Centrifugal fan

Abstract

A centrifugal fan includes a casing and an impeller module. The casing defines an accommodating space having an air inlet and an air outlet. The impeller module is mounted in the accommodating space for allowing air flow to enter from the air inlet and exit from the air outlet. The impeller module includes a body and a plurality of blade units connected to and annularly distributed along a circumference of the body. Each blade unit has a plurality of blades arranged equi-angularly. A blade spacing which is defined between each adjacent pair of the blades of one of the blade units is different from a blade spacing which is defined between each adjacent pair of the blades of another one of the blade units.

What is claimed is: 
     
         1 . A centrifugal fan comprising:
 a casing defining an accommodating space that has an air inlet and an air outlet; and   an impeller module mounted in said accommodating space and rotatable about an axis for allowing air flow to enter from said air inlet and exit from said air outlet, said impeller module including a body and a plurality of blade units connected to and annularly distributed along a circumference of said body, each of said blade units having a plurality of blades that are equi-angularly arranged along said circumference of said body, a blade spacing which is defined between each adjacent pair of said blades of one of said blade units being different from a blade spacing which is defined between each adjacent pair of said blades of another one of said blade units.   
     
     
         2 . The centrifugal fan as claimed in  claim 1 , wherein:
 said plurality of blade units includes at least three blade units;   the blade spacings among said blade units are different; and   said blade units are arranged in the order of size of the blade spacings.   
     
     
         3 . The centrifugal fan as claimed in  claim 1 , wherein said impeller module includes exactly three blade units. 
     
     
         4 . The centrifugal fan as claimed in  claim 1 , wherein said impeller module includes exactly four blade units. 
     
     
         5 . The centrifugal fan as claimed in  claim 4 , wherein said four blade units includes two first blade units with one blade spacing and two second blade units with a different blade spacing, said first and second blade units being arranged in alternate. 
     
     
         6 . A centrifugal fan comprising:
 a casing defining an accommodation space that has an air inlet and an air outlet; and   an impeller module mounted in said accommodating space and rotatable about an axis for allowing air flow to enter from said air inlet and exit from said air outlet, said impeller module including a body and a plurality of blade units connected to and annularly distributed in a rotational direction along a circumference of said body, each of said blade units having a plurality of blades with a blade spacing being defined between each adjacent pair of said blades;   wherein, for each of said blade units, the blade spacings among said blades are different, and said blades are arranged in a manner that the blade spacings increases in the rotational direction.   
     
     
         7 . The centrifugal fan as claimed in  claim 6 , wherein each blade unit has four blades.