Compliant foil hydrodynamic fluid film radial bearings are currently being utilized in a variety of high speed rotor applications. These bearings are comprised of an inner rotating element, non-rotating compliant fluid foil elements that surround the rotating element, non-rotating compliant spring foil elements that surround the fluid foil element and a non-rotating cartridge element that surrounds and provides attachments for the foil elements. The annular space between the rotating element and the cartridge element is filled with fluid (usually air) which envelops the foils. The space between the smooth rotating element and the fluid foil is subdivided into a plurality of fluid-dynamic wedge channels. These wedge channels are formed by overlapping the fluid and spring foils to form ramps in the inner surfaces of the fluid foils. The fluid wedge channels converge in thickness in the direction of the rotating element's motion. The rotating element's motion applies viscous drag forces to the fluid in the converging wedge channels. This results in increases in fluid pressure, especially near the trailing end of the wedge channels. If the rotating element moves toward the non-rotating element, the wedge channel's convergence angle increases causing the fluid pressure along the wedge channel to increase. If the rotating element moves away, the pressure rise along the wedge channel decreases. Thus, the fluid in the wedge channels exerts restoring forces on the rotating element that vary with and stabilize running clearances and prevent contact between the rotating and non-rotating elements of the bearing. Flexing and sliding of the foils causes coulomb damping of any orbital motion of the rotating element of the bearing.
At low rotor speeds, the rotating element of the bearing is in physical contact with the fluid foil element(s) of the bearing, resulting in bearing wear. Only when the rotor speed is above what is termed the lift-off/touch-down speed do the fluid dynamic forces generated in the wedge channels assure a running gap between the rotating and non-rotating elements.
Conventional, compliant foil hydrodynamic fluid film bearings have relied on backing springs and the spring properties of the elastically bent fluid foil to preload the fluid foil against the relatively moveable rotating element (rotor) to control foil nesting/position and to establish foil dynamic stability. This preload force significantly reduces the rotor speed at which the wedge channel effect is strong enough to lift the rotating bearing element out of physical contact with the non-rotating elements of the bearing. This preload force and the high lift-off/touch-down speed result in significant bearing wear each time the rotor is started or stopped. These bearings usually have high starting torques.
Conventional, compliant foil hydrodynamic fluid film bearings achieve spring properties for their spring foils before assembly into the bearing cartridge by imparting a permanently deformed series of, for example, convoluted spring portions. Therefore, the foil pack is relatively thick and has fairly large tolerances for foil stack height. The maximum rotor deflections that these bearings permit is fairly large (loose compliance control).
Most conventional compliant foil hydrodynamic fluid film bearings use a plurality of fluid foils and a plurality of spring foils. This results in reduced load capacity and higher bearing costs when compared to bearings with a single spring foil and a single fluid foil.
If a single fluid foil were to be used in lieu of a plurality of fluid foils, and that foil were formed as a flat, constant thickness sheet, which is subsequently formed to fit into the cartridge, the foil would not follow the contours of the inside of the cartridge near the foil ends. This is due to the fact that no bending moment can be applied to the ends of the foil and the foil's bending stiffness is constant throughout its length.
If a single fluid foil is utilized and it is attached to the cartridge at one end, the rotor can only rotate in one direction without risking foil to rotor lock-up and foil failure due to ever increasing rotor to foil friction and foil tension.
Previously, many types of compliant foil hydrodynamic fluid film radial bearings have been used to support, position and control the resonant motion of high speed rotating assemblies. These bearings have utilized cartridges with round apertures. Most bearings have used from five to nine fluid foils and from five to nine spring foils arrayed around the inside of the cartridge aperture. Many of the conventional, prior art bearings have the fluid foil welded to the spring foil, or when using a plurality of foils, attach the foils to the cartridge by bending the foils around bars or welding them to bars and then inserting the bars into wide slots provided for foil retention in the cartridge aperture.
A search of the prior-art has not disclosed any directly pertinent patents to the instant invention. Specifically, no art has been found that utilizes: 1) contoured cartridge apertures, 2) flat-formed spring foils with cantilever beams which stand erect when the foil is bent or formed for insertion into the cartridge, and 3) circumferential preloading of foils to force the foils to press against the cartridge aperture. However, the following U.S. patents are considered related:
______________________________________ U.S. PAT. NO. INVENTOR DATE ISSUED ______________________________________ 3,366,427 Silver Jan. 30, 1968 3,795,427 Licht Mar. 05, 1974 3,809,443 Cherubim May 07, 1974 3,957,317 Silver May 18, 1976 4,170,389 Eshel Oct. 09, 1979 4,178,046 Silver Dec. 11, 1979 4,213,657 Gray July 22, 1980 4,223,958 Gray Sep. 23, 1980 4,229,054 Miller Oct. 21, 1980 4,262,975 Heshmat Apr. 21, 1981 4,277,113 Heshmat July 07, 1981 4,415,281 Agrawal Nov. 15, 1983 4,552,466 Warren Nov. 12, 1985 4,743,126 Soum May 10, 1988 4,961,122 Sakai Oct. 02, 1990 5,129,739 Asai July 14, 1992 5,228,785 Saville July 20, 1993 ______________________________________
Silver (U.S. Pat. No. 3,366,427) discloses a bead 22, wide slots 18 and 19, rod 23 as elements for attaching foils to the cartridge while in the instant disclosure the foils are retained by pressing against the circumferential preload bar or are slid into electro discharge machined EDM fabricated slots. Silver also discloses ramps which are achieved by overlapping a plurality of foils, while in the instant invention there is no overlapping of foils and the lobes or ramps are achieved by contouring the cartridge aperture.
Licht (U.S. Pat. No. 3,795,427) discloses an overlapping single foil 61 or a plurality of overlapping foils 63, 64, and 65 which are secured to the cartridge by a retaining tab 78 at the end of the cartridge. In the instant invention, non-overlapping foils are secured by the circumferential preload bar along a line parallel to the cartridge axis.
Cherubim (U.S. Pat. No. 3,809,443) discloses a single spring foil element 23 and a single fluid foil element 25. But these foils are bonded together at one end, while in the instant invention the spring and fluid foils are not bonded. Cherubim discloses a spring foil that is formed into resilient surface elevations 27, while in the instant invention the spring foil is formed flat. Cherubim discloses a suitable restraining means (pin) 95 to secure the spring and fluid foils to the cartridge without circumferential preloading the foils, while in the instant invention a circumferential preload bar is used to preload the foils.
Silver (U.S. Pat. No. 3,957,317) discloses overlapping foils having herringbone or chevron shaped trailing edges that are attached to the cartridge by bars set in wide milled slots. These foils are preformed with radii that are greater than that of the round cartridge aperture. The intentional mismatch of the foil/cartridge radii causes the plurality of foils to be preloaded against the rotor. In the instant invention, the single fluid foil and single spring foil are preloaded away from the rotor and towards the contoured cartridge aperture.
Eshel (U.S. Pat. No. 4,710,389) discloses a ribbon-shaped thin steel foil member 41 which is stretched over a body of pressurized material which functions as a support media for fluid foils. He does not disclose a spring foil as a support for a fluid foil.
Silver (U.S. Pat. No. 4,178,046) discloses foils attached to the cartridge by mounting bars 14 and 44 and supported by springs with milled or chemically etched ridges 54 and grooves 56. In the instant invention, no bars are bonded to the foil or inserted into cartridge grooves nor are the spring foils formed to make ridges or grooves.
Gray (U.S. Pat. No. 4,213,657) discloses a spring comprised of tubular elements 22 and cage elements 24, while in the instant invention flat formed spring foils are utilized.
Gray (U.S. Pat. No. 4,223,958) discloses a spring foil having raised projections 42 fabricated in previously flat metal by the application of deforming forces. These projections function as cantilever beams. But in the instant invention, the cantilever beams are created in flat metal by chemical etch techniques, then they "stand proud" and function as springs only when the foil is bent or formed for insertion into the cartridge.
Miller (U.S. Pat. No. 4,229,054) discloses spacer blocks 25, the ends 23 of which are attached to the bore wall of the sleeve 15 by welding or other suitable means to prevent rotation of the bearing modules 13 relative to the sleeve 15. This welding or other suitable means presumably would also function to prevent axial translation of the bearing foil modules out of the sleeve. The bearing foil modules are also shown to reside in and be captured by the walls of a circumferential channel in the sleeve, presumable to also provide constraint against the bearing foil modules translating axially out of the sleeve. Miller does not disclose any element functioning as a circumferential preload bar, nor does he disclose any element functioning as anti-translation tabs or anti-translation grooves. Miller discloses a bi-directional journal bearing utilizing three bearing foil modules, each being 120 degrees long in arc length. But he does not identify any means to generate the circumferentially compressive stresses within the foils, between the foil attachment points to the sleeve and any foil to rotor contact points which would be required for bi-directional operation of single fluid foil bearings without tightening the fluid foil about the rotor to the point of foil failure. Miller does not utilize a contoured cartridge aperture, flat formed spring foils, or spring foil spring rates that vary along the arced length of the foil.
Heshmat (U.S. Pat. No. 4,262,975) discloses a compliant support element 54 which has a spring rate that varies along the length of the element due to variations in the spacing of ridges or bumps 56 in the element. In the instant invention, the spring rates vary due to variations in cantilever beam width and length, not variations in spacing of ridges or bumps. Heshmat also discloses a bearing pad assembly 40 which creates a ramped thickness change in the fluid foil. In the instant invention, there is a foil thickness variation, but it is in the spring foil, not the fluid foil, and it is achieved by varying the length of the cantilever beams.
Heshmat (U.S. Pat. No. 4,277,113) discloses a spring foil with elevation 52 that has a non-linear spring rate that increase with deflection. But in the instant invention, the non-linear spring rate is accomplished by wrapping the cantilever beam around the rotor radius so as to change the free length of the cantilever beam. This is a totally different means of achieving a non-linear spring than that utilized by Heshmat.
Agrawal (U.S. Pat. No. 4,415,281) discloses a convoluted spring foil 45 that has a non-linear spring rate that varies with deflection. This is accomplished by forming the foil in a plurality of sinusoidal shapes of varying height and spacing. Again, this method is different than in the instant invention.
Warren (U.S. Pat. No. 4,552,466) discloses foils with tabs 24 used for attachment to the cartridge. None of the disclosed tab configurations or attachment methods utilize electro discharge machine (EDM) technology.
Soum (U.S. Pat. No. 4,743,126) discloses a foil having side margins 3 that attach the foil to the end of the cartridge. In the instant invention, the foils are restrained against rotation in the cartridge by tabs oriented 90 degrees relative to those disclosed by Soum.
Sakai (U.S. Pat. No. 4,961,122) discloses a herringbone grooved bearing (the invention) and V-grooved bearings (the prior art) wherein the bearing has either grooves 160 or raised portions 260 in the shaft 4 and similar groove or raised portion patterns in the inner bore of the bearing housing 6 to induce local increases in the process fluid pressure when the shaft is rotated and displaced radially away from the centerline of the housing. The V grooves in the rotor and housing disclosed by Sakai are unrelated to the variable width V-shaped grooves used in the outer surface of the fluid foil of the instant invention.
Asai (U.S. Pat. No. 5,129,739) discloses a bearing with dynamic pressure grooves formed in the thermoplastic resin inner surface of a rigid metal cylinder 21 which functions as a fluid dynamic surface. This cylinder is not resiliently mounted to the bearing housing. In the fourth embodiment of the instant invention, the fluid sleeve does not have pressure grooves in its inner surface, is thin and flexible, and is resiliently mounted to the bearing cartridge aperture.
Saville (U.S. Pat. No. 5,228,785) discloses overlapping foils supported by convoluted spring foils having variable convolute height and variable convolute spacing to achieve non linear spring rates and ramps. In the instant invention, non-linear spring rates are achieved with variable cantilever beam width and length, and ramps are achieved by contouring the cartridge aperture and with variable cantilever beam length.