Fan

Abstract

A fan includes a motor and an impeller. The motor includes a stationary portion and a rotating portion. The stationary portion includes a stator and a bearing portion. The bearing portion includes a sleeve and a bearing housing. The rotating portion includes a rotor magnet, a shaft, and a thrust plate. A radial gap includes a radial dynamic pressure bearing portion arranged to generate a fluid dynamic pressure acting axially downward on a lubricating oil, while a thrust gap includes a thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure acting radially inward on the lubricating oil. A circulation hole extending in an axial direction is defined between the bearing housing and the sleeve. The radial gap is arranged to have a radial width in a range of about 5 μm to about 20 μm.

1 . A fan comprising:
 a motor; and   an impeller including a plurality of blades, and arranged to rotate about a central axis through the motor to produce air currents; wherein   the motor includes:
 a stationary portion; and 
 a rotating portion rotatably supported by the stationary portion; 
   the stationary portion includes:
 a stator; and 
 a bearing portion arranged inside of the stator; 
   the bearing portion includes:
 a sleeve defined by a metallic sintered body; and 
 a bearing housing arranged to cover an outer circumferential surface of the sleeve; 
   the rotating portion includes:
 a rotor magnet arranged radially outside the stator; 
 a shaft inserted in the sleeve, and having an upper portion fixed to the impeller directly or through one or more members; and 
 a thrust plate arranged to extend radially outward from a lower end of the shaft to be axially opposed to a lower surface of the sleeve; 
   a radial gap defined between an inner circumferential surface of the sleeve and an outer circumferential surface of the shaft includes a radial dynamic pressure bearing portion arranged to generate a fluid dynamic pressure acting axially downward on a lubricating oil, while a thrust gap defined between the lower surface of the sleeve and an upper surface of the thrust plate includes a thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure acting radially inward on the lubricating oil;   a circulation hole extending in an axial direction from an upper surface to the lower surface of the sleeve is defined between the bearing housing and the outer circumferential surface of the sleeve; and   the radial gap is arranged to have a radial width in a range of about 5 μm to about 20 μm.   
     
     
         2 . The fan according to  claim 1 , wherein the radial width of the radial gap is arranged to be greater than 5 μm. 
     
     
         3 . The fan according to  claim 1 , wherein an outer edge portion of the upper surface of the thrust plate includes an inclined surface arranged to be inclined downward with increasing distance from the central axis. 
     
     
         4 . The fan according to  claim 1 , wherein
 the stationary portion further includes a bearing bottom portion arranged axially opposite a lower surface of the thrust plate; and   another thrust gap defined between the lower surface of the thrust plate and an upper surface of the bearing bottom portion includes another thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure acting on the lubricating oil.   
     
     
         5 . The fan according to  claim 4 , wherein a sum of an axial width of the thrust gap and an axial width of the other thrust gap is arranged in a range of about 10 μm to about 40 μm. 
     
     
         6 . The fan according to  claim 1 , wherein
 the bearing housing includes an annular upper portion arranged to extend radially inward on an upper side of the sleeve; and   an inner circumferential surface of the annular upper portion and the outer circumferential surface of the shaft are arranged to together define a seal gap therebetween, the seal gap having a radial width gradually increasing with increasing height.   
     
     
         7 . The fan according to  claim 6 , wherein
 the inner circumferential surface of the sleeve includes an inclined surface arranged below and adjacent to the seal gap, and having a diameter gradually increasing with increasing height; and   the inclined surface is arranged to extend along the outer circumferential surface of the shaft when the shaft is tilted during rotation of the rotating portion.   
     
     
         8 . The fan according to  claim 7 , wherein the radial dynamic pressure bearing portion includes a dynamic pressure groove, and a portion of the dynamic pressure groove is defined in the inclined surface. 
     
     
         9 . The fan according to  claim 1 , wherein
 the radial dynamic pressure bearing portion includes an upper radial dynamic pressure bearing portion defined in an upper portion of the radial gap, and a lower radial dynamic pressure bearing portion defined in a lower portion of the radial gap; and   the upper radial dynamic pressure bearing portion is arranged to overlap with a center of gravity of a combination of the motor and the impeller in a radial direction.   
     
     
         10 . A fan comprising:
 a motor; and   an impeller including a plurality of blades, and arranged to rotate about a central axis through the motor to produce air currents; wherein   the motor includes:
 a stationary portion; and 
 a rotating portion rotatably supported by the stationary portion; 
   the stationary portion includes:
 a stator; and 
 a bearing portion arranged inside of the stator; 
   the bearing portion includes:
 a sleeve defined by a metallic sintered body; and 
 a bearing housing arranged to cover an outer circumferential surface of the sleeve; 
   the rotating portion includes:
 a rotor magnet arranged radially outside the stator; 
 a shaft inserted in the sleeve, and having an upper portion fixed to the impeller directly or through one or more members; and 
 a thrust plate arranged to extend radially outward from a lower end of the shaft to be axially opposed to a lower surface of the sleeve; 
   a radial gap defined between an inner circumferential surface of the sleeve and an outer circumferential surface of the shaft includes a radial dynamic pressure bearing portion arranged to generate a fluid dynamic pressure acting on a lubricating oil, while a thrust gap defined between the lower surface of the sleeve and an upper surface of the thrust plate includes a thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure acting on the lubricating oil;   a circulation hole extending in an axial direction from an upper surface to the lower surface of the sleeve is defined between the bearing housing and the outer circumferential surface of the sleeve; and   the lubricating oil is arranged to flow from the radial gap back to the radial gap through a gap above the upper surface of the sleeve, the circulation hole, and the thrust gap in an order named during rotation of the rotating portion.