New Concept Adaptive Controls for A High-Performance and High-Efficiency Engine

Continuously variable valve lift system (CVTL) can improve the fuel consumption of gasoline engines by reducing of pumping losses, and provide better torque and power characteristics than basic engines using throttles by the optimization of intake valve lift, opening and closing according to engine load and speed conditions. However, the conventional idle speed controller based on PID algorithm could not provide sufficient control performance of engine speed by using only CVTL. CVTL causes the dispersion of air-fuel ratio of combustion gas between cylinders. This deteriorates the control performance of air-fuel ratio and the conversion rate of a catalyst. In this research, new concept idle speed control using CVTL and ignition timing was designed by using cooperated algorithm based on a two-degree-of-freedom sliding-mode control. Moreover, the air-fuel ratio control on the basis of the output of switching lambda sensor downstream of the catalyst was re-designed by inserting delta-sigma modulator. These new controls were applied to an actual engine equipped with CVTL. As a result, the control performance of idle speed control was sufficiently improved without using any assistance of throttle, and the convergence behavior of the output of switching lambda sensor to an optimal set point was dramatically improved.