Ford Three-Way Catalyst and Feedback Fuel Control System

The objective of this paper is to describe the Ford Motor Company (Ford) approach of meeting exhaust emission regulations with a three-way catalyst and feedback control system. A pilot program was initiated to gain production experience with three-way catalyst systems in anticipation of expanded usage to meet future emission standards.

The Ford system consists of a three-way catalyst with feedback control monitoring the exhaust oxygen concentration and controlling the fuel flow to produce a stoichiometric exhaust mixture. Mixture control is critical since catalyst NOx conversion efficiency is diminished when the exhaust mixture deviates from stoichiometry. Briefly, the control loop consists of zirconium dioxide exhaust sensor to indicate oxygen concentration, an electronic control unit, a vacuum regulator to proportion a vacuum signal to the carburetor, and a feedback controlled carburetor with vacuum modulated main fuel system.

Highlights of the development program and system details are described.