Experimental comparison between mechanical resonance based feed-forward control strategies

Electromechanical devices based on double electromagnets have shown to be a promising solution to substitute classical cam systems to actuate engine valve and implement Variable Valve Actuation (VVA). On the other hand, this solution requires special care at the key-on engine for the first valve lift, when the valve must be shifted from the middle equilibrium position to the close one with bounded coil currents. Despite the central role of the first catching problem, few attempts have been done into the existing literature to tackle it systematically. In this report an experimental validation of two control strategies for the first lift of a double magnet Electro-Mechanical Valve Actuator (EMVA) system are presented and compared. For both the control actions the key idea is to induce valve oscillations exploiting the resonant behavior of the mechanical part. The common solution consists of injecting oscillating currents at the resonant frequency of the mechanical part. Instead, the other control solution the oscillating force acting on the armature is directly designed. To this end the Force-To-Current (FTC) inversion algorithm presented in \cite{GaGi:10} is here adopted to transform the sinusoidal control magnetic force into reference coil currents actuated via a multi-hysteresis control logic. Results of a wide experimental investigation show that performance strongly depend on the control parameters and control solutions are compared with respect to different performance indexes.