JP2012215218A - Fluid dynamic pressure bearing device and spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluid dynamic pressure bearing device which can suppress a torque upon starting and has high durability against a shock applied in the thrust direction.SOLUTION: In a first thrust bearing part 110 configured between the upper surface of a sleeve 103 and the lower surface of a hub 101, a second thrust bearing part 111 configured between the upper surface of a counter plate 104 and the lower end surface of a shaft 102 and a radial bearing part 113 configured between the outer circumferential surface of the shaft 102 and the inner circumferential surface of the sleeve 103, the shaft 102 and the hub 101 integrated with the shaft 102 are supported on the inside of the sleeve 103. Upon non-rotation of the shaft 102, the upper surface of the sleeve 103 in the first thrust bearing part 110 does not come in contact with the lower surface of the hub 101 and a gap 105 is secured and, upon the non-rotation, the lower end surface of the shaft 102 comes in contact with the upper surface of the counter plate 104 integrated with the sleeve 103, on the second thrust bearing part 111.

Description

  The present invention relates to a fluid dynamic bearing device and a spindle motor that are characterized by a structure of a bearing in a thrust direction.

  The following techniques are known for fluid dynamic bearing devices. For example, Patent Document 1 describes a structure (straight seal structure) of a fluid dynamic pressure bearing that has been reduced in size and reduced in thickness and improved in reliability of prevention of splashing of lubricant oil against impact and vibration applied when the rotating shaft is stationary. ing. Patent Document 2 describes a taper seal structure that enhances the external force retention performance of the bearing seal device and enables the bearing oil to be favorably retained.

  Patent Document 3 describes a structure that improves the circulation of the lubricating fluid at startup, reduces torque at startup, and prevents bearing damage. In Patent Document 3, a thrust bearing is disposed at one location in the thrust direction, and when not rotating, the rotor portion is supported by a stopper portion having a stopper surface provided on the upper stage side of the fixed shaft, and the dynamic pressure on the lower stage side is supported. The thrust fluid bearing in which the groove is formed describes a structure in which a bearing gap is maintained and the both bearing surfaces are not contacted. In this structure, dynamic pressure is generated in the lower thrust bearing during rotation, and the rotor part is lifted.

  Patent Document 4 describes a structure that suppresses inconvenience that the action of the dynamic pressure groove is hindered due to an error in machining accuracy. Patent Document 5 describes a structure for enabling easy and reliable filling of a bearing fluid with a lubricating fluid. Patent Document 6 describes a structure in which a stepped shape is formed in a taper seal part for the purpose of ensuring a structure in which the filling level of a lubricating fluid can be reliably confirmed by visual observation or the like. Patent Document 7 describes that on the thrust bearing surface, a bearing structure (dynamic pressure groove) may be formed in a range extending from the bearing hole to the outer end of the bearing sleeve. Patent Document 8 describes a configuration in which two thrust bearings are disposed and the bearing force due to the dynamic pressure generated in these thrust bearings is in the opposite direction.

JP 2005-351473 A Japanese Patent No. 2937833 JP 2010-281403 A JP 2009-222167 A JP 2010-121775 A German patent application DE 102007036790A1 German Patent Application Publication No. DE102009031219A1 DE Patent Application Publication No. DE102008062524A1

  The fluid dynamic pressure bearing device is used as a bearing of a spindle motor of a hard disk device, for example. Hard disk devices are required to have a structure that can suppress the torque at startup as much as possible from the viewpoints of low power consumption, improved durability, and startup speed. Patent Document 3 describes a configuration aimed at satisfying this requirement, but the resistance torque at the contact portion at the time of start-up is dry friction with no lubricating oil, so there is a limit to reducing the resistance torque. The function is not sufficient when further lower starting torque is required. In addition, various types of portable information devices are required to have resistance to impacts and vibrations, but in connection therewith, fluid dynamic bearing devices having high rigidity that can withstand impacts and vibrations are required. Further, it is also required that the lubricating fluid does not leak from the tapered seal portion of the fluid dynamic bearing device even when subjected to vibration or impact. However, in the structure described in Patent Document 8, two thrust bearings are configured in the axial direction. However, since the two bearings in the thrust direction are opposite in force direction due to dynamic pressure during rotation, On the contrary, the load capacity is lower than that of a single bearing, and the durability against the impact applied in the thrust direction described above is not improved. In such a background, the present invention can suppress the torque at the time of start-up, and has a highly resistant fluid dynamic bearing device capable of withstanding the impact and vibration applied in the thrust direction, and also suppresses the amplitude in response to the impact. It is an object of the present invention to obtain a fluid dynamic bearing device that prevents leakage of lubricating fluid from the taper seal portion.

  The invention described in claim 1 includes a shaft, a hub integrated with the shaft, a sleeve that holds the shaft in a rotatable state inside, and a top surface that faces the bottom surface of the hub. A counter plate that can contact a lower end surface, and at least one radial bearing portion that supports a load in a radial direction is configured between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve, and the upper surface of the sleeve And a first thrust bearing portion for supporting a load in the thrust direction is formed between the upper surface of the hub and the lower surface of the shaft. 2 thrust bearing portions are configured, and when the shaft is not rotating, the slits in the first thrust bearing portion are The upper surface of the hub and the lower surface of the hub are not in contact with each other, and a gap is formed, and the upper surface of the counter plate and the lower end surface of the shaft in the second thrust bearing portion are in contact with each other. The fluid dynamic pressure bearing device includes a fluid dynamic pressure bearing device that is continuously filled with a lubricating fluid, and when the shaft rotates, the clearance in the first thrust bearing portion is filled. The fluid dynamic pressure bearing device is characterized in that dynamic pressure is generated by the lubricating fluid, and the shaft floats from the counter plate.

  According to the first aspect of the present invention, when the shaft is not rotating, the first thrust bearing portion between the upper surface of the sleeve and the lower surface of the hub is not in contact with the second thrust bearing portion. The upper surface of the plate and the lower end surface of the shaft come into contact with each other to support the shaft. When the shaft starts to rotate, the hub receives a force that causes the hub to float with respect to the sleeve due to the dynamic pressure of the lubricating fluid in the gap between the first thrust bearing portions, and the shaft floats from the counter plate. Here, since the first thrust bearing portion is non-contact at the time of non-rotation, even if the area of the first thrust bearing is increased in order to effectively generate dynamic pressure, the contact resistance at the start of rotation Does not increase. On the other hand, since the contact area between the upper surface of the counter plate and the lower end surface of the shaft can be made relatively small, the turning radius becomes relatively small, and the contact resistance torque at the start of rotation can be made small. For this reason, compared with the conventional technique in which both bearing surfaces of the first thrust bearing portion are in contact with each other at the time of non-rotation, the torque at the time of starting is greatly suppressed.

  Since the load in the thrust direction is supported by the first thrust bearing portion and the second thrust bearing portion, the bearing rigidity in the thrust direction is higher than that in the case of one thrust bearing portion. Thereby, the response amplitude of the shaft when the fluid dynamic bearing device is subjected to an impact or the like is suppressed. In particular, even when the facing surface is in contact with the second thrust bearing portion, the first thrust bearing portion is in a state in which the facing surface is not in contact with the gap, so that the shaft is pushed in by an impact. At this time, the bearing action of the first thrust bearing portion is not lost, and the first thrust bearing portion does not come into contact, so that the problem that the bearing surface of the first thrust bearing portion is damaged does not occur.

  Further, even if the shaft is pushed in and the opposing surface of the second thrust bearing portion comes into contact, the contact resistance torque at that portion is relatively small as described above, and therefore the rotation of the shaft tends to be rapidly inhibited. It is small and is unlikely to cause inconveniences such as a sudden decrease in rotational speed. Further, even if the shaft is pushed in and the opposing surfaces of the second thrust bearing portion come into contact with each other, the first thrust bearing portion having a relatively large circumferential speed has a clearance, so that the dynamic pressure there Can be expected. This serves to maintain the bearing function in the thrust direction due to fluid dynamic pressure. In other words, even if the shaft receives an impact in the thrust direction and contact between the opposing surfaces of the second thrust bearing portion occurs, the function as the fluid dynamic bearing device is unlikely to be lost.

According to a second aspect of the present invention, in the first aspect of the present invention, the distance from the upper surface of the counter plate in the axial direction of the shaft to the upper surface of the sleeve constituting the first thrust bearing portion is L. _first and then, the distance to the lower surface of the hub constituting the first thrust bearing portion from the lower end surface of the shaft in the axial direction of the shaft when the L _2, L 1 _<relation L ₂ is satisfied It is characterized by doing.

  According to the second aspect of the present invention, there is provided a structure in which the upper surface of the counter plate contacts the lower end surface of the shaft when the shaft is not rotating, and a gap is formed between the upper surface of the sleeve and the lower surface of the hub in this state. can get.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the first and second thrust bearing portions are provided with dynamic pressure grooves, and the second thrust bearing portion. The depth of the dynamic pressure groove in the first thrust bearing portion is deeper than that in the dynamic pressure groove.

  The maximum bearing rigidity is obtained when the depth of the dynamic pressure groove is about 1.5 times the bearing clearance. On the other hand, the bearing rigidity decreases as it increases or decreases from about 1.5 times. According to the third aspect of the present invention, the depth of the dynamic pressure groove in the first thrust bearing portion in which the bearing gap is relatively large is made relatively deep, and the second thrust bearing in which the bearing gap is relatively small. By making the depth of the dynamic pressure groove in the portion relatively small, both the first and second thrust bearing portions can have high rigidity. Further, when the lower end surface of the shaft approaches the upper surface of the count plate due to impact or vibration, the rigidity of the second thrust bearing portion having the shallow dynamic pressure groove works effectively, which is advantageous in reducing the response amplitude.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the upper surface of the sleeve and the lower surface of the hub of the first thrust bearing portion are opposed to each other. In comparison, the second thrust bearing portion has a small contactable area between the upper surface of the counter plate and the lower end surface of the shaft.

  According to the invention described in claim 4, the friction torque generated at the time of starting can be suppressed as compared with the case where the area size relationship is reversed from that of the structure described in claim 4. According to the fourth aspect of the present invention, the bearing capacity in the thrust direction is more likely to be the first thrust bearing portion and the second thrust bearing portion to be the slave. As a result, it is possible to obtain a performance in which the thrust dynamic fluid dynamic bearing function is not easily lowered when the shaft contacts the counter plate due to the impact in the thrust direction.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein when viewed from the axial direction of the shaft, the outer diameter of the bearing of the second thrust bearing portion is the first. It is characterized by being smaller than the bearing outer diameter of one thrust bearing part.

  According to the fifth aspect of the present invention, the contact area of the second thrust bearing portion can be made smaller, and the radius of the second thrust bearing is smaller than the radius of the first thrust bearing. Friction torque in the thrust bearing portion 2 can be greatly suppressed.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein the hub has an inner peripheral surface facing the outer peripheral surface of the sleeve with a gap in a radial direction. A taper seal portion for preventing leakage of the lubricating fluid is provided in the radial clearance formed between the outer peripheral surface of the sleeve and the inner peripheral surface of the hub, and the taper seal portion Has a taper cross-sectional shape in which the radial gap gradually expands along the leakage direction of the lubricating fluid in the axial direction, and the taper cross-sectional shape is along the direction of leakage of the lubricating fluid, A structure having a first inclination angle portion and a second inclination angle portion having an inclination angle smaller than the first inclination angle following the first inclination angle portion. And

  According to the sixth aspect of the present invention, in the relatively large first inclination angle portion, the radial radial minimum gap is made as small as possible, and the second gap having a relatively large gap in a short distance in the axial direction. Can be obtained. As a result, the moving speed and amplitude of the lubricating fluid are absorbed in the portion of the second inclination angle having a large gap, and at the same time, the level of the lubricating fluid is maintained by the surface tension at the relatively small second inclination angle of this portion. By combining these two functions, a function of suppressing the leakage of the lubricating fluid can be obtained.

  According to a seventh aspect of the present invention, in the sixth aspect of the present invention, when the fluid dynamic pressure bearing device rotates normally, the liquid level of the lubricating fluid is located at the portion of the second inclination angle. It is characterized by.

  According to the seventh aspect of the present invention, since the liquid level of the lubricating fluid is located at a portion where the function of maintaining the liquid level by surface tension is obtained, the fluid dynamic bearing device rotates stably in a steady state. Thus, the sealing effect of the lubricating fluid can be effectively obtained. Since the width of the seal gap is limited, the volume of the first inclination angle portion cannot be increased so much. If the liquid level is located at the first inclination angle portion, the shaft vibrates in the vertical direction when the fluid dynamic bearing device receives an impact or the like, and the volume at the first inclination angle portion If the amount of movement of the lubricating fluid cannot be absorbed, the liquid level may reach the position of the first thrust bearing portion. In addition, even if there is room in the volume of the first inclination angle portion, the liquid level approaches the second inclination angle portion. Since the first tilt angle is relatively large, the effect of maintaining the liquid level due to surface tension is small compared to the portion of the second tilt angle, and the lubrication fluid in a steady state is rotating stably. The sealing effect is weaker than when the invention according to claim 7 is adopted.

  The invention according to claim 8 is the invention according to claim 6 or 7, wherein the tapered cross-sectional shape has an inclination larger than the second inclination angle, which continues from a terminal point of the second inclination angle portion. A third inclination angle portion having an angle; and a fourth inclination angle portion having an inclination angle smaller than the third inclination angle following the third inclination angle portion. And

  According to the eighth aspect of the present invention, when the fluid dynamic pressure bearing device receives an impact or the like and the lubricating fluid moves downward in the axial direction, the portion having the third large inclination angle is more effectively made of the lubricating fluid. It functions to absorb moving speed and amplitude. Further, when the fluid dynamic pressure bearing device receives vibration and the lubricating fluid moves upward in the axial direction from the position of the liquid level in the steady state, the second small inclination angle portion more effectively moves the lubricating fluid. And absorb amplitude. Then, the lubricating fluid exceeding the third tilt angle portion is sealed with a large surface tension without excessively increasing the seal gap of the fourth tilt angle portion having the small tilt angle. As a result, the sealing function that combines the inclination angle portion having the function of absorbing the moving speed and amplitude of the lubricating fluid and the inclination angle portion having the function of maintaining the liquid level of the lubricating fluid by surface tension in two stages. Arranged and a more thorough sealing function can be obtained. Further, when rotating stably in a steady state, the level of the lubricating fluid is located near the third inclination angle portion below the second inclination angle portion (see FIG. 4). .

  The invention according to claim 9 is the invention according to any one of claims 6 to 8, wherein the inner peripheral surface of the hub and the outer peripheral surface of the sleeve in the vicinity of the terminal position inside the tapered seal portion. An oil repellent agent that repels the lubricating fluid is applied to at least one of the above.

  According to the ninth aspect of the present invention, the inclination of the lubricating fluid level relative to the rotation axis due to the eccentricity of the shaft relative to the bearing can be suppressed by the action of the oil repellent to repel the lubricating fluid. Thereby, the amplitude of the lubricating fluid level due to the impact is suppressed, and the moving speed of the lubricating fluid is suppressed, so that a sealing function can be achieved.

  A tenth aspect of the present invention is the fluid dynamic pressure bearing device according to any one of the first to ninth aspects, a base plate to which the sleeve is fixed, and a rotor magnet disposed on the outer peripheral side of the hub. A spindle motor comprising: an electromagnet fixed to the base plate and disposed with a gap from the rotor magnet.

  According to the tenth aspect of the present invention, there is provided a spindle motor including a fluid dynamic bearing device having the advantages of the first aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the fluid dynamic pressure bearing apparatus which can suppress the torque at the time of starting, and has the high tolerance which resists the impact added to a thrust direction, and has a seal structure which resists an impact can be obtained.

It is sectional drawing of the fluid dynamic pressure bearing apparatus of embodiment. It is a top view of the sleeve in an embodiment. It is a bottom view of the shaft in an embodiment. It is sectional drawing of the seal part in embodiment. It is sectional drawing of the spindle motor of embodiment. It is sectional drawing of the other aspect of a seal | sticker part. It is sectional drawing of the other aspect of a seal | sticker part. It is sectional drawing which shows the other example of the shape of a shaft bottom face. It is sectional drawing which shows the other example of the shape of a shaft bottom face.

(Constitution)
FIG. 1 is a cross-sectional view of the fluid dynamic bearing device according to the embodiment. FIG. 1 shows a fluid dynamic bearing device 100. The fluid dynamic bearing device 100 is a device that supports a shaft 102 and a hub 101 serving as a rotor in a rotatable state. The fluid dynamic bearing device 100 includes a shaft 102, a hub 101, a sleeve 103 that faces the lower surface of the hub 101, and a counter plate 104 that can come into contact with the lower end surface of the shaft 102. The radial bearing portion 113 is between the inner peripheral surface of 103 and the first thrust bearing portion 110 is between the upper surface of the sleeve 103 and the lower surface of the hub 101, and the upper surface of the counter plate 104 and the lower end surface of the shaft 102. A second thrust bearing portion 111 is formed therebetween.

  The hub 101 is fixed to the shaft 102 and integrated with the shaft 102. The shaft 102 has a substantially cylindrical shape, and is held in a state where it can be freely rotated around the rotation shaft 102b inside the sleeve 103, which is a substantially cylindrical member. The sleeve 103 is a member on the stator side, and is fixed to a base plate 201 serving as a base. In this structure, the hub 101 and the shaft 102 integrated with each other rotate with respect to the sleeve 103 and the counter plate 104.

  There is a slight gap between the outer peripheral surface of the shaft 102 and the inner peripheral surface of the sleeve 103, which is filled with a lubricating fluid. In this portion, a herringbone type dynamic pressure groove 103c, which is a dynamic pressure generating means, is provided on the inner peripheral surface of the sleeve 103 facing the outer peripheral surface of the shaft 102. A radial bearing portion 113 that supports a radial load acting on the shaft 102 by a portion in which the inner peripheral surface of the sleeve 103 provided with the dynamic pressure groove 103c and the outer peripheral surface of the shaft 102 face each other with a gap therebetween. Is configured.

  The lower end surface of the shaft 102 is a flat bottom surface, and this bottom surface is in contact with the upper surface of the counter plate 104 having a flat structure when the shaft 102 is not rotating. The counter plate 104 is a member that supports the shaft 102 in the thrust direction, and is fixed to the sleeve 103 so as to be fitted into the sleeve 103.

When the shaft 102 is not rotating, the upper surface of the sleeve 103 does not contact the lower surface of the hub 101, and a slight gap 105 (for example, 2 to 3 μm) exists between the upper surface of the sleeve 103 and the lower surface of the hub 101. ) Is secured. That is, when the distance from the top surface of counter plate 104 to the upper surface of the sleeve 103 and _{L 1,} the distance from the lower end surface of the shaft 102 to the surface facing the upper surface of the sleeve 103 of the hub 101 and _{L 2, L 2> L} The dimension of each part is adjusted so that it may become ₁ relationship. The gap 105 is filled with a lubricating fluid 109.

  FIG. 2 is a top view of the sleeve 103 as viewed from above in FIG. On the upper surface of the sleeve 103 (the surface facing the lower surface of the hub 101), a spiral dynamic pressure groove 103a as a dynamic pressure generating means is formed. The dynamic pressure groove 103 a is formed up to the edge of the upper surface of the sleeve 103. A hollow portion 107 in which the shaft 102 is accommodated is provided at the center of the sleeve 103. In addition, openings of communication holes 106 also shown in FIG. 1 are formed at substantially equiangular positions when viewed from three axial directions on the upper surface of the sleeve 103. In order to make the dynamic pressure uniform, the relative positions of the openings of the three communication holes 106 with the dynamic pressure grooves are set to be substantially the same. In this example, the number of communication holes 106 is three, but the number is not limited to three.

  The upper surface of the sleeve 103 provided with the dynamic pressure groove 103a and the lower surface of the hub 101 opposed to the sleeve 103 constitute a first thrust bearing portion 110 that receives the shaft 102 and the load in the thrust direction applied to the hub 101. Yes.

  A communication hole 106 is provided in the sleeve 103. The upper part of the communication hole 106 is connected to the gap 105 of the first thrust bearing part 110, and the lower part of the communication hole 106 is connected to the vicinity of the end of the part where the upper surface of the counter plate 104 and the lower end surface of the shaft 102 face each other. Yes. Further, this portion is connected to the gap of the radial bearing portion 113. When the shaft 102 rotates, the hub 101 and the shaft 102, which serve as the rotor, are levitated by the support of the first thrust bearing portion 110 and the second thrust bearing portion 111, and between the upper surface of the counter plate 104 and the lower end surface of the shaft 102 A gap is formed. This gap is connected to the gap 105 through the communication hole 106. When the fluid dynamic pressure bearing device rotates, the flow from the first thrust bearing portion 110 to the radial bearing portion is caused by the strong pumping force of the first thrust bearing portion 110 and the pressure difference below the radial bearing portion 113. It circulates back to the outside of the first thrust bearing part 110 through the communication hole 106 from the lower side of the radial bearing part 113 to the 113.

  As described above, the lower end surface of the shaft 102 is in contact with the upper surface of the counter plate 104 when the shaft 102 does not rotate. The counter plate 104 is fitted into the lower portion of the sleeve 103 and is integrated with the sleeve 103. A dynamic pressure groove 102a is formed on the lower end surface of the shaft 102 facing the upper surface of the counter plate 104, and a DLC film (diamond-like carbon film) is formed on this surface and subjected to wear resistance treatment. Other methods such as a Teflon (registered trademark) coating treatment can be used for the abrasion resistance treatment. On the other hand, since both opposing surfaces of the first thrust bearing portion do not contact, the upper surface of the sleeve 103 in which the dynamic pressure groove 103a is formed does not require wear resistance treatment such as DLC. FIG. 3 shows a state where the shaft 102 is viewed from below (counter plate 104 side) in FIG. FIG. 3 shows a spiral-shaped dynamic pressure groove 102 a which is a dynamic pressure generating means provided on the lower end surface of the shaft 102.

  The upper surface of the counter plate 104 and the lower end surface of the shaft 102 provided with the dynamic pressure groove 102a constitute a second thrust bearing portion 111 that receives a load in the thrust direction applied to the hub 101 and the shaft 102. Further, the end portion of the shaft 102 is constituted by a flange shape protruding in the radial direction, and the flange portion 102c having this flange shape faces the step portion 103b of the sleeve 103, thereby functioning as a retaining member for the shaft 102. ing. The dynamic pressure groove 102a is formed up to the edge of the flange portion 102c. Further, a gap 114 is formed in a portion of a difference in diameter between the side peripheral surface of the flange portion 102 c and the inner peripheral surface of the sleeve 103. Then, the stepped portion 116 in which the flange portion 102 c as a function of preventing the shaft 102 from coming off projects from the bearing surface of the radial bearing portion of the sleeve 103 in the radial direction is set to be as small as possible.

  The depth of the dynamic pressure groove 102a is set to a smaller value than the depth of the dynamic pressure groove 103a. Further, the dimension is set so that the bearing area of the first thrust bearing 110 when viewed from the axial direction is larger than the bearing area of the second thrust bearing. By doing so, the dynamic pressure generated in the first thrust bearing portion 110 can be made to act larger, and the dynamic pressure generated in the second thrust bearing portion 111 can be made to act relatively small. The fluid dynamic pressure bearing function in the bearing portion 110 is mainly used, and the fluid dynamic pressure bearing function in the second thrust bearing portion 111 is subordinate.

  In the bearing structure shown in FIG. 1, the first thrust bearing portion 110 and the second thrust bearing portion 111 are separated from each other in the axial direction, and a radial bearing portion 113 that supports a radial load is formed therebetween. . Further, a hub 101 that is a relative heavy object is attached above the first thrust bearing portion 110. Therefore, in the first thrust bearing portion 110, the second thrust bearing portion 111 mainly receives a load in the thrust direction, and the first thrust bearing portion 110 supplementarily receives the load in the thrust direction. The main structure that mainly receives the load in the thrust direction and supplementarily receives the load in the thrust direction at the second thrust bearing portion 111 is more stable as a structure that holds the shaft 102 in a rotatable state. It is done.

  The lubricating fluid filled in the gap inside the fluid dynamic bearing device of FIG. 1 is prevented from leaking by the taper seal portion 108. Hereinafter, the taper seal portion 108 will be described. FIG. 4 is a cross-sectional view of the taper seal portion 108. In FIG. 4, the state of the inclination angle is exaggerated.

The taper seal portion 108 has a cross-sectional structure that opens downward. Speaking in more detail, a tapered seal portion 108, alpha ₁ of inclination downward in the open tapered portion 108a, beta ₁ of inclination downward in the open tapered portion 108b, alpha ₂ at the inclination angle tapered portion 108c opened downward, and a tapered portion 108d opened downward at an inclination angle of beta _2. Here, the inclination angles are set such that α ₁ > β ₁ , α ₂ > β ₂ , α ₁ > α ₂ , β ₁ = β ₂ are satisfied. Note that the present invention is not limited to this, and other settings are possible.

Here, the inclination angles indicated by α ₁ , α ₂ , β ₁ , and β ₂ are angles formed between the inner peripheral surface 101 a of the hub 101 facing the outer peripheral surface of the sleeve 103 and the outer peripheral surface of the sleeve 103. is there. The inner peripheral surface 101a may be parallel to the axial direction, but has a structure that has an inclination approaching the sleeve 103 as it goes downward. This is to obtain an effect of driving the lubricating fluid upward as much as possible by the centrifugal force when the hub 101 rotates.

  The taper part 108a and the taper part 108b constitute a first stage taper seal part, and the taper part 108c and the taper part 108d constitute a second stage taper seal part. That is, the taper seal portion 108 has a two-stage configuration. Then, when there is no movement of the lubricating fluid 109 due to an impact or the like, the position of the liquid surface 109a is set to be near the lower portion of the tapered portion 108b as shown in FIG. The bearing device can rotate stably in a steady state.

Hereinafter, the function of the taper seal portion 108 will be described. For example, it is assumed that the lubricating fluid 109 is moved due to an impact or the like, and the position of the liquid surface 109a of the lubricating fluid 109 shown in FIG. At this time, the sudden volume change of the lubricating fluid is first absorbed by the relatively large tapered portion 108c. By absorbing this sudden volume change, the moving speed and amplitude of the lubricating fluid are suppressed. That is, the moving speed and amplitude of the liquid surface 109a can be suppressed. On the other hand, the large angle of inclination alpha _1, it is possible to obtain a relatively large gap at short distance axially. Also, the smaller inclination angle beta _1, when the lubricating flow fluid surface 109a vibrates upward by vibration, the sealing gap is not suddenly reduced, the moving speed and the amplitude is suppressed. That is, the width of the rapid vertical movement of the liquid level 109a is suppressed. Even if the liquid surface 109a reaches the tapered portion 108d beyond the tapered portion 108c, the surface tension acts on the relatively small tapered portion 108d, so that the liquid surface 109a is moved upwardly from the original upper surface. The action of returning to the position works. This is the sealing effect by the combination of the tapered portions 108a and 108b and the tapered portions 108c and 108d.

  Here, a two-stage configuration in which a first-stage taper seal portion including the taper portion 108a and the taper portion 108b and a second-stage taper seal portion including the taper portion 108c and the taper portion 108d are described as an example. However, a configuration in which a third-stage tapered seal portion having a similar structure is arranged, and a multi-stage structure in which a similar fourth-stage taper seal portion is arranged are also possible.

Also, so as short as possible the distance between the position x ₂ of the inner circumferential surface of the position x ₁ and the hub 101 of the end portion of the bearing surface of the first thrust bearing portion 110 of the sleeve 103 upper surface. For example, the bearing surface of the first thrust bearing portion 110 formed to the upper surface of the edge of the sleeve 103, by increasing the inclination angle alpha _1, it is possible to obtain a relatively large seal gap at a short distance axially together, it is possible to minimize the distance between the x ₁ and x _2, it can be reduced the amount of movement of the lubricating fluid by volume change of the fluid dynamic bearing device internal clearance due to vibration of the shaft 102. By reducing the moving amount of the lubricating fluid, the moving speed and amplitude of the lubricating fluid level in the tapered seal portion are suppressed, and leakage of the lubricating fluid from the tapered seal portion can be prevented.

  Similarly, the flange portion 102c of the shaft 102 is set so that the portion 116 protruding in the radial direction from the radial bearing surface of the sleeve is as small as possible due to the volume change of the clearance in the fluid dynamic bearing device due to the vibration of the shaft. The amount of movement of the lubricating fluid can be reduced. By reducing the amount of fluid movement, the moving speed and amplitude of the fluid level in the seal can be suppressed, and leakage of the lubricating fluid from the taper seal can be prevented.

  In addition, the lubricating fluid 109 is repelled (repels) on a portion indicated by reference numeral 115 on the outer peripheral surface of the sleeve 103 and the inner peripheral surface 101a facing the outer peripheral surface of the sleeve 103 of the hub 101 near the terminal end in the taper seal portion 108. ) Property oil repellent (Barrier film) is applied. The oil repellent applied to the reference numeral 115 has the following functions. That is, when the shaft 102 is eccentric with respect to the sleeve 103, an inclination of the liquid surface 109a of the lubricating fluid 109 of the taper seal portion 108 with respect to the rotation axis occurs. When a part of the inclined liquid surface exceeds the tapered portion 108c of the taper seal portion 108, the lubricating fluid 109 is repelled in the portion 115, so that the inclination of the liquid surface is suppressed.

(Bearing function)
When not rotating, the hub 101 and the shaft 102 integrated with the hub 101 are supported by the upper surface of the counter plate 104 being in contact with the lower end surface of the shaft 102. At this time, since the gap 105 is formed, the lubricating fluid 109 exists in the gap 105, and the upper surface of the sleeve 103 and the lower surface of the hub 101 facing the sleeve 103 are not in contact with each other.

  When the hub 101 starts to rotate, at the same time, the shaft 102 starts to rotate with the lower end surface of the shaft 102 in contact with the upper surface of the counter plate 104. When the rotation speed increases, the dynamic pressure by the lubricating fluid 109 existing in the gap 105 is generated in the first thrust bearing portion 110 by the action of the dynamic pressure groove 103 a, and the hub 101 is lifted from the sleeve 103. At this time, the hub 101 further floats from the stationary state with respect to the sleeve 103. When the hub 101 is lifted, the lower end surface of the shaft 102 is separated from the counter plate 104, and the lubricating fluid 109 enters the gap formed there. As a result, due to the action of the dynamic pressure groove 102 a shown in FIG. 3, a force due to dynamic pressure that lifts the shaft 102 away from the counter plate 104 is generated in the second thrust bearing portion 111. At this time, the lubricating fluid 109 is supplied to the gap between the upper surface of the counter plate 104 and the lower end surface of the shaft 102 by the circulating flow of the lubricating fluid 109 performed through the communication hole 106.

  Thus, due to the dynamic pressure generated in the first thrust bearing portion 110 and the second thrust bearing portion 111, the shaft 102 and the hub 101 are lifted with respect to the sleeve 103 and the counter plate 104, which are the stators, and the load in the thrust direction is increased. The thrust dynamic pressure bearing functions so as to be supported by dynamic pressure. Further, the dynamic pressure groove 103c on the inner peripheral surface of the sleeve 103 causes dynamic pressure to be generated in the gap between the outer peripheral surface of the shaft 102 and the inner peripheral surface of the sleeve 103, so that a radial load is supported by the dynamic pressure. The radial dynamic pressure bearing functions.

(Spindle motor)
Hereinafter, an example of a spindle motor using the fluid dynamic bearing device of FIG. 1 will be described. FIG. 5 shows a cross-sectional structure of the spindle motor 200 of the embodiment. The spindle motor 200 has a structure in which a hub 101 is rotatably held by a fluid dynamic bearing device 100 shown in FIG. The spindle motor 200 includes a base plate 201 that is a base member on the stator side. A sleeve 103 is fitted and fixed to the base plate 201.

  A stator structure 203 in which a stator coil is wound around a stator core is fixed to the base plate 201. The stator structure 203 is an electromagnet that generates magnetic flux in the direction of a rotor magnet 207, which will be described later, and constitutes a magnetic pole on the stator side. The number of stator structures 203 such as four poles or six poles is arranged along the circumferential direction around the rotation axis 102b of the shaft 102. Note that the left and right sides of the figure are asymmetric and the cross-sectional state of the drawing of the stator structure 203 is different because different cross-sections are shown.

  An end portion of the winding of the stator coil of the stator structure 203 is drawn from the wiring lead portion 205 and connected to the flexible printed circuit board 206. The flexible printed circuit board 206 is drawn out to the outside, and wiring from a drive circuit (not shown) is connected to the portion drawn out to the outside.

  A rotor magnet 207, which is a magnetic pole on the rotor side, is disposed outside the stator structure 203 with a gap therebetween. The rotor magnet 207 extends to the outer peripheral side of the hub 101 and is fixed to the inner side of the outer peripheral side annular portion 101b having a width in the axial direction. Further, a magnet 208 for suppressing the vertical swing of the hub 101 in the axial direction is disposed on the base plate 201 at a position separated by a gap below the rotor magnet 207.

  For example, in the case of a hard disk device, a disk unit having a magnetic recording surface is fixed to the upper part of the hub 101. Then, a drive current is passed through the stator coil of the stator structure 203, and when it is switched at an appropriate timing, the direction of the magnetic flux generated by the stator structure 203, which is the magnetic pole on the stator side, is switched regularly. The magnetic attractive force and the magnetic repulsive force generated between the structure 203 and the rotor magnet 207 are regularly switched, and the hub 101 and the shaft 102 integrated with the hub 101 rotate. This principle is the same as that of a normal DC brushless motor. During this rotation, the hub 101 and the shaft 102 are supported by the bearing function of the fluid dynamic bearing device 100, and smooth rotation of the hub 101 and the shaft 102 is ensured.

(Superiority)
When the shaft 102 is not rotating, the lower end surface of the shaft 102 is in contact with the upper surface of the counter plate 104, and the upper surface of the sleeve 103 is not in contact with the lower surface of the hub 101, so that a gap 105 is secured. According to this structure, the torque at the time of starting can be suppressed, and the resistance to withstand an impact applied in the thrust direction can be increased.

  First, the superiority that can suppress the starting torque will be described. According to the above structure, the resistance generated in the situation where the rotation starts from the non-rotation time is mainly the frictional resistance between the upper surface of the counter plate 104 and the lower end surface of the shaft 102. Here, the bearing outer diameter of the second thrust bearing portion 111 is inside the bearing outer diameter of the first thrust bearing portion 110, and the bearing area of the second thrust bearing portion 111 is relatively smaller, Since the radius of the bearing is also relatively small, the resistance torque received at the start-up is higher than that in the case where the upper surface of the sleeve 103 and the lower surface of the hub 101 are in contact with each other in the first thrust bearing portion 110 when not rotating. Significantly smaller. The first thrust bearing portion 110 is far from the center of rotation and has a relatively high circumferential speed during rotation. However, since the physical contact is not performed here, the wear of the dynamic pressure groove 103a is reduced. It can be suppressed. Further, since the gap 105 is ensured at the time of starting and the lubricating fluid 109 is filled therewith, the circulation of the lubricating fluid 109 is quickly formed after the rotation is started, and the bearing is quickly and stable. In particular, since the first thrust bearing portion 110 is far from the center of rotation, the circumferential speed during rotation is relatively large, and the bearing area of the first thrust bearing portion 110 is relatively large, Dynamic pressure is generated more effectively and quickly. This also contributes to a reduction in starting torque. In addition, it is effective in that stable rotation can be obtained quickly.

  Next, the superiority that can withstand the impact applied in the thrust direction can be increased. According to the above structure, the first thrust bearing portion 110 between the upper surface of the sleeve 103 and the lower surface of the hub 101, and the second thrust bearing portion between the upper surface of the counter plate 104 and the lower end surface of the shaft 102. A thrust load is supported by two thrust bearings 111. According to this structure, in the first thrust bearing portion 110, a large area of the thrust bearing is ensured, so that the bearing rigidity is increased and the ability to withstand an impact applied in the thrust direction is enhanced.

  Further, when the shaft 102 is pushed downward due to some factor during rotation, the lower surface of the shaft 102 may come into contact with the upper surface of the counter plate 104, but the lower surface of the hub 101 contacts the upper surface of the sleeve 103. Never do. For this reason, the lower surface of the hub 101, which is a portion having a higher circumferential speed, contacts the upper surface of the sleeve 103, and the dynamic pressure groove 103a (see FIG. 2) provided on the sleeve 103 side is prevented from being damaged. Although there is a possibility that the dynamic pressure groove 102a (see FIG. 3) may be damaged due to contact between the upper surface of the counter plate 104 and the lower end surface of the shaft 102, this portion is a portion close to the rotation axis of the shaft 102. Since the circumferential speed is relatively small, the possibility is small as compared with the damage caused by the contact of the portion of the dynamic pressure groove 103a. In this respect as well, resistance to impact in the thrust direction is increased.

  When the dynamic pressure groove 102 a is provided on the lower end surface of the shaft 102, it is necessary to subject the lower end surface of the shaft 102 to wear resistance treatment by forming a DLC film. On the other hand, in the first thrust bearing portion 110, the upper surface of the sleeve 103 and the lower surface of the hub 101 are not in contact with each other, so that the upper surface of the sleeve 103 in which the dynamic pressure grooves are formed does not require wear resistance treatment such as DLC. As a result, the wear resistance treatment does not increase the number of steps and does not increase the manufacturing cost.

  A taper seal portion 108 is provided in which a structure constituted by two inclination angles is arranged in two stages. Accordingly, even if a force that ejects from the portion in which the lubricating fluid is sealed is applied for some reason, it can be suppressed. That is, a sudden volume change of the lubricating fluid is absorbed at a large inclination angle, and the moving speed and amplitude of the liquid surface of the lubricating fluid are suppressed. And at the small inclination angle, the function of maintaining the position of the liquid surface by the surface tension works. By doing so, the length of the taper seal can be suppressed while ensuring the sealing characteristics.

  By providing the communication hole 106, the lubricating fluid is circulated inside the fluid dynamic pressure bearing device, and the first thrust bearing portion 110 and the second thrust bearing portion provided at different positions in the axial direction are provided. The movement of the lubricating fluid is ensured with respect to 111. For this reason, the lubricating fluid is smoothly moved due to the variation in the gap between the two thrust bearing portions. For this reason, generation | occurrence | production of the negative pressure accompanying the rapid movement to the axial direction of the shaft 102 with respect to the sleeve 103 is suppressed, and generation | occurrence | production of cavitation is suppressed.

  Further, as shown in FIG. 2, the opening of the communication hole 106 is provided in a region where the dynamic pressure groove 103 a in the first thrust bearing portion 110 is provided. By doing so, the function of the communication hole 106 can be ensured while ensuring the effective area contributing to the dynamic pressure generation of the first thrust bearing portion 110, the mass of the hub 101, that is, the rotation, while suppressing the radial dimension. The body mass can be reduced. By reducing the mass of the rotating body, the amplitude when receiving an impact or the like can be reduced, and an effect of suppressing leakage of the taper seal can be obtained.

  Normally, the bearing has a slight eccentricity when it rotates due to the eccentricity of the center of gravity of the rotating object and the influence of the load. The bearing is also eccentric when the spindle motor is subjected to an impact in a horizontal posture. At this time, the lubricating fluid in the taper seal is inclined in the circumferential direction with respect to the rotation axis. In the present embodiment, an oil repellent (Barrier film) is applied in the vicinity of the end position inside the taper seal portion (in the range indicated by reference numeral 115 in FIG. 4), whereby the inclination of the lubricating fluid due to the eccentricity occurs, and the lubricating fluid When the oil reaches the position of the oil repellent, the lubricating fluid is repelled there, so that the inclination of the lubricating fluid is suppressed.

(Modification 1)
FIG. 4 shows a two-stage taper seal composed of a first-stage seal portion constituted by inclination angles α ₁ and β ₁ and a second-stage seal portion constituted by inclination angles α ₂ and β _2. Portion 108 is shown. As a modified example, a taper seal portion having a one-stage structure may be used. Hereinafter, an example of the taper seal portion having the one-stage structure will be described with reference to FIG. FIG. 6 shows a taper seal portion 300. The taper seal portion 300 includes a taper portion 301 having a relatively large inclination angle α and a taper portion 302 having a relatively small inclination angle β. Here, the angular relationship is α> β, and it is preferable that 45 ° ≧ α ≧ 30 ° and 0 ° <β <15 °. In this angular range, the tapered portion 301, it is possible to obtain a relatively large gap at short distance axially, it is possible to make as small as possible distance between x ₁ and x _2, the vibration of the shaft 102 The amount of movement of the lubricating fluid 109 due to the change in the volume of the gap in the fluid dynamic bearing device can be reduced. By reducing the moving amount of the lubricating fluid 109, the moving speed and amplitude of the liquid surface 109a of the lubricating fluid 109 in the taper seal portion can be suppressed. Further, the effect of suppressing the moving speed of the lubricating fluid by absorbing the moving amount of the lubricating fluid 109 through the relatively large gap of the tapered portion 302 and the effect of reducing the amplitude of the lubricating fluid 109 can be obtained. The function of holding the liquid surface 109a of the lubricating fluid 109 using the surface tension is obtained. In order to obtain these effects, when the fluid dynamic bearing device rotates stably in a steady state, the position of the liquid surface 109a of the lubricating fluid 109 may be the middle position of the tapered portion 302. preferable.

(Modification 2)
Another example of the taper seal structure will be described. FIG. 7 shows a taper seal portion 400. The taper seal portion 400 includes a taper portion 401 having a relatively small inclination angle β, a taper portion 402 having a relatively large inclination angle α, and a taper portion 403 having a relatively small inclination angle β. The first-stage seal portion is constituted by a second-stage seal portion constituted by a tapered portion 404 having a relatively large inclination angle α and a tapered portion 405 having a relatively small inclination angle β.

  The inclination angle of the tapered portions 402 and 404 is preferably 30 ° or less. When the fluid dynamic bearing device rotates stably in a steady state, the position of the liquid surface 109a of the lubricating fluid 109 is that of the taper portion 401 having a relatively small inclination angle β starting from the upper end portion of the hub 101. A lower position is preferred. By doing in this way, the taper parts 402 and 404 can obtain the effect of suppressing the moving speed of the lubricating fluid 109 and the effect of reducing the amplitude of the lubricating fluid by absorbing the moving amount of the lubricating fluid. In particular, the movement of the liquid surface 109a can be effectively suppressed by arranging the tapered portions in two stages. And since this taper seal part 400 has a staircase structure, there is no significant difference in the radial gap between the start end and the end of the taper seal, so that the taper seal part can be provided in more stages. is there.

(Modification 3)
A structure in which a concave portion is provided on one or both of the upper surface of the counter plate 104 and the lower end surface of the shaft 102 to limit the contact area between the two is also possible. FIG. 8 shows a cross section of a configuration in which a recess is provided on the lower end surface side of the shaft 102. FIG. 8A shows a first example, and FIG. 8B shows a second example. FIG. 8 shows a state in which the shaft 102 is not rotating, and the lower end surface of the shaft 102 is in contact with the upper surface of the counter plate 104.

  In the example of FIG. 8A, a recess 501 is provided at the center of the lower end surface of the shaft 102, and the shaft 102 and the counter plate 104 are prevented from coming into contact with each other at this portion. The example which reduced the contact area with the lower end surface of 102 is shown. FIG. 8B shows an example in which an annular recess 502 is formed at an equal distance from the rotation axis of the shaft 102, thereby reducing the contact area between the lower end surface of the shaft 102 and the upper surface of the counter plate 104. It is shown. FIG. 8 shows an example in which a depression is provided on the shaft 102 side to reduce the contact area between the upper surface of the counter plate 104 and the lower end surface of the shaft 102. The counter plate 104 side or the counter plate 104 side and the shaft 102 are shown. A structure in which depressions are provided on both sides of the lower end surface of the plate is possible. Further, the number of depressions is not limited to one, and can be plural. In this structure as well, it is preferable to provide a dynamic pressure groove on at least one of the upper surface of the counter plate 104 and the lower end surface of the shaft 102 so as to obtain a floating effect by the dynamic pressure.

(Modification 4)
A structure in which one or both of the upper surface of the counter plate 104 and the lower end surface of the shaft 102 is not flat and a gap is partially formed between the upper surface of the counter plate 104 and the lower end surface of the shaft 102 is also possible. FIG. 9A shows a cross-sectional view when the lower end surface of the shaft 102 is a bowl-shaped curved surface 503. FIG. 9B shows a cross-sectional view in the case where the lower end surface of the shaft 102 is a conical surface 504 with a sharpened center tip. According to these structures, since the contact between the upper surface of the counter plate 104 and the lower end surface of the shaft 102 is restricted, the torque at the time of starting can be reduced.

  In the illustration of FIG. 9, the counter plate 104 side has a flat structure, but the cross-sectional structure on the counter plate 104 side may be a curved surface or a conical shape. Also, a structure in which both the counter plate 104 side and the shaft 102 side are non-planar is possible. Also in this structure, it is possible to provide a dynamic pressure groove on at least one of the upper surface of the counter plate 104 and the lower end surface of the shaft 102.

(Other)
A structure in which no dynamic pressure groove is provided in the second thrust bearing portion 111 is also possible. In this case, the load capacity and rigidity of the bearing due to the dynamic pressure in the thrust direction are lower than in the structure of FIG. 1, but the structure is simplified.

  In the example shown in FIGS. 1 and 2, the dynamic pressure groove 103a in the first thrust bearing portion 110 is provided on the sleeve 103 side, and the surface of the facing hub 101 is a flat surface. Further, the dynamic pressure groove 102a of the second thrust bearing portion 111 is formed on the shaft 102 side, and the surface of the counter plate 104 facing the flat surface is a flat surface. Further, in the radial bearing portion 113, the dynamic pressure groove 103 c is provided on the inner peripheral surface of the sleeve 103, and the dynamic pressure groove is not provided on the outer peripheral surface of the opposed shaft 102. However, the formation of the dynamic pressure groove on each bearing surface is not limited to the above combination. For example, the dynamic pressure groove 103a in the first thrust bearing portion 110 may be provided not on the sleeve 103 side but on the surface of the opposing hub 101 side. Further, the dynamic pressure groove 102a of the second thrust bearing 111 may be provided not on the shaft 102 side but on the surface of the counter plate 104 facing the second thrust bearing 111. Further, in the radial bearing portion 113, a structure in which a dynamic pressure groove is provided on the outer peripheral surface of the opposed shaft 102 instead of providing the dynamic pressure groove on the sleeve 103 side is also possible. In addition, the dynamic pressure groove is not limited to only one side of the opposing surface, and a configuration in which the dynamic pressure groove is provided on both of the opposing surfaces is also possible.

  The shape of the dynamic pressure groove in each part is not limited to the exemplified one, and various shapes such as a tapered shape can be used as long as the dynamic pressure can be generated.

  In the case where it is allowed to increase the outer diameter of the sleeve, there is also a configuration in which a flat surface is provided outside the upper surface of the sleeve 103 where the dynamic pressure groove 103a is provided, and an opening on the upper side of the communication hole 106 is positioned there. Is possible.

  The fluid dynamic bearing device using the invention disclosed in this specification can be widely used as a bearing device in various drive sources such as portable information devices and optical disks. In addition, the spindle motor using the invention disclosed in this specification can be used as a drive source for rotating various members in addition to the use of driving a disk in a hard disk device.

  The aspect of the present invention is not limited to the individual embodiments described above, and includes various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the contents described above. That is, various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

  The present invention can be used for a fluid dynamic bearing device and a spindle motor using the fluid dynamic bearing device.

  DESCRIPTION OF SYMBOLS 100 ... Fluid dynamic pressure bearing apparatus, 101 ... Hub, 102 ... Shaft, 102b ... Shaft rotating shaft, 102c ... Flange part, 103 ... Sleeve, 103b ... Step part, 104 ... Counter plate, 105 ... 1st thrust bearing part 106 ... communication hole 107 ... hollow part 108 ... taper seal part 108a, 108b, 108c, 108d ... taper part 109 ... lubricating fluid 109a ... lubricating fluid level 110 ... first thrust bearing , 111 ... second thrust bearing part, 113 ... radial bearing part, 114 ... gap, 115 ... oil repellent application part, 116 ... step part of the flange part of the shaft, 200 ... spindle motor, 201 ... base plate, 203 ... stator Structure 205 ... Wiring lead-out part 206 ... Flexible printed circuit board 207 ... B Tamagnet, 208 ... Magnet, 300 ... Tapered seal portion, 301, 302 ... Tapered portion, 400 ... Tapered seal portion, 401, 402, 403, 404 ... Tapered portion, 501, 502 ... Depression, 503 ... Curved surface, 504 ... Conical surface.

Claims (10)

A shaft,
A hub integrated with the shaft;
A sleeve that holds the shaft in a rotatable state on the inside and has an upper surface facing the lower surface of the hub;
A counter plate capable of contacting the lower end surface of the shaft,
Between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve, at least one radial bearing portion that supports a radial load is configured,
A first thrust bearing portion configured to support a load in a thrust direction is configured between the upper surface of the sleeve and the lower surface of the hub,
Between the upper surface of the counter plate and the lower end surface of the shaft, a second thrust bearing portion that supports a load in the thrust direction is configured,
When the shaft does not rotate, a gap is formed without contacting the upper surface of the sleeve and the lower surface of the hub in the first thrust bearing portion, and in the second thrust bearing portion. A fluid dynamic bearing device having a configuration in which an upper surface of the counter plate and a lower end surface of the shaft are in contact with each other,
The fluid dynamic bearing device is continuously filled with a lubricating fluid,
When the shaft rotates, a dynamic pressure is generated by the lubricating fluid filled in the gap in the first thrust bearing portion, and the shaft floats from the counter plate. . The distance from the upper surface of the counter plate in the axial direction of the shaft to the upper surface of the sleeve constituting the first thrust bearing portion and L _1,
The distance from the lower end surface of the shaft in the axial direction of the shaft to the lower surface of the hub constituting the first thrust bearing portion when the L _2,
The fluid dynamic bearing device according to claim 1, wherein a relationship of L ₁ <L ₂ is established. The first and second thrust bearing portions are provided with dynamic pressure grooves on at least one surface of both bearing surfaces facing each other,
3. The fluid dynamic pressure according to claim 1, wherein a depth of the dynamic pressure groove in the first thrust bearing portion is deeper than that of the dynamic pressure groove in the second thrust bearing portion. Bearing device.   The upper surface of the counter plate and the lower end surface of the shaft in the second thrust bearing portion as compared to the area where the upper surface of the sleeve and the lower surface of the hub face each other in the first thrust bearing portion 4. The fluid dynamic bearing device according to claim 1, wherein an area in contact with the fluid dynamic pressure bearing device is small. 5.   The bearing outer diameter of the second thrust bearing portion is smaller than the bearing outer diameter of the first thrust bearing portion when viewed from the axial direction of the shaft. The fluid dynamic pressure bearing device according to one item. The hub has an inner peripheral surface facing the outer peripheral surface of the sleeve with a radial gap therebetween,
The radial gap formed between the outer peripheral surface of the sleeve and the inner peripheral surface of the hub is provided with a taper seal portion that prevents leakage of the lubricating fluid,
The tapered seal portion has a tapered cross-sectional shape in which the radial gap gradually increases along the axial direction;
The tapered cross-sectional shape has a first inclination angle portion and an inclination angle smaller than the first inclination angle following the first inclination angle portion along the leaking direction of the lubricating fluid. 6. The fluid dynamic bearing device according to claim 1, comprising a structure having a second inclined angle portion.   The fluid dynamic bearing device according to claim 6, wherein when the fluid dynamic bearing device rotates in a steady state, the liquid level of the lubricating fluid is located at the portion of the second inclination angle. .   The tapered cross-sectional shape includes a third inclination angle portion having an inclination angle larger than the second inclination angle, continuing from an end point of the second inclination angle portion, and a portion of the third inclination angle. The fluid dynamic bearing device according to claim 6, further comprising a fourth inclination angle portion having an inclination angle smaller than the third inclination angle, following the third inclination angle.   7. An oil repellent agent that repels the lubricating fluid is applied to at least one of the inner peripheral surface of the hub and the outer peripheral surface of the sleeve in the vicinity of a terminal position inside the tapered seal portion. The fluid dynamic pressure bearing device according to any one of claims 1 to 8. A fluid dynamic bearing device according to any one of claims 1 to 9,
A base plate to which the sleeve is fixed;
A rotor magnet disposed on the outer peripheral side of the hub;
A spindle motor comprising: an electromagnet fixed to the base plate and disposed with a gap from the rotor magnet.

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