Electromagnetically-operated fuel injection valve

Claim 1

An electromagnetically-operated fuel injection valve comprising: an electromagnetic coil for generating magnetic flux when energized by the electric current supplied thereto; a tubular stator core made of a magnetic material for said magnetic flux and carrying said electromagnetic coil thereon, said stator core having a central passage for flowing fuel therethrough; a generally cylindrical valve casing made of a magnetic material for said magnetic flux and coaxially encasing said electromagnetic coil and said stator core therein; an armature core made of a magnetic material for said magnetic flux and facing said stator core with an air gap therebetween, said armature core being movably disposed in said valve casing to be attracted toward said stator core when said electromagnetic coil is energized; a fuel metering member integrally connected to said armature core for opening a fuel injection port communicated with said central passage of said stator core when said armature core is attracted thereby to meter fuel to be injected; a spring positioned between said stator core and said armature core and biasing said armature core and said fuel metering member to close said fuel injection port; and a thinned wall section provided in a magnetic flux path formed by said stator core, said valve housing and said armature core; the thickness of said thinned wall section being so determined that the magnetic flux passing therethrough is saturated thereat substantially only at and after the time said armature core is fully attracted to move said metering member to open said injection port, whereby magnetic force generated just before deenergization of said coil is made constant irrespective of the electric current having been supplied to said coil.