Abnormality diagnosis system for an exhaust gas purification apparatus

An abnormality diagnosis system for an exhaust gas purification apparatus which includes:

• an NOx selective reduction catalyst that is arranged in an exhaust passage of the internal combustion engine, and reduces NOx in an exhaust gas by using ammonia as a reducing agent;
• and
• an ammonia supply device that is arranged in the exhaust passage at the upstream side of the NOx selective reduction catalyst, and supplies ammonia to the NOx selective reduction catalyst;
• wherein the abnormality diagnosis system is applied to the exhaust gas purification apparatus;
• wherein
• the abnormality diagnosis system comprising:
• an ammonia sensor that detects a concentration of ammonia in the exhaust gas at the downstream side of the NOx selective reduction catalyst;
• and
• a controller comprising at least one processor configured to carry out an abnormality diagnosis of the NOx selective reduction catalyst, wherein
• the controller
• estimates a first estimated adsorption amount which is an amount of adsorption of ammonia in the NOx selective reduction catalyst at the time when the NOx selective reduction catalyst is assumed to be in a predetermined abnormal state;
• estimates a second estimated adsorption amount which is an amount of adsorption of ammonia in the NOx selective reduction catalyst at the time when the NOx selective reduction catalyst is assumed to be in a predetermined normal state;
• calculates, based on the first estimated adsorption amount, a first slip development temperature which is a temperature of the NOx selective reduction catalyst at which ammonia begins to slip from the NOx selective reduction catalyst in the case where the NOx selective reduction catalyst is in the predetermined abnormal state;
• calculates, based on the second estimated adsorption amount, a second slip development temperature which is a temperature of the NOx selective reduction catalyst at which ammonia begins to slip from the NOx selective reduction catalyst in the case where the NOx selective reduction catalyst is in the predetermined normal state;
• carries out diagnostic temperature control to control the temperature of the NOx selective reduction catalyst to a temperature which is equal to or higher than the first slip development temperature and is less than the second slip development temperature, at the time of carrying out the abnormality diagnosis of the NOx selective reduction catalyst;
• and
• carries out the abnormality diagnosis of the NOx selective reduction catalyst based on the concentration of ammonia detected by the ammonia sensor when the diagnostic temperature control is carried out.