Patent ID: 7607288

Claim:
A catalyst deterioration diagnosis apparatus comprising: a catalyst converter interposed in an exhaust passage of an internal combustion engine; an upstream-side O2 sensor disposed in an upstream of the catalyst converter; a downstream-side O2 sensor disposed in a downstream of the catalyst converter; a running-state detection unit which detects a running state of the internal combustion engine which includes an engine revolution number and load information; weighted correction process unit which subjects an output signal of the upstream-side O2 sensor and an output signal of the downstream-side O2 sensor to weighted correction processes corresponding to output levels, when the weighted correction process unit has determined on the basis of the running state information that the running state falls within a catalyst deterioration diagnosis performance region previously set; calculation unit which calculates at least one of amplitude magnitudes and time integral value, the amplitude magnitudes are 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 the time integral values are time integral values of a difference between a first predetermined signal and the output signal of the upstream-side O2 sensor after the weighted correction processes and of a difference between a second predetermined signal and the output signal of the downstream-side O2 sensor after the weighted correction processes; deterioration-diagnosing-parameter calculation unit which calculates a deterioration diagnosing parameter on the basis of a combination or either of the amplitude magnitudes and the time integral values calculated by the calculation unit; deterioration decision unit which determines a 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 by the deterioration-diagnosing-parameter calculation unit; and warning unit which issues a warning when the deterioration decision unit has detected and has determined that the catalyst converter has been deteriorated.