Dynamic foil gas bearing

A dynamic foil gas bearing comprising:

• a hollow cylindrical member with a rotatable shaft inserted therein;
• and
• a foil group mounted on an inner circumferential surface of the hollow cylindrical member, the dynamic foil gas bearing supporting the rotatable shaft in a journal direction;
• wherein the foil group comprises a sheet-like bump foil, a sheet-like middle foil, and a sheet-like top foil which are arranged successively toward the central axis of the hollow cylindrical member;
• the middle foil including:
• a first fixed surface fixed to an inner circumferential surface of the hollow cylindrical member;
• and
• a first rotatable shaft holding surface extending along a direction in which the rotatable shaft rotates, the first rotatable shaft holding surface having an end joined to the first fixed surface by a first linkage surface and an opposite end as a free end, the first rotatable shaft holding surface serving to restrain the rotatable shaft circumferentially;
• the top foil including:
• a second fixed surface fixed to the inner circumferential surface of the hollow cylindrical member;
• and
• a second rotatable shaft holding surface extending along a direction opposite to the direction in which the rotatable shaft rotates, the second rotatable shaft holding surface having an end joined to the second fixed surface by a second linkage surface and an opposite end as a free end, the rotatable shaft holding surface serving to restrain the rotatable shaft circumferentially;
• wherein the first linkage surface is provided by an angularly bent portion of the middle foil, wherein the middle foil further comprises:
• a round portion that is provided circumferentially around the shaft that terminates at a first transition point where the middle foil is angularly bent,
• a straight portion beginning at the first transition point and continuing to a second transition point where the middle foil is angularly bent,
• a welded portion beginning at the second transition point, the welded portion being welded to the inner circumferential surface of the hollow cylindrical member, and
• the second linkage surface is provided by a curved portion of the top foil, as opposed to the bent shape found in the first linkage surface, wherein:
• the top foil includes a second round portion that is provided circumferentially around the shaft such that the round portion is concave towards the central axis of the hollow cylindrical member,
• the second round portion transitions into the second linkage surface wherein the top foil becomes convex towards the central axis of the hollow cylindrical member, and a portion of the top foil that is convex being the second linkage surface, and
• the second linkage surface terminating at an angularly bent portion that transitions into a second welded portion that is welded to the inner circumferential surface of the hollow cylindrical member.