Model-Based Nonlinear Multivariable Engine Control

Optimal solutions for simultaneous air and fuel control in a spark ignition engine with the electronic throttle control are investigated. In an optimization framework, the method uses the already identified nonlinear physical models of engine processes for simultaneous torque tracking and air- fuel ratio regulation at the stoichiometric value. Simple physical arguments are used to reformulate the infeasible direct optimization problem into the optimal model predictive control framework for which a solution is sought. In the reformulated optimization problem, the engine torque is directly related to the cylinder air charge so that simpler feasible solutions for real-time control are obtained. Based on the identified engine models and predictive interpretation of the driver torque demand in a throttle-by-wire control strategy, the throttle position and the amount of fuel injection at every engine event are determined. Simulation studies of the predictive control solutions over the aggressive US06 driving cycles indicate that significant improvements in the transient accuracy of the air-fuel ratio control and fast delivery of the diver´s torque request through more aggressive throttle actuation are possible.