Combustion control system for internal combustion engine adaptable to on and off of exhaust gas recirculation

For an internal combustion engine having an intake passage, an exhaust passage, and an exhaust gas recirculation system including an exhaust gas recirculation passage for recirculating exhaust gas from said exhaust passage to said intake passage, an exhaust gas recirculation control valve powered by a difference between atmospheric pressure and intake pressure in said intake passage for variably throttling said exhaust gas recirculation passage, and an exhaust gas recirculation on-off valve selectively put on or off so as, when put on, to supply said intake pressure to said exhaust gas recirculation control valve and, when put off, to interrupt supply of said intake pressure to said exhaust gas recirculation control valve,

• a combustion control system comprising:
• first means for determining a basic quantity of engine control parameter according to said intake pressure,
• second means selectively put on and off so as, when put on, to modify said basic quantity of engine control parameter so as thereby to provide a modified quantity of engine control parameter for adaptation to operation of the engine with exhaust gas recirculation and, when put off, to undo such modification to the basic quantity of engine control parameter, and
• third means for delaying the putting on and off of said second means from the time point of putting on and off of said exhaust gas recirculation on-off valve for a variable time duration determined according to the difference between atmospheric pressure and intake pressure of the engine in such a manner that said variable time duration is smaller as said difference is larger.