The evolution of increasingly stringent standards for passenger-car exhaust emissions has increased the need for more sophisticated engine controls. In the era prior to emissions control, the dependent variables were fuel economy, driveability, and convenience and cost to the customer. The principal independent variables were spark advance and air-fuel ratio. With the tailpipe emissions of unburned hydrocarbons, carbon monoxide, and oxides of nitrogen now added to the list of dependent variables, a number of additional concepts have been introduced on production automobiles. Among these are exhaust-gas recirculation (EGR), the oxidizing catalytic converter, and the three-way catalytic converter. These developments, in combination with tighter emission standards and new fuel-economy mandates, have complicated the engine control problem.
This presentation focuses on the definition of that problem. The effects of spark advance, air-fuel ratio, and EGR on emissions and fuel economy are reviewed. The needs for considering system deterioration, combustion knock, drive-ability, the cold start, dynamic effects, and control-system anomalies are delineated. The presentation thus provides an understanding of the challenges presented to the controls engineer by the modern homogeneous-charge passenger-car engine.