Patent ID: 9631535
Date: 2017-04-25
CPC Classifications: F01N,Y02C,Y02T

Claim:
1. A method of purifying exhaust gas exhausted from an internal combustion engine comprising an exhaust purification catalyst arranged in an engine exhaust passage and a hydrocarbon feed valve arranged in the engine exhaust passage upstream of the exhaust purification catalyst, a precious metal catalyst being carried on an exhaust gas flow surface of the exhaust purification catalyst, a basic layer being formed around the precious metal catalyst, and an air-fuel ratio of an exhaust gas flowing into the exhaust purification catalyst being made rich when releasing NO x which is stored in the basic layer from the exhaust purification catalyst, wherein when releasing the stored NOx from the exhaust purification catalyst, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is made rich by generating combustion gas of a rich air-fuel ratio in a combustion chamber or the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is made rich by injecting hydrocarbons from the hydrocarbon feed valve into the engine exhaust passage, wherein, for the temperature of the exhaust purification catalyst, an allowable lowest temperature which enables release of the stored NOx from the exhaust purification catalyst by generating the combustion gas of a rich air-fuel ratio in the combustion chamber and upper limit temperature higher than said allowable lowest temperature are set in advance, and wherein, when the temperature of the exhaust purification catalyst is between said allowable lowest temperature and said upper limit temperature, an amount of injection of hydrocarbons from the hydrocarbon feed valve is made greater as compared with when the temperature of the exhaust purification catalyst is higher than said upper limit temperature.