Higher order sliding mode air-to-fuel ratio in SI engines

In this work one presents a novel nonlinear control strategy for the normalized air to fuel ratio (represented by λ variable) for spark ignition engines. The control method is based on the high order sliding mode methodology that results to be robust to matched perturbations and alleviates the chattering problem. The dynamics for λ depends on the time derivative of the input control, i.e., the injected fuel mass flow ṁ_fi. This term is estimated by means of a well known robust sliding mode differentiator. Then, based on time delayed measurements given by an UEGO sensor, a high order sliding mode observer is proposed where the equivalent injected signal contains actual values. Finally, simulations based on a mean value engine model demonstrate the good performance of the proposed control method.