Control system for internal combustion engine

A control system for an internal combustion engine, for controlling internal EGR in which combustion gases are caused to remain in a cylinder by closing an exhaust valve before a piston reaches a top dead center, the engine having as a combustion mode, a homogeneous combustion mode and a stratified combustion mode, the system comprising:

• an exhaust-side variable valve-operating mechanism that controls an internal EGR amount by changing valve-closing timing of the exhaust valve;
• an intake-side variable valve-operating mechanism that changes valve-opening timing of an intake valve of the engine;
• target valve-opening timing-setting means for setting target valve-opening timing serving as a target of the valve-opening timing of the intake valve, such that length of a time period from the top dead center of the piston to the valve-opening timing of the intake valve becomes equal to length of a time period from the valve-closing timing of the exhaust valve to the top dead center;
• control means for controlling said intake-side variable valve-operating mechanism based on the set target valve-opening timing;
• operating condition-detecting means for detecting an operating condition of the engine;
• switching determining means for determining whether or not the combustion mode is being switched;
• target valve-closing timing-setting means for setting target valve-closing timing serving as a target of the valve-closing timing of the exhaust valve, according to the detected operating condition of the engine;
• and
• actual valve-closing timing-detecting means for detecting actual valve-closing timing of the exhaust valve,
• wherein said target valve-opening timing-setting means uses one of the actual valve-closing timing and the target valve-closing timing of the exhaust valve as the valve-closing timing of the exhaust valve, based on a result of comparison between the actual valve-closing timing and the target valve-closing timing of the exhaust valve, and
• wherein said target valve-opening timing-setting means calculates an average value of a difference between the actual valve-closing timing and the target valve-closing timing of the exhaust valve, and when it is determined that the combustion mode is being switched, uses a value obtained by adding the average value to the target valve-closing timing of the exhaust valve, as the valve-closing timing of the exhaust valve.