Fully hydrodynamic piston ring and cylinder assembly

Claim 1

In a machine having a piston which reciprocates in a cylinder and mounts a wrist pin extending perpendicularly to the central axis of the cylinder, a connecting rod is operatively connected to the wrist pin and with its other end connected to an engine crankshaft by suitable bearing means, said piston having a top portion mounting a means for sealing the piston with respect to the cylinder wall as it reciprocates therein, where the piston has a piston skirt assembly having opposed thrust surfaces extending downwardly from the piston top for engaging the wall of the cylinder in the manner of hydrodynamic bearings to support side thrust forces and to limit the angle of rocking of the piston within the cylinder, the piston being provided with a first peripheral groove in its upper portion, said groove having parallel upper and lower walls terminating in a back wall, a first sealing member having a "T" shaped cross section with the base of the T riding in the space between the upper and lower groove walls on a film of lubricant for free radial movement therein, said first sealing member being flexible with respect to cylinder wall deformations and having spring means operatively cooperating with the first sealing member whereby said first sealing member will conform on a scale relevant to the fluid mechanics of the lubricant film between the sealing member and the cylinder wall to any cylinder wall distortion which occurs in piston engine practice, that portion of the first sealing member engaging the lubricant film on the cylinder wall being curved to form a barrel-like crown surface along an arc parallel to the cylinder axis having a radius of curvature large enough so said surface acts as a good hydrodynamic bearing in interaction with the lubricant film on the cylinder wall, said barrel-like crown surface having a small enough radius of curvature so that said crown contacts the thin lubricant film covering the cylinder wall over the full range of rocking of said piston in the cylinder, the piston being provided with a second peripheral groove in its upper portion, said groove having parallel upper and lower walls terminating in a back wall, a second sealing member having a "T" shaped cross section with the base of the T riding in the space between the upper and lower groove walls on a film of lubricant for free radial movement therein, said second sealing member being flexible with respect to cylinder wall deformations and having spring means operatively cooperating with the second sealing member whereby said second sealing member will conform on a scale relevant to the fluid mechanics of the lubricant film between the second sealing member and the cylinder wall to any cylinder wall distortion which occurs in piston engine practice, that portion of the second sealing member engaging the lubricant film on the cylinder wall being curved to form a barrel-like crown along an arc relatively parallel to the cylinder axis with said crown radius of curvature smaller than that of the first sealing member to form a barrel-like surface acting as a good hydrodynamic bearing in interaction with the lubricant film on the cylinder wall, wherein all of the surfaces of said piston-seal assembly which slide against the lubricant film on the cylinder wall act in combination to leave a layer of lubricant on said cylinder wall sufficiently thick so that the sliding surface of said sealing members function in interaction with the cylinder wall as hydrodynamic bearings in the fully flooded or starved full film regime with substantially no cycle time for said sealing member surfaces in the boundary lubrication regime.