Adaptive Air-fuel Ratio Controls for Continuously Variable Valve Lift Gasoline Engines

Engines equipped with continuously variable valve lift (CVTL) system can improve the fuel consumption of gasoline engines and provide better torque and power characteristics than conventional engines using variable cam phasing or switcthable valve timing and lift mechanisms. However, the relationship between the intake valve lift and suction air volume to the cylinders changes drastically at low valve lift and low engine speed conditions. This causes air-fuel ratios between cylinders to differ and deteriorates control performance of the airfuel ratio during transient operations. These in turn reduce the catalyst conversion rate.

The purpose of this research is aimed at improving the control performance of the air-fuel ratio with a redesigned secondary O₂ feedback system using a delta-sigma modulation algorithm and a feed-forward compensation algorithm for suction air volume.