Foil thrust bearings.

Process fluid or gas bearings are now being utilised in an increasing number of diverse applications. These fluid bearings generally comprise two relatively movable elements with a predetermined spacing therebetween filled with a fluid such as air, which, under dynamic conditions, forms a supporting wedge sufficient to prevent contact between the two relatively movable elements.

More recently, improved fluid bearings, particularly gas bearings of the hydrodynamic type, have been developed by providing foils in the space between the relatively movable bearing elements. Such foils, which are generally thin sheets of a compliant material, are deflected by the hydrodynamic film forces between adjacent bearing surfaces and the foils thus enhance the hydrodynamic characteristics of the fluid bearings and also provide improved operation under extreme load conditions when normal bearing failure might otherwise occur. Additionally, these foils provide the added advantage of accommodating eccentricity of the relatively movable elements and further provide a cushioning and dampening effect.

The ready availability of relatively clean process fluid or ambient atmosphere as the bearing fluid makes these hydrodynamic, fluid-film-lubricated, bearings particularly attractive for high speed rotating machinery. While in many cases the hydrodynamic or self-acting fluid bearings provide sufficient load bearing capacity solely from the pressure generated in the fluid film by the relative motion of the two converging surfaces, it is sometimes necessary externally to pressurize the fluid between the bearing surfaces to increase the load carrying capability. While these externally pressurized or hydrostatic fluid bearings do increase the load carrying capacity, they do introduce the requirement for an external source of clean fluid under pressure.

In order properly to position the compliant foils between the relatively movable bearing elements a number of mounting means have been devised. In thrust bearings, it is conventional practice to mount a plurality of individually spaced foils on a foil bearing disc such as by spot welds and position the foil bearing disc on one of the bearing elements as exemplified in U.S. Patent No. 3,635,534.

To establish stability of the foils in most of these mounting means, a substantial pre-load is required on the foil. That is, the individual foils must be loaded against the relatively movable bearing element opposed to the bearing element upon which the foils are mounted. It has been conventional to provide separate compliant stiffener elements or underfoils beneath the foils to supply this required preload as exemplified in U.S. Patent Nos. 3,893,733 and 4,153,315.

In order to facilitate start-up and to reduce bearing wear, the individual foils may be coated with a high lubricity material such as a stratified fluorocarbon, molybdenum disulfide, graphite fluoride, or the like. The use of such coatings, while enhancing the life of the foil bearing, introduces certain operating temperature limitations thereon. As still higher temperature environments are envisaged for foil bearing operation, the temperature limitations of these coatings become critical since they cannot survive as high a temperature as the underlying metallic foil. Thus, higher temperature coatings must be developed or means found to limit the operating temperature at the coated foil surfaces. Examples of prior cooling schemes for foil bearings can be found in U.S. Patent Nos. 4,227,753 and 4,247,155.

As more widespread use is made of foil bearings, the ease and cost of manufacturing and assembly become of more concern. Simple construction with greater ease of manufacture and shorter axial heat conduction paths is needed. Examples of recent attempts in this direction can be found in U.S. Patent No. 3,747,997 and 3,809,443.

According to one aspect of the present invention a fluid thrust bearing assembly comprises first and second members arranged for relative rotation with respect to one another, a thrust member being operably disposed between the first and second members and being mounted on said first member, the thrust member having a number of compliant foils each of which has an operative face which inclines to a radial plane and which defines between it and the second member a generally wedge-shaped space for bearing fluid, and the direction of relative rotation of the first and second members being towards the narrower ends of said wedge shaped spaces and is characterised in that the compliant foils are integrally formed with the thrust member.

According to another aspect of the present invention a fluid thrust bearing assembly comprises first and second members arranged for relative rotation with respect to one another, a thrust member being operably disposed between the first and second members and being mounted on said first member, the thrust member having a number of compliant foils each of which has an operative face which inclines to a radial plane and which defines between it and the second member a generally wedge-shaped space for bearing fluid, and the direction of relative rotation of the first and second members being towards the narrower ends of said wedge shaped spaces and is characterised in that the thrust member comprises a ring having an external peripheral edge, and an internal peripheral edge surrounding a central aperture of the ring, and the foils are integrally formed from the material of the ring by bending each foil out of the plane of the remainder of the ring along a bend line which extends substantially radially of the ring.

According to yet another aspect of the present invention a fluid thrust bearing assembly comprises first and second members arranged for relative rotation with respect to one another, a thrust member being operably disposed between the first and second members and being mounted on said first member, the thrust member having a number of compliant foils each of which has an operative face which inclines to a radial plane and which defines between it and the second member a generally wedge-shaped space for bearing fluid, and the direction of relative rotation of the first and second members being towards the narrower ends of said wedge-shaped spaces, and is characterised in that the thrust member comprises a ring having an external peripheral edge, and an internal peripheral edge surrounding a central aperture of the ring, and the foils are each formed by an integral portion of the ring which is bounded by a pair of generally radial lines of which one line extends along an edge of the foil which is cut from the remainder of the ring by means of a generally radial slot formed in the ring.

According to a further aspect of the present invention a fluid thrust bearing assembly comprises first and second members arranged for relative rotation with respect to one another, a thrust member being operably disposed between the first and second members and being mounted on said first member, the thrust member having a number of compliant foils each of which has an operative face which inclines to a radial plane and which defines between it and the second member a generally wedge-shaped space for bearing fluid, and the direction of relative rotation of the first and second members being towards the narrower ends of said wedge-shaped spaces, and is characterised in that the compliant foils are integrally formed with the remainder of the thrust member, each foil being bent from the remainder of the thrust member along a generally radial bend line from whence the foil converges towards the adjacent face of the second member, the foil having an edge bounding said face at the narrower end of said wedge-shaped space, and the thrust member defining a ramped surface at the radially inner and/or radially outer edge of the foil said ramped surface or surfaces sloping in a direction opposite to the inclination of the operative face of the associated foil.

The invention may be carried into practice in various ways but certain specific embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none"><li>Figure 1 is an exploded perspective view of one embodiment of a foil thrust bearing according to the present invention;</li><li>Figure 2 is an enlarged plan view of the bearing disc of the foil thrust bearing of Figure 1;</li><li>Figure 3 is a side elevation of part of the bearing disc of Figure 2 viewed along the line 3-3 thereof;</li><li>Figure 4 is an enlarged view of a second embodiment of a bearing disc according to the present invention;</li><li>Figure 5 is a side elevation of part of the bearing disc of Figure 4 viewed along the line 5-5 thereof;</li><li>Figures 6 and 7 are similar views of a further embodiment of bearing disc according to the present invention;</li><li>Figures 8 and 9 are similar views of a further embodiment of bearing disc according to the present invention;</li><li>Figure 10 is an enlarged plan view of another embodiment of thrust disc according to the present invention;</li><li>Figure 11 is a cross-sectional view of the thrust disc of Figure 10 taken along the line 11-1 thereof;</li><li>Figure 12 is a top plan view of the underspring of the foil thrust bearing of Figure 1;</li><li>Figure 13 is a side elevation of part of the underspring of Figure 12 as viewed along the line 13-13 thereof, and</li><li>Figure 1 4 is a bottom plan view of the underspring of Figures 12 and 13.</li></ul>

Figures 1 to 3 illustrate a first embodiment of a thrust bearing of the present invention. As illustrated in Figure 1, a thrust runner 10 including shaft 12 is rotatably supported on a thrust plate 28 by means of a thrust bearing ring or disc 14 and a thrust bearing stiffener or underspring 22. The thrust bearing ring or disc 14 includes a plurality of integral bearing pads or foils 16. The thrust bearing underspring 22 includes a plurality of generally radially upper ridges 24 and lower ridges 26 alternately disposed thereon to provide preload and support for the thrust bearing disc 14.

As more fully shown in Figures 2 and 3, the thrust bearing disc 14 has an external periphery 14A and a central aperture 14B defined by an internal periphery 14C and comprises a plurality of thin compliant surface pads or foils 16 formed by and separated by radially extending slots 18. Each of these slots 18 is generally U-shaped having an outer leg 34 and an inner leg 36. Ramps 30 and 32 extend respectively between the outer leg 34 of the slot 18 and the outer periphery of the thrust bearing disc 14, and the inner leg 36 of the slot 18 and the inner periphery of the thrust bearing disc 14, around its central aperture. The ramps 30 and 32 are generally defined by radial lines, as seen in plan. The thrust bearing disc 14 thus provides alternate surface foils 16 and surface ramps 30 and 32. As shown in Figure 3, the foils 16 subtend a shallow angle to a radial plane. The thrust runner 10, which rotates above the foils, will, in practice, rotate in the direction of the arrow shown in Figure 1. This direction of rotary movement of the thrust runner is effectively to the right in Figure 3. Thus the foils 16 converge towards the underside of the thrust runner, in the direction of rotation of the latter so forming wedge-shaped spaces between the foils and the runner 10.

In contrast, the ramps 30 and 32 slope in the opposite direction, and quite steeply. Thus the ramps effectively diverge from the undersurface of the thrust runner, in the direction of rotation of the latter. With the generally U-shaped slot 18 extending between the ramps 30 and 32, the effective trailing edge 17 of the foil 16 continues to converge towards the thrust runner 10, as most clearly illustrated in Figure 3.

Figures 4 and 5 illustrate an alternate embodiment of the thrust bearing disc in which the slots 18 are generally L-shaped, having only an outer leg 34, but no inner leg 36. In addition, the ramps 30 and 32 are generally radially aligned with the slot in the embodiment of Figures 4 and 5. Alternately, the outer leg 34 of the slot 18 may be eliminated to leave a straight radial slot.

Also illustrated in Figure 4 is the relative position of the upper ridges 24 of the underspring 22 with respect to the foil 16 of the thrust bearing disk 14. The angle θ₁ is defined between the radial line extending from the base of the ramps 30 and 32 (the leading edge of the foil 16) and the radial centreline of the upper ridge 24. The angle 8₂ is defined between the leading edge of the foil 16 and the trailing edge 17 of the foil 16. In order to provide the proper preload and support for the individual foils 16, the ratio of the angles 6₁ and e₂ should be approximately 2:3 to provide optimum results in most operating conditions. It should be understood, however, that the ratio between 0₁ and 0₂ range can be from approximately 1:2 to almost 1:1. The relationship between 0₁ and 0₂ should, however, never be less than 1:2.

Another alternate embodiment of foil thrust disc 14 is illustrated in Figures 6 and 7. In this arrangement the L-shaped slot 18 opens directly to the inner periphery of the thrust bearing disc 14, and thus includes only a single outer ramp 30. The opening of the slot 18 at the inner periphery of the disc 14 is generally shown by numeral 40. As with the embodiment of Figures 4 and 5, a straight radial slot can be utilised in this embodiment also.

Figures 8 to 11 illustrate two alternate embodiments in which the thrust bearing disc 44 includes a plurality of foils 46 separated by ramps 48 which radially extend across the entire disc 44. In the embodiment of Figures 10 and 11 the ramps 48 include a plurality of cooling holes 50.

Figures 12 to 14 illustrate the underspring 22 utilised in the foil thrust bearing of this invention. Besides the upper ridges 24 and lower ridges 26, also shown are projections 25 which can be utilised to maintain the position of the underspring 22 with respect to the thrust plate 28. Similar cutouts 27 (see Figure 4) may be provided on the thrust bearing disc 14 for the same purpose.

As with conventional foil bearings, the bearing surface of the individual foils may be coated with a high lubricity material. The slots in the individual thrust bearing discs may be formed by photochemical machining or mechanical punching or someother similar process. The ramps can be produced by stamping orother similar mechanical techniques.

Since a portion of the heat generated in the hydrodynamic bearing film due to discous dissipation is conducted away through the foils and the disc, the integration of the foils and the disc provides a shorter heat conduction path as compared with individual foils mounted upon a separate disc. The simplicity in design will also provide ease in fabrication and thus lower cost, while still maintaining high bearing performance.

With respect to the embodiments of Figures 2 and 3 and Figures 4 and 5, it should be recognised that both of these embodiments may include only the ramps 30 at the outer periphery with no ramps at the inner periphery. Furthermore, there may be applications where the angle of divergence with respect to the underside of the thrust runner 10 and/or the length of the inner ramps 32 of these embodiments (and thus the ramp height) may vary from the angle of divergence and/or the length of the outer ramps 30. In some instances the outer ramp 30 may be eliminated altogether with only the inner ramp 32 remaining. Likewise, the angle of divergence and/or the length of the ramps in the embodiments of Figures 8 and 9 and Figures 10 and 11 can be varied in the radial direction.

The actual angle of divergence and height of the diverging ramps will be varied to provide for particular operating conditions. The integral foil thrust disc can provide a higher bearing load capacity than prior arrangements since there is a greater extent of converging surface facing the thrust runner 10 which generates the hydrodynamic pressure to support the thrust runner 10. The surface of the converging foils can be relatively flat or have a slight crown depending upon the desired operating characteristics. The height of the individual ramps would normally be between 0.00127 cm (0.0005 ins) to 0.0254 cm (0.010 ins) with a range of 0.00254 to 0.00508 cm preferred. The thrust bearing disc illustrated in Figures 6 and 7 would be thicker than the thrust bearing disc of Figures 2 and 3 to compensate for the loss of stiffness as a result of the opening 40. Likewise, the number of individual foils in a particular thrust bearing disc can be varied considerably depending upon the operating conditions in which the thrust bearing disc is to be utilised.