Diagnosis of deterioration in air/fuel ratio sensor

摘要

An air/fuel ratio sensor (4) and a three-way catalytic converter (3A) having an oxygen storage function are provided in an exhaust passage (2) of an internal combustion engine (1). A controller (6) runs the engine (1) under the alternating application of a stoichiometric air/fuel ratio and a rich air/fuel ratio, and a diagnosis of deterioration in the air/fuel ratio sensor (4) is performed on the basis of the amplitude of variation in the air/fuel ratio detected by the air/fuel ratio sensor (4). By executing the diagnosis only immediately after a fuel cut, the amount of oxygen stored in the three-way catalytic converter (3A) at the start point of the diagnosis is equal to the maximum amount. When the rich air/fuel ratio is applied, the converter (3A) releases the stored oxygen to maintain the exhaust gas purification performance of the converter (13).