Method of judging deterioration of emission gas control catalyst device

Abstract

A first exhaust gas sensor (air-fuel ratio sensor) and a second exhaust gas sensor (O sensor) are disposed respectively upstream and downstream of a catalytic converter. An exhaust system E which ranges from the exhaust gas sensor to the exhaust gas sensor and includes the catalytic converter is regarded as an object exhaust system E, and a behavior of the object exhaust system E is modeled. When an internal combustion engine is in operation, parameters to be set of the model of the object exhaust system E are sequentially identified based on the data of outputs of the exhaust gas sensors A deteriorated state of the catalytic converter is determined based on the data of the identified values. Concurrent with the determination of the deteriorated state, a target air-fuel ratio for the internal combustion engine is sequentially determined in order to converge the output of the exhaust gas sensor to a given target value, and the air-fuel ratio of the internal combustion engine is controlled to converge the output (the detected value of the air-fuel ratio) of the first exhaust gas sensor to the target air-fuel ratio, for thereby allowing the catalytic converter to achieve an optimum purifying capability. In this manner, the deteriorated state of the catalytic converter can be determined in various operation states of the internal combustion engine while keeping the purifying capability of the catalytic converter