Fuel injector

Abstract

A fuel injector of a fuel injection system for delivering gaseous fuel to an internal combustion engine, the fuel injector comprising a working fluid chamber (34), a gas delivery chamber (48), and a needle guide bore (24) extending from the working fluid chamber (34) to the gas delivery chamber, wherein the gas delivery chamber (48) communicates with a fuel injector outlet for delivering the gaseous fuel to the internal combustion engine. A valve needle (12) is movable within the needle guide bore (24) along a needle axis to open and close the fuel injector outlet, wherein a gap (26) is defined between an outer surface of the valve needle (12) and an inner surface of the needle guide bore (24); and a needle control valve (30) for controlling the movement of the valve needle (12) by controlling the pressure of a working fluid in the working fluid chamber (34). A seal member (60, 160, 260) is arranged between the valve needle (12) and the needle guide bore (24) to restrict the gap (26) and to permit a controlled volume of working fluid to leak between the valve needle (12) and the needle guide bore (24) into the gas delivery chamber (48), the seal member (60, 160, 260) defining an inner seal surface and an outer seal surface.

Description

[0001] PH24036-1

[0002] FUEL INJECTOR

[0003] FIELD OF THE INVENTION

[0004] This invention relates to a fuel injector for gaseous fuel. In particular, but not exclusively, the invention relates to a fuel injector for use in a fuel system of an internal combustion engine for a gaseous fuel such as hydrogen.

[0005] BACKGROUND

[0006] Gaseous fuels such as hydrogen are promising alternative fuels to gasoline and diesel due to their potential for low or zero emissions and there has been considerable interest in developing traditional internal combustion engines to run on ecologically produced hydrogen. High pressure injection of gaseous fuels into the combustion chamber of an internal combustion engine offers benefits, including reduced compression work, reduced susceptibility to uncontrolled auto-ignition and greater flexibility in combustion strategies resulting in improved efficiency. A servo method of operating gaseous fuel injectors is generally favoured and, in principle, the working fluid for servo operation of the injector valve needle could be the same gas as the gaseous fuel that is injected. However, the use of hydraulic oil as the working fluid offers the advantage of more accurate control due to the bulk modulus of the liquid.

[0007] In a known hydrogen gas injector, in a non-injecting state the hydraulic control fluid is maintained at a pressure above the pressure of the injectable gaseous fuel to ensure there is no risk of the gaseous fuel leaking into the control fluid circuit. The control fluid is separated from the gaseous fuel via a sliding seal along a guide for the valve needle, but an inevitable consequence of the rigid sliding seal is fluid leakage across the pressure differential. This can result in injection of hydraulic fluid in the gaseous fuel, which can lead to fouling of the combustion chamber surfaces, exhaust sensors and after treatment apparatus.

[0008] It is an object of the invention to provide to address this leakage problem. SUMMARY OF THE INVENTION

[0009] According to a first aspect of the invention, there is provided a fuel injector of a fuel injection system for delivering gaseous fuel to an internal combustion engine, the fuel injector comprising a working fluid chamber, a gas delivery chamber, and a needle guide bore extending from the working fluid chamber to the gas delivery chamber, wherein the gas delivery chamber communicates with a fuel injector outlet for delivering the gaseous fuel to the internal combustion engine; a valve needle movable within the needle guide bore along a needle axis to open and close the fuel injector outlet, wherein a gap is defined between an outer surface of the valve needle and an inner surface of the needle guide bore and a needle control valve for controlling the movement of the valve needle by controlling the pressure of a working fluid in the working fluid chamber. A seal member is arranged between the valve needle and the needle guide bore to restrict the gap and to permit a controlled volume of working fluid to leak between the valve needle and the needle guide bore into the gas delivery chamber.

[0010] The injector is an inwardly opening injector in which the valve needle is moveable inwardly, within an injector housing and along the needle axis, to open fuel injector outlet.

[0011] The seal member may be an annular seal which extends around the valve needle to define an inner seal surface which contacts the outer surface of the valve needle, and an outer seal surface which contacts the inner surface of the needle guide bore.

[0012] The seal may be conformable, and may be formed from polytetrafluoroethylene (PTFE), either filled or unfilled. The conformability of the seal permits a much lower working fluid leakage rate than can be achieved with metal interfaces alone.

[0013] A conduit may extend axially through the seal member to permit working fluid to leak between the valve needle and the needle guide bore into the gas delivery chamber.

[0014] The conduit may be provided as a groove or recess formed in one of the inner or outer seal surfaces of the seal member. In embodiments, at least one of the inner or outer seal surfaces may comprise a textured portion of the seal member configured to allow working fluid to leak between the textured portion of the seal member and the outer surface of the valve needle or between the textured portion of the seal member and the inner surface of the needle guide bore in contact with the textured portion of the seal member.

[0015] The portion of textured surface of the seal member may be knurled.

[0016] By way of example, the seal member may be seated within an annular groove so that one of the inner and outer seal surfaces defines a first seal surface and the other of the inner and outer seal surfaces defines a second seal surface, wherein the first seal surface defines a fixed interface with one of the valve needle and the needle guide bore when the valve needle moves, and the second seal surface defines a sliding interface with the other of the valve needle and the needle guide bore when the valve needle moves.

[0017] For example, the annular groove may be provided in the outer surface of the valve needle so that the sealing member and the valve needle are configured to move together.

[0018] In embodiments, the inner seal surface may have an inner sealing length and the outer seal surface has an outer sealing length, the first and second sealing lengths being defined in the axial direction, wherein the sealing member has a tapered cross-sectional profile such that the outer sealing length is shorter than the inner sealing length.

[0019] For example, the inner sealing length may be equal to or greater than a minimum seal length and the outer sealing length is shorter than the minimum seal length, wherein the minimum seal length defines the seal length required to prevent working fluid from leaking along the sliding interface.

[0020] The annular groove may comprise a portion of textured surface configured to allow the working fluid to leak along the fixed interface between the seal member and the annular groove. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order that the invention may be more readily understood, preferred non-limiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0022] Figure 1 is a schematic diagram of a known servo-actuated injection nozzle for use in a gaseous fuel injector;

[0023] Figure 2 is an enlarged view of a part of the injection nozzle in Figure 1 ;

[0024] Figure 3 is a schematic diagram of a part of a servo-actuated injection nozzle of a first embodiment;

[0025] Figure 4 is a schematic diagram of a part of a servo-actuated injection nozzle of a second embodiment;

[0026] Figure 5 is a schematic diagram of a part of a servo-actuated injection nozzle of a third embodiment;

[0027] Figure 6 is a schematic diagram of a part of a servo-actuated injection nozzle of a fourth embodiment; and

[0028] Figure 7 is a plan view of a sealing ring when implemented in the servo-actuated injection nozzle of Figure 3.

[0029] Throughout this description, terms such as ‘upper’ and ‘lower’, and other directional references, are used with reference to the orientation of the injector as shown in the accompanying drawings. However, it will be appreciated that such references are not limiting and that injectors according to the invention can be used in any orientation. DETAILED DESCRIPTION OF THE INVENTION

[0030] Referring to Figures 1 and 2, a known servo-actuated gaseous fuel injector includes an injection nozzle 10 comprising an injector valve needle 12 which is inwardly-opening within the injection nozzle 10 and is controlled by means of a servo-valve mechanism, referred to generally as 14. The fuel injector is arranged to inject gaseous fuel into a combustion chamber 16 of an internal combustion engine by moving the valve needle 12 towards and away from a valve needle seating 18 to control the gaseous fuel flow through one or more injector outlets 20. The valve needle is movable within a needle bore provided in an injection nozzle housing 22. An upper portion of the valve needle 12 is received within a needle guide portion 24 of a valve needle bore provided in the injection nozzle housing 22. The upper portion of the valve needle 12 has an outer surface 13 which defines an axially extending gap 26 with an inner surface 24a of the needle guide bore portion 24. The upper portion of the valve needle 12 is guided for movement within the needle guide bore portion 24.

[0031] As best seen in Figure 2, the servo-valve mechanism 14 comprises a valve member 30 which is operable by means of an electromagnetic actuator 32 to control fluid pressure within a working fluid chamber 34 defined at an upper end of the valve needle 12. The valve member 30 is movable within a bore provided in a valve housing 38, the valve housing 38 being in abutment with the injection nozzle housing 22. The valve member 30 is movable between first and second valve seats 40, 42. In the example shown the first valve seat 40 is defined by the bore within the valve housing 38 and the second valve seat 42 is defined by an upper surface of the injection nozzle housing 22. A low pressure drain passage 44 is provided in the injection nozzle housing 22 so that, when the valve member 30 is moved away from the second valve seat 42, into engagement with the first valve seat 40, the working fluid chamber 34 communicates with the drain 44 to allow control fluid within the working fluid chamber 34 to flow to low pressure. High pressure control fluid is supplied to the bore in the valve housing 38 so that when the valve member is moved away from the first valve seat 40, into engagement with the second valve seat 42, hence closing communication between the working fluid chamber 34 and the low pressure drain 44, high pressure control fluid is able to flow into the working fluid chamber 34.

[0032] A supply passage 46 is defined within the valve housing 38 and the injection nozzle housing 22 for supplying injectable gaseous fuel to the injection nozzle 10. The supply passage communicates with a gas delivery chamber 48 defined in the injection nozzle housing 22, with a spring 50 being housed within the gas delivery chamber 48. The spring 50 acts on the valve needle 12 to urge the valve needle into engagement with the valve needle seating 18, to prevent fuel injection into the combustion chamber 16. The actuator 32 is actuable to allow the valve needle 12 to lift away from the valve needle seating 18 to commence injection through the injector outlet 20.

[0033] The working fluid within the working fluid chamber 34 is typically hydraulic oil and the fluid for injection, within the gas delivery chamber 48 is gaseous fuel such as hydrogen. It is therefore important to isolate, as far as possible, the working chamber 34 from the gas delivery chamber 48. To this end, a sliding seal is formed in the gap 26 between the upper portion of the valve needle 12 and the adjacent region of the needle guide bore 24 within the injection nozzle housing 22. Due to the pressure difference across the sliding seal (between working fluid in the working chamber 34 and high pressure gaseous fuel in the gas delivery chamber 48), it is inevitable that some leakage occurs through the gap 26 across the sliding seal. Whilst tight tolerancing can minimise the fluid leakage rate, it is not always possible to eliminate this to a satisfactory level or controlled level.

[0034] Referring to Figure 3, embodiments of the invention overcome this problem by introducing a separate seal member into the injection nozzle. Similar parts to those shown in Figures 1 and 2 are denoted with the same reference numbers in Figure 3, and details will not necessarily be repeated. The upper portion of the valve needle 12 is provided with an annular groove or annulus 52 so that the valve needle 12 comprises three portions; an upper head portion 12a, a thinned portion 12b created by the annulus 52 and a main body portion or needle stem 12c. The upper head portion 12a comprises a frusto-conical portion which defines a flat end surface 12d. Working fluid within the working fluid chamber 34 is exposed to the frusto-conical head portion 12a. The outer diameter of the remainder of the upper head portion 12a is otherwise the same as the outer diameter of the needle stem 12c.

[0035] Within the annulus 52, an annular sealing ring 60 is provided so that the sealing ring 60 resides within the gap 26 between the valve needle 12 and the internal surface 24a of the needle guide bore 24. The sealing ring 60 defines an inner seal surface which seals against the outer surface of the valve needle 12, in the region of the annulus 52, and an outer seal surface which seals against the inner surface of the needle guide bore 24. The sealing ring 60 provides a tight seal under varying conditions including component dimension tolerance, thermal expansion, mechanical loading and varying working fluid and gas pressure. The leakage rate is considerably reduced through the gap 26 with the sealing ring 60 within the annulus 52, compared to the situation where the sealing relies only on the metal interfaces between the outer surface 13 of the valve needle 12 and the inner surface 24a of the needle guide bore 24. The sealing ring 60 may be formed from PTFE which has low sliding friction properties, excellent chemical resistance and good tolerance in operating temperatures ranging between -40°C to 120°C especially. The PTFE may be Virgin PTFE (PTFE without a filler) or filled PTFE.

[0036] It may be useful to have a small quantity (volume) of controlled fluid leakage through the gap 26 as this ultimately results in a small amount of lubrication at the valve needle seat 18. Providing a controlled quantity (volume) of lubricating fluid (such as oil) at the valve needle seat 18 has a benefit on wear of the valve needle 12 and / or of the valve seat 18. In other words, a controlled amount of leakage through the gap 26 may be desirable. Figure 4 shows an embodiment in which the outer surface of the valve needle 12 within the annulus 52 is provided with a textured portion 64. The textured portion 64 comprises a region of surface roughness provided on the outer surface of the valve needle 12. In this case the sealing ring 60 has a smooth inner surface (as in Figure 3) which cooperates with the textured portion 64 of the valve needle 12.

[0037] As an alternative, Figure 5 shows an embodiment in which a textured portion 164 is provided on the outer seal surface of the sealing ring 160 within the annulus 52. The surface roughness of the textured portion 64, 164, whether provided on the valve needle 12 or on the sealing ring 60, has the effect of controlling the leakage rate (of working fluid, e.g. hydraulic oil) through the gap 26, between the outer surface 13 of the valve needle 12 and the internal surface 24a of the needle guide bore 24. This is more beneficial than having an uncontrolled leakage through the gap 26, as with a smooth surface interface, and provides the benefit of a controlled amount of lubrication being delivered to the valve seat 18.

[0038] In a further alternative embodiment, as shown in Figure 6, the sealing ring 260 is profiled so that the outer seal surface creates a relatively short outer sealing length, extending in an axial direction along the valve needle 12, compared to the relatively longer sealing length of the inner seal surface, extending in an axial direction along the valve needle 12. In other words, the sealing ring 260 has a tapered cross- sectional profile such that the relative lengths of the outer and inner sealing lengths mean that the working fluid is more likely to leak along the sliding interface (between the sealing ring 260 and the surface 24a of the needle guide bore 24) than along the fixed sealing interface (between the valve needle 12 and the inner seal surface of the sealing ring 260).

[0039] In more detail, the sealing ring 260 includes a tapered outer profile in an upper portion 260a of the sealing ring 260 and a tapered outer profile in a lower portion 260c of the sealing ring 260 with the two tapered profiles meeting together in a uniform diameter central portion 260b of the sealing ring 260. The central portion 260b of the sealing ring 260 defines a sliding interface with the inner surface 24a of the needle guide bore 24 at the outer seal surface and serves to allow a controlled leakage flow, of hydraulic oil, through the gap 26 and into the gas delivery chamber 48, to provide a benefit of some lubrication at the valve needle seat 18. The relatively short sealing length on this sliding interface also reduces sliding friction to improve injector performance by minimising friction-related variability.

[0040] A still further embodiment is shown in Figure 7 in which a leakage groove 70 is provide in the outer periphery of the sealing ring 60, 160, 260 to define a conduit for fluid flow between the inner surface 24a of the needle guide bore 24 and the outer surface of the sealing ring 60, 160, 260, into the gas delivery chamber 48. Whereas the sealing ring in this embodiment presents a substantial seal between hydraulic oil in the working chamber 34 and gaseous fuel in the gas delivery chamber 48, the provision of the groove 70 allows a controlled leakage flow (of working fluid, e.g. hydraulic oil) through the gap 26. This also provides the aforementioned advantages of a degree of lubrication at the valve needle seat 18. Any of the embodiments described previously may be provided with such a leakage groove in addition to their other features.

Claims

Claims1 . A fuel injector of a fuel injection system for delivering gaseous fuel to an internal combustion engine, the fuel injector comprising: a working fluid chamber (34), a gas delivery chamber (48), and a needle guide bore (24) extending from the working fluid chamber (34) to the gas delivery chamber, wherein the gas delivery chamber (48) communicates with a fuel injector outlet for delivering the gaseous fuel to the internal combustion engine; a valve needle (12) movable within the needle guide bore (24) along a needle axis to open and close the fuel injector outlet, wherein a gap (26) is defined between an outer surface of the valve needle (12) and an inner surface of the needle guide bore (24); a needle control valve (30) for controlling the movement of the valve needle (12) by controlling the pressure of a working fluid in the working fluid chamber (34); and a seal member (60, 160, 260) arranged between the valve needle (12) and the needle guide bore (24) to restrict the gap (26) and to permit a controlled volume of working fluid to leak between the valve needle (12) and the needle guide bore (24) into the gas delivery chamber (48), the seal member (60, 160, 260) defining an inner seal surface and an outer seal surface.

2. A fuel injector according to claim 1 , wherein the seal member is an annular seal (60, 160, 260) which extends around the valve needle (12) so that the inner seal surface contacts the outer surface of the valve needle (12), and the outer seal surface which contacts the inner surface of the needle guide bore (24).

3. A fuel injector according to claim 1 or claim 2, wherein a conduit (70) extends axially through the seal member (60, 160, 260) to permit working fluid to leak between the valve needle (12) and the needle guide bore (24) into the gas delivery chamber (48).

4. A fuel injector according to claim 3, wherein the conduit is provided as a groove or recess (70) formed in one of the inner or outer seal surfaces of the seal member (60, 160, 260).

5. A fuel injector according to any of claims 1 to 4, wherein at least one of the inner or outer seal surfaces comprises a textured portion (164) of the seal member (160) which is configured to allow working fluid to leak between the textured portion (164) of the seal member and the outer surface of the valve needle (12) and / or between the textured portion (164) of the seal member (160) and the inner surface of the needle guide bore (24) in contact with the textured portion (164) of the seal member (160).

6. A fuel injector according to claim 5, wherein the textured portion (164) of the seal member (160) is knurled.

7. A fuel injector according to any of claims 1 to 6, wherein the seal member (60, 160, 260) is seated within an annular groove (52) provided in the outer surface of the valve needle (12) and so that the seal member (60, 160, 260) and the valve needle (12) are configured to move together.

8. A fuel injector as claimed in claim 7, wherein one of the inner and outer seal surfaces defines a first seal surface and the other of the inner and outer seal surfaces defines a second seal surface, wherein the first seal surface defines a fixed interface with one of the valve needle (12) and the needle guide bore (24) when the valve needle (12) moves, and the second seal surface defines a sliding interface with the other of the valve needle (12) and the needle guide bore (24) when the valve needle (12) moves.

9. A fuel injector according to claim 8, wherein the annular groove (52) comprises a portion of textured surface (64) configured to allow the working fluid to leak along the fixed interface between the seal member and the annular groove.

10. A fuel injector according to claim 9, wherein the portion of textured surface (64) of the annular groove (52) is knurled.

11. A fuel injector according to any of claims 1 to 4, wherein the inner seal surface has an inner sealing length and the outer seal surface has an outer sealing length, the first and second sealing lengths being defined in the axial direction,wherein the sealing member has a tapered cross-sectional profile such that the outer sealing length is shorter than the inner sealing length.

12. A fuel injector according to claim 11 , wherein the inner sealing length is equal to or greater than a minimum seal length and the outer sealing length is shorter than the minimum seal length, wherein the minimum seal length defines the seal length required to prevent working fluid from leaking along the sliding interface.

13. A fuel injector according to any of claims 1 to 12, wherein the seal member is made from polytetrafluoroethylene (PTFE).

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