DETERIORATION DIAGNOSIS DEVICE FOR AN EXHAUST GAS PURIFICATION APPARATUS

摘要

A deterioration diagnosis device for an exhaust gas purification apparatus which performs inducement processing when the internal combustion engine is operated at a lean air fuel ratio, measures, by means of air fuel ratio sensors, the air fuel ratio of exhaust gas flowing into the SCR catalyst and the air fuel ratio of exhaust gas flowing out from the SCR catalyst during a period while the inducement processing is performed, and diagnoses deterioration of the SCR catalyst based on a difference between the measured values of these sensors, wherein an amount of hydrogen produced by each of a three-way catalyst and an NSR catalyst is estimated based on the deterioration degree thereof, and an air fuel ratio of exhaust gas discharged from the internal combustion engine is feedback-controlled so that the air fuel ratio of the exhaust gas flowing into one of the three-way catalyst and the NSR catalyst in which the hydrogen production amount thus estimated is larger than that in the other becomes a target value.

主权项

1. A deterioration diagnosis device for an exhaust gas purification apparatus, comprising:
a first exhaust gas purification unit that is arranged in an exhaust passage of an internal combustion engine capable of a lean burn operation, and is equipped with a three-way catalyst which serves to promote a water gas shift reaction when an air fuel ratio of exhaust gas is a rich air fuel ratio which is lower than a stoichiometric air fuel ratio; a second exhaust gas purification unit that is arranged in the exhaust passage at the downstream side of the first exhaust gas purification unit, and is equipped with a storage reduction catalyst which serves to promote a water gas shift reaction when the air fuel ratio of exhaust gas is a rich air fuel ratio which is lower than the stoichiometric air fuel ratio; a third exhaust gas purification unit that is arranged in the exhaust passage at the downstream side of the second exhaust gas purification unit, and is equipped with a selective catalytic reduction catalyst which serves to store oxygen in exhaust gas when the air fuel ratio of the exhaust gas is a lean air fuel ratio higher than the stoichiometric air fuel ratio, and to desorb the oxygen thus stored when the air fuel ratio of the exhaust gas is equal to or lower than the stoichiometric air fuel ratio; a first air fuel ratio sensor that measures a physical quantity correlated with an air fuel ratio of exhaust gas flowing into the first exhaust gas purification unit; a second air fuel ratio sensor that measures a physical quantity correlated with an air fuel ratio of exhaust gas flowing into the second exhaust gas purification unit; a third air fuel ratio sensor that measures a physical quantity correlated with an air fuel ratio of exhaust gas flowing into the third exhaust gas purification unit; a fourth air fuel ratio sensor that measures a physical quantity correlated with an air fuel ratio of exhaust gas flowing out from the third exhaust gas purification unit; and a controller, comprising at least one processor, configured to: perform, when the air fuel ratio of the exhaust gas discharged from the internal combustion engine is a lean air fuel ratio, inducement processing of inducing a water gas shift reaction in each of the first exhaust gas purification unit and the second exhaust gas purification unit, by changing an air fuel ratio of exhaust gas discharged from the internal combustion engine to a rich air fuel ratio lower than the stoichiometric air fuel ratio; obtain a total sensor output difference which is a total sum of a sensor output difference in a period while the inducement processing is performed, by integrating the sensor output difference which is a difference between a measured value of the third air fuel ratio sensor and a measured value of the fourth air fuel ratio sensor in the period, and diagnose deterioration of the third exhaust gas purification unit by using the total sensor output difference as a parameter; and estimate, based on a deterioration degree of the three-way catalyst and a deterioration degree of the storage reduction catalyst, a first hydrogen production amount which is an amount of hydrogen produced by the first exhaust gas purification unit and a second hydrogen production amount which is an amount of hydrogen produced by the second exhaust gas purification unit while the inducement processing is performed; wherein the controller is further configured so as to perform the inducement processing by controlling the air fuel ratio of the exhaust gas discharged from the internal combustion engine in such a manner that in cases where the first hydrogen production amount is more than the second hydrogen production amount, a measured value of the first air fuel ratio sensor becomes a first predetermined rich air fuel ratio, and in cases where the second hydrogen production amount is more than the first hydrogen production amount, a measured value of the second air fuel ratio sensor becomes a second predetermined rich air fuel ratio.