Abstract:
An improved cooling fan ( 12 ) fan for cooling an electronic component includes a rotor ( 26 ) rotatably mounted in a housing ( 18 ) and having a plurality of fan blades ( 28 ). The housing ( 18 ) includes a first end ( 20 ), a second end ( 24 ), and a passage ( 24 ) interconnecting the first end and the second end to define an air flow path ( 25 ) therebetween. An entry port ( 16 ) is defined by an upstream portion of the housing ( 18 ) generally adjacent the housing first end ( 20 ), with the entry port ( 16 ) having a cross-sectional area greater than a cross-sectional area of the passage ( 24 ). The entry port ( 16 ) and the passage ( 24 ) being separated by a transition zone ( 30 ), with the entry port ( 16 ) and the transition zone ( 30 ) cooperating to define an abrupt step ( 36 ). The abrupt step ( 36 ) is adapted to at least partially affect the flow of air flowing along the flow path ( 25 ), thereby reducing the ambient noise level of the fan.

Description:
FILED OF THE INVENTION 
     The present invention relates generally to cooling fans for electronic components. More specifically, the present invention relates to an improved housing for such fans which lowers ambient noise levels, and further relates to a method of reducing the noise levels in existing fans. 
     BACKGROUND OF THE INVENTION 
     Power devices in electronic components produce heat, and the heat must be removed in order for the electronic component to function properly. In some cases, simple convection provides adequate cooling. However, in a wide variety of applications, simple convection may not be sufficient and thus cooling fans must be used. The cooling fans greatly improve airflow past the devices, thereby preventing overheating and premature failure. Unfortunately, the cooling fans add a significant amount of noise to the overall system. In many cases, this added noise is undesirable and/or unacceptable. 
     Designers of electronic components are constantly searching for ways to reduce fan noise, such as by altering a number of design parameters including the design, pitch and size of the fan blades and the clearance of the fan blade tips within the housing. Nevertheless, there is a continuing need for ever quieter cooling fans for electronic components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially exploded view isometric view of a muffin type cooling fan and an entry port therefor constructed in accordance with the teachings of the present invention; 
     FIG. 2 is an elevational view of a housing for the muffin-type cooling fan shown in FIG. 1, with the housing having an entry port constructed in accordance with the teachings of the present invention; 
     FIG. 3 is a cross-sectional view taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is an enlarged fragmentary cross-sectional view taken about the circumscribed portion of FIG. 3; and 
     FIG. 5 illustrates 13 different entry port profiles. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following descriptions of the preferred embodiments are not intended to limit the scope of the invention to the precise forms disclosed, but instead are intended to be illustrative of the principles of the invention so that others may follow its teachings. 
     Referring now to the drawings, FIG. 1 illustrates an entry shroud  10  constructed In accordance with the teachings of the present invention and which is shown with a muffin-type fan  12  of the type commonly employed for the cooling of electronic components (not shown). The shroud  10  may be constructed of a plate  14  having a port  16  defined therein, which plate  14  may be attached to a housing  18  of the fan  12  using suitable fasteners (not shown). Alternatively, the shroud  10  and its associated port  16  may be formed as part of the housing  18  of the fan  12  using known molding or other fabrication techniques. 
     The fan  12  includes the housing  18  having an inlet end  20 , an outlet end  22 , and a generally cylindrical passage  24  extending between the inlet end  20  and the outlet end  22 , such that air will flow through the housing  18  along a flow path indicated by the reference arrow  25 . As shown in FIG. 1, the fan  12  typically includes a fan rotor  26  having a plurality fan blades  28  extending radially therefrom, with the fan rotor  26  being rotatably supported in the housing  18  in a known manner and driven by an electrical motor (not shown) in a known manner. 
     The inlet end  20  of the housing  18  may include an outwardly flared transition  30 , which will have an entry diameter slightly greater than the three inch (3″) nominal diameter of the passage  24 . As shown in FIGS. 3 and 4, the flared transition is disposed between the entry port  16  and the passage  24 . 
     In the embodiment shown, the passage  24  has a length of about one and one-half inches (1.5″). The flared transition  30  terminates in a front mounting plate  32  having a generally fiat surface  34 . It will be understood that, if the shroud  10  is molded in conjunction with the housing  18  as alluded to above, then an upstream face  33  of the plate  14  will form the front mounting plate  32 . Similarly, the housing  18  may include a flared transition  35  adjacent the outlet end  22  as shown in FIG.  3 . It will be understood that the above-given dimensions for the fan  12  will vary depending on the size of the fan chosen for a particular application. 
     As shown in FIGS. 3 and 4, a step  36  is defined generally adjacent an interface  38  between the entry port  16  and the passage  24 . As best shown in the enlarged view of FIG. 4, the entry port  16  includes an inner surface  40 , which preferably has a generally flat cross section oriented generally parallel to the flow  25 , while an upstream portion of the flared transition  30  includes a surface  42 , which also preferably has a generally flat cross section oriented generally perpendicular to the flow  25 . It will be noted that the flared transition includes a surface  44 , which preferably has a generally curved cross section, which leads to a sloping portion  46 , preferably having a generally flat cross section and being disposed downstream towards the passage  24 . As shown, the inner surface  40  and the surface  42  intersect at a vertex  47  which is roughly 90 degrees. The vertex  47  may of course have a slight radius or other characteristics dictated by assembly or molding practices. Further, the cross section defined adjacent the intersection of the entry port  16  and the flared transition  30  may take a variety of shapes, as long as the flow interrupting step  36  is defined thereby. 
     Further, it will be understood that the cross-sectional shape defined by the intersection of the surfaces  40 ,  42 ,  44  and  46  together define a means  49  which protrudes at least partially into the flow path  25 , and which further forms cavities which recede away from the flow path  25 , all of which alters or at least partially interrupts the flow characteristics of air flowing along the flow path  25 . It will be understood that the means  49  may be defined by other combinations of intersecting surfaces, which may protrude into, away from, or partially into and partially away from the flow path  25 . 
     As shown in FIG. 1, the entry port  16  is sized to define or encompass a cross sectional area that is greater than the cross sectional area defined by the passage  24 . According to a preferred embodiment, the cross sectional area defined by the entry port will be between about 5% to about 10% greater than the cross sectional area of the passage  24 . Still preferably, for a fan  12  having a nominal diameter of three inches (3″), the entry port  16  will have a nominal diameter of about three and one-eighth inches (3⅛″). 
     The entry port  16  includes a length dimension  48 , which generally corresponds to a thickness of the plate  14  if the entry shroud  10  is formed of a separate piece. For a fan  12  having a passage  24  with a nominal length dimension  50  of one and ½ inches (1.5 inches), the plate  14  will have a thickness between about 0.06 inches and about 0.20 inches, which corresponds to a length dimension  48  for the entry port  16  between about 4% and about 13% of the length  50  of the passage  24 . 
     Referring again to FIG. 1, the entry port  16  includes a generally curved inner edge  52 , thus giving the entry port a generally round entry profile (see also, for example, the entry profiles illustrated in FIG.  5 ). Alternatively, depending on the dimensions of the fan  12 , the inner edge  52  of the entry port  16  may include a number of curved sections  54  and a number of generally straight sections  56 , giving the entry port  16  the entry profile shown in FIG.  2 . 
     Referring now to FIG. 5, a variety of possible entry ports are shown, with each having a different entry profile. The entry ports are labeled as entry ports  16 . 1  through  16 . 8 . The entry port  16 . 1  is substantially as described above and includes a flat surface  40 , and thus will not be described further. 
     The entry port  16 . 2  includes an inner surface  40 . 2  having a plurality of sharp fins  60 . 2  spaced about the inner circumference thereof, with each of the sharp fins  60 . 2  extending about 0.2 inches radially inwardly into the flow path  25 . 
     The entry port  16 . 3  includes an inner surface  40 . 3  having a plurality of sharp fins  60 . 3  spaced about the inner circumference thereof, with each of the sharp fins  60 . 3  extending about 0.2 inches radially inwardly into the flow path  25 . Each of the fins  60 . 3  is angled in a direction counter to the rotational direction  70  of the fan rotor  26 . 
     The entry port  16 . 4  includes an inner surface  40 . 4  having a plurality of sharp fins  60 . 4  spaced about the inner circumference thereof, with each of the sharp fins  60 . 4  extending about 0.2 inches radially inwardly into the flow path  25 . Each of the fins  60 . 4  is angled in a direction coinciding with the rotational direction  70  of the fan rotor  26 . 
     The entry port  16 . 5  includes an inner surface  40 . 5  having a plurality of lobes  60 . 5  spaced about the inner circumference thereof, with each of the lobes  60 . 5  extending about 0.2 inches radially inwardly into the flow path  25 . 
     The entry port  16 . 6  includes an inner surface  40 . 6  having a plurality of rounded fins  60 . 6  spaced about the inner circumference thereof, with each of the rounded fins  60 . 6  extending about 0.2 inches radially inwardly into the flow path  25 . Each of the fins  60 . 6  is angled in a direction counter to the rotational direction  70  of the fan rotor  26 . 
     The entry port  16 . 7  includes an inner surface  40 . 7  having a plurality of rounded fins  60 . 7  spaced about the inner circumference thereof, with each of the rounded fins  60 . 7  extending about 0.2 inches radially inwardly into the flow path  25 . Each of the fins  60 . 7  is angled in a direction coinciding with the rotational direction  70  of the fan rotor  26 . 
     The entry port  16 . 8  includes an inner surface  40 . 8  having a plurality of rounded indentations  60 . 8  spaced about the inner circumference thereof, with each of the rounded indentations  60 . 8  extending about 0.2 inches radially outwardly into the inner surface  40 . 8  (i.e., away form the flow path  25 ). 
     In operation, the shroud  10  may be constructed in a number of possible ways. If the shroud  10  is constructed of a separate plate  14 , then the plate  14  having the entry port  16  defined therein is mechanically fastened, glued, bonded, or otherwise secured to the housing  18  of the fan  12  along the interface  38 . Second, if the shroud  10  is formed integrally with the housing  18 , then the entire unit may be molded using conventional molding practices following the above outlined shape and/or dimensional characteristics for the entry port  16 . Third, the plate  14  may be formed in a mounting portion of the electronic component to be cooled (not shown), such that the step  36  is formed when the fan  12  is mounted to the electronic component. 
     Air is drawn through the housing  18  of the fan  12  in response to rotation of the rotor  26  and its attached fan blades  28  in a conventional manner. As air flows along the flow path  25 , the flow characteristics of the air is at least partially altered and/or interrupted as the air flows past the step  36 . The air flow may be further altered and or interrupted depending on the shape of the inner surface  40  of the entry port  16  (i.e., by substituting any one of the profiles  16 . 1  through  16 . 8  shown in FIG. 5 as outlined above). 
     Those skilled in the art will appreciate that, although the teachings of the invention have been illustrated in connection with certain embodiments, there is no intent to limit the invention to such embodiments. On the contrary, the intention of this application is to cover all modifications and embodiments fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.