Abstract:
A portable room air cleaner including a frame; at least one motor connected to the frame; at least two rotatable axial flow fans connected to the at least one motor; and a filter connected to the frame. The fans are rotated by the motor to additively build static air pressure in series for entry of the air into the filter.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an air cleaning system and, more particularly, to a multi-stage fan system for use in an air cleaning system.  
           [0003]    2. Brief Description of Prior Developments  
           [0004]    Most room air purifiers use a “squirrel cage” blower type of fan system which comprises a centrifugal flow fan. A problem exists with these types of systems in that they are relatively noisy for the amount of air being moved. A conventional axial fan could deliver more air flow at lower noise levels, but a conventional axial fan cannot develop enough static pressure for effective use with a filter in a room air purifier. There is a desire to provide a room air purifier which can provide a greater air flow and greater static pressure at a given noise level than conventional room air cleaners.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with one aspect of the present invention, a portable room air cleaner is provided including a frame; at least one motor connected to the frame; at least two rotatable axial flow fans connected to the at least one motor; and a filter connected to the frame. The fans are rotated by the motor to additively build static air pressure in series for entry of the air into the filter.  
           [0006]    In accordance with another aspect of the present invention, a portable room air cleaner is provided comprising a frame; a single motor connected to the frame; at least two spaced fans operably connected to the single motor; and a filter connected to the frame.  
           [0007]    In accordance with one method of the present invention, a method of moving air in a portable room air cleaner is provided comprising steps of rotating a first fan by a motor to propel air through a first stage of the portable room air cleaner; and rotating a second fan by the motor to propel air from the first stage through a second stage of the portable room air cleaner and into a filter of the air cleaner. The sequential multistage propulsion of air allows an increase in static air pressure for entry of the air into the filter without substantial noise from the rotating first and second fans. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein:  
         [0009]    [0009]FIG. 1 is a perspective view of a room air cleaner incorporating features of the present invention;  
         [0010]    [0010]FIG. 2 is a cross sectional view of the air cleaner shown in FIG. 1;  
         [0011]    [0011]FIG. 3 is a perspective view of the air cleaner shown in FIG. 1 with the inlet cover removed;  
         [0012]    [0012]FIG. 4 is a schematic cross-sectional view of an alternate embodiment of the present invention; and  
         [0013]    [0013]FIG. 5 is a cross sectional view of another alternate embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    Referring to FIG. 1, there is shown a perspective view of a room air cleaner  10  incorporating features of the present invention. Although the present invention will be described with reference to the embodiments shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used.  
         [0015]    Referring also to FIG. 2, the room air cleaner  10  generally comprises a frame  12 , a motor  14 , two fans  16 ,  18  and a filter  20 . In alternate embodiments, the room air cleaner could comprise additional or alternative components. In the embodiment shown, the room air cleaner  10  is a portable room air cleaner intended to be relatively easily relocated by a user to a desired position in a room. However, in alternate embodiments, the air cleaner  10  could be adapted to be located in a window opening or other semi-fixed or fixed position, such as in a non-portable air cleaner.  
         [0016]    The frame  12  generally comprises an inlet  22 , and outlet  24 , and a carry handle  26 . In an alternate embodiment, the carry handle  26  might not be provided. In the embodiment shown, the inlet  22  is located at an opposite end of the frame from the outlet  24 . However, in alternate embodiments, the outlet could be located at any suitable side(s) of the frame. In the embodiment shown, the frame  12  establishes a generally straight air conduit path between the inlet  22  and the outlet  24 . However, in alternate embodiments, the air conduit path through the frame  12  could be non-straight. In the embodiment shown, the frame  12  is generally adapted to be located on a floor, but could be located on a desktop or other suitable location.  
         [0017]    In the embodiment shown, the inlet  22  and outlet  24  comprise removable covers  23 ,  25 . However, in alternate embodiments, the covers  23 ,  25  might not be removable. The covers  23 ,  25  each comprise protective gratings  28  with holes therethrough to allow air to enter and exit the frame  12 , but prevent a user&#39;s fingers from inadvertently entering into the frame  12 . In alternate embodiments, the inlet and outlet could have any suitable type of shapes for allowing air to flow therethrough. The frame  12  forms a main air flow channel  34  and a filter receiving area  36  between the inlet  22  and the outlet  24 . The filter receiving area  36  is located proximate the outlet  24 .  
         [0018]    Referring also to FIG. 3, the inlet end of the air cleaner  10  is shown with the inlet cover  23  removed. The motor  14  is preferably an electric motor which can be attached to an electrical outlet by a plug  30 . The motor  14  is fixedly connected to the frame by support brackets  32 . The support brackets  32  allow the motor  14  to be supported in the center of the main air flow channel  34 . However, in alternate embodiments, the motor  14  could be supported on the frame  12  in any suitable position and in any suitable manner.  
         [0019]    The motor  14  comprises a drive shaft  38 . In the embodiment shown, the drive shaft  38  extends from the motor  14  on two opposite sides. The first fan  16  is directly fixedly attached to a first end  38   a  of the drive shaft. The second fan  18  is directly fixedly attached to the opposite second end  38   b  of the drive shaft. Thus, as the motor  14  rotates the drive shaft  38 , the motor will rotate both the first and second fans  16 ,  18 .  
         [0020]    The first and second fans  16 ,  18 , in the embodiment shown, are both axial flow fans. In a preferred embodiment, the fans  16 ,  18  have “high pitch” axial fans blades such as having a pitch of about 30%-40%. However, any suitable pitch could be provided. The two fans  16 ,  18  could be substantially the same as each other, or could be different from each other. Any suitable type of axial flow fans could be used. For example, the fans could comprise three, five or seven fan blades. In the embodiment shown, the main air flow channel  34  has a substantially uniform shape along its length. However, in an alternate embodiment, the cross sectional flow path of the main air flow channel  34  could change along its length, such as becoming narrower or larger proximate the second fan  18 . In a preferred embodiment, the first fan  16  has a pitch of about 30% and the second fan has a pitch of about 40%, but any suitable percentages or ratio of percentages could be provided.  
         [0021]    As noted above, the frame  12  comprises a filter receiving area  36 . The filter receiving area  36  is adapted to removably receive the filter  20 . In the embodiment shown, the filter  20  is preferably a cartridge filter which can be replaced by removing the cover  25 . However, in alternate embodiments, the filter  20  could be removably connected to the frame  12  in any suitable manner. Further, the filter  20  may comprise a plurality of removable filter elements. For example, a first filter element might be adapted to remove odors and a second filter element might be adapted to remove small particulate matter. The filter  20  is located in front of the outlet  24  such that air passing through the main air flow channel  34  must pass through the filter  20  in order to exit through the outlet  24 . The filter  20  could comprise any suitable type of filter. For example, the filter  20  could comprise a paper filter element, and/or a polymer mesh filter element and/or an activated carbon filter element. The filter element could comprises a high-efficiency particulate arrest (HEPA) filter.  
         [0022]    As the first fan  16  is rotated by the motor  14 , the first fan  16  pulls air through the inlet  22 , into the main air flow channel  34 , and propels the air towards the second fan  18 . As the air is pushed by the first fan  16  towards the second fan  18 , the velocity of the air increases and the static pressure of the air also increases. This forms a first stage for increasing the velocity and static air pressure of the air as it travels through the air cleaner. As the air comes to the second fan  18 , the second fan  18  propels the air towards the filter  20 . This forms a second stage for increasing the velocity and static air pressure of the air as it travels through the air cleaner. Thus, the two fans  16 ,  18  form a multistage fan system for increasing the velocity and static air pressure of the air before it reaches the filter  20 . The increase in static air pressure and velocity from the multi stage fan system imparts sufficient force on the air as its engages the filter  20  such that the air can pass through the filter  20  and exit the air cleaner through the outlet  24 .  
         [0023]    The present invention can provide more air flow and static pressure at a given noise level than a single stage axial fan system. This makes it particularly advantageous for use in an air purification system which is intended to move large quantities of air through a filter with the least possible noise. An axial fan system can move a larger quantity of air at a given noise level than a “squirrel cage” blower type of fan system. Thus, for a given noise level, the present invention can move a larger quantity of air than a “squirrel cage” blower type fan system and, can move more air flow and provide greater static pressure then a single stage axial fan system. Greater static air pressure can increase the ease at which the air passes through the filter  20 . A greater quantity of air flow through the cleaner  10  enables the cleaner  10  to be smaller in volume or size than a conventional air purifier, but with the same cleaning capacity and without an increase in the noise output from the cleaner. Alternatively, the air cleaner  10  could be adapted to provide a same quantity of air flow therethrough as a conventional air purifier, but with a smaller size and decreased noise output.  
         [0024]    Referring now to FIG. 4, a schematic diagram of components of an alternate embodiment of the present invention are shown. In this embodiment the air cleaner  40  generally comprises a frame  42 , the motor  14 , the fans  16 ,  18 , the filter  20 , and two transmissions  44 ,  46 . In this embodiment, the frame  42  forms a main air flow channel  48  which decreases in size along its length. This can help to increase static pressure rise along the length of the channel  48 . The two fans  16 ,  18  are connected to the opposite ends of the drive shaft of the motor  14  by the two transmissions  44 ,  46 . In an alternate embodiment, only one of the fans might be connected to the drive shaft by a transmission. The two transmissions  44 ,  46  allow the fans  16 ,  18  to be rotated at different rotational velocities relative to each other. The two transmissions  44 ,  46  can also maximize the driving power of the motor  14  for the different force levels encountered by the two fans  16 ,  18  as they propel air.  
         [0025]    Referring now to FIG. 5, another alternate embodiment of the present invention is shown. In this embodiment, the air cleaner  50  generally comprises a frame  52 , the motor  14 , the two fans  16 ,  18  and the filter  20 . In this embodiment the motor  14  is connected to the frame  52  by a first set of air vanes  54 . The first vanes  54  could be integrally formed with the frame  52 . The first vanes  54  are adapted to redirect air exiting from the first fan  16  for a more efficient flow into the second fan  18 . This can help to reduce static pressure losses and increase air velocity.  
         [0026]    The air cleaner  50  also comprises a second set of air vanes  56 . The second air vanes  56  could be integrally formed with the frame  52 . The second vanes  56  are adapted to redirect air exiting from the second fan  18  for a more efficient engagement with the front face of the filter  20 . In a preferred embodiment, the air exiting from the second air vanes  56  will engage the front face of the filter  20  substantially perpendicular to the front face. In an alternate embodiment, the air cleaner might comprise only one set of air redirection vanes. In another alternate embodiment, such as when the air cleaner comprises more than two fans, the air cleaner could comprise more than two sets of air redirection vanes. In another type of alternate embodiment, the air cleaner could comprise more than one motor and, could comprise more than one filter.  
         [0027]    The present invention can use two or more “high pitch” axial fan blades which are driven off a common motor drive shaft. Air can be drawn into the inlet opening, preferably unobstructed by any filters or fine screen. The air can then enter the first stage fan whereby its velocity and static pressure can rise. The air can then enter the second stage fan which results in a further increase in velocity and static pressure. This provides enough force to push the air through a filter located on the output side of the unit. Test results have shown an increase of about 21%-35% in the air flow, depending upon the specific filter tested, and about 40% in static pressure verses a single axial fan system when compared at the same sound level. In an alternate embodiment, more than two fan stages could be provided. The blade pitch of the fan blades at the inlet verses the outlet could be varied. The present invention could also be used with air vanes to optimize air flow. The multi-stage fan system can also be used as a cooling fan by providing a greater air flow quantity when compared to a single stage fan of similar size and noise level.  
         [0028]    It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.