Sensorless Control of Electromagnetic Actuators for Variable Valve Train

A promising approach for the variable valve actuation in spark ignition engines is based on electromagnetic actuators for the valve drive. The movement of the armature results from two opposite electromagnetic drives, supported by two springs. Without proper control of the current through the coils during flight time, the armature will hit the opposite position at high velocity, thus producing acoustical noise and reducing the lifetime of the actuator. This paper presents a new concept to achieve a soft landing with velocities in the range of 0.1 m/s. The applied control circuit requires no additional sensor for the valve position or speed and is only based on the observation of the electrical coil signals. Together with the optimized control strategy, the system complexity is minimized, which results into substantial cost savings. The complete system for a 4 cylinder / 16 valve engine has been tested under laboratory conditions and on a combustion test engine and has demonstrated its high robustness against variations of cylinder pressure and supply voltage.