Abstract:
Manufacturing method for impregnating with lubricant a porous bearing material retained in a bearing retaining cavity in a bearing retainer. Under a reduced-pressure space within a vacuum chamber, a bearing structural unit in which a porous bearing material is retained in a bearing retaining cavity in a bearing retainer is, with an opening in the bearing structural unit directed down, immersed in or contacted on lubricant to cover over the bearing-structural-unit opening; by then restoring chamber pressure, the porous bearing material is impregnated with the lubricant. The manufacturing method controls to a minimum adhesion of lubricant to the bearing-retainer exterior, to eliminate as far as possible the trouble of lubricant cleanup, and at the same time makes the impregnation of the porous bearing material with lubricant more sound and facilitates the impregnation job despite its being under a reduced-pressure atmosphere.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to methods of manufacturing fluid dynamic-pressure bearings furnished with a lubricant-impregnated porous bearing component; in particular, the present invention relates to methods of manufacturing fluid dynamic-pressure bearings that are installed in spindle motors for driving hard disks and like information-recording devices.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, in order to impregnate a porous substance with a lubricant, a method referred to as vacuum impregnation has been employed.  
         [0005]     For example, Japanese Patent No. 3,010,718 discloses a method of impregnating a porous object with lubricating fluid by evacuating a containment space containing the lubricating fluid, with the porous object being immersed in the fluid. It is possible to apply this method to a porous bearing component of a form in which the porous bearing material is retained in the interior of a bearing housing. One drawback with this method, however, is that because the bearing housing is immersed in the lubricating fluid, the fluid sticks to the outer surfaces of the bearing housing, making it necessary to wipe the lubricating fluid off the outer surfaces of the bearing housing after impregnating the porous bearing material with the lubricating fluid, which is a laborious task.  
         [0006]     Furthermore, if the bearing housing is in the form of a close-ended cylinder, the porous bearing material can be impregnated with lubricating fluid by putting the bearing housing open-end up, seating the porous bearing material within the housing and then, with lubricating fluid filling the bearing housing, in that state evacuating the environment surrounding the bearing housing. In this case, however, due to the bursting of air bubbles discharged from the voids in the porous bearing material, there is a likelihood of the lubricating fluid splattering and contaminating the outer periphery of the bearing housing, leading to difficulties similar to those described above. This also runs the risk, moreover, that the porous bearing material will not be sufficiently impregnated with the lubricating fluid.  
         [0007]     Another example is the vacuum-assisted resin impregnation technique—a method for impregnating a porous component with a synthetic resin—described in Japanese Unexamined Pat. App. Pub. No. H11-033389, in which a container holding synthetic resin is placed within vacuum atmosphere (a vacuum furnace), air within the vacuum atmosphere is removed, and then, under the vacuum atmosphere, a porous component is immersed in the synthetic resin within the container to impregnate the porous body with the synthetic resin. Although it is possible to use this technique to impregnate with lubricating fluid a porous bearing material retained in a bearing housing, the technique gives rise to the trouble of having to wipe off lubricating fluid adhering to the outside of the bearing housing, likewise as with the method described above. Moreover, the published application makes no mention of the specific way in which, within the vacuum furnace, the porous component from which air has been removed is introduced into the lubricant while the vacuum atmosphere is maintained. Although component introduction would be possible employing an actuator whose manipulation inside the vacuum furnace is possible from without, such equipment is generally expensive and would make for a heavy equipment-cost burden in a mass production situation.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is in providing a method of manufacturing a fluid dynamic-pressure bearing furnished with a porous bearing component, to enable reliable lubricant impregnation of a porous bearing material contained in a bearing retainer.  
         [0009]     Another object of the present invention is to provide a method of manufacturing a fluid dynamic-pressure bearing including a porous bearing component, whereby the impregnation work can be easily carried out despite its being done under a reduced-pressure atmosphere.  
         [0010]     Still another object of the present invention is to provide a method of manufacturing a fluid dynamic-pressure bearing including a porous bearing component, whereby labor of cleaning up lubricant can be eliminated to the extent possible by minimizing lubricant adhering to the exterior of the bearing retainer when impregnating with lubricant a porous bearing material housed in a bearing retainer.  
         [0011]     According to a method of manufacturing a lubricant-impregnated porous bearing component, and to a method of manufacturing a fluid dynamic-pressure bearing of the present invention to attain the above-described objects, a bearing structural unit is disposed in a vacuum chamber in which lubricant is contained, and one end portion of the bearing retainer is immersed in or contacted on the lubricant, with the one end of the bearing retaining cavity turned down, under a state in which the pressure in the vacuum chamber is reduced, and the lubricant is infiltrated into the inside of the bearing retainer while a state in which the one end of the bearing retaining cavity is occluded by the lubricant is maintained.  
         [0012]     Thus, by putting a bearing structural unit retaining the porous bearing material in the bearing retaining cavity of the bearing retainer under a reduced-pressure atmosphere, as compared to the case in which the lubricant infiltrates the inside of the bearing retaining cavity including the voids in the porous bearing material, air is removed and air pressure is reduced more easily and more certainly. By immersing in or contacting on the lubricant one end portion of the bearing structural unit in the lubricant arranged in a reduced air pressure space with the one end portion turned lower (namely, within a scope of the present invention, in the same direction as the gravitational direction, or in a direction inclined with respect to the gravitational direction), occluding the one end portion with the lubricant, it is possible to close off the inside of the bearing retaining cavity from the outside. Herein, a bearing structural unit in which the inside of the bearing retaining cavity has air tightness against the outside except for the one end portion is used as it is, whereas a bearing structural unit without such air tightness is used with the inside of the bearing retaining cavity except for the one end portion placed under airtightness.  
         [0013]     After that, when the pressure is restored while maintaining the lubricant-occluding state at the one end portion of the bearing retainer, the reduced pressure state of the inside of the bearing retaining cavity is maintained against the outside, and this makes the lubricant to move upward in the bearing retaining cavity. Thereby, by infiltrating the lubricant in the porous bearing material into the bearing retaining cavity, a porous bearing component impregnated with the lubricant can be acquired. Since the inside of the bearing retaining cavity including the gap of the porous bearing material is evacuated of air and the pressure is reduced, the splattering of lubricant due to the bursting of air bubbles is prevented.  
         [0014]     Since one end portion of the bearing structural unit is immersed in or contacts on the lubricant except for the inside of the bearing retaining cavity, and the outside of the bearing retainer does not contact the lubricant except for the one end portion thereof, and thus the lubricant is prevented from getting splattered due to the bursting of air bubbles, the time and trouble of cleanup work involving the wiping off of lubricant adhering to the exterior of the bearing retainer is curtailed.  
         [0015]     In addition, the porous bearing material retained in the bearing retaining cavity is immersed in or contacted on the lubricant with the one end of the bearing retaining cavity occluded by the lubricant by immersing the one end of the bearing structural unit in, or contacting it on, the lubricant arranged in the reduced-pressure space, with the one end portion turned down. In this case, once the porous bearing material retained in the bearing retaining cavity is immersed in or makes contact with the lubricant, the lubricant permeates the voids in the porous bearing material by the agency of surface tension, enabling the more certain impregnation of the porous bearing material with the lubricant.  
         [0016]     Further, the one end of the bearing retainer is occluded by the lubricant by immersing in or contacting on the lubricant the one end of the bearing structural unit to immerse in or contact on the lubricant the porous bearing material retained in the bearing retaining cavity, and then, after a predetermined time has passed, the pressure in the vacuum chamber is restored while maintaining the one end portion of the bearing retainer in the state in which it is occluded by the lubricant. Thereby, it is possible to more certainly impregnate the porous bearing material with the lubricant. In this case, the predetermined time may be about five minutes, for example; however, it is preferable that the predetermined time is changed in accordance with the kind of the lubricant used and the structure of the bearing.  
         [0017]     Thus, since the manufacturing method of the present invention can be practiced by performing the operation for changing the relative vertical positional relation between the bearing structural unit and the surface of the lubricant in a reduced-pressure space, even in the reduced-pressure space, the operation is easily carried out and the required material and equipment costs can be effectively reduced. In addition, because the outside of the bearing retainer does not contact the lubricant except for the one end portion thereof and the lubricant is prevented from getting splattered due to bursting of air bubbles, the time and trouble of cleanup involving the wiping off of lubricant adhering to the outside of the bearing retainer is curtailed. Further, in cases in which the open end of the bearing housing is directed upward, the lubricating fluid is pooled within the bearing housing, and the bearing housing is evacuated, it is necessary to measure the lubricating fluid and inject it into the bearing housing; however, according to the present invention, it is not necessary to measure the lubricating fluid, curtailing costs by that which would otherwise be expended to do so. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0018]     Referring now to the attached drawings that form a part of this original disclosure:  
         [0019]      FIG. 1A  is a sectional view of a bearing structural unit, wherein the situation under reduced pressure in the process of manufacturing a porous bearing component is represented;  
         [0020]      FIG. 1B  is a sectional view of the bearing structural unit, wherein a state, in the process of manufacturing the porous bearing component, in which part of the bearing structural unit is immersed in a lubricant is represented;  
         [0021]      FIG. 1C  is a sectional view of the bearing structural unit, wherein the situation when pressure is restored in the process of manufacturing a porous bearing component is represented;  
         [0022]      FIG. 2A  is a sectional view representing, in a pressure-reduction situation, a manufacturing apparatus for manufacturing the porous bearing component;  
         [0023]      FIG. 2B  is a sectional view representing, in an immersion situation, a manufacturing apparatus for manufacturing the porous bearing component;  
         [0024]      FIG. 3  is a sectional view of a fluid dynamic-pressure bearing furnished with the porous bearing component;  
         [0025]      FIG. 4  is a plan view of the bearing structural unit; and  
         [0026]      FIG. 5  is a sectional view of a spindle motor in which the fluid dynamic-pressure bearing is utilized. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     Embodiments of the present invention will be described below with reference to the drawings.  
         [0028]     (1) Fluid Dynamic-Pressure Bearing Structure  
         [0029]      FIG. 3  is a sectional view of a fluid dynamic-pressure bearing that is a manufacturing target. This fluid dynamic-pressure bearing is made up of a rotor  10  that is a shaft-end structural component of the motor, and a bearing structural unit  12 . As the bearing structural unit  12 , a porous bearing component impregnated with lubricant, manufactured through the steps shown in  FIGS. 1A  to  1 C is utilized. In the present embodiment, the rotor constitutes the shaft-end structural component but the configuration is not thereby limited; the shaft-end structural component may be provided on the stator end of the motor, or may be provided on the rotary or stationary end of the embodying device apart from the motor. Further with regard to alternative embodiments, although a fluid dynamic-pressure bearing furnished with a porous bearing component manufactured according to the present invention is particularly suited to utilization in spindle motors for driving information recording devices such as hard disks, the bearing is utilizable in rotating machines apart from spindle motors.  
         [0030]     The rotor  10  is constituted by a cuplike rotor hub  10   a,  and a shaft  10   b  that is anchored in a snug fit into the rotational center of the rotor hub  10   a.  On the inner circumferential surface of the outer circumferential wall of the rotor hub  10   a,  a rotor magnet  14  is attached by adhesive or like means.  
         [0031]     The bearing structural unit  12  has a housing  16  (a bearing retainer) in the form of a close-ended cylinder, and a bearing sleeve  18  (a porous bearing material) in the form of a hollow tube coaxially mounted within the housing  16 . A journaling bore  18   b  axially through which the shaft  10   b  penetrates is formed through the central portion of the bearing sleeve  18 .  
         [0032]     Sheet metal consisting of a material such as stainless steel or a copper-based or aluminum-based alloy is press-worked to form the housing  16  in the shape of an approximate cup whose bottom side is closed off. Nevertheless, the method of manufacturing the bearing retainer is not thereby limited.  
         [0033]     The bearing sleeve  18  is constituted from a porous sintered body, rendering the inner-circumferential-surface portion of the journaling bore  18   b  of the bearing sleeve  18  a porous surface. The substance of the bearing sleeve  18  is not particularly limited; molded and sintered substances in which powders of various metals, powders of metal compounds, or a nonmetal powders are the source material may be employed. Examples of such source materials include Fe—Cu, Cu—Sn, Cu—Sn—Pb, and Fe—C. The interior of the bearing sleeve  18  of porous sintered manufacture is impregnated with the same oil  15  that is retained in a later-described bearing gap.  
         [0034]     The shaft  10   b  is inserted through the journaling bore  18   b  in the bearing sleeve  18 . The outer circumferential surface of the shaft  10   b  radially opposes, across an interspace, the inner circumferential surface of the bearing sleeve  18 , and the leading-end face of the shaft  10   b  axially opposes, across an interspace, the inner surface of the closed-off end part  16   a  (closed-off end surface) in the bottom portion of the housing  16 . The bearing sleeve  18  is mounted so that its depth-wise endface (in  FIGS. 1A  to  1 C, the endface on the upper side; in  FIG. 3  and  FIG. 5 , the endface on the lower side) axially opposes, across an interspace, closed-off end part  16   a  of the housing  16 . The endfaces along the openings in the housing  16  and the bearing sleeve  18  axially oppose, across an interspace, a shaft-end ringlike planar surface  10   a   1  extending radially outward from the outer circumferential surface of the shaft  10   b  along where the shaft protrudes from the rotor hub  10   a.    
         [0035]     The interspace formed between the endfaces along the openings in the housing  16  and the bearing sleeve  18 , and the surface of the rotor hub  10   a  along where the shaft protrudes, the interspace formed between the inner circumferential surface of the bearing sleeve  18  and the outer circumferential surface of the shaft  10   b,  the gap formed between the inner surface of the closed-off end part  16   a  of the housing  16 , and the lower endface of the shaft  10   b,  and the adjoining gap formed between the depth-wise endface of the bearing sleeve  18  and the inner surface of the closed-off end part  16   a  of the housing  16  (hereinafter, each of these gaps—as well as the gap formed in a later-described communicating passage  19 —will together be denoted “the bearing gap”) are all continuous. The oil  15  is continuously retained in these continuous gaps without interruption, constituting a bearing of a full-fill structure.  
         [0036]     An axially directed groove  18   a  reaching from the endface on the upper side to the endface on the lower side of the bearing sleeve  18  is provided on the sleeve outer circumferential surface (cf.  FIGS. 1, 3  and  4 ). The axially directed groove  18   a  is formed to have a semicircular cross-sectional conformation by a pressing, milling or similar process on the sleeve. The cross-sectional shape of the axially directed groove  18   a  is not limited to being semicircular, and can have other geometries, such as an approximate rectangular form for example. Attaching the thus-structured bearing sleeve  18  to the inner circumferential surface of the housing  16  forms the communicating passage  19  from the axially directed groove  18   a  and the inner circumferential surface of the housing  16 , and the oil  15  is retained also within the communicating passage  19 . Both axial end portions of the gap formed between the inner circumferential surface of the bearing sleeve  18  and the outer circumferential surface of the shaft  10   b  communicate through the communicating passage  19 , via the gap formed between the endfaces along the openings in the housing  16  and the bearing sleeve  18 , and the surface of the rotor hub  10   a  along where the shaft protrudes, as well as the gap formed between the depth-wise endface of the bearing sleeve  18  and the inner surface of the closed-off end part  16   a  of the housing  16 .  
         [0037]     An annular flange portion  16   b  is provided at the circumferentially open end part of the housing  16 . The flange portion  16   b  is formed in a sloped-surface contour so as to project radially outward and so that the outer peripheral surface constricts as it separates from the open end. An annular wall part  10   c  is provided on the rotor hub  10   a,  standing out, in the same direction as the shaft  10   b,  shorter than the outer circumferential wall of the rotor hub  10   a,  from the shaft-end ringlike planar surface  10   a   1  along its outer periphery. An annular recess, the floor of which is the shaft-end ringlike planar surface  10   a   1 , is formed between the annular wall part  10   c  and the shaft  10   b.  The inner circumferential surface of the annular wall part  10   c  and the outer peripheral surface of the flange portion  16   b  radially oppose each other in a non-contacting state.  
         [0038]     By the outer peripheral surface of the flange portion  16   b  being formed in a sloped-surface contour, the radial gap measurement in the interspace between the inner circumferential surface of the annular wall part  10   c  (that is, the surface of a cylindrical surrounding wall), and the outer peripheral surface of the flange portion  16   b,  gradually increases heading toward a bracket  30 , represented in  FIG. 5 , (that is, in the direction of the leading-end portion of the annular wall part  10   c ). In other words, the inner circumferential surface of the annular wall part  10   c  and the outer peripheral surface of the flange portion  16   b  associatively constitute a taper seal section  28 . With regard to the oil  15  retained within the gaps described above, in the taper seal section  28  the surface tension of the oil  15  and the external air pressure balance, forming the boundary surface between the oil  15  and air into a meniscus.  
         [0039]     The taper seal section  28  functions as an oil reservoir, and the location of the oil boundary surface shifts appropriately in accordance with the volume of the oil retained in the taper seal section  28 . Accordingly, the oil  15  retained in the taper seal section  28  is supplied into a bearing section, to be explained later, in accordance with any amount by which the retained oil decreases; meanwhile any amount by which the volume of the oil  15  increases due to thermal expansion another cause is accommodated within the taper seal section  28 .  
         [0040]     Thus, forming a tapered interspace between the outer peripheral surface of the flange portion  16   b  of the housing  16 , and the inner circumferential surface of the annular wall part  10   c  of the rotor hub  10   a,  to constitute the surface-tension-exploiting taper seal section  28  enables the taper seal section  28  to be diametrically larger, and the axial dimension of the taper seal section  28  to be relatively large. Accordingly, the capacity within the taper seal section  28  is increased, and the taper seal section  28  can sufficiently follow the thermal expansion of the generous quantity of oil  15  retained in a full-fill structured dynamic pressure bearing.  
         [0041]     In order to induce fluid dynamic pressure in the oil  15  upon rotation of the rotor  10 , herringbone grooves  20   a  made up of linked pairs of spiral striations inclined in orientations running counter to the rotational direction are formed on the inner circumferential surface of the bearing sleeve  18  along its open end, wherein a radial bearing section  20  along the opening in the sleeve  18  is constituted by the herringbone grooves  20   a  and the outer circumferential surface of the shaft  10   b.  The axial dimension of the spiral-striation portions of the herringbone grooves  20   a  located toward the sleeve open end is determined so as to be greater than that of the spiral-striation portions located depth-wise, wherein the herringbone grooves  20   a  are formed so that, in response to rotation of the rotor  10 , maximum dynamic pressure is generated in a region biased depth-wise from the center, and at the same time, pressure pushing the oil  15  depth-wise is produced. Due to this depth-wise pressing force, the internal pressure of the oil  15  retained in the gap located deeper than the radial bearing section  20  along the open end is kept at atmospheric pressure (external air pressure) or greater.  
         [0042]     Likewise, in order to induce fluid dynamic pressure in the oil  15  upon rotation of the rotor  10 , herringbone grooves  22   a  made up of linked pairs of spiral striations inclined in orientations running counter to the rotational direction are formed on the inner circumferential surface of the bearing sleeve  18  along its bottom end, wherein a radial bearing section  22  along the depth-wise end of the sleeve  18  is constituted by the herringbone grooves  22   a  and the outer circumferential surface of the shaft  10   b.  The two sets of spiral striations forming the herringbone grooves  22   a  in the depth-wise radial bearing section  22  are configured so that groove fundamentals, such as axial dimension and angle of inclination with respect to the rotational direction, or groove width and depth, are the same in order that the two sets of spiral striations generate substantially equal pumping force. In other words, two sets of spiral striations are configured to have line symmetry with respect to where they link (a circumference of the bearing sleeve  18  at a given axial position). Accordingly, in the depth-wise radial bearing section  22 , the dynamic pressure maximum appears midway of the bearing axially.  
         [0043]     Further, pump-in spiral grooves  24   a —as represented in  FIG. 4 —that induce in the oil  15  radially inward-heading (toward the shaft  10   b ) pressure when the rotor  10  spins are formed in the endface (bearing-end ringlike planar face) along the open end of the housing  16 , and between the pump-in grooves  24   a  and the shaft-end ringlike planar surface  10   a   1  of the rotor hub  10   a,  a thrust bearing portion  24 , as indicated in  FIG. 3 , is constituted.  
         [0044]     The herringbone grooves  20   a  and  22   a  provided in the opening-ward radial bearing portion  20 , and the depth-wise radial bearing portion  22  can be formed by a pressing operation on a bearing sleeve  18  made of a sintered material. In addition, the spiral grooves  24   a  with which the thrust bearing portion  24  is provided can be formed at the same time the housing  16  is press-molded.  
         [0045]     It will be appreciated that the endface along the free end of the shaft  10   b,  and the inner surface of the closed-off end part  16   a  of the housing  16  function as a static pressure bearing section that exploits internal pressure of the oil  15  having been heightened by the spiral grooves  24   a  of the thrust bearing section  24 .  
         [0046]     A fluid dynamic bearing manufactured in this way can be utilized, for example, in a spindle motor as represented in  FIG. 5 . Specifically, the housing  16  is anchored into a round boss portion  30   a  provided in the bracket  30 , and a stator  27  is secured to the outer circumferential surface of the boss portion  30   a  so as to radially oppose the rotor magnet  14 . An annular retaining ring  25  is fastened by an adhesive or similar means to the leading end of the annular wall part  10   c  beyond the taper seal section  28 . The annular retaining ring  25  is fit together, in a non-contacting state, with the underside of the flange portion  16   b  ( FIG. 5 ) to prevent the rotor  10  (shaft-end structural component) from falling out of the housing  16  of the bearing structural unit  12 . Fitting information-recording discoid plate(s) externally over, and retaining the plate(s) on, the rotor hub  10   a  enables the spindle motor to be utilized as a disk drive.  
         [0047]     (2) Manufacture of a Lubricant-Impregnated Porous Bearing Component  
         [0048]     Porous bearing components impregnated with lubricant are manufactured utilizing the manufacturing apparatus represented in  FIG. 2A  and  FIG. 2B .  
         [0049]     The manufacturing apparatus is furnished with: an oil bath  52 , inside a vacuum constant-temperature vat  50 , in which the oil  15  (lubricant) is stored; a support frame  56  that is vertically driven by air-pressure actuated linear guides  54 ; and a pallet  58 , detachably supported on the support frame  56 , that moves vertically within the oil bath  52 . The pallet  58  is provided with a grip  64  on a carrying plate  62  evenly perforated by numerous small through-holes  60 . It will be appreciated that the means for vertically driving the pallet  58  and associated components can be selected as appropriate to a given implementation.  
         [0050]     In manufacturing a porous bearing component, as indicated in  FIG. 1A  and  FIG. 2A , in the vacuum constant-temperature vat  50 , a predetermined amount of oil  15  is pooled in the oil bath  52 . Then bearing structural units  12 , in which the bearing sleeves  18  are attached coaxially into the housings  16 , are placed with their open ends turned down on the carrying plate  62  on the pallet  58 , and the pallet  58  is loaded onto the support frame  56  having been positioned above the oil  15  in the oil bath  52 . In this state, the pressure inside the vacuum constant-temperature vat  50  is reduced to a predetermined vacuum level (for example, 0.1 torr or less, but the vacuum is not limited to being that level) with a vacuum pump or like device. Further, in order to reduce the viscosity of the oil  15 , the temperature within the vacuum constant-temperature vat  50  is kept at 70° C. Herein, although it is the case that the more the temperature is raised, the more the viscosity is lowered, maintaining a temperature in excess of 90° C. can lead to troubles with the manufacturing work. By the same token, a temperature less than 60° C. is undesirable because the viscosity of the oil  15  does not lower sufficiently.  
         [0051]     Then, the inside of the vacuum constant-temperature vat  50  is left under this reduced-pressure state for a predetermined time (for example, 40 minutes, but the duration is not limited to that), to reduce the pressure in, and reliably evacuate the air from, the inside of the housing  16  (the inside of the bearing retaining cavity), including the voids in the bearing sleeve  18 , bringing the bearing structural unit  12  down to a requisite vacuum level. It will be appreciated that in order to lower the viscosity of the oil  15 , the temperature of the oil  15  within the oil bath  52  may be maintained at above-noted necessary temperature.  
         [0052]     After that, the linear guides  54 , are driven to lower the support frame  56  and immerse, as illustrated in  FIG. 1B , in the oil  15  the carrying plate  62  on the pallet  58 , and the open-end portions, being the bottom ends, of the bearing structural units  12  (including the open ends of the bearing sleeves  18 ) set on the carrying plate  62 , occluding the bottom ends of the bearing structural units  12 , as indicated in  FIG. 2B . The housing  16  interior is in this way put into an occluded state, and that state is left as it is for five minutes. In that interval, the oil  15  permeates the voids in the bearing sleeve  18  by the agency of surface tension. During this immersion period, the height of the pallet  58  or the position of the oil  15  surface is adjusted so that the open ends of the bearing structural units  12  constantly remain immersed in the oil  15 . For example, occluding the open ends of the bearing structural units  12  with oil  15  can be realized by making the pallet  58  stationary and elevating the oil bath  52 , or by increasing the amount of oil  15  to elevate the oil surface.  
         [0053]     When the pressure inside the vacuum constant-temperature vat  50  is subsequently restored (normally it is restored to atmospheric pressure), because a reduced pressure state in the inside of the housing  16  including the inside of the journaling bore  18   b  is sustained, as shown in  FIG. 1C , the oil  15  infiltrates the housing  16  interior including the journaling bore  18   b  interior, sufficiently impregnating the bearing sleeve  18  with the oil  15 . In this case, it is preferable that the reduction and restoration of pressure are carried out so that the oil  15  rises to the upper end of the journaling bore  18   b.  Holding the inside of the vacuum constant-temperature vat  50  in this state for a requisite time (several minutes for example), enables the action of impregnating the bearing sleeve  18  with the oil  15  to be made the more certain. Gas introduced in restoring the pressure within the vacuum constant-temperature vat  50  may be an inert gas, such as helium or nitrogen, whose solubility with respect to the oil  15  is low.  
         [0054]     It should be understood that means can be adopted in order to make it so that before the oil  15  has sufficiently infiltrated the housing  16 , the occlusion of the open end of the bearing structural unit  12  by the oil  15  does not break due to the liquid surface of the oil bath  52  dropping when the oil  15  infiltrates the housing  16  interior. Such means include: (i) having the position of the pallet  58  with respect to the oil bath  52  when the lower end portion of the bearing structural unit  12  is immersed in the oil  15  be fixed and, taking into consideration the drop in the liquid surface of the oil bath  52 , setting the depth to which the lower end portion of the bearing structural unit  12  is immersed in the oil  15  so that the occlusion is not broken; (ii) in response to a drop in the liquid surface of the oil bath  52 , lowering the position of the pallet  58  with respect to the oil bath  52 ; and (iii) monitoring the height of the surface of the oil  15  with a sensor, and if the level drops below a prescribed height, automatically injecting oil into the bath  52 .  
         [0055]     Thereafter, by driving the linear guides  54  to elevate the support frame  56  (alternatively, by lowering the oil bath  52 , or externally discharging the oil  15  in the oil bath  52  to reduce the oil volume) the occlusion of the open end of the bearing structural unit  12  by the oil  15  is broken, whereby excess oil in the journaling bore  18   b  interior and other regions drains, yielding a lubricant-impregnated porous bearing component in which the bearing sleeve  18  is impregnated with the oil  15 .  
         [0056]     In this way carrying out the operation of varying the relative vertical positional relationship between the pallet  58  within the vacuum constant-temperature vat  50 , and the level of the oil in the oil bath  52  enables the manufacture of lubricant-impregnated porous bearing components to be performed, thanks to which operations in the vacuum constant-temperature vat  50  are facilitated, and material costs for the necessary machinery and facilities are effectively minimized. Furthermore, since the inside of the housing  16 , including the voids in the bearing sleeve  18 , is evacuated and reduced in pressure beforehand, bursting of air bubbles that splatters the oil  15  is prevented. In addition, except for the housing  16  interior, the bearing structural unit  12  is immersed single-ended in the oil  15 ; thus, due to the fact the exterior of the housing  16  except for the one end portion does not come into contact with the oil  15 , and to the fact that splattering of the oil  15  due to air bubbles bursting is prevented, the labor of wiping away lubricant adhering to the exterior of the housing  16  and of associated cleanup is curtailed.  
         [0057]     For bearing structural unit implementations in which the depth-wise end of the housing is open, a lubricant-impregnated porous bearing component can be obtained by using a jig or similar tool to temporally close off the depth-wise end of the housing and render it airtight against the exterior, and processing the unit likewise as above. The jig or similar tool employed in this case may be detached following completion of the oil-impregnation job.  
         [0058]     The present invention is not limited to the above-described embodiments and various changes or modifications are possible without deviating from the scope of the present invention.  
         [0059]     Specifically, the present invention is not limited to the dynamic pressure bearing, motor, or the recording disk drive illustrated in the foregoing embodiment. Further, the presence/absence of dynamic-pressure-generating grooves in, the components forming, or the geometry of, the bearing sections of the dynamic pressure bearing are not limited to those of the foregoing embodiment.  
         [0060]     Furthermore, with the embodiment illustrated in the figures, a description was made giving the example of a so-called shaft-rotating spindle motor in which the shaft  10   b  is fixed to the rotor hub  10   a  to constitute the rotor  10 ; however, the present invention is also applicable to so-called shaft-stationary spindle motors in which the shaft constitutes a portion of the stationary component.