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 injector axis (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 (2.1) that defines a valve seat (3) extending around an outlet opening (5); and - 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) to close the outlet opening (5), and a distal pintle position, in which it releases the outlet opening (5). In order to provide reliable means for preventing closing impact damage in an injector for gaseous fuel, the invention provides that the valve seat (3) comprises a first seat portion (3.1), a second seat portion (3.2) and a third seat portion (3.3), wherein the second seat portion (3.2) extends distally between the first seat portion (3.1) and the third seat portion (3.3) and is less inclined with respect to the injector axis (A) than the first seat portion (3.1) and the third seat portion (3.3), and wherein the pintle (10) comprises a first pintle portion (10.4) that is disposed adjacent to the first seat portion (3.1) in the proximal pintle position and a second pintle portion (10.5) radially outside of the first pintle portion (10.4) that is disposed adjacent to the second seat portion (3.2) in the proximal pintle position and that is disposed distally offset from the second seat portion (3.2) in the distal pintle position.

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 in an internal combustion engine.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 as compared to liquid fuels like gasoline or diesel. Specifically, while liquid fuel provides a considerable damping effect, in particular due to squeeze damping, such damping is negligible for a gaseous fuel. Accordingly, when a moving part of the injector engages another part during its movement in the injection cycle, the resulting impact is much more severe than in a comparable injector for liquid fuel. Also, the mass of the moving elements is oftentimes greater than in a liquid-fuel injector, which also increases the forces acting during impact. Over time, this may lead to deformation or even failure of a component. In particular, the injector valve may lose its sealing properties due to deformations of the injector pintle or the valve seat which the pintle engages during each injection cycle. The resulting injector leakage normally necessitates the replacement of the injector. Also, a severe impact may lead to a rebound of the pintle, thus increasing the time necessary to close the injector.

[0003] One option to alleviate this problem would be to reduce the closing speed of the armature and the pintle. In principle, this is possible by a brief electrical re-activation of the injector during closing. This so-called “soft-landing pulse” helps to slow down the pintle and thus reduce the impact load. However, it is difficult to sense the best timing for the pulse, wherefore satisfactory control of the pintle movement is hardly possible for the entire operating range of the injector.TECHNICAL PROBLEM

[0004] It is thus an object of the present invention to provide reliable means for preventing closing impact damage in an injector for gaseous fuel.

[0005] This problem is solved by a fuel injector according to claim 1.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. “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 injector axis from a proximal side to a distal side. The injector axis corresponds to an axial direction, and 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. The general flow direction of the fuel is from the proximal side to the distal side.

[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. During operation, fuel is ejected from the fuel passage through the outlet opening. As a rule, the injector body comprises several components that are connected to each other. Several components or portions of the injector body may be made of metal, normally stainless steel. The end portion of the injector body at the distal side defines a valve seat that extends around the outlet opening. Normally, the valve seat and the outlet opening are symmetric with respect to the abovementioned injector axis. Also, the fuel passage can be symmetric with respect to this axis. Usually, at least the end portion of the injector body is adapted to be inserted into a through-opening of a cylinder head, with the outlet opening being disposed near the inside of the cylinder head, i.e., near the combustion chamber.

[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 releases the outlet opening. The pintle is normally received in the injector body so that it can slide along theinjector axis. 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. 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. In the distal pintle position, it disengages from the valve seat, thereby opening the fuel passage via the outlet opening. The proximal pintle position can therefore be referred to as a closed position and the distal pintle position can be referred to as an open position. The portion of the pintle that engages the valve seat can normally be referred to as a pintle head, which radially protrudes from a pintle shaft. As a rule, the pintle is also made of metal like stainless steel.

[0010] The valve seat comprises a comprises a first seat portion, a second seat portion and a third seat portion, wherein the second seat portion extends distally between the first seat portion and the third seat portion and is less inclined with respect to the injector axis than the first seat portion and the second seat portion. The valve seat comprises at least the three portions as mentioned, but may also comprise more portions. As will become apparent below, the pintle normally does not engage all three portions in the proximal pintle position, but they are nevertheless considered as portions of the valve seat. Regarding their axial positions, i.e., their sequence with respect to the axial direction, the first seat portion is normally the proximal one, the second is the intermediate one and the third is the distal one. However, the axial positions of these portions may possibly overlap. In any case, the second seat portion extends distally between the first seat portion and the third seat portion. This means that a part of the second seat portion that is closest to (and normally connected to) the first seat portion is disposed further to the proximal side than a part that is closest to the third seat portion. With respect to their radial positions, the first seat portion is normally the innermost one, the second seat portion is the intermediate one and the third seat portion is the outermost one. Normally, the first seat portion is directly connected to the second seat portion, which is directly connected to the third seat portion. It is possible, though, that an additional portion is interposed between the first seat portion and the second seat portion and / or between the second seat portion and the third seat portion.

[0011] The second seat portion is less inclined with respect to the injector axis than the first seat portion and the second seat portion. It will be understood that the inclination refers to an alignment of the surface of the valve seat. In other words, the first, second and third seat portion are strictly speaking surface portions of the valve seat. An inclination refers to an inclination angle between the respective portion (or possibly a tangential plane of the portion) and the injector axis. In case of a rotation symmetry, this inclination angle may also be referred to as a cone angle. If the respective portion is parallel to the injector axis, theinclination is zero. The first, second and third seat portions do not all have the same inclination with respect to the injector axis, but the second seat portion is the least inclined, while both the first and the third seat portion are more inclined. One could also say that an inclination angle between the second seat portion and the injector axis is smaller than an inclination angle between the first seat portion and the injector axis and an inclination angle between the third seat portion and the injector axis. It is possible that at least one portion has a non-constant inclination. According to the described configuration, the surface of the valve seat is inclined further from the injector axis (and thus, further inclined towards the radial direction) in the first seat portion and in the third seat portion than in the second seat portion. Optionally, at least one of the first and third seat portion could be at least partially parallel to the radial direction. Also, the second seat portion can be at least partially parallel to the injector axis. In any case, the three portions define a “stepped” surface structure, i.e. , a step is defined by the second seat portion between the first and third seat portion.

[0012] In embodiments, the valve seat region, respectively injector body, is configured such as to maintain a large flow diameter below the pintle. This may be done by avoiding flow a geometry leading to a flow restriction distally from the third seat portion beyond the second pintle portion, e.g. by maintaining a flow passage corresponding to the diameter of the third seat portion or say a flow diameter at least corresponding to outer diameter of the second pintle portion.

[0013] The pintle comprises a first pintle portion that is disposed adjacent to the first seat portion in the proximal pintle position and a second pintle portion radially outside of the first pintle portion that is disposed adjacent to the second seat portion in the proximal pintle position and that is distally offset from the second seat portion in the distal pintle position. The first and second pintle portion are usually parts of a pintle head which radially protrudes from a pintle shaft. When the pintle is in the proximal position, the first pintle portion is disposed adjacent to the first seat portion, which includes the possibility that these portions engage each other. Likewise, the second pintle portion is disposed adjacent to the second seat portion, which includes the possibility that these portions engage each other. It will be understood that at least one pair of corresponding portions has to sealingly engage each other so that the outlet opening is closed in the proximal pintle position. When the pintle is in the distal pintle position, the second pintle portion is axially offset from the second seat portion, i.e., it is disposed further to the distal side than the second seat portion. One could also say that the second pintle portion is disposed distally of the second seat portion.

[0014] When the pintle is in the proximal pintle position, the outlet opening is closed. The first pintle portion and the second pintle portion are disposed adjacent to the first seat portion and the second seat portion, respectively. As the pintle moves towards the distal pintle position, its axial movement creates an increasing gap between the first pintle portion and the first seat portion. Depending on the shape and inclination of the second seat portion, the movement may also create an increasing gap between the second pintle portion and the second seat portion. However, since the second seat portion is less inclined with respect to the injector axis, the latter gap increases slower (or not even at all). Accordingly, during the first phase of the distal movement, the region between the second pintle portion of the second seat portion represents a bottleneck through which the pressurized fuel can only slowly exit the outlet opening. Therefore, there is an increased pressure difference between the proximal side of the pintle and the distal side of the pintle during this first phase of the movement, which helps to open the injector. At least in the final phase of the movement, as the pintle approaches the distal pintle position, the second pintle portion is distally offset from the second seat portion. Due to the alignment of the third seat portion, which is more inclined towards the radial direction than the second seat portion, the gap between the pintle and the seat now increases significantly faster, i.e. , the bottleneck is removed. Accordingly, pressurized fuel can escape through the outlet opening much faster, thereby enabling a sufficient amount of fuel to be injected, and the pressure difference between the proximal side and the distal side of the pintle is considerably reduced. On the other hand, when the pintle is moved from the distal pintle position towards the proximal pintle position, there is a considerable gap between the pintle and the seat during the first phase of the movement, wherefore gas exchange between the proximal side and the distal side of the pintle is relatively unhindered and has only minor influence on movement of the pintle. However, when the axial positions of the second pintle portion and the second seat portion begin to overlap, the above-mentioned bottleneck reduces the gas exchange so that pressurized fuel between the first seat portion and the first pintle portion cannot escape easily. The pressure difference between the proximal side of the pintle and the distal side leads to an effective force acting on the pintle towards the distal side. This force has a braking effect on the pintle, i.e., it at least reduces the proximal acceleration of the pintle, usually it even reduces the speed of the pintle. In any case, the pintle reaches the proximal pintle position with a “final” speed that is reduced with respect to a common design which does not provide the described bottleneck. Accordingly, the impact force between the pintle and the seat is reduced, which reduces the risk of wear or damage.

[0015] The space between the first pintle portion of the first seat portion can also be described as a damper space, corresponding to a pneumatic damping or braking effect.The inventive injector employs pneumatic damping. The working fluid for the damper can be the gaseous fuel that is available in the injector during operation at all times, i.e., no additional working fluid is necessary. The braking or dampening effect occurs as a result of the movement of the armature and does not require any sensor or actuator for its control. Accordingly, a properly timed damping effect can be achieved with comparatively simple, mechanical means, namely with a special design of the valve seat - and possibly the pintle. Consequently, the inventive design leads to a reduced risk of impact damage during the closing of the injector. As a bonus effect, it facilitates the opening movement by promoting the abovementioned pressure difference.

[0016] Normally, the injector further comprises an armature for actuating the pintle and being axially movable between a proximal armature position and a distal armature position, which corresponds to the distal pintle position. The armature may be made of a single piece or of several pieces, which are fixedly connected. It is adapted for actuating or operating the pintle, i.e., the pintle is movable by the armature. The armature may engage the pintle from the proximal side, i.e., it is at least partially disposed proximally of the pintle. This includes the possibility that it permanently engages the pintle or may even be fixedly connected thereto. The armature and the pintle could even be made as a single piece. In any case, the armature is movable within the injector body. As it is moved from the proximal armature position to the distal armature position, it moves the pintle into the distal pintle position (i.e., the open position). As it moves from the distal armature position to the proximal armature position, the pintle can move back to the proximal pintle position (i.e., the closed position). If the armature and the pintle are fixedly connected, they of course move together.

[0017] The armature may comprise an armature shaft that extends axially and an armature collar that is circumferentially disposed around the armature shaft and fixedly connected thereto. The armature shaft can be elongate in the injector axis. The armature collar and the armature shaft can be made of a single piece or several connected pieces. The armature collar and / or the armature shaft may comprise at least one axially extending armature channel, which is either in fluid communication with the fuel passage or can be regarded as a part of the fuel passage. The armature shaft may be received in at least one guide portion of the injector body. The guide portion guides the axial movement of the armature shaft and accordingly the movement of the armature as a whole.

[0018] The injector normally also comprises an actuator adapted to initiate a movement of the armature towards the distal position, i.e., a distal movement. Preferably the actuatorincludes a solenoid that is activatable to generate a magnetic field. This, in turn, moves the armature from the proximal armature position towards the distal armature position. As a rule, the magnetic field magnetizes at least one component of the injector body, thereby creating magnetic attraction. Specifically, the armature can be pulled towards the distal side. For instance, the injector body may comprise a magnetizable pole piece, which can be circumferentially disposed around the fuel passage. In some embodiments, a distal body portion of the injector body may be magnetizable and serve as a pole piece. When the solenoid is activated, the respective component (pole piece, distal body portion, etc.) is magnetized, thereby magnetically attracting the armature.

[0019] According to one option, the armature and the pintle could be fixedly connected or could even be made of a single piece. Alternatively, the armature and the pintle can be separate elements. In the latter case, the armature is adapted to engage the pintle and move it distally as the armature itself moves towards the distal armature position, and the pintle is adapted to engage the armature and move it proximally as the pintle itself moves towards the proximal pintle position. During the injection cycle, the pintle and the armature may be in permanent contact, or they may temporarily disengage. When the pintle is in the proximal pintle position (corresponding to a closed injector), the pintle and armature may be in contact with one another or separated by a gap, depending on embodiments.

[0020] Reliable contact between the pintle and the armature can be provided if a distal force acts on the armature. According to a preferred embodiment, an armature spring biases the armature towards the distal armature position. By the action of the armature spring, the armature is pressed against the pintle. Normally, the armature spring is interposed between the injector body and the armature. Preferably, the armature spring is a coil spring made of spring steel, but other materials or designs are possible, too. As a rule, the pintle is biased towards the proximal pintle position by a pintle spring. The pintle spring may be a coil spring circumferentially disposed around the pintle. It is normally a pressure spring that is interposed between the pintle and the injector body. It should be understood that the closing of the injector is caused by the action of the pintle spring. Also, during at least a part of the proximal movement, the pintle spring may act, through the pintle and the armature, against the above-mentioned armature spring. Accordingly, the force of the pintle spring has to be considerably greater than that of the armature spring in order to guarantee a reliable closing of the fuel injector. Although reference is made to “an armature spring” and “a pintle spring”, it will be understood that a plurality of armature springs and / or pintle springs could be employed.

[0021] Preferably, the first pintle portion sealingly engages the first seat portion in an annular sealing region when the pintle is in the proximal pintle position. Depending on the design of the first pintle portion of the first seat portion, the annular sealing region can be one-dimensional (corresponding to a ring with negligible width) or two-dimensional (corresponding to a ring with a non-negligible width). Normally, the sealing region is circular, i.e., symmetric with respect to the injector axis. Preferably, the sealing region is disposed in an inner half of the first seat portion, preferably in an innermost third of the first seat portion. Preferably, the annular sealing region represents the only contact region between the pintle and the seat.

[0022] According to a preferred embodiment, the ratio between an outer radius of the second pintle portion and an inner radius of the sealing region is between 1 ,2:1 and 1 ,5:1 , preferably between 1 ,3:1 and 1 ,4:1. Normally, the outer radius of the second pintle portion determines the effective cross-section of the pintle on which the lower pressure from the distal side is acting, and therefore the axial force component exerted by the gas pressure in the proximal direction. If there is no pressure difference between the proximal and the distal side of the pintle, this force component is neutralized by an equal force component acting from the proximal side. However, when the pintle is in the proximal pintle position, a higher pressure is acting on the area radially inside of the sealing region. This, in turn, influences the force needed to move the pintle out of the proximal pintle position. The abovementioned preferred ratio corresponds to a relatively large outer radius of the second pintle portion in relation to the inner radius of the sealing region. The large outer radius of the second pintle portion on the one hand may lead to an increased force differential between forces exerted by the gas pressure from the distal side and the proximal side. Another benefit is that for a given stroke length and a given axial dimension of the second seat portion, an annular flow area between the pintle and the seat is larger if the outer radius of the second pintle portion is larger. Here and in the following, “outer radius” refers to the maximum radial dimension, even if the respective object is not symmetric to the injector axis, while “inner radius” refers to the minimum radial dimension.

[0023] Since a relatively large outer radius of the second pintle portion is beneficial, it is also relatively large compared to the opening radius of the outlet opening. One embodiment provides that the ratio between a maximum opening radius of the outlet opening and the outer radius of the second pintle portion is between 1 ,1 :1 and 1 ,3:1 , preferably between 1 ,1 :1 and 1 ,2:1. In prior art designs, this ratio is usually above 1 ,3:1 , corresponding to a smaller outer radius of the second pintle portion. Normally, the maximum opening radius ofthe outlet opening refers to a location within the third seat portion or distally of the third seat portion.

[0024] It is also preferred that a distal-end inner radius of the valve seat, which is the inner radius of the valve seat at its distal end, corresponds to at least 80%, at least 90%, or at least 100% of the outer radius of the second pintle portion. The inner radius of the valve seat also defines a radius of the outlet opening. To this respect, it is preferred that the outlet opening widens from the second seat portion to the distal end, which includes the possibility that its radius may be partially constant.

[0025] It is highly preferred that an annular first flow area between the first pintle portion and the first seat portion is smaller than an annular second flow area between the first pintle portion and the third seat portion when the pintle is in the distal pintle position. The respective flow area corresponds to an annular area perpendicular to the surface of the pintle. It represents the area or cross section available for gas flow. As mentioned above, when the pintle is near the proximal pintle position, there is a bottleneck between the pintle and the seat that hinders the gas flow. This embodiment provides that when the pintle is in the distal pintle position, there is a sufficiently large second flow area between the first pintle portion and the third seat portion so that the bottleneck is eliminated. While the distance between the first pintle portion and the first seat portion may be greater than the distance between the first pintle portion and the third seat portion, the third seat portion is normally disposed radially outwards of the first seat portion, so that the second flow area has a greater radius than the first flow area. This embodiment usually corresponds to at least one of the abovementioned embodiments with a relatively large outer radius of the second pintle portion.

[0026] In some embodiments, it is possible that the second pintle portion and the second seat portion engage each other in the proximal pintle position. However, this is detrimental when the second seat portion has only a small or even zero inclination with respect to the injector axis. In such a case, considerable friction between the second seat portion and the second pintle portion could occur, which would detrimentally affect the mobility of the pintle and could reduce its service lifetime. To avoid this, it is preferred that the second pintle portion and the second seat portion are radially spaced by an annular radial gap when the pintle is in the proximal pintle position.

[0027] If the radial gap is too small, this could lead to friction between the second pintle portion and the second seat portion. On the other hand, if the radial gap is too large, thiscould lead to excessive gas exchange through the radial gap when the pintle is near the proximal pintle position. It is therefore preferred that a radial width of the radial gap is between 10 pm and 100 pm, preferably between 20 pm and 50 pm. the radial width of course corresponds to the dimension of the radial gap along the radial direction.

[0028] Preferably, a first inclination angle between the second seat portion and the injector axis is at maximum 15°, preferably at maximum 5°. It is conceivable that the first inclination angle is larger, but in this case, the size of the radial gap between the second pintle portion and the second seat portion will depend significantly on the axial position of the pintle. In particular, the above-mentioned bottleneck and the coinciding dampening effect will only be relevant for a small position interval near the proximal pintle position, even to an extent where the dampening effect is too small to provide significant benefit. According to a particularly preferred embodiment, the first inclination angle is zero, i.e., the second seat portion is parallel to the injector axis.

[0029] As mentioned above, it is preferred that the sealing region is relatively close to the inside of the first seat portion. This can be promoted if a second inclination angle between the first seat portion and the injector axis is greater than a third inclination angle between the first pintle portion and the injector axis. Accordingly, the distance between the first seat portion and the first pintle portion increases outwards along the radial direction. Normally, the difference between the second inclination angle and the third inclination angle is relatively small, though. For instance, the difference may be between 1° and 10° or between 2° and 7°.

[0030] One embodiment provides that at least one of the second inclination angle and the third inclination angle is between 45° and 90°, preferably between 50° and 80°. In combination with the second inclination angle being greater than the third inclination angle as in the abovementioned embodiment, the second inclination angle could be, e.g., between 50° and 90°, while the third inclination angle is between 45° and 85°.

[0031] The inclination of the first seat portion and the inclination of the third seat portion can be different. Normally, they are at least similar. According to a preferred embodiment, a fourth inclination angle between the third seat portion and the injector axis is between 45° and 90°, preferably between 50° and 80°.

[0032] In order for the second pintle portion to be sufficiently offset from the second seat portion when the pintle is in the distal pintle position, the “length” of the second seat portion must be smaller (in the axial direction) than the stroke length of the pintle. Preferably, anaxial dimension of the second seat portion is between 15% and 60%, preferably between 20% and 50%, of a stroke length of the pintle. The stroke length refers to the axial distance between the proximal pintle position and the distal pintle position. When the axial dimension of the second seat portion is e.g., 20% of the stroke length, the second pintle portion has moved beyond the second seat portion after 20% of the stroke length. If the second seat portion is parallel to the injector axis, a gap between the pintle and the seat begins to open at this stage and increases over the following 80% of the stroke. It will be understood that this percentage influences the size of the abovementioned second flow area.

[0033] In some embodiments, first, second and third seat portion are formed by a single component. On the other hand, it is possible that the first seat portion is formed by a first injector component and at least one of the second seat portion and the third seat portion is formed by a second injector component that is connected to the first injector component. The connection is normally gas-tight. It is also normally a fixed connection that prevents any relative movement between the injector components. The two injector components could e.g., be welded together or be connected by a press-fit. The first and second seat portion could be formed by the first injector component while the third seat portion could be formed by the second injector component. Alternatively, only the first seat portion could be formed by the first component while the second and third seat portion are formed by the second component.

[0034] According to one embodiment, the second injector component comprises a deflector portion that extends further distally than the pintle in the distal pintle position. In this case, the second injector component may also be referred to as a deflector cap. Such a component is used to influence the shape of the gas stream released from the fuel injector. In principle, such a component is known in the art and it is normally produced separately and then connected to the rest of the injector body. In this embodiment, it is used to provide at least one seat portion. This may help to facilitate the formation of the inventive seat structure without having to introduce a dedicated additional element.

[0035] The invention also provides a gaseous-fuel supply system for an internal combustion engine, comprising at least one inventive fuel injector, at least one fuel tank for pressurized gaseous fuel, and a supply piping which connects the at least one fuel tank to the at least one injector via a regulation module adapted for regulating a pressure of gaseous fuel supplied to the at least one injector. The gaseous-fuel supply system is adapted for supplying gaseous fuel to the engine. The gaseous fuel may in particular be hydrogen. It may comprise one or several fuel tanks. Each fuel tank is adapted for containing pressurizedgaseous fuel. “Pressurized” in general means that the pressure is above atmospheric pressure. Preferably, the fuel tank is adapted to contain fuel under a pressure of at least 30 bar(a), at least 50 bar(a) or at least 100 bar(a), wherein “(a)” indicates absolute pressure. Therefore, it can also be referred to as a pressurized tank or a pressure-resistant tank. As mentioned above, a “gaseous fuel” is gaseous under standard conditions, i.e., 15°C and 101 ,325 Pa. In some embodiments, the fuel may be in the gaseous state inside the fuel tank, while in other embodiments, it may be liquid due to the increased pressure inside the fuel tank. The supply piping may comprise one or several pipes adapted for containing and guiding gaseous fuel. It will be understood that the supply piping should be gas-tight and be pressure resistant. E.g., it may be pressure-resistant up to at least 20 bar(a), at least 30 bar(a) or at least 50 bar(a). The piping may be branched or unbranched. It may comprise one portion that connects the at least one fuel tank to the regulation module and one portion that connects the regulation module to the at least one fuel injector. In case of a plurality of fuel injectors, these injectors may be connected to a common fuel rail, which can be regarded as part of the supply piping. The regulation module can also be regarded as part of the supply piping. If the gaseous fuel is hydrogen, the regulation module can also be referred to as a hydrogen regulation module (HRM). It is adapted for regulating the pressure of gaseous fuel that is supplied to the injector(s). Preferably, this includes reducing the pressure from a tank side of the regulation module to an injector side, e.g., from 50 bar(a) to between 20 bar(a) and 40 bar(a). In addition to regulating the pressure, the regulation module may be adapted to regulate a temperature of the fuel, remove foreign particles from the fuel etc. It should be noted that the supply system may comprise additional elements, like a shut-off valve and / or a regulator valve between a fuel tank and the supply piping, a purge valve for releasing fuel to the atmosphere to avoid damage by overpressure, a pressure sensor, a temperature sensor, or others.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] 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 the inventive fuel injector with a pintle in a proximal pintle position;Fig.2 is a sectional view of the fuel injector from fig.1 with the pintle in a distal pintle position;Fig.3 is a detail view of fig.1 ;Fig.4 is a detail view of fig. 3;Fig.5 is a detail view of the fuel injector with the pintle in an intermediate position;Fig.6 is a detail view of fig.2;Fig.7 is a detail view of a second embodiment of the inventive fuel injector with the pintle in a proximal pintle position; andFig.8 is a schematic view of an inventive gaseous-fuel supply system.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] Figs. 1 - 6 show a first embodiment of the fuel injector 1 according to the present invention. The fuel injector 1 is adapted to inject a gaseous fuel, in particular H2, into a combustion chamber of an internal combustion engine 40( see fig.8). It can be used in an inventive gaseous-fuel supply system 30 that will be explained below with reference to fig. 8. The fuel injector 1 is mostly symmetrical to an injector axis A. It 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 a through-opening of the cylinder head. 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 closed 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 a proximal pintle position shown in figs.1 , 3 and 4. The pintle spring 11 engages a pintle perch 10.3 that protrudes from the pintle shaft 10.1.

[0039] Proximally of the pintle 10, an armature 15 is disposed inside the injector body 2. The armature 15 is biased by an armature spring 18 towards the distal side D. It comprises an elongate, roughly cylindrical armature shaft 16 and an annular armature collar 17 that circumferentially surrounds the armature shaft 16 and is connected thereto by welding. The armature collar 17 is axially movable within a cylinder portion 8 of the injector body 2. To facilitate the movement of the armature 15, the armature shaft 16 is received in a plurality of guide bearings 9.

[0040] Distally of the armature collar 17, the injector body 2 comprises a distal body portion 6 which is magnetizable by a solenoid 12, which generates a magnetic field when it is activated. In this embodiment, the distal body portion functions as a pole piece. By the magnetization of the distal body portion 6, the armature collar 17 and the entire armature 15 can be pulled towards the distal side D in a distal movement. Fig. 1 shows the armature 15 in a proximal armature position, in which the armature collar 17 and the distal bodyportion 6 are axially spaced apart. The armature shaft 16 engages the pintle shaft 10.1 , wherefore the armature 15 is forced into the proximal armature position through the action of the pintle spring 11 that acts on the pintle 10.

[0041] In order to optimize the opening as well as the closing of the injector 1 , the valve seat 3 and the pintle head 10.2 have a special structure, which can be seen in the detail views of figs. 3 and 4. Specifically, the valve seat 3 has a stepped surface with a first seat portion 3.1 , a second seat portion 3.2 and a third seat portion 3.3. With respect to the injector axis A, the second seat portion 3.2 has a first inclination angle a of 0°, i.e. , it is parallel to the injector axis A (see fig.4). The first inclination angle a could be nonzero but is preferably at maximum 15°. The first seat portion 3.1 has a second inclination angle p of 60° and the third seat portion 3.3 has a fourth inclination angle 8 of also 60°. These inclination angles could also be different but are preferably between 45° and 90°. The second seat portion 3.2 is less inclined with respect to the injector axis A than both the first seat portion 3.1 and the third seat portion 3.3. It forms a step between the first seat portion 3.1 and the third seat portion 3.3. In this embodiment, an axial dimension B of the second seat portion 3.2 is 40% of a stroke length S of the pintle 10. In other embodiments, it may be different, but it is preferably between 15% and 60% of the stroke length S.

[0042] The pintle head 10.2 comprises a first pintle portion 10.4 that engages the first seat portion 3.1 in an annular sealing region 19. The first pintle portion 10.4 has a third inclination angle y that is 55° in this example, but could be different, e.g., between 45° and 85°. Since this third inclination angle y is smaller than the second inclination angle p, the sealing region 19 is located near the radially innermost part of the first seat portion 3.1 . For the most part, the first pintle portion 10.4 is spaced from the first seat portion 3.1 , but is disposed adjacent thereto. Likewise, a second pintle portion 10.5, which is parallel to the injector axis A, is disposed adjacent to the second seat portion 3.2. It is spaced therefrom by an annular radial gap 14 (see fig.4). The radial width of the radial gap 14 may generally be e.g., between 10 pm and 100 pm, in this case it is 30 pm.

[0043] In the embodiment shown, the ratio between an outer radius R1 of the second pintle portion 10.5 and an inner radius R2 of the sealing region 19 is 1 ,35:1. In other embodiments, it may be e.g., between 1 ,2:1 and 1 ,5:1. The ratio between a maximum opening radius R3 of the outlet opening 5 and the outer radius R1 of the second pintle portion 10.5 is about 1 ,2:1. In other embodiments, it may be between 1 ,1 :1 and 1 ,3:1. When the injector is closed as shown in figs. 1 , 3 and 4, a significantly higher pressure acts on the area inside the sealing radius R2 than on other parts of the pintle head 10.2. The force exerted by thispressure acts towards the distal side D and complements the force by the armature spring 18, while a lower gas pressure in the cylinder head generates an opposite force, which complements the force of the pintle spring 11. In this embodiment, the maximum opening radius R3 is equal to a distal-end inner radius R4, which is the inner radius of the seat 3 at its distal end 3.4. The distal-end inner radius R4 corresponds to more than 100% of the outer radius R1 of the second pintle portion 10.5, in this case about 120% thereof. Accordingly, the outlet opening 5 widens between the second seat portion 3.2 and the distal end 3.4.

[0044] When the solenoid 12 is activated and magnetizes the distal body portion 6, the armature 15 is pulled towards the distal armature position. Since the armature shaft 16 engages the pintle 10, the pintle 10 is also pushed towards the distal pintle position (which is shown in figs.2 and 6) and the injector 1 starts to open. Fig.5 shows an intermediate position, in which the first pintle portion 10.4 is entirely removed from the first seat portion 3.1 , which allows gaseous fuel to flow into a damper space 13 in between. During the first part of the distal movement, however, there is still an axial overlap between the second pintle portion 10.5 and the second seat portion 3.2, wherefore fuel can only escape through the small radial gap 14. This leads to a considerable pressure difference between the proximal side P and the distal side D of the pintle head 10.2, which facilitates the distal movement of the pintle 10. After 40% of the stroke length S, the overlap between the second pintle portion 10.5 and the second seat portion 3.2 ends (as shown in fig.5), and the available flow area for the fuel increases, leading to a pressure drop in the damper space 13. Finally, when the pintle 10 has reached the distal pintle position shown in figs.2 and 6, an annular first flow area 20 between the first pintle portion 10.4 and the first seat portion 3.1 is smaller than an annular second flow area 21 between the first pintle portion 10.4 and the third seat portion 3.3. In other words, the second flow area 21 does not represent a bottleneck for the gas flow and therefore allows for an efficient injection into the cylinder head.

[0045] When the solenoid 12 is deactivated, the armature 15 is no longer attracted towards the distal body portion 6. Accordingly, the force of the pintle spring 11 pushes the pintle 10 towards the proximal pintle position and, accordingly, the armature 15 is pushed towards the proximal armature position in a proximal movement. During this time, the armature 15 is kept in contact with the pintle 10 by the force of the armature spring 18. As the armature 15 moves towards the proximal armature position and the pintle 10 moves towards the proximal pintle position, the second flow area 21 decreases. However, during the first 60% of the motion, there is still enough space between the first pintle portion 10.4 and the thirdseat portion 3.3 to allow for a pressure exchange. Then, when the pintle 10 reaches the intermediate position shown in fig.5, the only flow path is the narrow radial gap 14. Accordingly, the gas in the damper space 13 is under the increased pressure of the fuel channel 4, while the gas on the distal side D of the pintle head 10.2 is under a significantly lower pressure. Accordingly, the pressure difference leads to a pressure-induced force that acts towards the distal side D. This force decelerates the pintle 10. Accordingly, the speed of the pintle 10 during the final 40% of the motion is significantly reduced as compared to a conventional design. As a result of this, the impact force between the pintle head 10.2 and the seat 3 is comparatively small, which reduces the risk of wear and damage.

[0046] Figs.1-6 show a fuel injector 1 in which the seat portions 3.1-3.3 are formed by a single injector component, namely the distal body portion 6. Fig.7 shows an alternative embodiment, in which a deflector cap 7 is connected to the distal side D of the distal body portion 6. The function of the deflector cap 7 is to shape and guide the gaseous fuel stream that exits the outlet opening 5. For this purpose, the deflector cap 7 has a deflector portion 7.1 that extends further distally than the pintle 10 in the distal pintle position. The deflector cap 7 has an overall annular shape and can be press-fitted and / or welded onto the distal body portion 6. In the embodiment shown, the first seat portion 3.1 is formed by the distal body portion 6, while the second seat portion 3.2 and the third seat portion 3.3 are formed by the deflector cap 7. This design may simplify the production process since the shape of the distal body portion 6 is simpler.

[0047] Although not shown, the deflector cap 7 may, in embodiments, further define a hood portion that extends beyond the tip region of the nozzle and provides a fuel delivery guide.

[0048] The hood portion may be shaped to define a bulbous cavity or chamber which at least partially encloses the outlet opening 5 of the nozzle. In this way, the hood portion defines a sac volume of the nozzle which promotes mixing of air and fuel. The hood portion may be provided with a plurality of outlet openings, the positions of which are selected to achieve predetermined spray shape objectives.

[0049] Fig. 8 shows an inventive gaseous-fuel supply system 30 for an internal combustion engine 40. It will be understood that the depiction is highly simplified for sake of clarity. The system 30 comprises a fuel tank 31 for pressurized gaseous fuel, in particular hydrogen. In operational state, a pressure in the fuel tank 31 may be several hundred bar(a), e.g., up to 700 bar(a). A supply piping 32 connects the fuel tank 31 to four inventive fuel injectors 1 via a regulation module 33. All four injectors 1 are connected to a common fuel rail 34, whichis part of the supply piping 32. Each injector 1 is mounted to the engine 40 and adapted to inject fuel into a combustion chamber of a cylinder thereof. In this embodiment, the engine 40 may comprise four cylinders. Although not shown here, a regulator valve and / or a shutoff valve may be interposed between the fuel tank 31 and the supply piping 32, or they can be included in the fuel tank 31. The regulator valve can reduce the pressure of the fuel from several hundred bar(a) to e.g. 50 bar(a). The regulation module 33 is adapted for regulating the pressure of the gaseous fuel that is supplied to the injectors 1 . Specifically, it reduces the pressure from e.g., 50 bar(a) on a tank side to, e.g., between 20 bar(a) and 40 bar(a) on an injector side. In addition to regulating the pressure, the regulation module 33 may be adapted to regulate a temperature of the fuel, remove foreign particles from the fuel etc.Legend of Reference Numbers:1 fuel injector2 injector body2.1 end portion3 valve seat3.1 , 3.2, 3.3 seat portion3.4 distal end4 fuel passage5 outlet opening6 distal body portion7 deflector cap7.1 deflector portion8 cylinder portion9 guide bearing10 pintle10.1 pintle shaft10.2 pintle head10.3 pintle perch10.4, 10.5 pintle portion11 pintle spring12 solenoid13 damper space14 radial gap15 armature16 armature shaft17 armature collar18 armature spring19 sealing region20, 21 flow areaA injector axis a, p, y, 5 inclination angleB axial dimensionD distal sideP proximal sideR1 , R2, R3, R4 radiusS stroke length

Claims

CLAIMS:1 . A fuel injector (1) for direct injection of gaseous fuel, extending along an injector axis (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 (2.1) that defines a valve seat (3) extending around an outlet opening (5); and 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) to close the outlet opening (5), and a distal pintle position, in which it releases the outlet opening (5); wherein the valve seat (3) comprises a first seat portion (3.1), a second seat portion (3.2) and a third seat portion (3.3), wherein the second seat portion (3.2) extends distally between the first seat portion (3.1) and the third seat portion (3.3) and is less inclined with respect to the injector axis (A) than the first seat portion (3.1) and the third seat portion (3.3), and wherein the pintle (10) comprises a first pintle portion (10.4) that is disposed adjacent to the first seat portion (3.1) in the proximal pintle position and a second pintle portion (10.5) radially outside of the first pintle portion (10.4) that is disposed adjacent to the second seat portion (3.2) in the proximal pintle position and that is disposed distally offset from the second seat portion (3.2) in the distal pintle position.

2. The fuel injector according to claim 1 , further comprising: an armature (15) for actuating the pintle (10) and being axially movable between a proximal armature position and a distal armature position, which corresponds to the distal pintle position; and an actuator, preferably including a solenoid (12), adapted to initiate a movement of the armature (15) towards the distal armature position,3. The fuel injector according to any of the preceding claims, wherein the first pintle portion (10.4) sealingly engages the first seat portion (3.1) in an annular sealing region (19) when the pintle (10) is in the proximal pintle position.

4. The fuel injector according to any of the preceding claims, wherein the ratio between an outer radius (R1) of the second pintle portion (3.2) and an inner radius (R2) of the sealing region (19) is between 1 ,2:1 and 1 ,5:1 , preferably between 1 ,3:1 and 1 ,4:1.

5. The fuel injector according to any of the preceding claims, wherein the ratio between a maximum opening radius (R3) of the outlet opening (5) and the outer radius (R1) of the second pintle portion (10.5) is between 1 ,1 :1 and 1 ,3:1 , preferably between 1 ,1 :1 and 1 ,2:1.

6. The fuel injector according to any of the preceding claims, wherein an annular first flow area (20) between the first pintle portion (10.4) and the first seat portion (3.1) is smaller than an annular second flow area (21) between the first pintle portion (10.4) and the third seat portion (3.3) when the pintle (10) is in the distal pintle position.

7. The fuel injector according to any of the preceding claims, wherein the second pintle portion (3.2) and the second seat portion (10.5) are radially spaced by an annular radial gap (14) when the pintle (10) is in the proximal pintle position.

8. The fuel injector according to any of the preceding claims, wherein a radial width of the radial gap is between 10 pm and 100 pm, preferably between 20 pm and 50 pm.

9. The fuel injector according to any of the preceding claims, wherein a first inclination angle (a) between the second seat portion (3.2) and the injector axis (A) is at maximum 15°, preferably at maximum 5°.

10. The fuel injector according to any of the preceding claims, wherein a second inclination angle (P) between the first seat portion (3.1) and the injector axis (A) is greater than a third inclination angle (y) between the first pintle portion (10.4) and the injector axis (A).11 . The fuel injector according to any of the preceding claims, wherein at least one of the second inclination angle ( ) and the third inclination angle (y) is between 45° and 90°.

12. The fuel injector according to any of the preceding claims, wherein a fourth inclination angle (8) between the third seat portion (3.3) and the injector axis (A) is between 45° and 90°.

13. The fuel injector according to any of the preceding claims, wherein an axial dimension (B) of the second seat portion (3.2) is between 15% and 60%, preferably between 20% and 50%, of a stroke length (S) of the pintle (10).

14. The fuel injector according to any of the preceding claims, wherein the first seat portion (3.1) is formed by a first injector component (6) and at least one of the second seat portion (3.2) and the third seat portion (3.3) is formed by a second injector component (7) that is connected to the first injector component (6).

15. The fuel injector according to any of the preceding claims, wherein the second injector component (7) comprises a deflector portion (7.1) that extends further distally than the pintle (10) in the distal pintle position.

16. A gaseous-fuel supply system (30) for an internal combustion engine (40), comprising at least one fuel injector (1) according to one of the preceding claims, at least one fuel tank (31) for pressurized gaseous fuel, and a supply piping (32) which connects the at least one fuel tank (31) to the at least one injector (1) via a regulation module (33) adapted for regulating a pressure of gaseous fuel supplied to the at least one injector (1).

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