Cam-less electro-hydraulic variable valve actuation (EHVVA) systems offer full flexibility in regulating gas exchange processes, with strong potential for improving engine efficiency and reducing emissions. However, the lack of stable cycle-to-cycle valve operation has hindered their practical deployment. This study introduces a cycle-based closed-loop control strategy for precise and stable regulation of valve opening duration. Novel event-detection algorithms were developed to accurately identify valve timings from valve lift measurements, which provide direct feedback for the controller. Comparative experiments under diverse operating conditions demonstrate that the proposed method reduces steady-state errors by up to 55.2% and significantly improves cycle-to-cycle stability compared with open-loop control. Real-time tests further confirm robust adaptability to transient events such as engine startup and load variations. These findings verify the feasibility of fully flexible valve duration control in cam-less systems and highlight the potential of EHVVA technology to enhance combustion stability, support load management, and contribute to efficiency gains and emission reductions in next-generation high-efficiency engines.
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