Fuel injector

A diesel fuel injector (10) having a body (12) in which fuel (C) under pressure circulates between an inlet and an injection nozzle controlled by a needle. The needle moving axially under the influence of the pressure difference between a control chamber (16) arranged upstream of the needle and the injection nozzle downstream. The injector (10) further comprises a controlled valve (14) controlling the pressure in said control chamber (16) by opening or closing a discharge channel (18) extending from the control chamber (16) and opening into a cylindrical low-pressure return channel (20) of larger cross-section. The return channel (20) is provided with an enlarged zone (22) into which the discharge channel (18) opens so as to reduce the mechanical stresses linked to the passage of pressurized fuel (C) and to the cycles of the valve (14).