초록 ▼

An exhaust emission control system for an internal combustion engine diagnoses a NOx storage capacity of a NOx storage type three-way catalyst disposed in an exhaust passage. A control unit of the exhaust emission control system includes a calculating section which calculates a quantity of fuel to a

An exhaust emission control system for an internal combustion engine diagnoses a NOx storage capacity of a NOx storage type three-way catalyst disposed in an exhaust passage. A control unit of the exhaust emission control system includes a calculating section which calculates a quantity of fuel to a cylinder to bring an air fuel ratio of air-fuel mixture closed to a target ratio and to output an injection signal to a fuel injector based on the calculated quantity of fuel, an executing section which executes a rich-spike treatment for temporally enriching the air-fuel ratio of air-fuel mixture supplied to the engine in a lean condition, and a diagnosing section which diagnoses a NOx storage capacity of said NOx storage type three-way catalyst on the basis of a peak value of the air-fuel ratio during the rich-spike treatment.

대표청구항 ▼

[ What is claimed is:] [1.]1. An exhaust emission control system for an internal combustion engine, comprising:a nitrogen oxide storage type three-way catalyst disposed in an exhaust passage of the engine, said catalyst functioning to store nitrogen oxide of exhaust gases when an air-fuel ratio of a

[ What is claimed is:] [1.]1. An exhaust emission control system for an internal combustion engine, comprising:a nitrogen oxide storage type three-way catalyst disposed in an exhaust passage of the engine, said catalyst functioning to store nitrogen oxide of exhaust gases when an air-fuel ratio of air-fuel mixture supplied to the engine is leaner than a stoichiometric ratio and to release and reduce nitrogen oxide when the air-fuel ratio of the air-fuel mixture is richer than or equal to the stoichiometric ratio;an air-fuel sensor disposed downstream of said nitrogen oxide storage type three-way catalyst in the exhaust passage;a fuel injector injecting fuel to the engine according to an injection signal; anda control unit arrangedto calculate a quantity of fuel to bring the air fuel ratio of the air-fuel mixture close to a target ratio and to output the injection signal to said fuel injector based on the calculated quantity of fuel,to execute a first rich-spike treatment of temporally enriching the air-fuel ratio of the air-fuel mixture by adjusting the injection signalto execute a second rich spike treatment of temporally enriching the air-fuel ratio of the air-fuel mixture by adjusting the infection signal sequentially following the first rich-spike treatment, andto diagnose a nitrogen oxide storage capacity and an oxygen storage capacity of said nitrogen oxide storage type three-way catalyst on the basis of peak values of the detected air-fuel ratio during the first rich-spike treatment and second rich-spike treatment.