Egr control device and method for internal combustion engine

An EGR control device for an internal combustion engine comprising:

• an EGR passage through which an exhaust passage and an intake passage of the internal combustion engine communicate with each other;
• an EGR control valve across which the EGR passage extends and which controls a flow rate of EGR gas flowing from the exhaust passage to the intake passage;
• and
• an EGR controller that:
• acquires an operational state quantity of the engine;
• determines, on the basis of the detected operational state quantity, a target value of an EGR ratio, namely, a ratio of a flow rate of EGR gas sucked by the engine to a flow rate of gas sucked by the engine, as a target EGR ratio;
• determines, on the basis of the detected operational state quantity, a target value of a flow rate of air sucked by the engine, as a target air flow rate;
• acquires a true EGR ratio on the basis of the detected operational state quantity, as an actual EGR ratio;
• acquires, on the basis of the detected operational state quantity, an actual flow rate of air sucked by the engine, as an actual air flow rate;
• and
• defines a target converted EGR ratio as a value corresponding to a ratio of the target EGR ratio to a target excessiveness ratio as being a ratio of the target air flow rate to a command injection amount, and an actual converted EGR ratio as a value corresponding to a ratio of the actual EGR ratio to an actual excessiveness ratio as being a ratio of the actual air flow rate to the command injection amount,
• and controls an actual EGR ratio by controlling an opening of the EGR control valve in accordance with the converted actual EGR ratio and the target converted EGR ratio.

An EGR control method for an internal combustion engine provided with an EGR passage through which an exhaust passage and an intake passage of the internal combustion engine communicate with each other, and with an EGR control valve across which the EGR passage extends and which controls a flow rate of EGR gas flowing from the exhaust passage to the intake passage, comprising the steps of:

• acquiring an operational state quantity of the engine;
• determining, on the basis of the detected operational state quantity, a target value of an EGR ratio, namely, a ratio of a flow rate of EGR gas sucked by the engine to a flow rate of gas sucked by the engine, as a target EGR ratio;
• determining, on the basis of the detected operational state quantity, a target value of a flow rate of air sucked by the engine, as a target air flow rate;
• acquiring a true EGR ratio on the basis of the detected operational state quantity, as an actual EGR ratio;
• acquiring, on the basis of the detected operational state quantity, an actual flow rate of air sucked by the engine, as an actual air flow rate;
• and
• defining a target converted EGR ratio as a value corresponding to a ratio of the target EGR ratio to a target excessiveness ratio as being a ratio of the actual air flow rate to a command injection amount, and an actual converted EGR ratio as a value corresponding to a ratio of the actual EGR ratio to an actual excessiveness ratio as being a ratio of the actual air flow rate to the command injection amount, and
• controlling an actual EGR ratio by controlling an opening of the EGR control valve in accordance with the actual converted EGR ratio and the target converted EGR ratio.