An aerosol generating device

Abstract

A battery-powered aerosol generating device comprises a heater (14) for generating aerosol from a source (12) during a heating session and a controller (20) configured to determine whether a further heating session should be permitted. The determination involves simulating the further heating session to determine whether calculated values of one or more parameters of the battery (16) will reach a threshold value during the session. The parameters may include the remaining capacity of the battery (16) or indicators of its state of health including closed circuit voltage, impedance or temperature. The controller (20) may run simulations of successive further sessions until one of the threshold values is reached, as a way of estimating the remaining number of permissible heating sessions.

Description

[0001]TITLE AN AEROSOL GENERATING DEVICE DESCRIPTION Technical field The invention relates to battery-powered aerosol generating devices such as electronic cigarettes, which a user can operate for the purpose of inhaling an aerosol. The aerosol typically contains flavouring and optionally nicotine as a component. Background of the invention Heating devices for generating an aerosol or vapour for inhalation are known in the art. (In this specification, the term “aerosol” should hereafter be taken to include “vapour” as an alternative.) Such devices typically include a heater arranged to heat an aerosolizable product (i.e., an aerosol precursor), such as a “stick” that serves as an aerosol source of flavouring in a volatile form. In operation, the device heats the aerosol source with the heater to convert constituents of the product into an aerosol for the user to inhale. In some examples, the product may comprise tobacco and may be similar to a traditional cigarette; in other examples the product may be in liquid form. Such devices are powered using the energy stored in a rechargeable battery. Their users are often concerned that the stored energy might run out at a time or in a place where it is not convenient to recharge the battery so that they will be unable to make further use of the device. Accordingly, it is desirable to be able to provide the user with an accurate estimate of the number of heating sessions that they will be able to carry out based on the remaining capacity of the battery. This allows the user to plan their usage and / or recharging of the device in an optimal way. In some devices, the state of charge of the battery is indicated by a display, e.g. a row of LEDs on the housing of the device, which are all illuminated when the battery is full and are extinguished in turn as the remaining charge in the battery becomes depleted. This gives the user a general indication of when recharging might be required but cannot easily be converted into a remaining number of heating sessions because the energy consumed during each session varies depending on a number of internal and external conditions of the device. Published international patent application WO 2024 / 133510 A1 discloses an aerosol generation device comprising a battery, a controller and a battery monitor. The controller is configured to measure an energy level of the battery using the battery monitor and to calculate the number of heating sessions that can be powered according to a first heating profile. The expected energy consumption per session is determined using a fitting algorithm to extrapolate from the successive energy consumption values of previous sessions. While this might account for changes in energy consumption due to increasing age or P51768EP / 6652 usage of the device, it assumes that all other operating conditions of the device remain the same as in previous sessions. Moreover, it cannot predict changes in parameters of the battery other than the state of charge, which might make the device unsuitable for the intended further use. It is also desirable that such a device should not begin a heating session if it will not be able to complete it. If the reason is that the remaining capacity of the battery is insufficient, then to complete only part of the session would be wasteful of energy and the aerosolizable product, as well as unsatisfactory for the user. If the reason is that there exists a risk of a condition arising that causes harm to the user or to the device itself, then clearly it would be unacceptable to allow the session to continue. In this specification, the terms “heating session”, “smoking session” and “vaping session” are used interchangeably. Summary of the invention The invention provides an aerosol generating device comprising a heater for generating aerosol from a source during a heating session; a battery for supplying power to the heater; and a controller configured to determine whether a further heating session should be permitted, wherein the determination involves simulating the further heating session and calculating values of one or more battery parameters during the simulated further heating session to determine whether the calculated values of any of the battery parameters passes or reaches a respective threshold value for that parameter. By “simulating” a heating session, we mean that the controller performs calculations to track the values of one or more variables – which include the battery parameters – at successive times during the course of the simulated session. The calculated values predict, estimate or represent the values that the corresponding real variables would be expected to take if the device were to carry out an actual heating session under the same conditions. The variables are typically calculated at discrete times within the duration of the session, rather than continuously, and the simulation is typically not carried out in real time. By performing a simulation of the further heating session, the controller can more accurately determine how the values of the battery parameters may be expected to change if a corresponding actual session is performed on the device. The simulation process is more accurate than simply extrapolating from previous sessions because it can take account of current conditions that are internal and / or external to the device. It can also track the values of battery parameters during the course of a session, with the potential to indicate that they will pass or reach a critical threshold at some intermediate time. This would not be captured solely by calculating an extrapolated value such as total energy consumption, which relates to the session as a whole. P51768EP / 6652 The simulation of the further heating session may recurrently calculate the values of battery parameters. More concretely, the values of battery parameters at the next step (i.e., step n+1) may be calculated based on the values of battery parameters at current step (i.e., step n). At a first step of the recurrent calculations, the values of battery parameters, which are directly measured, may be inputted as initial values. This may lead to a more precise battery control, compared to simply taking account of current conditions that are internal and / or external to the device without simulating the further heating session. This invention will be understood from following perspective. Even if the present value of any battery parameter (i.e., before running the simulation) does not pass or reach a dedicated threshold, the controller may not permit a further heating session in the case that the value of this battery parameter is expected to pass or reach the dedicated threshold as a result of the simulation. Actual values of the respective thresholds may be found on a user guide, a user manual, or an official website of the aerosol generating device. Since the simulation of the further heating session may take account of various parameters, a result may differ even if the battery parameter is the same or substantially the same. The current conditions that are internal and / or external to the device and are independent from the battery, or other battery parameters may affect a result of the simulation. This invention will be also understood from following perspective. If the further heating session or a discharging simulating the heating session will forcibly run (e.g., by an external device) under a condition which the controller does not permit the further heating session, a value of any battery parameter passes or reaches a dedicated threshold. The device preferably further comprises a monitoring circuit configured to output one or more real values of the battery parameters; wherein the controller is further configured to calculate the values of the one or more battery parameters during the simulated further heating session, by using the one or more parameters of the battery outputted by the monitoring circuit as initial values. The values of the battery parameters calculated by the controller during the simulation will typically more closely reflect the values achieved during a real performance of the session if they use measured real values to determine the initial conditions of the simulation. It may also mean that a signal communication transmitted to the controller from the monitoring circuit may be performed before the simulation runs. The battery parameters may include not only a primary parameter (e.g., voltage, current or temperature), which can be directly measured from the battery, but also a secondary parameter (e.g., remaining capacity, state of charge, or state of health), for which a complicated calculation is required with reference to the primary parameter. Rather than implementing such a complicated calculation into the controller (e.g., microcontroller unit (MCU)), using a dedicated monitoring circuit may be also advantageous in a design and production of the aerosol generating devices. The calculated battery parameter may be one that varies with a state of health (SOH) of the battery or an impedance of the battery. Changes in the impedance of the battery might indicate that irreversible P51768EP / 6652 physical or chemical changes are occurring, such as its internal insulation breaking down, or that more temporary conditions are prevailing such as it operating at an excessive temperature. Accordingly, impedance can be used as one proxy to represent the state of health of the battery but there are other parameters that can be measured and / or calculated to provide alternative direct or indirect indications of its state of health. An actual impedance value may be used instead of the SOH. If the battery is in a poor state of health – or is predicted by the simulation to enter a poor state of health during the course of a further session – then it may be unable to complete the session and it may risk damage to the user or to the device, for example by overheating. The controller is preferably configured, during an actual heating session, to terminate the heating session if any of the one or more parameters of the battery inputted from the monitoring circuit reach or pass a respective value being equal to or lower than the respective threshold value. By making the threshold values used in the simulation the same as the threshold values used during an actual heating session, the controller can most accurately predict whether the further heating session is at risk of being terminated. The simulation will not be always perfect. Thus, by enabling the controller so that it terminates the actual heating session based on the same or similar criteria in the simulation, a safety and / or a precision of control of the aerosol generating device may be secured. As described above, threshold values may be found in a user guide, a user manual, or an official website of the aerosol generating device. This termination may be interpreted as the termination which is triggered during or directly after activation to prevent incomplete consumption of the aerosol source. The one or more battery parameters may include a closed circuit voltage of the battery. The open circuit voltage (OCV) of the battery varies with its state of charge. The closed circuit voltage (CCV) that the battery develops when supplying a load typically changes with time because the internal impedance of the battery includes reactive components that do not vary linearly with current. If the CCV drops too low, it can indicate that the battery is at risk of failure or that it will be unable to deliver the required power to the heater. The OCV and CCV will be also understood such that the OCV may indicate an ideal performance of the battery and the CCV may indicate a real performance of the battery. Thus, the CCV may lead to improve an accuracy of the control. The one or more battery parameters may include a temperature of the battery. If the temperature of the battery becomes too high, it can risk damage to the device or accelerate a degradation of the battery depending on the type of battery. For this purpose, the controller may use a thermal model of the battery to calculate the time-dependent temperature of the battery during the simulated further heating session, the temperature being derived from the open circuit voltage of the battery. As further described below, simulating the closed circuit voltage may precisely predict the heat generated in the battery. P51768EP / 6652 The controller may use an electrical model of internal impedances of the battery to calculate the time- varying closed circuit voltage of the battery during the simulated further heating session, the closed circuit voltage being derived from a simulated open circuit voltage of the battery and from a simulated current supplied by the battery to the heater. Modelling the battery as a circuit comprising various impedances enables equations to be derived, which can be used to predict how the value of the CCV changes with time when supplying different levels of current. The calculations may be performed using either continuous or discrete variables. The simulated current supplied by the battery to the heater is preferably varied with time to control the heater temperature. It may lead to improve an accuracy of the simulation. During the simulated further heating session, the simulated current supplied by the battery to the heater may be obtained from a stored value of the average current supplied during a pre-programmed heating session. The heating session is typically pre-programmed to control the temperature of the heater according to a predetermined profile over the duration of the session but the current levels required to achieve the desired profile can vary according to the prevailing internal and external conditions of the device. Accordingly, the simulation can be made more accurate by using a stored value of the average current that was found to be required during one or more previous sessions of operating the device according to the same temperature profile. The time-varying simulated current may well correspond with an actual electrical current profile in the latest heating session. Preferably, the pre-programmed heating session is divided into a plurality of phases and the simulated current is obtained from a series of stored values of average current supplied during the successive phases of the simulated further heating session. For example, the phases may include an initial warm-up phase that requires a high current to bring the heater from its initial temperature – which is typically the ambient temperature – up to a predetermined maximum temperature. In a subsequent phase, a lower current may be required to maintain the heater at a roughly constant temperature while the device is used for vaping. The simulation will be more accurate if it can model each of these phases separately. Preferably, the calculated values of each of the one or more battery parameters is compared with the respective threshold value for that parameter only at predetermined times during the simulated further heating session, the predetermined times including at least the beginning or end of each phase. The phases of the pre-programmed heating session are normally defined such that the current or power supplied from the battery is held approximately constant during each phase. Accordingly, the battery parameters may rise or fall over the duration of a single phase but within that period their values are unlikely to rise then fall again or fall then rise again. It follows that the parameters will normally only take their maximum or minimum value at the beginning or end of a phase and the calculation can be made more efficient by only carrying out the comparison of the battery parameters with the respective P51768EP / 6652 threshold values at those predetermined times. It may lead to accelerate the simulation or reduce a load of the simulation. Thus, a high performance controller may not be mandatory. Preferably, if the controller determines as a result of the simulation that a further heating session should not be permitted, it prevents the device from starting the further heating session. The alternative would be simply to issue a warning to the user by some means but this would entail a risk that the user might miss the warning or choose to ignore it. In some devices according to the invention, if the controller determines that the further heating session should not be permitted, it is configured to perform at least one alternative simulation of the further heating session using an alternative profile of supplying power from the battery to the heater during the session, repeating this process until either the controller determines that one of the additional simulated further heating sessions should be permitted or a predetermined maximum number of the additional simulations have been performed. It may provide a better user experience if, instead of simply blocking further use of the device, the controller is able to propose or effect an acceptable alternative heating profile that permits the further use of the device without any of the one or more battery parameters transgressing its predetermined threshold. The acceptable alternative heating profile may be of short duration and / or low power density. In some devices according to the invention, if the controller determines that the further heating session should be permitted, the controller performs simulations of successive further heating sessions until it determines that one of the successive further heating sessions should not be permitted; and the controller then notifies the number of permitted sessions to a user via a user interface. By simulating a continuing sequence of further sessions until a battery parameter transgresses a predetermined threshold, the controller is able to make a highly accurate prediction of the remaining number of heating sessions that the user will be able to carry out using the device. The last values of battery parameters in the present heating session will be taken over to the next heating session as the initial values of battery parameters, for implementing a control loop. The drawings Figure 1 is a schematic diagram of an aerosol generating device in accordance with the present invention. Figure 2 is a block diagram showing the overall flow of information in a device in accordance with the present invention. Figure 3 is a plot showing a temperature profile of a heating session. Figure 4 is a plot showing a power profile of the heating session of Figure 3. Figure 5 is a flowchart showing the operation of the LSS algorithm module of Figure 2. Figure 6 is a circuit diagram to explain a battery model used in embodiments of the present invention. P51768EP / 6652 Figure 7 is a diagram to explain a model of a heater external to the aerosol source, which may be used in embodiments of the present invention. Figure 8 is a diagram to explain a model of a heater internal to the aerosol source, which may be used in alternative embodiments of the present invention. Figure 9 is a diagram to explain a battery heating model, which may be used in embodiments of the present invention. Detailed description of the drawings Figure 1 schematically shows an aerosol generating device enclosed by a housing 2. An airflow path extends from an inlet 4, via a heating chamber 6 and a conduit 8 to a mouthpiece 10. An aerosol source 12, which may be in the form of a stick, is received in the heating chamber 6 so as to be capable of replacement when it has been exhausted. A heater 14 surrounds the chamber 6 so that, when the heater 14 is connected to a supply of electrical current from a battery 16, it generates heat and increases the temperature of the aerosol source 12 to evolve an aerosol into the heating chamber 6. A user can put their lips against the mouthpiece 10 and breathe in to draw air along the airflow path, which they can inhale together with the aerosol from the source 12. The aerosol may comprise components such as nicotine and flavour compounds. It should be understood that Figure 1 is purely schematic and the device could be configured in many different ways. For instance, although the heater 14 is illustrated as a resistance coil heating the aerosol source 12 radiatively, it could alternatively heat the source 12 by conduction or induction and at least a portion of the heater 14 could directly contact or penetrate the aerosol source 12. The airflow path does not need to be straight; its inlet could be provided independently of the mouth 4 of the heating chamber 6; and the mouthpiece 10 does not need to project from the housing 2 but could comprise a simple hole in the housing 2. The device operates under the control of a controller 20, which is typically in the form of a microprocessor unit or a microcontroller unit. Data and control lines are shown connecting the controller 20 to a memory 22, a user interface 24 located on the exterior of the housing 2, an ambient temperature sensor 26 also located on the exterior of the housing 2, a puff sensor 28 located in the conduit 8, and a switch 30 that can selectively connect or disconnect the supply of current from the battery 16 to the heater 14. For simplicity, Figure 1 does not show the further circuits by which the battery 16 also supplies power to the controller 20, memory 22 and user interface 24. Again, it should be understood that Figure 1 is purely schematic and the electronic components of the device could be configured in many different ways. For instance, the memory 22 could be included on the same microchip as the controller 20; the puff sensor 28 could be located anywhere along the airflow path, in particular close to the inlet 4; and the ambient temperature sensor 26 could also be located in the P51768EP / 6652 airflow path close to the inlet 4. The switch 30 may not be a simple on / off switch but a device such as a transistor that allows the controller 20 to control the level of current that flows from the battery 16 to the heater 14, either in an analogue fashion or by using pulse width modulation (PWM) or pulse frequency modulation (PFM). The user interface 24 is schematically shown as a screen on the exterior of the housing 2, by which information can be displayed to the user. Alternatively, a limited range of information could be conveyed by one or more LEDs. For the user to input commands to the device, the interface 24 could be a touch screen or one or more control buttons (not illustrated) could be provided. Additionally or alternatively to the built in interface 24, the device could comprise an antenna (not illustrated), by which the controller 20 transmits information to and receives commands from a smart phone and / or a smart watch. The user interface could accordingly be provided via an app on the smart phone, which could also be used as a source of data such as ambient temperature and location. Figure 2 is a block diagram that shows one possible configuration of the flow of information in software executed by the controller 20 to carry out the present invention. The controller 20 is embodied as a microcontroller unit (MCU). From a fuel gauge 40, the controller 20 receives data that represents the remaining capacity of the battery 16, and from a temperature sensor 42, the controller 20 receives data that represents the temperature of the heater 14. The temperature sensor 42 may be a negative temperature coefficient (NTC) thermistor. The fuel gauge 40 may be a dedicated integrated chip (IC) to periodically calculate the parameter of the battery 16 (e.g., the remaining capacity) based on inputs from various sensors, and to subsequently store these into an internal register by updating previous values. By periodically communicating with the fuel gauge 40, the controller 20 may obtain the latest values of the parameters of battery 16. In Figure 2, the parameter of the battery 16 is labelled as “batteryMeasurements”. A communication between the fuel gauge 40 and the controller 20 may be realized via any type of serial communication (e.g., I2C, SPI or UART). An actual calculation of the remaining capacity is rather complicated, so using the fuel gauge 40 may be advantageous in view of development and production of the aerosol generating device. The fuel gauge 40 may be also named as a gas gauge. The temperature sensor 42 is not limited to the NTC thermistor. Either one of a positive temperature coefficient (PTC) thermistor, a thermocouple or a thermopile may be alternatively or additionally employed. In Figure 2, the data representing the temperature of the heater 14 is labelled as “heaterTemperature”. The controller 20 optionally passes the battery data to a battery observer module 44, which outputs battery parameters to a battery model 46. The battery observer module 44 may calculate a future value P51768EP / 6652 of the parameter of the battery 16 passed from the controller 20, and / or convert the parameter of the battery 16 into a secondary parameter being more suitable for the battery model 46. Since the fuel gauge 40 is the IC being commercially available, original outputs of the fuel gauge 40 are not always suitable for the battery model 46. In Figure 2, the outputs of the battery observer module 44 are labelled as “batteryModelParams”. Of course, the outputs of the battery observer module 44 may also contain the parameter of the battery 16 obtained from the fuel gauge 40 as original. Details of the battery observer module 44 are described later. The battery model 46 maintains a model of the condition of the battery 16 over time – both during a heating session and over the charging cycle of the battery – for example to estimate whether its core temperature, surface temperature or closed circuit voltage (CCV) exceeds certain thresholds, which would indicate to the controller 20 that the device should not be used. The simulation carried out by the battery model 46 may make use of ambient temperature data received from the temperature sensor 26. The battery model 46 may contain a thermal model to estimate a temperature at a specific point of the battery 16 at a specific timing, and an equivalent circuit as an electrical model to estimate the CCV at a specific timing. In Figure 2, one directional communication from the battery observer module 44 to the battery model 46 is depicted, but actual communication may be bi-directional. Details of the battery model 46 are described later. The controller 20 also passes the heater temperature data to a heater observer module 48, which output heater parameters to a heater model 50. In Figure 2, the output from the heater observer module 48 is labelled as “heaterModelParams”. The heater model 50 also receives data from a heating protocol output control logic block 52 (HPOCL), which provides the temperature setpoints that the heater 14 should reach as its temperature varies over the course of a heating session. In Figure 2, the data from the HPOCL block 52 is labelled as “temperatureSetpoints”. As shown in Figure 3, each heating session preferably comprises a series of successive phases: for example, a ramp-up phase during which the heater is brought up to its maximum temperature, followed by a phase in which the current is cut off to allow the temperature to fall to a desired operating temperature. In a third phase, during which the user commences vaping, sufficient current is supplied to maintain the operating temperature for a predetermined time (135s in this example). Further phases may follow, in which the temperature is ramped up again, then maintained at a new, higher level for a further predetermined time. The profile of temperature setpoints can be specified by a user or can be adapted to different circumstances, e.g. to maximize battery life. The heater observer module 48 may calculate a future value of the heater temperature passed from the controller 20, and / or convert the heater temperature into a secondary parameter being more suitable for the heater model 50. Of course, the outputs of the heater observer module 48 may also contain the heater temperature obtained from the temperature sensor 42 as original. Details of the heater observer module 48 are described later. P51768EP / 6652 The heater model 50 uses the received data about the actual heater temperature and the desired temperature profile to control the current supply to the heater 14 (e.g. by pulse width modulation) in order to match as closely as possible the desired temperature profile. Strictly, the specified temperature profile should refer to the temperature of the aerosol source 12, not the heater itself, and the heater model 50 can also simulate the flow of heat from the heater 14 to the aerosol source 12. Alternatively, a temperature of the heater 14 may be used instead of the temperature of the aerosol source 12 to simplify and accelerating a calculation. Figure 4 shows examples of how the power supply to the heater 14 might be varied with time in order to achieve the temperature profile of Figure 3. (The horizontal timescales of Figures 3 and 4 are the same.) The outputs of the battery model 46 and the heater model 50 are received by an LSS (Last Smoking Session) assurance module 55. The LSS assurance module 55 also receives data from a key profile information module 58, which data may include information about the power profile of the last heating session. Based on the data it receives from the various sources, the LSS assurance module 55 carries out a basic check of whether the remaining energy in the battery 16 is sufficient carry out a further smoking session and, if so, it performs at least one simulation of the further smoking session to determine whether, according to predetermined criteria, it should be permitted to proceed. On the basis of its determination, the LSS assurance module 55 outputs information 60 about the outcome of the simulation, which is used to control the further behaviour of the device. If the simulation indicates that the further session should be permitted, it may commence straight away. If the determination is that the further session should not be permitted, then preferably it is blocked, with a suitable notification to the user via the interface 24. The notification may contain a further recommendation, for example that the battery 16 should be recharged or the heating chamber 6 should be cleaned. Devices according to some embodiments of the invention might only notify a warning to the user, without blocking the further smoking session, thereby allowing the user to make the decision about whether to proceed. This option could be enabled selectively, depending on which of the battery parameters has reached its respective threshold during the simulated session. Figure 5 is a flowchart that illustrates the functioning of the LSS assurance module 55. In a first step 102, data received from the battery observer module 44 is used to compute the state of energy (SoE) of the battery 16. The state of energy may be the remaining capacity, which is expressed in units of Watt-hour or Ampere-hour, of the battery 16 or the state of charge (SOC) of the battery 16, which is expressed in units of percentage. This value is supplied to a comparator 104, which also receives from the key profile information module 58 a value representing the energy used during the last heating session performed by the device. This representing value may be expressed in the same units as the value supplied in the step 102, and may be recorded by the battery observer module 44 into the memory 22 in advance. If the P51768EP / 6652 comparator 104 determines that the state of energy of the battery 16 is not greater than the energy used during the last session, this suggests that a further session will not be possible and the LSS assurance module 55 outputs a value of “False” (step 106). This in turn causes the controller 20 to generate a warning (step 108) that a further session cannot be started and preferably, as discussed above, actually to prevent the user from initiating the session. If the comparator 104 determines that the state of energy of the battery 16 is greater than the energy used during the last session, the process continues with step 110, in which the further smoking session is simulated. The comparator 104 (and optionally the step 102) may be omitted in an alternative embodiment. In the alternative embodiment, the simulation in the step 110 runs in regardless of the values of battery parameters. The simulation in the step 110 also uses data about the battery load profile, i.e. the profile of current or power that the battery must supply in order to heat the heater 14 to the desired temperature setpoints over the duration of the session. The simulation 110 further receives the current values of one or more battery parameters such as its open circuit voltage from the battery observer module 44. For each phase during the profile, the simulator 110 calculates the values of the prescribed battery parameters. It also stores the calculated values at predetermined times, which typically correspond to the end of each phase, when the battery parameters are likely to take their maximum or minimum values. At the end of the simulation or during the simulation, the stored values are output to a further comparator 112, which determines whether any of the battery parameters have reached or passed their respective thresholds. This output of the stored values may be triggered by a flag which is labelled as “ExitFlag” in Figure 5. The flag may be a completion of the simulation 110 or reaching a predetermined time in the simulation 110. In the illustrated example, the battery parameter of interest is the closed circuit voltage (CCV) of the battery 16. The comparator 112 compares each of the stored values of CCV with a predetermined minimum threshold value. If the CCV has not fallen below the threshold during the simulation, then the LSS assurance module 55 outputs a value of “True” (step 114). This in turn causes the controller 20 to operate the device to start the further smoking session (step 116). If the comparator 112 determines that the simulated value of the CCV has fallen below the minimum threshold at one of the predetermined times, then the further session cannot proceed on the basis of the load profile that was used during the simulation. In some embodiments of the invention, that may be the end of the process: the LSS assurance module will generate an output of “False” (step 106) and the further session will not start (step 108). In the illustrated embodiment, however, the device attempts to improve the user experience by trying to find an alternative load profile that will enable the further heating session to be performed without any of the battery parameters breaching their respective thresholds. Accordingly, P51768EP / 6652 the process passes to step 118, in which information received from the key profile information module 58 is used to update the load profile, for example by reducing one or more of the temperature setpoints or by increasing the time that is taken for the heater 14 to heat up, which will reduce the maximum level of power that the battery 16 needs to supply. The updated heating profile may be of short duration and / or low power density. The simulation process 110 is then repeated using the updated profile and the test by the comparator 112 is carried out again. If one of the battery parameters has again reached or passed its threshold, the process returns again to step 118, where a further iteration of updating the load profile may be carried out. On each pass through this cycle, a comparator 120 determines whether the number of iterations, which is labelled as “iter” in Figure 5, has exceeded a predetermined maximum number which is labelled as “maxIter” in Figure 5. If not, then the further simulation using the updated profile is allowed to continue in step 110. If the maximum number of iterations has been exceeded then the comparator 120 causes the LSS assurance module to generate a “False” output (step 106) and control passes to step 108 to notify the user that no further session can be performed. In the illustrated embodiment of the invention, the principal battery parameter that is calculated during the simulation is the closed circuit voltage (CCV) of the battery 16. When the battery is delivering current to a load such as the heater 14, its open circuit voltage (OCV) is reduced as a result of the internal impedance of the battery. This reduction of voltage is also referred as an IR drop. This may be modelled using an equivalent circuit such as the one shown in Figure 6, in which the impedance comprises a series connection of an ohmic resistor and one or more parallel RC circuits; in this case there are two such RC circuits. This equivalent circuit may be stored in the battery model 46, and parameters of the equivalent circuit may be provided from the battery observer module 44. The voltage across the series resistor is proportional to the current supplied to the heater but the voltages V1, V2 across the RC circuits are transient, decaying at a rate that depends on the respective time constants R1C1 and R2C2. On the assumption that the supplied current remains constant during each phase of the heating profile, an analytical approach may be used and the change in CCV over the duration of that phase can be calculated as: …(1) where: ^^̅^^is the current supplied to the heater Vi(0) is the voltage across circuit RiCiat the beginning of the phase t is the time since the beginning of the phase. P51768EP / 6652 This can clearly be generalized to any number of RC circuits. In Figure 6, Rohmic represents an ohmic resistance coming from a solution resistance, a first parallel RC circuit consisted by R1 and C1 represents an electric double layer on a surface of electrodes, and a second parallel RC circuit consisted by R2and C2represents a diffusion reaction inside electrodes. Hereinafter, a derivation of Equation (1) is described in detail. First, the CCV is a voltage which subtracts losses while discharging from the OCV. The losses of the equivalent circuit in Figure 6 are sum of voltage drops across the ohmic resistance, the first parallel RC circuit and second parallel RC circuit. It may be expressed by Equation (2) below.^^^^^^ = ^^^^^^ − ^^^^^ − ^^^^^ − ^^^^^^= ^^^^^^ − ^^^^^ − ^^^^^ − ^^^^^^ ∙ $^^^ …(2)According to Kirchhoff's first law, a current flowing through the equivalent circuit at time t can be described as follows: $^^^ + $ ^^^ = $^^^% ^& &$^ ^^^ + $ ^^^ = $ … '' ^^^A time-varying current following through a capacitor can be described as follow: be derived by substituting Equation (4) into Equation (3). Respective voltage V1, V2 across the first and second parallel RC circuits can be replaced into a current as follows: P51768EP / 6652 For solving the derivative equation, Equation (6) can be transformed as follows: Equation (6) can be generalized as follows: Now, parameters a, b are introduced for simplifying. Equation (8) can be transformed by substituting Equation (9) as follows: P51768EP / 6652 If the value of the heater current between 0 to t is constant or substantially constant, $^6^ can be replaced by ^^̅^^. By multiplying a resistance Ri onto Equation (11), a voltage Vi can be obtained. By substituting Equation (12) into Equation (2), Equation (1) can be derived as follows: P51768EP / 6652 For running the simulation, it’s preferable that Equation (1) is transformed into a discrete format. In the discrete format, the CCV may be calculated at every ∆^ elapsed, and time t is handled as the k th step.Thus, ? ∙ ∆^ is the elapsed time when the k th step is run. Equation (1) with the discrete format may beas follows: It’s known that the OCV depends on the stage of charge (SOC), so the OCV can be also described as follows:^^^@?A → ^^^^E^^@?A^ …(14)A change of the SOC can be described by below recurrence equation.E^^@?A = E^^@? − 1A − 3600 ∙ H^^…(15) The FCC stands for the fully charged capacity of the battery 16 and is expressed by a unit of Ampere- hour [Ah]. A recurrence equation suitable for the simulation can be derived by substituting Equation (15) into Equation (13). An initial value of the SOC may be obtained from the fuel gauge 40. The FCC may be recorded into either one of the fuel gauge 40, the controller 20 or the memory 22 in advance. P51768EP / 6652 The key profile information module 58 may store and update the constant current ^^̅^^in the memory 22 by averaging or smoothing a battery current measured by the fuel gauge 40, and may provide it to the LSS assurance module 55. Adopting several values into the constant current ^^̅^^may improve an accuracy of the simulation. Such the time-varying constant current ^^̅^^may be set based the temperature profile shown on Figure 3. The key profile information module 58 may divide the temperature profile into several sections, and subsequently store the respective constant current ^^̅^^for each section. Skilled person will be understood that such time-varying constant current ^^̅^^may show a similar or same trend as the power profile shown on Figure 4. The battery observer module 44 may provide the latest OCV value by inputting the SOC into a relationship with the SOC and the OCV (SOC-OCV curve) being recorded in advance. The SOC-OCV curve may be provided as a function or a look-up table. For the sake of precise calculation, a plurality of the functions or the look-up tables may be prepared for different temperatures of the battery 16 and / or states of health (SOH) of the battery 16. Otherwise, the function or the look-up table may become a multi-variable type including the temperature and / or the SOH of the battery 16. The temperature and / or the SOH of the battery 16 may be obtained from the fuel gauge 40. The respective values of parameters in the equivalent circuit Ri, Ci, and Rohmic may be provided from the battery observer module 44 to the battery model 46. If these parameters are handled as constant across whole of life of the battery 16, these parameters may be alternatively set in the battery model 46 in advance. In this alternative embodiment, the providing these parameters from the battery observer module 44 to the battery model 46 is unnecessary. The battery observer module 44 may vary the values of these parameters based on any parameter (e.g., temperature, SOH, or combination thereof) of the battery 16. If the simulation is successively performed across multiple heating sessions, these parameters may be kept to constant across the multiple heating sessions, otherwise these parameters may be updated once simulation for single heating session is completed. Such update of these parameters may be based on the expected value of temperature or SOH of the battery 16 at end timing of the simulation for previous heating session. The SOH may be updated based on an integration amount of discharged charges so far. The SOH may be defined as a ratio between a remaining useful capacity of the aged and new batteries. Here, the word “remaining useful capacity” may mean that available capacity when battery is fully charged. Details of a simulation algorithm for the battery temperature are described in later. An initial value of a voltage across the parallel RC circuit ^^^0^ may be deemed as zero. Without the assumption of constant current, it may be more practical to calculate the CCV by dividing the heating profile into small time intervals and using discrete variables to model how the current through each of the resistors develops from one interval to the next. P51768EP / 6652 Hereinafter, detail of this alternative approach is described in detail. First, Equation (10) is discrete as follows: In Equation (17), an integral term can be separated into a small fragment, which is from ^? − 1^ ∙ ∆^ to? ∙ ∆^, and a remaining. Equation (19) can be substituted into Equation (18) as follows: P51768EP / 6652In Equation (20), if ∆^ is sufficiently small so that $^6^ can be deemed as constant ^K^^^@? − 1A from^? − 1^ ∙ ∆^ to ? ∙ ∆^, Equation (20) can be transformed as follows: The constants a, b can be replaced in accordance with definition of Equation (9). Here, Equation (2) can be discrete and generalized as follows: The respective voltage can be described by a product of a resistance and a current, and Equation (22) can be substituted into Equation (23) as follows: P51768EP / 6652 5 By substituting Equation (15) into Equation (24), a recurrence equation suitable for the simulation can be derived.10 Since most parameters may be obtained in the same way as with Equation (16), only differences are explained. A current initially flows into only a capacitor in parallel RC circuit, thus an initial value of a 15 current flowing through a resistor in parallel RC circuit $^^@0Acan be deemed as zero. A total current supplied from the battery 16 between a small fragment ^K^^^may be provided from the heater model 50. Hereinafter, the heater model 50 in described in detail. The heater model 50 may be also explained as a heat transfer model among three bodies as shown on Figure 7. In this model, it’s treated that Joule heat 20 generated in the heater 14 is transported to a surface of the aerosol source 12 by mean of a gap between the heater 14 and the aerosol source 12 and heat received at the surface of the aerosol source 12 is transferred into an inside of the aerosol source 12. Such a heat transfer model among three bodies (i.e., the heater 14, the surface of the aerosol source 12, and the inside of the aerosol source 12) may be described as follows: 25 where: P51768EP / 6652^R^^^ , ^XU , and ^RZ^[^B are respectively heat capacities of the heater 14, the surface of the aerosolsource 12, and the inside of the aerosol source 12 S^^^, SU, and S^Yare respectively temperatures of the heater 14, the surface of the aerosol source 12, and the inside of the aerosol source 12 T^^^is the power consumed at the heater 14 ^XVW and ^RZ^[^B are respectively thermal resistance of the gap and the aerosol source 12.Equation (26) can be made discrete as follows: Equation (27) can be respectively solved for S^^^, SU, and S^Yas follows: The values of thermal parameters ^R^^^ , ^XU , ^RZ^[^B , ^XVW and ^RZ^[^B may be provided from the heaterobserver module 48 to the heater model 50, otherwise these are embedded into the heater model 50 in advance if they are treated as constant. Alternatively, they may be handled as variant changed by any user action (e.g., a puffing action or a cleaning of the heating chamber 6). In this alternative embodiment, the heater observer module 48 may update these values in response to a detection of a user action. The initial values of temperatures S^^^, SU, and S^Ymay be obtained from sensors including the temperature sensor 42. The initial values of temperatures of the surface and the inside of the aerosol source 12 may be deemed as to be same or be close to an atmosphere temperature. The atmosphere temperature is labelled as “externalTemperature” in Figure 2. If the simulation is successively performed across multiple heating sessions, the initial temperature of the heater 14 at each successive session may be set based on the last temperature of the heater 14 of the previous session. More concretely, the initial temperature of the heater 14 at successive session may be the same as the last temperature of the heater P51768EP / 6652 14 of the previous session, otherwise it may be bit lower than the last temperature of the heater 14 of the previous session considering a cooling effect coming from the interval between sessions. A power supplied to the heater 14 T^^^@^YA may be calculated based on the power profile shown on Figure 4, otherwise an actual output of PID controller when the previous heater temperature S^^^@^Y^^Ais inputted may be used. By dividing T^^^@^YA by the voltage of the battery 16 (either the CCV or OCV),^K^^^@^YA may be derived.Equation (28) can be transformed so that cooling effect coming from the puffing action is taken into account as follows: where: are respectively coefficients for the heater 14, the surface of the source 12, and the inside of the aerosol source 12. These coefficients reflect how strongly the puffing action affects each body, and may have a negative value. is a time-varying puff profile.If the heater 14 alternatively heats the aerosol source 12 from its inside as shown in Figure 8, Equations (26) and (28) are respectively described as follows: P51768EP / 6652 where: ^XVW is the heat capacity of the heating chamber 6SVWis the temperature of the heating chamber 6 ^XVW is the thermal resistance of the gap between the heating chamber 6 and the aerosol source 12.Equation (31) may be transformed so that the puffing action is taken into account, in the same way as Equation (29). In the above formulae, the open circuit voltage (OCV) of the battery 16 is shown as being dependent on time. In fact, the OCV is known to vary in a predicable way with the state of charge of the battery, which is known in turn by measuring – or, in the case of a simulation, calculating – the current that flows out of the battery. The battery model may further include hysteresis effects to accurately compute the battery OCV and available power at low state-of-charge. The battery parameters that are included in the simulation and are used for comparison to determine whether the further heating session should be permitted may additionally or alternatively include values of the core and / or surface temperature of the battery 16. Heat is generated in the battery because of current flowing through its internal impedance. The voltage across that impedance is the difference between CCV and OCV in the formulae above and multiplying it by the simulated current gives the power developed as heat. Heat is simultaneously lost by conduction to the surroundings, which may be assumed to include a flow of cooling air at approximately constant temperature while the device is in use. Otherwise, the flow of cooling air may be further precisely taken account by using a temperature sensor which measures an atmosphere temperature. If the initial temperature, thermal capacity and thermal conductivity of the battery 16 are known, as well as the temperature and thermal conductivity of its surroundings, then the change in core and surface temperatures with time can be modelled as part of the simulation. In alternative embodiments, it may be sufficient to estimate the core and / or surface temperature of the battery for the simulated current supply by using look-up tables derived from tests that have been carried out previously. This will avoid the need to perform a full simulation of the heat flow in the battery. P51768EP / 6652 Hereinafter, another aspect of the battery model 46 is described in detail. The battery model 50 may comprise a thermal model, which may be also referred as “battery thermal model” hereinafter, as shown in Figure 9. The battery thermal model may also be explained as a heat transfer model among three bodies. In this model, it’s treated that Joule heat due to an internal resistance of the battery occurs at only the core of the battery 16, and it’s successively transported to a surface of battery 16 and the atmosphere. It may be also deemed that the atmosphere temperature may be brought by air flow, and the temperature of the battery 16 may not affect the atmosphere temperature. In this embodiment, a cross-sectional shape of the battery 16 may be deemed as a circle. If the cross-sectional shape of the battery 16 has a different shape (e.g., rectangular), the following explanation will be adapted to a main surface of the battery 16. First, Equation 2 may imply that a difference between the OCV and the CCV represents a voltage drop inside the battery 16 as follows: An energy lost inside the battery 16 can be described as follows:T@^YA = ^^^^@^YA − ^^^@^YA^ ∙ ^^̅^^ …(33)Instead of the constant current ^^̅^^, the simulated current $@^YA explained in Equation (25) may be used. A respective derivative equation for a core and a surface temperature may be described as follows: where: X^^ and ^aZ are respectively the thermal capacities of the core of the battery 16 and the surface ofthe battery 16 S^, SZ, and S̀ are respectively the temperatures of the core of the battery 16, the surface of thebattery 16, and the atmosphere ^X^is the thermal resistances between the core and the surface of the battery 16 ^X_ is the thermal resistances between the surface of the battery 16 and the atmosphere.Equation (34) may be transformed into discrete format as follows: P51768EP / 6652 Equation (35) can be respectively solved for S^@^YA and SZ@^YA as follows: The values of thermal parameters X ^^, ^aZ , ^X^ and ^X_ may be provided from the battery observer module44 to the battery model 46, otherwise these are embedded into the battery model 46 in advance if these are treated as constant. Alternatively, these may be treated as variants changed by any parameter of the battery 16 (e.g., SOC, SOH, or combination thereof). In this alternative embodiment, the battery observer module 44 may update these values based on the parameter of the battery 16. The initial temperature of the core and the surface of the battery 16 may be deemed as the same and be set based on the temperature of the battery 16 provided from the fuel gauge 40. If the simulation is successively performed across multiple heating sessions, these battery temperatures at each successive session may be set based on the last battery temperatures of the previous session. More concretely, the initial battery temperatures at each successive session may be same as the last battery temperatures of the previous session, otherwise they may be a bit lower than the last battery temperatures of the previous session considering a cooling effect coming from the interval between sessions. Although not shown in the block diagram or flowchart for the illustrated embodiment of the invention, it will readily be understood that, instead of carrying out a single simulation of the next further heating session, the controller 20 could carry out simulations of multiple, successive heating sessions until a session is reached in which the charge of the battery is depleted or one of the other battery parameters passes its respective threshold. In this way, the simulation can provide a highly accurate estimate of the number of sessions that it will be possible to perform using the remaining capacity of the battery 16. Some assumptions may need to be made about the conditions under which the sessions will be carried out. In particular, if the sessions are performed consecutively, the heater 14 and aerosol source 12 will not have time to return fully to the ambient temperature in the interval between sessions, therefore less energy will be required to attain the desired operating temperature. In some embodiments of the P51768EP / 6652 invention, the device may record details of past sessions in order to develop a model of the user’s behaviour regarding parameters such as how frequently they perform consecutive smoking sessions. Although exemplary embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the appended claims. Thus, the breadth and scope of the claims should not be limited to the above-described exemplary embodiments. In Figure 2, the battery observer module 44, the battery model 46, the heater observer module 48, the heater model 50, the heating protocol output control logic block 52, the LSS assurance module 55, and the key profile information module 58 are depicted separately from the controller 20. However, at least one of these may be realized as a function implemented in the controller 20. Any combination of the above-described features in all possible variations thereof is encompassed by the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. P51768EP / 6652

Claims

CLAIMS 1. An aerosol generating device comprising: a heater for generating aerosol from a source during a heating session; a battery for supplying power to the heater; and a controller configured to determine whether a further heating session should be permitted, wherein the determination involves simulating the further heating session and calculating values of one or more battery parameters during the simulated further heating session to determine whether the calculated values of any of the battery parameters reaches or passes a respective threshold value for that parameter.

2. An aerosol generating device according to claim 1, further comprising a monitoring circuit configured to output one or more real values of the battery parameters; wherein the controller is further configured to calculate the values of the one or more battery parameters during the simulated further heating session, by using the one or more parameters of the battery outputted by the monitoring circuit as initial values.

3. An aerosol generating device according to claim 2, wherein at least one of the one or more battery parameters varies with a state of health of the battery or an impedance of the battery.

4. An aerosol generating device according to claim 2 or claim 3, wherein the controller is further configured, during an actual heating session, to terminate the heating session if any of the one or more parameters of the battery outputted by the monitoring circuit reach or pass a respective value being equal to or lower than the respective threshold value.

5. An aerosol generating device according to any preceding claim, wherein the one or more battery parameters include a closed circuit voltage of the battery.

6. An aerosol generating device according to any preceding claim, wherein the one or more battery parameters include a temperature of the battery.

7. An aerosol generating device according to claim 6, wherein the controller uses a thermal model of the battery to calculate the time-dependent temperature of the battery during the simulated further heating session, the temperature being derived from an open circuit voltage of the battery.

8. An aerosol generating device according to claim 5, wherein the controller uses an electrical model of internal impedances of the battery to calculate the time-varying closed circuit voltage of the battery during the simulated further heating session, the closed circuit voltage being derived from a P51768EP / 6652simulated open circuit voltage of the battery and from a simulated current supplied by the battery to the heater.

9. An aerosol generating device according to claim 8, wherein the simulated current supplied by the battery to the heater is obtained from a stored value of the average current supplied during a pre- programmed heating session.

10. An aerosol generating device according to claim 9, wherein the pre-programmed heating session is divided into a plurality of phases and the simulated current is obtained from a series of stored values of average current supplied during the successive phases of the simulated further heating session.

11. An aerosol generating device according to claim 10, wherein the calculated values of each of the one or more battery parameters is compared with the respective threshold value for that parameter only at predetermined times during the simulated further heating session, the predetermined times including at least the beginning or end of each phase.

12. An aerosol generating device according to claim 8, wherein the simulated current supplied by the battery to the heater is varied with time to control the heater temperature.

13. An aerosol generating device according to any of claims 1 to 12, wherein, if the controller determines that a further heating session should not be permitted, it prevents the device from starting the further heating session.

14. An aerosol generating device according to any of claims 1 to 12, wherein, if the controller determines that the further heating session should not be permitted, it is configured to perform at least one alternative simulation of the further heating session using an alternative profile of supplying power from the battery to the heater during the session, repeating this process until either the controller determines that one of the additional simulated further heating sessions should be permitted or a predetermined maximum number of the additional simulations have been performed.

15. An aerosol generating device according to any of claims 1 to 12; wherein, if the controller determines that the further heating session should be permitted: the controller performs simulations of successive further heating sessions until it determines that one of the successive further heating sessions should not be permitted; and the controller then notifies the number of permitted sessions to a user via a user interface. P51768EP / 6652

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