Advanced modeling ,control, and design of an electromechanical engine value drive system with a limited-angle actuator

Abstract

This thesis addresses a specific variable valve actuation (VVA) system ---- an electromechanical valvetrain ---- in order to provide variable valve timing (VVT) in internal combustion (IC) engines. This electromechanical valve drive (EMV) system was proposed by Dr. Woo Sok Chang and his colleagues in the Laboratory for Electromagnetic and Electronic Systems (LEES), who also validated the feasibility of the design to provide VVT. The goal of this thesis is to bring the MIT EMV system to a more practical level by achieving a smaller package (to fit in the limited space over the engine head), a faster transition time (to accommodate faster engine speed), and a lower power consumption, while still offering satisfactory valve transitions with timing control. This thesis reports four major achievements. First, a more accurate system model, including dynamics, loss flow and distributions, and nonlinear friction, has been established for better guidance in system control and design via numerical simulations. Second, different control strategies and cam designs have been explored in order to determine the most appropriate control strategy and cam design to achieve a lower torque requirement, reduced power consumption and a faster transition time. Third, a limited-angle actuator was custom designed and built for the valve actuation application in order to reduce the actuator size while maintaining the necessary torque and power output. Fourth, with the limited-angle actuator in place, the EMV system was evaluated experimentally for intake valve actuation and numerically for exhaust valve actuation with gas force disturbance taken into consideration. Based on this system evaluation, we are able to project the system's applicability to a real 4-cylinder 16-valve engine with independent valve control for each intake and exhaust valve.

(cont.) At the end of the thesis, the power consumption has been reduced from 140 W to 50 W (about 64%), the transition time has been reduced from 3.3 ms to 2.7 ms, and the final actuator volume has been reduced to 1/7 of that of the original motor. These significant improvements enabled the projection of independent valve actuation for a 4-cylinder 16-valve IC engine with reasonable power consumption and high engine speed.