Stepped foil journal foil bearing

A journal foil bearing comprising:

• a bushing member;
• a shaft member arranged for unidirectional relative rotation within said bushing member;
• a compliant foil assembly disposed between said shaft and bushing members, said foil assembly including a plurality of circumferentially evenly arrayed and overlapping like arcuate foil elements mounted to said bushing member, each foil element being of fine-dimension sheet material having a thickness and extending with a uniform axial width circumferentially between said shaft and bushing members, each foil element defining a surface portion having a circumferential dimension and confronting said shaft and in operation of said bearing defining an operating clearance therewith, and also including an overlapping portion and an overlapped portion respectively overlapping and overlapped by next adjacent foil elements of said plurality of foil elements, and a transition portion connecting said overlapped and overlapping portions;
• each foil element at said transition portion thereof defining a step-like discontinuity so that said transition portion connects overlapped and overlapping portions of said foil element and has a circumferential dimension which is from 5% to 15% inclusive of the circumferential dimension of said surface portion;
• wherein said discontinuity is one of arcuate curvature, said transition portion having a radial dimension substantially equal to said thickness;
• and wherein each of the foil elements has a uniform axial width over its entire circumferential length.

A journal foil bearing comprising:

• a bushing member;
• a shaft member arranged for unidirectional relative rotation within said bushing member;
• a compliant foil assembly disposed between said shaft and bushing members, said foil assembly including a plurality of circumferentially evenly arrayed and overlapping like arcuate foil elements mounted to said bushing member, each foil element being of fine-dimension sheet material having a thickness and extending with a uniform axial width circumferentially between said shaft and bushing members, each foil element defining a surface portion confronting said shaft and in operation of said bearing defining an operating clearance therewith, and also including an overlapping portion and an overlapped portion respectively overlapping and overlapped by next adjacent foil elements of said plurality of foil elements, and a transition portion connecting said overlapped and overlapping portions;
• each foil element at said transition portion thereof defining a step-like discontinuity so that said transition portion connects overlapped and overlapping portions of said foil element and presents to said shaft a transition surface which is from 5% to 15% inclusive of the circumferential dimension of said surface portion;
• wherein said discontinuity is one of foil thickness, said foil elements each defining an axial groove opening radially outwardly on said transition portion, whereby said groove provides a structurally weakened zone of increased pliability connecting said overlapped and overlapping portions.

A journal foil bearing comprising:

• a bushing member;
• a shaft member arranged for unidirectional relative rotation within said bushing member;
• a compliant foil assembly disposed between said shaft and bushing members, said foil assembly including a plurality of circumferentially evenly arrayed like arcuate foil elements mounted to said bushing member, each foil element being of fine-dimension sheet material having a thickness and extending with a uniform axial width circumferentially between said shaft and bushing members, each foil element defining a surface portion confronting said shaft and in operation of said bearing defining an operating clearance therewith, and also including an overlapping portion and an overlapped portion respectively overlapping and overlapped by next adjacent foil elements of said plurality of foil elements, and a transition portion connecting said overlapped and overlapping portions;
• each foil element at said transition portion thereof defining a step-like discontinuity so that said transition portion extends between overlapped and overlapping portions of said foil and presents to said shaft a transition surface which is from 5% to 15% inclusive of the circumferential dimension of said surface portion;
• wherein said discontinuity is one of foil thickness, said foil elements being of two-part construction with cooperating radially inner compliant portions and radially outer and stiffer spacer portions, said radially inner portion of each foil element having a circumferential extent in the direction of shaft rotation which is less than the circumferential extent of its respective spacer portion, said radially inner portion terminating in an edge defining a leading edge of said transition portion, and said spacer portion defining a radially inwardly disposed surface which defines said transition surface beyond said terminating edge of said radially inner portion.