Abstract:
A hydraulic dynamic bearing has a rotational assembly and a bearing member for rotationally supporting the rotational assembly. The bearing member has a main body having a recess portion and a cover for covering an open end of the recess portion. The rotational assembly has a shaft main body having an end portion extending into the recess of the bearing main body for undergoing rotation relative thereto and a ring member disposed in the recess of the bearing main body. The ring member is connected to the end portion of the shaft main body for rotation therewith. Axial dynamic pressure generating grooves are formed in upper and lower surface portions of the ring member for generating axial dynamic pressure during rotation of the rotational assembly. Radial dynamic pressure generating grooves are formed in an outer peripheral surface portion of the ring member for generating radial dynamic pressure during rotation of the rotational assembly. Spaces are formed between the bearing member and the rotational assembly for storing a lubricant.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a ring-like hydraulic dynamic bearing having axial dynamic pressure portions and a radial dynamic pressure portion contiguous to each other and to a spindle motor using the hydraulic dynamic bearing. 
     As a bearing for a spindle motor for a hard disk device, there is used a hydraulic dynamic bearing having a shaft portion and a bearing portion for supporting the bearing portion. The hydraulic dynamic bearing is formed with dynamic pressure generating grooves at either one of opposed faces of the shaft and bearing portions and is formed with a layer of a lubricant at high pressure in a very small clearance disposed between the shaft and bearing portions so that during rotation of the shaft portion noncontact rotation of the shaft portion is realized. 
     FIG. 8 is a sectional view showing a conventional ring-like hydraulic dynamic bearing. A ring-like hydraulic dynamic bearing  100  is provided with a shaft portion  103  constituted by fixing a ring  102  to an end portion  101 A of a shaft main body  101  by press fitting and a bearing portion  104  supporting the shaft portion  103  and is constituted such that the ring  102  at the shaft portion  103  rotatably contained in a recess portion  105 A of a main body  105  of the bearing portion  104  is prevented from coming out from the recess portion  105 A by a circular disk-like thrust holding member  106 . 
     An upper face  102 A and a lower face  102 B of the ring  102  are respectively formed with axial dynamic pressure generating grooves G 1  and G 2  and a peripheral face  102 C of the ring  102  is formed with radial dynamic pressure generating grooves G 3 . 
     A lubricant for generating dynamic pressure is held between the shaft portion  103  and the bearing portion  104  and accordingly, when the shaft portion  103  is rotated, axial dynamic pressure is generated between the upper face  102 A and the circular disk-like thrust holding member  106  by the axial dynamic pressure generating grooves G 1  and axial dynamic pressure is generated between the lower face  102 B and a bottom face of the recess portion  105 A by the axial dynamic pressure generating grooves G 2 . Further, radial dynamic pressure is generated between the peripheral face  102 C and an inner peripheral face of the recess portion  105 A by the radial dynamic pressure generating grooves G 3 . As a result, axial dynamic pressure bearings and a radial dynamic pressure bearing which are lubricant layers at high pressure are formed between the shaft portion  103  and the bearing portion  104  to thereby enable to rotate the shaft portion  103  by noncontact rotation. 
     As described above, according to the conventional ring-like radial dynamic bearing, there is constructed the constitution in which the radial dynamic pressure generating face and the axial dynamic pressure generating faces are contiguous to each other and accordingly, the following problem is posed. That is, when the shaft portion  103  is rotated, by the axial dynamic pressure generating grooves G 1 , the axial dynamic pressure generating grooves G 2  and the radial dynamic pressure generating grooves G 3  which are respectively formed at the upper face  102 A, the lower face  102 B and the peripheral face  102 C of the ring  102 , the lubricant is drawn to central portions of the respective dynamic pressure generating faces and negative pressure is produced at portions of the upper face  102 A and the peripheral face  102 C contiguous to each other and portions of the lower face  102 B and the peripheral face  102 C contiguous to each other. As a result of producing the negative pressure caused by mutual interference, air bubbles are liable to produce at the portions of the dynamic pressure generating faces contiguous to each other which hamper flow of the lubricant and accordingly, there causes a drawback in which sufficient dynamic pressure is not generated and the bearing rigidity is deteriorated. 
     SUMMARY OF THE INVENTION 
     Hence, it is an object of the invention to provide a hydraulic dynamic bearing capable of resolving the above-described problem in the conventional technology and to a spindle motor using the hydraulic dynamic bearing. 
     In order to resolve the above-described problem, according to an aspect of the invention, there is proposed a hydraulic dynamic bearing which is a ring-like hydraulic dynamic bearing comprising a shaft portion constituted by fixing a ring to an end portion of a shaft main body thereof and a bearing portion supporting the shaft portion via the ring wherein a radial dynamic pressure bearing portion and axial dynamic pressure bearing portions are formed contiguously to each other between the ring and the bearing portion and wherein spaces for storing a lubricant for generating dynamic pressure are provided along portions of the radial dynamic pressure bearing portion and the axial dynamic pressure bearing portions contiguous to each other. 
     When relative rotational motion is caused between the shaft portion and the bearing portion, the lubricant at the respective dynamic pressure bearing portions is drawn to respective central portions of the shaft and bearing portions to thereby generate required dynamic pressure. Therefore, at regions of the radial dynamic pressure bearing portion and the axial dynamic pressure bearing portions contiguous to each other, the lubricant is going to reduce. However, owing to the lubricant stored in the spaces provided along the portions of the two dynamic pressure bearing portions contiguous to each other, the reduction does not amount to produce mutual interference between the two dynamic pressure bearing portions and mutual operation between the two dynamic pressure bearing portions is alleviated. As a result, at the portions of the two dynamic pressure bearing portions contiguous to each other, generation of negative pressure is restrained and air bubbles can be restrained from generating in the lubricant and accordingly, the bearing rigidity can be made higher than that in the conventional bearing. 
     The radial dynamic pressure bearing can be formed by providing dynamic pressure generating grooves at an outer peripheral face of the ring or an inner face of the bearing portion opposed thereto. The axial dynamic pressure bearing can be formed by providing the dynamic pressure generating grooves at at least one of plane portions contiguous to an outer peripheral face of the ring. Alternatively, the dynamic pressure generating grooves may be formed at inner faces of the bearing portion opposed to the plane portions. 
     The spaces for storing the lubricant can be provided by forming ring-like recess portions at boundary regions between the outer peripheral face of the ring and the planes contiguous thereto. A sectional shape of the recess portion may be that of a circular arc or an arbitrary stepped shape of an L-like type. 
     According to another aspect of the invention, there is proposed a constitution in which a clearance is provided between an end face of the shaft main body and the bearing portion opposed thereto and paths for communicating the clearance with the atmosphere are formed at an inner peripheral face of the ring to thereby enable to circulate the lubricant by the clearance and the paths. 
     According to the constitution, in the case in which there is constructed a constitution in which axial dynamic pressure is generated between the plane portion on the end face side of the shaft main body in the plane portion of the ring and the bearing portion, even when the lubricant disposed in the clearance is drawn to the ring side in generating the dynamic pressure, owing to the lubricant circulating to the clearance by passing through the paths communicating with the atmosphere, the negative pressure can effectively be prevented from generating in the clearance. As a result, the dynamic pressure is excellently generated at the plane portion and the bearing rigidity can further be promoted. 
     Further, in either of the cases, the spaces for storing the lubricant are not limited to the constitution provided by machining the ring but in place thereof or in addition thereto, for example, there may be constructed a constitution in which the spaces are provided by forming ring-like grooves at corresponding portions of the bearing portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing an example of an embodiment of a ring-like hydraulic dynamic bearing according to the invention; 
     FIG. 2 is a perspective view enlarging a ring shown in FIG. 1; 
     FIG. 3 is a sectional view showing an example of an embodiment of a spindle motor constituted by using the ring-like hydraulic dynamic bearing shown in FIG. 1; 
     FIG. 4 is a sectional view showing another embodiment of a ring-like hydraulic dynamic bearing portion according to the invention; 
     FIG. 5 is a perspective view enlarging a ring shown in FIG. 4; 
     FIG  6  is perspective view enlarging a shaft portion shown in FIG. 4; 
     FIG  7  is a sectional view showing a modified example of a ring-like hydraulic dynamic bearing shown in FIG. 4; and 
     FIG. 8 is a sectional view showing a conventional ring-like hydraulic dynamic bearing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed explanation will be given of an examples of embodiments according to the invention in reference to the drawings as follows. 
     FIG. 1 is a sectional view showing an example of an embodiment of a ring-like hydraulic dynamic bearing according to the invention. The ring-like hydraulic dynamic bearing  1  is provided with a shaft assembly portion  4  constituted by fixing a ring  3  to an end portion  2 A of a shaft main body  2  by press fitting and a bearing assembly portion  5  supporting the shaft portion  4 . The bearing portion  5  comprises a bearing portion main body  6  and a circular disk-like thrust holding member  7  and is constructed by a constitution in which the ring  3  of the shaft portion  4  rotatably contained in a recess portion  6 A of the bearing portion main body  6  is held by the thrust holding member  7  which functions as a cover to thereby prevent the ring  3  from coming out from the recess portion  6 A. Further, a lubricant is held between the bearing portion  5  and the bearing portion main body  6 . 
     FIG. 2 shows an enlarged view of the ring  3 . An outer peripheral face  3 A of the ring  3  is formed with radial dynamic pressure generating grooves GR and axial dynamic pressure grooves GA 1  are formed at a plane portion  3 B contiguous to the outer peripheral face  3 A of the ring  3 . Axial dynamic pressure generating grooves GA 2  are similarly formed at a plane portion  3 C on a side opposed to the plane portion  3 B although not apparent in FIG. 2 (refer to FIG.  1 ). Both of the radial hydraulic pressure generating grooves GR and the axial dynamic pressure generating grooves GA 1  and GA 2  can be formed by a publicly-known method. 
     The ring  3  is formed as described above and accordingly, as shown by FIG. 1, when the ring  3  is rotated in the bearing portion  5  constituted by the bearing portion main body  6  and the thrust holding member  7 , a radial dynamic pressure portion is formed by the outer peripheral face  3 A and an inner peripheral face  6 A a  of the recess portion  6 A opposed thereto. Simultaneously therewith, an axial dynamic pressure portion is formed by the plane portion  3 B and a bottom face  7 A of the thrust holding member  7  opposed thereto and an axial dynamic pressure portion is formed by the plane portion  3 C and a bottom face  6 A b  of the recess portion  6 A opposed thereto. 
     The radial dynamic portion and the axial dynamic portions formed between the shaft portion  4  and the bearing portion  5  as described above, are contiguous to each other and accordingly, the radial dynamic pressure portion and the axial dynamic pressure portions are provided with a tendency of interfering with each other as has been explained already. 
     In order to improve the drawback of the mutual interference, there are provided ring-like stepped portions  3 D and  3 E at portions constituting boundaries between the radial dynamic pressure portion and the axial dynamic pressure portions. The ring-like stepped portion  3 D is a stepped portion having a section in an L-like shape and the outer peripheral face  3 A and the plane portion  3 B are separated by the ring-like stepped portion  3 D. Further, when the shaft portion  4  and the bearing portion  5  are integrated, the ring-like stepped portion  3 D forms a ring-like space  8  and is used for storing the lubricant for generating dynamic pressure in the ring-like space  8  (refer to FIG.  1 ). 
     Meanwhile, the ring-like stepped portion  3 E is similarly constituted by a stepped portion having a section in an L-like shape and the outer peripheral face  3 A and the plane portion  3 C are separated by the ring-like stepped portion  3 E. Further, when the shaft portion  4  and the bearing portion  5  are integrated, the ring-like stepped portion  3 E forms a ring-like space  9  and is used for storing the lubricant for generating dynamic pressure in the ring-like space  9  (refer to FIG.  1 ). 
     Further, as shown by FIG. 1, a very small space  10  is formed between a lower end face  2 B of the shaft main body  2  and the bottom face  6 A b  of the recess portion  6  and the lubricant is filled also in the very small space  10 . Meanwhile, a ring-like oil storage space  11  is provided at an upper end edge  3 F a  of an inner peripheral face  3 F of the ring  3 . The oil storage space  11  communicates with the atmosphere via a clearance between the shaft main body  2  and an inner peripheral face  7 B of the thrust holding member  7 . 
     The ring-like hydraulic dynamic bearing  1  is constituted as described above and accordingly, when the shaft portion  4  carries out rotational motion relative to the bearing portion  5 , the lubricant held between the shaft portion  4  and the bearing portion  5  is pressurized at the very small clearances between the shaft portion  4  and the bearing portion  5  by the radial dynamic pressure generating grooves GR and the axial dynamic pressure generating grooves G 1  and G 2 , thereby, the radial dynamic pressure portion and the axial dynamic pressure portions, described above, are formed contiguously to each other between the shaft portion  4  and the bearing portion  5 . 
     In this case, the ring-like space  8  is formed at the ring-like hydraulic dynamic bearing  1  and the lubricant is filled there and accordingly, the lubricant drawn toward the center of the outer peripheral portion  3 A by the radial dynamic pressure generating grooves GR and the lubricant drawn toward the center of the plane portion  3 B of the ring  3  by the axial dynamic pressure generating grooves GA 1 , are supplied by the lubricant in the ring-like space  8  without causing negative pressure at contiguous portions of the two dynamic pressure generating portions. Therefore, there is produced no mutual interference between the radial dynamic pressure portion formed by the radial dynamic pressure generating grooves GR and the axial dynamic pressure portion formed by the axial dynamic pressure generating grooves GA 1 , no air bubbles are produced in the lubricant and accordingly, excellent dynamic pressure property is achieved and high bearing rigidity can be realized. 
     Similarly, owing to the lubricant filled in the ring-like space  9 , the lubricant drawn toward the center of the outer peripheral portion  3 A of the ring  3  by the radial dynamic pressure generating grooves GR and the lubricant drawn toward the center of the plane portion  3 C of the ring  3  by the axial dynamic pressure generating grooves GA 2 , are supplied by the lubricant in the ring-like space  9  without producing negative pressure at contiguous portions of the two dynamic pressure generating portions. Therefore, mutual interference is not produced between the radial dynamic portion formed by the radial dynamic pressure generating grooves GR and the axial dynamic pressure portion formed by the axial dynamic pressure generating grooves GA 2  and no air bubbles are produced in the lubricant. As a result, the dynamic pressure function is significantly improved, high bearing rigidity is achieved and accordingly, stable rotation can be realized. 
     FIG. 3 is a sectional view showing an example of an embodiment of a spindle motor constituted by using the ring-like hydraulic dynamic bearing  1  shown by FIG.  1 . According to a spindle motor  21 , a base  22  is integrally assembled with the ring-like hydraulic dynamic bearing  1  shown by FIG.  1 . That is, the bearing portion main body  6  of the ring-like hydraulic dynamic bearing  1  is formed integrally with the base  22 . A hub  23  is fixed to the shaft main body  2  of the ring-like hydraulic dynamic bearing  1  and a rotor magnet  24  attached to the hub  23  and a stator coil  25  attached to the base  22  are opposed to each other via a very small clearance. 
     The spindle motor  21  is constituted as described above and accordingly, when current is made to flow in the stator coil  25 , the hub  23  rotatably supported by the ring-like dynamic bearing  1  can be rotated. In this case, since the ring-like hydraulic dynamic bearing  1  is constituted as described above, the dynamic pressure function is excellent and the axial rigidity is excellent and accordingly, the hub  23  can stably be rotated. Therefore, when a magnetic disk is attached to the hub  23  by publicly-known pertinent means, the magnetic disk can be rotated extremely stably and magnetic recording and reading can be carried out at an extremely high density. 
     FIG. 4 is a sectional view showing another embodiment of a ring-like hydraulic dynamic bearing portion according to the invention. Although the ring-like hydraulic dynamic bearing portion  31  is basically provided with a constitution similar to that of the ring-like hydraulic dynamic bearing  1  shown by FIG. 1, the ring-like hydraulic dynamic bearing portion  31  differs from the ring-like hydraulic dynamic bearing  1  shown by FIG. 1 only in that paths  32  and  33  for communicating the very small space  10  and the oil storage space  11  are provided at the inner peripheral face of the ring  3 . Therefore, among respective portions of the ring-like hydraulic dynamic bearing  31 , portions thereof in correspondence with the respective portions of the ring-like hydraulic dynamic bearing  1  are attached with the same notations and an explanation thereof will be omitted. 
     In reference to FIG.  5  and FIG. 6, in order to form the paths  32  and  33 , vertical grooves  3 G and  3 H are formed at the inner peripheral face  3 F of the ring  3  and accordingly, when the shaft main body  2  is fitted to the ring  3 , the paths  32  and  33  are formed between the ring  3  and the shaft main body  2  by the vertical grooves  3 G and  3 H. 
     By providing the paths  32  and  33 , when the lubricant in the very small space  10  is drawn to between the plane portion  3 C of the ring  3  and the bottom face  6 A b  of the recess portion  6 A by dynamic pressure produced by the axial dynamic pressure generating grooves GA 2 , the inside of the very small space  10  can be prevented from being brought under negative pressure. As a result, the dynamic pressure function of the axial dynamic pressure portion formed by the axial dynamic pressure generating grooves GA 2  can be promoted and the axial rigidity of the ring-like hydraulic dynamic bearing  31  can further be promoted. 
     FIG. 7 shows a modified example of the ring-like hydraulic dynamic bearing  31  shown by FIG.  4 . According to the ring-like hydraulic dynamic bearing  41 , by providing a ring-like groove  42  opposed to the ring-like stepped portion  3 D on the side of the bearing portion  5  and providing a ring-like groove  44  opposed to the ring-like stepped portion  3 D on the side of the thrust holding member  7  in the circular disk shape, enlargement of a capacity of the ring-like space  8  is achieved and further, a ring-like groove  43  opposed to the ring-like stepped portion  3 E is provided on the side of the bearing portion  5  to thereby achieve enlargement of a capacity of the ring-like space  9 . In this way, by achieving enlargement of the capacities of the ring-like spaces  8  and  9 , the mutual interference between the radial dynamic pressure portion and the axial dynamic pressure portions contiguous thereto can further be reduced. As a result, the axial rigidity of the ring-like hydraulic dynamic bearing  41  can be promoted in comparison with that of the ring-like hydraulic dynamic bearing  31 . Further, when the capacities may stay to be the same, dimensions of the ring-like stepped portions  3 D and  3 E are reduced and areas of the plane portions  3 B and  3 C are increased to thereby serve to generate larger dynamic pressure. 
     The ring-like hydraulic dynamic bearing  31  or  41  shown by FIG. 4 or FIG. 7 can be used in place of the ring-like hydraulic dynamic bearing  1  of the spindle motor  21  shown by FIG.  3  and similar effects can be achieved. 
     According to the invention, in the ring-like hydraulic dynamic bearing, there are provided the spaces for storing the lubricant at portions of the axial dynamic bearing portions and the radial dynamic bearing portion contiguous to each other and accordingly, mutual interference between the two dynamic pressure bearing portions can effectively be prevented, air bubbles are not produced in the lubricant in the contiguous regions, the axial rigidity can be promoted more than that in the conventional bearing and the hydraulic dynamic bearing having high function can be provided. 
     Further, since the very small spaces formed by the shaft main body and the bearing portion are communicated with the atmosphere by using circulation paths, the dynamic pressure properties of the dynamic pressure generating portions communicated with the very small spaces can significantly be improved. 
     Further, by constituting a spindle motor by using the hydraulic dynamic bearing, stable rotation is achieved and a spindle motor having higher function can be realized.