Air-fuel ratio control system for internal combustion engine

An air-fuel ratio control system for an internal combustion engine, comprising:

• an engine condition detecting unit detecting an engine operating condition of the internal combustion engine;
• a throttle valve varying a real intake air quantity of air to be supplied to the internal combustion engine;
• a fuel injector injecting a real fuel injection quantity of fuel into each combustion chamber of the internal combustion engine;
• and
• a control unit coupled to the engine condition detecting unit, the throttle valve and the fuel injector, the control unit being arranged,
• to calculate a target engine torque on the basis of the engine operating condition;
• to calculate a target EGR ratio, a target excess air ratio and a target intake air quantity on the basis of the engine operating condition and the target engine torque,
• to calculate a target equivalence ratio on the basis of the target EGR ratio and the target excess air ratio,
• to calculate a target injection quantity on the basis of the engine operating condition and the target equivalence ratio,
• to control the throttle valve and the fuel injector so as to bring the real intake air quantity to the target intake air quantity and to bring the real fuel injection quantity to the target fuel injection quantity.

An air-fuel ratio control system for an internal combustion engine, comprising:

• engine operating condition detecting means for detecting an engine operating condition of the internal combustion engine;
• first calculating means for calculating a target engine torque on the basis of the engine operating condition;
• second calculating means for calculating a target EGR ratio, a target excess air ratio and a target intake air quantity on the basis of the engine operating condition and the target engine torque;
• third calculating means for calculating a target equivalence ratio on the basis of the target EGR ratio and the target excess air ratio;
• fourth calculating means for calculating a target injection quantity on the basis of the engine operating condition and the target equivalence ratio;
• and
• controlling means for controlling an air-fuel ratio at a desired value by bringing a real intake air quantity to the target intake air quantity and by bringing a real fuel injection quantity to the target fuel injection quantity.

A method for controlling an air-fuel ratio of an internal combustion engine, comprising:

• detecting an engine operating condition of the internal combustion engine;
• calculating a target engine torque on the basis of the engine operating condition;
• calculating a target EGR ratio, a target excess air ratio and a target intake air quantity on the basis of the engine operating condition and the target engine torque;
• calculating a target equivalence ratio on the basis of the target EGR ratio and the target excess air ratio;
• calculating a target injection quantity on the basis of the engine operating condition and the target equivalence ratio;
• and
• controlling an air-fuel ratio at a desired value by bringing a real intake air quantity to the target intake air quantity and by bringing a real fuel injection quantity to the target fuel injection quantity.