Abstract:
A filter housing includes an inlet for receiving airflow, a cavity for receiving a filter and an airflow passage between the inlet and the filter. At least one vane is positioned in the airflow passage for partitioning the airflow passage into a plurality of ducts. Each vane has a non-linear shape in the direction of flow through the airflow passage. This helps to reduce acoustic emissions from the machine since sound waves emitted by the fan and/or motor are caused to bounce off the vanes, which allows the vanes to absorb some of the sound energy. The filter housing can form part of a vacuum cleaner.

Description:
FIELD OF THE INVENTION  
   The invention relates to a filter housing. Particularly, but not exclusively, the invention relates to a filter housing for use in a domestic appliance such as a vacuum cleaner. 
   BACKGROUND OF THE INVENTION 
   Vacuum cleaners are required to separate dirt and dust from an airflow. Dirt and dust-laden air is sucked into the appliance via either a floor-engaging cleaner head or a tool connected to the end of a hose and wand assembly. The dirty air passes to some kind of separating apparatus which attempts to separate dirt and dust from the airflow. Many vacuum cleaners suck or blow the dirty air through a porous bag so that the dirt and dust is retained in the bag whilst cleaned air is exhausted to the atmosphere. In other vacuum cleaners, cyclonic or centrifugal separators are used to spin dirt and dust from the airflow (see, for example, EP 0 042 723). Whichever type of separator is employed, there is commonly a risk of a small amount of dust passing through the separator and being carried to the fan and motor unit, which is used to create the flow of air through the vacuum cleaner whilst it is in operation. Also, with the majority of vacuum cleaner fans being driven by a motor with carbon brushes, such as an AC series motor, the motor emits carbon particles which are carried along with the exhaust flow of air. 
   In view of this, it is common for a filter to be positioned after the motor and before the point at which air is exhausted from the machine. Such a filter is often called a ‘post motor’ filter. 
   There is an increasing awareness among consumers of the problem of emissions, which can be particularly problematic for asthma sufferers. Thus, recent vacuum cleaner models are fitted with filters which have a large surface area of filter material, and the filters often comprise several types of filter material and a foam pad. Such filters are physically bulky and housing such filters in the cleaner is quite challenging. A vacuum cleaner called the Dyson DC05, manufactured and sold by Dyson Limited, houses a circular post motor filter beneath the dirt collection bin. Air flows towards a first face of the filter, passes through the filter and exhausts from the machine via a set of apertures in the cover above the filter. 
   U.S. Pat. No. 5,961,677 shows a vacuum cleaner exhaust filter in which air flows out of a central conduit, via a series of openings formed between angled vanes, before passing through an open space to a cylindrical filter which surrounds the central conduit. 
   SUMMARY OF THE INVENTION 
   The present invention seeks to provide an improved filter housing. 
   There is also a desire to increase the rate of flow of air through a vacuum cleaner. A higher rate of flow generally increases both the ability of the cleaner to pick up material from a surface and the ability of the cyclonic separator to separate material from the dirty airflow. However, an increased rate of airflow can cause the machine to be noisy in operation. It is possible to place acoustically absorbent material in the path of the exhaust air, but this increases the resistance of the path seen by the airflow. This has a detrimental effect on the overall rate of airflow through the machine in addition to adding both weight and cost to the machine. 
   Accordingly, the present invention provides a filter housing comprising an inlet for receiving an airflow, a cavity for receiving a filter, an airflow passage between the inlet and the cavity and at least one vane positioned in the airflow passage for partitioning the airflow passage into a plurality of ducts, wherein each vane has a non-linear shape in the direction of flow through the duct. 
   The non-linear vanes serve to reduce acoustic emissions from the machine since sound waves emitted by the fan and/or motor are caused to bounce off the vanes, which allows the vanes to absorb some of the sound energy. Thus, a reduction in noise is achieved without the use of dedicated noise reduction structures. 
   Although this invention is described in relation to a cylinder (canister) vacuum cleaner, it will be apparent that it can be applied to other kinds of vacuum cleaner, domestic appliances or machines which use a filter of some kind. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention will now be described with reference to the accompanying drawings in which: 
       FIG. 1  is a perspective view of a vacuum cleaner in which a filter housing according to the invention is embodied; 
       FIGS. 2 and 3  are side views of the vacuum cleaner of  FIG. 1 , showing some of the internal components of the cleaner; 
       FIG. 4  shows the filter housing of the vacuum cleaner of  FIGS. 1 to 3 ; 
       FIG. 5  shows the chassis of the vacuum cleaner and the conduit leading to the filter housing of  FIG. 4 ; 
       FIG. 6  is a plan view of the lower part of the filter housing of  FIG. 4 ; 
       FIGS. 7 and 8  illustrate the effect of vanes in reducing swirl in the airflow; 
       FIGS. 9 and 10  illustrate the effect of the shape of the vanes in the filter housing of  FIG. 6 ; and 
       FIG. 11  is a plan view of an alternative embodiment of the lower part of the filter housing. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 to 3  show an example of a vacuum cleaner  10  in which the invention is embodied. The vacuum cleaner  10  is a cylinder or canister type of vacuum cleaner comprising a chassis  12  with wheels  13 ,  15  for allowing the chassis  12  to be moved across a surface to be cleaned. The chassis  12  supports a chamber  20  which serves as a separator for separating dirt, dust and other debris from an airflow and also as a collector for the separated material. While a cyclonic separator is shown here, the separator can take any form and this is not important to the invention. Chamber  20  is removable from the chassis  12  such that a user can empty the chamber  20 . Although not shown for reasons of clarity, a hose connects to inlet  14  of the vacuum cleaner  10  and a user can fit a wand or tools to the distal end of the hose for use in cleaning various surfaces. 
     FIGS. 2 and 3  show some of the internal components of the vacuum cleaner  10  of  FIG. 1 . The chamber  20  communicates with the inlet  14  through which an airflow can enter the chamber in a tangential manner. The chamber  20  has an apertured shroud  21  mounted centrally within it. The region  22  externally of the shroud  21  forms a first cyclonic separation stage. The apertures  23  in the shroud  21  communicate with a second cyclonic separation stage comprising a set of frusto-conical separators  25  arranged in parallel. The outlets of the second stage separators  25  are connected, via a duct  29 , to a housing for a pre-motor filter  30 . The pre-motor filter  30  serves to trap any fine dust or microscopic particles which have not been separated by the two cyclonic separation stages  22 ,  25 . The downstream side of the pre-motor filter  30  communicates with a fan and motor housing  48 . This housing  48  accommodates an impeller  45  which is driven by a motor  40 . The outlet of the housing  48  communicates, via an aperture  50 , with a filter housing  60 . The filter housing  60  houses a post-motor filter  70  which serves to trap any particles remaining in the airflow, as well as carbon particles emanating from the motor  40 . The downstream side of the filter housing  60  communicates with an exhaust duct  90  having outlet apertures  95  at its furthest end. 
   The filter housing  60  will now be described in more detail with reference to  FIG. 4 . The filter housing  60  comprises a lower part  61 , which in this embodiment forms part of the chassis  12  of the vacuum cleaner  10 , and an upper part  62 . The upper part  62  fits removably to the lower part  61  by means of lugs  64  and a snap fastener  67 . Other types of fastener could, of course, be used. The lower part  61  defines an airflow passage which communicates at its upstream end with the aperture  50  which forms the outlet from the housing  48 . The space between the lower part  61  and the upper part  62  defines a cavity for housing the filter  70 . The upper part  62  has an outlet branch  63  which mates, in an airtight manner, with the lower end of the exhaust duct  90 . 
   A plurality of vanes  65   a ,  65   b ,  65   c  are located in the airflow passage. Two of the vanes  65   a ,  65   b  extend from the aperture  50  and into the area of the airflow passage which lies adjacent the cavity for receiving the filter  70 . In this area, the vanes  65   a ,  65   b  extend from the lower part  61  towards the upper part  62  so that they lie adjacent, or even contact, the filter  70 . A third vane  65   c  extends from the aperture  50  towards the area of the airflow passage which lies adjacent the cavity for receiving the filter  70  but terminates immediately before the said area. Three separate ducts  51 ,  52 ,  53  are formed between the vanes  65   a ,  65   b ,  65   c.    
   The vanes  65   a ,  65   b ,  65   c  serve to guide the airflow passing through the vacuum cleaner  10  to and from the filter  70 . The vanes  65   a ,  65   b ,  65   c  extend from the outlet  50  of the motor housing  48  along the lower surface of part  61 . The vanes  65   a ,  65   b  continue beneath the area where filter  70  is located. The vanes  65   a ,  65   b ,  65   c  have two uses: firstly they serve to distribute airflow across the surface of the filter  70  in a reasonably uniform manner, and secondly their non-linear shape serves to attenuate sound from the impeller  45 . Referring to  FIG. 5 , the vanes  65   a ,  65   b ,  65   c  divide outlet  50  into six apertures  51   a ,  51   b ,  52   a ,  51   b ,  53   a ,  53   b . In use, this causes the flow of air from the impeller  45  to be divided into six separate flows. Each aperture  51   a ,  51   b ,  52   a ,  52   b ,  53   a ,  53   b  forms an inlet to one of the ducts  51 ,  52 ,  53 . Each duct  51 ,  52 ,  53  communicates with a distinct and separate portion of the surface area of the filter  70 . The height of each vane  65   a ,  65   b  is chosen such that the distal edges thereof lie adjacent, and preferably touch, the surface of the filter  70  when the filter is fitted in the filter housing  60 . Thus, each duct  51 ,  52 ,  53  communicates with a separate and distinct portion of the filter  70  so that air flowing along each duct  51 ,  52 ,  53  is constrained to flow through the respective portion of the filter  70 . 
   Referring again to  FIG. 2  it can be seen that the upstream surface of the filter  70  lies, in use, at an acute angle (approximately 10°) with respect to the incoming airflow from the motor housing  48 . The division of the airflow into separate portions in the manner just described helps to distribute the airflow evenly across the surface of the filter  70 , even though the arrangement of the filter  70  with respect to the incoming airflow is not ideal for even distribution. It is particularly beneficial that each duct  51 ,  52 ,  53  serves a portion of the filter surface which is a different distance from the inlet  50 ; i.e. duct  51  serves the remote portion of the filter  70 , duct  52  the middle section, and duct  53  the nearest portion of the filter surface  70 . 
     FIG. 6  shows the lower part  61  of the filter housing  60  in plan view. The path taken by the airflow along part of the duct  52  is shown by arrow  85  while the path taken by sound waves is shown by arrow  86 . Due to the shape of the vanes  65   a ,  65   b , it can be seen that the sound waves are forced to bounce between the vanes  65   a ,  65   b  on multiple occasions or at the very least provide an obstruction to sound waves emanating from the motor housing  48 . Vanes  65   a ,  65   b ,  65   c  can be moulded or otherwise formed integrally with the lower part  61  of the filter housing  60  or they can be provided as a separate part or set of parts which locate within the lower part  61  of the filter housing  60 . 
   The provision of the vanes  65   a ,  65   b ,  65   c  described above is also particularly beneficial where the airflow inlet  50  is off-centre with respect to the filter housing  60 .  FIG. 7  shows the expected airflow without the presence of vanes of this sort. Air enters the filter housing  60  and swirls around the housing. This swirling airflow can cause added noise and can further reduce suction power.  FIG. 8  shows the effect of positioning vanes  65   a ,  65   b  within the filter housing  60 . Air entering the filter housing  60  is now unable to swirl to any noticeable degree. 
   The shape of the vanes  65   a ,  65   b ,  65   c  ensures a smooth transition between directions and section changes which helps to avoid ‘break away’ and turbulence which increase noise and back pressure. It is particularly desirable to minimise back pressure in a vacuum cleaner as it reduces suction power.  FIGS. 9 and 10  show the effect of ‘break away’ airflow by contrasting a smoothly curved duct ( FIG. 9 ) with a duct which is curved too sharply ( FIG. 10 ). 
   The position of the vanes  65   a ,  65   b ,  65   c  within the outlet aperture  50  of the motor housing  48  is chosen such that the cross sectional area of the inlet to each duct  51 ,  52 ,  53  is substantially proportional to the surface area of the filter portion served by that duct. This helps to ensure that the airflow is evenly distributed across the filter surface. The provision of two inlets to each duct (e.g. inlets  51   a ,  51   b  to duct  51 ) also helps to balance the airflow to the filter. 
   Filter  70  is shown here as a pleated filter, in which a cylindrical plastic case houses a pleated structure  72 . Other types of filter, e.g. a simple foam pad filter, could be used in place of what has been shown here. Preferably the post-motor filter is a HEPA (High Efficiency Particulate Air) filter. 
     FIG. 11  shows a plan view of an alternative embodiment of the lower part  61  of the filter housing  60 . In this embodiment, a set of vanes  165   a - 165   e  are positioned in a different manner to that shown in  FIG. 6 . Here, the vanes  165   a - 165   e  extend outwardly from the outlet aperture  50  of the motor housing  48  towards the furthermost side of the lower part  61  of the filter housing  60 . As before, this arrangement of vanes divides the area beneath the filter  70  into a plurality of ducts  151 - 156 , each duct communicating with a different portion of the filter surface. Each vane has a non-linear, sinuous shape which enhances the likelihood of sound waves colliding with at least one of the vanes. In use, incoming airflow will be divided into a plurality of separate portions, each portion flowing along a respective duct. As before, the cross-section of each inlet is proportional to the filter area served by the inlet. 
   The operation of the vacuum cleaner will now be described. In use, air is drawn by the motor-driven impeller  45 , through any floor tool and hose into inlet  14  of the vacuum cleaner  10 . The dirty air passes through the cyclonic separation stages  22 ,  25 , during which dirt and dust is removed from the airflow in a manner which is well documented elsewhere. Air flows from the outlet of cyclones  25 , along duct  29 , through pre motor filter  30  and into the motor housing  48 . Exhaust air is blown towards the aperture  50  and is there divided into six portions by the leading edges of the vanes  65   a ,  65   b ,  65   c . The divided portions of the airflow flow along the three ducts  51 ,  52 ,  53 . As described above, acoustic waves bounce along the ducts  51 ,  52 ,  53  between opposing vanes  65   a ,  65   b . Airflow from the ducts  51 ,  52 ,  53  then passes through the portion of the post-motor filter  70  with which each respective duct  51 ,  52 ,  53  communicates. After passing through the filter  70 , air passes to the inlet to the exhaust duct  90 . Some of the air vents to atmosphere via apertures  80  in the upper face of the filter housing part  62  (see arrows  82 ,  FIG. 3 ). The remainder of the air flows along the exhaust duct  90 . As the air flows along the exhaust duct  90 , it slows down because the duct  90  widens in the direction of flow. This air vents to atmosphere via apertures  95  (see arrows  85 ,  FIG. 3 ).