Spindle motor with fluid dynamic bearing system

Abstract

Spindle motor with a fluid dynamic bearing system, which includes: a base plate (10) with a cylindrical opening (11), a bearing bushing (12) and a shaft (14) rotatably mounted relative to the bearing bushing (12) as part of the fluid dynamic bearing system, wherein the bearing bushing (12) is closed by a cover plate (34) and arranged in the opening (11) of the base plate (10); and a rotor component (24) which is driven by an electromagnetic drive system (36, 38) in a rotating manner, characterized in that that the opening (11) in the base plate (10) below the bearing system is closed by a cylindrical plate (44), wherein the cylindrical plate (44) has a bore (46) which connects one end face of the cylindrical plate (44) to the other end face, and the bore (46) is closed by a sealing compound (48).

Description

Field of the invention

[0001] The invention relates to a spindle motor with a fluid-dynamic bearing system, according to the preamble of independent patent claim 1 or 3. Such a spindle motor is used, for example, to drive storage disk drives, fans or the like. State of the art

[0002] Spindle motors with fluid-dynamic bearing systems are known in a variety of designs. The motor comprises, for example, a stationary base plate to which the stationary component of the fluid-dynamic bearing system is attached. A rotating component of the bearing system supports a rotor component (hub), which is driven in rotation by an electromagnetic drive system consisting of a stator assembly and a rotor magnet. The stator assembly is held on the base plate, while the rotor magnet is attached to the rotor component. In a fluid-dynamic bearing system according to a known design, a shaft is rotatably mounted in a bearing bore of a bearing bush. The diameter of the bearing bore is slightly larger than the diameter of the shaft, so that a bearing gap filled with a bearing fluid remains between the surfaces of the bearing bush and the shaft.The facing surfaces of the shaft and / or the bearing bushing have pressure-generating bearing groove structures as part of at least one fluid-dynamic radial bearing. A free end of the shaft is connected to a rotor component (hub), the lower surface of which, together with an end face of the bearing bushing, forms a fluid-dynamic axial bearing. For this purpose, one or both of the facing surfaces of the rotor component or the bearing bushing are provided with pressure-generating bearing groove structures.

[0003] For some applications, it is necessary to use an existing fluid-dynamic bearing system in a spindle motor with an increased overall height. An increased overall height of a spindle motor to drive a hard disk drive is necessary, for example, in server applications where multiple storage disks are arranged one above the other on the hard disk drive to increase storage capacity. The fluid-dynamic bearing system has a lower overall height than the spindle motor, so that the bearing bush of the bearing system arranged in the opening of the base plate of the spindle motor does not completely fill this opening. Instead, an air space remains beneath the bearing system. This air space weakens the stability of the base plate and reduces its rigidity. This reduces the rigidity of the entire motor system and can lead to resonances in the upper frequency range above 1000 Hertz.These resonances are undesirable for a spindle motor used to drive a hard disk drive, as they lie exactly in the frequency range of the servo motor of the hard disk drive's read / write device and can interfere with data recording. Furthermore, such frequencies are also acoustically disruptive.

[0004] WO 2007 / 043 604 A shows a fluid dynamic bearing system with the features of the preamble of independent patent claim 1 and represents the closest prior art.

[0005] US 7 542 232 B2 discloses in Fig. 2 a cover plate which closes one end of the bearing bush or of a sleeve receiving the bearing bush.

[0006] JP H06 189 490 A shows a fluid dynamic bearing system with a rotating shaft in which not the bearing bush but only the base plate is closed by a plate.

[0007] JP 2007 092 783 A discloses a fluid dynamic bearing system with a fixed shaft, the bearing bush of which rotates, wherein the ends of the bearing bush are not closed.

[0008] WO 02 / 071 402 A1 discloses a fluid dynamic bearing system which has a bearing bush closed by a plate or a cup-shaped bearing bush or a cup-shaped sleeve surrounding the bearing bush.

[0009] US 5 810 480 A discloses a fluid dynamic bearing system with an axial journal bearing in which an opening in the base plate is closed by a plate.

[0010] DE 43 06 402 A1 concerns a sealing compound for a spark plug. Disclosure of the invention

[0011] It is the object of the invention to provide a spindle motor with an increased overall height, which has improved rigidity and freedom from resonance.

[0012] This object is achieved according to the invention by a spindle motor having the features of patent claim 1 or patent claim 3.

[0013] Preferred embodiments and further advantageous features of the invention are specified in the dependent claims.

[0014] According to the invention, the air space beneath the bearing is sealed by a component, preferably a metal component, thus increasing the structural rigidity of the base plate and also the overall rigidity of the spindle motor. At the same time, resonances are shifted to a higher frequency range, where they no longer interfere with the system frequencies of the hard disk drive's read / write device.

[0015] In a first embodiment of the invention, the opening in the base plate is closed by a cylindrical plate. The plate is relatively thick, i.e., its height is at least 30% of the outer diameter of the plate. The cylindrical plate is connected directly to the base plate and can preferably be pressed into the opening of the base plate, glued in, or welded to the base plate.

[0016] A preferably central bore is provided in the cylindrical plate so that the air trapped between the bearing and the cylindrical plate can escape when the opening in the base plate is closed.

[0017] This hole is sealed with a sealing compound. The sealing compound can be an electrically conductive compound, for example, to establish electrical contact between the cylindrical plate and a cover plate of the bearing. Fluid dynamic bearings are susceptible to static charges due to their bearing components being separated by bearing fluid, so good electrical contact between the bearing components and the base plate is necessary to allow the electrical charges to dissipate.

[0018] In another embodiment of the invention, the opening in the base plate is closed by a portion of the base plate itself, ie the opening in the base plate is a blind hole in the base plate in which the bearing bush is arranged.

[0019] In the area of ​​the section of the base plate that closes the opening, there is a hole which in turn serves to allow the air trapped in the cavity between the bearing bush and the base plate to escape when the bearing bush is installed.

[0020] The bore is in turn closed by a sealing compound, preferably an electrically conductive sealing compound, so that contact is established between a cover plate of the bearing and the base plate.

[0021] The described embodiments of the invention have the further advantage that the shock resistance of the bearing is improved since the deformation of the base plate is reduced in the event of a shock.

[0022] Furthermore, the acoustic properties of the motor are improved because the resonance frequencies are shifted to a higher, acoustically less disturbing frequency range.

[0023] The invention also relates in particular to a spindle motor such as can be used to drive hard disk drives.

[0024] The invention will now be explained in more detail using preferred embodiments with reference to the drawings described below. Further features, advantages, and possible applications of the invention will become apparent from these. Short description of the drawings Fig. 1 shows a section through a first embodiment of a spindle motor according to the invention with fluid dynamic bearing. Fig. 2 shows a section through a second embodiment of a spindle motor according to the invention with a fluid dynamic bearing. Fig. 3 shows a section through a non-claimed embodiment of a spindle motor with fluid dynamic bearing. Description of preferred embodiments

[0025] The Fig. Figure 1 shows a section through a spindle motor with a fluid-dynamic bearing system. The spindle motor comprises a base plate 10 with a central opening 11, into which a bearing bushing 12 is firmly received. The bearing bushing 12 is, for example, pressed into the opening 11 of the base plate 10 and forms the stationary component of the fluid-dynamic bearing system. The axial length of the opening 11 of the base plate 10 is significantly greater than the axial joining length of the bearing bushing 12 to the base plate 10.

[0026] The bearing bush 12, for example, has an outer diameter of approximately 6.5 mm and has a bearing bore with a diameter of approximately 2.5 mm. A shaft 14 is inserted into the bearing bore of the bearing bush 12, the diameter of which is slightly smaller than the diameter of the bearing bore, i.e., only a few micrometers. A bearing gap 16 a few micrometers wide remains between the surfaces of the bearing bush 12 and the shaft 14. The opposing surfaces of the shaft 14 and the bearing bush 12 form two fluid-dynamic radial bearings 20, 22, by means of which the shaft 14 is rotatably mounted in the bearing bush 12 about a rotational axis 18. The two radial bearings 20, 22 are characterized in a known manner by bearing groove structures that are applied to the surface of the shaft 14 and / or the bearing bush 12. The bearing gap 16 is filled with a suitable bearing fluid, for example a bearing oil.When the shaft 14 rotates, the bearing groove structures of the radial bearings 20, 22 exert a pumping effect on the bearing fluid located in the bearing gap 16 between the shaft 14 and the bearing bush 12, creating a hydrodynamic pressure in the bearing gap 16 that makes the radial bearings 20, 22 load-bearing. The upper radial bearing 20 preferably has asymmetrically designed bearing groove structures that pump the bearing fluid predominantly toward the lower radial bearing 22. The lower radial bearing 22 preferably comprises symmetrically designed bearing groove structures that generate a uniform pumping effect in both directions of the bearing gap 16.

[0027] A free end of the shaft 14 is connected to a rotor component 24, which has an approximately cup-shaped cross-section and partially surrounds the bearing bush 12. A hub 26, which can also be formed integrally with the rotor component 24, is arranged on the outer circumference of the rotor component 24. A lower, flat surface of the rotor component 24, together with an adjacent end face of the bearing bush 12, forms a fluid-dynamic axial bearing 28. In this case, the end face of the bearing bush 12 or the opposite surface of the rotor component 24, or both, is provided with preferably spiral-shaped bearing groove structures which, upon rotation of the shaft 14, exert a pumping action directed radially inward toward the upper radial bearing 20 on the bearing fluid located in the bearing gap 16 between the rotor component 24 and the upper end face of the bearing bush 12, so that the axial bearing 28 becomes load-bearing.A recirculation channel 30 can be provided in the bearing bush 12, which connects a section of the bearing gap 16 located at the radially outer edge of the axial bearing 28 with a section of the bearing located below the lower radial bearing 22 and enables circulation of the bearing fluid in the bearing.

[0028] The bearing bush 12 is surrounded by a stator assembly 36, which is arranged on the base plate 10 and consists of a ferromagnetic stator laminated core and corresponding stator windings. This stator assembly 36 is surrounded by a circumferential edge of the hub 26, on which an annular rotor magnet 38 is arranged. The rotor magnet 38 surrounds the stator assembly 36 in the radial direction, forming an air gap. An external rotor motor is shown. A ferromagnetic metal ring 40 can be arranged below the rotor magnet 38, which magnetically attracts the rotor magnet 40, resulting in a force directed downward toward the base plate 10. This force counteracts the bearing force of the axial bearing 28 and serves to axially preload the bearing system.

[0029] The bearing gap 16 comprises an axial section that extends along the shaft 14 and the two radial bearings 20, 22, and a radial section that extends along the end face of the bearing bush 12 and the axial bearing 28. At the radially outer end of its radial section, the bearing gap 16 transitions into a gap with a larger gap spacing, which acts as a reservoir and sealing gap 42 and is partially filled with bearing fluid. The gap initially extends radially outward from the bearing gap 16 and transitions into an axial section that extends along the outer circumference of the bearing bush 12 between the bearing bush 12 and a cylindrical section of the rotor component 24, forming the sealing gap 42. The outer surface of the bearing bush 12 and the inner surface of the rotor component 24 are largely cylindrical, but preferably slightly inclined in the direction of the rotational axis 18 and form the boundary of the sealing gap 42.Preferably, the inner diameter of the inner circumferential surface of the rotor component 24 decreases in the direction of the opening of the sealing gap 42 to a lesser extent than the outer diameter of the bearing bush 12, so that a substantially conical cross-section of the sealing gap 42 results.

[0030] Below the radial bearing 22, the bearing bush 12 has a recess whose diameter is significantly larger than the diameter of the bearing bore. The bearing bush 12 is closed on this side by a cover plate 34. The shaft 14 has a stopper ring 32 at this end, which is arranged within the recess of the bearing bush 12. The recess in which the stopper ring 32 is arranged is connected to the bearing gap 16 and the recirculation channel 30 and is completely filled with bearing fluid. In the event of excessive axial movement of the shaft 14, the stopper ring 32 abuts a step in the bearing bush formed by the transition between the bearing bore and the recess. The stopper ring 32 thus prevents the shaft 14 from falling out of the bearing bush 12.

[0031] According to the invention, the opening 11 in the base plate is closed with a cylindrical component, in particular a cylindrical plate 44. This gives the base plate 10 greater rigidity and reduces resonances.

[0032] To allow the cylindrical plate 44 to be secured in the opening 11 of the base plate, a bore 46 is provided in the plate 44 to allow the air trapped between the bearing system and the plate 44 to escape during installation of the plate 44. The bore 46 can be sealed with a sealing compound 48. Preferably, the sealing compound 48 is an electrically conductive sealing compound and is arranged deep within the bore 46 in the region of the cover plate 34 of the bearing, so that the cover plate 34 and the cylindrical plate 44 are electrically connected to one another.

[0033] Fig. 2 shows a section through a spindle motor in a modified design, which is largely identical to the design of Fig. 1. Identical components are designated by the same reference numerals.

[0034] In contrast to Fig. 1 is at Fig. 2 the base plate 110 is designed differently and comprises an opening 111 which is designed as a blind hole and is closed at the bottom.

[0035] The bearing bushing 12 is pressed, for example, into the opening 111 of the base plate 110. To allow any air trapped between the bearing bushing 12 and the base plate 110 to escape during assembly of the bearing bushing, a bore 146 is provided in the base plate 110 to vent this area. The bore 146 can preferably be sealed with a sealing compound 148.

[0036] This sealant is as in connection with Fig. 1 is preferably designed to be electrically conductive and connects the cover plate 34 of the storage system to the base plate 110 in an electrically conductive manner.

[0037] In this embodiment, the base plate 110 is designed without a through-opening, thus improving its structural rigidity. No additional component is required to close the opening 111.

[0038] Fig. 3 shows another, opposite Fig. 1 modified design of a spindle motor, in which the same components are designated by the same reference numerals. The design of Fig. 3 is not part of the invention.

[0039] In contrast to Fig. 1, a bearing bush 212 is inserted into the opening 11 of the base plate 10, the lower section of which is axially extended so that the entire axial length of the opening 11 is filled by the bearing bush 212.

[0040] A particularly thick cover plate 234 closes the bearing system at the bottom and is arranged in a recess in the bearing bushing 212. The thick cover plate 234 also closes the remaining opening 11 of the base plate 10 at the bottom. The thick cover plate 234 stiffens both the bearing bushing 212 and the base plate 10.

[0041] The extended bearing bush 212 makes a greater joining length between bearing bush 212 and base plate 10 possible.

[0042] A sealing compound 248 may be arranged between the bearing bush 212 and the base plate 10 and may preferably be electrically conductive to ensure good electrical contact between the bearing bush 212 and the base plate 10. List of reference symbols 10, 110 base plate 11, 111 Opening 12, 212 bearing bush 14 Wave 16 Bearing gap 18 Rotation axis 20 radial bearings 22 radial bearings 24 Rotor component 26 Hub 28 thrust bearings 30 Recirculation channel 32 stopper ring 34, 234 cover plate 36 Stator arrangement 38 rotor magnet 40 metal ring 42 Sealing gap 44 plate 46, 146 bore 48, 148, 248 Sealant

Claims

[1] Spindle motor with a fluid dynamic bearing system, which comprises: a base plate (10) with a cylindrical opening (11), a bearing bush (12) and a shaft (14) rotatably mounted relative to the bearing bush (12) as part of the fluid-dynamic bearing system, wherein the bearing bush (12) is closed by a cover plate (34) and is arranged in the opening (11) of the base plate (10); and a rotor component (24) which is driven in rotation by an electromagnetic drive system (36, 38), characterized by , that the opening (11) in the base plate (10) below the bearing system is closed by a cylindrical plate (44), wherein the cylindrical plate (44) has a bore (46) which connects one end face of the cylindrical plate (44) to the other end face, and the bore (46) is closed by a sealing compound (48). [2] Spindle motor according to claim 1, characterized bythat the height of the cylindrical plate (44) is at least 30% of its outer diameter. [3] Spindle motor with a fluid dynamic bearing system, which comprises: a base plate (110) with a cylindrical opening (111), a bearing bush (12) and a shaft (14) rotatably mounted relative to the bearing bush (12) as part of the fluid-dynamic bearing system, wherein the bearing bush (12) is closed by a cover plate (34) and is arranged in the opening (111) of the base plate (110); and a rotor component (24) which is driven in rotation by an electromagnetic drive system (36, 38), characterized by , that the opening (111) in the base plate (110) below the bearing system is closed by a portion of the base plate (110) itself, wherein the portion of the base plate (110) has a bore (146) connecting one side of the base plate (110) to the other side, and the bore (146) is closed by a sealing compound (148). [4] Spindle motor according to claim 1 or 3, characterized by that the sealing compound (48, 148) is electrically conductive and conductively connects the cylindrical plate (44) or the base plate (110) to a component of the bearing system.

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