The present invention relates to an aerosol-generating system comprising a liquid storage portion and a control unit by which the fill level of the liquid storage portion is determined. The present invention also relates to a corresponding method.

One type of aerosol-generating system comprises a liquid storage portion and a vaporizer comprising a wick and coil heater arrangement. The liquid aerosol-forming substrate is provided to the vaporizer via the wick by capillary forces. In such systems there is a risk that the coil heater is activated, although the liquid aerosol-forming substrate of the liquid storage portion is used up. As a result no aerosol is formed and the user will inhale heated air. Inhaling heated air may not only be unpleasant for the user, but may also result in the release of undesirable products which are then inhaled by the user.

It would therefore be desirable to provide an improved aerosol-generating system which ensures that upon activation of the system sufficient liquid aerosol-generating substrate is available in the liquid storage portion.

According to a first aspect of the invention there is provided an aerosol-generating system comprising a liquid storage portion, for holding liquid aerosol-forming substrate. The system further comprises a liquid pressure sensor provided within the liquid storage portion, and a control unit that is in communication with the liquid pressure sensor. The control unit is configured to determine the fill level of the liquid aerosol-forming substrate based on a pressure signal provided by the liquid pressure sensor.

The aerosol-generating system of the present invention allows to determine whether sufficient liquid aerosol-forming substrate is available in the liquid storage portion. The liquid pressure sensor is used to determine the pressure excerted by the liquid aerosol-forming substrate. The liquid pressure may be configured to be in direct contact with the liquid aerosol- forming substrate provide in the liquid storage portion. The liquid pressure sensor may be configured to be liquid-proof, such that the continued contact with the liquid aerosol-forming substrate does not negatively affect its proper function.

When the liquid pressure sensor is in contact with the liquid in the liquid storage portion, the total pressure measured by the liquid pressure sensor is, according to Pascals's law, the sum of the atmpospheric pressure and the pressure caused by the liquid column above the liquid pressure sensor. In case the liquid pressure sensor in the liquid storage portion detects that no or not sufficient fluid is available, the control unit of the aerosol-generating system may prevent activation of the vaporizer until the liquid storage portion has been replaced or refilled. The unpleasant user experience of inhaling hot air only is thus prevented. Upon detection of an empty liquid storage portion, the control unit may indicate via a display or similar devices that a fresh liquid storage portion must be supplied or that refilling is required.

The liquid pressure sensor may be provided at a bottom of the liquid storage portion. By providing the liquid pressure sensor at the bottom of the liquid storage portion, the height of the liquid column that has an effect on the pressure measurement is maximized. Moreover, in embodiments in which the liquid storage portion is of an elongated cylindrical form, and wherein the bottom of the liquid storage portion is defined by one of the end-faces of the cylindrical liquid storage portion, the liquid aerosol-forming substrate is in contact with the liquid pressure sensor over a rather wide range of orientations of the aerosol-generating system. Thus, in these orientations also a reliable determination as to whether sufficient liquid aerosol-forming substrate is available may be performed.

As used herein, the term "bottom" is to be understood in the configuration as depicted in the accompanying figures. Thus, the bottom of the liquid storage portion denotes the lower portion of the liquid storage portion, when the aerosol-generating system is in the desired orientation for performing the fill level check as depicted in the accompanying figures.

As used herein, the term "liquid pressure sensor" refers to any pressure sensor that is suitable to determine the pressure excerted by the liquid aerosol-forming substrate in the liquid storage portion.

The aerosol-generating system may further comprise a second pressure sensor in communication with the control unit. The second sensor may be configured for determining the atmospheric pressure of the environment. The second pressure sensor will therefore herein also be referred to as atmospheric pressure sensor. The control unit may be configured to receive the two pressure signals from the two pressure sensors comprised in the aerosol-generating system. The control unit is further configured to determine the fill level of the liquid aerosol- forming substrate based on a comparison of these two pressure signals.

When the liquid storage portion is filled with liquid aerosol-forming substrate and the liquid pressure sensor in the liquid storage is in contact with this liquid aerosol-forming substrate, the pressure that is measured by the liquid pressure sensor inside the liquid storage portion is higher than the ambient atmospheric pressure. Thus, a higher pressure reading inside the liquid storage portion as compared with the ambient atmospheric pressure is indicative of the presence of sufficient liquid aerosol-forming substrate in the liquid storage portion. In this configuration, the aerosol-generating system may be used by the user for inhalation purposes.

As the liquid storage portion is progressively emptied by the continued use of the aerosol-generating system, the pressure value measured in the liquid storage portion continuously decreases until it becomes identical to the ambient atmospheric pressure. When the two pressure values are identical, the liquid storage portion is empty and needs refilling. In order to prevent that the liquid storage portion is completely empty, the control unit may be configured to alert the user once the difference between the pressure values has reached a certain pre-determined threshold value. This threshold may be determined to be 10 percent above atmospheric pressure, 5 percent above atmospheric pressure, or 2 percent above atmospheric pressure.

Electronically operated aerosol-generating systems usually comprise a puff detection unit which indicates that a user draws a puff at the aerosol-generating system. In some of these systems the puff sensor is a pressure sensor, that measures the pressure in an air flow path within the aerosol-generating system. A pressure drop in the air flow path within the aerosol- generating system is indicative of a puff and triggers activation of the vaporizing unit of the aerosol-generating system. When no puff is drawn, the pressure reading of such puff sensor corresponds to the ambient atmospheric pressure. Thus, in an embodiment of the invention, the ambient atmospheric pressure may be determined by the pressure reading from the puff sensor used in the puff detection unit of the aerosol-generating system. By using an already existing pressure sensor for determination of the ambient atmospheric pressure, additional functionality of the aerosol-generating system may be obtained without requiring additional components, and, thus, without increasing complexity of the system.

The pressure reading obtained with the liquid pressure sensor inside the liquid storage portion may depend on the orientation of the aerosol-generating system and the liquid storage portion, respectively. In particular if the aerosol-generating system is a handheld system, it may well be possible that the aerosol-generating system is held upside down, such that the liquid pressure sensor is temporarily located at the top of the liquid storage portion. In this configuration the liquid pressure sensor may not be in contact with the liquid aerosol-forming substrate. If the control unit performs the fill level check in this configuration, it may be determined that the liquid storage portion is empty although in reality still sufficient liquid aerosol-forming substrate would still be available.

In order to avoid such erroneous fill level checks, the aerosol-generating system may comprise an orientation sensor that is in communication with the control unit. The orientation sensor may be provided to determine the orientation of the liquid storage portion. In embodiments in which the liquid storage portion is fixedly held within the aerosol-generating system, the orientation sensor may also be provided anywhere within the aerosol-generating system. In such embodiments the orientation of the aerosol-generating system may be used to determine the orientation of the liquid storage portion.

The control unit may therefore further be configured to initiate a fill level check only when the liquid storage portion is in the correct orientation. In this way an erroneous fill level check caused by misorientation of the liquid storage portion is avoided. The orientation sensor may be any suitable commercially available orientation sensor. The orientation sensor may be a gyroscope sensor.

The liquid storage portion may be refillable. To this end the liquid storage portion may be provided with a refill opening. The user may refill liquid aerosol-forming substrate whenever the aerosol-generating system indicates that the liquid storage portion does not comprise sufficient liquid aerosol-forming substrate anymore.

The liquid storage portion may be configured as a replaceable liquid storage portion. The liquid sensor may form part of the replaceable liquid storage portion. Upon replacement of the liquid storage portion the contact between the liquid storage portion and the control unit requires only that corresponding electric connections are established between these components. However, as the liquid sensor is part of the liquid storage portion, the manufacturing cost for such liquid storage portions is increased.

The aerosol-generating system may comprise a device portion which in turn comprises the power source and electronic circuitry including the control unit. The device portion may also comprise the orientation sensor. The aerosol-generating system may further comprise a cartridge which comprises the liquid storage portion and optionally further comprises a vaporizer assembly and a mouthpiece. The cartridge may be releasably attached to the device portion of the aerosol-generating system.

The liquid pressure sensor may be part of the device portion. Upon assembly of the aerosol-generating system or upon replacement of the cartridge, the liquid pressure sensor will be located within the liquid storage portion of the cartridge such that the liquid pressure sensor is brought into direct contact with the liquid aerosol-forming substrate in the liquid storage portion. In this embodiment, replacement of the cartridge therefore also requires not only electrical connections but also a fluid connection established between the device portion and the cartridge. However, as the cartridge does not comprise the liquid pressure sensor, resulting in no need of corresponding electric connections, the manufacturing cost of the individual cartridges is lower compared to cartridges comprising the liquid pressure sensor.

The liquid storage portion may also comprise pressurized liquid aerosol-forming substrate or may already be filled with pressurized aerosol. Such liquids under pressure might offer a more accurate pressure measurement to the system. In order to release the pressurized liquid or aerosol at a desired pressure for inhalation, a pressure regulator may be included in the aerosol-generating system.

According to a second aspect the present invention is also directed to a method for determining the fill level of a liquid storage portion in an aerosol forming system. The method comprises the steps of providing a liquid storage portion holding liquid aerosol-forming substrate, providing a liquid pressure sensor within the liquid storage portion and providing a control unit that is in communication with the liquid pressure sensor. The liquid pressure sensor in the liquid storage portion measures a pressure value and communicates this pressure signal to the control unit. The control unit is configured to evaluate the pressure signal and to determine the fill level of the liquid aerosol-forming substrate in the liquid storage portion.

When evaluation of the pressure signal of the liquid pressure sensor results in the finding that the fill level in the liquid storage portion is sufficiently high, the aerosol-generating system may be operated by the user as desired. When the control unit determines upon evaluation of the pressure signal that the liquid storage portion is empty or substantially empty, the consumer is notified accordingly and the aerosol-generating system cannot be activated before the liquid storage portion is refilled or replaced.

Fill level detection can generally be performed at any time during normal operation of the aerosol-generating system. It may be advantageous to perform fill level checks immediately before aerosol generation is started.

As the pressure reading of the liquid pressure sensor may depend on the correct orientation of the aerosol-generating system, the method may further comprise the steps of providing an orientation sensor for determining the orientation of the aerosol-generating system, and triggering the evaluation of the fill level depending on the determined orientation of the aerosol-generating system. Advantageously fill level detection is triggered only when the aerosol-generating system is in the correct orientation, in which the pressure sensor is located at the bottom of the liquid storage portion.

Features disclosed in combination with one aspect of the invention may readily be also used in combination with other aspects of the invention.

The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 shows an aerosol-generating system of the present invention;

Fig. 2 shows a cross-section of the liquid storage portion of the aerosol-generating system of Fig. 1 ;

Fig. 3 shows a further aerosol-generating system of the present invention;

In Figs. 1 to 3 an aerosol-generating system 10 is depicted that consists of a lower portion, the aerosol generating device 12, and an upper portion the aerosol generating article 20.

The aerosol-generating device 12 comprises a power source 14 and electric circuitry, including a control unit 16 and a puff detector 18. The aerosol-generating article 20 comprises a liquid storage portion 22, a vaporizer 24 and a mouth piece 26. Upon assembly of the aerosol- generating system 10 an electric connection is established between the aerosol-generating device 12 and the aerosol-generating article 20 such that the individual electric components of the aerosol-generating system 10 may communicate with each other.

The aerosol generating system 10 defines an air flow path from an air inlet, via the vaporizer 24 to the mouth piece 26.

Fig. 2 shows a cross-section through a portion of the aerosol-generating article 20 comprising the liquid storage portion 22. The liquid storage portion 22 comprises a housing 28 having an opening 30 through which the liquid aerosol-forming substrate 31 is delivered to the vaporizer. The fill level in the depicted liquid storage portion 22 is about 50 percent. In Figs. 1 to 3 the aerosol-generating system 10 is in an upright position with the mouth piece 26 pointing upwards. In this configuration, at the bottom 32 of the liquid storage 22 portion there is provided a liquid pressure sensor 34. The liquid pressure sensor 34 may be liquid-proofed to be in contact with the aqueous liquid aerosol-forming substrate. When the liquid pressure sensor 34 is in contact with the liquid aerosol-forming substrate 31 , the pressure measured by the liquid pressure sensor 34 is higher than the ambient atmospheric pressure. Further, the higher the liquid column above the liquid pressure sensor 34, the higher the measured pressure value. Thus, when the aerosol-generating article 20 is in the upright position as depicted in Figs. 1 to 3, the pressure value is a measure for the liquid fill level in the liquid storage portion 22. The liquid pressure sensor 34 is in electrical connection with the control unit 16. The control unit 16 is configured to evaluate the pressure signal from the liquid pressure sensor 34. If this pressure signal indicates that the liquid storage portion 22 is empty or nearly empty, the control unit 16 prevents activation of the vaporizer 24.

Fig. 3 shows a detailed cross-section of an aerosol-generating system 10 according to a further embodiment of the present invention. The general construction of this embodiment is similar to the construction of the embodiment depicted in Fig. 1 . The upper portion, representing the aerosol-generating article 20 comprises a liquid storage portion 22. Again, at the bottom of the liquid storage portion 22 a liquid pressure sensor 34 is provided. The liquid pressure sensor 34 is again connected to the control unit 16.

The system depicted in Fig. 3 also comprises a puff sensor and further comprises a gyroscope sensor 36. Puff sensor 18 and gyroscope sensor 36 are both provided in the device portion 12 and are also both connected to the control unit 16. The puff sensor 18 is a pressure sensor which is primarily used for detecting the pressure within the air flow path defined in the aerosol generating system 10. A pressure drop at the puff sensor 18 is indicative for a puff drawn by a user and as a response of the system, the vaporizer 24 is activated. When no puff is drawn at the aerosol-generating system 10, the pressure signal of the puff sensor 18 corresponds to the ambient atmospheric pressure. Thus, by comparing the pressure signals from the liquid pressure sensor 34 and the puff sensor 18, the fill level of the liquid aerosol- forming substrate may be determined. The larger the pressure difference between these two pressure signals, the more liquid aerosol-forming substrate is available in the liquid storage portion 22.

The gyroscope sensor 36 allows the control unit 16 to determine the orientation of the aerosol-generating system 10. The liquid storage portion is fixedly held with respect to the aerosol-generating system 10. Accordingly, the orientation of the liquid storage portion can be derived from the orientation of the aerosol-generating system 10.

As can be readily appreciated from the embodiment depicted in Figs. 1 and 3 the determined pressure value also depends on the orientation of the liquid storage portion 22. A reliable pressure reading may be obtained, if the pressure is determined when the liquid storage portion 22 is in the correct upright orientation as depicted in Figs. 1 to 3. To this end, the control unit 16 first ensures via the gyroscope sensor 36 the correct orientation of the liquid storage portion 22. When the control unit 16 has detected that the liquid storage portion 22 is in the correct orientation, the fill level determination may be triggered by the control unit 16.