Patent Application
20080075398
With reference to attached drawings, preferred embodiments of the present invention will be described in detail.
As illustrated in
The sleeve S has a hollow cylindrical shape having a radially inner surface defining a bearing hole 5 axially penetrating the sleeve, and the shaft 1 is inserted into the bearing hole 5. An opening arranged axially below the bearing hole 5 is sealed with a sealing cap 6, defining with the sleeve S a substantially cup shape having an axially upper opening. There is provided an axially lower portion of the sleeve S at which a diameter of the sleeve S radially outwardly expands, defining an oil pool portion 7 reserving the lubricating oil 2. The sleeve S further includes a circulation hole extending along the center axis and connecting the oil pool portion 7 and an axially upper end surface of the sleeve 7 to circulate the lubricating oil 2.
The sleeve S also includes a flange portion 9 radially outwardly extending at an axially upper end portion of the sleeve S. An axially upper portion of the radially outer surface of the sleeve S is constricted gradually toward the axially lower direction and radially opposes to the radially inner surface of the rotor hub R via a gap defined therebetween. With this configuration, the gap functions as a capillary seal portion preventing the outflow of the lubricating oil 2.
The rotor hub R includes a discoid portion 11 (a thrust plate) having a center through hole 10 in which an axially upper end portion of the shaft 1 is inserted, a cylindrical portion 12 axially downwardly extending from a the discoid portion, and a rotor flange portion 13 radially outwardly extending from a radially outer surface of the rotor hub R
The shaft 1 has a substantially column shape and the axially upper end portion of the shaft 1 is inserted into the center through hole 10 and is attached to the discoid portion 11 such that center axes of the rotor hub R and the shaft 1 are substantially aligned.
The shaft 1 is inserted into the sleeve S and the rotor hub R is supported in a rotatable manner. A retaining member 14 having a substantially ring shape is attached to the radially inner surface of the cylindrical portion 12. When a force to remove the rotor hub R from the sleeve S is applied in the axially upper direction, the retaining member 14 engages with the flange portion 9 of the sleeve S and prevents the rotor hub R from being removed.
In the present preferred embodiment of the present invention, the sleeve S is preferably made of ferritic stainless steel for the sake of facilitating the cutting process in the manufacture thereof, and the shaft 1 is preferably made of martensitic stainless steel having greater hardness than the ferritic stainless steel. It should be noted that the sleeve S may be defined with a plurality of members, e.g., the sleeve S may include a sleeve body made of porous sintered material essentially composed of copper and a sleeve housing made of phosphor bronze, having a substantially cup shape in which the sleeve body is attached.
There are provided gaps in between the sleeve S and the rotor hub R, in between the sleeve S and the shaft 1, and the gaps are filled with the lubricating oil 2 (e.g., ester oil). In particular, gaps are provided in the fluid dynamic bearing device, in between the radially inner surface of the cylindrical portion 12 of the rotor hub R, and the radially outer surface of the sleeve S, in between the axially lower surface of the discoid portion 11 of the rotor hub R, and the axially upper end surface of the sleeve S; in between the radially inner surface of the sleeve S, and the radially outer surface of the shaft 1; and in between the axially lower end surface of the shaft 1, and the axially upper surface of the sealing cap 6. Those gaps are filled with the lubricating oil 2 without interruption.
An annular rotor magnet 15 is attached to an axially lower surface of the flange portion 13. The rotor magnet 15 is magnetized in the circumferential direction such that S and N poles are alternately arranged. An armature (not illustrated in drawings) is arranged radially outside of the rotor magnet 15 such that the armature radially opposes the rotor magnet 15 via a gap defined therebetween. The armature interacts with the rotor magnet 15 upon energizing the armature, and the rotor hub R rotates about the center axis.
The sleeve S includes the radial bearing portion 3 and the thrust bearing portion 4 to support the rotor hub R in a non-contact manner when the rotor hub R rotates.
The radial bearing portion 3 is defined with a portion of the radially inner surface of the sleeve S, a portion of the radially outer surface of the shaft 1 radially opposing to the radially inner surface of the sleeve S, and the lubricating oil 2 filling the gap defined between the sleeve S and the e shaft 1. In addition, a plurality of dynamic pressure generating grooves (e.g., grooves arrayed in a herringbone shape, that is, a herringbone groove array 18) is arranged in the radially inner surface of the sleeve S. The dynamic pressure generating grooves generate the hydrodynamic pressure in the lubricating oil 2 by directing the lubricating oil to flow toward a predetermined portion along the rotational direction of the rotor hub R.
The thrust bearing portion 4 is defined with the axially upper end surface of the sleeve S, the axially lower surface of the discoid portion 11 of the rotor hub R, and the lubricating oil 2 filling the gap defined between the sleeve 4 and the discoid portion 11. In particular, as illustrated in
As illustrated in
When the rotor hub R rotates upon energizing the armature, the shaft 1 is supported in a manner without coming into contact with the radially inner surface of the sleeve S due to the dynamic pressure generated by the radial bearing portion, and the rotor hub R is supported in a manner axially lifted and without coming into contact with the sleeve S due to the dynamic pressure generated by the thrust bearing portion.
Recently, a motor incorporating the fluid dynamic bearing device has been installed into the portable devices, such as portable digital music players. When the devices are moved during its operation, the abnormal force is applied to the fluid dynamic bearing, and the rotor hub R and the sleeve S may come in contact with each other while the rotor hub R rotates.
In a storage disk drive, a data storage disk is mounted on the rotor hub and rotates therewith in a high speed, thus the rotor portion including the rotor hub and the data storage disk stores high angular momentum. Thus, when the storage disk drive is moved during the operation thereof, the rotor portion cannot follow the motion of the storage disk drive, and the rotor hub and/or the shaft comes into contact with the sleeve. The contact of the rotor hub and/or the shaft, and the sleeve during the rotor rotates generates an undesirable noise like the sound of frogs croaking. It is extremely undesirable that such undesirable noise is generated while the portable audio player is operated.
The inventors of the present invention discovered that the contact between the rotor hub and/or the thrust plate, and the sleeve at the thrust bearing portion generates the undesirable noise through the extensive research. Furthermore, the inventors of the present invention discovered that the contact in the thrust bearing portion mainly contributes to the generation of the undesirable noise. Generally, the thrust dynamic bearing portion is arranged radially outside of the radial dynamic bearing portion, and thus has a higher circumferential speed. When an abnormal force is applied to the fluid dynamic bearing device and the rotor portion is slanted relative to the sleeve, the rotor portion may come into contact with the sleeve at the radially outermost portion thereof having the highest circumferential speed. Generally, a thrust bearing surface arranged in the rotor hub and/or the thrust plate comes into contact with the sleeve, and due to their discoid shape, the undesirable noise is generated.
In the present preferred embodiment of the present invention, the fluid dynamic bearing device has a configuration in which the rotor hub R does not come into contact with the sleeve S when the rotor hub R is slanted as much as possible. Particularly, in the fluid dynamic bearing device according to the present preferred embodiment of the present invention, the axial clearance of the gap defining the thrust bearing portion is configured such that the rotor hub R does not come into contact with the sleeve S when the shaft 1 is slanted until the axially upper and lower portions of the shaft 1 come into contact with axially upper and lower ends of a radially inner surface of the sleeve S defining the bearing hole in which the shaft 1 is inserted, in the state that the rotor hub R is lifted to a rated flying height. In other words, when the shaft comes into contact with an axially upper end portion of the radially inner surface of the sleeve and an axially lower portion of the radially inner surface of the sleeve, the thrust plate and the sleeve do not come into contact with each other, wherein a line connecting one axial end portion and the other axial end portion passes the center axis. In order to realize the configuration described above, it is preferable, but not limited, that the thrust bearing portion 4 is arranged near the upper opening of the cup-shaped sleeve S.
Referring to
In the present preferred embodiment of the present invention, the fluid dynamic bearing device has an outer diameter of the thrust bearing portion 4, an axial length of the shaft 1, and a radial clearance of the gap defined between the shaft 1 and the sleeve S, each of which is preferably configured. As illustrated in
In the present preferred embodiment of the present invention, as illustrated in
Through the configuration illustrated in
According to the present preferred embodiment of the present invention, portions of the shaft 1 and the sleeve S that come into contact with each other may wear out after the prolonged period of operation of the fluid dynamic bearing device. It may result in enlarging the radial clearance of the gap between the shaft 1 and the sleeve S. With the enlarged radial clearance, the shaft 1 may be slanted greatly and the sleeve thrust bearing surface 20 and the rotor thrust bearing surface 21 come into contact with each other, generating undesired noise. In the present preferred embodiment of the present invention, the following configuration is adapted to the fluid dynamic bearing device to prevent wearing out of the shaft 1 and the sleeve S, and the generation of the undesired noise for a prolonged period.
In the present preferred embodiment of the present invention, the radial clearance of the gap defined between the shaft 1 and the sleeve S is preferably smaller than that of the general fluid dynamic bearing device (about 1.3 μm to about 2.5 μm in the present preferred embodiment of the present invention) to reduce the inclination of the shaft 1 relative to the center axis. When the radial clearance of the gap is smaller than about 1.3 μm, the friction resistance between the shaft 1 and the sleeve S drastically increases.
With the reduced radial clearance of the gap, the risk of the shaft 1 and the sleeve S coming into contact with each other and wearing out increases. Thus, in the present preferred embodiment of the present invention, super-finishing is applied to the shaft 1 or the sleeve S having greater hardness to have an extremely smoothed surface. The super-finishing is a surface-finishing process which produces a very fine, mirror-smooth finish for example. With this configuration, it is possible to prevent the shaft 1 or the sleeve S having the greater hardness from wearing the other. By applying the super-finishing process to the shaft 1 or the sleeve S, it is possible to delay that the shaft 1 or the sleeve S having the greater hardness wears out the other. However, it is preferable that the fluid dynamic bearing adapts the reduced radial clearance of the gap and the super-finishing process.
In the measurement, the fluid dynamic bearing device as follow was used. In the fluid dynamic bearing device, the shaft had about 3.3 mm axial length and about 2.5 mm diameter. The radial gap defined between the shaft and the sleeve was about 2.5 μm, and the rated flying height of the thrust bearing portion was about 10 μm. The shaft was made of stainless steel (SUS420J2 in accordance with JIS (Japanese Industrial Standards)). The surface of the shaft was smoothed by cutting and grinding. The arithmetical average of the surface roughness of the radially outer surface of the shaft is varied by changing the grinding configuration.
The sleeve was made of DHS-1 (registered mark), and the radially inner surface of the sleeve was processed with an appropriate surface finishing. The sleeve had Vickers hardness (VH) of about 290 (290 HV) at a portion to come into contact the shaft. The hardness of the shaft was about 700 HV at a portion to come into contact with the sleeve. The arithmetical average of the surface roughness was measured along the axial direction with the Surface Roughness Meter.
The fluid dynamic bearing was installed in a storage disk drive device, in which the 1.8 inch magnetic disk was mounted on the fluid dynamic bearing. Then, the storage disk drive was placed on a shaker table, which applied a rocking movement, rocking the storage disk drive back and force, centered on a pivot axis arranged in the shaker table and substantially perpendicularly across the rotational axis of the fluid dynamic bearing device. The angle of the rocking movement was approximately 90 degrees about the pivot axis, and frequency of the rocking movement was about 1.5 Hz. While the disk drive was operated, the one-minute rocking movement was applied thereto, and then, the fluid dynamic bearing device was taken out from the storage disk drive and the wearing amount was measured.
As illustrated in
When the shaft has the hardness greater than that of the sleeve, the hardness of the shaft on the radially outer surface is preferably configured to be about 500 HV to about 750 HV, and the hardness of the sleeve on the radially inner surface is preferably configured to be about 150 HV to about 200 HV. It should be noted that the hardness of the shaft and the sleeve maybe variously modified. The hardness of the shaft is preferably greater than about 100 HV and exceeds the hardness of the sleeve, and the hardness of the sleeve is less than about 600 HV and smaller than the hardness of the shaft.
When the arithmetical average surface roughness of the shaft 1, having the hardness greater than that of the sleeve, is about 0.03 μm or less, it is possible to prevent the sleeve from being worn, even if the shaft and the sleeve are made of different material from each other. In general, the conventional shaft used for the conventional fluid dynamic bearing has about 0.06 μm surface roughness.
In the foregoing description of the preferred embodiments of the present invention, the shaft 1 comes into contact with the axially upper and lower ends of the radially inner surface of the sleeve S when the shaft 1 is slanted as much as possible. It should be noted that the shaft 1 may come into contact with other portions of the sleeve S upon slanting the shaft 1 as much as possible. Such portions may be varied based on the shape and the like configuration of the sleeve. Furthermore, the sleeve and the shaft do not necessarily satisfy the hardness and surface roughness described above across the entire section thereof. The sleeve and the shaft may include contacting portions coming into contact with each other, having the preferable hardness and the preferable surface roughness described above.
With reference to
As illustrated in
There is provided a set of thrust bearing portions 4, one is arranged on the axially upper side of the thrust plate 30 (i.e., an upper thrust bearing portion) and the other is at the axially lower side thereof (i.e., a lower thrust bearing portion). In the following description, axially upper and lower surfaces of the thrust plate 20 are referred to as thrust plate bearing surfaces 21, and an axially upper surface of the counter plate 31 and an inner surface of the sleeve S radially inwardly extending to define the step portion 32 and axially opposing the thrust plate bearing surfaces 21, respectively, are referred to as sleeve thrust bearing surfaces 20. Those thrust bearing surfaces 20 and 21 include dynamic pressure generating grooves arrayed in the herringbone shape, respectively. In the present preferred embodiment of present invention, the upper thrust bearing portion and the lower thrust bearing portion generate the dynamic pressure in the lubricating oil directed in axially opposite directions from each other. The shaft 1 and the rotor R is lifted to the point where the dynamic pressures generated by the upper and lower thrust bearing portions are balanced. The fluid dynamic bearing device according to the present preferred embodiment of the present invention has a configuration in which the rotor hub R and the sleeve S, the thrust plate 30 and the sleeve S do not come into contact with each other when the shaft 1 is slanted until the axially upper and lower portions of the shaft 1 come into contact with axially upper and lower ends of a radially inner surface of the sleeve S defining the bearing hole in which the shaft 1 is inserted, in the state that the rotor hub R is lifted to a predetermined flying height, as illustrated in
The configuration of the radial gap defined between the shaft 1 and the sleeve S, the hardness, the surface roughness and the like is as described in the description of the first preferred embodiment of the present invention. With this configuration, the generation of the undesirable noise is restricted.
With reference to
As illustrated in
By adapting the fluid dynamic bearing device according to the preferred embodiments of the present invention, generation of the undesirable noise of the hard disk drive is restricted when the hard disk drive is moved during the operation thereof. Furthermore, since the wearing out of the fluid dynamic bearing device is restricted, the hard disk drive according to the present preferred embodiment of the present invention may be reliably used for extended period.
It is preferable that the magnetic disk having 2.5 inch or smaller diameters is mounted on the spindle motor 41. With this configuration, it is possible to reduce the weight of the rotor portion having the rotor hub R and the magnetic disk 42, reducing the load to be applied to the shaft 1 and the sleeve S. Thus, it is possible to further restrict the wearing out of the fluid dynamic bearing device and the generation of the undesirable noise.
With reference to
According to the present preferred embodiment of the present invention, the generation of the undesirable noise can be prevented when the portable device is moved during the operation thereof.
While preferred embodiments of the present invention have been described in the foregoing, the present invention is not limited to those detailed above, in that various modifications are possible.
In the first and second preferred embodiments of the present invention, the shaft 1 preferably has a greater hardness than that of the sleeve S. Alternatively, the sleeve may have a greater hardness than that of the shaft, and the surface of the sleeve S to come into contact with the shaft 1 may be smoothed by super-finishing. The sleeve S can be attached to the rotor hub R. In this case, the shaft 1 is attached to the stator portion and is inserted into the bearing hole 5 arranged in the sleeve S attached to the rotor hub R.
The preferable hardness and the preferable surface roughness of the shaft and the sleeve described above are not limited to those described above, they can be variously modified. For example, surfaces of the shaft and the sleeve to come into contact with each other may be coated with the diamond-like-carbon, in which the hardness of the surfaces maybe about 2000 HV to about 3000 HV. Through the configuration, it is possible to provide a fluid dynamic bearing device which is reliable and has a prolonged bearing life.
Only selected preferred embodiments have been chosen to illustrate the present invention. To those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the preferred embodiments according to the present invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-261756 | Sep 2006 | JP | national |
