The present invention is intended to provide a control system for an direct injection internal combustion engine capable of effectively reducing the amounts of both HC and NOx exhausted from a combustion chamber during a period from the start of the engine operation to the stop of the engine operation. It comprises an external EGR passage (11) for returning a part of exhaust gas from an exhaust pipe (10) to an intake pipe (5), an external EGR control valve (12) for controlling an amount of exhaust gas returned to the external EGR passage (11), and a valve timing varying mechanism (9A, 9B) for varying timing of opening and closing at least one of an intake valve and an exhaust valve. An ECU 100 controls the valve timing varying mechanism (9A, 9B) to always return internal EGR gas in an operation region where exhaust gas recirculation is required, and controls the external EGR control valve (12) to return exhaust gas in a combination of internal EGR and external EGR when an internal EGR rate provided by the valve timing varying mechanism (9A, 9B) is not sufficient to satisfy an EGR rate demanded depending on an operation state.
An EGR control system that is capable of controlling the amount of recirculation of high-temperature and low-temperature recirculated gases, with high accuracy, to thereby improve the control accuracy of in-cylinder temperature. An ECU of an ERG control system calculates a fresh intake air ratio, and sets a target value of the fresh intake air ratio. The ECU calculates a feedback correction coefficient for converging the fresh intake air ratio to the target value, with an I-PD control algorithm, and sets an external EGR ratio and an internal EGR ratio. The ECU controls the EGR amount whose ratio is the larger, according to the larger one of the two ratios and the feedback correction coefficient, and controls the EGR amount whose ratio is the smaller, according to the smaller of the ratios and the learned value thereof.
