Patent ID: 10465579

Abstract:
When the temperature of an NSR catalyst belongs to a specified NSR temperature range and the temperature of an SCR catalyst belongs to a specified SCR temperature range, urea water is added, and specified air-fuel ratio processing relating to an air-fuel ratio of exhaust gas flowing into the NSR catalyst is executed. The specified air-fuel ratio processing includes i) a first air-fuel ratio processing to cause the air-fuel ratio of the exhaust gas flowing into the NSR catalyst to be a first lean air-fuel ratio that causes emission of occluded NOx from the NSR catalyst and ii) a second air-fuel ratio processing to cause the air-fuel ratio of the exhaust gas to be a second lean air-fuel ratio leaner than the first lean air-fuel ratio. In the specified air-fuel ratio processing, the first air-fuel ratio processing and the second air-fuel ratio processing are alternately repeated.