Fuel injector for direct injection of gaseous fuel

Abstract

The invention relates to a fuel injector (1) for direct injection of gaseous fuel, extending along an axial direction (A) from a proximal side (P) to a distal side (D) and comprising: - an injector body (2) defining a fuel passage (4) and having a distally disposed end portion (3) that defines a valve seat (3.1) extending around an outlet opening (5); - an outward opening pintle (10) received in the injector body (2) to be axially movable between a proximal pintle position, in which it engages the valve seat (3.1) to close the outlet opening (5), and a distal pintle position, in which it disengages from the valve seat (3.1) to release the outlet opening (5); - a deflector cap (19) that is connected to the end portion (3) and extends distally beyond the end portion (3) and that defines at least one exit hole (22) communicating with the outlet opening (5). In order to provide improved means for connecting a deflector cap to a fuel injector, the invention provides that a connecting portion (20) of the deflector cap (19) has a coherent annular structure extending circumferentially in a tangential direction, at least a major part of the connecting portion (20) is disposed radially outwards of the end portion (3), and at least one retention element (23-25) is adapted to establish a form-fit connection between the connecting portion (20) and the end portion (3), which form-fit connection prevents a distal removal of the deflector cap (19) from the end portion (3).

Description

FUEL INJECTOR FOR DIRECT INJECTION OF GASEOUS FUELTECHNICAL FIELD

[0001] The present invention relates to a fuel injector for direct injection of gaseous fuel. It further relates to an engine assembly.BACKGROUND OF INVENTION

[0002] For automotive applications, hydrogen engines are considered as a promising alternative to gasoline or diesel engines since the emissions from a hydrogen engine consist mainly of water. However, using hydrogen as a fuel in a combustion engine brings about several difficulties, some of which stem from the combustion characteristics of hydrogen. Compared to other fuel types, hydrogen has a high laminar flame velocity, a low quenching distance, a large flammability range and a high flame temperature. These characteristics increase the heat input to a fuel injector that is installed to a cylinder head of the engine.

[0003] For instance, an outward opening fuel injector may be used, i.e. , a fuel injector with a pintle that opens towards the combustion chamber of the cylinder. To enhance the combustion quality of the engine, it is beneficial to direct the gas flow into the combustion chamber in a controlled manner. For this purpose, the fuel injector can be equipped at its end with a deflector cap that faces the combustion chamber. Apart from directing the gas flow, the deflector cap may also protect adjacent parts of the injector from heat inside the combustion chamber, e.g. by directly transferring heat to the cylinder head. A portion of the heat flow can thus be diverted away from the injector. The deflector cap can be produced as a separate part that is then assembled to an end portion of the injector. It is possible to connect the deflector cap and the end portion by welding. However, it has been found that in some instances, the welding connection has failed due to the extreme thermal conditions and the vibrations transferred through the cylinder head. In such a case, the deflector cap falls into the combustion chamber where it collides with the piston. This can result in a total loss of the engine.TECHNICAL PROBLEM

[0004] It is thus an object of the present invention to provide improved means for connecting a deflector cap to a fuel injector.

[0005] This problem is solved by a fuel injector according to claim 1 and by an engine assembly according to claim 15.GENERAL DESCRIPTION OF THE INVENTION

[0006] The invention provides a fuel injector for direct injection of gaseous fuel. In other words, the fuel injector is designed for an engine that is adapted for gaseous fuel combustion. “Gaseous fuel” normally refers to a fuel that is gaseous under standard conditions, i.e., 15°C and 101 ,325 Pa. Specifically, the gaseous fuel may be hydrogen (H2). The fuel injector is adapted for direct injection of the gaseous fuel into a combustion chamber of a cylinder of the respective engine. However, this does not exclude the possibility that the fuel injector could be used for indirect injection.

[0007] The fuel injector extends along an axial direction from a proximal side to a distal side. The axial direction can correspond to an injector axis, which may be a symmetry axis of at least some parts of the fuel injector. When the fuel injector is installed to the engine, the proximal side is the side that faces away from the engine, while the distal side faces the engine. In some embodiments, the proximal side corresponds to an upper side and the distal side corresponds to a lower side. The general flow direction of the fuel is from the proximal side to the distal side. The axial direction implicitly defines a radial direction and a tangential direction.

[0008] The fuel injector comprises an injector body defining a fuel passage and having a distally disposed end portion that defines a valve seat extending around an outlet opening. The fuel passage extends through the injector body and communicates with the outlet opening, which is disposed on the distal side of the injector body. The end portion of the injector body at the distal side defines a valve seat that extends around the outlet opening. The end portion can be made of metal, e.g. stainless steel. The other portions of the injector body, or the entire injector body, may also be made of the same metal. The term “metal” explicitly includes alloys, which may also comprise at least one semi-metal, semi-conductor and / or non-metal. Normally, the valve seat and the outlet opening are symmetric with respect to the abovementioned symmetry axis of the fuel injector. Also, the fuel passage can be globally symmetric with respect to this axis. Preferably, at least the end portion of the injector body is adapted to be inserted into a through-opening of a cylinder head. Then, when the fuel injector is installed, the outlet opening of the fuel injector is disposed near the inside of the cylinder head, i.e., near the combustion chamber. The through-opening axiallytraverses a wall of the cylinder head. The end portion can be adapted to the dimensions of the through-opening so that it can be inserted from the outside of the cylinder head.

[0009] The fuel injector further comprises an outward opening pintle received in the injector body to be axially movable between a proximal pintle position, in which it engages the valve seat to close the outlet opening, and a distal pintle position, in which it disengages from the valve seat to release the outlet opening. The pintle is normally received in the injector body so that it can slide along the axial direction. It can be biased towards the proximal pintle position by a spring element, while it can be moved towards the distal pintle position by an actuator, e.g. an electromagnetic actuator or piezoelectric actuator. There are various working principles known in the art for moving the pintle of a fuel injector, all of which are possible in the context of the invention. The term “outward opening” refers to a pintle that moves outward with regard to the fuel passage as it opens, i.e., towards the cylinder or towards the distal side. In the proximal pintle position, the pintle engages the abovementioned valve seat (in a gas-tight manner) to prevent fuel from exiting the fuel passage (injector closed). In the distal pintle position, it disengages from the valve seat, thereby opening the fuel passage via the outlet opening (injector open). As a rule, the pintle is also made of stainless steel.

[0010] Further, the fuel injector comprises a deflector cap that is connected to the end portion and extends distally beyond the end portion and that defines at least one exit hole communicating with the outlet opening. The term “deflector cap” is not to be construed in any limiting way as to the shape of the deflector cap. The deflector cap extends further to the distal side than the end portion. One could also say that it protrudes distally with respect to the end portion. Accordingly, it is closer to the cylinder than the end portion or possibly even disposed inside the cylinder. It comprises at least one exit hole that communicates with the outlet opening. Accordingly, gaseous fuel that exits the outlet opening can exit the fuel injector through the exit hole. Due to its position, the deflector cap is normally the part of the fuel injector that is exposed to the highest temperatures. As a rule, it is also made of metal like stainless steel. When the fuel injector is installed to the engine, the deflector cap can be in contact with the inner surface of the through-opening, thereby facilitating heat transfer from the deflector cap to the cylinder head. Such heat transfer may protect the end portion and possibly other components of the fuel injector from excessive temperatures.

[0011] A connecting portion of the deflector cap has a coherent annular structure extending circumferentially in a tangential direction, at least a major part of the connecting portion is disposed radially outwards of the end portion, and at least one retention element is adaptedto establish a form-fit connection between the connecting portion and the end portion, which form-fit connection prevents a distal removal of the deflector cap from the end portion. The connecting portion is normally only a part of the deflector cap, but it could also correspond to the entire deflector cap. This connecting portion has a coherent annular structure, which extends circumferentially in the tangential direction. “Annular” or “ring-like” refers to a structure that circumferentially surrounds an inner void. It does not imply that the crosssection has to be circular, although this may be true at least for some parts of the connecting portion. The annular structure is coherent, i.e., it corresponds to a full ring, not a partial ring. However, “coherent” is not to be understood as “solid”. In fact, the connecting portion may comprise local cavities like a through-opening or a slot. However, such a cavity does not extend over the entire length of the connecting portion along the axial direction, i.e., it does not fully interrupt the structure in the tangential direction. One could also say that such a cavity is axially limited. The coherent annular structure promotes the mechanical stability of the connecting portion. Also, although some parts of the connecting portion may be elastically and / or plastically deformable to change their radial position, the connecting portion as a whole is normally resistant against radial compression or expansion. This is in contrast to an open ring which can be deformed to adapt its radial dimension. Accordingly, the installation process of the deflector cap preferably does not rely on a deformation of the connecting portion. Therefore, it may be possible to use a cheaper material, e.g., with lower elasticity.

[0012] At least a major part of the connecting portion is disposed radially outwards of the end portion. The term “major part” refers to a sub-portion of the connection portion that represents at least 50% of its axial length. Hence, at least 50% of the length of the connection portion in the axial direction surrounds the end portion of the injector. Depending on the embodiment, the entire connecting portion may be disposed radially outwards of the end portion. One could say that the connecting portion at least partially surrounds the end portion (or a part thereof). It should be noted that the axial dimension of the connecting portion may be different from that of the end portion, e.g., smaller. Some parts of the connecting portion could extend radially into the end portion. The connecting portion may at least partially be in contact with the end portion. However, it may also at least partially be radially spaced from the end portion. A radial spacing may be beneficial to reduce heat transfer between the deflector cap and the injector body.

[0013] The fuel injector comprises at least one retention element that is adapted to establish a form-fit connection between the connecting portion and the end portion, which form-fit connection prevents a distal removal of the deflector cap from the end portion. The term“retention element” is not to be understood in that this has to be a dedicated element separate from the other aforementioned elements. E.g., it could be formed integrally with the end portion or the connecting portion. Through the retention element, a form-fit connection between the connecting portion and the end portion can be established. More specifically, the form-fit connection can be referred to as an axial form-fit connection in that it limits or prevents axial movement of the connecting portion relative to the end portion. Specifically, the form-fit connection prevents distal removal of the deflector cap from the end portion. Due to the connection, the deflector cap cannot be moved away from the end portion towards the distal side. This includes the possibility that the deflector cap can move distally to some extent, while its range of motion is limited by the form-fit connection. In other embodiments, the axial position of the deflector cap may be fixed by the form-fit connection. As will become apparent below, establishing the form-fit connection during assembly may require elastic and / or plastic deformation of the retention element. However, it preferably does not require deformation of the connecting portion. Unlike a welding connection, the form-fit connection is resistant to thermal stress and therefore extremely unlikely to fail. The deflector cap cannot fall off the injector body, which eliminates the risk of a collision inside the cylinder. Also, the continuous annular structure of the connecting portion, which normally maintains its radial dimension, helps to maintain the form-fit connection even when the injector has not been installed to the engine. In contrast to this, an open ring structure could require an outward restriction, e.g., by the walls of the through- opening, to maintain the connection.

[0014] In some embodiments, the deflector cap may be formed like a tube or sleeve that extends from the end portion towards the distal side. In such an embodiment, the outer diameter and the inner diameter of the deflector cap could be constant along the axial direction, or they show only minor variation. At its distal end, the deflector cap then defines a single, relatively large exit hole, according to the inner diameter of the deflector cap. According to another embodiment, the deflector cap comprises a hood portion spaced from the end portion and extending radially inwards from the connecting portion. The hood portion can extend radially inwards to form a hood or dome that is closed except for the at least one exit hole, which is / are normally disposed in the hood portion. These exit holes may be configured to guide the exiting fuel (or fuel-air mixture) differently from what could be achieved by the outlet opening alone. The hood portion may be provided with a plurality of exit holes, the positions of which can be selected to achieve a predetermined spray pattern. The hood portion forms a shield that extends perpendicular to the axial direction and can thus prevent hot gases and infrared radiation from directly impinging on the distal end of the end portion and the pintle. A cavity or chamber can be formed between the hoodportion and the end portion and / or the pintle. Such a chamber can promote mixing of air and fuel.

[0015] According to one embodiment, the connecting portion comprises a deflector-cap retention surface and the end portion comprises an injector-body retention surface, which retention surfaces are adapted to engage at least one retention element interposed between them for axial force transfer through the retention element. In this embodiment, there is preferably only a single retention element, but there could also be a plurality. The respective retention element is produced separately from the connecting portion and the end portion. Both regions can engage the retention element with respective retention surfaces. This includes the possibility that both retention surfaces permanently engage the retention element. The retention element is interposed between them, so that forces can be transferred between the end portion and the connecting portion through the retention element. Specifically, an axial force can be transferred, which prevents the distal movement of the deflector cap. In this embodiment, one could also say that the injector-body retention surface and the deflector-cap retention surface indirectly engage each other through the retention element. It will be understood that the injector-body retention surface is inclined relative to the axial direction towards the proximal side, while the deflector-cap retention surface is inclined towards the distal side. Thus, a distal force component can act on the deflector-cap retention surface while a proximal force component can act on the injectorbody retention surface. “Inclined relative to the axial direction” includes the possibility that the respective surface is perpendicular to the axial direction. Although there are other possibilities, at least one of the retention surfaces can be parallel to the tangential direction. Also, at least one of the retention surfaces can be annular in that it extends over 360° in the tangential direction.

[0016] It is also preferred that at least one of the end portion and the connecting portion defines a radially extending retention recess, which is limited in the axial direction and in which at least one retention element is at least partially received to establish the form-fit connection. The retention recess extends radially. In case of the end portion, it extends radially inwards, whereas in case of the connecting portion, it extends radially outwards. In some embodiments, the retention recess can extend radially through the respective portion, i.e. it can be a through-opening. At least one retention element is at least partially received in the retention recess. One could also say that the retention element extends into the retention recess. Since the retention recess is limited in the axial direction, axial movement of the retention element within the retention recess is also limited. Depending on the dimensions of the retention element and the retention recess, the axial position of theretention element in the retention recess could be completely fixed. In some embodiments, both connecting portions may define a retention recess and the retention element may be partially received in both retention recesses. While the retention recess is axially limited, it may extend along the tangential direction over 360°, i.e. it may be annular.

[0017] In one embodiment, the connecting portion comprises a deflector-cap recessed portion and a proximally adjacent deflector-cap protruding portion which protrudes radially inwards with respect to the deflector-cap recessed portion, wherein the deflector-cap retention surface is disposed in the deflector-cap recessed portion. The deflector-cap recessed portion is radially recessed, i.e., it recedes radially with respect to the adjacent deflector-cap protruding portion. The deflector-cap protruding portion, on the other hand, protrudes radially with respect to the adjacent deflector-cap recessed portion. Specifically, the deflector-cap protruding portion is proximally adjacent to the deflector-cap recessed portion. The deflector-cap recessed portion could also be referred to as a cap increased- radius portion, while the deflector-cap protruding portion could be referred as a cap reduced-radius portion. However, neither of the respective portions needs to have a single, constant radius or radial dimension. However, any (inner) radial dimension of the deflectorcap protruding portion is smaller than any radial dimension of the deflector-cap recessed portion. Accordingly, the deflector-cap recessed portion recedes radially outwards from the end portion, whereas the deflector-cap protruding portion protrudes radially towards the end portion. The deflector-cap retention surface is disposed in the deflector-cap recessed portion. One could also say that the deflector-cap recessed portion comprises the deflectorcap retention surface or forms the deflector-cap retention surface.

[0018] In another embodiment, the end portion comprises an injector-body recessed portion and a distally adjacent injector-body protruding portion which protrudes radially outwards with respect to the injector-body recessed portion, wherein the injector-body retention surface is disposed in the injector-body recessed portion. The injector-body recessed portion is radially recessed, i.e., it recedes radially with respect to the adjacent injector-body protruding portion. The injector-body protruding portion, on the other hand, protrudes radially with respect to the adjacent injector-body recessed portion. Specifically, the injectorbody protruding portion is distally adjacent to the injector-body recessed portion. The injector-body recessed portion could also be referred to as a body reduced-radius portion, while the injector-body protruding portion could be referred as a body increased-radius portion. Again, while neither of the respective portions needs to have a single, constant radius or radial dimension, any (outer) radial dimension of the injector-body protruding portion is greater than any radial dimension of the injector-body recessed portion.Accordingly, the injector-body recessed portion recedes radially inwards from the connecting portion, whereas the injector-body protruding portion radially protrudes towards the connecting portion. The injector-body retention surface is disposed in the injector-body recessed portion, one could also say that the injector-body recessed portion comprises the injector-body retention surface or forms the injector-body retention surface.Preferably, at least one recessed portion is disposed axially between two protruding portions which both radially protrude with respect to the recessed portion, whereby a retention recess is defined adjacent the recessed portion and axially between the protruding portions. This may pertain to the injector-body recessed portion and / or the deflector-cap recessed portion. In case of the injector-body recessed portion, it is disposed axially between a distal injector-body protruding portion and a proximal injector-body protruding portion. In case of the deflector-cap recessed portion, it is disposed axially between a distal deflector-cap protruding portion and a proximal deflector-cap protruding portion. It should be noted that although the recessed portion is recessed with respect to both protruding portions, the two protruding portions may have different radial dimensions.

[0019] Preferably, the retention element is an elastically deformable retention ring, which extends tangentially over at least 200°, preferably at least 300°, around the end portion. The retention ring is interposed between the end portion and the connecting portion. It is manufactured separately from the end portion and the connecting portion. While it is referred to as a retention “ring” it does not have to be fully annular. However, it extends over considerably more than 180°, namely at least 200°, in the tangential direction. It is elastically deformable and may e.g. be made of a steel with sufficiently high elasticity. Specifically, the radial dimension of the ring may be changeable by elastic deformation. The retention ring may have a circular cross-section, but other geometries are also possible. Apart from its function in establishing the form-fit connection, the retention ring may also provide a (possibly imperfect) seal between the end portion and the connecting portion, thereby hindering heat and / or hot gas from moving further in the proximal direction. In order to realize the elastic expansion and / or compression of the retention ring, there are various options. For instance, the retention ring may comprise an axially and radially extending slot. The slot may be straight and could be aligned along the axial direction. However, it could be aligned at an angle to the axial direction. It could also have a non-straight shape, e.g., an undulated or meandering shape. Anyhow, the slot facilitates deformation of the retention ring. Alternatively or additionally, the retention ring, in undeformed state, can have a corrugated profile along the tangential direction. In other words, as viewed in the radial- tangential plane, the profile of the retention ring undulates along the tangential direction,i.e., it alternatingly protrudes and recedes. Normally, the corrugation is in the radial direction, but it could also be in the axial direction, alternatively or additionally. It will be understood that the corrugated structure allows the retention ring to be deformed, thereby enabling expansion and compression, respectively. It could also be a laminar ring that forms a labyrinth seal with respect to the axial direction. Laminar rings are known in the art as sealing elements. The laminar ring is not closed in the tangential direction but comprises at least one element that is helically wound around the axial direction and overlaps itself. As a rule, each element is made of a metal band with an oblate cross section that is larger in the radial direction than in the axial direction. The open structure of each element facilitates radial deformation.

[0020] Preferably, the retention ring is elastically deformable so that it can be pressed into one retention recess during an assembly process of the deflector cap. In this embodiment, the elasticity of the retention ring, as well as the dimensions of the retention ring in relation to the retention recess, allow for the retention ring to be pressed into the respective retention recess. Thus, during assembly, the retention ring can be radially moved out of the way of the connecting portion or the end portion. For instance, if it is pressed into a retention recess in the of the connecting portion, it can axially move along the end portion without major interference. It may move over a (distal) injector-body protruding portion until it reaches a injector-body recessed portion. There, due to elastic restoring forces, it can contract and be received adjacent to the injector-body recessed portion. Specifically, it may be partially received in a injector-body retention recess in order to establish the form-fit connection. Alternatively, if it is pressed into a retention recess in the of the body portion, the connecting portion can axially move over the retention ring without major interference. A (proximal) deflector-cap protruding portion may move over the retention ring until a deflector-cap recessed portion reaches the position of the retention ring. Then, due to elastic restoring forces, the ring can expand and be received adjacent to the deflector-cap recessed portion. Specifically, it may be partially received in a deflector-cap retention recess in order to establish the form-fit connection. It should be noted that the described embodiments rely exclusively on a deformation of the retention ring and do not require any deformation of the end portion or the connecting portion.

[0021] In order to facilitate the assembly process, it is preferred that one of the connecting portion and the end portion comprises a deflection surface that is inclined relative to the axial direction and that is adapted to exert a radial force on the retention ring during a proximal movement of the deflector cap during the assembly process, thereby pressing the retention ring into the retention recess of the other portion. The deflection surface can bedisposed near a proximal end of the connecting portion or near a distal end of the end portion. For instance, if the retention ring is to be pressed radially inwards into a retention recess of the end portion, the deflection surface is disposed on the connecting portion, preferably near the proximal end thereof. First, the retention ring is placed partially inside the retention recess. Then, as the connecting portion moves proximally, its proximal end gets into contact with the retention ring and the deflection surface exerts a radial force on the ring which pushes it radially inwards. If, on the other hand, the retention ring is to be pressed radially outwards into a retention recess of the connecting portion, the deflection surface is disposed on the end portion, preferably near the distal end thereof. Also in this case, the retention ring is placed partially inside the retention recess. Then, as the connecting portion moves proximally together with the retention ring, the distal end of the end portion gets into contact with the retention ring and the deflection surface exerts a radial force on the ring which pushes it radially outwards.

[0022] According to one embodiment, the deflector-cap retention surface is more inclined relative to the axial direction than the injector-body retention surface. As specified above, an axial force is transferred between the retention surfaces through the retention element. The axial forces acting on the surfaces have the same absolute value but act in opposite directions. In general, if the retention surface is not perpendicular to the axial direction, the axial force is accompanied by a radial force which depends on the inclination of the surface. In this embodiment, the inclination of the deflector-cap retention surface is greater than the inclination of the injector-body retention surface, wherefore the radial force acting on the deflector-cap retention surface is smaller than that acting on the injector-body retention surface. Due to Newton’s third law, this leads to an overall force that acts radially outwards on the retention ring. Therefore, the retention ring is prevented from moving further radially inwards. If it is partially received in an injector-body retention recess, it is prevented from moving further into the recess, which could disrupt the form-fit connection. If, on the other hand, the retention ring is to be prevented from moving radially outwards, the deflector-cap retention surface should be less inclined relative to the axial direction than the injector-body retention surface.

[0023] A retention element like the retention ring is a separate element from the end portion and the connecting portion. There are alternatives, though. According to one embodiment, at least one retention element is permanently connected to the end portion or, preferably, to the connecting portion and protrudes radially towards the other portion. In particular, the retention element can be integrally formed with the respective portion. I.e., the retention element and the end portion or the connecting portion, respectively, can be made of a singlepiece. In some cases, there may not be a clear, unambiguous distinction between the connecting portion (or the end portion) and the retention element. Preferably, the retention element does not extend circumferentially over 360°, but is limited in the tangential direction.

[0024] According to one embodiment, at least one retention element is permanently connected to the connecting portion in a connecting region and is otherwise separate from the connecting portion so that it is movable from an assembly position, in which it can move proximally along the end portion during the assembly process, into a retention position, in which it establishes the form-fit connection with the end portion. Since the retention element is only connected to the connecting portion, it can be moved, by plastic and / or elastic deformation relative to the connecting portion. The movement may correspond to a bending of the retention element. In the assembly position, an inner radial position of the retention element may correspond to an inner radial position of the connecting portion. In the retention position, on the other hand, the retention element may protrude radially inwards from the connecting portion. It is conceivable that the retention position corresponds to a rest position of the retention element from which it is elastically deflectable into the assembly position, so that it moves spontaneously back into the retention position. In another embodiment, it can be moved into the retention position by plastic deformation. I.e. , once the deflector cap is in the desired position, a tool acts on the retention element and deforms it into its retention position, e.g. by bending. The retention element may have a shape similar to a tab, a blade, or a fin. It may be formed by a part of a cylindrical wall of the deflector cap which also forms the connecting portion. It may be separated from the connecting portion by a U-shaped slot, with the connecting region being disposed between the ends of the “U”. Preferably, in assembled state, the retention element is at least partially received in a retention recess of the end portion. To provide optimal support for the deflector cap, it may comprise a plurality of such retention elements, preferably between 2 and 6.

[0025] While the form-fit connection may in some embodiments be considered sufficient for securing the position of the deflector cap, it may be augmented by an additional connection. According to one such embodiment, the deflector cap is press-fitted onto the end portion. The press-fitting process involves a plastic and / or elastic deformation of the deflector cap and / or the end portion, which occurs as the deflector cap is axially pressed onto the end portion. As will be understood, the press-fit connection is mainly based on intense frictional forces which result from the deflector cap and the end portion pressing against each other. The connecting portion can be press-fitted onto the end portion, but it could also be a different portion of the deflector cap.

[0026] Another preferred embodiment provides that the deflector cap is materially bonded to the end portion. In particular, it may be welded to the end portion. Both the end portion and the deflector cap are usually made of stainless steel, wherefore a connection by welding can be easily established. The material bond between the deflector cap and the end portion provides a secure connection without any risk of misalignment e.g., when the fuel injector is inserted into the through-opening. If the material bond fails, however, the deflector cap is still retained by the form-fit connection.

[0027] Advantageously, the deflector cap comprises a lip portion protruding radially inwards and adapted to engage the end portion from the distal side to prevent a proximal movement of the deflector cap relative to the end portion. During assembly, the lip portion can engage the end portion when the deflector cap has reached an intended axial position relative to the end portion. Apart from defining the axial position of the deflector cap, the lip portion can also at least partially cover the end portion from the distal side, thereby protecting it from heat inside the cylinder. The lip portion extends preferably circumferentially in the tangential direction. It may be disposed adjacent to the exit hole.

[0028] The invention further relates to an engine assembly according to claim 15. The engine assembly is either a part of an engine or it comprises the entire engine. Specifically, it is an engine assembly for an engine for gaseous fuel. In some embodiments, the engine assembly can also be referred to as an injector assembly or a cylinder-head assembly. It comprises a cylinder head with an axial through-opening and a fuel injector for direct injection of gaseous fuel according to the present disclosure, at least partially received in the axial through-opening, in particular the injector end portion.

[0029] Preferred embodiments of the inventive engine assembly correspond to those of the inventive fuel injector.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:Fig.1 is a sectional view of a first embodiment of an inventive fuel injector;Fig.2 is a sectional view of a part of the fuel injector of fig.1 and a cylinder head;Figs.3A-3D show different stages of an assembly process of the fuel injector from fig.1 ;Fig.4 is a sectional view of a part of a second embodiment of an inventive fuel injector;Fig.5 is a perspective view of a deflector cap of the fuel injector from fig.4; andFigs.6A-6C show different stages of an assembly process of the fuel injector from fig.4.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] Fig. 1 shows an inventive fuel injector 1 according to a first embodiment of the present invention, while fig. 2 shows a detail of the fuel injector 1 as part of an inventive engine assembly 50. The engine assembly 50 comprises a cylinder head 51 that covers a combustion chamber 52 of a cylinder of an engine. The engine is adapted for a gaseous fuel, in this case hydrogen. A through-opening 53 (or bore) traverses the wall of the cylinder head 51 in an axial direction A, which implicitly defines a radial direction and a tangential direction.

[0032] The fuel injector 1 comprises an injector body 2 that is at least partially made of stainless steel. When installed to the engine, at least an end portion 3 of the injector body 2 is inserted into the through-opening 53 of the cylinder head 51 . The injector body 2 defines a fuel passage 4, which extends axially from a proximal side P towards a distal side D, where it communicates with an outlet opening 5. A pintle 10 is movably received inside the injector body 2. In a proximal pintle position, which is shown in fig. 1 , a pintle head 10.2, which radially protrudes from a pintle shaft 10.1 , closes the outlet opening 5. Specifically, the pintle head 10.2 rests against a valve seat 3.1 that is formed by the end portion 3 around the outlet opening 5. The pintle 10 is also made of stainless steel. It is biased by a pintle spring 11 towards the proximal pintle position. The pintle spring 11 engages a pintle perch 10.3 that protrudes from the pintle shaft 10.1.

[0033] Proximally of the pintle 10, an armature element 15 is disposed inside the injector body 2. The armature element 15 comprises an elongate, roughly cylindrical armature shaft 16 and an annular armature 17 that circumferentially surrounds the armature shaft 16 and is fixedly connected thereto, e.g. by press-fitting and / or by welding. To the distal side D, the armature 17 faces a pole piece 6 which is part of the injector body 2. The pole piece 6 is magnetizable by a magnetic actuator, in this case a solenoid 7, which generates a magnetic field when it is activated (energized). By way of the magnetic field (shaped by the pole piece 6), the armature 17 and the entire armature element 15 can be pulled towards the distal side D. Fig. 1 shows the armature element 15 in a proximal armature position, in which the armature 17 and the pole piece 6 are axially spaced apart.

[0034] The armature shaft 16 comprises an elongate, hollow sleeve portion 16.1 that circumferentially surrounds a shaft channel 16.2. During operation, gaseous fuel flows through the shaft channel 16.2. An armature spring 18 is interposed between the injector body 2 and the armature element 15. It biases the armature element 15 towards the distal side D. Since the armature shaft 16 is in contact with the pintle 10, the pintle spring 11 and the armature spring 18 act against each other and create opposing forces on the armature element 15. When the solenoid 7 is activated and magnetizes the pole piece 6, the armature element 15 is pulled towards the distal side D and, since the armature shaft 16 engages the pintle 10, the pintle 10 is also pushed towards the distal pintle position and the injector 1 starts to open. When the solenoid 7 is deactivated, the armature 17 is no longer attracted towards the pole piece 6. Accordingly, the force of the pintle spring 11 pushes the pintle 10 towards the proximal pintle position, and the armature element 15 is pushed towards the proximal armature position.

[0035] A deflector cap 19 is connected to the end portion 3 of the injector body 2. The deflector cap 19 comprises a connecting portion 20 that is circumferentially disposed around the end portion 3, forming a coherent annular structure. The deflector cap 19 extends distally beyond the end portion 3, where a lip portion 21 extends radially inwards. The lip portion 21 at least partially shields the end portion 3 from the distal side D, thereby protecting it from heat inside the combustion chamber 52. The deflector cap 19 defines an exit hole 22 that communicates with the outlet opening 5, wherefore fuel can be released through the outlet opening 5 and the exit hole 22 into the combustion chamber 52. In this embodiment the exit hole 22 is axially disposed and has a diameter greater than the outer diameter of the pintle head 10.2, respectively the valve seat 3.1. As can be seen in fig.2, the connecting portion 20 is connected to the end portion 3 by a welding connection, i.e. , a welding seam 26, and by a form-fit connection. The latter connection is established through a retention ring 24 serving as a retention element 23. The retention ring 24, which has a circular cross-section, comprises a radially and axially extending slot (forming a cut ring, not visible) so that it can be elastically compressed to a smaller radial dimension or be elastically expanded to a larger radial dimension. Fig.2 shows the retention ring 24 partially received in a injector-body retention recess 3.3 of the end portion 3 and partially in a deflector-cap retention recess 20.3 of the connecting portion 20. Each of the retention recesses 3.3, 20.3 extends circumferentially in the tangential direction. The deflector-cap retention recess 20.3 is disposed adjacent a deflector-cap recessed portion 20.4 that is axially interposed between two deflector-cap protruding portions 20.5. The injector-body retention recess 3.3 is disposed adjacent a injector-body recessed portion 3.4 that is axially interposed between two injector-body protruding portions 3.5. The deflector-cap recessed portion 20.4comprises a deflector-cap retention surface 20.2, while the injector-body recessed portion 3.4 comprises a injector-body retention surface 3.2. Both retention surfaces 3.2, 20.2 engage the retention ring 24, so that an axial force can be transferred between the end portion 3 and the connecting portion 20 through the retention ring 24. The injector-body retention surface 3.2 is less inclined relative to the axial direction A (see angle a1) than the deflector-cap retention surface 20.2 (see angle a2; a1 <a2). Therefore, if an axial force is transferred through the retention ring 23, this results in a total radial force on the retention ring 23 that is directed radially outwards. At a proximal end, the connecting portion 20 comprises an annular deflection surface 20.1 that is inclined against the axial direction A.

[0036] The assembly process of the deflector cap 19 to the end portion 3 will now be explained with reference to figs.3A to 3D. In a first step, which is shown in fig.3A, the retention ring 24 is moved from the distal side D axially over the end portion 3. During its movement along the injector-body protruding portion 3.5, the retention ring 24 is radially expanded. When it reaches the injector-body recessed portion 3.4, it contracts due to elastic restoring forces until it is partially received in the injector-body retention recess 3.3. Then, the connecting portion 20 of the deflector cap 19 is axially moved over the end portion 3. Fig. 3B shows a state in which the deflection surface 20.1 makes contact with the retention ring 24. Due to its inclination, the deflection surface 20.1 creates a radial force which pushes the retention ring 24 radially inwards into the injector-body retention recess 3.3. Therefore, the deflector-cap protruding portion 20.5 can be moved over the retention ring 24 without interference, as shown in fig.3C. Then, when the deflector-cap recessed portion 20.4 has reached the axial position of the retention ring 24, the latter can elastically expand into the deflector-cap retention recess 20.3, as shown in fig.3D. It will be appreciated that the formfit connection via the retention ring 24 not only limits a distal movement of the deflector cap 19, but also a proximal movement. Furthermore, the lip portion 21 can engage the end portion 3 from the distal side D, thereby limiting the proximal movement. In this embodiment, the form-fit connection is complemented by the welding seam 26, which is applied once the retention ring 24 is receive in both retention recesses 3.3, 20.3. However, it would be possible to omit the welding seam 26 and only rely on the form-fit connection. Also, it would be possible to complement the form-fit connection by press-fitting the connecting portion 20 over the end portion 3.

[0037] Fig.4 shows a cross-sectional view of a part of a fuel injector 1 according to a second embodiment of the present invention. This embodiment is largely identical to the first one and will insofar not be discussed again. A major difference is that the form-fit connection does not rely on a separate retention ring 24, but on two retention elements 23 that areintegrally formed with the connecting portion 20 of the deflector cap 19. In a retention position, which is shown in fig.4, each retention element 23, which can be referred to as a retention tab 25, is partially received in an injector-body retention recess 3.3 of the end portion 3. It establishes a form fit with the end portion 3 that prevents a distal movement of the deflector cap 19. Again, a proximal movement may be prevented by the lip portion 21 engaging the end portion 3 from the distal side D. In a variant not shown here, the form-fit connection could be complemented by a welding connection and / or by a press-fit connection.

[0038] The assembly process will now be explained with reference to figs. 6A-6C, as well as fig.5, which shows the deflector cap 19 before assembly. The overall shape of the deflector cap 19 is roughly cylindrical. The retention tabs 25 are realized by U-shaped slots 27 formed through the cylinder wall, which separate the connecting portion 20 from the respective retention tab 25. Each retention tab 25 is connected to the connecting portion 20 in a connecting region 28 between the tips of the “U”. The retention tabs 25 hence may have an overall square or rectangular shape, seen from the side (however following the curvature of the connecting portion 20 I deflector cap). During the initial phase of the assembly, which is shown in Fig.6A, the retention tabs 25 are in an assembly position, in which they are flush with the neighboring parts of the connecting portion 20. Thus, they can be moved axially over the end portion 3 without interference. The deflector cap 19 is moved proximally until each retention tab 25 is in the axial position of one injector-body retention recess 3.3, as shown in fig. 6B. This position can be defined by the lip portion 21 making contact with the end portion 3 from the distal side D. In order to establish the form-fit connection, a bending tool 30 exerts an inwardly radial force on each retention tab 25, which leads to a plastic deformation, specifically in the connecting region 28. During this process, a support 31 keeps the deflector cap 19 in position by exerting a force from the distal side D. Through the force of the bending tool 30, each retention tab 25 is moved from the assembly position into the retention position, as shown if fig.6C.Legend of Reference Numbers:1 fuel injector2 injector body3 end portion3.1 valve seat3.2 injector-body retention surface3.3 injector-body retention recess3.4 injector-body recessed portion3.5 injector-body protruding portion4 fuel passage5 outlet opening6 pole piece7 solenoid8 guide element10 pintle10.1 pintle shaft10.2 pintle head10.3 pintle perch11 pintle spring15 armature element16 armature shaft16.1 sleeve portion16.2 shaft channel17 armature18 armature spring19 deflector cap20 connecting portion20.1 deflection surface20.2 deflector-cap retention surface20.3 deflector-cap retention recess20.4 deflector-cap recessed portion20.5 deflector-cap protruding portion21 lip portion22 exit hole3 retention element4 retention ring 5 retention tab 6 welding seam 7 slot 8 connecting region0 bending tool 1 support 0 engine assembly 1 cylinder head 2 combustion chamber3 through-openingA axial directionD distal sideP proximal side

Claims

CLAIMS1 . A fuel injector (1) for direct injection of gaseous fuel, extending along an axial direction (A) from a proximal side (P) to a distal side (D) and comprising: an injector body (2) defining a fuel passage (4) and having a distally disposed end portion (3) that defines a valve seat (3.1) extending around an outlet opening (5); an outward opening pintle (10) received in the injector body (2) to be axially movable between a proximal pintle position, in which it engages the valve seat (3.1) to close the outlet opening (5), and a distal pintle position, in which it disengages from the valve seat (3.1) to release the outlet opening (5); a deflector cap (19) that is connected to the end portion (3) and extends distally beyond the end portion (3) and that defines at least one exit hole (22) communicating with the outlet opening (5), wherein a connecting portion (20) of the deflector cap (19) has a coherent annular structure extending circumferentially in a tangential direction, at least a major part of the connecting portion (20) is disposed radially outwards of the end portion (3), and at least one retention element (23-25) is adapted to establish a form-fit connection between the connecting portion (20) and the end portion (3), which form-fit connection prevents a distal removal of the deflector cap (19) from the end portion (3).

2. The fuel injector according to claim 1 , wherein the connecting portion (20) comprises a deflector-cap retention surface (20.2) and the end portion (3) comprises an injectorbody retention surface (3.2), which retention surfaces (3.2, 20.2) are adapted to engage at least one retention element (23-25) interposed between them for axial force transfer through the retention element (23-25).

3. The fuel injector according to any of the preceding claims, wherein at least one of the end portion (3) and the connecting portion (20) defines a radially extending retention recess (3.3, 20.3), which is limited in the axial direction (A) and in which at least one retention element (23-25) is at least partially received to establish the form-fit connection.

4. The fuel injector according to any of the preceding claims, wherein the connecting portion (20) comprises a deflector-cap recessed portion (20.4) and a proximally adjacent deflector-cap protruding portion (20.5) which protrudes radially inwards with respect to the deflector-cap recessed portion (20.4), wherein the deflector-cap retention surface (20.2) is disposed in the deflector-cap recessed portion (20.4).

5. The fuel injector according to any of the preceding claims, wherein the end portion (3) comprises an injector-body recessed portion (3.4) and a distally adjacent injector-body protruding portion (3.5) which protrudes radially outwards with respect to the injectorbody recessed portion (3.4), wherein the injector-body retention surface (3.2) is disposed in the injector-body recessed portion (3.4).

6. The fuel injector according to any of the preceding claims, wherein at least one recessed portion (3.4, 20.4) is disposed axially between two protruding portions (3.5, 20.5) which both radially protrude with respect to the recessed portion (3.4, 20.4), whereby a retention recess (3.3, 20.3) is defined adjacent the recessed portion (3.4, 20.4) and axially between the protruding portions (3.5, 20.5).

7. The fuel injector according to any of the preceding claims, wherein the retention element (23-25) is an elastically deformable retention ring (24), which extends tangentially over at least 200°, preferably at least 300°, around the end portion (3).

8. The fuel injector according to any of the preceding claims, wherein the retention ring (24) is elastically deformable so that it can be pressed into one retention recess (3.3, 20.3) during an assembly process of the deflector cap (19).

9. The fuel injector according to any of the preceding claims, wherein the deflector-cap retention surface (20.2) is more inclined relative to the axial direction (A) than the injector-body retention surface (3.2).

10. The fuel injector according to any of the preceding claims, wherein at least one retention element (23-25) is permanently connected to the end portion (3) or, preferably, to the connecting portion (20) and protrudes radially towards the other portion (3, 20).11 . The fuel injector according to any of the preceding claims, wherein at least one retention element (23-25) is permanently connected to the connecting portion (20) in a connecting region (28) and is otherwise separate from the connecting portion (20) so that it is movable from an assembly position, in which it can move proximally along the end portion (3) during the assembly process, into a retention position, in which it establishes the form-fit connection with the end portion (3).

12. The fuel injector according to the preceding claims, wherein in the retention position, the at least one retention element (25) is inwardly bent, by plastic deformation, suchthat it is partially received in an injector-body retention recess (3.3) of the end portion (3).

13. The fuel injector according to any of the preceding claims, wherein the deflector cap (19) is press-fitted onto the end portion (3).

14. The fuel injector according to any of the preceding claims, wherein the deflector cap (19) is materially bonded to the end portion (3).

15. The fuel injector according to any of the preceding claims, wherein the deflector cap(19) comprises a lip portion (21) protruding radially inwards and adapted to engage the end portion (3) from the distal side (D) to prevent a proximal movement of the deflector cap (19) relative to the end portion (3).

16. An engine assembly (50) with a cylinder head (51) comprising an axial through-opening(53) and a fuel injector (1) for direct injection of gaseous fuel according to any of the preceding claims at least partially received in said axial through-opening (53).

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