Development of Closed Loop Secondary Air Control Three-Way Catalyst System

The three-way catalyst system using a carburetor still needs a lot of improvement for meeting emission standards of U.S. for 1981, California for 1983, and Japanese for 1978. In order to improve air fuel ratio control capability of a carburetor three-way catalyst system, Toyota has developed a closed loop secondary air control system. In this system air fuel ratio is controlled not in the induction but in the exhaust. The short control loop of this system provides high air-fuel ratio oscillation frequency and rapid correction ability for maintaining the exhaust air-fuel ratio at stoichiometric. This gives the system a higher conversion efficiency. This paper describes the performance characteristics and an analysis of the system with regards to emission, driveability and fuel economy.