Injector and rail assembly

Abstract

An injector and rail assembly for a common rail fuel injection system. The fuel injector 22 comprises an injector body with a ring flange and an injector head end 22. The ring flange 48 has a ring ele

Description

FIELD OF THE INVENTION This invention relates to an injector and rail assembly for a common rail fuel injection system. In particular, the invention relates to an injector and a rail connection assembly for use in a common rail fuel injection system for an internal combustion engine. BACKGROUND In a gasoline direct injection fuel system, the fuel from a rail is supplied to a plurality of injectors via a plurality of corresponding rail sockets, with each pair of injectors and the rail sockets being connected using a mechanical connector assembly. In some injector mounting configurations, such as ‘seated’ injectors, a seat ring of the fuel injector rests on a ledge inside a pocket of an engine head. In such systems, a downward or ‘seating’ force is required to keep the fuel injector in place in the pocket of the engine head against a combustion gas pressure inside a cylinder of the engine during operation. A connector arrangement is generally used to establish a fuel supply path between a fuel rail socket and the injector. The respective position of each rail socket and corresponding injector pair is constrained by how the rail conduit is mounted onto the engine head and how the respective injector pockets in the engine head are located relative to the rail assembly. Due to these positional constraints and potential variations in the dimensions of the rail sockets, injectors, and the injector pockets, each rail socket and corresponding injector pair may be angularly and / or axially misaligned. In addition to this, the amount of angular and / or axial misalignment of each socket and injector pair may be different from that of the other pairs, leading to variation in the amount of misalignment along the rail conduit. Angular and / or axial misalignments can contribute to suboptimal orientations and positions of the injector spray tip, resulting in suboptimal fuel injection spray directions and profiles which can lead to inefficient fuel combustion. While metallic connector interfaces between a rail socket and injector are robust, using a rigid mechanical connection to force a correction to any of the above-mentioned misalignments may result in undesirable stresses and strains on the rail and the injector. Furthermore, if a misalignment is large, it could affect the sealing capabilities of the connector, which could in turn lead to fuel leakage between the rail socket and the injector. The mechanical connector assembly must therefore be robust, easy to mount, and prevent fuel leakage while allowing fuel to flow from the rail sockets to the injectors. Additionally, the mechanical connector assembly must be able to accommodate both unintended angular misalignment of the injector and rail socket central axes as well as unintended axial separation between the socket and the top head of the injector. Existing mechanical connector assemblies rely on elastomer O-rings at the injector-socket interface. However, there is an increasing demand to improve fuel efficiency and reduce exhaust emissions which means injection is required at high fuel pressures in excess of 500 bar, for example as in gasoline direct injection systems. This creates a challenge for the sealing requirements as the elastomer seals are prone to performance degradation and failure over a long service life. The wide temperature range to which the seals are subjected during their service lives are also prejudicial to seal performance. In addition, these elastomeric seals may not be reliable in injection systems using gaseous fuel such as hydrogen which can gradually diffuse into the elastomer and degrade the material and the sealing function. This degradation may aggravate in injection systems using hydrogen at very high pressure. It is against this background that the invention has been devised. SUMMARY OF THE INVENTION According to an aspect of the invention there is provided an injector and rail assembly for a common rail fuel injection system, the injector and rail assembly comprising a fuel injector comprising an injector body provided with a ring flange arrangement and an injector head end for receiving fuel, the ring flange arrangement comprising a flange and a ring element removably seated on a substantially planar first surface of the flange. The injector and rail assembly further comprises a common rail housing defining a reservoir volume for storing fuel at high pressure, the common rail housing comprising at least one socket having a bore for delivering high pressure fuel from the reservoir volume to the injector head end. The injector and rail assembly further comprises a mechanical connector assembly for sealingly mounting the fuel injector to the socket of the common rail housing. The mechanical connector assembly comprises an upper portion configured to threadably engage with an outer surface of the socket, a lower portion having a second surface configured to interface with a third surface of the ring element, and an internal channel configured to receive at least a portion of the head end of the fuel injector. The ring element has a substantially circular or elliptical cross-section. The second and third surfaces together define a rolling interface. The invention advantageously allows for corrections to be made to axial and / or angular misalignments which may occur between the injector and the socket. Furthermore, the invention provides an arrangement in which a curved surface (i.e. the third surface of the ring element) for the rolling interface between the ring flange arrangement and the mechanical connector assembly is provided without the need for curved or contoured surfaces to be machined into the injector body itself. Instead, the ring element is provided as a separate (curved outer surface) element to the injector body, that is seated on a substantially planar or flat surface of the injector body. The curved outer surface of the ring element provides for at least one or the second and third surfaces to define a curved surface for the rolling interface. The second surface may define a conical surface, and in particular may define a side face of a truncated cone. In other embodiments, the second surface may be contoured in a different manner complementary to the third surface of the ring element to produce the rolling interface between them. The upper portion of the mechanical connector assembly may comprise an internal surface having a threaded arrangement for cooperating with a threaded arrangement on the outer surface of the socket. The flange may be integral or removably coupled to the fuel injector. As such, the flange on which the ring element is seated or mounted may be an integral part of the injector body or a removably separate entity. Opposing ends of the ring element may be separated by a gap such that the ring element is circumferentially discontinuous. The ring element may comprise a radial recess that extends about the circumference of the ring element to define a radial split in the ring element. The ring element may comprise an outer wall that defines an annular space within. In some embodiments the annular space may be empty such that the ring element is substantially hollow. In some embodiments a spring element, such as a force resistive springy element, may be housed within the annular space. As such, the ring element may be solid or define a hollow or filled annular space within, and / or may be a radially or circumferentially split ring. In other words, the ring element may be continuous or discontinuous with a split (radially or circumferentially) and can be solid or annular with or without a spring element inside. The head end of the fuel injector may comprise an upper flange. The radial diameter of the upper flange may be less than the radial inner diameter of the socket bore. Inner surfaces of the socket and the upper flange may cooperate to define a sealing ring cavity. The upper flange, a sloping portion of the socket, and a lower internal wall of the socket may cooperate to define the sealing ring cavity. An annular sealing element may be housed in the sealing ring cavity. The annular sealing element may be formed of one of: a metal; and a composite material. The sealing element may be solid. The sealing element may comprise an annular space that may be empty such that the sealing element is hollow. The annular space may be fully or partially filled with another suitable material. Although using metallic sealing rings instead of elastomeric rings is known and can provide robust performance under high pressure and wide temperature conditions, using metallic sealing rings with an improperly designed connection arrangement may make the arrangement rigid or inflexible, for example not optimally accommodating angular or linear misalignments between the injectors and the rail sockets. The present invention overcomes this limitation using an advantageous mechanical connector assembly. The sealing provided by the annular sealing element housed in the sealing ring cavity may be the only sealing interface between the injector and the socket, common rail and mechanical connector assembly. This sealing interface prevents leakage out of the socket bore and towards the ring flange arrangement, such that the interfaces between the lower flange of the injector, the ring element, and the lower portion of the mechanical connector assembly, do not need to provide sealing. In this way, the ring flange arrangement and lower portion of the mechanical connector assembly can advantageously be optimised to provide the rolling interface without curved contours required to be machined into the injector body, without the added requirement of providing sealing between the ring flange arrangement and mechanical connector assembly, and elements of the ring flange arrangement itself. The mechanical connector assembly may comprise an extension wall that extends from the lower portion of the mechanical connector assembly to define an enclosure for housing the flange. The extension wall may comprise one or more openings arranged to receive a retaining element for retaining the injector with respect to the mechanical connector assembly. In embodiments, the retaining element may be a substantially U-shaped pin. In that case, the extension wall may comprise a pair of openings. Each opening of the pair of openings may be arranged to receive a leg of the substantially U-shaped pin, such that the legs of the pin engage and support an underside of the flange of the injector. The ring element or ring-like component may be primarily a load transfer member to hold down the injector onto its seat (which may be a ledge provided inside the engine pocket) with sufficient force. Another function of the ring element is to establish a rolling interface with the second surface on the lower end of the mechanical connector assembly, to accommodate angular misalignment between the socket and injector axes. The common rail housing may comprise a housing for a doser. The doser may be provided between the reservoir volume and the socket. The doser may be a unit to supply a regulated amount of a fluid to the injector, other than the reservoir fuel. The fluid could serve as a lubricant or any other function as required. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a front view of an injector and rail assembly including a rail socket, with the injector and rail socket connected via a mechanical connector according to an embodiment of the invention; Figures 2a, 2b, and 2c show non-limiting examples of angular and axial misalignment between an injector and its corresponding rail socket; Figures 3a is a cross-sectional view of a portion of the injector and rail assembly of Figure 1 denoted by area ‘A’; Figure 3b is a cross-sectional view of a portion of an injector and rail assembly according to another embodiment of the invention; Figure 4 shows a method of assembling the injector and rail assembly of Figure 1; and Figure 5 is a cross-sectional view of an injector and rail assembly according to another embodiment of the invention. DETAILED DESCRIPTION In general, embodiments of the invention provide arrangements for common rail fuel injection systems which provide improved management of angular and / or axial misalignment of a fuel injector with a socket, and more secure and adaptable means for preventing leakage of fuel from the interface between the injector and the socket, which may be subject to pressures up to and in excess of 500 bar. Embodiments of the invention are applicable to any such fuel injection systems, for example those used by vehicles such as automobiles, submersibles, and the like. The fuel used may be any liquid or gaseous fuel for use in such systems, such as hydrocarbon-based fuels, synthetic fuels such as electro-fuels, hydrogen or other alternative fuels and the like. The embodiments of the invention are also applicable to fuel injection systems that employ auxiliary systems, such as lubrication dosing systems for example. Embodiments of the invention are described in relation to a seated arrangement of the fuel injector, in which an injector seat ring rests on a ledge inside a pocket of an associated engine. It will be appreciated that the embodiments of the invention are compatible with other types of fuel rail arrangements, for example such as a hanging arrangement, in which the injector is retained against the socket and / or rail by a clip or pin. In the following description, directional or relative references such as ‘upper’, ‘lower’, ‘above’ and ‘below’, relate to the orientation of the features as illustrated in the drawings, but such references are not to be considered limiting. The skilled reader will appreciate that injector and rail assemblies in accordance with embodiments of the invention may be oriented differently to the manner depicted in the drawings in practice. Figure 1 shows an injector and rail assembly 10 for a fuel system of a gasoline direct injection engine which includes a common rail housing 12 including a conduit defining a rail volume or reservoir 14 for storing fuel at high pressure. The injector and rail assembly 10 also includes a socket 16 having a central axis L1 and a socket bore 18 defining a passage for delivering high pressure fuel from the rail volume 14 to a head end 20 of a fuel injector 22, also referred to as an injector head 20. An outlet 24 of the rail conduit (shown, for example, in Figures 3a and 3b) allows fuel to enter the socket 16 from the rail volume 14. The fuel injector 22 is mounted onto an associated engine head (not shown), and the socket 16 is typically forged or brazed onto the rail housing 12. A mechanical connector assembly or connector 26 connects the injector head 20 to the socket 16. The connector 26 may be made from, for example, metal, polymer, overmolded material, or fibre-reinforced polymer. In practice, several fuel injectors 22 may be clamped along the length of the rail housing 12 depending on the number of cylinders in the engine. A lock nut (not shown) may also be included on the socket 16 between the connector 26 and the rail housing 12 to counteract possible loosening of the connector 26 by engine vibrations. In rail systems which use a seated injector arrangement, the position of the socket axis L1 is typically constrained by the mounting of the rail housing 12 to the mounting boss on the engine head, while the injector position is constrained by the position of a seating ledge 105 defined in a pocket 100 of the engine head, on which the injector 22 is seated. Due to variance in manufacturing tolerances, the differences in these positions may result in axial misalignment of the fuel injector 22 with the socket 16, where when the fuel injector 22 is mounted inside the pocket 100 of the engine head there can be an axial gap / distance G between the fuel injector 22 and the socket 16, for example as illustrated in Figure 2c. Such misalignment can result in fuel leakage and improper contact engagement affecting the transfer of a downward or ‘seating’ force required to firmly secure the fuel injector 22 against the seating ledge 105 in the pocket 100 of the engine head. Forced correction of such misalignment or gapping by an intervening resilient or springy C-clip, for example, between the socket 16 and the fuel injector 22, or other inflexible mechanical connections such as metallic sealing rings, can lead to undesirable load on the rail housing 12 and fuel injector 22 which can affect their respective structural integrities. As will be described further below, if such an axial gap G is present then respective threading 58, 30 on the connector 26 and the socket 16 allows the connector 26 to be moved gradually closer to the engine head, until it bridges the gap, at which point the connector 26 can be tightened to the extent required to provide a secure downward or ‘seating’ force on the fuel injector 22. This adjusts for axial misalignment without over-loading the injector and rail assembly 10, including the fuel injector 22 and connector 26, which helps in improving the fatigue life and structural integrity of the associated components. The same mechanism can be used to accommodate differing operating pressure conditions. In addition to bridging an axial gap G in this manner, the same mechanism allows the connector 26 to address any axial misalignment in the opposite direction, for example excessive overlapping of the associated parts, by moving the connector 26 closer to the rail housing 12 (rather than the engine head) by turning. In addition, variance in manufacturing tolerances can lead to tilting of the fuel injectors 22 relative to the socket axis L1. Figure 2b shows an example of such tilting and an associated angular misalignment, ‘R’, of the fuel injector 22 and the socket 16 which, as will be described in more detail below, the invention can advantageously accommodate. For reference, Figure 2a shows an example of angular alignment of the fuel injector 22 and the socket 16. The correction or accommodation of such angular misalignment R using, for example, metallic sealing rings with inflexible connectors, can lead to fuel leakage, undesirable stressing / straining of the injector and rail assembly 10 and fuel injector 22 as well as the connector 26 itself, and undesirable deformation of these components. Turning now to Figure 3a, a cross-sectional view of a portion of the injector and rail assembly 10 of Figure 1 is shown, in accordance with an embodiment of the invention. The fuel injector 22 has a central longitudinal main axis L2 which is preferably axially aligned with the socket axis L1 (as illustrated in Figure 3a). The socket 16 has a radially outer surface 28 which comprises threads 30 that radially spiral around and along the socket axis L1. The threads 30 extend along the majority of the length of the socket 16 along the socket axis L1. As explained above, the provision of a threaded socket 16 can allow for the height of the connector 26 in relation to the socket 16 to be adjusted without providing an unnecessarily high preload to the rail housing 12 or compressing other components. The bore 18 of the socket 16 is circular and extends vertically along the socket axis L1, defining an upper internal wall 32, a sloping section 38, and a lower internal wall 34. The upper internal wall 32 protrudes slightly into the bore 18 towards the socket axis L1 such that the upper internal wall 32 has a diameter Duw which is smaller than the diameter Di_wof the lower internal wall 34. The sloping section 38 joins the upper internal wall 32 to the lower internal wall 34 and thus has a diameter which varies along the socket axis L1. The upper internal wall 32 and sloping section 38 therefore together define an internal protrusion 36. In other embodiments, the internal protrusion 36 may instead have a horizontal ledge or similar, such that the sloping section 38 instead extends substantially perpendicularly to the socket axis L1. The injector head 20 is substantially cylindrical with a diameter which is smaller than the diameter Duw of the bore upper internal wall 32, and has a top (upper) flange 40 with a diameter Dtf. Diameter Dtf is smaller than the diameter Dlw of the socket bore 18, such that there is a small gap 42 between the bore 18 lower internal wall 34 and the outer side wall of the top flange 40 when the injector head 20 is inserted into the socket bore 18. The small gap 42 allows for the injector and rail assembly 10 to accommodate a degree of angular misalignment or tilt of the fuel injector 22 when it is assembled into the socket 16, without loading the fuel injector 22 or the socket 16. The size of the small gap 42 depends on the angle of inclination of the fuel injector 22 to be accommodated. The angle of inclination depends on a number of factors, for example, control of manufacturing tolerance, constraints between the injector top flange 40 and internal protrusion 36, and so on. The top flange 40 is situated a distance below the top of the injector head 20, such that the top surface of the top flange 40, a portion of the lower internal wall 34 of the bore 18, the sloping section 38, and a portion of the injector head 20 together define a sealing ring cavity 44. The sealing ring cavity 44 houses an annular sealing element or ring 46 and prevents the sealing ring 46 from being easily dislodged. The sealing element 46 may be solid or may comprise an annular space within. The internal protrusion 36 is especially advantageous in securing the sealing ring 46 within this sealing ring cavity 44. However, in some embodiments it is possible for there to be no internal protrusion in the socket 16, in which case the sealing ring 46 rests on top of the top flange 40. One or more of these surfaces which interact to form the sealing ring cavity 44 may be curved or rounded to align more closely with the shape of the sealing ring 46. In embodiments, the annular sealing ring 46 is flexible and may be an O-ring, C-ring, E-ring, Y-ring or other similar element, and may be formed from an elastomeric material, metallic material, composite material, or the like. The sealing ring 46 may comprise an internal resilient media or a structural member, such as one or more springs for example, such that the sealing element may considered to be an energised ring. The sealing ring 46 could be plain or heat-treated or surface coated based on the application needs. The sealing ring 46 provides an internal seal between the fuel injector 22 and the engine environment, which prevents leakage from the interface between the fuel injector 22 and the socket 16, which in turn prevents subsequent leakage from the interface between the fuel injector 22 and the connector 26 via an internal connector channel 60 of the connector 26. In this way, this configuration does not require additional seals at other locations within the injector and rail assembly 10 to prevent fuel leakage, thus reducing complexity and the number of components required for the injector and rail assembly 10. The fuel injector 22 also comprises a ring flange arrangement situated below the injector head 20. The ring flange arrangement includes a lower flange 48 of the fuel injector 22 and a ring element 70 that is removably seated on the lower flange 48. In the embodiment of Figure 3a, the lower flange 48 is machined to be integral with the fuel injector body, but in other embodiments the lower flange 48 may be formed as a separate element that is rigidly and removably mounted on the fuel injector body. The lower flange 48 of this embodiment extends radially outwardly from the fuel injector body, away from and perpendicularly to the longitudinal axis L2 of the fuel injector 22. In this embodiment the lower flange 48 is stepped to define first and second lower flange sections, 48a and 48b, respectively. Turning now to the ring element 70, this component may be circular in cross-section as shown in Figure 3a, although in other embodiments may be differently contoured to define a different cross-section, for example ellipsoidal. In some embodiments, the ring element 70 is circumferentially continuous to form a closed annular ring. In other embodiments, the ring element 70 is a discontinuous ring having a gap or space between its opposing ends. In that case, the gap or space defines a circumferential split in the discontinuous ring element 70. The ring element 70 may be solid in some embodiments, as in the example of Figure 3a. In embodiments, the ring element 70 may include a radial split that defines a recess that extends partially through the ring element 70 in a radial direction. Such radial split may extend about some or all of the circumference of the ring element 70. In some embodiments, the ring element 70 may comprise an outer wall that surrounds and defines an annular space within. The annular space of the ring element 70 may be empty such that the ring element 70 is hollow. Alternatively, the annular space may house a resilient media, or a biased or force resistive element, to provide for more effective transfer of the downward seating force onto the fuel injector 22 and against the combustion gas pressure from the engine head. In radial split ring elements 70 such as those described above, it would also be possible for a resilient media, or a biased or force resistive element, to be provided in the radial recess. As illustrated in Figure 3a, the ring element 70 is seated on an upper surface 68 of the first lower flange section 48a and abuts an outer surface 67 of the second lower flange section 48b. The lower flange 48 thus supports the ring element 70, with the first lower flange section 48a supporting the ring element 70 from beneath in this embodiment. The upper surface 68 on which the ring element 70 sits is substantially planar or flat, and extends in a plane that is substantially perpendicular to the central axis L2 of the fuel injector 22 in this example, although other orientations of the upper surface 68 are possible. Turning now to the connector 26, in embodiments this element is shaped in the form of a hexagonal nut, to allow an appropriate tool to turn the connector 26 on the threads 58 described below. It will be appreciated that the form and configuration of the connector 26 may differ in accordance with other embodiments of the invention. Referring to Figure 3a, the connector 26 has an upper connector portion 50, a middle connector portion 52, a lower connector portion 54, and a lower extension wall 55. The internal connector channel 60 of the connector 26 is configured to receive at least a portion of the injector head 20, as well as at least a portion of the socket 16 when the socket 16 and connector 26 are threadably engaged. The upper connector portion 50, middle connector portion 52, lower connector portion 54 and the lower extension wall 55 of the connector 26 are all formed integrally with one another in this embodiment, although in other embodiments this may not be the case. The upper connector portion 50 has a radially inner surface 56 comprising the threads 58 noted already, which are configured to threadably engage with the threads 30 of the socket 16 (and thus with an outer surface of the socket 16). The threads 58 on the radially inner surface 56 spiral around and along the length of the radially inner surface 56 of the upper connector portion 50. The upper connector portion 50 transitions to the middle connector portion 52, which then transitions to the lower connector portion 54. The lower connector portion 54 extends radially inwards from the middle connector portion 52 to create a protrusion into the internal connector channel 60 of the connector 26, such that the inner diameter of the lower portion 54 is smaller than the inner diameter of the middle portion 52 or the upper portion 50. The inner diameter of the lower portion 54 is substantially the same or greater than the diameter Dlw of the lower internal wall 34 of the socket 16. The inner diameter of the lower portion 54 is sufficiently large to allow insertion of the top flange 40 of the fuel injector 22 into the connector 26 and associated socket 16 during assembly, for example when using an assembly method as described herein with respect to Figure 4. The lower connector portion 54 has a sloped surface 66 (or first surface) facing inwardly towards the socket axis L1. The sloped surface 66 is configured to form an interface with an outer surface 62 (or second surface) of the ring element 70 of the ring flange arrangement 48 of the fuel injector 22. Specifically, the sloped surface 66 of the connector 26 and the outer surface 62 of the ring element 70 together define a rolling interface. The sloped surface 66 on the lower portion 54 of the connector 26 has a conical profile extending to a lower corner end 51 of the lower portion 54. Specifically, the sloped surface 66 defines a curved side surface of a truncated cone that is centred about the socket axis L1 of the connector 26. It will be appreciated that the sloped surface 66 of the lower connector portion 54 may be differently contoured in accordance with other embodiments of the invention. For example, the sloped surface 66 may be contoured to have a part-spheroidal or part-ellipsoidal profile or shape and so on. As noted above, the sloped surface 66 of the lower portion 54 of the connector 26 and the outer surface 62 of the ring element 70 are configured in a complementary way to produce a rolling interface between the sloped surface 66 and the outer surface 62. This rolling interface between the connector 26 and the ring element 70 is capable of accommodating an angular misalignment or tilt and a degree of rolling interaction between the connector 26 and the fuel injector 22. As will be appreciated from Figure 3a, the sloped surface 66, the outer surface 67 and the upper surface 68 define a cavity for housing and retaining the ring element 70. Turning now to the lower extension wall 55, this wall 55 is integral with and extends downwardly from the lower connector portion 54. The lower extension wall 55 defines a cylindrical skirt-like housing that extends parallel to the socket axis L1 and defines an inner space 57. The inner space 57 is suitably dimensioned to allow the injector head 20 to be inserted into the connector 26, and to accommodate and house the lower flange 48 of the fuel injector body. It will be appreciated that the shape of the lower extension wall 55 may differ in other embodiments. For example, in some embodiments the lower extension wall 55 may define a divergent annular cone or the like. The lower extension wall 55 of the connector 26 includes a pair of holes 59 configured to accommodate a retaining element 49, such as a ll-pin, for example as illustrated in Figure 1. The ll-pin 49 is capable of supporting an underside surface 69 of the lower flange 48 of the fuel injector 22 to retain the upper portion of the fuel injector 22 within the connector 26. For use, legs of the ll-pin 49 that extend substantially perpendicularly from an end portion 53 of the ll-pin 49 are inserted through the openings 59 to support the fuel injector 22 with respect to the connector 26 from beneath the lower flange 48. Advantageously, the ll-pin 49 allows the fuel injector 22 and the connector 26 to be packaged and transported together as a preassembled unit to an assembly site or plant, such that the fuel injector 22 and connector 26 can be mounted as a unit onto the engine head. Alternatively, the rail housing 12 may be transported together with one or more fuel injectors 22, and corresponding connectors 26, sealing rings 46, and annular rings 70. In that case, the ll-pin 49 may facilitate transportation of these components of the rail assembly as a single preassembled and prepackaged unit. Subsequent assembly of the rail housing 12, connector 26, and fuel injector 22 to the engine head may thus be simplified. The ll-pin 49 may additionally be present before or after the lock nut is mounted to the injector and rail assembly 10. To enable the fuel injector 22 to remain seated on the ledge 105 of the pocket 100 inside the engine head against combustion gas pressure, a downward (seating) force on the injector 22 is required, as discussed above. This is achieved by turning the connector 26 on the socket 16 such that it engages with the ring element 70 positioned on the lower flange 48 of the fuel injector 22 to provide the downward seating force. Tightening the connector 26 increases the seating force on the fuel injector 22. The threaded connection of the connector 26 with the socket 16 helps to adjust for any axial gaps caused by misalignment, without inducing extraneous stresses and / or strains on the fuel injector 22 and injector and rail assembly 10, thus improving the durability of the injector and rail assembly 10. The rolling interface between the sloped surface 66 of the connector 26 and the ring element 70 of the ring flange arrangement of the injector 22 together with the gap 42 allows for angular misalignment R of the fuel injector 22 with respect to the aligned connector 26 and socket 16 axes, L1. Figure 3b shows another embodiment of the invention. The embodiment shown in Figure 3b is the same as the first embodiment of Figure 3a, except that in this embodiment the connector 26 does not include a lower extension wall 55. Instead, the connector 26 of the embodiment of Figure 3b terminates with the lower connector portion 54. Figure 4 shows a method for assembling the embodiment as shown in Figure 3a. It will be appreciated that other methods for assembly may be equally applicable in accordance with the embodiments of the invention. In the example shown in Figure 4, the lower flange 48 is integral with the fuel injector body, and the connector 26 comprises a single integral component. The ring element 70 and sealing ring 46, which are each provided as separate elements, are placed onto the fuel injector 22. Specifically, the ring element 70 is removably mounted or seated on the lower flange 48 and the sealing ring 46 is removably mounted or seated on the top flange 40. Advantageously, the ring element 70 and the sealing ring 46 are mounted on the same component, i.e. the fuel injector 22, and so can be assembled on the injector 22 in a single assembly step or setting. Once the ring element 70 and sealing ring 46 are assembled on the fuel injector 22, the injector 22 is inserted into the injector pocket 100 of the engine head such that an injector seating ring 102 of the injector 22 is seated on the ledge 105 of the pocket 100. Separately, the connector 26 is mounted onto the socket 16. The rail housing 12 and socket 16, which now includes the connector 26, can then be mounted over the injector head 20, which is already supported on the ledge 105 inside the pocket 100 of the engine head, on which the rail housing 12 is suitably mounted. The connector 26 can then be adjusted on the socket 16 as required via the complementary threading 30, 58 to provide a secure downward force on the fuel injector 22. The ll-pin 49 can then be inserted through the holes 59 in the lower extension wall 55 of the connector 26 when the connector 26 has been mounted over the injector head 20 such that the ll-pin 49 supports the underside surface 69 of the lower flange 48 of the fuel injector 22 and retains the fuel injector 22 inside the annular space 57 of the socket 16. In another example of a method of assembly, the rail housing 12, connector(s) 26, and fuel injector(s) 22 and associated annular sealing element(s) 46 and ring element(s) 70, and may be assembled to form a unit before being fitted to the engine. In that case, ll-pins 49 may be inserted through the holes 59 in the lower extension wall 55 of the connector(s) 26 to support the underside surface 69 of the lower flange 48 of the fuel injector(s) 22 and retain the fuel injector(s) 22 with respect to the rail housing 12 and connector(s) 26. Once assembled and secured in this way, the unit can be positioned such that the injector(s) 22 are received in respective pockets 100 of the engine head, and mounted via a mounting boss onto the engine head. The connector(s) 26 then may be adjusted to provide a downward seating force on the injector 22 as discussed above. The skilled person will appreciate that there is more than one suitable way of assembling and mounting the injector and rail assembly 10 on the engine head. This depends on the preference for packaging and transporting the components, and the suitability of mounting the rail and injector system (as described above) on the engine head at a facility or plant. Figure 5 shows an alternative configuration of a fuel injector 22 and rail assembly 110, preferably for use with gaseous fuels such as hydrogen gas, wherein the common rail housing 12 may have a housing 78 for an oil lubrication doser provided between the rail volume 14 and the socket 16. The doser is directly connected to an oil pump (not shown) which provides a small amount of oil into the housing 78 which is interspersed with the hydrogen gas such that droplets of oil can lubricate the walls of the fuel injector 22. It will be appreciated that the rail assembly 110 shown in Figure 5 is compatible with the described connector 26, fuel injector 22, and other embodiments of the invention. Other modifications and variations will be apparent to the skilled person without deviating from the scope of the appended claims. List of parts 10, 110 - injector and rail assembly 12 - rail housing 14 - reservoir / rail volume for fuel 16- socket 18- socket bore 20 - head end of fuel injector or injector head 22 - fuel injector 24 - outlet in rail conduit 26 - mechanical connector assembly or connector 28 - socket radially outer surface 30 - socket outer threads 32 - upper internal wall (of bore section) 34 - lower internal wall (of bore section) 36 - internal protrusion 38 - sloping portion (of bore section) 40 - injector top flange 42 - small gap between injector top flange 40 and lower internal wall 36 44 - sealing ring cavity 46 - solid or annular sealing element or ring 48 - injector lower flange arrangement 48a - first lower flange section 48b - second lower flange section 49 - ll-pin 51 - corner end of sloped surface 66 of connector 26 50 - upper connector portion 52 - middle connector portion 53 - end portion of ll-pin 54 - lower connector portion 55 - lowest connector portion 56 - radially inner surface of upper connector portion 57 - annular space at the centre enclosed by lowest connector portion 55 58 - connector threads 59 - holes on connector portion 55 to accommodate the ll-pin 60 - internal connector channel 62 - outer surface (second surface) of ring-like element 66 - sloped surface (first surface) of the lower connector portion 67 - annular surface of the lower flange 48 68 - stepped surface of the lower flange 48 69 - underside surface of lower flange 48 70 - Annular ring-like component resting on lower flange 48 78 - housing for an oil lubrication doser 100 - pocket of engine head 105 - ledge of pocket of engine head L1 - socket central axis L2 - longitudinal injector axis R - angular misalignment between socket 16 and fuel injector 22 G - axial gap between socket 16 and fuel injector 22 Duw - upper internal wall (of bore section) diameter Dtf - injector top flange diameter Dlw - lower internal wall (of bore section) diameter

Claims

1. An injector and rail assembly (10) for a common rail fuel injection system, the injector and rail assembly (10) comprising:a fuel injector (22) comprising an injector body provided with a ring flange arrangement and an injector head end (20) for receiving fuel, the ring flange arrangement comprising a flange (48) and a ring element (70) removably seated on a substantially planar first surface (68) of the flange (48);a common rail housing (12) defining a reservoir volume (14) for storing fuel at high pressure, the common rail housing (12) comprising at least one socket (16) having a bore (18) for delivering high pressure fuel from the reservoir volume (14) to the injector head end (20); anda mechanical connector assembly (26) for sealingly mounting the fuel injector (22) to the socket (16) of the common rail housing (12), the mechanical connector assembly (26) comprising:an upper portion (50) configured to threadably engage an outer surface (28) of the socket (16);a lower portion (54) having a second surface (66) configured to interface witha third surface (62) of the ring element (70); andan internal channel (60) configured to receive at least a portion of the head end (20) of the fuel injector (22);wherein the ring element (70) has a substantially circular or elliptical cross-section, and wherein the second and third surfaces (66 and 62 respectively) together define a rolling interface.

2. The injector and rail assembly (10) of Claim 1, wherein the second surface (66) defines a conical surface.

3. The injector and rail assembly (10) of Claim 2, wherein the second surface (66) defines a side face of a truncated cone.

4. The injector and rail assembly (10) of any preceding claim, wherein the upper portion (50) of the mechanical connector assembly (26) comprises an internal surface (56) having a threaded arrangement (58) for cooperating with a threaded arrangement on the outer surface (30) of the socket (16).

5. The injector and rail assembly (10) of any preceding claim, wherein the flange (48) is integral or removably coupled to the fuel injector (22).

6. The injector and rail assembly (10) of any preceding claim, wherein opposing ends of the ring element (70) are separated by a gap such that the ring element (70) is circumferentially discontinuous.

7. The injector and rail assembly (10) of any preceding claim, wherein the ring element (70) comprises a radial recess that extends about the circumference of the ring element (70) to define a radial split in the ring element (70).

8. The injector and rail assembly (10) of any preceding claim, wherein the ring element (70) comprises an outer wall that defines and surrounds an annular space within.

9. The injector and rail assembly (10) of Claim 8, wherein a spring element is housed within the annular space.

10. The injector and rail assembly (10) of any preceding claim, wherein the head end (20) of the fuel injector (22) comprises an upper flange (40).

11. The injector and rail assembly (10) of any preceding claim, wherein the radial diameter of the upper flange (40) is less than the radial inner diameter of the socket bore (18).

12. The injector and rail assembly (10) of any preceding claim, wherein inner surfaces of the socket (16) and the upper flange (40) cooperate to define a sealing ring cavity (44).

13. The injector and rail assembly (10) of Claim 11, wherein the upper flange (40), a sloping portion (38) of the socket (16), and a lower internal wall (34) of the socket (16) cooperate to define the sealing ring cavity (44).

14. The injector and rail assembly (10) of Claim 12 or Claim 13, wherein an annular sealing element (46) is housed in the sealing ring cavity (44).

15. The injector and rail assembly (10) of Claim 14, wherein the annular sealing element (46) is formed of one of: a metal; and a composite material.

16. The injector and rail assembly (10) of any preceding claim, wherein the mechanical connector assembly (26) comprises an extension wall (55) that extends from the lower portion (54) to define an enclosure for housing the flange (48).

17. The injector and rail assembly (10) of Claim 16, wherein the extension wall (55) comprises one or more openings (59) arranged to receive a retaining element (49) for retaining the injector (22) with respect to the mechanical connector assembly (26).

18. The injector and rail assembly (10) of Claim 17, wherein the retaining element (49) is a substantially U-shaped pin.

19. The injector and rail assembly (10) of Claim 18, wherein the extension wall (55) comprises a pair of openings (59) arranged to receive legs of the substantially U-shaped pin, such that the legs of the substantially U-shaped pin engage and support an underside of the flange (48) of the injector (22).

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