Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1999-04-14
2001-11-27
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S110000
Reexamination Certificate
active
06322252
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fluid dynamic bearings, and more specifically, the present invention relates to a self-contained, discrete fluid dynamic bearing which is a functional equivalent to, and/or replacement for a traditional ball bearing.
BACKGROUND OF THE INVENTION
The bearing assembly which supports a shaft and sleeve for relative rotation is of critical importance to the lifetime and stability of a motor, gyroscope or other devices based on relative rotation. However, ball bearing assemblies have many mechanical problems such as wear, run-out and manufacturing difficulties. Moreover, resistance to operating shock and vibration is poor, because of low damping. Thus, there has been a search for alternative bearing assemblies.
One alternative bearing design which has been investigated is a hydrodynamic bearing. In a hydrodynamic bearing, a lubricating fluid such as gas or a liquid provides a bearing surface between a fixed member of the housing and a rotating member of the disc hub. Typical lubricants include oil or ferromagnetic fluids. Hydrodynamic bearings spread the bearing interface over a large continuous surface area in comparison with a ball bearing assembly, which comprises a series of point interfaces. This is desirable because the increased bearing surface reduces wobble or run-out between the rotating and fixed members. Further, improved shock resistance and ruggedness is achieved with a hydrodynamic bearing. Also, the use of fluid in the interface area imparts damping effects to the bearing which helps to reduce non-repetitive runout.
However, to design an effective self-contained fluid dynamic bearing, the issue of fluid retention must be addressed. If fluid is lost during operation of the bearing, or in the event of shock, then the effectiveness of the bearing is diminished or lost.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a discrete, self-contained hydrodynamic bearing.
More specifically, it is an object of the invention to provide a self-contained hydrodynamic bearing which may be utilized as a direct substitute for a ball bearing.
A further objective of the invention is to provide a hydrodynamic bearing incorporating the functional equivalent of inner and outer races so that the hydrodynamic bearing may be easily used in a system which requires relative rotation of two parts with substantial stability.
Another objective of the invention is to provide a discrete fluid dynamic bearing which can be delivered for installation filled with fluid and with the bearing gap pre-established.
Yet another objective of the invention is to provide a discrete fluid dynamic bearing wherein a sleeve supports structure to serve as an inner race and a bearing seat serves as an outer race.
A further and related objective of the invention is to provide a self-contained hydrodynamic bearing where the bearing is substantially conical or spherical in shape so that it provides a measure of both radial and axial stability to the system being supported.
Yet another objective of the present invention is to provide a self-contained conical bearing which may be easily filled with the fluid which serves as the bearing surface.
Another objective of the invention is to provide a self-contained conical bearing which is easily filled with fluid.
A further objective of the invention is to provide a fluid-filled self-contained conical bearing incorporating means for sealing the fluid into the bearing located on either side of the bearing column.
Yet another objective of the invention is to provide means incorporated in the design and a procedure for easily filling the bearing with the required fluid level for efficient operation.
Yet another objective of the invention is to provide active sealing means on at least one side and preferably both sides of the bearing cone or sphere so that the fluid is actively maintained with the bearing while the system is rotating.
Yet another objective of the invention is to achieve a design for a seal system which actively pushes the oil back into the fluid dynamic bearing capsule while it is spinning; a further objective is to combine this approach with the use of capillary tension to hold the oil in the fluid dynamic bearing during stationary periods.
Yet another objective of the invention is to achieve a seal design which allows air, trapped within the seal and the associated fluid dynamic bearing, to be expelled, eliminating air bubbles from the fluid dynamic bearing.
These and other objectives of the present invention are achieved by providing a discrete, self-contained fluid dynamic bearing comprising a sleeve supporting on its outer surface a bearing cone and cooperating with a bearing seat having an inner surface; one of the surfaces has grooves to establish and maintain fluid pressures so that an effective fluid bearing is established. A fluid dynamic bearing is defined by providing for fluid to be maintained on the surface of the bearing cone. Typically, the fluid also is found in channels on the outer surfaces of the bearing cone, including grooves or channels between the bearing cone and the outer surface of the sleeve.
In one preferred embodiment, facing surfaces of a seal cone mounted on the sleeve adjacent the bearing cone and seal shield supported on the bearing seat provide a tapered gap through which fluid may be inserted into the active surfaces of the hydrodynamic bearing, the gap being tapered to form a meniscus to retard or prevent the flow of the fluid back out through this opening. The relative rotation of the seal shield and the seal cone create a pressure through centrifugal force which causes the bearing fluid to be forced toward the bearing cone. At the opposite end of the sleeve of the bearing, the fluid is retained in the bearing device either by providing slightly tapered surfaces for the bearing seat and the sleeve to form a meniscus, or by providing a grooved pumping seal which actively seals the fluid within the bearing.
In an especially preferred embodiment of the invention, an asymmetric sealing system and method is employed on either side of the hydrodynamic bearing in the bearing device. This asymmetric sealing technique incorporates, in addition to the above centrifugal capillary seal, a grooved pumping seal on the opposite side of each fluid dynamic bearing from the centrifugal capillary seal and between the fluid dynamic bearing and a central portion of the sleeve. This grooved pumping seal is a seal formed between a sleeve and the bearing seat, with pumping grooves being defined on at least part of the seat or sleeve. These pumping grooves retain bearing fluid within the grooved pattern when the sleeve and seat are stationary; when the parts are relatively rotating, the oil is pumped into a region of the seal which has very shallow or no grooves, dramatically enhancing the sealing stiffness of the sealing system. By one measurement, this grooved pumping seal is over 60 times stiffer than the centrifugal capillary seal which is on the opposite side of the fluid dynamic bearing.
In a further advantageous portion of this design, the surface of the fluid dynamic bearing uses a grooving pattern and, in some embodiments, a varying gap width which varies over the bearing surface of the cone (or sphere) with distance from the wider radius of the cone toward the narrower radius to provide a slightly unbalanced pressure distribution. Thus the fluid flow is in the direction from the centrifugal capillary seal to the grooved pumping seal; this is accomplished even with variations in manufacturing tolerances in parts and assembly. By establishing this pressure distribution over the surface of the fluid bearing, air bubbles are pushed to the apex of the bearing cone or bisphere and are expelled through the centrifugal capillary seal.
The invention further comprises means and a method for filling the discrete fluid dynamic bearing with fluid and setting the gap. Basically, the method comprises injecting a fixed amount of fluid into the bearing, and then p
Grantz Alan Lyndon
Heine Gunter Karl
Hannon Thomas R.
Seagate Technology LLC
Thomason, Moser & Patterson L.L.P.
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