WO2022200772A1

WO2022200772A1 - A prefilter and an air intake system

Info

Publication number: WO2022200772A1
Application number: PCT/GB2022/050703
Authority: WO
Inventors: Darren PEARCE; David Mark Williams; Mark Thomas Raymonds BAILEY
Original assignee: Vortexair Ltd
Priority date: 2021-03-24
Filing date: 2022-03-21
Publication date: 2022-09-29
Also published as: GB2605161A; GB202104124D0

Abstract

A prefilter, said prefilter comprising: a cyclone defining a volume, said cyclone comprising an inlet and an outlet, said cyclone further comprising an aperture for the egress of particulate matter from the cyclone, and said prefilter further comprising a cap member that is located within said volume and that divides said volume into a first portion and a second portion, said second portion extending between said cap member and said aperture, wherein said inlet and said outlet are arranged to generate a vortex within said first portion of said volume when the air pressure at said outlet is lower than the air pressure at said inlet, wherein said cap member is arranged to partially occlude said first portion from said second portion and to form one or more openings that allow fluid communication between said first portion and said second portion.. The inclusion and positioning the cap member is beneficial as it increases the amount of particulate matter that is removed from the airflow within the cyclone as it inhibits particulate matter than has hit the walls and slide towards the aperture from re-entering the cyclone and its vortex. An air intake system comprising the prefilter.

Description

A PREFILTER AND AN AIR INTAKE SYSTEM

Field of the Invention

The present invention relates to a prefilter and an air intake systems comprising a prefilter.

Background to the Invention

It is often necessary to filter or purify the air drawn into systems such as heating, ventilation and air-conditioning (HVAC) systems or internal combustion engines. This air filtration often aims to remove particulate matter such as debris, sand, dust, dirt, insects, pollen, mould and bacteria before the air enters the HVAC or engine system. By filtering the air and minimising particulate matter entering the system, the contamination and damage to the system can be reduced. As such, filters are typically used in the air intake systems of HVAC systems and engine systems to increase their lifespans and increase the time required between maintenance and servicing.

Air filters are often used to filter and purify the air of HVAC and engine systems. Air filters typically comprise porous or fibrous materials, as these materials are ideal for filtering particulate matter from the air drawn into the HVAC or engine system. These porous or fibrous materials act as a physical barrier that traps the particulates or debris from making their way further into the system and potentially into the engine.

However, as air filters are a physical barrier, over time they can become partially or entirely blocked by particulate matter filtered from the air. When an air filter becomes partially or entirely blocked, airflow into the engine is limited, concomitantly reducing the HVAC system's efficiency or engine system. Regular maintenance, inspection, cleaning or replacement of air filters is required to ensure the HVAC or engine system remains operating at peak efficiency.

One method of increasing the lifespan of air filters to provide what is known as a prefilter, pre filter, precleaner or pre-cleaner as part of the air intake system. Prefilters are typically positioned such that incoming air passes through them before subsequently passing through the air filter. Prefilters usually aim to remove a significant proportion of the particulate matter in the air before it passes through a subsequent air filter. Thus, prefilters typically increase the longevity of an air filter and, therefore, also improve the efficiency of the HVAC or engine system. Many prefilters are designed to utilise centrifugal forces to remove particulate matter from the air drawn through the air intake. One problem with current prefilter technology is that the systems require moving parts to rotate at speed to separate the particulate matter from the air. Prefilters of this nature are prone to becoming stiff or damaged by particulate matter working itself into the rotating mechanism. Where a prefilter has stiff moving parts, this can lead to excessive wear and an increase in resistance to rotation that can reduce fuel efficiency. Another type of prefilter is a cyclonic or vortex separator. These prefilter types are advantageous as they do not require moving parts to separate particulate matter from an airflow.

Many state-of-the-art prefilters are also designed to collect and accumulate the particulate matter removed from the air in a reservoir or tank that then needs to be cleaned and emptied at regular intervals. Self-cleaning prefilters have been developed to reduce the problem of cleaning and emptying, these systems typically using a system of aspiration (or scavenging) to self-clean. Aspiration involves supplying a secondary airflow, frequently from the exhaust, to remove the particulate matter accumulated by the prefilter. However, systems of this nature are undesirable, as they require complicated plumbing systems in tight spaces to supply the secondary airflow, increasing the cost and complexity of such solutions.

In our previous patent GB 2572658B, we presented a self-cleaning cyclonic prefilter that comprises a blocking member arranged to move and concomitantly occlude an aperture when the air pressure at the outlet of the cyclone is lower than the air pressure at the aperture. Accordingly, once the pressure within the cyclone dropped to a sufficient level, for example, when air is no longer flowing through the cyclone, the blocking member would move away from the aperture, and particulate matter is expelled through the aperture via gravity. However, this system has the drawback that particulate matter is only expelled in batches, and a certain amount of particulate matter can build-up and re-enter the vortex of the cyclone after it has been filtered but before it has been expelled.

Objects and aspects of the present claimed invention seek to alleviate at least these problems of the prior art.

Summary of the Invention

According to a first aspect of the present invention, there is provided a prefilter, said prefilter comprising: a cyclone defining a volume, said cyclone comprising an inlet and an outlet, said cyclone further comprising an aperture for the egress of particulate matter from the cyclone, and said prefilter further comprising a cap member that is located within said volume and that divides said volume into a first portion and a second portion, said second portion extending between said cap member and said aperture, wherein said inlet and said outlet are arranged to generate a vortex within said first portion of said volume when the air pressure at said outlet is lower than the air pressure at said inlet, wherein said cap member is arranged to partially occlude said first portion from said second portion and to form one or more openings that allow fluid communication between said first portion and said second portion.

It has been found to be advantageous to split the volume into a first portion above (i.e. between the cap member and the outlet) the cap member and a second portion below (i.e. between the cap member and the aperture) the cap member. The cap member is therefore arranged to disrupt the formation of vortices within the volume such that the vortex that separates particulate matter from the airflow is only formed within the first portion. In this way, the cyclonic separation occurs above the cap member and the cap member defines a base from which the airflow being filtered rises towards the outlet. The one or more openings allow particulate matter that has been separated from the airflow via collision or contact with the walls of the cyclone to fall under gravity from the first portion to the second portion. Once the particulate matter is in the second portion, it is inhibited from re-entering the vortex within the first portion and exiting the cyclone as the cap member acts as a physical barrier that inhibits such movement. That is, the cap member partially occludes the first portion from the second portion and vice versa.

Overall, the inclusion and positioning of the cap member is beneficial as it increases the amount of particulate matter that is removed from the airflow within the cyclone as it inhibits particulate matter than has hit the walls and slide towards the aperture from re-entering the cyclone and its vortex. Thus, for a given size and shape of prefilter and cyclone, the prefilter of the present invention more efficiently separates particulate matter from the airflow compared to the state of the art. Additionally, the cap member can guide airflow within the first portion towards the outlet and thereby reduce turbulence within the first portion. Reducing turbulence within the cyclone also increases the efficiency of separation of the prefilter.

Preferably, the one or more openings are located adjacent to a wall of the cyclone. It is advantageous to position the one or more openings adjacent to a wall of the cyclone such that particulate matter that has collided with a wall of the cyclone can more easily travel through the one or more openings. That is, the wall of the cyclone acts as a guide to guide the particulate matter separated from the airflow towards the one or more openings and the second portion. In this way, the efficiency of the prefilter is increased as less particulate matter can re-enter the vortex.

More preferably, the one or more openings are located between an edge of the cap member and the wall of the cyclone. In this way, both the cap member and the wall of the cyclone can act as guides for guiding the particulate matter separated from the airflow towards the one or more openings.

Even more preferably, the edge of the cap member and the wall of the cyclone are attached at two or more locations, and wherein the spaces between the two or more locations are the one or more openings. Attaching the cap member to the wall member at two or more locations enables designs with minimal attachments between these components and, therefore, maximum space for openings, thereby increasing the amount of particulate matter that can travel from the first portion to the second portion.

Alternatively, the cap member may comprise the one or more openings that allow fluid communication between the first portion and the second portion.

Preferably, the one or more openings extend around the majority of the cap member. More preferably, the one or openings extend around at least 95% of the periphery of the cap member.

Preferably, the cap member is shaped to be complementary to part of the wall of the cyclone. More preferably, an edge of the cap member is angled to be parallel with part of the wall of the cyclone.

Preferably, the surface of the cap member facing towards the first portion is angled towards the one or more openings. The surface of the cap member facing towards the first portion can also be described as facing towards the inlet, facing towards the outlet, facing away from the aperture, and facing away from the second portion. The surface of the cap member facing towards the first portion is also called the upper surface of the cap member herein. Angling the upper surface of the cap member towards the one or more openings is advantageous to guide particulate matter that has collided with the cap member towards the one or more openings.

Preferably, the surface of the cap member facing towards the first portion is angled away from the aperture. Preferably, the surface of the cap member facing towards the first portion is angled towards the first portion. Preferably, the surface of the cap member facing towards the first portion is angled towards the outlet. Angling the upper surface of the cap member in these orientations is advantageous for guiding particulate matter towards the openings and for guiding the airflow within the first portion towards the outlet, thereby improving separation efficiency and reducing turbulence within the prefilter.

Preferably, the cap member is centrally aligned with the outlet. Preferably, the cap member is centrally aligned with the aperture. Preferably, the cap member is centrally aligned within the cyclone and its volume.

Preferably, the surface of the cap member facing towards the first portion is a cone-shaped surface. More preferably, the apex of the cone-shaped surface is centrally aligned with the outlet. Typically, the outlet is centrally aligned with the cyclone, as such; it is preferable that the apex of the cone-shaped surface is centrally aligned with cyclone and its volume. The upper surface having a cone shape has been found to be particularly beneficial for guiding particulate matter towards the one or more openings and guiding the airflow within the first portion towards the outlet. Thus, the cone-shaped surface is thought to improve the efficiency of the prefilter and reduce turbulence within the cyclone.

Alternatively, the surface of the cap member facing towards the first portion is a frustoconically- shaped surface. In this alternative embodiment, it is preferable that the frustum of the cone- shaped surface is centrally aligned with the outlet.

Preferably, the surface of the cap member facing towards the second portion is angled towards the one or more openings. The surface of the cap member facing towards the second portion can also be described as facing towards the aperture, facing away from the first portion, facing away from the outlet, and facing away from the inlet. The surface of the cap member facing towards the second portion is also called as the lower surface of the cap member herein. Angling the lower surface of the capper member towards the one or more openings is advantageous to guide particulate matter away from the one or more openings once it has travelled through the one or more openings. In this way, the particulate matter is less likely to re-enter the first portion from the second portion, increasing the efficiency of separation of the prefilter.

Preferably, the surface of the cap member facing towards the second portion is angled away from the aperture. Preferably, the surface of the cap member facing towards the second portion is angled towards the outlet. Preferably, the surface of the cap member facing towards the second portion is angled towards the first portion. Angling the lower surface of the cap member in these orientations is advantageous for guiding particulate matter away from the one or more openings, thereby improving the efficiency of the prefilter. Additionally, angling the lower surface of the cap member in these orientations increases the volume of the second portion enabling it to hold more particulate matter during use, thereby improving the separating efficiency of the prefilter.

Preferably, the surface of the cap member facing towards the second portion is a frustoconically-shaped surface. More preferably, the frustum of the frustoconically-shaped surface is centrally aligned with the outlet. Typically, the outlet is centrally aligned with the aperture, and, as such, it is preferable that the frustum of the frustoconically-shaped surface is centrally aligned with the aperture. The lower surface having a frustoconical shape has been found to be particularly beneficial for trapping and/or collecting particulate matter within the second portion. In this way, the particulate matter in the second portion is more likely to egress from the cyclone via the aperture, thereby improving the separating efficiency of the prefilter. Furthermore, the frustoconical shape increases the volume of the second portion.

Alternatively, the surface of the cap member facing towards the second portion is a cone- shaped surface. More preferably, the apex of the cone-shaped surface is centrally aligned with the outlet.

Preferably, the surface of the cap member facing towards the outlet and the surface of the cap member facing away from the outlet are arranged in a spaced relationship. By having the upper surface and lower surface of the cap member in a spaced relationship the two surfaces are spatially separated and the cap member has a body between them. The body of the cap member can be hollow or solid. The upper and lower surfaces are not considered to have a spaced relationship if they are merely just opposite sides of a sheet or plane. By having the upper surface and lower surface in a spaced relationship, it is possible for the upper surface and lower surfaces to have different shapes or be angled at different pitches. Accordingly, the spaced relationship allows each of the upper surface and lower surface to be optimised for their respective functions independently of one another.

Preferably, the first portion has a frustoconical shape. This shape is beneficial for the cyclonic separating action of the cyclone. Preferably, the second volume has frustoconical shape. This shape is beneficial for guiding the particulate matter from the one or more openings towards the aperture.

Preferably, the prefilter further comprises a blocking member arranged to move and concomitantly occlude the aperture when the air pressure at the outlet is lower than the air pressure at the aperture.

In this way, there is advantageously provided a self-cleaning, low-maintenance prefilter for use in an air intake system of an engine. The blocking aperture is only occluded when there is a pressure difference between the aperture and outlet. As such, when there is no airflow through the cyclone, the aperture is not occluded by the blocking member as the pressure at the outlet and aperture will be substantially the same. The aperture provides fluid communication between the internal volume of the cyclone and the exterior of the cyclone, such that particulate matter in the second portion cab egress from the prefilter through the aperture. This egress of the particulate matter when there is no airflow through the cyclone results in this preferred embodiment of the prefilter being self-cleaning.

The combination of the blocking member and the cap member of the present invention is particularly advantageous. In the state of the art, the blocking member can cause a build-up of particulate matter proximate the aperture. Thus, in the state of the art, some of this built- up particulate matter can re-enter the vortex and reduce the separating efficiency of the prefilter. In this preferred embodiment, this problem with the prior art is solved as the cap member inhibits particulate matter that has built up proximate the aperture (i.e. within the second portion) from re-entering the first portion. As such, this preferred embodiment of the present invention provides a self-cleaning prefilter that has improved separating efficiency. Furthermore, any particulate matter that does not egress through the aperture when the blocking member is not occluding the aperture is less likely to be drawn into the vortex once airflow begins again in the cyclone. Again, this improves the separating efficiency of the prefilter.

Preferably, the blocking member is arranged to completely occlude the aperture when air pressure at the outlet is lower than the air pressure at the aperture. More preferably, the occlusion of the aperture by the blocking member when air pressure at the outlet is lower than the air pressure at the aperture is substantially airtight. Even more preferably, when the aperture is occluded by the blocking member, the blocking member abuts the entire perimeter of the aperture to form an airtight seal. In this way, the air pressure within the cyclone can be more closely controlled such that the prefilter operates at higher efficiencies.

Preferably, the blocking member is located outside the volume of the cyclone. Preferably, the blocking member is completely located outside the volume of the cyclone until the blocking member occludes the aperture when a portion of the blocking member protrudes into the volume of the cyclone. Preferably, the protruding portion of the blocking member is a curved surface of the blocking member. This positioning of the blocking member reduces the turbulence within the cyclone, compared to embodiments where the blocking member is located within the cyclone, and improves the operation of the prefilter.

Preferably, the blocking member is held proximate to the aperture by a cage that surrounds the aperture. Preferably, the cage is located outside of the volume of the cyclone. Preferably, the longitudinal axis of the cage is parallel and coaxial to the longitudinal axis of the cyclone.

Preferably, the blocking member is arranged to move and concomitantly occlude the aperture when the air pressure at the outlet is lower than the air pressure at the aperture under the influence of air passing through the aperture. Air passes through the aperture, as the air pressure inside the volume of the cyclone is lower than the air pressure external to the volume of the cyclone.

Preferably, the blocking member has a curved surface. More preferably, the curved surface of the blocking member is configured to abut the aperture. Even more preferably, the blocking member is substantially spherical. Even more preferably, the blocking member is a ball.

According to a second aspect of the present invention, there is provided an air intake system, the air intake system comprising the prefilter of the first aspect of the invention. The air intake system of the second aspect may be suitable for use in heating, ventilation and air-conditioning (HVAC) systems. Furthermore, the air intake system of the second aspect may be suitable for use in engine systems such as internal combustion engine systems.

Detailed Description

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is a skeletal view of a first embodiment of a prefilter in accordance with the present invention;

Figure 2 is a sectional view of the first embodiment of the prefilter of Figure 1 ;

Figure 3 is a perspective view of a second embodiment of a prefilter in accordance with the present invention; and

Figure 4 is a perspective sectional view of the prefilter of Figure 3.

Figure 5a is a skeletal view of a computational fluid dynamic (CFD) simulation of the prefilter of Figure 3 showing the computed distribution of sand particles within the cyclone, where the sand particles have a diameter of 5 micrometers and are enlarged 1000 times for visualisation in the figure;

Figure 5b is a skeletal view of a computational fluid dynamic simulation of a prior art prefilter not in accordance with the present invention showing the computed distribution of sand particles within the prefilter, where the sand particles have a diameter of 5 micrometers and are enlarged 1000 times for the visualisation in the figure;

Figures 1 , 2 and 3a depict a first embodiment of a prefilter 10 in accordance with of the present invention. The prefilter 10 comprises a cyclone 12, where the cyclone 12 is a housing that substantially surrounds and defines a volume 14. The volume 14 of the cyclone 12 is divided into a first portion 16 and a second portion 18 by a cap member 20.

The housing of the cyclone 12 is shaped such that it comprises two parts: a frustoconical part 22 and a shoulder part 24. The interior surfaces of both the frustoconical part 22 and shoulder part 24 are substantially smooth. The shoulder part 24 and its curved sidewalls extend from the upper edge of the frustoconical part 22 such that the shoulder part 24 has substantially the same cross-sectional area as the upper edge of the frustoconical part 22.

The height of the frustoconical part 22 along its longitudinal axis is greater than the height of the shoulder part 24. The combined height of the shoulder part 24 and the frustoconical part 22 is greater than the diameter of the shoulder part 24 such that the longitudinal axis of the cyclone 12 extends centrally through both the frustoconical part 22 and the shoulder part 24 of the cyclone 12.

The frustum 26 of the frustoconical part 22 comprises an aperture 28. In this embodiment, the aperture 28 occupies the entire frustum 26 of frustoconical part 22. The shoulder part 24 and the aperture 28 are located at opposing ends of the cyclone 12 and prefilter. The aperture 28 is substantially circular and lies in a plane substantially perpendicular to the longitudinal axis of the cyclone 12. The aperture 28 allows fluid communication between the second portion 18 of the volume 14 and the exterior of the cyclone 12. In this way, particulate matter 30 separated from airflow within the cyclone 12 can be egressed from the prefilter 10 and cyclone 12 through the aperture 28.

The air, or airflow, that is to be cleaned by the prefilter 10 enters the first portion 16 of the volume 14 of the cyclone 12 by an inlet 32. The inlet 32 is a tube, pipe or hose that extends into the first portion 16 of the volume 14 of the cyclone 12 through its sidewalls in a spiral configuration. The inlet 32 and the should part 24 are configured to assist in directing the airflow to form a vortex within the first portion 16 of the volume 14. The longitudinal axis of the inlet 32 and the direction of airflow through the inlet 32 are both orientated substantially perpendicular to the longitudinal axis of the cyclone 12.

The air, or airflow, that has been cleaned by the prefilter 10 and cyclone 12 leaves the first portion 16 of the volume 14 of the cyclone 12 by an outlet 34. The outlet 34 is a tube, pipe or hose that extends into the volume 14 of the cyclone 12 through the centre of the shoulder part 24. The outlet 34 is centrally aligned with the cyclone 12 and is orientated in a direction that is substantially perpendicular to the inlet 32 and substantially parallel to the longitudinal axis of the cyclone 12. The outlet 34 and aperture 28 are situated at opposing ends of the cyclone 12. Both the outlet 34 and aperture 28 are centrally aligned with the longitudinal axis of the cyclone 12, such that the longitudinal axes of the cyclone 12 and the frustoconical part 22 extend through both the outlet 34 and aperture 28 respectively. The outlet 34 extends from the exterior of the prefilter 10 into the first portion 16 of the volume 14 towards the aperture 28 and cap member 20, such that the outlet is closer to the aperture 28 and the cap member 20 than the inlet 32.

The cap member 20 divides the volume 14 in the first portion 16 and the second portion 18. That is, the cap member 20 defines the boundary between the two portions 16, 18. The first portion 16 extends between the outlet cap member 20 and the top of the cyclone 12, the outlet 32 or the inlet 34. The second portion 18 extends between the cap member 20 and the aperture 28. Both the first portion 16 and the second portion 18 are frustoconical in shape. The first portion 16 of the volume 14 is substantially larger than the second portion 18 of the volume 14, such the largest diameter and circumference of the second portion 18 is less than or equal to the smallest diameter and circumference of the first portion 16. Also, the height of the first portion 16 is greater than the height of the second portion 18.

The cap member 20 is centrally aligned with the aperture 20, the outlet 34, the first portion 16, the second portion 18 and the cyclone 12. The cap member 20 is fixed in place within the cyclone 12. In this embodiment, the cap member is attached to the interior of the wall 38 of the frustoconical part 22 of the cyclone 12 at six different locations around an outer edge 36 of the cap member 20. The outer edge 36 represents the periphery of the cap member 20. The six attachments are evenly spread around the outer edge 36 of the cap member 20.

The gaps between the attachment locations provide six openings 40 for particulate matter 30 to travel between the first portion 16 and the second portion 18. The openings 40 extend around the majority of the periphery, or circumference, of the cap member 20 and only a fraction of the area between the outer edge 36 and wall 38 is blocked by the attachments. In this embodiment, each of the six openings 40 are identically sized and shaped.

The cap member 20 is a member with a circular circumference such that its shape is complementary to the circular cross-section of the frustoconical part 22. Moreover, the outer edge 36 is angled such that it is substantially parallel, and therefore complementary, to the wall 38 of the frustoconical part 22.

The cap member 20 further comprises an upper surface 42 and a lower surface 44. The upper surface 42 faces towards the outlet 34, the inlet 32, the first portion 16 and faces away from the aperture 28 and the second portion 18. The lower surface 44 faces away from the outlet 34, the inlet 32, the first portion 16 and faces towards from the aperture 28 and the second portion 18. Typically, in use, the upper surface 42 is above the lower surface as the prefilter 10 is orientated such that particulate matter 30 can egress via the aperture 28 under gravity.

The upper surface 42 of the cap member 20 is a cone-shaped surface that extends from the outer edge 36 to an apex 46 that extends into the first portion 16. The apex 46 is orientated towards the outlet 34 and away from the outer edge 36 and wall 38. In this way, the sloped curved walls of the cone-shaped upper surface 42 are angled towards the openings 40, the first portion 16 and the outlet 34. Furthermore, the sloped curved walls of the cone-shaped upper surface 42 are angled away from second portion 18 and the aperture 28. This shape of the upper surface 42 has been found to be particularly beneficial for the present invention. By sloping or angling the upper surface 42 towards the openings 40, the upper surface 42 guides particulate matter 30 that has been separated from the airflow towards the openings 40 and into the second portion 18. Additionally, the upper surface 42 helps reduce turbulence within the cyclone 12 by directing airflow proximate to the upper surface 42 towards the column of air rising through the centre of the vortex within the first portion 16 and exiting the cyclone 12 via the outlet 34.

The lower surface 44 of the cap member 20 is a frustoconically-shaped surface that extends from the outer edge 36 to a frustum such that the outer edge 36 is closer to the aperture 28 than the frustum 48. In this way, the sloped curved walls of the frustoconically-shaped lower surface 44 are angled towards the opening and away from the aperture 28. In this way, the lower surface 44 can guide particulate matter 30 that has entered the second portion 18 towards its frustum 48 such that the particulate matter 30 is collected proximate the frustum 48. The sloped walls of the lower surface 44 then act as a barrier making it difficult for the particulate material to re-enter the first portion 16 via the openings 40.

The upper surface 42 and the lower surface 44 have a spaced relationship such that the cap member 20 comprises a hollow or solid body between them. This spaced relationship gives the outer edge 36 its height and allows lower surface 44 and upper surface 42 to have different shapes and configurations. In this embodiment, the curved sloped walls of the lower surface 44 are steeper than the curved slope walls of the upper surface 42.

Due to the configuration of the inlet 32, the outlet 34 and the cyclone 12, vortices are formed within the volume 14 of the cyclone 12 such that particulate matter drawn into the prefilter 10 through the inlet 32 alongside the air is separated from the air by a process known as cyclonic separation or vortex separation. The shape of the cyclone 12, causes air entering the volume 14 to flow in a downward vortex, the entering air spiralling down the increasingly narrow frustoconical part 22. The high-speed rotation of the airflow in volume 14 causes particulate matter in the air, in particular, larger and denser particulate matter, to collide with the walls of the cyclone 12 as the inertia of these particles results in their ejection from the increasingly tight downward vortex. The axes of the vortices formed within the cyclone 12 are substantially coaxial with the longitudinal axis of the cyclone 12.

In use, air, or an airflow, comprising particulate matter 30 is injected into the prefilter 10 via the inlet 32. The shoulder part 24 and the frustoconical part 22 of the cyclone 12 guide the airflow creating a vortex within the first portion 16 of the volume 14. The vortex spirals downwards towards the aperture 28 and cap member 20. The inertia of the particulate matter 30 can be too large such that it cannot stay within the vortex and instead collides with the wall 38 of the cyclone 12, thereby separating it from the airflow. The wall 38 guides the separated particulate matter 30 towards the openings 40, past the cap member 20 and through into the second portion 18. The cap member 20 prevents the vortex within the first portion 16 from extending into the second portion 18, and the vortex rises from the cap member 20 to exit the cyclone 12 via the outlet 34. Thus, the separated particulate matter 30 remains below the cap member 20 and can egress from the cyclone 12 via the aperture 28 under its own gravity.

Figures 3 and 4 depict a prefilter 100 that is a particularly preferred embodiment of the present invention. The prefilter 100 comprises all the features of the prefilter 10. Specifically, the prefilter 100 comprises a cyclone 12, a volume 14, a first portion 16, a second portion 18, a cap member 20, a frustoconical part 22, a shoulder part 24, a frustum 26, an aperture 28, an inlet 32, an outlet 34, an outer edge 36 of the cap member 20, a wall 38 of the cyclone 12, openings 40, and an upper surface 42 and lower surface 44 of the cap member 20, an apex 46 and a frustum 48 that was substantially identical as the first embodiment.

Compared to the first embodiment, the prefilter 100 additionally comprises a blocking member 102 that is arranged to obscure, occlude, block, stopper or plug the aperture 28 at certain times during the operation of the prefilter 100.

The blocking member 102 is located proximate to the aperture 28. The blocking member 102 is substantially spherical and ball-shaped and is located externally to both the volume 14 and the cyclone 12. The curvature and size of the blocking member 102 are designed and arranged to be such that the blocking member 102 can occlude the aperture 28. In this embodiment, the blocking member 102 completely occludes the aperture 28 to form a substantially airtight seal when air pressure at the outlet 34 is lower than the air pressure at the aperture 28. As the aperture 28 occupies the entire frustum 26, the perimeter of the aperture 28, defined by the wall 38 of the frustoconical part 22, is abutted by the blocking member 102.

The blocking member 102 is contained within a substantially cylindrical cage 104 located outside of the volume 14 of the cyclone 12. The cage 104 has a cylindrical profile with an open end 106 that allows particulate matter 30 egressed from the cyclone 12 to pass through. The cage 104 comprises a retaining member 106 that prevents the blocking member 102 from being removed from the cage 104 in use. In use, the prefilter 100 is installed, positioned and orientated such that force of gravity acts to move the blocking member 102 away from the position where it is occluding the aperture 28 to a position where it is abutting the cage 104 and the aperture 28 is open. As such, in rest or in when there is no airflow through the cyclone, the aperture 28 is open.

The cage 104 prevents the blocking member 102 from moving more than a relatively small distance in any direction perpendicular to the longitudinal axis of the cyclone 12. In this way, the majority of the freedom of movement of the blocking member 102 is towards and away from the aperture 28 for occluding the aperture 28.

In operation, air enters the volume 14 of the cyclone 12 through the inlet 32 and exits via the outlet 34 due to the pressure difference between the inlet 32 and outlet 34. The air pressure at the outlet 34 is also lower than at the aperture 28.

The flow of the air through the cyclone 12 causes the pressure inside the volume 14 of the cyclone 12 to be lower than the pressure outside the cyclone 12. Thus, there is airflow through the aperture 28 that brings the blocking member 102 into contact with the aperture 28 such that the blocking member 102 occludes the aperture 28. The pressure differential between the volume 14 and the external environment outside of the cyclone 12 acts to fix and secure the blocking member 102 in a position where it occludes the aperture 28 by virtue of a suction force.

In this embodiment, the blocking member 102 completely occludes the aperture to provide a substantially airtight seal. To occlude the aperture 28, the blocking member 102 moves substantially along the longitudinal axis of the cage 104.

As described previously, in use, particulate matter 30 separated from the air, or airflow, accumulates in the second portion 18 proximate the aperture 28. In this embodiment, the particulate matter 30 is prevented from egressing the aperture 28 via the blocking member 102. The cap member 20 inhibits the accumulated particulate matter 30 from moving inot the first portion and exiting the cyclone 12. Thus, the acculumated particulate matter 30 is collected in the second portion 18 ready to be expelled once the blocking member 102 is no longer occluding the aperture 28.

When airflow through the prefilter 100 ceases, or is sufficiently reduced, the pressure difference between the volume 14 and the exterior of the cyclone 12 decreases and equalises. The pressure holding the blocking member 102 in its occluding position weakens until gravity is the predominant force. When gravity is the predominant force, the blocking member 102 drops away from the aperture 28 such that the aperture 28 is no longer occluded and the aperture 28 is thus open.

When the aperture 28 opens, particulate matter 30 that has accumulated in the second portion 18 proximate the aperture 28 can egress from the cyclone 12 through the aperture 28. This egress is under the influence of gravity, assisted by the sloped nature of the internal surfaces of the frustoconical part 22. When the aperture 28 is no longer occluded by the blocking member 102, the particulate matter 30 can egress from the prefilter 100 without any further user interaction, providing self-cleaning functionality of this embodiment.

The aperture 28 may also be opened when there is airflow through the prefilter 100 and cyclone 12. In use, the accumulated particulate matter 30 can reduced the suction force acting on the blocking member 102. The combination of the reduction in suction force and the weight of the accumulated particulate matter 30 acting on the blocking member 102 can displace the blocking member 102 from its occluding position of the aperture 28. This displacement can occur despite there being a flow of air between the inlet 32 and outlet 34 of the prefilter 100. In other words, the prefilter 100 can eject and egress accumulated particulate matter 30 whilst still cleaning air passing through cyclone 12.

The displacement of the blocking member 102 results in the egress of the accumulated particulate matter 30 through the aperture 28. The removal of particulate matter 30 from the second portion 18 of the volume 14 results in an increased suction force acting on the blocking member 102 and less weight acting on the blocking member 102. As such, after the egress of the accumulated particulate matter 30, the blocking member 102 can then move back to occlude the aperture 28 as described previously

Figures 5a and Figures 5b depict computational fluid dynamics (CFD) simulations comparing the prefilter 100 in accordance with the present invention (Figure 3a) and a prior art prefilter 1 (Figure 3b). The prior art prefilter 1 has the same dimensions and features as the prefilter 100 in accordance with the present invention except that it does not comprise a cap member 20 such that its volume 14 is not divided into two portions. In this way, the first portion 16 of the prefilter 1 is the same size as its volume 14 as it does not comprise a second portion 18.

Specifically, the prefilter 1 comprises a cyclone 12, a volume 14, a frustoconical part 22, a shoulder part 24, a frustum 26, an aperture 28, an inlet 32, an outlet 34 and a wall 38, blocking member 102 and cage 104 substantially identical to those discussed for the prefilter 100. In the CFD calculations, the blocking member 102 is assumed to be closed the aperture 28 and the blocking member 102 and its cage 104 are omitted from Figures 5a and 5b for clarity.

The CFD simulations of Figure 5a and Figure 5b were performed by calculating a discrete phase model (DPM) by simulating the injection of five thousand sand particles within an airflow (i.e. particulate matter 30) into the prefilter 100 and the prior art prefilter 1. The sand particles of this simulation have a diameter of five micrometres. The positions of each of the sand particles 30 was then calculated at 0.2 seconds after injection and depicted at 1000 times their actual size for visualisation purposes. The positions of the sand particles (5 pm) at 0.2 seconds are summarised below in Table 1.

Table 1

The CFD simulations were also performed by calculating a discrete phase model (DPM) by simulating the injection five thousand sand particles within an airflow into the prefilter 100 and the prior art prefilter 1. The sand particles of this simulation have a diameter of one micrometre. The positions of each of the sand particles (1 pm) were then calculated at 0.2 seconds and summarised in Table 2.

Table 2

From the results of the CFD calculations summarised in Table 1 and Table 2, the prefilter 1 in accordance with the prior art expels a greater number of sand particles of either size through the outlet 34. Thus, the prior art prefilter 1 is less efficient at separating particulate matter 30 from airflow than the prefilter 100 in accordance with the present invention. The two prefilters 100, 1 are substantially identical except for the presence of the cap member 20. Thus, it can be concluded that the cap member 20 improves the separating efficiency of the prefilter 100.

Claims

1. A prefilter, said prefilter comprising: a cyclone defining a volume, said cyclone comprising an inlet and an outlet, said cyclone further comprising an aperture for the egress of particulate matter from the cyclone, and said prefilter further comprising a cap member that is located within said volume and that divides said volume into a first portion and a second portion, said second portion extending between said cap member and said aperture, wherein said inlet and said outlet are arranged to generate a vortex within said first portion of said volume when the air pressure at said outlet is lower than the air pressure at said inlet, wherein said cap member is arranged to partially occlude said first portion from said second portion and to form one or more openings that allow fluid communication between said first portion and said second portion.

2. The prefilter of claim 1 , wherein said one or more openings are located adjacent to a wall of said cyclone.

3. The prefilter of claim 2, wherein said one or more openings are located between an edge of the cap member and the wall of the cyclone.

4. The prefilter of claim 3, wherein the edge of the cap member and the wall of the cyclone are attached two or more locations, and wherein the spaces between said two or more locations are the said one or more openings.

5. The prefilter of anyone preceding claim, wherein the surface of said cap member facing towards said first portion is angled towards said one or more openings.

6. The prefilter of any one preceding claim, wherein the surface of said cap member facing towards said first portion is angled away from said aperture.

7. The prefilter of claim 6, wherein the surface of said cap member facing towards said first portion is angled towards said outlet.

8. The prefilter of claim 5, claim 6 of claim 7, wherein the surface of said cap member facing towards said first portion is a cone-shaped surface.

9. The prefilter of claim 8, wherein the apex of said cone-shaped surface is centrally aligned with said outlet.

10. The prefilter of any one preceding claim, wherein the surface of said cap member facing towards said second portion is angled towards said one or more openings.

11. The prefilter of any one preceding claim, wherein the surface of said cap member facing towards said second portion is angled away from said aperture.

12. The prefilter of claim any one preceding claim, wherein the surface of said cap member facing towards said second portion is angled towards said outlet.

13. The prefilter of claim 10, claim 11 or claim 12, wherein the surface of said cap member facing towards said aperture is a frustoconically-shaped surface.

14. The prefilter of claim 13, wherein the frustum of the frustoconically-shaped surface is centrally aligned with said outlet.

15. The prefilter of any one preceding claim, wherein the surface of said cap member facing towards said outlet and the surface of said cap member facing away from said outlet are arranged in a spaced relationship.

16. The prefilter of any one preceding claim, wherein first portion has a frustoconical shape.

17. The prefilter of claim any one preceding claim, wherein said second volume has frustoconical shape.

18. The prefilter of any one preceding claim, wherein said prefilter further comprises a blocking member arranged to move and concomitantly occlude said aperture when the air pressure at said outlet is lower than the air pressure at said aperture.

19. The prefilter of claim 18, wherein said blocking member is arranged to completely occlude said aperture when air pressure at said outlet is lower than the air pressure at said aperture.

20. The prefilter of claim 19, wherein the occlusion of said aperture by said blocking member when air pressure at said outlet is lower than the air pressure at said aperture is substantially airtight.

21. The prefilter of any of claims 18 to 20 , wherein said blocking member is located outside said volume of said cyclone.

22. The prefilter of claim 21 , wherein said blocking member is held proximate said aperture by a cage that surrounds said aperture.

23. The prefilter of claim 21 or claim 22, wherein said blocking member is arranged to move and concomitantly occlude said aperture when the air pressure at said outlet is lower than the air pressure at said aperture under the influence of air passing through said aperture.

24. The prefilter of any one of claims 17 to 23, wherein said blocking member is a ball.

25. An air intake system, said air intake system comprising the prefilter of any one of claims 1 to 24.