Electromagnetic fuel injector with selectively hardened armature

Claim 1

In an electromagnetic fuel injector of the type having a hollow tubular body with a stepped bore therethrough providing a fuel chamber therein intermediate its ends adapted to receive fuel, a fuel injector nozzle positioned in the stepped bore at one end of the body to define a spray tip at one end and an annular valve seat encircling a discharge passage upstream of the spray tip in communication with the fuel chamber, a valve positioned in the stepped bore for movement into and out of engagement with the valve seat, the valve being flat on one side thereof and being spherical opposite the flat to form a spherical seating surface for valve closing engagement with the valve seat, and a solenoid means including a stationary pole piece and a movable cylindrical armature for actuating the valve for controlling flow from the fuel chamber to the discharge passage; the improvement comprising a non-magnetic guide pin fixed to the pole piece to extend axially toward the valve seat substantially concentric therewith, the armature having a central axial guide bore therein of a diameter to slidably receive said guide pin whereby said armature is axially guided by said guide pin, and wherein at least the internal wall material of said armature defining said guide bore is wear resistant whereby frictional wear between said guide pin and said armature will be substantially reduced during extended operation of the electromagnetic fuel injector, at least the remainder of said armature in the magnetic circuit of the solenoid being of magnetically soft material.