Fuel injector

Abstract

A gaseous fuel injector 200 comprising a gas delivery chamber 48 and housing body 22 defining a working fluid chamber 34 and needle guide bore 24. A valve needle 212 is movable within the guide bore,

Description

FIELD OFTHE INVENTION 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. BACKGROUND 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. 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 a leakage of hydraulic fluid in the gaseous fuel, which can lead to fouling of the combustion chamber surfaces, exhaust sensors, and after treatment apparatus. It is an object of the present invention to provide a fuel injector which addresses this leakage problem. SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a fuel injector of for delivering gaseous fuel to an internal combustion engine, the fuel injector comprising a gas delivery chamber defining an opening for delivering the gaseous fuel therethrough to the internal combustion engine; a housing body defining a working fluid chamber and a needle guide bore extending from the working fluid chamber to the gas delivery chamber; a valve needle movable within the needle guide bore along a valve needle axis to open and close the opening defined by the gas delivery chamber; and a needle control valve for controlling movement of the valve needle by controlling a pressure of a working fluid in the working fluid chamber. An annular groove is defined in the valve needle between the valve needle and the needle guide bore to define a thinned portion of the valve needle; and an annular seal member arranged at least partially within the annular groove configured to provide a seal between an outer surface of the valve needle and an internal surface of the needle guide bore. The seal member comprises a passage extending therethrough and is movable within the annular groove from a first position to a second position in the event of a malfunction resulting in the pressure of working fuel in the working fluid chamber being less than the pressure of the gaseous fuel in the gas delivery chamber, wherein, in the first position, the passage is blocked to prevent the working fluid from flowing through the passage of the seal member into the gas delivery chamber; and, in the second position, the passage is unblocked to allow the gaseous fuel to leak through the passage of the seal member into the working fluid chamber. The injector is an inwardiy opening injector in which the valve needle is moveable inwardly, within an injector housing and along the needle axis, to open fuel injector outlet. The above-described fuel injector is advantageous at least in that the seal member is movable to permit a flow of gaseous fuel into the working fluid chamber providing a system capable self-correction in the event that there is a malfunction in the supply of working fluid to the working fluid chamber. In the case that the supply of working fluid to the working fluid chamber cannot repressurise the working fluid chamber, the pressure in the gas delivery chamber will exceed the pressure in the working fluid chamber. The pressure difference between the gas delivery chamber and the working fluid chamber will force the valve needle away from the valve seat defined by the gas delivery chamber and open the injector. Given that the working fluid chamber cannot repressurise, the injector will remain open for an extended period of time -which may damage the internal combustion engine. The present invention is configured to permit a flow of gaseous fuel from the gas delivery chamber into the working fluid chamber in the above case. When the gaseous fuel flows into the working fluid chamber, via the passage formed in the seal member, the pressure either side of the valve needle will equalise and the injector will be closed through the force applied to the valve needle by a biasing spring for valve needle closure. The needle axis may define an axial direction and the seal member may be configured to slide in the axial direction between the first and second positions. The seal member may be made from polytetrafluoroethylene (PTFE), either filled or unfilled. The passage may extend from an upper end face of the seal member at a first end of the passage to a lower end face of the seal member at a second end of the passage, wherein the upper end face faces towards the working fluid chamber and the lower end face faces towards the gas delivery chamber. The first end of the passage may be arranged radially apart from the annular groove and the second end of the passage may be arranged radially with in the annular groove. The annular groove may be configured to block the second end of the passage when the seal member is in the first position. For example, a radially outer surface of the valve needle within the annular groove ora lower radial shoulder define by the groove may be configured to block the second end of the passage when the seal member is in the first position. Agroove axis defined perpendicular to the valve needle axis may pass radially through the centre of the thinned portion of the valve needle and, correspondingly, through both the seal member and the annular groove. The seal member and the annular groove may comprise corresponding asymmetric profiles about the groove axis. The seal member may comprise a trapezoidal cross section defining an upper end face which faces towards the gas delivery chamber and an opposing lower end face which faces towards the gas delivery chamber. An outer surface may extend from the upper end face to the lower end face parallel to the valve needle axis, and a conical inner surface may extend from the upper end face to the lower end face at an angle to the valve needle axis. The conical inner surface may be angled towards the valve needle axis such that the upper end face may be wider than the lower end face in a radial direction. For example, the annular groove may define an upper radial shoulder which faces towards the gas delivery chamber and against which the upper end face of the annular seal member abuts when the seal member is in the second position. Optionally, the annular groove may define a lower radial shoulder which faces towards the working fluid chamber and against which the lower end face of the seal member abuts when the seal member is in the first position. Optionally, the annular groove may define a conical groove surface extending between the upper and lower radial shoulder, wherein the conical groove surface corresponds to the conical inner surface of the seal member. For example, the seal member may be movable within the annular groove from the first position to the second position when the valve needle is moving to close the opening. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood, preferred nonlimiting embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a known servo-actuated injector for use in a gaseous fuel injector; Figure 2 is an enlarged view of a part of the injector in Figure 1; Figure 3 is a schematic diagram of a part of a servo-actuated injector; Figure 4 is an enlarged view of a part of the injector in Figure 3; Figure 5 is a schematic diagram of a part of a servo-actuated injector of a first embodiment; Figure 6 is an enlarged view of a part of the injector in Figure 5; Figure 7 is a schematic diagram of the servo-actuated injector of the first embodiment during a malfunction event; and Figure 8 is a schematic diagram of a part of a servo-actuated injector of a second embodiment. Throughout this description, terms such as ‘upward’, ‘downward’, ‘upper’, ‘lower’, ‘inner’, ‘outer’, 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 present invention can be used in any orientation. DETAILED DESCRIPTION OFTHE INVENTION Referring to Figures 1 and 2, a known servo-actuated gaseous fuel injector includes an injector 10 comprising an injector valve needle 12, defining a valve needle axis 12’ which is controlled by means of a servo-valve mechanism, referred to generally as 14. The fuel injector 10 is arranged to inject gaseous fuel into a combustion chamber (not shown) of an internal combustion engine (not shown) by moving the valve needle 12 towards and away from a valve needle seat 18 to control the gaseous fuel flow through one or more injector outlets 20. The valve needle 12 is movable within a needle bore provided in a housing body 22. The fuel injector is of the inwardly-opening type in which the valve needle 12 moves inwardly, within the housing body 22, to open away from the valve needle seat 18. An upper portion of the valve needle 12 is received within a needle guide portion 24 of the needle bore provided in the housing body 22 (hereinafter referred to as a needle guide bore 24). The upper portion of the valve needle 12 has an outer surface 13 which defines an axially extending gap 26 with an internal surface 24a of the needle guide bore 24. The upper portion of the valve needle 12 is guided for movement within the needle guide bore 24. The servo-valve mechanism 14 comprises a needle control valve 30 which is operable by means of an electromagnetic actuator 32 to control a working fluid pressure within a workingfluid chamber 34 defined at an upper end ofthe valve needle 12. The needle control valve 30 is movable within a bore provided in a valve housing 38, the valve housing 38 being in abutment with the housing body 22. The needle control valve 30 is movable between a first valve seat 40 and a second valve seat 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 housing body 22. A low pressure drain 44 is provided in the housing body 22 so that, when the needle control valve 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 low pressure 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, info 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. A supply conduit 46 is defined within the valve housing 38 and the housing body 22 for supplying injectable gaseous fuel to the injector 10. The supply conduit 46 communicates with a gas delivery chamber 48 defined in the housing body 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 12 into engagement with the valve needle seat 18, to prevent fuel injection into the combustion chamber. The actuator 32 is actuable to raise the needle control valve 30 and cause the valve needle 12 to lift away from the valve needle seat 18 to commence injection through the injector outlet 20. 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 typically gaseous fuel, such as hydrogen. It is therefore important to isolate, as far as possible, the working fluid 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 internal surface 24a of the needle guide bore 24. Due to the pressure difference across the sliding seal (between working fluid in the working fluid 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 leakage rate, it is not always possible to eliminate this to a satisfactory, controlled level. Referring to Figures 3 and 4, one example of a fuel injector 100 which may overcome this problem introduces a seal member 60 into the injector 10, as described in our co-pending UK patent application. Similar parts to those shown in Figures 1 and 2 are denoted with the same reference numbers in Figures 3 and 4, and detailswill not necessarily be repeated. The upper portion of the valve needle 112 is provided with an annular groove 52 so that the valve needle 112 comprises three portions; an upper head portion 112a, a thinned portion 112b created by the annular groove 52, and a main body portion or needle stem 112c. The upper head portion 112a comprises a frusto-conical portion which defines a flat end surface 112d and an upper cylindrical outer surface 113a. The thinned portion 112b defines a thinned cylindrical outer surface 113b which extends perpendicular to the working fluid chamber 34. The needle stem 112c defines a lower cylindrical outer surface 113c. The annular groove 52 defines an upper radial shoulder 52a and a lower radial shoulder 52c on the valve needle 112. The upper radial shoulder 52a faces towards the gas delivery chamber 48 and the lower radial shoulder 52c faces towards the working fluid chamber 34. The upper and lower radial shoulders 52a, 52c are joined by the cylindrical groove surface 113b which is symmetrically arranged about the valve needle axis 112’. The flat end surface 112d of the frusto-conical head portion 112a is exposed to the working fluid within the working fluid chamber 34. The diameter of the upper cylindrical outer surface 113a of the upper head portion 112a is otherwise the same as the diameter of the lower cylindrical outer surface 113c of the needle stem 112c. The seal member 60 resides within the annular groove 52, within a gap defined between the thinned cylindrical outer surface 113b and the internal surface 24a of the needle guid bore 24. The seal member 60 defines an inner seal surface 60d which seals against the outer thinned cylindrical surface 113b and an outer surface 60c which seals against the internal surface 24a. The seal member 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 seal member 60 disposed within the annular groove 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 internal surface 24a of the needle guide bore 24, as seen in Figures 1 and 2. The seal member 60 may be formed from PTFE (either virgin PTFE which is unfilled or filled PTFE) which has low sliding friction properties, excellent chemical resistance, and good tolerance in operating temperatures ranging between -40:'C to 120°C especially. Whilst flow of gaseous fuel into the working fluid chamber 34 is generally considered undesirable, if the injector 10 were to malfunction and the supply pressure of the working fluid was suddenly lost, e.g. in the case of a hydraulic pump failure, the gaseous fuel pressure in the gas delivery chamber 48 would cause the valve needle 12 to move away from the valve needle seat 18 such that the injector 10 would be open. Given that the working fluid in the working fluid chamber 34 cannot repressurise due to the malfunction, the injector 10 would then remain open. This uncontrolled injection could pose a risk to damage in the engine. In order to overcome the aforementioned problem, the fuel injector 100 embodiment shown in Figures 5, 6, and 7 comprises an seal member 600 configured to inhibit the flow of working fluid from the working fluid chamber 34 into the gas delivery chamber 48 but to permit the flow of gaseous fuel from the gas delivery chamber 48 into the working fluid chamber 34 in the case where the gaseous fuel pressure is greater than the working fluid pressure during non-injection (i.e. in the case where a malfunction occurs when the injector is not supposed to be injecting). In Figures 5, 6, and 7, similar parts to those shown in Figures 1 to 4 are denoted with the same reference numbers and details will not necessarily be repeated. By enabling some gaseous fuel to flow into the working fluid chamber 34, the pressure in the working fluid chamber 34 will equalise with the pressure in the gas delivery chamber 48. Acting in combination with the spring 50, the force due to fuel pressure in the working fluid chamber 34 will push the valve needle 112 into contact with the valve needle seat 18, preventing uncontrolled injection. Similarly to Figures 3 and 4, the valve needle 112 of Figures 5, 6 and 7 is provided with an annular groove 502 so that the valve needle 212 comprises three portions; an upper head portion 212a, a thinned portion 212b created by the annular groove 502, and a main body portion or needle stem 212c. The upper head portion 212a comprises a frusto-conical portion which defines a flat end surface 212d and an upper cylindrical portion which defines an outer surface 213a. However, in Figures 5, 6 and 7, the thinned portion 212b comprises a further frusto-conical portion and defines a frusto-conical groove surface 502b. The further frusto-conical portion of the thinned portion 212b of the valve needle tapers so that the lower end is wider than the upper end (referencing the orientation in the figures). The frusto-conical groove surface 502b is upwardly directed towards the working fluid chamber 34 and defines an angle to the axis 212’ of the valve needle 212 which is less than 90 degrees but typically more than 20 degrees. In summary, therefore, thethinned portion 212b created by the annulargroove 502 is of axially varying thickness, wherein the region of the thinned portion 212b axially closest to the gas delivery chamber 48 has a larger thickness than the region of the thinned portion 212b axially furthest from the gas delivery chamber 48. The thinned portion 212b has a trapezoidal cross section. The needle stem 212c defines a lower cylindrical outer surface 213c. The annular groove 502 defines an upper radial shoulder 502a and a lower radial shoulder 502c. The upper and lower radial shoulders 502a, 502c are joined by the conical groove surface 213b which is symmetrically arranged about the valve needle axis 212’. It is noted that the upper head portion 212a and the needle stem 212c are of substantially equal diameter. It is also noted that the needle guide bore 24 is of constant diameter and, therefore, the gap 26 between the outer surface 213 of the valve needle 212 and the needle guide bore 24 has a uniform flow cross section both above and below the annular groove 502. A seal member 600 resides within the annular groove 502. The configuration of the seal member 600 is such that it is suitable to seal the communication path between the working fluid chamber 34 and the gas delivery chamber 48 in normal operating positions, but to be operable to open up the communication path in the event of a malfunction. A groove axis 502’ is defined perpendicular to the valve needle axis 212’ and extends through the centre of the thinned portion 212b of the valve needle 212 and, correspondingly, both the seal member 600 and the annular groove 502. The seal member 600 and the annular groove 502 have corresponding asymmetric profiles about the groove axis 502’. The seal member 600 has a trapezoidal or wedged-like cross section and defines an upper end face 600a and a lower end face 600b. The seal member 600 is shaped to define a conical inner surface 600d which seals against the conical groove surface 213b of the thinned portion 212b of the valve needle 212’ and an outer surface 600c which seals against the internal surface 24a of the needle guide bore 24. Given the trapezoidal cross section of the seal member 600, the upper end face 600a is wider than the lower end face 600b in a radial direction. In normal operation, when the injector is functioning correctly, the seal member 600 provides a tight seal under various conditions including component dimension tolerance, thermal expansion, mechanical loading, and varying working fluid and gas pressure. The leakage rate through the gap 26 is considerably reduced with the seal member 600 disposed within the annular groove 502, 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 internal surface 24a of the needle guide bore 24 (as is the case in Figures 1 and 2). The seal member 600 may be formed from PTFE (either unfilled or filled PTFE) which has low sliding friction properties, excellent chemical resistance, and good tolerance in operating temperatures ranging between -40°C to 120°C especially. When the working fluid in the working fluid chamber 34 is at a greater pressure than the pressure of gaseous fuel in the gas delivery chamber 48, the valve needle 212 is in contact with the valve seat 18. As can be seen from Figures 5 and 6, and as has already been described with reference to Figures 3 and 4, high pressure workingfluid is proneto leakout from the working fluid chamber 34 through the gap 26 between the valve needle 212 and the internal surface 24a of the needle guide bore 24. The flow of high pressure working fluid is incident on the upper end face 600a of the seal member 600 and provides a force which pushes the seal member 600 axially in the direction of the gas delivery chamber 48. Given the wedge-like formation of the seal member 600, as the seal member 600 is forced towards the gas delivery chamber 48, and thus towards the narrower portion of the annular groove 502, the outer and inner surfaces 600c, 600d of the seal member 600 will be compressed towards each other. Squeezing the seal member 600 in this way increases the contact pressure between the seal member 600 and both the internal surface 24a of the needle guide bore 24 and the conical groove surface 213b of the valve needle 212, whilst urging the seal member 600 against the lower radial step 502c. This results in a tight seal between the valve needle 212 and the seal member 600, and between the seal member 600 and the internal surface 24a, and hence reduces the likelihood of fluid leakage into the gas delivery chamber 48. In order to optimise the above benefit associated with a wedgelike formation of the seal member 600, the narrowest portion of the groove 502 should be narrower than the narrowest portion of the seal member 600, at its lower end. The seal member 600 further comprises a passage 602 which extends from the upper end face 600a of the seal member 600 at a first end to the inner surface 600d of the seal member 600 at a second end. The first end of the passage 602 is arranged radially away from the annular groove 502 and the second end of the passage 602 is arranged radially within the annular groove 502. In normal working operation of the injector 100, as shown in Figures 5 and 6, the second end of the passage 602 is closed by the conical groove surface 213b of the thinned portion 212b of the valve needle 212 so that working fluid is not able to flow out of the working fluid chamber 34, through the gap 26 between the internal surface 24a of the needle guide bore 24 and the outer surface 213a of the upper head portion 212a of the valve needle 212, and through the passage 602 into the gas delivery chamber 48. However, in the event of an injector malfunction when the injector 100 is not injecting, the supply pressure of working fluid to the working fluid chamber 34 drops and the lower end face 600b of the seal member 600 is lifted away from the upper radial shoulder 502a of the valve needle 212, due to higher pressure within the gas delivery chamber 48. This position of the seal member 600 is shown in Figure 7. When the lower end face 600b of the seal member 602 is lifted from the lower radial shoulder 502c, a gap opens up between the thinned portion 212b of the valve needle 212 and the inner surface 600d of the seal member 600 so that the passage 602 is no longer closed against the valve needle 212 at its first end. Gaseous fuel is therefore able to flow from the higher pressure gas delivery chamber 48 into the lower pressure working fuel chamber 34 through the passage 602. Once the pressure either side of the seal member 600 is equalised, the forces due to fluid pressure acting on the valve needle 212 are equalised and the biasing spring 50 serves to maintain the valve needle 212 against the valve seat 18, therefore preventing the injector 100 from becoming stuck open. Without the presence of the passage 602, a failure in the supply pressure of working fluid to the working chamber 34 would otherwise result in the valve needle 212 becoming stuck open, with insufficient force to act against fuel pressure within the gas delivery chamber 34 to close the valve needle against the valve seat 18. From the foregoing description it will be appreciated that the seal has two modes of operation: in a first mode it provides an effective seal against an unwanted flow of fluid between the working chamber 34 and the gas delivery chamber 48, and in a second mode it opens up a flow path for gaseous fuel to flow to the working chamber 34 when it is required to reestablish high pressure in the working chamber 34 in the event of a malfunction. It is noted that, referring back to the example in Figures 3 and 4, and as shown in Figure 8, a passage 62 may additionally be provided in an annular seal member 60 having a uniform outer diameter along its axial length. A passage 62 extends between the upper end face 60a of the annular seal member 60 and the lower end face 60b of the annular seal member 60, with the upper end of the passage 62 communicating with the gap 26 between the inner surface 24a of the needle guide bore 24 and the outer surface 113a of the head portion 112a of the valve needle 112. The lower end of the passage 62 opens at the lower end face 60b of the annular seal member 60 so that it is closed by the lower radial shoulder 52c defined by the annular groove 52, when in normal operating conditions, but opens up if the annular seal member 60 lifts away from the lower radial shoulder 52c. In circumstances in which the pressure of working fluid within the working fluid chamber 34 is reduced, the annular seal member 60 is lifted away from the lower radial shoulder 52c, due to the pressure imbalance across the annular seal member 60, and gaseous fuel may flow from the gas delivery chamber 48 into the working fluid chamber 34 through the passage 62. Given that the pressure in the gas delivery chamber 48 is greater than the pressure in the working fluid chamber 34, the gaseous fuel will flow through the passage 60 until the pressure either side of the seal member 60 is equal. Once the pressure either side of the seal member 60 is equalised, the forces due to fluid pressure acting on the valve needle 112 are equalised and the biasing spring serves to maintain the valve needle against the valve seat 18, therefore preventing the injector 100 from becoming stuck open. In one embodiment of the invention, the working fluid supplied to the working fluid chamber 34 is a lubrication fluid. In this case, it may be useful to have a small quantity of controlled working fluid leakage through the gap 26 as this ultimately results in a small amount of lubrication fluid at the valve needle seat 18. Providing a controlled quantity of lubricating fluid (such as oil) at the valve needle seat 18 has a benefit on the wear of the valve needle 212 and / or of the valve needle seat 18. In other words, a controlled amount of leakage through the gap 26 may be desirable. As has been described previously, axial motion of the valve needle 212 is driven by changing the pressure of the working fluid in the working fluid chamber 34. More specifically, the actuator 32 has been operated to lift the valve needle 212 away from the valve seat 18. The control valve 30 is actuated so that it is no longer in contact with the valve seat 42 defined by the housing body 22, working fluid flows through the low pressure drain 44 and hence the pressure of the working fluid in the working fluid chamber 34 decreases. In these circumstances the pressure of the gaseous fuel in the gas delivery chamber 48 urges the valve needle 212 away from the valve seat 18, against the closing force of the spring 50. The seal member 600 is also driven along the needle axis 212’ towards the working fluid chamber 34 by the pressure of the gaseous fuel in the gas delivery chamber 48. In other words, both the valve needle 212 and the seal member 600 are urged to move axially in a direction away from the valve seat 18 by the high pressure gaseous fuel in the gas delivery chamber 48. When injector is in a second operating state the valve needle 212 is moving axially toward the valve needle seat 18 such that the injector 200 is ‘closing’. High pressure control fluid is supplied to the bore in the valve housing 38 so that when the valve member 30 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. Therefore, the pressure of the working fluid in the working fluid chamber 34 will increase. When the pressure in the working fluid chamber 34 increases such that the force acting on the valve needle 212 due to fluid pressure of the working fluid is greater than the force acting on the valve needle 212 in the other direction, due to fuel pressure of the gaseous fuel in the gas delivery chamber 48, the valve needle 212 moves into contact with the valve seat 18. During this axial motion of the valve needle 212, the seal member 600 is also in axial motion towards the valve seat 18. A flow path is provided between the working fluid chamber 34 and the gas delivery chamber 48, through the passage 602. Given that, during motion of the valve needle 212 towards the valve seat 18, the pressure of the working fluid in the working fluid chamber 34 is greater than the pressure of gaseous fuel in the gas delivery chamber 48, working fluid will flow through the passage 602 into the gas delivery chamber 48. Due to its higher density, this workingfluid will travel down and through the gas delivery chamber 48 providing the valve seat 18 with a small amount of working fluid, which acts as a lubricant. It may be possible that, when the fuel injector 100 is closing, a greater frictional force is experienced by the seal member 60 causing it to lag behind movement of the valve needle 121. In this case, when the valve needle 112 is urged axially towards the valve seat 18, fluid communication is provided between the working fluid chamber 34 and the gas delivery chamber 48 via the gap 26 between the outer surface 113a of the upper head portion 112a and the internal surface 24a of the needle guide bore 24 so that the valve seat 18 is provided with some working fluid, which acts as a lubricant. It will be appreciated that other embodiments are envisaged beyond those described here, without departing from the scope of the invention set out in the appended claims.

Claims

1. A fuel injector (100, 200) for delivering gaseous fuel to an internal combustion engine, the fuel injector (100, 200) comprising:a gas delivery chamber (48) defining an opening (20) for delivering the gaseous fuel therethrough to the internal combustion engine;a housing body (22) defining a workingfluid chamber (34) and a needle guide bore (24) extending from the working fluid chamber (34) to the gas delivery chamber (48);a valve needle (112, 212) movable within the needle guide bore (24) along a valve needle axis (112’, 212’) to open and close the opening (20) defined by the gas delivery chamber (48);a needle control valve (30) for controlling movement of the valve needle (112, 212) by controlling a pressure of a working fluid in the working fluid chamber (34);an annular groove (52, 502) defined in the valve needle (112, 212) between the valve needle (112, 212) and the needle guide bore (24) to define a thinned portion (112b, 212b) of the valve needle (112, 212); andan annular seal member (60,600) arranged at least partially within the annular groove (52, 502) configured to provide a seal between an outer surface (113,213) of the valve needle (112,212) and an internal surface (24a) of the needle guide bore (24), wherein the seal member (60,600) comprises a passage (62, 602) extending therethrough and is movable within the annular groove (52, 502) from a first position to a second position in the event of a malfunction resulting in the pressure of working fuel in the working fluid chamber (34) being less than the pressure of the gaseous fuel in the gas delivery chamber (48), wherein:in the first position, the passage (62, 602) is blocked to prevent the working fluid from flowing through the passage (62, 602) of the seal member (60, 600) into the gas delivery chamber (48); andin the second position, the passage (62, 602) is unblocked to allow the gaseous fuel to leak through the passage (62, 602) of the seal member (60, 600) into the working fluid chamber (34).

2. Afuel injector (100,200) accordingto claim 1, wherein the needle axis (112’, 212’) defines an axial direction and the seal member (60, 600) is configured to slide in the axial direction between the first and second positions.

3. A fuel injector (100, 200) according to claim 1 or 2, wherein the seal member (60, 600) is made from polytetrafluoroethylene (PTFE).

4. A fuel injector (100, 200) according to any preceding claim, wherein the passage (62, 602) extends from an upper end face (60a, 600a) of the seal member (60, 600) at a first end of the passage (62, 602) to a lower end face (60b, 600b) of the seal member (60, 600) at a second end of the passage (62, 602), wherein the upper end face (60a, 600a) faces towards the working fluid chamber (34) and the lower end face (60b, 600b) faces towards the gas delivery chamber (48).

5. Afuel injector (100, 200) accordingto claim 4, wherein the first end of the passage (62, 602) is arranged radially apart from the annular groove (52, 502) and the second end of the passage (62, 602) is arranged radially within the annular groove (52, 502).

6. A fuel injector (100, 200) according to claim 5, wherein the annular groove (52,502) is configured to block the second end of the passage (62,602) when the seal member (60, 600) is in the first position.

7. A fuel injector (200) according to any preceding claim, wherein a groove axis (502’) is defined perpendicular to the valve needle axis (212’) andpasses radially through the centre of the thinned portion (212b) of the valve needle (212) and, correspondingly, through both the seal member (600) and the annular groove (502), and the seal member (600) and the annular groove (502) comprise corresponding asymmetric profiles about the groove axis (502’).

8. A fuel injector (200) according to claim 7, wherein the seal member (600) comprises a trapezoidal cross section defining an upper end face (600a) which faces towards the gas delivery chamber (34), an opposing lower end face (600b) which faces towards the gas delivery chamber (48), an outer surface (600c) extending from the upper end face (600a) to the lower end face (600b) parallel to the valve needle axis (212’), and a conical inner surface (600d) extending from the upper end face (600a) to the lower end face (600b) at an angle to the valve needle axis (212’), wherein the conical inner surface (600d) is angled towards the valve needle axis (212’) such that the upper end face (600a) is wider than the lower end face (600b) in a radial direction.

9. A fuel injector (200) according to claim 8, wherein the annular groove (502) defines:an upper radial shoulder (502a) which faces towards the gas delivery chamber (48) and against which the upper end face (600a) of the annular seal member (600) abuts when the seal member (600) is in the second position;the lower radialshoulder (502c) which faces towards the working fluid chamber (34) and against which the lower end face (600b) of the seal member (600) abuts when the seal member (600) is in the first position; anda conical groove surface (213b) extending between the upper and lower radial shoulders (502a, 502c), wherein the conical groove surface (213b) corresponds to the conical inner surface (600d) of the seal member (600).

10. A fuel injector according to any preceding claim, wherein the seal member (60, 600) is movable within the annular groove (52, 502) from thefirst position to the second position when the valve needle (112, 212) is moving to close the opening.

Images