초록 ▼

A diagnosis of deterioration and/or normality of an exhaust gas purifying catalyst is made by comparing a ratio of reversal frequencies of outputs from oxygen sensors disposed on opposite sides of the exhaust gas purifying catalyst with a threshold ratio. Discrimination is performed on both normalit

A diagnosis of deterioration and/or normality of an exhaust gas purifying catalyst is made by comparing a ratio of reversal frequencies of outputs from oxygen sensors disposed on opposite sides of the exhaust gas purifying catalyst with a threshold ratio. Discrimination is performed on both normality and deterioration in a standard gas quantity zone, on only normality in a large gas quantity zone, and on only deterioration in a small gas quantity zone, and nothing is made in an extra large gas quantity zone.

대표청구항 ▼

[ What is claimed is:] [1.] A diagnostic system for performing diagnosis of functional states of an exhaust gas purifying catalyst installed in an exhaust system of an engine based on comparison between value relating to a ratio of frequencies of reversal of outputs from oxygen (O.sub.2) sensors dis

[ What is claimed is:] [1.] A diagnostic system for performing diagnosis of functional states of an exhaust gas purifying catalyst installed in an exhaust system of an engine based on comparison between value relating to a ratio of frequencies of reversal of outputs from oxygen (O.sub.2) sensors disposed on the opposite sides of the exhaust gas purifying catalyst and a threshold value while the engine operates in a specified operating state, said catalyst diagnostic system comprising:engine operating condition detecting means for detecting an engine operating condition in said specified operating state;exhaust gas detecting means for detecting an amount of exhaust gas flowing through the exhaust gas purifying catalyst; anddiagnostic means for performing discrimination as to whether the exhaust gas purifying catalyst is normal or has been deteriorating while said engine operating condition is in a specified first zone where said amount of exhaust gas is in a specified range, prohibiting said discrimination but performing discrimination of normality of the exhaust gas purifying catalyst while said engine operating condition is in a specified second zone where said amount of exhaust gas is greater than said specified range, and terminating said diagnosis of functional states of the exhaust gas purifying catalyst when the exhaust gas purifying catalyst is discriminated to be normal.