| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve the accuracy of diagnosis of catalyser deterioration by determinating the existence of catalyser according to an output of downstream air-fuel ratio sensor when an intake air quantity is within a specified determination execution range during control of air-fuel ratio feed-back, and setting the execution range according to difference between an upstream sensor output and a target output. SOLUTION: An air-fuel(A/F) sensor 45 is arranged upstream of a catalyser converter 38 arranged at an exhaust pipe 34 of an engine 20 while an oxygen sensor 46 is arranged downstream thereof. An output signal of each sensor is input to an ECU 70, and the quantity of fuel ignition is feed-back controlled so that an engine air-fuel ratio becomes a theoretical air-fuel ratio according to an output of the A/F sensor 45. During the control operation, when the quantity of intake air of engine detected by an air flow meter 40 is within a specified determination execution range. the existence of deterioration in exhaust emission control catalyzer is determinated according to an output of an oxygen sensor 46. The determination execution range relating to this catalyser deterioration determination is set according to difference between an output of the A/F sensor 45 and a target output corresponding to the theoretical air-fuel ratio.</p> |
