Gas injector

Abstract

Injector (1) for direct injection of gas into a combustion chamber (16), having: - a stationary 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 passage openings of the nozzle (4) and to open towards the outside of the injector (1), wherein the closing element comprises an upper needle (5) and a lower needle (6), the motion of which is guided by an axial guide (40), - an actuator (20) for actuating the closing element (5, 6), - a supply connection (12), wherein the contact between the upper needle (5) and the lower needle (6) occurs by means of at least one pair of surfaces, each pair having a concave surface and the other convex or two surfaces both convex.

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 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. 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 an opening 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] A significant technical challenge for gas injectors is their considerable length requirement due to the internal components required to meet performance standards. These components include bellows, springs, solenoids, inlets, and injector nozzles. High-static-flow gas injectors are typically approximately 200 mm long. This requirement requires the design of a long, thin needle with a diameter-to-length ratio of less than 2%.

[0011] The production of such needles is challenging and complex, as maintaining minimal overall runout is essential to ensure proper operation. One possible solution is to divide the needle into two elements, an upper needle and a lower needle. However, this introduces an additional technical challenge: maintaining parallelism between the axes of the two needles. Any slight angular misalignment can lead to excessive constraint, causing the needles to jam or generating significant stick-slip phenomena, which can compromise functionality.

[0012] When technological constraints require the use of two needles, achieving a single needle with a diameter / length ratio of less than 2% is impractical due to the strict eccentricity tolerances required. The main problem in using two needles lies in their guiding interface. Referring to Figures 3 and 4, these figures schematically depict an upper needle 5, a lower needle 6, and an axial guide 40 (for simplicity, the same references as those used below in the description of the invention are used). From these figures, it can be observed that, as long as the needles remain perfectly parallel, the guiding conditions and tolerances are maintained without problems (Figure 3). However, even a slight misalignment can significantly deteriorate the contact conditions (Figure 4). The misaligned needle, in this example the lower needle 6, begins to run on its edges Ps, leading to increased wear of the axial guide 40, wear that can quickly become destructive.

[0013] Therefore, there is a need to design a gas injector that is free of, or at least minimizes, the aforementioned drawbacks.

[0014] Summary of the Invention

[0015] To substantially solve the technical problems highlighted above, an aim of the present invention is to define a gas injector in which there are two needles having contact surfaces that are not flat, but concave / convex or both convex.

[0016] Therefore, according to the present invention, a gas injector is provided having the characteristics set forth in the independent claim, attached to the present description.

[0017] Further embodiments of the invention, preferred and / or particularly advantageous, are described according to the characteristics set forth in the dependent claims attached.

[0018] Brief Description of the Drawings

[0019] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting embodiments, in which:

[0020] - Figure 1 is a cross-section of a gas injector according to a preferred embodiment of the present invention;

[0021] - Figure 2 shows, on an enlarged scale, a detail of the injector of Figure 1;

[0022] - Figure 3 schematically illustrates a first operating condition of a prior art injector;

[0023] - Figure 4 schematically illustrates a second operating condition of the prior art injector of Figure 3; and

[0024] - Figure 5 schematically illustrates an operating condition of the injector of Figure 1.

[0025] Detailed Description

[0026] 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 with 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.

[0027] With reference to Figure 1, injector 1 is a direct-injection gas injector that injects gaseous fuel directly into a combustion chamber 100, of a known type and therefore only schematically depicted, of an internal combustion engine. The combustion chamber is not part of the present invention.

[0028] Throughout this description and the claims, terms and expressions indicating positions such as "proximal" and "distal" refer to the distance from the combustion chamber 100. Terms such as "radially internal" or "radially external" refer to an axisymmetric X-axis of the injector. For what is relevant for the purposes of the present 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.

[0029] The injector 1 comprises:

[0030] - a distal upper body 2, substantially cylindrical in shape,

[0031] - a proximal lower body 3, also substantially cylindrical in shape, integrally connected to the upper body,

[0032] - a nozzle 4, integrally positioned at the proximal end of the lower body 3 and equipped with openings for the passage of gas from the injector to the combustion chamber,

[0033] - an injector closing element made of two parts in axial contact with each other: 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 example shown in 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.

[0034] The closing 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 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 explained in more detail below. Both the upper needle 5 and the lower needle 6 are operated 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 inside 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. The armature 9 is radially internal with respect to the solenoid 8 and to a collar 11, distal with respect to the solenoid 8 and which has the function of axially guiding the armature 9. The armature 9 is integral with the upper pin 6 and in non-operating conditions it abuts against a stop element 13.

[0035] The closing 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 the nozzle 4, allowing gas to flow into the combustion chamber.

[0036] At the end of an injection, the injector closing element is reset in a known manner by an elastic element 10, such as a coil spring. The upper needle 5 and lower needle 6 are in axial contact with each other throughout the injection cycle thanks to the preload of the coil spring 10.

[0037] The fuel gas enters the injector 1 through a supply connection 12. The supply connection 12 is located distal to the upper body 2. The gas travels along a predominantly axial path, finally reaching the seal 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.

[0038] The injector 1 also includes an elastomeric gasket 14 that seals the injector and dampens shocks during closing. The use of the elastomeric seal has, in fact, the advantage that during the closing process of the lower needle it is possible to obtain such damping as to avoid or reduce to a minimum the so-called "rebound" of the lower needle with consequent unwanted reopening of the injector.

[0039] Injector 1 also includes a resilient element made of metal or plastic, such as a bellows 17, configured to compress when external pressure is applied. Bellows 17 is concentric and radially external to the lower needle 6. Bellows 17 is designed so that its hydraulic diameter, the diameter on which gas pressure acts, coincides with the sealing diameter of gasket 14.

[0040] With the use of bellows component 17, the pressure acting on the sealing diameter of gasket 14 is balanced, enabling the design of an injector that operates dynamically independent of gas supply pressure. In other words, the pressure acting on the sealing area of 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.

[0041] The use of 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 behavior of the injector as the gas supply pressure varies. The pressure balancing effect provided by the bellows offers the advantage of designing a smaller actuator, consequently allowing for an overall reduction in the external diameters of the injector.

[0042] According to the present invention, contact between the upper needle 5 and the lower needle 6 occurs via one or more pairs of surfaces, each pair comprising one concave surface and the other convex, or two convex surfaces.

[0043] With reference to Figure 2, a first embodiment of the invention comprises a sphere 30 located on the axis between the upper needle 5 and the lower needle 6 and within the axial guide 40.

[0044] The interposition of a sphere, within the axial guide, between the upper and lower needles defines a ball joint that provides an additional degree of freedom to the two-part closing element. Specifically, and with reference also to Figure 5, this involves a rotation around the X-axis of the injector, which relieves the parallelism constraint between the upper and lower needles. By allowing rotational motion, the needles can operate effectively without the strict requirement of perfectly parallel alignment, thus improving reliability and reducing the likelihood of problems such as sticking or stick-slip.

[0045] According to the embodiment shown in Figure 2, contact between the upper needle 5 and the lower needle 6 occurs via two pairs of surfaces:

[0046] - a concave conical surface 5s located on the proximal end of the upper needle 5, and a convex spherical surface 30s of the sphere 30, and - the spherical surface 30s with a concave conical surface 6s located on the distal end of the lower needle 6.

[0047] The concave shape of the conical surfaces 5s and 6s helps maintain contact between the needles and the sphere under all operating conditions of the injector. For this reason, preferably, the cone angle, for both conical surfaces 5s and 6s is between 70° and 150°, with a diameter of the sphere 30 between 2.5 and 3.5 mm.

[0048] Advantageously, in a second embodiment of the invention not illustrated, the ball 30 is welded to the upper needle 5 or to the lower needle 6. In this way, the ball 30 is prevented from rotating freely, with consequent increase in wear of the axial guide 40. In this embodiment, assuming for example that the ball 30 is welded to the lower needle 6, the contact between the upper needle 5 and the lower needle 6 is achieved by means of the conical surface 5s of the upper needle 5, which is concave, and the spherical surface 30s of the ball 30, which is evidently convex. Similarly, with sphere 30 welded to the upper needle 5, contact between the upper and lower needles will be achieved by means of the concave conical surface 6s of the lower needle 6 and the spherical surface 30s of the sphere 30.

[0049] Following the same inventive idea, there could be no third component, the sphere, but only the two needles, one with a concave conical surface and the other with a spherical surface (for example, the surface of a spherical cap).

[0050] According to a further variant, not illustrated because it is intuitive to understand, each of the two needles could have a sphere welded to the ends that come into contact. In this way, axial contact between the upper and lower needles occurs between two convex surfaces, specifically spherical ones. Furthermore, according to this variant, a double contact surface is defined with the axial guide.

[0051] Ultimately, this invention solves the technical problem of wear due to misalignment between the upper and lower needles.

[0052] The main advantages of the proposed solution include:

[0053] 1. Improved alignment flexibility: the guided ball allows for rotational movement, reducing the need for perfectly parallel alignment of the two needles.

[0054] 2. Improved reliability: the design minimizes the risk of stick-slip or sticking, leading to more consistent injector performance.

[0055] 3. Reduced wear: by alleviating the parallelism constraint, guiding conditions are less stringent. This reduces wear on the axial guide bushing, extending the life of the injector.

[0056] 4. Simplified manufacturing: the additional degree of freedom simplifies the manufacturing process by reducing the precision required for the parallelism of the two needles. Consequently, it becomes easier to produce the needles within acceptable tolerances.

[0057] 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 gas 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 closing 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), wherein the closing element comprises an upper needle (5) and a lower needle (6), the motion of which is guided by an axial guide (40),- an actuator (20) for actuating the closing element (5, 6),- a supply connection (12) the injector (1) being characterized in that the contact between the upper needle (5) and the lower needle (6) occurs by means of at least one pair of surfaces, each pair having a concave surface and the other convex or two surfaces both convex.

2. Injector (1) according to claim 1, comprising a sphere (30) located on the axis between the upper needle (5) and the lower needle (6) and inside the axial guide (40).

3. Injector (1) according to claim 2, wherein the contact between the upper needle (5) and the lower needle (6) occurs by means of two pairs of surfaces:- a conical surface (5s), concave and located on the proximal end of the upper needle (5), and a spherical surface (30s) of the sphere (30), convex, and- the spherical surface (30s) with a conical surface (6s), concave and located on the distal end of the lower needle (6).

4. Injector (1) according to claim 3, wherein the cone angle, for both conical surfaces (5s) and (6s) is between 70° and 150°.

5. Injector (1) according to claim 2 or 3, wherein the sphere (30) is welded to the lower needle (6).

6. Injector (1) according to claim 5, wherein the contact between the upper needle (5) and the lower needle (6) is made by means of the conical surface (5s) of the upper needle (5) and the spherical surface (30s) of the sphere (30).

7. Injector (1) according to claim 2 or 3, wherein the sphere (30) is welded to the upper needle (5).

8. Injector (1) according to claim 7, wherein the contact between the upper needle (5) and the lower needle (6) is made by means of the conical surface (6s) of the lower needle (6) and the spherical surface (30s) of the sphere (30).

9. Injector (1) according to claim 1, wherein the contact between the upper needle (5) and the lower needle (6) is made by the fact that one pin has a concave conical surface and the other pin has a spherical surface.

10. Injector (1) according to claim 1, wherein both the upper needle (5) and the lower needle (6) have, at the ends that come into contact, a welded sphere and the contact between the upper needle (5) and the lower needle (6) is made between two spherical surfaces.

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