Abstract:
A high speed centrifugal air impeller assembly with rearwardly curved blades has it impeller backplate directly cooperating with an adjacent housing wall portion to provide a narrow annular sound attenuating passageway from an impeller chamber to a motor and discharge chamber.

Description:
RELATED APPLICATIONS  
       [0001]     Provisional Application No. 60/508,325, titled “Internal Muffler for Backward Inclined Blower” filed Oct. 2, 2003, inventor David A. Curtis, incorporated herein by reference. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     This invention relates to a high speed centrifugal air impeller with rearwardly curved blade and more particularly to sound attenuation means therefore. Impellers of the type under consideration are relatively low flow high speed devices, which operate in the neighborhood of a blade tip speed up to approximately 550 feet per second.  
         [0003]     Air flow is three dimensional. Air enters the impeller axially through inlet openings in the housing and impeller. In the plane of rotation there is a circulation that flows outwardly and is collected by the housing for approximately 300 degrees of rotation. Typically an outlet section makes up the remaining flow, usually a cylindrical section whose axis is substantially tangent to the impeller outer diameter.  
         [0004]     As will be apparent, the high speed operation of these devices results in substantial noise generation. One method of noise reduction used involved the provision of an impeller housing having two discrete chambers, one containing the impeller and the other the air outlet or discharge section. Thus, a muffler effect can be provided for by means of a rapidly changing cross-sectional opening. In the prior art a divider piece is provide in one design and cooperates with the impeller backplate to define a narrow annular opening spaced radially inwardly from the housing wall but interconnecting the impeller and discharge chambers. Sound waves passing through the opening along with the air are substantially attenuated. The additional part, however, adds significantly to manufacturing cost and assembly complexity and the overall cost of the impeller assembly is adversely affected.  
         [0005]     It is the general object of the present invention to provide a high speed centrifugal air impeller assembly having rearwardly curved blades with improved sound attenuation means which can be manufactured at economic advantage and which also enhances impeller performance.  
         [0006]     In fulfillment of the foregoing object and in accordance with the present invention, an impeller housing is provided with air inlet and discharge openings. An air impeller with an annular backplate is disposed in the housing with a circumaxially spaced series of long narrow rearwardly inclined air moving blades on its backplate and with its inlet opening in communication with the housing inlet opening. The annular backplate of the impeller cooperates with an annular potion of the housing inner surface to define a narrow annular passageway and discrete chambers on opposite sides thereof. Although the impeller may be otherwise driven, it preferably has its backplate connected with and driven by an electric motor mounted in the chamber on the side opposite the blades. With this arrangement, the air flow created by the impeller blades is constrained to flow through the narrow annular passageway connecting the impeller and motor chambers and the sound waves accompanying the flow are substantially attenuated in flow through the passageway. It should also be noted that the air flow is not required to reverse direction on reaching the housing wall in order to flow radially inwardly and then through the annular passageway as the prior art design. Confinement of the motor in its chamber within the housing also contributes significantly to overall sound reduction.  
     
    
     DESCRIPTION OF DRAWINGS  
       [0007]      FIG. 1  of the drawings shows a prior art design in sectional schematic form,  
         [0008]      FIG. 2  illustrates the improved design of the present invention also in sectional schematic form. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]     Referring initially to  FIG. 1 , it will be observed that an impeller housing is indicated generally at  10 . Mating upper and lower cup-shaped members form a generally cylindrical housing with an annular third housing member  15  clamped therebetween. The member  15  has a radially inwardly projecting annular extension  16  which cooperates with an impeller backplate  18  to define an annular passageway  20  spaced radially inwardly from the inner wall of the housing  10 . The extension  16  and the backplate  18  cooperatively define upper and lower chambers  22  and  24  in the housing and the latter carries a circumaxially spaced series of long narrow rearwardly curved air moving blades  26 , 26 . A housing inlet opening  28  receives an inlet member  30  of the impeller and the air is conducted generally radially outwardly where it is forced to reverse direction at the housing wall and travels radially inwardly before passing through the passageway  20  to the upper chamber  22 . The chamber  22  contains electric motor  32  driving the impeller through connection with backplate  18  and a discharge opening  34 , which extends in a direction generally tangent to the housing wall.  
         [0010]     As will be apparent, a degree of sound attenuation will be realized with the design of  FIG. 1 . As mentioned above, however, it will also be apparent that the third housing part  15  will add substantial cost in manufacturing and assembly time. Further, the inefficient reversing flow pattern is obviously detrimental to impeller performance.  
         [0011]     Referring now to  FIG. 2 , the improved impeller assembly of the present invention has a housing indicated generally at  40  which may vary widely in form but which preferably comprises a pair of mating cup-shaped members  42 , 44  as in  FIG. 1 . The members  42 , 44  are attached directly to each other at their open ends to provide a desirably simple two part construction. At the junction between the members on the interior surface of the housing a narrow annular portion  46  thereof is provided irrespective of the remaining configuration of the housing. This portion of the housing cooperates with an enlarged backplate  48  to define a narrow annular air passageway  50  for the passage of air and the attenuation of accompanying noise. The backplate also serves to define a lower chamber  52  which houses an impeller  54  and from which air flows through the passageway  50  to an upper chamber. The lower surface of the backplate  48  also carries a circumaxial series of long narrow rearwardly inclined air moving blades  56 , 56  and an inlet tube  58  which is received in inlet opening  60  in the lower wall of the housing member  44 . As will be apparent, air drawn inwardly through the inlet tube  58  will be discharged radially outward from the impeller blades and will then make a direct right angle turn through the passageway  50  without any reversal in flow and resulting turbulence.  
         [0012]     As mentioned above, various configurations may be employed for the chambers  52 ,  54 . In this regard it should be observed that the diameter of the narrow annular portion which defines the opening  50  in cooperation with the backplate  48  should in all cases be at least as large as that of the inlet chamber  52 .  
         [0013]     The upper chamber  54  preferably houses an electric motor  62  for rotating the backplate of the impeller and thus driving the impeller. Also located in the chamber  54  is a discharge tube which has its axis substantially tangent to the wall of the housing. As mentioned confining the electric motor in the housing also serves to reduce noise generated by the assembly.