Self-Filtering Apparatus for Hydrodynamic Bearing Gas

This invention relates generally to hydrodynamic or self-acting gas bearings, and more particularly to bearing arrangements in which the replenishment gas is drawn through a filter as required by the operating bearings.

Low friction, self-acting gas bearings rely on the relative rotation of the bearing members to form the supporting bearing film from the ambient atmosphere. This atmosphere is usually air, but may be other gases if the bearing is sufficiently isolated. The gap or clearance between the surface of the rotating member and that of the stationary member is frequently on the order of one hundred microinches. Gas borne particles larger than this size can be sucked or drawn into the dynamically changing film and damage one or both of the mating bearing surfaces.

In some gas bearings, the gas required for the supporting film is supplied directly to the bearing from a pressurized source and is known as jacking fluid. Gas entering the source can be selected or filtered to prevent the entrance of oversized particles. Self-acting gas bearings, however, are usually started, stopped, and operate in an environment that includes the bearing drive or load or is amidst wear particles that are produced by nearby mechanisms. It then becomes difficult to insure that replenishment gas for the bearing film is clear of occasional oversize particles that can spall or gouge the bearing surface.

Attempts have been made to trap the damaging bits with filters in self-acting gas bearings, but the filters have been placed either at the entrance to the mechanism chamber enclosing the bearing, drive and load, which are themselves particle generators, or have been placed at the exit for the gas from the bearing. Typical of such arrangements are U.S. Pat. Nos. 4,656,545, issued Apr. 7, 1987 to K. Kakuta and 4,547,081, issued Oct. 15, 1985 to K. Tanaka et al. In each of these references, the gas for the supporting bearing film is either filtered as it enters a chamber enclosing a motor and disc drive or after the gas has passed through a drive motor and the gas bearing. The bearing gas is filtered too late to intercept wear or dirt particles and prevent them entering the narrow gas film opening crucial to bearing operation.

It is accordingly a primary object of this invention to provide a hydrodynamic gas bearing for which ambient gas entering the bearing is required to be drawn through filtering means immediately prior to use as a support film in the bearing to insure that the gas is free of damaging particles.

Another important object of this invention is to provide a method of supplying filtered gas for hydrodynamic journal or thrust bearings to which the filtered gas is supplied according to the demand of the bearings.

Yet another important object of this invention is to provide a pumping arrangement for the gas supply of a hydrodynamic or self-acting thrust or journal bearing in which a surplus of filtered gas is drawn adjacent to the bearing to further assure that unfiltered gas is not consumed in the bearing.

The foregoing objects are attained in accordance with the present invention by providing thrust or journal hydrodynamic or self-acting gas bearings with gas pumping means for their necessary support film supply and limiting the supply channels for the gas to only paths that incorporate filtering means. The filtering means is capable of removing airborne particles of sizes sufficient to damage the bearing components. The gas pumping means is of a capacity to draw the required gas or an excess quantity of gas to the entrance to the bearing opening and thus prevent unfiltered ambient gas and particles from entering the bearing gaps.

The present inventive arrangement has the advantage of avoiding bearing shielding or confinement or the requirement that the bearing be supplied with externally pressurized gas. Pumping capability can be easily and inexpensively provided for the hydrodynamic bearings. Since the demand for replacement gas is not great in high quality hydrodynamic bearings, the supply channels and filtering means do not require significant structure and can be kept small. Bearing clearance can be minimized since filtered gas is assured.

Additional objects, features and advantages of the invention will become apparent from the following, more particular description of a preferred embodiment of the invention with reference to the accompanying drawing.

FIG. 1 is sectional elevation view of a hydrodynamic gas bearing incorporating a filter arrangement constructed in accordance with the principles of the invention;

FIG. 2 is sectional view taken along the line 2--2 shown in FIG. 1;

FIG. 3 is a sectional view taken along the line 3--3 in FIG. 1; and

FIG. 4 is a modification of the embodiment of the invention shown in FIGS. 1-3.

Referring to the figures, right circular cylinder 10 is fixed on an input/output shaft 11 and rotates within stationary journal sleeve 12 on a film of gas in the narrow gap or clearance 13. The gas film in this instance may be assumed to be air from the ambient atmosphere, and the film is formed by the relatively rotating adjacent surfaces of the cylinder and sleeve. The air film serves as the supporting lubricant as in a typical gas or air bearing. The sleeve and cylinder are finished to geometric accuracies of ten microinches and are dimensioned to provide a radial gap of approximately 100 microinches.

Shaft 11 has annular shoulders 14 and surfaces 16, 17 to which exemplary driving or driven elements 18, 19 can be secured by nuts 20. For example, element 18 can be the rotor of a drive motor and element 19 may be a magnetic disc hub or fan. Sleeve 12 has secured at either end thereof an end plate 21 that accomodates shoulder 16 or 17 of the rotating shaft with clearance. Each end plate is formed with at least one radially extending channel 22 and counterbore 23 that communicates with the end plate opening at a shoulder 14 of the shaft. In FIG. 1, two oppositely disposed channels 22 have been shown in each end plate 21 and additional ones may be provided. Each counterbore 23 is filled with suitable submicron filter material 24, such as "Microfibre" from Balston, Inc., Lexington, Mass., that will intercept airborne particles equal to or larger than those expected to damage the inner surface of sleeve 12 or outer surface of cylinder 10 rotating adjacent to the sleeve.

Inner face 25 of each end plate 21 lying next to the ends 10a of cylinder 10 is formed with a plurality of spiral or "Whipple" grooves or flutes 26, best seen in FIG. 2. These grooves are commonly used to pump the gas and produce a supporting end thrust film at the cylinder ends that serve as thrust bearings. Gas is also urged into the journal bearing. The grooves extend only part way along the coextensive surfaces of endplates 21 and cylinder 10. Clamped between each shoulder 14 and input or output element 18 or 19 is a washer 27 having on its face 28 adjacent to shoulder 14 a pattern of radial ribs 29, FIG. 3, that serve to evacuate gas from the opening near shoulder 14. The ribs pump the gas outwardly between element 18 or 19 and end plate 21 to insure a surplus flow of gas through channels 22. Ribs 29 can be of various configuration, such as those forming grooves 26 on face 25 of end plate 21 or the washer surface can be plain. Pumping action will still occur since pumping depends on speed, clearance and washer diameter. The clearance between shoulders 14 and the mating openings in end plates 21, and the washer 27 and the end plate is much larger than that of the bearing air gap between sleeve and cylinder or between end plate and cylinder. The bearing clearance may be only a fifth or tenth that of the other clearances.

In operation, cylinder 10 and its shaft 11 are rotated within stationary sleeve 12 by an input source of energy, such as element 18. The relative motion between the ends of cylinder 10 and journal sleeve 12 with its end plate grooves 26 forms a radial support gas film and end thrust gas film on which the cylinder and shaft move. The pumping grooves or flutes 26 urge the gas into the thrust bearing and journal bearing gap, thus drawing any replenishment gas from the shoulder-end of channels 22 after the gas has passed through filters 24. This assures entrapment of potentially damaging particulate prior to its entry into the radial and thrust bearings. Gas is also forced outward between end plates 21 and input or output elements 18 and 19. The larger clearances, however, decrease the effective pumping action so that the gas is drawn in continually and slowly through channels 22, but without producing a significant negative pressure or overcoming the pumping of grooves 26. The outward flow of gas away from the bearing film assures that any necessary gas has been filtered.

In a different embodiment, in FIG. 4, gas supply channels 22, counterbores 23 with filters 24 can be placed near the center of journal sleeve 12 between end plates 21 and grooves 26 can be reversed and arranged to pull gas through the filters into the journal first, then between the thrust surfaces of the ends of cylinder 10 and end plates 21, and out to the atmosphere adjacent shoulders 14. Washers 27 would continue to provide an exhaust function for the gas as it passes from the journal through the thrust bearings. A region of decreased atmospheric pressure is created in the journal bearing in this embodiment.

The self-cleaning gas bearing described above can be modified in several other aspects: for example, the bearing may be oriented with shaft 11 being vertical or at some other acute angle with respect to the horizontal; this would require only a single thrust bearing. Although the bearing has been illustrated with a rotating cylinder 10, sleeve 12 may be rotated instead; self-cleaning is functional with relative rotation of the bearing members. Pumpimg grooves 26 can be formed on the ends 10a of cylinder 10, and along with ribs 29 can be modified as necessary to provide the desired bearing film of gas flow through the supply channels. In addition, the number and location of channels 22 can be varied to meet the particular bearing arrangement.

Even though the illustrative bearing has been disclosed as an air bearing, the entire mechanism can be enclosed in an atmosphere of another gas and function as described. Manufacturing devices may have to operate in gas atmospheres, such as nitrogen, and the filtering arrangement of the invention is equally effective in these environments.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.