| 摘要 |
PROBLEM TO BE SOLVED: To conduct prompt switching of combustion mode while preventing deterioration of combustion stability or emission at a transition stage of combustion mode switching. SOLUTION: An engine control unit is provided with; a circulating gas concentration detector (air/fuel ratio calculating means in an EGR tube) 60s for obtaining circulating gas concentration which is equivalent to the air/fuel ratio in the EGR gas, in the vicinity of an EGR valve during a transition stage for switching between a lean state in which the air/fuel ratio in a combustion chamber is larger than a theoretical air/fuel ratio, and a rich state in which the air/fuel ratio in the combustion chamber is smaller than a substantially theoretical air/fuel ratio or a theoretical air/fuel ratio; and an emission circulation rate corrector 60t for correcting the circulation rate of emission, which compares the circulating gas concentration with a target air/fuel ratio in the combustion chamber in the transition stage, and as a result drives the EGR valve in the direction of reducing valve travel in the case where the circulating gas concentration is larger than the target air/fuel ratio, and drives the EGR valve in the direction of increasing valve travel in the case where the circulating gas concentration is smaller than the target air/fuel ratio. COPYRIGHT: (C)2003,JPO
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