Emission control apparatus with reduced hangover time to switch from open- to closed-loop control modes

摘要

A closed-loop emission control apparatus for internal combustion engines includes exhaust composition sensor for feedback control of the air-fuel mixture. When the temperature in the exhaust passage is lower than the operating temperature of the sensor, control is switched to an open-loop mode. The feedback control signal is fluctuated above and below a predetermined DC bias at periodic intervals during the open-loop mode to switch the control to the closed-loop mode in a minimum transition time as soon as the sensor's temperature condition warrants feedback control.