Dust separation unit

Abstract

A dust separation unit for a vacuum cleaner, the separation unit comprises a chamber 22 having an airflow inlet 38 through which an airflow enters the chamber and a core 24 located in the chamber. The

Description

Field of the Invention The present invention relates to a dust separation unit for a vacuum cleaner. Background Vacuum cleaners are devices that remove dirt, dust or other particulates from surfaces, such as floors. They can comprise a separation unit to separate dirt or dust from an airflow drawn through the vacuum cleaner. Summary of the Invention According to an aspect disclosed herein, there is provided a dust separation unit for a vacuum cleaner, the separation unit comprising: a chamber having an airflow inlet through which an airflow enters the chamber; and a core located in the chamber, the core comprising: a primary filter for filtering a first portion of the airflow; and an auxiliary filter for filtering a second portion of the airflow; wherein the separation unit further comprises: a primary valve for controlling the flow of air through the primary filter; and / or an auxiliary valve for controlling the flow of air through the auxiliary filter. By controlling the flow of air through the primary filter and / or the auxiliary filter, the dust separation efficiency of the vacuum cleaner can be improved. For example, by obstructing or blocking only the primary filter, such that airflow through the primary filter is blocked but airflow through the auxiliary filter is permitted, any dust and / or dirt that has accumulated in or around the primary filter can be pulled away from the primary filter. In particular by preventing the airflow through the primary filter, the force holding the dust or dirt to the primary filter is removed. The dust and / or dirt can then be entrained in and carried by the airflow towards the auxiliary filter, and away from the primary filter. Thus, the primary filter can be unblocked and the separation efficiency of the vacuum cleaner improved. By obstructing or blocking the auxiliary filter, the separation efficiency of the vacuum cleaner at different flow rates can be improved. As used herein, filtering a portion of an airflow may be understood as filtering dust, fluff, fibres and / or dirt from the portion of the airflow. Optional features will now be set out. Controlling the flow of air may include increasing and / or decreasing the flow of air through the primary filter and / or the auxiliary filter, for example. Controlling the flow of air may include decreasing the flow of air by at least partially blocking / obstructing the flow of air through the primary filter and / or auxiliary filter. The primary and / or auxiliary valve may each comprise an active valve. The primary and / or auxiliary valve may each comprise a passive valve. Active valves may control (e.g., open or close) the flow of air in response to an external input. Passive valves may control (e.g., open or close) the flow of air in response to changes in the airflow rate itself, e.g., without an external input. The separation unit may comprise a primary outlet passage and an auxiliary outlet passage. In use, the first portion of the airflow may flow from the airflow inlet through the primary filter and along the primary outlet passage. The second portion of the airflow may flow from the airflow inlet through the auxiliary filter and along the auxiliary outlet passage. The primary filter may be at an upstream end of the primary outlet passage. The auxiliary filter may be at an upstream end of the auxiliary outlet passage. The core may comprise a single auxiliary filter. In other examples, the core may comprise a plurality of (i.e. two or more) auxiliary filters. Where there is a plurality of auxiliary filters, the separation unit may comprise a plurality of auxiliary valves e.g. with each auxiliary valve associated with a respective one of the auxiliary filters. Where there is a plurality of auxiliary filters, the separation unit may comprise a plurality of auxiliary outlet passages e.g. with each auxiliary valve / filter associated with a respective one of the auxiliary outlet passages. For example, the core may comprise a first auxiliary filter and a second auxiliary filter, a first auxiliary valve configured to control the flow of air through the first auxiliary filter along the first auxiliary passage, and a second auxiliary valve configured to control the flow of air through the second auxiliary filter along the second auxiliary passage. In examples with more than one auxiliary filter, the additional auxiliary filters may be as described herein with respect to a single auxiliary filter. The core may extend along a longitudinal axis and have a substantially U-shaped transverse crosssection. The core may comprise an outer profile comprising a concave portion and a convex portion. The concave portion may form a front outwardly-facing surface of the core and the convex portion may form the opposing back outwardly-facing surface of the core. The concave portion may define an arcuate surface which is concave in the transverse direction (perpendicular to the longitudinal axis of the core). The convex portion may define an arcuate surface which is convex in the transverse direction (perpendicular to the longitudinal axis of the core). The concave portion may comprise the primary filter. The convex portion may comprise the auxiliary filter(s) e.g. the first and second auxiliary filters. The first and second auxiliary filters may be circumferentially-spaced around the arcuate surface of the convex portion. The primary filter may comprise a porous shroud, which may be positioned at the concave portion of the core. The primary filter may comprise a perforated region or mesh having a plurality of holes. The holes of the mesh of the primary filter may have a hole size (i.e., diameter or equivalent diameter) of between 0.1 mm and 0.5 mm. The mesh of the primary filter may have an open area of between 15% and 35%, The auxiliary filter(s) may (each) comprise a porous shroud, which may be positioned at the convex portion of the core. The / each auxiliary filter may comprise a perforated region or mesh having a plurality of holes. The holes of the mesh of the / each auxiliary filter may have a hole size of between 0.1 mm and 0.5 mm. The mesh of the / each auxiliary filter may have an open area of between 20% and 40%. The auxiliary filter(s) may have a (combined) total open area that is less than the total open area of the primary filter. The primary filter and / or the auxiliary filter(s) may be formed of metal. The dust separation efficiency of the vacuum cleaner is particularly improved when the core of the separation unit has such a U-shaped cross-section, with the primary filter comprised in the concave portion, and the auxiliary filter(s) comprised in the convex portion. In use, this shape may result in air flowing from the air-flow inlet, along an air flow channel defined by the outwardly facing surface of the concave portion and in a direction parallel to the longitudinal axis of the core. The air may therefore flow over the primary filter. The first portion of the airflow may flow through the primary filter, to be filtered by the primary filter. The second portion of the airflow may flow over the primary filter and then over and around the convex portion to the auxiliary filter(s) in the convex portion. The primary filter may extend over a primary opening in the concave portion. The / each auxiliary filter may extend over a respective auxiliary opening in the convex portion. The core may be hollow. The core may comprise internal walls that partition the interior of the core. The core may comprise the primary outlet passage, and / or the auxiliary outlet passage(s). In particular, the internal walls may define the primary outlet passage, and / or the auxiliary outlet passage(s). A downstream end of the / each auxiliary outlet passage may be in fluid communication with the primary outlet passage, and in particular, a part of the primary outlet passage downstream of the primary filter. The core may have a substantially U-shaped transverse cross-section along its length (in a direction parallel to the longitudinal axis). It may have a substantially uniform cross-section along its length. The concave portion, and in particular the outwardly facing surface of the concave portion, may define an airflow channel that extends from the airflow inlet, in a direction parallel to the longitudinal axis of the core. In examples where the separation unit comprises one or more auxiliary valves, the auxiliary valve(s) may be adapted to reduce the flow of air through the auxiliary filter(s) as the airflow rate through the separation unit increases. It has been found that the separation efficiency of the separation unit changes with flow rate depending on whether or not air can flow through the auxiliary filter(s). In particular, when air is allowed to flow through the auxiliary filter(s) (e.g., when the auxiliary valve(s) is / are open), the separation efficiency of the separation unit decreases as flow rate increases. When air is (substantially) prevented from flowing through the auxiliary filter(s) (e.g., when the auxiliary valve(s) is / are (substantially) closed), the separation efficiency of the separation unit increases as the flow rate increases. Therefore, by reducing the flow of air through the auxiliary filter(s) as the airflow rate increases (e.g., by substantially closing the auxiliary valve(s)), and by increasing the flow of air through the auxiliary filter(s) as the airflow rate decreases (e.g., by opening the auxiliary valve(s)), a higher separation efficiency of the separation unit can be maintained regardless of the flow rate through the separation unit. The / each auxiliary valve may be positioned in the (respective) auxiliary outlet passage. In these examples, the auxiliary valve(s) may be positioned downstream of the auxiliary filter (s). In examples having two auxiliary outlet passages, the first valve may be positioned in the first auxiliary outlet passage to selectively control (e.g., restrict, block or obstruct) the flow of air through the first auxiliary filter upstream of the first valve and the second valve may be positioned in the second auxiliary outlet passage to selectively control (e.g., restrict, block or obstruct) the flow of air through the second auxiliary filter upstream of the second valve . In other examples, the auxiliary valve(s) may be positioned upstream of the auxiliary filter(s). The auxiliary valve (e.g. the first and / or second auxiliary valve) may comprise a passive valve biased into a substantially open position in the absence of airflow through the separation unit. The passive valve(s) may be arranged to progressively close as the airflow rate through the separation unit increases. The / each passive valve may comprise a resilient deformable valve. It / they may comprise a spring-loaded valve, or a flap valve, for example. The passive valve may comprise rubber, and / or another suitable resiliently deformable material. The auxiliary valve (e.g. the first and / or second auxiliary valve) may comprise an active valve configured to control the flow of air through the auxiliary filter in response to an external input. The external input may be a control input from a controller of the vacuum cleaner. The active valve(s) may be configured to control the flow of air through the auxiliary filter(s) in response to one or more sensor readings, e.g., in response to a detected dust particle size and / or dust particle quantity, for example. The detected dust particle size may be an average dust particle size detected, for example, by a piezoelectric acoustic sensor. Accordingly, the separation unit may comprise a dirt detection assembly configured to sense a number and / or a size of particulate matter entrained within the airflow. The dirt detection assembly may comprise a piezoelectric acoustic sensor configured to sense a number and / or a size of particulate matter entrained within the airflow and colliding with the piezoelectric acoustic sensor. In examples with (at least) two auxiliary filters, the separation unit may comprise a first active auxiliary valve for selectively restricting the flow of air through the first auxiliary filter, and a second active auxiliary valve for selectively restricting the flow of air through the second auxiliary filter. The first active auxiliary valve and the second active auxiliary valve may be independently controllable. In this way, blocking of the first and second auxiliary filters may be asymmetrical. In other examples, the first and second active auxiliary valves may be controlled together, such that blocking of the first and second auxiliary filters is symmetrical. In examples where the dust separation unit comprises a primary valve, the primary valve may be adapted to selectively prevent the flow of air through the primary filter. During use of the vacuum cleaner, and particularly at lower flow rates, lightweight fluff and dust can block the primary filter, e.g., by accumulating in the concave portion of the core. By temporarily blocking the flow of air through the primary filter, all of the air travels through the auxiliary filter(s), which in turn pulls the accumulated fluff and dust away from the primary filter. Thus, the primary filter can be cleared, enabling continuation of the dust loading and improving the separation efficiency of the separation unit. The primary valve may be configured to prevent the flow of air through the primary filter for a predefined period of time (e.g., in the range of 0.1-10 seconds, more preferably in the range of 0.5-8 seconds, more preferably in the range of 0.5-4 seconds, more preferably in the range 0.5-2 seconds). The flow of air may be prevented for a predefined time period of less than or equal to 4 seconds, more preferably less than or equal to 3 seconds, more preferably less than or equal to 2 seconds. The primary valve may comprise an active primary valve configured to prevent the flow of air through the primary filter in response to an external input. The external input may be an input from outside of (e.g., external to) the separation unit. The active primary valve may be adapted to selectively prevent the flow of air through the primary filter in response to a user input. The user input may be manual user input via a button or switch on the vacuum cleaner. In this way, the user can choose when to remove accumulated dust and dirt from the primary filter. This may be particularly useful in examples where the chamber is transparent or translucent, such that the user can see the primary filter, and thus can see when dust and dirt has accumulated at the primary filter. The primary valve may be adapted to selectively prevent the flow of air through the primary filter in response to a detection that a pressure difference between a point upstream of the primary filter and a point downstream of the primary filter meets one or more predefined criteria. The one or more predefined criteria may be a predefined threshold. For example, the primary valve may be configured to prevent the flow of air through the primary filter in response to the pressure difference (or a rate of change of pressure difference) exceeding a predefined threshold. The pressure difference may be indicative of dust and / or dirt accumulating on the primary filter and thus at least partially blocking the primary filter. The primary valve may be positioned in the primary outlet passage. In these examples, the primary valve may be positioned downstream of the primary filter. In other examples, the primary valve may be positioned upstream of the primary filter. The separation unit may comprise both a primary valve and one or more auxiliary valve(s), wherein the primary valve is configured to control the flow of air through the primary filter and the auxiliary valve(s) is / are configured to control the flow of air through the auxiliary filter(s). The separation unit may be a non-cyclonic separation system. According to a second aspect, there is provided a vacuum cleaner comprising the dust separation unit of the first aspect. The vacuum cleaner may further comprise a main unit, a wand and a cleaner head. The wand and the cleaner head may be removable from the main unit. The main unit may comprise the dust separation unit. The main unit may additionally comprise a suction motor for generating the airflow through the dust separation unit. The main unit may further comprise a battery assembly, one or more additional dust separation units, and / or a controller. The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided. Summary of the Figures Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which: Figure 1 is a perspective view of a vacuum cleaner; Figure 2 is a perspective view of a main unit of a vacuum cleaner; Figure 3a is a perspective sectional view of a dust separation unit for a vacuum cleaner; Figure 3b is a front perspective view of a dust separation unit for a vacuum cleaner; Figure 3c is a top-down sectional view of a dust separation unit for a vacuum cleaner; Figure 4 is a sectional slice through a dust separation unit for a vacuum cleaner; Figure 5 is a bottom plan view of a core of a dust separation unit; Figure 6 is a graph showing the separation efficiency of a dust separation unit at different flow rates of air through the dust separation unit; Figure 7a is a schematic sectional slice through a dust separation unit for a vacuum cleaner; Figure 7b is a schematic sectional slice through Section A-A of the dust separation unit of Figure 7a; Figure 7c is a schematic sectional slice through Section B-B of the dust separation unit of Figure 7a; Figure 8a is a schematic sectional slice through a dust separation unit for a vacuum cleaner showing air flow during normal vacuuming during which airflow is allowed through both a primary filter and an auxiliary filter; and Figure 8b is a schematic sectional slice through the dust separation unit of Figure 9a showing airflow through the dust separation unit when air flow is prevented through the primary filter. Detailed Description of the Invention Aspects and embodiments will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference. A vacuum cleaner is illustrated in Figure 1. The vacuum cleaner 1 comprises a main unit 10, a wand 1000 and a cleaner head 1100. The vacuum cleaner 1 may be referred to as a stick vacuum cleaner. In use, the main unit 10 provides a suction force, which entrains dust and dirt in an airflow which is sucked from the cleaner head 1100, through the wand 1000 to the main unit 10. The wand 1000 and the cleaner head 1100 are removable from the main unit 10, which can then be used as a standalone handheld vacuum cleaner, as shown in Figure 2. The main unit 10 is illustrated in Figure 2. The main unit 10 comprises a dust separation unit 20 for separating dust and dirt from airflow through the dust separation unit 20. The main unit 10 may also comprise additional dust separation units or filter units 400, a suction motor 600 for generating the airflow through the dust separation unit, a battery assembly 800 and / or a controller, e.g., a PCB assembly (not shown in Figure 2). A dust separation unit 20 is shown in Figures 3a-3c. The dust separation unit 20 comprises a chamber 22, and a core 24 positioned within the chamber 22. As best shown in Figure 3b, the core extends along a longitudinal axis and has a substantially U-shaped transverse cross-section. The transverse cross-sectional shape of the core is substantially uniform along its length. The outer profile of the core 24 comprises a concave portion 26 and a convex portion 28. The outwardly-facing surface of the concave portion 26 defines a trough or airflow channel 30 that extends along the length of the core 24 parallel to the longitudinal axis of the core. The core 24 may be thought of as comprising a first arm 32 and a second arm 34, each of which is arcuate and forms one half of the U-shaped core 24. The core 24 extends from a first end 36 of the chamber 22 to an opposing second end 38 of the chamber 22 along a longitudinal axis parallel to the longitudinal axis of the core 24. The chamber 22 may be cylindrical and may completely surround the core 24. The airflow channel 30 defined by the concave portion 26 of the core 24 may extend in a direct parallel to the longitudinal axis of the cylindrical chamber 22. The chamber 22 comprises an airflow inlet 38, which may be defined by a nozzle 58 at the first end 36 of the chamber 22. The chamber 22 also comprises an airflow outlet 44, which may be defined in the second end 38 of the chamber 22. In use, dust and / or dirt separation from the airflow by the dust separation unit 20 may collect in the chamber. The chamber 22, and in particular the curved lateral outer wall of the cylindrical chamber, may be transparent or translucent so that a user can see when the chamber 22 is full of dust and / or dirt. Optionally, one end of the chamber 22, for example the first end 36) can be opened (e.g., by a hinged connection 60), so that the chamber 22 can be emptied when it is full of dust / dirt. The core comprises a primary filter 46 and two auxiliary filters 48a, 48b for filtering the airflow through the dust separation unit 20. The primary filter 46 is for filtering a first portion of the airflow, and the two auxiliary filters 48a, 48b are for filtering a second portion of the airflow. Although in the examples shown in Figures 3a-3c, the core comprises two auxiliary filters 48a, 48b, in other examples, there may be one single auxiliary filter, or more than two, e.g., three, four, etc... auxiliary filters. The primary filter 46 is attached to the concave portion 26 of the dust separation unit 10, and in particular to overlie an opening defined through the concave portion 26. The two auxiliary filters 48a, 48b are attached to the convex portion 28 of the dust separation unit 20, and in particular to overlie a respective opening in the convex portion 28. As best shown in Figures 3b and 4a, the core 24 is hollow. The core 24 comprises internal walls that partition an interior of the core 24 (see e.g., Figure 7). The interior walls define a primary outlet passage 40 and two auxiliary outlet passages 42a, 42b. The primary outlet passage 40 and the auxiliary outlet passages 42a, 42b extend to the second end 38 of the chamber, and in particular to one or more airflow outlets therein. The primary outlet passage 40 is in fluid communication with the primary filter 46, at an upstream end of the primary outlet passage 40. Each auxiliary outlet passage 42a, 42b is in fluid communication with a respective one of the auxiliary filters 48a, 48b. Accordingly, in use, a first portion of the airflow is filtered by the primary filter 46 and then flows through the primary outlet passage 40, and a second portion of the airflow is filtered by the two auxiliary filters 48a, 48b and then flows through the two auxiliary outlet passages 42a, 42b. Each auxiliary filters may have its own respective auxiliary outlet passage. A downstream end of the auxiliary outlet passages 42a, 42b may be in fluid communication with the primary outlet passage (e.g., via ducts into the primary outlet passage). In these examples, there may be a single airflow outlet 44 in the second end 38 of the chamber, and air from the auxiliary outlet passages 42a, 42b may flow into the primary outlet passage 40 via respective ducts, and exit the chamber 22 through the single airflow outlet 44. In some examples, the auxiliary outlet passages may join into a single auxiliary outlet passage before joining the primary outlet passage 40. Operation of the dust separation unit 20 will now be described. Airflow enters the chamber 22 through the nozzle 58 at the first end 36 of the chamber 22. The airflow is directed towards the core 24, and in particular, along the airflow channel 30 defined by the outwardly-facing surface of the concave portion 26 of the core 24. The primary filter 46 is positioned on the concave portion 26 of the core, and a first portion of the airflow (which may be a majority of the airflow) sinks through the primary filter 46 into the primary outlet passage 40 in the interior of the core 24 (as best shown in Figure 3a). Dust and dirt filtered from the first portion of the airflow by the primary filter 46 is collected in the chamber 22. In particular, a recirculating second portion of the airflow (which is the remainder of the airflow that has not passed through the primary filter 46) is directed by the shape of the core 24 over the first and second arms 32, 34 of the core 24, and over the convex portion 28 of the core. The dust and dirt can then collect in the container 22, behind the convex portion 28 of the core 24. The second portion of the airflow then passes through the two auxiliary filters 48a, 48b positioned on the convex portion 28 of the core 24, and into the two auxiliary outlet passages 42a, 42b in the interior of the core 24. The two auxiliary filters 48a, 48b filter dust and dirt from the second portion of the airflow. The first and second portions of the airflow filtered by the primary filter 46 and two auxiliary filters 48a, 48b travel through the outlet passages and out of the dust separation unit 20 through the airflow outlet 44. Providing auxiliary filters in the core 24 reduces the component of flow travelling through the concave portion 26 to the interior of the core 24, whilst the flow across the concave portion 26 of the core 24 is maintained (as the velocity of the airflow entering the chamber 22 is unchanged). This may result in a reduced amount of dirt or dust collecting in and blocking (also known as “blinding”) the primary filter 46, and improved separation efficiency of the dust separation unit 20. Additionally, the recirculating flow helps to collect the separated dust and dirt towards the base of the chamber 22, towards the first end 36 of the chamber 22. This may improve the loading of the chamber 22 with dust and dirt, so that the dust and dirt is compactly collected, and more dust and dirt can be collected before the chamber 22 needs to be emptied. The dust separation unit 20 comprises a primary valve for controlling the flow of air through the primary filter 46 and / or auxiliary valves for controlling the flow of air through the auxiliary filters 48a, 48b. In particular, the valves are arranged to restrict or allow (e.g., reduce or increase) the flow of air through the filters. The one or more valves may be controlled (e.g., by a controller of the vacuum cleaner) to open (and thus increase the amount of air flowing through a respective filter) and close (and thus reduce the amount of air flowing through a respective filter). The valves may be controlled to transition between a fully closed position (e.g., blocking 100% of airflow), to one or more partially closed positions (e.g., reducing the airflow but not blocking it completely), and / or to a completely open position (e.g., not preventing the flow of air at all). Each filter may have a corresponding valve for controlling the flow of air through that valve. For example, the primary filter 46 may have a corresponding valve for controlling the flow of air through the primary filter 46 and each auxiliary filter 48a, 48b may have a corresponding valve for controlling the flow of air through the auxiliary filters 48a, 48b. Alternatively, only the primary filter 46 may have a corresponding valve for controlling the flow of air through the primary filter, or only the auxiliary filters 48a, 48b may have corresponding valves for controlling the flow of air through the auxiliary filters. The valves may include active valves and / or passive valves, as described in further detail below. A dust separation unit 20 with two auxiliary valves 50a, 50b for controlling the flow of air through two auxiliary filters 48a, 48b is shown in Figure 4. The two auxiliary valves 50a, 50b are configured to reduce the flow of air through the two auxiliary filters 48a, 48b as the airflow rate through the dust separation unit 20 increases. As shown in graph 90 shown in Figure 6, it has been found that the separation efficiency of the dust separation unit changes with flow rate depending on whether the auxiliary filters (and in particular, the auxiliary valves) are open or closed. Graph 90 shows target behaviour of China clay separation efficiency across flow rates for a dust separation unit, such as dust separation unit 20 shown in Figures 3a-3c. When the two auxiliary valves 50a, 50b are in an open state, such that air can flow through the auxiliary filters, the separation efficiency of the separation unit decreases as the flow rate increases (see e.g., line labelled “Auxiliary valve open” in graph 90 of Figure 6). The lower separation efficiency at higher flow rates, when the auxiliary valves are in an open state, may be due to excess emissions of fine dust via the auxiliary filters or high flow speed in the container 22 that prevents dust and / or dirt accumulating on the auxiliary filters. In contrast, when the two auxiliary valves 50a, 50b are in a (at least partially) closed state, such that air is (at least partially) prevented from flowing through the auxiliary filters, the separation efficiency of the dust separation unit increases as the flow rate increases (see e.g., line labelled “Auxiliary valve closed” in graph 90 of Figure 6). The lower separation efficiency at low flow rates, when the auxiliary valves are in a closed state, may be because the dust and dirt is collected less compactly in the chamber 22, and / or because the dust covers or blocks the primary filter. Therefore, by reducing the flow through the auxiliary filters (by at least partially blocking the auxiliary filters) as the airflow rate increases (e.g., by substantially closing the auxiliary valves), and by increasing the flow of air through the auxiliary filters as the airflow rate decreases (e.g., by opening the auxiliary valves), a higher separation efficiency of the separation unit can be maintained regardless of flow rate. This is illustrated in graph 90 by the line labelled “Dynamically controlled auxiliary valve opening”. Accordingly, at higher flow rates (e.g., when the vacuum cleaner is in a high-power mode and / or when the flow rate is greater than a predefined threshold), the auxiliary valves are arranged to transition into a closed state. The auxiliary valve closed state is illustrated in the left-hand side 70a of the schematic of core 24 shown in Figure 4, where auxiliary valve 50a is substantially closed such that there is less flow through auxiliary filter 48a. At lower flow rates (e.g., when the vacuum cleaner is in a normal mode, or eco mode, and / or when the flow rate is less than a predefined threshold), the auxiliary valves are arranged to shift into an open state. This is illustrated in the right-hand side 70b of the schematic of the core 24 shown in Figure 4, where auxiliary valve 50b is open such that there is increased flow through auxiliary filter 48b. A high airflow rate (e.g., an airflow rate in a high-power mode of the vacuum cleaner) may be greater than or equal to 101 / s, for example. A low airflow rate (e.g., an airflow rate in a low-power mode, normal mode, or eco mode of the vacuum cleaner) may be less than 101 / s, for example. The auxiliary filters may be arranged to be in the open state when the airflow rate is less than a predefined threshold (which may be e.g., approximately 101 / s), and in the closed state when the airflow rate is more than the predefined threshold (e.g., of approximately 101 / s). The shift between states may be immediate (e.g., a step-like shift between open and closed), or gradual (e.g., gradually closing the auxiliary valves, for example). As described herein, a closed state may mean a substantially closed state, e.g., the valve is at least 60% closed, 70% closed, 75% closed, 80% closed, 85% closed, 90% closed, 95% closed etc. For example, auxiliary valve 50b shown in Figure 5 may be considered to be in a closed state, even though it is only 75% closed (25% open). This is an example position of an auxiliary valve at higher flow rates. An open state may mean a substantially open state, e.g., the valve at least 60% open, 70% open, 75% open, 80% open, 85% open, 90% open, 95% open etc. For example, auxiliary valve 50a shown in Figure 5 may be considered to be in an open state, as it is 95% open. This is an example position of an auxiliary valve in an open state. The auxiliary valves 50a, 50b are positioned in the auxiliary outlet passages 42a, 42b, inside the core 24 (see e.g., Figure 4). Accordingly, the first auxiliary valve 50a for controlling the flow of air through the first auxiliary filter 48a, is positioned in the first auxiliary outlet passage 42a, downstream of the first auxiliary filter 48a. The second auxiliary valve 50b for controlling the flow of air through the second auxiliary filter 48b is positioned in the second auxiliary outlet passage 42b, downstream of the second auxiliary filter 48b. In other examples, the auxiliary valves 50a, 50b may be positioned upstream of the auxiliary filters 48a, 48b. In examples where the auxiliary outlet passages 42a, 42b join the primary outlet passage 40, the valves 50a, 50b are upstream of the join to the primary outlet passage 40. The auxiliary valves 50a, 50b, may be active valves (e.g., which open and close in response to an external input) or passive valves (e.g., which open and close without external input / without external power). If the auxiliary valves are passive valves, they may be biased into a substantially open position in the absence of airflowthrough the separation unit (and / or at low flow rates). They may progressively close as the airflow rate through the separation unit increases, in response to the increase in airflow. Alternatively, they may be arranged to suddenly close when the airflow rate passes a predefined threshold. These types of valves do not require any external input, power supply, or active control from the controller of the vacuum cleaner. Example passive valves may include resiliently deforming valves, e.g., spring-loaded valves, flap valves or bistable live hinge mechanisms, for example. If the auxiliary valves are active valves, they may be configured to control the flow of air through the auxiliary filters in response to an external input. For example, the auxiliary valves may be configured to control the flow of air through the auxiliary filters based on a flow rate detected by the controller of the vacuum cleaner 1 and / or a pressure difference between a point upstream of one or more of the auxiliary filters (e.g., at the dirt detection assembly in the chamber 22, or near the nozzle 58) and a point downstream of one or more of the auxiliary filter (e.g., in the auxiliary outlet passage). The external input may be a control input from the controller of the vacuum cleaner 1. The active valves may be configured to control the flow of air through the auxiliary filters 48a, 48b in response to one or more sensor readings. The sensor readings may be indicative of a rate of airflow, a detected dust particle size and / or dust particle quantity, for example. The detected dust particle size may be an average dust particle size detected by a piezoelectric acoustic sensor. Accordingly, the separation unit 20 may comprise a dirt detection assembly configured to sense a number and / or a size of particulate matter entrained within the airflow. The dirt detection assembly may comprise a piezoelectric acoustic sensor configured to sense a number and / or a size of particulate matter entrained within the airflow and colliding with the piezoelectric acoustic sensor. The dirt detection assembly may be positioned on the concave portion 26 of the core 24, adjacent to the primary filter 46. It may be positioned upstream of the primary filter 46, between the primary filter 46 and the airflow inlet 38. It may comprise an impact area, which forms part of the surface of the concave portion 26 of the core 24. In use, the airflow entrained with dust and dirt entering the dust separation unit 20 may be directed towards the impact area of the dirt detection assembly, and as the airflow hits the impact area, the piezoelectric acoustic sensor may be arranged to sense a number and / or or a size of the particulate matter entrained within the airflow. The active valves may be controlled to be in an open state at lower flow rates (e.g., below 10l / s), higher dust particle sizes and / or lower dust particle quantities. Then active valves may be controlled to be in a closed state at higher flow rates (e.g., above 10l / s), lower dust particle sizes, and / or higher dust particle quantities (particularly when there are higher quantities of fine particles with lower dust particle sizes) . This dynamic switching between opening and closing the active valves may be particularly useful when the dust / dirt is detected as comprising fine particulate matter without any fibres, hair and / or other types of fluff. As such, if it is detected that there is a higher flow rate with larger particles, then the active valves may be controlled to be in an open state. The active valves may be controlled to be in an open state at lower flow rates regardless of dust composition, quantity and / or particle size. The first auxiliary valve 50a and the second auxiliary valve may be independently controllable, e.g., so that one auxiliary valve is in an open state, and the other is in a closed state at the same time. Alternatively, they may be controllable together so that both auxiliary valves 50a, 50b are always in the same state at the same time. The dust separation unit 20 may alternatively / additionally comprise a primary valve 52 for selectively controlling the flow of air through the primary filter 46. This can be useful for a number of reasons. In particular, during use of the dust separation unit 20, lightweight fluff, hair and dust may load in the concave portion of the core 24 so that this area gets clogged / blogged, and leaving space in the container 22, for example behind the concave portion of the core 24 unused. This is particularly problematic at lower flow rates. By temporarily closing the primary valve 52 such that airflow is prevented from flowing through the primary filter 46, all of the airflow is diverted through the auxiliary filters 48a, 48b. This pulls the fluff, dirt and dust accumulated in the concave portion of the core 24 out and towards the concave portion, to compactly load the container 22. The primary valve 52 may be configured to prevent the flow of air for a predefined period of time, which is preferable in the range of 0.1-10 seconds, more preferably 0.5-2 seconds. The primary valve 52 may be an active valve configured to selectively prevent the flow of air through the primary filter 46 in response to a user input. For example, a user may press a button on the vacuum cleaner (e.g., on the main unit 10 of the vacuum cleaner), to temporarily close the primary valve 52 and prevent the flow of air therethrough. Alternatively / additionally, the primary valve 52 may close in response to a detection that a pressure difference between a point upstream of the primary filter (e.g., at the dirt detection assembly in the chamber 22, or near the nozzle 58) and a point downstream of the primary filter (e.g., in the primary outlet passage 40) meets or exceeds a predefined threshold. This pressure difference may indicate that dust, dirt and / or fluff has accumulated in the concave portion and / or blocked the primary filter 46. As shown in Figure 7a, the primary valve 52 may be positioned in the primary outlet passage 40, downstream of the primary filter 46. Figures 7a-7c show the relative positioning of the primary outlet passage 40, an auxiliary outlet passage 42a, a primary filter 46 and an auxiliary filter 48a. In this example, only one auxiliary outlet passage 42a and one auxiliary filter 48a is shown. At least one internal wall 62 in the interior of the core 24 divides the interior of the core into the primary outlet passage 40 and the auxiliary outlet passage 42a, which then join to a single outlet 44 at a downstream end thereof. The primary valve 52 is positioned at the downstream end of the primary outlet passage 40 to selectively prevent airflow through the primary outlet passage 40. Figures 7b and 7c show section views across planes A-A and B-B shown in Figure 7a, respectively. When the primary valve 52 is in an open (or at least partially open) position, as shown in Figure 8a, air may flow through both the primary filter 46 and the auxiliary filter 48a. The portion of the airflow flowing through the primary filter 46 may be larger than the portion of airflow flowing through the auxiliary filter 48a. This may be considered a normal use of the vacuum cleaner. However, when it is determined that the primary filter 46 should be cleaned such that fluff and dirt is removed from the primary filter, the primary valve 52 may transition into a closed position, such as that shown in Figure 8b. In the closed position, air can only flow through the auxiliary filter 48a, and air is prevented from flowing through the primary filter 48a. This may pull the fluff and dirt away from the primary filter and may more efficiently load the fluff and dirt in container 22. As described above, the primary valve 52 may open and close automatically, e.g., based on the detection of a pressure difference between the container 22 and the primary outlet passage 40, or manually, e.g., using a button on the vacuum cleaner activated by the user when desired. Although not shown in Figures 8a and 8b, the dust separation unit may have both a primary valve 52 and one or more auxiliary valves 50a, which may be independently controllable. The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention. For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations. Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / -10%.

Claims

1. A dust separation unit for a vacuum cleaner, the separation unit comprising:a chamber having an airflow inlet through which an airflow enters the chamber; anda core located in the chamber, the core comprising:a primary filter for filtering a first portion of the airflow; and an auxiliary filter for filtering a second portion of the airflow;wherein the separation unit further comprises:a primary valve for controlling the flow of air through the primary filter; and / or an auxiliary valve for controlling the flow of air through the auxiliary filter.

2. The separation unit of claim 1, wherein the core comprises a first auxiliary filter and a second auxiliary filter, a first auxiliary valve for controlling the flow of air through the first auxiliary filter, and a second auxiliary valve for controlling the flow of air through the second auxiliary filter..

3. The separation unit of claim 1 or claim 2, wherein the core extends along a longitudinal axis, and has a substantially U-shaped transverse cross-section and an outer profile comprising a concave portion and a convex portion, wherein:the concave portion comprises the primary filter; and / or the convex portion comprises the auxiliary filter.

4. The separation unit of any preceding claim, wherein the separation unit comprises an auxiliary valve and the auxiliary valve is adapted to reduce the flow of air through the auxiliary filter as the airflow rate through the separation unit increases.

5. The separation unit of claim 4, further comprising an auxiliary outlet passage, and wherein, in use, the second portion of the airflow flows through the auxiliary filter and along the auxiliary outlet passage, and wherein the auxiliary valve is positioned in the auxiliary outlet passage.

6. The separation unit of claim 4 or claim 5, wherein the auxiliary valve comprises a passive valve biased into a substantially open position in the absence of airflow through the separation unit, and arranged to progressively close as the airflow rate through the separation unit increases.

7. The separation unit of claim 6, wherein the passive valve comprises a spring-loaded valve or a flap valve.

8. The separation unit of any of claims 4 to 7, wherein the auxiliary valve comprises an active valve configured to control the flow of air through the auxiliary filter in response to an external input.

9. The separation unit of claim 8, wherein the separation unit comprises a first auxiliary filter, a second auxiliary filter, a first active valve for selectively restricting the flow of air through the first auxiliary filter, and a second active valve for selectively restricting the flow of air through the second auxiliary filter, wherein the first active valve and second active valve are independently controllable.

10. The separation unit of any preceding claim, wherein the separation unit comprises a primary valve adapted to selectively prevent the flow of air through the primary filter.

11. The separation unit of claim 10, wherein the primary valve is configured to prevent the flow of air through the primary filter for a predefined period of time.

12. The separation unit of claim 10 or claim 11, wherein the primary valve comprises an active valve configured to prevent the flow of air through the primary filter in response to an external input.

13. The separation unit of any of claims 10-12, wherein the primary valve is adapted to selectively prevent the flow of air through the primary filter in response to a user input.

14. The separation unit of any of claims 10-13, wherein the primary valve is adapted to selectively prevent the flow of air through the primary filter in response to a detection that a pressure difference between a point upstream of the primary filter and a point downstream of the primary filter meets one or more predefined criteria.

15. The separation unit of any of claims 10-14, further comprising a primary outlet passage, and wherein, in use, the first portion of the airflow flows through the primary filter and along the primary outlet passage, and wherein the primary valve is positioned in the primary outlet passage.17

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