DE10231962B4 - Hydrodynamic bearing, spindle motor and hard disk drive - Google Patents

Abstract

Hydrodynamic bearing with
a shaft (10),
a bearing sleeve (12) which surrounds the shaft at a small radial distance to form a concentric bearing gap (24),
a compensation volume (20) having a passage opening (20 '),
at least one connecting gap (26) which connects the bearing gap (24) via the passage opening (20 ') with the compensating volume (20), wherein the connecting gap (26) between a front end of the bearing sleeve and one, with a small distance parallel to the front end arranged, on the bearing sleeve (12) mounted annular disc (28) is formed, and wherein the passage opening (20 ') at a distance from the bearing gap (24), is arranged radially outside thereof.

Description

The The invention relates to a hydrodynamic bearing, a spindle motor and a hard drive.

Usually there is a spindle motor for one Hard disk drive consisting of a rotating component, the rotor, the a ring-shaped Permanent magnet is assigned, and a stationary component, the Stator, which is associated with a coil-wound laminated core, with the rotor facing the stator is rotatably mounted by means of a suitable storage system.

there Hydrodynamic bearings are increasingly being used in addition to the rolling bearings that have been used for a long time for use. A hydrodynamic bearing is an advanced one Slide bearing, which consists of a bearing sleeve with cylindrical inner bearing surface and one in the sleeve used shaft formed with cylindrical bearing outer surface is. The diameter of the shaft is slightly smaller than the sleeve inner diameter, whereby a concentric bearing gap between the two bearing surfaces resulting in the formation of a coherent capillary film with a Lubricant, preferably with oil, filled is.

The WO 02/10602 A discloses a hydrodynamic bearing with a compensation volume, which is formed by grooves in a lower hood of the bearing becomes. additionally At the open end of the bearing, an oil stop disc is provided. which prevents in Series of bumps of oil from the Warehouse exit. While the filling process is oil between the oil stop disc and that of porous sintered Material existing bearings. The oil then diffuses in this sintered bearing. Oil escaping from the bearing collects in the grooves in the lower hood and diffuses partially back into the sintered material bearing.

Around to prevent bearing oil from the hydrodynamic bearing exits, this is a front end the bearing sleeve is hermetically sealed. At the opposite open end between the motor shaft and bearing surface can be a concentric, conically widening free space be formed equally as a lubricant reservoir and serves as expansion volume. This free space takes over also the function of sealing the bearing.

The in the space between the motor shaft and conical outlet opening of the bearing sleeve located oil forms under the influence of Capillary forces one stable, coherent Liquid film, which is why this type of seal also called capillary seal becomes.

A such solution For example, U.S. Pat. Patent 5,667,309. The bearing sleeve has at the front end a conical area, whereby between shaft and bearing sleeve a concentric, cone-shaped expanding space arises. This serves as expansion volume, in which the bearing oil can ascend when the liquid level increases with increasing temperature. This prevents bearing oil from the bearing bush exit. The free space also serves as a "lubricant reservoir" for the replacement of evaporating Bearing oil. The bearing is deliberately "overfilled" to the effective liquid level to keep approximately constant in the bearing gap despite evaporation of the bearing oil. Of the concentric free space thus serves as a kind of overflow volume, at the same time is a lubricant reservoir. The disadvantage is that the retention capacity and so that the sealing effect of the concentric, widening conically Freiraums because of the growing outward Cross-section decreases.

One Another disadvantage of this known solution is that the usable Length of the Bearing and thus the bearing stiffness by the axial length of a such a "capillary seal" so concentric, conical expanding free space, is reduced. Here are the axial height of the "seal" cone and the associated angle of inclination dependent of the desired Filling volume and the viscosity of the bearing oil. Low viscosity bearing oils require a smaller acute angle and thus at the same Filling volume a larger length. For fluid bearings with bearing sleeve open on both sides reduces the for the hydrodynamic radial bearing usable length equal at both ends the bearing sleeve. additionally becomes the retention capacity of the warehouse on the bearing oil film worsened by the widening cross-section at the ends of the bearing sleeve. In principle therefore hydrodynamic bearings are closed on one side bearing sleeve preferred for better retention. Another disadvantage arises from the fact that at higher speeds considerable centrifugal forces on the bearing oil acting on the bearing oil ascend to the edge of the bearing sleeve in the conical space can let so that Risk that this is thrown off, rises.

An important criterion for the suitability of hydrodynamic bearings in hard disk drives, especially in portable devices, is the lowest possible power loss of the bearing. One way to achieve this goal is to use a low viscosity bearing oil which, as described above, has a suitably adapted one The dimensioning of a hydrodynamic radial bearing with sufficient rigidity is thereby severely limited and may no longer be possible with very small spindle motors.

It Thus, it is an object of the invention to provide a hydrodynamic bearing a suitable, non-contact To specify a seal that is as small as possible Power loss, high bearing stiffness and a long service life Has.

These Task is by a hydrodynamic bearing with the features of claim 1 solved. The invention also provides a spindle motor according to claim 13 and a hard disk drive according to claim 14 ago.

The The invention provides a hydrodynamic bearing for a spindle motor, with a shaft with a rotating or a stationary component connected, and an associated preferably cylindrical bearing sleeve which surrounds the shaft. Due to a small diameter difference between shaft and cylindrical bearing sleeve creates a bearing gap, which is filled with a bearing fluid. In the area of the bearing gap is in the shaft and / or in the cylindrical bearing sleeve formed at least one radial bearing portion. This one will, like known in the art by structuring in particular the Inside of the bearing sleeve formed with a groove pattern. In the hydrodynamic invention Bearing is also provided a compensation volume for the bearing fluid, which is at the same time expansion volume, in which the bearing fluid can expand as the fluid level increases with increasing temperature, and as a lubricant reservoir for the replacement of evaporating bearing fluid serves. This compensating volume is according to the invention via at least a connecting gap, in particular a micro-gap with the bearing gap connected, wherein the micro-gap, the bearing gap with an opening of the Compensating volume connects, in the radial direction outside, with Distance to the bearing gap is arranged. The micro-gap is according to the invention between a front end of the bearing sleeve and one arranged at a small distance parallel to the front end Ring disc formed. This creates between the two opposite surfaces an annular gap of the inner diameter of the bearing sleeve to to or near its outer diameter enough. The distance between the front end of the bearing sleeve and Ring disc is sized so that between these a capillary film can form.

The opening of the Compensation volume can be one or more parts, in the form of an annular gap-shaped passage, be realized one or more individual Duchgänge.

The Invention has the advantage that the Compensation volume not along the usable storage length in one Part of the storage gap must be formed, but that it outside arranged the bearing gap and laid, in particular radially outward can be and connected to the bearing gap over the micro gap becomes. This allows the bearing sleeve with more than the entire bearing length unchanged Diameter are formed, resulting in a bearing gap with maximum usable length. The radial bearing sections of the hydrodynamic bearing can therefore closely adjacent the respective ends of the bearing with maximum Distance from each other are formed, creating an optimal bearing stiffness is reached.

The Forming a compensation volume is preferably at least a front end of the bearing sleeve intended.

There the compensation or storage volume in the hydrodynamic according to the invention Warehouse outside the bearing gap, preferably substantially perpendicular to the axis of rotation, is arranged and has a radially outwardly tapering cross section, at its radially outer end the connection is made to the micro-gap, this bearing is equally for engines with rotating or stationary shaft and / or both sides open bearing sleeve suitable. In a preferred embodiment the compensating volume is adjacent to the front end of the bearing sleeve and runs essentially parallel to the micro-gap arranged underneath.

The hydrodynamic bearings according to the invention can be used in electric motors and in particular at Spindle motors for Hard disk drives.

The Compensating or storage volume is arranged and configured, that this bearing fluid contained therein at any time due to capillary forces especially with axial shock load effectively tied up becomes.

This Effect is in engines with rotating bearing sleeve by the on the bearing fluid acting centrifugal forces still significantly supported, so that too at radially acting acceleration forces by dripping caused centrifuging of bearing fluid is almost impossible.

Both by the arrangement of the compensation volume outside of the bearing gap over the micro-gap as well as by its configuration with radially outwardly tapering cross-section leakage of bearing oil is effectively prevented, so that in addition to an increase in life in particular the reliability of the hydrodynamic bearing is significantly improved.

at an embodiment According to the invention, the micro gap directly adjoins the radial bearing section in the storehouse, while in another embodiment the invention of the micro-gap over one piece the bearing gap indirectly connected to the radial bearing section is. It is essential in both embodiments that between the radial bearing section and the micro-gap a capillary connection exists, so that the Bearing fluid a coherent Capillary film from the bearing gap over the Micro gap forms in the compensation volume.

Of the Micro-gap is preferably wholly or at least partially in the bearing sleeve formed and extends from the inner diameter of the bearing sleeve, starting radially outward, where the connection to the equalization volume takes place. At a special advantageous embodiment the invention is the micro-gap as circumferential of the inner diameter the bearing sleeve outgoing capillary annular gap formed, the radial bearing section or connects the bearing gap with the compensation volume.

Preferably the equalization volume is approximately parallel to the micro gap in a region which encloses an angle "α" with the axis of rotation, due to the simpler Making an angle of 90 ° is preferred becomes.

Preferably has the annular disc on its outer circumference Recesses that connect between the micro-gap and the Compensating volume form.

The Compensation volume is preferably between this annular disc and a arranged on the front side of the bearing sleeve cover formed, wherein the cover depending on the embodiment of the hydrodynamic Bearing a face plate, a bearing sleeve surrounding the pot or the like can be. Particularly preferably, the compensation volume is a formed concentric, rotationally symmetric cavity whose Cross section tapers from the inside to the outside radially, wherein the longitudinal axis of the V-shaped Cross section spans a sectional plane which is substantially perpendicular runs to the axis of rotation.

The Connection between equalization volume and micro gap takes place in the outer edge area over the arranged there recesses, so that on the micro-gap a continuous capillary film between bearing gap and compensation volume sets.

in the Area of the front ends of the bearing sleeve can be a paragraph on the shaft be provided by an annular disc and / or a cover at least partially radially overlapped is to fix the shaft in the axial direction or secure. This radial overlap granted additional Protection against clogging of bearing fluid with appropriate shock load.

The The invention is described below with reference to preferred embodiments closer to the drawings explained. In the figures show:

1 shows a schematic longitudinal section through a hydrodynamic bearing according to a first embodiment of the invention.

2 shows a schematic longitudinal sectional view of a modified embodiment of the hydrodynamic bearing of 1 ;

3 shows a schematic longitudinal sectional view of another embodiment of the hydrodynamic bearing according to the invention;

4 shows a longitudinal sectional view of a modified embodiment of the hydrodynamic bearing of 3 ;

5 shows a schematic longitudinal sectional view of another embodiment of the hydrodynamic bearing according to the invention;

6a shows a plan view of an annular disc for use in a hydrodynamic bearing according to the invention;

6b shows a plan view of a modification of the annular disc of 6a ,

In all Drawings are corresponding components with the same reference numerals designated.

This in 1 shown hydrodynamic bearing comprises a shaft 10 in a cylindrical bearing sleeve 12 is included. The wave 10 indicates at its from the bearing sleeve 12 enclosed end a pressure plate (thrust plate) 14 on, with the bearing sleeve 12 at this end by an abutment (counter plate) 16 is completed, the axial bearing force acting on the shaft 10 acts, over the pressure plate 14 receives. The bearing sleeve 12 is with the interposition of a spacer ring 46 in a Holding cup or pot 18 used. With the help of the spacer ring 46 can the gap between pressure plate 14 and abutments 16 be set.

The wave 10 is at her shaft end 10 ' from the bearing sleeve 12 led out. The bearing sleeve 12 is at this end through the floor 18 ' of the pot 18 completed, a central opening 18 '' having.

The bearing sleeve 12 is at her one front end 12 ' thus formed - in the embodiment shown, it has a radially inner, annular recess - that between the front end 12 ' and an annular disc 28 leading to the front end 12 ' is aligned substantially parallel, a micro-gap 26 is formed, the axis of rotation 22 of the hydrodynamic bearing is substantially perpendicular. In a practical implementation, the recess may have a depth of about 2-10 μm, in particular about 5 μm.

Between the wave 10 and the bearing sleeve 12 is a storage gap 24 formed over the micro-gap 26 at the front 12 ' the bearing sleeve 12 and at least one passage opening 20 ' in the ring disk 28 with the compensation volume 20 , which is explained in more detail below, is connected. The micro-gap 26 is formed by the fact that the annular disc 28 with a very small distance to the front side 12 ' the bearing sleeve 12 is attached, so that a circumferential annular gap is formed, which is a capillary connection between the bearing gap 24 and the equalization volume 20 forms and maintains. The thickness of the micro gap 26 corresponds approximately to the thickness of the bearing gap 24 ,

The compensation volume 20 is between the annular disc 28 and the bearing sleeve 12 surrounding pot 18 arranged and is formed in the embodiment shown in that the central opening 18 '' of the pot bottom 18 ' as in 1 shown conically bent to form a concentric conical annular space, wherein the cone base, the at least one arranged in the outer edge region of the annular disc passage opening 20 ' at least partially overlaps and so the connection between the compensation volume 20 and the micro-gap 26 manufactures. The passages 20 ' be through corresponding recesses in the outer edge region of the annular disc 28 formed, see 6a and 6b ,

In the embodiment shown are preferably on the inner diameter of the bearing sleeve 12 Radial bearing sections (not shown) by a groove structure on the inner diameter of the bearing sleeve 12 educated. Additionally, in the area of the printing plate 14 and the abutment 16 be formed in known per se thrust bearing sections. Because the equalization volume 20 and the bearing gap 24 with the compensation volume 20 connecting micro-gap 26 at the front end 12 ' the bearing sleeve 12 are formed, is the entire length of the bearing sleeve 12 for the training of one or more radial bearing sections available. In particular, two radial bearing portions at the respective end portions of the bearing sleeve 12 be formed with a maximum distance from each other, so that a maximum bearing stiffness is achieved.

After mounting the hydrodynamic bearing according to the invention, the bearing gap 24 and part of the equalization volume 20 filled with bearing fluid, in particular with a storage oil-based fluid.

The degree of filling of the compensation volume 20 with fluid is chosen so that on the one hand sufficient lubricant can be introduced to ensure permanent lubrication of the hydrodynamic bearing over the entire life.

On the other hand, in the filled part of the compensation volume 20 remain sufficient space into which the bearing fluid can expand, if at a temperature rise currency end of the operation, the total volume of the fluid due to different thermal expansion coefficients increases.

The non-bearing fluid filled part of the compensation volume 20 will accumulate as a result of the evaporation rate of the bearing fluid with gaseous fluid, with increasing saturation of the evaporation process is increasingly delayed.

If bearing fluid from the bearing gap 24 It evaporates through its boundary surface into the surrounding atmosphere, through the compensation volume 20 located bearing fluid through the contiguous and by means of the micro-gap 26 stabilized capillary film connection between the bearing gap 24 and equalization volume is replaced.

In this way it can be ensured that the bearing gap 24 is completely filled with bearing fluid over the entire life, so that in the hydrodynamic bearing according to the invention caused by lack of lubrication due to dry running "scuffing" is excluded.

In particular, when installing the hydrodynamic bearing according to the invention in engines in which the bearing sleeve 12 Part of the rotor is, so rotates together with the rotor, are the centrifugal forces caused by the rotation, which in the compensation volume 20 and in the micro-gap 26 located bearing fluid, essentially in Balance. As the amount of in the compensation volume 20 bearing fluid is usually slightly larger than that of the bearing fluid in the micro-gap 26 Due to the centrifugal forces, the bearing fluid tends to be in the compensation volume 20 stronger outward, thus ensuring that the Kapillarfilmverbindung the bearing fluid from the bearing gap 24 over the micro gap 26 into the equalization volume 20 does not break off.

In the embodiment shown, the shaft 10 and the bearing sleeve 12 made of steel and the pot 18 made of aluminum, wherein the skilled person can choose other suitable materials depending on the specific requirements.

2 shows a schematic longitudinal sectional view of a modification of 1 , wherein corresponding parts are designated by the same reference numerals. The embodiment of the 2 differs from 1 in that, instead of the hydrodynamic thrust bearing, a spur bearing (pivot type bearing) 30 is provided. All functional elements are in the correspondingly designed bearing sleeve 12 mounted so that the pot 18 or the support cup can be omitted.

The hill-top camp 30 the in 2 As shown in the prior art is known per se. The at the shaft end of the shaft 10 Trained toe supports itself against the abutment 16 from. In the embodiment of the 2 is a wave 10 with a radial bearing section 32 shown. The skilled person will understand, however, that all embodiments of the invention one or more, in particular two such radial bearing sections in the region of the longitudinal extension of the shaft 10 or the bearing sleeve 12 can have.

The micro-gap 26 that the bearing gap 24 over the opening 20 ' with the compensation volume 20 connects is in the embodiment of the 2 between a depression in the front end 12 ' the bearing sleeve 12 and an annular disc 28 educated. The ring disk 28 has at its periphery recesses which the openings) 20 ' form as in 2 right from the axis of rotation 22 by the radial shortening of the annular disc 28 indicated.

The front end 12 ' the bearing sleeve 12 is in the embodiment of the 2 further formed so that there is a cover plate 34 can take, which in a matching recess in the front end 12 ' the bearing sleeve 12 fitted and secured with this by welding, gluing, screwing or other suitable connection and is hermetically sealed.

2 shows, for example, a weld 36 for fixing the cover plate 34 in the bearing sleeve 12 , The cover plate 34 is provided with a chamfer or countersink, so that between this and the annular disc 28 a conical compensating volume 20 that forms radially inward, towards the shaft 10 is widened.

The embodiment of the 2 differs from 1 further characterized in that the shaft 10 at their "free" end 10 ' a paragraph 10 '' that is from the inner edge of the annular disc 28 and the cover plate 34 is overruled. This will provide a mechanical backup of the shaft 10 formed against axial displacement and ensures that no impact fluid from the bearing gap at impact loads of the hydrodynamic bearing 24 cums in the axial direction.

With reference to the 1 and 2 were unilaterally closed bearing sleeves 12 described for hydrodynamic bearings where the shaft 10 only at one end, the free end 10 ' is led out of the bearing sleeve.

The embodiments of the 3 to 5 refer to two-sided open bearing sleeves, have at least one compensating volume of the type described. If necessary, two equalization volumes can be provided.

3 shows a first embodiment of the bearing according to the invention with open on both sides bearing sleeve. This in 3 shown hydrodynamic bearing according to the invention comprises a stepped shaft 10 with a shaft shoulder 10 '' each in the area of the front end 12 ' . 12 '' the bearing sleeve. The wave 10 has a central pressure plate 14 for forming a thrust bearing. The bearing sleeve is in two parts with an outer sleeve portion 12b and an inner sleeve portion 12a built up. The inner sleeve section 12a is in a corresponding recess of the outer sleeve portion 12b as in 3 shown used. In the area of the printing plate 14 is between the outside and the inside bearing sleeve section 12a . 12b a spacer ring 46 used, with the help of the bearing gap 24 in the area of the printing plate 14 can be adjusted. The printing plate 14 rests against the bearing sleeve sections 12a . 12b from, so that they also take over the function of an axial abutment.

bearing gap 24 in the area of the printing plate 14 can be adjusted. The printing plate 14 rests against the bearing sleeve sections 12a . 12b from, so that they also take over the function of an axial abutment.

The inner sleeve section 12a can in the outer sleeve section 12b turned fit, pressed, glued, welded or otherwise connected to this.

The micro-gap 26 and the equalization volume 20 are in the respective front ends 12 ' . 12 '' of the inner sleeve section 12a or the outer sleeve portion 12b in the same way as with respect to 2 described trained.

4 shows a similar embodiment as 3 , It differs from the embodiment of the 3 by the two-part construction of the bearing sleeve with two mirror-symmetrical in axial directions, successively arranged bearing sleeve sections 12c . 12d through a spacer ring 46 are spaced as in 4 shown. The axial bearing sleeve sections 12c . 12d and the spacer ring 46 are similar to the embodiment of the 1 in a holder cup or pot 18 used, in particular in these pressed or shrunk. The spacer ring 46 again has the function, the bearing gap 24 in the area of the printing plate 14 , So the thrust bearing, set.

In the open, in the drawing lower end of the pot 18 are the micro-gap 26 and the equalization volume 20 similar to 3 by inserting an annular disk 28 and a cover plate 34 , adjacent to the front end 12 '' of the bearing sleeve section 12d educated. At the opposite end of the front 12 ' of the bearing sleeve section 12c are the micro-gap 26 and the equalization volume 20 similar to the embodiment of the 1 between the front end 12 ' of the bearing sleeve section 12c , the ring disk 28 and the floor 18 ' of the pot 18 educated.

4 shows an embodiment of the hydrodynamic bearing with centrally disposed along the longitudinal axis of the bearing pressure plate 14 , which together with the corresponding end faces of the bearing sleeves 12c and 12d two acting in opposite directions hydrodynamic thrust bearing forms, it will be understood by those skilled in the art that this in the pressure plate 14 formed thrust bearing depending on the application along the axis of rotation 22 , in the 4 up or down, can be moved. Further shows 4 an embodiment in which the pot 18 the bearing sleeve 12c . 12d enveloped along its entire length. The skilled person will understand that a similar operation can be achieved with a pot that has a lower height than the length of the bearing sleeve. The pot 18 can be considered as an injection molded part, a turned part or a deep-drawn part, similar to in 1 , or manufactured in any other suitable manner. The bearing sleeve sections 12c . 12d be in the pot 18 preferably held in a press fit.

5 shows a further embodiment of the hydrodynamic bearing according to the invention. The embodiment of the 5 includes a stepped shaft 10 with a shaft shoulder 10 '' and a printing plate 14 , The wave 10 is in a bearing sleeve 12 held at her one front end 12 '' a recess for receiving a spacer ring 46 and an abutment 16 having. At this front end 12 '' is between printing plate 14 and abutments 16 formed a hydrodynamic thrust bearing. At the opposite end of the front 12 ' is similar to, for example, with reference to 2 described by an annular disk 28 and a cover plate 34 a micro-gap 26 and a compensation volume 20 formed for the bearing fluid. The embodiment of the 5 differs in this respect from the embodiment of the 2 in that only the cover plate 34 the shaft heel 10 '' overlaps to prevent clogging of bearing fluid under impact load. With regard to the above-described various embodiments of the hydrodynamic bearing according to the invention the skilled person will further modifications of the bearing with one side closed or open on both sides bearing sleeve, with or without pot, with different realization of micro gap and compensating volume, with different arrangement and design of the axial and radial bearing sections as well as numerous other modifications.

The 6a and 6b show two possible embodiments of the annular disc 28 to limit the micro gap 26 between the front end 12 ' the bearing sleeve and said washer 28 , Characteristic feature of the illustrated embodiment of the annular disc 28 is that these recesses on its outer circumference 38 which, when installed, the openings) 20 ' form over which the connection between the micro-gap 26 and the equalization volume 20 (please refer 1 to 5 ) will be produced. Of course, this can also be achieved by differently shaped shaping of the edge regions or by bores, preferably in the outer edge region, of the annular disc 28 respectively. The ring disk 28 can be produced for example by punching or injection molding.

The in the forgoing description, claims and drawings Features can both individually and in any combination for the realization of the invention in various embodiments of importance.

10

wave

10 '

shaft end

10 ''

shaft shoulder

12

bearing sleeve

12 ', 12' '

front end the bearing sleeve

12a, 12b, 12c, 12d

Bearing sleeve sections

14

printing plate

16

abutment

18

pot

18 '

pot base

18 ''

central opening

20

compensating volume

20 '

Opening, passage

22

axis of rotation

24

bearing gap

26

Micro-gap, communication gap

28

washer

30

Pivot-bearing

32

Radialllagerabschnitt

34

cover plate

36

Weld

38

recesses

46

spacer ring

Claims (14)

Hydrodynamic bearing with a shaft ( 10 ), a bearing sleeve ( 12 ), which the shaft with a small radial distance to form a concentric bearing gap ( 24 ), a compensation volume ( 20 ) with a passage opening ( 20 ' ), at least one connecting gap ( 26 ), which the bearing gap ( 24 ) via the passage opening ( 20 ' ) with the compensation volume ( 20 ), whereby the connection gap ( 26 ) between a front end of the bearing sleeve and one, arranged at a small distance parallel to the front end, on the bearing sleeve ( 12 ) attached annular disc ( 28 ) is formed, and wherein the passage opening ( 20 ' ) at a distance from the bearing gap ( 24 ) is disposed radially outside thereof. Hydrodynamic bearing according to claim 1, characterized in that the connecting gap ( 26 ) directly to the bearing gap ( 24 ) or radial bearing section adjacent. Hydrodynamic bearing according to claim 1, characterized in that at least one radial bearing in the region of the bearing gap ( 24 ) is formed and the connecting gap ( 26 ) over a section of the storage gap ( 24 ) is connected to the radial bearing. Hydrodynamic bearing according to one of the preceding claims, characterized by a bearing fluid which seals the bearing gap ( 24 ) and the connecting gap ( 26 ) and the compensation volume ( 20 ) at least partially fills, wherein the bearing fluid has a continuous fluid film between the bearing gap ( 24 ) and the equalization volume ( 20 ). Hydrodynamic bearing according to one of the preceding claims, characterized in that the connecting gap ( 26 ) at least partially in the bearing sleeve ( 12 ) is trained. Hydrodynamic bearing according to one of the preceding claims, characterized in that the connecting gap ( 26 ) one to the inner diameter of the bearing sleeve ( 12 ) adjacent circumferential capillary annular gap. Hydrodynamic bearing according to one of the preceding claims, characterized in that the annular disc ( 28 ) has at its periphery recesses, via which a fluid connection between the in the connecting gap ( 26 ) and in the equalization volume ( 20 ) located bearing fluid. Hydrodynamic bearing according to one of the preceding claims, characterized in that the compensating volume ( 20 ) between the annular disc ( 28 ) and one on the front side of the bearing sleeve ( 12 ) arranged cover is formed. Hydrodynamic bearing according to one of the preceding claims, characterized in that the connecting gap ( 26 ) at an angle of approximately 90 degrees to an axis of rotation ( 22 ) of the bearing extends. Hydrodynamic bearing according to one of the preceding claims, characterized in that the compensating volume ( 20 ) is formed as a conical cavity whose base via the passage opening ( 20 ' ) and the connecting gap ( 26 ) with the bearing gap ( 24 ) connected is. Hydrodynamic bearing according to one of the preceding claims, characterized in that the compensating volume ( 20 ) substantially perpendicular to a rotation axis ( 22 ) of the bearing and at its the bearing gap ( 24 ) facing the end is widened. Hydrodynamic bearing according to one of the preceding claims, characterized in that the shaft ( 10 ) in the region of a front end ( 12 ' ) of the bearing sleeve ( 12 ) a paragraph ( 10 '' ) extending from one end ( 12 ' ) associated cover ( 34 ) and / or the annular disc ( 28 ) is at least partially covered. Spindle motor with a hydrodynamic bearing after one of the preceding claims. Hard disk drive with a spindle motor after Claim 13.