Fully hydrodynamic piston ring and piston assembly with elastomerically

Abstract

A piston ring and piston assembly designed for operation with the piston skirt fully flooded with oil and with the piston rings operating as fully hydrodynamic sliders is disclosed. Geometries of rings and piston skirt are arranged to conform elastically to the real out-of-round deformations of cylinder walls in such a fashion as to maximize the advantages of full film lubrication physics. The rings are loaded in circumferential compression and are flexible. This elastic configuration makes the rings conform instantaneously to cylinder wall out-of-round to a scale of microinches. This conformability is required to maintain oil control (zero oil pumping to the top of the cylinder wall) with fully hydrodynamic conditions between the rings and the cylinder wall. The piston has a piston skirt which is flexible enough to conform to cylinder wall out-of-round and maximize squeeze film effects. The piston skirt is arranged to superimpose squeeze film and pivoted pad slider physics. The piston is equipped with a heat piped internal heat transfer structure which maintains the piston in a near isothermal condition. The piston skirts are nearly isothermal. This controls expansion for improved hydrodynamic geometry. The great majority of heat transfer from the piston crown to the cylinder passes through the piston skirt oil film to the cylinder wall. The assembly utilizes component deformations to maximize hydrodynamic and squeeze film lubrication effects to minimize engine friction and wear.