Abstract:
A furnace blower has an inexpensive and compact coaxially arranged simplified construction that includes an electric motor having a shell with radially projecting fins that is press-fit into a cylindrical blower housing and a combustion tube that is also press-fit into the blower housing where the interior of a combustion tube is positioned in close proximity to a fan on the motor shaft. The press-fit assembly of the motor into the blower housing as well as the combustion tube into the blower housing simplifies the construction of the furnace blower and reduces its manufacturing costs. The furnace blower is also smaller than prior art furnace blowers which enables it to be readily retrofit into conventional furnaces in place of prior art furnace blowers.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention pertains to a furnace blower having a co-axially arrange and simplified construction. More specifically, the furnace blower comprises an electric motor press-fit into a cylindrical blower housing and a nozzle that is also press-fit into the blower housing. The motor has a shaft with a fan mounted on the shaft and positioned in the nozzle. The press-fit assembly of the motor into the blower housing as well as the nozzle into the blower housing simplifies the construction of the furnace blower and reduces its manufacturing costs. The furnace blower is also smaller than prior art furnace blowers which enables it to be readily retrofit into conventional furnaces in place of the prior art furnace blower. 
     (2) Description of the Related Art 
     A prior art furnace blower  10  is shown in FIGS. 1 and 2. Prior art furnace blowers, and in particular oil burner furnace blowers typically include an electric motor  12  mounted to the side of a fan housing  14  that encloses a squirrel cage fan (not shown). The fan housing  14  also supports an oil pump  16  of the furnace and a blower nozzle  18  that directs a flow of air generated by the squirrel cage fan into the combustion chamber of the furnace. 
     The fan housing of these prior art furnace blowers is constructed of two housing sections  22 ,  24  that are cast of metal. With the housing sections being cast, it is necessary to machine surfaces on the exterior of the housing sections to provide flat, smooth surfaces to which the motor  12 , the oil pump  16  and the blower nozzle  18  can be mounted. The two housing sections  22 ,  24  are also machined to provide flat, smooth surfaces where they are joined together. It is also necessary to machine interior surfaces of the cast housing sections that receive axially aligned bearings (not shown) that support the shaft of the squirrel cage fan. The machining steps required of the fan housing sections significantly contribute to the overall cost of manufacturing the furnace blower. 
     In addition, the motor, oil pump and blower nozzle are secured to the fan housing sections by fasteners, for example, threaded screws and bolts. Assembling these component parts to the housing sections with the threaded fasteners contributes significantly to the time required to assemble the furnace blower and thereby also increases the assembly&#39;s cost of manufacture. 
     SUMMARY OF THE INVENTION 
     What is needed to overcome the disadvantages of the prior art furnace blower constructions is an improved construction of a furnace blower that reduces the number of component parts of the blower and simplifies its assembly. The furnace blower of the invention provides these advantages. 
     The furnace blower of the invention is contained in a cylindrical housing having inlet and outlet ends at axially opposite ends of the housing. The shell of the electric motor employed in the blower is formed of extruded aluminum and has three radially projecting fins. The radially projecting fins are press-fit into the interior of the cylindrical blower housing and center the electric motor coaxially in the housing with a radial spacing between the motor shell and the interior surface of the housing. The radial spacing allows a flow of air through the inlet end of the housing and around the motor as the motor is operated, thereby cooling the motor. A shaft of the motor projects into the motor housing and a fan is mounted on the shaft. The fan is not a squirrel cage fan as employed in prior art blowers, but a fan with radially projecting blades. 
     A combustion tube is also coaxially press fit into the interior of the blower housing. The combustion tube has an inlet opening and an axially opposite outlet opening and tapers as its extends between its inlet and outlet openings. In the preferred embodiment the combustion tube tapers through a curve as it extends from its inlet opening to its outlet opening. The inlet opening of the combustion tube is press fit into the interior of the cylindrical housing. The cylindrical housing has a circular end wall at its outlet end and the end wall has a circular opening that engages around an intermediate portion of the combustion tube and provides further support to the combustion tube in the housing. 
     The construction of the furnace blower of the invention is smaller than that of prior art furnace blowers which enables the furnace blower to be retrofit into most exiting furnaces. The combustion tube outlet end is dimensioned the same size as prior art furnace blowers which also facilitates retrofitting the furnace blower of the invention to existing furnaces. The simplified press fit construction of the furnace blower reduces the number of its component parts and the time required for its manufacture, thus significantly reducing its cost of manufacture from that of prior art furnace blowers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features of the invention are set forth in the following detailed description of the preferred embodiment of the invention and in the drawing figures wherein: 
     FIG. 1 is a perspective view of a prior art furnace blower; 
     FIG. 2 is a perspective view of the prior art furnace blower showing the opposite side of the blower from that of FIG. 1; 
     FIG. 3 is a partially cut away side perspective view of the furnace blower of the invention; 
     FIG. 4 is a side perspective view of the motor and fan of the furnace blower; and 
     FIG. 5 is an end view of the motor and fan of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The furnace blower  32  of the invention is shown in FIGS. 3,  4  and  5 . The furnace blower has a more simplified construction from those of the prior art and is basically comprised of a blower housing  32 , a motor  36 , a fan  38  and a combustion tube  42 . 
     The blower housing  34  is formed as a stamped steel construction as opposed to case iron employed in manufacturing blower housings of the prior art. The housing  34  is formed as a cylindrical tube with an axial length between a first end  44  and a second end  46  of the cylinder that is sufficiently large to contain the motor  36  within the housing. The housing has an exterior surface  48  and an opposite interior surface  52  that surrounds a hollow interior volume  54  of the housing. The first end  44  of the housing defines an inlet end  56  of the furnace blower as will be explained. A circular housing end wall  58  is press-fit into the second end  46  of the cylindrical housing  34 . The end wall  58  is also preferably of stamped steel construction as opposed to the cast iron construction of prior art furnace blower housings. The end wall  58  is formed with an annular shoulder  62  around its periphery that is press-fit into the blower housing second end  46  and engages in a friction fit connection against the housing interior surface  52  as shown in FIG.  3 . By a press-fit connection between the blower housing  34  and the end wall shoulder  62  what is meant is a tight friction fit or interference fit between these component parts that enables them to be held securely together without the use of separate fasteners as is necessary in assembling cast iron housing sections of prior art furnace blowers. The housing end wall  58  is also provided with a circular opening  64  at its center that defines the second end opening of the blower housing  34 . 
     The motor  36  employed in the furnace blower  32  could be any electrical motor but in the preferred embodiment is an induction motor which provides the advantages of high speed operation and the ability to control speeds of operation. The novel feature of the motor of the furnace blower  32  is that it is constructed with a cylindrical, extruded aluminum shell  66  that includes a plurality of fins  68  that are formed as one piece or monolithically with the cylindrical shell  66 . The extruded aluminum construction of the shell  66  and its fins  68  provides the benefit of improved heat transfer from the motor  36  over that of stamped steel construction often used in shells of prior art electric motors. The radial fins  68  also function as a mounting mechanism for the motor as will be explained. The fins  68  preferably extend the axial length of the motor shell  66  and all extend the same radial distance from the motor shell. In the preferred embodiment there are three fins  68  spacially arranged around the motor as shown in FIG.  5 . The motor  36  also includes opposite end caps  72 ,  74 . The two end caps support a pair of bearings  76 ,  78  that also support a shaft  82  of the motor. The motor also supports the oil pump  84  attached to one of its end caps. 
     The fan  38  is secured to an end of the motor shaft  82  that projects from the motor  36  into the housing interior volume  54 . The blower fan  38 , unlike prior art furnace blower squirrel cage fans, is a bladed fan with a plurality of fan blades  86  that extend radially outwardly from a center hub  88  of the fan. The use of an induction motor  36  and its high speed operation enable the use of a bladed fan  38  in the furnace blower  32 . The high speed operation of the motor and fan enables the fan to push a flow of air through the blower housing  34  that is comparable to that of a squirrel cage fan employed in prior art furnace blowers. In addition, the use of the bladed fan  38  instead of a squirrel cage fan reduces the overall size of the furnace blower  32 . 
     The combustion tube  42  is also preferably of stamped steel construction. As seen in FIG. 3, the combustion tube  42  has a general conical configuration with an axial length between an input end  92  and output end  94  of the combustion tube. The combustion tube input end  92  defines a circular inlet opening  96  of the combustion tube. The input end has a cylindrical dimension that enables the input end  92  to be press-fit into the interior of the blower housing  34  where the exterior surface  98  of the nozzle engages in a tight friction fit or interference fit with the interior surface  52  of the housing. As shown in FIG. 3, the combustion tube tapers through a curve as it extends from its input end  92  to its output end  94  which is positioned outside the blower housing  34 . As the combustion tube tapers toward its output end  94  its exterior surface  98  engages in a press-fit connection with the housing second end opening  64  in the center of the housing end wall  58 . In addition, as the combustion tube tapers from its input end to its output end  94  the combustion tube interior surface  102  comes in close proximity to the fan blades  86  of the fan  38  mounted on the motor shaft  82 . This enables the fan  38  to produce air at a high static pressure through the furnace blower  32 . 
     In assembling the component parts of the furnace blower  32 , the fan  38  is first mounted on the motor shaft  82  at a predetermined axial position on the motor shaft and is secured in place. The motor  36  is then inserted into the blower housing  34  through the first end  44  of the housing. The radial fins  68  of the motor are press-fit against the housing interior surface  52  as the motor is inserted, providing a tight connection between the motor and the housing. The motor is inserted to the extent that the ends of the radial fins  68  opposite the fan  38  are aligned with the first end opening  56  of the housing. This properly positions the fan  38  relative to other component parts of the furnace blower to be assembled. The radiating fins  68  also function to provide a radial spacing  104  between the motor shell  66  and the housing interior surface  52 . This radial spacing between the motor shell and the blower housing provides a flow path of air into the housing from the first end opening or the inlet end of the blower  56  that passes over and cools the motor. By constructing the motor shell  66  and the fin  68  as one monolithic piece of extruded aluminum the heat transfer ability of the motor is improved, thus enhancing the cooling effect of the air flow over the motor shell. 
     The combustion tube  42  is next assembled into the blower housing  34  with the input end  92  being inserted through the housing second end  46 . The combustion tube input end  92  engages in a press-fit connection with the housing interior surface  52  that securely holds the combustion tube in the housing. The combustion tube input end  92  is inserted to the extent that it abuts against the ends of the motor shell fins  68 , thus properly positioning the combustion tube  42  relative to the motor  36  and the blower housing  34  and properly positioning the fan  38  on the motor shaft  82  in the tapered intermediate portion of the combustion tube in close proximity to the interior surface  102  of the combustion tube. 
     The housing end wall  58  is then assembled onto the second end  46  of the blower housing with the end wall annular shoulder  62  fitting in a press-fit connection against the housing interior surface  52 . As the end wall  58  is assembled to the blower housing  34  the combustion tube  42  passes through the end wall center opening  64 . As the end wall shoulder  62  is press-fit against the housing interior surface at the housing second end  46  the end wall opening  64  is press-fit around the exterior surface  98  of the combustion tube, thus further supporting the tube in the furnace blower  32 . 
     The furnace blower  32  constructed of the component parts described above and in the manner described above provides a more compact construction and a more economical construction for a furnace blower than that of prior art furnace blowers. The construction of the furnace blower is comprised of basically four component parts, the housing, the motor, the fan and the combustion tube. Each of these component parts are assembled to each other by press-fit connections, eliminating the need for mechanical fasteners and the time required in attaching component parts by mechanical fasteners. The stamped steel construction of the furnace blower housing also eliminates the machining steps required by prior art furnace blower housings and further reduces the manufacturing costs of the furnace blower. 
     While the present invention has been described by reference to specific embodiment, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the invention defined in the following claims.