Shaft Member For Hydrodynamic Bearing Apparatuses And A Method For Producing The Same

Abstract

A shaft member for hydrodynamic bearing apparatuses having higher dimensional accuracy produced at low costs and a method for producing the same are provided. Moreover, a shaft member for hydrodynamic bearing apparatuses having hydrodynamic grooves processed with high accuracy and a method for producing the same are provided without a large increase in the processing costs. A shaft material 10 integrally having a shaft portion 11 and a flange portion 12 is formed by a forging process, and the cylindricity of a part or the entire outer circumferential surface 11 a of the shaft portion 11 is corrected. The end face 11 b of the shaft portion of the shaft material 10 and the end face 12 b of the flange portion 12 on the opposite side of the shaft portion are ground relative to the corrected face 13 mentioned above, and the outer circumferential surface 10 b of the shaft material 10 is ground relative to these end faces 11 b , 12 b . This renders the cylindricity of the radial bearing faces 23 a , 23 b formed on the outer periphery of the shaft portion 21 of the produced shaft member 2 to be 3 μm or lower. Moreover, in a common forging step, a shaft material 110 integrally having the shaft portion 111 and flange portion 112 is formed, while simultaneously thrust hydrodynamic groove regions 112 a , 112 b are formed on both end faces of the flange portion 112. After the forging process, in a common rolling step, radial hydrodynamic groove regions 113 a , 113 b are formed on the outer circumferential surface 111 a of the shaft portion 111. In a grinding step following the rolling process, the radial hydrodynamic groove regions 113 a , 113 b and the thrust hydrodynamic groove regions 112 a , 112 b are ground.

1 . A shaft member for hydrodynamic bearing apparatuses comprising a shaft portion and a flange portion each formed by forging, a radial bearing face which faces a radial bearing gap and is formed on the outer periphery of the shaft portion, and said radial bearing face having a cylindricity of 3 μm or lower.  
   
   
       2 . A shaft member for hydrodynamic bearing apparatuses according to  claim 1 , wherein the perpendicularity of both end faces of the flange portion and the perpendicularity of an end face of the shaft portion relative to said radial bearing face are each 5 μm or lower.  
   
   
       3 . A shaft member for hydrodynamic bearing apparatuses according to  claim 1 , wherein said shaft portion and flange portion are integrally formed by forging.  
   
   
       4 . A shaft member for hydrodynamic bearing apparatuses according to  claim 1 , wherein both end faces of said shaft member are grinding surfaces.  
   
   
       5 . A shaft member for hydrodynamic bearing apparatuses according to  claim 1 , wherein a slanting recess portion is formed at the corner between said shaft portion and flange portion.  
   
   
       6 . A hydrodynamic bearing apparatus comprising a shaft member for hydrodynamic bearing apparatuses according to  claim 1;  a bearing sleeve into which said shaft member is inserted at its inner surface; 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 surface 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 which occurs in a 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 a 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.  
   
   
       7 . A hydrodynamic bearing apparatus according to  claim 6 , 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 surface of the bearing sleeve facing this outer circumferential surface.  
   
   
       8 . A motor comprising the hydrodynamic bearing apparatus according to  claim 6 , a rotor magnet and a stator coil.  
   
   
       9 . A method for producing a shaft member for hydrodynamic bearing apparatuses, the method comprising the step of forming the shaft material which integrally has the shaft portion and the flange portion by a forging process; and the step of correcting the cylindricity of a part or the entire outer circumferential surface of the shaft portion.  
   
   
       10 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 9 , wherein said correcting step is performed by rolling.  
   
   
       11 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 9 , wherein a first grinding process is performed on both end faces of the shaft material relative to said corrected face, and a second grinding process is performed on at least the outer circumferential surface of the shaft material relative to said both end faces.  
   
   
       12 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 11 , wherein the first grinding process is performed on the other hand end face of the flange portion and on the end face of the shaft portion.  
   
   
       13 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 11 , wherein said second grinding process is performed on at least a portion which serves as a radial bearing face facing a radial bearing gap on the outer periphery of the shaft portion of the shaft material.  
   
   
       14 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 13 , wherein the other end face of the flange portion is ground further in the second grinding process.  
   
   
       15 . A metallic shaft member for hydrodynamic bearing apparatuses which integrally comprises a shaft portion and a flange portion, and a radial hydrodynamic groove region which comprises a plurality of hydrodynamic grooves and demarcation portions demarcating each hydrodynamic groove being formed on the outer periphery of said shaft portion by plastic processing, and said outer circumferential surfaces of the demarcation portions in the radial hydrodynamic groove region being grinding surfaces.  
   
   
       16 . A shaft member for hydrodynamic bearing apparatuses according to  claim 15 , wherein a thrust hydrodynamic groove region comprising a plurality of the hydrodynamic grooves and demarcation portions demarcating each hydrodynamic groove is formed by plastic processing on both end faces of said flange portion, and the end face in the axial direction of the demarcation portion in said thrust hydrodynamic groove region is a grinding surface.  
   
   
       17 . A shaft member for hydrodynamic bearing apparatuses according to  claim 15 , wherein said radial hydrodynamic groove region is formed by a rolling process or a forging process.  
   
   
       18 . A shaft member for hydrodynamic bearing apparatuses according to  claim 16 , wherein said thrust hydrodynamic groove region is formed by a forging process.  
   
   
       19 . A shaft member for hydrodynamic bearing apparatuses according to  claim 15 , wherein said shaft portion and said flange portion are integrally formed by forging.  
   
   
       20 . A hydrodynamic bearing apparatus comprising a shaft member for hydrodynamic bearing apparatuses according to  claim 15;  and a sleeve member into which said shaft member is inserted at its inner surface to form a radial bearing gap between itself and said shaft member, wherein said shaft member and said sleeve member being retained in a non-contact manner by said hydrodynamic effect of the fluid occurring in the radial bearing gap.  
   
   
       21 . A hydrodynamic bearing apparatus according to  claim 20 , wherein the sleeve member is formed of an oil-containing sintered metal.  
   
   
       22 . A hydrodynamic bearing apparatus according to  claim 20 , wherein hydrodynamic grooves for producing the hydrodynamic effect of the fluid are formed asymmetrically in the axial direction on the outer circumferential surface of the shaft portion facing the radial bearing gap.  
   
   
       23 . A motor comprising a hydrodynamic bearing apparatus according to  claim 20 , a rotor magnet and a stator coil.  
   
   
       24 . A method for producing a shaft member for hydrodynamic bearing apparatuses comprising a shaft portion and a flange portion integrally, and a radial hydrodynamic groove region which comprises a plurality of hydrodynamic grooves and demarcation portions demarcating each hydrodynamic groove being formed on the outer periphery of said shaft portion, 
 the method comprising forming said radial hydrodynamic groove region by plastic processing on the outer periphery of the shaft portion of the shaft material, and then grinding a portion including the outer diameter portion of the demarcation portion in said radial hydrodynamic groove region.    
   
   
       25 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 24 , the method comprising forming said shaft material and said radial hydrodynamic groove region both by forging, and simultaneously performing forging of both.  
   
   
       26 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 24 , wherein forming said radial hydrodynamic groove region and correcting said cylindricity of a portion including the radial hydrodynamic groove region of the shaft portion are both performed by rolling, and the rolling process of both are simultaneously performed.  
   
   
       27 . A method for producing a shaft member for hydrodynamic bearing apparatuses according to  claim 24 , wherein forming said shaft material and forming the thrust hydrodynamic groove region comprising the hydrodynamic grooves and demarcation portions demarcating each hydrodynamic groove on both end faces of the flange portion are both performed by forging, and the forging process of both is performed simultaneously.