Abstract:
A bearing comprises a rotating shaft, a sleeve which surrounds the outer wall of the rotating shaft and supports the rotating shaft in such a manner that the rotating shaft is rotatable, and a thrust bearing plate which is fixed to the sleeve and supports one end of the rotating shaft. A first herringbone pattern and a second herringbone pattern are formed either on the rotating shaft or on the sleeve, wherein the first herringbone pattern is located at a first side and the second herringbone pattern is located at a second side, wherein the first side is the side where the thrust bearing plate is located, and the second side is the side opposite the first side. The relation between width-A and width-B in the first herringbone pattern is expressed by 0&lt;(A−B)&lt;0.2x(A+B), where A denotes the dimension from a turning point of the first herringbone pattern to the end thereof in the first side, and B denotes the dimension from the turning point to the end thereof in the second side, and, the relation between width-C and width-D in the second herringbone pattern is expressed by 0 ((D(C) (0.2((D+C), where C denotes the dimension from a turning point of the second herringbone pattern to the end thereof in the first side, and D denotes the dimension from the turning point to the end thereof in the second side. The above structure enables the reduction of the radial runout of the rotating shaft of the bearing and the improvement of the durability of the bearing.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a hydrodynamic bearing for a motor and the motor having the same, which is used for a data processing apparatus such as a data storing apparatus having a disk drive, or a printer, or, for an entertainment apparatus having a disk drive for recording or reproducing images or sounds, or the like. 
     BACKGROUND OF THE INVENTION 
     In recent years, under the circumstance that the reduction of size and weight, high density recording, high speed data processing and the like are required in a data processing apparatus or in an entertainment apparatus, the improvement of the performance of a motor (small spindle motor in this occasion) used for the apparatus is also required. 
     In regard to the improvement of the performance of the motor, the reduction of the rotational runout of the rotor of the motor, the reduction of the noise and the improvement on the durability of the motor are mostly required, for which the improvement of the performance of a bearing used for the motor is also required. 
     The runout of the rotor and the noise of the motor are caused by the magnetic attraction and repulsion between the rotor magnet and the stator of the motor. That is, the rotating shaft of the rotor radially vibrates and bumps against the bearing of the rotor when the rotor is rotated. A conventional motor having a bearing whose bearing is made of sintered oleo-metal can hardly reduce the runout and the noise of the motor to a sufficiently low level. 
     For the improvement on the above problems, a hydrodynamic bearing has been developed, and the bearing is now being put into practical use. The hydrodynamic bearing comprises, which denotes the dimension from the turning point  163  to the end thereof in the second side. That is, the second herringbone pattern  157  is asymmetrical. 
     An oil reserving groove  159  is formed on the inner wall of the sleeve  155 . The oil reserving groove  159  is located at the position which corresponds to the intermediate portion between the first herringbone pattern  156  and the second herringbone pattern  157  of the rotating shaft  154 . A through-hole  160  is formed through the wall of the sleeve  155  in such a manner that the through-hole  160  radially extends from the oil reserving groove  159  to the outside of the sleeve  155 . 
     In the above conventional structure, the dynamic pressure of the oil  161 , which is generated at the herringbone pattern  157  when the shaft  154  is rotated, forms a stream of the oil  161 , which flows toward the second side (i.e., the side where the shaft end  162  is located) since the width-E is larger than the width-F, which causes the occurrence of air bubbles in the oil  161  since air comes into the space in the sleeve  155  from the through-hole  160 . Then the air bubbles further push the oil  161  outward from the space in the sleeve  155 , which result in the shortage of oil  161  and causes the increase of the runout of the shaft  154  and the damage on the durability of the motor having the bearing. 
     FIG. 16 is a partially schematic sectional view showing another example of the structure of the hydrodynamic bearing. This type of bearing, which is also known in general, is disclosed in Japanese Utility Model Publication No.2560501. 
     In FIG. 16, a rotating shaft  164  is rotatably supported by a sleeve  165 . A thrust bearing plate  168  is fixed to the sleeve  165  and supports one end of the shaft  164 . Oil  169  is filled in the space formed with the sleeve  165 , the rotating shaft  164  and the thrust bearing plate  168 . On the outer wall of the rotating shaft  164 , a first herringbone pattern  167  and a second herringbone pattern  166  are formed. The first herringbone pattern  167  is located at a first side (i.e., the side where the thrust bearing plate  168  is located). The second herringbone pattern  166  is located at a second side (i.e., the side opposite the first side). for example, a cylindrical rotating shaft and a sleeve, and, a fluid (oil, in most cases) is filled in a space formed with the sleeve and the rotating shaft which is inserted into the sleeve. A herringbone pattern is formed either on the shaft or on the sleeve. In the above structure, when the rotor is rotated, the rotating shaft is supported by the dynamic pressure of the fluid, which is generated at the herringbone pattern. 
     The hydrodynamic bearing has advantages that the size of the bearing can be reduced since the mechanical components and portions of the bearing share relatively small space comparing with that in the other bearings. Also, since the rotating shaft is supported by the sleeve via the fluid, the noise of the motor can be reduced, and the motor having the bearing is durable against shock. Also, since the load on the rotating shaft is supported by the whole circumference of the shaft (which generates an integral effect), the runout of the shaft is reduced. As is described above, the hydrodynamic bearing is structurally superior for the spindle motor. 
     In the hydrodynamic bearing, the structure disclosed in Japanese Non-Examined Patent Publication H6-137320 is known in general. The structure disclosed in the publication is described hereinafter with reference to FIG. 15 which is a partially schematic sectional view showing the structure of the bearing. 
     In FIG. 15, a rotating shaft  154  is rotatably supported by a sleeve  155 . A thrust bearing plate  158 , which is fixed to the sleeve  155 , supports one end of the shaft  154 . Oil  161  is filled in the space formed with the sleeve  155 , the shaft  154  and the thrust bearing plate  158 . On the outer wall of the shaft  154 , a first herringbone pattern  156  and a second herringbone pattern  157  are formed. The first herringbone pattern  156  is located at a first side (i.e., at the side where the thrust bearing plate  158  is located). The second herringbone pattern  157  is located at a second side (i.e., the side opposite the first side). 
     In the second herringbone pattern  157 , width-E, which denotes the dimension from the turning point  163  of the pattern  157  to the end thereof in the first side, is larger than width-F 
     In the second herringbone pattern  166 , width-G, which denotes the dimension from the turning point of the pattern  166  to the end thereof in the second side, is larger than width-H which denotes the dimension from the turning point of the pattern  166  to the end thereof in the first side. 
     Also, in the first herringbone pattern  167 , width-I, which denotes the dimension from the turning point of the pattern  167  to the end thereof in the second side, is larger than width-J which denotes the dimension from the turning point of the pattern  167  to the end thereof in the first side. That is, both patterns  166  and  167  are respectively asymmetrical. 
     Also, two through-holes  170  and  171  are formed through the thrust bearing plate  168 . 
     In the above structure, the oil  169  flows outside from both through-holes  170  and  171 , such that the oil  169  has to be refilled for the continuous operation of the motor having this type of bearing. That is, the bearing is not suitable for continuous long time operation. 
     When the through-holes  170  and  171  are closed for preventing the leakage of the oil  169 , the pressure around the thrust bearing plate  168  becomes high and air bubbles occur there, such that the shaft  164  enters into a state of unstable floating relative to the thrust bearing plate  168 , which results in a serious problem, for instance, that the disk of a disk drive touches the pickup head of the disk drive when such a bearing is used for the spindle motor of the disk drive, due to the axial runout of the rotating shaft. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to address the problems in the conventional hydrodynamic bearing and to provide a durable hydrodynamic bearing in which the uniform and stable thickness of the oil film for the hydrodynamic bearing is realized for reducing both radial and axial runout of the rotating shaft. Another object of the present invention is to provide a motor having the durable bearing and a disk drive having the motor. 
     For realizing the above object, the bearing of the present invention comprises: 
     (a) a rotating shaft, 
     (b) a sleeve which surrounds the outer wall of the rotating shaft and supports the rotating shaft in such a manner that the shaft is rotatable, and 
     (c) a thrust bearing plate which is fixed to the sleeve and supports one end of the rotating shaft, 
     where in a first herringbone pattern and a second herringbone pattern are formed either on the rotating shaft or on the sleeve, wherein the first herringbone pattern is located at a first side and the second herringbone pattern is located at a second side, wherein the first side is the side where the thrust bearing plate is located, and the second side is the side opposite the first side, 
     wherein the relation between width-A and width-B in the first herringbone pattern is expressed by 
     
       
         0&lt;( A−B )&lt;0.2 x ( A+B ) 
       
     
     where A denotes the dimension from the turning point of the first herringbone pattern to the end thereof in the first side, and B denotes the dimension from the turning point to the end thereof in the second side, and, the relation between width-C and width-D in the second herringbone pattern is expressed by 
     
       
         0&lt;( D−C )&lt;0.2 x ( D+C ) 
       
     
     where C denotes the dimension from the turning point of the second herringbone pattern to the end thereof in the first side, and D denotes the dimension from the turning point to the end thereof in the second side. 
     The above structure enables the improvement of both durability and stiffness of the bearing. 
     Also, another structure of the bearing for realizing the above object comprises: 
     (a) a rotating shaft, 
     (b) a sleeve which surrounds the outer wall of the rotating shaft and supports the rotating shaft in such a manner that the shaft is rotatable, and 
     (c) a thrust bearing plate which is fixed to the sleeve and supports one end of the rotating shaft, 
     wherein a first herringbone pattern and a second herringbone pattern are formed either on the rotating shaft or on the sleeve, and an oil reserving groove is formed on the sleeve, wherein the oil reserving groove is located at the position which corresponds to the intermediate portion between the first herringbone pattern and the second herringbone pattern, and a through-hole and an air-bubble-holding-hollow are formed in the wall of the sleeve, wherein the through-hole extends from the thrust bearing plate up to the oil reserving groove, also up to the air-bubble-holding-hollow. 
     In the above structure, since oil can be reserved in the through-hole too, the shortage of the oil is more surely prevented, and also, air bubbles in the bearing can be more surely eliminated, such that the further improvement of the durability of the bearing can be realized. 
     Also, still another structure of the bearing for realizing the above object comprises: 
     (a) a rotating shaft, 
     (b) a sleeve which surrounds the outer wall of the rotating shaft and supports the rotating shaft in such a manner that the shaft is rotatable, and 
     (c) a thrust bearing plate which is fixed to the sleeve and supports one end of the rotating shaft, 
     wherein a first herringbone pattern and a second herringbone pattern are formed either on the rotating shaft or on the sleeve, wherein the turning point of the first herringbone pattern and the turning point of the second herringbone pattern are located on a same phantom line axially extended on the surface of the rotating shaft. 
     In the above structure, the phase of dynamic pressure (i.e., the operating phase of the stiffness of the bearing) at the first herringbone pattern agrees with that at the second herringbone pattern, such that the runout including Non-Repeatable Runout (NRRO) of the rotating shaft can be reduced. 
     Also, for realizing the above object, the motor of the present invention comprises: 
     (a) a rotor having a rotating shaft fixed thereto, 
     (b) a bearing, and 
     (c) a stator having the bearing, 
     wherein the bearing used for the motor is one of the above bearings. 
     The above structure enables the motor to have advantages of the bearing described above. 
     Also, for realizing the above object, the disk drive of the present invention has a motor comprising: 
     (a) a rotor which has a rotating shaft fixed thereto and rotates a disk, 
     (b) a bearing, and 
     (c) a stator having the bearing, 
     wherein the bearing used for the motor is one of the above bearings. 
     The above structure enables the disk drive to have advantages of the bearing described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially schematic sectional view showing the structure of a bearing in a first exemplary embodiment of the present invention, 
     FIG. 2 is a partially schematic sectional view showing the structure of a bearing in a second exemplary embodiment of the present invention, 
     FIG. 3 is a partially schematic sectional view showing the structure of a bearing in a third exemplary embodiment of the present invention, 
     FIG. 4 is a partially schematic sectional view showing the structure of a bearing in a fourth exemplary embodiment of the present invention, 
     FIG. 5 shows a spiral pattern formed on a thrust bearing plate in the exemplary embodiments of the present invention, 
     FIG. 6 shows a herringbone pattern formed on the thrust bearing plate in the exemplary embodiments of the present invention, 
     FIG. 7 is a partially schematic sectional view showing the structure of a motor in a fifth exemplary embodiment of the present invention, 
     FIG. 8 is a partially schematic sectional view showing the structure of a motor in a sixth exemplary embodiment of the present invention, 
     FIG. 9 is a partially schematic sectional view showing the structure of a motor in a seventh exemplary embodiment of the present invention, 
     FIG. 10 is a partially schematic sectional view showing the structure of a motor in an eighth exemplary embodiment of the present invention, 
     FIG. 11 is a partially schematic sectional view showing an example of the structure of a disk drive in a ninth exemplary embodiment of the present invention, 
     FIG. 12 is a partially schematic sectional view showing another example of the structure of the disk drive in the ninth exemplary embodiment of the present invention, 
     FIG. 13 is a partially schematic sectional view showing an example of the structure of a disk drive in a tenth exemplary embodiment of the present invention, 
     FIG. 14 is a partially schematic sectional view showing another example of the structure of the disk drive in the tenth exemplary embodiment of the present invention, 
     FIG. 15 is a partially schematic sectional view showing an example of the structure of a conventional bearing, and 
     FIG. 16 is a partially schematic sectional view showing another example of the structure of the conventional bearing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter exemplary embodiments of the present invention are described on reference to illustrations. 
     First Exemplary Embodiment 
     FIG. 1 is a partially schematic sectional view showing the structure of a bearing in the first exemplary embodiment of the present invention. 
     In FIG. 1, a rotating shaft  1  is rotatably supported by a sleeve  2 . One end of the shaft  1  is spherically shaped. A thrust bearing plate  3  is fixed to the sleeve  2  and supports the spherical end of the shaft  1 . The sleeve  2  supports the radial load of the shaft  1 , and the thrust bearing plate  3  supports the axial load of the shaft  1 . On the outer wall of the shaft  1 , a first herringbone pattern  4  and a second herringbone pattern  5  are formed. The first herringbone pattern  4  is located at a first side (i.e., the side where the thrust bearing plate  3  is located), and the second herringbone pattern  5  is located at a second side (i.e., the side opposite the first side, and where shaft end  10  is located). An oil reserving groove  7  is formed on the inner wall of the sleeve  2 . The oil reserving groove  7  is located at the position which corresponds to the intermediate portion between the first herringbone pattern  4  and the second herringbone pattern  5  of the rotating shaft  1 . Oil  6  is filled in a space formed with the sleeve  2 , shaft  1  and the thrust bearing plate  3 . 
     In the first herringbone pattern  4 , the relation between width-A and width-B is expressed by 
     
       
         0&lt;( A−B )&lt;0.2 x ( A+B ) 
       
     
     where A denotes the dimension from a turning point  8  of the first herringbone pattern  4  to the end thereof in the first side, and B denotes the dimension from the turning point  8  to the end thereof in the second side. 
     On the other hand, in the second herringbone pattern  5 , the relation between width-C and width-D is expressed by 
      0&lt;( D−C )&lt;0.2 x ( D+C ) 
     where C denotes the dimension from a turning point  9  of the second herringbone pattern  5  to the end thereof in the first side, and D denotes the dimension from the turning point  9  to the end thereof in the second side. 
     In the above structure of the bearing having the asymmetrical herringbone patterns  4  and  5 , when the rotating shaft  1  is rotated, the oil  6  flows toward the oil reserving groove  7  along arrows  12  and  11  respectively since the dynamic pressure generated at the side of width-A and that generated at the side of width-D in the herringbone patterns  4  and  5  are respectively larger than those generated at the sides of width-B and width-C. That is, the oil  6  does not leak outside, and the space formed with the sleeve  2 , the shaft  1  and the thrust bearing plate  3  is always filled with the oil  6 . As a result, the durability of the bearing is improved. 
     In the above structure, when the dimensional differences between A and B, and between C and D are too large, the dynamic pressure at the sides having smaller width (i.e., B and C) becomes too low and a bearing span between the herringbone patterns  4  and  5  decreases, which causes a decrease of the stiffness of the bearing. According to the results of experiments, the preferable dimensional differences between A and B, and between C and D are respectively 0%-20% of the respective total widths (A+B, D+C) in the respective patterns. The ratio has been determined taking the practical preciseness in forming the patterns into consideration. In the above range of difference, superior effects are obtained in both durability and stiffness of the bearing. 
     In the above description, the herringbone patterns  4  and  5  are formed on the outer wall of the shaft  1 . However, a similar effect is obtained by forming the patterns on the inner wall of the sleeve  2 . 
     Second Exemplary Embodiment 
     FIG. 2 is a partially schematic sectional view showing the structure of a bearing in the second exemplary embodiment of the present invention. The reference numerals for the components in FIG. 2 are identical with those for their corresponding components in FIG. 1 of the first exemplary embodiment, and the description of the components having the identical numerals is omitted in this exemplary embodiment. 
     In FIG. 2, as in FIG. 1 of the first exemplary embodiment, an oil reserving groove  17  is formed on the inner wall of the sleeve  2 , wherein the oil reserving groove  17  is located at the position which corresponds to the intermediate portion between a first herringbone pattern  15  and a second herringbone pattern  16 , and also, a space between the sleeve  2  and the thrust bearing plate  3  forms an oil reservoir  18 . In this exemplary embodiment, different from the first exemplary embodiment, in the wall of the sleeve  2 , a through-hole  13  and an air-bubble-holding-hollow  14  are formed. The through-hole  13  extends along the axial direction of the shaft  1  from the oil reservoir  18  up to the oil reserving groove  17 , and also up to the air-bubble-holding-hollow  14 . The oil reservoir  18  is located at one end of the through-hole  13  (i.e., at the side where the thrust bearing plate  3  is located) and the air-bubble-holding-hollow  14  is located at the other end of the through-hole  13  (i.e., at the side where the shaft end  10  is located). 
     In the above structure, since the oil  6  can be reserved in the through-hole  13  too, the shortage of the oil  6  can be more surely prevented, and also air bubbles in the bearing can be more surely eliminated since the air bubbles move upward and stay in the air-bubble-holding-hollow  14 . As a result, a more stable rotation of the rotating shaft is realized, and also the durability of the bearing is further improved. 
     Third Exemplary Embodiment 
     FIG. 3 is a partially schematic sectional view showing the structure of a bearing in the third exemplary embodiment of the present invention. The reference numerals for the components in FIG. 3 are identical with those for their corresponding components in FIG. 1 of the first exemplary embodiment and in FIG. 2 of the second exemplary embodiment, and the description of the components having the identical numerals is omitted in this exemplary embodiment. 
     In FIG. 3, a first herringbone pattern  20  and a second herringbone pattern  21  are formed in such a manner that a turning point  22  of the first herringbone pattern  20  and a turning point  25  of the second herringbone pattern  21  are located on a same phantom line  28  which axially extends on the outer wall of the rotating shaft  1 . In a manner similar to the above description, turning points  23  and  24  of the first herringbone pattern  20  and turning points  26  and  27  of the second herringbone pattern  21  are respectively located on the same respective axial phantom lines  29  and  30 . 
     In the above structure, the phase of the dynamic pressure (i.e., the operating phase of the stiffness of the bearing) generated at the first herringbone pattern  20  agrees with that generated at the second herringbone pattern  21 , such that the runout including the Non-Repeatable Runout (NRRO) of the rotating shaft can be reduced (i.e., mechanical preciseness in the rotation of the shaft is improved). 
     Fourth Exemplary Embodiment 
     FIG. 4 is a partially schematic sectional view showing the structure of a bearing in the fourth exemplary embodiment of the present invention. The reference numerals for the components in FIG. 4 are identical with those for their corresponding components in FIG. 1 of the first exemplary embodiment, in FIG. 2 of the second exemplary embodiment, and in FIG. 3 of the third exemplary embodiment, and the description of the components having the identical reference numerals is omitted in this exemplary embodiment. 
     In FIG. 4, as in FIG. 1 of the first exemplary embodiment, the relation between width-A and width-B, and, the relation between width-C and width-D in the herringbone patterns  4  and  5  are respectively expressed by 
     
       
         0&lt;( A−B )&lt;0.2 x ( A+B ) 
       
     
     and 
     
       
         0&lt;( D−C )&lt;0.2 x ( D+C ). 
       
     
     Also, in this exemplary embodiment, the through-hole  13  is formed between the oil reserving groove  17  and the oil reservoir  18  as in FIG. 2 of the second exemplary embodiment. 
     In the structure described above, the oil  6  circulates along a circulating stream, for instance, from the oil reservoir  18  to the first herringbone pattern  4 , then to the oil reserving groove  17 , then to the through-hole  13 , then back to the oil reservoir  18 . In this case, since the oil  6  can be reserved in the through-hole  13  too, the oil  6  is more steadily circulated along the above circulating stream, such that the rise of temperature at the point-contact formed with the shaft  1  (having a pivot structure) and the thrust bearing plate  3  (i.e., the rise of temperature at the point-contact of the thrust bearing section of the bearing) can be surely suppressed. 
     Also, in this exemplary embodiment, the structure of a hydrodynamic bearing can be applied to the thrust bearing section of the bearing. That is, a thrust bearing plate  31  of FIG. 5 having a spiral pattern  32 , or, a thrust bearing plate  33  of FIG. 6 having a herringbone pattern  34  can be used in place of the thrust bearing plate  3 . 
     When the thrust bearing plate  31  or the thrust bearing plate  33  is used in place of the thrust bearing plate  3 , the oil  6  flows along the pattern formed on the plate, and dynamic pressure is generated at the pattern when the shaft  1  is rotated, such that the shaft  1  enters into the state of floating relative to the thrust bearing plate. In this case, the stable and precise state of floating of the shaft  1  is realized since the oil  6  is steadily circulated via the through-hole  13  where the sufficient volume of the oil  6  is reserved. 
     Fifth Exemplary Embodiment 
     FIG. 7 is a partially schematic sectional view showing a motor in the fifth exemplary embodiment of the present invention. The reference numerals for the components in FIG. 7 are identical with those for their corresponding components in the illustrations of the embodiments described above, and the description of the components having the identical reference numerals is omitted in this exemplary embodiment. 
     In FIG. 7, the structure of a bearing  35  is identical with that of FIG. 1 in the first exemplary embodiment. A sleeve of the bearing  35  is fixed to abase  38  by adhesive bonding or the like, and a winding assembly  36  is also fixed to the base  38 , and a stator  80  is formed. A hub  40  is fixed to a shaft of a rotor  70  by pressure bonding or the like, and a rotor magnet  41  is fixed to the hub  40 . The magnet  41  of the rotor  70  faces the winding assembly  36  of the stator  80  via an air gap. 
     In the motor having the above structure, the rotor  70 , which is rotatably supported by the bearing  35 , rotates when electricity is applied to the winding assembly  36  since a magnetic circuit is formed between the winding assembly  36  and the magnet  41  by the application of electricity. 
     In the above structure, as is described in the first exemplary embodiment, the bearing  35  has superior durability since the oil steadily circulates in the bearing without leaking outside. As a result, a durable motor is realized by using the durable bearing. 
     Sixth Exemplary Embodiment 
     FIG. 8 is a partially schematic sectional view showing the structure of a motor in the sixth exemplary embodiment of the present invention. The reference numerals for the components in FIG. 8 are identical with those for their corresponding components in the illustrations of the embodiments described above, and the description of the components having the identical reference numerals is omitted in this exemplary embodiment. 
     In FIG. 8, the structure of a bearing  42  is identical with that of FIG. 2 in the second exemplary embodiment. 
     In the above structure, as is described in the second exemplary embodiment, since the oil is reserved in the through-hole too, the oil circulates more steadily in the bearing. Also, air bubbles in the bearing can be more surely eliminated since the air bubbles move upward and stay in the air-bubble-holding-hollow. As a result, a durable motor is realized by using the durable bearing. 
     Seventh Exemplary Embodiment 
     FIG. 9 is a partially schematic sectional view showing the structure of a motor in the seventh exemplary embodiment of the present invention. The reference numerals for the components in FIG. 9 are identical with those for their corresponding components in the illustrations of the embodiments described above, and the description of the components having the identical reference numerals is omitted in this exemplary embodiment. 
     In FIG. 9, the structure of a bearing  43  is identical with that of FIG. 3 in the third exemplary embodiment. 
     In the above structure, as is described in the third exemplary embodiment, the phase of the dynamic pressure generated at the first herringbone pattern agrees with that generated at the second herringbone pattern. As a result, the motor having the rotor whose radial runout is reduced can be realized. 
     Eighth Exemplary Embodiment 
     FIG. 10 is a partially schematic sectional view showing the structure of a motor in the eighth exemplary embodiment of the present invention. The reference numerals for the components in FIG. 10 are identical with those for their corresponding components in the illustrations of the embodiments described above, and the description of the components having the identical reference numerals is omitted in this exemplary embodiment. 
     In FIG. 10, the structure of a bearing  44  is identical with that of FIG. 4 in the fourth exemplary embodiment. 
     In the above structure, as is described in the fourth exemplary embodiment, the rise of temperature at the point-contact of the thrust bearing section of the bearing is suppressed since the oil steadily circulates around the point-contact. Also, in the case where the hydrodynamic structure is applied to the thrust bearing section by using the thrust bearing plate having the spiral pattern or the herringbone pattern described in the fourth exemplary embodiment, a stable state of floating of the shaft can be realized since the oil is steadily circulated via the through-hole where the sufficient volume of the oil is reserved. As a result, the motor having the rotor whose rotating shaft is in the state of stable floating can be realized. 
     Ninth Exemplary Embodiment 
     FIG. 11 is a partially schematic sectional view showing an example of the structure of a disk drive in the ninth exemplary embodiment of the present invention, and FIG. 12 is a partially schematic sectional view showing another example of the structure of the disk drive in the same. The reference numerals for the components in FIG.  11  and FIG. 12 are identical with those for their corresponding components in the illustrations of the embodiments described above, and the description of the components having the identical reference numerals is omitted in this exemplary embodiment. 
     In each of FIG.  11  and FIG. 12, the structure of a motor  46  is identical with that of FIG. 8 in the sixth exemplary embodiment. That is, the bearing of the motor  46  has the through-hole  13  and the air-bubble-holding-hollow  14  whose details are shown in FIG. 2 of the second exemplary embodiment. 
     In this exemplary embodiment, as shown in FIG. 11, the motor  46  is installed to the disk drive in such a manner that the rotating shaft  1  of the motor  46  enters into a vertical state, and that the air-bubble-holding-hollow  14  is located above the thrust bearing plate  3  in the field where gravitational attraction works vertically. On the other hand, in FIG. 12, the motor  46  is installed to the disk drive in such a manner that the rotating shaft  1  enters into a horizontal state, and that the air-bubble-holding-hollow  14  is located above the rotating shaft  1  in the field where gravitational attraction works vertically. 
     Also, each of the disk drives of FIG.  11  and FIG. 12 in this exemplary embodiment has the structure that a plurality of disks  47  are fixed to a hub of the motor  46  with a damper  49  and a screw  50 , and a spacer  48  is disposed for spatially separating the respective disks  47  each other. Also, a cover  51  is disposed for protecting the motor  46  and the disks  47 . 
     In each of the disk drives of FIG.  11  and FIG. 12 in this exemplary embodiment having the above structure, air bubbles in the bearing of the motor  46  are more surely eliminated since the air bubbles move upward and stay in the air-bubble-holding-hollow  14 , such that the oil is more steadily circulated in the bearing of the disk drive. As a result, a durable disk drive can be realized by installing the bearing in such a manner as is described above. 
     Tenth Exemplary Embodiment 
     FIG. 13 is a partially schematic sectional view showing an example of the structure of a disk drive in the tenth exemplary embodiment of the present invention, and FIG. 14 is a partially schematic sectional view showing another example of the structure of the disk drive of the present invention. The reference numerals for the components in FIG.  13  and FIG. 14 are identical with those for their corresponding components in the illustrations of the embodiments described above, and the description of the components having the identical reference numerals is omitted in this exemplary embodiment. 
     In each of FIG.  13  and FIG. 14, the structure of a motor  53  is identical with that of FIG. 10 in the eighth exemplary embodiment. That is, the bearing of the motor  53  has the through-hole  13  and the air-bubble-holding-hollow  14 , and the herringbone patterns have the structure shown in FIG. 4 of the fourth exemplary embodiment. 
     In FIG. 13, the motor  53  is installed to the disk drive in such a manner that the rotating shaft  1  of the motor  53  enters into a vertical state, and that the air-bubble-holding-hollow  14  of the bearing is located above the thrust bearing plate  3  in the field where gravitational attraction works vertically. On the other hand, in FIG. 14, the motor  53  is installed to the disk drive in such a manner that the rotating shaft  1  enters into a horizontal state, and that the air-bubble-holding-hollow  14  of the bearing is located above the rotating shaft  1  in the field where gravitational attraction works vertically. 
     In each of the disk drives of FIG.  13  and FIG. 14 in this exemplary embodiment having the above structure, the air bubbles in the bearing of the motor  53  can be more surely eliminated since the air bubbles move upward and stay in the air-bubble-holding-hollow  14 , such that the oil is more steadily circulated in the bearing of the disk drive. 
     Also, as is described in the fourth exemplary embodiment, since the oil is circulated around the point-contact of the thrust bearing section of the bearing, the rise of the temperature at the point-contact is surely suppressed. As a result, a durable disk drive can be realized. 
     In the above exemplary embodiments, the herringbone patterns are formed on the outer wall of the rotating shaft. However, the similar effect can be obtained by forming the herringbone patterns on the inner wall of the sleeve. 
     As is described above, in the hydrodynamic bearing of the present invention, the radial and axial runout of the rotating shaft of the bearing can be reduced, and also the durability of the bearing is improved. Also, in a motor having the durable bearing, the effectiveness and the durability of the motor can be improved, and also the power-consumption-increase with the-passage-of-time in the motor can be suppressed, such that the saving of power consumption is realized. Also, in a disk drive having the durable motor, the durability of the disk drive is also improved, such that, for example, the data in a storing unit having the durable disk drive can be safely stored for a long period of time.