Patent ID: 8978367
Filing Date: 2015-03-17
Classification: F01N,F02D,Y02A,Y02T

Abstract:
1. An exhaust gas purifying system of an internal combustion engine comprising: a selective reduction catalyst which is provided in an exhaust passageway of an internal combustion engine and has a function of reducing NOx under the presence of NH3 and absorbing any one of or both NO2 and a NO2 compound in the exhaust gas; a reducing agent supply device which supplies NH3 or its precursor to the selective reduction catalyst; an upstream catalyst which is provided at the upstream side of the selective reduction catalyst in the exhaust passageway and has a three-way purification function; a NOx correlation value calculating unit which calculates the value of a NOx correlation parameter that increases in response to the NOx discharge amount of the engine; an air-fuel ratio control unit which controls an air-fuel ratio of an air-fuel mixture to stoichiometry when the value of the NOx correlation parameter is larger than a stoichiometry determination threshold value; a NO2 storage amount estimating unit which calculates an NO2 storage amount corresponding to the amount of NO2 and a NO2 compound absorbed to the selective reduction catalyst; and a threshold value setting unit which sets the stoichiometry determination threshold value to a smaller value as the NO2 storage amount increases.