DIAGNOSTIC DEVICE FOR EXHAUST EMISSION CONTROL DEVICE

摘要

PROBLEM TO BE SOLVED: To enhance the accuracy of diagnosing the degradation of an adsorption catalyst by enabling only the degradation of the adsorption catalyst to be diagnosed regardless of the degree of degradation of a catalytic converter rhodium located upstream of the adsorption catalyst. SOLUTION: An A/F sensor 24 is placed between a catalytic converter rhodium 22 and an absorption catalyst 23, and a sensor 25 providing an output proportional to the concentration of oxygen in exhaust is placed downstream of the adsorption catalyst 23. A control means 26 performs air-fuel ratio feedback control according to the output of the oxygen concentration sensor 25 located downstream of the adsorption catalyst 23, and a measuring means 27 measures the amplitude of exhaust air-fuel ratio between the catalytic converter rhodium 22 and the adsorption catalyst 23 by use of the output of the A/F sensor 24 during the air-fuel ratio feedback control. A determination means 28 determines whether or not the adsorption catalyst 23 has degraded according to the air-fuel ratio amplitude.