Device for determining deterioration of a catalytic converter for an engine

摘要

A device for determining a deterioration of the catalytic converter for an engine equipped with a catalytic converter disposed in the exhaust passage and upstream and downstream air-fuel ratio sensors disposed in the exhaust passage upstream and downstream of the catalytic converter, respectively. The device also determines whether the three-way catalyst in the catalytic converter has deteriorated based on the output signal of the downstream air-fuel ratio sensor when the air-fuel ratio of the engine is feedback controlled by the output of the upstream air-fuel ratio sensor, wherein the execution of the determining operation of catalyst deterioration is prohibited when the period of the cycle of the air-fuel ratio feedback control becomes longer than a predetermined value, thereby preventing errors from accuracy in the determination.