| A model has been developed for determining the lubrication regime under which the piston and piston rings operate in the internal combustion engine, and for calculating the friction force of each component at each crank angle.; The ring is assumed to have a circular profile in the direction of motion. The profile changes in time because tilting of the ring is taken into account. In the circumferential direction two cases are examined. In the first the ring is assumed to be a perfect circle, and the bore cross-section elliptic. The Finite Element Method (FEM) is used to solve the two-dimensional Reynolds equation. In the second the clearance between ring and bore is assumed to be constant, and the one-dimensional Reynolds equation is used. The ring is treated as infinitely long, and an integration of the Reynolds equation is performed.; The piston is treated like the one-dimensional case of the ring, except that a correction factor is used to take care of the fact that the piston skirt has dimensions of the same magnitude in both directions. For all cases mixed lubrication is considered when the oil film thickness becomes lower than a specified value. This value depends upon the roughness of the surfaces which are in contact. The friction coefficient for this type of lubrication is taken as a function of the oil film thickness and the surface roughness.; The friction results of the model are compared with experimental friction data for a given engine under motoring conditions. The agreement between the theoretical results and the experimental data is very good. Also the effect of several parameters of the rings and of the engine on the FMEP of a ring pack is examined. These parameters are the curvature and the offset of the profile, the ring width and tension, the roughness of the surfaces, the bore ellipticity, the engine speed, the oil temperature and viscosity. Some of these parameters have an optimum value for which the FMEP is minimum. For values smaller or larger than the optimum the FMEP increases in some cases very sharply. |
