CATALYST DIAGNOSTIC DEVICE FOR INTERNAL COMBUSTION ENGINE

摘要

PROBLEM TO BE SOLVED: To detect the deteriorated state of a catalytic converter with high accuracy without being affected by fluctuation factors such as fluctuation in the exhaust has quantity. SOLUTION: A judgement part 22 judges whether a catalyst is in the diagnostic area or not, and an output judging part 19 judges whether a signal S4 is near the stoichiometric air amount or not. When the signal S4 is not near the stoichiometric air amount, it is supplied to a lean-rich side judging part 20, and whether the signal is on the lean side or on the rich side is judged. A shift factor calculation part 21 determines a factor with which an air fuel ratio is shifted to the rich side or the lean side to supply the factor to an air fuel ratio feedback calculation part 8. The calculation part 8 corrects a correction factorαand supplies it to a fuel injection quantity calculation part 9. When the signal S4 is near the stoichiometric air amount, the signal is supplied to a correlation function calculation part 18, and a sequential deterioration indexϕi is calculated by an autocorrelation function-maximum value (x) and a cross-correlation function-maximum value (y). A calculation part 16B determines a final deterioration index I, a comparison part 16E compares the deterioration index I and a judged value ID, and a judgement output part 17 judges whether a catalytic converter 2 is deteriorated or not.