Electromagnetic actuator driving method, in particular for actuating valves in an internal combustion engine.

A servo drive for a valve in an internal combustion engine has an armature (4) fitted at right angles to the valve stem (3). The armature is held midway between two solenoids (6,7) by opposing springs and is displaced in either direction by the solenoids. A displacement sensor on the valve stem enables the control circuit (11) to monitor the exact position of the valve and to calculate the rate at which the valve is displaced. This enables the control system to achieve accurate valve action irrespective of the ambient conditions e.g. viscosity of the lubricant, temperature variation etc.