A fuel injector includes a collar, which may be formed of a porous, sintered material, the collar being located around the needle and allowing a restricted fluid pathway, such as orifices through the collar, between first and second volumes of fuel, the collar being located in a section of the nozzle body which has a greater cross-sectional area than the rest of the bore.
1. A fuel injector comprising:
a piston guide section;
a nozzle body;
a barrel section located between the piston guide section and the nozzle body;
a valve needle, movable along a longitudinal axis of the fuel injector, within a bore comprising a piston guide bore section, a bore provided in the barrel section, and a bore provided in the nozzle body, and wherein the valve needle comprises a first end region within the nozzle body, and a second end region within the piston guide section;
a nozzle control valve, for controlling fuel pressure within a control chamber surrounding the second end region of the valve needle, and thereby controlling the magnitude of a force applied to a pressure surface provided at the second end region of the valve needle, by fuel pressure within the control chamber; wherein the valve needle is movable, under the control of the nozzle control valve, between a fully closed position, in which a first surface provided at the first end region of the valve needle is in contact with a first seating region, provided in the nozzle body, and wherein ejection of fuel out of the nozzle body through at least one spray hole is prevented, and a fully open position, wherein a second surface provided at the second end region of the valve needle is in contact with a second seating region provided in the piston guide section, and wherein ejection of fuel out of the nozzle body through the at least one spray hole is enabled; and
a needle motion control means comprising a collar, located in a collar locating section of the bore provided in the nozzle body, the collar allowing a restricted fluid pathway between a first volume of fuel, and a second volume of fuel, located further away from the piston guide section than the first volume of fuel;
wherein the collar locating section comprises a section of the bore provided in the nozzle body, and has a cross-sectional area which is greater than that of a remainder of the bore provided in the nozzle body; and
wherein the collar has a cross sectional area which is greater than that of the bore provided in the barrel section.
2. The fuel injector as claimed in claim 1 , wherein a first face of the collar, adjacent the first volume of fuel, and a second face of the collar, each have a surface area which is greater than a surface area of the pressure surface.
3. The fuel injector as claimed in claim 1 , wherein a clearance between the collar and the collar locating section prevents fuel from flowing through the clearance between the first volume of fuel and the second volume of fuel.
4. The fuel injector as claimed in claim 1 , wherein the restricted fluid pathway comprises at least one orifice, provided through the collar.
5. The fuel injector as claimed in claim 4 wherein the collar is provided with two orifices located at opposing positions on the collar either side of the valve needle, at equal distances from the valve needle.
6. The fuel injector as claimed in claim 1 , wherein the collar comprises a porous material.
7. The fuel injector as claimed in claim 6 , wherein the collar is at least partially formed of a sintered material.
8. The fuel injector as claimed in claim 1 , wherein the collar is formed integrally with a spring seat against which an end of a spring, which biases the valve needle towards a closed position, abuts.
9. The fuel injector as claimed in claim 8 , wherein the spring abuts a contact surface of the spring seat, and wherein the contact surface is axially separated from the collar.
10. A method of a assembling the fuel injector as claimed in claim 1 , the method comprising push fitting the collar onto the valve needle in an interference fit.