| This work explores the use of adaptive control as a practical means of precisely controlling the air-fuel ratio in a spark-ignition engine. Accurate control of the air-fuel ratio delivered to the engine is critical in order for an automotive system to satisfy future federal and California emissions requirements. This objective is made difficult by the highly nonlinear and time-varying dynamics of a production engine. Therefore, a control-oriented dynamic model has been developed that includes both air and fuel dynamics, significant process delays and sensor dynamics. This model can be represented as a time-varying linear system amenable to on-line adaptation. With this model, the state-space control and estimator design are constructed to regulate air-fuel ratio on an engine cycle-to-cycle basis. Adaptation is provided by on-line system identification that updates model parameters according to sensed input and output data. Identification techniques utilized include a nonlinear least-squares method and a novel method that uses quadratic programming to determine a linear system through a partially known, possibly nonsmooth, nonlinear sensor. Stability is analyzed using Lyapunov theory and convex optimization. Performance is investigated with simulations and experimental tests on a single-cylinder engine. |
