US20060002642A1 - Fluid dynamic pressure bearing apparatus - Google Patents
Fluid dynamic pressure bearing apparatus Download PDFInfo
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- US20060002642A1 US20060002642A1 US11/188,161 US18816105A US2006002642A1 US 20060002642 A1 US20060002642 A1 US 20060002642A1 US 18816105 A US18816105 A US 18816105A US 2006002642 A1 US2006002642 A1 US 2006002642A1
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- Prior art keywords
- dynamic pressure
- thrust
- bearing
- depth
- plate
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C17/00—Sliding-contact bearings for exclusively rotary movement
- F16C17/10—Sliding-contact bearings for exclusively rotary movement for both radial and axial load
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C17/00—Sliding-contact bearings for exclusively rotary movement
- F16C17/04—Sliding-contact bearings for exclusively rotary movement for axial load only
- F16C17/045—Sliding-contact bearings for exclusively rotary movement for axial load only with grooves in the bearing surface to generate hydrodynamic pressure, e.g. spiral groove thrust bearings
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C25/00—Bearings for exclusively rotary movement adjustable for wear or play
- F16C25/02—Sliding-contact bearings
- F16C25/04—Sliding-contact bearings self-adjusting
- F16C25/045—Sliding-contact bearings self-adjusting with magnetic means to preload the bearing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
- F16C33/02—Parts of sliding-contact bearings
- F16C33/04—Brasses; Bushes; Linings
- F16C33/06—Sliding surface mainly made of metal
- F16C33/10—Construction relative to lubrication
- F16C33/1025—Construction relative to lubrication with liquid, e.g. oil, as lubricant
- F16C33/106—Details of distribution or circulation inside the bearings, e.g. details of the bearing surfaces to affect flow or pressure of the liquid
- F16C33/107—Grooves for generating pressure
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B19/00—Driving, starting, stopping record carriers not specifically of filamentary or web form, or of supports therefor; Control thereof; Control of operating function ; Driving both disc and head
- G11B19/20—Driving; Starting; Stopping; Control thereof
- G11B19/2009—Turntables, hubs and motors for disk drives; Mounting of motors in the drive
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2240/00—Specified values or numerical ranges of parameters; Relations between them
- F16C2240/40—Linear dimensions, e.g. length, radius, thickness, gap
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
- F16C2370/00—Apparatus relating to physics, e.g. instruments
- F16C2370/12—Hard disk drives or the like
Abstract
A fluid dynamic pressure bearing apparatus includes a radial dynamic pressure bearing formed in a gap portion between a bearing member and a shaft member. The apparatus also includes a thrust dynamic pressure bearing having a first thrust bearing portion formed between a top surface of the thrust plate and a first facing member opposing thereto in the axial direction and a second thrust bearing portion formed between a bottom surface of the thrust plate and a second facing member opposing thereto in an axial direction. Dynamic pressure generating grooves are formed on the radial dynamic pressure bearing and the thrust dynamic pressure bearing. The shaft member and the bearing member are rotated together as a rotation member, such that the rotation member is supported in a position such that a gap space L1 of the first thrust bearing portion is larger than a gap space L2 of the second thrust bearing portion and the depth of the dynamic pressure generating grooves where the gap space is smaller is formed shallower than that where the gap space is larger.
Description
- 1. Field of the Invention
- The present invention relates to a fluid dynamic pressure bearing apparatus and more particularly, to a fluid dynamic pressure bearing apparatus having a rotating shaft member and a bearing sleeve member wherein the rotating shaft member and the bearing sleeve member are supported in a relatively rotatable state by a dynamic pressure generated from a lubrication fluid disposed between a dynamic pressure surface of the rotating shaft member and a dynamic pressure surface of the bearing sleeve member.
- 2. Related Art
- In recent years, various fluid bearing apparatuses have been proposed for rotatably supporting a rotator body such as magnetic disks, optical disks, or polygon mirrors in a high-speed rotation.
- For example, a dynamic pressure bearing apparatus is used in a spindle motor such as a hard disk drive (HDD) shown in
FIG. 7 . Abearing sleeve 13 acts as a bearing member and is mounted for supporting a rotatingshaft member 21. A dynamic pressure surface provided on an outer peripheral surface of the rotatingshaft member 21 and a dynamic pressure surface provided on the internal circumference of thebearing sleeve 13 radially face each other in proximity to form a narrow gap. A radial dynamic pressure bearing RB is formed by filling a lubricating fluid such as oil or air within the narrow gap. In addition, dynamic pressure surfaces provided on both sides of athrust plate 23 fixed to the rotatingshaft member 21 and a dynamic pressure surface of thebearing sleeve 13 or a dynamic pressure surface of acounter plate 16 mounted in an opening portion of thebearing sleeve 13 face each other in proximity to form a narrow gap in an axial direction. The lubricating fluid is filled to form thrust dynamic pressure bearings SBa and SBb. - At least one surface of the dynamic pressure surfaces of the radial dynamic pressure bearing RB and the thrust dynamic pressure bearings SBa or SBb is provided with a fluid pressuring means such as dynamic pressure generating grooves. A lubrication fluid is pressurized by means of a pumping operation created by the dynamic pressure generating grooves (not shown) to generate a dynamic pressure. Due to the generated dynamic pressure, a rotating member is rotatably supported with respect to a stationary member in an elevated state in a radial and a thrust direction, respectively.
- In such a fluid bearing device described above, when the rotating member rotates, the rotating member moves in a non-contact position with respect to the stationary fixed member by the lubrication fluid. When the rotating member stops rotating, one side of the two thrust bearing portions comes in contact with the rotating member and the fixed member. For example, in a spindle motor for HDDs, after a hard disk supported by the rotating member rotates at a particular speed, a recording/reproducing head moves over a disk via a guide member and recording/reproducing is performed in a non-contact state. When the motor stops, the rotating member moves downward from an elevated position to a contacting position due to gravitational forces.
- While this operation is performed, the hard disk is separated from the guide member having the recording/reproducing magnetic head so that the hard disk does not come into contact with the guide member. However, when the motor is placed in an upside down position or an extremely large shock is added to the motor from the outside, the rotating member becomes displaced to a larger extent than the elevated height and the hard disk may come into contact with the guide member, which damages the disk and/or the guide member.
- In order to solve this problem, a motor having a magnetic plate is attached to the fixed member so as to face a motor drive magnet provided on the rotor. The magnetic plate and the motor drive magnet are magnetically attracted to each other by the magnetic attraction force of the drive magnet. As a result, the rotating member is attracted towards the fixed member.
- However, the gap dimension between the magnetic plate and the motor drive magnet varies according to the assembling process of the motor or errors in the dimensions of various component parts. Thus, the magnetic attraction force also varies. The variation of the magnetic attraction force results in a fluctuation of the spaces of the thrust dynamic pressure bearings SBa and SBb. Hence, the required thrust dynamic pressure may not be obtained. In addition, when the gap space of the thrust dynamic pressure bearing is made smaller due to a stronger magnetic attraction force during rotation, the viscosity of the lubrication fluid increases and a loss of torque in the motor also increases.
- Generally, the amount a bearing wears is proportional to the product of the rotational speed and the contacting time of the rotating member. Therefore, the amount the bearing wears can be reduced by making the rotating member elevate even at a low speed of rotation such as when the motor first starts. However, when the rotating member and the fixed member are magnetically attracted to each other, the needed time for elevating the rotating member will increase because it is necessary to generate a force of dynamic pressure greater than the magnetic attraction force. That is, the time both members are in contact with each other increases and this causes the bearing to wear down.
- The present invention provides a fluid dynamic pressure bearing apparatus with a high reliability, wherein the restrictions as to the position of the motor in use is eliminated. The present invention also provides a fluid dynamic pressure bearing apparatus wherein a required dynamic pressure can be generated readily in a thrust dynamic pressure bearing and the wearing of the thrust dynamic pressure bearing is reduced.
- A fluid dynamic pressure bearing apparatus includes a radial dynamic pressure bearing formed in a gap portion between a bearing member and a shaft member. The apparatus also includes a thrust dynamic pressure bearing having a first thrust bearing portion formed between a top surface of the thrust plate and a first facing member opposing thereto in the axial direction and a second thrust bearing portion formed between a bottom surface of the thrust plate and a second facing member opposing thereto in an axial direction. Dynamic pressure generating grooves are formed on the radial dynamic pressure bearing and the thrust dynamic pressure bearing. The shaft member and the bearing member are rotated together as a rotation member, such that the rotation member is supported in a position that a gap space L1 of the first thrust bearing portion is larger than a gap space L2 of the second thrust bearing portion and the depth of the dynamic pressure generating grooves where the gap space is smaller is formed shallower than that where the gap space is larger.
- In this configuration, the shallower depth of the thrust dynamic pressure generating grooves generates larger dynamic pressure at a low speed of rotation. As a result, the rotating member is able to elevate from the fixed member in the thrust bearing portion even at a low speed of rotation such that the wearing of the contact sliding of both members is decreased. Accordingly, a fluid dynamic pressure bearing which is superior to its durability is obtained and a larger thrust dynamic pressure is obtained even in the thrust bearing portion in which the opposing gap space is small.
- In accordance with one embodiment of the present invention, the depth of the dynamic pressure generating grooves in the thrust bearing portion in which the gap space is smaller is determined in such a manner that the coefficient of elasticity of the thrust bearing portion is set to be generally at a maximum value. Therefore, a large bearing rigidity is obtained.
- For this purpose, it is preferable to establish the depth of the dynamic pressure generating grooves in the dimension of 0.8 times to 2.8 times of its gap space.
- In accordance with one embodiment of the present invention, each of the depths of the dynamic pressure generating grooves in the first and the second thrust bearing portions is determined in such a manner that each of the coefficients of elasticity of the thrust bearing portions is respectively set to be a generally maximum value. Therefore, a large bearing rigidity is obtained and further, a desired coefficient of elasticity can be obtained even if the real peak value of the coefficient of elasticity is displaced by residual stress or distortion produced in the thrust plate.
- In accordance with one embodiment of the present invention, the second facing member is formed from a material of greater hardness than that of the first facing member and a biasing means is provided for urging the thrust plate to elevate from the second thrust bearing portion.
- In this configuration, the thrust plate elevates from the side of the material of greater hardness and thus the wear of the thrust dynamic pressure bearing is restrained, regardless of the position of the motor in use, and the reliability of the bearing is improved.
- Other features and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings that illustrate, by way of example, various features of embodiments of the present invention.
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FIG. 1 is a sectional view of a spindle motor provided with a fluid dynamic pressure bearing apparatus according to an embodiment of the present invention. -
FIG. 2 is a plane explanatory view of one example of dynamic pressure generating grooves formed in a thrust plate. -
FIG. 3 is a partially cross-sectional view of the spindle motor provided with a fluid dynamic pressure bearing apparatus in a suspended state according to an embodiment of the present invention. -
FIG. 4 is a partially cross-sectional view of the spindle motor provided with a fluid dynamic pressure bearing apparatus in a rotation state according to an embodiment of the present invention. -
FIG. 5 is a schematic illustration which shows a simulation result of the coefficient of elasticity in the thrust dynamic pressure bearing with respect to the depth of the thrust dynamic pressure generating groove SG as a parameter of the floating amount of the thrust plate. -
FIG. 6 is a cross-sectional view of a fluid dynamic pressure bearing apparatus according to another embodiment of the present invention. -
FIG. 7 is a sectional view of a conventional fluid bearing apparatus. - Various embodiments of the present invention will be explained below. First, an overall structure of a hard disk drive (HDD) device to which the present invention may be applied will be explained in reference to the accompanying drawings.
- A shaft rotation-type spindle motor for a HDD shown in
FIG. 1 generally includes astator assembly 10, which is a fixed member, and arotor assembly 20, which is a rotating member assembled on top of thestator assembly 10. Thestator assembly 10 has afixed frame 11 screwed onto a fixed base or chassis of the drive apparatus (not shown). The fixedframe 11 is formed of an aluminum metal material to reduce its weight. A cylindricalsleeve holding portion 12 is formed upright in the generally center area of the fixedframe 11. A bearingsleeve 13 in a hollow cylinder shape, which is a fixed bearing member, is attached to an inner circumference of the bearingholder 12 and joined to thebearing holder 12 through press fit or shrink fit. The bearingsleeve 13 is formed from a copper alloy material, such as phosphorous bronze, in order to facilitate the machining of holes with small diameter. - On the outer circumference mounting surface of the bearing
holder 12 is mounted astator core 14 including a stacked layered body of electromagnetic steel plates. Adrive coil 15 is wound on each of the salient pole sections provided on thestator core 14. - A bearing hole (not shown) is provided in the center of the bearing
sleeve 13, and a part of therotor assembly 20, which is arotating shaft 21, is inserted inside the bearing hole. The rotatingshaft 21 in the present embodiment is formed from stainless steel. This means that the bearingsleeve 13 which is a bearing member, is formed from a material with more resilience than the rotatingshaft 21, which is a shaft member. On the inner circumference surface of the bearing hole of the bearingsleeve 13 is formed a dynamic pressure surface, which is positioned to face in the radial direction a dynamic pressure surface formed on the outer circumference surface of therotating shaft 21, such that a radial dynamic pressure bearing section RB is created in minute bearing gap between the dynamic pressure surfaces. More specifically, the dynamic pressure surface on the bearingsleeve 13 side and the dynamic pressure surface on therotating shaft 21 side in the radial dynamic pressure bearing section RB face each other across a minute gap of a few μm; this minute gap forms a bearing space into which lubricating fluid is continuously charged in the axial direction. The lubricating fluid is, for example, lubricating oil such as from an ester series or a poly-α-olefin series, magnetic fluid, or air. - Radial dynamic pressure generating grooves (not shown) in a herringbone shape, for example, are provided on at least one of the dynamic pressure surfaces on the bearing
sleeve 13 and therotating shaft 21 in two blocks of concave ring shapes separated in the axial direction. When the rotation takes place, the pumping action of the grooves pressurizes the lubricating fluid to generate a dynamic pressure, so that the rotatingshaft 21 and the rotatinghub 22 are shaft-supported in the radial direction. - A capillary seal portion RS is provided at the top of the bearing space in the figure that forms the radial dynamic pressure bearing section RB. The capillary sealing section RS is structured by an angle surface formed on the
rotating shaft 21 or on the bearingsleeve 13 that gradually widens the bearing gaps towards the outside of the bearing, and has a gap dimension of about 20 μm to about 300 μm, for example. The surface level of the lubricating fluid is positioned within the capillary sealing section RS in both the motor rotation and stop states. - A rotating
hub 22 that along with the rotatingshaft 21 forms therotor assembly 20 is formed from a generally cup-shaped member made of an aluminum metal, so that a recording medium such as a magnetic disk (not shown) can be mounted on the rotatinghub 22. In the center area of the rotatinghub 22 is provided a joint hole 22 d, which is joined in a unitary fashion through press fit or shrink fit with the top area of therotating shaft 21. - The rotating
hub 22 has a generally cylinder-shapedbody section 22 a on whose outer circumference a disk is mounted, and on the bottom inner circumference wall of thebody section 22 a is mounted via aback yoke 22 b and a ring-shapeddrive magnet 22 c. Themagnet 22 c is positioned to face the outer circumference end surface of thestator core 14. - At the bottom end of the
rotating shaft 21 is fixed a disk-shapedthrust plate 23. Thethrust plate 23 is contained in a cylinder-shaped concave recess formed at the bottom center of the bearingsleeve 13. In the recess of the bearingsleeve 13, the dynamic pressure surface provided on the top surface of thethrust plate 23 faces in close proximity the dynamic pressure surface provided on the bearingsleeve 13. A dynamic pressure generating groove is formed on at least one of the two facing dynamic pressure surfaces, and a top thrust dynamic pressure bearing section Sba is formed in the gap between the dynamic pressure surfaces of thethrust plate 23 and the bearingsleeve 13 facing each other. - In close proximity to the bottom dynamic pressure surface of the
thrust plate 23 is acounter plate 16, which is formed from a disk-shaped member with a relatively large diameter. Thecounter plate 16 closes off the bottom opening area of the bearingsleeve 13. A dynamic pressure generating groove is also formed between the dynamic pressure surface provided at the top of thecounter plate 16 and the dynamic pressure surface on the bottom of thethrust plate 23, which forms a bottom thrust dynamic pressure bearing section SBb. - The two dynamic pressure surfaces of the
thrust plate 23 and the dynamic pressure surface of the bearingsleeve 13 and of thecounter plate 16 that faces them together constitute a set of thrust dynamic pressure bearing sections SBa and SBb next to each other in the axial direction and are in each case arranged so that the opposing dynamic pressure surfaces face each other across a minute gap of a few μm; and the lubricating fluid is charged continuously into the minute gaps in the axial direction via a path provided on the outer circumference of thethrust plate 23. - Furthermore, normal herringbone-shaped thrust dynamic pressure generating grooves in a ring shape are provided on at least one of the dynamic pressure surfaces of the
thrust plate 23 and that of the bearingsleeve 13, and on at least one of the dynamic pressure surfaces of thethrust plate 23 and that of thecounter plate 16. As a result, when rotation takes place, the pumping action of the thrust dynamic pressure generating grooves pressurizes the lubricating fluid to generate dynamic pressure and therotating shaft 21 and the rotatinghub 22 are supported in the thrust direction. A further option for the thrust dynamic pressure generating grooves is that they may be formed on the dynamic pressure surface of the bearingsleeve 13 at the top thrust dynamic pressure bearing section SBa and may be formed on the dynamic pressure surface of thecounter plate 16 at the bottom thrust pressure bearing section SBb. - In the spindle motor shown in
FIG. 1 , a ring shapedmagnetic attraction plate 17 made of magnetic material is mounted on fixedframe 11. Themagnetic attraction plate 17 is fixed on the fixedframe 11 to face onto the bottom surface of thedrive magnet 22 c and therefore includes a biasing means. Themagnetic attraction plate 17 attracts therotor assembly 20 towards theframe 11 by a magnetic attraction force between thedrive magnet 22 c and themagnetic attraction plate 17. The magnitude of the force is larger than the gravitational force applied on theentire rotor assembly 20 when the motor is placed upside down. - Therefore, the
magnetic attraction plate 17 can always pull therotor assembly 20 towards the fixedframe 11, even if the motor is placed upside down and the gravitational force is applied to therotor assembly 20. Thus, when therotor assembly 20 does not rotate, thecounter plate 16 contacts with the bottom surface of thethrust plate 23 of the bottom thrust dynamic pressure bearing section SBb. - When a current is applied to the
drive coil 15 and therotor assembly 20 rotates by the electromagnetic action between thestator core 14 and thedrive magnet 22 c, thethrust plate 23 elevates from thecounter plate 16. When rotation is suspended, thethrust plate 23 returns to be in contact with thecounter plate 16 again. - In addition, regarding the top thrust dynamic pressure bearing section SBa which includes the upper surface of the
thrust plate 23 and the bottom surface of the bearingsleeve 13, the bottom surface of the bearingsleeve 13 does not form a flat surface because the surface is provided with cut streaks. Furthermore, the bearingsleeve 13 is formed from a comparatively soft metal such as copper or copper alloy. This is for easy workability of the top thrust dynamic pressure bearing section SBa as well as radial dynamic pressure generation grooves formed on its internal circumference surface. - On the other hand, regarding the bottom dynamic pressure bearing section SBb which includes the under surface of the
thrust plate 23 and the upper surface of thecounter plate 16, the upper surface of thecounter plate 16 has a flat surface which is achieved by lapping work or polishing work. Further, thecounter plate 16 is formed of a hard material which is a heat-treated rustless steel. - As described above, when the
rotor assembly 20 stops rotating, the bottom face of thethrust plate 23 remains in contact with thecounter plate 16 of the bottom thrust dynamic pressure bearing surface SBb. In a low-speed rotating state such as just after starting or before stopping, both members remain slightly in contact with each other. However, since the upper surface of thecounter plate 16 is flat and hard, the wearing of the dynamic pressure surfaces of thecounter plate 16 and thethrust plate 23 can be greatly reduced. - The structure of the thrust dynamic pressure bearing according to an embodiment of the present invention is described below in detail with reference to
FIG. 3 andFIG. 4 .FIG. 3 is a sectional view of a spindle motor for a HDD in a stopped state in an embodiment of the present invention.FIG. 4 is a sectional view of the motor in a rotating state. - In
FIG. 3 , thethrust plate 23 is fixed to one end of therotating shaft 21 and is provided within the recessedportion 13 a formed within the bearingsleeve 13. Thrust dynamic pressure generating grooves SGa having a depth d1 are formed on theupper surface 23 a of thethrust plate 23. Theupper surface 23 a faces onto a dynamic pressure surface of the bearing sleeve 13 (the first facing member) and the top thrust dynamic pressure bearing section SBa is formed by the bearing gap space between theupper surface 23 a and the bearingsleeve 13. Also, thrust dynamic pressure generating grooves SGb having a depth d2 are formed on thebottom surface 23 b of thethrust plate 23. Thebottom surface 23 b faces onto a dynamic pressure surface of the counter plate 16 (the second facing member) and the bottom thrust dynamic pressure bearing surface SBb is formed by the bearing gap space between thebottom surface 23 b and thecounter plate 16. When the motor stops, thebottom surface 23 b of thethrust plate 23 and the dynamic pressure surface of thecounter plate 16 make contact by a force of the biasing means including that of themagnetic attraction plate 17. - The depth d1 of the thrust dynamic pressure generating grooves SGa formed on the
upper surface 23 a and the depth d2 of the thrust dynamic pressure generating grooves SGb formed on thebottom surface 23 b are so determined as to satisfy the relationship of d1>d2, that is, the depth d1 is deeper than the depth d2 in thethrust plate 23. - When the
rotating shaft 21 and thethrust plate 23 start rotating, the dynamic pressure in the bottom thrust dynamic pressure bearing surface SBb increases to make thethrust plate 23 elevate. At a specified number of rotations, the dynamic pressure of the bottom thrust dynamic pressure bearing surface SBb and the dynamic pressure of the top thrust dynamic pressure bearing surface SBa balance each other so that thethrust plate 23 will continue to rotate in a state that thethrust plate 23 maintains a specified elevation as shown inFIG. 4 . - In this case, the relationship between the gap dimension L1 in the top thrust dynamic pressure bearing section SBa and the gap dimension L2 in the bottom thrust dynamic pressure bearing section SBb is as follows; L1>L2, that is, the rotation is performed in a state that the gap L2 is smaller than the gap L1. This is because the
rotor assembly 20 is attracted to theframe 11 by the biasing means described above. -
FIG. 5 is a schematic illustration which shows the simulation results of the coefficient of elasticity in the thrust dynamic pressure bearing, that is, the magnitude of the repulsive force by the dynamic pressure with respect to the depth of the thrust dynamic pressure generating groove SG as a parameter of the elevated amount of thethrust plate 23. InFIG. 5 , three cases of the elevated amount (gap dimension) of thethrust plate 23 as 5.0 μm, 7.5 μm, and 10.0 μm are plotted to show how the coefficient of elasticity in the thrust dynamic pressure bearing varies depending on the depth of the thrust dynamic pressure generating groove SG. - As a result, when the groove's depth is progressively increased by 1 m with the elevated amount or gap dimension maintaining a constant value of 5.0 μm, the coefficient of elasticity rapidly increases within the range of about 8 μm of the depth of the dynamic pressure generating groove and the peak value of the coefficient of elasticity reaches about 110,000 N/m.
- Especially, when the groove's depth is in the range of 1 times to 2 times of the elevated amount (5.0 μm), that is, the groove's depth is in the range of about 5 μm to 10 μm, a sufficient coefficient of elasticity around 90% of the coefficient of elasticity of the peak can be obtained. In addition, when the groove's depth is in the range of about 0.8 times to 2.8 times of the elevated amount (5.0 μm), that is, the groove's depth is in the range of about 4 μm to 14 μm, the coefficient of elasticity reaches a value larger than 70% of the peak. On the other hand, when the depth of the dynamic pressure generating groove is larger than about 8 μm, the coefficient of elasticity decreases gradually, and when the groove's depth is about 20 μm, the coefficient of elasticity reaches approximately one-third of the peak.
- Next, when the elevated amount is a constant value of 7.5 μm and the depth of the dynamic pressure generating groove is progressively increased, the coefficient of elasticity increases gradually up to around 12 μm and the peak value of the coefficient of elasticity reaches about 33,000 N/m. That is a similar result to the case of the elevated amount of 5.0 μm. When the groove's depth is in the range of about one times to two times of the elevated amount, that is, when the groove's depth is in the range of about 7.5 μm to 15 μm, the coefficient of elasticity is reached to a value of about 90% of the peak. Also, when the groove's depth is in the range of about 0.8 times to 2.8 times of the elevated amount, that is, the groove's depth is in the range of 6 μm to 21 μm, the coefficient of elasticity reaches to a value larger than 70% of the peak. The curve of the elevated amount of 7.5 μm in
FIG. 5 varies more gradually than the curve of 5.0 μm, and after the peak of the coefficient of elasticity, the coefficient of elasticity decreases according to the increase of the groove's depth. - When the elevated amount is a constant value of 10.0 μm and the depth of the dynamic pressure generating groove is progressively increased, the coefficient of elasticity increases gradually up to around 16 μm and the peak value of the coefficient of elasticity reaches about 15,000 N/m. Similar to the case when the elevated amount is 5.0 μm, when the groove's depth is in the range of about one times to two times of the elevated amount, that is, when the groove's depth is in the range of about 10 μm to 20 μm, the coefficient of elasticity reaches a value about 90% of the peak. When the groove's depth is in the range of about 0.8 times to 2.8 times of the elevated amount, that is, when the groove's depth is in the range of about 8 μm to 28 μm, the coefficient of elasticity reaches a value larger than 70% of the peak. The curve of the elevated amount of 10.0 μm varies more gradually than the curve of 7.5 μm in the figure, and after the peak of the coefficient of elasticity, the coefficient of elasticity decreases slightly according to the increase of the groove's depth.
- From the results described above in
FIG. 5 , it is understood that when the amount of the thrust plate's elevation is smaller, the coefficient of elasticity is larger with relatively smaller depths of the dynamic pressure generating grooves. On the otherhand, when the amount of the thrust plate's elevation is larger, the coefficient of elasticity is larger with relatively larger depths of the dynamic pressure generating grooves. - As described above and as illustrated in
FIG. 4 , the thrust dynamic pressure bearing is structured in such a manner that the gap dimension L2 of the bottom thrust dynamic pressure bearing section SBb is narrower than the gap dimension L1 of the top thrust dynamic pressure bearing section SBa in a rated rotation state. (Please define the term “rated rotation state”.) Further, a larger coefficient of elasticity and a bearing rigidity can be achieved by setting the depth of a dynamic pressure generating groove in the smaller elevation amount side of the thrust plate 23 (the bottom thrust dynamic pressure bearing section SBb) smaller than the depth in the larger elevation amount side. At this time, the depth of the dynamic pressure generating groove is preferably in the range of about 0.8 times to 2.8 times of the elevation amount (gap dimension) of thethrust plate 23 in a rated number of rotations. Further, when the depth of the dynamic pressure generating groove is set in the range of about one times to two times of the floating amount (gap dimension), the coefficient of elasticity can be achieved near the peak coefficient of elasticity in the bottom thrust dynamic pressure bearing section SBb. - On the other hand, a larger coefficient of elasticity and a bearing rigidity can be achieved by setting the depth of a dynamic pressure generating groove in the larger elevation amount side of the thrust plate 23 (the top thrust dynamic pressure bearing section SBa) larger than the depth in the smaller elevated amount side. At this time, the depth of the dynamic pressure generating groove is desirably in the range of about 0.8 times to 2.8 times of the elevated amount of the
thrust plate 23 in a rated number of rotations. Further, when the depth of the dynamic pressure generating groove is set in the range of about one times to two times of the elevated amount, the coefficient of elasticity can be achieved near the peak coefficient of elasticity in the top thrust dynamic pressure bearing section SBa. - As described above, when the coefficient of elasticity is set to be near to the maximum value of the coefficient of elasticity, close to the desired value of the coefficient of elasticity can be obtained in each of the thrust bearing portions SBa and SBb respectively, even if the real value of the coefficient of elasticity is shifted a little from the peak value by the residual stress or the distortion applied to the
thrust plate 23 when the dynamic pressure generating grooves are formed on thethrust plate 23 or when thethrust plate 23 is fitted to therotor shaft 21. Therefore, when the rotating member begins to rotate, a dynamic pressure with a high coefficient of elasticity occurs even at a slow speed and thethrust plate 23 begins to elevate. As a result, a sliding period with thecounter plate 16 can be reduced to a short time and wear in the thrust dynamic pressure bearing can be reduced. Consequently, a fluid dynamic pressure bearing apparatus having a high reliability can be provided. - Next, another embodiment according to the present invention is described with reference to
FIG. 6 , which is a sectional view of a shaft fixed-type HDD spindle motor. InFIG. 6 , the same reference symbols are used for the same members as the shaft rotation-type HDD spindle motor shown inFIG. 1 , and its description is omitted. - The HDD spindle motor shown in
FIG. 6 includes astator assembly 30 as a fixed member and arotor assembly 40 as a rotation member which is rotatably supported to thestator assembly 30. Thestator assembly 30 is provided with aframe 31 fixed to a main chassis of the drive apparatus (not shown) by a screw, etc. A fixedshaft 35 as a shaft member is mounted in a center area of theframe 31, and its upper end portion is provided with a tapped hole for a screw to the drive chassis. This construction is known as a motor where both ends of the shaft are fixed. - A cup-shaped
hub 22 formed unitarily with a bearingsleeve 41 is rotatably mounted to an outer periphery of the fixedshaft 35 via the bearingsleeve 41 as a bearing member, including therotor assembly 40. A ring-shapeddrive magnet 22 c is mounted on an inner wall surface of thehub 22 via aback yoke 22 b. - In an internal peripheral surface of a center hole of the bearing
sleeve 41, a pair of radial bearing portions are formed apart from each other in an axial direction. These radial bearing portions face opposite to an outer peripheral surface of the fixedshaft 35. A pair of radial dynamic pressure bearings RB are provided between the dynamic pressure surfaces which are formed on the internal peripheral surface of these bearing portions of the bearingsleeve 41 and the dynamic pressure surface formed on the outer peripheral surface of the fixedshaft 35. Thehub 22 is rotatably supported to the fixedshaft 35 in a radial direction by these radial dynamic pressure bearings RB. - A
thrust plate 36 is fixed to the upper end portion of theshaft 35 and is disposed in a recessed portion formed in an upper central part of the bearingsleeve 41. The top thrust dynamic pressure bearing section SBa is formed between a dynamic pressure surface, an upper surface of the bearingsleeve 41 as a first facing member and a dynamic pressure surface provided on a bottom surface of thethrust plate 36 in a proximate state in an axial direction. - In addition, the counter plate 44 (the second facing member) having a larger diameter than the
thrust plate 36 is mounted in an opening portion of the bearingsleeve 41 so as to oppose a dynamic pressure surface of the upper side of thethrust plate 36 in a proximate state. The bottom thrust dynamic pressure bearing section SBb is positioned between the dynamic pressure surface provided on an under surface of the counter plate 44 and the dynamic pressure surface provided on the upper surface of thethrust plate 36. A lubricating fluid such as lubricating oil, magnetic fluid, or air is filled into the top and the bottom thrust dynamic pressure bearing surfaces SBa and SBb and the radial dynamic pressure bearings RB. - In a spindle motor shown in
FIG. 6 , a biasing means, such as a ring shapedmagnetic attraction plate 17 made of a magnetic material, is fixed on theframe 31 so as to oppose a bottom end surface of thedrive magnet 22 c. Themagnetic attraction plate 17 attracts therotor assembly 40 to the side of theframe 31 with the magnetic attraction force that is larger than the magnitude of the gravitational force relating to therotor assembly 40. Therefore, even when the motor is used in an upside down manner, themagnetic attraction plate 17 still attracts therotor assembly 40 to theframe 31 given the gravity applied to therotor assembly 40. Thus, when therotor assembly 40 does not rotate, the upper surface of thethrust plate 36 and the bottom surface of the counter plate 44 of the bottom thrust dynamic pressure bearing section SBb are in contact with each other. - In a shaft fixed-type HDD spindle motor described above, the counter plate 44 and the bearing
sleeve 41 are formed to rotate with respect to thethrust plate 36 attached to the fixedshaft 35. To the contrary, in a shaft rotation-type HDD spindle motor described above, thethrust plate 23 is fixed to therotating shaft 21 which rotates with respect to the bearingsleeve 13, and thecounter plate 16 is mounted to the fixed member. These two embodiments differ from each other in the fixed member and the rotating member, but they are similar in basic construction according to the present invention. - That is, in a shaft fixed-type HDD spindle motor shown in
FIG. 6 , when therotor assembly 40 rotates with respect to thestator assembly 30 in a rated speed, the gap dimension L2 of the bottom thrust dynamic pressure bearing section SBb is constructed so as to be smaller than the gap dimension L1 of the top thrust dynamic pressure bearing section SBa. The depth of the dynamic pressure generating grooves in the bottom thrust dynamic pressure bearing section SBb is formed shallower than the depth of the dynamic pressure generating grooves in the top thrust dynamic pressure bearing section SBa. - In addition, the depth of the dynamic pressure generating grooves in the bottom thrust dynamic pressure bearing section SBb, of which the gap dimension L2 is smaller than the gap dimension L1, is established so that the coefficient of elasticity of the bottom thrust dynamic pressure bearing section SBb has generally the greatest value. More specifically, the depth of the dynamic pressure generating grooves of the bottom thrust dynamic pressure bearing section SBb is established in the dimension of 0.8 times-2.8 times with respect to the gap dimension L2. For example, when the gap dimension L2, that is, the elevated amount of the
thrust plate 36 in a rated rotation is 5 μm, the depth of the dynamic pressure generating grooves of the bottom thrust dynamic pressure bearing section SBb is established between 4 μm and 14 μm. More preferably, the coefficient of elasticity of near the maximum value can be obtained by setting the groove depth between 5 μm and 10 μm. - In addition, the depth of the dynamic pressure generating grooves in the top thrust dynamic pressure bearing section SBa, which is the larger side in the gap dimension, is preferably set so that the coefficient of elasticity of the top thrust dynamic pressure bearing section SBa has generally the greatest value.
- In this embodiment, a
magnetic attraction plate 17 is provided on theframe 31 for urging the rotation member to theframe 31. Thus, the counter plate 44 as a second facing member is formed by a material of greater hardness than the bearingsleeve 41 as a first facing member, and thethrust plate 36 can always elevate from the bottom thrust dynamic pressure bearing surface SBb. In addition, the surface roughness of the dynamic pressure surface of the counter plate 44 is formed more smoothly than the surface roughness of the dynamic pressure surface of the bearingsleeve 41. - Therefore, even when the counter plate 44 and the
thrust plate 36 slide together at a slow speed of rotation such as when starting to rotate, the wear of the dynamic pressure surfaces of the counter plate 44 and thethrust plate 36 can be extremely reduced because the dynamic pressure surface of the counter plate 44 can be formed smoothly and formed by a material of greater hardness. - The embodiments of the invention are described above. However, the present invention is not limited to the embodiments described above, and many modifications can be made without departing from the subject matter of the present invention.
- In the above-mentioned embodiments, for example, the thrust dynamic pressure generating grooves SG are formed on both surfaces of the
thrust plate sleeves counter plates 16 or 44 as the second facing member in an axial direction. - Also, in the above-mentioned embodiments, the
magnetic attraction plate 17 is arranged at a position so as to oppose against thedrive magnet 22 c as a biasing means in an axial direction. However, instead of arranging themagnetic attraction plate 17, therotor assembly frame drive magnet 22 c with respect to a magnetic center of thestator core 14 in a reverse direction of the frame. - In addition, the
shaft member plate FIG. 2 . - Furthermore, the present invention can be similarly applied to motors of one side shaft fixed-type motor instead of both side shaft fixed-type motor shown in
FIG. 6 . - While the description above refers to particular embodiments of the invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention.
- The disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (10)
1-12. (canceled)
13. A fluid dynamic pressure bearing apparatus comprising:
a radial dynamic pressure bearing formed in a gap portion between a bearing member and a shaft member; and
a thrust dynamic pressure bearing including a first thrust bearing portion formed between a top surface of the thrust plate and a first facing member opposing thereto in the axial direction and a second thrust bearing portion formed between a bottom surface of the thrust plate and a second facing member opposing thereto in an axial direction;
wherein the second facing member is formed from a material harder that than the first facing member and a biasing means is provided for urging the thrust plate to elevate from the second thrust bearing portion.
14. The apparatus according to claim 13 further comprising a lubricating fluid filled within the radial dynamic pressure bearing and the thrust dynamic pressure bearing.
15. The apparatus according to claim 13 further comprising dynamic pressure generating grooves on the radial dynamic pressure bearing and the thrust dynamic pressure bearing.
16. The apparatus according to claim 15 , wherein the depth of the dynamic pressure generating grooves in the thrust bearing portion in which the gap is smaller is determined by the maximum value of coefficient of elasticity of the thrust bearing portion.
17. The apparatus according to claim 15 , wherein the depth of the dynamic pressure generating grooves of the thrust bearing portion in which the gap is smaller is in the range of about 0.8 times to about 2.8 times of its gap space dimension.
18. The apparatus according to claim 15 , wherein each of the depths of the dynamic pressure generating grooves in the first and second thrust bearing portions is determined by the coefficients of elasticity having a maximum value.
19. The apparatus according to claim 13 , wherein the first facing member is the bearing member and the second facing member is a counter plate mounted to the bearing member.
20. The apparatus according to claim 13 , wherein the surface of the second facing member is formed more smoothly that the surface of the first facing member.
21. The apparatus according to claim 15 , wherein the depth of the dynamic pressure generating grooves in the second thrust bearing portion is formed shallower than the depth of the dynamic pressure generating grooves in the first thrust bearing portion.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US11/188,161 US20060002642A1 (en) | 2001-03-05 | 2005-07-22 | Fluid dynamic pressure bearing apparatus |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2001060761A JP2002266861A (en) | 2001-03-05 | 2001-03-05 | Fluid dynamic pressure bearing device |
JP2001-060761 | 2001-03-05 | ||
US10/090,419 US6962443B2 (en) | 2001-03-05 | 2002-02-28 | Fluid dynamic pressure bearing apparatus |
US11/188,161 US20060002642A1 (en) | 2001-03-05 | 2005-07-22 | Fluid dynamic pressure bearing apparatus |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/090,419 Division US6962443B2 (en) | 2001-03-05 | 2002-02-28 | Fluid dynamic pressure bearing apparatus |
Publications (1)
Publication Number | Publication Date |
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US20060002642A1 true US20060002642A1 (en) | 2006-01-05 |
Family
ID=18920142
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/090,419 Expired - Fee Related US6962443B2 (en) | 2001-03-05 | 2002-02-28 | Fluid dynamic pressure bearing apparatus |
US11/188,161 Abandoned US20060002642A1 (en) | 2001-03-05 | 2005-07-22 | Fluid dynamic pressure bearing apparatus |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/090,419 Expired - Fee Related US6962443B2 (en) | 2001-03-05 | 2002-02-28 | Fluid dynamic pressure bearing apparatus |
Country Status (4)
Country | Link |
---|---|
US (2) | US6962443B2 (en) |
JP (1) | JP2002266861A (en) |
CN (1) | CN1206466C (en) |
SG (1) | SG111931A1 (en) |
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Publication number | Priority date | Publication date | Assignee | Title |
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DE10162675A1 (en) * | 2001-12-19 | 2003-07-10 | Gerhard Wanger | Dynamic gas storage of a shaft with a polygon mirror with a vacuum polygon chamber |
DE10240634B4 (en) * | 2002-03-12 | 2007-07-19 | Minebea Co., Ltd. | Hydrodynamic bearing for a spindle motor |
US6982513B2 (en) * | 2002-09-27 | 2006-01-03 | Nidec Corporation | Recording disk drive motor, recording disk drive employing the motor, a method of manufacturing a stator used in the recording disk drive motor, and core plate that is used in the manufacture of the stator |
CN101413531B (en) * | 2003-03-31 | 2012-08-08 | Ntn株式会社 | Fluid bearing device |
US7063463B2 (en) * | 2003-06-13 | 2006-06-20 | Nippon Densan Co., Ltd. | Conical hydrodynamic bearing device and a recording disk drive equipped with it, and a method of manufacturing a conical hydrodynamic bearing device |
US7201517B2 (en) * | 2003-06-23 | 2007-04-10 | Nidec Corporation | Hydrodynamic bearing device and a recording disk drive equipped with it |
CN1957184B (en) * | 2004-03-30 | 2011-05-25 | Ntn株式会社 | Fluid dynamic pressure bearing device |
CN100406193C (en) * | 2004-06-28 | 2008-07-30 | 日本电产株式会社 | Method for producing thrust plate and method for producing shaft for hydrodynamic bearing |
JP4610973B2 (en) * | 2004-09-08 | 2011-01-12 | Ntn株式会社 | Method for manufacturing shaft member for hydrodynamic bearing device |
TWI273187B (en) | 2005-01-28 | 2007-02-11 | Foxconn Tech Co Ltd | Fluid dynamic bearing |
CN100370159C (en) * | 2005-02-25 | 2008-02-20 | 富准精密工业(深圳)有限公司 | Fluid bearing |
JP4979950B2 (en) * | 2006-01-19 | 2012-07-18 | Ntn株式会社 | Shaft member for hydrodynamic bearing device |
JP2007192369A (en) * | 2006-01-20 | 2007-08-02 | Jtekt Corp | Performance determining method of dynamic pressure bearing and dynamic pressure bearing |
US8016554B2 (en) * | 2006-02-01 | 2011-09-13 | Borgwarner Inc. | Combination hydrodynamic and rolling bearing system |
JP4829039B2 (en) * | 2006-08-22 | 2011-11-30 | アルファナテクノロジー株式会社 | Fluid dynamic bearing device and motor equipped with the same |
JP2008082414A (en) * | 2006-09-27 | 2008-04-10 | Nippon Densan Corp | Fluid dynamic bearing device, magnetic disk device and portable electronic equipment |
JP5220339B2 (en) * | 2007-05-07 | 2013-06-26 | Ntn株式会社 | Hydrodynamic bearing device |
KR20090002337A (en) * | 2007-06-28 | 2009-01-09 | 엘지이노텍 주식회사 | Spindle motor |
EP2042753A1 (en) * | 2007-09-26 | 2009-04-01 | ABB Turbo Systems AG | Hydrodynamic axial bearing |
DE102009054341A1 (en) * | 2009-11-24 | 2011-05-26 | Minebea Co., Ltd. | Bearing surface for fluid dynamic axial bearing, has bearing grooves of fluid-dynamic axial-bearing, where bearing surface is assigned to another bearing surface |
JP2019027501A (en) * | 2017-07-28 | 2019-02-21 | パナソニックIpマネジメント株式会社 | Bearing structure |
US10422373B1 (en) * | 2018-04-04 | 2019-09-24 | General Electric Company | Machine thrust bearing assembly |
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US5357163A (en) * | 1992-05-08 | 1994-10-18 | Matsushita Electric Industrial Co., Ltd. | Motor with dynamic-pressure type bearing device |
US6132094A (en) * | 1998-12-21 | 2000-10-17 | Fmc Corporation | Multiple groove thrust bearing |
US20010022869A1 (en) * | 2000-02-24 | 2001-09-20 | Nsk Ltd | Fluid bearing device |
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DE3901265A1 (en) * | 1989-01-18 | 1990-07-19 | Glyco Metall Werke | Hydrodynamic sliding thrust (locating, plain)-bearing segment |
JPH09158744A (en) * | 1995-12-08 | 1997-06-17 | Toyota Motor Corp | Thrust bearing of turbocharger |
JPH1113748A (en) | 1997-06-21 | 1999-01-22 | Sankyo Seiki Mfg Co Ltd | Thrust dynamic pressure bearing device |
JP2001295833A (en) * | 2000-04-18 | 2001-10-26 | Matsushita Electric Ind Co Ltd | Thrust dynamic pressure bearing |
JP2002061637A (en) | 2000-08-23 | 2002-02-28 | Ntn Corp | Dynamic pressure type bearing device |
-
2001
- 2001-03-05 JP JP2001060761A patent/JP2002266861A/en not_active Withdrawn
-
2002
- 2002-02-28 US US10/090,419 patent/US6962443B2/en not_active Expired - Fee Related
- 2002-03-04 SG SG200201118A patent/SG111931A1/en unknown
- 2002-03-05 CN CNB021069565A patent/CN1206466C/en not_active Expired - Fee Related
-
2005
- 2005-07-22 US US11/188,161 patent/US20060002642A1/en not_active Abandoned
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US5357163A (en) * | 1992-05-08 | 1994-10-18 | Matsushita Electric Industrial Co., Ltd. | Motor with dynamic-pressure type bearing device |
US6132094A (en) * | 1998-12-21 | 2000-10-17 | Fmc Corporation | Multiple groove thrust bearing |
US20010022869A1 (en) * | 2000-02-24 | 2001-09-20 | Nsk Ltd | Fluid bearing device |
Also Published As
Publication number | Publication date |
---|---|
SG111931A1 (en) | 2005-06-29 |
US20020122609A1 (en) | 2002-09-05 |
CN1206466C (en) | 2005-06-15 |
CN1382919A (en) | 2002-12-04 |
JP2002266861A (en) | 2002-09-18 |
US6962443B2 (en) | 2005-11-08 |
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