Fuel injection nozzle

Claim 1

In a fuel injection nozzle through which pressurized fuel is delivered to an internal combustion engine, the nozzle including: a nozzle body in which a bore is defined leading to a plurality of injection openings through which the fuel is injected; a valve needle having at least one end thereof extending into said bore for controlling the opening extent of said injection openings; a closing spring mounted to engage the valve needle and exert a force against the valve needle to move said valve needle toward the injection openings; and an adjusting piston mounted in axial alignment with the valve needle, the adjusting piston being mounted to exert an additional force against the valve needle tending to move the valve needle toward the injection openings, the improvement wherein: said nozzle body and said valve needle include complementally formed engaging surfaces capable of preventing fuel flow when said valve needle is depressurized; said bore defined by said nozzle body includes a blind bore into which the injection openings open; said valve needle includes a frontal portion that cooperates with said blind bore to define a first chamber, a cylindrical section at said at least one end thereof, radially sealable in said blind bore, channel means in said cylindrical section of said valve needle arranged to deliver fuel from a pressure chamber to said first chamber wherein said channel means are closed to fuel delivery when said complementally formed sealing surfaces are in engagement, and at least a pair of pressure receiving surfaces displaced axially relative to each other along the valve needle, such that the pressure exerted against the pressure receiving surfaces when said pressure receiving surfaces are exposed to the pressurized fuel results in a force on each surface tending to move the valve needle away from the injection openings against the spring force and said additional force; said valve needle having a two-stage opening stroke, whereby a portion of the injection openings are opened by the radially sealed cylindrical section of said valve needle for fuel passage therethrough as a result of the fuel pressure acting against at least one of said pair of pressure receiving surfaces, and the remainder of the injection openings are opened by the radially sealed cylindrical section of said valve needle for fuel passage therethrough as a result of the force acting against all of the pressure receiving surfaces.