Foil bearing assembly including perforated inner foil assembly and compressor including same
A bearing system includes a bearing housing and a foil bearing assembly. The bearing housing includes a sleeve defining a cylindrical bore, and a mounting structure for connecting the bearing system to a compressor housing. The foil bearing assembly is positioned within the cylindrical bore and includes an inner foil assembly and a bump foil assembly. The bump foil assembly includes a plurality of bump foils disposed circumferentially about the inner foil assembly. Each bump foil is spaced circumferentially from an adjacent bump foil to define a gap therebetween. The inner foil assembly includes a cylindrical inner surface defining a plurality of perforations extending radially therethrough. Each perforation is radially aligned with one of the gaps between adjacent bump foils.
1. A bearing system comprising:
a bearing housing including:
a sleeve defining a cylindrical bore; and
a mounting structure for connecting the bearing system to a compressor housing; and
a foil bearing assembly positioned within the cylindrical bore and including:
an inner foil assembly including a cylindrical inner surface; and
a bump foil assembly positioned radially outward from the inner foil assembly, the bump foil assembly including a plurality of bump foils disposed circumferentially about the inner foil assembly, wherein each of the bump foils is spaced circumferentially from an adjacent bump foil to define a gap therebetween, wherein each of the bump foils comprises a plurality of bump foil strips extending from a first edge to a second edge, wherein each bump foil strip is spaced axially from an adjacent bump foil strip to define an axial gap therebetween;
wherein the cylindrical inner surface of the inner foil assembly defines a plurality of perforations extending radially therethrough, wherein each of the plurality of perforations is radially aligned with one of the gaps between adjacent bump foils and is positioned at a common axial position with one of the axial gaps defined between adjacent bump foil strips.
2. The bearing system of claim 1 , wherein each of the plurality of perforations has an at least partially polygonal shape.
3. The bearing system of claim 1 , wherein each of the plurality of bump foils extends from a first edge to a second edge and comprises a plurality of bumps, each of the bumps having a height, and wherein the height of each of the plurality of bumps increases between the first edge and the second edge.
4. The bearing system of claim 1 , wherein the plurality of perforations comprises at least one subset of perforations, wherein each of the perforations in the at least one subset of perforations is axially aligned with the other perforations in the at least one subset, and wherein each of the at least one subset of perforations is radially aligned with one of the gaps defined between adjacent bump foils.
5. The bearing system of claim 1 , wherein the plurality of perforations comprises a single perforation radially aligned with one of the gaps defined between adjacent bump foils, and axially aligned with each of the axial gaps defined between adjacent bump foil strips.
6. The foil bearing assembly of claim 1 , wherein each of the plurality of perforations has an opening area and the sum of the opening areas of each of the plurality of perforations is a total opening area, wherein the inner foil assembly has a total foil area, and wherein a ratio of the total opening area to the total foil area is between 0.48% and 4.27%.
7. The bearing system of claim 1 , wherein each of the plurality of perforations has a width, and wherein a ratio of the width of each of the plurality of perforations to a width of the gap with which the perforation is radially aligned is between 0.100 and 0.300.
8. A foil bearing assembly comprising:
an inner foil assembly including a cylindrical inner surface; and
a bump foil assembly positioned radially outward from the inner foil assembly, the bump foil assembly including a plurality of bump foils disposed circumferentially about the inner foil assembly, wherein each of the bump foils is spaced circumferentially from an adjacent bump foil to define a gap therebetween, wherein each of the bump foils comprises a plurality of bump foil strips extending from a first edge to a second edge, wherein each bump foil strip is spaced axially from an adjacent bump foil strip to define an axial gap therebetween,
wherein the cylindrical inner surface of the inner foil assembly defines a plurality of perforations extending radially therethrough, wherein each of the plurality of perforations is radially aligned with one of the gaps between adjacent bump foils and is positioned at a common axial position with one of the axial gaps defined between adjacent bump foil strips.
9. The foil bearing assembly of claim 8 , wherein each of the plurality of perforations has an at least partially polygonal shape.
10. The foil bearing assembly of claim 8 , wherein each of the plurality of bump foils extends from a first edge to a second edge and comprises a plurality of bumps, each of the bumps having a height, and wherein the height of each of the plurality of bumps increases between the first edge and the second edge.
11. The foil bearing assembly of claim 8 , wherein the plurality of perforations comprises at least one subset of perforations, wherein each of the perforations in the at least one subset of perforations is axially aligned with the other perforations in the at least one subset, and wherein each of the at least one subset of perforations is radially aligned with one of the gaps defined between adjacent bump foils.
12. The foil bearing assembly of claim 8 , wherein each of the plurality of perforations has an opening area and the sum of the opening areas of each of the plurality of perforations is a total opening area, wherein the inner foil assembly has a total foil area, and wherein a ratio of the total opening area to the total foil area is between 0.48% and 4.27%.
13. The foil bearing assembly of claim 8 , wherein each of the plurality of perforations has a width, and wherein a ratio of the width of each of the plurality of perforations to a width of the gap with which the perforation is radially aligned is between 0.100 and 0.300.
14. A compressor comprising:
a compressor housing;
a shaft rotatably supported within the compressor housing;
an impeller connected to the shaft and operable to impart kinetic energy to incoming refrigerant gas upon rotation of the shaft;
a bearing housing mounted to the compressor housing and including a sleeve defining a cylindrical bore; and
a foil bearing assembly rotatably supporting the shaft and positioned within the cylindrical bore, the foil bearing assembly including:
an inner foil assembly including a cylindrical inner surface; and
a bump foil assembly positioned radially outward from the inner foil assembly, the bump foil assembly including a plurality of bump foils disposed circumferentially about the inner foil assembly, wherein each of the bump foils is spaced circumferentially from an adjacent bump foil to define a gap therebetween, wherein each of the bump foils comprises a plurality of bump foil strips extending from a first edge to a second edge, wherein each bump foil strip is spaced axially from an adjacent bump foil strip to define an axial gap therebetween,
wherein the cylindrical inner surface of the inner foil assembly defines a plurality of perforations extending radially therethrough, wherein each of the plurality of perforations is radially aligned with one of the gaps between adjacent bump foils and is positioned at a common axial position with one of the axial gaps defined between adjacent bump foil strips.
15. The compressor of claim 14 , wherein each of the plurality of bump foils extends from a first edge to a second edge and comprises a plurality of bumps, each of the bumps having a height, and wherein the height of each of the plurality of bumps increases between the first edge and the second edge.
16. The compressor of claim 15 , wherein the shaft is configured to rotate about a rotational axis of the shaft in a first direction, and wherein the height of each of the plurality of bumps increases between the first edge and the second edge of each bump foil in a second direction opposing the first direction.
17. The compressor of claim 16 , wherein rotation of the shaft causes the cylindrical inner surface of the inner foil assembly to deflect such that at least one of the plurality of perforations is oriented obliquely relative to the first direction.
18. The compressor of claim 14 , wherein the plurality of perforations comprises at least one subset of perforations, wherein each perforation in the at least one subset of perforations is axially aligned with the other perforations in the at least one subset, and wherein each of the at least one subset of perforations is radially aligned with one of the gaps defined between adjacent bump foils.