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An Improved Friction Model for Spark-Ignition Engines

2003; Linguagem: Inglês

10.4271/2003-01-0725

2688-3627

Daniel Sandoval, John B. Heywood,

Industrial Technology and Control Systems

The details of a modified model that predicts friction mean effective pressure (fmep) for spark-ignition engines are described.The model, which was based on a combination of fundamental scaling laws and empirical results, includes predictions of rubbing losses from the crankshaft, reciprocating, and valvetrain components, auxiliary losses from engine accessories, and pumping losses from the intake and exhaust systems.These predictions were based on engine friction data collected between 1980 and 1989.Some of the terms are derived based on lubrication theory.Other terms are derived empirically from measurements of individual friction components, rather than the basic processes themselves.Current engine developments (improved oils, surface finish on piston liners, valve train mechanism) suggested that the model needed modification to predict modem engine losses due to friction.Modifications in oil viscosity, piston ring tension and gas pressure contribution on piston assembly, liner roughness, and valvetrain mechanism were made.The sum of the predictions now gives reliable estimates of sparkignition engine fmep.The inclusion of oil viscosity scaling with temperature results in cold engine friction predictions about twice the value for warmed up engines.This agrees with the limited engine friction data used to modify the friction model.