Fuel injector

1. A mobile valve member that is designed to be arranged in a nozzle body of a fuel injector, the mobile valve member extending along a main axis between a top end and a bottom end that is provided with a mobile valve seat designed to cooperate with a static seat arranged on an inner face of the nozzle body about a circular line of an effective diameter, the mobile valve member being designed to slide between a closed position in which the mobile valve seat and the static seat are in sealing contact about the circular line to prevent fuel injection, and an open position in which the mobile valve seat and the static seat are separated from one another to enable fuel injection, the mobile valve member comprising:

a piston made up of a first male cylinder of the effective diameter forming the top end of the mobile member and a second cylinder with an external diameter that is greater than the effective diameter, the second cylinder provided with an internal cylindrical bore having the effective diameter extending axially in the second cylinder as far as a back face; and

a shutoff member made up of a cylindrical body comprising a male cylindrical shaft having the effective diameter that fits slidingly with a clearance in the internal cylindrical bore of the piston, and a male pointed cylindrical member with a diameter that is greater than the effective diameter, the male pointed cylindrical member extending as far as a pointed end including the mobile valve seat and forming the bottom end of the mobile valve member;

wherein the mobile valve member is hydraulically balanced and a length between the top end and the bottom end thereof is variable as a result of a sliding of the male cylindrical shaft in the internal cylindrical bore of the piston.

2. A mobile valve member as claimed in claim 1 , also including a first spring compressed between the piston and the shutoff member that permanently stresses the piston and the shutoff member to extend the mobile valve member.

3. A mobile valve member as claimed in one of claim 1 , wherein the shutoff member also has a disk flange arranged between the male cylindrical shaft and the male pointed cylindrical member, the disk flange extending radially from the cylindrical body of the shutoff member to a peripheral edge which fits slidingly against the inner face of the nozzle body, the disk flange having an upper face facing the piston and an opposing lower face facing the static seat, the disk flange also defining a first restricted orifice and a second restricted orifice, both of which extend between the upper face of the disk flange and the opposing lower face of the disk flange, enabling pressurized fuel to flow at reduced speed from one side to the other of the disk flange, creating a pressure difference between the upper face of the disk flange and the opposing lower face of the disk flange.

4. A mobile valve member as claimed in claim 3 , in which the internal cylindrical bore has a first section of greater diameter than the effective diameter and a second section having the effective diameter, such that the piston includes a circular end forming a sealing lip cooperating with a circular annular surface of the upper face of the disk flange, the first restricted orifice being arranged on an outside of the circular annular surface and the second restricted orifice being arranged on an inside of said circular annular surface.

5. A mobile valve member as claimed in claim 4 , wherein the mobile valve member is limited in extension by an anchoring means preventing the shutoff member from becoming detached from the piston, and in compression by the sealing lip butting sealingly against the upper face of the disk flange.

6. A mobile valve member as claimed in claim 1 , wherein the piston also has a return channel extending from the back face of the internal cylindrical bore and opening out at the top end of the first male cylinder.

7. An injection nozzle of a high-pressure fuel injector, the injection nozzle comprising:

a nozzle body that is elongate along a main axis and that has a cylindrical lateral peripheral wall that is tapered at one end, and an upper wall at the other end, the upper wall having a pressurized fuel inlet orifice and an axial through-bore forming an annular guide such that the axial through-bore has an effective diameter, the tapered end being formed on an inner face of the cylindrical lateral peripheral wall of the nozzle body of a static seat arranged close to injection holes extending across the cylindrical lateral peripheral wall; and

a mobile valve member extending along the main axis between a top end and a bottom end that is provided with a mobile valve seat designed to cooperate with the static seat of the nozzle body about a circular line of the effective diameter, the mobile valve member being designed to slide between a closed position in which the mobile valve seat and the static seat are in sealing contact about the circular line to prevent fuel injection, and an open position in which the mobile valve seat and the static seat are separated from one another to enable fuel injection, the mobile valve member comprising:

a piston made up of a first male cylinder of the effective diameter forming the top end of the mobile member and a second cylinder with an external diameter that is greater than the effective diameter, the second cylinder provided with an internal cylindrical bore having the effective diameter extending axially in the second cylinder as far as a back face; and

a shutoff member made up of a cylindrical body comprising a male cylindrical shaft having the effective diameter that fits slidingly with a clearance in the internal cylindrical bore of the piston, and a male pointed cylindrical member with a diameter that is greater than the effective diameter, the male pointed cylindrical member extending as far as a pointed end including the mobile valve seat and forming the bottom end of the mobile valve member;

wherein the mobile valve member is hydraulically balanced and a length between the top end and the bottom end thereof is variable as a result of a sliding of the male cylindrical shaft in the internal cylindrical bore of the piston; and

wherein the mobile valve member is arranged axially to slide in an internal space of the nozzle body, the first male cylinder of the piston fitting slidingly with a clearance in the annular guide, such that the mobile valve seat cooperates with the static seat and that the mobile valve member slides along the main axis between the closed position and the open position in which the mobile valve seat is separated from the static seat.

8. A fuel injector comprising:

an actuator; and

an injection nozzle comprising:

a nozzle body that is elongate along a main axis and that has a cylindrical lateral peripheral wall that is tapered at one end, and an upper wall at the other end, the upper wall having a pressurized fuel inlet orifice and an axial through-bore forming an annular guide such that the axial through-bore has an effective diameter, the tapered end being formed on an inner face of the cylindrical lateral peripheral wall of the nozzle body of a static seat arranged close to injection holes extending across the cylindrical lateral peripheral wall; and

a mobile valve member extending along the main axis between a top end and a bottom end that is provided with a mobile valve seat designed to cooperate with the static seat of the nozzle body about a circular line of the effective diameter, the mobile valve member being designed to slide between a closed position in which the mobile valve seat and the static seat are in sealing contact about the circular line to prevent fuel injection, and an open position in which the mobile valve seat and the static seat are separated from one another to enable fuel injection, the mobile valve member comprising:

a piston made up of a first male cylinder of the effective diameter forming the top end of the mobile member and a second cylinder with an external diameter that is greater than the effective diameter, the second cylinder provided with an internal cylindrical bore having the effective diameter extending axially in the second cylinder as far as a back face; and

a shutoff member made up of a cylindrical body comprising a male cylindrical shaft having the effective diameter that fits slidingly with a clearance in the internal cylindrical bore of the piston, and a male pointed cylindrical member with a diameter that is greater than the effective diameter, the male pointed cylindrical member extending as far as a pointed end including the mobile valve seat and forming the bottom end of the mobile valve member;

wherein the mobile valve member is hydraulically balanced and a length between the top end and the bottom end thereof is variable as a result of a sliding of the male cylindrical shaft in the internal cylindrical bore of the piston;

wherein the mobile valve member is arranged axially to slide in an internal space of the nozzle body, the first male cylinder of the piston fitting slidingly with a clearance in the annular guide, such that the mobile valve seat cooperates with the static seat and that the mobile valve member slides along the main axis between the closed position and the open position in which the mobile valve seat is separated from the static seat; and

wherein the actuator is an electromagnet including a static coil and a mobile magnetic armature attached directly to the piston.