Fluid dynamic bearing apparatus and motor comprising the same

Abstract

A fluid dynamic bearing apparatus with an increased adhesive strength between a component having an adhesion fixing face and a bracket is provided by appropriately controlling the adhesion gap. Materials for a bracket 6 and a housing 7 are selected so that the value obtained by dividing the linear expansion coefficient of the housing 7 fixed to the inner periphery of the bracket 6 by the linear expansion coefficient of the bracket 6 having a portion 6 b for mounting a stator coil 4 of a motor is not lower than 0.5 but not higher than 2.0. An adhesion fixing face 7 e formed on the outer periphery of the housing 7 is adhesively fixed to the inner circumferential surface 6 a of the bracket 6 with an anaerobic adhesive or an epoxy-based adhesive.

1 . A fluid dynamic bearing apparatus comprising a shaft member, a bracket, and a radial bearing portion which rotatably supports the shaft member in the radial direction by a fluid film formed in a radial bearing gap, and an adhesion fixing face which is adhesively fixed to the inner circumferential surface of the bracket,
 wherein the value obtained by dividing a linear expansion coefficient of the component having the adhesion fixing face by a linear expansion coefficient of the bracket is not lower than 0.5 but not higher than 2.0.   
   
   
       2 . A fluid dynamic bearing apparatus according to  claim 1  which further comprises a bearing sleeve whose inner circumferential surface forms a radial bearing gap between itself and the outer circumferential surface of the shaft member, and a housing in which the bearing sleeve is fixed on its inner periphery and an adhesion fixing face is formed on its outer periphery. 
   
   
       3 . A fluid dynamic bearing apparatus according to  claim 1  which further comprises a bearing member whose inner circumferential surface forms a radial bearing gap between itself and the outer circumferential surface of the shaft member and in which an adhesion fixing face is formed on its outer circumferential surface. 
   
   
       4 . A fluid dynamic bearing apparatus according to  claim 1 , wherein an adhesive used in the adhesive fixing between the component having the adhesion fixing face and the bracket is an anaerobic adhesive or an epoxy-based adhesive. 
   
   
       5 . A fluid dynamic bearing apparatus according to  claim 1 , wherein one or both of the component having the adhesion fixing face and the bracket are formed from a metallic material. 
   
   
       6 . A fluid dynamic bearing apparatus according to  claim 1 , wherein one or both of the component having the adhesion fixing face and the bracket are formed from a resin composition. 
   
   
       7 . A fluid dynamic bearing apparatus according to  claim 6 , wherein polyphenylene sulfide (PPS) is contained in the resin composition as a base resin. 
   
   
       8 . A fluid dynamic bearing apparatus according to  claim 6  or  7 , wherein carbon fiber is contained in the resin composition as a filler. 
   
   
       9 . A fluid dynamic bearing apparatus according to  claim 6  or  7 , wherein an inorganic compound is contained in the resin composition as a filler. 
   
   
       10 . A housing for fluid dynamic bearing apparatuses according to  claim 6  or  7  which is a resin composition having the amount of Na contained of 2000 ppm or lower. 
   
   
       11 . A housing for fluid dynamic bearing apparatuses according to  claim 7 , wherein polyphenylene sulfide (PPS) is of the linear type. 
   
   
       12 . A housing for fluid dynamic bearing apparatuses according to  claim 8 , wherein the pull strength of the carbon fibers is 3000 MPa or higher. 
   
   
       13 . A housing for fluid dynamic bearing apparatuses according to  claim 8 , wherein the carbon fiber is a PAN-based fiber. 
   
   
       14 . A housing for fluid dynamic hearing apparatuses according to  claim 8 , wherein the aspect ratio of the carbon fibers is 6.5 or higher. 
   
   
       15 . A housing for fluid dynamic bearing apparatuses according to  claim 8 , wherein the carbon fiber is contained in the resin composition in an amount of not lower than 10 vol. % but not higher than 35 vol. %. 
   
   
       16 . A housing for fluid dynamic bearing apparatuses according to  claim 9 , wherein the inorganic compound is aluminum borate whisker. 
   
   
       17 . A motor comprising a fluid dynamic bearing apparatus according to  claim 1 , a stator coil, and a rotor magnet which produces excitation between itself and the stator coil.