Search Results

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.

New cylinder impulse charge systems permit higher torque at low speed and promise substantial downsizing potential ongoing with reduced fuel consumption and lower emissions. Their immediate response avoids the disturbing delay of turbochargers. Using a fast switching valve in the air intake manifold, they generate a dynamic pressure increase, which provides higher cylinder air mass filling. The short transient times needed for the valve opening and closing process together with the required low air leakage rate call for an effective drive. Electromagnetic spring-mass actuators are well suited for this task. They generate high control forces over long distances and can be designed for transient times below 2 ms. However, they suffer from high impact energies at the stop positions und cannot be used without movement control for the armature. Tight commercial conditions restrict the application of sensors and complex hard- and software.