Patent Publication Number: US-8528158-B2

Title: Cleaner head

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of United Kingdom Application No. 0906353.8, filed Apr. 14, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a cleaner head for a cleaning appliance. In its preferred embodiment, the present invention relates to a cleaner head for a vacuum cleaning appliance. 
     BACKGROUND OF THE INVENTION 
     An upright vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head mounted on the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere. 
     The suction opening is directed downwardly to face the floor surface to be cleaned. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement. The present invention is not concerned with the nature of the separating apparatus and is therefore applicable to vacuum cleaners utilizing any of the above arrangements or another suitable separating apparatus. 
     A driven agitator, usually in the form of a brush bar, is supported in the cleaner head so as to protrude to a small extent from the suction opening. The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. The brush bar may be driven by an air turbine or by an electric motor powered by a power supply derived from the main body of the cleaner. The brush bar may be driven by the motor via a drive belt, or may be driven directly by the motor, so as to rotate within the suction opening. Rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust, and pick up debris. The suction of air causes air to flow underneath the sole plate and around the brush bar to help lift the dirt and dust from the surface of the carpet and then carry it from the suction opening through the cleaner head towards the separating apparatus. 
     For example, GB 2,388,306 describes a cleaner head having a brush bar chamber housing a rotatable brush bar. A turbine for driving the brush bar is located in a turbine chamber disposed behind a rectangular air outlet from the brush bar chamber so as to be driven by the airflow emitted from the brush bar chamber. The turbine is connected to the brush bar by a timing belt which extends into the brush bar chamber to one side of the air outlet. The timing belt is located within a belt housing which divides the brush bar chamber into a relatively large first section and a relatively small second section each containing part of the brush bar. As the air outlet is located wholly within the first section of the brush bar chamber, a pressure differential can be generated between the two sections of the brush bar chamber during use of the cleaner head, which can compromise the passage of air from the second section of the brush bar chamber to the air outlet and thereby compromise the pick up performance of the cleaner head. 
     SUMMARY OF THE INVENTION 
     The present invention provides a cleaner head for a cleaning appliance, comprising a housing having an air outlet, a rotary brush bar assembly located within a chamber of the housing, the chamber having an air outlet which is in fluid communication with the air outlet of the housing, and a drive mechanism for driving the brush bar assembly, the drive mechanism extending into the chamber between first and second side walls of the chamber, wherein the brush bar assembly comprises a first brush bar section located within a first section of the chamber between the drive mechanism and the first side wall of the chamber, and a second brush bar section located within a second section of the chamber between the drive mechanism and the second side wall of the chamber, and wherein the air outlet of the chamber extends between and into both sections of the chamber. 
     To minimise the pressure difference between these two sections of the brush bar chamber, and to enable the dirt and dust agitated from the floor surface by both brush bar sections to be conveyed rapidly to the air outlet of the cleaner head, the air flow is preferably drawn through both of the brush bar chamber sections. In view of this, the air outlet from the brush bar chamber extends between, and into, both sections of the brush bar chamber. 
     Each brush bar section may comprise an individual brush bar which is connected to the drive mechanism. Alternatively, the brush bar sections may be continuous, with the drive mechanism comprising a pulley or gear which extends about the brush bar assembly and which divides the brush bar assembly into the first and second sections. 
     The air outlet from the brush bar chamber is preferably in the form of a slot, which preferably has an aspect ratio of at least 3:1, more preferably of at least 5:1. 
     Each brush bar section preferably comprises a first set of bristles and a second set of bristles which are different from the first set of bristles. Each set of bristles preferably comprises a plurality of clusters arranged in a helical formation at regular intervals along the brush bar section, with the helical pattern of the clusters of the second set of bristles being angularly spaced from the helical pattern of the clusters of the first set of bristles. The first set of bristles preferably comprises relatively long, stiff bristles for plush pick up, whereas the second set of bristles preferably comprises relatively short, soft bristles for fibre pick up. 
     The brush bar assembly is preferably driven by a motor located in a motor housing. To provide a balanced cleaner head in which the weight of the motor is spread evenly about the lower surface of the cleaner head, the motor is preferably located centrally above the air outlet of the brush bar chamber. Consequently, the drive mechanism may extend into the brush bar chamber, between the side walls of the chamber and closer to one side wall than the other. In this case, the brush bar assembly may comprise a first, relatively long brush bar section located between the drive mechanism housing and a first side wall of the chamber, and a second, relatively short brush bar section, preferably co-axial with the first brush bar section and located between the drive mechanism housing and a second side wall of the chamber. 
     Alternatively, the brush bar assembly may be driven by a turbine located in a turbine chamber, and which is rotated by the airflow which passes from the air outlet of the chamber to the air outlet of the housing, or by an airflow which enters the housing through a separate air inlet. The drive mechanism may comprise gears or a belt, located within a drive mechanism housing so that the drive mechanism is isolated from the air passing through the housing. 
     Where the drive mechanism comprises a belt connecting the motor to the brush bar assembly, wear of the belt during use of the cleaner head can cause the belt to expand. In turn, this can cause the belt to slip, which can result in damage to the motor and/or other components of the drive mechanism. In view of this, the drive mechanism connecting the motor to the brush bar assembly preferably comprises a rotatable input drive member connected to the motor, a rotatable output drive member connected to the brush bar assembly and moveable relative to the input drive member in a direction orthogonal to the axes of rotation of the drive members, a belt connecting the input drive member to the output drive member, and a belt tensioning member located between the drive members for tensioning the belt by urging the output drive member away from input drive member. This can maintain the tension of the belt at a substantially constant level during the life of the belt. 
     The output drive member is preferably moveable relative to the input drive member in a direction extending between the axes of rotation of the drive members. The belt tensioning member is preferably also moveable relative to the drive members in this direction. 
     Preferably, the output drive member is rotatably supported by a housing for the drive mechanism, with the belt tensioning member being arranged to move the housing relative to the input drive member. The belt tensioning member is preferably mounted on a spigot connected to the housing, which spigot is preferably substantially parallel to the axes of rotation of the drive members. The belt tensioning member is preferably moveable along the spigot, and is thus moveable in a direction substantially perpendicular to the direction of the relative movement between the axes of rotation of the drive members. 
     The belt tensioning member is preferably urged away from the input drive member by an abutment member connected to the motor. Engaging portions of the abutment member and the belt tensioning member are preferably wedge-shaped. A resilient member or other means is preferably provided for urging the belt tensioning member against the abutment member. This resilient element may be conveniently located between the belt tensioning member and the housing. 
     The cleaner head preferably comprises a sole plate comprising a suction opening through which dirt-bearing air enters the cleaner head, and a flexible annular seal located between the sole plate and the housing for allowing relative movement between the housing and the sole plate. 
     When an air flow is generated through the suction opening, the pressure difference between the air passing through the cleaner head and the external environment causes the housing of the cleaner head to be sucked down towards the floor surface, whereas the fibres of a carpeted surface are lifted towards the housing of the cleaner head. Due to the presence of the flexible annular seal, which may be in the form of a flexible skirt or membrane, between the housing and the sole plate, the housing is capable of moving relative to the sole plate. Consequently, only a relatively small amount of force, if any, is applied to the sole plate by the housing, thereby preventing the sole plate from being pushed into the pile of the carpet by the housing. In turn, this means that the sole plate does not cause significant resistance to the movement of the cleaner head over the floor surface, and does not unduly restrict the flow of air into the cleaner head. 
     The flexible annular seal preferably extends about the suction opening to provide an air-tight seal between the sole plate and the housing. The flexible annular seal may thus define part of a suction passage for conducting the dirt-bearing air from the suction opening to an air outlet. Thus, in comparison to a cleaner head using air channels to restrict the force acting on the cleaner head by allowing air to enter the suction passage from the external environment, the use of a flexible annular seal can enable an improved air flow into the cleaner head from around the periphery thereof and through a carpeted flow surface therebeneath to be achieved for a given air pressure within the housing of the cleaner head, thereby improving pick up performance. 
     The majority of the air flow entering the suction opening of the sole plate will pass beneath the edges of the sole plate and, when the sole plate is located on a carpeted surface, through the carpet pile. As the sole plate is not being urged against the floor surface by the housing of the cleaner head, the air flow passing beneath the edges of the sole plate can tend to lift the sole plate away from the floor surface, particularly when the amount of suction provided at the suction opening is relatively high. This could have the effect of increasing the pressure within the cleaner head, and in turn reducing the speed of the air flow through the suction opening and compromising the pick up performance of the cleaner head. 
     To inhibit lifting of the sole plate from the floor surface during use, the sole plate may be provided with sufficient mass as to resist movement away from the floor surface under the action of the air flow passing beneath the sole plate. Alternatively, the flexible annular seal may be formed from resilient material having an elasticity selected so that an amount of the force acting on the cleaner head is transferred to the sole plate through compression of the flexible annular seal. In the preferred embodiment the flexible annular seal is formed from a material comprising latex. Additionally, or as another alternative, one or more springs or other resilient members may be provided between the housing and the sole plate for applying a force to the sole plate. In the preferred embodiment the flexible annular seal comprises a bellows seal element to facilitate the compression and expansion of the skirt as the cleaner head is moved, for example between a hard floor surface and a carpeted surface. 
     The downwards force acting on the sole plate, either under its own weight or in combination with the force applied through the flexible annular seal and/or other resilient members(s), is preferably sufficient to minimise the risk of the sole plate lifting from the floor surface during use while minimising the resistance to the maneuvering of the cleaner head over the floor surface. This force is preferably less than 10 N, and in the preferred embodiment is between 2 and 7 N. 
     The cleaner head preferably comprises features which limit the extent of the relative movement between the sole plate and the housing to avoid over-compression of the flexible member. The relative movement between the sole plate and the housing is preferably restricted to less than 20 mm, more preferably less than 15 mm. 
     In order to assist movement of the cleaner head over a deep pile carpeted floor, in the preferred embodiment the leading edge of the sole plate is moveable relative to the housing by a greater amount than the trailing edge of the sole plate. This allows the leading edge to move relative to the housing when the movement of the trailing edge of the sole plate relative to the housing is inhibited. In the preferred embodiment the extent of the movement of the rear of the sole plate relative to the housing is restricted to a distance of around 5.5 to 6.5 mm, whereas the extent of the movement of the front of the sole plate relative to the housing is restricted to a distance of around 6.5 to 8 mm. 
     The sole plate comprises a bottom surface which, in use, faces the floor surface to be cleaned, and which has a leading section and a trailing section located on opposite sides of the suction opening. The sole plate also comprises a front wall and a rear wall which each upstand from the bottom surface of the sole plate and define, in part, the suction opening. The rear wall is preferably inclined forwardly relative to the bottom surface to guide fibres of a carpeted floor surface beneath the trailing section of the bottom surface of the sole plate as the cleaner head is maneuvered over the floor surface. 
     The flexible annular seal is preferably connected at one end thereof to the sole plate so as to surround the suction opening. The other end of the flexible annular seal is preferably connected to a chassis which is detachably connected to the housing. This can enable the sole plate, flexible annular seal and the chassis to be removed as a single detachable unit from the cleaner head, for example to provide access to the brush bar assembly, without compromising the integrity of the seal between the chassis and the sole plate. 
     The cleaner head preferably comprises guide means for guiding relative movement between the housing and the sole plate. The guide means preferably comprises a plurality of guide members, which may in the form of rods, bars, pins or other elongate members, connected to one of the sole plate and the chassis or housing. In this case, the other of the sole plate and the chassis or housing may comprise a plurality of guide retaining members each for receiving a respective guide member and within which the guide members move with movement of the housing towards or away from the sole plate. In the preferred embodiment the sole plate comprises a plurality of guide members which are received within guide members connected to, or integral with, the chassis. 
     The guide means preferably also serve to inhibit relative movement between the sole plate and the housing in the direction of movement of the cleaner head across the floor surface. Alternatively, separate means may be provided for inhibiting relative movement between the sole plate and the housing in the direction of movement of the cleaner head across the floor surface. The guide means may preferably comprise means for limiting the extent of the movement of the sole plate away from the chassis, and/or means for limiting the extent of the movement of the sole plate towards the chassis. 
     In a second aspect the present invention provides a cleaning appliance, preferably a vacuum cleaner, comprising a cleaner head as aforementioned. 
    
    
     
       BRIEF DESCRIPTION OF TILE DRAWINGS 
       An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a front perspective view of a cleaner head; 
         FIG. 2  is a rear perspective view of the cleaner head of  FIG. 1 ; 
         FIG. 3  is an underside view of the cleaner head of  FIG. 1 ; 
         FIG. 4  is a front perspective view of the chassis and sole plate of the cleaner head of  FIG. 1 ; 
         FIG. 5  is a rear perspective view of the chassis and sole plate of  FIG. 4 ; 
         FIG. 6  is an oblique underside view of the cleaner head of  FIG. 1 , with the brush bars removed; 
         FIG. 7  is a cross-sectional view taken along line X-X in  FIG. 3 ; 
         FIG. 8  is part of a cross-sectional view taken along line Y-Y in  FIG. 3 ; 
         FIG. 9  is a side view of the cleaner head of  FIG. 1  when located on a hard floor surface; 
         FIG. 10  is a side view of the cleaner head of  FIG. 1  when located on a carpeted surface; 
         FIG. 11  is a cross-sectional view taken along line Z-Z in  FIG. 7  of the drive mechanism for the brush bar assembly; and 
         FIG. 12  is a perspective view of the drive mechanism of  FIG. 11 , with the cover of the drive mechanism removed. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference first to  FIGS. 1 and 2 , a cleaner head  10  for a vacuum cleaner comprises a housing  12  and a lower plate, or sole plate  14 , comprising a suction opening  16  through which a dirt-bearing fluid flow enters the cleaner head  10 . The housing  12  defines a suction passage  17  (indicated in  FIG. 7 ) extending from the suction opening  16  to a fluid outlet  18  located at the rear of the housing  12 . The fluid outlet  18  is dimensioned to connect to a main body or a hose of an upright vacuum cleaner. 
     The sole plate  14  is illustrated in more detail in  FIGS. 3 to 5 . The sole plate  14  comprises a bottom surface which, in use, faces the floor surface to be cleaned and, as described in more detail below, engages the surface of a carpeted floor surface. The bottom surface of the sole plate  14  is generally planar, and comprises two opposing side sections  20 , a leading section  22  and a trailing section  24  which extend about the suction opening  16 . 
     The suction opening  16  is generally rectangular in shape, and is delimited by relatively short side walls  26 , a relatively long front wall  28  and a relatively long rear wall  30  which each upstand from the bottom surface of the sole plate  14 . These walls also delimit the start of the suction passage  17  through the cleaner head  10 . A plurality of rug strips  32  for guiding the movement of the cleaner head  10  over a rug or deeply piled carpeted floor surface, extend across the suction opening  16  from the front wall  28  to the rear wall  30 , and are substantially parallel with the side walls  26 . 
     The front wall  28  of the suction opening  16  is substantially orthogonal to the bottom surface of the sole plate  14 . A front working edge  34  of the sole plate  14  is located at the intersection between the leading section  22  of the bottom surface and the front wall  28 , and extends substantially uninterruptedly between the side walls  26 . An inclined front lip  36  extends upwardly and forwardly from the front of the leading section  22 , and in use sweeps the fibres of a rug or deeply piled carpeted floor surface beneath the leading section  22  as the cleaner head  10  is maneuvered over that floor surface, thereby lowering the resistance to motion of the cleaner head  10 . 
     The rear wall  30  of the suction opening  16  is also inclined forwardly relative to the bottom surface of the sole plate  14  to sweep the fibres of a rug or deeply piled carpeted floor surface beneath the trailing section  24  as the cleaner head  10  is maneuvered over the floor surface. The angle of inclination of the rear wall  30  relative to the bottom surface is substantially the same as the angle of inclination of the front lip  36  relative to the bottom surface, and is preferably in the range from 40 to 50°. A rear working edge  38  of the sole plate  14  is located at the intersection between the rear section  24  of the bottom surface and the rear wall  32 , and extends substantially uninterruptedly between the side walls  26 . Two rear lips  40  curve upwardly and rearwardly from the rear of the trailing section  24 , and are located on opposite sides of the fluid outlet  18 . 
     The sole plate  14  is connected to a chassis  50 . The chassis  50  is substantially rectangular in shape, and comprises relatively short side walls  52 , a relatively long front wall  54  and a relatively long rear wall  56 . The chassis  50  is annular in shape, with these walls delimiting a substantially rectangular aperture for receiving the dirt-bearing fluid flow drawn into the cleaner head  10  through the suction opening  16 , and thus also delimit part of the suction passage  17  through the cleaner head  10 . This aperture has a size which is similar to that of the suction opening  16 . 
     The chassis  50  is releasably connected to the housing  12  of the cleaner head  10 . With reference also to  FIG. 8 , the chassis  50  comprises an annular projection  58  upstanding from the upper surfaces of the walls  52 ,  54 ,  56  of the chassis  50  which locates within an annular groove  60  defined by an L-shaped flange  62  extending about the housing  12  of the cleaner head  10 . An annular sealing member, preferably in the form of a rope seal, may be located within the groove  60  for engaging with the projection  58  to ensure that an air-tight seal is formed between the housing  12  and the chassis  50 . The front wall  54  of the chassis  50  comprises a plurality of forwardly extending lugs  64 . To attach the chassis  50  to the housing  12 , the chassis  50  is angled relative to the housing  12  to allow each of these lugs  64  to be located within a respective recess formed in the front of the housing  12 . The chassis  50  is then pivoted about these lugs  64  and towards the housing  12  to insert the annular projection  58  within the groove  60 . The chassis  50  also comprises a first pair of annular lugs  66  connected to the rear wall  56  and each arranged to engage with a respective one of a pair of lugs  68  connected to the rear of the housing  12  when the annular projection  58  is fully inserted within the annular groove  60 . A screw  69  is inserted into each engaging pair of lugs  66 ,  68  to secure the chassis  50  to the housing  12 . 
     The sole plate  14  is connected to the chassis  50  by a flexible annular seal, which in this example is in the form of a flexible skirt  70 . One end of the skirt  70  is connected to the upper surfaces of the walls  26 ,  28 ,  30  of the sole plate  14  so as to surround the suction opening  16 , while the other end of the skirt  70  is connected to the lower surfaces of the walls  52 ,  54 ,  56  of the chassis  50  so as to surround the aperture of the chassis  50 . Consequently, the skirt  70  also delimits part of the suction passage  17  through the cleaner head  10 , and the chassis  50 , skirt  70  and sole plate  14  together form a unit which is detachable from the housing  12  of the cleaner head  10 . The presence of the skirt  70  allows relative movement between the housing  12  and the sole plate  14  during a cleaning operation, as described in more detail below. With reference to  FIG. 7 , the rear wall  30  of the sole plate  14  has a raised portion  71  to prevent sharp debris entering the housing  12  through the suction opening  16  from damaging or otherwise compromising the integrity of the seal between the sole plate  14  and the skirt  70 . 
     The cleaner head  10  is arranged to constrain relative movement between the sole plate  14  and the housing  12  to a direction extending substantially orthogonal to the bottom surface of the sole plate  14 . With reference to  FIGS. 4 and 5 , the sole plate  14  comprises a pair of rectangular guide members  72  extending upwardly from the front of the sole plate  14 . Each rectangular guide member  72  passes through an aperture  74  formed in a respective guide retaining member  76  projecting forwardly from the front wall  54  of the chassis  50 . The rectangular guide members  72  and the guide retaining members  76  are shaped to enable sliding relative movement therebetween in a direction extending substantially orthogonal to the bottom surface of the sole plate  14 , and inhibit both relative rotation between the chassis  50  and the sole plate  14  and relative movement between the chassis  50  and the front of the sole plate  14  in the direction of the movement of the cleaner head  10  across the floor surface. 
     Each rectangular guide member  72  preferably has a head portion  78  projecting forwardly therefrom and located above its guide retaining member  76 . The head portion  78  is shaped to engage the upper surface of the guide retaining member  76 , and thereby limit the movement of the front of the sole plate  14  away from the housing  12 . The movement of the front of the sole plate  14  towards the housing  12  may be limited by the abutment of the front lip  36  of the sole plate  14  with the lower surface of the guide retaining members  76 . Alternatively, other features may be located on the front of the housing  12  for engaging the front lip  36  of the sole plate  14  to limit the movement of the front of the sole plate  14  towards the housing  12 . In this example, the extent of the movement of the front lip  36  of the sole plate  14  relative to the housing  12  is restricted to a distance of around 6.5 to 8 mm. 
     The sole plate  14  also comprises a pair of cylindrical guide members  80  extending upwardly from the rear of the sole plate  14 . Each cylindrical guide member  80  is retained by a respective guide retaining member  82  projecting rearwardly from the rear wall  56  of the chassis  50 . Each guide retaining member  82  preferably comprises a pair of ribs extending about the cylindrical guide member. Again, the cylindrical guide members  80  and the guide retaining members  82  are shaped to enable sliding relative movement therebetween in a direction extending substantially orthogonal to the bottom surface of the sole plate  14 . Each cylindrical guide member  80  preferably has a head portion  84  projecting forwardly therefrom and located above its guide retaining member  82 . The head portion  84  is shaped to engage the upper surface of the guide retaining member  82 , and thereby limit the movement of the rear of the sole plate  14  away from the housing  12 . The movement of the rear of the sole plate  14  towards the housing  12  is limited by the abutment of fins  86  extending radially outwardly from each cylindrical guide member  80  with the lower surface of the guide retaining member  82 . When the chassis  50  is connected to the housing  12 , the head portions  84  of the cylindrical guide members  80  are each received within a respective one of a second pair of annular lugs  88  located on the rear of the housing  12 , inwardly from the first pair of annular lugs  68 , and within which the head portions  84  of the cylindrical guide members  80  are slidably moveable. The guide retaining members  82  and the annular lugs  88  are preferably shaped so as to inhibit relative movement between the chassis  50  and the rear of the sole plate  14  in the direction of the movement of the cleaner head  10  across the floor surface. The housing  12  comprises a bumper  90  mounted on the front of housing  12  for reducing the risk of impact between the sole plate  14  and objects such as items of furniture or walls during a cleaning operation, which could otherwise cause damage to the guide members  72 ,  80  and the guide retaining members  76 ,  82 . 
     In this example, the extent of the movement of the rear lip  40  of the sole plate  14  relative to the housing  12  is restricted to distance of around 5.5 to 6.5 mm, that is, shorter than the extent of the movement of the front lip  36  of the sole plate  14  relative to the housing  12 . Consequently, the front of the sole plate  14  is able to pivot slightly about the points of contact between the guide retaining members  82  and the fins  86  once movement of the rear of the sole plate  14  towards the housing  12  has been restricted. 
     The skirt  70  is preferably in the form of a bellows-type element to facilitate repeated compression and extension of the skirt  70  due to relative movement between the sole plate  14  and the housing  12  during a cleaning operation. The skirt  70  is preferably formed from a resilient material, which preferably comprises latex. 
     With reference now to  FIGS. 3 and 7 , the cleaner head  10  comprises an agitator for agitating dirt and dust located on the floor surface. In this example the agitator comprises a rotatable brush bar assembly  100  which is mounted within a brush bar chamber  102  of the housing  12 . The chassis  50  and the skirt  70  extend about the brush bar assembly  100 . The removal of the chassis  50  from the housing  12  enables a user to access the brush bar assembly  100 , for example for cleaning and/or removal from the brush bar chamber  102 . 
     The brush bar assembly  100  is driven by a motor  104  located in a motor housing  106  of the housing  12 . The brush bar assembly  100  is connected to the motor  104  by a drive mechanism  107 , described in more detail below, located within a drive mechanism housing  108  so that the drive mechanism  107  is isolated from the air passing through the suction passage  17 . To provide a balanced cleaner head  10  in which the weight of the motor  104  is spread evenly about the bottom surface of the sole plate  14 , the motor housing  106  is located centrally above, and rearward of, the brush bar chamber  102 . Consequently, the drive mechanism  107  extends into the brush bar chamber  102  between the side walls  110 ,  112  of the brush bar chamber  102 , closer to side wall  110  than to side wall  112 . 
     In view of this, the brush bar assembly  100  comprises a first, relatively long brush bar  114  located between the drive mechanism housing  108  and side wall  110  of the brush bar chamber  102 , and a second, relatively short brush bar  116 , co-axial with the first brush bar  114  and located between the drive mechanism housing  108  and side wall  112  of the brush bar chamber  102 . Each brush bar  114 ,  116  has one end connected to the drive mechanism  107  to enable the brush bars  114 ,  116  to be driven by the motor  104 . The other ends of the brush bars  114 ,  116  are rotatably supported by end caps  118  mounted on the side walls  110 ,  112  of brush bar chamber  102 . Each brush bar  114 ,  116  comprises a first set of relatively long, stiff bristles  120  and a second set of relatively short, soft bristles  122 . Each set of bristles  120 ,  122  comprises a plurality of clusters arranged in a helical formation at regular intervals along the brush bar  114 ,  116 , with the helical pattern of the clusters of the second set of bristles  122  being angularly spaced from the helical pattern of the clusters of the first set of bristles  120 . 
     The brush bar chamber  102  provides part of the suction passage  17  extending from the suction opening  16  to the fluid outlet  18  located at the rear of the housing  12 . Consequently, the brush bar chamber  102  comprises a chamber air outlet  130  through which the air flow leaves the brush bar chamber  102 , and enters a conduit  132  extending beneath the motor housing  106  for conveying the air flow to the fluid outlet  18 . With reference to  FIG. 6 , in which the brush bars  114 ,  116  have been omitted for clarity, the first brush bar  114  is located within a first section  102   a  of the brush bar chamber  102  and the second brush bar  116  is located within a second section  102   b  of the brush bar chamber  102 . To enable the air flow to pass rapidly from each section  102   a ,  102   b  of the brush bar chamber  102  into the conduit  132 , the air outlet  130  is in the form of an elongate aperture which extends between, and into, both sections  102   a ,  102   b  of the brush bar chamber  102 . The air outlet  130  from the brush bar chamber  102  is preferably in the form of a slot, which preferably has an aspect ratio of at least 3:1, more preferably of at least 5:1. In contrast, the fluid outlet  108  is in the form of a substantially circular aperture, and so the conduit  132  is shaped so that its cross-section changes gradually and smoothly from an elongate shape to a circular shape. 
     The fluid outlet  18  of the cleaner head  10  is connected to a main body of a cleaning appliance (not shown), which contains dirt and dust separating apparatus and a motor-driven fan unit for drawing dirt-bearing air through the suction opening  16  from the floor surface. In use, the dirt-bearing air passes through the suction passage  17  and into the main body of the cleaning appliance, wherein dirt and dust is separated from the air before it is expelled to the atmosphere. 
     When an air flow is generated through the suction passage  17 , a pressure difference is generated between the air passing through the cleaner head  10  and the external environment. This pressure difference generates a force which acts downwardly on the housing  12  of the cleaner head  10  towards the floor surface. Due to the presence of the flexible skirt  70  between the housing  12  and the sole plate  14 , the housing  12  moves relative to the sole plate  14 . Consequently, only a relatively small amount of force, if any, is applied to the sole plate  14  by the housing  12 , preventing the sole plate  14  from being urged against the floor surface by the housing  12 . As a result, the flow of air into the suction opening  16  from beneath the bottom surface of the sole plate  14  is not unduly restricted, and the sole plate  14  does not cause significant resistance to the movement of the cleaner head  10  over the floor surface. 
     To prevent the housing  12  from being forced against the sole plate  14  through extensive compression of the skirt  70 , the cleaner head  10  comprises a plurality of floor engaging support members for restricting the movement of the housing  12  towards the sole plate  14 . Returning to  FIGS. 2 and 3 , this plurality of floor engaging support members comprises a pair of rear support members  140 . Each of the rear support members  140  is connected to the end of an arm  142  rigidly connected to and extending rearwardly from a respective side wall  110 ,  112  of the brush bar chamber  102  so that each of the rear support members  140  is located behind the sole plate  14 . The plurality of floor engaging support members also comprises a further support member  143  located in front of the rear support members  140  to prevent the cleaner head  10  from pivoting about these rear support members  140  and “digging” into the floor surface during use. In this example, the further support member  143  is mounted on the drive mechanism housing  108  so as to protrude through the suction opening  16  of the cleaner head  10 . 
     Each support member  140 ,  143  comprises a support having a substantially cylindrical upper portion  144 , and a curved, preferably substantially hemispherical, lower portion  146 . Each support member  140 ,  143  also comprises a floor engaging rolling element  148  mounted within a recess formed in the outer surface of the lower portion  146  so as to protrude from the support. The rolling element  148  is preferably in the form of a cylindrical rolling element which rolls along the floor surface as the cleaner head  10  is maneuvered over the floor surface during a cleaning operation to minimise the resistance to the movement of the support members  140 ,  143 , particularly over a hard floor surface. The rolling element  148  is preferably arranged so that the point of contact between the rolling element  148  and the floor surface is substantially coincident with a locus  149  described by the lower surface of the support member  140 ,  143 . In other words, the outer surface of the rolling element  148  is preferably substantially coincident with the lowest point of a virtual hemispherical shape which is concentric with, and has the same radius of curvature as, the lower portion  146  of the support. 
     When the cleaner head  10  is located on a hard floor surface  160 , as indicated in  FIG. 9 , only the rolling elements  148  of the support members  140 ,  143  engage the hard floor surface  160 . Under the weight of the sole plate  14 , the head portions  78 ,  84  of the guide members  72 ,  80  come into contact with the upper surfaces of their respective guide retaining members  76 ,  82  to restrict the movement of the sole plate  14  towards the hard floor surface  160  so that the sole plate  14  is spaced from the hard floor surface  160 . This allows dirt-bearing air to flow unrestrictedly beneath the bottom surface of the sole plate  14  and into the suction passage  17  through the suction opening  16 . 
     When the cleaner head  10  is moved on to a carpeted floor surface  170 , as illustrated in  FIG. 10 , the force acting on the housing  12  pushes the support members  140 ,  143  into the fibres of the carpet so that the hemispherical surfaces of the lower portions  146  of the support members  140 ,  143  engage the carpeted floor surface  170 . The hemispherical shape of the lower portions  146  of the support members  140 ,  143  provides a substantially constant resistance to movement of the cleaner head  10  across the carpeted floor surface  170  in any direction, and minimises the resistance to movement of the cleaner head  10  across the carpeted floor surface. As the rolling elements  148  do not protrude beyond the locus described with the curved shape of the lower portions  146  of the support members  140 ,  143 , the rolling elements  148  provide minimal resistance to the movement of the cleaner head  10  over the floor surface  170 . 
     As the support members  140 ,  143  sink into the carpet, the bottom surface of the sole plate  14  comes into contact with the carpeted floor surface  170 . Due to the compression of the flexible skirt  70  located between the housing  12  and the sole plate  14 , further sinking of the support members  140 ,  143  into the carpet causes the guide retaining members  76 ,  82 , which are connected to the housing  12  by the chassis  50 , to move downwardly away from the head portions  78 ,  84  of the guide members  72 ,  80  connected to the sole plate  14 . Consequently, the housing  12  moves relative to the sole plate  14 , which remains located on the upper surface of the carpeted floor surface  170 . Depending on the pile of the carpeted floor surface  170 , some of the fibres of the carpet may protrude through the suction opening  16  as the sole plate  14  sinks slightly into the carpet under its own weight. The dirt and dust within these fibres can be agitated by the rotating brush bar assembly  100  located within the housing  12  and become entrained within the air flow drawn into the suction passage  17 . 
     Thus, only a relatively small amount of force is applied to the sole plate  14  by the housing  12 , thereby preventing the sole plate  14  from being pushed into the pile of the carpet by the housing  12 . In turn, this means that the sole plate  14  does not cause significant resistance to the movement of the cleaner head  10  over the carpeted floor surface  170 , and does not unduly restrict the flow of air into the cleaner head  10 . The lower portions  146  of the support members  140 ,  143  preferably have a radius in the range from 10 to 20 mm so as to not sink so far into the fibres of the carpet that the housing  12  starts to exert a significant force on the sole plate  14  once the fins  86  abut with the lower surface of the guide retaining member  82 . 
     To inhibit lifting of the sole plate  14  away from the carpeted floor surface  170  under the action of the air flow passing beneath the sole plate  14 , the flexible skirt  70  preferably has an elasticity selected so that an amount of the force acting on the housing  12  of the cleaner head  10  is transferred to the sole plate  14  by the compression of the flexible skirt  70 . The amount of this force is preferably less than 10 N, and in the preferred embodiment is between 2 and 7 N. This pushes the sole plate  14  into the carpeted floor surface, resulting in the protrusion of carpet fibres through the suction opening  16  for agitation by the brush bar assembly  100 . 
     The drive mechanism  107  for connecting the brush bar assembly  100  to the motor  104  will now be described with reference to  FIGS. 11 and 12 . The drive mechanism  107  comprises a rotatable input drive member  180 , preferably in the form of a pulley, mounted on the drive shaft  182  of the motor  104  for rotation about the longitudinal axis of the drive shaft  182 . The drive mechanism  107  further comprises a rotatable output drive member  184 , also preferably in the form of a pulley, connected to the input drive member  180  by a drive belt  186 . The axis of rotation of the output drive member  184  is substantially parallel to the axis of rotation of the input drive member  180 . The output drive member  184  is rotatably supported within the drive mechanism housing  108  by a rolling bearing  188 . A first drive dog  190  is mounted on one side of the output drive member  184  for connection to the first brush bar  114 , and a second drive dog  192  is mounted on the opposite side of the output drive member for connection to the second brush bar  116 . 
     The drive mechanism housing  108  is moveable relative to the motor  104  in a direction substantially orthogonal to the axes of rotation of the drive members  180 ,  184 , and so the output drive member  184  is similarly moveable relative to the input drive member  180 . Guide members (not shown) may be provided for restricting the movement of the housing  108  relative to the motor  104  to this direction. 
     A belt tensioning member  194  is located between the drive members  180 ,  184  for tensioning the belt  186  by urging the output drive member  184  away from input drive member  180 . The belt tensioning member  194  is annular, and is mounted on a spigot  196  connected to the drive mechanism housing  108  and located between the rotational axes of the drive members  180 ,  184 . The spigot  196  extends substantially parallel to the rotational axes of the drive members  180 ,  184 . The belt tensioning member  194  is moveable along the spigot  196 . Part of the annular outer surface of the belt tensioning member  194  is shaped to define a wedge-shaped portion  198  which is inclined to the longitudinal axis of the spigot  196 . The wedge-shaped portion  198  of the belt tensioning member  194  is urged against a conformingly wedge-shaped portion  200  of a mounting plate  202  connected to the motor  104  by a resilient member  204  located between the belt tensioning member  194  and a cover  206  of the drive mechanism housing  108 . This causes the resilient member  204  to be urged away from the input drive member  180  by the wedge-shaped portion  200  of the mounting plate  202 . As the belt tensioning member  194  extends about part of the drive mechanism housing  108 , namely the spigot  196 , this results in the drive mechanism housing  108 , and the output drive member  184  supported thereby, being urged away from the input drive member  180  to maintain the belt  186  in a fully tensioned state. 
     The invention is not limited to the detailed description given above. Variations will be apparent to the person skilled in the art.