Foil bearing and fluid machinery

Fluid machinery comprising:

• a rotary member;
• an impeller configured to compress a fluid by rotating integrally with the rotary member;
• an impeller housing accommodating the rotary member and the impeller;
• and
• a foil bearing, the foil bearing comprising:
• a bearing housing including an insertion hole through which the rotary member is to be inserted;
• a tubular top foil including a bearing surface that faces the rotary member;
• and
• a sheet-shaped bump foil located between the top foil and the bearing housing, the bump foil including multiple crest portions in contact with an outer circumference surface of the top foil and multiple trough portions in contact with an inner circumference surface of the bearing housing, the crest portions and the trough portions being arranged alternately in a rotation direction of the rotary member, and the crest portions and the trough portions being configured to expand in the rotation direction so as to elastically support the top foil, wherein
• the bump foil is configured to, when a load received by the bearing surface from the rotary member is less than or equal to a threshold value, support the top foil with gaps formed between the crest portions and the bearing housing and with gaps formed between the trough portions and the top foil,
• the bump foil is configured to, when the load received by the bearing surface from the rotary member exceeds the threshold value, support the top foil with the crest portions in contact also with the inner circumference surface of the bearing housing and with the trough portions in contact also with the outer circumference surface of the top foil so that the top foil and the bump foil locally form a plain bearing and support the rotary member,
• the impeller housing includes a shroud surface that covers an outer circumference of the impeller, and
• a tip clearance between the impeller and the shroud surface is greater than 0 even when the top foil and the bump foil locally form the plain bearing.

Fluid machinery comprising:

• a rotary member;
• an impeller configured to compress a fluid by rotating integrally with the rotary member;
• an impeller housing accommodating the rotary member and the impeller;
• and
• a foil bearing, the foil bearing comprising:
• a bearing housing including an insertion hole through which the rotary member is to be inserted;
• a tubular top foil including a bearing surface that faces the rotary member;
• and
• a sheet-shaped bump foil located between the top foil and the bearing housing, the bump foil including multiple crest portions in contact with an outer circumference surface of the top foil and multiple trough portions in contact with an inner circumference surface of the bearing housing, the crest portions and the trough portions being arranged alternately in a rotation direction of the rotary member, and the crest portions and the trough portions being configured to expand in the rotation direction so as to elastically support the top foil, wherein
• the bump foil is configured to, when a load received by the bearing surface from the rotary member is less than or equal to a threshold value, support the top foil with gaps formed between the crest portions and the bearing housing and with gaps formed between the trough portions and the top foil,
• the bump foil is configured to, when the load received by the bearing surface from the rotary member exceeds the threshold value, support the top foil with the crest portions in contact also with the inner circumference surface of the bearing housing and with the trough portions in contact also with the outer circumference surface of the top foil so that the top foil and the bump foil locally form a plain bearing and support the rotary member,
• the impeller housing includes a shroud surface that covers an outer circumference of the impeller, and
• a distance between an outer circumference surface of the bump foil at the crest portion and the inner circumference surface of the housing in a radial direction of the rotary member is H1 in a state in which no load acts on the bearing surface from the rotary member, and a minimum value of a gap between the impeller and the shroud surface in the radial direction is greater than H1.