Modeling and control of an electric variable valve timing system for SI and HCCI combustion mode transition

This paper models an electric variable valve timing (VVT) system and develops the corresponding controller for the electric VVT system. The studied electric VVT uses a planetary gear system for engine cam timing control; and a cyclic torque disturbance is applied to the cam shaft. The main motivation of utilizing the electric VVT system is for the mode transition control between the spark ignited (SI) and homogeneous charge compression ignition (HCCI) combustions due to its fast response time. During the combustion mode transition between SI and HCCI operations, it is required for the engine cam timing to follow a desired trajectory to make the smooth combustion mode transition possible. This is mainly due to the fact that the engine valve timings effect the engine recompression operation that is directly associated with the start of HCCI combustion. A control oriented electric VVT model was developed and closed-loop control strategies were developed to maintain the cam phase at a desired level, as well as to follow a desired trajectory during the combustion mode transition. Simulation results are included.