Catalyst deterioration diagnosis apparatus and catalyst deterioration diagnosis method for internal combustion engine

A catalyst deterioration diagnosis apparatus for an internal combustion engine as has a catalyst converter which is interposed in an exhaust passage of the internal combustion engine, an upstream-side O2 sensor which is disposed in an upstream of the catalyst converter, a downstream-side O2 sensor which is disposed in a downstream of the catalyst converter, running-state detection means for detecting that running state of the internal combustion engine which includes an engine revolution number and load information, basic-injection-quantity setting means for setting a basic fuel injection quantity in accordance with the running state information from the running-state detection means, feedback control means for executing a feedback control on the basis of a signal of the upstream-side O2 sensor and for correcting the feedback control on the basis of a signal of the downstream-side O2 sensor, and fuel-injection-quantity correction means for correcting the basic fuel injection quantity in accordance with a control magnitude based on the feedback control, comprising:

• weighted correction process means for subjecting the output signal of said upstream-side O2 sensor and the output signal of said downstream-side O2 sensor to weighted correction processes corresponding to output levels, when it has been decided on the basis of the running state information that the running state falls within a catalyst deterioration diagnosis performance region previously set;
• calculation means for calculating both or either of amplitude magnitudes of the output signal of said upstream-side O2 sensor and the output signal of said downstream-side O2 sensor after the weighted correction processes, and time integral values of differences between predetermined signals and the output signal of said upstream-side O2 sensor and the output signal of said downstream-side O2 sensor after the weighted correction processes;
• deterioration-diagnosing-parameter calculation means for calculating a deterioration diagnosing parameter on the basis of a combination or either of the amplitude magnitudes and the time integral values calculated by said calculation means;
• deterioration decision means for deciding deterioration of said catalyst converter on the basis of a result of a comparison between a predetermined deterioration decision threshold value and the deterioration diagnosing parameter calculated by said deterioration-diagnosing-parameter calculation means;
• and
• warning means for issuing warning when it has been decided by said deterioration decision means that said catalyst converter has been deteriorated.

A catalyst deterioration diagnosis method for an internal combustion engine as has a catalyst converter which is interposed in an exhaust passage of the internal combustion engine, an upstream-side O2 sensor which is disposed in an upstream of the catalyst converter, a downstream-side O2 sensor which is disposed in a downstream of the catalyst converter, running-state detection means for detecting that running state of the internal combustion engine which includes an engine revolution number and load information, basic-injection-quantity setting means for setting a basic fuel injection quantity in accordance with the running state information from the running-state detection means, feedback control means for executing a feedback control on the basis of a signal of the upstream-side O2 sensor and for correcting the feedback control on the basis of a signal of the downstream-side O2 sensor, and fuel-injection-quantity correction means for correcting the basic fuel injection quantity in accordance with a control magnitude based on the feedback control, comprising:

• a weighted correction process step of subjecting the output signal of the upstream-side O2 sensor and the output signal of the downstream-side O2 sensor to weighted correction processes corresponding to output levels, when it has been decided on the basis of the running state information that the running state falls within a catalyst deterioration diagnosis performance region previously set;
• a calculation step of calculating both or either of amplitude magnitudes of the output signal of the upstream-side O2 sensor and the output signal of the downstream-side O2 sensor after the weighted correction processes, and time integral values of differences between predetermined signals and the output signal of the upstream-side O2 sensor and the output signal of the downstream-side O2 sensor after the weighted correction processes;
• a deterioration-diagnosing-parameter calculation step of calculating a deterioration diagnosing parameter on the basis of a combination or either of the amplitude magnitudes and the time integral values calculated at said calculation step;
• a deterioration decision step of deciding deterioration of the catalyst converter on the basis of a result of a comparison between a predetermined deterioration decision threshold value and the deterioration diagnosing parameter calculated at said deterioration-diagnosing-parameter calculation step;
• and
• a warning step of issuing warning when it has been decided at said deterioration decision step that the catalyst converter has been deteriorated.