A foil bearing allows bi-directional rotation of a shaft. The foil bearing includes a plurality of thin compliant foils secured to a housing, and spring segments underlying the foils. Each spring segment has a first stiffness profile in a first zone and a second stiffness profile in a second zone. The first stiffness profile allows rotation in one direction, and the second stiffness profile allows rotation in an opposite direction.

The present invention provides a foil bearing (1), comprising: a stationary mount member (2) surrounding an outer circumferential surface of a journal (13) of a rotating member via an annular gap (G); and a plurality of centripetal force producing foils (e.g., middle foils 12) arranged in a circumferential direction in the annular gap, where each of the centripetal force producing foils has one end fixed to the stationary mount member, wherein portions of the stationary mount member located between fixed ends of adjoining ones of the centripetal force producing foils are formed with an axially extending slit (4).

The present invention provides a foil bearing (1), comprising: a stationary mount member (2) surrounding an outer circumferential surface of a journal (13) of a rotating member via an annular gap (G); and a plurality of centripetal force producing foils (e.g., middle foils 12) arranged in a circumferential direction in the annular gap, where each of the centripetal force producing foils has one end fixed to the stationary mount member, wherein portions of the stationary mount member located between fixed ends of adjoining ones of the centripetal force producing foils are formed with an axially extending slit (4).

A fluid bearing includes a foil assembly that supports a journal inside a stationary retaining member includes a cylindrical top foil that is positioned radially inward, a cylindrical mid-foil that is positioned outside the top foil and corrugated bump foils positioned outside the mid-foil. In order to suppress a small amplitude vibration of the journal in the low rotational rate region, the bump foils, are separated into six in the circumferential direction. In order to suppress the synchronous vibration instability phenomenon, the top foil and the mid-foil are wound in opposite directions from each other. In order to suppress the whirl instability phenomenon, the sum of the frictional damping forces generated by the lower bump foils is set to be larger than the sum of the frictional damping forces generated by the upper bump foils.

A hydrodynamic fluid film bearing has a stationary retaining member (12) having a cylindrical opening (14) to receive for rotation therein a rotatable shaft (16). The inner surface (20) of the opening (14) is lined by a generally cylindrical-shaped foil assembly (18) comprised of a plurality of foil sub-assemblies (24) each comprised of spring foils (26), contact foils (30) and, optionally, inner foils (32). Each foil sub-assembly (24) subtends a rotational segment, less than all, of the inner surface (20), e.g., from about 45 degrees to 120 degrees of rotation. The spring foils (26) and contact foils (30) are affixed to the retaining member (12) in such a way that sliding travel of the spring foils (26) along the inner surface (20) is in the opposite rotational direction of sliding travel of the contact foils (30) along the inner surface (20). The foil sub-assemblies (24) may be affixed to the retaining member (12) by means of keyways (22a-22e) within which the foil sub-assemblies (24) are mounted.