The axial motion of the piston ring in the top ring groove of a gasoline engine

Abstract

Abstract The top ring groove is host to some of the harshest operating conditions in the internal combustion engine. The temperature is high due to the close proximity of the combustion chamber. This is likely to inhibit the efficacy of the lubricant, the supply of which is severely limited by design to minimise oil consumption and harmful exhaust emissions. The relative motion of the components is limited by the small clearances and this does not promote effective entrainment of lubricant. Furthermore, the cyclic rapid movement of the ring axially across the groove results in regular impacts between the two components. There is field evidence the poor tribological design of this interface can lead to failure mechanisms associated with a phenomenon generally referred to as piston ring micro-welding, essentially transfer and adhesion of piston material to the piston ring flank, and ring groove pounding, which is severe deformation of the piston groove. This paper describes analytical studies of the axial motion of the piston ring within the piston groove due to the balance of gas pressure, inertia, hydrodynamic and contact forces. Contact reactions at the ring flank include impact loading following ring lifting as well as longer lasting forces such as those due to gas pressure. Deformation of the groove due to ring pounding depends on the rate of the tranist of the ring across the groove. Previous models of ring dynamics have described the lifting as an instantaneous action, but closer inspection enables the calculation of impact speed allowing prediction of the resultant surface damage. Values of impact velocity, duration, peak force and stresses are predicted for a typical automotive case.