US Patent 7252282 Armature with vent passages for vehicle actuator

In a vehicle solenoid valve, the spool that holds the actuation coil is formed with a hexagonal or octagonal inner chamber in which a cylindrical armature can slide. Owing to the different cross-sectional shapes between the spool and armature, a longitudinal fluid vent passageway is established along each edge of the chamber between the non-cylindrical walls of the chamber and the cylindrical armature so that movement of hydraulic fluid relative to the armature is promoted when the armature moves. The face of the spool that is oriented toward the valve end can be formed with radial vent grooves to further facilitate fluid venting when the armature moves.