Exhaust emission control device for internal combustion engine and NOx purification catalyst deterioration determination method

摘要

An exhaust emission control device includes a first detection unit for detecting a NOx adsorption amount and an oxygen storage amount of a three-way catalyst and a NOx purification catalyst during rich spike, a second detection unit for detecting the oxygen storage amount of the three-way catalyst and the NOx purification catalyst until the output of a second air-fuel sensor becomes lean after the rich spike, and a deterioration determination unit for determining deterioration of the NOx purification catalyst based on a detected value of the first detection unit and that of the second detection unit.

主权项

1. An exhaust emission control device for an internal combustion engine, comprising:
a NOx purification catalyst provided in an exhaust system of the internal combustion engine; a three-way catalyst provided upstream of the NOx purification catalyst and having oxygen storage capacity; an upstream side air-fuel ratio sensor provided upstream of the three-way catalyst and configured to detect an exhaust gas air-fuel ratio; a downstream side air-fuel ratio sensor provided downstream of the NOx purification catalyst and configured to detect the exhaust gas air-fuel ratio; a rich spike unit configured to change the air-fuel ratio of exhaust gas discharged from the internal combustion engine from lean to rich and to return the air-fuel ratio to lean after the elapse of a predetermined time to reduce and purify the NOx absorbed by the NOx purification catalyst; a first detection unit configured to detect a NOx absorption amount and an oxygen storage amount of the three-way catalyst and the NOx purification catalyst based on an output value of the upstream side air-fuel ratio sensor and that of the downstream side air-fuel ratio sensor during rich spike by the rich spike unit; a second detection unit configured to detect the oxygen storage amount of the three-way catalyst and the NOx purification catalyst based on the output value of the upstream side air-fuel ratio sensor and that of the downstream side air-fuel ratio sensor until the exhaust gas air-fuel ratio changes to lean after the rich spike and the output of the downstream side air-fuel ratio sensor becomes lean; and a deterioration determination unit configured to determine deterioration of the NOx purification catalyst based on a detected value of the first detection unit and that of the second detection unit.