Estimation of automotive engine parameters: Part I: Discharge coefficient of throttle body

A novel method of estimating the coefficient of discharge of the throttle body model in an automotive gasoline engine is presented in this paper. The coefficient of discharge is estimated as an engine signal. Air mass flow across the throttle body of gasoline engine is a critical variable to maintain the air fuel ratio closer to the ideal value; which is necessary to minimize the pollution contents in exhaust gases of the automotive engine. The correct prediction of air mass flow into the engine cylinders depends primarily upon the accurate estimation of model parameters of throttle body model. Coefficient of discharge C_d of butterfly valve of throttle body, in the air intake system of automobile gasoline engine is dealt as an uncertain parameter and is taken to be a model perturbation. A sliding mode observer (SMO) drives these perturbations into online parameter values. The sliding surface is steered to compensate for the effect of uncertainty in the parameter and estimated parameter value is found. This results in a more accurate description of the air path across the throttle body. The coefficient of discharge estimated then is used for compensation of modeling errors and unmodeled dynamics. The estimated parameters can also be used for engine fault diagnosis work.