OXIDATION CATALYST FAULT DIAGNOSIS UNIT AND OXIDATION CATALYST FAULT DIAGNOSIS METHOD AND INTERNAL COMBUSTION ENGINE EXHAUST PURIFICATION APPARATUS

摘要

To provide an oxidation catalyst fault diagnosis unit and fault diagnosis method that can perform fault diagnosis of an oxidation catalyst with good precision in a desired time period and an internal combustion engine exhaust purification apparatus equipped with the oxidation catalyst fault diagnosis unit.;An oxidation catalyst fault diagnosis unit which, in an exhaust purification apparatus of an internal combustion engine that delivers a reducing agent capable of generating ammonia to an exhaust passage on the upstream side of a reduction catalyst and selectively reduces and purifies NO_x in exhaust with the reduction catalyst, is for performing fault diagnosis of an oxidation catalyst placed on the downstream side of the reduction catalyst, the oxidation catalyst fault diagnosis being equipped with a reducing agent dosage calculating portion that sets a dosage of the reducing agent such that a predetermined quantity of the ammonia flows out to the downstream side of the reduction catalyst, an oxidation efficiency calculating portion that obtains the efficiency with which the predetermined quantity of ammonia flowing out to the downstream side of the reduction catalyst is oxidized by the oxidation catalyst when the predetermined quantity of ammonia passes through the oxidation catalyst, and a fault determining portion that performs determination of whether or not the oxidation catalyst is faulty by comparing the oxidation efficiency with a predetermined reference value.