Abstract:
An impeller for a radial-flow heat dissipating fan includes a hub and a plurality of blades surrounding the hub. The blades are connected to a circumference of the hub to allow joint rotation of the hub and the blades. More than one blade include an air inlet side edge and an air outlet side edge. The air inlet side edge of each of the more than one blade has a radial length smaller than that of the air out side edge, thereby increasing an air inlet amount and smoothly changing incoming axial airflow into centrifugal airflow.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an impeller for a radial-flow heat dissipating fan. In particular, the present invention relates to an impeller for a radial-flow heat dissipating fan with increased air inlet amount. 
   2. Description of Related Art 
     FIG. 1  of the drawings illustrates a conventional radial-flow heat dissipating fan. The radial-flow heat dissipating fan in  FIG. 1  comprises a casing  1  and a cover  2 . The casing  1  includes a compartment  11  and a side outlet  12 . The cover  2  is mounted to the casing  1  and includes an inlet  21 . An impeller  3  is rotatably mounted in the compartment  11  of the casing  1  and includes a hub  31 , a supporting member  32  extending from the hub  31 , and a plurality of blades  33  each having an edge mounted on a side of the supporting member  32 . 
     FIG. 2  illustrates another conventional radial-flow heat dissipating fan, wherein a connecting ring  34  extends across the other edges of the blades  33  to improve the strength. In operation, turning of the blades  33  of the impeller  3  drives axial airflow into the casing  1  via the inlet  21  of the cover  2 . Then, the axial airflow is driven by the blades  33  to exit the casing  1  via the side outlet  12  for dissipating an object such as a fin. 
   Although the above radial-flow heat dissipating fans are widely used in computers, there are still several problems. First, the other edge  33   a  of each blade  33  is located at the same level as a top face of the hub  31 . After assembly, the top face of the hub  31  is very close to the inlet  21  of the cover  2 . Thus, the incoming air can only pass through the inlet  21  via the gap between the blades  33 , resulting in limitation to the amount of the incoming axial airflow. In this case, if the other edge  33   a  of each blade  33  has a relatively long radial length, the other edge  33   a  interferes with entrance of the incoming axial airflow via the inlet  21 . The air inlet amount could not be increased, the air outlet amount and the wind pressure are reduced. Secondly, if the other edge  33   a  of each blade  33  has a relatively long radial length, the incoming axial airflow entering the casing  1  via the inlet  21  is directly guided by the rotation of the edge  33   a  and thus turns into centrifugal airflow, leading to blowing noise and adversely affect to the rotational efficiency of the impeller. 
   OBJECTS OF THE INVENTION 
   An object of the present invention is to provide an impeller for a radial-flow heat dissipating fan for increasing air inlet amount and air outlet amount. 
   Another object of the present invention is to provide an impeller for a radial-flow heat dissipating fan for increasing outlet wind pressure. 
   A further object of the present invention is to provide an impeller for a radial-flow heat dissipating fan for lowering blowing noise. 
   SUMMARY OF THE INVENTION 
   In accordance with an aspect of the present invention, an impeller for a radial-flow heat dissipating fan comprises a hub, a plurality of blades surrounding the hub, and means for connecting the blades to a circumference of the hub, allowing joint rotation of the hub and the blades. 
   More than one blade include an air inlet side edge and an air outlet side edge. The air inlet side edge of each of the more than one blade has a radial length smaller than that of the air out side edge, thereby increasing an air inlet amount and smoothly changing incoming axial airflow into centrifugal airflow. 
   In an embodiment, the inner edge of each blade includes a first section and a second section having a slope or curvature different from that of the first section. In another embodiment, the inner edge of each blade includes a shoulder. 
   In an embodiment, each blade includes an axial length greater than that of the hub, defining a buffering space between a top of the hub and the inner edges of the blade for increasing an air inlet area and for assisting in change of the axial incoming airflow into the centrifugal airflow. 
   In another embodiment, the impeller includes a first set of blades and a second set of blades that are alternately disposed. Each of the first set of blades has a rectilinear inner edge such that the air inlet side edge of each of the first set of blades has a radial length the same as that of the air outlet side edge of each of the first set of blades. The air inlet side edge of each of the second set of blades has a radial length smaller than that of the air outlet side edge of each of the second set of blades. 
   In an embodiment, a connecting ring extends across the air inlet side edge of each blade and another connecting ring extends across the air outlet side edge of each blade. At least one of the blades is connected by a supporting member to the circumference of the hub. 
   In a further embodiment, an annular plate extends from the circumference of the hub, and the blades are mounted on a side of the annular plate. 
   Other objects, advantages and novel features of this invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of a conventional radial-flow heat dissipating fan; 
       FIG. 2  is an exploded perspective view of another conventional radial-flow heat dissipating fan; 
       FIG. 3  is a perspective view, partly cutaway, of a first embodiment of an impeller for a radial-flow heat dissipating fan in accordance with the present invention; 
       FIG. 4  is a side view of the impeller in  FIG. 3 ; 
       FIG. 5  is a view similar to  FIG. 4 , illustrating operation of the impeller; 
       FIG. 6  is a side view illustrating a second embodiment of the impeller in accordance with the present invention; 
       FIG. 7  is a perspective view, partly cutaway, of a third embodiment of the impeller in accordance with the present invention; 
       FIG. 8  is a side view of the impeller in  FIG. 7 ; 
       FIG. 9  is a perspective view of a fourth embodiment of the impeller in accordance with the present invention; and 
       FIG. 10  is side view of the impeller in  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 3 and 4 , a first embodiment of an impeller  4  in accordance with the present invention comprises a hub  41 , at least one supporting member  42 , a plurality of blades  43 , and at least one connecting ring  44 ,  45 . The impeller  4  may be coupled with a motor (not shown) and assembled with a casing  1  and a cover  2  (see  FIGS. 1 and 2 ) to form a complete radial-flow heat dissipating fan. The motor is mounted inside the hub  41  that is rotatably mounted in a compartment  11  in the casing  11 . In this embodiment, a plurality of supporting members  42  are provided, with each supporting member  42  being connected between a circumference of the hub  41  and an associated one of the blades  43 . Preferably, each supporting member  42  is a wave-like rib extending from the circumference of the hub  41  to the associated blade  43 . A first connecting ring  44  extends across an air inlet side edge  43   a  of each blade  43 , and a second connecting ring  45  extends across an air outlet side edge  43   b  of each blade  43 , providing a structure with improved strength. 
   Still referring to  FIGS. 3 and 4 , each blade  43  further includes an inner edge facing the hub  41  and an outer edge  43   d  facing away from the hub  41 . The inner edge of each blade  43  includes at least one section. In this embodiment, the inner edge of each blade  43  includes a first section  43   c   1  adjacent to the air inlet side and a second section  43   c   2  adjacent to the air outlet side. The inner edges of some of the blades  43  are connected to the supporting members  42 . The first section  43   c   1  and the second section  43   c   2  have different slopes or different curvatures such that a radial length of the air inlet side edge  43   a  of each blade  43  is smaller than that of the air outlet side edge  43   b  of each blade  43 , thereby avoiding interference to drawing of the air into the casing  1  via the inlet  21 . Further, the outer edge  43   a  of each blade  43  is parallel to a rotational axis  40  of the impeller  43  without any change in the radial length. Further, an axial level of the impeller  43  is preferably above the hub  41  such that a buffering space  400  is defined between a top face of the hub  41  and the first sections  43   c   1  of the inner edges of the blades  43 . The air inlet area is increased, and airflow can be smoothly changed from the axial direction to the centrifugal direction. 
   Referring to  FIG. 5 , when the blades  43  of the impeller  4  turns, axial airflow is drawn into the buffering space  400  via the inlet  21  of the cover  2 . Since the first section  43   c   1  of the inner edge of each blade  43  is slanted or curved, the air inlet side edge  43   a  of each blade  43  has a relatively smaller radial length. Thus, the buffering space  400  can be enlarged to the maximum. When the axial airflow enters the buffering space  400 , the buffering space  400  provides a sufficient space for changing the axial airflow into centrifugal airflow. Thus, pressurized centrifugal airflow is obtained and exits the casing  1  via the outlet  12 . The slopes or curvatures of the first and second sections  43   c   1  and  43   c   2  of the inner edges of the blades  43  provide the lower portions of the blades  43  with a greater air driving power such that air flows easily in the lower portions of the blades  43 . Namely, the directional change from the axial direction to the centrifugal direction is not completely carried out at the upper portions of the blades  43 , which lowers the blowing noise of the blades  43 . 
     FIG. 6  illustrates a second embodiment of the invention, wherein the first section  43   c   3  and the second section  43   c   4  of the inner edge of each blade  43  are rectilinear to form a shoulder. This embodiment provides advantages the same as those of the first embodiment. 
     FIGS. 7 and 8  illustrate a third embodiment of the invention, wherein the impeller  4  comprises two sets of alternately disposed blades  43  and  43 ′ having different shapes. Each of a first set of blades  43  has a structure the same as that in the first embodiment. Each of a second set of blades  43 ′ has a rectilinear inner edge  43   c ′ throughout an axial length of the blade  43 ′. In other words, the inlet side edge of each of the second set of blades  43 ′ has a radial length the same as that of the outlet side edge of each of the second set of blades  43 ′. Drawing of air into the casing  1  via the inlet  21  of the cover  2  is not interfered. Further, a buffering space  400  is defined between the inner edges  43   c   1  of the blades  43 , the inner edges  43   c ′ of the blades  43 ′, and a top face of the hub  41 . Similar to the first embodiment, the air inlet area is increased, the airflow can be smoothly changed from the axial direction to the centrifugal direction, and the blowing noise is lowered. 
     FIGS. 9 and 10  illustrate a fourth embodiment of the invention, in this embodiment, the impeller  5  includes a hub  51 , a plate-like supporting member  52  extending radially outward from a circumference of the hub  51 , and a plurality of blades  53  provided on a side of the supporting member  52 . Each blade  53  includes an inner edge  53   c , a rectilinear outer edge  53   d , an air inlet side edge  53   a , and an air outlet side edge  53   b . The inner edge  53   c  is slanted. Alternatively, the inner edge  53   c  may include two sections similar to the first embodiment. The air outlet side edge  53   b  has a radial length longer than that of the air inlet side edge  53   a . Thus, drawing of air into the casing  1  via the inlet  21  of the cover  2  is not interfered. The axial height of each blade  43  is greater than that of the hub  51 . Thus, a buffering space  500  is defined between the inner edges  53   c  of the blades  53  and a top face of the hub  51 . Similar to the first embodiment, the air inlet area is increased, the airflow can be smoothly changed from the axial direction to the centrifugal direction, and the blowing noise is lowered. 
   While the principles of this invention have been disclosed in connection with specific embodiments, it should be understood by those skilled in the art that these descriptions are not intended to limit the scope of the invention, and that any modification and variation without departing the spirit of the invention is intended to be covered by the scope of this invention defined only by the appended claims.