Observer design of critical states for air path flow regulation in a variable geometry turbocharger exhaust gas recirculation diesel engine

Abstract

Modern automotive diesel engines rely on control strategies that must optimally manage the flows of fresh air and recirculated exhaust gas to achieve the best trade-off between torque demand and engine out emissions. An important aspect of the gas exchange regulation problem is the complex interaction between the variable geometry turbocharger (VGT) and the exhaust gas recirculation (EGR) valve and their associated flows. Control strategies that seek to optimize these flows must either have direct flow measurements or have access to the state variables that provide information on these flows. Furthermore, while the precise control of high-pressure (HP) EGR flow is essential, minimizing its usage is desirable given the engine durability concerns related to the excessive use of HP EGR, such as EGR valve coking and sticking, plugged EGR cooler, cylinder deposits, and valve deposits, to name a few. Exhaust gas recirculation may be optimally used if information on the level of inertness or leanness (oxygen content) of the exhaust gases is available. This paper presents the systematic design of observers for state variables that facilitate the design of such an optimal gas exchange control policy, thereby eliminating the need for direct sensing of the state variables for which the observer designs are proposed.