Identification of the Twin Independent Variable Cam Timing Engines for AFR Control

Abstract

A control-oriented air-fuel ratio path model is developed to represent a spark-ignited, port-fuel-injected, twin-independent variable cam timing engine. Following a recent publication [Genç et al., SAE 2002-01-2752 (2002)] showing that cam timing not only affects the cylinder air flow but also the transient cylinder fuel flow, this paper constructs a mean value model that describes both air and fuel dynamics. While steady-state engine tests have been performed in order to identify the air path dynamics, a combination of linear and nonlinear identification methods have been used in order to identify the fuel path model including the wall-wetting dynamics. The resulting parameter-varying model has been validated with independent experimental data and can be used in powertrain controller design and development.