Fuel injector

Abstract

Injector (1) for direct fuel injection into a combustion chamber (16), comprising: - a body (2, 3), - a nozzle (4) provided with passage openings for the fuel from the injector to the combustion chamber, - a closing element (5, 6) configured to unlock and close the nozzle passage openings (4) and to open outwards, - an actuator (20) for operating the dosing element (5, 6), and - a supply fitting (12) - a seal (14, 24, 34) made of elastomeric material which seals the injector (1) in the closed state of the injector, and - an elastic element (17) configured to be compressed when pressure is applied externally, wherein - a hydraulic diameter (Di) of the elastic element (17) is equal to a sealing diameter (Dt) of the seal (14, 24, 34).

Description

[0001] FUEL INJECTOR

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

[0003] Technical field of the invention

[0004] The present invention relates to a fuel injector. The injector is 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. Typically, these injectors are operated electromagnetically, using a solenoid that can be electrically energized to generate a magnetic field. This magnetic field causes an armature made of magnetic material, which is typically attached to an opening element or needle of an injector nozzle, 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 start of the 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 towards the nozzle orifice, which means that the armature must counteract the force of the spring to open the nozzle orifice. Once the nozzle orifice is opened, a specified amount of fuel within the injector can flow into a combustion chamber, typically found in an internal combustion engine.

[0008] 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 fuel-wetted surfaces, which helps open or close the valve needle from the nozzle orifice.

[0009] Fuel injectors typically retain the fluid internally when not actuated, either by a metal-to-metal seal between two components or by an elastomeric seal. Failure of this seal could result in fuel leaking from the nozzle tip.

[0010] Gas injectors offer high static flow rates due to their lower volumetric energy density compared to liquid fuels. However, this advantage introduces several design challenges. The need for larger flow sections and overall dimensions, unlike liquid fuel injectors, complicates their integration into engine heads. To accommodate these larger dimensions, modifications to the engine head are often required and may require adjustments to critical components such as the camshaft, coolant passages and valve arrangements. These modifications are complex and present substantial design and integration hurdles.

[0011] Managing high gas flow rates further complicates the problem. The larger injector size introduces a level of complexity to engine modifications, involving various engine components that may require redesign or specific adjustments to accommodate the larger gas injector size. This cascade of required modifications highlights the challenges and potential difficulties of integrating gas injectors into existing engine designs.

[0012] In addition, the high-pressure operation of gas injectors introduces additional challenges. Specifically, outward-opening configurations, where the nozzle needle extends outside the injector body when closed, present a significant challenge. In these configurations, the gas pressure attempts to open the nozzle needle, requiring substantial spring preload to ensure closure. Additionally, the design of these injector configurations must account for a wide range of pressures. The significant difference in pneumatic forces between maximum and minimum pressure requires a solenoid capable of generating a large magnetic force. This often limits the operating pressure range of such injectors and requires a higher drive current at lower pressures, complicating the design and requiring a larger solenoid diameter. This adds further challenges to retrofitting such injectors.

[0013] The large gas flow cross-sections also mean large contact surfaces between components, reducing the contact pressure for the same overall force. This reduction in contact pressure compromises the effectiveness of meta I -to- meta I seals, especially because gas molecules can escape through the smallest imperfections. Many designs therefore use elastomeric seals to provide gas sealing at lower contact pressures. However, the use of elastomers in close proximity to the combustion chamber is problematic due to the poor resistance of these materials to high temperatures and exposure to combustion gases, representing another significant obstacle to the development of efficient and durable gas injectors.

[0014] Finally, due to the injector layout, gas injectors cannot be calibrated because their geometry does not allow for the provision of a calibration spring housing and accessibility. Failure to calibrate injectors increases the variation in gas dosage from injector to injector.

[0015] There is therefore a need to define a fuel injector that is free from or at least minimizes the drawbacks inherent in the loss of efficiency and noise mentioned above.

[0016] Summary of the invention

[0017] In order to substantially solve the technical problems highlighted above, an object of the present invention is to define a fuel injector, particularly a gas injector, equipped with an elastomeric seal that is indifferent to the fuel supply pressure.

[0018] Therefore, according to the present invention, a fuel injector is provided having the characteristics set forth in the independent claim, attached to this description.

[0019] Further preferred and / or particularly advantageous embodiments of the invention are described according to the characteristics set forth in the attached dependent claims.

[0020] Brief description of the drawings

[0021] The invention will now be described with reference to the attached drawings, which illustrate some non-limiting examples of its implementation, in which:

[0022] - Figure 1 is a section of an injector according to a preferred embodiment of the present invention,

[0023] - Figure 2 illustrates, on an enlarged scale, a detail of the injector of Figure 1,

[0024] - Figure 3 illustrates, on an enlarged scale, a detail of the injector of Figure 1 in a second embodiment, and

[0025] - Figure 4 illustrates, on an enlarged scale, a detail of the injector of Figure 1 in a third embodiment. Detailed description

[0026] By way of example and not limitation, the present invention will now be described with reference to the aforementioned figures.

[0027] The fuel injector, object of the present invention, is particularly suitable for application in the presence of gaseous fuels and therefore, in the following, will be called gas injector. As can be seen from the following description, the same injector can, however, be used for the injection of gaseous fuel, for example natural gas or hydrogen, but also for the injection of liquid fuels, for example liquid natural gas, ammonia, methanol and the like.

[0028] With reference to figure 1, the 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 schematized, of an internal combustion engine. The combustion chamber is not part of the present invention.

[0029] 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 in any case unless explicitly stated otherwise, the injector 1 and its main components are substantially axially symmetrical with respect to the X axis.

[0030] The injector 1 comprises:

[0031] - an upper body 2, distal, of substantially cylindrical shape,

[0032] - a lower body 3, proximal, also of substantially cylindrical 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] - an injector closing element which, in the example illustrated in figure 1, is made of two parts axially in contact with each other: upper needle 5, distal, and lower needle 6, proximal. The closing element is configured to open outwards. In other words, the lower needle 6 is more proximal to the combustion chamber 100 than the nozzle 4. The hermetic closure of the injector to the passage of the gas flow is achieved by a seal between the lower needle 6 and the nozzle 4, as will be better explained below.

[0035] Both the upper needle 5 and the lower needle 6 are operated by an actuator, for example 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 inside the upper body 2 and integral with it. A solenoid 8 is integrally mounted on the electromagnetic core 7. Finally, the actuator comprises a movable armature 9. The armature 9 is radially internal with respect to the solenoid 8 and is integral with the upper needle 6. The actuation of the closing element occurs to start a gas injection phase. Due to the movement of the armature 9 in the axial direction and towards the combustion chamber, the upper needle and the lower needle will also move axially towards the combustion chamber and the lower needle will uncover the openings of the nozzle 3 allowing the gas to flow into the combustion chamber.

[0036] At the end of an injection, the injector closure element is reset in a known manner by means of an elastic element 10, for example a helical spring. The upper needle 5 and lower needle 6 are in axial contact with each other for all injection transients thanks to the preload of the elastic element 10.

[0037] Although the preferred solution, illustrated in figure 1, provides a closure element comprising two separate components - upper needle 5 and lower needle 6, an alternative solution is certainly the one in which the closure element is a single needle. This solution is advantageous with regard to the dynamics of the closure element as it avoids the possibility that the two separate needles can detach and bounce off each other. On the other hand, this solution poses problems of technological feasibility due to the excessive length that the closure element made of a single component would have.

[0038] Furthermore, a further alternative always included in the dictates of this injection is the one in which the upper needle and the lower needle are not in contact with each other. In this case, during the opening phase of the injector, a so-called "free lift" of the upper needle is carried out before it comes into contact with the lower needle, carrying out the actual opening of the injector. The "free lift" solution exploits the kinetic energy accumulated on the upper needle that carries out the free lift to open the lower needle on which the pressure and spring forces act. This alternative is particularly suitable in the case of injectors with inward opening (needle that moves away from the combustion chamber). The path 11 of the fuel gas starts from the supply by means of a supply fitting 12. The supply fitting 12 is located in a distal position with respect to the upper body 2 and the seal between the fitting and the upper body can be achieved by means of a meta I -to- meta I connection or with an O-ring connection 13. The gas then proceeds in a cavity obtained between the upper body 2 and a cavity 2a concentric and radially internal with respect to the upper body 2 and for this reason the injector is also defined as an external flow injector as the gas does not lick the components of the actuator 20. Finally, it reaches the area where there is a seal between the lower needle 6 and the nozzle 4 and, when the injector opens, in the area of the openings of the nozzle 4.

[0039] Advantageously, all the components and the gas passage areas are sized to obtain a minimum pressure load loss between the inlet supply pressure (corresponding to the pressure of a supply manifold of the injection system) and injection pressure in the combustion chamber.

[0040] According to the present invention and also with reference to figure 2, the injector 1 also comprises a gasket 14 made of elastomeric material that seals the injector and dampens impacts during closing. The use of the elastomer gasket has, in fact, the advantage that during the closing process of the lower needle it is possible to obtain a damping that avoids or minimizes the so-called "rebound" of the lower needle with consequent unwanted reopening of the injector.

[0041] The gasket 14 is mounted integrally and concentrically with the lower needle 6 and, when the injector 1 is in the closing phase, it creates a conical seal against a stop element 15 mounted integrally on the lower body 3, concentrically and radially internal to the lower body 3 itself. The conical seal can be either vulcanized on a metal support element 16 or housed by interference.

[0042] The injector is mounted so that the gasket 14 is compressed by a fixed amount generating the gas sealing function. The geometric design of the rubber is made such that the sealing diameter Dt is defined by the design and the variability between injector and injector is minimized.

[0043] At the same time, when the gasket 14 is compressed, the support element, preferably a poppet valve 16, proximal to the gasket 4 and mounted concentrically on the lower needle 6, shields the internal volume of the injector from the combustion chamber, protecting it from the hot gases and contaminants present in the combustion chamber.

[0044] The injector 1 also comprises an elastic element made of metal or plastic material, for example a bellows 17, configured to be compressed when pressure is applied externally. The bellows 17 is concentric and radially external to the lower needle 6. The bellows 17 is designed so that its hydraulic diameter Di, the diameter on which the gas pressure acts, coincides with the sealing diameter Dt of the gasket 14.

[0045] With the use of the bellows component 17, the pressure acting on the sealing diameter Dt of the gasket 14 is balanced, allowing the design of an injector that has a dynamic operation independent of the gas supply pressure. In other words, the pressure acting on the sealing area of the elastomer gasket 14 generates a force in the opening direction of the injector, while the pressure acting on the hydraulic diameter Di of the bellows generates a force in the closing direction of the injector. The use of the bellows 17 in combination with the elastomer gasket 14 allows the gasket to have a constant compression determined solely by the preload of the elastic element 10. If this were not the case, the compression of the gasket would also depend on the internal pressure of the gas, causing the injector to behave differently as the gas supply pressure varies. The pressure balance effect provided by the bellows gives the advantage of designing a smaller actuator, thus allowing a general reduction in the external diameters of the injector.

[0046] The use of the bellows 17 therefore generates an area that is not influenced by the gas pressure and that remains at ambient pressure. The actuator and the injector guides are positioned in this area.

[0047] Advantageously, the injector 1 comprises an externally accessible calibration pin 18, concentric and radially internal to the supply fitting 12, and distal to the armature 9. The calibration pin 18 compresses a calibration spring 19 which, in turn, acts on the armature 9. The ability to calibrate the injector in the gas flow or in the magnetic flow has a beneficial effect in reducing the variability of performance from injector to injector regarding the injected quantities and the transient behavior.

[0048] The design of the injector supply by means of the supply fitting 12, allows the electrical supply wires of the solenoid 8 to be brought out of the gas path without the use of special gaskets. The gas enters the upper body 2 of the injector 1 by means of a plurality of holes 20, obtained inside the supply connection 12 and inclined with respect to the X axis of the injector 1. Preferably the number of holes 20 can vary from 6 to 10. This number of holes 20 allows to reduce to a minimum the pressure drop at the injector inlet. This design allows to have an internally hollow supply connection 12 and therefore to house the calibration pin 18 inside it.

[0049] With reference to figure 3, in a second embodiment of the invention, the seal can be achieved by means of an O-ring 24 mounted on a support 26 and which seals against the stop element 15, rather than by means of a conical-sealing elastomer gasket.

[0050] With reference to figure 4, according to a third embodiment of the invention, the seal can be achieved by means of a square-section ring 34 mounted on a support 36 and which seals against the stop element 15. Obviously, both in the configuration of figure 3 and in the configuration of figure 4, the equality between the sealing diameter Dt and the hydraulic diameter Di of the bellows 17 must always be verified.

[0051] Ultimately, the present invention allows the following advantages to be achieved:

[0052] - excellent sealing of the combustible gas by means of the elastomer gasket,

[0053] - protection of the gasket and the combustible gas thanks to the use of a poppet valve which shields from the temperature of the combustion gases,

[0054] - high static flow thanks to large flow areas that allow a static flow rate greater than 15 g / s at an injection pressure of 40 bar at room temperature,

[0055] - injector body diameter, i.e. maximum external diameter of the injector comparable to that of standard injectors, for example a diesel engine injector of about 20 mm in diameter, - pressure balance inside the injector thanks to the use of bellows,

[0056] - possibility of calibrating using a calibration pin accessible from the outside in order to reduce performance variations between different injectors. In addition to the embodiment of the invention, as described above, it is to be understood that numerous other variations exist. It is also to be understood that such embodiments are exemplary only and do not limit the scope of the invention, its applications, or its possible configurations. Conversely, while the above description enables the skilled craftsman to carry out the present invention at least according to one exemplary embodiment thereof, it should be understood that many variations of the described components are possible without departing from the scope of the invention, as defined in the appended claims, which are construed literally and / or according to their legal equivalents.

Claims

C LA I M S1. Injector (1) for direct fuel injection into a combustion chamber (16), comprising:- a body (2, 3),- a nozzle (4) provided with passage openings for the fuel from the injector to the combustion chamber,- a closing element (5, 6) configured to unlock and close the nozzle passage openings (4) and to open outwards,- an actuator (20) for operating the closing element (5, 6), and- a supply fitting (12) the injector (1) being characterized by the fact that it also includes in combination:- a seal (14, 24, 34) made of elastomeric material which seals the injector (1) in the closed state of the injector, and- an elastic element (17) configured to be compressed when pressure is applied externally, wherein- a hydraulic diameter (Di) of the elastic element (17) is equal to a sealing diameter (Dt) of the seal (14, 24, 34).

2. Injector (1) according to claim 1, further comprising a calibration pin (18), accessible from the outside of the injector, concentric with the supply fitting (12), which compresses a calibration spring (19) which, in turn acts on an armature (9) of the actuator (20).

3. Injector (1) according to claim 1 or 2, wherein the seal (14) is configured to provide a conical seal.

4. Injector (1) according to claim 1 or 2, wherein the seal is an O- ring (24).

5. Injector (1) according to claim 1 or 2, wherein the seal is a ring (34) with a square section.

6. Injector (1) according to any of the previous claims, wherein the closing element comprises an upper needle (5) and a lower needle (6) axially in contact with each other.

7. Injector (1) according to any of claims 1 to 5, wherein the closing element is realized as a single component.

8. Injector (1) according to one of claims 1 to 5, wherein the closing element is made of two components not in contact with each other in the closed state of the injector.

9. Injector (1) according to any of the previous claims, in which the supply fitting (12) is provided with a plurality of internal holes (20), inclined with respect to an axis (X) of the injector (1).

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

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