Internal combustion engine fuel injector

A fuel injector for an internal combustion engine;

• the injector having a nozzle for injecting fuel into a relative cylinder of the engine, and comprising:
• a hollow injector body extending in an axial direction;
• a control rod movable axially with respect to said injector body to open and close said nozzle;
• a control servo valve housed in said injector body and comprising:
• a) an electro-actuator;
• b) a control chamber, which is bounded axially at one side by said control rod, communicates with a fuel inlet, and has a discharge passage comprising a calibrated portion;
• and
• c) a sleeve movable axially, under the control of said electro-actuator, between a closed position, in which it closes said discharge passage, and an open position, in which it opens said discharge passage to vary the pressure in said control chamber and so produce axial movement of said control rod;
• wherein said control servo valve also comprises an axial rod fixed with respect to said injector body and an outer lateral surface through which said discharge passage comes out;
• said sleeve being fitted to said outer lateral surface to slide axially in substantially fluidtight manner, and, in said closed position, being effective to close said discharge passage so as to be subjected to substantially zero resultant axial pressure by the fuel;
• and
• wherein said calibrated portion is formed close to the outlet of said discharge passage to produce swirl or cavitation in the fuel outflow near to the closing area between said sleeve and said axial rod,
• characterized in that said control chamber is bounded radially by a tubular portion in turn defining outwards an annular chamber connecting said control chamber to said inlet;
• said annular chamber comprising a first annular gap housing a sealing ring interposed between said tubular portion and said injector body, and a second annular gap bounded axially by a shoulder of said tubular portion and smaller radially than said first annular gap.

A fuel injector for an internal combustion engine;

• the injector having a nozzle for injecting fuel into a relative cylinder of the engine, and comprising:
• a hollow injector body extending in an axial direction;
• a control rod movable axially with respect to said injector body to open and close said nozzle;
• a control servo valve housed in said injector body and comprising:
• a) an electro-actuator;
• b) a control chamber, which is bounded axially at one side by said control rod, communicates with a fuel inlet, and has a discharge passage comprising a calibrated portion;
• and
• c) a sleeve movable axially, under the control of said electro-actuator, between a closed position, in which it closes said discharge passage, and an open position, in which it opens said discharge passage to vary the pressure in said control chamber and so produce axial movement of said control rod;
• wherein said control servo valve also comprises an axial rod fixed with respect to said injector body and an outer lateral surface through which said discharge passage comes out;
• said sleeve being fitted to said outer lateral surface to slide axially in substantially fluidtight manner, and, in said closed position, being effective to close said discharge passage so as to be subjected to substantially zero resultant axial pressure by the fuel;
• and
• wherein said calibrated portion is formed close to the outlet of said discharge passage to produce swirl or cavitation in the fuel outflow near to the closing area between said sleeve and said axial rod,
• wherein said closing area is formed between an end of said sleeve and a shoulder integral with said rod,
• said rod is integral with said a body bounding axially said control chamber, said shoulder being formed between said rod and a portion of said body having a diameter larger than the one of said rod,
• wherein said rod is provided with a cylindrical lateral surface slidably engaging a cylindrical inner surface of said shutter substantially in a fluid tight manner, and wherein an annular chamber is formed between said lateral surface and said inner surface and is located between said discharge passage and said closing area.

A fuel injector for an internal combustion engine;

• the injector having a nozzle for injecting fuel into a relative cylinder of the engine, and comprising:
• a hollow injector body extending in an axial direction;
• a control rod movable axially with respect to said injector body to open and close said nozzle;
• a control servo valve housed in said injector body and comprising:
• a) an electro-actuator;
• b) a control chamber, which is bounded axially at one side by said control rod, communicates with a fuel inlet, and has a discharge passage comprising a calibrated portion;
• and
• c) a sleeve movable axially, under the control of said electro-actuator, between a closed position, in which it closes said discharge passage, and an open position, in which it opens said discharge passage to vary the pressure in said control chamber and so produce axial movement of said control rod;
• wherein said control servo valve also comprises an axial rod fixed with respect to said injector body and an outer lateral surface on the axial rod through which said discharge passage comes out;
• said sleeve being fitted to said outer lateral surface to slide axially in substantially fluidtight manner, and, in said closed position, being effective to close said discharge passage so as to be subjected to substantially zero resultant axial pressure by the fuel;
• and
• wherein said calibrated portion is formed in the axial rod close to the outlet of said discharge passage to produce swirl or cavitation in the fuel outflow near to the closing area between said sleeve and said axial rod,
• said discharge passage is formed entirely in a single fixed body comprising said axial rod and axially defining said control chamber at the opposite side to said control rod,
• said control chamber is bounded radially by a tubular portion forming part of a valve body distinct from said fixed body;
• said fixed body comprising a base portion larger in diameter than said axial rod, axially defining said control chamber, and gripped axially against said valve body.