INTERNAL COMBUSTION ENGINE CONTROL METHOD AND CONTROL DEVICE

PROBLEM TO BE SOLVED: To eliminate a possibility that at the time of reduction of EGR where a target EGR rate is reduced, combustion becomes unstable under influence of EGR gas left in an intake passage.SOLUTION: A fresh mixture supply passage 41 capable of supplying fresh mixture not including EGR gas is arranged at one of cylinder groups #1, #3 of odd-number combustion order or cylinder groups #2, #4 of even-number combustion order. At the time of low EGR where a target EGR rate set in response to an engine operating state, an EGR control vale 28 is controlled to be closed in response to a reduction of the target EGR rate. At this time, a fresh mixture flow rate control valve 42 arranged at the fresh mixture supply passage 41 is opened and the fresh mixture gas not containing the EGR gas is supplied to one group of cylinders to continue combustion state and the other group of cylinders stop the combustion.SELECTED DRAWING: Figure 1 【課題】目標ＥＧＲ率が低下するＥＧＲ低下時には、吸気通路内に残存するＥＧＲガスの影響で燃焼が不安定になるおそれがある。【解決手段】燃焼順序が奇数番目の気筒群＃１，＃４又は偶数番目の気筒群＃２，＃３の一方に、ＥＧＲガスを含まない新気を供給可能な新気供給通路４１を設ける。機関運転状態に応じて設定される目標ＥＧＲ率が低下するＥＧＲ低下時には、目標ＥＧＲ率の低下に応じてＥＧＲ制御弁２８を閉じる方向に制御する。このとき、新気供給通路４１に設けた新気流量制御弁４２を開いて一方の気筒群に対してＥＧＲガスを含まない新気を供給し、燃焼を継続させる一方、他方の気筒群では燃焼を停止させる。【選択図】図１