DE102012023854A1 - Fluid dynamic bearing system for spindle motor used in disk drive, has axially extending portion that is limited by outer circumferential surface of bearing component and radially opposite inner peripheral surface of rotor component - Google Patents

Abstract

The system has bearing components (16,18) that are arranged at mutual distance on fixed shaft (12). A rotor component (14) is mounted on bearing component relative to shaft. Dynamic journal bearing is positioned along axial portion of oil filled bearing gap (20) formed at both ends of adjacent surfaces of shaft of components. An axially extending portion (38a) of air gap (38) formed on sealing gap (34) that seals open end of bearing gap, is limited by outer circumferential surface of bearing component and radially opposite inner peripheral surface of rotor component. Independent claims are included for the following: (1) the spindle motor; and (2) the hard disk drive.

Description

Field of the invention

The invention relates to a fluid dynamic bearing system for a spindle motor according to the features of the preamble of claim 1. Spindle motors with such fluid dynamic bearing systems are used for example for driving disk drives.

State of the art

Fluid dynamic bearing systems usually comprise at least two relatively rotatable bearing parts, the bearing surfaces between one another with a bearing fluid, for. B. a bearing oil, filled bearing gap form. In a known manner bearing groove structures are applied to the bearing surfaces. The bearing groove structures produce relative to each other within the bearing gap a hydrodynamic pressure with relative rotation of the bearing parts. This hydrodynamic pressure makes the bearing viable.

A disadvantage of fluid dynamic bearing systems is that the bearing fluid used in the fluid dynamic bearing evaporates over time. It is therefore necessary to provide a sufficient stock of bearing fluid for the specified service life in the bearings. This fluid supply must be greater, the higher the expected operating temperature and the required service life.

Another factor influencing the evaporation rate of the bearing fluid is the size of the interface of the fluid with the ambient air. A small interface also reduces fluid loss. If the fluid in the storage volume in motion, for example, because rotating parts border the volume, this increases the interface and thus the evaporation rate. Last but not least, the state of the surrounding air is decisive for the evaporation rate. When the interface is surrounded by moving air, the rate of evaporation is greater than at an interface adjacent to a relatively non-moving volume of air already enriched with fluid vapors.

From the prior art, a number of different designs for fluid dynamic bearings are known. For example, the DE 10 2008 052 469 A1 a spindle motor having a fluid dynamic bearing having a bushing rotatably supported about a fixed shaft connected to the base plate of a spindle motor, the bearing gap between the fixed and rotating parts of the bearing being open on both sides and sealed by capillary seals. As a result, the bearing fluid is in contact with the ambient air on two sides of the bearing, which leads to an additional increase in the evaporation rate. At the top of the bearing, the gap is therefore covered by a cap. At a lower, axially extending sealing gap, a thin axial air gap follows, which is formed between an outer diameter of the hub fixedly connected to the bearing bush and the inner diameter of a raised edge of the base plate of the spindle motor. This raised edge also serves at its outer diameter for attachment of the stator assembly of the spindle motor.

The US 2010/0296190 A1 and the DE 10 2009 035 125 A1 show designs of spindle motors with fluid dynamic bearing systems, in which a lower, axially extending sealing gap is present, which is followed directly in the axial extension of a thin air gap. The seal gap and the air gap are defined by an outer peripheral surface of a rotor member (bushing) and an inner peripheral surface of a stationary bearing member connected to the base plate.

A disadvantage of the above-described embodiments of the air gap is that, due to the predetermined dimensions of the spindle motor, the air gap compared to the sealing gap can be measured only relatively short, which reduces the sealing effect against leakage of fluid vapor at this point.

Another problem with the realization of such an air gap is that the walls of the central opening of the base plate can deform by the pressing of the stutter assembly. If the air gap is delimited by a wall of an edge of the base plate, a deformation or undesired change in the gap diameter also occurs in the area of the air gap.

Another disadvantage is that the fluid-dynamic bearing or the first bearing component is glued into the opening of the base plate and also slight tolerances can occur when gluing, which affect the width of the air gap. Due to these problems described above, the air gap can not be made arbitrarily small, since the corresponding tolerances must be observed.

Moreover, in such an arrangement of the air gap in the axial extension of the capillary seal gap disadvantageous that as a result of shocks or vibrations from the surface of the bearing fluid squirting oil droplets in the constriction of the air gap due to Attach capillary action and do not get back into the fluid reservoir.

Disclosure of the invention

It is the object of the invention to further develop a fluid dynamic bearing for a spindle motor to effectively prevent leakage of bearing fluid and in particular fluid vapor from the bearing and thus increase the life of the spindle motor.

This object is achieved by a fluid dynamic bearing system with the features of claim 1.

Preferred embodiments of the invention and further advantageous features are indicated in the dependent claims.

The fluid dynamic bearing system comprises a fixed shaft and a first and a second bearing member, which are arranged at a mutual distance on the shaft. Relative to the shaft and the two bearing components, a rotor component is arranged rotatably about a rotation axis. Between the adjacent surfaces of the shaft, the rotor member and the bearing components extends a bearing gap open on both sides, which is filled with a bearing fluid. Along the bearing gap at least one fluid dynamic radial bearing and at least one fluid dynamic thrust bearing are arranged. For sealing an open end of the bearing gap at least a first sealing gap is provided. Beyond the first sealing gap, an air gap with a small gap diameter is arranged, which has at least one axially extending section.

According to the invention, the axially extending section of the air gap is delimited by an outer peripheral surface of the first bearing component and an inner circumferential surface of the rotor component.

Since the air gap is neither limited by surfaces of the base plate, nor is it in direct axial extension of the sealing gap, it is substantially independent of corresponding mounting tolerances and the height of the fluid dynamic bearing and can therefore be made very narrow and relatively long.

From the surface of the bearing fluid in the sealing gap constantly evaporates bearing fluid. The amount of vaporization depends on the temperature of the bearing fluid as well as the size of the boundary surface of the bearing fluid to the surrounding air. The resulting fluid vapor can escape to the atmosphere outside the bearing and condense within the engine.

According to the invention, a narrow air gap adjoins the sealing gap, which has at least one section running axially and preferably parallel to the axis of rotation of the motor. This axially extending portion of the air gap is limited in a preferred embodiment of the invention by an outer peripheral surface of the first bearing member and an inner peripheral surface of an annular recess of the rotor member.

Since the air gap is no longer in direct extension of the sealing gap but substantially radially outside and parallel to the sealing gap, the limited height of the bearing is optimally utilized. Furthermore, so that the entire design of the bearing is independent of the structure of the base plate, since the air gap is determined exclusively by components of the storage system.

According to the invention, it is provided that the gap spacing in the air gap is very small and its axial length parallel to the axis of rotation is as large as possible. Due to the small gap width and the large axial length of the air gap no or only very small air vortices will form in the region of the air gap, and due to the small cross section and the relatively large length of the air gap, only a small amount of fluid vapor can escape from the sealing gap and over the air gap , Thus, the storage system according to the invention has only low fluid losses and the life is increased compared to conventional two-sided open bearings.

In a preferred embodiment of the invention, the rotor component has an annular recess on its side facing the first bearing component. An upper edge of the first bearing component extends into this groove, wherein the axially extending portion of the air gap is formed by radially opposite surfaces of the edge of the bearing member and the recess. Especially with very flat fluid dynamic bearings this puncture is advantageous because not only the length of the axial extending portion of the air gap can be increased, but also the axial length of the sealing gap can be increased, since the first bearing member partially in this groove of the rotor component extends and overlaps with the rotor component.

The air gap also comprises a more or less long radially extending portion which is arranged between the axially extending portion of the air gap and the first sealing gap. The radially extending portion of the air gap is preferably bounded by a bottom surface of the recess and an end face of the edge of the first bearing member and has a larger gap width, as the axially extending portion of the air gap.

Preferably, the bottom surface of the recess and / or the end face of the edge of the first bearing component are provided with a bearing fluid-repellent coating. This coating prevents droplets of bearing fluid from depositing on these surfaces and can continue to migrate toward the axially extending portion of the air gap.

Preferably, a recirculation channel arranged in the rotor component and filled with bearing fluid is provided, which connects together mutually remote regions of the bearing gap. An opening of the recirculation channel opens into a region between the radially extending portion of the bearing gap radially outside of the thrust bearing and the first sealing gap. The other opening of the recirculation channel opens into a region of the bearing gap between the upper radial bearing and the second sealing gap.

The fluid-dynamic bearing system according to the invention is in particular provided for the rotational mounting of a spindle motor, as used to drive a hard disk drive.

The invention will be explained in more detail by means of exemplary embodiments, wherein further features and advantages of the invention will become apparent from the following description and the drawing.

Brief description of the drawings

1 shows a section through a spindle motor with a preferred embodiment of a bearing according to the invention.

2 shows a section through a spindle motor with a slightly modified embodiment of the bearing of the invention 1 ,

Description of the preferred embodiments of the invention

The 1 shows a spindle motor with a fluid dynamic bearing according to the invention. Such a spindle motor can be used to drive disks of a hard disk drive.

The spindle motor comprises a base plate 10 having a substantially central cylindrical opening in which a first bearing member 16 is included. The first bearing component 16 is about cup-shaped with a thick bottom and a peripheral edge 17 formed and includes a central opening, in which the shaft 12 is attached. At the free end of the fixed shaft 12 is a second bearing component 18 arranged, which formed as a stopper member and preferably annular and integral with the shaft 12 is trained. The named components 10 . 12 . 16 and 18 form the fixed component of the spindle motor.

The fluid dynamic bearing comprises a rotor component 14 with a molded bushing 14a in one by the shaft 12 and the two bearing components 16 . 18 formed intermediate space is rotatably arranged relative to these components. The upper bearing component 18 is in an annular recess of the rotor component 14 arranged. Adjacent surfaces of the shaft 12 , the rotor component 14 and the bearing components 16 . 18 are by a bearing gap open on both sides 20 separated from each other, which is filled with a bearing fluid, such as a bearing oil.

The bearing bush 14a has a cylindrical bore, on whose inner circumference two cylindrical bearing surfaces are formed, which by a circulating separator gap between them 24 are separated with increased gap width. The bearing surfaces of the bearing bush 14a enclose the standing wave 12 at a distance of a few microns to form an axially extending portion of the bearing gap 20 and are provided with herringbone bearing groove structures, so that they with the respective opposite bearing surfaces of the shaft 12 two fluid dynamic radial bearings 22a and 22b form.

To the lower radial bearing 22b closes a radially extending portion of the bearing gap 20 on, by radially extending annular bearing surfaces of the bearing bush 14a and corresponding opposite bearing surfaces of the first bearing component 16 is formed. These bearing surfaces form a fluid dynamic thrust bearing 26 , The fluid dynamic thrust bearing 26 is characterized in a known manner by spiral bearing groove structures, either on the front side of the bearing bush 14a , the first bearing component 16 or both parts can be attached. The bearing groove structures of the thrust bearing 26 preferably extend over the whole, annular bearing surface of the thrust bearing, ie from the inner edge to the outer edge.

Advantageously, all are for the radial bearings 22a . 22b and the thrust bearing 26 necessary Lagerrillenstrukturen on the bearing bush 14a arranged what the production of the bearing, in particular the shaft 12 and the bearing component 16 simplified.

To the radially extending portion of the bearing gap 20 radially outside of the thrust bearing 26 closes a proportionately filled with bearing fluid first sealing gap 34 on, passing through an outer peripheral surface of the bearing bush 14a and an inner peripheral surface 17 of the edge 16a of the first bearing component 16 is limited. The sealing gap 34 seals the end of the bearing gap on this side of the fluid bearing system against leakage of the bearing fluid from the bearing gap. The first sealing gap 34 includes one opposite the bearing gap 20 widened radially extending portion into which an opening of the recirculation channel opens, and a nearly axially extending portion which opens conically starting from the radially extending portion in its course. In addition to the function as a capillary seal, the sealing gap is used 34 as a fluid reservoir and provides the required for the life of the storage system amount of bearing fluid. Furthermore, through the sealing gap 34 Filling tolerances and a possible thermal expansion of the bearing fluid can be compensated. The two of the conical section of the sealing gap 34 forming surfaces on the bearing bush 14a and the first bearing component 16 can each be relative to the axis of rotation 46 slightly inclined radially inwards. At least, however, is the outer surface 15 the bearing bush 14a relative to the axis of rotation 46 inclined inwards. As a result, the bearing fluid in a rotation of the bearing due to the centrifugal force inward in the direction of the bearing gap 20 pressed. Preferably, the inner surface 17 of the bearing component 16 as well as the outer surface 15 the bearing bush 14a axially above the maximum level of the bearing fluid within the seal gap 34 parallel to the axis of rotation 46 aligned.

On the other side of the fluid bearing system is the bearing bush 14 following the upper radial bearing 22a designed so that it forms a radial extending surface, which with a corresponding opposite surface of the second bearing component 18 forms a radially extending gap. At the radially extending gap, an axially extending second sealing gap closes 32 on, which seals the bearing gap at this end. The second sealing gap 32 includes starting from the bearing gap 20 preferably a pump seal characterized by corresponding grooves 36 and widens in the further course with preferably conical cross-section. The sealing gap 32 is made by opposing surfaces of the bearing bush 14 and the bearing component 18 limited and can by an annular cap 30 be covered. The inner edge of the cap 30 forms together with the outer circumference of the shaft 12 a gap seal 31 out. This increases the safety against leakage of bearing fluid from the sealing gap 32 and further reduces leakage of vaporized bearing fluid from the seal gap 32 ,

The structured bearing surfaces of the fluid bearing system are preferably all on a single component, preferably the bearing bush 14 so that they can be made relatively easily with the required accuracy in a single operation. Due to the mounting of the bearing in the first bearing component 16 as a flange for connection to the base plate 10 serves, it is possible to mount the fluid bearing as a unit to fill with bearing fluid and test before the fluid bearing as a unit with the base plate 10 is connected.

The electromagnetic drive system of the spindle motor is formed in a known manner by a on the base plate 10 arranged stator arrangement 42 and a ring-shaped permanent magnet surrounding the stator assembly at a distance 44 at an inner circumferential surface of the rotor component 14 ,

In the case that the spindle motor only a fluid dynamic thrust bearing 26 having a force in the direction of the second bearing component 18 generated, a corresponding counterforce or biasing force must be provided on the movable bearing part, which holds the bearing system axially in balance. For this, the base plate 10 a ferromagnetic ring 40 have, the rotor magnet 44 axially opposite and is magnetically attracted by this. Alternatively, it is possible that the base plate 10 at least partially in the area below the rotor magnet 44 made of ferromagnetic material. This magnetic attraction acts against the force of the thrust bearing 26 and keeps the bearing axially stable. Alternatively or in addition to this solution, the stator assembly 42 and the rotor magnet 44 axially offset from each other, in such a way that the rotor magnet 44 axially further away from the base plate 10 is arranged as the stator assembly 42 , As a result, an axial force is built up by the magnet system of the motor, which also opposite to the thrust bearing 26 acts. Alternatively or additionally, between the bearing component 18 and the bearing bush 14 a second thrust bearing 50 be provided with spiral bearing grooves, the thrust bearing 26 counteracts.

In order to ensure a continuous flushing of the storage system with bearing fluid, in a known manner, a recirculation channel 28 intended. The recirculation channel 28 is also completely filled with bearing fluid.

Preferably, the rotor component comprises 14 at his the first bearing component 16 facing side an annular groove 14b in which a border 16a of the first bearing component 16 extends. The surfaces of the edge 16a form together with the surfaces of the puncture 16a an air gap 38 out. An axially extending section 38a of the air gap 38 is between an inner peripheral surface of the groove 14b of the rotor component 14 and an outer peripheral surface of the rim 16a arranged the first bearing component. A radially extending section 38b of the air gap 38 is between the axial section 38a of the air gap 38 and the first sealing gap 34 arranged and is through a bottom surface of the groove 14b and an end face of the edge 16a limited. The radially extending section 38b of the air gap 38 has a significantly greater gap width than the axially extending portion 38a of the air gap 38 ,

The radial gap width of the axially extending section 38a of the air gap 38 is for example between 0.02 and 0.1 mm. The axial length of the air gap 38a is for example 0.4 to 1.5 mm. The radially extending section 38b of the air gap 38 has an axial gap width of, for example, 0.1 to 0.3 mm. The radial gap width of the first sealing gap 34 is at its narrowest point typically 0.05 to 0.15 mm and widens in the direction of the radially extending portion of the air gap 38 for example, 0.18 to 0.4 mm. The axial length of the first sealing gap is for example 2.5 to 3.5 mm.

Due to the small gap width and the largely axial course arise in the narrow axially extending air gap 38a only very small centrifugal forces that can act on the fluid vapor. This ensures that the evaporated bearing fluid only very slowly through the air gap 38 can escape (diffuse). Instead, the fluid vapor collects in the region of the first sealing gap 34 , Due to the high concentration of fluid vapor above the interface additionally slows the evaporation rate.

2 shows a spindle motor with fluid dynamic bearings, which is substantially identical to the fluid dynamic bearing 1 , The same components are designated by the same reference numerals.

In contrast to 1 is the puncture 114b in the rotor component 114 wider and also the edge 116a of the first bearing component 116 has a distribution on its upper side. As a result, in particular, the radially extending portion 138b the air gap longer and the puncture 114b or the edge 116a The bearing component can be made easier due to the larger dimensions and larger tolerances.

The structure and functioning of the air gap 138 are the same as related to 1 has been described.

LIST OF REFERENCE NUMBERS

10

baseplate

12

wave

14, 114

rotor component

14a, 114a

bearing bush

14b, 114b

puncture

15

outer surface

16, 116

bearing component

16a, 116a

edge

17

18

bearing component

20

bearing gap

22a, 22b

radial bearings

24

separator gap

26

thrust

28

recirculation

30

cap

31

gap seals

32

second sealing gap

34

first sealing gap

36

pump seal

38, 138

air gap

38a, 138a

axially extending section

38b, 138b

radially extending section

40

ferromagnetic ring

42

stator

44

permanent magnet

46

axis of rotation

50

thrust

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008052469 A1 [0005]
• US 2010/0296190 A1 [0006]
• DE 102009035125 A1 [0006]

Claims (10)

Fluid dynamic bearing system, comprising: a fixed shaft ( 12 ), a first and a second bearing component ( 16 . 116 . 18 ) spaced at the shaft ( 12 ) are arranged, one relative to the shaft ( 12 ) and the bearing components ( 16 . 116 . 18 ) about a rotation axis ( 46 ) rotatably mounted rotor component ( 14 . 114 ), a bearing gap open on both sides ( 20 ) filled with a bearing fluid, the adjacent surfaces of the shaft ( 12 ), of the rotor component ( 14 . 114 ) and at least the first bearing component ( 16 . 116 ), at least one fluid dynamic radial bearing ( 22a . 22b ), which is arranged along an axially extending portion of the bearing gap, at least one fluid dynamic thrust bearing ( 26 ) along a radially extending portion of the bearing gap (FIG. 20 ), a first sealing gap ( 34 ) which is at least partially filled with bearing fluid and for sealing an open end of the bearing gap ( 20 ), at least one air gap ( 38 . 138 ) beyond the first sealing gap ( 34 ) is arranged and at least one axially extending portion ( 38a . 138a ), characterized in that the axially extending portion ( 38a . 138a ) of the air gap ( 38 . 138 ) by an outer peripheral surface of the first bearing component ( 16 . 116 ) and a radially opposite inner peripheral surface of the rotor component ( 14 . 114 ) is limited. Fluid dynamic bearing system according to claim 1, characterized in that the rotor component ( 14 . 114 ) at its first bearing component ( 16 . 116 ) facing side an annular groove ( 14b . 114b ), in which an upper edge ( 16a . 116a ) of the first bearing component ( 16 . 116 ), and the axially extending portion ( 38a . 138a ) of the air gap ( 38 . 138 ) by radially opposite surfaces of the edge ( 16a . 116a ) and the puncture ( 14b . 114b ) is formed. Fluid dynamic bearing system according to claim 1 or 2, characterized in that the upper edge ( 116a ) of the first bearing component ( 116 ) has a thickening. Fluid dynamic bearing system according to one of claims 1 to 3, characterized in that between the axially extending portion ( 38a . 138a ) of the air gap ( 38 . 138 ) and the first sealing gap ( 34 ) a radially extending section ( 38b . 138b ) of the air gap, which is defined by a bottom surface of the recess ( 14b . 114b ) and an end face of the edge ( 16a . 116a ) of the first bearing component ( 16 . 116 ) is limited and has a greater gap width than the axially extending portion ( 38a . 138a ) of the air gap. Fluid dynamic bearing system according to one of claims 1 to 4, characterized in that the bottom surface of the recess ( 14b . 144b ) and / or the end face of the edge ( 16a . 116a ) are provided with a bearing fluid-repellent coating. Fluid dynamic bearing system according to one of claims 1 to 5, characterized in that the axially extending portion ( 38a . 138a ) of the air gap radially outside the first sealing gap ( 34 ) is arranged and parallel to the axis of rotation ( 46 ) runs. Fluid dynamic bearing system according to one of claims 1 to 6, characterized in that in the rotor component ( 14 . 114 ) and filled with bearing fluid recirculation channel ( 28 ) is provided which connects mutually remote areas of the bearing gap with each other, wherein a first opening of the recirculation channel ( 28 ) in an area between the radially extending portion of the bearing gap ( 20 ) and the first sealing gap ( 34 ) opens. Fluid dynamic bearing system according to one of claims 1 to 7, characterized in that the first opening of the recirculation channel ( 28 ) in the plane of the radially extending portion of the bearing gap ( 20 ) opens. Spindle motor having a stator and a rotor, which is rotatably mounted relative to the stator by means of the fluid dynamic bearing system according to claims 1 to 8, and an electromagnetic drive system ( 42 . 44 ) for driving the rotor. Hard disk drive with a spindle motor according to claim 9 for the rotary drive of at least one magnetic storage disk, and a writing and reading device for writing and reading data on or from the magnetic disk.

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