Centrifugal fan

Abstract

A centrifugal fan includes an impeller including a blade portion having plural elongated blades arranged at a predetermined pitch in the circumferential direction and a motor for rotating the impeller. The impeller and the motor are arranged side by side in the axial direction. A diameter of the impeller is less than or equal to 25 millimeters. A radius r of the impeller and a length h in the axial direction of the impeller satisfies the relationship of 2r<=h<=20r. Among elements that constitute the motor, a torque generating portion including an armature and a field magnet, and a bearing portion that retains a rotational member in a rotatable manner to a fixed member are arranged side by side in the axial direction.

1 . A centrifugal fan comprising: 
 an impeller including a blade portion having plural elongated blades arranged at a predetermined pitch in the circumferential direction, said blade portion having a radius r and a length h in the axial direction of the impeller with satisfying a relationship 2r<=h<=20r;    a rotational member including said impeller;    a rotor magnet secured to said rotational member;    a stator armature which composes a stational member;    a torque generating portion including said stator armature and said rotor magnet;    a bearing portion which retains said rotational member in a rotatable manner to said stational member arranged tandem in the axial direction with said torque generating portion; and    a motor including said rotor, said stator, said torque generating portion and said bearing portion.    
   
   
       2 . The centrifugal fan according to  claim 1 , wherein the rotational speed of the impeller is set more than or equal to 10,000 revolutions per minute.  
   
   
       3 . The centrifugal fan according to  claim 1 , wherein said rotational member rotates as one element; and the bearing portion is disposed at a barycenter of the element or at vicinity of the barycenter of the same.  
   
   
       4 . The centrifugal fan according to  claim 2 , wherein said rotational member rotates as one element; and the bearing portion is disposed at a barycenter of the element or at vicinity of the barycenter of the same.  
   
   
       5 . The centrifugal fan according to  claim 1 , wherein an outer diameter of the blade portion of the impeller is substantially the same as an outer diameter of the torque generating portion of the motor.  
   
   
       6 . The centrifugal fan according to  claim 2 , wherein an outer diameter of the blade portion of the impeller is substantially the same as an outer diameter of the torque generating portion of the motor.  
   
   
       7 . The centrifugal fan according to  claim 1 , wherein the motor is a DC brushless motor.  
   
   
       8 . The centrifugal fan according to claims  1 , wherein the bearing portion is a pair of ball bearings that are arranged separately in the axial direction.  
   
   
       9 . The centrifugal fan according to claims  2 , wherein the bearing portion is a pair of ball bearings that are arranged separately in the axial direction.  
   
   
       10 . The centrifugal fan according to  claim 8 , wherein the pair of ball bearings are preloaded by pressing inner ring portions or outer ring portions of the ball bearings in the opposite direction to each other along the axial direction.  
   
   
       11 . The centrifugal fan according to  claim 1 , wherein the bearing portion is a sleeve bearing including 
 a rotational shaft that is connected to the rotational member;    a sleeve having a cylindrical shape that engages the outer surface of the rotational shaft with a minute gap,    and the centrifugal fan further comprises    a cylindrical portion in which the sleeve is held;    a supporting portion that retains the cylindrical portion to a base portion;    a sleeve holder that includes the cylindrical portion and the supporting portion;    a stator armature constituting the torque generating portion which is fixed to the outer surface of the supporting portion of the sleeve holder.    
   
   
       12 . The centrifugal fan according to  claim 2 , wherein the bearing portion is a sleeve bearing including 
 a rotational shaft that is connected to the rotational member;    a sleeve having a cylindrical shape that engages the outer surface of the rotational shaft with a minute gap,    and the centrifugal fan further comprises    a cylindrical portion in which the sleeve is held;    a supporting portion that retains the cylindrical portion to a base portion;    a sleeve holder that includes the cylindrical portion and the supporting portion;    a stator armature constituting the torque generating portion which is fixed to the outer surface of the supporting portion of the sleeve holder.    
   
   
       13 . The centrifugal fan according to  claim 3 , wherein the bearing portion is a sleeve bearing including 
 a rotational shaft that is connected to the rotational member;    a sleeve having a cylindrical shape that engages the outer surface of the rotational shaft with a minute gap,    and the centrifugal fan further comprises    a cylindrical portion in which the sleeve is held;    a supporting portion that retains the cylindrical portion to a base portion;    a sleeve holder that includes the cylindrical portion and the supporting portion;    a stator armature constituting the torque generating portion which is fixed to the outer surface of the supporting portion of the sleeve holder.    
   
   
       14 . The centrifugal fan according to  claim 1 , wherein the bearing portion is a sleeve bearing including a fixed shaft that is fixed to the stational member and a sleeve having a cylindrical shape that engages the outer surface of the fixed shaft with a radial minute gap, and a stator armature constituting the torque generating portion is fixed to the outer surface of the fixed shaft.  
   
   
       15 . The centrifugal fan according to  claim 2 , wherein the bearing portion is a sleeve bearing including a fixed shaft that is fixed to the stational member and a sleeve having a cylindrical shape that engages the outer surface of the fixed shaft with a radial minute gap, and a stator armature constituting the torque generating portion is fixed to the outer surface of the fixed shaft.  
   
   
       16 . The centrifugal fan according to  claim 3 , wherein the bearing portion is a sleeve bearing including a fixed shaft that is fixed to the stational member and a sleeve having a cylindrical shape that engages the outer surface of the fixed shaft with a radial minute gap, and a stator armature constituting the torque generating portion is fixed to the outer surface of the fixed shaft.