Electromagnetic valve with permanent magnet armature

Abstract

A modulating valve is described for controlling the flow of a working fluid through a flow orifice. The valve includes a encapsulated armature having a permanent magnet and a pair of soft iron pole pieces within its interior. The armature is axially movable by the passage of current through one or a dual pair of solenoid coils surrounding the armature. A thin webbed sealing disk is stretched over the end of an armature housing extension and acts to close or modulate flow of working fluid by varying the axial clearance between the disk and a stationary annular seat of the flow orifice. The armature is supported on flexure guide springs that allow armature axial motion when axial magnetic forces are applied to the armature. These axial forces are provided by the interaction of the solenoid coil(s) and the field of the permanent magnet. A magnetic field gradient produced by the permanent magnet allows the coil to apply a force to the armature in either the valve opening or valve closing direction, depending on the coil current polarity. An armature velocity signal is used in a closed loop servo control of valve position to suppress valve oscillation and over shoot when a change in valve position is commanded.