Patent ID: 7685812

Claim:
An exhaust purification device for an internal combustion engine having, a NO x storing catalyst arranged in an engine exhaust passage, the NO x storing catalyst being comprised of a precious metal catalyst and a NO x absorbent and, when an air-fuel ratio of inflowing exhaust gas is lean, cold storing nitrogen dioxide NO 2 contained in the exhaust gas in the NO x absorbent when not activated and hot storing cold stored nitrogen dioxide NO 2 in the NO x absorbent when activated, said exhaust purification device for an internal combustion engine making the nitrogen dioxide NO 2 contained in the exhaust gas be cold stored in the NO x absorbent in the state where said NO x storing catalyst is not activated and executing a NO x storing catalyst restoring control including at least raising the temperature of said NO x storing catalyst to a predetermined temperature to activate it when a predetermined NO x storing catalyst restoring condition is met so as to restore the cold storing capability of said NO x absorbent in the state where said NO x storing catalyst is not activated, wherein said NO x storing catalyst is a NO x storing catalyst having the function of hot storing nitrogen oxides NO x contained in exhaust gas in the NO x absorbent when said NO x storing catalyst is activated and the air-fuel ratio of the exhaust gas flowing into the NO x storing catalyst is lean, said device has a NO x release speed estimating means for estimating a release speed of nitrogen oxides NO x from said NO x absorbent when making said NO x storing catalyst said predetermined temperature and a NO x storing speed estimating means for estimating a storing speed of nitrogen oxides NO x to said NO x absorbent when making said NO x storing catalyst said predetermined temperature, and said NO x storing catalyst restoring condition is deemed to be met when the NO x release speed estimated by said NO x release speed estimating means becomes greater than or equal to a predetermined speed set to not more than said NO x storing speed based on the NO x storing speed estimated by said NO x storing speed estimating means.