Dynamic pressure bearing apparatus and fan

Abstract

A dynamic pressure bearing apparatus includes a bearing portion; a shaft; a substantially annular bushing; a radial dynamic pressure bearing portion; and a seal gap. A minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing. The seal gap is arranged to be in communication with an exterior space through the horizontal gap.

1 . A dynamic pressure bearing apparatus comprising:
 a bearing portion;   a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion;   a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members;   a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and   a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; wherein   a minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing; and   the seal gap is arranged to be in communication with an exterior space through the horizontal gap.   
     
     
         2 . The dynamic pressure bearing apparatus according to  claim 1 , wherein
 a minute vertical gap extending in an axial direction is defined between a circumferential surface of the bearing portion and a circumferential surface of the bushing;   the vertical gap is connected with a radially outer end portion of the horizontal gap; and   the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the vertical gap.   
     
     
         3 . The dynamic pressure bearing apparatus according to  claim 2 , wherein
 one of the bushing and the bearing portion includes an annular portion arranged to project toward the other one of the bushing and the bearing portion;   the other one of the bushing and the bearing portion includes an annular recessed portion arranged to be recessed in a direction away from the one of the bushing and the bearing portion, and arranged axially opposite the annular portion;   the annular portion is arranged in the annular recessed portion; and   the vertical gap is defined between an inner circumferential surface of the annular portion and an outer circumferential surface of the other one of the bushing and the bearing portion which defines a portion of the annular recessed portion.   
     
     
         4 . The dynamic pressure bearing apparatus according to  claim 2 , wherein
 the bushing includes an annular portion arranged to extend downward; and   the vertical gap is defined between an inner circumferential surface of the annular portion and an outer circumferential surface of the bearing portion.   
     
     
         5 . The dynamic pressure bearing apparatus according to  claim 2 , wherein a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of an opening of the seal gap. 
     
     
         6 . The dynamic pressure bearing apparatus according to  claim 1 , wherein an outside diameter of the bushing is arranged to be substantially equal to or smaller than an outside diameter of the bearing portion. 
     
     
         7 . The dynamic pressure bearing apparatus according to  claim 1 , wherein a minimum axial width of the horizontal gap is arranged to be smaller than a maximum radial width of an opening of the seal gap. 
     
     
         8 . The dynamic pressure bearing apparatus according to  claim 1 , wherein
 an inclined gap arranged in a shape of a conical surface centered on the central axis is defined between the bearing portion and the bushing on a radially outer side of the horizontal gap;   a minimum width of the inclined gap is arranged to be smaller than a maximum radial width of an opening of the seal gap; and   the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the inclined gap.   
     
     
         9 . The dynamic pressure bearing apparatus according to  claim 1 , wherein
 the bushing includes an annular projecting portion arranged to project radially inward from an inner circumferential surface thereof; and   the projecting portion is arranged to be in contact with an upward facing surface of the shaft.   
     
     
         10 . The dynamic pressure bearing apparatus according to  claim 1 , wherein the bearing portion is defined by a single member made of a metal. 
     
     
         11 . The dynamic pressure bearing apparatus according to  claim 1 , wherein
 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 bearing housing includes an annular upper portion arranged to extend radially inward on an upper side of the sleeve; and   the seal gap is defined between an inner circumferential surface of the annular upper portion and the outer circumferential surface of the shaft.   
     
     
         12 . The dynamic pressure bearing apparatus according to  claim 1 , further comprising a thrust plate arranged to extend radially outward from a lower end of the shaft to be axially opposed to the bearing portion, wherein a thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure in the lubricating oil is defined in a thrust gap defined between axially opposing surfaces of the bearing portion and the thrust plate. 
     
     
         13 . The dynamic pressure bearing apparatus according to  claim 12 , further comprising a cap member arranged to close a bottom portion of the bearing portion below the thrust plate, wherein another thrust dynamic pressure bearing portion arranged to generate a fluid dynamic pressure in the lubricating oil is defined in another thrust gap defined between the thrust plate and the cap member. 
     
     
         14 . The dynamic pressure bearing apparatus according to  claim 12 , wherein the lubricating oil is arranged continuously in a gap having a bladder structure and including the seal gap, the radial gap, and the thrust gap, and the surface of the lubricating oil defined in the seal portion is a sole surface of the lubricating oil. 
     
     
         15 . 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:
 the dynamic pressure bearing apparatus of  claim 1 ; 
 a stationary portion including a stator; and 
 a rotating portion including a rotor magnet arranged radially outside the stator. 
   
     
     
         16 . The fan according to  claim 15 , wherein the impeller is made of a resin and fixed to the bushing. 
     
     
         17 . The fan according to  claim 15 , wherein
 the rotating portion further includes a rotor holder made of a metal and fixed to the bushing; and   the impeller is fixed to the rotor holder.   
     
     
         18 . A dynamic pressure bearing apparatus comprising:
 a bearing portion;   a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion;   a substantially annular bushing fixed to the shaft on an upper side of the bearing portion, and arranged to allow an impeller to be attached to an outer circumferential surface thereof directly or through one or more members;   a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, an outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil; and   a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; wherein   a horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the bushing;   a minute vertical gap extending in an axial direction is defined between a circumferential surface of the bearing portion and a circumferential surface of the bushing;   the vertical gap is connected with a radially outer end portion of the horizontal gap; and   the seal gap is arranged to be in communication with an exterior space through the horizontal gap and the vertical gap.   
     
     
         19 . 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:
 the dynamic pressure bearing apparatus of  claim 18 ; 
 a stationary portion including a stator; and 
 a rotating portion including a rotor magnet arranged radially outside the stator. 
   
     
     
         20 . The fan according to  claim 19 , wherein the impeller is made of a resin and fixed to the bushing. 
     
     
         21 . The fan according to  claim 19 , wherein
 the rotating portion further includes a rotor holder made of a metal and fixed to the bushing; and   the impeller is fixed to the rotor holder.   
     
     
         22 . A dynamic pressure bearing apparatus comprising:
 a bearing portion;   a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members;   a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil;   a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and   an annular member arranged in an annular shape, fixed to the shaft axially between the seal portion and the attachment surface, and arranged to extend radially outward beyond an opening of the seal gap; wherein   a minute horizontal gap extending radially is defined between an upper surface of the bearing portion and a lower surface of the annular member; and   the seal gap is arranged to be in communication with an exterior space through the horizontal gap.   
     
     
         23 . The dynamic pressure bearing apparatus according to  claim 22 , wherein
 the annular member includes:
 a top cover portion arranged substantially in a shape of an annular plate centered on the central axis, and fixed to the shaft axially between the seal portion and the attachment surface; and 
 a tubular portion arranged to extend downward from the top cover portion, and arranged radially opposite an outer circumferential surface of the bearing portion; 
   the horizontal gap is defined between the upper surface of the bearing portion and a lower surface of the top cover portion;   a minute vertical gap extending in an axial direction is defined between an inner circumferential surface of the tubular portion and the outer circumferential surface of the bearing portion;   the vertical gap is connected with a radially outer end portion of the horizontal gap; and   the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the vertical gap.   
     
     
         24 . The dynamic pressure bearing apparatus according to  claim 22 , wherein
 the bearing portion includes an annular projection portion arranged to project upward from the upper surface thereof;   the annular member is arranged substantially in a shape of an annular plate centered on the central axis;   an outer circumferential surface of the annular member is arranged radially opposite an inner circumferential surface of the annular projection portion;   a minute vertical gap extending in an axial direction is defined between the outer circumferential surface of the annular member and the inner circumferential surface of the annular projection portion;   the vertical gap is connected with a radially outer end portion of the horizontal gap; and   the seal gap is arranged to be in communication with the exterior space through the horizontal gap and the vertical gap.   
     
     
         25 . The dynamic pressure bearing apparatus according to  claim 23 , wherein a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of the opening of the seal gap. 
     
     
         26 . The dynamic pressure bearing apparatus according to  claim 24 , wherein a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of the opening of the seal gap. 
     
     
         27 . The dynamic pressure bearing apparatus according to  claim 22 , wherein a minimum axial width of the horizontal gap is arranged to be smaller than a maximum radial width of the opening of the seal gap. 
     
     
         28 . 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:
 the dynamic pressure bearing apparatus of  claim 22 ; 
 a stationary portion including a stator; and 
 a rotating portion including a rotor magnet arranged radially outside the stator. 
   
     
     
         29 . The fan according to  claim 28 , wherein a lower end of the bearing portion is arranged at a level higher than that of a lower end of the impeller. 
     
     
         30 . The fan according to  claim 28 , wherein the impeller includes a channel arranged to bring a space above the impeller into communication with a space above the stator. 
     
     
         31 . A dynamic pressure bearing apparatus comprising:
 a bearing portion;   a shaft inserted in the bearing portion, and arranged to rotate about a central axis relative to the bearing portion, an outer circumferential surface of the shaft including an attachment surface to which an impeller is to be attached directly or through one or more members;   a radial dynamic pressure bearing portion defined by an inner circumferential surface of the bearing portion, the outer circumferential surface of the shaft, and a portion of a lubricating oil which exists in a radial gap defined between the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft, and arranged to generate a fluid dynamic pressure in the portion of the lubricating oil;   a seal gap defined by the inner circumferential surface of the bearing portion and the outer circumferential surface of the shaft on an upper side of the radial dynamic pressure bearing portion, the seal gap including a seal portion having a surface of the lubricating oil defined therein; and   an annular member arranged in an annular shape, and fixed to an upper portion of the bearing portion; wherein   a minute vertical gap extending in an axial direction is defined between the outer circumferential surface of the shaft and an inner circumferential surface of the annular member;   a minimum radial width of the vertical gap is arranged to be smaller than a maximum radial width of an opening of the seal gap; and   the seal gap is arranged to be in communication with an exterior space through the vertical gap.   
     
     
         32 . The dynamic pressure bearing apparatus according to  claim 31 , wherein
 the bearing portion includes an annular projection portion arranged to project upward from an upper surface thereof;   the annular member is fixed to the upper surface of the bearing portion on a radially inner side of the annular projection portion; and   at least a portion of an outer circumferential surface of the annular member is arranged to be in contact with an inner circumferential surface of the annular projection portion.   
     
     
         33 . 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:
 the dynamic pressure bearing apparatus of  claim 31 ; 
 a stationary portion including a stator; and 
 a rotating portion including a rotor magnet arranged radially outside the stator. 
   
     
     
         34 . The fan according to  claim 33 , wherein a lower end of the bearing portion is arranged at a level higher than that of a lower end of the impeller. 
     
     
         35 . The fan according to  claim 33 , wherein the impeller includes a channel arranged to bring a space above the impeller into communication with a space above the stator.