Abstract:
A marine in line bilge blower and a method of manufacturing same are described. The blower, or fan, includes a housing in which a motor, airfoils, a fan wheel hub, and straightening vanes are positioned. Specifically, numerous airfoils are positioned on a fan wheel hub, which is in connection with a motor. The motor is mounted on one of several straightening vanes. The housing includes a base with a pair of feet. To protect the circumference of the housing from physical and thermal stress, strengthening rings are positioned on the circumference.

Description:
BACKGROUND 
     The invention relates generally to an exhaust fan and more particularly to an axial-flow exhaust fan for use as a bilge blower in marine environments. 
     Two industrial forms of fans or blowers predominate, axial-flow fans and centrifugal, or radial-flow, fans. In centrifugal fans, air flows through the fan wheel in a mostly radially outward direction, while air flows in an axial-flow fan in an axial direction with almost no radial component. 
     Axial-flow fans operate by deflecting axially directed air on airfoils, or blades. This deflection causes the air flow to take on a helical flow pattern past the airfoils. This flow shape has two flow components, tangential velocity and axial velocity. Of the two flow components, the axial velocity is the more important component for moving air through the fan. Guide vanes positioned either upstream or downstream of the airfoils serve to translate the tangential velocity component of the air flow into the axial velocity component. 
     There are two methodologies for determining the size, dimensions, and number and positioning of blades for an axial-flow fan. One method is testing a first axial-flow fan design to ascertain the air volume and static pressure of the fan. Rarely does a first design meet the desired running parameters, and thus redesigning one or more times becomes necessary. Redesigning costs man-hours, and often the result is a fan which is larger than originally anticipated that runs at higher speeds and consumes more brake horsepower than needed. In addition, redesigning often leads to uneven and turbulent air flow and to the creation of stalling effects in certain parts of the blades. 
     A second methodology, which improves over the first methodology, is to design the axial-flow fan based upon desired outcome parameters as well as desired structural and design parameters. Such parameters may include high efficiency and low sound output over a wide range of operation, non-overloading brake horsepower, a steep pressure curve (little variation in air delivery), a large free delivery of air, large pressure safety margin, and compactness. 
     One problem experienced with conventional axial fans used in marine environments is that the fan housings are subjected to physical and thermal stresses which may alter the diameter of the housings. 
     SUMMARY 
     The invention provides an axial-flow fan which includes a plurality of airfoils extending from a rotatable fan wheel hub, a motor engaged with the fan wheel hub through a shaft, and a housing into which the fan wheel hub and the motor are positioned. The housing has a circumference with a diameter and at least one supporting element surrounding the circumference of the housing. The supporting element inhibits variation in the diameter of the circumference of the housing. 
     The invention further provides a method of manufacturing an axial-flow fan. The method includes the steps of engaging a fan wheel hub with a motor through a shaft, mounting at least one straightening vane from an inner surface of a housing, positioning the fan wheel hub and the motor within the housing such that the motor is mounted on one of the straightening vanes, and surrounding the housing with at least one supporting element which inhibits variation in the diameter of the circumference of the housing. 
     With these and other objects, advantages and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an axial-flow fan constructed in accordance with an embodiment of the invention. 
     FIG. 2 is a partial cross-sectional view of the fan of FIG.  1 . 
     FIG. 3 is another perspective view of the fan of FIG.  1 . 
     FIG. 4 is another perspective view of the fan of FIG.  1 . 
     FIG. 5 is a top view of the fan of FIG. 1 coupled with a pair of ventilation hoses. 
     FIG. 6 is a partial cross-sectional view showing the interior of the fan of FIG.  1 . 
     FIG. 7 is a perspective view of an axial-flow fan constructed in accordance with another embodiment of the invention. 
     FIG. 8 is a partial cut-out view from the side of the fan of FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1-5 illustrate an axial-flow fan  10  constructed according to a preferred embodiment of the invention. The fan  10  includes a housing  18  extending from a first end  11  to a second end  13 . Positioned within the housing  18  between the ends  11 ,  13  is a fan apparatus which includes a fan wheel hub  12 . A plurality of airfoils  14  extend from the hub  12  leaving a small space between the inner surface of the housing  18  and the farthest extent of the airfoils  14 . The airfoils  14  are designed similarly to wings on an airplane, wherein the side of the airfoils  14  facing the inlet end  11  has a greater surface area than the side of the airfoils  14  facing the outlet end  13 . 
     The diameter of the hub  12  is chosen to maximize the airflow through the fan  10 . Hubs having a smaller diameter relative to the diameter of the housing experience greater turbulence, especially at or near the midpoint of the housing. As the diameter of a hub, such as the hub  12 , increases, the amount of turbulence experienced diminishes. For a housing  18  inside diameter of four inches, preferably the hub  12  diameter is two and one-half inches. For a three inch diameter housing  18 , the hub  12  diameter is preferably two inches. 
     The hub  12  is physically connected to a motor  46  through one end of a motor shaft  47 . Located between the hub  12  and the end  13  are one or more straightening vanes  26  extending from an inner surface of the housing  18 . The motor  46 , which is mounted to one of the straightening vanes  26 , drives the hub  12 , via the shaft  47 , causing the hub  12  to rotate. The rotation of the airfoils  14  draws air into the fan apparatus through end  11 . As the air is drawn over the airfoils  14 , it takes on a corkscrew shape due to the tangential velocity component. As the air continues to be drawn through the vanes  26 , the tangential velocity component is translated into an axial velocity component by the curvature of the vanes  26 . Through this design, the fan  10  moves more air in a more efficient manner in that it draws less current and is quieter. 
     The dimensions and number of the airfoils  14  and straightening vanes  26  may be determined by an algorithm for optimizing the performance of the fan  10 . The algorithm is available in Bleier, Frank P.,  FAN HANDBOOK Selection, Application, and Design  (1998). 
     The diameter of the housing  18  should remain relatively constant and not vary. For example, since the fan  10  has been designed based on various desired output parameters, a change in the diameter of the housing  18  or its profile may affect the output parameters. Further, if the diameter of the housing  18  is made smaller where the airfoils  14  are located, the airfoils  14  may strike the inner surface of the housing  18  during rotation, most likely leading to premature wear of the airfoils  14  and certainly leading to decreased efficiency of the fan. 
     One or more strengthening portions, such as, for example, stiffening rings  20  are placed around the circumference of the housing  18  to provide support for the housing and to serve as a positive stop for positioning and mounting ventilation hoses (described below). Preferably, at least one of the rings  20  is provided on the circumference of the housing  18  surrounding the airfoils  14 . With this added strength, the housing  18  is better able to remain in its intended shape and is more resistant to physical and/or thermal forces, such as caused by clamping hoses on the ends  11 ,  13 , which may tend to warp or misshape the housing  18 . In addition, the stiffening rings  20  provide a positive stop along the circumference of the housing  18  for positioning hoses placed over either end of the fan  10 . 
     A tapered collar  22  is located at the end  11 , and another tapered collar  24  is located at the end  13 . The tapered collars  22 ,  24  each include one or more collar tabs  25 . The collar tabs  25  assist in attaching the hoses  38 ,  40  to the collars  22 ,  24  by extending radially higher than the collars  22 ,  24 . The tabs  25  do not extend around the circumference of the fan housing  18 . If the tabs  25  did extend around the circumference, their added height would render impossible attempts to attach the hoses  38 ,  40  to the collars  22 ,  24 . 
     A dimple  16  is provided on the hub  12 . The dimple  16  is sized and configured to mate with an assembly fixture (not shown) during assembly of the fan  10 . Specifically, the dimple  16  ensures proper alignment of the hub  12  with the motor  46  through the shaft  47 . 
     Marine environments are prone to the effects of moisture. Moisture can lead to corrosion, and so it is important to minimize the amount of moisture contacting the motor  46  and the shaft  47 . Only one of the ends of the shaft  47  is protected from the moisture. The first end of the shaft  47  is attached to the hub  12 . The shaft  47  extends from the hub, through a shaft pocket  30  of a sealing chamber  28  (FIG. 3) located in a back side of the fan wheel hub  12 , and into the motor  46 . Preferably, an elastomeric washer is placed over the first end, and some grease is applied to the first end, which is then fitted snuggly into the shaft pocket  30 . Nonetheless, a portion of the shaft  47  near the first end remains exposed. 
     A second end of the shaft  47  is protected from moisture by a protective boot  32  (FIG.  4 ). The boot  32 , which is preferably formed of vinyl, covers the second end of the shaft  47  coming from the motor  46 . Openings  34  are created in the boot  32  to allow for a pair of wires  36  to be squeezed out. The motor  46  is also protected from moisture by a spray coating of a protectant, such as, for example, dichromate. 
     The entire housing  18  is supported on a hollow base  42  having a pair of feet  44 . The feet  44  each contain an opening  45  which may be utilized to attach the fan  10  to some base substrate (not shown). The hollowness of the base  42  adds strength while lessening weight of the fan  10 . 
     FIGS. 7 and 8 illustrate a second embodiment of the invention. Specifically, an axial-flow fan  110  is shown having a housing  18  extending between a first end  11  and a second end  13  and housing a fan apparatus including a fan wheel hub  112 . A plurality of airfoils  114  extend from the hub  112 . The chief difference between the hub  12  and the hub  112  is the diameter of the hub. While the hub  12  in a housing with an inside diameter of four inches is in the range of two and one-half inches and the hub  12  in a housing  18  with a diameter of three inches is about two inches, the hub  112  within a four inch diameter housing  18  and within a three inch diameter housing is in the range of, respectively, two and 1.65 inches. The diameter of the hub  112  approximates the diameter of the motor  46 , and does not cause an impediment to naturally occurring air flow. 
     Certain Coast Guard regulations require that a boat cabin have a natural air source, i.e., a source of naturally circulated, and not circulated under power, air so that a predetermined amount of fresh air is circulated through the cabin. Most boat manufacturers build a single shaft into a cabin. Thus, for boats that must follow the Coast Guard regulations and that have only a single shaft into the cabin, the axial-flow fan  10 ,  110  must be placed in the shaft or a second shaft must be created to fit the fan. 
     If a second shaft is not to be created in the cabin, then the fan fitting within the single shaft must allow a certain predetermined amount of naturally circulated fresh air. In such an instance, the hub must be a smaller diameter to allow a greater amount of naturally circulating air in. 
     The base  42  includes a flow direction section  140  which provides an arrow to indicate the designed air-flow direction to installers of the fan  110 . 
     The above description and drawings are only illustrative of preferred embodiments of the inventions, and are not intended to limit the inventions thereto. For example, while stiffening rings  20  have been described as the strengthening portions, other forms of strengthening portions may be used for providing circumferential support to the housing  18 . Examples of other suitable strengthening portions may include axially directed elements which are positioned about the circumference of the housing or radially directed elements which extend around only a portion of the circumference of the housing. Any subject matter or modification thereof which comes within the spirit and scope of the following claims is to be considered part of the present inventions.