Closed loop NOx control by discrete time sliding mode

Nitrogen oxides (NO_x) are besides particulate matter (PM), especially for diesel engines, the most relevant emission components. Against this background and the fact that passenger car emission legislation is permanently becoming stricter, there is still a growing interest in minimizing these pollutants. Beside the highly nonlinear behavior of engines also the tradeoff between PM and NO_x is a challenging task for the evaluation of a control scheme. In this work the NO_x emissions are addressed and a discrete time sliding mode controller (DSMC) is proposed to control the exhaust gas recirculation (EGR) valve in order to provide tracking of a time varying NO_x reference while disturbances are rejected. The method presented in this report avoids the common use of intermediate variables like intake fresh air or inlet manifold pressure and shows proper results in both simulation and measurements with a Euro 5 engine.