DE102010048027A1 - Spindle motor of hard disk drive assembly, has stopper element that limits backlash of shaft and faces bearing bush collar, where radial length of overlap portion between stopper element and collar is preset percentage of collar radius - Google Patents

Abstract

The spindle motor has a fixed bearing bush (12) that is arranged in an opening of a base plate (10), and a shaft (26) which is rotatably mounted in an axial bore of bearing bush by fluid dynamic bearing, and connected with a hub. An electromagnetic drive unit rotationally drives the hub. A stopper element (38) limits the axial backlash of shaft, and faces a collar (12a) of bearing bush where the stopper element is separated from the collar by an axial gap. The radial length (L) of overlap portion between stopper element and collar is 15% of the radius (R) of collar.

Description

Field of the invention

The invention relates to a spindle motor with a fluid dynamic bearing with stopper function, in particular for driving a disk drive.

State of the art

From the prior art a variety of different constructions of spindle motors with fluid dynamic bearing is known.

For example, the US Pat. No. 6,834,996 B2 a spindle motor with a fluid dynamic bearing system. The storage system comprises a bearing bush and a rotatably mounted therein shaft whose bearing surfaces are separated by a bearing gap. The bearing surfaces of bearing bush and shaft form two radial bearings. A thrust bearing is formed in the region of the open end of the bearing gap between an end surface of the bearing bush and a lower surface of the rotor (hub) of the spindle motor. The radial and axial bearings are characterized by bearing structures that exert a pumping action on the bearing fluid during rotation of the bearing and generate a corresponding bearing pressure. At an open end of the bearing gap, a compensation volume or a sealing gap is provided which receives a supply of bearing fluid or prevents leakage of the bearing fluid from the bearing. So that the bearing fluid can circulate in the bearing gap, a recirculation bore is preferably provided, which connects the closed end of the bearing gap with the open end of the bearing gap. In order to prevent falling out of the combination of shaft and hub of the bearing bush, a so-called stopper element is arranged on the hub, which cooperates with a arranged on the bearing bushing stopper edge. This is a so-called wet-stopper system in which the stopper surfaces are surrounded by bearing fluid and are located in the region of the sealing gap.

The stopper element is fastened during assembly of the bearing in a ring shoulder of the hub. During operation of the bearing, the bearing surfaces run without contact on a fluid film. The stopper surfaces do not touch either. In the event of extreme axial shock on the bearing, the stopper surfaces perform their function by abutting each other, with large acceleration forces acting on the rotor of the spindle motor.

A sufficiently large axial shock overcomes the bearing force of the thrust bearing, so that the stopper surfaces touch and hitting each other hard. During operation of the bearing, a gap section filled with bearing fluid is located between the stopper surfaces, the bearing fluid located in this gap section being pushed out during shock action. This is relatively easy, as join the gap section between the stopper surfaces further column, which have a relatively large gap distance, so that the bearing fluid is not opposed to much resistance and this can easily escape from the gap section. The stopper surfaces thus beat almost undamped and hard together and have an amplification factor of about one. This is defined as the quotient of the excited acceleration and the excitation acceleration.

Disclosure of the invention

It is the object of the invention to provide a spindle motor with fluid dynamic bearing system, which has an improved axial damping, so that the effects of axial shock are reduced.

This object is achieved by a spindle motor with the features of claim 1.

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

Described is a spindle motor with fluid dynamic storage system, in particular for the drive of storage disks of a hard disk drive. The spindle motor comprises a base plate, a fixed bearing bush arranged in an opening of the base plate and a shaft rotatably mounted in an axial bore of the bearing bush by means of the fluid-dynamic bearing system. A hub is attached to the shaft. Further, a stopper member for limiting the axial play of the shaft is present, which is axially opposite a collar of the bearing bush, separated by a gap and forms an overlap therewith. The hub is driven in rotation by an electromagnetic drive system. According to the invention, the radial length of the overlap between the stopper element and the collar of the bearing bush is at least 15% of the radius of the collar.

The stopper member is disposed in a space formed by surfaces of the hub and the bearing bush and disposed on the hub or a member connected to the hub.

Due to the radial overlap between the stopper element and the collar of the bearing bush is a perpendicular or oblique to the axis of rotation extending and filled with bearing fluid gap section educated. The length of the overlap, that is, this gap section, is at least 15% of the radius of the collar according to the invention. This means that there is a relatively large amount of bearing fluid in the gap section between the stopper surfaces, much more than in comparable stopper arrangements of known spindle motors. Due to this enlarged "fluid supply" in the gap section, an increased damping effect is achieved in the case of an axial shock, since a significantly greater resistance is counteracted by the longer gap section and the bearing fluid flows out of the gap section much more slowly in the event of an axial shock. This reduces the speed of approaching the two stopper surfaces. This has the consequence that the forces acting on the rotor acceleration forces are much lower, since the stop between the stopper surfaces is significantly attenuated and less hard. Further, with a larger pulse width of the exciting vibration, the gain becomes smaller.

The gap section is arranged between a gap with a significantly greater gap spacing, which adjoins a radial section of the bearing gap, and a sealing gap, which is arranged beyond the gap section. Although these above-mentioned gap and the sealing gap have gap spacings which are many times greater than the gap distance of the bearing gap, a significantly better damping effect is achieved by the relatively large length of the gap portion between the stopper surfaces and it is difficult to the bearing fluid, in the adjacent Drain column with larger gap distance.

The stopper surfaces are surrounded by the bearing fluid, wherein an inner peripheral surface of the stopper element defines together with an outer peripheral surface of the bearing bush the sealing gap which is partially filled with bearing fluid.

The fluid dynamic bearing comprises at least one radial bearing, which is arranged between the shaft and the bearing bush, and a thrust bearing between the bearing bush and hub. The radial and axial bearings are characterized by suitable bearing groove structures, which are arranged on the bearing surfaces and generate a hydrodynamic pressure in the bearing gap upon rotation of the bearing components.

A recirculation bore disposed in the bearing bush connects one end of the bearing gap to the other end and allows circulation of the bearing fluid from one end of the bearing gap to the other. In this case, the upper end of the recirculation bore can open either radially inside or outside or in the middle of the axial bearing region.

The invention also relates to a storage disk drive having at least one storage disk which is driven in rotation by a spindle motor designed according to the invention. The disk drive includes means for writing and reading data to and from the disk arranged in a closed housing together with the spindle motor and the disk.

Preferred embodiments of the invention will be explained in more detail with reference to the drawings. In this case, 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 according to a first embodiment of the invention.

2A shows a section of the spindle motor according to the first embodiment accordingly 1 ,

2 B shows a section of a spindle motor according to a second embodiment of the invention.

3 : shows a diagram in which the expected during an axial shock acceleration force is shown on the rotor as a function of the diameter of the collar of the bearing bush.

Detailed descriptions with the preferred embodiments of the invention

1 shows a section through a structure of a fluid dynamic bearing system according to the invention or a rotatably mounted by means of the bearing system spindle motor.

The spindle motor includes a stationary motor assembly and a rotating motor assembly rotatably supported by the bearing system relative to the fixed assembly. The fixed arrangement comprises a base plate 10 to which the remaining engine components are attached. The base plate 10 comprises a central sleeve-shaped part with a central bore, in which a substantially hollow cylindrical bearing bush 12 is fastened, for example by pressing, gluing or welding. The base plate 10 For example, may be made of light metal, such as aluminum, while the bearing bush 12 may consist of suitable metals / alloys or ceramics. A wave 14 For example, made of steel or ceramic, is in the bore of the bearing bush 12 around a rotation axis 16 rotatably arranged. The wave 14 has a slightly smaller diameter than the bore in the bearing bush 12 , so between the shaft 14 and the bearing bush 12 a bearing gap 18 remains, which is filled with a bearing fluid, such as bearing oil. In an axial section of the bearing gap 18 are at a mutual distance two fluid dynamic radial bearings 20 and 22 arranged, which by corresponding bearing groove structures on the surface of the bore of the bearing bush 12 or the peripheral surface of the shaft 14 Marked are. With a rotation of the shaft 14 in the bearing bush 12 becomes through these bearing groove structures of the radial bearings 20 . 22 in the storage gap 18 generates a pumping action on the bearing fluid, through which a hydrodynamic pressure in the bearing gap 18 is built. The radial bearings 20 . 22 preferably have a pumping action in a specific axial direction, preferably in the direction of the closed end of the bearing, through a cover plate 24 is closed, in a recess of the bearing bush 12 is attached and the bearing bush 12 Air and oil seal closes. Between the end of the wave 14 and the cover plate 24 a gap remains which is connected to the bearing gap and filled with bearing fluid.

A free end of the wave 14 , which from the bore of the bearing bush 12 protrudes, is with a hub 26 connected, which has a cup-shaped cross-section and partially encloses the storage system. The hub 26 is for example on the free end of the shaft 14 pressed. The hub 26 has a circumferential approximately cylindrical edge, on the inner diameter of a rotor magnet 28 is attached. The rotor magnet 28 surrounds a stator assembly 30 attached to a sleeve-shaped approach of the base plate 10 is attached. The stator arrangement 30 forms with the rotor magnet 28 the electromagnetic drive system of the spindle motor. The stator arrangement 30 consists of a magnetic core and corresponding phase windings wound on the magnetic core. If the spindle motor is used to drive a disk drive, be on the hub 26 For example, one or more disks attached and rotated by this.

The upper end face of the bearing bush 12 attached to the bottom of the hub 26 adjacent, is formed as an axial bearing surface, as well as the adjacent surface of the underside of the hub 26 , The two bearing surfaces of the bearing bush 12 and the hub 26 are by the radially extending in this area bearing gap 18 separated from each other and form a thrust bearing 32 , which also like the two radial bearings 20 . 22 characterized by Lagerrillenstrukturen on the surface of the bearing bush 12 and / or the surface of the hub 26 are arranged. The thrust bearing 32 is along a radially extending portion of the bearing gap 18 arranged, which adjoins the axially extending portion of the radial bearing gap. The thrust bearing 32 includes, for example, spiral or herringbone bearing groove structures, one in the direction of the axially extending portion of the bearing gap 18 generate directed pumping action and the bearing fluid in the interior of the bearing gap 18 in the direction of the radial bearings 20 . 22 promote.

In the axial direction opposite the rotor magnet 28 is a ferromagnetic ring 34 provided, which of the rotor magnet 28 magnetically attracted and a thrust bearing 32 oppositely directed force on the hub 26 generated.

Preferably, in the bearing bush 12 a recirculation hole 42 provided, which is the closed end of the bearing, ie the area of the gap below the shaft 14 with the open end of the bearing in the area of the thrust bearing 32 connects with each other. As a result, the bearing fluid in the bearing gap 18 and the recirculation bore 42 circulate. The circulation of the bearing fluid is through the next to the bearing gap 18 or the recirculation bore 42 Arranged arrows marked.

Radially outward of the thrust bearing 32 the bearing gap widens 18 in a gap 36 with a larger gap distance, which then kinks approximately at right angles and on a stopper element 38 meets. The stopper element 38 is on an inner circumference of an annular projection of the hub 26 attached and lies a bunch 12a the bearing bush 12 axially opposite. The stopper element 38 and the covenant 12a the bearing bush 12 prevent excessive axial displacement of hub 26 and wave 14 and falling out of the arrangement of hub and shaft from the bearing bush. The gap 36 kinks in the area of the stopper element 38 one more time and runs along a substantially radially extending gap portion 36a between the stopper element 38 and the federal government 12a , The gap section 36a defines the overlap between the stopper element and the collar 12a the bearing bush 12 , The gap section 36a kinks again and opens into a substantially axially extending sealing gap 40 , which is designed as a capillary seal, in particular as a conical capillary seal. The sealing gap 40 is limited by an outer peripheral surface of the bearing bush 12 and an opposite inner circumferential surface of the stopper element 38 , The the sealing gap 40 limiting surfaces of the bearing bush 12 and the stopper element 38 For example, they can be parallel to the axis of rotation 16 However, they are preferably slightly inward in the direction of the axis of rotation 16 inclined. Preferably, the inner diameter of the stopper member increases 38 in the direction of the opening of the sealing gap 40 to a lesser extent than the outer diameter of the bearing bush 12 . so that a substantially conical cross section of the sealing gap 40 results.

According to the invention, the gap section 36a between the two stopper surfaces, ie between the stopper element 38 and the federal government 12a the bearing bush 12 especially long trained. The gap section 36a in this case according to the invention has a radial length L, ie a length perpendicular to the axis of rotation 16 at least 15% of the radius R of the bushing 12 in the area of the federal government 12a is. The gap section 36a is between the gap 36 and the sealing gap 40 arranged, both of which have a significantly greater gap distance, as the bearing gap 18 , For example, in a spindle motor for driving a 2.5 inch hard disk drive, the diameter of the shaft is 2.5 mm. The diameter of the bearing bush 12 in the area of the federal government 12a is for example between 7 mm and 8 mm. The gap distance of the bearing gap 18 is in the range of the axial bearing, for example, 20-30 microns. The gap distances of the gap 36 and the sealing gap 40 Both are more than 100 microns. Due to the length L of the gap section 36a For example, if larger than 0.7 mm is selected, there will be a relatively large amount of bearing fluid in the gap section 36a , which in case of an axial shock effect on the bearing in the direction of the gap 36 or the sealing gap 40 is pushed out. By increasing the length L of the section 36a however, the time required for the gap portion increases 36a to completely deflate in a shock, which period determines the relative axial damping of the bearing in the axial direction. As a result, the maximum occurring acceleration forces on the rotor at a contact of the stopper surfaces of stopper element 38 and edge 12a the bearing bush 12 significantly reduced. Experiments have shown that the maximum occurring acceleration forces can be reduced by up to a factor of 4.

2A shows a section of the bearing of the spindle motor according to 1 , 2 B shows a section through a second embodiment of a storage system according to the invention. One recognizes those in the bearing bush 112 rotatably mounted shaft 114 as well as on the shaft 114 arranged hub 126 , on the outer edge of the stopper element 138 is arranged. The stopper element 138 opposite is the federal government 112a the bearing bush 112 , In contrast to the first embodiment of the invention is in the embodiment 2 B the gap section 136a obliquely to the axis of rotation 116 arranged, ie the respective stopper surfaces of the stopper element 138 and the federal government 112a run obliquely, for example, at an angle of 45 ° to the axis of rotation 16 , At the gap section 138a In turn, the wide gap is bounded 136 and the conically widening sealing gap 140 at. Due to the inclination of the gap section 138a corresponds to the radial length L of the gap portion 138a not the absolute length of the gap section 138a but is a little lower due to the angle. The absolute length of the gap section 138a is chosen according to the invention, the radial length L of the gap portion 138a at least 15% of the radius R of the federal government 112a is.

3 shows a diagram in which schematically the expected in an axial shock maximum acceleration forces on the rotor 26 depending on the diameter of the federal government 12a the bearing bush 12 are shown. In the example shown according to 1 and 2 has the bearing system of the spindle motor or the bearing bush 12 an outside diameter in the area of the covenant 12a for example, from 7 to 8 millimeters, with the shaft about 2.5 millimeters in diameter. The entire spindle motor with rotor then has about 20 to 25 millimeters in diameter.

One recognizes 3 that with increasing outside diameter of the covenant 12a the bearing bush 12 Starting at about 6.9 millimeters to about 7.95 millimeters, the maximum acceleration force acting upon contact of the stopper surfaces with the rotor rapidly decreases from about 4500 G to substantially below 1000 G. An increasing outside diameter of the bush of the bush 12 means according to the invention an increase in the length L of the gap portion 36a respectively. 136a , by which the axial damping of the bearing is increased, whereby the maximum acceleration force acting on the rotor in shock, is reduced. Of course, according to the invention not only the outer diameter of the Federal 12a the bearing bush 12 be increased, but also the opposite surface of the stopper element 38 . 138 , so that a correspondingly long gap section 36a respectively. 136a can be achieved.

LIST OF REFERENCE NUMBERS

10

baseplate

12, 112

bearing bush

12a, 112a

Collar (bearing bush)

14, 114

wave

16

axis of rotation

18

the bearing gap

20

radial bearings

22

radial bearings

24

cover

26, 126

hub

28

rotor magnet

30

stator

32

thrust

34

Ferromagnetic ring

36, 136

gap

36a, 136a

gap section

38, 138

stopper member

40, 140

seal gap

42

Rezirkulationsbohrung

L

radial length of the gap section 36a . 136a

R

Radius of the covenant 12a . 112a

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

• US 6834996 B2 [0003]

Claims (10)

Spindle motor with fluid dynamic bearing system, in particular for the drive of storage disks of a hard disk drive, with a base plate ( 10 ), one in an opening of the base plate ( 10 ) fixed bearing bush ( 12 . 112 ), a rotatably mounted in an axial bore of the bearing bush by means of the fluid dynamic bearing system shaft ( 14 . 114 ), a hub connected to the shaft ( 26 . 126 ), a stopper element ( 38 . 138 ) for limiting the axial play of the shaft, which is a collar ( 12a . 112a ) of the bushing is separated axially by a gap and forms an overlap therewith, and an electromagnetic drive system ( 28 . 30 ), characterized in that the radial length L of the overlap between the stopper element ( 38 . 138 ) and the federal government ( 12a . 112a ) of the bearing bush is at least 15% of the radius R of the federal government. Spindle motor according to claim 1, characterized in that the stopper element ( 38 . 138 ) in one through surfaces of the hub ( 26 . 126 ) and the bearing bush ( 12 . 112 ) formed free space is arranged. Spindle motor according to one of claims 1 or 2, characterized in that by the overlap between the stopper element ( 38 . 138 ) and the federal government ( 12a . 112a ) of the bearing bush a perpendicular or oblique to the axis of rotation ( 16 ) extending and filled with bearing fluid gap portion ( 36a . 136a ) is formed. Spindle motor according to one of claims 1 to 3, characterized in that a radial portion of the bearing gap ( 18 ) into a gap filled with bearing fluid ( 36 . 136 ) merges with a significantly larger gap distance. Spindle motor according to one of claims 1 to 5, characterized in that an inner circumferential surface of the stopper element ( 38 . 138 ) together with an outer peripheral surface of the bearing bush ( 12 . 112 ) a partially filled with bearing fluid sealing gap ( 40 . 140 ) trains. Spindle motor according to one of claims 1 to 5, characterized in that the gap section ( 36a . 136a ) between the gap ( 36 . 136 ) and the sealing gap ( 40 . 140 ), wherein the gap distances of the gap ( 36 . 136 ) and the sealing gap ( 40 . 140 ) are many times larger than the gap distance of the bearing gap ( 18 ). Spindle motor according to one of claims 1 to 6, characterized in that at least one radial bearing ( 20 . 22 ) by mutually facing bearing surfaces of the bearing bush ( 12 . 121 ) and the wave ( 14 . 114 ), wherein these bearing surfaces by an axially extending portion of the bearing gap ( 18 ) are separated from each other. Spindle motor according to one of claims 1 to 7, characterized in that a thrust bearing ( 32 ) by mutually facing bearing surfaces of the bearing bush ( 12 . 112 ) and the hub ( 26 . 126 ), wherein these bearing surfaces by a radially extending portion of the bearing gap ( 18 ) are separated from each other. Spindle motor according to one of claims 1 to 8, characterized in that a recirculation bore ( 42 ) separated from each other sections of the storage gap directly connects. A disk drive with a spindle motor according to any one of the preceding claims.

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