Patent Publication Number: US-8534998-B2

Title: Centrifugal fan

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to centrifugal fans, and particularly to a centrifugal fan with strong airflow. 
     2. Description of Related Art 
     Thermal modules incorporated with a centrifugal fan are often applied to dissipate heat from heat generating components, such as central procession units (CPUs) in computers. The centrifugal fan is used to provide airflow to evacuate heat from the thermal module.  FIG. 4  shows a commonly used centrifugal fan  900 , which includes a casing  92  and an impeller  94  received in the casing  92 . The casing  92  includes a volute sidewall  922  with an air outlet  920  defined at one side thereof. As shown in the coordinate system, four regions I, II, III, IV are formed respectively at four corners of the casing  92 , and the sidewall  922  includes a curved section extending from a position in the region II anticlockwise through to the 0° axis. The casing  92  defines a corner portion  924  at the region III. During operation of the centrifugal fan  900 , a dead airspace is formed in the corner portion  924  of the centrifugal fan  900 , wherein air in the corner portion  924  receives little or no impetus to flow towards the air outlet  920 . Thus the airflow efficiency of the centrifugal fan  900  is limited. 
     Accordingly, it is desired to overcome the described shortcomings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded, isometric view of a centrifugal fan in accordance with an exemplary embodiment. 
         FIG. 2  is a top plan view of the centrifugal fan of  FIG. 1 , but omitting the cover and showing airflow paths inside the centrifugal fan. 
         FIG. 3  is a bottom plan view of the centrifugal fan of  FIG. 2 . 
         FIG. 4  is a bottom plan view of a commonly used centrifugal fan. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  show a centrifugal fan  100  in accordance with an exemplary embodiment. The centrifugal fan  100  includes a casing  10 , and an impeller  20  received in the casing  10 . The impeller  20  includes a hub  22 , and a plurality of blades  24  extending radially and outwardly from an outer periphery of the hub  22 . The casing  10  includes a top cover  12 , a bottom plate  14  corresponding to the top cover  12 , and a volute sidewall  16  interconnecting circumferential portions of the top cover  12  and the bottom plate  14 . The top cover  12 , the bottom plate  14  and the sidewall  16  cooperatively define a receiving space (not labeled) therein. The impeller  20  is received in the receiving space. 
     The top cover  12  defines a through hole  120  in a central area thereof, the through hole  120  functioning as an air inlet  120 . The impeller  20  is mounted to the bottom plate  14 , and aligned with the air inlet  120  of the top cover  12 . The sidewall  16  extends perpendicularly upwardly from a circumference of the bottom plate  14 , with an air outlet  160  defined between two ends of the sidewall  16 . The impeller  20  is spaced from the sidewall  16 , with an air channel  17  defined between the sidewall  16  and the outermost free ends of the blades  24  of the impeller  20 . 
     The sidewall  16  includes, along a clockwise rotation direction of the impeller  20  as viewed in  FIG. 2 , a first linear section  161 , a first curved section  162  connected with the first linear section  161 , a second curved section  163  connected with the first curved section  162 , and a second linear section  164  connected with the second curved section  163 . In other words, the first linear section  161 , the first curved section  162 , the second curved section  163  and the second linear section  164  are connected with each other along the rotation direction of the impeller  20 . An upstream end of the first curved section  162  is connected to a downstream end of the first linear section  161 . A downstream end of the first curved section  162  is connected to an upstream end of the second curved section  163 . A downstream end of the second curved section  163  is connected to an upstream end of the second linear section  164 . The first linear section  161  and the second linear section  164  are located at two opposite sides of the air outlet  160 , with the air outlet  160  defined therebetween. A width of the air channel  17  gradually increases along the rotation direction of the impeller  20 . 
     An air guide plate  15  is perpendicularly formed on the bottom plate  14 . In the present embodiment, the air guide plate  15  is integrally formed with the bottom plate  14 . That is, the air guide plate  15  and the bottom plate  14  are portions of single, one-piece, monolithic body of the same material. Alternatively, the air guide plate  15  can be fixed on the bottom plate  14  after the air guide plate  15  and the bottom plate  14  have been separately formed. The air guide plate  15  extends from the air outlet  160  to approximately a midway point of the air channel  17 . The midway point of the air channel  17  is located directly behind the impeller  20  far away from the air outlet  160 . In particular, an imaginary line drawn perpendicularly from the air outlet  160  to the midway point of the air channel  17  passes through the center of the impeller  20 . The air guide plate  15  is spaced from the sidewall  16  and the outermost free ends of the blades  24  of the impeller  20 , to thereby divide a downstream portion of the air channel  17  into a first branch channel  171  and a second branch channel  172 . The first branch channel  171  is located between the air guide plate  15  and the outermost free ends of the blades  24  of the impeller  20 , and the second branch channel  172  is located between the air guide plate  15  and the sidewall  16 . In the embodiment, the second branch channel  172  is wider than the first branch channel  171  along entire lengths of the first and second branch channels  171 ,  172 . 
     Referring also to  FIG. 3 , the centrifugal fan  100  is divided into four regions I, II, III, IV by a 0° axis, a 90° axis, a 180° axis and a 270° axis. As viewed from the bottom of the centrifugal fan  100 , the first curved section  162  of the sidewall  16  is located in the region II, and extends along a part of an Archimedes spiral from the downstream end of the first linear section  161  of the sidewall  16  anticlockwise through to the 180° axis. Alternatively, the first curved section  162  of the sidewall  16  can extend along a part of a logarithmic spiral. The broken line  169  connected with the downstream end of the first curved section  162  is an imaginary extension line  169  of the first curved section  162  along the Archimedes spiral or the logarithmic spiral. The first curved section  162  together with the extension line  169  thereof coincides with the curved section of the sidewall  922  of the commonly used centrifugal fan  900  (see above). Note that in  FIG. 3 , the part of the extension line  169  in the region IV extending from the 270° axis to the 0° axis coincides with and is obscured by the broken lines shown for the inner section  151 . 
     The second curved section  163  is located in the regions III, IV, and extends from the 180° axis anticlockwise through to the 0° axis. The second curved section  163  is located outside of the extension line  169  of the first curved section  162 . In other words, the second curved section  163  is located farther away from the outermost free ends of the blades  24  of the impeller  20  than the extension line  169  of the first curved section  162 . Thereby, a curvature of the second curved section  163  is less than that of the extension line  169  of the first curved section  162 . Accordingly, the curvature of the second curved section  163  is less than that of the curved section of the sidewall  922  of the commonly used centrifugal fan  900 . The casing  10  defines a corner portion  174  at approximately the middle of the air channel  17 . The corner portion  174  is located in the region III corresponding to an upstream side of the second curved section  163  of the sidewall  16 . 
     The air guide plate  15  includes an inner section  151  and an adjoining outer section  152 . The outer section  152  of the air guide plate  15  extends linearly from the air outlet  160  clockwise through to the 0° axis. A free end of the outer section  152  of the air guide plate  15  is located near the center of the air outlet  160 . As viewed from the bottom of the centrifugal fan  100  ( FIG. 3 ), the inner section  151  of the air guide plate  15  curves from the 0° axis clockwise through to the 270° axis. In this embodiment, the outer section  152  of the air guide plate  15  is parallel to the second linear section  164  of the sidewall  16 . The inner section  151  of the air guiding plate  15  extends to the midway point of the air channel  17 . The inner section  151  of the air guide plate  15  coincides with a corresponding portion of the extension line  169  of the first curved section  162  of the sidewall  16 . A width of the first branch channel  171  gradually increases along the rotation direction of the impeller  20 . A width of the second branch channel  172  gradually increases from the 270° axis to the 0° axis, and remains constant from the 0° axis to the air outlet  160  along the rotation direction of the impeller  20 . 
     The curvature of the second curved section  163  of the sidewall  16  is less than that of the curved section of the sidewall  922  of the commonly used centrifugal fan  900 , thus reducing flow resistance in the air channel  17  corresponding to the second curved section  163  of the sidewall  16 . Thereby, air in the corner portion  174  is efficiently guided to the air outlet  160 . Accordingly, the dead airspace of the commonly used centrifugal fan  900  is mitigated or not formed at all in the centrifugal fan  100 , and airflow to the air outlet  160  is thus increased. In addition, the air guide plate  15  divides airflow in the air channel  17  into two portions to respectively flow through the first branch channel  171  and the second branch channel  172 , such that pressure and velocity of airflow to the air outlet  160  is increased. Furthermore, as guided by the air guide plate  15 , more air may flow to portions of the air outlet  160  further away from the second linear section  164 . For example, much air may flow through the first and second branch channels  171 ,  172  to portions of the air outlet  160  spanning from the second linear section  164  to nearly the center of the air outlet  160 . Thus distribution of the airflow at the air outlet  160  can be more uniform. 
     It is to be understood, however, that even though numerous characteristics and advantages of the exemplary embodiment(s) have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.