Importance

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Abstract

There is provided an exhaust gas recirculation control system and method and an engine control unit for an internal combustion engine, which is capable of properly controlling an exhaust gas recirculation rate in advance according to the NOx-eliminating performance of a catalyst, thereby reducing exhaust emissions. An internal combustion engine eliminates NOx in exhaust gases by a catalytic converter, and recirculates the exhaust gases into an intake pipe. An exhaust gas recirculation control system for the engine includes an ECU. The ECU calculates a NOx exhaust estimate based on the intake pipe absolute pressure and the engine rotational speed detected by the respective sensors, calculates an estimated NOx elimination ratio of the catalytic converter based on an estimated catalyst temperature and the space velocity through the catalytic converter. The ECU calculates an uneliminated NOx estimate based on the NOx exhaust estimate and the estimated NOx elimination ratio, and calculates a target valve lift amount of an EGR control valve based on the uneliminated NOx estimate.

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First Claim