Gas injector

Abstract

Injector (1) for direct injection of fuel into a combustion chamber (16), having: - a stationary body (2, 3), - a nozzle (4) provided with openings for the passage of fuel from the injector to the combustion chamber, - a movable element (5, 6) configured to unlock and close the passage openings of the nozzle (4) and to open towards the outside of the injector (1) in an axial direction, in which the movable element comprises an upper needle (5) and a lower needle (6), - an actuator (20) for actuating the movable element (5, 6), comprising a stationary ferromagnetic core (7) and an armature (9) movable axially together with the movable element (5, 6), - a supply connection (12), made of metallic material, - a damping element (13) made of elastomeric material, distal to the armature (9) and which it is configured as a limit switch element of the armature (9) of the actuator (20).

Description

[0001] GAS INJECTOR

[0002] D E S C R I PTI O N

[0003] Technical Field of the Invention

[0004] The present invention relates to an injector particularly suitable for use with gaseous fuels.

[0005] Background Art

[0006] Fuel injectors for internal combustion engines— including gas injectors— are well-known components in the field of internal combustion engine fuel systems. These injectors are typically actuated electromagnetically, using a solenoid located inside the injector body. This solenoid can be electrically energized to generate a magnetic field. This magnetic field induces the movement of a magnetic armature, typically connected to a movable element or needle in the injector nozzle, causing it to move along its axis.

[0007] The needle, moving in tandem with the armature, controls the opening or closing of the nozzle orifice at its tip. The initial opening of the nozzle orifice during the injection process is regulated by a spring element located inside the fuel injector. This spring pushes the needle toward the nozzle orifice, meaning the armature must counteract the spring force to open the nozzle orifice. Once the nozzle orifice is opened, a specified amount of fuel inside the injector can flow into a combustion chamber, typically found in an internal combustion engine.

[0008] Fuel injectors typically retain gaseous fuel internally when not actuated, either through contact between two metal parts or by means of a rubber sealing gasket.

[0009] In the case of high-pressure injectors, the magnetic force must overcome not only the spring preload but also the pneumatic / hydraulic pressure acting on the surfaces wetted by the fuel fluid, which helps open or close the needle at the nozzle orifice.

[0010] All injector types (gasoline, diesel, and natural gas) suffer from needle bounce, resulting in re-opening and post-injections, where postinjections are defined as unwanted injections that occur after a brief period of injector closure. These effects are caused by the dynamic behavior of the injector, and many features are designed to mitigate this effect, which is detrimental to the engine. One example is decoupling between the armature and the needle to reduce impact energy.

[0011] Dynamic effects can be mitigated by using elastomers to exploit their damping effect. Elastomeric elements, for example, can be used to stop the armature, the moving element of the injector's electromagnetic actuator. However, when considering injectors that inject gasoline or diesel fuel, the use of elastomeric materials for damping purposes is ruled out for several critical reasons:

[0012] - fuel compatibility and aging: elastomeric materials are not compatible with gasoline and diesel fuel blends. Prolonged exposure to these fuels can cause elastomer degradation, resulting in a loss of structural integrity and functionality. This degradation process is accelerated by the chemical composition of gasoline and diesel fuel, which can deteriorate the elastomer over time, - manufacturing tolerances: elastomeric components typically have manufacturing tolerances that are larger than the very tight stroke requirements of injector moving parts. Injectors require extremely tight tolerances to function properly, and the variability in the dimensions of the rubber parts can result in significant variability from one injector to another. This inconsistency can negatively impact the performance and reliability of injectors,

[0013] - magnetic interference: the placement of the elastomer within the injector poses significant challenges. Injectors rely on magnetic forces to function, and the introduction of elastomer elements can reduce the amount of magnetic material that can be used. This reduction in magnetic material directly decreases the available magnetic force, which is essential for the injector's operation. Furthermore, the placement of the elastomer element within the magnetic space can interfere with the magnetic field, further compromising the injector's performance.

[0014] In the case of gas-injecting injectors, these use elastomeric components, but some issues still arise:

[0015] - fluid compatibility: the elastomer in gas injectors must be carefully selected to withstand the specific fluids it will come into contact with. There is always the risk of compatibility issues that can lead to material deterioration over time,

[0016] - magnetic air gap interference: even in gas injectors, elastomeric elements can be used as stops for the armature stroke, within the magnetic air gap. This increases the stroke length required to achieve the required static flow rate, and consequently reduces the magnetic force available for proper injector operation.

[0017] The conflicting design requirements— on the one hand, dampening the bouncing of the moving element and the resulting injector reopening to avoid late injections, and on the other hand, ensuring the required static flow rate with the necessary magnetic force— lead to inefficiencies and potential performance problems.

[0018] Therefore, there is a need to design a gas injector that is free of, or at least minimizes, the aforementioned drawbacks.

[0019] Summary of the Invention

[0020] To substantially solve the technical problems highlighted above, one object of the present invention is to define a gas injector that solves the problem of bouncing of its moving element and the resulting late injections (post-injection).

[0021] Therefore, according to the present invention, a gas injector is provided having the features set forth in the independent claim, appended to this specification.

[0022] Further preferred and / or particularly advantageous embodiments of the invention are described according to the features set forth in the appended dependent claims.

[0023] Brief Description of the Drawings

[0024] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting examples of its implementation, in which:

[0025] - Figure 1 is a cross-section of a gas injector according to a preferred embodiment of the present invention, and

[0026] - Figure 2 shows, on an enlarged scale, a detail of the injector of Figure 1.

[0027] Detailed Description

[0028] By way of example and not limitation, the present invention will now be described with reference to the aforementioned figures. The fuel injector, the subject of the present invention, is particularly suitable for use in the presence of gaseous fuels and will therefore be referred to hereinafter as a gas injector. Specifically, this gas injector can be used for the injection of natural gas or hydrogen. However, the present injector solution is also suitable for use in the injection of liquid fuels, such as liquid natural gas, ammonia, or methanol.

[0029] With reference to Figure 1, injector 1 is a direct injection gas injector that injects the gaseous fuel directly into a combustion chamber 100, of a known type and therefore only schematically illustrated, of an internal combustion engine. The combustion chamber is not part of the present invention.

[0030] Throughout this specification and the claims, terms and expressions indicating positions such as "proximal" and "distal" are intended to refer to the distance from the combustion chamber 100. Terms such as "radially internal" or "radially external" are intended to refer to an X-axis of axisymmetry of the injector. For the purposes of this invention, and unless explicitly stated otherwise, the injector 1 and its main components are substantially axially symmetrical with respect to the X axis.

[0031] The injector 1 comprises: - a distal upper body 2, substantially cylindrical in shape,

[0032] - a proximal lower body 3, also substantially cylindrical in shape, integrally connected to the upper body,

[0033] - a nozzle 4, integrally positioned at the proximal end of the lower body 3 and provided with openings for the passage of gas from the injector to the combustion chamber,

[0034] - a movable injector element made of two parts axially in contact with each other or in any case consecutive: the distal upper needle 5 and the proximal lower needle 6. The two needles are each provided with at least one axial guide 40. In the exemplary solution of figure 1, the axial guide 40 is a bushing, stably connected to a fixed element of the injector (in the example a ferromagnetic core 7), and is interlocked with the axial guide of both the upper needle 5 and the lower needle 6. Advantageously, the mobile element can also comprise a sphere 30 located on axis between the upper needle 5 and the lower needle 6 and inside the axial guide 40. The interposition of a sphere, inside the axial guide, between the upper needle and the lower needle defines a spherical joint which provides a further degree of freedom to the mobile element made in two parts.

[0035] The movable element is configured to open outward. In other words, the lower needle 6 is more proximal to the combustion chamber 100 than the nozzle 4. The injector's hermetic closure to the passage of the gas flow is achieved by a seal between the lower needle 6 and the nozzle 4, as will be explained in more detail below.

[0036] Both the upper needle 5 and the lower needle 6 are actuated by an actuator, such as an electromagnetic actuator or a piezoelectric actuator. In the embodiment illustrated in Figure 1, the actuator is an electromagnetic actuator 20 and comprises a stationary ferromagnetic core 7 housed within the upper body 2 and integral with it. A solenoid 8 is integrally mounted on the ferromagnetic core 7. Finally, the actuator comprises a movable armature 9. Armature 9 is radially internal to the solenoid 8 and a collar 11, distal to the solenoid 8, which serves as an axial guide for armature 9. The armature 9 is integral with the upper needle 6 and, in non-operating conditions, abuts against a limit element 13.

[0037] The movable element is actuated to initiate a gas injection phase. As the armature 9 moves axially toward the combustion chamber, the upper and lower needles will also move axially toward the combustion chamber, and the lower needle will uncover the openings of nozzle 4, allowing gas to flow into the combustion chamber.

[0038] At the end of an injection, the movable element of the injector is reset in a known manner by an elastic element 10, such as a helical spring. The upper needle 5 and the lower needle 6 are in axial contact with each other for all injection transients thanks to the preload of the helical spring 10. The elastic element 10 is housed between a support 50 integral with the lower body 3 and a cup-shaped element 60 integral with the lower needle 6.

[0039] The fuel gas enters injector 1 through a supply connection 12. The supply connection 12 is located distal to the upper body 2. The gas flows along a predominantly axial path, finally reaching the seal area between the lower needle 6 and the nozzle 4 and, when the injector opens, the nozzle 4 opening area. Advantageously, all components and gas passage areas are sized to achieve minimal pressure loss between the inlet supply pressure (corresponding to the pressure of an injection system supply manifold) and the injection pressure in the combustion chamber.

[0040] Injector 1 also includes an elastomeric gasket 14 that seals the injector and dampens shocks during closing. The use of an elastomeric seal has the advantage of providing sufficient damping during the closing process of the lower needle to prevent or minimize the so-called "bounce" of the lower needle, which would result in unwanted reopening of the injector.

[0041] The injector 1 also includes an elastic element made of metal or plastic, such as a bellows 17, configured to be compressed when external pressure is applied. The bellows 17 is concentric and radially external to the lower needle 6. The bellows 17 is designed so that its hydraulic diameter, the diameter on which the gas pressure acts, coincides with the sealing diameter of the gasket 14.

[0042] With the use of the bellows component 17, the pressure acting on the sealing diameter of the gasket 14 is balanced, enabling the design of an injector that has dynamic operation independent of the gas supply pressure. In other words, the pressure acting on the sealing area of the elastomeric gasket 14 generates a force in the injector's opening direction, while the pressure acting on the hydraulic diameter of the bellows 17 generates a force in the injector's closing direction.

[0043] The use of the bellows 17 in combination with the elastomeric gasket 14 allows the seal to have a constant compression determined solely by the preload of the elastic element 10. Otherwise, the compression of the seal would also depend on the internal gas pressure, resulting in variable injector behavior as the gas supply pressure varies. The pressure-balancing effect provided by the bellows offers the advantage of designing a smaller actuator, thus allowing for an overall reduction in the injector's external diameters.

[0044] According to the present invention and with reference also to Figure 2, the injector 1 is provided with a damping element 13, distal to the armature 9, which functions as a limit switch for the armature 9 of the electromagnetic actuator 20.

[0045] In fact, a proximal annular surface 13' thereof is in contact with a corresponding distal annular surface 9' of the armature 9, in non-injection conditions, that is, once the electrical power supply to the actuator 20 has ceased and, consequently, the effect of the magnetic force attracting the armature 9 towards the ferromagnetic core 7 has ceased.

[0046] The elastomeric material used for the damping element must be a compound with high damping properties. Preferably, this material could be:

[0047] - an "Ethylene-Propylene Diene Monomer" (EPDM), which is a terpolymer obtained from the union of two copolymers of ethylene and propylene and a diene monomer (hence the acronym EPDM),

[0048] - an ethylene-acrylic compound (AEM),

[0049] - a "Hydrogenated Nitrile Butadiene Rubber" (HBNR), which is a synthetic elastomer based on hydrogenated acrylonitrile butadiene.

[0050] Advantageously, the geometry of the damping element is ringshaped with dimensions that are at least 2 mm in height and a difference of 3 mm between the outer and inner radii of the ring.

[0051] The resulting damping capacity of the damping element 13 therefore depends on the volume of compressed elastomeric material and the material itself.

[0052] The elastomeric damper 13 plays a crucial role in dissipating residual energy present in the armature 9 due to its magnetic actuation. This energy dissipation prevents further movement of the movable element 5, 6 of the injector 1 (particularly the lower needle 6), thus preventing involuntary reopening after injection and other undesirable behaviors that could negatively impact engine performance.

[0053] Preferably, the fuel connection 12, which is a metal component, is equipped with an elastomeric damper 13, proximal to the fuel connection 12 itself.

[0054] Advantageously, the damper 13 can be easily installed into the fuel connection 12 via a simple snap-fit assembly process, eliminating the need for in-situ vulcanization of the elastomeric material.

[0055] Naturally and alternatively, the elastomeric material of the damping element 13 can be vulcanized in situ onto the supply connection 12.

[0056] Ultimately, this invention solves the technical problem of late injections in the injector due to the reopening of the injector's moving element.

[0057] The main advantages of the proposed solution include:

[0058] - reduced or eliminated late injections (post injection),

[0059] - increased injector life due to low-energy impacts within the injector itself, - simple design that does not require vulcanization or other costly and difficult processes.

[0060] In addition to the embodiment of the invention, as described above, it should be understood that numerous other variations exist. It should also be understood that such embodiments are only exemplary and do not limit either the scope of the invention, nor its applications, nor its possible configurations. On the contrary, although the description above allows the person skilled in the art to implement the present invention at least according to one of its exemplary embodiments, it should be understood that many variations of the described components are possible, without thereby departing from the scope of the invention, as defined in the appended claims, which are interpreted literally and / or according to their legal equivalents.

Claims

C LA I M S1. Injector (1) for direct injection of fuel into a combustion chamber (16), comprising:- a stationary body (2, 3),- a nozzle (4) provided with passage openings for the fuel from the injector to the combustion chamber,- a movable element (5, 6) configured to unlock and close the passage openings of the nozzle (4) and to open towards the outside of the injector (1) in an axial direction, wherein the movable element comprises an upper needle (5) and a lower needle (6),- an actuator (20) for actuating the movable element (5, 6), comprising a stationary ferromagnetic core (7) and an armature (9) axially movable together with the movable element (5, 6),- a supply connection (12), made of metallic material, the injector (1) being characterized in that it comprises a damping element (13) made of elastomeric material, distal to the armature (9) and which is configured as a lift stopper element of the armature (9) of the actuator (20).

2. Injector (1) according to claim 1, wherein the damping element (13) is provided with an annular surface (13'), in contact with a corresponding annular surface (9'), distal, of the armature (9), in conditions of absence of injection.

3. Injector (1) according to claim 1 or 2, wherein the geometry of the damping element (13) is ring-shaped with dimensions that are at least2 mm in height and at least 3 mm difference between the external and internal radius of the ring.

4. Injector (1) according to anyone of the preceding claims, wherein the elastomeric material of the damping element (13) is:- a terpolymer union of two copolymers of Ethylene and Propylene and a Diene Monomer, or- an ethylene-acrylic blend, or- a hydrogenated acrylonitrile butadiene.

5. Injector (1) according to anyone of the preceding claims, wherein the damping element (13) is housed in the supply connection (12), proximal to the supply connection (12) itself.

6. Injector (1) according to claim 5, wherein the damper element (13) is stably fixed in the supply connection (12) by means of a snap-fit assembly process.

7. Injector (1) according to claim 5, wherein the damper element (13) is stably fixed in the supply connection (12) by means of a vulcanization process.

8. Injector (1) according to anyone of the preceding claims, wherein the fuel is a gaseous fuel.

9. Injector (1) according to claim 8, wherein the gaseous fuel is hydrogen.

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