| 摘要 |
<p>PURPOSE:To keep high level NOx reduction effect in a high load area of an engine which is provided with a means for varying a valve overlapping time of an intake valve and an exhaust valve. CONSTITUTION:A valve overlapping time where an intake valve and an exhaust valve are closed at the same time is set small in a low speed low load area, for securing stability in combustion. On the other hand, a large valve overlapping time is provided in a partial load area II, so that NOx and pumping loss are reduced by means of a large amount of inner EGR. When a load in the partial load area is smaller than a specified load L2, a theoretical air-fuel ratio is set. When the load is equal to the specified load L2, an equation for showing NOx reduction effect, for instance, A/F=21, is set. When the load exceeds the specified load L2, a lean degree is gradually increased according to increase of the load. Accordingly, when the load is not less than the specified load L2, NOx is reduced through a leaned condition of an air-fuel ratio.</p> |
