Model-Based Control and Cylinder-Event-Based Logic for an Ultra-Low Emissions Vehicle

Improvements in several areas are required to convert current technology light-duty vehicles into low-emissions vehicles suitable for meeting California's Ultra-Low Emissions Vehicle (ULEV) standards. This paper discusses one of those areas, the engine and aftertreatment control system algorithms. The approach was to use model-based air and fuel flow calculations to maintain accurate air-fuel ratio control, and to interface the aftertreatment requirements with engine air-fuel ratio control during the cold- and hot-start parts of the cycle. This approach was applied to a 1993 Ford Taurus operating on Ed85 (85% denatured alcohol, 15% gasoline).

Algorithms discussed in this paper include: a manifold airflow model for predicting airflow and exhaust gas recirculation (EGR) into and out of the intake manifold; a manifold absolute pressure (MAP) observer for predicting MAP with lead information compared with a MAP sensor; manifold air pressure control to reduce the likelihood of misfires during decelerations; a transient volumetric efficiency correction model; dual tau (τ), epsilon (ε) type transient compensation models, cylinder-event-based control for starting, and an aftertreatment control system for rapid catalyst light-off.