Fuel injector with a control rod controlled by the fuel pressure in an control chamber

The injector (7) has a control rod (17) controlled by the fuel pressure in a control chamber (52), and a nozzle (13) having an injection chamber (31) supplied with pressurized fuel for injection. The nozzle (13) has at least one injection orifice (16) normally closed by a pin (19) connected to the rod (17) and activated by the fuel pressure in the injection chamber (31). The control chamber (52) has a pressurized-fuel intake conduit (57), and a fuel discharge conduit (59) which is normally closed and is opened for a variable length of time depending on the amount of fuel to be injected. The pin (19) and the rod (17), and/or the intake conduit (57) and the discharge conduit (59), are so sized as to keep the pin (19) and the rod (17) hydraulically balanced in the maximum-lift position to open the orifice (16).