Nicholas Fekete

Model-Based Control of the VGT and EGR in a Turbocharged Common-Rail Diesel Engine: Theory and Passenger Car Implementation

In this article model-based controller design techniques are investigated for the transient operation of a common-rail diesel engine in order to optimize driveability and to reduce soot emissions. The computer-aided design has benefits in reducing controller calibration time. This paper presents a nonlinear control concept for the coordinated control of the exhaust gas recirculation (EGR) valve and the variable geometry turbocharger (VGT) in a common-rail diesel engine. The overall controller structure is set up to regulate the total cylinder air-charge with a desired fresh air-charge amount by means of controlling the intake manifold pressure and estimating the fresh air-charge inducted into the cylinders. During varying engine operating conditions the two control loops are coordinated by a compensation of the EGR valve action through the VGT controller. A nonlinear exhaust pressure controller is designed to regulate the estimated turbocharger power which compensates all EGR valve actions and results in the desired turbocharger power management. The VGT and EGR controllers, the cylinder air-charge observer and the turbocharger identification algorithm are developed based on a nonlinear diesel engine model. The benefits of the coordinated controller structure are demonstrated with transient engine measurements in a passenger car.

Observer Based Air-Fuel Ratio Control

Abstract Reduced automotive exhaust emissions strongly depend on precise control of air-fuel ratio (AFR) during both steady and transient engine operation. Furthermore, precise transient control of AFR is required for acceptable driveability of lean engines. A discrete nonlinear fuel injected SI engine model was developed and used for the design of AFR control algorithms using an observer structure. The engine model includes intake manifold air dynamics, fuel wall-wetting dynamics, and the process delays inherent in the four-stroke engine cycle. The control scheme used an electronic throttle and exhaust gas oxygen measurements. Use of a mass airflow sensor or manifold pressure sensor was not required for warmed-up operation. It has been demonstrated on a 4 cylinder automotive engine to provide 0.8% RMS accuracy in steady state with peak errors on the order of 2% during transient stoichiometric operation.