Experimental investigation of a double magnet EMVA at key-on engine: a mechanical resonance based control strategy

Nowadays, developing of effective camless engine systems, allowing Variable Valve Actuation (VVA), is one of the fundamental automotive challenge to increase engine power, reduce fuel consumption and pollutant emissions, as well as improve the engine efficiency significantly. Electromechanical devices based on double electromagnets have shown to be a promising solution to actuate engine valves during normal engine cycle due to their efficient working principle. Conversely, 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 closing one with limited coil currents and power requirements as well. Despite the central role of the first catching problem, few attempts have been done into the existing literature to tackle it systematically. This paper presents an experimental validation of a control strategy for the first lift of a double magnet Electro Mechanical Valve Actuator (EMVA) system. The key idea is to induce valve oscillations exploiting the resonant behavior of the mechanical part. Since the actuator produces a magnetic force as a nonlinear function of the coil currents and valve position, a proper force-to-current inversion algorithm, previously presented by the authors, has been here adopted to transform 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, i.e. the amplitude and the frequency of the exciting periodic force, with respect to different performance indexes. The performance of the proposed control strategy have been compared experimentally with those provided by an empirical solution involving pulsing coil currents with constant amplitude.