Gas foil thrust bearings having top foils incorporating pocket recesses

1. A gas foil thrust bearing comprising:

multiple arcuate bearing pads, each bearing pad including a top foil and a compliant support element, each top foil having a leading edge, a trailing edge, and a top surface that extends from the leading edge to the trailing edge, the top foil having a taper-flat-recess configuration in which the top surface includes a taper region located near the leading edge, a flat land region located near the trailing edge, and a pocket recess defined by a base, opposed side walls, and an end wall,

wherein a majority of the pocket recess exists within the taper region, and

wherein the pocket recess has a leading opening that extends across a majority of a radial width of the top foil.

2. The gas foil thrust bearing of claim 1 , wherein the pocket recess also extends along a portion of the flat land region.

3. The gas foil thrust bearing of claim 1 , wherein the side walls of the pocket recess are parallel.

4. The gas foil thrust bearing of claim 1 , wherein the side walls of the pocket recess are nonparallel.

5. The gas foil thrust bearing of claim 4 , wherein the side walls of the pocket intersect at a point.

6. The gas foil thrust bearing of claim 1 , wherein a ratio between a taper angle and a pad angle of each top foil is approximately 0.1 to 0.7.

7. The gas foil thrust bearing of claim 1 , wherein the compliant support elements comprise corrugated bump foils.

8. The gas foil thrust bearing of claim 7 , wherein corrugations of the bump foils extend in a radial direction of the bearing.

9. The gas foil thrust bearing of claim 7 , wherein corrugations of the bump foils extend in a circumferential direction of the bearing.

10. The gas foil thrust bearing of claim 1 , wherein the compliant support elements extend only along the flat land region of the top foils.

11. The gas foil thrust bearing of claim 1 , wherein the compliant support elements extend along the flat land region and a portion of the taper region of the top foils.

12. The gas foil thrust bearing of claim 1 , wherein the leading edges of the top foils are supported by shims.

13. The gas foil thrust bearing of claim 1 , wherein the leading edges of the top foils are formed as inwardly extending lips configured to directly contact a backing plate of the bearing.

14. An arcuate top foil configured for use in a gas foil thrust bearing, the top foil comprising:

a leading edge;

a trailing edge; and

a top surface that extends from the leading edge to the trailing edge, the top foil having a taper-flat-recess configuration in which the top surface includes a taper region located near the leading edge, a flat land region located near the trailing edge, and a pocket recess defined by a base, opposed side walls, and an end wall,

wherein a majority of the pocket recess exists within the taper region, and

wherein the pocket recess has a leading opening that extends across a majority of a radial width of the top foil.

15. The top foil of claim 14 , wherein the pocket recess also extends along a portion of the flat land region.

16. The top foil of claim 14 , wherein the side walls of the pocket recess are parallel.

17. The top foil of claim 14 , wherein the side walls of the pocket recess are nonparallel.

18. The top foil of claim 14 , wherein a ratio between a taper angle and a pad angle of each top foil is approximately 0.1 to 0.7.

19. The top foil of claim 1 , wherein the arcuate pocket recess extends along the entire length of the taper region.