Patent ID: 7086223

Claim:
An exhaust gas purification device of an internal combustion engine arranging a catalyst suitable for reduction of NOx in exhaust gas by ammonia in the presence of excess oxygen in an engine exhaust passage, said device comprising: feeding means for feeding a liquid containing an ammonia generating compound to the catalyst; feed control means for controlling the amount of feed of the liquid, the catalyst storing inside it at least part of the ammonia generating compound contained in the liquid fed to the catalyst and having the function of causing the release of ammonia a little at a time from the ammonia generating compound stored in the catalyst along with the rise of temperature of the catalyst and reducing the NOx in the exhaust gas by the ammonia released; decision means for deciding if the temperature of the catalyst is in an ammonia generating compound storage region which stores the ammonia generating compound contained in the liquid fed to the catalyst inside the catalyst and releases almost no ammonia from the stored ammonia generating compound, or if the temperature of the catalyst is in an ammonia release region which causes the ammonia to be released a little at a time from the stored ammonia generating compound; calculating means for calculating the amount of the ammonia generating compound stored in the catalyst per unit time and the amount of the ammonia released from the catalyst per unit time; and estimating means for estimating the amount of storage of the ammonia generating compound stored in the catalyst on the basis of a result of calculations by said calculating means; wherein said feed control means stops the feed of the liquid if the estimated amount of storage of the ammonia generating compound exceeds a predetermined maximum amount of storage when the temperature of the catalyst is lower than a temperature at which ammonia is released all at once from the catalyst, and said feed control means feeds the liquid irrespective of the amount of the liquid stored in the catalyst when the temperature of the catalyst is in a state where ammonia is released all at once from the catalyst.