Modeling and Control of an Electric Variable Valve Timing System

This paper presents a model of an electric variable valve timing (EVVT) system and its closed-loop control design with experimental validation. The studied EVVT uses a planetary gear system to control the engine cam timing. The main motivation of utilizing the EVVT system is its fast response time and the accurate timing control capability. This is critical for the combustion mode transition control between the spark ignition (SI) and homogeneous charge compression ignition (HCCI) combustion, where the engine cam timing needs to follow a desired trajectory to accurately control the engine charge and recompression process. A physics-based model was developed to study the characteristics of the EVVT system, and a control oriented EVVT model, with the same structure as the physics-based one, was obtained using closed-loop system identification. The closed-loop control strategies were developed to control the EVVT to follow a desired trajectory. Both simulation and bench test results are included.