Gas bearing piston assembly

• US 4,455,974 A
• Filed: 01/08/1981
• Issued: 06/26/1984
• Est. Priority Date: 01/08/1981
• Status: Expired due to Term

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Shapiro, Wilbur, Bupara, Sargit S.
• Primary Examiner(s): Feinberg, Craig R.
• Application Number:
  US06/223,314
• Time in Patent Office: 1,265 Days
• Field of Search: 123/47 R, 123/47 AB, 123/193 R, 123/193 P, 92/162, 92/182, 92/183, 92/199, 277/174
• US Class Current: 123/47.00R
• CPC Class Codes: F16C 32/0685 for radial load only
• CPC Class Codes: F16J 1/02 Bearing surfaces

Abstract

A gas bearing supported piston assembly (2) for an internal combustion engine including a piston body (14, 14'"'"') and a segmented piston ring (3) arranged to expand to compensate for wear. A piston supporting gas layer (27) is formed between the cylinder walls (8) and the exterior surface of each piston ring segment (32) by means of a plurality of restricted flow passages (40) formed in each segment (32) and extending between the inner and outer surfaces of the segment (32). In one embodiment, gas under pressure is supplied to the ring segments (32) through a single annular cavity (36) formed in piston body (14). In another embodiment, gas under pressure is supplied to the ring segments (32) through a plurality of corresponding holes (70) in piston body (14'"'"').

Claims

1. A piston assembly for reciprocating movement within a cylinder to form a variable volume chamber containing fluid gas under varying pressure conditions comprising:

(A) a piston body having a peripheral wall shaped to form a slight clearance space with an interior wall of the cylinder when said piston body is co-axially positioned for reciprocating movement within the cylinder, said piston body containing an annular recess formed in said peripheral wall and opening toward the interior wall of the cylinder;

(B) a source of gas under pressure including a gas reservoir chamber contained in said piston body and gas trapping means for allowing gas to flow from the variable volume chamber into said gas reservoir chamber when the gas pressure in the variable volume chamber is above the gas pressure within said gas reservoir chamber and for impeding reverse flow when the gas pressure in the variable volume chamber is below the gas pressure within said gas reservoir chamber; and

(C) bearing means for generating a gas layer within the clearance space between said piston body and the interior wall of the cylinder to hold said peripheral wall out of contact with the interior wall of the cylinder during reciprocating movement of said piston assembly, said bearing means including a radially expandable and compressible ring formed in equal arcuate segments extending end-to-end around said piston body positioned within said annular recess in contact with the gas layer, said bearing means further including gas flow restriction means in communication with said source of gas for establishing a controlled flow of gas into the gas layer to cause the gas layer to impart a radially inwardly directed force on said ring which varies circumferentially between limits in inverse proportion to the radial thickness of the corresponding circumferential portion of the gas layer, biasing means for imparting to said ring an outwardly directed radial force having a magnitude intermediate the magnitude limits of said radially inwardly directed force imparted to said ring by the gas layer to cause each circumferential portion of said ring to seek such a force balanced radial position, wherein said biasing means includes gas pressure means for subjecting a predetermined area of an interior surface of each said ring segment defined by a pair of annular resilient seals positioned between said piston body and each said ring segment to provide a predetermined radially outward bias to each said ring segment to gas pressure from said reserovir chamber, and joint sealing means for rendering the end-to-end joints between adjacent ring segments substantially impervious to radial gas flow, wherein each said joint sealing means includes an interior insert spanning circumferentially between said segments and extending axially between said resilient seals and further includes an exterior insert assembly spanning circumferentially between said segments and extending axially along the entire axial extent of said piston segments.

2. A piston assembly as defined in claim 1, wherein said exterior insert assembly includes an upper exterior insert and a lower exterior insert, said upper and lower exterior inserts including radially inwardly directed legs, and wherein said ring segments include complementary notch portions positioned to reverse said radially inwardly directed legs to retain said exterior inserts axially.

3. A piston assembly as defined in claim 2, wherein said interior insert incudes end portions shaped to contact an exterior surface of said resilient seals.

4. A piston assembly for reciprocating movement within a cylinder to form a combustion chamber of an internal combustion engine comprising:

(A) a piston body having a peripheral wall shaped to form a slight clearance space with an interior wall of the cylinder when said piston body is co-axially positioned for reciprocating movement within the cylinder, said piston body containing a gas reservoir chamber for storing gas supplied from the combustion chamber and an annular recess formed in said peripheral wall and opening toward the interior wall of the cylinder;

(B) gas trapping means for allowing gas to flow from the combustion chamber into said reservoir chamber when the gas pressure in the variable volume chamber is above the fluid pressure within said reservoir chamber and for impeding reverse flow when the gas pressure in the variable volume chamber is below the gas pressure within said reservoir chamber; and

(C) bearing means for generating a gas layer within the clearance space between said piston body and the interior wall of the cylinder to hold said peripheral wall out of contact with the interior wall of the cylinder during reciprocating movement of said piston assembly, said bearing means including

(1) a radially expandable and compressible ring positioned within said annular recess externally in contact with the gas layer,

(2) gas flow restriction means contained within said ring in communication internally with said gas reservoir chamber for establishing a controlled flow of gas from said reservoir chamber into the gas layer to cause the gas layer to impart a radially inwardly directed force on said ring which varies circumferentially between limits in inverse proportion to the radial thickness of the corresponding circumferential portion of the gas layer, and

(3) biasing means for imparting to said ring an outwardly directed radial force having a magnitude intermediate the limits of said radially inwardly directed force imparted to said ring by the gas layer to cause each circumferential portion of said ring to seek a force balanced radial position.

5. A piston assembly as defined in claim 4, wherein said ring is formed in equal arcuate segments extending end-to-end around said piston body.

6. A piston assembly as defined in claim 5, wherein said biasing means includes gas pressure means for subjecting a predetermined area of an interior surface of each said ring segment to gas pressure from said reservoir chamber.

7. A piston assembly as defined in claim 6, wherein said biasing means includes an expandable gas cavity, each said ring segment forming a movable wall of said expandable gas cavity.

8. A piston assembly as defined in claim 7, wherein said gas flow restriction means includes at least one restricted flow passage formed in each said ring segment extending between said expandable gas cavity and an exterior surface of said ring segment.

9. A piston assembly as defined in claim 8, wherein the area on the exterior surface of each said ring segment subjected to gas pressure by the gas layer is greater than the area of the interior surface of each said ring segment subjected to gas prssure by said gas pressure means.

10. A piston assembly as defined in claim 9, wherein each said ring segment has an axial length substantially greater than its radial thickness, each said ring segment having an upper axial end closest to the combustion chamber and a lower axial end furtherest from the variable volume chamber.

11. A piston assembly as defined in claim 10, wherein each said flow passage opens into the exterior surface of each said ring segment intermediate the upper and lower axial ends thereof, and wherein said annular recess is formed to cause the interior surface of each said ring segment immediately adjacent said upper axial end to be subjected to the same gas presure as exists within adjacent portions of the gas layer to tend to balance bending moments imparted to said ring segment caused by increasing gas pressure within the combustion chamber.

12. A piston assembly as defined in claim 10, wherein each said ring segment includes a radially inwardly directed flange adjacent said upper axial end, said annular recess including an annular groove shaped and positioned to receive said inwardly directed flange.

13. A piston assembly for reciprocating movement within a cylinder to form a variable volume chamber containing fluid gas under varying pressure conditions comprising:

(A) a piston body having a peripheral wall shaped to form a slight clearance space with an interior wall of the cylinder when said piston body is co-axially positioned for reciprocating movement within the cylinder, said piston body containing an annular recess formed in said peripheral wall and opening toward the interior wall of the cylinder;

(B) a source of gas under pressure; and

(C) bearing means for generating a gas layer within the clearance space between said piston body and the interior wall of the cylinder to hold said peripheral wall out of contact with the interior wall of the cylinder during reciprocating movement of said piston assembly, said bearing means including a radially expandable and compressible ring positioned within said annular recess externally in contact with the gas layer, and said bearing means further including therein gas flow restriction means in communication internally with said source of gas for controllably directing gas under pressure from said source to position a portion of said gas layer between said ring and the interior wall of the cylinder to hold said ring out of contact with said interior wall during operation of the piston assembly and for establishing a controlled flow of gas into the gas layer to cause the gas layer to impart a radially inwardly directed force on said ring, said gas flow restriction means including as a means for providing said controlled flow of gas a flow passage contained within said ring and communicating at one end with said source of gas and at another end with said gas layer.

14. A piston assembly as defined in claim 13, wherein said bearing means further includes

biasing means for imparting to said ring an outwardly directed radial force having a magnitude intermediate the magnitude limits of said radially inwardly directed force imparted to said ring by the gas layer to cause each circumferential portion of said ring to seek such a force balanced radial position.

15. A piston assembly as defined in claim 14, wherein said source of gas under pressure includes a gas reservoir chamber contained in said piston body and gas trapping means for allowing gas to flow from the variable volume chamber into said gas reservoir chamber when the gas pressure in the variable volume chamber is above the gas pressure within said gas reservoir chamber and for impeding reverse flow when the gas pressure in the variable volume chamber is below the gas pressure within said gas reservoir chamber.

16. A piston assembly as defined in claim 15, wherein said ring is formed in equal arcuate segments extending end-to-end around said piston body, thereby forming end-to-end joints between adjacent segments.

17. A piston assembly as defined in claim 16, wherein said biasing means includes gas pressure mens for subjecting a predetermined area of an interior surface of each said ring segment to gas pressure from said reservoir chamber.

18. A piston assembly as defined in claim 17, wherein said predetermined area is defined by a pair of annular resilient seals positioned between said piston body and each said ring segment to provide a predetermined radially outward bias to each said ring segment.

19. A piston assembly as defined in claim 18, wherein said bearing means further includes joint sealing means for rendering the end-to-end joints between adjacent ring segments substantially impervious to radial gas flow.

20. A piston assembly as defined in claim 17, wherein said biasing means includes an expandable gas cavity, each said ring segment forming a movable wall of said expandable gas cavity.

21. A piston assembly as defined in claim 20, wherein said gas flow restriction means includes at least one restricted flow passage formed in each said ring segment extending between a corresponding expandable gas cavity and an exterior surface of said ring segment.

22. A piston assembly as defined in claim 21, wherein the area on the exterior surface of each said ring segment subjected to gas pressure by the gas layer is greater than the area of the interior surface of each said ring segment subjected to gas pressure by said gas pressure means.

23. A piston assembly as defined in claim 22, wherein each said ring segment has an axial length substantially greater than its radial thickness, each said ring segment having an upper axial end closest to the variable volume chamber and a lower axial end furtherest from the variable volume chamber.

24. A piston assembly as defined in claim 23, wherein each said flow passage opens into the exterior surface of each said ring segment intermediate the upper and lower axial ends thereof, and wherein said annular recess is formed to cause the interior surface of each ring segment immediately adjacent said upper axial end to be subjected to a gas pressure same as that which exists within adjacent portions of the gas layer to tend to balance bending moments imparted to said ring segment caused by increasing gas pressure within the variable volume chamber.

25. A piston assembly as defined in claim 23, wherein each said ring segment includes a radially inwardly directed flange adjacent said upper axial end, said annular recess including an annular groove shaped and positioned to receive said inwardly directed flange.