Abstract:
A debris blowing and/or vacuum appliance. The appliance comprises a body including a fluid inlet, a fluid outlet for exhausting fluid externally of the body, a volute located in a flowpath between the fluid inlet and the fluid outlet and a centrifugal impeller located within the volute and rotatable by a motor to generate a flow of fluid, and a diffuser located immediately downstream of the centrifugal impeller between the centrifugal impeller and a volute outlet region. The diffuser comprises an annular channel surrounding the centrifugal impeller and has substantially constant radial width such that the impeller is radially spaced from the volute walls by at least the width of the diffuser. By providing such an arrangement, the efficiency of the impeller can be improved.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a blower vacuum, vacuum or blower appliance. More particularly, the present invention relates to a blower vacuum, vacuum or blower appliance having improved efficiency. 
         [0002]    In general, blower vacuum appliances comprise a motor and fan arrangement. The motor is usually either petrol or electrically powered. The fan comprises a centrifugal impeller enclosed within a toroidal enclosure known as a volute. The impeller is configured, in use, to draw air in along the axis of rotation of the centrifugal impeller and expel air out radially. The volute comprises a fluid inlet surrounding the eye of the impeller and aligned with axis of rotation of the impeller, and a fluid outlet located at a point on the periphery of the volute. The shape of the volute essentially directs the radially-moving air towards the fluid outlet. 
         [0003]    Blower vacuum appliances generally have two modes of operation: blowing and vacuuming. In the blowing mode, clean air is drawn into the volute from the atmosphere via the fluid inlet and is expelled via the fluid outlet. A blower tube is attached to the outlet in order to focus and direct the expelled air into a jet. This jet of air may be aimed through manipulation of the blower tube or blower vacuum to move or gather garden waste. 
         [0004]    When in the vacuuming mode, garden waste may be collected up a suction tube connected to the blower vacuum. There are two common structural arrangements for a blower vacuum appliance having a vacuum mode: dirty fan and clean fan configurations. 
         [0005]    In a dirty fan arrangement, a suction tube having a suction inlet is connected to the fluid inlet of the volute and a debris collector (which may comprise separation means such as a semiporous bag or container) for garden waste is attached in direct fluid connection to the fluid outlet of the volute. Therefore, in this arrangement, the fan is located directly in the flowpath from the suction inlet to the debris collector. Consequently, garden waste or debris entrained in the air passing into the suction inlet passes through the fluid inlet of the volute and collides with the fan before being passed via the fluid outlet of the volute into the debris collector. This arrangement enables garden waste or debris to be broken down or mulched into smaller particles for efficient collection in the debris collector. 
         [0006]    In a clean fan arrangement, a debris collector (which may comprise separation means such as a semi-porous bag or container) for garden waste is also attached in direct fluid connection to the fluid outlet of the volute. However, in contrast, a suction tube comprising a suction inlet is connected downstream of the fluid outlet of the volute. 
         [0007]    Therefore, in the same manner as for the blowing mode, in use air is drawn into the fluid inlet of the volute from the atmosphere and expelled from the volute through the fluid outlet towards the debris collector. The flow of air from the fluid outlet and into and through the debris collector causes a pressure differential between the proximal and distal ends of the suction tube. This causes air to be drawn into the suction inlet, through the suction tube and into the debris collector. Consequently, any garden waste or debris entrained in the air passing into the suction tube will be deposited into the debris collector. 
         [0008]    This arrangement has the advantage that the fan is supplied with a clean stream of air at all times and so can operate under optimal conditions with relatively little chance of blockages forming. 
         [0009]    An alternative arrangement of device is simply a blower appliance without a vacuum function. This arrangement operates in the same manner as the blower mode of the clean fan arrangement. Clean air is drawn into a volute from the atmosphere via afluid inlet and is expelled via a fluid outlet. A blower tube attached to the fluid outlet focuses and directs the expelled air into a jet. This jet of air may be aimed through manipulation of the blower tube or blower vacuum to move or gather garden waste. 
         [0010]    Blower vacuum and/or blower appliances are often required to generate high flow rates of air through the impeller to produce a powerful jet of air (in the blower mode) or powerful suction (in the vacuum mode, where appropriate) in order to clear an external environment of debris and waste. Therefore, it is beneficial to minimise losses in the appliance in order to maximise the available airflow. 
         [0011]    Commonly, in a volute arrangement comprising a centrifugal impeller, air is directed through the eye of the impeller and is then directed radially outwardly therefrom. From the outlet of the impeller, the airflow passes into a volute which directs the airflow to an outlet. However, in conventional arrangements, the location of the impeller with regard to the walls of the volute mean that the pressure distribution created at the outlet to the impeller may not be constant. This reduces the efficiency of the impeller. As a result, there is a need in the art to provide an impeller arrangement which has lower losses than known arrangements. 
       SUMMARY OF THE INVENTION 
       [0012]    According to a first aspect of the present invention, there is provided a debris blowing and/or vacuum appliance comprising a body including: a fluid inlet; a fluid outlet for exhausting fluid externally of the body; a volute located in a flowpath between the fluid inlet and the fluid outlet; and a centrifugal impeller located within the volute and rotatable by a motor to generate a flow of fluid between the fluid inlet and the fluid outlet, the volute comprising: volute walls delimiting a volute outlet region in communication with the fluid outlet; and a diffuser located immediately downstream of the centrifugal impeller between the centrifugal impeller and the volute outlet region, the diffuser comprising an annular channel surrounding the centrifugal impeller and having substantially constant radial width such that the impeller is radially spaced from the volute walls by at least the width of the diffuser. 
         [0013]    By providing such an arrangement, the efficiency of the impeller can be improved. The use of such a diffuser configuration in an appliance enables the pressure drop across the impeller to be substantially even around the circumference thereof, improving the performance of the impeller. In a debris blowing and/or vacuum appliance, this enables a greater airflow to be supplied per unit of supplied power. Therefore, an appliance having improved performance for blowing and/or vacuuming dirt and debris can be provided without, for example, increasing power consumption. This is of relevance to battery powered appliances, where improved efficiency may provide stronger performance and a longer operating run time for a given battery size and charge. 
         [0014]    In one embodiment, the diffuser is vaneless. A vaneless diffuser is particularly efficient for guiding an airflow from an impeller to the volute outlet region. 
         [0015]    In one embodiment, the diffuser comprises planar annular walls defining the annular channel. By providing planar annular walls, losses in the diffuser are minimised. 
         [0016]    In one embodiment, the volute walls define a volute outlet region having an expanding cross-sectional area in the downstream direction. By providing an outlet region with an expanding cross-sectional area, the pressure of the air moving towards the outlet can be reduced. 
         [0017]    In one embodiment, the cross-sectional area increases smoothly in the downstream direction. This arrangement reduces losses due to sudden volume changes as the air moves downstream of the impeller. 
         [0018]    In one embodiment, the volute walls define a scroll-type volute outlet region having a substantially circular cross section. Such an arrangement provides an efficient configuration with reduced losses. 
         [0019]    In one embodiment, the volute outlet region further comprises a tangential portion extending downstream towards the fluid outlet. By providing such a tangential portion, the airflow can be directed into a linear stream to be passed to the fluid outlet. 
         [0020]    In one embodiment, the volute further comprises a volute tongue delimiting at least a part of the tangential portion. 
         [0021]    In one embodiment, the volute tongue is radially spaced from the impeller by a distance at least equal to the width of the diffuser. By spacing the volute tongue from the impeller by at least the width of the diffuser, localised pressure drops can be reduced downstream of the impeller outlet. This improves the efficiency of the impeller. 
         [0022]    In one embodiment, the appliance is in the form of a vacuum appliance or a combined debris blowing and vacuum appliance, wherein the fluid inlet comprises a suction inlet arranged, in use, to draw dirt and debris therethrough. Such a configuration is an efficient device for cleaning and/or directing debris and waste from an area such as, for example, a garden. 
         [0023]    In one embodiment, the appliance further comprises a suction tube, the suction inlet being located at a distal end of the suction tube. The suction tube enables a dire- and debris-entrained stream of air to be drawn efficiently into the appliance. 
         [0024]    In one embodiment, the centrifugal impeller is arranged, in use, to receive and to mulch dirt and debris drawn in through the suction inlet. By providing such an arrangement, dirt and debris can be mulched (i.e. broken up) by the impeller into smaller sections. This enables the dirt and debris leaving the appliance to be packed more tightly and efficiently. 
         [0025]    In one embodiment, the appliance further comprises a debris collector located downstream of the fluid outlet and arranged, in use, to collect dirt and debris drawn in through the suction inlet. This enables the dirt and debris drawn into the appliance to be captured securely for disposal. 
         [0026]    In one embodiment, the appliance is in the form of a debris blowing appliance and further comprises a blower tube, the fluid outlet being located at a distal end of the blower tube. The blower tube enables a concentrated stream of air to be directed accurately as required by a user of the appliance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which: 
           [0028]      FIG. 1  is a side view showing the general configuration of a blower appliance; 
           [0029]      FIG. 2  is a side view showing the general configuration of a blower vacuum appliance; 
           [0030]      FIG. 3  is a cross-sectional view of a volute according to an embodiment of the present invention; 
           [0031]      FIG. 4  is a sectional plan view of the volute of  FIG. 3 ; 
           [0032]      FIG. 5  is a perspective view of part of the volute of  FIG. 3 ; 
           [0033]      FIG. 6  is a perspective view of an impeller according to an embodiment of the present invention; 
           [0034]      FIG. 7  is a perspective view showing the impeller of  FIG. 6  located in a part of the volute of  FIG. 3 ; and 
           [0035]      FIG. 8  is a detailed cross-sectional view of a part of the volute of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]    The present invention provides an impeller and volute arrangement which reduces inlet losses to the impeller when compared to known arrangements. Barrier means provided on the shroud of an impeller are located in close relationship with a complementary portion of the volute adjacent the air inlet. 
         [0037]    The interaction between these components defines a convoluted or labyrinthine pathway between the shroud and the volute housing, reducing the likelihood of air passing therebetween and improving the flow of air into the eye of the impeller. 
         [0038]    The general configuration of a blower appliance and a blower vacuum appliance will now be described with reference to  FIGS. 1 and 2 . 
         [0039]      FIG. 1  shows an example of a blower (or sweeper) appliance  10  in which embodiments of the present invention may be used. The blower appliance  10  is an electrically-powered appliance which comprises a battery pack. However, alternatively the blower appliance  10  may be mains-powered or comprise an internal combustion engine and fuel tank. 
         [0040]    The blower appliance  10  comprises a body  12  which may be formed from a hardened plastic material. The body  12  comprises a volute  14  and a graspable handle  16 . A removable power source  18  (in the form of a battery pack) is located at the base of the handle  16 . 
         [0041]    The volute  14  is essentially disc shaped and houses a motor and impeller arrangement (not shown in  FIG. 1 ) for generating an airflow through the blower appliance  10 . The volute  14  comprises an air inlet  20  located at the centre of the disc-shaped volute  14  and an air outlet  22  extending tangentially away from the disc shaped portion of the volute  14 . 
         [0042]    The impeller is operable to draw an airflow through the air inlet  20  and exhaust the airflow through the air outlet  22 . The air inlet  20 , as shown, is covered by a grille or cover  24  which prevents a user contacting rotating parts located therein. The spacing of the grille  24  is such to prevent insertion of a human finger according to existing safety standards. 
         [0043]    A detachable blower tube  26  is connected to the air outlet  22  and comprises an exhaust outlet  28  at a distal end thereof. The blower tube  26  narrows from the adjacent the air outlet  22  to the exhaust outlet  28  to focus and direct the airflow into a powerful jet. 
         [0044]    A blower vacuum appliance  30  is shown in  FIG. 2  in which embodiments of the present invention may be used. The blower vacuum appliance  30  is similar in configuration to the blower appliance  10  of  FIG. 1  and is an electrically-powered appliance which comprises a battery pack. 
         [0045]    The blower vacuum appliance  30  comprises a body  32  comprising a volute  34  and a graspable handle  36 . A removable power source  38  (in the form of a battery pack) is located at the base of the handle  36 . 
         [0046]    The volute  14  is essentially the same as that of the blower appliance  10  and houses a motor and impeller arrangement (not shown in  FIG. 2 ) for generating an airflow through the blower vacuum appliance  30 . However, in this instance, the blower vacuum appliance  30  is a dirty-fan arrangement and so the impeller is configured to receive debris and mulch the debris. 
         [0047]    The volute  34  comprises an air inlet  40  located at the centre of the disc-shaped volute  34  and an air outlet  42  extending tangentially away from the disc shaped portion of the volute  34 . In this arrangement, a suction tube  44  is connected to the air inlet  40  and comprises a suction inlet  46  at a distal end thereof. The suction tube  44  is configured to draw air and entrained debris through the suction inlet  46  and into the volute  34  where the debris is mulched. 
         [0048]    A debris collector  48  is connected directly to the air outlet  42  and provides a collection receptacle for the mulched debris passed through the volute  34 . The debris collector  48  is semi-porous so that air can escape therethrough and may comprise, for example, a nylon bag or other collection means. 
         [0049]    The blower vacuum appliance  30  as described above is shown in a vacuum mode of operation. In order to operate in a blower mode, the suction tube  44  can be detached and connected to the air outlet  42  in the manner of the blower appliance  10 . A grille (not shown) can then be connected to the air inlet. 
         [0050]      FIGS. 3 to 7  show the arrangement according to the present invention.  FIGS. 3 to 7  shows a section through a volute assembly  100  according to an embodiment of the present invention. 
         [0051]    Referring to  FIGS. 3 to 6 , the volute assembly  100  comprises first and second clamshell portions  102 ,  104 . The clamshell portions  102 ,  104  define a central hub  106  and a scroll portion  108  located outwardly of the hub  106 . 
         [0052]    The hub  106  comprises an air inlet  110  located centrally at an upper portion thereof. The air inlet  110  is covered by a grille  112 . An impeller  200  is located at the centre of the hub  106  in communication with the air inlet  110 . The impeller  200  is mounted on a drive shaft  202  connected to a motor  204 . The impeller  200 , in use, is operable to rotate on the drive shaft  202  about an axis X-X which is coincident with the centre of the hub  106 . 
         [0053]    A diffuser  114  is located radially outwardly, and downstream, of the impeller  200  and comprises an annular channel delimited by two diffuser walls  116 ,  118 . The diffuser  114  is located between the hub  106  and the scroll portion  108  of the volute  100  and has a narrower height that either the hub  106  or the scroll region  108 . 
         [0054]    The diffuser  114  is vaneless. That is to say no vanes, projections or guides are located in the annular channel comprising the diffuser  114  and the diffuser  114  essentially comprises a substantially smooth annular channel defined by the two planar, spaced apart annular walls  116 ,  118 . The diffuser  114  is symmetrical about the axis X-X and has a constant height and width. 
         [0055]    The scroll portion  108  is located in the flowpath immediately downstream of the diffuser  114 . The scroll portion  108  comprises a spiral, scroll cavity  120  defined by volute walls  122 . The volute walls  122  have a circular cross section which increases smoothly in diameter in an anticlockwise direction (as shown in  FIG. 4 ) from a position adjacent a volute tongue  124  located adjacent the outer portion of the diffuser  114  to terminate in an air outlet  126 . In other words, the cross-sectional area of the volute outlet portion (scroll cavity  120 ) increases smoothly and constantly in the downstream direction towards the air outlet  126 . 
         [0056]    The air outlet  126  is formed at a distal end of a tangential section  128  of the scroll portion  108 . As shown in  FIG. 4 , the volute tongue  124  delimits a portion of the tangential section  128  leading to the air outlet  126 . 
         [0057]    As shown in  FIGS. 3 and 4 , the diffuser  114  functions to space the impeller  200  radially from the walls  122  of the scroll cavity  120 . The impeller  200  is spaced radially from the walls  122  by at least the width of the diffuser walls  116 ,  118 . This arrangement ensures that the pressure distribution at the outlet of the impeller  200  is substantially constant around the circumference of the impeller  200 . This prevents localised pressure variations, improving the efficiency of the impeller  200 . 
         [0058]    The impeller  200  will now be described in detail with reference to  FIGS. 6 to 8 . In  FIG. 6 , the impeller  200  is shown removed from the volute arrangement  100 . In  FIG. 7 , the impeller  200  is shown located on the lower clamshell portion  104  with the upper clamshell portion  102  removed. 
         [0059]    The impeller  200  includes a base  206 , a shroud  208  and a plurality of fan blades  210  located therebetween. The base  206  extends radially from the axis X-X of the drive shaft  202  parallel to the diffuser  114 . The fan blades  210  extend perpendicularly from the base  206  and are curved for aerodynamic efficiency. The shroud  208  delimits an axially-arranged inlet  212  to the eye of the impeller  200 . When fitted in the volute  100 , the inlet  212  to the impeller  200  is co-axial with, and located adjacent, the air inlet  110  formed in the hub  106  of the volute  100 . 
         [0060]    The shroud  208  comprises barrier means  214  located on a surface thereof facing away from the base  206 . The barrier means  214  comprise two annular ribs  216 ,  218  which project away from the shroud  208  and surround the inlet  212 . The innermost annular rib  216  forms a part of the boundary wall delimiting the inlet  212 . 
         [0061]    The annular ribs  216 ,  218  define an annular channel  220  therebetween. This is shown in  FIG. 8 .  FIG. 8  shows a cross-sectional view (similar to  FIG. 3 ) through the volute  100  showing the impeller located in the hub  106  of the volute  100 . 
         [0062]    As shown in  FIG. 8 , a complementary annular volute rib  130  is formed on the inner surface of the wall of the hub  106  of the volute  100 . The annular volute rib  130  extends into the annular channel  220  formed by the annular ribs  216 ,  218 , defining a convoluted or labyrinthine path from the air inlet  110  through the annular channel  220 . 
         [0063]    The volute rib  130  is spaced from the annular ribs  216 ,  218  in both axial and radial directions to ensure that, in use, tolerances are sufficient to prevent contact between the volute rib  128  and the annular ribs  216 ,  218  (which will be rotating with the impeller  200 ). 
         [0064]    As shown in  FIG. 8 , an internal inlet wall  132  of the inlet  110  is located at the same radial spacing as the inner annular wall  216  to define an essentially smooth (with the exception of the necessary axial spacing between the annular wall  216  and the internal inlet wall  132 ) inlet flowpath for air entering the inlet  110  and passing through the inlet  212  into the eye of the impeller  200 . 
         [0065]    In use, when the motor  204  is activated by a user, the drive shaft  202  will be caused to rotate. The impeller  200 , which is secured to the drive shaft  202 , will also be caused to be rotated. Thus, an airflow is drawn in through the volute inlet  110  and through the inlet  212  of the impeller  200 . The air is then guided onto the fan blades  210  where it is accelerated and dispersed radially outwardly by the fan blades  210 . This causes a pressure drop across the impeller  200  since the air downstream of the impeller  200  is moving faster than the upstream airflow. This, in turn, causes further air to be drawn into the volute inlet  110  and into the impeller  200 . 
         [0066]    In conventional centrifugal impeller arrangements, the pressure drop at the outlet of the impeller may not be substantially constant around the circumference of the impeller. This is due to the varying radial distance between the outlet of the impeller and the walls of the volute in conventional arrangements. This reduces the efficiency of the impeller. 
         [0067]    However, in the present invention, the provision of the vaneless diffuser  114  provides a constant-width outlet region with no projections or unnecessary contact surfaces to disturb the airflow exiting the impeller. The pressure drop at the impeller outlet is, thus, substantially constant around the circumference of the impeller  200 . As a result, the impeller  200  is able to operate at a high efficiency. 
         [0068]    The airflow then passes through the fan blades  210 , across the diffuser  114  and is exhausted into the scroll portion  108  of the volute  100 . The airflow is then directed around the volute walls  122  towards the tangential portion  128  and through the air outlet  126 . 
         [0069]    Variations of the above embodiments will be apparent to the skilled person. The precise configuration of components may differ and still fall within the scope of the present invention. 
         [0070]    Whilst the above embodiment has been described with reference to a “clean fan” impeller arrangement, the invention is equally applicable to “dirty fan” impeller arrangements in which dirt and debris is drawn into the impeller inlet and broken up (or mulched) by the impeller before being passed out of the impeller outlet into the volute outlet region and out of the fluid outlet. The mulched dirt and debris may then be collected in a suitable debris collector such as a semi-porous bag. 
         [0071]    Further, whilst the present invention has been described with reference to blower or blower vacuum appliances generally for use in a domestic environment, the invention is readily applicable to other machines comprising centrifugal impellers. For example, the present invention is equally applicable to a domestic or industrial vacuum cleaner. 
         [0072]    Embodiments of the present invention have been described with particular reference to the examples illustrated. While specific examples are shown in the drawings and are herein described in detail, it should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular form disclosed. It will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.