combines with the reference resistor 51 to form a low pass filter to filter out noise in the frequency range of the varying magnetic field, i.e. between 5 kHz and 500 kHz or higher. A filter circuit based on the example of FIG. 8B using a capacitor 53 having a capacitance C of 94 nF has been found to be particularly effective at reducing residual noise in the signal.

[0128] FIG. 9 shows the filter circuit 400b of FIG. 8B connected to a microcontroller 220 which forms part of the control circuitry 208 of FIG. 6. The microcontroller 220 can be used to determine the resistance Rs of temperature sensor 13 by determining output voltage Vo using a built-in analogue to digital converter. Once output voltage Vo has been determined, the microcontroller can calculate resistance Rs as follows.

[0129] The current I through reference resistor 51 is equal to Vo divided by Rr (that is, I=Vo/Rr). The current I through temperature sensor 13 is equal to the difference between the supply voltage Vcc and output voltage Vo divided by the resistance Rs of temperature sensor 13 (that is I=(Vcc−Vo)/Rs). Given that the current I through temperature sensor 13 is equal to the current I through reference resistor 51, equating and rearranging the two foregoing equations gives an equation for the resistance Rs:

Rs=Rr×(Vcc−Vo)/Vo

[0130] Once Rs has been determined, the temperature of the temperature sensor 13 and hence the susceptor can be determined by applying a function relating temperature and resistance or using a look up table of resistance and corresponding temperature values.

[0131] In tests, the temperature sensor 13 of FIG. 1 was shown to have a nominal resistance of 10.5 ohm at 23° C. and to have a temperature coefficient of resistance of 0.00288 K.sup.−1 (compared to a theoretical value for Cu: 0.00386 K.sup.−1). It exhibited an approximately linear relationship between temperature and resistance over the temperature range 0 to 200° C.