Method for estimating exhaust gas state of engine, method for determining abnormality of catalyst, and catalyst abnormality determination device for an engine

A non-transitory computer readable medium including executable instructions, which when executed by a computer cause the computer to execute a method, the method comprising:

• estimating an ammonia adsorption amount of a NOx selective reduction catalyst, the NOx selective reduction catalyst being provided in an exhaust passage of an engine, the NOx selective reduction catalyst reducing NOx in an exhaust gas by using a supplied reducing agent, ammonia or a precursor of the ammonia being supplied as the reducing agent to the NOx selective reduction catalyst by a reducing agent supplier;
• detecting a catalytic temperature of the NOx selective reduction catalyst;
• and
• estimating a slip amount of ammonia that is an amount of ammonia discharged into a portion of the exhaust passage on a downstream side of the NOx selective reduction catalyst based on the estimated ammonia adsorption amount and the detected catalytic temperature, wherein
• in the estimating of the slip amount of ammonia, for a same catalytic temperature, the slip amount of ammonia is estimated to be larger in a case where the estimated ammonia adsorption amount is a first value than in a case where the estimated ammonia adsorption amount is a second value that is smaller than the first value, and
• in the estimating of the slip amount of ammonia, for a same estimated ammonia adsorption amount, the slip amount of ammonia is estimated to be larger in a case where the detected catalytic temperature is a third value than in a case where the detected catalytic temperature is a fourth value that is smaller than the third value.

A device, comprising:

• a catalytic temperature detector configured to detect a temperature of a NOx selective reduction catalyst, the NOx selective reduction catalyst being provided in an exhaust passage of an engine, the NOx selective reduction catalyst reducing NOx in an exhaust gas by using a supplied reducing agent, ammonia or a precursor of the ammonia being supplied as the reducing agent to the NOx selective reduction catalyst by a reducing agent supplier;
• a NOx sensor that is disposed in the portion of the exhaust passage on the downstream side of the NOx selective reduction catalyst, an output value of the Nox sensor varying in accordance with an amount of NOx and an amount of ammonia in the exhaust gas;
• and
• processing circuitry configured to
• estimate an ammonia adsorption amount of the NOx selective reduction catalyst;
• estimate a slip amount of ammonia that is an amount of ammonia discharged into a portion of the exhaust passage on a downstream side of the NOx selective reduction catalyst based on the estimated ammonia adsorption amount and the detected catalytic temperature;
• perform an abnormality determination on whether the NOx selective reduction catalyst is abnormal based on the output value of the NOx sensor;
• and
• restrict the abnormality determination in a case where the estimated slip amount of ammonia is equal to or larger than a specified slip amount, wherein
• in the estimating of the slip amount of ammonia, for a same catalytic temperature, the slip amount of ammonia is estimated to be larger in a case where the estimated ammonia adsorption amount is a first value than in a case where the estimated ammonia adsorption amount is a second value that is smaller than the first value, and
• in the estimating of the slip amount of ammonia, for a same estimated ammonia adsorption amount, the slip amount of ammonia is estimated to be larger in a case where the detected catalytic temperature is a third value than in a case where the detected catalytic temperature is a fourth value that is smaller than the third value.