Abstract: A control system for an internal combustion engine, which is capable of positively preventing a misfire or knocking during a compression ignition combustion mode by switching from the compression ignition combustion mode to a spark ignition combustion mode in appropriate timing. The engine is operated while switching between the compression ignition and spark ignition combustion modes. The control system (ECU) sets a target operating gas temperature to which the temperature of operating gases in a combustion chamber is to be controlled in the compression ignition combustion mode, sets a target internal EGR amount to which the internal EGR amount is to be controlled, such that the temperature of operating gases in the combustion chamber becomes equal to the target operating gas temperature, and switches the combustion mode to the spark ignition combustion mode depending on the target internal EGR amount.

Abstract: An internal EGR control system for an internal combustion engine, which is capable of controlling the internal EGR amount with accuracy, when controlling the internal EGR by changing both the exhaust cam phase and the exhaust valve lift. An internal EGR control system for an internal combustion engine controls internal EGR in which combustion gases are caused to remain in a cylinder. An ECU sets a target cam phase serving as a target of the exhaust cam phase, and controls a variable exhaust cam phase mechanism such that the exhaust cam phase becomes equal to the target cam phase. ECU 2 sets a target lift of an exhaust valve according to a detected actual cam phase and calculated valve-closing timing, and controls a variable exhaust valve lift mechanism such that the lift of the exhaust valve becomes equal to the target lift.