Fast solenoid valve, particularly a fuel injection pilot valve for diesel engines

Claim 1

An electromagnetically-controlled fuel injection valve for diesel engines, including: a hollow body housing an injection chamber and a control chamber both supplied with fuel under pressure, an injection nozzle provided at one end of said hollow body and communicating with said injection chamber, a needle operatively associated with said nozzle to control communication between said injection chamber and said nozzle, piston means secured to said needle and cooperating with said control chamber to keep said needle in a position closing said communication by the sole action of said fuel under pressure, and an electromagnetic metering valve mounted at the other end of said hollow body, said metering valve comprising: a discharge port communicating with said control chamber, the opening of which causes a drop in the pressure of said control chamber to cause said piston to move said needle to a position opening said communication, an obturator normally closing said discharge port, a selectively energizable cylindrical solenoid secured to said hollow body, an armature secured to said obturator and operable by said solenoid to cause said obturator to open said discharge port, said armature having a surface facing said solenoid and having a generally circular shape with a diameter slightly less than the one of said solenoid, and a floating annular element of non-magnetic material interposed between said armature and said solenoid, said annular element having an outer diameter substantially equal to the one of said facing and an inner diameter such that said element ovelaps said facing surface only partially, whereby any sticking action of the mutual contact on said facing surface is prevented without reducing the magnetic inductance of said armature.