| 摘要 |
<p>PURPOSE:To keep precision of deterioration judgment regardless of the deterioration of a sensor by setting a control constant just before the output value of a second exhaust sensor is inverted as an air-fuel ratio control constant in the deterioration judgment by a catalyst deterioration judging means at the time of catalyst deterioration judgment. CONSTITUTION:The detection value of a first exhaust sensor 12 on the upper stream side of a catalytic converter 11 disposed on the exhaust passage 6 of an engine 1 and the detection value of a second exhaust sensor 13 on the lower stream side of the catalystic converter 11 are inputted, and feedback control of air-fuel ratio is conducted on the basis of the detection value of the first exhaust sensor 12. In an ECU 14 which judges the deterioration of the catalytic convertor 12 on the basis of the detection value of the second exhaust sensor 13, an air-fuel ratio control constant is changed so that the detection value of the second exhaust sensor 13 is inverted at the time of detecting the catalyst deterioration. Further, the air-fuel ratio control constant just before the detection value of the second exhaust sensor 13 is inverted is set as a catalyst deterioration judging control constant, whereby the judging precision of catalyst deterioration can be held.</p> |
