DE102019107232A1 - Spindle motor and shaft or bearing bush for this spindle motor - Google Patents

Abstract

The invention relates to a spindle motor with a stationary motor component, which comprises a bearing bush (10), and a rotatable motor component, which comprises a shaft (12) rotatably mounted in the bearing bush (10) and a hub (20) connected to it, which by means of a Press connection is connected to a shaft journal (12a) of the shaft (12) and wherein the shaft has a bearing surface (22a) of a fluid dynamic radial bearing (22) adjoining the shaft journal (12a), at least part of the bearing surface (22a) of the shaft (12) has a conical widening (28), the diameter of the shaft (12) increasing in the area of the conical widening (28) in the direction of the shaft journal (12a).

Description

The invention relates to a spindle motor and a shaft or a bearing bush for this spindle motor according to the preamble of the independent claims.

Spindle motors are usually electrical DC machines that are used for a variety of drive purposes, such as hard disk drives, lasers, optical devices or other purposes.

Two basic designs are common here, on the one hand motors with a rotating shaft that is rotatably mounted in a bearing bush and carries the hub of the spindle motor, and spindle motors with a fixed shaft on which a rotating bearing bush is mounted, with the bearing bushing in this design the hub is connected.

The present invention relates to all types of spindle motors with a rotating shaft which have an axial threaded bore arranged in the shaft. This threaded hole is used to fasten a holder for fastening a load on the hub of the spindle motor, the holder being fixed in the threaded hole by means of a screw.

Such a spindle motor generally comprises a stationary motor component which comprises a base plate and a bearing bush connected thereto, and a rotatable motor component which comprises the shaft rotatably mounted in the bearing bush and the hub connected thereto. One end of the shaft preferably has a shaft journal that is connected to the hub by means of a press connection.

As a rule, such a spindle motor comprises a fluid dynamic bearing system which, for example, has two radial bearings which are arranged along an axially running bearing gap between bearing surfaces of the shaft and bearing surfaces of the bearing bush. The axial forces are absorbed by one or more axial bearings.

The first fluid dynamic radial bearing has bearing surfaces which adjoin the shaft journal in the axial direction. The second fluid dynamic radial bearing with corresponding bearing surfaces is arranged at a distance from this first fluid dynamic radial bearing.

For use in hard disk drives or, for example, laser scanners, the running accuracy of the spindle motors is becoming increasingly demanding. The components must therefore be manufactured and assembled very precisely in order to achieve the specified running accuracy of the spindle motors.

The problem here is that the shaft is connected to the hub by means of a press connection, with very high forces acting on the shaft through this press connection. As a result of the forces acting on the shaft, the shaft is deformed radially inward, in particular in the area of the press connection and in the area of the adjacent bearing surface of the upper fluid dynamic radial bearing.

This deformation is reinforced by the fact that the shaft has an axial threaded hole in the area of the shaft journal and the first radial bearing for fastening the retaining screw.

Forces are also generated by screwing the retaining screw into the axial bore of the shaft, which, however, act radially outward on the shaft.

The DE 10 2013 022 267 A1 deals with this problem and reveals in 3 a spindle motor of the type described above with a central retaining screw, in which the influence of the expansion of the shaft by the retaining screw in the area of the radial bearing is to be reduced, as the thread of the retaining screw is only below the radial bearing, i.e. between the two fluid dynamic radial bearings in the so-called separator area with an enlarged gap width, is arranged.
As a result, the expansion of the shaft by screwing in the retaining screw has no negative influence on the geometry of the radial bearing surfaces or the gap width of the bearing gap in this shaft section.

It is the object of the invention to provide a spindle motor with a shaft or bearing bush suitable for this spindle motor, in which the risk of deformation of the shaft, in particular due to the press connection between shaft and hub, can be largely compensated for.

According to the invention, this object is achieved by a spindle motor and a shaft or a bearing bush having the features of the independent claims.

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

According to the invention, a spindle motor is proposed in which part of the bearing surface of the first radial bearing, which adjoins the shaft journal, has a conical widening such that the diameter of the shaft in the area of conical expansion in the direction of the shaft journal increases.

This conical widening of the bearing surface is, for example, one or more micrometers and is selected such that the amount of the constriction or deformation of the bearing surface due to the press connection between the shaft and the hub is compensated as far as possible.

The expansion of the shaft in the area of the bearing surface, which is caused by the fastening screw in the central bore of the shaft, must also be taken into account.

However, this widening is relatively small in comparison with the constriction caused by the press connection, so that the constriction caused by the fastening screw is only slightly reduced.

The greatest compensation for the constriction of the shaft caused by the press connection can therefore be achieved by the conical expansion of the shaft.

In a preferred embodiment of the invention, the conical widening extends over at least half of the bearing surface of the first radial bearing closest to the shaft journal, since in this area of the bearing surface in particular a significant constriction of the shaft is caused by the influence of the press connection.

A shaft for a fluid dynamic bearing system is also claimed which has a shaft journal and a first bearing surface of a fluid dynamic radial bearing adjoining the shaft journal, at least part of this bearing surface of the shaft having a conical widening such that the diameter of the shaft in the area this conical widening increases in the direction of the shaft journal.

Of course, in the context of the invention, it is also possible not to use the shaft in a spindle motor 12th in the area of the storage area 22a with a conical widening 28 to be provided, but it can also be provided in reverse, the hole in the bearing bush 10 to be designed so that the bearing surface of the bearing bush 10 in the area of the upper radial bearing 22nd and especially above the apex line 26th has a conical constriction.

I.e. in this case the diameter of the bearing bore is the bearing bush 10 not constant, but decreases above the apex line 22nd in the direction of the shaft journal 12a or the closest face of the bearing bush 10 each by the amount d / 2 .

• 1 zeigt eine Ansicht einer Welle eines Spindelmotors mit aufgepresster Nabe und einer in die axiale Gewindebohrung eingedrehten Befestigungsschraube.
• 2 zeigt einen vergrößerten Schnitt von 1 im Bereich der Welle mit schematischer Darstellung der Lagerbuchse.
• 3 zeigt ein Diagramm der Deformation der Welle durch äußere Einflüsse.
• 4 zeigt eine Ansicht der erfindungsgemäßen Welle.
• 5 zeigt ein vergrößertes Detail der erfindungsgemäßen Welle von 4.

The invention is explained in more detail below with reference to the drawings. This results in further features and advantages of the invention.

• 1 shows a view of a shaft of a spindle motor with a pressed-on hub and a fastening screw screwed into the axial threaded bore.
• 2 shows an enlarged section of 1 in the area of the shaft with a schematic representation of the bearing bush.
• 3 shows a diagram of the deformation of the shaft due to external influences.
• 4th shows a view of the shaft according to the invention.
• 5 FIG. 8 shows an enlarged detail of the shaft according to the invention from FIG 4th .

1 shows a section of part of a spindle motor, in particular the shaft 12th of the spindle motor and the hub 20th , which by means of a press connection on a shaft journal 12a the wave 12th is arranged.

On one end of the shaft 12th is an axial threaded hole 12b provided in which a screw 14th can be rotated, which is used to attach a load or a bracket (not shown) to fix a load on the hub 20th serves.

2 shows an enlarged view of the shaft 12th from 1 .

The wave 12th includes a shaft journal at its upper end 12a on which the hub 20th is pressed on by means of a press connection.

The axial threaded hole can also be seen 12b on the upper face of the shaft 12th extending over much of the axial length of the shaft 12th extends.

In this threaded hole 12b becomes the fastening screw 14th screwed in to attach a load to the hub 20th serves.

The wave 12th is rotatable in a bearing bush 10 stored, which is shown here only schematically.

The bearing bush 10 includes a bearing bore that is slightly larger than the outer diameter of the shaft 12th so that between the shaft 12th and the bearing bush a bearing gap 18th remains, which is filled with a bearing fluid, for example a bearing oil. The lower end of the bearing bush 10 is by means of a cover 16 locked.

On the one in the bearing bush 10 located end of the shaft can be a stopper ring 12c be arranged in an enlarged recess of the bearing bush 10 is recorded and a falling out of the shaft 12th from the bearing bush 10 prevented.

Along the axial course of the bearing gap 18th are on the wave 12th and the bearing bush 10 Storage areas 22a , 24a arranged, which together a first fluid dynamic radial bearing 22nd and a second fluid dynamic radial bearing 24 form. The bearing surfaces on the shaft 12th and the bearing bush 10 are through the annular bearing gap filled with bearing fluid 18th separated from each other.

In the area of the shaft journal 12a is the hub 20th by means of a press connection with the shaft 12th joined.

Due to this press connection in the area of the shaft journal 12a and especially by the weakening of the wave 12th through the axially running threaded hole 12b the shaft is deformed 12th radially inwards predominantly in the area of the press connection, i.e. in the area of the shaft journal 12a , but also in the area of the shaft journal 12a subsequent storage area 22a the wave 12th .

Due to the fact that the storage area 22a the wave 12th in the area of the upper first radial bearing 22nd deformed inwards, the width of the bearing gap increases 18th in the area of the first radial bearing 22nd .

The bearing gap is usually a few micrometers wide, so that a widening of the bearing gap by 0.5 to 1 micrometer has a significant impact on the bearing properties of the radial bearing.

The wave 12th deforms more strongly in the area of the press connection than in the lower area further away from the press connection, so that an approximately conical deformation and conical widening of the bearing gap occurs in the area of the first radial bearing 22nd results.

This is how the individual areas of the radial bearing act 22nd unevenly strong and produce uneven bearing forces that reduce the performance of the bearing, in particular this upper radial bearing 22nd absorbs a large part of the bearing forces of the bearing system, since it is close to the center of gravity.

3 shows a schematic diagram of the radial deformation of the shaft 12th over their length, caused on the one hand by the press connection and on the other hand by the additional use of the fastening screw 14th .

The deformation is shown in relation to a zero line, with the radial deformation of the shaft on the ordinate 12th is shown in both directions perpendicular to its longitudinal axis.

The curves 30th and 32 show the total deformation of the shaft 12th caused by the press connection between the shaft 12th and hub 20th .

The axial length of the shaft is on the abscissa 12th applied, being along the area 22 ' the wave 12th the storage area 22a of the first radial bearing 22nd extends and along the area 24 ' the wave 12th the storage area 24a of the second radial bearing 24 .

The storage areas 22a , 24a are provided with bearing groove structures which are arranged obliquely to the direction of rotation and to the left and right of an apex line 26th a differently directed pumping action on the bearing fluid in the bearing gap 18th exercise.

It can be seen that according to the curves 30th and 32 the constriction of the shaft 12th by the press connection mainly in the area 22 ' the storage area 22a to the left of the apex line 26th , ie in close proximity to the shaft journal 12a he follows.

In this case, the maximum constriction of the shaft is approximately one micrometer, which results in a maximum diameter reduction of the shaft of two micrometers in the area of the press connection.
To the right of the apex line 26th a deformation of the bearing surface can hardly be seen, not even in the further course of the shaft or in the radial bearing area 24 ' of the second radial bearing 24 .

By screwing in the fastening screw 14th into the threaded hole 12b the wave 12th becomes the wave 12th stretched slightly radially outwards, so that according to the curves 34 and 36 overall a smaller diameter constriction of the shaft 12th results in the closest point to the shaft journal 12a is a maximum of 2 × 0.75 micrometers and also approximately to the apex line 26th enough.

By screwing in the fastening screw 14th becomes the diameter reduction of the shaft 12th reduced by about a quarter, which, however, still means a total constriction of the diameter of 1.5 micrometers.

With a gap width of the bearing gap 18th The constriction of the shaft is three to four micrometers 12th by up to 1.5 micrometers to an increase in the width of the bearing gap by 30% and more, what the performance of the bearing just in the area to the left of the apex line 26th significantly deteriorated.

In the 3 shown constriction of the shaft 12th has an approximately conical shape, ie starting approximately from the apex line 26th the diameter of the shaft decreases 12th in the direction of the shaft journal 12a continuously.

According to the invention it is according to the 4th and 5 provided that in the field 22 ' of the first radial bearing 22nd the storage area 22a or part of the storage area 22a the wave 12th above the apex line 26th a conical expansion 28 receives.

In 5 is shown that the shaft 12th starting from the apex line 26th the storage area 22a is made in such a way that its diameter D extends in the direction of the shaft journal 12a enlarged in the form of a conical widening 28 .

The diameter D of the shaft 12th increases in the direction of the shaft journal by an amount d , with the amount d or 2 * d / 2 of the expansion 28 about the amount of constriction starting from the central axis of the shaft 12th according to 3 corresponds.

According to the examples 3 can for the amount d / 2 about 0.75 micrometers, so that the diameter enlargement d the shaft is 1.5 microns.

The shaft diameter D is, for example, 3.5 millimeters, the diameter of the threaded hole 12b for the threaded screw 14th depending on the version of the spindle motor is between 1.3 and 1.6 millimeters.

Through this expansion of the diameter D of the shaft 12th by the amount d in the area of the storage area 22a of the upper radial bearing 22nd , especially part of the storage area 22a , the constriction of the shaft caused by the press connection 12th essentially compensated so that the shaft diameter D is in the range 22 ' the storage area 22a of the upper radial bearing 22nd remains approximately constant and corresponds to the specified shaft diameter D.

The gap width of the bearing gap thus changes 18th in the area of the upper radial bearing 22nd not, and the radial bearing retains its full capacity.

List of reference symbols

10

Bearing bush

12

wave

12a

Shaft journal

12b

Threaded hole

12c

Stop ring

14th

screw

16

cover

18th

Bearing gap

20th

hub

22nd

fluid dynamic radial bearing

22a

storage area

22 '

storage area

24

fluid dynamic radial bearing

24a

storage area

24 '

storage area

26th

Apex line

28

conical expansion

30th

Curve

32

Curve

34

Curve

36

Curve

D.

Outer diameter shaft

d

Amount of deformation of the shaft diameter

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102013022267 A1 [0012]

Claims (12)

Spindle motor with a stationary motor component, which comprises a bearing bush (10), and a rotatable motor component, which comprises a shaft (12) rotatably mounted in the bearing bush (10) and a hub (20) connected to it, which by means of a press connection with a shaft journal (12a) is connected to the shaft (12) and wherein the shaft has a bearing surface (22a) of a fluid dynamic radial bearing (22) adjoining the shaft journal (12a), characterized in that at least part of the bearing surface (22a) of the shaft ( 12) has a conical widening (28), the diameter of the shaft (12) increasing in the area of the conical widening (28) in the direction of the shaft journal (12a). Spindle motor after Claim 1 , characterized in that the conical widening (28) of the shaft (12) extends at least from the apex line (26) of the bearing surface (22a) over that part of the bearing surface (22a) of the shaft which is closest to the shaft journal (12a). Spindle motor according to one of the Claims 1 or 2 , characterized in that the conical expansion (28) of the diameter of the shaft (12) is one or more micrometers. Spindle motor with a stationary motor component, which comprises a bearing bush (10), and a rotatable motor component, which comprises a shaft (12) rotatably mounted in a bearing bore of the bearing bush (10) and a hub (20) connected to it, which by means of a press connection with a shaft journal (12a) of the shaft (12) is connected, and wherein the bearing bush (10) has a bearing surface (22a) of a fluid dynamic radial bearing (22) adjacent to the shaft journal (12a), characterized in that at least part of the bearing surface of the bearing bore the bearing bush (10) has a conical constriction, the diameter of the bearing bore of the bearing bush (10) decreasing in the area of the conical constriction in the direction of the shaft journal (12a). Spindle motor after Claim 4 , characterized in that the conical constriction of the bearing bore of the bearing bush (10) extends over at least half of the part of the bearing surface (22a) of the bearing bush (10) which is closest to the shaft journal (12a). Spindle motor according to one of the Claims 4 or 5 , characterized in that the conical constriction of the diameter of the bearing bore of the bearing bush (10) is one or more micrometers. Shaft (12) for a fluid dynamic bearing system with a shaft journal (12a) and a bearing surface (22a) of a fluid dynamic radial bearing (22) adjoining the shaft journal (12a), characterized in that at least part of the bearing surface (22a) of the shaft ( 12) has a conical widening (28), the diameter of the shaft (12) increasing in the area of the conical widening (28) in the direction of the shaft journal (12a). Wave after Claim 7 , characterized in that the conical widening (28) of the shaft (12) extends over at least half of that part of the bearing surface (22a) which is closest to the shaft journal (12a). Spindle motor according to one of the Claims 7 or 8th , characterized in that the conical widening (28) of the diameter of the shaft (12) is one or more micrometers. Bearing bush (10) for a fluid dynamic bearing system with a bearing bore and a bearing surface of a fluid dynamic radial bearing (22) adjacent to an end face, characterized in that at least part of the bearing surface of the bearing bush (10) has a conical constriction, the diameter of the bearing bore being in Area of the conical constriction decreases in the direction of the adjacent end face. Bearing bush after Claim 10 , characterized in that the conical constriction of the bearing bore of the bearing bush (10) extends over at least half of the part of the bearing surface (22a) closest to the end face of the bearing bush (10). Spindle motor according to one of the Claims 10 or 11 , characterized in that the conical constriction of the diameter of the bearing bore of the bearing bush (10) is one or more micrometers.

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