The Employment of a 1D Simulation Model for A/F Ratio Control in a VVT Engine

An experimentally derived map of the engine volumetric efficiency is usually employed to control the A/F ratio in a SI-ICE. In the case of a variable valve timing (VVT) engine, a different efficiency map must be considered at each camshaft position, as a consequence of the influence on the air flow exerted by the actual position of the intake/exhaust camshaft. In this paper, an attempt is reported to theoretically derive a correlation of the volumetric efficiency as a function of engine speed, manifold absolute pressure, and camshaft position. The correlation is not based on experimental data but on the results of a one-dimensional simulation model (1Dime code) developed at DIME. An extensive validation of the 1D model is preliminary reported in the first part of the paper. The procedure is developed with reference to a four-cylinder, SI engine, equipped with a phased intake and exhaust VVT device. The latter includes a “slider” which deactivates a tumble-flow inducing port for burning speed enhancement at part-load. The derived correlation also accounts for the variations of ambient conditions and can be directly included within the classical strategies for A/F Ratio control, programmed inside the ECU. The whole methodology allows to greatly reduce the experimental efforts required to fully characterize the VVT engine and to develop its control logic.