Modeling and control of a linear electro-mechanical actuator (LEMA) for operating engine valves

In today's engines, the valves for air induction are controlled mechanically and their open and closing timings are fixed relative to engine crankshaft position. It has been demonstrated that engine fuel economy will be increased by 10-15% and the emission will be reduced significantly if the valve open and closing timing can be adjusted according to engine load and speed. The linear electromechanical actuator (LEMA) is one of the mechanisms to realize this function. In this paper, the design and operation of a linear electromechanical actuator are described. For the purpose of control design, a nonlinear magnetic model is developed and validated experimentally. Then, a dynamic model of the system is developed and a current pulse modulation control strategy is proposed and implemented on an experimental prototype system. Finally, test results are presented to show satisfied operation with good soft seating for initialization, closed-to-open transition and open-to-closed transition.