Patent Abstract:
Embodiments of the invention provide a magnetic disk drive having improved vibration characteristics and a reduced size. In one embodiment, a magnetic disk drive comprises: a motor shaft for rotating a magnetic disk; a sleeve for rotatably supporting the motor shaft; and a motor hub into which the motor shaft is press fit. The motor hub supports the magnetic disk and includes a projection portion having an inner surface and an outer surface. The inner surface is in contact with the press-fit motor shaft in directions perpendicular to the rotational axis of the motor shaft. The outer surface faces the sleeve.

Full Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. JP2005-040793, filed Feb. 17, 2005, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a magnetic disk drive, and more particularly to a technique of improving the vibration characteristics of a magnetic disk drive and reducing its size. 
     In recent years, there has been a need to miniaturize magnetic disk drives such as hard disk drives. Some such magnetic disk drives employ a cantilever type spindle motor and a fluid bearing as shown in  FIG. 11 . 
     The magnetic disk drive  100  includes: a motor shaft  101  for rotating a magnetic disk (not shown); a motor hub  102  into which the motor shaft  101  is press fit and which supports the magnetic disk; and a sleeve  103  for rotatably supporting the motor shaft  101  through oil X. 
     Since such a cantilever type magnetic disk drive  100  is susceptible to external vibrations, etc., the stiffness of the radial bearing has been increased to improve the vibration characteristics. See, e.g., Patent Document 1 (Japanese Patent Laid-open No. 2001-339899). 
     BRIEF SUMMARY OF THE INVENTION 
     The above conventional magnetic disk drive  100  must have a thickness large enough to accommodate the following lengths: the length Y 1  of the portion of the motor shaft  101  press fit into the motor hub  103 ; the length Y 2  of the oil buffer for holding the excess portion of the oil X held between the motor shaft  101  and the sleeve  103 ; and the length Y 3  of the radial bearing portion of the sleeve  103  for supporting the motor shaft  101 . 
     Therefore, there is a limit to the miniaturization of the above conventional magnetic disk drive  100 ; it is difficult to reduce the thickness of the drive. 
     The present invention has been devised in view of the above problems. It is, therefore, a feature of the present invention to provide a magnetic disk drive having improved vibration characteristics and a reduced size. 
     To solve the above problems, a magnetic disk drive according to an embodiment of the present invention comprises: a motor shaft for rotating a magnetic disk; a sleeve for rotatably supporting the motor shaft; and a motor hub into which the motor shaft is press fit, the motor hub supporting the magnetic disk and including a projection portion having an inner surface and an outer surface, the inner surface being in contact with the press-fit motor shaft in directions perpendicular to the rotational axis of the motor shaft, the outer surface facing the sleeve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a first example of a magnetic disk drive according to an embodiment of the present invention, taken along the rotational axis P. 
         FIG. 2  is a cross-sectional view of the motor hub of the first example according to the embodiment, taken along the rotational axis P. 
         FIG. 3  is a cross-sectional view of the sleeve of the first example according to the embodiment, taken along the rotational axis P. 
         FIG. 4  is a cross-sectional view of the sleeve of the first example according to the embodiment, taken along the rotational axis P, wherein unbalancing grooves are formed in the buffer inner surface. 
         FIG. 5  is a cross-sectional view of a second example of the magnetic disk drive according to the embodiment, taken along the rotational axis P. 
         FIG. 6  is a cross-sectional view of the motor hub of the second example according to the embodiment, taken along the rotational axis P. 
         FIG. 7  is a cross-sectional view of the sleeve of the second example according to the embodiment, taken along the rotational axis P. 
         FIG. 8  is a cross-sectional view of the second example of the magnetic disk drive according to the embodiment, taken along the rotational axis P, wherein an oil circulation flow path is formed in the sleeve. 
         FIG. 9  is a plan view of the sleeve of the second example according to the embodiment, wherein the oil circulation flow path is formed in the sleeve. 
         FIG. 10  is a cross-sectional view of the sleeve shown in  FIG. 9  taken along line H-H. 
         FIG. 11  is a cross-sectional view of a conventional magnetic disk drive. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description will be given below of a magnetic disk drive according to an embodiment of the present invention with reference to the accompanying drawings.  FIG. 1  is a cross-sectional view of a first example of the magnetic disk drive (hereinafter referred to as disk drive  1 ) of the present embodiment. 
     As shown in  FIG. 1 , the disk drive  1  includes: a motor hub  10  for supporting a magnetic disk (not shown); a motor shaft  20  press fit into the motor hub  10 ; and a sleeve  30  for rotatably supporting the press-fit motor shaft  20  through oil O. 
     Further, the disk drive  1  also includes a coil stator  40  and a magnet  41  which are disposed between the motor hub  10  and the sleeve  30  to generate a magnetic field for rotating the motor shaft  20 . 
     A characteristic of the disk drive  1  is that the motor hub  10  and the sleeve  30  are disposed such that the upper portion of the motor hub  10  and the sleeve  30  partially overlap each other in the direction of the rotational axis P of the motor shaft  20 . At least a portion of the length L 2  of the oil buffer A overlaps the length L 1  of the portion of the motor shaft  20  press fit into the motor hub  10 . 
     That is, the oil buffer A of the sleeve  30  is formed such that its upper surface is higher than the lowest point of the portion or hole of the motor hub  10  into which the motor shaft  20  is press fit. That portion of the motor hub  10  downwardly extends inside the oil buffer A in the direction of the rotational axis P of the motor shaft  20 . 
       FIG. 2  is a cross-sectional view of the motor hub  10  of the disk drive  1 . As shown in the figure, the motor hub  10  includes: a central portion  12  including the inner surface  11  of the hole B into which the motor shaft  20  is press fit; a top plate portion  13  having a disk shape and extending from the central portion  12  in directions approximately perpendicular to the rotational axis P; a side plate portion  14  downwardly extending from the outer circumference of the top plate portion  13 ; and a disk-receiving portion  15  extending from the lower end of the side plate portion  14  in directions approximately perpendicular to the rotational axis P and supporting the magnetic disk (not shown). 
     Further, the central portion  12  includes a projection portion  50  provided on its back surface side, that is, the side facing the sleeve  30 . The projection portion  50  downwardly extends from the back surface  16  of the top plate portion  13 . 
     The projection portion  50  has: a projection portion inner surface  51  in contact with the motor shaft  20  press fit into the hole B for press fitting in directions perpendicular to the rotational axis P; and a projection portion outer surface  52  facing a portion, described later, of the sleeve  30 . 
     The projection portion inner surface  51  constitutes a portion of the inner surface  11  of the hole B for press fitting opened at the center of the projection portion  50 . Further, the projection portion outer surface  52  is formed at an angle with the rotational axis P. 
     The length from the back surface  16  of the top plate portion  13  to the lowest point of the projection portion  50 , that is, the length L 3  of the projection portion  50 , is approximately equal to the length L 2  of the oil buffer A. In the disk drive  1 , a portion of the length L 2  of the oil buffer A overlaps the length L 3  of the projection portion  50 , as shown in  FIG. 1 . 
     The length of the inner surface  11  of the hole B for press fitting is equal to the length L 1  of the portion of the motor shaft  20  press fit into the motor hub  10  and is the sum of the length L 4  from the central portion upper surface  17  to the top plate portion back surface  16  and the length L 3  of the projection portion  50 . 
       FIG. 3  is a cross-sectional view of the sleeve  30  of the disk drive  1 . As shown in the figure, the sleeve  30  has: a buffer inner surface  31  facing approximately parallel to the projection portion outer surface  52 ; and a bearing inner surface  32  for rotatably supporting the motor shaft  20  through the oil O. 
     Naturally, the dimension of the buffer inner surface  31  in the direction of the rotational axis P is equal to the length L 2  of the oil buffer A. Further, in the disk drive  1 , as shown in  FIG. 1 , the buffer inner surface  31  forms a hole C for receiving therein the projection portion  50  having the length L 3 . That is, the disk drive  1  is configured such that the outer surface  52  of the projection portion  50  received within the projection-portion-receiving hole C and the buffer inner surface  31  facing the projection portion outer surface  52  form the oil buffer A therebetween. 
     Thus, the disk drive  1  includes: the projection portion inner surface  51  in contact with the motor shaft  20  press fit into the motor hub  10  in directions perpendicular to the rotational axis P; and the projection portion outer surface  52  and the buffer inner surface  31  facing each other and forming the oil buffer A therebetween. 
     Further, the bearing inner surface  32  is cylindrical and forms a bearing hole D into which the motor shaft  20  is inserted (see  FIG. 1 ). In the disk drive  1 , the oil O is held between the bearing inner surface  32  and the motor shaft  20  inserted into the bearing hole D, as shown in  FIG. 1 . 
     The bearing inner surface  32  includes a plurality of radial bearing regions  33 ,  34  having grooves formed therein to generate dynamic pressure by the action of the oil O so as to rotatably support the motor shaft  20  and thereby function as a fluid bearing. 
     More specifically, the bearing inner surface  32  includes an upper radial bearing region  33  and a lower radial bearing region  34  spaced a predetermined distance apart along the direction of the rotational axis P. 
     In the lower portion having the length L 5  of the upper radial bearing region  33 , a plurality of balancing grooves E are formed to generate dynamic pressure by the action of the oil O. Further, in the upper portion having the length L 6  above the balancing grooves E, a plurality of unbalancing grooves F are formed such that they follow the balancing grooves E to prevent the oil O from leaving the bearing hole D or the oil buffer A. It should be noted that unlike the upper radial bearing region  33 , only balancing grooves E are formed in the lower radial bearing region  34 . 
     It should be further noted that unbalancing grooves F may be formed in the buffer inner surface  31  of the sleeve  30 , as shown in  FIG. 4 . In this case, only the balancing grooves E need to be formed in the upper radial bearing region  33  of the bearing inner surface  32 , allowing the sleeve  30  to have the upper radial bearing region  33  at a higher position than shown in  FIG. 3 . This makes it possible to more stably support the motor shaft  20 . 
       FIG. 5  is a cross-sectional view of a second example of the disk drive  1 .  FIGS. 6 and 7  are cross-sectional views of the motor hub  10  and the sleeve  30 , respectively, of this example. It should be noted that the second example includes components of the first example. The detailed description of these components will not be repeated below. 
     In the second example, the motor hub  10  of the disk drive  1  includes a projection portion  50  having: a projection portion outer surface  52  approximately parallel to the rotational axis P; and a projection portion undersurface  53  approximately perpendicular to the rotational axis P and connecting between the projection portion outer surface  52  and the projection portion inner surface  51  (see  FIGS. 5 and 6 ). 
     Further, the sleeve  30  of this disk drive  1  has: a buffer inner surface  31  approximately parallel to the projection portion outer surface  52  of the motor hub  10 ; and a buffer bottom surface  35  approximately parallel to the projection portion undersurface  53  (see  FIGS. 5 and 7 ). 
     In this sleeve  30 , the projection-portion-receiving hole C is formed by the buffer inner surface  31  and the buffer bottom surface  35 . 
     In this disk drive  1 , the buffer inner surface  31  and the buffer bottom surface  35  of the sleeve  30  face the outer surface  52  and the undersurface  53 , respectively, of the projection portion  50  received within the projection-portion-receiving hole C; these surfaces form therebetween the oil buffer A for holding the oil O. 
     Also in the second example, the motor hub  10  and the sleeve  30  are disposed such that the upper portion of the motor hub  10  and the sleeve  30  partially overlap each other in the direction of the rotational axis P of the motor shaft  20 . At least a portion of the length L 8  of the oil buffer A overlaps the length L 7  of the portion of the motor shaft  20  press fit into the motor hub  10 . It should be noted that the sleeve  30  shown in  FIG. 7  may have balancing grooves E and unbalancing grooves F as shown in  FIGS. 3 and 4 . 
     Further, in this disk drive  1 , an oil circulation flow path G for circulating the oil O may be formed between the buffer inner surface  31  and the bearing inner surface  32  of the sleeve  30 , as shown in  FIG. 8 . 
       FIG. 9  is a plan view of such a sleeve  30 , and  FIG. 10  is a cross-sectional view taken along line H-H in  FIG. 9 . In this sleeve  30 , the oil circulation flow path G is formed between the buffer inner surface  31  and the bearing inner surface  32  such that the path is located at points on the circumference of a circle concentric with the buffer inner surface  31  and the bearing inner surface  32  centered at the rotational axis P, as shown in  FIG. 9 . 
     As shown in  FIGS. 8 and 10 , the oil circulation flow path G is made up of through holes running downward from the buffer bottom surface  35  along the length L 9  of the bearing inner surface  32 . The oil circulation flow path G also functions to allow fine bubbles generated between the motor shaft  20  and the sleeve  30  to escape, for example. 
     In this disk drive  1  configured as described above, a magnetic field is generated between the magnet  41  fixed to the side plate portion  14  of the motor hub  10  and the coil stator  40  fixed to the sleeve  30  so as to face the magnet  41 , thereby integrally rotating the motor hub  10 , the magnetic disk supported by the disk-receiving portion  15  of the motor hub  10 , and the motor shaft  20  press fit into the motor hub  10 . 
     It should be noted that as the motor shaft  20  rotates, the oil O held between the motor shaft  20  and the sleeve  30  is gathered through the balancing grooves E formed in the radial bearing regions  33  and  34  of the bearing inner surface  32 , thereby generating dynamic pressure which allows the motor shaft  20  to float within the bearing hole D and rotate smoothly. 
     It is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Technology Classification (CPC): 5