Patent ID: 8099950

Claim:
An exhaust gas purifying apparatus for an internal combustion engine comprising: an additive fuel injector that adds fuel into an exhaust passage, a catalyst providing an oxidation function, a first air-to-fuel ratio sensor that measures an air-to-fuel ratio, a NOx catalyst that occludes and reduces NOx, and a second air-to-fuel ratio sensor that measures an air-to-fuel ratio, the additive fuel injector, the catalyst, the first air-to-fuel ratio sensor, the NOx catalyst, and the second air-to-fuel ratio sensor being arranged in the exhaust passage in sequence from an upstream side of the exhaust passage; a setting unit that sets commanded values of an amount and a period of injection from the additive fuel injector such that an air-to-fuel ratio within the exhaust passage is a target air-to-fuel ratio that is leaner than a theoretical air-to-fuel ratio; an adding controlling unit that injects fuel from the additive fuel injector for a predetermined period in accordance with the commanded values set by the setting unit; a determining unit that determines whether or not a high-accuracy measurement state has been entered in which a difference between a measurement value of the first air-to-fuel ratio sensor and a measurement value of the second air-to-fuel ratio sensor is within a predetermined range, during a period in which the air-to-fuel ratio within the exhaust passage is affected by the injection of fuel by the adding controlling unit; a calculating unit that calculates, when the determining unit determines that the high-accuracy measurement state has been entered, a deviation between the commanded value and a true value of the amount of injection in the injection by the adding controlling unit as a correction value of the amount of injection, from at least one of the measurement value of the first air-to-fuel ratio sensor and the measurement value of the second air-to-fuel ratio sensor; and a correcting unit that adds the correction value to the commanded value of the amount of injection.