THRUST BEARINGS

Abstract: A foil thrust bearing comprising a pair of members (10, 28) arranged for relative rotation with respect to one another, and, disposed between said pair of members, a compliant foil bear­ ing (14) and an under spring (22). The under spring (22) in­ cludes a pluratlity of upper ridges (24) and lower ridges (26) al­ ternatively disposed thereon, the upper ridges (24) having a height (t1) greater than the height (t2) of the lower ridges (26).

Description: Thrust Bearings Process fluid or gas bearings are now being utilized 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 sedge 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 disk such as by spot welds and position the foil bearing disk 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 undersprings beneath the foils to supply this required preload as exemplified in U.S. Patent Nos. 3,893,733 and 4,153,315. Under extremely high load, however, the compliance of these underfoils may be exceeded and the undersprings 'bottom out', thus destroying the load carrying capability of the bearing. In one aspect of the present invention the bearing underspring is characterised by a plurality of upper ridges and lower ridges alternately disposed thereon, the upper ridges having a height greater than the height of the lower ridges. In another aspect of the present invention a foil sitffener disk is included having a plurality of upper and lower ridges alternately transversely disposed therearound between the thrust disk and the thrust plate, the upper ridges having a height generally between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges. According to a third aspect of the present invention a foil stiffener disk has a plurality of upper and lower ridges alternately transversely disposed therearound between the thrust disk and the thrust plate, the upper ridges outwardly diverging radially, the lower ridges outwardly diverging radially, the space between adjacent lower ridges outwardly converging radially, and the upper ridges having a height generally between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges. According to a fourth aspect of the present invention an underspring for a foil thrust bearing comprises a compliant ring disk having a plurality of upper ridges disposed on one surface of the disk and a plurality of lower ridges disposed on the other surface of the disk generally between adjacent upper ridges, the upper ridges having a height generally between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges. According to a fifth aspect of the present invention an underspring for a foil thrust bearing comprises a compliant ring disk having a plurality of upper ridges disposed on one surface of the disk and a plurality of lower ridges disosed on the other surface of the disk generally between adjacent upper ridges, the upper ridges outwardly diverging radially, the lower ridges outwardly diverging radially, the space between adjacent lower ridges outwardly converging radially, and the height of the upper ridges being between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges. The invention may be carried into practice in various ways, but one specific embodiment will now be described, by way of example with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of a foil thrust bearing according to the present invention; Figure 2 is an enlarged top plan view of the thrust bearing underspring of the foil thrust bearing of Figure 1; Figure 3 is a side elevation of the thrust bearing bearing underspring of Figure 2 taken along line 3-3 thereof; Figure 4 is an enlarged under plan view of the thrust bearing underspring of Figure 2; Figure 5 is an enlarged sectional view of the foil thrust bearing of Figure 1 in a static condition; and Figure 6 is an enlarged sectional view of the foil thrust bearing of Figure 1 in a dynamic condition. Figure 1 illustrates a thrust runner 10 including shaft 12, the runner 10 being rotatably supported on a thrust plate 28 by means of a thrust bearing disk 14 and a thrust bearing stiffener or underspring 22. The thrust bearing disk 14 has a plurality of bearing pads or foils 16 mounted thereon, while the thrust bearing underspring 22 includes a plurality of upper ridges 24 and lower ridges 26 alternately disposed thereon to provide stiffness for the thrust bearing disk 14. As more fully shown in Figures 2-4, the thrust bearing underspring 22 generally comprises a thin compliant ring ranging in thickness td between 0.00254 cm and 0.508 cm and can be produced by conventional chemical etching techniques. The upper ridges of this thrust bearing underspring 22 have a height defined as t1. The upper ridges 24 diverge radially outwardly in width as best illustrated in Figure 2. The width of these upper ridges 24 is generally defined by W1 with the width at the outer periphery defined as WO (Figure 2) and the width at the inner periphery defined as Wi (Figure 2). The outer periphery width WO is generally from 0 to 30% greater than the inner periphery width Wi. In the underspring 22 illustrated in Figure 2, the upper ridges 24 are laterally defined by radially emanating lines. Certain of the upper ridges 24 may include outer projections 25 have cutouts 29 which can be utilised to maintain the position of the underspring 22 with respect to the thrust plate 28. As shown in Figure 1, similar projections 27 may be spaced around the thrust bearing disk 14. The upper ridges 24 may also include inner projections 23 which extend radially inward of the inner periphery of the central aperture of the underspring 22. The lower ridges 26 include struck-out spring-like tabs 34 extending toward the thrust plate 28. These tabs 34 may be provided near the outer periphery of the lower ridges 26, or near the inner periphery of the lower ridges 26, or alternating between these two positions as shown in Figure 2. The tabs 34 provide the initial pre-load for the bearing assembly to maintain static contact between the thrust plate 28, the stiffener or underspring 22, the thrust disk 24, and the thrust runner 10. These relatively soft tabs 34 readily deform under hydrodynamic pressure such that the lower ridges 26 will contact the thrust plate 28 as illustrated most clearly in Figure 6. As shown in Figure 3, the height of the lower ridges 26 is defined as t2 with their width generally defined as W2. The lower ridges 26 also diverge outwardly radially with the width at the inner periphery defined as Wa (Figure 4) and the width at the outer periphery defined as Wb. As is best illustrated in Figure 4, the outward divergence of the lower ridges 26 is considerably greater than the radial outward divergence of the upper ridges 24. Thus the lateral edges of the lower ridges 26 are defined by a pair of non-radial lines which intersect much closer to the inner periphery of the underspring than the centre point of the underspring. The spacing between the upper ridges 24 and the lower ridges 26 thus outwardly converges as shown by a comparison of Figures 3 and 4. The dimension for the height t1 of the upper ridges 24 will always be greater than the dimension for the height t2 of the lower ridges 26. While the relationship between t1 and t2 may vary considerably, depending upon different operating conditions, t1 will generally be greater than t2 by between 0.00254 cm to 0.0254 cm in order to accommodate deflection of the thrust disk due to hydrodynamic pressure. The resiliency or spring rate of the underspring 22 can be varied by changing its thickness or the dimensions of the upper and lower ridges 24,26. The space between adjacent lower ridges 26, defined as W3 in Figure 3, has a marked effect on the stiffness and will generally outwardly converge at least slightly in order better to accommodate the hydrodynamic pressure forces which increase radially. Additionally, as shown in Figure 2, slots 30,32 can be provided transversely across the upper ridges 24 to divide the upper ridges into three separate sections. With the radially diverging upper ridges 24 divided into three separate sections, the stiffness of the upper ridges will more closely conform to the radially increasing hydrodynamic pressure forces. The foil thrust bearing of the present invention is shown further enlarged in Figure 5 (static condition) and Figure 6 (dynamic condition). For purposes of better illustrating the invention, the size of the underspring 22 has been enlarged considerably, more particularly in the axial direction, than the thrust bearing disk 14. It is important, however, to stress the relative position of the disk 14 and its foils 16 with respect to the upper and lower ridges 24,26 respectively of the underspring 22 and in particular the interaction therebetween in the dynamic condition of Figure 6. In the static or non-operating condition of Figure 5, the foils 16 of the thrust bearing disk 14 are shown as having the upper ridges 24 of the underspring 22 generally under the trailing edge half thereof. In this staticcondition neither the disk 14 nor the underspring 22 will be deflected and both will be substantially transverse to the eventual axis of rotation. The arrow provided on the thrust runner 10 indicates the direction of rotational movement that the runner will take with respect to the foils 16 on the disk 14. In order to assist the establishment of the hydrodynamic film between the foils 16 and the thrust runner 10, the foils 16 may be curved as shown in Figure 5 or the leading edge of the foils may be tapered to a thinner thickness than the rest of the foil. Once relative rotational movement is established between the thrust runner 10 and thrust plate 28, a hydrodynamic fluid film is developed between the thrust disk foils 16 and the thrust runner #0 and the dynamic condition illustrated in Figure 6 will occur. The fluid film pressure gradient established above an individual foil 16 is generally shown by the varying length of arrows provided above the leftmost foil of Figure 6. This pressure is least at the leading edge of the foil and gradually increases over the converging or wedge portion of the foil before the position of the upper ridge 24 of the underspring 22 therebeneath. The maximum pressure occurs in that portion of the foil directly over the upper ridge 24 and then markedly declines to zero near the trailing edge of the foil. While the dynamic operation of the foil thrust bearing will deform the thrust bearing disk and foils as generally shown in Figure 6, the pressure developed therein will also deflect the underspring 22 as likewise illustrated in Figure 6. The position of the underspring 22 above the lower ridges 26 will not change, but the distance between the underspring 22 above the lower ridges 26 and the underspring side of the disk 14, defined as d1 will generally be 0.00254 cm to 0.0127 cm less than t1 while still providing suitable operation of the thrust bearing. In addition, under dynamic conditions, the underspring 22 beneath the upper ridges 24 will be deflected towards the thrust plate 28 a distance defined as d2, such that the spacing between the disk 22 and the thrust plate 28 in this region will be less than the height of the lower ridges t2. This spacing, t2-d2 depends on the bearing stiffness and hydrodynamic film pressure. With t1 at least 0.0127 cm greater than t2, even if d2 approaches or actually equals t2 (bottoms out), the upper ridges 24 will still provide support for the thrust disk 14 so that the hydrodynamic forces will conform the foils to the shape generally shown in Figure 6. If t1 were to be equal to t2, and d2 equal to t1, then the top of the upper ridges 24 would then be no higher than the upper surface of the underspring 22 and the foils 16 would no longer be deflected to form the pressure forming surface as shown.

Claims: Claims: 1. A fluid thrust bearing comprising a pair of members arranged for relative rotation with respect to one another, one of said pair of members being adapted rotatably to support the other; and a compliant foil bearing (14,16) operably disposed between said pair of relatively rotatable memebrs (10,28) and mounted on one of said pair of relatively rotatable members (28), said compliant foil bearing (14,16) comprising a thrust disk (14)having a plurality of compliant foils (16) and an underspring (22) characterised in that the underspring (22) includes a plurality of upper ridges (24) and lower ridges (26) alternately disposed thereon, the upper ridges (24) having a height greater than the height of the lower ridges (26). 2. A fluid thrust bearing comprising a thrust runner (10), a thrust plate (28) rotatably to support the thrust runner (10); and a compliant foil bearing (14,16) operably disposed between said thrust runner (10) and said thrust plate (28) and mounted on said thrust plate (28), said compliant foil bearing (14,16) including a thrust disk (14) having a plurality of compliant foils (16) thereon which are disposed towards said thrust runner (10), characterised by a foil stiffener disk (22) having a plurality of upper (24) and lower (26) ridges alternately transversely disposed therearound between the thrust disk (1 4) and the thrust plate (28), the upper ridges (24) having a height generally between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges (26). 3. A fluid thrust bearing comprising a thrust runner (10), a thrust plate (28) rotatably to support the thrust runner (10); and a compliant foil bearing (14,16) operably disposed between said thrust runner (10) and said thrust plate (28) and mounted on said thrust plate (28), said compliant foil bearing including a thrust disk (14) having a plurality of compliant foils (16) thereon which are disposed towards said thrust runner (10), characterised by a foil stiffener disk (22) having a plurality of upper (24) and lower (26) ridges alternately transversely disposed therearound between the thrust disk (14) and the thrust plate (28), the upper ridges (24) outwardly diverging radially, the lower ridges (26) outwardly diverging radially, the space between adjacent lower ridges (26) outwardly converging radially, and the upper ridges having a height generally between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges. 4. The fluid thrust bearing of any one of claims 1 to 3 characterised in that the compliant foils are individually mounted upon said thrust disk. 5. The fluid thrust bearing of any one of claims 1 to 3 characterised in that the compliant foils are integral with said thrust disk. 6. The fluid thrust bearing of claim 1 or claim 2 characterised in that the space between adjacent ridges (26) radially converges. 7. The fluid thrust bearing of claim 1 or claim 2 characterised in that the upper ridges (24) outwardly diverge radially. 8. The fluid thrust bearing of claim 1 or claim 2 characterised in that lower ridges outwardly diverge radially. 9. The fluid thrust bearing of any one of the preceding claims characterised in that the upper ridges each have at least one transverse slot dividing the upper ridges into at least two segments. 10. An underspring for a foil thrust bearing comprising a compliant ring disk, characterised by a plurality of upper ridges (24) disposed on one surface of the disk and a plurality of lower ridges (26) disposed on the other surface of the disk generally between adjacent upper ridges (24), the upper ridges having a height generally between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges (26). 11. An underspring for a foil thrust bearing comprising a compliant ring disk and characterised by a plurality of upper ridges (24) disposed on one surface of the disk and a plurality of lower ridges (26) disposed on the other surface of the disk generally between adjacent upper ridges (24), the upper ridges (24) outwardly diverging radially, the lower ridges (26) outwardly diverging radially, the space between adjacent lower ridges (26) outwardly converging radially, and the height of the upper ridges between 0.00254 cm and 0.0254 cm greater than the height of the lower ridges.

Inventors: LEE-VAN GU, ALSTON
Applicants: ALLIED-SIGNAL INC.
Application year: 1985
Main classification: F16C27
IPC codes: F16C17