Method for controlling heating of a susceptor in an aerosol generating device - Patent Application 20070123633

Abstract

A method for controlling the heating of a susceptor (7) of an aerosol generation device (1) is described. The susceptor (7) is inductively heated by an oscillating circuit driven by an inverter. The method includes a pre-heating phase of the aerosol generation device (1) followed by a heating phase of the aerosol generation device (1). A step of estimating or determining the temperature of the aerosol generation device (1) is performed during the pre-heating phase and the heating phase. At the start of the pre-heating phase, the estimation or determination of the temperature is based on a determined resonant frequency of the oscillating circuit (6) or a determined index electrical value of the oscillating circuit, e.g. a capacitor voltage. The determination or estimation of the temperature proceeds to a scheme based on a measured internal temperature of the aerosol generation device (1).

Description

[Technical field]

[0001] The present disclosure generally relates to a method for controlling heating of a susceptor of an aerosol generating device, and an aerosol generating device including a controller adapted to carry out said method. [Background technology]

[0002] Aerosol generating devices generally include at least one reservoir configured to store an aerosol-generating (or vaporizable) material, which may be a solid or liquid. The aerosol-generating material is heated, without combustion, to generate an aerosol for inhalation. The aerosol is emitted into a flow path extending between an inlet and an outlet of the device. The outlet may be configured as a mouthpiece through which a user inhales to deliver the aerosol. Summary of the Invention [Problem to be solved by the invention]

[0003] In some aerosol generating devices, the aerosol generating material is stored in a removable cartridge, so that when the aerosol generating material is consumed, the cartridge can be easily removed and replaced.

[0004] The aerosol-generating material can be heated in different ways. One method is by means of induction heating. Such an aerosol-generating device therefore includes an induction heating system which typically includes an induction coil, an inductively heatable susceptor and a power supply unit.

[0005] A power supply unit or battery supplies electrical energy to the induction coil. The induction coil thus generates an alternating electromagnetic field. The susceptor couples with the electromagnetic field to generate heat, which is transferred, for example by conduction, to the aerosol-forming material. Finally, the heated aerosol-forming material generates an aerosol.

[0006] For optimal operation of an aerosol generating device, it is necessary to maximize the energy efficiency during induction heating.

[0007] The present disclosure aims to provide an improved method for controlling the inductive heating of a susceptor of an aerosol generating device, more precisely, to improve the energy efficiency in heating the susceptor, and further aims to provide a consistent, high quality inhalation experience for users of the aerosol generating device.

[0008] The heating system of the aerosol generating device is desirably capable of heating the aerosol generating material without burning it, and can heat the aerosol generating material according to a predetermined heating profile to provide a more comfortable user experience.

[0009] Accurate temperature control is crucial for heating in an aerosol generating device. The aerosol generating material may, for example, heat up too slowly or too quickly. This may result in the aerosol generating material burning and / or a poor user experience. The present disclosure aims to provide optimal temperature estimation during different operational phases of an aerosol generating device, in particular the initial pre-heating phase and the subsequent heating phases. [Means for solving the problem]

[0010] According to a first aspect of the present disclosure, there is provided a method for controlling heating of a susceptor of an aerosol generating device, the susceptor being inductively heated by an oscillating circuit driven by an inverter.

[0011] The method includes a pre-heating phase of the aerosol generation device followed by a heating phase of the aerosol generation device, and a step of estimating or determining the temperature of the aerosol generation device performed during the pre-heating phase and the heating phase, where at the start of the pre-heating phase, the temperature estimation or determination is based on a determined resonant frequency of the oscillator circuit or a determined index electrical value of the oscillator circuit (i.e., the temperature estimation or determination of the aerosol generation device is based on the ``oscillator circuit parameters'' determined at the start of the pre-heating phase), transitioning to a scheme where the temperature estimation or determination is based on the measured internal temperature of the aerosol generation device.

[0012] The indicator electrical value may be a function of the resonant frequency of the oscillator circuit, or the operating frequency at which the inverter drives the oscillator circuit, or any value related or proportional to frequency. The indicator electrical value may be, for example, a current, a voltage, an impedance, etc. The indicator electrical value may be, for example, a voltage on a capacitor of the oscillator circuit, etc.

[0013] The indicator electrical value may be determined using a sensor such as a voltage sensor or a current sensor.

[0014] The pre-heating phase is generally intended to pre-heat the aerosol generating material (or vaporizable material) stored in the aerosol generating device, e.g., in a reservoir or compartment of the aerosol generating device, and the heating phase is generally intended to heat the aerosol generating material to generate an aerosol.

[0015] At the start of the pre-heat phase, a temperature estimation or determination is initially made based on predetermined parameters of the oscillator circuit, thereby providing an accurate temperature estimation or determination during highly dynamic operation of the aerosol-generating device, where the temperature of the susceptor increases rapidly towards a target temperature, which may be in a narrow range, for example, about 230-320° C. It will be appreciated that the estimated or determined temperature of the aerosol-generating device is typically the temperature of the susceptor, but may also be the temperature of any suitable part of the aerosol-generating device, such as, for example, the aerosol-generating material (or vaporizable material) or a reservoir or compartment of the device storing the aerosol-generating material, which may optionally be related to the temperature of the susceptor, for example within an offset value.

[0016] The temperature estimation or determination is then transferred to a method based on the measured internal temperature of the aerosol generating device. Using the internal temperature measurements allows for accurate temperature estimation or determination when the temperature of the susceptor is relatively stable. It is known that temperature estimation or determination based on internal temperature measurements provided by one or more temperature sensors is less susceptible to parameter variations of the susceptor and the oscillator circuit. For example, estimating the temperature of the susceptor using the resonant frequency of the oscillator circuit may be more sensitive to the exact position of the susceptor relative to the induction coil of the oscillator circuit.

[0017] The pre-heat phase may be initiated by the controller, for example, when a user activates an inhale button, or by a trigger event, such as detection of a user puff. During the pre-heat phase, heating of the susceptor may be based on a predetermined pre-heat temperature profile.

[0018] The pre-heating phase may be performed for a predetermined time after start-up of the aerosol generating device. The duration of the pre-heating phase may be fixed. For example, the duration may be less than about 10 seconds. The duration of the pre-heating phase may be variable and may be determined by the controller based on other parameters. For example, the duration of the pre-heating phase may be determined as a function of the ambient temperature. At the end of the pre-heating phase, the controller initiates a heating phase during which the heating of the susceptor is based on a predetermined heating temperature profile of the aerosol generation.

[0019] The temperature estimation or determination may transition to using the internal temperature measurements when the aerosol generating device transitions from the pre-heating phase to the heating phase, i.e., at the end of the pre-heating phase ("initial transition"). However, the temperature estimation or determination may transition to using the internal temperature measurements during the pre-heating phase (i.e., before the end of the pre-heating phase) or after the heating phase has already been initiated by the controller. In other words, the initial transition to using the internal temperature measurements to estimate or determine the temperature of the aerosol generating device may not coincide with the end of the pre-heating phase.

[0020] The temperature estimation or determination may be based on a predetermined parameter of the oscillator circuit (e.g., resonant frequency or index electrical value) for a predetermined time after the start of the preheat phase or after start-up of the aerosol generating device before transitioning to a regime based on the measured internal temperature of the aerosol generating device. However, it may be preferred that the temperature determination or estimation transitions to a regime based on the measured internal temperature of the aerosol generating device when the rate of change of the estimated or determined temperature falls below a first predetermined value. For example, the first predetermined value may be about 3 to about 7°C / s, most preferably about 5°C / s. In this case, the temperature is initially estimated or determined based on the parameter of the oscillator circuit during the preheat phase when the rate of change of the estimated temperature exceeds the first predetermined value. At some point, the rate of change of the estimated temperature begins to decrease as the heating of the susceptor is controlled, e.g., as the target temperature is reached or approached. When the rate of change of the estimated or determined temperature falls below the first predetermined value, the determination of the estimated or determined temperature transitions to a regime based on internal temperature measurements. Switching between using oscillator circuit parameters with an estimated or determined rate of change of temperature and using a measured internal temperature means that the process of estimating or determining the temperature of the aerosol generation device is independent of other control triggers, such as the end of a pre-heating phase, allowing the device to operate with optimal accuracy.

[0021] After the initial transition, the temperature of the aerosol generating device may be estimated or determined based on the measured internal temperature of the aerosol generating device until the end of the heating phase.

[0022] Alternatively, after the initial transition, the determination of the estimated or determined temperature may transition between a scheme based on the measured internal temperature of the aerosol generating device and a scheme based on a predetermined parameter of the oscillator circuit. In particular, after the initial transition, the determination of the estimated or determined temperature may transition to a scheme based on a predetermined parameter of the oscillator circuit if the rate of change of the estimated temperature exceeds a second predetermined value. For example, the second predetermined value may be about 8 to about 12°C / s, most preferably about 10°C / s. The determination of the estimated or determined temperature may then transition to a scheme based on the measured internal temperature if the rate of change of the estimated temperature falls below the first predetermined value (or another predetermined value). The transition or switch between using the measured internal temperature and using the parameters of the oscillator circuit for the estimation or determination of the temperature of the aerosol generating device may continue until the end of the heating phase, thereby providing optimal accuracy during periods when the temperature of the susceptor increases or decreases rapidly (dynamic response) and periods when the temperature is relatively stable. In some configurations, the threshold for transitioning or switching can be selected such that a user puff during the heating phase does not result in a transition between using the parameters of the oscillator circuit and using the measured internal temperature of the aerosol generating device.

[0023] If the temperature is estimated or determined using parameters of the oscillator circuit, including a resonant frequency or an index electrical value, such as a voltage on a capacitor of the oscillator circuit, the controller may continue to receive internal temperature measurements from one or more temperature sensors. However, the internal temperature measurements are not used in the process of estimating or determining the temperature of the aerosol generating device to control the heating of the susceptor. Similarly, if the temperature is estimated or determined using internal temperature measurements, the controller may continue to determine the resonant frequency of the oscillator circuit or continue to receive index electrical value measurements, as described in more detail below. However, the determined resonant frequency or index electrical value is not used in the process of estimating or determining the temperature of the aerosol generating device to control the heating of the susceptor.

[0024] The resonant frequency may be determined by measuring the phase angle between the current in the inductor and the voltage on a capacitor of the oscillator circuit, the resonant frequency corresponding to the frequency when the phase angle is substantially equal to 90°.

[0025] The resonant frequency may be determined by minimizing an error function calculated using measurements of electrical indices in the oscillator circuit.

[0026] The method may further include an initialization step including determining an initial resonant frequency of the oscillator circuit when the susceptor is at ambient temperature. The resonant frequency in the initialization step may be determined as follows: Sweeping frequencies over a range; Measuring a characteristic electrical value in the oscillator circuit; and This may be determined by selecting a resonant frequency within the range where an extreme value of the index electrical value is obtained.

[0027] The estimated or determined temperature of the aerosol generating device may be the temperature of the susceptor.

[0028] The temperature of the susceptor can be estimated or determined using a predetermined linear function between the resonant frequency of the oscillator circuit and the temperature of the susceptor, for example, a predetermined linear function in which the resonant frequency at ambient temperature corresponds to the initial resonant frequency. The temperature of the susceptor may also be estimated or determined using a predetermined polynomial function between the resonant frequency of the oscillator circuit and the temperature of the susceptor.

[0029] The determination or estimation of the temperature may proceed based on the measured internal temperature of the aerosol-generating device and a predefined offset value. In many cases, the temperature of the susceptor cannot be measured directly using a temperature sensor due to its location. For example, the susceptor may be located within the aerosol-generating material. One or more temperature sensors may therefore be located adjacent to or within a reservoir of the aerosol-generating device and configured to measure the temperature of the aerosol-generating material rather than the temperature of the susceptor. However, the temperature of the aerosol-generating material may differ from that of the susceptor by an offset value that can be empirically determined. It is therefore possible to perform a heating phase in which the heating of the aerosol-generating material is precisely controlled based on the internal temperature measurements provided by the temperature sensors and a predefined offset value. The predefined offset value may be a constant value over time such that the same value of the offset value is used throughout the heating phase.

[0030] The estimated or determined temperature of the aerosol-generating device is preferably used to control the heating of the susceptor during the pre-heating and heating phases. For example, the estimated or determined temperature can be used by a controller to control the operation of an inverter or to vary the output voltage of a power converter, such as a boost converter, connected between the power supply unit and the inverter. Thus, the temperature of the aerosol-generating material can be controlled in an optimal manner to ensure an optimal user experience.

[0031] The heating of the susceptor can be controlled based on a comparison of an estimated or determined temperature of the aerosol generating device to a target temperature or temperature profile, such as a pre-heating temperature profile or a heating temperature profile. The temperature profile for controlling the heating can be determined by a user depending on their preference.

[0032] The aerosol generating device may further include a power converter connected between the power supply unit and the inverter, and the estimated or determined temperature may be used to vary an output voltage of the power converter or to control operation of the inverter to control heating of the aerosol generating material.

[0033] According to a second aspect of the present disclosure, there is provided a method for controlling heating of a susceptor of an aerosol generating device, the susceptor being inductively heated by an oscillating circuit driven by an inverter.

[0034] The method includes a pre-heating phase of an aerosol generating device followed by a heating phase of the aerosol generating device, and a step of estimating or determining the temperature of the aerosol generating device performed during the pre-heating phase and the heating phase, wherein at the start of the pre-heating phase, the temperature estimation or determination is based on a first parameter, and the temperature estimation or determination transitions to a regime based on a second parameter different from the first parameter if the rate of change of the estimated or determined temperature falls below a first predetermined value.

[0035] The first parameter may be a parameter of the oscillator circuit. The first parameter may be, for example, an indicated electrical value of the oscillator circuit or a resonant frequency of the oscillator circuit. The indicated electrical value may be a function of the resonant frequency of the oscillator circuit or an operating frequency at which the inverter drives the oscillator circuit, or any value related or proportional to frequency. The indicated electrical value may be, for example, a current, a voltage, an impedance, etc. The indicated electrical value may be, for example, a voltage on a capacitor of the oscillator circuit, etc. The resonant frequency of the oscillator circuit may be determined as described herein.

[0036] The second parameter may for example be a measured internal temperature of the aerosol generating device and optionally a predefined offset value. The second parameter may be a parameter of an oscillator circuit.

[0037] The first predetermined value may be about 3 to about 7° C. / sec, and most preferably about 5° C. / sec.

[0038] Further details of the first aspect of the present disclosure also apply to the second aspect of the present disclosure.

[0039] According to a third aspect of the present disclosure, an inductively heatable susceptor; an oscillator circuit configured to generate a time-varying electromagnetic field to inductively heat the susceptor; an inverter configured to drive an oscillator circuit; A temperature sensor for measuring an internal temperature of the aerosol generating device; An aerosol generating device is provided that includes a controller adapted to carry out the method of controlling heating of a susceptor described above.

[0040] The aerosol generating device may further include a power converter connected between the power supply unit and the inverter.

[0041] The aerosol generating device may include a reservoir or compartment for storing the aerosol generating material (or vaporizable material). The temperature sensor may be located adjacent to or within the reservoir or compartment. [Brief description of the drawings]

[0042] [Figure 1a] 1A-1C are schematic diagrams illustrating portions of an aerosol generating device according to two embodiments of the present disclosure; [Figure 1b] 1A-1C are schematic diagrams illustrating portions of an aerosol generating device according to two embodiments of the present disclosure; [Figure 2a] 1 shows a schematic diagram of the electronic circuit of the aerosol generating device. [Figure 2b] 1 illustrates a schematic of a control loop system according to an embodiment of the present disclosure. [Diagram 3] 3a-3c show several examples of oscillator circuits for use in inductive heating in an aerosol generating device. [Figure 4a] 1 shows a theoretical example of an oscillator circuit that can be used for inductive heating of an aerosol generating device. [Figure 4b] 4 shows an equivalent circuit of the oscillator circuit of FIG. 4a. [Figure 4c] 4b shows a vector representation of the currents in the oscillator circuit of FIG. [Figure 4d] 4b shows a vector representation of the currents in the oscillator circuit of FIG. [Diagram 5]1 shows the linear dependence of the resonant frequency of the oscillator circuit on the temperature of the susceptor of the aerosol generating device. [Figure 6] 1 shows the temperature of the susceptor of the aerosol generating device during the pre-heating and heating phases. [Figure 7a] 1 shows the temperature of the susceptor of the aerosol generating device during the pre-heating and heating phases. [Figure 7b] 1 shows the temperature of the susceptor of the aerosol generating device during the pre-heating and heating phases. [Figure 8a] 1 shows a flow diagram of a control method according to the present disclosure. [Figure 8b] 1 shows a flow diagram of a control method according to the present disclosure. [Figure 9] 1 shows a heating controller for an aerosol generating device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Several embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0044] Although exemplary embodiments have been described in the above paragraphs, it should be understood that various modifications can be made to these embodiments without departing from the scope of the appended claims, and therefore, the scope and scope of the claims should not be limited to the exemplary embodiments described above.

[0045] Any possible combination of the features described above is encompassed by the present disclosure unless otherwise expressly stated herein or clearly contradicted by context.

[0046] Unless the context clearly indicates otherwise, throughout this specification and the claims, the words "comprise", "including", and the like are intended to be construed in an inclusive sense, i.e., "including but not limited to", rather than an exclusive or exhaustive sense.

[0047] The term "aerosol generating device" or "device" as used herein may include an inhalation device that delivers an aerosol, including an aerosol for inhalation, to a user by means of an aerosol generating unit (e.g., an aerosol generating element that generates a vapor that condenses into an aerosol before being delivered to the outlet of the device at the mouthpiece for inhalation by the user). The device may be portable. "Portable" may refer to a device that is held by a user for use. The device may be adapted to generate a variable amount of aerosol that can be controlled by a trigger, for example, by operating a heater system for a variable time (rather than a metered dose of aerosol). The trigger may be activated by the user, such as an inhale button and / or an inhale sensor. The inhale sensor may be sensitive to the duration of the inhale as well as the strength of the inhale (to mimic the effect of smoking a conventional combustible smoking article, such as a cigarette, cigar, pipe, etc.) to provide a variable amount of vapor.

[0048] As used herein, the term "aerosol" may include a suspension of vaporizable material as one or more of solid particles, liquid droplets, and / or gas. The suspension may be in a gas, including air. Aerosol herein may generally refer to / include a vapor. Aerosol may include one or more components of vaporizable material.

[0049] As used herein, the term "aerosol-forming material" or "vaporizable material" is used to refer to any material that can be vaporized in air to form an aerosol. Vaporization generally occurs by raising the temperature of the vaporizing material to a temperature below the boiling point, e.g., 400°C, preferably 350°C. The vaporizable material may include or consist of an aerosol-forming liquid, a gel, a wax, a foam, etc., an aerosol-forming solid that may be in the form of a rod containing processed tobacco material, a crimped sheet or oriented strip of reconstituted tobacco (RTB), or any combination thereof. The vaporizable material may include one or more of nicotine, caffeine, or other active ingredients. The active ingredients may be carried by a carrier, which may be a liquid. The carrier may include propylene glycol or glycerin. Flavorings may also be included. Flavorings may include ethyl vanillin (vanilla), menthol, isoamyl acetate (banana oil), and the like.

[0050] Figures 1a and 1b show schematic diagrams of parts of an aerosol generating device 1 according to two different embodiments of the present disclosure. Figures 1a and 1b both show schematic diagrams of the mechanical configuration of the aerosol generating device, whereas Figure 2a shows an example of the electronic circuitry of the aerosol generating device.

[0051] The aerosol generating device generally comprises a body 2 and a cartridge 3 .

[0052] The cartridge 3 includes a first end 30 configured for engagement with the body 2 and a second end 31 configured as a mouthpiece portion (not shown) having a vapor outlet.

[0053] The cartridge 3 further includes at least one reservoir 32 configured to store an aerosol-forming material 33. The cartridge 3 may be disposable.

[0054] Reservoir 32 is configured to receive a correspondingly shaped aerosol-forming material 33. The aerosol-forming material 33 and / or reservoir 32 may be a disposable item or stick.

[0055] The mouthpiece is removably attached to allow access to the reservoir for the purpose of inserting or removing aerosol-forming material 33.

[0056] The heated temperature sensor 21 is configured to measure the temperature of the aerosol-forming material 33. As shown in Figures 1a and 1b, the heated temperature sensor 21 may be adjacent to at least one wall of the cartridge housing, for example. The heated temperature sensor may be located within the aerosol generating device or within the reservoir of the reservoir 32. The heated temperature sensor may be positioned to contact the aerosol-forming material 33. The heated temperature sensor 21 may correspond to known sensors, such as, for example, a "PT100" sensor.

[0057] The aerosol generating device 1 includes an induction heating system configured to enable the aerosol generating material 33 to be heated.

[0058] The induction heating system generally comprises a power supply unit or battery 4 located within the body 2, an inverter 5 and a controller 9 (visible in Figure 2b).

[0059] The inverter 5 is configured to convert the direct current from the battery 4 into an alternating high frequency current. Here, the inverter 5 includes two switches or transistors T0, T1. The transistors T0, T1 operate at the same frequency and a given duty cycle. In particular, the duty cycle of the two transistors T0, T1 of the inverter 5 is equal to 50%.

[0060] The induction heating system further includes an oscillator circuit 6. The oscillator circuit includes an inductance created by a coil 60.

[0061] Here, coil 60 is a helical induction coil that extends around reservoir 32. Induction coil 60 is powered by a power supply unit and controller.

[0062] The induction heating system also includes one or more inductively heatable susceptors 7. A susceptor is an element made of an electrically conductive material and used to heat non-conductive materials.

[0063] The inductively heatable susceptor 7 can be in direct or indirect contact with the aerosol-generating material 33 such that once the susceptor 7 is inductively heated by the induction coil 60, heat is transferred from the susceptor 7 to the aerosol-generating material to heat the aerosol-generating material and thereby generate an aerosol.

[0064] 1a, the susceptor 7 extends into the reservoir 32 with the aerosol-forming material 33. The susceptor is preferably disposed within the aerosol-forming material 33.

[0065] 1b, the susceptor 7 extends outside the aerosol-forming material 33. The susceptor 7 preferably extends along the side wall 320 of the reservoir 32.

[0066] The controller 9 is configured to operate other electronic components including the inverter 5 .

[0067] The controller 9 is arranged to control the oscillator circuit, for example by controlling the voltage supplied to the oscillator circuit from the battery 4 and the operating frequency at which the oscillator circuit is driven.

[0068] FIG. 2 a shows an oscillator circuit 6 including a battery circuit 40 , an inverter circuit 50 , a coil circuit 61 and a susceptor circuit 62 .

[0069] The aerosol generating device 1 also includes a boost converter 8 in a circuit 80 shown in FIG. 2a. In some aerosol generating devices, the boost converter can be omitted and the inverter 5 can be directly connected to the battery 4. Whether a boost converter is required depends on the characteristics of the susceptor and the oscillator circuit. If the aerosol generating device does not include a boost converter, the heating of the susceptor can be controlled by operating the inverter. For example, the inverter can be periodically turned on and off (or periodically controlled to be in an on and off state) with a duty cycle that can be varied to control the heating of the susceptor. Such operation is sometimes referred to as a "global" pulse width modulation (PWM) control scheme, where the time (or "pulse width") that the inverter is turned on varies. During the period when the inverter is on (or on state), the transistors T0 and T1 of the inverter 5 can be operated with a predetermined duty cycle. During the period when the inverter is off (or off state), both transistors T0 and T1 are off.

[0070] One end of the boost converter 8 is connected to the battery 4 , and the other end is connected to the inverter 5 .

[0071] The boost converter 8 is configured to boost the voltage, i.e. to convert a DC voltage to a higher value DC voltage. More precisely, the boost converter 8 converts the input voltage V in The higher output voltage V is supplied to the inverter 5. out The voltage is configured to be boosted to

[0072] The boost converter 8 is an advantageous solution for increasing the voltage in a minimum space.

[0073] A boost converter is a type of switched mode power supply. In particular, it uses a main switch, e.g. a transistor, to switch part of a circuit on and off at a fixed rate. Boost converter 8 includes an active switch T2 and a passive switch T3.

[0074] The active switch T2, i.e. the main switch, is here a MOSFET transistor (Metal Oxide Semiconductor Field Effect Transistor). The passive switch T3, i.e. the auxiliary switch, is here a diode. The boost converter is therefore an asynchronous boost converter.

[0075] In another embodiment, the passive switch T3 may be a MOSFET transistor. The boost converter 8 may therefore be a synchronous boost converter.

[0076] The boost converter 8 further includes an inductor 81 and a capacitor 82 .

[0077] The controller 9 is here arranged to control the boost converter 8 , in particular to control the output voltage delivered to the inverter 5 .

[0078] An example of a control loop system that can be used in the present disclosure is shown in Figure 2b: a controller 9 is connected on the one hand to an inverter 5 and on the other hand to a boost converter 8.

[0079] The controller 9 is, for example, a proportional-integral-derivative controller (PID controller).

[0080] Other types of topologies or controllers may be used to obtain more sophisticated control and better performance. The controller 9 may for example be a model-based controller. Such a controller has the advantage that it takes into account the dynamic response of the system as it changes with the operating conditions. Model-based controllers provide significantly better performance and are much less sensitive to variations in system characteristics compared to normal PID controllers. For example, the temperature can be increased or decreased quickly if required.

[0081] In yet another particular embodiment, the controller 9 may be a model predictive controller or a model-based predictive controller. Such a controller may also represent the behavior of a dynamic system and may further use a model of the system to make predictions regarding the future behavior of the system.

[0082] Some kind of hybrid or mixed control may be used. For example, if the aerosol generating device 1 includes a boost converter 8, the boost converter may be controlled by the controller 9 for some operation of the aerosol generating device (e.g. during preheating), whereas for other operation (e.g. during heating or inhalation phases) the boost converter may be bypassed or stopped and the inductive heating of the susceptor 7 controlled by an inductor, for example using the "global" PWM control scheme described above. During preheating, more power is required so it may be desirable for the boost converter 8 to provide a higher output voltage for the inverter 5. A higher voltage means less current is needed to obtain the same power, reducing losses. Then, less power is needed during the heating phase and the boost converter 8 is not needed. Bypassing the boost converter 8 therefore reduces conduction losses.

[0083] Induction heating is generally based on the series, parallel or series-parallel resonance principle. The present aerosol generating device uses the series-parallel resonance principle. Furthermore, the resonant circuit commonly used in induction heating is an RLC circuit. However, such a circuit has high losses because a high-voltage current flows through the components at the oscillation frequency. Furthermore, the components of the circuit need to be large, making it expensive.

[0084] To overcome these shortcomings, other circuits can be used, such as those shown in Figures 3a, 3b and 3c, in fact LLC, LCL and CLL circuits can be used instead of the standard RLC circuit.

[0085] LLC, LCL, and CLL circuits, when operated at parallel resonance, consume minimal current when operating at the resonant frequency and limit inrush current, allowing the components in the circuit to be scaled down to lower values ​​and smaller components to be used.

[0086] These circuits are digitally controllable, allowing measurements of the resonant frequency to be made.

[0087] An example of an oscillator circuit for an aerosol generating device is shown in Fig. 4a. This oscillator circuit is used for theoretical explanation before explaining the heating control in the aerosol generating device. The equivalent circuit of induction heating is further transferred to a simpler circuit in Fig. 4b.

[0088] To determine the frequency of the oscillator circuit, it is necessary to determine a parameter electrical value of the oscillator circuit. The parameter electrical value may be any value that is a function of the operating frequency at which the inverter 5 drives the oscillator circuit. The parameter electrical value may be, for example, a current, a voltage, an impedance, etc.

[0089] In this embodiment, the index electrical value is a voltage. This is specifically because a parallel resonant circuit is implemented, however, as mentioned above, either voltage or impedance may be used as the index electrical value depending on the type of oscillator circuit implemented in the system.

[0090] The index electrical value in the oscillator circuit can be determined by means of a sensor. In the embodiment of FIG. 2a, a voltage sensor 10 is arranged to read the voltage value across the capacitor of the oscillator circuit 6.

[0091] The resonant frequency of the oscillator, f r is affected by the values ​​of inductance L, resistance R, and capacitance C, and is given by the following equation:

number

[0092] The resonant frequency of the oscillator, f r teeth, the correct positioning of the susceptor 7 relative to the inductor 60 of the oscillator circuit 6, and - Depends on the resistance of the susceptor 7, which varies with the temperature of the susceptor. This variation in resistance may also be affected by manufacturing tolerances.

[0093] The determined resonant frequency of the oscillator circuit 6 can therefore be used to track the change in total resistance and hence the temperature of the susceptor 7 .

[0094] More specifically, the resonant frequency f r varies linearly with temperature as shown in FIG. 5. The functional form describing the temperature T of the susceptor 7 as a function of the frequency characteristic F can be written as F(T)=aT+b, where "a" and "b" are constant parameters of the functional form. Parameter "a" corresponds to the slope value of the frequency curve. Parameter "b" corresponds to the y-intercept. The functional form may be a polynomial function. However, in practice the circuit is usually optimized for the aerosol generating device to operate in a linear region, i.e., the locally linear region of the polynomial function.

[0095] The different curves in figure 5 represent the change in frequency of the oscillator circuit as a function of temperature and the position of the susceptor 7. Indeed, as explained above, the resonant frequency depends on the position of the susceptor 7 relative to the oscillator circuit. This therefore changes the y-intercept of the frequency curve. This is clearly visible in figure 5, where the slope a is the same for all curves, while the y-intercept is different for each curve.

[0096] In the illustrated embodiment, the y-intercept or b-parameter corresponds to the initial resonant frequency f i Corresponding to the initial resonant frequency f i indicates the resonant frequency of the oscillator circuit before heating the susceptor 7. In other words, it corresponds to the resonant frequency when the susceptor 7 is at the ambient temperature, i.e., around 20°C.

[0097] The curves shown therefore show that an improper insertion of the susceptor 7 into the aerosol generating device can be taken into account.

[0098] A method for controlling the heating of the susceptor 7 of the aerosol generation device 1 according to an embodiment of the present disclosure will now be described.

[0099] First, the initial resonant frequency of the oscillator, f i This first step is also called the initialization step. The initialization step is carried out when the susceptor 7 is at ambient temperature, ie before heating.

[0100] initial resonance frequency f i In order to determine the output voltage V of the boost converter, the oscillator circuit is supplied with low power energy. In particular, only the transistor T0 of the inverter 5 is turned on, while the transistor T1 remains off. out is set to a low value, preferably below a predetermined voltage, for example about 8V.

[0101] By reducing the power supplied to the oscillation circuit 6, the power supply to the susceptor 7 can be avoided.

[0102] Then, the frequency is swept over a certain range and the indicated electrical value in the oscillator circuit is measured. In practice, the initial resonant frequency f is determined as the frequency at which the extreme value of the indicated electrical value is obtained. i Select .

[0103] By extreme value is meant minimum or maximum value depending on the type of index electrical value determined. The resonant frequency corresponds to a maximum voltage or current value and a minimum impedance value.

[0104] Preferably, the duration of a range sweep is short, for example a sweep lasting no more than 50 milliseconds.

[0105] Preferably, the frequency sweep is performed multiple times, for example 4 to 12 times. i is the average value of the resonant frequencies obtained by multiple sweeps.

[0106] When the susceptor is being heated, both transistors T0, T1 of the inverter 5 typically operate at a 50% duty cycle. out is usually set to a high value as an initial value. That is, the output voltage V out is set to the desired output voltage. The desired output voltage is sufficient to provide reasonable losses if heating of the susceptor is required, and in some embodiments the desired voltage may be greater than 8V. The desired output voltage may depend on susceptor characteristics such as resistance, shape, size, etc. The output voltage V out may be adjusted to control the heating.

[0107] With reference to FIG. 6, the method for controlling an inhalation session includes a pre-heating phase PHP intended to pre-heat the aerosol-forming material 33, and a heating phase HP.

[0108] The pre-heating phase PHP is initiated by the controller 9 upon detection of a triggering event, such as activation of the inhale button by the user or detection of, for example, a puff by the user. During this pre-heating phase PHP, the controller 9 controls the induction heating system to heat the aerosol-generating material 33 based on a pre-defined pre-heating temperature profile and the estimated temperature of the susceptor 7. The pre-defined pre-heating temperature profile may, for example, be empirically determined to ensure an optimal user experience. According to another embodiment, the pre-defined pre-heating temperature profile is selected by the user depending on his or her preferences.

[0109] At the start of the preheat phase PHP, the resonant frequency is continuously tracked and used to estimate the temperature of the susceptor 7 .

[0110] One method, a direct method, is to measure the phase of the current in the inductor and the voltage across the capacitor of the oscillator circuit 6. The resonant frequency f r corresponds to the frequency obtained when the current and voltage are 90° out of phase.

[0111] An alternative, or indirect, method uses electrical measurements of the oscillatory circuit, such as current measurements, and is described with reference to Figure 4b, which shows an equivalent circuit for induction heating, and Figures 4c and 4d, which are vector representations of the currents in the equivalent circuit when it is close to and at phase resonance, respectively.

[0112] As can be seen in FIG. 4c, at near-resonance conditions, the following relationship is obtained:

number

[0113] As can be seen in Figure 4d, at resonance the phase angle α is equal to 90°. Therefore, we obtain

number

[0114] To track the resonant condition, an error function is defined. The error function is defined as the difference between the squared value of the measured or actual induction coil current and the squared value of the resonant induction coil current. In other words, the error function is expressed as follows:

number

number

[0115] The error function can be simplified as follows: ε=-2I r I f cos(α)

[0116] Therefore, at resonance with α=90°, the error ε is equal to zero.

[0117] When close to resonance, the current can be considered as the peak value of a sine wave. Therefore, the error function can be rewritten as

number

[0118] The induction heating system may further include an estimator that drives the controller 9 and is adapted to minimize this error function.

[0119] Since the resonant frequency is tracked continuously at the beginning of the preheat phase, the temperature can be determined continuously using the curves of Figure 5. In practice, the same curve corresponding to the initial resonant frequency is used to determine the temperature of the susceptor.

[0120] The curves shown in Figure 5 are fitted after determining the initial resonant frequency. These curves may or may not then be shifted depending on the equations implemented in the controller.

[0121] In another embodiment, these curves may be implemented as a look-up table, which may be stored in the memory of the aerosol generating device.

[0122] In one embodiment of the present disclosure, the controller or aerosol generating device includes a memory configured to store data including parameters of a functional form describing temperature as a function of frequency characteristics and position of the susceptor 7.

[0123] In practice, the initial resonant frequency f i If the resonant frequency at the ambient temperature is known, the initial resonant frequency f i The corresponding curve is selected taking advantage of the fact that the initial resonant frequency f i therefore represents a reference frequency which makes it possible to select a curve for determining the temperature of the susceptor 7.

[0124] The temperature of the susceptor 7 can then be determined by the value of the resonant frequency simply by reading the corresponding curve. The temperature is thus updated while the resonant frequency is updated.

[0125] By using the above described method of controlling the heating, the temperature of the susceptor 7 can be continuously and accurately determined at the start of the preheat phase in case the temperature of the susceptor rises rapidly.

[0126] The duration of the preheat phase PHP is fixed to a predetermined time, which may be, for example, less than about 10 seconds. In this case, the controller 9 detects the end of the predetermined time and initiates the heating phase HP. The duration of the pre-heating phase PHP can also be dynamically determined by the controller 9 as a function of the ambient temperature or other parameters. During the heating phase HP, the controller 9 controls the induction heating system to heat the aerosol-generating material 33 based on a predetermined heating temperature profile and the estimated temperature of the susceptor 7. The predetermined heating temperature profile is determined empirically, for example, to ensure an optimal user experience. According to another embodiment, the predetermined pre-heating temperature profile is selected by the user depending on his / her preferences. The predetermined heating temperature profile may be selected to maintain the aerosol-generating material 33 at the same temperature during the inhalation session or to vary the temperature over time.

[0127] 7a and 7b show a period during which temperature estimation is based on the determined resonant frequency of the oscillator circuit 6 (labeled "RF") and an internal temperature measurement (labeled "ITM"). The rate of change of the estimated temperature is tracked by the controller 9. At the start of the preheat phase, the rate of change of the estimated temperature is relatively high because the susceptor is heating up rapidly. This can be seen in FIGS. 6, 7a, 7b, and 8, with a steep slope at the start of preheat. If the rate of change of the estimated temperature falls below a first predetermined value (e.g., about 5°C / sec), then rather than using the resonant frequency of the oscillator circuit, the temperature of the susceptor 7 can be determined using the internal temperature measurement provided by the heating temperature sensor 21. In the example shown in FIGS. 7a and 7b, the initial transition from using the resonant frequency to measuring the internal temperature generally coincides with the end of the preheat phase. At the start of the heating phase, the temperature of the susceptor is relatively stable for a period of time. The temperature then drops rapidly, remains relatively stable at a lower temperature for a period of time, rises rapidly, remains relatively stable at a higher temperature for a period of time, and then drops rapidly. In Fig. 7a, throughout the heating phase, the controller 9 controls the operation of the induction heating system based on the internal temperature measurements provided by the heating temperature sensor 21 and a predefined offset value. The predefined offset value is shown in Fig. 6 and corresponds to the difference between the temperature of the susceptor 7 and the temperature measured by the heating temperature sensor 21, i.e., the temperature measurement of the aerosol-generating material 33. The offset value may be a constant value over time or may vary over time. In both cases, the offset value can be empirically determined. In some cases, the offset value may be a function of at least one characteristic of the aerosol-generating material (e.g., composition, size and shape) or the device (e.g., reservoir or susceptor design, susceptor material, susceptor placement within the reservoir, etc.). The offset value can be proportional to the difference between the susceptor 7 and the temperature sensor 21. In Fig. 6, the curve L1 corresponds to the temperature of the aerosol-generating material provided, for example, by the heating temperature sensor 21, and the curve L2 corresponds to the temperature measurement of the susceptor 7. It can be seen that the behavior of the curves L1, L2 during the preheating phase and the heating phase is significantly different. In particular, the temperature of the susceptor increases significantly during the preheat phase compared to the aerosol generating material temperature.These maximum differences D can be several times larger than the offset value during the heating phase. However, as mentioned above, the temperature of the susceptor during the preheating phase is estimated using the resonant frequency of the oscillator circuit, which can improve accuracy during highly dynamic operation. During the heating phase, the difference between the temperature of the susceptor and the temperature of the aerosol-generating material is more constant and can be modeled by an offset value. An accurate temperature estimation during the heating phase is therefore performed using the internal temperature measurement provided by the heating temperature sensor 21 and a predefined offset value.

[0128] In FIG. 7b, the temperature estimation is performed by repeatedly switching between the method using the resonant frequency and the method using the internal temperature measurement. In particular, after an initial transition to the method using the internal temperature measurement, the temperature estimation is performed based on the internal temperature measurement provided by the heating temperature sensor 21. This continues for a period during which the temperature is relatively stable. However, if the temperature of the susceptor drops sharply, the rate of change of the estimated temperature exceeds a second predetermined value (e.g., about 10° C. / s). The temperature estimation then switches to a method based on the resonant frequency of the oscillator circuit. It is not important whether the estimated temperature is increasing or decreasing, only that the rate of change exceeds the second predetermined value. Once the rate of change of the estimated temperature falls below the first predetermined value (e.g., about 5° C. / s) and the temperature stabilizes at a low temperature as shown in FIG. 7b, the temperature estimation switches to a method based on the internal temperature measurement. This continues for a period during which the temperature is relatively stable. However, if the temperature of the susceptor rises sharply, the rate of change of the estimated temperature exceeds the second predetermined value. The temperature estimation then switches to a method based on the resonant frequency of the oscillator circuit. If the rate of change of the estimated temperature falls below the first predetermined value and the temperature stabilizes at a high temperature as shown in Figure 7b, the temperature estimation transitions to a scheme based on the internal temperature measurement. This continues for a period of time during which the temperature is relatively stable. However, if the temperature of the susceptor drops suddenly, the rate of change of the estimated temperature exceeds the second predetermined value. The temperature estimation then transitions to a scheme based on the resonant frequency of the oscillator circuit.

[0129] 8a and 8b are flow diagrams illustrating how the temperature of the susceptor is estimated or determined during the preheat and heat up phases shown in FIGS. 7a and 7b, respectively.

[0130] FIG. 9 illustrates an example of a temperature controller 100 according to the present disclosure.

[0131] The internal temperature measurements T from the heating temperature sensor 21 are fed to a temperature estimation block 102, which also receives electrical measurements EM on the oscillator circuit to determine the resonant frequency using the selected curve. (Alternatively, the temperature estimation block may receive the determined resonant frequency from another functional block). The temperature estimation block 102 outputs an estimated temperature ET based on measurements of (a) the resonant frequency of the oscillator circuit or (b) the internal temperature, and transitions between calculating and outputting the estimated temperature based on these different inputs depending on the rate of change of the estimated temperature (see, for example, Figs. 8a, 8b). An error E between the estimated temperature ET and the temperature profile TP is calculated and used to control the induction heating system 104. In particular, the error E is fed to a control block 106, which can control the inverter (e.g., using a "global" PWM control scheme) or vary the output voltage of the boost converter 8.

[0132] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present disclosure and without diminishing its attendant advantages. Accordingly, such changes and modifications are intended to be included within the scope of the appended claims.

[0133] For example, it will be appreciated that other functional forms may be used to determine the dependence between the susceptor resonant frequency and temperature, for example non-linear functional forms such as appropriately parameterized polynomial functions.

[0134] Thus, the present disclosure provides a method for controlling inductive heating within an aerosol generating device that allows for optimized energy efficiency.

[0135] The determination of the resonant frequency of the oscillator circuit and the temperature of the aerosol-generating material is applicable to any type of susceptor and takes into account differences in the placement of the susceptor relative to the inductor. Additionally, the temperature determination accommodates changes in the susceptor or any element of the oscillator circuit that is replaceable, for example, after a certain number of uses or after damage.

Claims

1. A method for controlling the heating of a susceptor (7) of an aerosol generation device (1), the susceptor (7) being inductively heated by an oscillator circuit (6) driven by an inverter (5), the method comprising a pre-heating phase (PHP) of the aerosol generation device (1) followed by a heating phase (HP) of the aerosol generation device (1), a step of estimating or determining the temperature of the aerosol generation device (1) being carried out during the pre-heating and heating phases (PHP, HP), at the start of the pre-heating phase (PHP), the estimation or determination of the temperature being based on a determined resonant frequency of the oscillator circuit (6) or a determined index electrical value of the oscillator circuit (6), and the determination or estimation of the temperature being transitioned to a method based on a measured internal temperature of the aerosol generation device (1).

2. 10. The method of claim 1, wherein the temperature estimation or determination transitions if the rate of change of the estimated or determined temperature falls below a first predetermined value, eg, about 3 to about 7 degrees Celsius per second.

3. The method described in claim 1, wherein after the initial transition, the temperature estimation or determination is based on the measured internal temperature of the aerosol generating device until the end of the heating phase (HP).

4. The method of claim 1, wherein after an initial transition, the temperature estimation or determination transitions to a method based on a determined resonant frequency of the oscillator circuit (6) or a determined index electrical value of the oscillator circuit (6) if the rate of change of the estimated or determined temperature exceeds a second predetermined value, for example, about 8 to about 12°C / second.

5. 2. The method of claim 1, wherein the estimation or determination of the temperature at the start of the preheating phase (PHP) is based on a determined resonant frequency of the oscillator circuit (6), the resonant frequency being determined by measuring a phase angle between a current in an inductor (60) and a voltage on a capacitor of the oscillator circuit (6), the resonant frequency corresponding to a frequency when the phase angle is substantially equal to 90°.

6. 2. The method of claim 1, wherein the estimation or determination of the temperature at the start of the preheating phase (PHP) is based on a determined resonant frequency of the oscillator circuit (6), the resonant frequency being determined by minimizing an error function calculated using measurements of electrical index values ​​of the oscillator circuit (6).

7. 2. The method of claim 1, wherein the estimated or determined temperature of the aerosol generating device (1) is the temperature of the susceptor (7).

8. 8. The method according to claim 7, wherein the estimation or determination of the temperature at the start of the preheating phase (PHP) is based on a determined resonant frequency of the oscillator circuit (6), and the temperature of the susceptor (7) is estimated or determined using a predetermined linear or polynomial function between the resonant frequency of the oscillator circuit (6) and the temperature of the susceptor (7).

9. 2. The method according to claim 1, wherein the estimation or determination of the temperature at the start of the preheating phase (PHP) is based on an indicator electrical value of the oscillator circuit (6).

10. 2. The method according to claim 1, wherein the temperature determination or estimation is based on a measured internal temperature of the aerosol generating device (1) and a predetermined offset value.

11. 2. The method of claim 1, wherein the estimated or determined temperature of the aerosol generating device (1) is used to control the heating of the susceptor (7) during the preheating and heating phase (PHP, HP).

12. 12. The method of claim 11, wherein the heating of the susceptor (7) is controlled based on a comparison of the estimated or determined temperature with a target temperature or temperature profile.

13. 12. The method according to claim 11, wherein the aerosol generating device (1) further comprises a power converter (8) connected between the power supply unit (4) and the inverter (5), and the estimated temperature is used to vary the output voltage of the power converter (8) or to control the operation of the inverter (5).

14. An aerosol generating device (1), comprising: an inductively heatable susceptor (7); an oscillator circuit (6) configured to generate a time-varying electromagnetic field to inductively heat the susceptor (7); an inverter (5) configured to drive the oscillator circuit (6); a temperature sensor (21) for measuring the internal temperature of the aerosol generating device (1); a controller (9) adapted to carry out the method for controlling the heating of a susceptor (7) according to any one of claims 1 to 13; An aerosol generating device (1) comprising:

15. 15. The aerosol generating device (1) according to claim 14, further comprising a power converter (8) connected between the power supply unit (4) and the inverter (5).

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