Air bearing arrangement for electrically driven compressors
An air foil bearing for supporting a high speed rotating assembly such as in a turbocharger, a high speed centrifugal separator or the like. The foil bearing includes at least one bump foil and at least one top foil. The top foil leading edge is bent radially outwards forming a bevel or step. This feature serves as an air guide to prevent air of the preceding pad flowing into the gap between the pads, and then between the bump foil and the top foil, causing the top foil to bear against the rotor, causing severe wear.
1. A foil bearing, comprising:
a bush ( 3 ) having an axial bore;
at least one bump foil ( 4 ) having a leading edge ( 4 a ) and a trailing edge, having undulations between the leading and trailing edge, said undulations having a radial height, and anchored at the leading edge to the bush ( 3 ), the undulations having a wavelength;
a top foil ( 5 ) for each bump foil ( 4 ), the top foil having a leading edge and a trailing edge ( 5 a ), and anchored at the trailing edge ( 5 a ) to the bush ( 3 ), wherein:
the top foil ( 5 ) has, in a non-tensioned state, a larger diameter than the shaft diameter,
the top foil, after assembly of the foil bearing, is in a tensioned state,
a circumferential gap ( 8 ) is formed between the top foil ( 5 ) leading edge and its trailing edge if there is only one top foil or an adjacent trailing edge ( 5 a ) if there is more than one top foil,
the gap also extends radially a radial height, and
a bevel or step is formed in the leading edge of the top foil extending circumferentially and radially,
wherein the circumferential length of the bevel or step is one tenth of the wavelength of the undulations in the bump foil or more and
in the radial direction the bevel or step extends one fifth of the radial height of the bump foil or more.
2. The foil bearing of claim 1 , wherein the undulations in the bump foil ( 4 ) are nearly uniform.
3. The foil bearing of claim 1 , wherein said bevel or step is a concave or convex curved shape.
4. The foil bearing of claim 1 , wherein said top foil ( 5 ) is provided with a dry lubricant surface coating.
5. The foil bearing of claim 1 , wherein said top foil is provided with a wear-in surface coating.
6. The foil bearing of claim 1 , wherein said top foil ( 5 ) trailing edge forms a retaining lug ( 5 a ), wherein the bush ( 3 ) is provided with at least one slot, and wherein top foil retaining lug ( 5 a ) is inserted into the slot in the bush ( 3 ).
7. The foil bearing of claim 1 , wherein said top foil ( 5 ) trailing edge is spot welded to the bush.
8. A foil bearing, comprising:
a bush ( 3 ) having an axial bore;
at least one bump foil ( 4 ) having a leading edge ( 4 a ) and a trailing edge, having undulations between the leading and trailing edge, and anchored at the leading edge to the bush ( 3 );
a top foil ( 5 ) for each bump foil ( 4 ), the top foil having a leading edge and a trailing edge ( 5 a ), and anchored at the trailing edge ( 5 a ) to the bush ( 3 ),
wherein the top foil ( 5 ) has, in a non-tensioned state, a larger diameter than the shaft diameter,
wherein the top foil, after assembly of the foil bearing, is in a tensioned state,
wherein a circumferential gap ( 8 ) is formed between the top foil ( 5 ) leading edge and an adjacent trailing edge ( 5 a ), the gap also extends radially from the top foil trailing edge ( 5 a ) to the bump foil,
wherein a bevel or step is formed in the leading edge of the top foil, extending into the circumferential gap, and
wherein said bevel or step is step-shaped.