Patent Abstract:
A bearing unit and a rotating apparatus which prevent leakage of lubricating oil to the utmost and are superior in reliability are disclosed. A radial bearing and a thrust bearing support a shaft for rotation, and a path forming member and a path forming member lid form a communicating path having a function of short-circuiting pressure generated when the shaft and the radial bearing rotate relative to each other. A housing has a function of covering and holding the members mentioned while the housing is open at one end of the shaft with a small void left therebetween. Lubricating oil is filled in the void. The path forming member and the path forming member lid fully cover the members mentioned except a shaft opening side portion of the radial bearing. The housing is made of a molded resin material.

Full Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     The present invention contains subject matter related to Japanese Patent Application JP 2005-217763 filed in the Japanese Patent Office on Jul. 27, 2005, the entire contents of which being incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a bearing unit which incorporates a countermeasure for preventing leakage of lubricating oil and a rotating apparatus which incorporates a bearing unit of the type described.  
         [0004]     2. Description of the Related Art  
         [0005]     First, a bearing unit of a related art is described with reference to FIGS.  6  to  9 .  
         [0006]     In particular,  FIG. 6  is a side elevational sectional view showing the bearing unit of the related art mentioned.  FIGS. 7A  to  7 C show a path forming member which is a component of the bearing unit shown in  FIG. 6 , and wherein  FIG. 7A  is a perspective view of the entire path forming member;  FIG. 7B  is a top plan view of the path forming member; and  FIG. 7C  is a sectional view taken along line C-C of  FIG. 7B . Further,  FIG. 8  is a perspective view of a path forming member lid which is a component of the bearing unit shown in  FIG. 6  and cooperates with the path forming member shown in  FIG. 6 .  FIG. 9  is a perspective view of a radial bearing which is another component of the bearing unit shown in  FIG. 6 .  
         [0007]     Referring first to  FIG. 6 , the bearing unit of the related art is denoted by a numeral  30 . The bearing unit  30  is same as a bearing unit disclosed in Japanese Patent Laid-Open No. 2005-69382 (pages 9 to 18,  FIG. 3 ). The bearing unit  30  includes a radial bearing  33 , a path forming member  34 , a path forming member lid  40 , and a housing  60 . The radial bearing  33  supports a shaft  31  in a circumferential direction at a portion  31   a  thereof which is supported for rotation by dynamic pressure and has dynamic pressure generating grooves  32  formed on an outer periphery thereof. The radial bearing  33  has a shaft opening side end face  33   a  and a thrust bearing side end face  33   b  formed thereon. The path forming member  34  covers a circumferential face of part of the radial bearing  33  and has a thrust bearing  46  formed at a bottom portion thereof. The path forming member lid  40  has a shaft fitting hole  40   h  formed at a central portion thereof as particularly seen in  FIG. 8  and having a diameter sufficient to allow the shaft  31  to pass through the shaft fitting hole  40   h.  The path forming member lid  40  covers the shaft opening side end face  33   a  of the radial bearing  33 .  
         [0008]     Referring to  FIG. 9 , the radial bearing  33  has a cylindrical structure and has a through-hole  33   h  formed axially at a central portion thereof. The upper end face of the radial bearing  33  is formed as a shaft opening side end face  33   a  while the lower end face of the radial bearing  33  is formed as a thrust bearing side end face  33   b.  The radial bearing  33  further has a plurality of grooves, three in the arrangement shown, first grooves  51  formed on an outer circumferential face thereof. The radial bearing  33  further has an equal number of second grooves  52  and an equal number of third grooves  53  formed on the thrust bearing side end face  33   b  and the shaft opening side end face  33   a  thereof, respectively, and both communicating with the first grooves  51  to form communicating paths  50 .  
         [0009]     Referring now to  FIGS. 7A  to  7 C, the path forming member  34  has a cup-shaped configuration and has a thrust bearing  46  formed on a bottom face thereof. An upper cylindrical portion of the path forming member  34  has three arcuate plates  36  separated by three cutaway portions  35  for covering the communicating paths  50  to assure voids for the grooves of the communicating paths  50 . The path forming member  34  has a space  37  and another space  38  formed at a central portion of the bottom portion thereof. The space  37  can be expanded outwardly to accommodate a flexible coming off preventing washer  49  when the shaft  31  is pushed into the same while the space  38  can accommodate a lower end portion  31   b  of the shaft  31  therein. The spaces  37  and  38  form a thrust space which is communicated also with the communicating paths  50  such that lubricating oil  42  can be circulated. Further, engaging pawls  39  are formed to extend inwardly from a circumferential edge of the path forming member  34  at the upper opening.  
         [0010]     Referring now to  FIG. 8 , the path forming member lid  40  has a donut-shaped flat disk shape and has a shaft fitting hole  40   h  formed at a central portion thereof. The path forming member lid  40  has a size a little greater than the diameter of the engaging pawls  39  formed at the opening of the path forming member  34  and is fitted in through the engaging pawls  39  while pushing away the engaging pawls  39 . The path forming member lid  40  is locked by the engaging pawls  39  so that it does not remove upwardly.  
         [0011]     Upon assembly of the bearing unit  30 , the coming off preventing washer  49  is disposed in the space  37  of the path forming member  34  in advance, and the radial bearing  33  is fitted into the coming off preventing washer  49  with the thrust bearing side end face  33   b  directed downwardly. Then, the path forming member lid  40  is fitted in from above the path forming member  34  and is secured by the engaging pawls  39  such that it closely contacts with the shaft opening side end face  33   a  of the radial bearing  33 .  
         [0012]     Where the bearing unit  30  is assembled in this manner, the three third grooves  53  of the radial bearing  33  are closed up with the path forming member lid  40  to form pipe-shaped space paths, and the three first grooves  51  of the radial bearing  33  are closed up with the arcuate plates  36  of the path forming member  34  to form pipe-shaped space paths. Further, the three second grooves  52  of the radial bearing  33  are open to the space  37  to form space paths. The space paths formed in this manner form communicating paths  50  through which lubricating oil  42  can be supplied and circulated to the dynamic pressure generating grooves  32  of the shaft  31  and which have a function of short-circuiting pressure which is generated when the shaft  31  and the radial bearing  33  rotate relative to each other.  
         [0013]     If an outer surface of the path forming member  34  and an upper face of the path forming member lid  40  are sealed with a resin material using a metal mold while the bearing unit  30  is in the assembled state described above, then the bearing unit  30  can be covered with the housing  60  of the resin material. In particular, the housing  60  made of a resin material can cover the bearing unit  30  over part of the outer circumferential face of the radial bearing  33  which is exposed by the cutaway portions  35  of the path forming member  34  and the outer surface of the arcuate plates  36  and over the upper surface of the path forming member lid  40 .  
         [0014]     Thereafter, if the shaft  31  is inserted and pushed through the shaft fitting hole  40   h  of the path forming member lid  40  and the through-hole  33   h  of the radial bearing  33  into a central portion of the coming off preventing washer  49 , then the bearing unit  30  having the structure shown in  FIG. 6  is obtained. After the bearing unit  30  is completed, the lubricating oil  42  is poured in from the shaft opening end  30   a  side of the bearing unit  30  so as to fill between the shaft fitting hole  40   h  of the radial bearing  33  and the shaft  31  and the communicating paths  50 .  
         [0015]     The bearing unit  30  is assembled in such a manner as described above.  
       SUMMARY OF THE INVENTION  
       [0016]     The bearing unit  30  having such a configuration as described above can be suitably used as a bearing for a motor of a heat radiating apparatus incorporated in an electronic apparatus such as a computer, particularly a portable computer. Therefore, leakage of the lubricating oil  42  should be prevented to the utmost.  
         [0017]     As described above, in the bearing unit  30  of the related art, the arcuate plates  36  of the path forming member  34  cover the communicating paths  50 . However, part of the radial bearing  33  contacts directly with the housing  60  due to the presence of the cutaway portions  35  of the path forming member  34 .  
         [0018]     When the shaft  31  rotates relative to the radial bearing  33 , the lubricating oil  42  filled in the internal voids of the bearing unit  30  circulates in the voids in the bearing unit  30  as described above. However, there is the possibility that part of the lubricating oil  42  may come round to the surface of the path forming member  34  from the location where the radial bearing  33  contacts directly with the housing  60 .  
         [0019]     The housing  60  is formed by outsert molding or the like of a resin material, and the path forming member  34  has a pawl structure formed from the three arcuate plates  36  by the cutaway portions  35 . Therefore, the housing  60  is structured such that the molding resin material which forms the housing  60  has a comparatively small thickness at the portions of the path forming member  34  at which the arcuate plates  36  exist but has a comparatively great thickness at the other portions of the path forming member  34  at which the arcuate plates  36  do not exist.  
         [0020]     Therefore, upon molding of the housing  60 , molten resin material flows but not uniformly and does not run uniformly. Therefore, a weld (joint of the resin material upon molding) is likely to appear. Further, since the path forming member  34  has a pawl structure, it is compressed diametrically upon molding of the housing  60 . However, where the bearing unit  30  is placed under a high temperature environment, the arcuate plates  36  of the path forming member  34  are inclined to open outwardly by internal residual stress, and there is the possibility that a crack may appear at a portion of the housing  60  at which a difference in thickness exists.  
         [0021]     If such a weld or a crack occurs with the housing  60 , then the surface of the path forming member  34  is communicated with the outside and the lubricating oil  42  leaks to the outside from the inside of the radial bearing  33  through the weld or crack. Thus, the bearing unit  30  of the related art has a subject to be in that good lubrication is difficult to achieve readily, resulting in deterioration of the reliability.  
         [0022]     Therefore, it is desirable to provide a bearing unit and a rotating apparatus using the bearing unit which prevent leakage of lubricating oil to the utmost and are superior in reliability.  
         [0023]     According to an embodiment of the present invention, there is provided a bearing unit including a radial bearing and a thrust bearing configured to support a shaft for rotation, a path forming member and a path forming member lid configured to form a communicating path having a function of short-circuiting pressure generated when the shaft and the radial bearing rotate relative to each other, a housing having a function of covering and holding the shaft, radial bearing, thrust bearing, path forming member and path forming member lid while the housing is open at one end of the shaft with a small void left therebetween, and lubricating oil filled in the void, the path forming member and the path forming member lid cooperating with each other to fully cover the shaft, radial bearing, thrust bearing, path forming member and path forming member lid except a shaft opening side portion of the radial bearing, the housing being made of a molded resin material.  
         [0024]     According to another embodiment of the present invention, there is provided a bearing unit including a radial bearing having a through-hole formed at a central portion thereof and configured to support a shaft fitted therein for rotation in a circumferential direction, the radial bearing further having a shaft opening side end face and a thrust bearing side end face, a path forming member having a thrust bearing formed at a bottom portion thereof and covering an overall outer circumferential face of the radial bearing, and a path forming member lid having a shaft fitting hole formed at a central portion thereof and having a diameter sufficient to allow the shaft to be fitted in the shaft fitting hole, the path forming member lid covering the shaft opening side end face of the radial bearing, the bearing unit having an integral structure wherein the radial bearing is fitted coaxially in the path forming member with the overall outer circumferential face thereof covered with the path forming member and is closed up with the path forming member lid with the shaft opening side end face thereof covered with the path forming member lid such that a plurality of lubricating oil circulating paths are formed such that a space between the shaft opening side end face of the radial bearing and an inner face of the path forming member lid, another space between the outer circumferential face of the radial bearing and the inner circumferential face of the path forming member, a further space in the proximity of the thrust bearing and the through-hole of the radial bearing are communicated with each other while lubricating oil is enclosed in the lubricating oil circulating paths and the overall bottom face and the overall outer circumferential face of the path forming member and the upper face of the path forming member lid except a portion in the proximity of the shaft fitting hole are covered with the housing.  
         [0025]     Preferably, the radial bearing is made of a sintered metal material. Alternatively, the radial bearing may be formed from a dynamic pressure fluid bearing having a dynamic pressure generating groove formed on an inner circumferential face of through-hole formed therein.  
         [0026]     Preferably, the bearing unit further includes a shaft coming off preventing element provided in a bottom space of the path forming member.  
         [0027]     Preferably, the housing is formed as a unitary member from a molded article of a synthetic resin material.  
         [0028]     According to a further embodiment of the present invention, there is provided a rotating apparatus including a radial bearing having a through-hole formed at a central portion thereof and configured to support a shaft fitted therein for rotation in a circumferential direction, the radial bearing further having a shaft opening side end face and a thrust bearing side end face, a path forming member having a thrust bearing formed at a bottom portion thereof and covering an overall outer circumferential face of the radial bearing, and a path forming member lid having a shaft fitting hole formed at a central portion thereof and having a diameter sufficient to allow the shaft to be fitted in the shaft fitting hole, the path forming member lid covering the shaft opening side end face of the radial bearing, the bearing unit having an integral structure wherein the radial bearing is fitted coaxially in the path forming member with the overall outer circumferential face thereof covered with the path forming member and is closed up with the path forming member lid with the shaft opening side end face thereof covered with the path forming member lid such that a plurality of lubricating oil circulating paths are formed such that a space between the shaft opening side end face of the radial bearing and an inner face of the path forming member lid, another space between the outer circumferential face of the radial bearing and the inner circumferential face of the path forming member, a further space in the proximity of the thrust bearing and the through-hole of the radial bearing are communicated with each other while lubricating oil is enclosed in the lubricating oil circulating paths and the overall bottom face and the overall outer circumferential face of the path forming member and the upper face of the path forming member lid except a portion in the proximity of the shaft fitting hole are covered with the housing, the shaft being fitted in and supported for rotation by the through-hole of the radial bearing such that the thrust end side portion of the shaft contacts with the thrust bearing of the path forming member.  
         [0029]     The rotating apparatus may be a motor including a stator and a rotor, and a rotary shaft of the rotor may be supported for rotation relative to the stator by the bearing unit. Preferably, the bearing unit includes a shaft coming off preventing member provided in a bottom space of the path forming member, and the thrust end portion of the shaft is locked in a center hole of the shaft coming off preventing member.  
         [0030]     In the bearing units and the rotating apparatus, the housing can be made of a material, particularly a synthetic resin material, having a uniform thickness over the overall outer periphery of the radial bearing.  
         [0031]     With the bearing units and the rotating apparatus, the housing is formed in a housing structure wherein the dynamic pressure generating portion is sealed fully with the path forming member lid except the shaft fitting hole and the radial bearing is formed with a substantially uniform thickness over the overall outer periphery thereof. Therefore, the lubricating oil filled in the bearing unit is not likely to suffer from leakage, and consequently, the bearing unit and the rotating apparatus which uses the bearing unit such as a motor are superior in reliability.  
         [0032]     The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]      FIG. 1  is a sectional view of a motor to which the present invention is applied;  
         [0034]      FIG. 2  is a vertical sectional side elevational view of a bearing unit according to a first embodiment of the present invention which is used in the motor of  FIG. 1 ;  
         [0035]      FIGS. 3A  to  3 C show a path forming member suitable for use with the bearing unit of  FIG. 2  and wherein  FIG. 3A  is a perspective view of the entire path forming member,  FIG. 3B  is a top plan view of the path forming member and  FIG. 3C  is a vertical sectional side elevational view taken along line C-C of  FIG. 3B ;  
         [0036]      FIG. 4  is a perspective view, partly in section, of the radial bearing of  FIG. 3  which has dynamic pressure generating grooves formed on an inner circumferential face thereof;  
         [0037]      FIG. 5  is an exploded perspective view showing a configuration of communicating paths formed between a path forming member and a radial bearing which are used in a bearing unit according to a second embodiment of the present invention;  
         [0038]      FIG. 6  is a vertical sectional side elevational view of a bearing unit of a related art;  
         [0039]      FIGS. 7A  to  7 C show a path forming member which is a component of the bearing unit shown in  FIG. 6  and wherein  FIG. 7A  is a perspective view of the entire path forming member,  FIG. 7B  is a top plan view of the path forming member and  FIG. 7C  is a vertical sectional side elevational view taken along line C-C of  FIG. 7B ;  
         [0040]      FIG. 8  is a perspective view of a path forming member lid which is another component of the bearing unit shown in  FIG. 6  and cooperates with the path forming member shown in  FIG. 6 ; and  
         [0041]      FIG. 9  is a perspective view of a radial bearing which is a further component of the bearing unit shown in  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0042]     In the following, bearing units to which the present invention is applied and a motor which is an example of a rotating apparatus which uses the bearing units are described. According to the present invention, the bearing units and the motor of the embodiments are generally configured such that the bearing unit is formed as a unitary member by fully covering a radial bearing except a shaft opening end portion while the cutaway portions of the path forming member of the bearing unit of the related art are eliminated.  
         [0043]     First, a motor which is an example of a rotating apparatus to which the present invention is applied is described with reference to  FIG. 1 . The motor mentioned is suitable for use with electronic apparatus which perform arithmetic operation processing, recording and reproduction and so forth of various kinds of information such as computers, particularly notebook type computers. Particularly, the motor is suitable for use with small size electronic apparatus and is formed suitably as a motor for a heat radiating apparatus.  
         [0044]     A heat radiating apparatus is provided in the inside of an electronic apparatus such as a notebook type computer. The heat radiating apparatus includes a base made of a metal material, a motor  1  attached to the base, a fan  3  driven to rotate by the motor  1 , a fan case  4  for accommodating the fan  3  therein, and a heat sink (not shown). The motor  1  for driving the fan  3  of the heat radiating apparatus to rotate is described in detail below.  
         [0045]     The motor  1  which uses a bearing unit  30 A to which the present invention is applied as hereinafter described includes a rotor  11  and a stator  12 .  
         [0046]     The stator  12  is provided integrally on a top plate  4   a  of the fan case  4  in which the fan  3  which is driven to rotate by the motor  1  is accommodated together with the motor  1 . The stator  12  includes a stator yoke  13 , a bearing unit  30 A to which the present invention is applied, a coil  14 , and a core  15  on which the coil  14  is wound. The stator yoke  13  may be formed integrally with the top plate  4   a  of the fan case  4 , that is, may be formed from part of the fan case  4  or otherwise may be formed as a separate member from the fan case  4 . The stator yoke  13  is formed from, for example, iron. The bearing unit  30 A is secured to a holder  16  formed tubularly at a central portion of the stator yoke  13  by force fitting or adhesion or by force fitting and adhesion.  
         [0047]     It is to be noted that the holder  16  in which the bearing unit  30 A is force fitted is formed tubularly integrally with the stator yoke  13 . The core  15  on which the coil  14  to which driving current is supplied is attached to an outer periphery of the holder  16  formed integrally on the stator yoke  13  as seen in  FIG. 1 .  
         [0048]     The rotor  11  which forms the motor  1  together with the stator  12  is attached to a shaft  31  supported for rotation on the bearing unit  30 A such that it rotates together with the shaft  31 . The rotor  11  includes a rotor yoke  17  and a fan  3  rotatable integrally with the rotor yoke  17  and having a plurality of blades  19 . The blades  19  of the fan  3  are formed integrally with the rotor yoke  17  by outsert molding on an outer circumferential face of the rotor yoke  17 .  
         [0049]     A ring-shaped rotor magnet  20  is provided on an inner circumferential face of a tubular portion  17   a  of the rotor yoke  17  in an opposing relationship to the coil  14  of the stator  12 . The rotor magnet  20  is a plastic magnet having S poles and N poles magnetized alternately in a circumferential direction, and is secured to an inner circumferential face of the rotor yoke  17  by a bonding agent.  
         [0050]     The rotor yoke  17  is attached for integral rotation to the shaft  31  by force fitting of a hub (boss) portion  21  provided at a central portion of a flat plate portion  17   b  of the rotor yoke  17  and having a through-hole  21   a  provided therein in an attaching portion  31   c  provided at an end portion of the shaft  31  supported by the bearing unit  30 A.  
         [0051]     In the motor  1  having such a configuration as described above, driving current is supplied to the coil  14  of the stator  12  in accordance with a predetermined energization pattern from a driving circuit section not shown provided outside the motor  1 . Thereupon, a magnetic field is generated from the coil  14 , and the rotor  11  rotates integrally with the shaft  31  by an action between the magnetic field generated from the coil  14  and a magnetic field from the rotor magnet  20  of the rotor  11 . As the rotor  11  rotates, also the fan  3  attached to the rotor  11  and having the blades  19  thereon rotates integrally with the rotor  11 . As the fan  3  rotates, air outside the apparatus is sucked into a housing of the computer through an opening formed in the housing and is circulated in the housing. Thus, after the air is circulated in a heat sink provided in the housing, it is exhausted to the outside of the housing through a through-hole formed in the housing. Consequently, heat generated from heat generating elements in the computer is radiated to the outside of the computer body by the air to cool the computer body.  
         [0052]     Now, the bearing unit  30 A according to the first embodiment which is suitable for use with the motor  1  is described with reference to FIGS.  2  to  4 .  
         [0053]     The bearing unit  30 A which supports the shaft  31  of the motor  1  for rotation includes a radial bearing  33  for supporting the shaft  31  in a circumferential direction, and a path forming member  34 A formed on the outer side of the radial bearing  33 . The bearing unit  30 A further includes a housing  60 A in which the path forming member  34 A is accommodated and communicating paths  50  formed between the path forming member  34 A and the radial bearing  33 .  
         [0054]     The bearing unit  30 A is configured in such a structure that the path forming member  34 A covers the overall periphery of the radial bearing  33 . In particular, the radial bearing  33  is covered fully with the path forming member lid  40  and the path forming member  34 A except a portion of the shaft opening end  30   a  side thereof.  
         [0055]     It is to be noted that the radial bearing  33  and the path forming member lid  40  have a structure similar to that of the related art arrangement described hereinabove with reference to  FIGS. 9 and 8 , respectively, and therefore, overlapping description of them is omitted herein to avoid redundancy.  
         [0056]     A structure of the path forming member  34 A which can be suitably applied to the bearing unit  30 A shown in  FIGS. 1 and 2  is shown in an enlarged scale in  FIGS. 3A  to  3 C. Referring to  FIGS. 3A  to  3 C, the path forming member  34 A shown has a generally cup-shaped configuration and has a cylindrical structure capable of fully covering over an outer periphery of the radial bearing  33 . In other words, the path forming member  34 A does not have, at an upper portion thereof, such cutaway portions  35  as are provided on the path forming member  34  of the arrangement of the related art described hereinabove, and is formed in such a size that the voids of grooves of the communicating paths  50  can be assured.  
         [0057]     At a central portion of a bottom portion of the path forming member  34 A, a space  37  which can accommodate a flexible coming off preventing washer  49 , which is flexibly expanded when the shaft  31  is inserted into the coming off preventing washer  49 , and another space  38  which can accommodate a lower end portion  31   b  of the shaft  31  are formed concentrically. The spaces  37  and  38  serve also as a thrust space which is communicated with the communicating paths  50  and through which the lubricating oil  42  can be circulated. Further, an engaging pawl  39  is formed inwardly along an overall circumferential edge of the top opening of the path forming member  34 A.  
         [0058]     In assembly of the bearing unit  30 A, the coming off preventing washer  49  is disposed in advance in the space  37  of the path forming member  34 A, and the radial bearing  33  is fitted into the coming off preventing washer  49  with the thrust bearing side end face  33   b  side thereof directed downwardly. Then, the path forming member lid  40  is fitted from above into the path forming member  34 A until that it is engaged with and secured by the engaging pawl  39  so that it contacts closely with the shaft opening side end face  33   a  of the radial bearing  33 .  
         [0059]     As a result of such assembly, the three third grooves  53  of the radial bearing  33  are closed up with the path forming member lid  40  to form pipe-shaped space paths. Further, the three first grooves  51  of the radial bearing  33  are closed up with the cylindrical portion of the path forming member  34 A to form pipe-shaped space paths. Further, the three second grooves  52  of the radial bearing  33  are opened to the space  37 . Consequently, lubricating oil  42  can be supplied and circulated to dynamic pressure generating grooves  32  of the shaft  31  through the communicating paths  50  formed from the space paths mentioned.  
         [0060]     It is to be noted that, while, in the embodiment described above, the communicating paths  50  each formed from a first groove  51 , a second groove  52  and a third groove  53  are formed at angular intervals of 120 degrees, the number of the communicating paths  50  is not limited to three but may be, for example, one. However, the radial bearing  33  preferably has a plurality of communicating paths provided symmetrically therearound as in the present embodiment.  
         [0061]     In this assembled state, the assembly is sealed over the outer surface of the path forming member  34 A and the upper face of the path forming member lid  40  except the shaft fitting hole  40   h  with a resin material using a metal mold. By the sealing, the overall outer surface of the path forming member  34 A and the upper face of the path forming member lid  40  can be covered with the housing  60 A made of a resin material.  
         [0062]     Thereafter, the shaft  31  is inserted and forced into the shaft fitting hole  40   h  ( FIG. 8 ) of the path forming member lid  40 , the through-hole  33   h  ( FIG. 9 ) of the radial bearing  33  and the central portion of the coming off preventing washer  49 . As a result, the bearing unit  30 A having such a structure as shown in  FIG. 2  is obtained.  
         [0063]     After the bearing unit  30 A is completed, lubricating oil  42  is poured into the axial opening end  30   a  side of the bearing unit  30 A so that it is spread to the space between the shaft fitting hole  40   h  of the radial bearing  33  and the shaft  31  and into the communicating paths  50 . The lubricating oil  42  thus functions to short-circuit pressure which is generated when the shaft  31  and the radial bearing  33  rotate relative to each other.  
         [0064]     A coming off preventing washer  49  is provided as a coming off preventing element for the shaft  31  on the bearing unit  30 A to enhance the convenience in use. The coming off preventing washer  49  may be made of a resin material such as nylon or polyimide or a metal material.  
         [0065]     The bearing unit  30 A is assembled in such a manner as described above.  
         [0066]     The radial bearing  33  does not contact directly with the housing  60 A because it is covered fully with the path forming member lid  40  and the path forming member  34 A except the axial opening portion thereof. Therefore, the lubricating oil  42  filled in the void in the inside of the bearing unit  30 A does not at all come round to the outer side of the path forming member lid  40  and the path forming member  34 A.  
         [0067]     Further, since the path forming member  34 A has a full circumference structure, the thickness of the housing  60 A in the diametrical direction is uniform. Therefore, resin upon molding of the housing  60 A flows uniformly to the overall circumference. Consequently, appearance of a weld of resin which appears in the bearing unit  30  of the related art can be suppressed to the utmost.  
         [0068]     Further, since the path forming member  34 A has a full circumference structure, it has a higher rigidity than the path forming member  34  of the related art which has a pawl structure, and this is effective also for prevention of appearance of a crack.  
         [0069]     Accordingly, since no weld or no crack appears upon molding of the housing  60 A, a stabilized molding condition can be maintained.  
         [0070]     From the foregoing, since the configuration of the path forming member  34 A has a full circumference structure, a bearing unit which is superior in reliability in that it is less likely to suffer from leak of lubricating oil can be obtained due to reinforcement of the sealing structure for lubricating oil and also to stabilization of a resin molding condition.  
         [0071]     While, in the bearing unit  30 A according to the first embodiment, dynamic pressure generating grooves are provided on the shaft  31 , dynamic pressure generating grooves  43  and  44  may be provided on an inner circumferential face of a radial bearing  33 A as seen in  FIG. 4 .  
         [0072]     As a material for the radial bearing  33  or  33 A, a metal material such as sintered metal, brass or stainless steel or a resin material may be used.  
         [0073]     Further, the thrust bearing element may be a dynamic pressure fluid bearing or a pivot type bearing. In  FIG. 2 , a pivot thrust bearing element is used wherein the shaft  31  has a spherical lower end and the path forming member  34 A is made of a resin material.  
         [0074]     Further, in the bearing unit of the present embodiment, the communicating paths  50  are provided to short-circuit a dispersing dynamic pressure generated between the two dynamic pressure generating grooves  32  upon rotation of the shaft  31  and a dispersing static pressure generated together with a rise of the dynamic pressure.  
         [0075]     If the dynamic pressure and the static pressure are not short-circuited between the dynamic pressure generating grooves  32 , then when the dynamic pressure on the non-opening side of the shaft  31  is lower than that on the opening side of the shaft  31 , the static pressure becomes relatively higher. Consequently, force acting to push up the shaft  31  is generated. If the shaft  31  is pushed outwardly by the force, then the bearing unit  30 A may not exhibit a function as a bearing unit.  
         [0076]     The amount of dynamic pressure generated in the dynamic pressure generating grooves  32  depends upon the depth of the dynamic pressure generating grooves, the void amount between the dynamic pressure generating grooves and the shaft, the mechanical accuracy of the groove angle and so forth. However, it is very difficult to adjust the mechanical accuracy to an equal level. Therefore, it is desirable to provide the communicating paths  50  between the dynamic pressure generating grooves  32  to short-circuit the dynamic pressure and the static pressure.  
         [0077]     Further, although the material of the housing  60 A is not limited particularly, the housing  60 A in the present embodiment is formed by outsert molding of a resin material such as POM (polyoxymethylene), polyimide, LCP (liquid crystal polymer) or the like.  
       Second Embodiment  
       [0078]     Now, another bearing unit to which the present invention is applied is described with reference to  FIG. 5 . It is to be noted that a sectional view of the bearing unit similar to that of  FIG. 2  is omitted for the convenience of illustration.  
         [0079]     The communicating paths  50  in the bearing unit  30 A of the first embodiment described hereinabove are configured such that the first grooves  51 , second grooves  52  and third grooves  53  are provided on the radial bearing  33  and are closed up with the path forming member  34 A and the path forming member lid  40  to form pipe-like space paths. However, in the bearing unit according to the second embodiment of the present invention shown in  FIG. 5 , such communicating paths are formed in such a manner as seen in  FIG. 5 . In particular, referring to  FIG. 5 , such first grooves  51 ,  52  and  53  as described hereinabove are not provided on the outer periphery and the opposite upper and lower end faces of the radial bearing  33 A. Instead, for example, three grooves  54   a,    55   a  and  56   a  are formed in an axial direction on an inner circumferential face of a path forming member  34 B, and three grooves (not shown) are provided toward the center also on the bottom face of the path forming member  34 B in a communicating relationship with the grooves  54   a,    55   a  and  56   a.  Further, three grooves  54   b,    55   b  and  56   b  are formed in an equally angularly spaced relationship around a shaft fitting hole  40   h  on an inner face (lower face or rear face) of a path forming member lid  40 A, which closes up an opening at the upper end of the path forming member  34 B, in a communicating relationship with the grooves  54   a,    55   a  and  56   a,  respectively.  
         [0080]     Meanwhile, a radial bearing  33 B used in the present bearing unit does not have any groove on an outer circumferential face and an upper end face thereof. The radial bearing  33 B having such a structure as just described is fitted into the path forming member  34 B, and then the path forming member lid  40 A is fitted into the radial bearing  33 B from above. Consequently, the outer circumferential face of the radial bearing  33 B closes up the three grooves  54   a,    55   a  and  56   a  formed on the inner circumferential face of the path forming member  34 B to form three space paths. Further, the flat upper end face of the radial bearing  33 B closes up the three grooves  54   b,    55   b  and  56   b  formed on the path forming member lid  40 A to form three space paths. The space paths are communicated with each other to form communicating paths  50  similar to those in the bearing unit  30 A of the first embodiment described hereinabove.  
         [0081]     Accordingly, also in the bearing unit of the second embodiment having such a structure as described above, lubricating oil  42  encapsulated in the bearing unit can be circulated through the communicating paths  50 .  
         [0082]     It is to be noted that, while, in the embodiments described above, a motor is applied as a rotating apparatus, the bearing unit to which the present invention is applied is not limited to a bearing unit for use with a bearing for a rotary shaft of a motor. In particular, the bearing unit to which the present invention is applied can be applied also to bearings for guide rollers, idlers, capstans, pinch rollers and so forth which are used in apparatus which involve takeup of a linear article such as a yarn or a wire or a belt-like article such as a wide film or a magnetic tape.  
         [0083]     While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purpose, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

Technology Classification (CPC): 5