Fuel injector
A fuel injector for use in an internal combustion engine, comprising a supply passage for high pressure fuel and an injection nozzle for receiving high pressure fuel. The injection nozzle includes a valve needle which is engageable with a valve needle seating to control fuel delivery from the injector. A surface associated with the valve needle is exposed to fuel pressure within a control chamber and a first restricted flow path provides communication between the supply passage and the control chamber. A supplementary flow path also provides communication between the supply passage and the control chamber under the control of a control valve, so as to allow high pressure fuel to flow from the supply passage into the control chamber through two flow paths when it is required to terminate an injection of fuel.
1. A fuel injector for use in a fuel system for an internal combustion engine, the fuel injector comprising:
a supply passage for high pressure fuel,
an injection nozzle including a valve needle which is engageable with a valve needle seating to control fuel delivery from the injector, a surface associated with the valve needle being exposed to fuel pressure within a control chamber,
a first restricted flow path providing communication between the supply passage and the control chamber,
a control valve for controlling fuel pressure within the control chamber, and
a supplementary flow path controlling communication between the supply passage and the control chamber under the control of the control valve, so as to allow high pressure fuel to flow between the supply passage and the control chamber,
wherein the supplementary flow path includes a second restricted flow path and wherein the control valve is operable to control whether fuel flows through the second restricted flow path either (i) between the control chamber and a low pressure drain or (ii) between the supply passage and the control chamber.
2. The fuel injector as claimed in claim 1 , wherein communication between the control chamber and the supply passage through the first restricted flow path is continuous.
3. The fuel injector as claimed in claim 1 , wherein the control valve has a control valve member defining first and second seating surfaces for engagement with a respective one of first and second valve seats, the control valve having a first operating position in which the supply passage communicates with the control chamber through the supplementary flow path to allow high pressure fuel to flow into the control chamber; and in which first operating position communication between the control chamber and the low pressure drain through the second restricted flow path is prevented.
4. The fuel injector as claimed in claim 3 , wherein the control valve has a second operating position in which the control chamber communicates with the low pressure drain through the second restricted flow path, and in which second operating position communication between the supply passage and the control chamber through the supplementary flow path is prevented.
5. The fuel injector as claimed in claim 4 , wherein the control valve member is provided with a drilling through which fuel flows when the second restricted flow path communicates with the low pressure drain.
6. The fuel injector as claimed in claim 3 , wherein at least one of the first and second seating surfaces is of frusto-conical form.
7. The fuel injector as claimed in claim 6 , wherein the first seating surface is of frusto-conical form and wherein the second seating surface is defined by an end surface of the control valve member.
8. The fuel injector as claimed in claim 3 , further comprising an arrangement for ensuring communication between the control chamber and the low pressure drain through the second restricted flow path is broken once the valve needle has moved a predetermined distance away from the valve needle seating, thereby to limit the loss of pressurised fuel between the control chamber and the low pressure drain during injection.
9. The fuel injector as claimed in claim 8 , wherein the predetermined distance is maximum lift of the valve needle.
10. The fuel injector as claimed in claim 8 , wherein the arrangement includes a further surface associated with the valve needle and an entry port of the second resticted flow path which communicates with the control chamber, and wherein the valve needle is movable away from the valve needle seating into a position in which the further surface covers the entry port.
11. The fuel injector as claimed in claim 10 , wherein the further surface of the valve needle is defined by an end piece.
12. The fuel injector as claimed in claim 11 , wherein the end piece forms an integral part of the valve needle.
13. The fuel injector as claimed in claim 1 , wherein the control valve includes an electromagnetic actuator.
14. The fuel injector as claimed in claim 1 , wherein the control valve includes a piezoelectric actuator.
15. The fuel injector as claimed in claim 1 , wherein the surface associated with the valve needle is either defined by the valve needle itself or by a piston coupled to the valve needle.
16. The fuel injector as claimed in claim 1 , wherein the injection nozzle and the control valve are formed within a common injector unit.
17. A common rail fuel injection system including a plurality of fuel injectors as claimed in claim 1 and a common source of high pressure fuel for supplying to the plurality of injectors.
18. A fuel injection system including a plurality of injectors as claimed in claim 1 and a dedicated high pressure pump for supplying pressurised fuel to the injector supply passage of an associated one of the injectors.