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A nozzle able to be arranged in a diesel injection system of the internal combustion engine of a vehicle comprises a fixed member provided with a nozzle seat at the center of which there opens a discharge orifice, the fixed member comprising a cylindrical tubular part defining an inner guide cylinde

A nozzle able to be arranged in a diesel injection system of the internal combustion engine of a vehicle comprises a fixed member provided with a nozzle seat at the center of which there opens a discharge orifice, the fixed member comprising a cylindrical tubular part defining an inner guide cylinder extending axially from an open first end as far as the seat that forms the closed end of the guide cylinder, and a shut-off member arranged and guided in the guide cylinder, the shut-off member being able to move between a closed state (EF) when the shut-off member is in abutment against the seat and an open state (EO) when the shut-off member opens the discharge orifice.

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1. A valve for regulating the pressure of the fuel in the common rail of the diesel injection system of a vehicle internal combustion engine, the valve comprising a body, a shaft, an actuator and a nozzle itself comprising a fixed member provided with a nozzle seat in the center of which there opens

1. A valve for regulating the pressure of the fuel in the common rail of the diesel injection system of a vehicle internal combustion engine, the valve comprising a body, a shaft, an actuator and a nozzle itself comprising a fixed member provided with a nozzle seat in the center of which there opens a discharge orifice connecting the common rail to a discharge duct; the shaft, arranged axially sliding in a central bore of the body such that the shaft is guided by the central bore, the shaft being moved by the actuator in such a way as to cause the nozzle to switch between the discharge orifice being in an open state (EO) when the pressure in the common rail is above a pre-established limit (L), and the discharge orifice being in a closed state (EF) when the pressure in the common rail is below the pre-established limit (L), characterized in thatthe valve further comprises a shutoff member arranged between the shaft and the seat so that in the closed state (EF) the shaft pushes the shutoff member into abutment against the seat shutting off the discharge orifice and in the open state (EO) the pressurized fuel pushes the shutoff member back and opens the discharge orifice, the shaft itself being pushed back by the shutoff member,the fixed member of the nozzle comprising a tubular part defining an interior guide cylinder extending axially from an open first end as far as the seat forming the bottom end of the guide cylinder, the shutoff member arranged and guided in the guide cylinder independently of the shaft, the guide cylinder being in fluidic communication with the discharge duct. 2. The valve as claimed in claim 1, in which the tubular part of the fixed member is provided with a connecting orifice connecting the guide cylinder to the discharge duct so that when the nozzle is in the open state (EO), the fuel emerging from the common rail passes in succession through the discharge orifice, the guide cylinder, the connecting orifice and the discharge duct. 3. The valve as claimed in claim 2, in which the body is provided with a housing in which the tubular part is arranged, these between them defining an intermediate tubular space into which the discharge duct and the connecting orifice emerge so that when the nozzle is in the open state (EO) the fuel emerging from the common rail passes through the intermediary tubular space before entering the discharge duct. 4. The valve as claimed in claim 1, in which the fixed member of the nozzle is additionally provided with an axial cylindrical base extending between two radial surfaces so as to position the fixed member by arranging the base in a complementary counterbore, one of the two surfaces being in abutment with the end of the counterbore. 5. The valve as claimed in claim 1, in which the counterbore is provided in the body of the valve, the fixed member of the nozzle being secured to the body. 6. The valve as claimed in claim 1, in which the end of the shutoff member collaborating with the seat has a spherical surface, the seat for its part having a conical surface the vertex of which faces towards the rail. 7. The valve as claimed in claim 1, in which the actuator is the plunger of an electromagnet controlled by a central unit. 8. The valve as claimed in claim 1, in which the actuator is a compression spring constantly urging the shaft with an axial force rated at the pre-established pressure limit (L), so that the shaft urges the nozzle towards the closed state (EF). 9. The valve as claimed in claim 1, in which the dimensional tolerance between the diameters of the axial bore and of the shaft is 30 μm. 10. The valve as claimed in claim 1, in which the axial bore in which the shaft is guided has a surface roughness of less than Ra 3.2. 11. A common rail of a motor vehicle internal combustion engine diesel injection system comprising amongst other things a counterbore capable of accepting a nozzle arranged in a valve produced as claimed in claim 1, the base fitting into the counterbore, the fixed member being secured to the common rail. 12. A diesel fuel injection system of the common rail type comprising a valve produced as claimed in claim 1. 13. The injection system as claimed in claim 12, comprising a common rail produced as claimed in claim 11.