Abstract: Air-fuel ratio control system for an engine having a catalyst purifying exhaust gases, first oxygen sensor disposed upstream of the catalyst, and second oxygen sensor disposed downstream. Intake air flow rate is detected. An amount of oxygen flowing into the catalyst is calculated using oxygen concentration detected by the first sensor and the detected intake air flow rate. The air-fuel ratio is alternately controlled to lean and rich by comparison between the calculated oxygen amount and target values. A rich oxygen amount and a lean oxygen amount are calculated. A correction amount for correcting the first sensor output is calculated based on the rich oxygen amount, the lean oxygen amount, and an accumulated value of the detected intake air flow rate. The oxygen concentration corrected with the correction amount is used for calculating the inflowing oxygen amount, the rich operation oxygen amount, and the lean operation oxygen amount.

Abstract: A deterioration detecting apparatus for a purifying catalyst in an exhaust system of an engine. A first oxygen concentration sensor is disposed upstream of the catalyst. A second oxygen concentration sensor is disposed downstream. An amount of oxygen flowing into the catalyst is calculated from the oxygen concentration detected by the first sensor and the detected intake air flow rate. A control command value of an air-fuel ratio is alternately switched between a first value corresponding to a lean air-fuel ratio and a second value corresponding to a rich air-fuel ratio according to a result of comparison between the calculated inflowing oxygen amount and target values. Excessive inflowing oxygen amounts are calculated. The target values are corrected with the excessive inflowing oxygen amount. A deterioration degree of the catalyst is detected based on an output of the second sensor when performing the switching of the control command value using the corrected target values.

Abstract: An air-fuel ratio control system for an internal combustion engine having a catalyst provided in an exhaust system of the engine for purifying exhaust gases and a first oxygen concentration sensor disposed upstream of the catalyst is disclosed. The air-fuel ratio control system controls an air-fuel ratio of an air-fuel mixture supplied to the engine. A degree of response deterioration of the first oxygen concentration sensor is detected. A response delay of the first oxygen concentration sensor is compensated according to the detected degree of deterioration to calculate a compensated sensor output. The air-fuel ratio is controlled so that a detected air-fuel ratio calculated from the compensated sensor output coincides with a target air-fuel ratio. A frequency characteristic of the compensation is adjusted according to the detected degree of deterioration.

Abstract: Air-fuel ratio control system for an engine having a catalyst purifying exhaust gases, first oxygen sensor disposed upstream of the catalyst, and second oxygen sensor disposed downstream. Intake air flow rate is detected. An amount of oxygen flowing into the catalyst is calculated using oxygen concentration detected by the first sensor and the detected intake air flow rate. The air-fuel ratio is alternately controlled to lean and rich by comparison between the calculated oxygen amount and target values. A rich oxygen amount and a lean oxygen amount are calculated. A correction amount for correcting the first sensor output is calculated based on the rich oxygen amount, the lean oxygen amount, and an accumulated value of the detected intake air flow rate. The oxygen concentration corrected with the correction amount is used for calculating the inflowing oxygen amount, the rich operation oxygen amount, and the lean operation oxygen amount.

Abstract: An air-fuel ratio control system for an internal combustion engine having a catalyst provided in an exhaust system of the engine for purifying exhaust gases and a first oxygen concentration sensor disposed upstream of the catalyst is disclosed. The air-fuel ratio control system controls an air-fuel ratio of an air-fuel mixture supplied to the engine. A degree of response deterioration of the first oxygen concentration sensor is detected. A response delay of the first oxygen concentration sensor is compensated according to the detected degree of deterioration to calculate a compensated sensor output. The air-fuel ratio is controlled so that a detected air-fuel ratio calculated from the compensated sensor output coincides with a target air-fuel ratio. A frequency characteristic of the compensation is adjusted according to the detected degree of deterioration.

Abstract: A deterioration detecting method for a catalyst in an exhaust system of an internal combustion engine for purifying exhaust gases. The system includes a first oxygen concentration sensor and a second oxygen concentration sensor disposed, respectively, upstream and downstream of the catalyst. Intake air flow rate of the engine is detected. An amount of oxygen flowing into the catalyst is calculated according to an oxygen concentration detected by the first sensor and the detected intake air flow rate. An air-fuel ratio of an air-fuel mixture supplied to the engine is controlled by alternately switching between lean and rich with respect to the stoichiometric ratio according to a result of comparison between the calculated and target values of the inflowing oxygen amount. A deterioration degree of the catalyst is detected based on an output of the second sensor when performing the switching control of the air-fuel ratio.

Abstract: A deterioration detecting apparatus for a purifying catalyst in an exhaust system of an engine. A first oxygen concentration sensor is disposed upstream of the catalyst. A second oxygen concentration sensor is disposed downstream. An amount of oxygen flowing into the catalyst is calculated from the oxygen concentration detected by the first sensor and the detected intake air flow rate. A control command value of an air-fuel ratio is alternately switched between a first value corresponding to a lean air-fuel ratio and a second value corresponding to a rich air-fuel ratio according to a result of comparison between the calculated inflowing oxygen amount and target values. Excessive inflowing oxygen amounts are calculated. The target values are corrected with the excessive inflowing oxygen amount. A deterioration degree of the catalyst is detected based on an output of the second sensor when performing the switching of the control command value using the corrected target values.