Airpath-Control of boosted Diesel engines
Coupling effects between the manipulated and controlled variables of a combustion engine affect, that demands concerning fuel consumption, power, emissions and reliability often are in conflict among each other. In the last years technologies were developed to defuse this trade-offs. Beside the classical variables like injection-parameters, today there exist further possibilities, among other things the variables of the air path, to manipulate the system. The fresh air flow respectivly the rate of the recirculated exhaust gas and the intake manifold pressure can be controlled by an adjustable exhaust gas recirculation (EGR) and a turbocharger with variable geometry of its turbine (VGT). Because of the physical coupling of both actuators, caused in the common air duct, interactions are unavoidable. In series production often separeted control loops are combined, so the full potential can not be utilized. However progresses in the available computing power of electronic control units allow modelbased multivariable control mechanism.
At the Institut of Automatic Control concepts for controlling based on the modelpredictive control have been developed and implemented on different engines in the context of national and international projects. Detailed models of the airpath, based on physical modelling and implemented in Matlab/Simulink and Modelica/Dymola, provide as base for the development of the observer and prediction model. With the help of dynamical measurements from the engine the models are fitted to the real behaviour by an optimization process. Base for the modelfitting are responses of the boost pressure and the airflow/egr-rate for steps in the vtg/egr-actuator.