Image Number 4 for United States Patent #5448886.
A catalyst deterioration-determining device for an internal combustion engine having first and second exhaust sensors positioned in an exhaust path of the internal combustion engine upstream downstream, respectively, of a catalyzer located in the exhaust path. The internal combustion engine further including a control station for effecting feedback control to match an air-fuel ratio with a desired value in accordance with first and second detection signals from the first and second exhaust sensors, respectively. The catalyst deterioration-determining device including a determining section provided in the control station which obtains a deterioration-determined value from calculations based on a rich determination delay time, a lean determination delay time, a lean response delay time and a rich response delay time when a deteriorated state of the catalyzer is determined. The lean response delay time and the rich response delay time extend from the beginning of a decrease and an increase in the first feedback control-corrected quantity to a lean inversion time and a rich inversion time of the second detection signal in response to rich and lean inversions of the first detection signal. The rich determination delay time and the lean determination delay time extend from a rich inversion time and a lean inversion time of the first detection signal to the beginning of the decrease and increase in the feedback control-corrected quantity. The determining section performs calculations in accordance with the deterioration-determined value to determine the deteriorated state of the catalyzer.