EXHAUST PURIFICATION SYSTEM AND METHOD FOR RESTORING NOx PURIFICATION CAPACITY

An exhaust purification system comprising:

• a NOx reduction catalyst that is disposed on an exhaust passageway of an internal combustion engine to reduce and purify NOx in an exhaust gas;
• an exhaust gas temperature sensor that is provided on a downstream side of the NOx reduction catalyst on the exhaust passageway to detect a temperature of the exhaust gas as a first exhaust gas temperature;
• and
• a control unit configured to:
• control at least one of an intake air flow rate and a fuel injection amount of the internal combustion engine;
• wherein
• execute a regeneration process of restoring a NOx purification capacity of the NOx reduction catalyst by controlling at least one of the intake air flow rate and the fuel injection amount so as to make the exhaust gas rich;
• execute an exhaust gas temperature estimating process of calculating a second exhaust gas temperature in which a temperature of the exhaust gas is estimated based on an operating state of the internal combustion engine;
• and
• execute an abnormality detecting process of detecting an abnormality in the regeneration process based on the first exhaust gas temperature that is detected by the exhaust gas temperature sensor and the second exhaust gas temperature calculated by the exhaust gas temperature estimating process in the midst of execution of the regeneration process.

A method for restoring a NOx purification capacity in an exhaust purification system having an internal combustion engine and a NOx reduction catalyst that is disposed on an exhaust passageway of the internal combustion engine to reduce and purify NOx in an exhaust gas, the method comprising:

• restoring the NOx purification capacity of the NOx reduction catalyst by controlling at least one of an intake air flow rate and a fuel injection amount of the internal combustion engine so as to make the exhaust gas rich;
• detecting a temperature of the exhaust gas as a first exhaust gas temperature;
• calculating a second exhaust gas temperature in which a temperature of the exhaust gas is estimated based on an operating state of the internal combustion engine;
• and
• detecting an abnormality in the regeneration process based on the first exhaust temperature and the second exhaust temperature in the midst of execution of the regeneration process.