| 摘要 |
<p>PROBLEM TO BE SOLVED: To precisely judge degradation of a catalytic converter without being affected from divergence of air-fuel ratio of a specific air-cylinder. SOLUTION: Upstream air-fuel ratio sensors 13A, 13B on the upstream of a catalytic converter 16 which is placed in an exhaust path of an engine 1, and a downstream O2 sensor 17 is placed in its upstream. An engine controlling circuit 10 controls engine's air-fuel ratio close to a stoichiometric air-fuel ratio and judges exiting of degradation of a catalytic converter based on locus length of output from the upstream air-fuel ratio sensors and the downstream O2 sensor. The controlling circuit performs moderating control of the output from the upstream air-fuel ratio sensors using moderating factor which increases according to engine speed, and calculates the locus length of the output from the upstream air-fuel ratio sensors based on fluctuation of the derived moderating value. Therefore, effect from divergence of air-fuel ratio of a specific air- cylinder is removed satisfactorily maintaining following property to actual air-fuel ratio fluctuation in a low rotational region.</p> |
