Fluid dynamic bearing device

Abstract

A weld line formed by injection molding of a sealing member is formed at a circumferential position out of deepest portions of axial grooves, which form thinned portions of the sealing member (optimally, in a region of a cylindrical surface between the axial grooves in a circumferential direction). Thus, the sealing member is prevented from being provided with parts having locally markedly low strength, and hence damage to be caused by press-fitting is prevented.

1 . A fluid dynamic bearing device, comprising:
 a shaft member;   a bearing sleeve having an inner periphery along which the shaft member is inserted;   a housing having an inner periphery by which the bearing sleeve is held;   a sealing member comprising an injection-molded product of a resin and having:
 a large-diameter inner peripheral surface which is fixed to an outer peripheral surface of an end portion of the bearing sleeve by press-fitting; and 
 a small-diameter inner peripheral surface; 
   a radial bearing portion for generating a dynamic pressure action of a lubricating oil in a radial bearing gap between an outer peripheral surface of the shaft member and an inner peripheral surface of the bearing sleeve so as to support the shaft member in a radial direction;   a first seal space formed between the small-diameter inner peripheral surface of the sealing member and the outer peripheral surface of the shaft member so as to seal the lubricating oil filling an inside of the housing;   a second seal space formed between an outer peripheral surface of the sealing member and an inner peripheral surface of the housing so as to seal the lubricating oil filling the inside of the housing; and   a communication path formed between the sealing member and the bearing sleeve so as to communicate the first seal space and the second seal space to each other,   wherein an axial groove is formed in the large-diameter inner peripheral surface of the sealing member so as to form the communication path, and   wherein a weld line as a result of injection molding is formed at a circumferential position out of a deepest portion of the axial groove.   
     
     
         2 . A fluid dynamic bearing device according to  claim 1 ,
 wherein the axial groove formed in the large-diameter inner peripheral surface of the sealing member comprises a plurality of axial grooves, and   wherein the weld line is formed in a region between the plurality of axial grooves in a circumferential direction.   
     
     
         3 . A fluid dynamic bearing device according to  claim 1 ,
 wherein a radial groove is formed in an inner end surface of the sealing member so as to form the communication path, and   wherein the weld line is formed at a circumferential position out of a deepest portion of the radial groove.   
     
     
         4 . A fluid dynamic bearing device according to  claim 1 , wherein a linear expansion coefficient of the sealing member is larger than a linear expansion coefficient of the bearing sleeve. 
     
     
         5 . A fluid dynamic bearing device according to  claim 1 ,
 wherein a diameter of the shaft member ranges from 2 mm to 4 mm, and   wherein a press-fitting margin of the sealing member and the bearing sleeve is 40 μm or more.   
     
     
         6 . A fluid dynamic bearing device according to  claim 1 , wherein the lubricating oil comprises an ester-based lubricating oil. 
     
     
         7 . A fluid dynamic bearing device according to  claim 1 , wherein the sealing member is made of a crystalline resin. 
     
     
         8 . A fluid dynamic bearing device according to  claim 7 , wherein the crystalline resin is selected from a group consisting of PPS, ETFE, PEEK, PA66, PA46, PA6T, and PA9T. 
     
     
         9 . A fluid dynamic bearing device according to  claim 1 ,
 wherein an axial groove is formed in an outer peripheral surface of the bearing sleeve, and   wherein the communication path is formed of the axial groove formed in the outer peripheral surface of the bearing sleeve and the axial groove of the sealing member.   
     
     
         10 . A fluid dynamic bearing device according to  claim 1 ,
 wherein the axial groove formed in the large-diameter inner peripheral surface of the sealing member comprises an odd number of axial grooves, and   wherein a gate for injection molding of the sealing member is provided at a circumferential position of one of the odd number of axial grooves.   
     
     
         11 . A fluid dynamic bearing device according to  claim 10 ,
 wherein the sealing member comprises an injection-molded product formed by injecting a resin from a side gate, and   wherein a gate mark with respect to the side gate is formed at a position lower than an axial position of an outer end surface of the sealing member.