Controller for controlling an electromagnetic actuator

Abstract

A controller for an electromagnetic actuator is provided that enables detection of a minute movement of the armature leaving the seating position and carries out pullback operation responsive to such detection. The electromagnetic actuator has a pair of springs acting on opposite directions, and an armature coupled to a mechanical element such as a exhaust/intake valve of an automobile engine. The armature is held in a neutral position given by the springs when the actuator is not activated. The actuator includes a pair of electromagnets for driving the armature between two end positions. The controller having current supplying means for supplying holding current to the electromagnet corresponding to one of the end positions when holding the armature in said one of the end positions. The controller includes determining that the armature is leaving (falling or lifting) the seated position when the holding current increases more than a predetermined value while the holding current is supplied to the electromagnet corresponding to said end position. Leaving armature is detected based on the variation of the holding current, which allows earlier detection of the leaving armature.