US Patent 7388461 Electromagnetic apparatus

An electromagnetic apparatus includes a solenoid having a movable core for being attracted to a fixed core when a coil is energized, a shaft coupled to the movable core for displacement in unison with the movable core, and a valve mechanism having a ball for selectively opening and closing a passageway between an inlet port and an outlet port in response to the displacement of the shaft. The movable core has a nonmagnetic layer formed on an outer surface thereof and having a predetermined thickness.