Improved robustness and energy consumption for sensorless electromagnetic valve train

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Improved robustness and energy consumption for sensorless electromagnetic valve train

Gunselmann, C. / Melbert, J.

The sensorless control of electromagnetic actuators for a variable valve train derives the information about the valve movement directly from the current and voltage of the operating coils, i.e. no further sensor is used at the actuator. The movement of armature and valve is heavily influenced by the cylinder pressure, especially, during opening of the exhaust valve. Between two consecutive openings, this pressure can vary by up to 3 bars. An early detection of pressure variation is essential in order to adjust the proper catching energy of the active coil. At the beginning of the armature movement, a degradation of the magnetic flux through the coils occurs being caused by eddy-currents and magnetic remanence and evokes an induced voltage. The information about the required energy adjustment of the catching coil can be calculated from this voltage. The algorithm allows for a safe and soft landing at pressure variations of up to 3 bars. Further improvement has been achieved by an advanced control strategy during the final swing period. The new algorithm adjusts the current shape and catching energy as well as the current switch-off time, thereby substantially increasing the robustness of a low landing velocity. Furthermore, ideal current shapes for minimum energy consumption have been derived. Consequently, the new control strategy is adapted to these current shapes and leads to a delayed current switch-on time. The combination of the three introduced methods results in a new generation of sensorless control, thus at the same time realising very low landing velocities, high robustness, and a low energy consumption.