Adjustable metering servovalve for a fuel injector

A metering servovalve for the fuel injector of an internal-combustion engine, comprising:

• a valve body and an open/close element controlled by an armature of an electromagnet, said servovalve being housed in a cavity of a casing of said injector;
• said servovalve comprising:
• a magnetic core provided with an annular shoulder,
• a support for said magnetic core having a bottom edge engaging said annular shoulder of the magnetic core, said support being provided with another annular shoulder engaged by a threaded ring nut screwed on an external thread of said casing to fix said support and said magnetic core in said cavity;
• said armature being designed to perform a given travel defined by a pair of opposed arrest elements, and said threaded ring nut being screwed on said external thread of said casing with a pre-set tightening torque adapted to prevent any accidental loosening of said threaded ring nut;
• an adjustment ring shim being set between said magnetic core and a shoulder of said cavity;
• wherein said adjustment ring shim is positioned in contact with said magnetic core and has a cross section configured to prevalently undergo flexure deformation caused by the axial load produced by the pre-set tightening torque of the threaded ring nut on the thread of the casing with a compression between the magnetic core and the adjustment ring shim, said adjustment ring shim being formed of a material softer than that of said magnetic core to prevent any plastic deformation of the magnetic core by the axial load produced by said pre-set tightening torque, the material of said adjustment ring shim being such that said axial load guarantees a predetermined elastic deformation of a height of said adjustment ring shim.