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 openings for the passage of 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), - an actuator (20) for actuating the closing element (5, 6) comprising at least one ferromagnetic core (7), a solenoid (8) and an armature (9), - a supply connection (12), and - at least two elements provided with a coating (30) of polymeric material, present on a metal substrate and with anti-wear characteristics.

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 very challenging technical issue for gas injectors is the wear and resulting durability of the contact surfaces and the surfaces in relative motion (needle and body or nozzle surfaces), since there are no fluids such as gasoline, diesel, or ethanol that improve lubrication and reduce contact forces. This lack of "lubricating" fluid can lead to increased surface wear, affecting the longevity and performance of the injector.

[0011] To address wear and durability issues, occasional lubrication via a special oil circuit is sometimes used, although this can lead to additional soot and increased carbon dioxide (CO2) emissions in the internal combustion engine.

[0012] An alternative solution to the problems of wear on contact surfaces is represented by high-hardness coatings such as DLC (Diamond Like Carbon), which combines excellent wear resistance with its particular selflubricating capacity, or WC / C, a layer composed of tungsten carbide flakes alternating with amorphous carbon flakes, featuring excellent hardness and good wear resistance. These coatings, despite their very high hardness and low friction, have the disadvantage of being very thin, which leads to scraping or chipping of the coating, resulting in destructive abrasive wear.

[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 object of the present invention is to define a gas injector in which there are coatings made of polymeric material with an axial guide function for the injector needle and / or the armature.

[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; and

[0022] - Figure 3 shows, on an enlarged scale, a component of the injector of Figure 1.

[0023] Detailed Description

[0024] 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.

[0025] 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 illustrated, of an internal combustion engine. The combustion chamber is not part of the present invention.

[0026] 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 axial symmetry 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 axisymmetric with respect to the X-axis.

[0027] The injector 1 comprises:

[0028] - a distal upper body 2, substantially cylindrical in shape,

[0029] - a proximal lower body 3, also substantially cylindrical in shape, integrally connected to the upper body,

[0030] - 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,

[0031] - an injector closing element which, in the example illustrated in Figure 1, is made of two parts axially in contact with each other: the distal upper needle 5 and the proximal lower needle 6. 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 injector's hermetic seal against the passage of gas flow is achieved by a seal between the lower needle 6 and the nozzle 4, as will be explained in more detail below.

[0032] 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 needle 6 and in non-operating conditions abuts against a stop element 13.

[0033] The closing element is actuated to initiate a gas injection phase. Due to the axial movement of armature 9 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.

[0034] 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 phase thanks to the preload of the coil spring 10.

[0035] An alternative solution, still within the scope of this injection, is one in which the upper and lower needles are not in contact with each other. In this case, when the injector opens, a so-called "free lift" of the upper needle occurs before it contacts the lower needle, effectively opening the injector. The "free lift" solution uses the kinetic energy accumulated on the upper needle during the free lift to open the lower needle, which is acted upon by the pressure and spring forces. This alternative is particularly suitable for inward-opening injectors (needle moving away from the combustion chamber). Another alternative solution is for the needle to be a single component.

[0036] 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 travels 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 area of the nozzle 4 openings.

[0037] 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] Injector 1 also includes an elastomeric gasket 14 that seals the injector and dampens shock during closing. The use of an elastomeric gasket has the advantage of providing sufficient damping during the closing process of the lower needle, thus preventing or minimizing the so-called "bounce" of the lower needle, which would result in unwanted reopening of the injector.

[0039] Injector 1 also includes an elastic 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 the gas pressure acts, coincides with the sealing diameter of the 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 the gas supply pressure. In other words, the pressure acting on the sealing area of the elastomeric 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 a 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, the injector 1 features coatings 30 made of self-lubricating polymer material that serve as axial guides for the injector needle, namely the upper needle 5 and the lower needle 6, as well as for the armature 9 of the actuator 20.

[0043] These coatings 30 are made on a metal substrate, which may be steel, stainless steel, bronze, aluminum, titanium, or plastic. The polymer coating 30 is applied to the substrate surface through a spraying process similar to a painting process.

[0044] With reference to Figure 2, the coating 30 can advantageously be applied to a radially external cylindrical surface 9a of the armature 9: this is the sliding surface of the armature within the collar 11 and is therefore particularly exposed to frictional wear. Similarly, the coating 30 can be applied to a distal annular surface 9b of the armature 9: in this case, this surface is the stop surface of the armature 9 against the stop element 13 and is therefore a surface subject to impact wear. Therefore, the coating, according to this method of implementation, is made on a metal substrate which is the armature 9 itself.

[0045] According to an alternative embodiment of the invention and with reference to figure 3, in areas where the spraying process is impractical or should take place in completely inaccessible areas, it is possible to use a coated bushing 40 with the coating 30 pre-applied on the metal substrate of the uncoated bushing 45 and precisely on a radially internal cylindrical surface 45a of the bushing 45. After its production, the coated bushing 40 is inserted into the designated position inside the injector housing 1. For example, and returning to figure 1, a coated bushing 40 could be inserted by interference into the ferromagnetic core 7 so as to create an axial guide of the upper needle 5 which during sliding would be in contact with the cylindrical surface 45a provided with the polymeric coating 30. According to another example, the coated bushing 40 could be inserted by interference into the nozzle 4 so as to create an axial guide for the lower needle 6 which, during sliding, would be in contact with the cylindrical surface 45a provided with the polymeric coating 30.

[0046] In the example illustrated in figure 1, there are three guides in which the coating 30 can be applied: the armature guide with the coating 30 applied to the armature itself, the upper needle 5 guide and the lower needle 6 guide with the coated bushings 40 applied. The same solution, as can be easily understood, can be applied to a different number of guides. For example, there could be only two guides, one on the armature and one on the needle made from a single piece; or there could be five guides: one for the armature with the coating 30 applied to the armature itself, two guides for the upper needle 5, and two guides for the lower needle 6, with a total of four coated bushings 40 applied. It is clear that further combinations are possible and that the functionality of this solution is guaranteed both with only coatings 30 and with only coated bushings 40.

[0047] The same functionality is also achieved:

[0048] - when the polymer coating 30 is applied to an element whose surface comes into contact with a metal surface, therefore without polymer coating 30, of a second element, for example, the coated surface of the armature 9 against the metal surface of the ferromagnetic core 7;

[0049] - when both surfaces of the two elements in contact with each other have the polymer coating 30.

[0050] Polymer coatings have not previously been used in gasoline or diesel injectors due to their poor chemical compatibility with these fuels. However, they exhibit better chemical compatibility with gaseous fuels.

[0051] Specifically, the following are suitable for application according to the present invention:

[0052] - polyether ether ketone (PEEK), a colorless organic thermoplastic polymer. PEEK is a semi-crystalline thermoplastic polymer with excellent mechanical and chemical resistance properties that are maintained even at high temperatures;

[0053] - polyimide (PI), a polymer of imide monomers. Thermosetting polyimides are known for their thermal stability, good chemical resistance, and excellent mechanical properties even at high temperatures;

[0054] - polyamide-imides (PAI). It is used for high-temperature applications (250°C continuously) and offers an excellent combination of mechanical performance and dimensional stability;

[0055] - polytetrafluoroethylene (PTFE), a polymer belonging to the perfluorocarbon class that exhibits almost complete chemical inertness, complete insolubility in water and any organic solvent, excellent dielectric properties, fire resistance, and surface smoothness.

[0056] In applications according to the present invention, PEEK and PI have demonstrated the best resistance at higher temperatures.

[0057] The metal substrate of the bushing 45 or a component of the injector 1 (e.g., the armature 9) provides structural stability and rigidity, while the polymer coating 30 provides self-lubricating properties. By carefully selecting the materials, the coefficient of friction can be minimized and the wear rate can be low enough to ensure billions of strokes without coating failure. The coatings are thick enough to tolerate minor wear without compromising functionality.

[0058] Ultimately, the present invention solves the technical problem of wear between contacting surfaces, particularly those with relative sliding motion.

[0059] The main advantages of the proposed solution include:

[0060] 1. Increased durability and longevity: the combination of metal substrates and polymer coatings provides structural stability and selflubricating properties, significantly reducing wear. This ensures that the injector can withstand billions of strokes without failure, resulting in a longer lifespan.

[0061] 2. Improved chemical compatibility: the coatings used are chemically compatible with gaseous fuels such as natural gas and hydrogen, making them suitable for use in gas injectors. This overcomes the compatibility issues previously encountered with gasoline and diesel injectors.

[0062] 3. Reduced friction: the self-lubricating properties of the polymer coating reduce the friction coefficient, resulting in smoother operation and less energy loss during injector operation. This improves the efficiency and precision of the injection process.

[0063] 4. Fuel versatility: the design is adaptable to gaseous fuels (such as natural gas and hydrogen), making it versatile and suitable for a wide range of applications.

[0064] 5. Ease of fabrication and assembly: the use of metal bushings with pre-applied coatings allows for simpler fabrication and assembly processes. This method is particularly useful in areas where direct application of coatings is impractical.

[0065] 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 openings for the passage of 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),- an actuator (20) for actuating the closing element (5, 6) comprising at least one ferromagnetic core (7), a solenoid (8) and an armature (9), and- a supply connection (12) the injector (1) being characterized in that it also comprises at least two elements provided with a coating (30) of polymeric material, present on a metal substrate and with anti-wear characteristics.

2. Injector (1) according to claim 1, wherein the coating (30) is present on a cylindrical surface (9a), radially external, of the armature (9).

3. Injector (1) according to claim 1 or 2, wherein the coating (30) is present on an annular surface (9b), distal, of the armature (9).

4. Injector (1) according to anyone of the preceding claims, comprising at least one coated bushing (40) having:- a metal bushing (45) provided with a cylindrical surface (45a), radially internal, and- the coating (30) arranged on the cylindrical surface (45a).

5. Injector (1) according to claim 4, wherein the coated bushing (40) is mounted by interference in the ferromagnetic core (7) with the function of axially guiding an upper needle (5).

6. Injector (1) according to claim 4 or 5, wherein the coated bushing (40) is mounted by interference in the nozzle (4) with the function of axially guiding a lower needle (6).

7. Injector (1) according to claim 5, wherein the upper needle (5) is axially guided by two coated bushings (40).

8. Injector (1) according to claim 6, wherein the lower needle (5) is axially guided by two coated bushings (40).

9. Injector (1) according to anyone of the preceding claims, wherein the coating (30) is made of polyether ether ketone.

10. Injector (1) according to anyone of the preceding claims, wherein the coating (30) is made of polyimide (PI).

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