| 摘要 |
An EGR control device is provided with an EGR control valve ( 52 ) and an electronic control unit ( 60 ). An exhaust gas recirculation pipe ( 51 ) extends across the EGR control valve ( 52 ). The electronic control unit calculates a target EGR ratio, a target air flow rate, an actual EGR ratio, and an actual air flow rate, on the basis of operational state quantities of an engine. The electronic control unit then calculates, as a target converted EGR ratio, a ratio of the target EGR ratio to the target air flow rate, calculates, as an actual converted EGR ratio, a ratio of the actual EGR ratio to the actual air flow rate, and controls an opening of the EGR control valve such that the target converted EGR ratio becomes equal to the actual converted EGR ratio. An actual converted EGR ratio is proportional to an intake-air oxygen concentration, and an actual converted EGR ratio and a target converted EGR ratio are calculated independently of a command injection amount. Therefore, a desired intake-air oxygen concentration is obtained irrespective of flow rate characteristics of injection valves. |
