Cleaner head for a vacuum cleaner

Abstract

A cleaner head for a vacuum cleaner including an agitator in the form of a brush bar, the brush bar including a plurality of radially extending bristles and a sealing material disposed between the bristles. The sealing material extends over substantially the entire circumferential and axial extent of the regions of the brush bar between the bristles. The cleaner head further includes a housing defining a chamber which at least partially surrounds the brush bar, a dirty air inlet in a lower part of the chamber and a front opening that exposes the brush bar at the front of the housing. The brush bar is supported for rotation with respect to the housing and arranged in the chamber such that the brush bar seals against the housing thereby restricting flow of air through the front opening.

Claims

1 . A cleaner head for a vacuum cleaner, comprising: an agitator in the form of a brush bar, the brush bar comprising a sealing material extending over the circumferential and axial extent of the brush bar, the sealing material comprising a tufted material; a housing defining a chamber which at least partially surrounds the brush bar, a dirty air inlet in a lower part of the chamber and a front opening that exposes the brush bar at the front of the housing, and the brush bar being supported for rotation with respect to the housing and arranged in the chamber, wherein the front opening is defined by an upper front edge of the housing, when the brush bar is driven in a forward direction a boundary-layer effect in the vicinity of the sealing material causes rotational flow within the chamber in the direction of rotation of the brush bar, and the rotational flow dynamically seals a gap between the brush bar and the upper front edge. 2 . The cleaner head of claim 1 , wherein the upper front edge is above the rotational axis of the brush bar. 3 . The cleaner head of claim 1 , wherein the upper front edge is below the top of the brush bar. 4 . The cleaner head of claim 1 , wherein a top portion of the housing extends forwardly over a top of the brush bar to form a guard that prevents debris from being flung upwardly by the brush bar away from the housing. 5 . The cleaner head of claim 1 , wherein the tufted material is made from nylon filaments. 6 . A cleaner head for a vacuum cleaner, comprising: an agitator in the form of a brush bar, the brush bar comprising a sealing material extending over the circumferential and axial extent of the brush bar, the sealing material comprising a tufted material; a housing defining a chamber which at least partially surrounds the brush bar, a dirty air inlet in a lower part of the chamber and a front opening that exposes the brush bar at the front of the housing, the brush bar being supported for rotation with respect to the housing and arranged in the chamber, wherein the housing comprises a sole plate which extends transversely from one side wall to another side wall of the housing, each side wall has a lower edge that defines a side peripheral edge of the dirty air inlet, the sole plate has a leading edge that defines a rear peripheral edge of the dirty air inlet, and the brush bar defines a forward peripheral edge of the dirty air inlet. 7 . The cleaner head of claim 6 , wherein the cleaner head comprises a rear sealing strip provided along the underside of the sole plate adjacent the leading edge, and side sealing strips provided along the lower edges of the side walls, and the sealing strips together with a lower periphery of the sealing material of the brush bar seal against a surface being cleaned. 8 . The cleaner head of claim 7 , wherein the sealing strips comprise a tufted material. 9 . The cleaner head of claim 6 , wherein the cleaner head comprises wheels supported by the sole plate, and the wheels are set into the sole plate so that only a lower portion of each wheel protrudes from the sole plate. 10 . The cleaner head of claim 6 , wherein the front opening is defined by an upper front edge and opposing side edges of the housing. 11 . The cleaner head of claim 10 , wherein the upper front edge is above the rotational axis of the brush bar. 12 . The cleaner head of claim 10 , wherein the upper front edge is below the top of the brush bar. 13 . The cleaner head of claim 6 , wherein a top portion of the housing extends forwardly over a top of the brush bar to form a guard that prevents debris from being flung upwardly by the brush bar away from the housing. 14 . The cleaner head of claim 6 , wherein the tufted material is made from nylon filaments. 15 . A cleaner head for a vacuum cleaner, comprising: an agitator in the form of a brush bar, the brush bar comprising a sealing material extending over the circumferential and axial extent of the brush bar, the sealing material comprising a tufted material; a housing defining a chamber which at least partially surrounds the brush bar, a dirty air inlet in a lower part of the chamber and a front opening that exposes the brush bar at the front of the housing, the brush bar being supported for rotation with respect to the housing and arranged in the chamber, wherein a partition is arranged within the chamber between the brush bar and an outlet of the chamber, the partition extends transversely and divides the chamber into an agitating region and a settling chamber, and the partition comprises a wall that extends tangentially to the brush bar and is inclined rearwardly. 16 . The cleaner head of claim 15 , wherein the wall of the partition has a lower edge that extends along the length of the wall, and the lower edge defines a debris opening beneath the front wall. 17 . The cleaner head of claim 15 , wherein the front opening is defined by an upper front edge and opposing side edges of the housing. 18 . The cleaner head of claim 17 , wherein the upper front edge is above the rotational axis of the brush bar. 19 . The cleaner head of claim 17 , wherein the upper front edge is below the top of the brush bar. 20 . The cleaner head of claim 15 , wherein a top portion of the housing extends forwardly over the top of the brush bar to form a guard that prevents debris from being flung upwardly by the brush bar away from the housing. 21 . The cleaner head of claim 15 , wherein the tufted material is made from nylon filaments. 22 . A cleaner head for a vacuum cleaner, comprising: an agitator in the form of a brush bar, the brush bar comprising a sealing material extending over the circumferential and axial extent of the brush bar, the sealing material comprising a tufted material; a housing defining a chamber which at least partially surrounds the brush bar, a dirty air inlet in a lower part of the chamber and a front opening that exposes the brush bar at the front of the housing, the brush bar being supported for rotation with respect to the housing and arranged in the chamber, wherein the brush bar comprises a core in the form of a rigid tube within which a motor and a transmission are disposed, the motor and the transmission are arranged to drive the brush bar, and the sealing material is secured to an outer surface of the core. 23 . The cleaner head of claim 22 , wherein the front opening is defined by an upper front edge and opposing side edges of the housing. 24 . The cleaner head of claim 23 , wherein the upper front edge is above the rotational axis of the brush bar. 25 . The cleaner head of claim 23 , wherein the upper front edge is below the top of the brush bar. 26 . The cleaner head of claim 22 , wherein a top portion of the housing extends forwardly over the top of the brush bar to form a guard that prevents debris from being flung upwardly by the brush bar away from the housing. 27 . The cleaner head of claim 22 , wherein the tufted material is made from nylon filaments.
[0001] REFERENCE TO RELATED APPLICATIONS [0002] This application is a continuation of U.S. patent application Ser. No. 14/909,399, filed Feb. 1, 2016, which is a national stage application under 35 USC 371 of International Application No. PCT/GB2014/052259, filed Jul. 24, 2014, which claims the priority of United Kingdom Application No. 1313707.0, filed Jul. 31, 2013, the entire contents of which are incorporated herein by reference. FIELD OF THE INVENTION [0003] This invention relates to a cleaner head for a vacuum cleaner, and particularly, although not exclusively, relates to a cleaner head for a hand-held vacuum cleaner. BACKGROUND OF THE INVENTION [0004] Cleaner heads for vacuum cleaners typically comprise a brush bar located within a housing. A suction opening is provided in a lower surface of the housing, which is commonly known as a sole plate, through which dirt bearing air is drawn into the cleaner head. [0005] A problem associated with conventional cleaner heads is that the close proximity required between the sole plate and the surface being cleaned in order to maintain pick-up performance means that large debris tends to be pushed across the surface being cleaned by the cleaner head rather than being drawn through the suction opening into the cleaner head. SUMMARY OF THE INVENTION [0006] According to a first aspect of the invention there is provided a cleaner head for a vacuum cleaner, comprising an agitator in the form of a brush bar, the brush bar comprising a plurality of radially extending bristles and a sealing material disposed between the bristles, the sealing material extending over substantially the entire circumferential and axial extent of the regions of the brush bar between the bristles; a housing defining a chamber which at least partially surrounds the brush bar, a dirty air inlet in a lower part of the chamber and a front opening that exposes the brush bar at the front of the housing, the brush bar being supported for rotation with respect to the housing and arranged in the chamber such that the brush bar seals against the housing thereby restricting flow of air through the front opening. [0007] The sealing material may be a deformable material. In particular, the sealing material may be a resiliently deformable material. [0008] The brush bar may substantially occlude the front opening. [0009] The radial extent of the bristles may be equal to the radial extent of the sealing material. The radial extent of the bristles may be greater than the radial extent of the sealing material. [0010] The cleaner head may be provided with a support for supporting the cleaner head on a surface being cleaned, the brush bar being arranged such that, in use, the bristles contact the surface being cleaned. The bristles may extend below the support. [0011] The sealing material may be arranged such that, in use, the sealing material is spaced away from the surface being cleaned by the support. [0012] The front opening may be defined by an upper front edge and opposing side edges of the housing. The upper front edge may be above the rotational axis of the brush bar. The upper front edge may be below the top of the brush bar. [0013] The front opening may extend in a plane which is forward of the longitudinal axis of the brush bar. At least a portion of the brush bar may protrude through the front opening. [0014] A top portion of the housing may extend forwardly over the top of the brush bar to form a guard that prevents debris from being flung upwardly by the brush bar away from the housing. [0015] The sealing material may seal against an inner surface of the front portion of the housing. [0016] The bristles may be arranged in a plurality of rows (starts) extending longitudinally with respect to the brush bar. The sealing material may comprise a tufted material. [0017] The bristles may comprise carbon fibre bristles having a stiffness which is greater than the stiffness of the sealing material in a radial direction. [0018] The cleaner head may comprise a rear roller. [0019] According to a second aspect of the invention there is provided a vacuum cleaner comprising a cleaner head in accordance with the first aspect of the invention. [0020] According to a third aspect of the invention there is provided a brush bar comprising a plurality of radially extending bristles and a sealing material disposed between the bristles, the sealing material extending over substantially the entire circumferential and axial extent of the regions of the brush bar between the bristles. [0021] The sealing material may be a deformable material. In particular, the sealing material may be a resiliently deformable material. [0022] The radial extent of the bristles may be equal to the radial extent of the sealing material. [0023] The radial extent of the bristles may be greater than the radial extent of the sealing material. [0024] The sealing material may comprise a tufted material. The sealing material may have a surface resistivity in the range from 1×105Ω/sq to 1×1012Ω/sq. [0025] The bristles may comprise carbon fibre bristles. The carbon fibre bristles may have a stiffness which is greater than the stiffness of the sealing material in a radial direction. [0026] The carbon fibre bristles may have a surface resistivity between 1×103Ω/sq and 1×106Ω/sq. The selection of material having a surface resistivity in this range can ensure that any static electricity on the floor surface is effectively discharged by the second agitating means. Values of surface resistivity discussed herein are as measured using the test method ASTM D257. [0027] The diameter of each bristle may be not greater than 10μm. The bristles may be arranged in a plurality of rows extending longitudinally with respect to the brush bar. The width of each row may be not greater than 5 mm, for example not greater than 2 mm The rows of bristles may be arranged in a generally helical configuration extending around, or partially around, the brush bar. [0028] The bristle density of the bristles is not less than 10,000 bristles per 10 mm in length. A bristle density of not less than 10,000 bristles is particularly effective because it provides effective sealing of the brush bar against the housing. A brush bar comprising rows of bristles having widths less than 2 mm and bristle densities greater than 10,000 are expected to provide excellent sealing characteristics and fine dust pick-up performance. The length of each bristle may be between 4 mm and 8 mm [0029] In particular, a brush bar comprising carbon fibre bristles having a diameters which are not greater than 10μm and lengths which are between 4 mm and 8 mm and which are arranged in rows having a bristle density which is not less than 10,000 bristles per 10 mm is expected to be particularly effective at picking up dirt and dust from hard surfaces. BRIEF DESCRIPTION OF THE DRAWINGS [0030] In order to better understand the present invention, and to show more clearly how the invention may be put into effect, the invention will now be described, by way of example, with reference to the following drawings: [0031] FIG. 1 is a perspective view of a hand-held vacuum cleaner; [0032] FIG. 2 is a perspective view of the cleaner head of the vacuum cleaner shown in FIG. 1 ; [0033] FIG. 3 is a front view of the cleaner head shown in FIG. 2 ; [0034] FIG. 4 is a side view of the cleaner head shown in FIG. 2 ; [0035] FIG. 5 is a rear view of the cleaner head shown in FIG. 2 ; [0036] FIG. 6 is an underside view of the cleaner head shown in FIG. 2 ; and [0037] FIG. 7 is a sectional view in the transverse direction of the cleaner head shown in FIG. 2 . DETAILED DESCRIPTION OF THE INVENTION [0038] FIG. 1 shows a hand-held vacuum cleaner 2 comprising a main body 4 , a wand 6 and a cleaner head 8 . [0039] The main body 4 comprises a separating system 10 , in the form of a cyclonic separator, a motor and impeller (not visible) arranged to draw air through the separating system 10 , and a power supply 12 , in the form of a battery, for powering the motor. The main body 4 has a handle 14 which is gripped by a user, and a clean air outlet 16 through which air that has passed through the separating system 10 is discharged. [0040] The wand 6 is attached at one end to the main body 4 and at the other end to the cleaner head 8 . The wand 6 provides fluid communication between the cleaner head 8 and the separating system 10 , and supports the cleaner head 8 during use. [0041] FIGS. 2 to 7 show the cleaner head 8 in isolation. The cleaner head 8 comprises an agitator in the form of a brush bar 18 , a rear roller 20 , and a housing 22 which defines a chamber 24 within which the brush bar 18 and the rear roller 20 are at least partially disposed. [0042] The housing 22 is connected to the wand 6 by a pivoting arrangement 26 comprising upper and lower pivotal joints 28 , 30 which enable the cleaner head 8 to be pivoted in yaw and pitch with respect to the wand 6 . A flexible hose 32 extends from a connecting portion 34 of the pivoting arrangement 26 into an upper region of the chamber 24 . The end of the hose 32 that extends into the chamber 24 defines a dirty air outlet 36 (shown in FIGS. 6 and 7 ) from the chamber 24 through which air is drawn into the wand 6 and through the separating system 10 . [0043] The brush bar 18 and the rear roller 20 are supported at each of their respective ends by side walls 38 , 40 of the housing 22 . The brush bar 18 and the rear roller 20 are each rotatably supported by the side walls 38 , 40 so that they can rotate with respect to the housing 22 . [0044] With reference to FIG. 7 , the brush bar 18 comprises a core 42 in the form of a rigid tube within which a brush bar motor (not shown) and a transmission 44 are disposed. The motor and the transmission 44 are arranged to drive the brush bar 18 . The brush bar 18 comprises four bristle strips 46 , also known as “starts”, spaced circumferentially about the core 42 . The bristle strips 46 are spaced apart from each other by the same separation angle (i.e. 90 degrees). Each bristle strip 46 comprises a row of radially extending bristles which are held by a locating strip 48 . The bristles may be densely packed, or spaced apart either in clumps or individually. [0045] Each bristle strip 46 extends both longitudinally and circumferentially with respect to the brush bar 18 in a generally helical configuration. Each bristle strip 46 extends circumferentially through an angle of 90 degrees over the length of the brush bar 18 . The locating strip 48 of each bristle strip 46 is secured to the core 42 within a corresponding groove 50 provided in the outer surface of the core 42 . Each groove 50 has opposing lips along each edge of the groove 50 which interlock with the locating strip 48 to secure the bristle strip 46 to the core 42 . [0046] Strips of a sealing material 52 are secured to the outer surface of the core 42 between the bristle strips 46 . The sealing material is locally deformable so that debris pressed into the material is at least partially enveloped by the material. The sealing material may also be resilient so that once debris has been extracted, the material returns to a nominal shape. However, it will be appreciated that centrifugal forces acting on the brush bar 18 during use may return the sealing material to its nominal shape. [0047] In the embodiment shown, the sealing material is a tufted material. The material may, for example, be a tufted material having a short dense pile and may be formed by filaments woven to a fabric substrate. The filaments of the pile may be made from nylon, or other suitable material having a relatively low stiffness. The stiffness of a tufted sealing material will depend on the elastic properties of the material, the filament diameter, filament length and pile density. In the embodiment shown, the tufted material is made from nylon and has a filament diameter of between 30μm and 50μm (preferably 30μm), a filament length of 0.005 m and a pile density of 60,000 filaments/25 mm2. The sealing material need not be a tufted material, but could be a foam material such as a closed cell foam material or other suitable material that provides adequate flow restriction. It will be appreciated that although a deformable sealing material is preferred, this is not essential. [0048] There are four strips of sealing material 52 in total. The thickness (i.e. radial depth) of each strip of sealing material 52 is substantially constant, and the sealing strips 52 are substantially identical. [0049] Each strip of sealing material 52 extends over substantially the entire radial and axial extent of the outer surface of the rigid tube 42 between adjacent bristle strips 46 . For example, each strip of sealing material 52 may extend over an angle of 75 to 90 degrees, preferably 80 to 90 degrees of the circumferential extent of the brush bar 18 . A gap 54 may be formed between one or more of the bristle strips 46 and an adjacent strip of sealing material 52 . In the embodiment shown, each strip of sealing material 52 extends over an angle of 80 degrees and each a gap 54 extending through an angle of 5 degrees is formed each side of each bristle strip 46 (reference signs are provided for the gaps 54 on opposite sides of only one of the bristle strips 46 ). The gaps 54 allow the bristle strips 46 to flex slightly without contacting the strips of sealing material 52 . It will be appreciated that the strips of sealing material 52 may abut the bristle strips 46 so that no gaps are provided between the strips of sealing material 52 and the bristles. This is expected to improve sealing effectiveness. [0050] Fewer or more bristle strips 46 may be provided, in which case a corresponding number of strips of sealing material 52 are used. For example, two or three bristle strips 46 may be provided. [0051] The radial extent of the bristle strips 46 is greater than the radial extent of the strips of sealing material 52 . That is, the radial distance between the tips of the bristle strips 46 and the rotational axis of the brush bar 18 is greater than the radial distance between the periphery of the strips of sealing material 52 and the rotational axis of the brush bar 18 . The radius of the brush bar 18 is defined as the distance between the axis of the brush bar 18 and the tips of the bristle strips 46 . [0052] The bristles of the bristle strips 46 are preferably made from a material which is stiffer than the sealing material disposed between the bristle strips 38 . The bristle strips may comprise carbon fibre filaments having a thickness of between 5μm and 10μm, preferably 7μm. In the embodiment shown, the carbon fibre filaments are 5.9 mm in length and the bristle density (i.e. the number of filaments per millimetre in length of the bristle strips 38 ) of the bristle strips 38 is 12,000 bristles per 10 mm The bristles are arranged in bundles that are spaced apart from each other in the longitudinal direction of each bristle strip 38 . There are 6 bundles per 10 mm of the length of each bristle strip 38 . [0053] The rear roller 20 comprises a core 56 in the form of a solid shaft wrapped in a strip of a tufted material. The tufted material may be the same as the tufted material of the brush bar 18 . [0054] The underside of the housing 22 is open. In the embodiment shown, the housing 22 comprises a rear sole plate 58 (see FIG. 6 ) which extends transversely with respect to the cleaner head 8 from one of the side walls 38 , 40 of the housing 22 to the other. A support in the form of wheels 60 are supported by the sole plate 58 . The wheels 60 are set into the sole plate 58 so that only a lower portion of each wheel 60 protrudes from the sole plate 58 . [0055] Each side wall 38 , 40 has a lower edge 62 , 64 . The sole plate 28 has a leading edge 66 , which is a working edge, that extends from one of the lower edges 62 , 64 to the other. The lower edges 62 , 64 of the side walls 38 , 40 and the leading edge 66 of the sole plate 58 together define the side and rear peripheral edge of a dirty air inlet 68 of the chamber 24 . [0056] The forward peripheral edge of the dirty air inlet 68 is defined by the brush bar 18 . In particular, the forward periphery of the dirty air inlet 68 is defined by the lowermost radial periphery of the strips of sealing material 52 . [0057] The wheels 60 support the cleaner head 8 on a surface being cleaned such that the sole plate 58 , the side walls 38 , 40 and the strips of sealing material 52 are spaced from the surface. In the embodiment shown, the brush bar 18 is arranged such that strips of sealing material 52 are spaced from the surface being cleaned by an amount that provides clearance of the strips of sealing material 52 from the surface, but which does not impair the sealing effectiveness between the strips of sealing material 52 and the surface. [0058] The sole plate 58 and the side walls 38 , 40 are spaced further from the surface being cleaned than the strips of sealing material 52 . A rear sealing strip 70 is therefore provided along the underside of the sole plate 58 adjacent the leading edge 66 . Side sealing strips 71 , 72 are also provided along the lower edges 62 , 64 of the side walls 38 , 40 . The sealing strips 70 , 71 , 72 are arranged to seal against the surface being cleaned during use. The sealing strips 70 , 71 , 72 comprise a material having a pile, for example a tufted fabric/brush-like fabric having filaments made of a suitable material, such as nylon. [0059] The housing 22 has an upper front edge 74 which extends transversely with respect to the cleaner head 8 . The upper front edge 74 is above the rotational axis of the brush bar 18 and below the top of the brush bar 18 . The brush bar 18 extends forwards of the upper front edge 74 . The upper front edge 74 and the front edges 75 , 77 (shown in FIGS. 3 and 4 ) of the side walls 38 , 40 define a front opening of the chamber 24 . [0060] The inner surface of a front region of the housing 22 which defines part of the chamber 24 curves over the top of the brush bar 18 . The radius of curvature of the inner surface of the chamber 24 corresponds to the radius of the tips of the bristle strips 46 . The front region of the housing 22 adjacent the front edge 74 provides a guard which prevents debris from being flung upwardly and/or forwardly by the brush bar 18 during use. However, it will be appreciated that in alternative embodiments the housing need not be arranged as a guard and need not extend forwardly of the top of the brush bar 18 . It will be appreciated that a small clearance may be provided to prevent interference between the tips of the bristles and the housing 22 . The brush bar 18 is arranged so that the sealing material restricts flow between the brush bar 18 and the inner surface of the housing adjacent the front edge 74 . [0061] A partition 76 is arranged within the chamber 24 between the brush bar 18 and the chamber outlet 36 . The partition 76 extends transversely with respect to the cleaner head 8 and divides the chamber 24 into a settling region 24 a, between the partition 76 and the chamber outlet 36 , and an agitating region 24 b, forward of the partition 76 . [0062] The partition 76 comprises a front wall 78 and a rear wall 80 which extend across the chamber 24 . The front wall 78 is supported at each end by the side walls 38 , 40 of the housing 22 . The front wall 78 extends in a plane which is substantially tangential to the brush bar 18 , and inclined rearwardly with respect to the upright direction of the cleaner head 8 . The front wall 78 has a lower edge 82 and an upper edge 84 which extend along the length of the front wall 78 . The lower edge 82 and the sidewalls 38 , 40 define a first debris opening 86 beneath the front wall 78 in the form of a slot. The first debris opening 86 extends in a direction which is parallel with the rotational axis of the brush bar 18 . [0063] The rear wall 80 is disposed between the front wall 78 and the chamber outlet 36 , and extends downwardly from an upper region of the chamber 24 in a direction which is substantially parallel with the front wall 78 . [0064] The rear wall 80 has a joining portion 88 which abuts the housing 22 . The joining portion 88 has a front edge 90 . The upper edge 84 of the front wall 78 and the front edge 90 of the joining portion 88 define a second debris opening 92 in the form of a slot. The second debris opening 92 extends in a direction which is parallel with the rotational axis of the brush bar 18 . The front edge 90 is substantially level with the rotational axis of the brush bar 18 and forms a lip that overhangs the upper edge 84 of the front wall 78 (i.e. the front edge 90 projects radially inwardly of the upper edge 84 with respect to the rotational axis of the brush bar 18 ). [0065] The front wall 78 and the rear wall 80 define a debris recovery passageway which extends downwardly and forwardly from the second debris opening 92 . The passageway opens at the lower end into the settling region 24 a of the chamber 24 . A portion of the joining portion 88 between the rear wall 80 and the front edge 90 has an inclined front surface 94 which is inclined forwardly at an angle of between 35 degrees and 65 degrees to the upright direction of cleaner head 8 . The inclined front surface 94 forms a deflector for deflecting debris downwardly along the passageway defined by the front and rear walls 78 , 80 . [0066] In use, the cleaner head 8 of the vacuum cleaner 2 is placed on a floor, for example a floor having a hard surface. The cleaner head 8 is supported on the surface by the rollers 60 so that the sealing strips 70 , 71 , 72 , together with the lower periphery of the sealing material of the brush bar 18 , seal against the surface being cleaned. The chamber 24 is therefore sealed around the periphery of the dirty air inlet 68 by the sealing strips 70 , 71 , 72 and the sealing material 52 of the brush bar 18 . In addition, the brush bar 18 seals against the upper inner surface of the housing 22 adjacent the front edge 74 . [0067] In the context of the specification, the term “seal” should be understood to mean capable of maintaining a predetermined pressure difference during use of the vacuum cleaner 2 . For example, the chamber 24 can be regarded as being sealed provided that the flow of air through the chamber 24 is restricted to an amount that is sufficient to maintain a pressure difference of at least 0.65 kPa between the inside of chamber 24 and ambient during normal use (e.g. when used to clean a hard/firm surface). Similarly, the brush bar 18 can be considered to be sealed against the housing 22 if the flow of air through the front opening is restricted by the brush bar 18 such that a pressure difference of at least 0.65 kPa between the inside of chamber 24 and ambient is maintained during normal use. [0068] The motor and the impeller draw air into the chamber 24 through the dirty air inlet 68 in the housing 22 and upwardly through the chamber outlet 36 , through the wand 6 and into the separating system 10 . Dirt is extracted from the air by the separating system 10 before being exhausted through the clean air outlet 16 . [0069] The brush bar 18 is driven in a forward direction which is the counter-clockwise direction in FIG. 7 . The brush bar 18 is driven at a relatively high rotational speed, for example between 600 rpm and 3000 rpm, preferably between 600 rpm and 1400 rpm. Increasing the rotational speed can be expected to improve fine dust pick up performance The boundary layer effect in the vicinity of the sealing material 52 and the bristle strips 46 causes rotational flow within the agitating region 24 b of the chamber 24 in the direction of rotation of the brush bar 18 . The rotational flow dynamically seals the gap between the brush bar 18 and the front edge 74 of the housing 22 . This dynamic sealing of the chamber 24 helps to maintain pressure within the chamber 24 by further restricting flow of air between the brush bar 18 and the housing 22 . [0070] As the cleaner head 8 is moved across the surface being cleaned, the tips of the bristles of the bristle strips 46 contact the surface and sweep debris rearwardly towards the first debris opening 86 . The bristles are particularly effective at removing fine dust from crevices and agitating dust that has been compacted on the surface being cleaned. The gaps 54 extending along each side of the bristle strips 46 accommodate flexing of the bristles as they are pressed against the surface of the floor. [0071] As the cleaner head 8 is moved over large debris (i.e. debris that is larger than the clearance between the periphery of the sealing material 52 and the floor), for example grains of rice, oats, pasta, cereals or similar, the sealing material 52 is deformed locally by the debris. [0072] Local deformation of the sealing material 52 ensures that, for most large debris, the cleaner head 8 does not ride-up over the debris, which would reduce sealing effectiveness between the sealing strip 70 , 71 , 72 , the sealing material 52 on the brush bar 18 and the floor surface. Sealing between the brush bar 18 and the surface being cleaned is therefore not adversely affected, and so effective pick-up performance is maintained. The large debris, which has been substantially enveloped by the sealing material 52 , is then released rearwardly through the first debris opening 86 into the settling region 24 a of the chamber 24 . Smaller debris or debris which clings to the floor, such as compacted dust, is agitated by the bristle strips 46 and swept rearwardly through the first debris opening 86 into the settling region 24 a of the chamber 24 . The debris, as well as other debris which may have been drawn directly up through the dirty air inlet 68 , is sucked through the chamber outlet 36 to the separating system 10 , as described above. [0073] It will be appreciated that the sealing material 52 also deforms to accommodate small variations in the surface being cleaned without causing scratching of the surface. [0074] In some circumstances, debris having relatively high inertia such as large debris, for example rice or large dust particles, rebounds off the rear wall of the settling region 24 a of the chamber 24 back though the first debris opening 86 without being sucked up through the chamber outlet 36 . Such debris collides with the brush bar 18 and is swept either back through the first debris opening 86 or else is driven upwardly along the front surface of the front wall 78 of the partition 76 towards the second debris opening 92 . The overhanging front edge 90 intercepts the debris and directs the debris rearwardly towards the inclined front surface 94 of the joining portion 88 . The overhanging front edge 90 therefore prevents the debris from being swept along the inner surface of the chamber 24 and out through the front opening by the brush bar 18 . [0075] Debris which collides with the inclined front surface 94 is directed downwardly along the passageway between the front and rear walls 78 , 80 of the partition 76 into the settling region 24 a of the chamber 24 . Each collision of the debris with the front and rear walls 78 , 80 dissipates some of the kinetic energy of the debris, thereby reducing its inertia. Consequently, debris that falls down along the passageway into the settling region 24 a is entrained by the air flowing through the chamber 24 and sucked the chamber outlet 36 to the separating system 10 . [0076] The front opening of the housing 22 allows the brush bar 18 to be pushed up against an object on the surface being cleaned or against a wall so the brush bar can pick up debris adjacent the object or wall. This improves overall pick up performance. [0077] The rear roller 20 is arranged to roll of debris on the surface being cleaned. Therefore, debris is not scraped along the surface being cleaned which could otherwise scratch the surface. [0078] The cleaner head 8 is effective at picking up both small and large debris as well as dust that has been compacted. The cleaner head 8 is particularly effective on hard floors in which large debris stands proud of the surface, or on which dust has been compacted.

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