Gas injector for an internal combustion engine

Abstract

A gas injector (10,fig.1) comprising an outwardly-opening pintle (26,fig.1) having a hollow pintle shaft 28 and a pintle head (30,fig.1). In the closed state, the pintle head engages a valve seat (24,fig.1). A magnetic armature 32 is mechanically coupled to the pintle shaft. The injector comprises a proximal flexible sealing means (40,fig.1) and a distal flexible sealing means (40’,fig.1) which extend between the injector body 12 and pintle shaft. The sealing membranes are axially spaced and are configured to sealingly isolate the axial gas passage from an intermediate portion (44,fig.1) of the gas injector. The intermediate portion is adapted to contain lubricating fluid. The armature is arranged within the intermediate portion and comprises at least one through-hole 48 to allow flow of lubricating fluid. Damping means 50 is arranged within the intermediate portion to obturate the flow cross section through the through-hole during axial movement of the armature. A fuel delivery system using the gas injector is also claimed.

Description

Technical field The present invention generally relates to a gas injector for injection of gaseous fuel in an internal combustion engine. Background Art For automotive applications, hydrogen engines are considered as a promising alternative to gasoline or diesel engines. Indeed, emissions from hydrogen internal combustion engines consist mainly of water and do not comprise nearly as much pollutants as those from traditional engines. When designing hydrogen engine components, inspiration is naturally drawn from those of currently available thermal engines, which are typically powered by liquid fuel such as gasoline or diesel. In their simplest form, the fuel delivery systems of such liquid fueled combustion engines typically comprise a liquid fuel tank with a low-pressure pump, a high-pressure pump connected thereto, a fuel rail and a plurality of fuel injectors. However, the components of liquid fueled engines cannot be carelessly used in gaseous fueled internal combustion engines and must instead be adapted to meet specific technical requirements. In particular, when designing gaseous fuel delivery systems, care must be taken to anticipate possible fuel leaks and / or excessive pressure drops, which occur much more frequently with gaseous fuels than with their liquid counterparts. Moreover, gaseous fuels may lack some advantageous properties of liquid fuels such as self-lubrication or squeeze damping properties. Finally, some gaseous fuel such as hydrogen may cause embrittlement of some components, in particular components made from martensitic stainless steels. Technical problem It is an object of the present invention to provide a gas injector suitable for injection of gaseous fuel, which overcomes the aforementioned drawbacks. General Description of the Invention The present invention provides a gas injector for an internal combustion engine as claimed in claim 1. The gas injector extends along an injector axis from a proximal side to a distal side and comprises: an injector body defining a channel extending from a proximal inlet portion to a distal outlet portion having an outlet opening surrounded by a valve seat; an outwardly-opening pintle having a pintle shaft and pintle head; wherein the pintle is movable along the injector axis between a closed position, in which the pintle head engages said outlet valve seat to prevent gas flow through the outlet opening, and an open position, in which the pintle head is distally spaced from the valve seat to enable flow of gas through the outlet opening; a magnetic armature mechanically coupled to said pintle shaft in the direction of the injector axis to be axially proximally and distally moveable therewith; a spring arranged to bias said pintle towards its closed position; the pintle shaft comprises a hollow length extending along the injector axis, and the pintle comprises a proximal aperture and a distal aperture, thereby defining an axial gas passage between the inlet portion and the outlet portion; at least two flexible sealing membranes extend between the injector body and the pintle shaft, the sealing membranes being axially spaced and configured to sealingly isolate the axial gas passage from an intermediate portion of the gas injector, the intermediate portion at least partially surrounding the pintle shaft and being adapted to contain lubricating fluid. It will be appreciated that the armature is arranged in said intermediate portion and comprises at least one axial through-hole to allow flow of lubricating fluid between distal and proximal armature sides. Furthermore, damping means are arranged is said intermediate portion and are configured to at least partially obturate the flow cross section through the through-hole during at least part of a distal movement and / or proximal movement of the armature. The damping means are arranged in the intermediate portion to, depending on the embodiment, limit or fully obstruct the flow cross-section through the armature through holes, during part of a stroke or during an entire armature stroke. This reduction of flow cross-section will reduce the armature speed and hence reduce the impact of the armature against other components. As it will appear from the present disclosure, the invention provides embodiments that can be easily implemented to provide damping effects, while allowing rapid movement dynamics. In embodiments, the damping means comprise one proximal flexible blade per armature through-hole arranged to cooperate with the through-hole from a proximal armature side, the blade having an obturating portion adapted to partially obturate through-hole during at least part of a proximal displacement, the obturating portion having one or more apertures therein defining a flow cross section that is narrower than that of the respective though hole. The proximal flexible blade may be mounted to the armature on the proximal armature side. In particular, the proximal flexible blade(s) is / are mounted to the armature with some spacing with respect to the proximal armature side, whereby the proximal flexible blade comes to cover the through-hole only after a predetermined proximal displacement. In such case the flexible blades are effective during part of the armature stroke. Alternatively, such spacer may be dispensed with, and the blades are in direct contact with the proximal armature side, in which case the flow cross-section is limited during the entire proximal stroke. In both cases the closing speed is limited, hence reducing armature impact speed at closure. In embodiments, the damping means comprise one distal flexible blade per armature through-hole arranged to cooperate with the through-hole from the distal armature side, the blade having an obturating portion adapted to partially obturate through-hole during at least part of a distal displacement, the obturating portion having one or more apertures therein defining a flow cross section that is narrower than that of the respective though hole. The distal flexible blade(s) may be mounted to the armature with some spacing with respect to the distal armature side, whereby said distal flexible blade(s) comes to cover the through-hole only after a predetermined distal displacement. In embodiments, the armature comprises a plurality of though holes, each associated with at least one of a respective proximal flexible blade and a respective distal flexible blade, wherein the proximal flexible blades, respectively the distal flexible blades, extend inwardly from an annular ring that is mounted to the armature. In an alternative embodiment, the damping means include the proximal flexible blade(s) that is / are fixedly mounted in the intermediate portion proximally to the armature, and arranged to come into contact with the armature (from proximal side) from a predetermined position along the proximal movement of the armature. In still another alternative embodiment, the damping means comprise a ring-shaped element arranged proximally to the armature in the intermediate portion, the ring element being axially moveable and positioned to come into contact with the proximal armature side from a predetermined position along the armature proximal movement. The ring-shaped element is preferably spring biased in distal direction. The ring-shaped element may be arranged to be moveable in a recess, in which an annular spring member is arranged proximally to the ring-shaped element. In general, the sealing membranes may be expandable and / or elastically deformable in the direction of the injector axis. The sealing membranes mayfor example be corrugated bellows. The sealing membranes may be made of metal, preferably austenitic stainless steel, copper, copper alloy, nickel or nickel alloy In embodiments, each sealing membrane is sealingly connected to an outer surface of the pintle shaft and to an inner surface of the injector body, thereby preventing flow of fluid between axial gas passage and the intermediate portion In embodiments, the proximal sealing membrane extends proximally from the proximal aperture of the pintle shaft along the injector axis. According to another aspect, the invention relates to a fuel delivery system comprising a gaseous fuel tank configured to store pressurized gaseous fuel, and a fuel rail fluidly coupled to at least one gas injector according to the present disclosure. The system may further comprise pressure regulating means configured to decrease the pressure of fuel flow therethrough, wherein the pressure regulating means is serially connected between the fuel tank and the fuel rail. Brief Description of the Drawings Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a cross sectional view through a gas injector according to an embodiment of the invention; Fig. 2 is an enlarged view around the armature in figure 1; Figs. 3 and 4 a principle diagram of a second embodiment of the invention; Fig. 5 is a top view of the armature of Fig.2; Fig. 6 is a principle diagram illustrating a third embodiment of the invention; Fig. 7 is a principle diagram illustrating a fourth embodiment of the invention. Description of Preferred Embodiments Figure 1 shows a first embodiment of the gas injector 10 according to the present invention. The gas injector 10 is adapted to inject a gaseous fuel, in particular hydrogen (H2) or natural gas (CH4), into a combustion chamber of an internal combustion engine (not shown). The term “gaseous fuel” generally includes combustible fluids which are in their gaseous state when exposed to nominal operating conditions of the injector and the engine, e.g. pressure and temperature. Regarding more specifically hydrogen as gaseous fuel for an ICE, it typically consists of a gas with at least 90% hydrogen (H2), preferably pure hydrogen with no more than 2% impurities. The gas injector 10 is mostly symmetrical about an injector axis A and comprises an injector body 12, which may be made of one or several pieces. The injector body 12 comprises a main body 12a and a lower body 12b, which are here separate parts fixed together, but could alternatively be integral. The injector 10 includes an inlet portion 14 on a proximal side P and an outlet portion 18 on a distal side D, where an outlet opening 22 is surrounded by a valve seat 24. The inlet portion 14 is typically fluidly coupled to a fuel rail 106 at the proximal side P for supply of pressurized gaseous fuel to the gas injector 10. When installed on the engine, the injector body portion with the outlet portion 18, i.e. lower body 12.b, is arranged in a bore in the cylinder head, which opens into a combustion chamber (not shown) of the engine. The injector body 12 defines a channel 20, which extends along injector axis A from the inlet portion 14 to the outlet portion 18. The channel 20 forms an internal, elongate passageway (or cavity) that extends throughout the injector body 12, from an inlet opening 21 to the outlet opening 22. Depending on the design, the channel 20 may comprise sections of different shapes or cross-sections along its length. Where the body is made of several pieces, they are assembled together in a fluid-tight manner. The valve seat 24 defines an annular surface 25 that faces outwardly, i.e. away from the channel 20, and which may typically be a conical surface. A pintle 26 is axially movable between closed and open positions to control flow of gaseous fuel through the outlet opening 22. The pintle 26 comprises a pintle shaft 28, which extends along the injector axis A and is moveably received inside channel 20, and a pintle head 30, which radially protrudes from the pintle shaft 28 at the distal end thereof. Pintle head 30 forms a valve member (or plug) that is adapted to cooperate with the valve seat 24. When the pintle 26 is in its closed position (as shown in Fig. 1), the pintle head 30 engages the valve seat 24, thereby preventing gas flow through the outlet opening 22. Conversely, when the pintle 26 is in its open position (not shown), the pintle head 30 is distally spaced from the valve seat 24, thereby enabling fuel flow through the outlet opening 22. It may be noted that the pintle head 30 is located downstream (in gas flow direction) of the valve seat 24 and the pintle 26 opens in flow direction; hence the gas injector 10 is said to open outwardly. Reference sign 36 designates a solenoid coil that cooperates with a magnetic armature 32 to actuate the pintle 26. The armature 32 is mechanically coupled to the pintle shaft 28, such that it moves therewith in the direction of the injector axis A. In embodiments, the armature 32 is fixedly attached to the pintle shaft 28, e.g. by welding (as is the case here), press-fit, or screwing, or through form combination. Hence, the pintle shaft 28 extends from the pintle head 30 up to the armature 32, and in the presented embodiment extends proximally beyond the armature 32. A coil spring 34 surrounding the pintle shaft 28 is arranged to bias the pintle 26 towards its closed position. In the embodiment of Fig. 1, the coil spring 34 is arranged distally from a pintle perch 29, with its proximal end engaging the latter and its distal end engaging a distal annular guide ring 42. Other spring configurations can be envisaged. In use, to perform an injection event where gas is discharged through the outlet opening 22, the solenoid 36 is energized to create a magnetic field that attracts the armature 32 in the distal direction and causes the pintle 26 to move distally in an open position, when the force due to the magnetic field overcomes the spring force. Reference sign 38 designates a pole piece arranged distally from the armature 32 to enhance and shape the magnetic field. More specifically, the pole piece 38 is arranged between the armature 32 and the lower body 12b. To guide the magnetic field, a non-magnetic ring 39 is incorporated in the main body; alternatively, the wall thickness of the main body 12a can be locally reduced to form a so-called shunt. The pintle shaft 28 comprises a hollow length 28.1 extending from proximal side P to the distal side D. The pintle 26 further comprises a proximal aperture 26.1 and a distal aperture 26.2. As will be understood, the pintle shaft 28 defines an axial gas passage that enables to convey gas from the inlet portion 14 to the outlet portion 18. In this embodiment, the pintle shaft 28 is realized as a straight tube having a proximal axial open end which forms the proximal aperture 26.1, and an opposite distal axial closed end. The distal aperture 26.2 is laterally or radially arranged, here about the distal end of the pintle shaft 28. In the embodiment of Fig.1, the distal aperture 26.2 is formed by a plurality of holes in the peripheral wall of the pintle shaft 28 proximal to the pintle head 30. The size and number of the holes may depend on the desired flow rate. When the pintle 26 is moved distally, a flow passage is opened between the pintle head 30 and valve seat 24, through which gaseous fuel is discharged. The present injector 10 thus provides a design with a straight gas passage extending throughout the injector length. Gas entering the gas passage at the inlet portion 14 exits through the distal aperture 26.2 near the outlet opening 22 and upstream of the valve seat 24. A straight gas passage is thus provided, thereby avoiding significant pressure drops as undergone in conventional designs with solid pintle shafts, where the fuel has to flow around the pintle and through the armature and spring. At the top of the pintle shaft 28, i.e. at the proximal side P, gaseous fuel enters through the axially located proximal aperture 26.1. As can be seen, an inlet member 15 is arranged to close the injector cavity 20 on the proximal side (inserted through opening 21) and is sealingly fixed to the injector body 12 by a continuous, gas-tight weld. The inlet member 15 is a globally tubular element defining a central passage 15.1 centered on the injector axis A. A rail adapter (not shown) may be mounted on the inlet member 15, which is an application dependent element for coupling to the rail. In this embodiment, on the distal side D, the gas injector 10 comprises a seat member 23 which is arranged at the distal end. The seat member 23 has a generally annular shape (coaxial with injector axis A), with an inward annular protrusion (or lip) surrounding the outlet opening 22 so as to define the valve seat 24. Hence, when the pintle 26 is in the closed position, flow through the outlet opening 22 is prevented, and an inner volume 18.1 of the outlet portion 18 defines a plenum chamber in fluid communication with the inner volume 28.1 of the hollow pintle shaft 28. Conversely, when the pintle 26 is in the open position, the chamber 18.1 is open and pressurized gaseous fuel is discharged in the engine’s combustion chamber. It will be noted that the gas injector 10 further comprises a proximal and a distal sealing membrane 40, 40’, which are elastically deformable along the injector axis A. The sealing membranes 40, 40’ have a generally tubular shape, with one end sealingly connected to an outer surface of the pintle shaft 28 and the opposite end sealingly connected to an inner surface of the injector body 12. The membranes have fluid-tight walls and connected in a fluid-tight manner at both ends. In this embodiment, the sealing membranes are corrugated bellows. The proximal sealing membrane 40 is welded at one end 40.1 to the pintle shaft 28, extends proximally from the proximal aperture 26.1 of the pintle shaft 28 along the injector axis A, and is welded at the other end 40.2 to the injector body 12 near the inlet (via a fixing ring 41). Hence the axial gas passage between the inlet portion 14 and the outlet portion 18 is defined by both the proximal sealing membrane 40 and the hollow pintle shaft 28. The axial guiding of the pintle 26 on the proximal side is here achieved by the controlled annular clearance between armature 32 and injector body 12. Meanwhile, the axial guiding of the pintle 26 on the distal side is achieved by the distal guide 42’ which is not submerged in lubricating fluid. The guide 42’ should thus be made of a material able to resist the sliding motion of the pintle without lubrication, such as e.g. a copper-alloy or a high-temperature resistant technical polymer compound, e.g. carbon filled PEEK. The distal sealing membrane 40’ is sealingly welded at one end 40’. 1 to the pintle shaft 28 and at the other end 40’.2 to a fixing ring 41, itself sealingly welded to the injector body 12. The proximal and distal sealing membranes 40, 40’ thus sealingly isolate the inlet portion 14 and the outlet portion 18 from an intermediate portion 44, within which the coil spring 34, pintle perch 29, armature 32 and pole piece 38 are advantageously arranged. In other words, gaseous fuel flowing through the injector 10 never enters the intermediate portion 44, and instead flows along the axial gas passage from the inlet portion 14 through the inner volume 28.1 of the pintle shaft 28 and the distal aperture 26.2, to the inner volume 18.1 of the outlet portion 18. Hence, none of the gas flowing through the injector 10 flows around the armature 32, pole piece 38 and coil spring 34, which are normally regions of the flow where high pressure drops tend to occur. As the intermediate portion 44 is sealingly isolated from the axial gas passage, its volume may be filled with a lubricating fluid via a sealable aperture 46, which may subsequently be plugged by press-fitting of a spherical ball made from stainless steel. Said lubricating fluid is typically a liquid having advantageous lubricating and squeeze damping properties, such as a low viscosity synthetic oil with appropriate doping additives. Some volume of gas (e.g. air, nitrogen or other inert gas) may also be enclosed in the intermediate portion 44, to allow for lubricant expansion and avoid local overpressures. The injector body 12 is typically made of metallic material, in particular steel or stainless steel. As the coil spring 34 is immersed in lubricants, this component is not susceptible to hydrogen embrittlement and can thus be made of conventional martensitic stainless steels. In other words, only the valve seat 24 and the pintle 26 are in direct contact with hydrogen. These components could thus be made of austenitic stainless steels, thereby reducing the risk of hydrogen embrittlement. The sealing membranes 40 can be made of metal, preferably austenitic stainless steel, copper (alloy), nickel (alloy); however, these should not be construed as limiting and other appropriate materials may be employed. The seat member 23 can be made integral with the injector lower body 12b or can be a pre-fabricated piece securely fixed thereon in a gas-tight manner, e.g. by welding, as shown on figure 1. Likewise, the pintle head 30 can be made integral with the pintle shaft 28 or can be a pre-fabricated piece securely fixed thereon, e.g. by interference fit, welding, etc. Figure 2 shows a detailed view of the region around the armature 32 in Figure 1. As it can be seen, the armature 32 divides the intermediate portion 44 into a proximal sub-portion 44a and a distal sub-portion 44b. The armature 32 comprises a plurality of through-holes 48 to promote flow of fluid through the armature 32, i.e. between the proximal sub-portion 44a and the distal sub-portion 44b. As the armature is fixedly mounted to the pintle, an armature rest (or proximal) position is defined that corresponds to the pintle being in closed position, and an armature active (or distal) position corresponding to the pintle being in (fully) open position. The displacement of the armature 32 from the rest position to the active position is referred to as opening or distal stroke, whereas the return movement is referred to as closing or proximal stroke. During motion of the armature 32, the volume of each sub-portion 44a, 44b varies. More specifically, when the pintle 26 moves into its open position, the armature 32 moves distally, thereby increasing the volume of the proximal sub-portion 44a and decreasing the volume of the distal sub-portion 44b. Conversely, when the pintle 26 moves into its closed position, the armature 32 moves proximally, thereby increasing the volume of the distal sub-portion 44b and decreasing the volume of the proximal sub-portion 44a. In this embodiment, on the proximal side 32.1 of the armature 32, in the embodiment of figure 1, the armature 32 and the inlet member 15 are arranged such that, when the pintle 26 is in its closed position, a relatively narrow gap exists between the armature 32 and the inlet member 15. The armature 32 and the inlet member 15 thus define an annular chamber on the proximal side, within the proximal sub-portion 44a. The volume of this chamber decreases during the closing motion of the pintle 26, therefore leading to a pressure increase on the proximal side of the armature 32. This increase in pressure on the proximal side of the armature 32 results in a hydraulic braking force which slows down the closing motion of the pintle 26, thereby reducing the impact speed of the pintle head 30 against the valve seat 24 and improving their durability. It will be appreciated that, in order to attenuate the force of the impact of the armature 32 against the inlet member 15, at least one damping means is arranged in the intermediate portion 44 and is configured to partially obturate the flow cross section through the armature through-holes 48 during armature 32 movements, here during the proximal stroke. In this embodiment, the damping means comprise one proximal flexible blade 50 per armature through-hole 48 arranged to cooperate with the through-hole 48 from the proximal armature side 32.1. The flexible blades 50, which are illustrated in Fig.5, have an obturating portion 53 adapted to partially obturate the through-hole 48 during the proximal stroke (or at least part thereof), the obturating region 53 having an aperture 53.1 therein defining a flow cross section that is narrower than that of the respective through-hole 48. There could be several apertures 53.1 in one obturating portion 53, in which case the cumulative cross-section offered by the set of apertures 53.1 is less than that of the respective through-hole 48. As will be understood, when the armature 32 moves distally (opening stroke), the proximal flexible blades 50.1 will tend to move away from the proximal armature side 32.1, hence full flow cross-section will be available for the lubricating fluid to move from the distal sub-portion 44b to the proximal sub-portion 44a. However, when the armature 32 will move back to the closed injector configuration (closing stroke), the proximal flexible blades 50 will be applied onto the proximal armature side 32.1 and hence operate a flow restriction. That is, when the proximal flexible blades 50 are applied onto the proximal armature side 32.1 and the armature 32 moves proximally, the flow cross section for the fluid through the through holes 48, from the proximal sub-portion 44a to the distal sub-portion, is limited by the apertures 53.1 in the flexible blades. Hence, the lubricant flow is reduced during the closing stroke, leading to a reduction in armature speed and hence of impact speed. A second embodiment of armature with damping means using flexible blades 50 will now be explained with reference to Figs.3 and 4. Figure 3 is a principal drawing where one will recognize the armature 32 arranged in the intermediate portion 44, where a plurality of through-holes 48 (two in the plane of the Figure) extend from the proximal 32.1 to distal 32.2 armature sides, to allow flow of lubricating fluid between distal 32.2 and proximal 32.1 armature sides. In the example, proximal 50.1 and distal 50.2 flexible blades are provided on the armature 32 and configured to partially obturate the flow cross section through the through-hole 48 during at least part of a distal, resp. proximal movement of the armature. In this embodiment, the proximal 50.1 and distal 50.2 flexible blades are mounted to their respective proximal 32.1 and distal 32.2 armature side with proximal 51.1 and distal 51.2 spacer with respect to the proximal 32.1 and distal 32.2 armature side. Therefore, a proximal spacer 51.1 is interposed between the proximal flexible blades 50.1 and the proximal armature side 32.1 and a distal spacer 51.2 is interposed between the distal flexible blades 50.2 and the proximal armature side 32.2. Due to the presence of these spacers 51.1 and 51.2, the proximal 50.1 and distal 50.2 flexible blades will only come to cover the respective through-holes 48 after a given proximal and distal displacement. One could thus say that the spacers 51.1 &51.2 delay the entry into effect of the flexible blades 50. Suppose that in Fig.3 the armature 32 is in its rest position (closed injector). In case the actuator is energized to operate an injection event, the armature 32 will move distally (opening stroke - downward in the Figure). As explained with respect to Fig.2, the proximal flexible blades 50.1 will not affect the flow cross-section. On the distal side, the distal flexible blades 50.2 are initially spaced from the distal armature side 32.2, due to the distal spacer 51.2. Hence, they will not restrict the flow through the through-holes 48 during a first part of the opening stroke. However, as the armature 32 will move further distally, the distal flexible blades 50.2 will come into contact with the distal armature side 32.2and cover the through-holes 48. This is the configuration illustrated in Fig.4. From that moment on, the flow of lubricant from the distal chamber to the proximal will be restricted, causing a dampening effect by reducing armature 32 speed. It may be noted that during the distal movement of the armature 32, the distal flexible blades 50.2 also tend to be attracted towards the distal armature side 32.2 due to a suction effect caused by the fluid flowing through the through-hole 48. Then when the armature 32 moves proximally to return to the closed position, the proximal flexible blades 50.1 will enter into action and operate in a similar manner. It is understood that in principle the distal 50.2 and proximal 50.1 flexible blades do not operate at the same time, but each in turn according to the movement of the armature 32. It is to be noted that whereas Figs. 3 and 4 show proximal 50.1 and distal 50.2 flexible blades, they may only be implemented on a single armature side to achieve a damping effect in one axial direction only, as is the case in the embodiment of Figs. 1 and 2 using proximal flexible blades 50.1 only. Turning now to Figure 5, the armature 32 is shown from the proximal side 32.1 with its damping means and its associated flexible blades 50. In the present variant, the flexible blades 50 (namely 4) are integral with a fixing ring 52, forming a blade member 55. The flexible blades 50 extend inwardly from the fixing ring 52, toward the associated through-holes 48. The fixing ring 52 is attached to the proximal armature side 32.1 by any appropriate means, e.g. by welding. Depending on the desired dampening effect, a spacer may be interposed between the fixing ring and the proximal armature surface (as shown in Fig.4). That is, such spacer is not provided in the embodiment of Fig.2. Accordingly, the through-holes 48 are obstructed by the blades 50.1’ during the full closing stroke. However, an embodiment provides that such spacer may be present; e.g. an annular spacer of same width and diameter as the fixing ring 52. It remains to be noted that although the blade member 55 is here represented as annular, other shapes may be considered. As shown, each flexible blade 50 comprises of a flat stem 54 ending with the obturating portion 53.1 provided with aperture 53.1. The obturating portion 53 is preferentially circular with a diameter greater than the respective through hole that is to be covered. The aperture 53.1 in the obturating region is centrally arranged. The embodiment described in Figure 6 mainly differs from the embodiment in Figures 2 to 5 in that the damping effect is provided by proximal flexible blades 50 (only one being shown in the Fig.) that are not connected to the armature 32 but fixed to the injector body 12, namely here to the inlet member 15. In the configuration of Fig.6, the armature 32 is in distal position. As can be seen, the proximal flexible blade 50 is fixedly mounted in the intermediate portion 44 proximally to the armature 32, and arranged to come into contact with the proximal armature side 32.1 from a predetermined position along the proximal movement of the armature 32, towards the end of the closing stroke. Advantageously, the flexible blade 50 extends in a cantilevered manner transversally to the injector axis, over a proximal recess 56 in the inlet member 15. The free end of the flexible blade 50 is held in rest position by a stop element 57, avoiding that the blade is suck down during the opening stroke. On the proximal armature side 32.1, a protruding annular collar 58 is arranged that forms an axial continuation of the through-hole 48. As will be understood, during the armature 32 proximal stroke, the armature 32 will first move without flow restriction. Towards the end of the proximal stroke, the protruding annular collar 58 will come into contact with the proximal flexible blade 50, whereby the flow cross-section will be reduced. The armature 32 will move flexible blade 50 upwardly until it comes into its rest position. As it will be noted, for proper operation of the shown embodiment, the protruding height H58 is greater than the edge height H57 of stop member 57. Figure 7 shows a further embodiment that incorporates damping means composed of a ring-shaped element 60 coupled to an elastic member 62, e.g. an elastic shim. The ring-shaped element 60 is arranged proximally to the armature 32 in the intermediate portion 44, here in a recess 64 in the body (specifically in inlet member 15). The ring-shaped element 60 is axially moveable around the pintle shaft 28.1 within the recess 64. It is configured to come into contact with the proximal armature side 32.1 at a predetermined axial position along the armature distal movement. In the figure, the ring-shaped element 60 is in its rest position, defined by an abutment 66. This rest position is chosen along the injector axis such that the ringshaped element 60 is contacted by the armature 32 toward the end of the closing stroke. The fluid trapped between the element 60 and the armature 32 will provide hydraulic damping, leading to so-called “squish damping”. From that moment the through hole 48 is also proximally closed by ring-shaped element 60, to hinder fluid flow there-trough. The amount of fluid in the recess 64 also provides some hydraulic braking effect. The spring 62 further provides some damping effect, and biases the ring-shaped element 60 in its rest position. The position of the ring-shaped element 60 along the axis and its proximal displacement is designed to avoid a hard surface that would lead to a statically indeterminate structure, considering the fact that in closed position the pintle position is determined by the valve seat. Although not shown, one or more channels may be provided in element 60 or in a wall portion surrounding the recess 64, to allow lubricant escape from recess 64 as the provided in element 60 moves therein. In the shown embodiment, for the armature 32 to properly push against element 60, the abutment 66 is radially beyond the periphery or armature 32, so that the armature can fit inside recess 64. As a corollary, the radial length of element 60 is greater than that of the armature 32.

Claims

1. A gas injector (10) for an internal combustion engine, extending along an injector axis (A) from a proximal side (P) to a distal side (D) and comprising:an injector body (12) defining a channel (20) extending from a proximal inlet portion (14) to a distal outlet portion (18) having an outlet opening (22) surrounded by a valve seat (24);an outwardly-opening pintle (26) having a pintle shaft (28) and pintle head (30);wherein the pintle (26) is movable along the injector axis (A) between a closed position, in which the pintle head (30) engages said outlet valve seat (24) to prevent gas flow through the outlet opening (22), and an open position, in which the pintle head (30) is distally spaced from the valve seat (24) to enable flow of gas through the outlet opening (22);a magnetic armature (32) mechanically coupled to said pintle shaft (28) in the direction of the injector axis (A) to be axially proximally and distally moveable therewith;a spring (34) arranged to bias said pintle (26) towards its closed position;the pintle shaft (28) comprises a hollow length (28.1) extending along the injector axis, and the pintle comprises a proximal aperture (26.1) and a distal aperture (26.2), thereby defining an axial gas passage between the inlet portion (14) and the outlet portion (18),at least two flexible sealing membranes (40, 40’) extend between the injector body (12) and the pintle shaft (28), the sealing membranes (40, 40’) being axially spaced and configured to sealingly isolate the axial gas passage from an intermediate portion (44) of the gas injector (10),the intermediate portion (44) at least partially surrounding the pintle shaft (28) and being adapted to contain lubricating fluid,characterized in that the armature is arranged in said intermediate portion and comprises at least one axial through-hole to allow flow of lubricating fluid between distal and proximal armature sides,wherein damping means are arranged is said intermediate portion (44) and are configured to at least partially obturate the flow cross section through the through-hole during at least part of a distal movement and / or proximal movement of the armature.

2. The gas injector (10) according to claim 1, wherein the damping means comprise one proximal flexible blade (50.1) per armature through-hole (48) arranged to cooperate with the through-hole from a proximal armature side, the blade having an obturating portion (53) adapted to partially obturate the through-hole during at least part of a proximal displacement, the obturating portion having one or more apertures (53.1) therein defining a flow cross section that is narrower than that of the respective though hole.

3. The gas injector (10) according to claim 2, wherein the proximal flexible blade (50.1) is mounted to the armature on the proximal armature side (32.1).

4. The gas injector (10) according to claim 2 or 3, wherein said proximal flexible blade is mounted to said armature with some spacing with respect to the proximal armature side, whereby said proximal flexible blade comes to cover the through-hole only after a predetermined proximal displacement.

5. The gas injector (10) according to any of the preceding claims, wherein the damping means comprise one distal flexible blade (50.2) per armature through-hole arranged to cooperate with the through-hole (48) from the distal armature side (32.2), the blade having an obturating portion (53) adapted to partially obturate through-hole during at least part of a distal displacement, the obturating portion having one or more apertures (53.1) therein defining a flow cross section that is narrower than that of the respective though hole.

6. The gas injector (10) according to claim 5, wherein said distal flexible blade (50.2) is mounted to said armature with some spacing with respect to the distalarmature side, whereby said distal flexible blade comes to cover the through-hole only after a predetermined distal displacement.

7. The gas injector (10) according to any of claims 2 to 6, wherein the armature comprises a plurality of though holes, each associated with at least one of a respective proximal flexible blade and a respective distal flexible blade, wherein the proximal flexible blades, respectively the distal flexible blades, extend inwardly from an annular ring that is mounted to the armature.

8. The gas injector (10) according to claim 2, wherein the proximal flexible blades (50) are fixedly mounted in the intermediate portion (44) proximally to the armature, and arranged to come into contact with the armature from a predetermined position along the proximal movement of the armature.

9. The gas injector (10) according to claim 1, wherein the damping means comprise a ring-shaped element (60) arranged proximally to the armature in the intermediate portion (44), the ring element being axially moveable and positioned to come into contact with the proximal armature side from a predetermined position along the armature proximal movement.

10. The gas injector (10) according to claim 9, wherein the ring-shaped element is spring biased in distal direction.

11. The gas injector (10) according to claim 10, wherein ring-shaped element is moveable in a recess (64), in which an annular spring member (62) is arranged.

12. Fuel delivery system (100) comprising a gaseous fuel tank configured to store pressurized gaseous fuel, and a fuel rail fluidly coupled to at least one gas injector (10) according to any of the preceding claims.

13. Fuel delivery system (100) according to claim 12, further comprising pressure regulating means configured to decrease the pressure of fuel flow therethrough, wherein the pressure regulating means is serially connected between the fuel tank and the fuel rail.

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