Patent Publication Number: US-7210903-B2

Title: Lobed joint draft inducer blower

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to air moving devices, and in particular, to blowers of the type which are used with high efficiency (e.g., 90% or higher efficiency) furnaces for drawing air from outside of a building into the furnace to support combustion and to expel combustion exhaust products outside of the building. More particularly, the present invention relates to a blower which provides more efficient air flow through the blower housing with decreased blower noise. 
     2. Description of the Related Art 
     In high efficiency furnaces, standard chimney air-draw effects are not sufficient to assure the required air flow through the furnace heat exchangers, and therefore, high efficiency furnaces utilize draft inducer blowers to provide sufficient air flow through the furnace. In particular, the blowers of high efficiency furnaces pull flue gases through the furnace heat exchangers and then push the flue gases out through exhaust piping to the exterior of the building. The length of the flue piping is limited by the static pressure induced on the flue gases by the draft inducer blower, and higher static pressures typically allow longer runs of flue piping. One measure of the efficiency of the draft inducer blower is the static pressure generated by the blower on the flue gases at a given air flow rate, wherein a blower is more efficient if it can generate higher pressures and air flows for a given power input to the electric motor which drives the blower impeller. 
     One known blower for a high efficiency furnace is shown in  FIGS. 1–4 , and generally includes a blower housing  20  having a housing body  22  and a housing cover  24 . Housing body  22  is typically formed as a molded plastic component, having a cylindrical outer wall  26 , a planar, annular top wall  28 , and an axially recessed, planar, circular wall  30  to which electric motor  32  is mounted. Housing body  22  further includes an integral, tubular exhaust transition  34  projecting tangentially therefrom, having a circular outlet  36  to which an exhaust pipe (not shown) is connected. Housing cover  24  is a substantially flat, molded plastic circular plate which is attached to housing body  22  by being captured between housing body  22  and wall  38  of a furnace, as shown in  FIG. 4 . Specifically, a plurality of bolts  40  are inserted through respective mounting lugs  42  in housing body  22  and into a set of corresponding holes  44  in furnace wall  38  to thereby attach the blower housing  20  to the furnace. Holes  44  in furnace wall  38  are disposed in a standard pattern with a predetermined, fixed diameter, typically about 9.25 inches. An impeller  46 , shown in  FIGS. 2–4 , is disposed within the interior of blower housing  20  between housing body  22  and housing cover  24 , and is mounted for rotation upon drive shaft  48  ( FIG. 4 ) of motor  32 . 
     In operation, rotation of impeller  46  by motor  32  draws exhaust gases through a centrally disposed circular inlet  50  ( FIG. 4 ) in housing cover  24  from the furnace into the blower housing  20 , and the exhaust gases are discharged through outlet  36  of exhaust transition  34 . Although the foregoing blower housing has proven to be effective for use with high efficiency furnaces, improvements to same are desired. 
     First, during the molding of housing body  22 , tubular exhaust transition  34  is formed by a cylindrical-shaped exhaust transition mold (not shown). After the plastic material of housing body  22  cures, the exhaust transition mold is pulled outwardly from housing body  22  in a tangential or radial direction with respect to housing body  22 . At least one other larger inner mold (not shown), which is cylindrically-shaped, is used to form the interior of housing body  22  and, after the plastic material of housing body  22  cures, is pulled away from housing body  22  along the axial direction with respect to housing body  22 . Notably, it is not practical to shape the inner end of the exhaust transition mold to fit perfectly tangentially along the cylindrical outer surface of the housing body interior mold. Therefore, the exhaust transition mold is shaped to project radially outwardly from the cylindrical outer surface of the housing body interior mold a short distance. Thus, when housing body  22  is molded, the exhaust transition mold forms a recessed area  52  in exhaust transition  34 , best shown in  FIG. 3 , which is radially offset from outer wall  26  of housing body  22 . Problematically, this recessed area  52  defines an abrupt outward step or “bump” in the air flow through exhaust transition  34  which, as shown by the air flow arrows in  FIG. 3 , causes undesired turbulence and swirl in the air flow in recessed area  52  as the air flow passes through exhaust transition  34  toward outlet  36  of housing body  22 . 
     Additionally, as may be seen from  FIGS. 2 and 3 , the intersection of the cylindrical exhaust transition mold and the cylindrical housing body interior mold which are used to form housing body  22  forms a sharp exhaust cutoff  54  within housing body  22 , which is present in blower housing  20  and in many other known blower housings. Cutoff  54  is located proximate exhaust transition  34 , and defines the point within blower housing  20  which separates the air flow through exhaust transition  34  from the remainder of the air flow within blower housing  20 . As may be seen in  FIGS. 2 and 3 , the outer edge of impeller  46  is disposed very close to cutoff  54  to maximize the efficiency of air flow in blower housing  20  and to prevent back flow of air through the gap between impeller  46  and cutoff  54  into exhaust transition  34 . As represented by the air flow arrows in  FIG. 3 , as impeller  44  rotates, a blade pass noise is generated as pressure waves exhausting the blade passages of impeller  46  impinge upon cutoff  54 . 
     Known blower housings have included features for masking the foregoing blade pass noise. For example, a blower housing disclosed in U.S. Pat. No. 5,316,439 includes either a noise cancellation rod located within the outlet of the blower housing, or a nose-like projection projecting inwardly from the exhaust transition. Noise generated from one of the foregoing components interferes with, and substantially cancels out, the blade pass noise generated by the impeller blades passing the sharp cutoff. U.S. Pat. No. 5,484,259 to Ahmed et al. discloses a blower housing having a fin near the cutoff to provide a vortex in the air flow near the cutoff to reduce noise. However, these and similar methods only mask the blade pass noise, rather than eliminating such noise. 
     What is needed is a draft inducer blower housing for high efficiency furnaces which is an improvement over the foregoing. 
     SUMMARY OF THE INVENTION 
     The present invention provides a draft inducer blower for high efficiency furnaces, including a blower housing which facilitates maximum air flow efficiency through the blower housing while reducing air flow noises. The blower housing generally includes a housing body and housing cover which define an exhaust transition therebetween, which transitions the air flow from the circular main cavity of the blower housing to the blower housing outlet. The housing body and housing cover are attached to one another via a lobed joint along the exhaust transition, and each include complementary, smoothly contoured inner surfaces to facilitate smooth air flow through the exhaust transition toward the outlet. Additionally, the housing body and housing cover include cooperating cutoff surfaces which form a broadly radiused cutoff within the blower housing to reduce or eliminate the blade pass noise associated with contact of the air flow from the impeller with the cutoff. 
     In particular, the housing body and housing cover are attached to one another along a primary joint line which extends around the outer peripheries thereof, and are also attached to one another along a secondary, lobed joint line which extends along the exhaust transition and slopes upwardly in the axial direction toward the exhaust outlet. The foregoing construction allows the inner surfaces of the housing body and housing cover to be molded as smoothly contoured and complementary surfaces in the area of the exhaust transition to facilitate smooth air flow through the exhaust transition toward the outlet. In this manner, the air flow does not encounter obstructions in the exhaust transition which would induce turbulence in the air flow, generating noise and compromising the air flow efficiency of the blower housing. 
     The housing body and housing cover each include broadly radiused cutoff portions which, when the housing cover is joined to the housing body, cooperate with one another via a pin-and-hole joint to define a broadly radiused cutoff to reduce or eliminate blade pass noise associated with the cutoff. Additionally, the pin-and-hole joint between the cutoff portions of the housing body and housing cover aids in locating the housing body with respect to the housing cover, and also forces the mutually facing surfaces of the housing body and housing cover into tight engagement with one another to assure minimum edge mismatches due to part warpage, for example, such that no protruding edges cause turbulence in the air flow. 
     Advantageously, the internal and external features of the housing body are configured such that the housing body may be formed according to a molding process using a pair of molds which may be separated from the housing body along the Z-axis direction after the plastic material of the housing body cures. Only one additional mold is needed to form the circular outlet of the housing body, which mold may conveniently take the form of a short, cylindrical mold which is separated from the housing body in the radial or X- or Y-axis direction after the plastic material of the housing body cures. In a similar manner, the features of the housing cover are configured to allow the housing cover to be formed via a molding process including a pair of molds which may be separated from the housing cover in the axial direction after the plastic material of the housing cover cures. In this manner, manufacture of the blower housing from plastic material, via a molding process such as injection molding, is simplified. 
     In one form thereof, the present invention provides a blower housing defining perpendicular axial and radial directions, including a first housing member including a substantially cylindrical outer wall, and a circular outlet projecting in the radial direction from the outer wall; a second housing member including a substantially circular base wall; an exhaust transition defined by at least one of the first and second housing members; and a broadly radiused cutoff disposed within the blower housing adjacent the exhaust transition, the cutoff defined by at least one of the first and second housing members. 
     In another form thereof, the present invention provides a blower housing defining perpendicular axial and radial directions, including a first housing member including a substantially cylindrical outer wall and a circular outlet projecting in the radial direction from the outer wall; a second housing member including a substantially circular base wall; an exhaust transition extending toward the outlet, the exhaust transition defined by the first and second housing members; and a first joint line between the first and second housing members, the first joint line extending along the exhaust transition and sloping in the axial direction toward the outlet. 
     In further form thereof, the present invention provides a blower housing defining perpendicular axial and radial directions, including first and second housing members connected to one another to define a circular main cavity therebetween; a plurality of mounting lugs disposed in spaced relation around an outer periphery of the blower housing; a circular outlet projecting in the radial direction from the blower housing, the outlet formed by at least one of the first and second housing members; an exhaust transition extending from the main cavity toward the outlet, the exhaust transition defined by the first and second housing members; and each of the first and second housing members including smoothly contoured interior surfaces extending along the exhaust transition from the main cavity toward the outlet. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a known blower and blower housing for high efficiency furnaces; 
         FIG. 2  is another perspective view of the blower housing of the blower of  FIG. 1 , with a portion of the housing body and housing cover cut away to show the interior of the blower housing in the exhaust transition and cutoff thereof; 
         FIG. 3  is a horizontal sectional view through the blower of  FIG. 1 , taken along line  3 — 3  of  FIG. 1  and looking downwardly, with the air flow through the blower housing shown by arrows; 
         FIG. 4  is a vertical sectional view through the blower of  FIG. 1 , taken along line  4 — 4  of  FIG. 1 ; 
         FIG. 5  is a perspective view of a blower for high efficiency furnaces, including a blower housing according to the present invention; 
         FIG. 6  is a first exploded view of the housing body and housing cover of the blower housing, looking downwardly; 
         FIG. 7  is a second exploded view of the housing body and housing cover of the blower housing, looking upwardly; 
         FIG. 8  is a horizontal sectional view through the blower of  FIG. 5 , taken along line  8 — 8  of  FIG. 5  and looking downwardly; 
         FIG. 9  is a vertical sectional view through the blower of  FIG. 5 , taken along line  9 — 9  of  FIG. 5 ; 
         FIG. 10  is a first perspective view of the housing body, looking upwardly; 
         FIG. 11  is a second perspective view of the housing body, looking downwardly; 
         FIG. 12  is a first perspective view of the housing cover, looking downwardly; and 
         FIG. 13  is a second perspective view of the housing cover, looking downwardly. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION 
     Referring first to  FIGS. 5–7 , a blower  60  for a high efficiency furnace according to the present invention is shown. Blower  60  generally includes blower housing  62 , electric motor  64  mounted to blower housing  62 , and an impeller ( FIGS. 7 and 8 ), described below, mounted to the output shaft  66  of motor  64  and disposed within blower housing  62 . Blower housing  62  generally includes a first housing member or housing body  68 , and a second housing member or housing cover  70 . Housing body  68  and housing cover  70  may be formed of metal or plastic according to an injection molding process, for example. Suitable plastics for housing body  68  and housing cover  70  include polypropylene or other thermoplastics. Housing body  68  includes a generally cylindrical outer wall  72 , an annular top wall  74 , an inner wall  76 , and a circular, recessed wall  78 . Motor  64  is attached to recessed wall  78  by a plurality of fasteners  80  which pass through mounting flanges  82  of motor  64  and into holes in recessed wall  78  of housing body  68 . Housing body  68  additionally includes a plurality of reinforcement ridges  83  extending along outer wall  72 , top wall  74 , inner wall  76 , and recessed wall  78  for providing structural strength and rigidity to housing cover  70 . Generally, blower housing  62  defines an axial or Z-axis direction which is aligned along the axis of output shaft  66  of motor  64 , as well as radial or X- and Y-axis directions which are aligned perpendicular to the axial or Z-axis direction. 
     Housing body  68  additionally includes a plurality of mounting lugs  84  integrally formed therewith, which are disposed radially outwardly of sidewall  72  in spaced relationship around the outer periphery of blower housing  62 . Alternatively, at least a portion of mounting lugs  84  may be formed with housing cover  70 . Mounting lugs  84  include slot-like or oval openings  86  for receipt of bolts  88  to attach blower housing  62  to wall  38  ( FIG. 4 ) of a furnace. As shown in  FIG. 9 , bolts  88  extend downwardly through mounting lugs  84  of housing body  68 , adjacent recesses  102  in lug feet  100  of housing cover  70  (discussed below), and into holes  44  ( FIG. 4 ) in furnace wall  38  to rigidly secure blower housing  62  to wall  38  of the furnace, with housing cover  70  captured between housing body  68  and furnace wall  38 . Additionally, housing body  68  includes a plurality of locating lugs  90  integrally formed therewith, which are disposed radially outwardly of outer wall  72  and spaced around the outer periphery of housing cover  70 . Locating lugs  90  include openings for receipt of upwardly-projecting locating pins  94  of housing cover  70  to thereby positively locate housing cover  70  with respect to housing body  68  during assembly of blower housing  62 . Optionally, housing body  68  includes one or more attachment lugs  92  for receipt of fasteners (not shown) which pass therethrough and also through one or more corresponding optional attachment lugs  93  of housing cover  70  to secure blower housing  62  to furnaces having an alternate furnace mounting bolt pattern. Further details of housing body  68  are discussed below. 
     Housing cover  70  cooperates with housing body  68  to define an enclosed, circular main cavity therebetween. Housing cover  70  includes a centrally disposed, inwardly-projecting, circular lip  96  defining a circular inlet opening  98 . Housing cover  70  also includes a plurality of lug feet  100  having recesses  102  which align with the openings  86  of mounting lugs  84 . As may be seen from  FIG. 9 , lug feet  100  of housing cover  70  and mounting lugs  84  of housing body  68  cooperate to support blower housing  62  on the wall of a furnace with a slight air gap between housing cover  70  and furnace wall  38  ( FIG.4 ). A gasket may be provided between housing cover  70  and the furnace wall to provide an air seal therebetween. Further details of housing cover  70  are described below. 
     Referring to  FIGS. 6 ,  7 , and  9 – 11 , housing body  68  includes a downwardly-projecting tongue  104  disposed about the periphery thereof, which is received within a corresponding groove  106  about the periphery of housing cover  70 , shown in  FIGS. 6 ,  9 ,  11 , and  12 , in a snap-fit manner to thereby secure housing cover  70  to housing body  68  along a primary joint line which extends around outer wall  72  from the cutoff region of blower housing  62  to the exhaust transition of blower housing  62 , discussed below, and thence around the lobed joint of blower housing  62  back to the cutoff region. Further details regarding the snap-fit attachment of housing cover  70  to housing body  68  provided by tongue  104  and groove  106  are described in detail in U.S. Pat. No. 5,954,476 to Stewart et al., assigned to the assignee of the present invention, the disclosure of which is expressly incorporated therein by reference. Alternatively, housing body  68  may include groove  106 , and housing cover  70  may include tongue  104 . Optionally, a gasket or other seal (not shown) formed of a suitable resilient material, such as rubber or EPDM foam cording, for example, may be fitted between tongue  104  and groove  106  to enhance the seal therebetween. As may be seen from  FIG. 9 , when blower housing  62  is attached to the wall of a furnace, lug feet  100  of housing cover  70  contact the wall of the furnace to maintain axial pressure on the snap-fit primary joint line between tongue  104  of housing body  68  and groove  106  of housing cover  70 . 
     As shown in  FIGS. 5–8  and  10 – 13 , housing body  68  and housing cover  70  cooperate to define an exhaust transition  108  which extends tangentially from the last mounting lug  84  of housing body and the last lug foot  100  of housing cover  70  in the air flow path to circular exhaust outlet  110  of housing body  68 . The last mounting lug  84  of housing body  68  and lug foot  100  of housing cover  70  in the air flow path will hereinafter be designated with reference numerals  84   a  and  100   a , respectively. An exhaust pipe or other duct structure (not shown) may be attached to exhaust outlet  110  in a suitable manner, such as with clamps or other fasteners. Further details of exhaust transition  108  are described below. 
     Referring to  FIGS. 8 and 9 , impeller  114  includes central hub  116 , which is secured to output shaft  66  of motor  64  in a suitable manner for rotation within blower housing  62 , and also includes lower plate  118  and upper plate  120  having a plurality of backward-curved blades  122  extending from central hub  116  between lower plate  118  and upper plate  120 . A plurality of blade passages  124  are defined between each pair of blades  122  radially around impeller  114 . Impeller  114  also includes a plurality of auxiliary blades  126  projecting upwardly from upper plate  120 , and a plurality of balancing lugs  128  projecting from upper plate  120  and spaced radially about upper plate  120 . Impeller  114  may be made of a lightweight metal, or from a lightweight yet durable plastic material, for example. 
     Housing body  68  of blower housing  62  defines radial X- and Y- axis dimensions which correspond to the diameter of sidewall  72  of housing body  68 , as well as an axial or Z-axis dimension which is co-axial with the rotation axis of impeller  114  and drive shaft  66  of motor  64 , and which corresponds to the height of outer wall  72  of housing cover  70 . Outer wall  72 , top wall  74 , and inner wall  76  of housing body  68  cooperate to define a volute  130  of housing body  68  which extends around the circumference and outer periphery of blower housing  62  and increases in cross-sectional area from cutoff  132  of blower housing  62  to exhaust transition  108  of housing body  68 , as described in further detail in co-pending U.S. patent application Ser. No. 10/934,004, entitled DRAFT INDUCER BLOWER WITH Z-AXIS VOLUTE, filed on Sep. 3, 2004, assigned to the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference. Volute  130  is curved around the outer periphery of blower housing  62  through an angle of at least 180° and, as shown in  FIG. 5 , volute  130  curves around the outer periphery of blower housing  62  from cutoff  132  to transition section through an angle slightly greater than 270°. 
     According to the present invention, blower housing  62  includes a lobed joint between housing body  68  and housing cover  70  at exhaust transition  108 , in addition to the planar, circular primary joint provided between tongue  104  of housing body  68  and groove  106  of housing cover  70 . As shown by the air flow arrows in  FIG. 8  and discussed in further detail below, the lobed joint provided between housing body  68  and housing cover  70  facilitates smooth, uninterrupted air flow through exhaust transition  108  from the circular main cavity of blower housing  62  toward outlet  110  of blower housing  62 , and provides a broadly radiused cutoff  132  for reducing or eliminating blade pass noise in blower housing  62 , while allowing housing body  68  and housing cover  70  to be molded primarily with molds that conveniently separate from housing body  68  and housing cover  70  in the Z-axis direction. 
     Referring to  FIGS. 6 ,  7 ,  10 , and  11 , housing body  68  additionally includes wall  134  aligned in the axial or Z-axis direction, which is connected to outer wall  72  at cutoff  132 , and is also connected to exhaust transition  108 . Cylindrical outlet wall  136  projects outwardly from wall  134  in the radial direction to define outlet  110  of blower housing  62 . A lobed joint line  138 , which may be considered a secondary joint line with respect to the primary joint line between housing body  68  and housing cover  70  described above, extends between housing body  68  and housing cover  70  along exhaust transition  108 . A transition point  140  is defined between housing body  68  and housing cover  70  immediately downstream of mounting lug  84   a  of housing body and lug foot  100   a  of housing cover  70 , where lobed joint line  138  begins to extend from the primary joint line. Lobed joint line  138  slopes upwardly in the axial or Z-axis direction from joint transition point  40  toward wall  134  of housing body  68 . As may be seen in  FIGS. 7 ,  10 , and  11 , tongue  104  of housing body  68 , which cooperates with groove  106  of housing cover  70  to form the primary joint line, extends around housing body  68  beneath exhaust transition  108  and wall  134 . 
     A recess  142  is defined in exhaust transition  108  of housing body  68  beneath lobed joint line  138 , and a groove  144  is formed in housing body  68  along lobed joint line  138  above recess  142 . As may be seen in  FIGS. 6 ,  10 , and  11 , from transition point  140  immediately downstream of mounting lug  84   a  and lug  100   a , outer wall  72 , top wall  74 , and inner wall  76  of housing body  68  merge with one another to define a smoothly contoured, curved inner surface  146  of housing body  68  along exhaust transition  108 . 
     A recess  148  is defined within housing body  68  proximate wall  134  and outlet wall  136  at the beginning of outer wall  72  beneath a first cutoff portion or cutoff hub  150 . Cutoff hub  150  is broadly radiused, wherein cutoff hub  150  does not include sharp edges. A pin  152  projects downwardly from cutoff hub  150  into recess  148  in the axial or Z-axis direction. 
     Referring to  FIGS. 6 ,  7 ,  12 , and  13 , housing cover  70  generally includes a circular base wall  154  having groove  106  defined around the outer periphery thereof which, as described above, receives tongue  104  of housing body  68  to define the primary joint line between housing body  68  and housing cover  70 . Lip  96  extends upwardly from base wall  154  to define inlet opening  98  in housing cover  70 . Housing cover  70  additionally includes other features, such as an annular depression in base wall  154  which cooperates with housing body  68  to form volute  130 , as well as an annular ridge and a conically-shaped, sloped wall between the annular ridge and lip  96 . The foregoing features, and the advantages provided by same, are described in further detail in the above-incorporated co-pending U.S. patent application Ser. No. 10/934,004. 
     Housing cover  70  additionally includes a lobe  156  having an upper edge which slopes upwardly in the axial or Z-axis direction along lobed joint line  138  from transition point  140  to wall  134  of housing body  68 . The upper edge of lobe  156  includes a tongue  158  shaped to fit within groove  144  of housing body  68  to form lobed joint line  138  between housing body  68  and housing cover  70 . Optionally, a gasket or other seal (not shown) formed of a suitable resilient material, such as rubber or EPDM foam cording, for example, may be fitted between groove  144  and tongue  158  to enhance the seal therebetween. As may be seen from  FIGS. 9 ,  10 ,  13 , and  14 , groove  106  of housing cover  70 , which cooperates with tongue  104  of housing body  68  to form the primary joint therebetween, extends around lobe  156  beneath exhaust transition  108  and wall  134  of housing body  68 . Lobe  156  includes a smoothly, curved, contoured inner surface  160  extending from transition point  140  to an outer wall  162  of lobe  156  which is fitted against wall  134  of housing body  68  when housing cover  70  is joined to housing body  68 . 
     Housing cover  70  additionally includes a broadly-radiused second cutoff portion or cutoff projection  164  projecting from base wall  154  of housing cover  70  in the axial or Z-axis direction, which includes a hole  166  in the upper end thereof which is aligned in the axial or Z-axis direction. Also, the cutoff surface of cutoff projection  164  is sloped upwardly in the axial or Z-axis direction from base wall  154  to the upper end of cutoff projection  164 . When housing cover  70  is joined to housing body  68 , pin  152  of cutoff hub  150  of housing body  68  is fitted within hole  166  of cutoff projection  164  of housing cover  70  to locate housing cover  70  with respect to housing body  68  and to tightly engage the mating surfaces of housing cover  70  and housing body  68 . Alternatively, cutoff hub  150  may include hole  166  and cutoff projection  164  may include pin  152 , or cooperating structure other than a pin-and-hole fitting may be provided between cutoff hub  150  and cutoff projection  164 . Also, when housing cover  70  is joined to housing body  68 , the radially outer wall  168  of lobe  156  is received within recess  142  of housing body  68 . 
     Advantageously, as shown in  FIGS. 6–8 , the broadly-radiused surfaces of cutoff projection  164  of housing cover  70  and cutoff hub  150  of housing body  68  cooperate to define a broadly radiused cutoff  132  within blower housing  62 , which is spaced from the outer edge of impeller  114 . Also, the cutoff surface of cutoff projection  164  is advantageously sloped upwardly in the axial or Z-axis direction from base wall  154  to the upper end of cutoff projection  164 , as best shown in  FIG. 12 . In this manner, as impeller  114  rotates within blower housing, air flow through blade passages  124  of impeller  114  smoothly contacts the broadly radiused and upward-sloped surface of cutoff  132  such that the air flow is only gradually “sliced” or separated from exhaust transition  108  at cutoff  132 , and does not create significant blade pass noise during operation of blower  60 . This is in contrast with the cutoff  54  of known blower housing  20 , shown in  FIGS. 1–4  and described above, which includes a sharp cutoff edge which abruptly chops the air flow from the impeller to generate a loud blade pass noise. 
     Additionally, as shown in  FIGS. 10–13 , the smooth contours of inner surface  146  of exhaust transition  108  of housing body  68  and inner surface  160  of lobe  156  of housing cover  70  cooperate with one another to define a smoothly contoured region between the housing body  68  and housing cover  70  along exhaust transition  108  for minimal disruption of air flow therethrough from the circular main cavity of blower housing  62  to outlet  110  of blower housing  62  for maximum air flow efficiency. 
     As may be seen from  FIGS. 10 and 11 , the overall shape of housing body  68  allows same to be easily formed via a molding process, such as injection molding, using a minimum number of molds. Specifically, the overall shape of housing body  68 , including the features of mounting lugs  84 , tongue  104 , exhaust transition  108  with inner surface  146 , recess  142 , cutoff hub  150 , and pin  152 , allow housing body  68  to be molded using a pair of molds (not shown) which may be separated from housing body  68  in the axial or Z-axis direction after the plastic material of housing body  68  cures. Only a relatively small cylindrical mold (not shown) is needed to form outlet wall  136 , which mold penetrates housing body  68  in the radial or X- or Y-axis direction only up to wall  134 , and which is separated from housing body  68  in the radial or X- or Y-axis direction after the plastic material of housing body  68  cures. Similarly, as may be seen from  FIGS. 12 and 13 , the overall shape of housing cover  70 , including the features of lip  96  and inlet opening  98 , groove  106 , lobe  156  with inner surface  160 , cutoff projection  164  and hole  166 , allow housing cover  70  to be molded using a pair of molds (not shown) which may be separated from housing cover  70  in the axial or Z-axis direction after the plastic material of housing cover  70  cures. 
     In a further embodiment, molded guide vanes and/or other air guiding devices (not shown) may be employed within exhaust transition  108  as a portion of one or both of housing body  68  and housing cover  70  to guide air flow between the circular main cavity of blower housing  62  and outlet  110  to efficiently direct air flow towards outlet  110  that might otherwise begin to spiral towards cutoff  132 . 
     Finally, although blower housing  62  is shown in  FIGS. 5–13  configured in a “clockwise” orientation, in which the shape of blower housing  62  is configured for clockwise rotation of impeller  114 , blower housing  62  may alternatively be configured in a “counterclockwise” orientation, in which the shape of blower housing  62  is configured for counterclockwise rotation of impeller  114 . 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.