Control System Design for an Electrohydraulic Fully Flexible Valve Actuator with Mechanical Feedback for a Camless Engine

This paper deals with the control system design of an electrohydraulic fully flexible valve actuator (EHVA) with a mechanical feedback for a camless engine. A model of the actuator was obtained using a frequency response identification method in a closed loop configuration from which a fifth-order linear model was subsequently derived. The problem was formulated using quantitative feedback theory (QFT), primarily because of the presence of structured as well as unstructured uncertainties. Results show improved results at the low-speed range but not at the high-speed range. This was due to several factors one of which was the introduction of significant lag into the system due to the need to have an underlap at the low- pressure port of the spool valve and an overlap at the high-pressure port.