Shaft Member for Fluid Lubrication Bearing Apparatuses and a Method for Producing the Same

Abstract

A shaft member for hydrodynamic bearing apparatuses which can restore the pressure balance in a thrust bearing gap formed on both axial sides of the flange portion in an early stage is provided at low costs. A shaft material 10 integrally having a shaft portion 11 and a flange portion 12 is formed as a through-hole 19 opening to its both end faces 12 a , 12 b on the flange portion 12 of the shaft material 10 is formed in a common forging step. As a result, the through-hole 29 is formed to open to the inner diameter side of these bearing gap W 1 , W 2 avoiding thrust bearing gaps W 1 , W 2 formed on both end faces of the flange portion 22 of the shaft member 2 as a finished product.

1 . A shaft member for hydrodynamic bearing apparatuses comprising
 a flange portion, and being supported in a non-contact manner in the thrust direction by the pressure produced by hydrodynamic effect of a fluid which occurs in a thrust bearing gap on both axial sides of the flange portion,   a through-hole opening to both end faces of the flange portion being formed on the flange portion, and   the inner periphery of the through-hole being processed by plastic processing.   
   
   
       2 . A shaft member for hydrodynamic bearing apparatuses according to  claim 1  further comprising a shaft portion formed integrally with the flange portion by forging. 
   
   
       3 . A shaft member for hydrodynamic bearing apparatuses according to  claim 1 , wherein the through-hole is formed in the vicinity of the shaft portion. 
   
   
       4 . A hydrodynamic bearing apparatus comprising a shaft member according to  claim 1 ; a bearing sleeve into which the shaft member is inserted at its inner periphery; a radial bearing portion which produces pressure by the hydrodynamic effect of a fluid which occurs in a radial bearing gap between the outer periphery of the shaft portion and the inner periphery of the bearing sleeve to support the shaft portion in the radial direction in a non-contact manner; a first thrust bearing portion which produces pressure by the hydrodynamic effect of a fluid occurring in the thrust bearing gap on one end side of the flange portion to support the flange portion in the thrust direction in a non-contact manner; and a second thrust bearing portion which produces pressure by the hydrodynamic effect of the fluid occurring in the thrust bearing gap on the other end side of the flange portion to support the flange portion in the thrust direction in a non-contact manner. 
   
   
       5 . A hydrodynamic bearing apparatus according to  claim 4 , wherein hydrodynamic grooves for producing the hydrodynamic effect of the fluid are formed asymmetrically in the axial direction on one of the outer circumferential surface of the shaft portion facing the radial bearing gap and the inner periphery face of the bearing sleeve opposing this outer circumferential surface. 
   
   
       6 . A motor comprising a hydrodynamic bearing apparatus according to  claim 4 ; a rotor magnet and a stator coil. 
   
   
       7 . A method for producing a shaft member for hydrodynamic bearing apparatuses which comprises a shaft portion and a flange portion and is supported in a non-contact manner by the pressure produced by hydrodynamic effect of a fluid which occurs in a thrust bearing gap on both axial sides of the flange portion in the thrust direction,
 the method comprising integrally forming the shaft portion and the flange portion by forging, and forming a through-hole opening to both end faces of the flange portion on the flange portion by forging, and these forging being performed simultaneously.   
   
   
       8 . A metallic shaft member for fluid lubrication bearing apparatuses in which a threaded hole is formed on its one end portion and a radial bearing face facing a radial bearing gap is formed on the outer periphery,
 wherein said threaded hole is formed by plastic processing.   
   
   
       9 . A shaft member for fluid lubrication bearing apparatuses according to  claim 8 , wherein said threaded hole has a prepared hole formed by a forging process;
 and a thread portion formed on the opening side of said prepared hole by a rolling process.   
   
   
       10 . A shaft member for fluid lubrication bearing apparatuses according to  claim 9 , wherein said prepared hole comprises a conical surface; and a cylinder face which is disposed on the opening side of said conical surface and is smoothly continuous with said conical surface via a radially curved surface. 
   
   
       11 . A shaft member for fluid lubrication bearing apparatuses according to  claim 10 , wherein said conical surface has a shape with its top removed. 
   
   
       12 . A shaft member for fluid lubrication bearing apparatuses according to  claim 8 , wherein the shaft portion and the flange portion are integrally formed by forging. 
   
   
       13 . A shaft member for fluid lubrication bearing apparatuses according to  claim 8 , wherein the coaxiality of the center line of the pitch circle of said thread portion is 0.2 mm or lower. 
   
   
       14 . A fluid lubrication bearing apparatus comprising a shaft member for fluid lubrication bearing apparatuses according to  claim 13 ; and a sleeve member into which said shaft member is inserted at its inner periphery and which forms the radial bearing gap between itself and said shaft member, the fluid lubrication bearing apparatus retaining the shaft member and the sleeve member in a non-contact manner by a lubricating film of a fluid produced in said radial bearing gap. 
   
   
       15 . A motor comprising a fluid lubrication bearing apparatus according to  claim 14 ; a rotor magnet and a stator coil. 
   
   
       16 . A method for producing a shaft member for fluid lubrication bearing apparatuses which comprises a threaded hole formed on its one end and a radial bearing face formed on its outer periphery facing a radial bearing gap,
 the method comprising forming a prepared hole of the threaded hole by forging on a metallic shaft material, and then forming a thread portion in the prepared hole by rolling to form said threaded hole.   
   
   
       17 . A method for producing a shaft member for fluid lubrication bearing apparatuses according to  claim 16 , wherein said shaft material is formed and said prepared hole is formed in a common forging step. 
   
   
       18 . A metallic shaft member for fluid lubrication bearing apparatuses which comprises a shaft portion and a flange portion,
 at least the shaft portion being formed by forging, and the shaft portion having a concave formed on its tip face, the concave comprising a plastically processed surface.   
   
   
       19 . A shaft member for fluid lubrication bearing apparatuses according to  claim 18 , wherein the concave has a shape whose diameter gradually decreases from the tip of the shaft portion toward the center of the shaft portion. 
   
   
       20 . A fluid lubrication bearing apparatus comprising a shaft member for fluid lubrication bearing apparatuses according to  claim 18 ; and a radial bearing gap formed between the outer circumferential surface of the shaft portion and the face facing the same, the apparatus relatively rotatably supporting said shaft member by a lubricating film of a fluid which occurs in a radial bearing gap. 
   
   
       21 . A method for producing a metallic shaft member for fluid lubrication bearing apparatuses which comprises a shaft portion and a flange portion, the method comprising forming the shaft portion by forging, and forming a concave at the tip portion of the shaft portion by plastic processing during the forging process to cause the tip portion of the shaft portion to overhang by a plastic flow. 
   
   
       22 . A method for producing a shaft member for fluid lubrication bearing apparatuses according to  claim 21 , wherein the concave is formed by plastic processing to cause the tip portion of the shaft portion to overhang until the tip portion reaches at least a final finished shape. 
   
   
       23 . A method for producing a shaft member for fluid lubrication bearing apparatuses according to  claim 22 , wherein the final finished shape of the tip portion of the shaft portion is defined by the outer circumferential surface of the tip of the shaft portion, the tip face of the shaft portion and a chamfer between the two faces.