Patent ID: 8857161

Claim:
An exhaust gas purification apparatus for an internal combustion engine comprising: NO x sensor that is arranged in an exhaust passage of the internal combustion engine and is configured to detect a concentration of NO x in an exhaust gas; an addition unit configured to add a reducing agent derived from ammonia as an additive agent into the exhaust passage; a catalyst that is arranged at a downstream side of the NO x sensor and the addition unit so as to receive a supply of the additive agent from the addition unit; and an electronic control unit having control logic that causes the electronic control unit to: determine whether detection accuracy of the NO x sensor drops due to the additive agent to be added from the addition unit; and stop the detection of the concentration of NO x in the exhaust gas by the NO x sensor in cases where it is determined by the electronic control unit that the detection accuracy of the NO x sensor drops.