Compliant foil fluid film radial bearing

Abstract: A multi-segment radial bearing including a bushing (12) with an interior bore having a plurality of anti-rotation retainers (22) which are equally spaced and extend the axial length of the interior bore. The generally T-shaped retainers (22) divide the interior bore of the bushing (12) into a like plurality of lobes, with each lobe having a compliant foil (16) and a foil underspring (18) disposed between adjacent generally T-shaped retainers (22).

Description: TECHNICAL FIELD This invention relates to the general field of compliant foil fluid film bearings and more particularly to an improved multi segment compliant foil fluid film radial bearing. BACKGROUND OF THE INVENTION Compliant foil fluid film radial bearings are currently being utilized in a variety of high speed rotor applications. These bearings are generally comprised of a bushing, a rotating element such as a rotor or shaft adapted to rotate within the bushing, non-rotating compliant fluid foil members mounted within the bushing and enclosing the rotating element, and non-rotating compliant spring foil members mounted within the bushing underneath the non-rotating compliant fluid foil members. The space between the rotating element and the bushing is filled with fluid (usually air) which envelops the foils. Conventionally, the compliant fluid foil elements are divided into a plurality of individual compliant foils to form a plurality of wedge shaped channels which converge in thickness in the direction of the rotation of the rotor. The motion of the rotating element 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 convergence angle of the wedge channel increases, causing the fluid pressure rise along the channel to increase. Conversely, 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 axial or overturning motion of the rotating element of the bearing. Owing to preload spring forces or gravity forces, the rotating element of the bearing is typically in physical contact with the fluid foil members of the bearing at low rotational speeds. This physical contact results in bearing wear. It is only when the rotor speed is above what is termed the lift-off/touch-down speed that the fluid dynamic forces generated in the wedge channels assure a running gap between the rotating and non-rotating elements. Compliant foil fluid film radial bearings typically rely on backing springs to preload the fluid foils against the relatively movable rotating element so as to control foil position/nesting and to establish foil dynamic stability. The bearing starting torque (which should ideally be zero) is directly proportional to these preload forces. These preload forces also significantly increase the rotor speed at which the hydrodynamic effects in the wedge channels are strong enough to lift the rotating element of the bearing out of physical contact with the non-rotating members of the bearing. These preload forces and the high lift-off/touch-down speeds result in significant bearing wear each time the rotor is started or stopped. Conventional compliant foil fluid film radial bearings operate with extremely small running clearances and moderate, as opposed to low, drag and power consumption. The clearances between the non-rotating fluid foil's converging channel ramp trailing ends and the rotating element are typically less than inch 0.00254 mm (100 micro-inches) at operating conditions. While most prior compliant foil fluid film radial bearings utilize a plurality of individual compliant foils and individual spring foils with a cylindrically bored bushing, there are instances where a single compliant foil and a single spring foil have been proposed with a cam shaped or lobed bushing. An example of this type of radial bearing can be found in United States Patent No. 5,427,455 issued June 27, 1995 to Robert W. Bosley, entitled "Compliant Foil Hydrodynamic Fluid Film Radial Bearing". DE-A-28 38 768 discloses a bearing comprising a bushing having an interior bore that has a plurality (three) of axially extending grooves defined therein. Three spring plates are provided in the interior bore with their respective edges secured in the grooves. The spring plates define a non-circular bore in which a shaft is supported for rotation. WO-A-92 11469 discloses a bearing comprising a bushing having an interior bore that has a plurality of axially extending grooves defined therein. Compliant foils and undersprings are mounted in the grooves. SUMMARY OF THE INVENTION The invention provides a compliant foil fluid film radial bearing comprising: a bushing having an interior bore including a plurality of equally spaced axially extending retainers projecting into said interior bore and a like plurality of lobes between adjacent said retainers; a plurality of compliant foils, with an individual said compliant foil disposed in said interior bore of said bushing between adjacent said retainers; and a plurality of foil undersprings, with a said underspring disposed beneath each of said compliant foils between said adjacent retainers. BRIEF DESCRIPTION OF THE DRAWINGS Having thus described the present invention in general terms, reference will now be made to the accompanying drawings in which: Figure 1 is an end view of the compliant foil fluid film radial bearing of the present invention; Figure 2 is an enlarged sectional view of a portion of the compliant foil fluid film radial bearing of Figure 1; Figure 3 is an exploded perspective view of the compliant foil fluid film radial bearing of Figures 1 and 2; and Figure 4 is an enlarged sectional view of a portion of an alternate compliant foil fluid film radial bearing of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Illustrated in Figures 1-3 is the compliant foil fluid film radial bearing 10 of the present invention. This multi-segment radial bearing 10 generally comprises a bushing 12, a shaft or rotor 14, a plurality of compliant foils 16 (shown as three), and a like plurality of foil undersprings 18. As best seen in Figure 3, interior bore 20 of the bushing 12 includes a plurality of anti-rotation devices or retainers 22 (shown as three, generally T-shaped retainers) which are equally spaced and extend the axial length of the interior bore 20. The retainers 22 divide the interior bore 20 of the bushing 12 into a like plurality of lobes 24. The compliant foils 16 and the foil undersprings 18 are disposed in each lobe 24 between adjacent generally T-shaped retainers 22. While the shaft or rotor 14 is cylindrical, the interior bore 20 of the bushing 12 may or may not be cylindrical. If the interior bore 20 is not cylindrical, the generally T-shaped retainers 22 will divide the interior bore 20 into a plurality of shaped or contoured lobes 24. On the other hand, if the interior bore 20' of the bushing 12' is cylindrical, the generally T-shaped retainers will divide the interior bore 20' into a plurality of lobes in the form of equally spaced arc segments of a cylinder and the converging wedges will be formed via the compliant foil 16' and/or the foil undersprings 18' as generally shown in Figure 4. The height of the foil undersprings 18' may increase from the leading edge of the compliant foil 16' to the trailing edge of the compliant foil 16' in order to form the converging wedge. Alternately, the stiffness of the foil underspring can vary from the leading edge to the trailing edge to produce the same result, or shims of varying height can be positioned underneath the foil underspring. The generally T-shaped retainers 22 may be symmetrical or conform to the leading edge and trailing edge of the contoured lobes 24. Non-symmetrical T-shaped retainers 22 will retain the foils 16 at different radii from the geometric center with the leading edge of the foils retained at a greater geometric radius than the trailing edge. The generally T-shaped retainers 22 are formed as part of the contoured interior bore 20 of the bushing 12 with the base 26 thereof extending radially inwards from the interior bore 20. The cross piece of the generally T-shaped retainers 22 has a leading edge 30 and a trailing edge 28, with the leading edge 30 having a greater thickness or width than the trailing edge 28 as best shown in Figure 2. Since the inner diameter of the cross piece is the same at both the leading edge 30 and the trailing edge 28, this provides a greater diameter or depth for the trailing edge of the contoured lobe 24 which is under the thicker leading edge 30 of the generally T-shaped retainers 22. The contoured surface of the lobes 24 can be derived from one or a series of radii of a defined profile. For example, in the case of three (3) foil segments, the contour of the lobes 24 in which the compliant foils 16 and underspring foils 18 rest upon can be a multiple of, or a fraction of, a specific number. Also, an appropriate contour can be constructed from vertices of an equilateral triangle of specific length side with circles formed from these vertices intersecting to give the contoured surface which may be machined, ground, EDM'ed or broached. While the compliant foil fluid film radial bearing 10 is shown with three (3) compliant foil segments 16 and three (3) foil undersprings 18, a greater number of compliant foils segments 16 and foil undersprings 18 can be utilized. For example, five (5) or more segments may be equally appropriate for the compliant foil fluid film radial bearing 10. The compliant foils 16 and foil undersprings 18 are trapped and held between adjacent T-shaped retainers 22. The compliant foils 16 would normally have a preformed arcuate shape as shown in Figure 3. The foil undersprings 18 may have a preformed radius or simply be a rectangular sheet. In either case, the compliant foils 16 and foil undersprings 18 are axially inserted, either separately or together, into the interior bore 20 of bushing 12 between adjacent T-shaped retainers 22. Also, while the foil undersprings 18 are illustrated as a wavy springform, any conventional bearing underspring can be utilized, including the spring described in US Patent No. 5,427,455. The underspring 18 may have variable spring rates or tapered heights from the leading edge to the trailing edge as shown in Figure 4. When trapped between adjacent T-shaped retainers 22, the compliant foils 16 would be pre-loaded in compression between the adjacent T-shaped retainers 22. In some instances, however, the compliant foils 16 may be merely retained in position between adjacent T-shaped retainers 22 without preloading. The foil undersprings 18 would, however, normally be pre-loaded in compression between adjacent T-shaped retainers 22. The foil underspring 18 may contribute to the contoured shape of the compliant foils 16. In most instances, the compliant foils 16 and foil underspring 18 would be separate and would be capable of sliding movement therebetween. There may, however, be instances where the compliant foils 16 and foil underspring 18 will be joined together into a single assembly. The greater thickness of the leading edge 30 of the T-shaped retainer crosspiece produces a greater depth at the trailing edge of the compliant foils 16 to serve as a means to pull the compliant foils 16 away from the trailing edge of the converging wedge. The trailing edge 28 of the T-shaped retainers 22 has less thickness thereby allowing the leading edge of the foils to rest closer to the shaft, which will facilitate development of the fluid film wedges. Also, while the complaint foil fluid film radial bearing 10 can function hydrodynamically, by providing an external source of fluid under pressure, a hydrostatic aspect can be realized. The external pressurized fluid may be introduced axially at the ends of the bushing or through radial holes 40 in the bushing 40 axially along and through the T-shaped retainers 22. The hydrostatic aspect will provide cooling fluid to the interior bore 20 of the bushing 12, which will increase bearing life especially in a gas turbine application. Hydrostatic operation will also increase the load capacity of the bearing. The radial bearing 10 of the present invention allows for automation by mass production and the components can easily be assembled by hand. The compliant foils 16 may be stamped or fine blanked and there is no requirement for spot welding or chemical etching. The large clearances between the compliant foils 16 and the shaft 14 at the T-shaped retainers 22 allow improved cooling of the shaft 14 and compliant foils 16. The design can accommodate a variety of underspring types and the T-shaped retainers 22 permit more design flexibility with respect to the shaft, foil and spring interaction.

Claims: A compliant foil fluid film radial bearing comprising: a bushing (12) having an interior bore (20;20') including a plurality of equally spaced axially extending retainers (22) projecting into said interior bore and a plurality of lobes (24) between adjacent retainers; a plurality of compliant foils (16) each disposed in said interior bore (20, 20') of said bushing (12) between respective adjacent retainers (22), and a plurality of foil undersprings (18) each disposed beneath a respective compliant foil (16) between said adjacent retainers (22). The compliant foil fluid film radial bearing of claim 1, wherein said retainers (22) are generally T-shaped, said interior bore (20') is cylindrical and said individual compliant foils (16) and said individual foil undersprings (18) beneath said individual complaint foils (16) establish a converging wedge between said adjacent generally T-shaped retainers (22). The compliant foil fluid film radial bearing of claim 1, wherein said retainers (22) are generally T-shaped, said interior bore is non-cylindrical (20), generally contoured said lobes (24) are formed between said adjacent retainers (22), and said individual compliant foils (16) and said individual foil undersprings (18) generally conform to the shape of said contoured lobes (24) to establish a converging wedge. The compliant foil fluid film radial bearing of claim 1, wherein said bushing (12) has a cylindrical interior bore (20') such that said lobes (24) comprise respective arc segments between said adjacent retainers (22); and the radial height of each said foil undersprings (18) increases from its leading edge to its trailing edge to establish a converging wedge on the surface of the respective compliant foil (16) that, in use, faces a shaft (14) that is rotatably supported in said interior bore of the bushing (12). The compliant foil fluid film radial bearing of claim 1, wherein said bushing (12) has a non-cylindrical interior bore (20) such that said lobes comprise respective contoured lobes (24) between said adjacent retainers (22); and the contour of each lobe (24) establishes a converging wedge on the surface of the respective compliant foil (16) that, in use, faces a shaft (14) that is rotatably supported in said interior bore of said bushing (12). The compliant foil fluid film radial bearing of claim 4 or 5, wherein said retainers (22) are generally T-shaped. The compliant foil fluid film radial bearing of claim 6, wherein said generally T-shaped retainers (22) are asymmetrical. The compliant foil fluid film radial bearing of claim 7, wherein said generally T-shaped asymmetrical retainers (22) have a crosspiece with a leading edge (30) and a trailing edge (28), with the leading edge thicker than the trailing edge. The compliant foil fluid film radial bearing of any of claims 2, 3 or 6 to 8, wherein said generally T-shaped retainers (22) include radial openings (40) to provide cooling flow to said interior bore of said bushing (12). The compliant foil fluid film radial bearing of any of the preceding claims, wherein the radial stiffness of each said foil underspring (18) increases from its leading edge to its trailing edge. The compliant foil fluid film radial bearing of any of the preceding claims wherein said bearing is hydrodynamic. The compliant foil fluid film radial bearing of any of claims 1 to 11, wherein said bearing is hydrostatic. The compliant foil fluid film radial bearing of any of the preceding claims including means to provide cooling flow axially into said interior bore of said bushing. An installation comprising the complaint foil fluid radial bearing of any of the preceding claims and a shaft (14) rotatably supported within said interior bore (20;20') of said bushing (12).

Inventors: WEISSERT DENNIS H, WEISSERT, DENNIS H.
Applicants: CAPSTONE TURBINE CORP, CAPSTONE TURBINE CORPORATION
Application year: 1998
Main classification: F16C17
IPC codes: F16C27, F16C17