| 摘要 |
PURPOSE:To improve operability and surely decrease a discharge quantity of NOx by detecting concentration of the NOx in exhaust gas, and controlling an air-fuel ratio within a range between lean limitation of burn variation and allowable limitation of the discharge quantity of the NOx. CONSTITUTION:A burn variation condition is calculated by a burn variation rate calculation means 24 from the detected result of inter-cylinder pressure in an engine main body, and a discharge quantity of NOx in an engine is calculation by a NOx discharge quantity calculation 29 from the detected result of the NOx concentration in the exhaust gas. A burn variation condition is judged (27) by a calculated burn variation rate and a standard rate of the burn variation rate subjected to map-retrieving, and the NOx discharged condition is judged (32) by the calculated NOx discharge quantity and the standard value of the NOx discharge quantity subjected to map-retrieving. An air-fuel ratio is subjected to rich correction when the burn variation rate becomes larger than the standard value of the lean limitation, and then the air-fuel ratio is subjected to lean correction when the NOx discharged quantity becomes larger than the standard value of the allowable limitation of the NOx discharge quantity under respective operation conditions. |
