To promote activity of catalyst extended to a low temperature region, by controlling a frequency and an amplitude amount in a perturbation condition of exhaust air-fuel ratio, correcting to the perturbation condition in accordance with a applied catalytic system, and further properly correcting in accordance with an exhaust temperature and exhaust amount exposed to the catalyst.
A precatalyst 12 and main catalyst 13 are interposed in an exhaust passage 11, each signal of detection means 16 detecting an operating condition of an engine 10 and a signal output from an O2 sensor 14 are input to a CPU 17, each signal is received to the CPU, and proper air-fuel ratio is set from the time when the engine is started at a low temperature. A control signal is output to an air-fuel ratio setting means 19 controlling a fuel supply means 18 of fuel injection valve or the like so as to obtain this setting air-fuel ratio. Based on a detection signal output respectively from the detection means, O2 sensor and two exhaust temperature sensors 15, an amplitude amount setting means 21 and frequency setting means 22 respectively of airfuel ratio are provided, and a correction means 23 is provided which corrects an amplitude amount and frequency of perturbation in accordance with a catalytic condition.
TAYAMA AKIRA
OTA TADAKI
