Abstract:
A generator incorporating a double sided fan operable to generate dual, spaced apart, simultaneous cooling airflows within the generator to more efficiently cool internal components located on opposite sides of the fan. The double sided fan generates a first cooling airflow into a permanent magnet generator (PMG) assembly and a second cooling airflow through an electronics assembly. The first cooling airflow cools a stator disposed within the PMG assembly, while the second cooling airflow cools a plurality of circuit boards disposed within the electronics assembly. The fan exhausts both cooling airflows radially outwardly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from U.S. Ser. No. 60/479,022 filed Jun. 17, 2003, the disclosure of which is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention relates to generators, and more particularly to a portable generator having a pair of cooling airflow paths formed to simultaneously cool a circuit board and a rotor/stator assembly of the generator through the use of a single fan. 
   BACKGROUND OF THE INVENTION 
   Generators are used in a wide variety of applications to provide AC or DC power to power electrical tools or implements. In particular, portable generators typically make use of an internal combustion engine which drives a rotor having a plurality of permanent magnets affixed thereto, and where the rotor is coupled to an output shaft of the engine. The rotor is disposed within a stator. Cooperatively these components form a portion of a permanent magnet generator. 
   Typically one or more electronic circuit boards are disposed adjacent the rotor and stator. Since these components can become quite hot during prolonged use, it is necessary to provide a cooling airflow that not only cools both the rotor and stator, but also the electronic circuit boards that control operation of the generator. Traditionally, this has been accomplished by the use of more than one fan. For example, one fan may be positioned to draw air in through an opening in a housing within which the stator and rotor is disposed, while a separate fan is positioned within a different location in order to draw a cooling airflow around the electronic circuit boards. 
   Other attempts at addressing the important issue of cooling the internal components of a generator have involved the use of a single fan which generates a main airflow, which is then subsequently divided and channeled into different areas of the generator. 
   In view of the foregoing, there still exists a need for even more effective cooling of the internal components of a generator. More particularly, there still exists a need for a cooling arrangement which can effectively cool the stator/rotor assembly located within a housing of the generator, as well as the electronic circuit board(s) located remotely from the stator/rotor assembly. It would be particularly desirable to provide an arrangement wherein a single fan disposed strategically within the generator could be used to generate two distinct cooling airflow paths to optimally cool both the rotor/stator assembly as well as an electronics circuit board that is located remotely from the rotor/stator assembly. The use of a single cooling fan that more effectively cools the stator/rotor assembly, as well as the electronic circuit board(s) of the generator would serve to reduce the overall cost of the generator, further improve reliability and simplify the construction of the generator. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a generator which makes use of a single fan to generate a plurality of distinct cooling airflows within interior structure of the generator. The plurality of cooling airflows are used to effectively cool both a rotor/stator assembly of the generator as well as an electronic printed circuit board assembly disposed within the generator but remotely from the rotor/stator assembly. 
   In one preferred form the generator includes a double sided fan coupled to an output shaft of an internal combustion engine of the generator. The double sided fan is disposed in between a rotor/stator assembly, which is also coupled to the output shaft, and an electronics printed circuit board assembly. A housing of the generator encloses the rotor/stator assembly and has openings at one end thereof through which the double sided fan can draw in a first cooling airflow. The first cooling airflow flows through the stator windings to effectively cool these windings during operation. The double sided fan further is positioned adjacent to an electronic control assembly which houses the electronics printed circuit board assembly components that control operation of the generator. The double sided fan draws a second cooling airflow path in through the electronic control assembly and exhausts it out through an exhaust outlet region together with the first cooling airflow. Accordingly, two distinct cooling airflows are drawn into the generator from different inlet points to simultaneously cool both the rotor/stator assembly and the printed circuit boards within the electronic control assembly. This makes for a very compact, yet effective airflow cooling arrangement that only requires a single fan to implement. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of a portable generator in accordance with a preferred embodiment of the present invention; 
       FIG. 2  is an exploded perspective view of certain of the internal components of the generator of  FIG. 1 ; 
       FIG. 3  is a simplified partial side cross sectional view of the components of  FIG. 2  shown in assembled relationship illustrating the dual cooling airflows generated by a double sided fan of the generator; 
       FIG. 4  is a side view of the fan shown in  FIG. 3 ; and 
       FIG. 5  is an end view of the fan of  FIG. 4  taken in accordance with directional line  5 — 5  in FIG.  4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   Referring to  FIGS. 1 and 2 , a generator  10  in accordance with a preferred embodiment of the present invention is shown. The generator forms a portable generator which is supported on a frame  12  and by at least a pair of wheels  14 . The generator  10  comprises an internal combustion (IC) engine  16  which is operatively coupled to a permanent magnet generator (assembly  39  in  FIG. 2 ) and an electronics control assembly  44  (component  44  in FIG.  2 ), both of which are hidden from view in  FIG. 1. A  control panel  22  ( FIG. 1 ) is also operatively coupled with the electronics control assembly to enable the user to control operation of the generator and to make use of its generated electrical power. 
   Referring specifically to  FIG. 2 , certain components of the generator  10  can be seen in exploded fashion. The internal combustion engine  16  includes an output shaft  16   a  which extends through an opening  24  in a front end bell  26 . The front end bell  26  encloses a position sensor housing  28 , a pair of insulating end rings  30  and  32 , a stator  34  disposed in between the end rings  30  and  32 , a rotor  36  and a fan baffle  38 . A back end bell  40  encloses a double sided fan  42 . The back end bell is coupled to the electronic control assembly  44 . The electronic control assembly  44  is comprised of a cover  46 , a box  48 , a pair of printed circuit boards  50  and  52 , and a battery charger assembly  54 . An air cone seal  56  is disposed on an inside surface  58  of cover  46  to provide a seal with the back end bell  40 , which will be described in further detail momentarily. 
   With continued reference to  FIG. 2 , the front end bell  26  also includes a plurality of circular airflow openings  60  and a pair of tabs  62  which are used to mount the position sensor housing  28  coaxially within the opening  24 . Tabs  62  can be secured with external fastening elements (not shown) that extend through an arcuate slot  64  in the sensor housing  28  to enable rotational adjustment of the position of the sensor housing  28 . 
   With further reference to  FIG. 2 , the stator  34  is supported in conventional fashion within the front end bell  26  and is sandwiched between the insulating end rings  30  and  32 . The output shaft  16   a  of the IC engine  16  extends through a central opening  66  in the sensor housing  28 , through the insulating end rings  30 ,  32  and through the stator  34  into a fitting  68 . The fitting  68  is press fit into the rotor  36 . The rotor  36  is thus fixedly attached to the output shaft  16   a  to rotate therewith. Components  26 ,  28 ,  30 ,  32 ,  34 ,  36 ,  38 ,  40 ,  42  and  68  form the permanent magnet generator (PMG) assembly  39 . 
   Also attached to the output shaft  16   a  is the double sided fan  42 . The fitting  68  extends through a central opening  70  in a hub  71  of the double sided fan  42  so that the fan can be press fit onto the output shaft  16   a . The double sided fan  42  has a diameter just slightly smaller than an internal diameter of the back end bell  40  such that it is able to rotate freely within the back end bell. A flange  72  of the back end bell  40  extends through a central opening  74  in the panel  46  and is engaged around its periphery by the air cone seal  56 . The air cone seal  56  may be formed from any suitable, flexible sealing material, but in one preferred form it is comprised of rubber. 
   Referring briefly to  FIGS. 4 and 5 , the double sided fan  42  can be seen in greater detail. The fan generally comprises a central or base portion  76  having a plurality of orthogonally extending fan blades  78  extending from opposite sides of the base portion  76 . Opening  70  is sized to be press fit over a portion of the fitting  68  of the PMG  39 . The blades  78  serve to draw air towards the fan in the direction of arrows  80  and  82  in FIG.  5  and then radially away from the fan in accordance with arrows  84  and  86  in FIG.  5 . The fan  42  may be made from a variety of materials but is preferably formed from high strength plastic, steel or aluminum. In one preferred form the fan  42  comprises a total of  38  independent fan blades  78  spaced evenly, circumferentially about its periphery, and has a diameter of about 7.9 inches (200 mm). However, it will be appreciated that this dimension and the number, as well as the shape, of the blades  78  could vary considerably depending on the cooling airflow requirements needing to be met. 
   Referring to  FIG. 3 , there is shown a simplified cross sectional view of the components comprising the IC engine  16 , the PMG assembly  39  and the electronics assembly  44 . In operation, the output shaft  16   a  drives the fan  42  rotationally which causes the fan to induce a pair of airflows  88  and  90 . Airflows  88  enter an interior area of the PMG  39 , and more specifically through the openings  60  in the front end bell  26 . Airflows  90  enter the electronics assembly  44  through openings or slots  92  formed in an end wall  94  of the cover  48 . 
   Airflows  88  flow inbetween the stator and the front end bell  26 , to thus help cool the stator  34  windings. The seal created by end bell  26  and the stator  34  around the inner diameter of the stator prevents air flows  88  from entering the gap between stator  34  and rotor  36 . Airflows  90  flow around circuit boards  50  and  52 , out through the opening  74  in the panel  46 , and into the back end bell  40  through opening  73 . Both airflows  90  and  88  are then directed radially outwardly by the fan  42  out through openings  96  in the back end bell  40 . Accordingly, the single double sided fan  42  is used to create separate cooling airflows from spaced apart locations to more effectively cool the various internal components of the PMG  39  and the electronics assembly  44 . The use of only a single fan  42  saves appreciable space within the generator  10 , simplifies its construction and reduces its overall cost and complexity. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.