DE102013008049A1 - Fluid dynamic storage system - Google Patents

Abstract

A fluid dynamic bearing system is described which comprises a fixed bearing component and a rotatable bearing component which is rotatably mounted about an axis of rotation relative to the fixed bearing component. A bearing gap, which is filled with a bearing fluid, is arranged between mutually opposite surfaces of the two bearing components, at least one fluid dynamic radial bearing and at least one fluid dynamic axial bearing being arranged along the bearing gap. The fixed component comprises a shaft with a stopper component, a filling reservoir for the bearing fluid being arranged between the stopper component and the rotatable bearing component. The invention is characterized in that the shaft has a circumferential groove in the form of a fillet in the area of the stopper component.

Description

Field of the invention

The invention relates to a fluid dynamic bearing system according to the features of the preamble of claim 1. Such fluid dynamic bearing systems are used, for example, for the rotational mounting of spindle motors, as they are in turn used to drive storage disk drives.

State of the art

Fluid dynamic bearing systems usually comprise at least two relatively rotatable bearing components, the bearing surfaces between each other a few microns wide and with a bearing fluid, for. B. bearing oil, filled bearing gap form. In a known manner, the bearing surfaces assigned and acting on the bearing fluid Lagerrillenstrukturen are provided. In fluid dynamic bearings, the bearing groove structures in the form of depressions or elevations are usually applied to individual or both bearing surfaces. These bearing groove structures arranged on corresponding bearing surfaces of the bearing partners serve as bearing and / or pumping structures which generate a hydrodynamic pressure upon relative rotation of the bearing components within the bearing gap. In radial bearings, for example, sinusoidal, parabolic or herringbone ("herringbone") bearing groove structures are used, which are arranged distributed on a surface parallel to the axis of rotation of the bearing components over the circumference of at least one bearing component. In axial bearings, for example, helical or herringbone bearing groove structures are used, which are arranged in a plane transverse to the axis of rotation.

There are known fluid dynamic bearing systems for spindle motors with fixed shaft and both sides open bearing gap. These storage systems include, for example, two axially spaced-apart fluid dynamic radial bearings and a fluid dynamic thrust bearing, which is often biased by an oppositely acting magnetic thrust bearing. A decisive advantage of a fixed shaft is that it can be firmly clamped at both ends. This gives such a storage system a very high structural rigidity, making it particularly suitable for spindle motors with high load, for example for driving hard disk drives for server application or hard disk drives with increased or special requirements, such as today in many mobile applications with steadily growing Data density and at the same time during normal operation existing vibrations occur.

An important step in the production of such a bearing is the filling of the bearing gap with bearing fluid. The bearing fluid is usually filled in the bearing gap after assembly of the bearing components. In a known filling method, a precisely measured amount of bearing fluid is introduced by means of a metering device in a specially designed annular filling reservoir. The filling reservoir is arranged, for example, between the rotor component and the shaft and connected to the bearing gap. The filled bearing fluid forms a closed ring of bearing fluid in the filling reservoir. The bearing fluid in the filling reservoir creeps into the bearing gap due to capillary forces. By vacuum process or rotation of the bearing, the filling process can be accelerated or optimized.

In order for the filling reservoir to be able to hold the entire amount of bearing fluid for filling the bearing at once, it must have a certain volume. The filling reservoir is usually located between the shaft and the bearing bush or the rotor component of the bearing, wherein the diameter of the shaft is co-determining the available size and geometry of the filling reservoir.

As the fluid dynamic bearings become smaller and smaller, the attachment of the shaft at its upper end plays an increasingly important role in order to improve the tendency of vibration and stability of the bearing. In particular, the frontal bearing surface of the shaft for attachment to a housing must have a certain size, d. H. have a certain diameter. Given the small space available in a fluid-dynamic bearing, increasing the shaft diameter in the region of the filling reservoir would mean a reduction in the volume of the filling reservoir. The upper surface of the shaft must also be large enough for the introduction of a hole, which is provided for the screw-fastening of a housing cover (top cover).

However, a reduced volume of the filling reservoir is unfavorable for the filling process. If, during the filling process, the intended amount of storage fluid for the bearing can not be accommodated at once in the filling reservoir, there is a risk that the filling reservoir adjacent surfaces of the shaft or the central bore of the shaft are contaminated with bearing fluid. To prevent this, a more complex process management, for example, a multi-stage filling process is necessary.

A reduction of the axial height of the bearing automatically leads to a reduced axial height of the filling reservoir and thus to a reduced filling volume.

There is therefore the need to provide a sufficiently large filling reservoir for fluid-dynamic bearings with a reduced overall height or with a larger shaft diameter.

Disclosure of the invention

It is the object of the invention to provide a fluid-dynamic bearing system, in particular for a spindle motor for driving a storage disk drive, in which despite reduced overall height and / or larger shaft diameter easy filling with bearing fluid is guaranteed.

This object is achieved by a storage system with the features of claim 1.

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

The fluid-dynamic bearing system comprises a fixed bearing component and a rotatable bearing component which is rotatably mounted relative to the stationary bearing component about a rotation axis. Between opposing surfaces of the two bearing components, a bearing gap is arranged, which is filled with a bearing fluid, wherein along the bearing gap at least one fluid dynamic radial bearing and at least one fluid dynamic thrust bearing are arranged. The fixed component comprises a shaft with a stopper component, wherein between the stopper member and the rotatable bearing member, a filling reservoir for the bearing fluid is arranged, the volume of which is sufficient to accommodate preferably the entire storage fluid required in the storage system.

The invention is characterized in that the shaft has a circumferential groove in the form of a groove in the region of the stopper component.

Due to the hollowed-out design of the shaft in the region of the filling reservoir, the volume of the filling reservoir is increased without reducing the diameter of the shaft as a whole or having to increase the overall height of the storage system. According to the invention, in particular the smallest diameter of the stopper component is arranged in the region of the groove, d. h., The smallest diameter of the groove is smaller than the diameter of the free end of the stopper member having an upper mounting surface.

So that no residues of bearing fluid remain in the filling reservoir after the fluid has been introduced into the bearing gap, it is preferred that the surface of the stopper component in the region of the filling reservoir has rounded shapes without sharp edges or burrs, on which the bearing fluid could adhere.

With the inventive construction of the shaft in the region of the stopper component, an enlargement of the contact area between the end face of the stopper component and a housing component can be realized. In other words, the stopper component may have a relatively large diameter at the upper end face, without the height of the bearing system or the diameter of the shaft or the stopper component would have to be increased.

With a suitable design can be achieved by suitable shaping of the groove that the bearing fluid is deflected by shock during the action of the groove and thus can not leave the area of the filling reservoir and escape to the outside.

In particular, the smallest diameter of the stopper component is in the region of the groove.

In this case, the groove is formed so that the surface of the stopper member has in the region of the groove at least at one point parallel to the axis of rotation extending Tangende.

The invention is particularly suitable for a fluid-dynamic bearing with a fixed shaft, which is accommodated with one end in a first bearing component and having a stopper component at another end.

The rotating component of the bearing system is preferably formed by a bearing bush or a bearing component having a rotor component, wherein the bearing bush between the fixed bearing member and the stopper member is rotatably mounted on the shaft.

In the embodiment according to the invention of a fluid-dynamic bearing, the bearing gap has two open ends, which are sealed by sealing means, for example capillary seals or dynamic pump seals. The filling reservoir is disposed adjacent to the sealing means, i. H. the sealing means are located between the bearing gap and the filling reservoir.

The described bearing system is suitable for the rotary mounting of a spindle motor, which has a stator and a rotor, wherein the rotor is driven by an electromagnetic drive system.

Preferred embodiments of the invention will be explained in more detail with reference to the drawings. This result from the Drawings and their description further features and advantages of the invention.

Brief description of the drawings

1 : shows a section through a spindle motor with a storage system according to the invention.

2 : shows an enlarged view of the filling and sealing area of the storage system of 1 ,

3 : shows an enlarged view of a modified embodiment of the filling and sealing region of the storage system of 1 ,

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The 1 shows a spindle motor with a fluid dynamic bearing system 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 bearing member 16 is included. The bearing component 16 is approximately cup-shaped and comprises a central opening, in which one end of a shaft 12 is attached. The attachment of the shaft 12 in the bearing component 16 can be done for example by a press fit. At the other end of the fixed shaft 12 is a stopper component 18 arranged, preferably annular and integral with the shaft 12 is formed and has a larger diameter than the remaining portions of the shaft 12 , The named components 10 . 12 . 16 and 18 form the fixed component of the storage system.

The bearing system comprises a rotor component in the form of a hub with integrated bearing bush 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 stopper component 18 is in an annular recess of the bearing bush 14a arranged. Adjacent surfaces of the shaft 12 , the bearing bush 14a and the bearing components 16 . 18 are through a narrow, open on both sides bearing gap 20 separated from each other. The bearing gap 20 is filled with a bearing fluid, such as a bearing oil. In principle, it is also possible, the rotor component 14 and the bearing bush 14a as two separate parts form.

The bearing bush 14a has a cylindrical bore on the inner circumference of two cylindrical radial bearing surfaces are formed, which opposite radial bearing surfaces of the shaft. These radial bearing surfaces have bearing groove structures 22a . 24a on that in connecting grooves 22b and 24b end and serve to ensure the pumping action despite axial tolerances in the manufacture and pressure equalization in the circumferential direction. The bearing groove structures 22a and 24a form two arranged in an axial distance fluid dynamic radial bearings 22 and 24 passing through an intervening separator gap 21 are separated. The radial bearing surfaces have a distance of a few microns during operation of the bearing to form the axially extending bearing gap 20 , The separator gap 21 is significantly wider than the bearing gap 20 and is about 50 to 100 microns.

To the lower radial bearing 24 closes a radially extending portion of the bearing gap 20 on, by radially extending thrust bearing surfaces of the bearing bush 14a and corresponding opposite thrust bearing surfaces of the bearing component 16 , which is at least in the region of the thrust bearing to increase the bearing life with DLC (diamond like carbon) is coated formed. These thrust bearing surfaces form a fluid-dynamic thrust bearing 26 in the form of an axis of rotation 46 vertical circular ring. The fluid dynamic thrust bearing 26 is in a known manner by, for example, spiral thrust grooves 26a marked either on the front side of the bearing bush 14a , the bearing component 16 or both parts can be attached. The axial bearing grooves 26a of the thrust bearing 26 preferably extend over the entire end face of the bearing bush 14a that is, from the inner edge to the outer edge.

Advantageously, all are for the radial bearings 22 . 24 , the thrust bearing 26 and possibly a pump seal 36 necessary bearing or pump groove structures on the bearing bush 14a arranged what the production of the bearing, in particular the shaft 12 and the bearing components 16 . 18 simplified.

At the radial portion of the bearing gap 20 in the area of the thrust bearing 26 closes a proportionately filled with bearing fluid first sealing gap 32 on, by opposing surfaces of the bearing bush 14a of the rotor component 14 and the bearing component 16 is formed and seals the relevant end of the storage gap. The first sealing gap 32 includes one opposite the bearing gap 20 widened radially extending portion that merges into a conically opening nearly axially extending portion of an outer peripheral surface of the bearing bush 14a and an inner peripheral surface of the bearing member 16 is limited. In addition to the function as a capillary seal, the sealing gap is used 32 as a fluid reservoir and provides the for the life of the storage system required amount of fluid ready. Furthermore, filling tolerances and a possible thermal expansion of the bearing fluid can be compensated. The two of the conical section of the sealing gap 32 forming surfaces on the bearing bush 14a and the bearing component 16 can each relative to the axis of rotation 46 to be 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.

On the other side of the storage system is the bearing bush 14a following the upper radial bearing 22 designed so that it forms a radial extending surface, which with a corresponding opposite surface of the stopper member 18 forms a radial gap. At the radial gap, an axially extending second sealing gap closes 34 on, the bearing gap 20 seals at this end. This sealing gap 20 is preferably made of an axially extending pump seal 36 with pump groove structures 36a and a capillary seal 35 together. Beyond the pump seal 36 expands the capillary seal 35 preferably with a conical cross section. The second sealing gap 34 is made by opposing surfaces of the bearing bush 14a and the stopper member 18 limited and can by an annular cap 30 be covered. The cap 30 is at a stage 38 of the rotor component 14 held and there, for example, glued, pressed and / or welded. The inner edge of the cap 30 can be together with the outer circumference of the shaft 12 a gap seal 31 form. This increases the safety against leakage of bearing fluid, for example by evaporation, from the second sealing gap 34 ,

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 is arranged.

Since the spindle motor only a fluid dynamic thrust bearing 26 having a force in the direction of the stopper member 18 generated, a corresponding counterforce or biasing force must be provided on the movable bearing component, 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. 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 magnetic center of the rotor magnet 44 axially further away from the base plate 10 is arranged as the magnetic center of the stator assembly 42 , As a result, an axial force is built up by the magnet system of the motor, which is opposite to the thrust bearing 26 acts.

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 as axially or slightly inclined channel in the bearing bush 14a is formed and is preferably at an acute angle with respect to the axis of rotation 46 of the warehouse. The recirculation channel 28 connects the two radial sections of the bearing gap 20 between the bearing areas and the sealing areas directly to each other and preferably ends in the radially outer portion of the thrust bearing 26 in that the axial gap distance is greater than the part of the thrust bearing gap which is closer to the shaft 12 is arranged adjacent. Due to the directed pumping action of the bearing groove structures of the thrust bearing 26 and the radial bearing 22 . 24 results in the bearing gap 20 preferably a flow of the bearing fluid from the thrust bearing 26 , over the lower radial bearing 24 to the upper radial bearing 22 and via the recirculation channel 28 back again. In addition, the bearing fluid in the recirculation channel 28 due to the effect of centrifugal force in the inclined channel downwards in the direction of the thrust bearing 26 promoted, so that sets a stable fluid circuit.

Due to the centrifugal force acting on the bearing fluid within the channel, it is necessary to maintain a flow of the bearing fluid in the bearing gap 20 sufficient if the lower radial bearing 24 total upwardly pumping asymmetric bearing structures, ie the lower branches of the radial bearing grooves 24a are slightly longer than the upper branches of the radial bearing. The upper radial bearing 22 On the other hand, it can be largely symmetrical.

2 shows an enlarged view of the bearing of 1 in the area of the stopper component 18 , You can see the wave 12 and that at the end of the wave 12 arranged stopper component 18 , one opposite the shaft 12 having enlarged outer diameter. The bearing bush 14a is around the wave 12 rotatably arranged.

Between the wave 12 and the bearing bush 14a runs the axial portion of the bearing gap 20 , In this section is also the upper radial bearing 22 with corresponding radial bearing grooves 22a arranged.

Above the radial bearing 22 ends the axial portion of the bearing gap 20 in a groove and then kinks in the radial direction to the outside, before he again kinks in the axial direction and there in the sealing gap 34 empties.

The sealing gap 34 widens conically at its end and merges into a filling reservoir 48 , which by an outer peripheral surface of the stopper member 18 and an inner peripheral surface of the rotor member 14 or the bearing bush 14a is formed. The volume of the filling reservoir 48 is preferably large enough to hold the entire required amount of bearing fluid for the bearing.

The filling reservoir 48 is through a cover 30 covered. The cover 30 forms with the stopper component 18 a gap seal 31 out.

Along the sealing gap 34 is a dynamic pump seal 36 arranged by pump groove structures 36a which is on the surface of the stopper member 18 or preferably on the inner peripheral surface of the bearing bush 14a are arranged.

Upon rotation of the bearing bush 14a around the shaft 12 generate these pump groove structures 36a a pumping action on the bearing fluid in the sealing gap 34 and promote it in the direction of the bearing gap 20 ,

The pump seal 36 forms a first sealing area 50 , Above the pumping seal widens the sealing gap 34 on and forms another sealing area 52 in the form of a capillary seal 35 , This sealing area 52 must not over the inner peripheral surface 58 go out so that no bearing fluid is thrown out of the camp during operation of the bearing due to the centrifugal force. When the bearing is at a standstill, this decreases in the sealing gap 34 Bearing fluid present the level shown, and forms a meniscus along the sealing area 52 the capillary seal. Above the sealing area of the pump seal 50 the filling area starts 54 , Below the sealing area of the pump seal 50 there is a rest area 49 which prevents air from entering the bearing fluid circuit during operation of the bearing.

The filling reservoir 48 is formed by an inner circumferential surface of the bearing bush 14a extending from an initially axial inner peripheral surface 58 radially outward in the form of a curved surface 60 expands.

Opposite is the filling reservoir 48 by a radially inwardly curved surface 62 the stopper component 18 formed, which is a groove 56 formed. Through this groove 56 can the volume of the filling reservoir 48 be increased accordingly, depending on the groove of the groove 56 Without the diameter of the shaft or the stopper component would have to be reduced overall. The radius of the groove 56 should be at least 0.25 mm, so that some of the bearing fluid does not stick in the groove.

The diameter D3 of the stopper component 18 in the area of the throat 56 is smaller than the diameter D4 on the front side of the stopper component 18 to which this component is attached to a housing component.

Further, the diameter D3 is smaller than the diameter D2 of the stopper member 18 in the field of dynamic pumping seal 36 , In addition, the diameter D2 of the stopper member 18 greater than the diameter D1 of the shaft 12 , The following relation holds: D3 <D4 <D2 and D1 <D2. The diameter D4 is at least 1.2 times larger than the diameter D1.

After assembly of the warehouse is located in the bearing gap 20 and in the sealing gaps 34 . 32 still no bearing fluid. For filling the bearing is therefore the required amount of storage fluid in the filling reservoir 48 brought in. Preferably, the filling reservoir 48 a sufficient volume to accommodate the entire amount of storage fluid needed to fill the bearing.

By capillary forces and / or application of a vacuum process now wanders in the filling reservoir 48 located bearing fluid through the sealing gap 34 in the storage gap 20 and takes the in 2 shown level at which the bearing fluid into the capillary sealing area 52 enough.

Axial above the sealing area of the capillary seal 52 There is no oil during operation.

The in the filling area 54 extending surface 62 the stopper component 18 is gently curved and goes into the groove 56 above.

3 shows a modified embodiment of the in 2 shown area of the storage system of 1 ,

The difference to 2 exists in particular in the course (contour) of the surface 62 the stopper component 18 showing the inner boundary of the filling reservoir 48 forms. Starting from the axially extending outer peripheral surface of the stopper member 18 in the area of the sealing gap 34 the radius of the stopper component decreases 18 essentially linear, so that there is a relatively straight surface 62 ' yields, which then at its end in a curved surface of the groove 56 passes.

In essence, the area can be 62 respectively. 62 ' be configured arbitrarily and the groove 56 form. However, it is only necessary to pay attention to the angle that the area 62 bw. 62 ' with the rotation axis 46 includes, is a relatively acute angle, for example, less than 50 °, so that is ensured that in the filling reservoir 48 introduced bearing fluid completely into the sealing gap 34 and bearing gap 20 flows in and not on the surfaces of the filling reservoir 48 remains.

Above the throat 56 the diameter D3 of the stopper component widens 18 back to the diameter D4 and forms an end surface for attachment of the stopper member 18 on a housing component.

LIST OF REFERENCE NUMBERS

10

baseplate

12

wave

14

rotor component

14a

bearing bush

16

bearing component

18

stop member

20

bearing gap

21

separator gap

22

radial bearings

22a

Radial grooves

22b

connecting grooves

24

radial bearings

24a

Radial grooves

24b

connecting grooves

26

thrust

26a

Axiallagerrillen

28

recirculation

30

cap

31

gap seals

32

seal gap

34

seal gap

35

capillary

36

pump seal

36a

Pumping groove structures

38

step

40

ferromagnetic ring

42

stator

44

rotor magnet

46

axis of rotation

48

Einfüllreservoir

49

rest area

50

Sealing area pump seal

52

Sealing area capillary seal

54

filling area

56

fillet

58

Inner circumferential surface

60

area

62, 62 '

area

D1

diameter

D2

diameter

D3

diameter

D4

diameter

R

Radius of the fillet

Claims (13)

Fluid dynamic bearing system, comprising: at least one stationary bearing component ( 12 ; 16 ; 18 ), at least one rotatable bearing component ( 14 ; 14a ), which relative to the fixed bearing component about an axis of rotation ( 46 ) is rotatably mounted, a bearing gap ( 20 ) formed between opposed surfaces of the fixed and rotatable bearing components and filled with a bearing fluid, at least one fluid dynamic radial bearing ( 22 ; 24 ) and at least one fluid dynamic thrust bearing ( 26 ) along sections of the storage gap ( 20 ) are arranged, wherein the fixed component is a shaft ( 12 ) with a stopper component ( 18 ), wherein between the stopper component ( 18 ) and the rotatable bearing component ( 14a ) a filling reservoir ( 48 ) is arranged for the bearing fluid, characterized in that the shaft ( 12 ) in the region of the stopper component ( 18 ) a circumferential groove in the form of a groove ( 56 ) having. Fluid dynamic bearing system according to claim 1, characterized in that the stopper component ( 18 ) in the region of the groove ( 56 ) has its smallest diameter D3. Fluid dynamic bearing system according to one of claims 1 or 2, characterized in that the stopper component ( 18 ) has in the region of its end face a diameter D4 which is greater by at least a factor of 1.2 than the diameter D1 of the shaft ( 12 ) in the region of the fluid dynamic radial bearing ( 22 ; 24 ). Fluid dynamic bearing system according to one of claims 1 to 3, characterized in that the surface of the stopper component ( 18 ) in the region of the groove ( 56 ) at least at one point one parallel to the axis of rotation ( 46 ) has running tangent. Fluid dynamic bearing system according to one of claims 1 to 4, characterized in that the surface of the stopper component ( 18 ) in the region of the filling reservoir ( 48 ) has rounded contours without sharp edges. Fluid dynamic bearing system according to claim 5, characterized in that the radius of the groove ( 56 ) is at least 0.25 mm. Fluid dynamic bearing system according to one of claims 1 to 6, characterized in that the fixed component is a bearing component ( 16 ) in the bearing component ( 16 ) recorded wave ( 12 ) and arranged on the shaft stopper member ( 18 ), wherein the components ( 16 ; 18 ) at a mutual distance on the shaft ( 12 ) are arranged. Fluid dynamic bearing system according to one of claims 1 to 7, characterized in that the rotating component is a bearing bush ( 14a ) or a rotor bushing having a bearing bush ( 14 ), wherein the bearing bush ( 14a ) between the two components ( 16 ; 18 ) on the shaft ( 12 ) is rotatably arranged. Fluid dynamic bearing system according to one of claims 1 to 8, characterized in that the bearing gap ( 20 ) has two open ends which are sealed by sealing means ( 32 ; 35 ; 36 ) are sealed. Fluid dynamic bearing system according to claim 9, characterized in that the sealing means capillary seals ( 32 ; 35 ). Fluid dynamic bearing system according to claim 9 or 10, characterized in that the sealing means at least one dynamic pumping seal ( 36 ). Fluid dynamic storage system according to one of claims 1 to 11, that the filling reservoir ( 48 ) adjacent to one of the sealants ( 34 ) is arranged. Spindle motor with a stator ( 42 ) and a rotor ( 14 ) and a fluid dynamic bearing system according to one of claims 1 to 12 for pivotal mounting of the rotor ( 14 ) generated by an electromagnetic drive system ( 42 ; 44 ) is driven.

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