Improved Robustness and Energy Consumption for Sensorless Electromagnetic Valve Train

The sensorless control of electromagnetic actuators for variable valve train derives the information about the valve movement directly from the current and voltage of the operating coils, no further sensor 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 opening events, 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 which is caused by eddy-currents and magnetic remanence and results into an induced voltage. The information about the required energy adjustment of the catching coil can be calculated from this voltage. The algorithm allows 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. By this means, the robustness of a low landing velocity can be increased substantially. Furthermore, ideal current shapes for minimum energy consumption have been derived. Consequently, the new control strategy is adapted to these current shapes and yields into a delayed current switch-on time.

The combination of the three introduced methods results in a new generation of sensorless control which realizes very low landing velocities, high robustness and a low energy consumption at the same time.