A fuel injector for delivering fuel to an internal combustion engine includes a nozzle having a valve needle which is movable with respect to a valve needle seat. The valve needle travels through a range of movement between a closed position and an open position to control fuel delivery through at least one nozzle outlet. The valve needle cooperates with a needle sleeve or a control member which is located in a piston guide. The valve needle is movable relative to the needle sleeve or the control member. The needle sleeve or the control member is movable relative to the piston guide.
1. A fuel injector for use in delivering fuel to an internal combustion engine, the fuel injector comprising:
a nozzle having a valve needle which is movable with respect to a valve needle seat through a range of movement between a closed position and an open position to control fuel delivery through at least one nozzle outlet;
a needle sleeve which is located in a piston guide with which the valve needle cooperates;
the needle sleeve having a guide bore which receives a guide portion of the valve needle such that an outer circumference of the valve needle abuts an inner circumference of the guide bore to guide the valve needle throughout movement of the valve needle relative to the needle sleeve;
the valve needle is movable relative to the needle sleeve; and the needle sleeve is movable relative to the piston guide between a retracted position and an advanced position;
a first control chamber which controls the position of the valve needle relative to the needle sleeve;
a second control chamber which controls the position of the needle sleeve relative to the piston guide;
a first nozzle control valve being provided which controls the pressure in the first control chamber; and
a second nozzle control valve being provided which controls the pressure in the second control chamber;
wherein movement of the valve needle with respect to the valve needle seat, toward the open position, is limited by the needle sleeve such that the retracted position of the needle sleeve provides greater separation between the valve needle and the valve needle seat than the advanced position of the needle sleeve;
wherein the valve needle in the closed position together with the needle sleeve simultaneously in the retracted position does not open a nozzle outlet; and
wherein the valve needle contacts the valve needle seat in the closed position.
2. A fuel injector as claimed in claim 1 , wherein the valve needle comprises a first end for cooperating with the valve needle seat and a first contact surface for cooperating with a needle sleeve seat such that a fluid pathway from the first control chamber is open when the first contact surface is unseated from the needle sleeve seat and such that the fluid pathway from the first control chamber is closed when the first contact surface is seated with the needle sleeve seat.
3. A fuel injector as claimed in claim 2 , wherein the first contact surface forms a second valve for sealingly engaging the needle sleeve seat.
4. A fuel injector as claimed in claim 3 , wherein the valve needle further comprises a first aperture for providing a first fluid pathway past the needle sleeve seat.
5. A fuel injector as claimed in claim 1 , wherein the retracted position of the needle sleeve causes a spring to be compressed more than in the advanced position of the needle sleeve.