Input observer-based individual cylinder air-fuel ratio control: Modelling, design and validation

A general approach is proposed to address the cylinder-to-cylinder air-fuel ratio (AFR) balancing control problem using a single universal exhaust gas oxygen (UEGO) sensor. Using the multirate sampling technique, a control-oriented engine model, well combining the fuel delivery dynamics and exhaust gas dynamics, is established. Gas mixing phenomena is characterized by a gas mixing matrix, which is valid both for equal-length and unequal-length exhaust runners. Based on the developed model, the observability of the individual cylinder AFR estimation problem is analyzed using the input observability concept. An input observer using the one-step forward feedback is proposed to design the estimator. Using the estimated AFR, a decoupled PI compensator is designed for each cylinder to compensate the cylinder-by-cylinder variations. Finally, the proposed approach is verified by simulation and experimental results.