Exhaust gas purification system abnormality diagnosing device and abnormality diagnosing method, and exhaust gas purification system

An exhaust gas purification system including an abnormality diagnosing device for diagnosing an abnormality occurring in an exhaust gas purification system equipped with a selective reduction catalyst that is capable of adsorbing ammonia and is for using the ammonia to reduce NOx in exhaust gas emitted from an internal combustion engine, the exhaust gas purification system comprising:

• a specified gas concentration sensor that is disposed on a downstream side of the selective reduction catalyst and responds at least to the NOx and the ammonia;
• a sensor value detecting means that reads a sensor signal of the specified gas concentration sensor to detect a gas concentration;
• a limiting device controlling means which, when the gas concentration has become equal to or greater than a predetermined start-of-diagnosis threshold value or when a difference obtained by subtracting from the gas concentration an estimated NOx concentration on the downstream side of the selective reduction catalyst obtained by computation has become equal to or greater than a predetermined start-of-diagnosis threshold value, increases the quantity of the ammonia capable of being adsorbed by the selective reduction catalyst by raising the pressure inside the exhaust gas passageway with a passageway area limiting device disposed on the downstream side of the selective reduction catalyst;
• and
• a determining means that determines the abnormal state in which abnormal outflows of ammonia or NOx are occurring on the basis of the gas concentration detected downstream of the selective reduction catalyst or the difference obtained by subtracting from the gas concentration detected downstream of the selective reduction catalyst and an estimated NOx concentration on the downstream side of the selective reduction catalyst obtained by computation after the pressure inside the exhaust gas passageway has been raised;
• and
• a reducing agent supply device that supplies a reducing agent derived from the ammonia to the inside of an exhaust gas passageway on an upstream side of the selective reduction catalyst, wherein an operation of the reducing agent supply device is modified based on the determination of the determining means.

An exhaust gas purification system abnormality diagnosing method for diagnosing an abnormality occurring in an exhaust gas purification system equipped with a selective reduction catalyst that is capable of adsorbing ammonia and is for using the ammonia to reduce NOx in exhaust gas emitted from an internal combustion engine, a reducing agent supply device that supplies a reducing agent derived from the ammonia to the inside of an exhaust gas passageway on an upstream side of the selective reduction catalyst, and a specified gas concentration sensor that is disposed on a downstream side of the selective reduction catalyst and responds at least to the NOx and the ammonia, the exhaust gas purification system abnormality diagnosing method comprising:

• raising the pressure inside the exhaust gas passageway with a passageway area limiting device disposed on the downstream side of the selective reduction catalyst to increase the quantity of the ammonia capable of being adsorbed by the selective reduction catalyst when a gas concentration detected by the specified gas concentration sensor has become equal to or greater than a predetermined start-of-diagnosis threshold value or when a difference obtained by subtracting from the gas concentration an estimated NOx concentration on the downstream side of the selective reduction catalyst obtained by computation has become equal to or greater than a predetermined start-of-diagnosis threshold value,
• determining the abnormal state in which abnormal outflows of ammonia or NOx are occurring on the basis of the gas concentration detected downstream of the selective reduction catalyst or the difference obtained by subtracting from the gas concentration detected downstream of the selective reduction catalyst and an estimated NOx concentration on the downstream side of the selective reduction catalyst obtained by computation, and
• operating the reducing agent supply device based on the determination of the step of determining.