Patent ID: 7832199

Claim:
An exhaust purification system for an internal combustion engine comprising: a storage-reduction type NOx catalyst that is disposed in an exhaust passage of said internal combustion engine and purifies NOx in exhaust; a reducer-adding unit that is disposed on an upstream side of said storage-reduction type NOx catalyst in said exhaust passage and adds a reducer to exhaust; and an exhaust amount-reducing unit that reduces an amount of exhaust flowing to said storage-reduction type NOx catalyst, wherein a reduction treatment of NOx is performed for said storage-reduction type NOx catalyst by at least said reducer-adding unit adding said reducer to exhaust while said exhaust amount-reducing unit reduces said amount of exhaust flowing to said storage-reduction type NOx catalyst, said exhaust purification system for an internal combustion engine further comprising: an upstream-side air-fuel ratio detecting unit that is disposed upstream of said storage-reduction type NOx catalyst in said exhaust passage and downstream of said reducer-adding unit, and that detects an air-fuel ratio of exhaust; and a downstream-side air-fuel ratio detecting unit that is disposed downstream of said storage-reduction type NOx catalyst in said exhaust passage, and that detects an air-fuel ratio of exhaust, wherein said reducer-adding unit changes a reducer-adding timing, such that a difference between an air-fuel ratio value detected by said upstream-side air-fuel ratio detecting unit and an air-fuel ratio value detected by said downstream-side air-fuel ratio detecting unit, during a predetermined period subsequent to said reducer-adding unit adding said reducer, becomes a predetermined target value.