Abstract:
A debris blower with a radial flow fan having an impeller that includes a set of impeller blades that are spaced about a rotary axis of the impeller in a predetermined manner such that at least two spacing angles are used to space the impeller blades circumferentially apart from one another. The use of a plurality of spacing angles operates to distribute the noise that is generated by the rotating impeller blades over several tones or frequencies.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention generally relates to radial flow fans and more particularly to a debris blower including a radial flow fan having an impeller with a noise reducing blade configuration.  
         BACKGROUND OF THE INVENTION  
         [0002]    Debris blowers are known in which an impeller or a fan driven by a motor creates an air stream which is directed into a duct. The air stream discharged from the open end of the duct is employed to blow debris off walks, driveways and lawns. Known higher performance blowers employ a radial flow fan in order to efficiently generate the pressure and volumetric flow rate required for the application. These devices tend to be relatively noisy such that their use is often unpleasant for the user and those in the vicinity of the blower.  
           [0003]    The scale of the impeller, the practical speeds at which it can be driven, and a practical number of blades results in blade passing frequencies that create tonal noise emission. Tonal emission at the blade passing frequency typically falls within the frequency range over which the human ear is sensitive and creates an unpleasant sound quality. Further, as the impeller blades of these devices are typically spaced apart evenly around the circumference of the impeller, the noise emission contains one or more discrete tones at frequencies related to the blade passing rate. It is this concentration of noise at one or more particular frequencies, rather than the overall amplitude of the noise, that most people find unpleasant.  
           [0004]    Given the design criteria of modern high performance debris blowers, along with issues relating to its overall size, weight and cost, changes to the size of the impeller, its rotational speed and/or the number of impeller blades to change the frequency of the noise that is generated by the passing impeller blades to a frequency that is outside the sensitive range of human hearing have not been practicable.  
           [0005]    It is therefore an object of the present invention to provide a radial flow fan having an impeller with a blade configuration that spreads the blade passing noise out over several frequencies to improve the quality of the noise that is generated during the operation of the radial flow fan.  
         SUMMARY OF THE INVENTION  
         [0006]    In one preferred form, the present invention provides a radial flow fan having a housing having at least one inlet, an outlet and an impeller cavity in fluid connection with the inlet and the outlet, and an impeller. The impeller is rotatably supported in the impeller cavity on a rotary axis and includes an annular flange member and a plurality of impeller blades that are fixedly coupled to the annular flange member such that each of the impeller blades is adjacent another of the impeller blades in a predetermined circumferential direction. Each adjacent pair of the impeller blades defines a spacing angle. The impeller is configured such that a first predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a first predetermined spacing angle and a second predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a second predetermined spacing angle that is not equal to the first predetermined spacing angle. The plurality of first impeller blades are configured to intake a compressible fluid in a first direction generally parallel the rotary axis and to expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity. The use of a plurality of spacing angles operates to distribute the noise that is generated by the rotating impeller blades over several tones or frequencies.  
           [0007]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein:  
         [0009]    [0009]FIG. 1 is a side view of a blower constructed in accordance with the teachings of the present invention;  
         [0010]    [0010]FIG. 2 is a sectional view of the blower of FIG. 1 taken along its longitudinal axis;  
         [0011]    [0011]FIG. 3 is an end view of a portion of the blower of FIG. 1, illustrating the set of first impeller blades in greater detail;  
         [0012]    [0012]FIG. 4 is an end view of the impeller illustrating the set of second impeller blades in greater detail;  
         [0013]    [0013]FIG. 5 is a perspective view of the impeller illustrating the set of first impeller blades; and  
         [0014]    [0014]FIG. 6 is a perspective view of the impeller illustrating the set of second impeller blades. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0015]    With reference to FIGS. 1 and 2 of the drawings, a blower constructed in accordance with the teachings of the present invention is generally indicated by reference numeral  10 . The blower  10  is shown to include a power source  12 , a switch assembly  14  for selectively controlling the power source, a housing  16 , an impeller  18  and a discharge tube assembly  20 . In the particular embodiment illustrated, the power source  12  is illustrated to include a motor assembly  30  having an electric motor  32  with a pair of terminals  34  and an output shaft  36 . The motor assembly  30  and switch assembly  14  are conventional in their construction and operation and need not be discussed in significant detail. Briefly, the switch assembly  14  is coupled to a source of electric power (e.g., via a power cord  40 ) and via the terminals  34 , selectively provides the motor  32  with electricity in a predetermined manner that is related to the amount by which a trigger button  46  on the switch assembly  14  is depressed.  
         [0016]    The housing  16  is illustrated to include a pair of housing shells  50  that collectively define a motor mounting portion  52 , a switch mounting portion  54  and a volute  58  having an impeller cavity  60 , a primary inlet  62 , a secondary inlet  64  and an outlet  68 . The motor and switch mounting portions  52  and  54  are conventional in their construction and operation, being employed to fixedly couple the motor assembly  30  and the switch assembly  14 , respectively, within the housing  16 . When the motor assembly  30  is coupled to the housing  16  by the motor mounting portion  52 , the distal end of the output shaft  36  extends rearwardly into the impeller cavity  60 .  
         [0017]    The impeller cavity  60  extends radially around the output shaft  36  and is substantially enveloped on its forward and rearward sides by a pair of annular endwalls  70  and  72 , respectively, into which the secondary and primary inlets  62  and  64 , respectively, are formed. A plurality of vent apertures  76  that are skewed to the rotary axis  80  of the output shaft  36  are formed through the housing  16  forwardly of the endwall  70 . A plurality of circumferentially extending inlet apertures  86  are spaced around the housing  16  rearwardly of the endwall  72 . The circumference of the portion of the housing  16  into which the inlet apertures  86  are formed is illustrated to be larger than the diameter of the primary inlet  62 . The outlet  68  intersects the impeller cavity  60  generally tangent to the outer diameter of the impeller cavity  60  in a manner that is conventionally known. However, the outlet  68  turns forwardly after this intersection and extends along an axis that is offset both vertically and horizontally from the rotary axis  80  of the output shaft  36 . The outlet  68  terminates at a coupling portion  90  that is configured to releasably engage a mating coupling portion  92  on the proximal end  94  of the discharge tube assembly  20 .  
         [0018]    With reference to FIGS. 2 through 6, the impeller  18  is illustrated to include a mounting hub  100 , a flange member  102 , a set of first impeller blades  104  and a set of second impeller blades  106 . The mounting hub  100  is generally cylindrical and includes a mounting aperture  110 , which is sized to engage the distal end of the output shaft  36  in a press-fit manner to thereby couple the impeller  18  to the motor assembly  30  for rotation about the rotary axis  80 . Those skilled in the art will readily understand that although press-fitting is employed to fix the impeller  18  for rotation with the output shaft  36 , any appropriate coupling means may be utilized for this purpose. The flange member  102  is coupled to the mounting hub  100  and extends radially outwardly therefrom in a continuous manner to thereby completely segregate the sets of first and second impeller blades  104  and  106  from one another.  
         [0019]    During the operation of the blower  10 , the impeller  18  rotates within the impeller cavity  60 . Rotation of the set of first impeller blades  104  imparts momentum to the air that is disposed between each adjacent pair of first impeller blades  104 , slinging the air radially outwardly toward the outlet  68 . The air exiting the outlet  68  as a result of the momentum imparted by the set of first impeller blades  104  creates a negative pressure differential that generates a primary air flow  120  that enters the housing  16  through the inlet apertures  86  and is directed into the set of first impeller blades  104  by the primary inlet  62  in a direction generally parallel the rotary axis  80 .  
         [0020]    Similarly, rotation of the set of second impeller blades  106  imparts momentum to the air that is disposed between each adjacent pair of second impeller blades  106 , slinging the air radially outwardly toward the outlet  68 . The air exiting the outlet  68  as a result of the momentum imparted by the set of second impeller blades  106  creates a negative pressure differential that generates a secondary air flow  122  that enters the housing  16  through the vent apertures  76 . The housing  16  is constructed such that the motor  32  rejects heat to the secondary air flow  122  before it travels through the secondary inlet  64 . The secondary inlet  64  directs the secondary flow  122  into the set of second impeller blades  106  in a direction generally parallel the rotary axis  80  and opposite the primary air flow  120 .  
         [0021]    The primary and secondary air flows  120  and  122  combine in the outlet  68  and are discharged through the coupling portion  90  into the discharge tube assembly  20 . In the example provided, the height of the first impeller blades  104  is substantially larger than that of the second impeller blades  106  and as such, the mass flow rate of the primary air flow  120  will be substantially larger than the mass flow rate of the secondary air flow  122 . As the flange member  102  is continuous, the primary and secondary flows  120  and  122  cannot travel in an axial direction beyond the flange member  102  until they have been slung radially outwardly of the impeller  18 .  
         [0022]    The set of first impeller blades  104  is fixedly coupled to a first side  150  of the flange member  102  such that each pair of the first impeller blades  104  (e.g., first impeller blades  104   a  and  104   b ) is separated by a predetermined spacing angle  152 , wherein one of the pair of first impeller blades  104  (e.g., first impeller blade  104   b ) is spaced apart from the other one of the pair of first impeller blades  104  (e.g., first impeller blade  104   a ) in a predetermined circumferential direction by the spacing angle  152 . The set of first impeller blades  104  are spaced about the flange member  102  such that spacing angles  152  having at least two different magnitudes are employed to space the first impeller blades  104  apart. Preferably, the set of first impeller blades  104  are spaced apart with a spacing angles  152  having a multiplicity of magnitudes, wherein the spacing angles  152  are distributed in a predetermined pattern that is repeated around the circumference of the impeller  18 .  
         [0023]    Similarly, the set of second impeller blades  106  is fixedly coupled to a second side  160  of the flange member  102  such that each pair of the second impeller blades  106  (e.g., second impeller blades  106   a  and  106   b ) is separated by a predetermined spacing angle  162 , wherein one of the pair of second impeller blades  106  (e.g., second impeller blade  106   b ) is spaced apart from the other one of the pair of second impeller blades  106  (e.g., second impeller blade  106   a ) in a predetermined circumferential direction by the spacing angle  162 . The set of second impeller blades  106  are also spaced about the flange member  102  such that spacing angles  162  having at least two different magnitudes are employed to space the second impeller blades  106  apart. As with the set of first impeller blades  104 , the set of second impeller blades  106  are preferably spaced apart with spacing angles  162  having a multiplicity of magnitudes, wherein the spacing angles  162  are distributed in a predetermined pattern that is repeated around the circumference of the impeller  18 . Also preferably, the magnitudes and pattern of spacing angles  162  for the set of second impeller blades  106  is different from the magnitudes and pattern of the spacing angles  152  for the set of first impeller blades  104 .  
         [0024]    In the particular embodiment illustrated, the pattern of spacing angles  152  that is employed for the set of first impeller blades  104  is configured such that a first one of the first impeller blades  104  (e.g., first impeller blade  104   b ) is adjacent a first one of the other first impeller blades (e.g., first impeller blade  104   a ) and cooperates to define a first area  170  on the flange member  102  therebetween, and each of the first impeller blades  104  (e.g., first impeller blade  104   b ) is also adjacent a second one of the other first impeller blades (e.g., first impeller blade  104   c ) and cooperates to define a second area  172  on the flange member  102  therebetween. The spacing of the first impeller blades  104  is such that none of the first and second areas  170  and  172  that are adjacent any one of the first impeller blades  104  is equal in magnitude.  
         [0025]    Each of the first impeller blades  104  is shown to begin at an inward point  174  and terminate at an outward point  176 . Each of the first impeller blades  104  (e.g., first impeller blade  104   b ) is configured such that its inward point  174  is radially inward of the outward point  176  of the first one of the other first impeller blades  104  (e.g., first impeller blade  104   a ) and its outward point  176  is radially outward of the inward point  174  of the second one of the other first impeller blades  104  (e.g., first impeller blade  104   c ). Accordingly, a first straight line passes through the mounting aperture  110  through the inward point  174  of the first impeller blade  104   b  and the outward point  176  of the first impeller blade  104   a  and a second straight line passes through the mounting aperture  110  through the inward point  174  of the first impeller blade  104   c  and the outward point  176  of the first impeller blade  104   b . Each first impeller blade  104  is arcuately shaped from its inward point  174  to its outward point  176 . Each first impeller blade  104  tapers outwardly away from the flange member  102  from its inward point  174  to an intermediate point  178  between the inward and outward points  174  and  176 .  
         [0026]    Similarly, the pattern of spacing angles  162  that is employed for the set of second impeller blades  106  is configured such that each of the second impeller blades  106  (e.g., second impeller blade  106   b ) is adjacent a first one of the other second impeller blades (e.g., second impeller blade  106   a ) and cooperates to define a third area  180  on the flange member  102  therebetween, and each of the second impeller blades  106  (e.g., second impeller blade  106   b ) is also adjacent a second one of the other second impeller blades (e.g., second impeller blade  106   c ) and cooperates to define a fourth area  182  on the flange member  102  therebetween. The spacing of the second impeller blades  106  is such that none of the third and fourth areas  180  and  182  that are adjacent any one of the second impeller blades  106  is equal in magnitude.  
         [0027]    Each of the second impeller blades  106  begins at an inward point  184  and terminates at an outward point  186 . Each of the second impeller blades  106  (e.g., second impeller blade  106   b ) is configured such that its outward point  186  is radially outward of the inward point  184  of the first one of the other second impeller blades  106  (e.g., second impeller blade  106   a ) and its inward point  184  is radially inward of the outward point  186  of the second one of the other second impeller blades  106  (e.g., second impeller blade  106   c ). Each second impeller blade  106  is arcuately shaped from its inward point  184  to its outward point  186 . Accordingly, a first straight line passes through the mounting aperture  110  through the inward point  184  of the first impeller blade  106   b  and the outward point  186  of the first impeller blade  106   c  and a second straight line passes through the mounting aperture  110  through the inward point  184  of the first impeller blade  106   a  and the outward point  186  of the first impeller blade  106   b . Each second impeller blade  106  tapers outwardly away from the flange member  102  from its inward point  184  to an intermediate point  188  between the inward and outward points  184  and  186 .  
         [0028]    Preferably, the spacing between any adjacent pair of impeller blades is not equal to any other spacing between an adjacent pair of any of the other first and second impeller blades  104  and  106  to thereby distribute the noise energy over a maximum number of frequencies. Construction in this manner, however, is extremely difficult, particularly where the impeller  18  is formed in a molding process, due to the unsymmetrical distribution of material in the impeller  18 . The unsymmetrical distribution of material tends to facilitate distortion in the molded impeller  18  as it cools, as well as offsets its rotational center of gravity about its axis of rotation so that it vibrates when it is rotated.  
         [0029]    In view of these difficulties, the set of first impeller blades  104  are instead divided into a plurality of identically configured first blade groups  200 , wherein each of the first blade groups  200  includes an identical quantity of the first impeller blades  104  which are spaced apart in a predetermined first blade spacing pattern. In the example provided, each of the first blade groups  200  includes a total of four (4) of the first impeller blades  104   a ,  104   b ,  104   c  and  104   d , with the first impeller blade  104   a  being spaced apart from predetermined reference point (e.g. the first impeller blade  104   d  in another first blade group  200 ) by an angle of 57°, the first impeller blades  104   a  and  104   b  being spaced apart with a spacing angle  152  of 41°, the first impeller blades  104   b  and  104   c  being spaced apart with a spacing angle  152  of 49° and the first impeller blades  104   c  and  104   d  being spaced apart with a spacing angle  152  of 33°. The first blade groups  200  are fixed to the first side  150  of the flange member  102  such that they are offset from one another by a predetermined angular spacing (e.g., 57°).  
         [0030]    Similarly, the set of second impeller blades  106  are divided into a plurality of identically configured second blade groups  220 , wherein each of the second blade groups  220  includes an identical quantity of the second impeller blades  106  which are spaced apart in a predetermined second blade spacing pattern. In the example provided, each of the second blade groups  220  includes a total of three (3) of the second impeller blades  106   a ,  106   b  and  106   c , with the second impeller blade  106   a  being spaced apart from predetermined reference point (e.g. the second impeller blade  106   c  in another second blade group  220 ) by an angle of 40°, the second impeller blades  106   a  and  106   b  being spaced apart with a spacing angle  162  of 32° and the second impeller blades  106   b  and  106   c  being spaced apart with a spacing angle  162  of 48°. The second blade groups  220  are fixed to the second side  170  of the flange member  102  such that they are offset from one another by a predetermined angular spacing (e.g., 40°).  
         [0031]    While noise attenuation is primarily achieved through the configuration of the impeller  18 , the geometry of the housing  16  is also employed to aid in the attenuation of the noise that is generated during the operation of the blower  10 . In this regard, noise that results from the rotation of the impeller  18  is not discharged in a direct or straight-line manner from the housing  16  but rather is reflected off several various interior surfaces within the housing  16  as shown in FIG. 2. For example, noise  250  that is directed rearwardly from the impeller  18  is reflected off the rearward wall  252  before it is reflected outwardly through the inlet apertures  86 . Similarly, noise  250  that is directed forwardly from the impeller  18  is reflected off the walls  254  of the outlet  68  before it is discharged through the outlet  68 . The reflecting of noise  250  off the various interior surfaces of the housing  16  permits the housing  16  to absorb some of the energy of the noise  250  to thereby attenuate the level of noise  250  that is transmitted out of the housing  16 .  
         [0032]    While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.