Patent Publication Number: US-2007110572-A1

Title: Centrifugal fan and impeller thereof

Description:
BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The invention relates to a fan and, in particular, to a centrifugal fan.  
      2. Related Art  
      Since the present electronic products are rapidly developed towards the goals of high performance, high frequency, high speed and compactness, the generated heat of the electronic products becomes greater. However, the electronic products may be unstable in the high temperature, which results in the poor reliability thereof. Thus, the heat dissipation has become an important issue of the present electronic products.  
      The fan is commonly used as a heat dissipating device for the electronic product.  FIG. 1   a  and  FIG. 1   b  are top views of two kinds of conventional centrifugal fans  1  and  1 ′, both of which have a plurality of blades. Based on the arrangement, the blades may be forward leaning blades  11  (shown in  FIG. 1   a ) or backward leaning blades  11 ′ (shown in  FIG. 1   b ). The rotation directions of the blades are shown by the arrows in  FIGS. 1   a  and  1   b . Under the same rotation speed, the forward leaning blades  11  can output higher air pressure for providing better heat dissipation effect. However, the loading of the motor increases, and the power consumption is higher. Contrariwise, the backward leaning blades  11 ′ provide a heat dissipation effect not as good as that provided by the forward leaning blades  11 , but the power consumption of the backward leaning blades  11 ′ is lower. Therefore, the manufacturer can choose different types of the blades according to the actual needs of power consumption.  
      As shown in  FIG. 2 , a conventional centrifugal fan  2  includes an impeller  21  and a motor  22 . The impeller  21  includes a base plate  213 , a hub  211 , and a plurality of backward leaning blades  212 . The base plate  211  is connected to the hub  211 , and the blades  212  are disposed on the base plate  211  and around the hub  211 . The impeller  21  further includes a connecting ring  214 , which is connected to a side of the blades  212  opposite to another side thereof facing the base plate  213 . The motor  22  is accommodated in the hub  211  for driving the impeller  21  to rotate.  
      When the impeller,  21  rotates, airflow enters. the center of the impeller  21 . Then, the blades  212  force the airflow to radiately flow out of the blades  212 . Since the air pressure provided by the backward leaning blades is smaller than that of the forward leaning blades, the fan  2  utilizing the backward leaning blades provides inferior heat dissipation effect.  
      It is therefore an important subject of the invention to improve the heat dissipation efficiency of the backward leaning blades with lower power consumption.  
     SUMMARY OF THE INVENTION  
      In view of the foregoing, the invention is to provide a centrifugal fan and an impeller thereof that can improve the efficiency thereof for enhancing the heat dissipation effect with lower power consumption.  
      To achieve the above, an impeller of the invention includes a base plate, a hub, and a plurality of blades. The hub is connected to the base plate. The blades are disposed on the base plate and around the hub. In the invention, the blades are backward leaning structures and each blade has at least one inversely inflective portion located at a tail of the blade.  
      To achieve the above, a centrifugal fan of the invention includes an impeller and a motor accommodated underneath the impeller. The impeller includes a base plate, a hub, and a plurality of blades. The hub is connected to the base plate. The blades are disposed on the base plate and around the hub. In the invention, the blades are backward leaning structures and each blade has at least one inversely inflective portion located at a tail of the blade.  
      As mentioned above, the centrifugal fan and impeller of the invention have the blades of the backward leaning structures, each of which has at least one inversely inflective portion located at a tail of the blade. Thus, when the airflow flows through the tails of the blades, the inversely inflective portion is capable of increasing the airflow quantity of the fan. As a result, the efficiency of the fan can be efficiently improved for enhancing the heat dissipation effect with lower power consumption. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:  
       FIG. 1   a  is a top view of a conventional centrifugal fan that has forward leaning blades;  
       FIG. 1   b  is a top view of a conventional centrifugal fan that has backward leaning blades;  
       FIG. 2  is a schematic view of a conventional centrifugal fan;  
       FIG. 3   a  is a top view of a centrifugal fan and an impeller thereof according to a preferred embodiment of the invention;  
       FIG. 3   b  is an enlarged diagram showing an inversely inflective portion shown in  FIG. 3   a;    
       FIG. 4  is a three dimensional view of the centrifugal fan according to the preferred embodiment of the invention; and  
       FIG. 5  is a schematic diagram showing efficiency curves of the conventional centrifugal fan and the centrifugal fan of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be apparent from the following detailed description, which proceeds with reference to the accompanying drawings, wherein the same references relate to the same elements.  
       FIG. 3   a  is a top view of a centrifugal fan and an impeller thereof according to a preferred embodiment of the invention, and  FIG. 4  is a three dimensional view of the centrifugal fan and the impeller. The centrifugal fan  3  includes an impeller  31  and a motor  32 . The impeller  31  includes a base plate  312 , a hub  311 , and a plurality of blades  313 . The motor  32  is accommodated in the hub  311  for coupling to the impeller  31  and driving it to rotate. The hub  311  is connected to the base plate  312 . The blades  313  are disposed on the base plate  312  and around the hub  311 . In the embodiment, the base plate  312  is ring-shaped, and the base plate  312 , the hub  311  and the blades  313  are integrally formed as a single unit. The blades  313  are backward leaning structures, and each blade  313  has an inversely inflective portion  3131  located at a tail of the blade  313 .  FIG. 3   b  is an enlarged diagram showing the inversely inflective portion  3131 . The inversely inflective portion  3131  has a smooth surface and is used to increase the airflow quantity and efficiency of the impeller  31 . In practice, the present invention may provide several inversely inflective portions at the tail of each blade according to the actual needs.  
      The impeller  31  further includes a connecting ring  314 , which is connected to a side of the blades  313  opposite to another side thereof facing the base plate  312 . Similarly, the connecting ring  314  and the blades  313  may be integrally formed.  
      With reference to  FIG. 5 , an experimental analysis is obtained by comparing the conventional centrifugal fan and the centrifugal fan of the present invention. Herein, the X axis represents the airflow quantity, and the Y axis represents the air pressure. Under the same rotation speed of 4060 RPM, the centrifugal fan of the invention can provide better efficiency than the conventional one according to the efficiency curve of the experimental analysis.  
      In summary, the centrifugal fan and impeller of the invention have the blades of the backward leaning structures, each of which has at least one inversely inflective portion located at a tail of the blade. Thus, when the airflow flows through the tails of the blades, the inversely inflective portion is capable of increasing the airflow quantity of the fan. As a result, the efficiency of the fan can be efficiently improved for enhancing the heat dissipation effect with lower power consumption.  
      Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.