Technical Paper
Engine Air-Fuel Ratio Control Using an Event-Based Observer
1993-03-01
930766
Better fuel economy, reduced exhaust emissions and better drivability strongly depend on precise control of air-fuel ratio (AFR) during both steady and transient engine operations. A discrete, nonlinear fuel-injected SI engine model was developed and used for the design of AFR control algorithms. The engine model includes intake manifold air dynamics, fuel wall-wetting dynamics, and cycle delays inherent in the four-stroke engine processes. The sampling period is synchronous with crank angle (“event-based”) as opposed to the conventional time synchronous sampling scheme (“time-based”). The model was validated with test data over a wide range of engine operating conditions. The exhaust O2 sensor can only provide a delayed and lagged AFR signal to the controller. This inherent delay in the measurement will slow down the system response if conventional feedback control design is used.