Patent Publication Number: US-7585154-B2

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 high performance, high frequency, high speed and compactness, the generated heat of the electronic products becomes greater. However, the electronic products are unstable in the high temperature, which affects the reliability thereof. Thus, the heat dissipation has become an important issue of the present electronic products. 
   The fan is a common heat dissipating device for the electronic product. As shown in  FIG. 1 , a conventional centrifugal fan  1  includes an impeller  11  and a motor  12 . The impeller  11  includes a base plate  113 , a hub  111  disposed at the center of the base plate  113 , and a plurality of blades  112 . The base plate  113  is connected to the hub  111 , and the blades  112  are disposed on the base plate  113  with respect to the hub  111  as a center. The blades  11  further includes a connecting ring  114 , which is connected to a side of the blades  112  opposite to another side thereof facing the base plate  113 . The motor  12  is accommodated in the hub  111  for driving the impeller  11  to rotate. 
   When the impeller  11  rotates, airflow enters the center of the impeller  11 . Then, the rotated blades  112  force the airflow to radiately flow out of the blades  112 . Since the airflow may have the counterflow, backflow, and separation phenomenon in the impeller  11 , the flow field after entering the impeller  11  becomes very complicated. 
   In more details, since the speed of the airflow near the hub  111  is lower than that at other places, the utility efficiency of the airflow near the hub  111  is poor. If this utility efficiency is appropriately enhanced, the performance of the whole fan can be better so as to increase the heat dissipation effect. It is therefore an important subject of the invention to improve the entire working efficiency of the centrifugal fan and the impeller thereof for obtaining higher heat dissipation effect. 
   SUMMARY OF THE INVENTION 
   In view of the foregoing, the invention is to provide a centrifugal fan and an impeller thereof that can efficiently improve the entire working efficiency for enhancing the heat dissipation effect. 
   To achieve the above, an impeller of the invention is applied to a centrifugal fan and includes a base plate, a plurality of first blades, and a hub. The first blades are disposed on the base plate with respect to the hub as a center. The hub is connected to the base plate, and has a plurality of second blades disposed around an outer wall of the hub. 
   To achieve the above, a centrifugal fan of the invention includes an impeller and a motor. The impeller includes a base plate, a hub, and a plurality of first blades. The first blades are disposed on the base plate with respect to the hub as a center. The hub is connected to the base plate, and has a plurality of second blades disposed around an outer wall of the hub. The motor is coupled to the impeller for driving the impeller to rotate. 
   As mentioned above, the centrifugal fan and impeller of the invention have a plurality of second blades disposed around the outer wall of the hub. Due to the second blades, the utility efficiency of the airflow near the hub can be appropriately enhanced so as to increase the heat dissipation effect. Furthermore, the centrifugal fan of the invention may have the superior performance at a high air pressure area. 

   
     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  is a schematic view of the conventional centrifugal fan; 
       FIG. 2  is a three dimensional view of a centrifugal fan according to a preferred embodiment of the invention; 
       FIG. 3  is a three dimensional view of another centrifugal fan according to the preferred embodiment of the invention; and 
       FIG. 4  is a schematic diagram showing efficiency curves of the conventional centrifugal fan and the centrifugal fan according to the preferred embodiment in  FIG. 3 . 
   

   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. 2  is a three dimensional view of a centrifugal fan and an impeller thereof according to a preferred embodiment of the invention. As shown in  FIG. 2 , the centrifugal fan  2  includes an impeller  21  and a motor  22 . The impeller  21  includes a base plate  212 , a hub  211 , and a plurality of first blades  213 . The motor  22  is accommodated in the hub  211  for coupling to the impeller  21  and driving it to rotate. The hub  211  is connected to the base plate  212 . The first blades  213  are disposed on the base plate  212  with respect to the hub  211  as a center. The hub  211  has a plurality of second blades  2111  disposed around its outer wall. In the embodiment, the base plate  212  is ring-shaped, and the base plate  212 , the hub  211  and the first blades  213  are integrally formed as a single unit. The second blades  2111  are forward leaning blades and the hub  211  and the second blades  2111  are integrally formed as a single unit. In other words, the second blades  2111 , the hub  211 , the base plate  212  and the first blades  213  are integrally formed as a single unit. To be noted, the second blades  2111  still can either be backward leaning blades or in any other curved shape. A plane parallel to the base plate  212  intersects the first blades  213  and the second blades  2111 . 
   The impeller  21  further includes a connecting ring  214 , which is connected to a side of the first blades  213  opposite to another side thereof facing the base plate  212 . In the embodiment, the connecting ring  214  and the first blades  213  integrally formed. Moreover, please refer to  FIGS. 2 and 3 , the first blades  213  and the second blades  2111  are both located substantially perpendicularly to the base plate  212 . The impeller  21  is the centrifugal impeller. The first blades  213  and the second blades  2111  are the centrifugal blades. 
     FIG. 3  is a three dimensional view of another centrifugal fan and the impeller thereof according to the preferred embodiment of the invention. With reference to  FIG. 3 , a centrifugal fan  2 ′ has a plurality of second blades  2111 ′ in plate shapes. Except the shapes and number of the second blades  2111 ′, the elements in the centrifugal fan  2 ′ are the same as those in  FIG. 2 . 
   With reference to  FIG. 4 , an experimental analysis by comparing the conventional centrifugal fan and the centrifugal fan of the invention as shown in  FIG. 3  is obtained. 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 produce higher air pressure and larger airflow quantity. More particularly, the increase of the air pressure is much obvious. According to the experimental analysis, the centrifugal fan of the invention can provide more working efficiency than the conventional one. 
   In these embodiments, the second blades  2111  or  2111 ′ and the first blades  213  are, but not limited to, forward leaning blades, backward leaning blades, plate blades, or their combinations. The number of the second blades  2111  or  2111 ′ is not limited and is unnecessary to have an absolute relation with the number of the first blades  213 . In addition, the positions of the second blades  2111  or  2111 ′ are unnecessary to have a relation with the positions of the first blades  213 . In conclusion, the shapes and number of the second blades and the relationship between the first and second blades are determined according to the actual needs. 
   In summary, the centrifugal fan and impeller of the invention have a plurality of second blades disposed around the outer wall of the hub. Due to the second blades, the utility efficiency of the airflow near the hub can be appropriately enhanced so as to increase the heat dissipation effect. Furthermore, the centrifugal fan of the invention may have the superior performance at the high air pressure area. 
   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.