Airpath control of a SI engine with Variable Valve Timing actuators

We address the control of the airpath of a turbocharged SI engine equipped with variable valve timing (VVT) actuators. VVT devices are used to produce internal exhaust gas recirculation, providing beneficial effects in terms of consumption and pollutant emissions reduction. However, VVT actuators affect the fresh air charge in the cylinders. This has an impact on the torque output (leading to driveability problems), and on the air/fuel ratio (AFR) (leading to pollution peaks). To compensate these undesirable effects, a new approach is proposed. We model the intake dynamics as a first order system using a balance equation in which the VVT actuators play the role of a measured disturbance in the volumetric efficiency of the aspiration phenomenon. In view of practical implementation, two types of modeling errors are considered. We address them by an integral term and an observer. Convergence is proven. This strategy is sufficient to control the engine air mass. As a consequence, the AFR management is improved. These points are supported by experimental results.