DETERIORATION DIAGNOSIS DEVICE FOR AN EXHAUST GAS PURIFICATION APPARATUS

摘要

In an deterioration diagnosis device for the exhaust gas purification apparatus in which in a period of time in which inducement processing is carried out which is to induce a water-gas-shift-reaction in a catalyst disposed at the upstream side of the SCR catalyst, by changing an air fuel ratio of exhaust gas discharged from an internal combustion engine from a lean air fuel ratio into a predetermined rich air fuel ratio, an air fuel ratio of exhaust gas flowing into the SCR catalyst and an air fuel ratio of exhaust gas flowing out from the SCR catalyst are measured by the air fuel ratio sensors, respectively, so that deterioration of the SCR catalyst is diagnosed based on a difference between the measured values of these sensors, wherein an end time of the execution of the inducement processing is adjusted in such a manner that an amount of hydrogen oxidized in the SCR catalyst during the period of the execution of the inducement processing becomes constant.

主权项

1. A deterioration diagnosis device for an exhaust gas purification apparatus comprising:
a first exhaust gas purification device that is arranged in an exhaust passage of an internal combustion engine which can be operated in a lean burn state, and is equipped with a 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 device that is arranged in the exhaust passage at the downstream side of the first exhaust gas purification device, and is equipped with a selective catalytic reduction catalyst which serves to store oxygen in the exhaust gas when the air fuel ratio of the exhaust gas is a lean air fuel ratio higher than the stoichiometric air fuel ratio, but to desorb the oxygen thus stored when the 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 second exhaust gas purification device; a second air fuel ratio sensor that measures a physical quantity correlated with an air fuel ratio of exhaust gas flowing out from the second exhaust gas purification device; and a controller comprising at least one processor configured to: start inducement processing, which is to induce a water-gas-shift-reaction in the first exhaust gas purification device by changing an air fuel ratio of exhaust gas flowing into the first exhaust gas purification device to a predetermined rich air fuel ratio lower than the stoichiometric air fuel ratio, when an air fuel ratio of exhaust gas discharged from an internal combustion engine is a lean air fuel ratio, estimate, after the start of the inducement processing, an amount of hydrogen oxidized per unit time in a predetermined state of the selective catalytic reduction catalyst based on a measured value of the first air fuel ratio sensor, integrate an estimated value thus obtained for each unit time, and end the inducement processing when an integrated value thus obtained becomes equal to or more than a predetermined target amount; and obtain a total sensor output difference, which is a total sum of a sensor output difference in a period of time from the start to the end of the inducement processing, by integrating the sensor output difference which is a difference between the measured value of the first air fuel ratio sensor and a measured value of the second air fuel ratio sensor in the period of time, and diagnose deterioration of the second exhaust gas purification device by using the total sensor output difference as a parameter.