EXHAUST GAS PURIFICATION SYSTEM, AND NOx PURIFICATION CAPACITY RESTORATION METHOD

An exhaust gas purification system comprising:

• a NOx storage-reduction catalyst that is disposed on an exhaust passageway of an internal combustion engine to store and reduce a nitrogen compound contained in exhaust gas discharged from the internal combustion engine;
• and
• a control unit for controlling an air-fuel ratio of the exhaust gas, wherein
• the control unit is configured to execute:
• a deterioration degree estimation process of estimating a degree of deterioration of the NOx storage-reduction catalyst;
• a regeneration process of shifting the air-fuel ratio to a rich state to restore a NOx storage capacity of the NOx storage-reduction catalyst;
• a target interval setting process of setting a target interval that is a time interval from an end of the regeneration process to a start of the subsequent regeneration process;
• a target interval correction process of correcting the target interval based on the estimated degree of deterioration;
• and
• a regeneration repeating process of repeating the regeneration process when the corrected target interval is over after an end of the regeneration process.

A NOx purification capacity restoration method for an exhaust gas purification system that includes an internal combustion engine and a NOx storage-reduction catalyst that is disposed on an exhaust gas passageway of the internal combustion engine to store and reduce a nitrogen compound contained in exhaust gas discharged from the internal combustion engine, the NOx purification capacity restoration method comprising:

• estimating a degree of deterioration of the NOx storage-reduction catalyst;
• executing a regeneration process by shifting an air-fuel ratio of the exhaust gas to a rich state to restore a NOx storage capacity of the NOx storage-reduction catalyst;
• setting a target interval that is a time interval from an end of the regeneration process to a start of the subsequent regeneration process;
• correcting the target interval based on the estimated degree of deterioration;
• and
• repeating the regeneration process when the corrected target interval is over after an end of the regeneration process.