Resilient plastic piston ring

Abstract

A plastic ring for internal combustion engine pistons. In a preferred embodiment, the ring has a flat outer diameter adapted to engage the inner diameter of a compression piston ring and an inner diameter adapted to engage the backwall of the ring groove. An axial groove slightly spaced from the outer diameter extends into the ring from the top thereof, whereby combustion gases will expand the ring so that it acts as a circumferential expander for the compression ring while preventing blowby of gases through the ring groove. In another modification, the ring is used with its outer diameter acting against the cylinder wall.

We claim as our invention: .[.1. A piston and piston ring combination for use in internal combustion engines comprising a piston having a plurality of ring grooves therein, a plurality of piston rings in said grooves, at least one of said piston rings having its inner diameter spaced from the inner diameter of a ring groove, a plastic piston ring positioned radially interiorly of said piston ring in the groove, said plastic piston ring comprising an annular ring of plastic material having inner and outer diameters and an axial thickness, an axially extending groove extending into said plastic piston ring from the top thereof, said axial groove terminating in spaced relation to the bottom of the said plastic piston ring, said groove dividing said ring into radially inner and radially outer spaced-apart portions in the area of the axial groove, the outer diameter of the radially outer portion abutting the inner diameter of the said one piston ring, the radially outer portion of the said plastic piston ring having an axial height less than the axial height of the said ring groove, and the said radially outer portion movable with respect to the radially inner portion in dependent response to the presence of a high pressure in the said axial groove..]. .[.2. The combination of claim 1 wherein the said plastic piston ring is a 360° continuous ring..]. .[.3. The combination of claim 2 wherein the said plastic piston ring is constructed of a polyimide resin which is structurally stable at a temperature greater than 500° F..]. .[.4. A piston and piston ring combination for use in internal combustion engines comprising: a piston, at least one ring groove in said piston, said ring groove having a metal split piston ring received therein, said metal piston ring having an axial height less than the height of the ring groove, a plastic piston ring concentric with said metal ring groove, a plastic piston ring concentric with said metal ring received in said ring groove radially interiorly of said metal ring, said plastic piston ring being substantially U-shaped in cross section with the opening of the U extending upwardly, the outer diameter leg of the said U having an axial height less than the axial height of the ring groove, the inner diameter leg of the said U having an axial height greater than the outer diameter leg, said plastic piston ring bottomed in the said ring groove, the radially outer leg of the plastic piston ring circumferentially contacting the inner diameter of the said metal piston ring and the said radially outer leg movable with respect to the said radially inner leg in dependent response to the presence of pressure in the opening of the said U-shaped ring, whereby high-pressure gases entering the ring groove above the said metal piston ring will enter the said opening and press the inner diameter leg into sealing engagement with the bottom of the ring groove and the outer diameter leg into sealing engagement with the inner diameter of the metal piston ring thereby entrapping the said gas in the said ring groove..]. .[.5. The combination of claim 4 wherein the outer diameter of the said plastic piston ring is circumferentially curved in an axial direction..]. .[.6. The combination of claim 4 wherein the outer diameter of the said plastic piston ring is circumferentially tapered in an axial direction..]. .[.7. The combination of claim 4 wherein the inner diameter of the said plastic piston ring is axially tapered..]. .[.8. The combination of claim 4 wherein the inner diameter of said plastic piston ring is axially curved..]. .[.9. A piston and piston ring combination for use in internal combustion engines comprising: a piston having at least one ring groove therein, a plurality of axially thin split annulus piston rings received in said groove projecting radially beyond said groove, said piston rings positioned one atop the other in said groove, the inner diameters of said piston rings terminating in spaced relationship to the bottom of said groove, a plastic piston ring received in said groove radially inwardly of said metal piston ring, the said plastic piston ring having its inner diameter bottomed on the bottom of the ring groove and its outer diameter contacting the inner diameters of the said metal piston rings, an axially extending groove projecting into the said plastic piston ring intermediate the inner and outer diameters thereof, the said axial groove projecting into the said ring from the top axial end thereof and terminating in spaced relationship to the bottom axial end thereof, the said plastic piston ring resilient whereby the outer diameter is movable with respect to the inner diameter in dependent response to the presence of high pressure fluid in the said axial groove..]. .[.10. The combination of claim 9 wherein portions of the material of the said plastic piston ring extend from its outer diameter into the gaps in the split annulus metal rings, the said gaps being circumferentially spaced from one another whereby the said metal rings are restrained against independent rotation with respect to one another..]. .[.11. The combination of claim 10 wherein the said plastic piston ring is a 360° continuous ring constructed of a high-temperature plastic..]. .[.12. The combination of claim 10 wherein the plastic piston ring has a radial groove in the ring from its inner diameter, the said ring groove positioned intermediate the axial ends of the said plastic piston ring..]. .[.13. The combination of claim 12 wherein the said plastic piston ring has a second axial extending groove positioned intermediate the inner and outer diameters thereof extending into the ring from the bottom axial end thereof and the said radial groove and axial groove bottom in spaced relationship from one another..]. .[.14. In an internal combustion engine having at least one piston reciprocatingly positioned in a cylinder, the piston having ring grooves therearound with metal piston rings therein, the improvement of at least one of said grooves having a plastic piston ring received therein positioned radially interiorly of the metal piston ring, said plastic piston ring being resilient and having a pressure-receiving axial groove therein, the plastic piston ring being responsive to the presence of pressures in said ring groove radially behind the said metal ring by sealing contact between the plastic piston ring and the backwall of the ring groove and inner diameter of the metal ring..]. .Iadd. 15. A piston and piston ring combination for use in an internal combustion engine comprising a piston movable in opposite directions in a cylinder and having at least one ring groove therein, a plurality of axially thin metal piston rings received in said groove one atop the other and projecting radially beyond said groove, each piston ring being split axially so as to have a circumferential gap, the gaps in said piston rings being circumferentially spaced, radially inner peripheries of said piston rings terminating in spaced relationship to a radially inner periphery of said groove, an expander ring for sealingly engaging the inner periphery of said groove and for sealingly engaging the inner peripheries of said piston rings and for restraining said piston rings against independent rotation with respect to one another during movement of the piston in said opposite directions, said expander ring comprising a one-piece body of elastomeric material that is stable at temperatures up to at least 900°  F. which may be present in an internal combustion engine during its operation, said expander ring body having a radial cross-section which includes an annular radially inner portion to sealingly engage said radially inner surface of the groove in the piston, an annular radially outer portion to sealingly engage radially inner surfaces of the piston rings and providing a single annular area of sealing engagement with the inner surfaces of the piston rings which spans each joint between abutting radially extending side surfaces of the piston rings and an annular connector portion which is disposed between and connects said inner and outer portions of said expander ring body, an axially extending groove projecting into said expander ring intermediate the inner and outer diameters thereof, the said axial groove projecting into said ring from the top axial end thereof and terminating in spaced relationship to the bottom axial end thereof, said expander ring having an axial extent which is at least as great as a major portion of the combined axial extents of the piston rings so that said single annular area of sealing engagement will have an axial extent which is at least as great as a major portion of the combined axial extents of the inner surfaces of the piston rings and said expander ring will be extruded radially into the gap in each piston ring to hold each piston ring against circumferential movement relative to the other. .Iaddend..Iadd. 16. A piston and piston ring combination of claim 15 wherein the said expander ring is a 360°  continuous ring. .Iaddend..Iadd. 17. A piston and piston ring combination as defined in claim 15 wherein said annular area of sealing engagement is cylindrical and extends from axially opposite edges of said annular radially outer portion. .Iaddend. .Iadd. 18. A piston and piston ring combination as defined in claim 15, 16 or 17 wherein a radially extending cicumferential groove is formed in the radially inner portion of the expander ring body intermediate radially inner axial ends of said expander ring, said circumferential groove opening toward the bottom of the ring groove. .Iaddend..Iadd. 19. A piston and piston ring combination as defined in claim 15, 16 or 17 wherein the expander ring is constructed of a polyimide resin. .Iaddend..Iadd. 20. A piston and piston ring combination for use in an internal combustion engine, comprising a piston movable in opposite directions and having at least one ring groove therein, a plurality of axially thin metal piston rings received in said groove one atop the other and projecting radially beyond said groove, each piston ring being split axially so as to have a cicumferential gap, the gaps in said piston rings being circumferentially spaced, radially inner surfaces of said piston rings terminating in spaced relationship to the bottom of said groove, a continuous annular expander ring received in said groove radially inwardly of said piston ring, said expander ring being formed from a resilient high temperature plastic stable at temperatures from 500°  F. to 900°  F. encountered in an internal combustion engine and having a radially inner surface sealingly bottomed on said bottom of the ring groove and a radially outer surface contacting the inner surfaces of said piston rings, a first annular groove projecting axially into said expander ring intermediate the radially inner and outer surfaces thereof from a top axial end thereof and terminating in spaced relationship to a bottom axial end thereof thereby to provide radially inner and radially outer portions of the expander ring, a radial groove formed in the radially inner surface of the expander ring intermediate the axial ends of said ring, a second axially projecting annular groove positioned intermediate the radially inner and radially outer surfaces of the expander ring and extending into the ring from the bottom axial end thereof, said radial groove and axially projecting grooves terminating in spaced relationship from one another, the radially outer surface of said expander ring being a continuous cylindrical surface for sealing engagement with the inner surfaces of the piston rings and spanning each joint between abutting radially extending surfaces of the piston rings, said cylindrical outer surface having an axial extent which is substantially the same as the combined axial extent of the inner surfaces of said piston rings, and portions of the material of the said expander ring extending from the outer surfaces of the expander ring into the gaps in the split piston rings whereby said piston rings are restrained against rotation with respect to one another. .Iaddend. .Iadd. 21. A piston and piston ring combination as defined in claim 20 wherein said expander ring is constructed of a polyimide resin. .Iaddend.