Engine control device

An engine control device for controlling an engine provided with a fuel injection valve for injecting fuel directly into a combustion chamber of the engine, an ignition timing controller for controlling ignition timing, an NOx-absorbing material arranged in an exhaust passage for discharging exhaust gas from the combustion chamber for absorbing NOx in an oxygen-rich atmosphere, and releasing NOx and absorbing sulfur content when the oxygen concentration drops, and an air-fuel ratio controller for controlling an air-fuel ratio, the engine control device comprising:

• a NOx-absorbing state judging unit for judging whether the amount of NOx absorbed in the NOx-absorbing material has reached a predetermined quantity;
• a NOx releasing controller for switching the air-fuel ratio from lean to rich over a first period of time to release the absorbed NOx from the NOx-absorbing material;
• an absorbed sulfur state judging unit for judging whether the amount of sulfur absorbed by the NOx-absorbing material has reached a predetermined quantity;
• a sulfur absorbing state judging unit for judging whether the amount of sulfur absorbed in the NOx-absorbing material has reached a predetermined quantity;
• and
• a desulfurization controller for causing the fuel injection valve to inject the fuel at least twice during a time period from an intake stroke to a succeeding compression in such a manner as to retard the ignition timing more in high-load condition than in the low-load condition over a second period of time that is longer than the first period of time to release the absorbed sulfur from the NOx-absorbing material when the amount of sulfur absorbed in the NOx-absorbing material is judged by the absorbed sulfur state judging unit to have reached the predetermined quantity.