Description

The present invention relates to a filter for a smoking article.

Typically, smoking articles are provided with filters for removing constituents from the smoke. A conventional filter for a smoking article passes gaseous smoke from a tobacco rod through a fibrous filtration material, in particular, cellulose acetate tow.

Various embodiments of the present invention provide a filter for a smoking article comprising: a flow restrictor configured to cause an increase in velocity of smoke drawn through the filter; and at least one guide surface configured to promote swirling motion of the increased velocity smoke, such that constituents of the smoke impact and are captured by the filter.

Various embodiments of the present invention further provide a filter for a smoking article comprising: a filtration chamber configured such that swirling smoke impacts a surface of the filtration chamber and constituents of the smoke are retained in the filtration chamber, wherein the filtration chamber has an inlet and an outlet configured such that the smoke at least initially travels in the filtration chamber from the inlet with a component in a first longitudinal direction , and the smoke travels towards the outlet and/or from the outlet and away from the chamber with a component in a second longitudinal direction different to the first longitudinal direction.

Various embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure l is a perspective view of the filter for a smoking article;

Figure 2 is a cut-away side elevation view of the filter;

Figure 3 is a schematic side elevation view of flow in a part of the filter;

Figure 4 is a perspective view of an interior part of the filter;

Figure 5 is a side elevation view of the interior part of the filter,

Figure 6 is a front elevation view of the interior part of the filter; and

Figure 7 is a cut-away side elevation view of an exterior part of the filter. Figures l and 2 show a filter l for a smoking article. Some embodiments of the filter l are configured to generate swirling flow of smoke from a smoking article in a filtration chamber. The smoke comprises a gaseous flow in which

constituents are initially entrained, which will be termed as "smoke" for simplicity. The constituents may be defined as any component of the smoke to be captured by the filter, for example, entrained particulates. The constituents to be filtered or particulates may also be known as particulate matter. The

constituents may be, for example, solid particles and/or entrained liquids. The parts of the smoke which may be retained by the filter will be referred to generally as constituents. The term "constituents" which may be captured may be replaced by "particulates" or "particles" or "particulate matter" throughout the specification. Any of these terms is intended to cover one or more of the components of the smoke, of any phase, which may be captured by the filter. In some embodiments, the swirling flow causes constituents of the smoke to be retained by one or more walls of the filtration chamber, and so filter the smoke. In some aspects, the filter ι may be considered as a capture device to capture particulate matter from the smoke. Generally, the smoke is from combustion of tobacco. The smoking article may be an article which generates smoke and/or vapour. For example, the smoking article may be a cigarette, cigar or cigarillo, whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco or tobacco substitutes and also heat-not-burn products (i.e. products in which flavour is generated from a smoking material by the application of heat without causing combustion of the material).

The filter according to various embodiments of the present invention receives a smoking article. The smoking article may not have a separate filter, for example, the smoking article may be only a tobacco rod. Alternatively, the smoking article may comprise a filter, for example, a fibrous filter.

In some examples, the filter l according to various embodiments comprises an elongate body having a forward end 2 for receiving a smoking article, and a rearward end 4 forming a mouthpiece 9 for a user. The rearward end 4 defines an opening 6 through which the filtered smoke exits the filter. In some embodiments, an exterior wall 8 of the filter 1 forward of the mouthpiece 9 is substantially cylindrical. The mouthpiece 9 may comprise fins 9a to effectively transfer heat generated in the filter 1 to the surrounding atmosphere.

Figure 2 shows a cross-section through the filter 1. A socket 10 is dimensioned to receive an end of a smoking article, and has interior dimensions to tightly fit around a periphery of the smoking article and retain the smoking article in the filter. In some embodiments, the cylindrical socket 10 defines a flange 12 at a rearward end, on which the smoking article can abut to limit rearward movement of the smoking article into the filter 1. In some examples, the flange 12 is an annular step around a periphery of the rearward end of the socket 10. In various embodiments, an intake cavity 14 is located rearwardly of the socket 10 and flange 12. In some examples, the intake cavity 14 is open to the socket 10, over the whole area within the flange 12. Smoke from the smoking article is freely drawn into the intake cavity 14 from the smoking article. In some examples, a rearward end of the intake cavity 14 tapers to reduce in diameter, and is, for example, substantially hemi-spherical. In various embodiments, the intake cavity 14 is radially centrally located in the filter 1.

In various embodiments, the intake cavity 14 defines an aperture 16 through which smoke is drawn into a preliminary chamber 20. In some examples, the plane of the aperture 16 extends in a substantially radial direction, and may also or alternatively extend at least partially rearwardly. In some examples, the aperture 16 is a single aperture 16, such that all smoke passes through the single aperture 16. The intake cavity 14 and aperture 16 form an intake of the smoking article.

In some embodiments, the preliminary chamber 20 receives smoke from the aperture 16. For example, the preliminary chamber 20 is a substantially annular chamber or passageway, on a periphery of the filter 1. In various embodiments, a radially exterior surface of the preliminary chamber 20 is defined by the outer wall 8. The exterior wall 8 extends at a uniform radius around the preliminary chamber 20. In various embodiments, the cross-sectional area of the preliminary chamber 20 decreases in an axial direction away from the intake. In various embodiments, a radially inner surface of the preliminary chamber is defined by a chamber wall 32. For example, the chamber wall 32 increases in radius towards a rearward end of the preliminary chamber 20, and for example, is frusto-conical. In various embodiments, the lateral (i.e. radial) extent of the preliminary chamber 20 decreases in a rearward direction from the aperture 16.

In various embodiments, the preliminary chamber 20 is defined by a rear wall 28 at rearward end of the exterior wall 8. The preliminary chamber 20 also extends forwardly of the aperture 16, around the intake cavity 14 and socket 10. The preliminary chamber 20 is also defined by a front wall 29, in the form of an annular wall around the socket 10 at the forward end of the filter 1. Alternatively, the preliminary chamber 20 does not extend forwardly of the aperture 16, or only extends around a part of the intake cavity 14 and socket 10.

In various embodiments, the preliminary chamber 20 is configured to guide smoke in a rearward longitudinal direction. The smoke travels rearwardly from the aperture 16 to an inlet 34 of a filtration chamber 30. In some examples, the filter is configured to promote the smoke to be swirling or rotating on entering the filtration chamber 30. In some embodiments, at least a part of the angular momentum to form the swirling motion is imparted to the smoke in the preliminary chamber 20. In some aspects, the preliminary chamber has a larger cross-section than the inlet 34. Thus, the speed of the smoke flow through the preliminary chamber is slower than through the inlet 34, reducing friction losses in the preliminary chamber.

In some examples, the preliminary chamber 20 is provided with one or more guide surfaces configured to promote a swirl to the smoke as the smoke travels through the preliminary chamber. The one or more guide surfaces may be configured to at least partially cause the swirl. The one or more surfaces may be located on one or more curved fins. The fins 22 are shown in Figure 5 and 6. In various embodiments, the fins 22 extend radially from the chamber wall 32 to exterior wall 8. The fins 22 are may be attached to the chamber wall 32, and may be integrally formed with the chamber wall 32. The fins 22 are at least partly curved in a circumferential direction, such that smoke following a fin 22 is urged in a circumferential direction. In some embodiments, all of the fins are curved in the same direction. In various embodiments, the fins 22 extend the whole length and depth of the preliminary chamber 20, and so a plurality of fins 22 divide the preliminary chamber 20 into separate circumferential compartments. For example, the filter 1 comprises two fins 22. The two fins 22 divide the preliminary chamber into two compartments. The fins may be equally spaced, such that the compartments are of equal size. Smoke preferably enters the preliminary chamber through a single aperture 16, and so smoke only passes through a single one of the compartments.

In some examples, the aperture 16 and inlet 34 to the filtration chamber are located within the same compartment. The aperture 16 is located diametrically opposite to the inlet 34. The aperture 16 is located adjacent a first fin, and the inlet 34 is adjacent a second fin. The smoke may interact with both of the curved first and second fins 22 defining the compartment.

In some embodiments, the inlet 34 to the filtration chamber 30 is at or adjacent a rearward end of the preliminary chamber 20. The inlet 34 is on a peripheral side of the filtration chamber 30, preferably defined by an aperture in the chamber wall 32 which faces substantially radially. In some embodiments, the inlet 34 is at or adj acent the rear wall 28 of the preliminary chamber 20. The smoke passes through the inlet 34, which is a passageway through the chamber wall 32. In some circumstances, the inlet 34 may be a single inlet 34, i.e. the only inlet into the filtration chamber 30.

In some embodiments, the filter comprises a flow restrictor to cause an increase in velocity of smoke drawn through the filter. The flow restrictor may be a restriction at a single point, or may be a restriction which extends over a length, for example, as formed by a tube. For example, the flow restrictor may be formed by the inlet 34 being dimensioned to cause a restriction on the flow of smoke. The restriction causes an increase in the speed of the smoke, and a reduction in pressure, following Bernoulli's principle. The inlet 34 is sufficiently large to avoid becoming blocked by depositions from the smoke, and to provide an acceptable draw resistance. The inlet 34 may have an area of from 0.3mm ² to 2mm ² , preferably from 0.5mm ² to 0.8mm ² , and preferably has an area of approximately 0.65mm ² . The inlet 34 may be substantially square in plan view, the inlet 34 preferably having dimensions of from 0.7mm x 0.7mm to 0.9mm x 0.9mm, and preferably approximately 0.8mm x 0.8mm. These dimensions of the inlet are examples only, and the inlet may have a larger or smaller cross- section to provide the required flow-rate and speed. In various embodiments, the smoke enters the filtration chamber 30 through the inlet 34. A rearward end of the filtration chamber 30 is defined by the common rear wall 28. For example, the inlet 34 is adjacent the rear wall 28 of the filtration chamber 30, and so the smoke enters the filtration chamber at or adjacent the rearward end of the filtration chamber 30. The inlet 34 is on a radial periphery of the filtration chamber 30. Further details of the inlet 34 are described with respect to Figures 5 and 6. In one example, the filtration chamber 30 is defined by the chamber wall 32, and the rear wall 28. The chamber wall 32 is frusto-conical, such that the filtration chamber 30 is substantially frusto-conical. The diameter of the filtration chamber 30 increases from a forward end towards the rearward end of the filtration chamber 30. In various embodiments, the diameter increases linearly with longitudinal position.

In various embodiments, the chamber wall 32 is integrally formed with the wall defining the socket 10. The chamber wall 32 defines both an exterior wall of the filtration chamber 30, and an interior wall of the preliminary chamber. The preliminary chamber 20 extends around a periphery of the filtration chamber 30. The filtration chamber 30 may located radially within the preliminary chamber 20, reducing the length of the filter 1 for the equivalent path length of the smoke. In at least some embodiments, the chamber wall 32 defines an interior surface 36 which is in contact with the swirling smoke in the filtration chamber 30. In some embodiments, the interior surface 36 is circular in cross-section, and extends laterally to the longitudinal axis of the filtration chamber. In some examples,

the curved interior surface 36 may form one or more guide surfaces which promote the swirling of the smoke. The one or more guide surfaces may be configured to at least partially cause the swirl.

In various embodiments, the swirling smoke forms a vortex in the filtration chamber 30. The filtration chamber 30 is configured to generate and/or support the vortex, for example, by having a circular cross-section. The filtration chamber 30 is configured such that smoke constituents impact and are retained in the filtration chamber 30. For example, the smoke constituents may adhere to an interior surface, for example, at least the interior surface 36. The interior surface 36 provides a relatively large area on which smoke constituents can be retained. A build-up of collected smoke constituents on the interior surface 36 does not have a significant effect on the pressure required to draw smoke through the filter. Smoke constituents may also impact and be retained by other surfaces in the filtration chamber and in the filter. The velocity of the swirling smoke in the filtration chamber is sufficiently high such that constituents of the smoke impact and remain on the interior surface 36. A user increasing draw pressure of the smoke will tend to increase the velocity of the smoke through the filter, increasing the amount of smoke constituents filtered.

In one example, the interior surface 36, or any surface in the filter, may be treated to improve retention of smoke constituents. For example, the interior surface 36 may be treated with a catalyst. Alternatively, the interior surface 36 may not be treated.

In various embodiments, the filtration chamber 30 comprises an outlet 40 through which the smoke is configured to exit the filtration chamber 30. The outlet 40 is spaced from all walls of the filtration chamber. For example, the outlet 40 is spaced from a rearward end of the filtration chamber 30. In particular, the outlet 40 is spaced longitudinally of the rearward end of the filtration chamber 30. In various embodiments, the longitudinal axis is defined by the axis of the filtration chamber around which the smoke swirls. In at least one example, the longitudinal axis of the filtration chamber may be substantially coincident with the longitudinal axis of the filter and/or the smoking article. For example, the outlet 40 is located forwardly of the rear wall 28. In some aspects, the outlet 40 is spaced from the inlet 34 in an axial direction of the filtration chamber.

In various embodiments, the outlet 40 is positioned between a forward end and a rearward end of the filtration chamber 30. The location of the outlet 40 is such that smoke is forced to travel at least initially in a forward direction in the filtration chamber 30 from the inlet 34. For example, the smoke travels at least partially in a longitudinal direction of the filtration chamber. In some embodiments, the longitudinal axis of the filtration chamber may be defined by the axis around which the smoke circulates. The components of the direction, i.e. longitudinal motion, radial motion and the swirling motion of the smoke are considered separately. Thus, a defined longitudinal movement does not indicate any particular rotational or radial motion.

In various embodiments, the outlet 40 is located in a radially central position within the filtration chamber 30. Thus, the smoke in the vortex also travels from the inlet at a radial periphery of the filtration chamber to the outlet at a radial centre before exiting.

In some embodiments, the longitudinal spacing of the inlet 34 and outlet 40 of the filtration chamber 30 means that the smoke cannot travel directly in a radial direction from the inlet 34 to the outlet 40. The configuration of the inlet 34 and outlet 40 provides for the smoke to swirl for an increased length of time, increasing the retention of smoke constituents to the interior surface 36 of the filtration chamber 30. In addition, the smoke travels radially outwardly by its angular momentum, and so initially circulates away from the radially central outlet 40. The outlet 40 is located forwardly of the rear wall 28, such that smoke travelling rearwardly on a periphery of the filtration chamber 30 will not be guided into the outlet 40 by the rear wall 28.

For example, the outlet 40 is an opening on a forward end of an exit channel 42. The channel 42 forms a passageway for the smoke from the outlet 40 to an opening 6 at a rearward end of the filter. In some examples, the smoke travels in a longitudinally rearward direction of the filter in the channel 42. In various embodiments, the channel 42 extends longitudinally in a hollow tube 41 within the filtration chamber 30. The channel 42 may also extends rearwardly of the filtration chamber 30 as a hollow tube to form mouthpiece 9. The smoke may continue to swirl in the channel 42.

In some examples, the channel 42 may vary in lateral extent along its length. In some embodiments, the channel is circular in cross-section, in which case the lateral extent is a diameter. The channel 42 may comprise a first section 44a, second section 44b and a third section 44c. The first section 44a within the filtration chamber 30 may have a first, uniform, lateral extent. The second section 44b may have a lateral extent which increases with longitudinal position in a rearward direction. The lateral extent of the channel increases linearly. The third section 44c may have a substantially uniform lateral extent, or may increase a relatively small amount per unit length. The lateral extent of the third section 44c, at a rearward end of the channel 42, may be greater than the first section 44a. In some examples, the opening 6 may have a larger area than the outlet 40. Alternatively, the channel 42 may have a substantially constant lateral extent or diameter along its length. Figure 3 shows a flow of smoke through the filtration chamber 30, according to some embodiments. The filter 1 is configured such that a predetermined flow is formed as smoke is drawn through the outlet 40. In some embodiments, the filtration chamber 30 is configured such that a reverse flow cyclone is

established in the chamber 30. The reverse flow cyclone referred to is considered to have a defined meaning in this specification. A reverse flow cyclone has smoke circulating (i.e. swirling) in two columns in opposite axial directions. The two columns are generally concentric. The axial direction relates to the axis of the filtration chamber 30. As shown in Figure 3, smoke 100 enters the filtration chamber 30 through inlet 34. The smoke 100 enters tangentially, and circulates or swirls around the periphery of the chamber. The swirling smoke travels axially away from the inlet 34, in an outer vortex 102. In some embodiments, the inlet may be angled slightly towards a forward end 37 of the chamber 30, distal to the inlet 34, to promote the vortex 102 to travel axially. Particulates entrained in the smoke impact against the walls 36 of the filtration chamber 30, and are captured.

In some embodiments, as the circulating smoke travels towards the forward end 37, the vortex is confined within a reducing diameter due to the reducing diameter of the filtration chamber 30. As the diameter of the outer vortex 102 reduces, the rotational velocity of the smoke within the outer vortex 102 increases, due to conservation of angular momentum. The mean radius of circulation of a particle may depend on its weight. The increase in velocity may result in further particulates, which were entrained within the smoke at a smaller angular velocity, impacting against the walls 37. In various aspects, the outer vortex 102 reaches the distal end 37 of the filtration chamber 30, and the flow is reflected to form an inner vortex 104. Thus, the axial direction of travel of the circulating smoke reverses in the filtration chamber. The inner vortex 104 is circulating or swirling smoke within the outer vortex 102. The smoke in the inner vortex 104 travels axially in the opposite direction to the outer vortex 102, i. e. from the forward end 37 towards the outlet 40. The inner vortex 102 forms a co-axial column from the forward end 37 to the outlet 40, through which the smoke then exits the filtration chamber 30. From the outlet 40, the smoke continues to swirl through channel 42 as flow 106.

In some aspects, the arrangement of the filter to form a reverse flow cyclone is advantageous for capturing particulates from the smoke. The reverse flow cyclone ensures that the smoke is swirling within the filtration chamber for a relatively long length of time, and so completes a high number of circulations. This amount of circulation of the smoke within the filtration chamber 30 provides for the effective capture of particulates. In some embodiments, the reverse flow cyclone is at least partially generated by the reduction in cross- section (diameter) of the filtration chamber away from the inlet. Alternatively, the filter 1 may not be configured to induce a reverse cyclone flow. The filter may be configured to cause swirl of the smoke within the filtration chamber, without having a differentiated inner column of swirling smoke within an outer vortex. The smoke may swirl as a substantially single body of rotating smoke within the chamber.

In use of various embodiments, a user draws smoke from a smoking article located in the socket 10. The smoke contains at least some constituents to be filtered out. The smoke is drawn through intake cavity 14 and aperture 16 into preliminary chamber 20. The smoke is drawn rearwardly through the

preliminary chamber, and is forced to swirl. For example, the smoke is rotated by the fins 22 and/or the inlet 34 and/or surfaces of the filtration chamber.

The smoke enters the filtration chamber 30 and forms a vortex in the filtration chamber 30. The smoke impacts against the interior surface 36 of the interior surface 36, and smoke constituents attach to the interior surface 36. The particulate constituents entrained in the smoke tend to move radially outwardly, due to the centrifuge effect, dependent on mass of the constituent and rotational velocity of the smoke. In some examples, the filter may be configured such that the amount of retention of a constituent by the filter may depend on the mass of the constituent.

In some examples, the smoke is forced to travel at least initially in a forward direction in the filtration chamber 30 from the inlet 34. The configuration of the filtration chamber causes the axial direction of the swirling smoke to reverse, and form a radially inner swirling column. The smoke exits the filtration chamber 30 through the outlet 40, and travels in a rearward direction away from the filtration chamber 30.

In various embodiments, the smoke is forced to change longitudinal direction at least once in the filter 1. Preferably, the smokes changes from a rearward motion in the preliminary chamber 20, to a forward motion in the filtration chamber 30, to a rearward motion in the filtration chamber 30 and into the outlet channel 42. Thus, the smoke travels in a first longitudinal direction from the inlet 34 in the filtration chamber, and in a second longitudinal direction from the outlet 40 away from the filtration chamber. The first and second longitudinal directions are preferably opposite directions. The smoke is drawn through the preliminary chamber in the second longitudinal direction.

Referring to Figures 4 to 7, the filter 1 may be formed in two pieces, a core 50 and a body 60. The core 50 defines the socket 10, front wall 29, intake cavity 14, chamber wall 32, fins 22. The components of the core are preferably integrally formed, or alternatively, may be assembled from more than one part.

In various embodiments, the body 60 defines the exterior wall 8, rear wall 28 of the preliminary chamber 20 and filtration chamber 30, the tube 41 providing the channel 42 and outlet 40 and mouthpiece 9. The components of the body are preferably integrally formed, or alternatively, may be assembled from more than one part.

The body and core may be formed by any suitable method, for example, moulding. The body and core may be formed from a plastics material, for example, polylactic acid (PLA) . Figure 4 shows the core 50 of the filter 1. The socket 10, front wall 29, intake cavity 14, chamber wall 32, fins 22 are substantially as described above. In various embodiments, the components of the core are preferably integrally formed, or alternatively, may be assembled from more than one part. The fins 22 are shown as a first fin 22a and a second fin 22b. The first fin 22a is curved, as described above, and with reference to Figure 5. The inlet 34 is adjacent the first fin 22a. The second fin 22b may not be curved, as described above. The second fin 22b extends straight and longitudinally from the front wall 29 to the rearward end of the chamber wall 32 to abut the rear wall 28.

In some examples, the fins 22a,22b extend to a uniform radius, to fit closely with the cylindrical inner surface of the body. An exterior of the socket 10 is provided with two supports 18. The supports 18 extend radially outwardly from the wall defining the socket 10. The supports 18 extend to the same radius as the fins 22a, 22b and fit closely with the cylindrical inner surface of the body. The supports 18 and fins 22 are equally spaced around the circumference of the core 50. The supports 18 and fins 22 securely locate the core 50 centrally within the body. Figure 5 shows a side elevation view of the core 50. The fin 22a is shown, guiding the smoke to rotate and enter inlet 34. In various embodiments, the fin 22a comprises a first section 24a which extends substantially straight in a

longitudinal direction. The fin 22a may further comprise a second section 24b, at a rearward end of the first section 24a, which is curved to allow the smoke to rotate about a longitudinal axis. The second section 24b may curve through approximately 90 degrees to extend circumferentially. The circumferentially extending part of the second section 24b extends adjacent the inlet 34, i.e.

longitudinally forward of the inlet 34. The smoke (not shown) is drawn from left to right, and above, fin 22a as shown in Figure 5. The smoke is guided

circumferentially (downwardly, as shown), by the curved second section 24b, into the inlet 34.

In various embodiments, the fin 22a may further comprise a third section 24c which extends longitudinally, at a rearward end of the second section 24b. The third section 24c extends to the rearward end of the core 50, and is configured to abut against rear wall 28. The third section 24c extends adjacent the inlet, and in particular, extends circumferentially of the inlet 34. The third section 24c may allow the smoke into the inlet 34 from the preliminary chamber 20, and prevents the smoke from passing into the adjacent compartment of the preliminary chamber 20. In some aspects, the filter comprises a guide surface extending longitudinally and/or circumferentially adjacent to the passageway defining the inlet to the filtration chamber, such that the guide surface guides smoke into the inlet. For example, the guide surface is formed by the fin 22a.

In some examples, the inlet 34 is defined by a recess or notch in the chamber wall 32, which is open to the rearward end of the core 50. The open side of the recess in the chamber wall 32 is closed by the rear wall 28, part of the body, to define the inlet 34. Alternatively, the inlet 34 may be defined within the chamber wall 32 only, as an aperture in the chamber wall 32. Figure 6 shows a rearward end of the core 50. In various embodiments, the fins 22a,22b and supports 18 extend radially outwardly from the chamber wall 32. The inlet 34 may be defined in the chamber wall 32. The inlet defines a passageway 35 through the chamber wall 32. The passageway 35 is not directed to the centre of the filtration chamber 30, but is angled thereto. In some examples, the passageway 35 is configured to direct the air tangentially to an adjacent interior surface 36 of the chamber wall 32. The passageway 35 has surfaces which may define one or more guide surfaces configured to promote swirl of the smoke in the filtration chamber. The one or more guide surfaces may be configured to at least partially cause the swirl. In various embodiments, the offset of the direction of the passageway from the radial centre of the filtration chamber generates and/or conserves the rotational motion of the smoke. In some aspects, the angle of the passageway away from the radial centre of the filtration chamber 30 is the main cause of swirl within the filtration chamber. In some examples, the curved surface of the chamber wall may guide the smoke to swirl. The angled passageway 35 and/or filtration chamber wall may function to guide air in the tangential direction, maintaining or increasing the swirling motion of the smoke, and so assist in creating the vortex.

In various examples, the inlet 34 may be formed by a curved passageway 35 through the chamber wall 32. The curved passageway 35 may be curved such that the rotating smoke is allowed to continue to travel circumferentially through the passageway, such that the passageway does not substantially reduce the rotation of the smoke. Alternatively, the passageway 35 may extend as a straight passageway through the chamber wall. In various embodiments, the third section 24c of the fin 22a defines a surface which is an extension of one side of the passageway 35. The third section 24c may be angled, and optionally curved, to assist in guiding the smoke to circulate about a longitudinal axis. As shown from the rearward end, as in Figure 6, the vortex in filtration chamber 30 will circulate anti-clockwise.

In some embodiments, the inlet 34 defines a flow restrictor which limits the area in which the smoke can flow, as described above. As the smoke enters the filtration chamber, the area in which the smoke can initially flow is limited to the area of the cross-section of the outer vortex 102. Thus, the reverse flow cyclone limits flow to a virtual cross-section. The virtual cross-section reduces in an axial direction away from the inlet. The virtual cross-section may be substantially the same, larger or smaller than the cross-section of the inlet 34. The virtual cross- section limiting flow within the filtration chamber 30 means that the speed of the smoke is maintained at a relatively high level, at least compared to smoke which is not substantially contained. Thus, the high speed of the flow through the flow restrictor is at least partially maintained in the filtration chamber 30.

Figure 7 shows a cut-away side elevation view of the body 60, forming the filter 1 in combination with the core 50. In various embodiments, the body 60 is open at a forward end 2 to receive the core 50. The exterior wall 8, rear wall 28 of the preliminary chamber 20 and filtration chamber 30, the tube 41 providing the channel 42 and outlet 40, and mouthpiece 9 with fins 9a, are as described above. The components of the core may be integrally formed, or alternatively, may be assembled from more than one part. In particular, the tube 41 configured to extend into the filtration chamber may be integrally formed with the remainder of the body 60, or may be a separately formed hollow tube inserted into the channel 42 and extending rearwardly into the filtration chamber 30.

After a tobacco rod has been used, the tobacco rod may be removed from the socket of the filter 1. The filter 1 may be re-used by inserting a fresh tobacco rod. Alternatively, the filter 1 may be permanently attached to a source of smokable material, e.g. a tobacco rod. The tobacco rod and filter would be discarded together once the tobacco has been smoked.

In one or more examples, the filter is described as configured to generate swirl by the one or more fins. Alternatively, the filter may not comprise fins, or the fins may not generate swirl of the smoke. The swirl of the smoke is generated solely by the passageway from the preliminary chamber to the filtration chamber and/or at least one wall of the filtration chamber. For example, the passageway may direct smoke at an angle away from the centre of the filtration chamber to cause rotation of the smoke, and/or the curvature of the filtration chamber wall may cause rotation of the smoke.

In some examples, the filter l may be used as the only filter for a smoking article. Alternatively, the filter l may be used in combination with a conventional fibrous filter. The conventional filter may be part of the smoking article received in socket 10, or may be in a section (not shown) of the filter l, before or after the filtration chamber 30.

In some embodiments, the filter 1 may provide for entry of ventilating air. The filter 1 may comprise one or more air permeable areas to allow air to be drawn into the filter, as smoke is drawn through. Preferably, the permeable areas are ventilation apertures. In some embodiments, the filter is configured to intake ventilation air upstream of the filtration chamber 30. The ventilation air may be considered as bypass air. For example, the preliminary chamber may comprise one or more air permeable areas, in particular ventilation apertures, on a radial surface and/or on a forward surface around the socket. Alternatively, ventilation air may be introduced to the smoke at any stage of the filter. For example, ventilation air may be introduced to or after the filtration chamber, or prior to the preliminary chamber. When ventilation air is introduced into the smoke, not all of the subsequent flow will have been derived from the smoking article through the socket 10. The subsequent composite flow is still termed as smoke for ease of reference. The introduction of ventilation air may reduce draw resistance of the smoke through the filter. A smoking article system according to the present invention may comprise a smoking article and connected filter 1, as described. The filter provides a resistance to drawing smoke from the smoking article. The presence of a resistance to smoke flow allows a higher level of ventilation to be used.

In a conventional fibrous filter, a pressure drop over the filter is typically approximately proportional to flow rate through the filter. In a cyclone filter of the type described, the pressure drop may be greater than proportional to flow rate through the filter. For example, the pressure drop may be approximately proportional to a square of the flow rate, or have an approximately exponential relationship with the flow rate. The exact relationship may be complicated, and not have a simple dependence.

In the cyclone filter described, the relationship between the pressure drop and flow rate means that in order to increase the flow rate, a relatively high increase in pressure drop is required. Thus, if a user draws harder on the cyclone filter, the flow rate will increase less than in a conventional fibrous filter. Thus, the cyclone filter provides a more uniform flow rate of smoke as a pressure drop through the filter increases, and it is relatively difficult to obtain a higher flow rate. In addition, as the flow rate increases, the efficiency of the cyclone filter ι increases. At higher flow rates, the air swirls at a higher velocity, and thus centripetal forces on the particulates increase. The higher centripetal forces provide for smaller weight particulates to travel radially outwardly to impact the side of the filtration chamber. A higher pressure drop through the filter may increase the flow rates and the speed of the smoke, resulting in increased impaction of particulates in the filtration chamber.

In some embodiments, the filtration chamber has been described as having a cross-section or diameter which varies with longitudinal position, e.g. the filtration chamber is at least a part of a cone. The varying cross-section promotes the reverse flow cyclone. Alternatively, the filtration chamber may have a uniform cross-section. For example, the filtration chamber may be a cylinder. The preliminary chamber surrounding the filtration chamber may by annular with a substantially constant cross-section around the filtration chamber. The constant cross-section may be used in particular with a single swirling flow in the filtration chamber, or alternatively, the filtration chamber may be configured such that a reverse flow cyclone is formed.

In some embodiments, the filtration chamber has a longitudinal axis around which the smoke swirls which is substantially coincident with the longitudinal axis of the filter and/or smoking article. Alternatively, the filtration chamber may have a longitudinal axis which extends at an angle to the longitudinal axis of the filter and/or smoking article, for example, substantially perpendicularly to the longitudinal axis of the filter and/or smoking article.

The longitudinal axis of the filtration chamber may be parallel and co-axial with the longitudinal axis of the filter and/or smoking article. Alternatively, the longitudinal axis of the filtration chamber may be laterally offset from the longitudinal axis of the filter and/or smoking article. In this embodiment, the filtration chamber may be located adjacent to an exterior wall of the filter body at a first circumferential point of the filter. In some examples, a preliminary chamber does not extend to this first circumferential point, such that the filtration chamber may be closer to the exterior wall of the filter at this first point. The preliminary chamber and inlet to the filtration chamber is spaced from the first circumferential point. For example, the inlet may be located diametrically opposite to the first circumferential point. This arrangement has the advantage that the overall diameter of the filter may be smaller for the same size of filtration chamber. In some examples, the exterior of the filter is described as having fins 9a for the efficient dispersal of heat. Alternatively, the filter 1 may not comprise the fins 9a. The exterior of the mouthpiece 9 may be a cylinder of uniform cross-section, or may vary in cross-section. In various embodiments, the filter has been described as having a single filtration chamber. Alternatively, the filter may comprise more than one filtration chamber. A swirl of smoke may be generated in a plurality of filtration chambers. The plurality of filtration chambers may be arranged in series such that smoke passes sequentially through the plurality of filtration chambers, or in parallel such that parts of the smoke pass through different filtration chambers. The filtration chamber has been described as having a single inlet. Alternatively, the filtration chamber may have one or more inlets. In some aspects, the filtration chamber may have a first inlet and a second inlet. Any feature of any embodiment may be used in combination with any other feature. In particular, any feature in a claim may be used in combination with any other feature in the same or another claim.