The present invention relates to an aerosol-generating system with a pump having an inlet and an outlet, the inlet being connectable to a liquid storage portion and a fluid channel. The present invention also relates to a method for generating an aerosol.

One type of aerosol-generating system comprises a liquid storage portion, a pump and a vaporiser. During a puff of the user a stream of liquid aerosol-generating substrate such as e-liquid is actively pumped from the liquid storage portion to the vaporiser by means of the pump. In such a system - when the liquid in the liquid storage portion is used up - the vaporiser may be heated, while no liquid aerosol-generating substrate is provided to the vaporiser. As a result, the user will inhale heated air, which does not contain a generated aerosol. Inhaling heated air only may be unpleasant for the user and is thus unwanted. Also, heating of the vaporiser or a wicking material when there is no liquid present may result in the release of undesirable products.

It would therefore be desirable to provide an improved aerosol-generating system which prevents activation of the system once the liquid aerosol-generating substrate in the liquid storage portion is used up.

According to a first aspect of the invention there is provided an aerosol-generating system, comprising a pump having an inlet and an outlet, the inlet being connectable to a liquid storage portion. The system also comprises a fluid channel fluidly connected to the pump and a fluid sensor. The fluid sensor is configured to determine a presence of liquid aerosol-forming substrate in the fluid channel preferably by measuring an electrical property of the fluid comprised in the fluid channel.

The aerosol-generating system of the present invention allows detection of the presence of liquid aerosol-forming substrate in the fluid channel. Beneficially, a vaporiser can be deactivated when the sensor detects that no fluid is present in the fluid channel. The inhalation of only hot air is thus prevented, thereby prohibiting an unpleasant experience for the user and the generation of undesirable products. The detection of the sensor that no more liquid aerosol-forming substrate is present in the fluid channel may be utilized to indicate that a fresh liquid storage portion must be supplied.

The aerosol-generating system may further comprise a dispensing device for dispensing the liquid aerosol-forming substrate, wherein the dispensing device is in fluid communication with the outlet of the pump. The fluid channel and the fluid sensor may be provided between the pump and the dispensing device. The fluid sensor may be provided adjacent to the dispensing device, wherein the dispensing device may be provided adjacent to the vaporiser. However, the fluid sensor may be provided anywhere in the system between the liquid storage portion and the dispensing device.

If the fluid sensor is provided downstream of the pump between the pump and the dispensing device, the liquid aerosol-forming substrate can be optimally used, since all of the liquid aerosol-forming substrate is consumed before the sensor detects that no more liquid is present in the fluid channel. In more detail, even if the liquid in the liquid storage portion is used up, liquid may still be present in the fluid channel. In this case, the system will still operate, until the fluid in the fluid channel downstream of the pump is used up. Thus, the liquid storage portion may be completely depleted of liquid aerosol-forming substrate before the fluid sensor detects that no more substrate is present.

The fluid sensor may be configured to measure an electrical property of the fluid comprised in the fluid channel. The electric property measured by the fluid sensor may be the electrical resistance of the fluid comprised in the fluid channel.

Typical fluids in the fluid channel are ambient air or liquid aerosol-forming substrate. When the liquid storage portion still comprises liquid aerosol-forming substrate and the substrate is pumped towards the dispensing device by the pump, the substrate will be present in the fluid channel. If, however, the liquid storage portion is emptied of substrate, no more substrate will subsequently be pumped through the fluid channel. Thus, ambient air will be present in the fluid channel. The electrical resistance of ambient air is different from the electrical resistance of liquid aerosol-forming substrate. Typically, the electrical resistance of ambient air is higher than the electrical resistance of liquid aerosol-forming substrate. Thus, by measuring the electrical resistance of the fluid comprised in the fluid channel, the sensor may determine whether air or substrate is present in the fluid channel.

For measuring the electrical resistance of the fluid comprised in the fluid channel, the fluid sensor may comprise a first electrode and a second electrode.

The resistance between the first electrode and the second electrode may depend on the amount of liquid aerosol-forming substrate held in the liquid channel. For example, the electrical resistance may increase as the amount of liquid aerosol-forming substrate held in the fluid channel decreases.

The electrodes are preferably arranged at walls of the fluid channel. For example, the first electrode is provided at a first channel wall of the fluid channel and the second electrode is provided at a second channel wall of the fluid channel. The electrodes may preferably be in direct contact with the fluid comprised in the fluid channel. The first electrode may be disposed opposite to the second electrode. The electrodes may alternatively be arranged in the liquid channel. The first electrode and the second electrode may be arranged at opposite ends of the liquid channel. At least one of the first and second electrodes may be arranged at or in contact with the wall of the liquid channel. The first and second electrodes may be arranged to each partially surround the liquid channel. The first and second electrodes may be arranged concentrically about a common axis of the liquid channel.

The second electrode may substantially follow the path of the first electrode. This may enable the spacing between the first and second electrodes to remain consistent along the length of the first and second electrodes. The second electrode may be arranged substantially parallel to the first electrode.

The electrodes may be any suitable type of electrode. For example, suitable types of electrodes include point electrodes, ring electrodes, plate electrodes or track electrodes. The first electrode and the second electrode may be the same type of electrode. The first electrode and the second electrode may be different types of electrodes.

The electrodes may by any suitable shape. For example, the electrodes may be: square, rectangular, curved, arcuate, annular, spiral or helical. The electrodes may be substantially cylindrical. The electrodes may comprise one or more sections that are substantially linear, non-linear, planar or non-planar. The electrodes may be rigid. This may enable the electrodes to maintain their shape. The electrodes may be flexible. This may enable the electrodes to conform to the shape of the fluid channel.

The electrodes may have a length, a width and a thickness. The length of the electrodes may be substantially greater than the width of the electrodes. In other words, the electrodes may be elongate. The thickness of the electrodes may be substantially less than the length and the width of the electrodes. In other words, the electrodes may be thin. Thin electrodes and elongate electrodes may have a larger surface area to volume ratio. This may improve the sensitivity of measurements.

The electrodes may comprise any suitable material. The electrodes may comprise any suitable electrically conductive material. Suitable electrically conductive materials include metals, alloys, electrically conductive ceramics and electrically conductive polymers. The materials may include gold and platinum. The electrodes may be coated with a passivation layer. The electrodes may comprise or be coated in material that is sufficiently non-reactive so as not to react with or contaminate the liquid aerosol-forming substrate. The electrodes may comprise transparent or translucent material.

For measuring the electrical resistance, the fluid sensor may comprise a voltage divider circuit. A voltage divider circuit enables the measurement of the electric resistance between the first and second electrode of the fluid sensor. However, any known method of measuring the resistance of the fluid between the two electrodes may be employed.

The measured electrical property of the fluid may also be the dielectric constant of the fluid. In this regard, the electrodes may constitute a capacitor. The fluid between the electrodes serves - in this case - as a dielectric medium, wherein the dielectric constant of this fluid may be measured by measuring the capacitance of the capacitor or any known method. The dielectric constant of air is different from the dielectric constant of liquid aerosol- forming substrate and can be used to distinguish these fluids.

The electric property, preferably the electric resistance or dielectric constant of the fluid in the fluid channel may be indicative of the specific fluid. By determining the electrical resistance of the fluid in the fluid channel, it may be possible to identify the chemistry of the liquid. In this regard, the electrical resistance of the fluid in the fluid channel may depend upon the chemistry of the liquid. Thus, it may be identified whether or not the correct type of liquid is used. For example, different liquid aerosol-forming substrates may be used in the system by subsequently providing liquid storage portions with different substrates. These different substrates may have different electric properties, which may be detectable by the fluid sensor. The fluid sensor may not only detect whether or not substrate is present in the fluid channel, but additionally detect what kind of substrate is present in the fluid channel. Beneficially, the system may be operated on basis of the detection of the specific substrate by the fluid sensor. For example, the temperature of a vaporiser may be controlled depending on the used substrate. Also, the heating time may be controlled depending on the used substrate.

The dispensing devise may be a nozzle or a tubing segment, also referred to as tube. The dispensing devise may comprise a tube and a nozzle at the distal end of the tube. The tube may comprise any appropriate material, for example glass, metal, for example stainless steel, or plastics material, for example PEEK. The size of the tube may match that of the pump outlet. For example, the tube may have a diameter of about 1 to 2 millimetres but other sizes are possible. The tube may be connected to the pump outlet via silicon tubing. The tube may be directly connected to the pump outlet.

The dispensing devise may be provided to deliver the liquid aerosol-forming substrate to a vaporiser. The vaporiser may comprise a heater for heating the supplied amount of liquid aerosol-forming substrate. The heater may be any device suitable for heating the liquid aerosol-forming substrate and volatilizing at least a part of the liquid aerosol-forming substrate in order to form an aerosol. The heater may exemplarily be a heated coil, a heated capillary, a heated mesh or a heated metal plate. Preferably, the vaporiser is provided as a heating coil extending - with respect to the dispensing device - in a longitudinal direction of the dispensing device. The diameter of the heating coil may be chosen such that the heating coil can be mounted around the dispensing device. The heating coil may be mounted transverse to the dispensing device. The heating coil may overlap with the nozzle of the dispensing device. In some examples, there may be a distance between the nozzle of the dispensing device and the heating coil. The length of the heating coil may be 2 millimetres to 9 millimetres, preferably 3 millimetres to 6 millimetres. The diameter of the heating coil may be 1 millimetre to 5 millimetres, preferably 2 millimetres to 4 millimetres.

The heater may comprise only a single heating element or a plurality of heating elements. The temperature of the heating element or elements is preferably controlled by electric circuitry.

The electric circuitry may comprise a microprocessor, which may be a programmable microprocessor. The microprocessor may be part of a controller. The electric circuitry may comprise further electronic components. The controller may be configured to regulate a supply of power to the vaporiser. Power may be supplied to the vaporiser continuously following activation of the system or may be supplied intermittently, such as on a puff-by-puff basis. The power may be supplied to the vaporiser in the form of pulses of electrical current. Preferably, the supply of power to the vaporiser is controlled depending upon the measurement of the fluid sensor. When the fluid sensor detects that no more liquid is present in the fluid channel, power supply to the vaporiser may be prohibited. Additionally or alternatively, the power supply to the vaporiser may be controlled on basis of the type of liquid aerosol-forming substrate in the fluid channel. For example, the specific heating regime may be executed on basis of the type of substrate.

For supplying power to the vaporiser, the system may comprise a power supply, typically a battery. As an alternative, the power supply may be another form of charge storage device such as a capacitor. The power supply may require recharging and may have a capacity that allows for the storage of enough energy for one or more smoking experiences; for example, the power supply may have sufficient capacity to allow for the continuous generation of aerosol for a period of several minutes. In another example, the power supply may have sufficient capacity to allow for a predetermined number of puffs or discrete activations of the vaporiser. The controller may be connected to the power supply to control the supply of power from the power supply to the vaporiser.

The vaporiser may also be provided as a piezoelectric transducer or vibrating membrane.

The pump may be a micro pump. The pump may also be provided as a micro stepper motor pump or a piezoelectric pump.

The pump may be controlled by the controller. The controller may stop the operation of the pump when the fluid sensor detects that no more liquid aerosol-forming substrate is present in the fluid channel. Power may be supplied to the pump by means of the power supply. The pump and preferably the vaporiser may be triggered by a puff detection system. Alternatively, the pump and preferably the vaporiser may be triggered by pressing an on-off button, held for the duration of the user's puff.

The puff detection system may be provided as a sensor, which may be configured as an airflow sensor and may measure the airflow rate. The airflow rate is a parameter characterizing the amount of air that is drawn through the airflow path of the system per time by the user. The initiation of the puff may be detected by the airflow sensor when the airflow exceeds a predetermined threshold.

The liquid storage portion may be adapted for storing the liquid aerosol-forming substrate to be supplied to the dispensing device. The liquid storage portion may be configured as a container or a reservoir for storing the liquid aerosol-forming substrate.

Preferably, the liquid storage portion is capable of being coupled to the pump inlet by a respective coupling hermetically sealed against surrounding atmosphere. Preferably, the couplings are configured as self-healing pierceable membranes. The membranes avoid undesired leaking of the liquid aerosol-forming substrate stored in the liquid storage portion. For coupling the replaceable liquid storage portion to the pump a respective needle-like hollow tube may be pierced through a respective membrane. When the pump is coupled to the liquid storage portion, the membranes avoid undesired leaking of the liquid aerosol- forming substrate and leaking of air from and into the liquid storage portion.

The liquid storage portion may be any suitable shape and size. For example, the liquid storage portion may be substantially cylindrical. The cross-section of the liquid storage portion may, for example, be substantially circular, elliptical, square or rectangular.

The liquid storage portion may be a disposable article replaced once the liquid storage portion is empty or below a minimum volume threshold. The system may output a signal such as an optical or acoustical signal when the fluid sensor detects that the fluid channel is empty of liquid aerosol-forming substrate. The signal may indicate that a new liquid storage portion must be provided to replace the old empty liquid storage portion or that the liquid storage portion needs to be refilled.

The aerosol-forming substrate is a substrate capable of releasing volatile compounds that can form an aerosol. The volatile compounds may be released by heating the aerosol- forming substrate. The aerosol-forming substrate may comprise plant-based material. The aerosol- forming substrate may comprise tobacco. The aerosol-forming substrate may comprise a tobacco-containing material containing volatile tobacco flavour compounds, which are released from the aerosol-forming substrate upon heating. The aerosol-forming substrate may alternatively comprise a non-tobacco-containing material. The aerosol-forming substrate may comprise homogenised plant-based material. The aerosol-forming substrate may comprise homogenised tobacco material.

The aerosol-generating system may be an electrically operated system. Preferably, the aerosol-generating system is portable. The aerosol-generating system may have a size comparable to a conventional cigar or cigarette. The smoking system may have a total length between approximately 30 millimetres and approximately 150 millimetres. The smoking system may have an external diameter between approximately 5 millimetres and approximately 30 millimetres.

According to a second aspect of the invention, there is provided a method for generating an aerosol. The method comprises the step of providing a pump for pumping liquid aerosol-forming substrate, the pump having an inlet and an outlet, the inlet being connectable to a liquid storage portion. A fluid channel is provided fluidly connected to the pump. Furthermore, a fluid sensor is provided, wherein the fluid sensor determines a presence of liquid aerosol-forming substrate in the fluid channel.

Features described in relation to one aspect may equally be applied to 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 illustrative cross section of the inventive aerosol-generating system;

Fig. 2 shows an illustrative cross section of the inventive sensor and the fluid channel;

Fig. 3 shows an illustrative wiring diagram of a voltage divider circuit which may be employed in the inventive sensor;

Fig. 4 shows an exemplary measurement diagram of the inventive sensor;

and

Fig. 5 shows an further exemplary measurement diagram of the inventive sensor.

The aerosol-generating system shown in Fig. 1 comprises a fluid sensor 10. The fluid sensor 10 is arranged between a pump 12 and a dispensing device 14. The fluid sensor 10 is arranged at a fluid channel 16. The fluid sensor 10 measures the electrical resistance of the fluid in the fluid channel 16. Thereby, the fluid sensor 10 determines whether liquid aerosol- forming substrate is present in the fluid channel 16. The pump 12 is configured to pump liquid aerosol-forming substrate from a liquid storage portion 18 towards the fluid channel 16 and the fluid sensor 10. The pump 12 is fluidly connected with the liquid storage portion 18 by means of an additional fluid channel 20.

After the liquid aerosol-forming substrate passes the fluid channel 16 and the fluid sensor 10, the liquid aerosol-forming substrate is delivered towards the dispensing device 14. The dispensing device 14 is configured as a tubing segment ending in a nozzle 22. Around the dispensing device 14, a heater 24 is arranged. The heater 24 is configured as a heating coil.

The heater 24 heats the liquid aerosol-forming substrate in the dispensing device 14 such that an aerosol is delivered from the nozzle 22 towards a mouth end 26 of the aerosol- generating system. The aerosol is subsequently inhaled by a user. The heater 24 is powered by a battery 28.

The fluid sensor 10, pump 12, dispensing device 14, fluid channel 16, nozzle 22, heater 24, mouth end 26 and battery 28 are arranged in a housing 30. The housing 30 confines a main body of the system. The housing 30 also comprises a controller 32. The controller 32 controls the activation of the heater 24. When the fluid sensor 10 detects that no liquid aerosol-forming substrate is present in the fluid channel 16, the controller 32 will deactivate the heater 24. The controller 32 also controls the pumping action of the pump 12. The controller 32 is part of electric circuity which may also determine the type of fluid in the fluid channel 16 on basis of the electric resistance of the fluid. The controller 32 may deactivate the heater 24, if an undesired fluid is present in the fluid channel 16.

In Fig. 1 , the liquid storage portion 18 is also arranged in the housing 30. However, the liquid storage portion 18 may be configured as a separate replaceable cartridge which may be attachable to an inlet of the pump 12.

Fig. 2 depicts the fluid sensor 10 in more detail. In this regard, Fig. 2 shows the fluid channel 16, wherein a first electrode 34 and a second electrode 36 of the fluid sensor 10 are arranged at the wall of the fluid channel 16.

The first electrode 34 is arranged at the wall of the fluid channel 16 such that the tip of the first electrode 34 is in direct contact with the fluid in the fluid channel 16. The second electrode 36 is arranged on the opposite site of the wall of the fluid channel 16 also in direct contact with the fluid in the fluid channel 16. The first and second electrodes 34, 36 are arranged to measure the electrical resistance of the fluid between the electrodes 34, 36 and thus of the fluid in the fluid channel 16. The electrodes 34, 36 are supported in a carrier 38 for dimensional stability. The fluid sensor 10 has a length and width of 1 millimetre to 1 centimetre and preferably around 3 millimetre. The thickness of the fluid sensor 10 is 0,5 millimetre to 3 millimetre and preferably around 1 ,5 millimetre. The electrodes have a diameter of 0,9 millimetre. The electrodes have a length of 1 to 5 millimetre and preferably around 3 millimetre. The distance between the electrodes should be as small as possible without impeding the flow of liquid, ideally 1 millimetre or the internal diameter of the tube.

Fig. 3 shows a voltage divider circuit which is used to determine the electrical resistance of the fluid in the fluid channel 16.

In Fig. 3, a conventional voltage divider circuit is modified in that a conventional first resistor is replaced by the first and second electrode 34, 36 and the fluid in the fluid channel 16 between the electrodes 34, 36. Apart thereof, the voltage divider circuit consists of the known elements of a voltage divider circuit. In more detail, a second resistor 40 is provided. The electrical resistance of the second resistor 40 is known. The electrical resistance of the second resistor can be chosen as required and is chosen suitable with respect to the electrical resistance of the liquid aerosol-forming substrate. The electrical resistance of the second resistor is chosen in the range of 5 to 20 Megaohm and preferably around 12 Megaohm or approximately equal to the resistance between the two electrodes when liquid is present. Different aerosol forming substrates will present different resistances therefore this may need to be specified during the design process. However most resistor values in this range will provide a significant voltage difference when liquid is present vs when it is not. The electrical resistance of the liquid aerosol-forming substrate is comparable within different liquid aerosol-forming substrates such as e-liquids. A known voltage is applied to the circuit. An analog-to-digital converter 42 is connected to the center tap of the voltage divider circuit. By using the measured voltage, the known electrical resistance of the second resistor 40 and the known applied voltage, the controller, which is connected with the analog-to-digital converter 42, computes the electrical resistance of the first resistor. Since the electrical resistance of the electrodes 34, 36 is also known, the controller 32 thus computes the electrical resistance of the fluid in the fluid channel. At the analog-to-digital converter 42, the measured voltage decreases if the electrical resistance of the fluid between the electrodes increases and vice versa.

Fig. 4 shows an exemplary measurement of the fluid sensor 10. Fig. 4 depicts the voltage which is measured at the analog-to-digital converter 42. The diagram shows the voltage over time. The electrical resistance of the second resistor 40 was set to 12 Megaohm. At first, no liquid aerosol-forming substrate is present in the fluid channel 16. Only air is present in the fluid channel 16. Thus, the measured voltage is low, corresponding to a high electric resistance of the fluid in the fluid channel 16. The electric resistance was determined to be 18 Megaohm when no substrate was present in the fluid channel 16. This measurement is denoted by reference sign 44. Before the fluid channel 16 is fully filled with liquid aerosol-forming substrate, bubbles emerge, i.e. a mixture of liquid aerosol-forming substrate and air. Thus, fluctuating electrical resistance values are determined by the fluid sensor 10. This measurement is denoted by reference sign 46. When the fluid channel 16 is fully filled with liquid aerosol-forming substrate, the measured voltage is high, corresponding to a comparatively low electric resistance of the liquid aerosol-forming substrate in the fluid channel 16 (reference sign 48). The electric resistance was determined to be 10 Megaohm when the fluid channel 16 was fully charged with liquid aerosol-forming substrate. The same principle applies when - at first - liquid aerosol-forming substrate is present in the fluid channel and - subsequently - air is present in the fluid channel. In this case, liquid aerosol- forming substrate will be followed by bubbles and eventually by air.

Fig. 5 is another exemplary measurement of the fluid sensor 10 with other parameters than the parameters used in Fig. 4. In the measurement as used in Fig. 5, the electrical resistance of the second resistor 40 was set to 5,6 Megaohm. The measurement was conducted with different fluids in the fluid channel 16. The fluids used were water 50, a fluid 52 with glycerol, denoted 80PG/20VG, and a further fluid 54 with higher glycerol content, denoted 20PG/80VG. Between measurements of the different fluids, the fluid channel 16 was cleaned using isopropanol and water to prevent contamination of the fluid channel 16. The measurements were delayed until the respective fluids 50, 52, 54 had filed the fluid channel 16 and a stable measurement signal could be obtained. Fig. 5 shows the measured resistance against the time.

The measurement depicted in Fig. 5 shows that the three fluids 50, 52, 54 could clearly be distinguished from one another based upon the measured electrical resistance. It has been observed that the measured electrical resistance increased over time. Without being bound to any theory, it is believed that this increase was a result of polarization of the fluids 50, 52, 54. Particularly the fluid 54 with high glycerol content was prone to polarization, since glycerol does not dissociate in water and so the fluid 54 contained a low initial ion count resulting in faster and more pronounced polarization. To avoid an increase of the measured electrical resistance over time, alternating current could be used for measuring the electrical resistance.

The exemplary embodiments described above illustrate but are not limiting. In view of the above discussed exemplary embodiments, other embodiments consistent with the above exemplary embodiments will now be apparent to one of ordinary skill in the art.