Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1999-03-18
2001-02-06
Marmor, Charles A (Department: 3681)
Bearings
Rotary bearing
Fluid bearing
C384S113000
Reexamination Certificate
active
06183135
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of hydrodynamic bearing assemblies of the type which provide support and rotation for high speed spindle elements. More specifically, the present invention relates to hydrodynamic bearing assemblies with a simplified fluid circulation scheme.
BACKGROUND OF THE INVENTION
Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle the information being accessed by means of read/write heads generally located on a pivoting arm which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by means of an electric motor generally located inside the hub or below the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted by means of two ball bearing systems to a motor shaft disposed in the center of the hub. One of the bearings is typically located near the top of the spindle and the other near the bottom. These bearings allow for rotational movement between the shaft and the hub which maintaining accurate alignment of the spindle to the shaft. The bearings themselves are normally lubricated by grease or oil.
The conventional bearing system described above is prone, however, to several shortcomings. First is the problem of vibration generated by the balls rolling on the raceways. Ball bearings used in hard disc drive spindles run under conditions that generally guarantee a physical contact between raceways and balls, this in spite of the lubrication layer provided by the bearing oil or grease. Hence, bearing balls running on the generally even and smooth, but microscopically uneven and rough raceways, transmit this surface structure as well as their imperfections in sphericity in the form of vibration to the rotating disk. This vibration results in misalignment between the data tracks and the read/write transducer. This source of vibration limits therefore the data track density and the overall performance of the disc drive system.
Another problem is related to the application of hard disk drives in portable computer equipment and the resulting requirements in shock resistance. Shocks create relative acceleration between the disks and the drive casting which in turn shows up as a force across the bearing system. Since the contact surfaces in ball bearings are very small, the resulting contact pressures may exceed the yield strength of the bearing material and leave permanent deformation and damage on raceways and balls.
Moreover, mechanical bearings are not always scalable to smaller dimensions. This is a significant drawback since the tendency in the disc drive industry has been to continually shrink the physical dimensions of the disc drive unit.
As an alternative to conventional ball bearing spindle systems, researchers have concentrated much of their efforts on developing a hydrodynamic bearing. In these types of systems, lubricating fluid-either gas or liquid-functions as the actual bearing surface between a stationary base or housing and the rotating spindle or rotating hub and the stationary surrounding portion of the motor. For example, liquid lubricants comprising oil, more complex ferromagnetic fluids, or even air have been utilized for use in hydrodynamic bearing systems.
Thus, in the case of a hydrodynamic bearing employing a liquid lubricant, the lubricating fluid and its components must be sealed within the bearing to avoid loss of lubricant which results in reduced bearing load capacity. Loss of a seal or failure to control the fluid level within the bearing system could cause contamination of the hard disk drive with lubricant particles and droplets as well as outgassing-related condensation particles.
Many earlier hydrodynamic bearings incorporated a reservoir extending up the central axis of the shaft and connected by cross-bores to the journal bearing. However, this design was impeded by lubricant thermal expansion issues, leading to a search for an alternative approach.
Therefore, a design for establishing and maintaining fluid distribution over a bearing surface remains highly desirable.
SUMMARY OF THE INVENTION
Therefore, it is an objective of the present invention to provide a hydrodynamic bearing which is simple in construction and whose design is highly scalable.
A further objective of the invention is to provide a hydrodynamic bearing in which the fluid level and pressure distribution across the surface of the journal bearing and/or thrust bearing is stable and easily maintained.
Another objective of the invention is to provide a hydrodynamic bearing in which the lubricant thermal expansion issue in the overall bearing design is minimized.
Another objective of the invention is to provide a hydrodynamic bearing design including a shaft and a thrust plate wherein the pressure distribution across the journal bearing on the shaft and across the thrust bearings is maintained, while providing a lower cost implementation of the design.
Another objective of the invention is to provide a bearing design with optimized boundary conditions between the various bearing sections to optimize the fluid distribution and insensitivity to temperature and machining tolerances, thereby providing a greater consistency of dynamic performance of the invention.
In summary, the present invention incorporates a shaft having a thrust plate at or near one end, and a sleeve cooperating with the shaft to define one or more journal bearings and a counterplate (which may be supported by the sleeve or defined by the sleeve) defining at least one counter thrust surface in cooperation with the thrust plate. In order to maintain an enhanced fluid distribution across the journal bearing and maintain pressure distribution boundary conditions as desired, one or more grooves are defined along the shaft extending behind or between the thrust plate and the shaft. The grooves typically extend from one radial side of the thrustplate behind the thrustplate and up to a point on the shaft adjacent or nearly adjacent to one of the journal bearings. Alternatively, the slot or slots may extend to a point between two journal bearings. In this way, the pressure from the distal axial surface of the thrust bearing to the point where the slot terminates is equalized, enhancing the stablility of the boundary conditions over each of the journal bearings and equalizing the pressure at the opposite ends of the fluid distribution slot.
Other features and advantages of the present invention will become apparent to a person of skill in the art who studies the present description of a preferred embodiment given in conjunction with the accompanying drawings.
REFERENCES:
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patent: 5427456 (1995-06-01), Hensel
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patent: 5516212 (1996-05-01), Titcomb
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patent: 5988886 (1999-11-01), Takahashi
Aiello Anthony
Kloeppel Klaus
Riegler Peter R.
Flehr Hohbach Test Albritton & Herbert LLP
Ho Ha
Marmor Charles A
Seagate Technology LLC
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