Patent ID: 7347043

Claim:
An exhaust gas purifier for an internal combustion engine, including an additive supplying unit supplying an additive to the exhaust gas, a catalyst device having a function of promoting oxidation of said additive, and an exhaust filter arranged downstream of said catalyst device and having functions of trapping particulate matter and of promoting oxidation of said additive, comprising: a processing unit increasing, when a condition for purifying the particulate matter trapped by said exhaust filter is satisfied, temperature of said exhaust filter to a target temperature by supplying the additive from said additive supplying unit; and a control unit changing the target temperature of said exhaust filter to a higher value, when deterioration of catalytic function of said catalyst device is detected, wherein said control unit determines, using temperature of exhaust gas in an exhaust passage downstream of said catalyst device and upstream of said exhaust filter as a reference exhaust gas temperature, that catalytic function of said catalyst device is deteriorated, when a degree of deviation between said reference exhaust gas temperature estimated based on a state of operation of said internal combustion engine and the reference exhaust gas temperature measured by an exhaust gas temperature sensor exceeds a reference value.